Theoretical Investigation of the Effect of the Surface Parameters on Cathodoluminescence Signal
历届IPho试题-历届IPho试题-ipho_Problemand9thIPhO86_fin
Problems of the 2nd and 9th International Physics Olympiads(Budapest, Hungary, 1968 and 1976)Péter VankóInstitute of Physics, Budapest University of Technical Engineering, Budapest, HungaryAbstractAfter a short introduction the problems of the 2nd and the 9th International Physics Olympiad, organized in Budapest, Hungary, 1968 and 1976, and their solutions are presented.IntroductionFollowing the initiative of Dr. Waldemar Gorzkowski [1] I present the problems and solutions of the 2nd and the 9th International Physics Olympiad, organized by Hungary. I have used Prof. R ezső Kunfalvi’s problem collection [2], its Hungarian version [3] and in the case of the 9th Olympiad the original Hungarian problem sheet given to the students (my own copy). Besides the digitalization of the text, the equations and the figures it has been made only small corrections where it was needed (type mistakes, small grammatical changes). I omitted old units, where both old and SI units were given, and converted them into SI units, where it was necessary.If we compare the problem sheets of the early Olympiads with the last ones, we can realize at once the difference in length. It is not so easy to judge the difficulty of the problems, but the solutions are surely much shorter.The problems of the 2nd Olympiad followed the more than hundred years tradition of **petitions in Hungary. The tasks of the most important Hungarian theoretical **petition (Eötvös Competition), for example, are always very short. Sometimes the solution is only a few lines, too, but to find the idea for this solution is rather difficult.Of the 9th Olympiad I have personal memories; I was the youngest member of the Hungarian team. The problems of this Olympiad were collected and partly invented by Miklós Vermes, a legendary and famous Hungarian secondary school physics teacher. In the first problem only the detailed investigation of the stability was unusual, in the second problem one could forget to subtract the work of the atmospheric pressure, but the fully “open” third problem was really unexpected for us.The experimental problem was difficult in the same way: in contrast to the Olympiads of today we got no instructions how to measure. (In the last years the only similarly open experimental problem was the investigation of “The magnetic puck” in Leicester, 2000, a really nice problem by Cyril Isenberg.) The challenge was not to perform many-many measurements in a short time, but to find out what to measure and how to do it.Of course, the evaluating of such open problems is very difficult, especially for several hundred students. But in the 9th Olympiad, for example, only ten countries participated and the same person could read, compare, grade and mark all of the solutions.2nd IPhO (Budapest, 1968)Theoretical problemsProblem 1On an inclined plane of 30° a block, mass m 2 = 4 kg, is joined by a light cord to a solid cylinder, mass m 1 = 8 kg, radius r = 5 cm (Fig. 1). Find the acceleration if the bodies are released. The coefficient of friction between the block and the inclined plane μ = 0.2. Friction at the bearing and rolling friction are negligible.SolutionIf the cord is stressed the cylinder and the block are moving with the same acceleration a . Let F be the tension in the cord, S the frictional force between the cylinder and the inclined plane (Fig. 2). The angular acceleration of the cylinder is a /r . The net force causing the acceleration of the block:F g m g m a m +-=αμαcos sin 222, and the net force causing the acceleration of the cylinder:F S g m a m --=αsin 11.The equation of motion for the rotation of the cylinder:I ra r S ⋅=.(I is the moment of inertia of the cylinder, S ⋅r is the torque of the frictional force.) Solving the system of equations we get:()221221cos sin rIm m m m m g a ++-+⋅=αμα,(1)()2212212cos sin rI m m m m m g r I S ++-+⋅⋅=αμα, (2)αm 1m 2Figure 1αm 2g sin α Figure 2F Fμ m 2g cos αSm 1g sin αr2212212sin cos rIm m r I r I m g m F ++-⎪⎭⎫ ⎝⎛+⋅=ααμ.(3)The moment of inertia of a solid cylinder is 221r m I =. Using the given numerical values:()2s m 3.25==+-+⋅=g m m m m m g a 3317.05.1cos sin 21221αμα,()N 13.01=+-+⋅=2122115.1cos sin 2m m m m m g m S αμα,()N 0.192=+-⋅=21125.1sin 5.0cos 5.1m m m g m F ααμ.Discussion (See Fig. 3.)The condition for the system to start moving is a > 0. Inserting a = 0 into (1) we obtain the limit for angle α1:0667.03tan 2121==+⋅=μμαm m m , ︒=81.31α.For the cylinder separately 01=α, and for the block separately ︒==-31.11tan 11μα. If the cord is not stretched the bodies move separately. We obtain the limit by inserting F = 0 into (3):6.031tan 212==⎪⎪⎭⎫⎝⎛+⋅=μμαI r m , ︒=96.302α.The condition for the cylinder toslip is that the value of S (calculated from (2) taking the same coefficient of friction) exceeds the value of αμcos 1g m . This gives the same value for α3 as we had for α2. The acceleration of the centers of the cylinder and the block is the same: ()αμαcos sin -g , the frictional force at the bottom of the cylinder is αμcos 1g m , the peripheral acceleration of the cylinder is αμcos 21g I r m ⋅⋅.Problem 2There are 300 cm 3 toluene of C 0︒ temperature in a glass and 110 cm 3 toluene of C 100︒ temperature in another glass. (The sum of the volumes is 410 cm 3.) Find the final volume after the two liquids are mixed. The coefficient of volume expansion of toluene()1C 001.0-︒=β. Neglect the loss of heat. β r, ag α0︒30︒60︒ 90︒F, S (N)α1α2=α31020FSβ raFigure 3SolutionIf the volume at temperature t 1 is V 1, then the volume at temperature C 0︒ is ()11101t V V β+=. In the same way if the volume at t 2 temperature is V 2, at C 0︒ we have ()22201t V V β+=. Furthermore if the density of the liquid at C 0︒ is d , then the masses are d V m 101= and d V m 202=, respectively. After mixing the liquids the temperature is212211m m t m t m t ++=.The volumes at this temperature are ()t V β+110 and ()t V β+120. The sum of the volumes after mixing:()()()()()212201102202011010221120102122112120102010201020101111V V t V t V t V V t V V d t m dt m V V m m t m t m d m m V V t V V V V t V t V +=+++==+++=⎪⎭⎫⎝⎛+++==++⋅+⋅++==+++=+ ++βββββββββThe sum of the volumes is constant. In our case it is 410 cm 3. The result is valid for any number of quantities of toluene, as the mixing can be done successively adding always one more glass of liquid to the mixture.Problem 3Parallel light rays are falling on the plane surface of a semi-cylinder made of glass, at an angle of 45︒, in such a plane which is perpendicular to the axis of the semi-cylinder (Fig. 4). (Index of refraction is 2.) Where are the rays emerging out of the cylindrical surface?SolutionLet us use angle ϕ to describe the position of the rays in the glass (Fig. 5). According to the law of refraction 2sin 45sin =︒β, 5.0sin =β, ︒=30β. The refracted angle is 30︒ for all of the incoming rays. We have to investigate what happens if ϕ changes from 0︒ to 180︒.Figure 4Figure 5ϕα βACDOBEIt is easy to see that ϕ can not be less than 60︒ (︒=∠60AOB ). The critical angle is given by 221sin ==n crit β; hence ︒=45crit β. In the case of total internal reflection ︒=∠45ACO , hence ︒=︒-︒-︒=754560180ϕ. If ϕ is more than 75︒ the rays can emerge the cylinder. Increasing the angle we reach the critical angle again if ︒=∠45OED . Thus the rays are leaving the glass cylinder if:︒<<︒16575ϕ, CE, arc of the emerging rays, subtends a central angle of 90︒.Experimental problemThree closed boxes (black boxes) with two plug sockets on each are present for investigation. The participants have to find out, without opening the boxes, what kind of elements are in them and measure their characteristic properties. AC and DC meters (their internal resistance and accuracy are given) and AC (5O Hz) and DC sources are put at the participants’ disposal .SolutionNo voltage is observed at any of the plug sockets therefore none of the boxes contains a source. Measuring the resistances using first AC then DC, one of the boxes gives the same result. Conclusion: the box contains a simple resistor. Its resistance is determined by measurement. One of the boxes has a very great resistance for DC but conducts AC well. It containsa capacitor, the value can be computed as CX C ω1=.The third box conducts both AC and DC, its resistance for AC is greater. It contains a resistor and an inductor connected in series. The values of the resistance and the inductance can be computed from the measurements.9th IPhO (Budapest, 1976)Theoretical problemsProblem 1A hollow sphere of radius R = 0.5 m rotates about a vertical axis through its centre with an angular velocity of ω = 5 s -1. Inside the sphere a small block is moving together with the sphere at the height of R /2 (Fig. 6). (g = 10 m/s 2.)a) What should be at least the coefficient of friction to fulfill this condition? b) Find the minimal coefficient of friction also for the case of ω = 8 s -1. c) Investigate the problem of stability in both cases,α) for a small change of the position of the block,β) for a small change of the angular velocity of the sphere.Solutiona) The block moves along a horizontal circle of radius αsin R . The net force acting on the block is pointed to the centre of this circle (Fig. 7). The vector sum of the normal force exerted by the wall N , the frictional force S and the weight mg is equal to the resultant: αωsin 2R m .The connections between the horizontal and **ponents:αααωcos sin sin 2S N R m -=,ααsin cos S N mg +=.The solution of the system of equations:⎪⎪⎭⎫⎝⎛-=g R mg S αωαcos 1sin 2,R/2Figure 6Figure 7Sαm ω2R sin αmg N R⎪⎪⎭⎫⎝⎛+=g R mg N αωα22sin cos . The block does not slip down if0.2259==+-⋅=≥2333sin cos cos 1sin 222gR gR NSa αωααωαμ.In this case there must be at least this friction to prevent slipping, i.e. sliding down.b) If on the other hand1cos 2>gR αω somefriction is necessary to prevent the block to slip upwards. αωsin 2R m must be equal to the resultant of forces S , N and mg . Condition for the minimal coefficient of friction is (Fig. 8):=+-⋅=≥gR gR NSb αωααωαμ222sin cos 1cos sin0.1792==2933.c) We have to investigate μa and μb as functions of α and ω in the cases a) and b) (see Fig. 9/a and 9/b ):In case a): if the block slips upwards, it comes back; if it slips down it does not return. If ω increases, the block remains in equilibrium, if ω decreases it slips downwards.In case b): if the block slips upwards it stays there; if the block slips downwards it returns. If ω increases the block climbs upwards -, if ω decreases the block remains in equilibrium.Problem 2α90︒μ a0.590︒μ b0.5ω = 5/sω < 5/sω > 5/sαω > 8/sω = 8/sω < 8/sFigure 9/aFigure 9/bSαm ω2R sin αmgNFigure 8The walls of a cylinder of base 1 dm 2, the piston and the inner dividing wall are perfect heat insulators (Fig. 10). The valve in the dividing wall opens if the pressure on the right side is greater than on the left side. Initially there is 12 g helium in the left side and 2 g helium in the right side. The lengths of both sides are 11.2 dm each and the temperature is C 0︒. Outside we have a pressure of 100 kPa. The specific heat at constant volume is c v = 3.15 J/gK, at constant pressure it is c p = 5.25 J/gK. The piston is pushed slowly towards the dividing wall. When the valve opens we stop then continue pushing slowly until the wall is reached. Find the work doneon the piston by us.SolutionThe volume of 4 g helium at C 0︒ temperature and a pressure of 100 kPa is 22.4 dm 3 (molar volume). It follows that initially the pressure on the left hand side is 600 kPa, on the right hand side 100 kPa. Therefore the valve is closed.An **pression happens until the pressure in the right side reaches 600 kPa (( = 5/3).35356002.11100V ⋅=⋅, hence the volume on the right side (when the valve opens):V = 3.82 dm 3.From the ideal gas equation the temperature is on the right side at this pointK 5521==nRpVT . During this phase the whole work performed increases the internal energy of the gas:W 1 = (3.15 J/gK) ⋅ (2 g) ⋅ (552 K – 273 K) = 1760 J.Next the valve opens, the piston is arrested. The temperature after the mixing has **pleted:K 313145522273122=⋅+⋅=T .During this phase there is no change in the energy, no work done on the piston. An **pression follows from 11.2 + 3.82 = 15.02 dm3 to 11.2 dm3:323322.1102.15313⋅=⋅T ,henceT 3 = 381 K.The whole work done increases the energy of the gas:W 3 = (3.15 J/gK) ⋅ (14 g) ⋅ (381 K – 313 K) = 3000 J. The total work done:W total = W 1 + W 3 = 4760 J.The work done by the outside atmospheric pressure should be subtracted:11.2 dm 11.2 dm 1 dm 2 Figure 10W atm = 100 kPa ⋅ 11.2 dm 3 = 1120 J. The work done on the piston by us:W = W total – W atm = 3640 J .Problem 3Somewhere in a glass sphere there is an air bubble. Describe methods how to determine the diameter of the bubble without damaging the sphere.SolutionWe can not rely on any value about the density of the glass. It is quite uncertain. The index of refraction can be determined using a light beam which does not touch the bubble. Another method consists of immersing the sphere into a liquid of same refraction index: its surface becomes invisible.A great number of methods can be found.We can start by determining the axis, the line which joins the centers of the sphere and the bubble. The easiest way is to use the “tumbler -over ” method. If the sphere is placed on a horizontal plane the axis takes up a vertical position. The image of the bubble, seen from both directions along the axis, is a circle.If the sphere is immersed in a liquid of same index of refraction the spherical bubble is practically inside a parallel plate (Fig. 11). Its boundaries can be determined either by a micrometer or using parallel light beams.Along the axis we have a lens system consisting, of two thick negative lenses. The diameter of the bubble can be determined by several measurements **plicated calculations.If the index of refraction of the glass is known we can fit a plano-concave lens of same index of refraction to the sphere at the end of the axis (Fig. 12). As ABCD forms a parallel plate the diameter of the bubble can be measured using parallel light beams.Focusing a light beam on point A of the surface of the sphere (Fig. 13) we get a diverging beam from point A inside the sphere. The rays strike the surface at the other side and illuminate a cap. Measuring the spherical cap we get angle ϕ. Angle ψ can be obtained in a similar way at point B. Fromd R r +=ϕsin and dR r-=ψsinFigure12A BC DArdψϕRBFigure13 Figure11we haveϕψϕψsin sin sin sin 2+⋅=R r , ϕψϕψsin sin sin sin +-⋅=R d .The diameter of the bubble can be determined also by the help of X-rays. X-rays are not refracted by glass. They will cast shadows indicating the structure of the body, in our case the position and diameter of the bubble.We can also determine the moment of inertia with respect to the axis and thus the diameter of the bubble.Experimental problemThe whole text given to the students:At the workplace there are beyond other devices a test tube with 12 V electrical heating, a liquid with known specific heat (c 0 = 2.1 J/g ︒C) and an X material with unknown thermal properties. The X material is insoluble in the liquid.Examine the thermal properties of the X crystal material between room temperature and 70 ︒C. Determine the thermal data of the X material. Tabulate and plot the measured data.(You can use only the devices and materials prepared on the table. The damaged devices and the used up materials are not replaceable.)SolutionHeating first the liquid then the liquid and the crystalline substance together two time-temperature graphs can be plotted. From the graphs specific heat, melting point and heat of fusion can be easily obtained.Literature[1] W. Gorzkowski: Problems of the 1st International Physics Olympiad Physics Competitions 5, no2 pp6-17, 2003[2] R. Kunfalvi: Collection of Competition Tasks from the Ist through XVth International Physics Olympiads 1967-1984 Roland Eötvös Physical Society in cooperation with UNESCO, Budapest, 1985 [3] A Nemzetközi Fizikai Diákolimpiák feladatai I.-XV.Eötvös Loránd Fizikai Társulat, Középiskolai Matematikai Lapok, 1985。
dotcom references
The first reference is the big theoretical/empirical reference for the program. The second, third, and fourth references are the three volumes of the users manual for the computer program. Notice the difference in the titles: The 4-volume paper reference is called DATCOM; the computer program is called Digital Datcom.1. Fink, R.: USAF Stability and ControlDATCOM.. AFWAL-TR-83-3048. McDonnell DouglasCorporation, Douglas Aircraft Division, for the Flight ControlsDivision, Air Force Flight Dynamics Laboratory,Wright-Patterson AFB, Ohio. October 1960, revised November 1965, revised April 1978.2. The USAF Stability And Control Digital Datcom, Volume I,Users Manual. USAF TechnicalReport AFFDL-TR-79-3032 (AD A086557), April 1979.3. The USAF Stability And Control Digital Datcom, Volume II,Implementation of Datcom Methods. USAF TechnicalReport AFFDL-TR-79-3032 (AD A086558), April 1979.4. The USAF Stability And Control Digital Datcom, Volume III, PlotManual. USAF Technical Report AFFDL-TR-79-3032 (ADA086559), April 1979.5. Pitts, William C.; Nielsen, Jack N.; and Kaattari, George E.: Liftand Center of Pressure of Wing-Body-Tail Combinations atSubsonic, Transonic, and Supersonic Speeds.NACA Report1307, July 1953.6. Hopkins, Edward J.: A Semi Empirical Method for Calculatingthe Pitching Moment of Bodies of Revolution at Low MachNumbers.NACA Research Memorandum A51C14, May 1951.7. Kaattari, George E.; Nielsen, Jack N.; and Pitts, WilliamC.: Method for Estimating Pitching Moment Interference ofWing-Body Combinations at Supersonic Speeds.NACAResearch Memorandum A52B06, April 1952.8. Ashley, Holt; and Landahl, Marten: Aerodynamics of Wings andBodies. Addison Wesley, 1965 (Now available from Dover inlow-cost edition).9. Wieselsburger, C.: Airplane Body (Non-Lifting System) Dragand Influence on Lifting System. Influence of the Airplane Body on the Wings. Vol. IV of Aerodynamics Theory, div. K, ch. III.sec. 1, W. F. Durand, ed., Julius Springer (Berlin), 1934, pp.152-157.10. Hopkins, Edward J., and Carel, Hubert C.: Experimental andTheoretical Study of the Interference at Low Speed Between Slender Bodies and Triangular Wings. NACA ResearchMemorandum A53A14, 1953.11. Nielsen, Jack N., and Pitts, William C.: Wing-Body Interferenceat Supersonic Speeds with an Application to Combinations with Rectangular Wings. NACA Technical Note 2677, 1952.12. Ferrari, Carlo: Interference Between Wing and Body atSupersonic Speeds. Theory and Numerical Application. Journal of the Aeronautical Sciences, vol. 15, no. 6, June 1948, pp.317-336.13. Morikawa, George K.: The Wing-Body Problem for LinearizedSupersonic Flow. PhD. Thesis, Calif. Inst. of Tech., 1949.14. Nielsen, Jack N., Katzen, Elliott D., and Tang, Kenneth K.: Liftand Pitching-Moment Interference Between a PointedCylindrical Body and Triangular Wings of Various Aspect Ratios at Mach Numbers of 1.50 and 2.02.NACA Technical Note 3795, 1956. (Supersedes NACA Research Memorandum A50F06) 15. Silverstein, Abe: Toward a Rational Method of Tail-PlaneDesign. Journal of the Aeronautical Sciences, vol. 6, no. 9, July 1939, pp. 361-369.16. Silverstein, Abe; and Katzoff, S.: Design Charts for PredictingDownwash Angles and Wake Characteristics Behind Plain and Flapped Wings.NACA Report 648, 1939.17. Morikawa, George: Supersonic Wing-Body-TailInterference. Journal of the Aeronautical Sciences, vol. 19, no.5, May 1952, pp. 333-340.18. Lomax, Harvard, and Byrd, Paul F.: Theoretical AerodynamicCharacteristics of a Family of Slender Wing-Tail-BodyCombinations. NACA Technical Note 2554, 1951.19. Lagerstrom, Paco A., and Graham, Martha E.: AerodynamicInterference in Supersonic Missiles. SM-13743, DouglasAircraft Co., Inc., Santa Monica, July 1950.20. Alden, Henry L., and Schindel, Leon H.: The Calculations ofWing Lift and Moments in Nonuniform Supersonic Flows. M. I. T.Meteor Report 53, May 1950.21. Spreiter, John R.: The Aerodynamic Forces on Slender Plane-and Cruciform-Wing and Body Combinations.NACA Report962, 1950. (Formerly NACA TN's 1662 and 1897)22. Morikawa, George: Supersonic Wing-Body Lift. Journal of theAeronautical Sciences, vol. 18, no. 4, Apr. 1951, pp. 217-228.23. Allen, H. Julian, and Perkins, Edward W.: A Study of Effects ofViscosity on Flow Over Slender Inclined Bodies ofRevolution.NACA Report 1048, 1951.24. Jones, Robert T.: Properties of Low-Aspect-Ratio PointedWings at Speeds Below and Above the Speed of Sound.NACA Report 835, 1946.25. Beskin, L.: Determination of Upwash Around a Body ofRevolution at Supersonic Velocities. Report No. CM-251, Johns Hopkins Univ., Applied Physics Lab., May 27, 1946.26. Nielsen, Jack N.: Quasi-Cylindrical Theory of Wing-BodyInterference at Supersonic Speeds and Comparison WithExperiment.NACA Report 1252, 1956.27. Lagerstrom. Paco A., and Van Dyke, M. D.: GeneralConsiderations About Planar and Non-Planar LiftingSystems. SM-13432, Douglas Aircraft Co., Inc., Santa Monica, June 1949.28. Jones, Robert T.: Thin Oblique Airfoils at SupersonicSpeed.NACA Report 851, 1946. (Formerly NACA TN 1107) 29. Lagerstrom, P. A.: Linearized Supersonic Theory of ConicalWings.NACA Technical Note 1685, 1950.30. Heaslet, Max. A., and Spreiter, John R.: Reciprocity Relationsin Aerodynamics. NACA Technical Note 2700, 1952. {notscanned yet}31. DeYoung, John, and Harper, Charles W.: TheoreticalSymmetric Span Loading at Subsonic Speeds for Wings Having Arbitrary Plan Form.NACA Report 921, 1950.32. Spreiter, John R., and Sacks, Alvin: The Rolling-Up of theTrailing Vortex Sheet and Its Effect on Downwash BehindWings. Journal of the Aeronautical Sciences, vol. 18, no. 1, Jan.1951, pp. 21-32, 72.33. Rogers, Arthur W.: Application of Two-Dimensional VortexTheory to the Prediction of Flow Fields Behind Wings ofWing-Body Combinations at Subsonic and SupersonicSpeeds.NACA Technical Note 3227, 1954.34. Lawrence, H. R.: The Lift Distribution on Low Aspect RatioWings at Subsonic Speeds. Journal of the AeronauticalSciences, vol. 18, no. 10, Oct. 1951, pp. 683-695.35. McDevitt,John B.: A Correlation by Means of TransonicSimilarity Rules of Experimentally Determined Characteristics of a Series of Symmetrical and Cambered Wings ofRectangular Plan Form.NACA Report 1253, 1955.36. Dugan, Duane W., and Hikido, Katsumi: TheoreticalInvestigation of the Effects on Lift of a Gap Between Wing and Body of a Slender Wing-Body Combination.NACA Technical Note 3224, 1954.37. Johnson, Ben H., Jr., and Rollins, Francis W.: Investigation ofa Thin Wing of Aspect Ratio 4 in the Ames 12-Foot PressureWind Tunnel. V - Static Longitudinal Stability and ControlThroughout the Subsonic Speed Range of a Semispan Model of a Supersonic Airplane.NACA Research Memorandum A9I01, 1949.38. Cahn, Maurice S., and Bryan, Carroll R.: A Transonic-WingInvestigation in the Langley 8-Foot High-Speed Tunnel at High Subsonic Mach Numbers and at a Mach Number of 1.2.Wing-Fuselage Configuration Having a Wing of ZeroSweepback, Aspect Ratio 4.0, Taper Ratio 0.6, and NACA65A006 Airfoil Section.NACA Research Memorandum L51A02, 1951.39. Weber and Kehl: Wind-Tunnel Measurements on the HenschelMissile "Zitterrochen" in Subsonic and SupersonicVelocities.NACA Technical Memorandum 1159, 1948.40. Anderson, Adrien E.: An Investigation at Low Speed of aLarge-Scale Triangular Wing of Aspect Ratio Two. III.Characteristics of Wing With Body and Vertical Tail.NACAResearch Memorandum A9H04, 1949.41. Polhamus, Edward C., and King, Thomas J., .Jr.: AerodynamicCharacteristics with Fixed and Free Transition of a ModifiedDelta Wing in Combination with a Fuselage at High Subsonic Speeds.NACA Research Memorandum L50C21, 1950.42. House, Rufus O., and Wallace, Arthur R.: Wind TunnelInvestigation of Effect of Interference on Lateral-StabilityCharacteristics of Four NACA 23012 Wings, and Elliptical and a Circular Fuselage, and Vertical Fins.NACA Report 705, 1941.43. McKay, James M., and Hall, Albert W.: The Effects on theAerodynamic Characteristics of Reversing the Wing of aTriangular Wing-Body Combination at Transonic Speeds asDetermined by the NACA Wing-Flow Method.NACA Research Memorandum L54H23, 1954.44. Hall, Albert W., and Morris, Garland J.: AerodynamicCharacteristics at a Mach Number of 1.25 of a 6-Percent-Thick Triangular Wing and 6- and 9-Percent-Thick Triangular Wings in Combination With a Fuselage. Wing Aspect Ratio 2.31.Biconvex Airfoil Sections.NACA Research MemorandumL50D05, 1950.45. Ellis, Macon C., Jr., and Grigsby, Carl E.: AerodynamicInvestigation at Mach Number 1.92 of a Rectangular Wing andTail and Body Configuration and Its Components. NACAResearch Memorandum L9L28a, 1950. {not scanned yet}46. Jaeger, B. F., and Brown, A. E.: The AerodynamicCharacteristics at Mach Number 2.0 of 14- and 18-CaliberFin-Stabilized Rockets with Varying Body and FinParameters. U. S. Naval Ordnance Test Station, Inyokern, Calif., NAVORD Report 1244, Jan. 20, 1950.47. Stivers, Louis S., Jr., and Malick, Alexander W.: Wind-TunnelInvestigation at Mach Numbers from 0.50 to 1.29 of anAll-Movable Triangular Wing of Aspect Ratio 4 Alone and with a Body.NACA Research Memorandum A9L01, 1950.48. Niewald, Roy J., and Moul, Martin T.: The Longitudinal Stability,Control Effectiveness, and Control Hinge-MomentCharacteristics Obtained from a Flight Investigation of a Canard Missile Configuration at Transonic and SupersonicSpeeds.NACA Research Memorandum L50I27, 1950.Order a CD with all of the programs from Public Domain Computer Programs for the Aeronautical Engineer.Last updated: 24 June 2013 by Ralph Carmichael, webmaster@ Public Domain Aeronautical SoftwareP.O. Box 1438 Santa Cruz CA 95061 USA。
BIIN
statistical mechanics Surface tension Bismuth Indium Alloys
abstract
The mixing behaviour of liquid Bi–In alloys has been described in terms of energetics and structure through the study of their thermodynamic, surface and structural properties by using the Complex Formation Model (CFM) in the weak interaction approximation and by postulating BiIn-chemical complexes as energetically favoured. The new Bi, In and Bi–In surface tension experimental data set, obtained by the large drop method in the temperature range 553–873 K, has been analysed in the framework of the CFM and compared with the calculated values as well as with corresponding literature data. The structural characteristics of Bi–In melts are described by the two microscopic functions, i.e. the concentration fluctuations in the long-wavelength limit and the Warren–Cowley short-range order parameter.
综合主观评价在整车开发中的应用
d. 为了提高评价的精确性，建议评价得分 精确到 0.5 分；得分高于 8 分的评价项给出优 点；得分低于 6 分评价项给出问题点并记录路 面状态、车辆的速度、档位等等详细情况。
THEORETICAL INVESTIGATION | 理论探讨
时代汽车
综合主观评价在整车开发中的应用
张静涛 奇瑞汽车股份有限公司汽车工程技术研究总院 安徽省芜湖市 241009
摘 要：综合主观评价是代表顾客评价车辆的一个重要手段，也是整车开发过程中问题解决和判定目标是否实现的手 段之一。文章指出了整车综合主观评价的类型以及不同类型的主观评价在整车开发不同阶段的不同作用，明 确提出采用的评分标准及注意事项，并以国内某自主品牌的在产品开发过程中综合主观评价的应用为例说明。 同时，丰富的综合主观评价经验对产品目标的设定具有良好的指导意义。
a. 评价人员相对固定。在同一个项目开发 过程中，评价人员应该是固定的，这一条至关 重要。评价人员的高矮、胖瘦、性别、年龄等 不同，可能会导致较大的评价结果，为了提高 主观评价的一致性，评价人员应该相对固定。
b. 评价的车辆状态应满足产品开发阶段的 设计目标要求。为保证评价的有效性，车辆状
表 1 SAE（J1060）主观评价评分标准
则以产品工程验收为目的。
3 综合主观评价的评分标准及整车开发 中的注意事项
3.1 综合主观评价的评分标准 “SAE 建议执行的汽车主观标定尺度主要 应用于在给定的场地及道路上，对汽车进行不 同的操作并对该汽车进行评价” [2]。 SAE J1060（Subjective Rating Scale for Evaluation of Noise and Ride Comfort Characteristics Related to Motor Vehicle Tires）[3] 是一个与轮胎有关的噪音和驾驶舒适性主观评 价相关的评分标准。如表 1 所示。本标准采用 10 分制，5 分为分界线，低于 5 分为不可接受， 高于 5 分为可以接受。该标准在评价人员的维 度上提出了要求并给出了 1~10 分的得分释义。 目前，在汽车工业领域中，评价体系的种 类 较 多， 其 中 既 包 含 基 于 数 字（ 评 分） 的 体
------Lateral Dynamics of Commercial Vehicle Combinations-A Literature Survey(Vehicle System Dynami
As compared with single vehicle units, the road vehicle trains are characterized by some specific features among which particularly the following should be noted (Fig. 2): a ) jackknifing b) trailer swing c ) trailer lateral oscillations Under conditions of high vehicle velocities the articulated vehicles tend to yaw oscillations causing large amplitudes of lateral trailer oscillations. The combinations truck-trailer are more prone to lateral oscillations than the tractorsemitrailer sets. Under braking conditions on wet slippery roads the blocking of one or more wheels causes jackknifing or a swing of the semitrailer or trailer. The combination TS (tractor-semitrailer) appears to be more sensitive to these effects. The tractor has to transmit a part of the mass of the semitrailer and, consequently, also a part of the braking power indispensable for braking the semitrailer, and thus considerable forces are exerted at the kingpin connecting the tractor and the trailer. When the tractor rear wheels are blocked, the tractor swings around the kingpin. In case the semitrailer wheels get blocked, the semitrailer starts to yaw by skidding around the axis of the connecting mechanism (i.e. the fifth wheel). The lateral stability and braking performance of articulated vehicles are problematic, in particular for the following reason: owing to forces in the connection
CES疗法对焦虑症、创伤应激后遗症
Cranial electrotherapy stimulation (CES) is a noninva-sive, prescriptive medical treatment approved by the Food and Drug Administration for anxiety, insom-nia, and depression. About the size of a smart phone, a CES device uses electrodes typically placed on both ear lobes to send a low level (less than 1 mA), pulsed electrical current transcranially through the brain.1 An EEG analysis of 30 subjects who received one 20 min-ute CES treatment showed significant increases in alpha activity (increased relaxation) and decreases in delta ac-tivity (increased alertness) and theta activity (increased ability to focus attention).2 These changes induce a calm, relaxed, yet alert state. A recent functional magnetic resonance imaging (fMRI) study provides irrefutable proof that CES causes cortical brain deactivation in the midline frontal and parietal regions of the brain after one 20 minute treatment.3 Many psychiatric and sleep problems are thought to be caused by cortical activation from anxiety or attention disorders.4,5 Thus, the fMRI study provides additional insight into the mechanism for the effectiveness of CES.Since the early 2000s, Department of Defense (DoD) and Department of Veterans Affairs (VA) practitioners have prescribed CES for the treatment of anxiety, Post-traumatic stress disorder (PTSD), insomnia, depression, pain, and headaches.6,7 CES is classed as a tier II modal-ity for pain by The Army Surgeon General’s Pain Man-agement Task Force.8 When CES is used primarily for centralized pain, it also can decrease anxiety, insomnia, and depression, common comorbidities of pain. Tan and colleagues9compared service members’ and veterans’ preferences for 5 different therapeutic modalities for de-creasing stress, anxiety, insomnia, and pain at a veterans’ outpatient pain management clinic. Participants could choose which device they wanted to use and could use a different device if they chose at future clinic visits. Cra-nial electrotherapy stimulation was selected 73% of the time (n=144), while the other 4 stress reducing modali-ties were selected from 4% to 11% of the time (n=53).The purpose of this nonprobability, purposive sampling survey was to examine service members’ and veterans’ perceptions of the effectiveness and safety of CES for the treatment of anxiety, PTSD, insomnia, and depres-sion. It was part of a postmarketing surveillance report for the Food and Drug Administration.S AFETYCranial electrotherapy stimulation has an excellent safe-ty profile. Electromedical Products International, Inc (EPI) (Mineral Wells, TX) reported, based on a surveyMilitary Service Member and Veteran SelfReports of Efficacy of Cranial Electrotherapy Stimulation for Anxiety, Posttraumatic Stress Disorder, Insomnia, and DepressionDaniel L. Kirsch, PhD Jeffrey A. Marksberry, MDLarry R. Price, PhD Katherine T. Platoni, PsyDFrancine Nichols, PhD, RNA BSTRACTCranial electrotherapy stimulation (CES) is being prescribed for service members and veterans for the treatment of anxi-ety, posttraumatic stress disorder (PTSD), insomnia and depression. The purpose of this study was to examine service members’ and veterans’ perceptions of the effectiveness and safety of CES treatment. Service members and veterans (N=1,514) who had obtained a CES device through the Department of Defense or Veterans Affairs Medical Center from 2006-2011 were invited to participate in the web based survey via email. One hundred fifty-two participants returned questionnaires. Data were analyzed using descriptive statistics. Participants reported clinical improvement of 25% or more from using CES for anxiety (66.7%), PTSD (62.5%), insomnia (65.3%) and depression (53.9%). The majority of these participants reported clinical improvement of 50% or more. Respondents also perceived CES to be safe (99.0%). Those individuals who were not taking any prescription medication rated CES more effective than the combined CES and prescription medication group. CES provides service members and veterans with a safe, noninvasive, nondrug, easy to use treatment for anxiety, PTSD, insomnia, and depression that can be used in the clinical setting or self-directed at home.Financial DisclosureDr Kirsch is a major shareholder and officer of Electromedical Products International, Inc.Dr Marksberry is an employee of Electromedical Products International, Inc.46 /amedd_journal.aspxof Alpha-Stim CES users, that during 2007-2011 there was a total of 8,248,920 Alpha-Stim CES treatments (1,982,520 individual users treatments plus 6,266,400 in-office treatments by practitioners).Any side effects that occurred were mild and self-limiting. Reported side effects from all sources (EPI survey and the scientific literature) are 1% or less. These include dizziness, skin irritation at electrode sites, and headaches. Headaches and dizziness are usually associated with a current set-ting too high for the individual. The symptoms normally resolve when the current is decreased. Irritation at the electrode site can be decreased by using alternate sites for placement of electrodes. There have been no seri-ous adverse effects reported from using CES during 31 years on the market in the United States.10E FFICACYThe first scientific investigations of the effect of CES were performed by Russian scientists in the 1950s and 1960s. These studies focused on the effect of CES on inducing sleep. After the 1966 International Symposia for Electro-therapeutic Sleep and Electroanesthesia in Graz, Austria, American scientists began investigating the effectiveness of CES for treating anxiety, insomnia, depression, and substance abuse. Numerous publications on these topics appeared during the 1970s. These early studies were typ-ically small and had methodological limitations reflect-ing the research designs used in the time period during which they were conducted. However, the findings from the studies were consistently positive, showing CES de-creased anxiety, insomnia, and depression.1October – December 2014 47Over the past 15 years or so, the sophistication of the research designs and the quality of CES research im-proved substantially. Four randomized clinical trials (RCTs) investigated the efficacy of CES in treating state anxiety (Table 1).Three of the RCTs, used a double-blind sham controlled design, while one RCT used an investigator-blind de-sign. In these RCTs, the active CES group had signifi-cantly lower scores on state anxiety outcome measures than the sham or control group. Three RCTS on anxi-ety included Cohen’s d effect sizes that ranged from d=-0.60 (moderate) to d=-0.88 (high). Two open clini-cal studies found a significant difference from base-line to the endpoint of the study, with subjects having lower state anxiety scores at the endpoint of the study. Bystritsky and colleagues reported Cohen’s d effects sizes for 2 anxiety outcome measures: d=-1.53 on the Hamilton Anxiety Rating Scale (very high) and d=-0.75 (moderate) on the Four-Dimensional Anxiety and De-pression Rating Scale. Cranial electrotherapy stimula-tion was also shown to significantly decrease insomnia and depression (Table 2). All studies that investigated the effect of CES used reliable and valid scales for the measurement of outcomes.M ETHODSThe CES DeviceThe Alpha-Stim CES device with ear clips electrodes (0.5 Hz, 100–600 μA, 50% duty cycle, biphasic asym-metrical rectangular waves) was used in this study. Two electrodes that clip onto the ear lobes are used to send a mild electrical current through the brain. Treatment duration is a minimum of 20 minutes, but may be an hour at least one time daily. PTSD patients sometimes do a one hour CES treatment several times a day. Dur-ing acute PTSD episodes, patients may use CES for ex-tended periods of time (several hours) until symptoms decrease. While CES treatments should last a minimum of 20 minutes to achieve the desired effect, extended use of CES has no adverse side effects and is well tolerated. The QuestionnaireOne thousand five hundred fourteen (N=1,514) active duty service members and veterans who obtained an Alpha-Stim CES device through the DoD or VA medical centers from 2006 to 2011 were invited to participate in the web-based survey via email. Email addresses were obtained from prescription information for CES devices that was on file at EPI, the manufacturer of the device. All of the potential participants had been taught, using a standardized DoD or VA CES protocol, how to use self-directed CES at home. Participants either voluntarily chose to respond or not to respond to the questionnaire. Survey Monkey is the professional website (http://www. ) for survey research that was used for this study. Respondents completed the questionnaireon-line from September 1, 2011, to October 1, 2011. Of the 1,514 persons who were invited to participate in the survey, 152 (N) responses to the questionnaire were re-ceived, yielding a response rate of 10%. Although re-sponse rates vary by the population sampled, a response rate somewhere between 15% and 40% is common for web-based surveys.19,20The questionnaire contained 27 questions that covered demographic information, prescription medication use, and current exercise activity, as well as questions asking respondents to rate the effectiveness of CES technology for treating anxiety, PTSD, insomnia, and depression. A single item, 7-point Likert scale, which has established validity in the literature,21 was used to measure respon-dents’ perceived effectiveness of CES for anxiety, PTSD, insomnia, and depression. A sample question follows:If you are using CES for your PTSD, since starting CES, rate your improvement as:a. Worse (negative change)b. No change (0%)c. Slight improvement (1% to 24%)d. Fair improvement (25% to 49%)e. Moderate improvement (50% to 74%)f. Marked improvement (75% to 99%)g. Complete recovery (100%)R ESULTSData were analyzed using descriptive statistics. The characteristics of respondents, their use of CES technol-ogy, conditions for which they used CES, how often they used CES, and the length of time they had used CES are shown in Table 3. In addition to analysis of improve-ment-related questions on anxiety, PTSD, insomnia, and depression, questions were also interpreted in consid-eration of respondents’ use of prescription medication while using CES. There were 152 responses to the ques-tionnaire. Seven questionnaires did not include any ef-fectiveness and safety data. Thus, the valid sample size was N=145 for the analysis of these questions.Safety and Overall Perceived EfficacyOf the 145 persons responding to “Do you consider CES safe and effective?”, 99% reported that they view CES as safe and effective. Of the 1% of respondents (n=2) report-ing CES as unsafe or ineffective, the reasons given were (1) that they were never shown how to use CES properly, and (2) CES was ineffective for their medical condition.MILITARY SERVICE MEMBER AND VETERAN SELF REPORTS OF EFFICACY OF CRANIAL ELECTROTHERAPY STIMULATION FOR ANXIETY, POSTTRAUMATIC STRESS DISORDER, INSOMNIA, AND DEPRESSION48 /amedd_journal.aspxTHE ARMY MEDICAL DEPARTMENT JOURNALAnxietyThirty-one subjects (21.3%) reportedthat they were not currently usingCES for anxiety. One hundred four-teen subjects (combined sample tak-ing and not taking prescription medi-cations regularly) using CES for anx-iety responded to, “If you are usingCES for anxiety, since starting CES,rate your improvement as ….” Figure1 shows the results for the total group(N=114), the CES only no medica-tion group (n=26), and the CES andmedication group (n=88).Posttraumatic Stress DisorderFifty-six of the subjects (38.6%)reported not using CES for PTSD.Although PTSD is an anxiety dis-order, it was included as a separatevariable because of its importancein the treatment of service membersand veterans.22 Eighty-eight subjects(combined sample taking and nottaking prescription medication regu-larly) using CES for PTSD respondedto “If you are using CES for PTSD, since starting CES, rate your improvement as....” The findings of the total group (N=88), CES only no medication group (n=18), and CES and medication group (n=70) are shown in Fig-ure 2.InsomniaForty-six subjects (31.7%) reported that they did not use CES for insomnia. Ninety-eight subjects (combined sample taking and not taking prescription medication regularly) who used CES for insomnia responded to , “If you are using CES for insomnia, since starting CES, rate your improvement as….”The findings of the total group (N=98), CES only no medication group (n=21), and CES medication group (n=77) are shown in Figure 3. DepressionFifty-six subjects (38.6%)reported that they were not using CES for depression. Eighty-nine subjects (sub-jects combined sample taking and not taking prescrip-tion medication regularly) using CES for depression re-sponded to “If you are using CES for depression, since starting CES, rate your improvement as….” The find-ings of the total group (N=89), CES only no medication group (n=13), and CES medication group (n=76) are shown in Figure 4.Determining Important Clinical ImprovementDworkin and colleagues23 defined the criteria for impor-tant clinical improvement as follows:Improvement of moderate clinical importance is 30% to 49%, and improvement of substantial clinical impor-tance, the highest category, is 50% or more.While the criteria were developed to evaluate clini-cal trial outcomes on chronic pain, it provides a useful framework for the assessment of clinical improvement in anxiety, PTSD, insomnia, and depression as well. For this study, improvement of moderate clinical impor-tance was defined as 25% to 49% because the Likert scale which has been validated for use in measuring CES outcomes used 25% increments for categories. Using a conservative approach, the “Slight Improvement” (1% to 24%) category on the 2011 Alpha-Stim CES service members and Veterans survey was excluded, leaving the top 4 categories of “Fair Improvement” (25% to 49%), “Moderate Improvement” (50% to 74%), “Marked Im-provement” (75% to 99%) and “Complete Improvement” (100%). Participants reported clinical improvement of 25% or more from using CES for anxiety (66.7%), PTSD (62.5%), insomnia (65.3%), and depression (53.9%). The majority of service members and veterans who report-ed improvement of 25% or more had improvement inOctober – December 20144950/amedd_journal.aspxthe highest category, “substantial clinical importance,” (50% or more) on all variables: anxiety, PTSD, insomnia, and depression, as shown in Figure 5.Prescription Medication Use Of the 112 respondents who reported they took at least one prescription medication, 98 provided the name of the drug or condition for which it was taken. The number of prescription medications taken ranged from one to 11, with a mean of 2.6 and a median of 2.0. The typesof medications taken are shown in Table 4. Medica-tions that are used clinically for anxiety and depression were placed in the anxiety category.24 Medications used primarily for depression were placed in the depressionNo Change (0%)Slight (1%-24%)Fair (25%-49%)Moderate (50%-74%)Marked (75%-99%)9.7%7.7%32.5%14.0%15.4%19.2%26.9%21.6%10.2%20.2%25.0%23.7%30.8%34.1%9.1%Total GroupCES OnlyCES with Medications353025201510504017.1%16.7%14.8%22.7%22.9%22.2%22.2%24.3%23.9%31.8%31.4%33.3%5.6%6.8%4.3%Total GroupCES OnlyCES with MedicationsNo Change Slight Fair Moderate Marked 35302520151050MILITARY SERVICE MEMBER AND VETERAN SELF REPORTS OF EFFICACY OF CRANIAL ELECTROTHERAPYSTIMULATION FOR ANXIETY, POSTTRAUMATIC STRESS DISORDER, INSOMNIA, AND DEPRESSIONOctober – December 201451THE ARMY MEDICAL DEPARTMENT JOURNALcategory. Only those medications catego-rized as sedative hypnotics were placed in the insomnia category. Only those drugs speci fically approved for migraine head-aches were included in the migraine head-ache category, while all narcotic and other pain medications were included in the pain category, the subject of a separate paper.Comparison of CES with Drug Therapy Several of the most common drugs used to treat anxiety, PTSD, insomnia, depression, pain and headaches were compared to the findings of the Alpha-Stim service member and civilian surveys as shown in Figure 6. CES data from October 2011 Military Service Member and Veterans study (N=152) and the CES Ci-vilian User Survey (N=1,745) August 2011 were used. Pharmaceutical Survey Data were obtained from on-line WebMD user surveys (/drugs).The Alpha-Stim CES civilian survey was conducted in August 2011 from data collected between July 2006 and July 2011 (). The final sam-ple size from the civilian survey was 1,745 responders from a mail survey of 4,590 (38% useable responses). The WebMD drug survey asked civilians the question:“This medication has worked for me?” Respondents could choose to answer in one of 5 categories, with “1” being the lowest to “5” being the most effective. The sample size for the drugs selected ranged from N=62 to N=2,238. The CES survey questionnaire asked respondents to rate their improve-ment for a speci fic condition based on us-ing CES. Subjects could choose one of 7 categories: worse (negative change), no improvement (0%), slight improvement (1% to 24%), fair improvement (25% to 49%), moderate improvement (50% to74%), marked improvement (75% to 99%),and complete recovery (100%). While the questions in the WebMD and CES sur-veys were slightly different, all surveys asked questions about effectiveness. The WebMD data were changed to percentages and ranged from 1% to 100%. Two catego-ries were excluded from the CES survey as they were not included in the WebMD survey: worse (negative change) and no change (0%). The categories of “worse (negative change)” or “no change” re flected less than 1% of the responses in all instances (ie, on all questions).The upper 5 categories which ranged from 1% to 100%were used for comparison. The scale was the same, 1% to 100% for the data from all surveys. The comparison of the data from the 2 surveys is both appropriate and justi fiable based on the item content (ie, content/con-struct validity) and the format of item response.19C OMMENTIt is not surprising that the response rate to the survey was not higher. The majority of persons asked to par-ticipate in the survey were active duty service members.Table 4. Prescription Medi-cations Use by Condition.Anxiety 45.9%Depression 44.8%Pain 38.7%Insomnia 27.5%Hypertension 16.3%Seizure Control 11.2%Migraine Headache 9.0%Schizophrenia/Bipolar 9.0%19.5%15.6%14.3%21.4%18.1%16.3%18.4%20.4%22.0%23.8%23.4%21.4%42.9%Total GroupCES OnlyCES with Medications3530252040455052/amedd_journal.aspxMany email addresses may not have been valid because the survey covered a 6-year period and some may have moved, were discharged, or may have elected not to re-spond to the email if they were no longerusing CES. This study supports the ef-ficacy and safety of CES technology for the treatment of anxiety, PTSD, insomnia,and depression in service members andveterans. The findings are consistent with findings of previous research studies on CES. The effectiveness of CES in a mili-tary population was comparable to theeffectiveness of drugs commonly used in the treatment of the same conditions in the civilian population.Ninety-nine percent of subjects in this survey considered CES technology to be safe. An important safety bene fit of CES is that it leaves the user alert and relaxed after treatment, in contrast to drugs that can have adverse side effects and affect service members’ ability to function on missions that require intense focus and attention.25 This is particularly true in the combat theater of operations.The information on prescription medica-tion use provides a general view of drugsused by respondents for their speci fic condition(s). The findings that a high percentage of respondents took pre-scription medications for anxiety (45.9%), depression 13.5%10.5%30.1%25.0%22.5%23.0%17.1%18.0%15.4%26.3%24.7%21.0%21.4%23.1%3530252015Total GroupCES OnlyCES with Medications20.2%46.5%21.6%43.2%15.4%57.7%66.7%, N=7664.8%, n=5773.1%, n=1960.0%, n=4272.2%, n=1362.5%, N=5559.8%, n=4665.2%, N=6423.9%38.6%24.3%35.7%22.2%50.0%20.4%44.8%19.5%40.3%Total Group CES CES & Med Total Group CES & MedCES CES & Med Total Group Improved 25% to 49%Improved 50% or more MILITARY SERVICE MEMBER AND VETERAN SELF REPORTS OF EFFICACY OF CRANIAL ELECTROTHERAPYSTIMULATION FOR ANXIETY, POSTTRAUMATIC STRESS DISORDER, INSOMNIA, AND DEPRESSIONOctober – December 2014 53THE ARMY MEDICAL DEPARTMENT JOURNAL(44.8%), pain (38.7%), and insomnia (27.5%) is consistent with the literature.6,7The importance of controlling for medi-cation type and dosage in future CES studies is a valuable outcome of this sur-vey. It would also be helpful to classify the severity of illness of the subjects in future studies. While it appears that med-ication may in fluence the effectiveness of CES technology, it is possible that respon-dents taking prescription medication had far more serious symptoms and medical and psychological conditions than the no medication group. The group sizes were group was considerably smaller, ranging from 13 to 26 subjects, in comparison to the CES medication groups that ranged from 53 to 88 subjects. This may account for the differences in scores between the groups. However, the effect of medication appears to be an important confounding variable when investigating the ef ficacy of CES.C ONCLUSIONSThe results of this survey are compelling and provide the foundation for a rigorous placebo controlled RCT that investigates the effectiveness of CES for treating anx-iety, PTSD, insomnia, and depression in service mem-bers and veterans. In addition, this study also examines the in fluence of medication on CES ef ficacy outcomes. This study provides evidence that service members and veterans perceived CES as an effective treatment for anxiety, PTSD, insomnia, and depression. CES can be used either as an adjunct to pharmaceutical therapy or as a standalone therapy, providing service members and veterans with a safe, noninvasive, nonpharmacologic treatment for anxiety, PTSD, insomnia, and depression that can be used in the clinic setting, including the war-time theater clinics, or self-directed at home.R EFERENCES1.Kirsch D. The Science Behind Cranial Electro-therapy Stimulation . Edmonton, Alberta, Canada: Medical Scope Publishing; 2002.2.Kennerly R. QEEG analysis of cranial electro-therapy: a pilot study [abstract]. J Neurother . 2004;8(2):112-113. Available at: /wp-content/uploads/CES_Research/kennerly-qeeg.pdf. Accessed July 11, 2014.3.Feusner JD, Madsen S, Moody TD, Bohon C, Hem-bacher E, Bookheimer SY, Bystritsky A. Effects of cranial electrotherapy stimulation on resting state brain activity. Brain Behav . 2012;2(3):211-220.4.Y assa MA, Hazlett RL, Stark CE, Hoehn-Saric R. Functional MRI of the amygdala and bed nucleus of the stria terminalis during conditions of uncer-tainty in generalized anxiety disorder. J Psychiatr Res, 2012;46(8):1045-1052.5.Bonnet MH, Arand DL. Hyperarousal and in-somnia: state of the science. Sleep Med Rev. 2010;14(1):9-15.6.Bracciano AG, Chang WP , Kokesh S, Martinez A, Moore K. Cranial electrotherapy stimulation in the treatment of posttraumatic stress disorder. a pilot study of two military veterans. J Neurother . 2012;16(1):60-69.7.Tan G, Rintala D, Jensen MP, et al. Ef ficacy of cranial electrotherapy stimulation for neuro-pathic pain following spinal cord injury. a multi-site randomized controlled trial with a secondary 6-month open-label phase. J Spinal Cord Med . 2011;34(3):285-296.8.Pain Management Task Force: Final Report . Wash-ington, DC: US Dept of the Army, Of fice of the Surgeon General; May 2010.70%67%83%56%78%84%68%81%Sonata (n=62) 462) 163)98)1198)2028) 311)89)Service MembersCiviliansWebMD Survey9. Tan G, Dao TK, Smith DL, Robinson A, JensenMP. Incorporating complementary and alterna-tive medicine (CAM) therapies to expand psycho-logical services to veterans suffering from chronicpain. Psychol Serv. 2010;7(3):148-16110. Petitioner Presentation to Neurological DevicesPanel for Reclassification of Alpha-Stim CES De-vices From Class III to Class II. Mineral Wells, TX:Electromedical Products International, Inc; Febru-ary 10, 2012. Available at: http://www.alpha-stim.com/wp-content/uploads/EPIs-fda-presentation.pdf. Accessed July 11, 2014.11. Kim HJ, Kim WY, Lee YS, Chang M, Kim JH, ParkYC. The effect of cranial electrotherapy stimula-tion on preoperative anxiety and hemodynamic re-sponses. Korean J Anesthesiol. 2008;55(6):657-661.12. Cork RC, Wood PM, Norbert C, Shepherd JE, PriceL. The effect of cranial electrotherapy stimulation(CES) on pain associated with fibromyalgia. Inter-net J Anesthesiol[serial online]. 2004;8(2). Avail-able at: /IJA/8/2/12659. AccessedJuly 11, 2014.13.Lichtbroun AS, Raicer MC, Smith RB. The treat-ment of fibromyalgia with cranial electrotherapystimulation. J Clin Rheumatol. 2001;7(2):72-78. 14. Winick RL. Cranial electrotherapy stimulation(CES): a safe and effective low cost means ofanxiety control in a dental practice. Gen Dent.1999;47(1):50-55.15. Bystritsky A, Kerwin L, Feusner J. A pilot studyof cranial electrotherapy stimulation for gen-eralized anxiety disorder. J Clin Psychiatry.2008;69:412-417.16. Overcash SJ. Cranial electrotherapy stimulationin patients suffering from acute anxiety disorders.Am J Electromedicine. 1999;16(1):49-51.17. Taylor AG, Anderson JG, Riedel SR, Lewis JE,Kinser PA, Bourguignon C. Cranial electrical stim-ulation improves symptoms and functional statusin individuals with fibromyalgia. Pain Manag Nurs.2013;14(4):327-335.18. Mellon RR, Mackey W: Reducing sheriff’s officers’symptoms of depression using cranial electrothera-py stimulation (CES): a control experimental study.Correct Psychologist. 2009;41(1):9-15.19. Dillman D. Mail and Internet Surveys. 2nd ed.Hoboken, NJ: John Wiley & Sons; 2007.20. Czaja R, Blair J. Designing Surveys: A Guide toDecisions and Procedures. 2nd ed. Thousand Oaks,CA: Pine Forge Press; 2005.21. Davey HM, Barratt AL, Butow PN, Deeks JJ. Aone-item question with a Likert or visual analogscale adequately measured current anxiety. J ClinEpidemiol. 2007;60(4):356-360.22. US Department of Veterans Affairs, National Cen-ter for PTSD. Available at: /.Accessed May 10, 2012.23.Dworkin RH, Turk DC, Wyrwich KW, et al. Inter-preting the clinical importance of treatment out-comes in chronic pain clinical trials: IMMPACTrecommendations. J Pain. 2008;9(2):105-121.24. Mental Health Indications: What medications areused to treat anxiety disorders?. National Insti-tute of Mental Health Website; 2008. Availableat: /health/publications/mental-health-medications/index.shtml. AccessedJuly 11, 2014.25. Tilghman A, McGarry B. Medicating the military:use of psychiatric drugs has spiked; concerns surfaceabout suicide, other dangers. Army Times. March 17,2010. Available at: /art i c l e/20100317/N E W S/3170315/M e d icating-military. Accessed July 11, 2014.A UTHORSDr Kirsch is President, American Institute of Stress, Fort Worth, Texas.Dr Price is Director of Faculty Research and Professor of Psychometrics and Statistics, College of Education and Department of Mathematics, Texas State University, San Marcos, Texas.Dr Nichols is a research consultant and retired Professor, Georgetown University, Washington, DC.Dr Marksberry is Director, Science and Education, Elec-tromedical Products International, Inc, Minerals Wells, Texas.When this article was written, COL Platoni was Army Reserve Psychology Consultant to the Chief, US Army Medical Services Corp. Now retired from the Army Reserve, Dr Platoni is in private practice in Centerville, Ohio.MILITARY SERVICE MEMBER AND VETERAN SELF REPORTS OF EFFICACY OF CRANIAL ELECTROTHERAPY STIMULATION FOR ANXIETY, POSTTRAUMATIC STRESS DISORDER, INSOMNIA, AND DEPRESSION54 /amedd_journal.aspx。
Shockley-Quisser-limit
An Investigation of Shockley-Queisser Limit of Single p-n Junction Solar Cells2.997 Project Report Bolin Liao Wei-Chun HsuAbstractShockley-Queisser limit has long been recognized as the theoretical limit of the efficiency of an ideal single p-n junction solar cell, which is based on the most fundamental physical laws.Despite its profound significance and widely accepted concepts, we found ambiguities in the derivation of the Shockley-Queisser limit in their seminal paper published in 1961. In this project, we look into the basic physical principles of the p-n junction solar cells, move on to clarify the details of the derivation process and finally try to give out a contemporary interpretation of this limit.1. IntroductionThe solid-state solar energy conversion technology utilizing semiconductor solar cells has become an important candidate for the next generation energy exploitation. By the end of 2006,the total installed PV capacity since 1991 had reached more than 7 GW worldwide [1]. In the meantime, how to further improve the efficiency of photovoltaic solar cells has become an essential issue.The most prevalent bulk material for solar cells is doped silicon with n-type or p-type impurities.In 1961, William Shockley and Hans J. Queisser showed that a single p-n junction solar cell hasa theoretical limit of efficiency, which is known as Shockley-Queisser limit or the detailed balance limit [2]. Instead of predicting the efficiency limit based on empirical data and semi-empirical modeling, Shockley and Queisser built up their insight purely on the basis of the detailed balance principle, which is deeply rooted in the second law of thermodynamics. Thislimit is one of the most fundamental theories to solar energy production, and is considered to be one of the most important contributions in the field. In addition to the situation with a specific semiconductor model, R. Ross and T. Hsiao generalized this limit to all photochemical solar energy conversion systems in 1977[4]. In 1980, C. Henry [3] further extended the approach of Shockley and Queisser along 4 directions, 1) using an intuitive graphical analyzing method to show the magnitudes of the intrinsic losses, 2) considering both single and multiple energy gap cells, 3) using the actual terrestrial solar spectrum instead of a blackbody spectrum, 4) considering the effect of concentrated sunlight, and finally reached the practical efficiency limitof an applicable conversion device.Miscellaneous factors are involved with the efficiency issue of a photochemical solar energy converter. Among these factors, some are not intrinsic, thus can be eliminated theoretically by improved fabrication technology and optimized device design. Examples include the series resistance and reflection loss, etc. Other than these factors, there exists another kind of loss factors, which are either intrinsic to the device characteristics, or determined by fundamental physical laws, which thus cannot be avoided by advanced manufacturing techniques or other methods. It is exactly these intrinsic losses that set the limit of the efficiency for a photochemical solar energy converter. The most important loss due to the device characteristics is the energy gap for photon absorption. Incident photons with energy higher than the energy gap can be absorbed, exciting electrons to higher electronic bands, while those with lower energy are not absorbed, either reflected or transmitted. Moreover, the portion of the absorbed energy greater than the energy gap is dissipated in the process of electrons relaxation by the form of heat, resulting in further loss of the absorbed energy. After absorption, not all absorbed energy can be converted into useful power, which is the electrical power in the case of a solar cell. Only the free energy (the Helmholtz potential) that is not associated with entropy can be extracted from the device, which is determined by the second law of thermodynamics. In the situation of a p-n junction solar cell, this effect manifests itself in the radiative recombination process, the inverse process of photon absorption. In equilibrium, any part of a system must emit exactly the same energy as that absorbed in every direction, at every moment and every frequency interval, which is known as the detailed balance principle, inferred by the second law of thermodynamics. Furthermore, the inevitable irreversibility when actual load is connected will lower the achievable power under the maximum available free energy.To recapitulate, the main factors considered by Shockley and Queisser to derive the limit efficiency include the energy gap, the radiative recombination and the load matching loss. In this report we will discuss these factors in detail and try to interpret the physical meaning behind the effects. At the last of the report, the discussion is extended to taking other non-ideal factors in practical application into account. Using the same notations as Shockley and Queisser’s original paper, the total efficiency of a single p-n junction solar cell can be expressed as the product of four terms:( ) ( ) ( )is called “ultimate efficiency”, only taking into consideration the loss due to the energy gap. denotes the ratio of the operational output voltage to the energy gap.is the impedance matching factor, and the probability that incident photons with solar cell surrounded by the black body with temperature will produce a hole-electron pair, which is assumed unity when the limit efficiency achieved. We will discuss and derive how these factors come from in the following sections.2. Energy Gap LossBefore we start to introduce several factors of the total efficiency of the solar cell, notations and parameters are defined as follows:: Planck's constant = 6.626068 × 10-34 ;: Boltzmann constant = 1.3806503 × 10-23: The electronic charge: Temperature of sun: Temperature of solar cell: Energy gap of the solar cell, and the cut-off frequencyIn the original paper, the authors use equivalent voltages to express , , and for convenience:; ;Also defined are two ratios among , , and .;The ultimate efficiency describes that when photons are incident on a solar cell, only photons with energy larger than the band gap of the solar cell will excite electrons, thus be absorbed. The absorbed electrons only contribute the amount of energy as the band gap, and the absorbed energy can be totally converted into electrical power, by the means of a output voltage , the equivalent voltage of the energy gap. Following this concept, Shockley and Queisser set a situation as Fig.1 to derive this efficiency. We assume a spherical black body with temperature surrounds a spherical pn junction with temperature (this condition is to ensure the there is no radiative recombination inside and the output voltage is exactly . We will discuss this later). Therefore, the ultimate efficiency can be calculated as the ratio of generated photon energy to input power.( )where is the number of quanta of frequency greater than incident per unit area per unit time for black body radiation of temperature , and the total incident power.Figure 1 demonstration of ultimate efficiency situationand can be calculated from the Plank’s law of blackbody radiation:( ) ∫ ∫∫∫Therefore, the ultimate efficiency can be expressed as a function of :∫∫ ∫ ∫ ( ) We plot the efficiency versus the energy gap as follow (consider the sun as a source of blackbody radiation with temperature 5800K):Figure 2 dependence of the ultimate efficiency on energy gapsThe maximum efficiency is 43.96%, corresponding to an energy gap around 1.08 eV.3. Detailed Balance PrincipleNow we consider a more realistic situation, depicted in Fig.3. Two factors will be taken into account, namely, the view factor of the sun seen from the solar cell, and the loss due to radiative recombination.Assume and are the surface areas of the sun and the solar cell plate respectively. Then the projected area of on the radiation sphere of the sun is , thus the view factor from theUltimate Efficiency Vs. Energy GapEnergy Gap (eV)U l t i m a t e E f f i c i e n c y , (%)sun to the solar cell is , where L is the distance between the sun and the earth. So the actual incident power is(*(*()where R is the radius of the sun, the solid angle subtended by the sun. We define the geometrical factor to lump the all geometric effects:Similarly, the generation rate of electron-hole pairs due to incident solar radiation can be calculated as:where is the probability of an incident photon exciting an electron-hole pair.Figure 3 demonstration of a realistic modelNow we evaluate the crucial point in deriving the Shockley-Queisser limit: the recombination process. Not all excited electron-hole pairs can be extracted by connected load, and a large portion of them will recombine and lose the energy. Generally two kinds of recombination processes will happen inside a solar cell: radiative recombination and non-radiative recombination. The latter one can be eliminated theoretically by ideal fabrication conditions, while the former one is intrinsic due to the detailed balance principle. The detailed balance principle states that: in equilibrium, any part of a system must emit exactly the same energy as it absorbs, in every direction, at every frequency and time interval. In other words, wherever absorption happens, emission (thus radiative recombination) must happen.To determine the radiative recombination rate, we first imagine the solar cell in equilibrium with a surrounding blackbody radiation field with temperature (without incident solar radiation). Due to the detailed balance principle, the recombination rate must be the same everywhere in thewhole system, including at the surface of the solar cell, where the recombination rate is just equal to the incident radiation exciting rate:( ) ∫and is the probability of an incident photon exciting an electron-hole pair, and the coefficient 2is because both sides of the solar cell can absorb the incident radiation. Then the radiative recombination rate inside the solar cell is just everywhere.Now we expose the solar cell to solar radiation, and the equilibrium inside the cell is disrupted. Excessive electron-hole pairs are generated due to the incident radiation, and the built-inpotential in the p-n junction will drive the excessive carriers to either side of the cell, resulting in the split of the single Fermi-level in equilibrium to quasi-Fermi levels in non-equilibrium in both sides. The energy band diagrams before and after exposure to solar radiation are shown in Fig.4.Figure 4 Energy Band Diagram in equilibrium and non-equilibriumThe relations between the quasi-Fermi level and non-equilibrium carrier concentration are given as:andTo determine the open-circuit voltage that can be obtained, we consider the question that how much the energy of the electron-hole gas system is lowered by removing an electron-hole pair out of the system. If just the internal energy is considered, the answer should be , the energy possessed by an electron-hole pair. But it is not correct. Since there will be an entropy change during this process, the system must exchange some heat with the environment. According to Ross[5], this entropy change is:Then the total energy change is:which is not very surprising, since this is exactly the change of the Helmholtz free energy. So instead of, the open circuit voltage that can be obtained is just.In non-equilibrium condition, the radiative recombination rate will deviate from the equilibrium value. As a first-order approximation, we assume the recombination rate is proportional to the product of the concentrations of electrons and holes. So the non-equilibrium recombination rate can be written as:(*where is the voltage between the two electrodes, as analyzed above. It is obvious to observe that if there are more photons absorbed by the solar cell, the will be larger, and the voltage will become larger as well.After external load is connected, the output voltage will drop below the open-circuit voltage. To obtain the I-V characteristics of the solar cell, we consider the balance among miscellaneous generation and recombination mechanisms and the external current:where R(0) and R(V) are the generation rate and recombination rate due to non-radiative processes. To avoid detailed consideration of non-radiative processes, a fraction coefficient is defined as the ratio of the radiative recombination rate to total recombination rate:We can now obtain the current-voltage relation:[ (*][ (*]where is the short circuit current, and is the reverse saturation current. By letting total current be zero, the open circuit voltage can also be derived:( *( *(*(*(∫∫)where is defined as the lumped factor of the radiative fraction , geometrical factor , and the exciting probabilities and :Assume an energy gap E g=1.12eV, and , which is the ideal condition, we plot the open circuit voltage as a function of operational temperature T c:Figure 5We can tell from this plot that when T c approaches zero, the open circuit voltage approaches V g =1.12V , which is the largest achievable open circuit voltage. This result can be easily verified by applying L'Hôpital's rule to the expression of the open voltage to get the limit behavior. Accordingly we can define a dimensionless ratio between the open-circuit voltage and the band gap voltage as:( )( ∫∫) ( ∫∫)If assume T c =300K ,, we can plot this factor as below:Figure 6Open Circuit Voltage Vs. Operational TemperatureOperational Temperature Tc (K)O p e n C i r c u i t V o l t a g e , V100Open Circuit Voltage Ratio Vs. Energy GapEnergy Gap (eV)O p e n C i r c u i t V o l t a g e R a t i o , (%)4. Impedance Matching FactorIn a practical device, the maximal values of current and voltage, namely I sh and V op cannot be achieved simultaneously. Instead, an optimized load can gain an optimized power, which is only a portion of the product of I sh and V op, as shown in Fig.7.Figure 7 the practical achievable powerBefore proceeding to consider the optimal load, we first assume the solar cell has not yet been connected to any load, the nominal efficiency is defined as the ratio of open-circuit voltage times the short-circuit current to the incident power.If the generation rate of electron-hole pairs by the sun is large enough, we can assume:( ) ( )Now we define an impedance matching factor as:( )Then the practical efficiency can be written as:( ) ( ) ( )To find the optimal power, we follow the extremum-finding routine:(*(*This is a transcendental equation, and can be solved numerically. Assume T c =300K ,, the impedance matching factor ( ) can be plotted as follow:Figure 8Now that we have all the ingredients to obtain the practical efficiency limit of a single p-n junction solar cell, the Shockley-Quesser limit can be plotted as below, with T c =300K,400K,500K , and.Figure 9The maximum efficiency is around 30% with an energy gap of 1.28 eV when T c =300K.100Impedance matching factor Vs. Energy GapI m p e d a n c e m a t c h i n g f a c t o r , %Energy Gap, eVEnergy Gap, eVE f f i c i e n c y , %Schockley-Queisser LimitReferences:[1] Electric Power Reach Institute (EPRI). An EPRI Technology Innovation White Paper. Dec. 2007. /docs/SEIG/1016279_Photovoltaic_White_Paper_1207.pdf[2] Shockley, W., Queisser, H.J., Journal of Applied Physics, 32, 510 (1961).[3] Henry, C.H., Journal of Applied Physics, 51, 4494 (1980)[4] Ross, R.T., Hsiao, T.L., Journal of Applied Physics, 48, 4783 (1977)[5] Ross, R.T., Journal of Applied Physics, 46, 4590 (1967)。
英文文献-溶胶-凝胶法制备LiFePO4改进其电化学性能
Electrochimica Acta 92 (2013) 248–256Contents lists available at SciVerse ScienceDirectElectrochimicaActaj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /e l e c t a c taGel-combustion synthesis of LiFePO 4/C composite with improved capacity retention in aerated aqueous electrolyte solutionMilica Vujkovi´c a ,Ivana Stojkovi´c a ,Nikola Cvjeti´canin a ,Slavko Mentus a ,b ,∗,1a University of Belgrade,Faculty of Physical Chemistry,P.O.Box 137,Studentski trg 12-16,11158Belgrade,Serbia bThe Serbian Academy of Sciences and Arts,Kenz Mihajlova 35,11158Belgrade,Serbiaa r t i c l ei n f oArticle history:Received 2October 2012Received in revised form 3January 2013Accepted 5January 2013Available online 11 January 2013Keywords:Aqueous rechargeable Li-ion battery Galvanostatic cycling Gel-combustion Olivine LiFePO 4LiFePeO 4/C compositea b s t r a c tThe LiFePO 4/C composite containing 13.4wt.%of carbon was synthesized by combustion of a metal salt–(glycine +malonic acid)gel,followed by an isothermal heat-treatment of combustion product at 750◦C in reducing atmosphere.By a brief test in 1M LiClO 4–propylene carbonate solution at a rate of C/10,the discharge capacity was proven to be equal to the theoretical one.In aqueous LiNO 3solu-tion equilibrated with air,at a rate C/3,initial discharge capacity of 106mAh g −1was measured,being among the highest ones observed for various Li-ion intercalation materials in aqueous solutions.In addition,significant prolongation of cycle life was achieved,illustrated by the fact that upon 120charg-ing/discharging cycles at various rates,the capacity remained as high as 80%of initial value.The chemical diffusion coefficient of lithium in this composite was measured by cyclic voltammetry.The obtained val-ues were compared to the existing literature data,and the reasons of high scatter of reported values were considered.© 2013 Elsevier Ltd. All rights reserved.1.IntroductionThanks to its high theoretical Coulombic capacity (170mAh g −1)and environmental friendliness,LiFePO 4olivine became a desir-able cathodic material of Li-ion batteries [1,2],competitive to other commercially used cathodic materials (LiMnO 4,LiCoO 2).As evidenced in non-aqueous electrolyte solutions,a small vol-ume change (6.81%)that accompanies the phase transition LiFePO 4 FePO 4enables Li +ion insertion/deinsertion reactions to be quite reversible [1–3].The problem of low rate capability,caused by low electronic conductivity [4,5],was shown to be solv-able to some extent by reduction of mean particle size [6].Further improvements in both conductivity and electrochemical perform-ances were achieved by forming composite LiFePO 4/C,where in situ produced carbon served as an electronically conducting con-stituent [5,7–27].Ordinarily,both in situ formed carbon and carbon black additive,became unavoidable constituent of the LiFePO 4-based electrode materials [28–37].Zhao et al.[27]reported that Fe 2P may arise as an undesirable product during the synthesis of LiFePO 4/C composite under reducing conditions,however,other authors found later that this compound may contribute positively∗Corresponding author at:University of Belgrade,Faculty of Physical Chemistry,P.O.Box 137,Studentski trg 12-16,11158Belgrade,Serbia.Tel.:+381112187133;fax:+381112187133.E-mail address:slavko@ffh.bg.ac.rs (S.Mentus).1ISE member.to the electronic conductivity and improve the electrochemical per-formance of the composite [28–30].Severe improvement in rate capability and capacity retention was achieved by partial replace-ment of iron by metals supervalent relative to lithium [31–37].Thus one may conclude that the main aspects of practical applica-bility of LiFePO 4in Li-ion batteries with organic electrolytes were successively resolved.After the pioneering studies by Li and Dahn [38,39],recharge-able Li-ion batteries with aqueous electrolytes (ARLB)attracted considerable attention [40–50].The first versions of ARLB’s,suf-fered of very low Coulombic utilization and significantly more pronounced capacity fade relative to the batteries with organic electrolyte,regardless on the type of electrode materials [43].For the first time,LiFePO 4was considered as a cathode material in ARLB’s by Manickam et al.in 2006[44].He et al.[46],in an aqueous 0.5M Li 2SO 4solution,found that LiFePO 4displayed both a surprisingly high initial capacity of 140mAh g −1at a rate 1C and recognizable voltage plateau at a rate as high as 20C,which was superior relative to the other electrode materials in ARLB’s.Recently,the same authors reported a high capacity decay in aer-ated electrolyte solution,amounting to 37%after only 10cycles [48].In the same study,they demonstrated qualitatively by a brief cyclovoltammetric test,that a carbon layer deposited from a vapor phase over LiFePO 4particles,suppressed the capacity fade [48].Inspired by the recent discoveries about excellent rate capa-bility [46]but short cycle life [48]of LiFePO 4in aerated aqueous solution,we attempted to prolong the cycle life by means of protecting carbon layer over the LiFePO 4particles.Therefore we0013-4686/$–see front matter © 2013 Elsevier Ltd. All rights reserved./10.1016/j.electacta.2013.01.030M.Vujkovi´c et al./Electrochimica Acta92 (2013) 248–256249synthesized LiFePO4/C composite by a fast and simple glycine-nitrate gel-combustion technique.This method,although simpler than a classic solid state reaction method combined with ball milling[44,48],was rarely used for LiFePO4synthesis[19,27].It yielded a porous,foamy LiFePO4/C composite,easily accessible to the electrolyte.Upon the fair charging/discharging performance was confirmed by a brief test in organic electrolyte,we examined in detail the electrochemical behavior of this material in aqueous electrolyte,by cyclic voltammetry,complex impedance and cyclic galvanostatic charging/discharging methods.In comparison to pure LiFePO4studied in Ref.[48],this composite displayed markedly longer cycle life in aerated aqueous solutions.The chemical dif-fusion coefficient of lithium was also determined,and the reasons of its remarkable scatter in the existing literature were considered.2.ExperimentalThe LiFePO4/C composite was synthesized using lithium nitrate, ammonium dihydrogen phosphate(Merck)and iron(II)oxalate dihydrate(synthesized according to the procedure described else-where[51])as raw materials.Our group acquired the experience in this synthesis technique on the examples of spinels LiMn2O4 [52]and LiCr0.15Mn1.85O4[53],where glycine served as both fuel and complexing/gelling agent to the metal ions.A stoichiometric amount of each material was dissolved in deionized water and mixed at80◦C using a magnetic stirrer.Then,first glycine was added into the reaction mixture to provide the mole ratio of glycine: nitrate of2:1,and additionally,malonic acid(Merck)was added in an amount of60wt.%of the expected mass of LiFePO4.The role of malonic acid was to decelerate combustion and provide con-trollable excess of carbon[14].After removing majority of water by evaporation,the gelled precursor was heated to initiate the auto-combustion,resulting in aflocculent product.The combustion product was heated in a quartz tube furnacefirst at400◦C for3h in Ar stream,and then at750◦C for6h,under a stream of5vol.%H2in Ar.This treatment consolidated the olivine structure and enabled to complete the carbonization of residual organic matter.The VO2powder prepared by hydrothermal method was used as an active component of the counter electrode in the galvanostatic experiments in aqueous electrolyte solution.The details of the syn-thesis and electrochemical behavior of VO2are described elsewhere [54,55].The considerable stoichiometric excess of VO2was used,to provide that the LiFePO4/C composite only presents the main resis-tive element,i.e.,determines the behavior of the assembled cell on the whole.The XRD experiment was performed using Philips1050diffrac-tometer.The Cu K␣1,2radiation in15–70◦2Ârange,with0.05◦C step and2s exposition time was used.The carbon content in the composite was determined by its com-bustion in theflowing air atmosphere,by means of thermobalance TA SDT Model2090,at a heating rate of10◦C min−1.The morphology of the synthesized compounds was observed using the scanning electron microscope JSM-6610LV.For electrochemical investigations,the working electrode was made from LiFePO4/C composite(75%),carbon black-Vulcan XC72 (Cabot Corp.)(20%),poly(vinylidenefluoride)(PVDF)binder(5%) and a N-methyl-2-pyrrolidone solvent.The resulting suspension was homogenized in an ultrasonic bath and deposited on electron-ically conducting support.The electrode was dried at120◦C for 4h.Somewhat modified weight ratio,85:10:5,and the same drying procedure,were used to prepare VO2electrode.The non-aqueous electrolyte was1M LiClO4(Lithium Corpo-ration of America)dissolved in propylene carbonate(PC)(Fluka). Before than dissolved,LiClO4was dried over night at140◦C under vacuum.The aqueous electrolyte solution was saturated LiNO3solution.The cyclic voltammetry and complex impedance experiments were carried out only for aqueous electrolyte solutions,by means of the device Gamry PCI4/300Potentiostat/Galvanostat.The three electrode cell consisted of a working electrode,a wide platinum foil as a counter electrode,and a saturated calomel electrode(SCE) as a reference one.The experiments were carried out in air atmo-sphere.The impedance was measured in open-circuit conditions, at various stages of charging and discharging,within the frequency range10−2−105Hz,with7points per decade.Galvanostatic charging/discharging experiments were carried out in a two-electrode arrangement,by means of the battery testing device Arbin BT-2042,with two-terminal connectors only.In the galvanostatic tests in non-aqueous solution,working electrode was a2×2cm2platinum foil carrying2.3mg of compos-ite electrode material(1.5mg of olivine),while counter electrode was a2×2cm2lithium foil.The cell was assembled in an argon-filled glove box and cycled galvanostatically within a voltage range 2.1–4.2V.The galvanostatic tests in the aqueous electrolyte solution were carried out in a two-electrode arrangement,involving3mg of cathodic material,as a working electrode,and VO2in a multi-ple stoichiometric excess,as a counter electrode.According to its reversible potential of lithiation/delithiation reaction[55],VO2per-formed as an anode in this cell.The4cm2stainless steel plates were used as the current collectors for both positive and negative electrode.The cell was assembled in room atmosphere,and cycled within the voltage window between0.01and1.4V.3.Result and discussion3.1.The XRD,SEM and TG analysis of the LiFePO4/C compositeFig.1shows the XRD patterns of the composite LiFePO4/C pre-pared according to the procedure described in the Experimental Section.As visible,the diffractogram agrees completely with the one of pure LiFePO4olivine,found in the JCPDS card No.725-19. The narrow diffraction lines indicate complete crystallization and relatively large particle dimensions.On the basis of absence of diffraction lines of carbon,we may conclude that the carbonized product was amorphous one.Fig.2shows the SEM images of the LiFePO4/C composite at two different magnifications.Theflaky agglomerates,Fig.2left,with apparently smooth surface and low tap density,are due to a partial liquefaction and evolution of gas bubbles during gel-combustion procedure.These agglomerates consist of small LiFePO4/CFig.1.XRD patterns of LiFePO4/C composite in comparison to standard crystallo-graphic data.250M.Vujkovi´c et al./Electrochimica Acta 92 (2013) 248–256Fig.2.SEM images of LiFePO 4/C composite at two different magnification,20000×and 100000×.composite particles visible better at higher magnification,Fig.2,ly at the magnification of 100,000×,one may see that the size of majority of composite particles was in the range 50–100nm.The mean particle diameter,2r,as per SEM microphotograph amounted to 75nm.This analysis evidences that the gel-combustion method may provide nanodisprsed particles,desirable from the point of view of rate capability.For instance,Fey et al.[16]demonstrated that particle size reduction from 476to 205nm improved the rate capa-bility of LiFePO 4/C composite in organic electrolyte,illustrated by the increase of discharge capacity from 80mAh g −1to 140mAh g −1at discharging rate 1C.Also,carbon matrix prevented particles from agglomeration providing narrow size distribution,contrary to often used solid state reaction method of synthesis,when sintering of ini-tially nanometer sized particles caused the appearance of micron sized agglomerates [22].The SEM microphotograph (Fig.2)alone did not permit to rec-ognize carbon constituent of the LiFePO 4/C composite.However,carbonized product was evidenced,and its content measured,by means of thermogravimetry,as described elsewhere [9].The dia-gram of simultaneous thermogravimetry and differential thermal analysis (TG/DTA)of the LiFePO 4/C composite performed in air is presented in Fig.3.The process of moisture release,causing a slight mass loss of 1%,terminated at 150◦C.In the temperature range 350–500◦C carbon combustion took place,visible as a drop of the TG curve and an accompanying exothermic peak of the DTA curve.However,the early stage of olivine oxidation merged to some extent with the late stage of carbon combustion,and therefore,the minimum of the TG curve,appearing at nearly 500◦C,was not so low as to enable to read directly the carbon content.Fortunately,as proven by XRD analysis,the oxidation of LiFePO 4at tempera-ture exceeding 600◦C,yielded only Li 3Fe 2(PO 4)3and Fe 2O 3,whatFig.3.TGA/DTA curve of LiFePO 4/C under air flow at heating rate of 10C min−1.corresponded to the relative gain in mass of exactly 5.07%[9].Therefore,the weight percentage of carbonaceous fraction in the LiFePO 4/C composite was determined as equal to the difference between the TG plateaus at temperatures 300and 650◦C,aug-mented for 5.07%.According to this calculation the carbon fraction amounted to 13.4wt.%,and by means of this value,the electro-chemical parameters discussed in the next sections were correlated to pure LiFePO 4.Specific surface area of LiFePO 4,required for the measurement of diffusion constant,was determined from SEM image (Fig.2).Assuming a spherical particle shape and accepting mean particle radius r =37.5nm,the specific surface area was estimated on the basis of equation [17,22,45,46]:S =3rd(1)where the bulk density d =3.6g cm −3was used .This calculation resulted in the value S =22.2m 2g −1.In this calculation the contri-bution of carbon to the mean particle radius was ignored,however the error introduced in such way is more acceptable than the error which may arise if standard BET method were applied to the com-posite with significant carbon ly,due to a usually very developed surface area of carbon,the measured specific sur-face may exceed many times the actual surface area of LiFePO 4.3.2.Electrochemical measurements3.2.1.Non-aqueous electrolyte solutionIn order to compare the behavior of the synthesized LiFePO 4/C composite to the existing literature data,available predominantly for non-aqueous solutions,a brief test was performed in non-aqueous 1M LiClO 4+propylene carbonate solution by galvano-static experiments only.The results for the rates C/10,C/3and C,within the voltage limits 2.1–4.2V,were presented in Fig.4.The polarizability of the lithium electrode was estimated on the basis of the study by Churikov [56–67],who measured the current–voltage curves of pure lithium electrode in LiClO 4/propylene carbon-ate solutions at various temperatures.To the highest rate of 1C =170mA g −1in nonaqueous electrolyte,the corresponding cur-rent amounted to 0.25mA,which was equal to the current density of 0.064mA cm −2through the Li counter electrode.According to Fig.2in Ref.[67],for room temperature,the corresponding over-voltage amounted to only 6mV.Since lithium electrode is thus practically non-polarizable in this system,the voltages presented on the ordinate of the left diagram are the potentials of the olivine electrode expressed versus Li/Li +reference electrode.The clear charge and discharge plateaus at about 3.49V and 3.40V,respec-tively,correspond to the LiFePO 4 FePO 4phase equilibria [5].At discharging rate of C/10,the initial discharge capacity,within the limits of experimental error,was close to a full theoreticalM.Vujkovi´c et al./Electrochimica Acta 92 (2013) 248–256251Fig.4.The initial charge/discharge curves (a)and cyclic performance (b)of LiFePO 4/C composite in 1M LiClO 4+PC at different rates within a common cut-off voltage of2.1–4.2V.Fig.5.Charge/discharge profile and corresponding cyclic behavior of LiFePO 4/C in 1M LiClO 4+PC at the rate of 1C.capacity of LiFePO 4(170mAh g −1).This value is higher than that for LiFePO 4/C composite obtained by glycine [19],malonic acid [14]and adipic acid/ball milling [15]assisted methods.As usual,the discharge capacity decreased with increasing discharging rate (Fig.4b),and amounted to 127mAh g −1at C/3,and 109mAh g −1at 1C.For practical application of Li-ion batteries,a satisfactory rate capability and long cycle life are of primary importance.The charge/discharge profiles and dependence of capacity on the cycle number at the rate 1C are presented in Fig.5.The capacity was almost independent on the number of cycles,similarly to theearlier reports by Fey et al.[37–39].For comparison,Kalaiselvi et al.[19],by a glycine assisted gel-combustion procedure,with an additional amount (2wt.%)of carbon black,produced a similar nanoporous LiFePO 4/C composite displaying somewhat poorer per-formance,i.e.,smaller discharge capacity of 160mAh g −1at smaller discharging rate of C/20.On the other hand,better rate capability of LiFePO 4/C com-posite,containing only 1.1–1.8wt.%of carbon,in a non-aqueous solution,was reported by Liu et al.[21].For instance they mea-sured 160mAh g −1at the rate 1C,and 110at even 30C [21].This may be due to a thinner carbon layer around the LiFePO 4olivine particles.However the advantage of here applied thicker carbon layer exposed itself in aqueous electrolyte solutions,as described in the next section.3.2.2.Aqueous electrolyte solution3.2.2.1.Cyclic voltammetry.By the cyclic voltammetry method (CV)the electrochemical behavior of LiFePO 4/C composite in satu-rated aqueous LiNO 3solution was preliminary tested in the voltage range 0.4–1V versus SCE.The cyclic voltammograms are pre-sented in Fig.6.The highest scan rate of 100mV s −1,tolerated by this material,was much higher than the ones (0.01–5mV s −1)used in previous studies in both organic [13,24,25]and aqueous electrolyte solutions [47,48].Since one deals here with the thin layer solid redox electrode,limited in both charge consumption and diffusion length,the voltammogram is more complicated for interpretation comparing with the classic case of electroactive species in a liquid solution.A sharp,almost linear rise of current upon achieving reversible potential,with overlapped rising parts at various scan rates,similar to ones reported elsewhere [21,25],resembles closely the voltammogram of anodic dissolution ofaFig.6.Cyclic voltammograms of LiFePO 4/C in saturated LiNO 3aqueous electrolyte with a scan rate of 1mV s −1(left)and at various scan rates in the range 1–100mV s −1.252M.Vujkovi´c et al./Electrochimica Acta 92 (2013) 248–256Fig.7.Anodic and cathodic peak current versus square root of scan rate forLiFePO 4/C composite in aqueous LiNO 3electrolyte solution.thin metal layer [56],which proceeds under constant reactant activity.Since the solid/solid phase transitions LiFePO 4 FePO 4accompanies the redox processes in this system [5,8,57,58],the positive scan of the voltammograms depict the phase transition of LiFePO 4to FePO 4,while the negative scan depicts the phase transi-tion FePO 4to LiFePO 4.As shown by Srinivasan et al.[5],LiFePO 4may be exhausted by Li not more than 5mol.%before to trans-form into FePO 4,while FePO 4may consume no more than 5%Li before to transform into LiFePO 4,i.e.cyclic voltammetry exper-iments proceeds under condition of almost constant activity of the electroactive species.Although these aspects of the Li inser-tion/deinsertion process do not fit the processes at metal/liquid electrolyte boundary implied by Randles–Sevcik equation:i p =0.4463F RT1/2C v 1/2AD 1/2(2)this equation was frequently used to estimate apparent diffusion coefficient in Li insertion processes [5,17,21,46,59].To obtain peak current,i p ,in amperes,the concentration of lithium,C =C Li ,should be in mol cm −3,the real surface area exposed to the electrolyte in cm 2,chemical diffusion coefficient of lithium through the solid phase,D =D Li ,in cm 2s −1,and sweep rate,v ,in V s −1.The Eq.(2)pre-dicts the dependence of the peak height on the square root of sweep rate to be linear,as found often in Li-ion intercalation processes [17,21,25,59,60].This condition is fulfilled in this case too,as shown in Fig.7.The average value of C Li may be estimated as a reciprocal value of molar volume of LiFePO 4(V M =44.11cm 3mol −1),hence C Li =2.27×10−2mol cm −3.The determination of the actual surface area of olivine is a more difficult task,due to the presence of carbon in the LiFePO 4/C ly,classical BET method of sur-face area measurement may lead to a significantly overestimated value,since carbon surface may be very developed and participate predominantly in the measured value [15].Thus the authors in this field usually calculated specific surface area by means of Eq.(1),using mean particle radius determined by means of electron microscopy [17,22,45,46].Using S =22.2m 2g −1determined by means of Eq.(1),and an actual mass of the electroactive substance applied to the elec-trode surface (0.001305g),the actual electrode surface area was calculated to amount to A =290cm 2.This value introduced in Randles–Sevcik equation yielded D Li ∼0.8×10−14cm 2s −1.From the aspect of capacity retention,the insolubility of olivine in aqueous solutions is advantageous compared to the vanadia-based Li-ion intercalation materials,such as Li 1.2V 3O 8[61],LiV 3O 8[62]and V 2O 5[63],the solubility of which in LiNO 3solution was perceivable through the yellowish solutioncoloration.Fig.8.The Nyquist plots of LiFePO 4/C composite in aqueous LiNO 3solution at var-ious stages of delithiation;inset:enlarged high-frequency region.3.2.2.2.Impedance measurements.Figs.8and 9present the Nyquist plots of the LiFePO 4/C composite in aqueous LiNO 3solution at various open circuit potentials (OCV),during delithiation (anodic sweep,Fig.8)and during lithiation (cathodic sweep,Fig.9).The delithiated phase,observed at OCV =1V,as well as the lithi-ated phase,observed at OCV =0V,in the low-frequency region (f <100Hz)tend to behave like a capacitor,characteristic of a surface thin-layered redox material with reflective phase bound-ary conditions [64].At the OCV not too far from the reversible one (0.42V during delithiation,0.308V during lithiation),where both LiFePO 4and FePO 4phase may be present,within the whole 10−2–105Hz frequency range,the reaction behaves as a reversible one (i.e.shows the impedance of almost purely Warburg type).The insets in Figs.8and 9present the enlarged parts of the impedance diagram in the region of high frequencies,where one may observe a semicircle,the diameter of which corresponds theoretically to the charge transfer resistance.As visible,the change of open circuit potential between 0and 1V,in spite of the phase transition,does not cause significant change in charge transfer resistance.The small charge transfer resistance obtained with the carbon participation of 13.4%,being less than 1 ,is the smallest one reported thus far for olivine based materials.This finding agrees with the trend found by Zhao et al.[27],that the charge transfer resistance scaleddownFig.9.The Nyquist plots of LiFePO 4/C composite in aqueous LiNO 3solution at var-ious stages of lithiation;inset:enlarged high-frequency region.M.Vujkovi´c et al./Electrochimica Acta 92 (2013) 248–256253Fig.10.The dependence Z Re vs.ω−1/2during lithiation at 0.308V (top)and delithi-ation at 0.42V (down)in the frequency range 72–2.68Hz.to 1000,400and 150 when the amount of in situ formed carbon in the LiFePO 4/C composite increased in the range 1,2.8and 4.8%.For OCV corresponding to the cathodic (0.42V)and anodic (0.308V)peak maxima,the Warburg constant W was calculated from the dependence [21]:Z Re =R e +R ct + W ω−1/2(3)In the frequency range 2.7–72Hz,almost purely Warburg impedance was found to hold (i.e.the slope of the Nyquist plot very close to 45degrees was found).At the potential of cathodic current maximum (0.42V),from Fig.10, W was determined to amount to 7.96 s −1/2.At the potential of anodic maxima,0.308V, W was determined to amount to 9.07 s −1/2.In the published literature,for the determination of diffusion coefficient on the basis of impedance measurements,the following equation was often used [66,68,69]:D =0.5V M AF W ıE ıx2(4)where V M is molar volume of olivine,44.1cm 3, W is Warburg con-stant and ıE /ıx is the slope of the dependence of electrode potential on the molar fraction of Li (x )for given value of x .However,the potentials of CV maxima in the here studied case correspond to the x range of two-phase equilibrium,where for an accurate deter-mination of ıE /ıx a strong control of perturbed region of sample particles is required [69],and thus the determination of diffusion coefficients was omitted.3.2.2.3.Galvanostatic measurements.The galvanostatic measure-ments of LiFePO 4/C in saturated LiNO 3aqueous solution were performed in a two-electrode arrangement using hydrother-mally synthesized VO 2[55]as the active material of thecounterFig.11.Capacity versus cycle number and charge/discharge profiles (inset)for thecell consisting of LiFePO 4/C composite as cathode,and VO 2in large excess as anode,in saturated LiNO 3aqueous electrolyte observed at rate C/3.electrode.Preliminary cyclovoltammetric tests of VO 2in saturated LiNO 3solution at the sweep rate 10mV s −1,evidenced excellent cyclability and stable capacity of about 160mAh g −1during at least 50cycles.The voltage applied to the two-electrode cell was cycled within the limits 0and 1.4V.Due to a significant stoichiometric excess of VO 2over LiFePO 4/C composite (5:1)the actual voltage may be considered to be the potential versus reference VO 2/Li x VO 2electrode.Fig.11shows the dependence of the discharging Coulombic capacity of the LiFePO 4/C composite on the number of galvano-static cycles at discharging rate C/3,as well as (in the inset)the voltage vs.charging/discharging degree for 1st,2nd and 50th cycle.The charge/discharge curves do not change substantially in shape upon cycling,indicating stable capacity.For an aqueous solution,a surprisingly high initial discharge capacity of 106mAh g −1and low capacity fade of only 6%after 50charge/discharge cycles were evidenced.This behavior is admirable in comparison to other elec-trode materials in aqueous media reported in literature (LiTi 2(PO 4)3[42],LiV 3O 8[57]),and probably enabled by a higher thermody-namic stability of olivine structure [1].Fig.12presents the results of cyclic galvanostatic investigations of LiFePO 4/C composite in aqueous LiNO 3solution at various dis-charging rates.The charging/discharging rate was initially C/3for 80cycles and then was increased stepwise up to 3C.ThecapacityFig.12.Cyclic performance of LiFePO 4/C in saturated LiNO 3aqueous electrolyte at different charging/discharging rates.。
Research Proposal 的写作主要包括以下几个部分
Research Proposal 的写作主要包括以下几个部分：1. Statement of your hypothesis2. Review of Related Literature3. Methodology4. Analysis of the problems or significant issues involved. (Statistics)5. Summary of your findings and your conclusions and recommendationsResearch Proposal 一般的长度控制在2000-3000 词左右,必须回答下列问题: What you plan to accomplish, why you want to do it and how you are going to do it.必须要让读者相信you have an important research idea, 重要的研究想法that you have a good grasp of the relevant literature and the major issues, 对主要问题和相关文献有很好的把握and that your methodology is sound.方法是对路的【题目】：简单描述性，An investigation of可以省略【摘要】：300词，包括the research question, the rationale for the study, the hypothesis (if any), the method and the main findings. Descriptions of the method may include the design, procedures, the sample and any instruments that will be used.【Introduction】：为研究的问题提供主要的背景首先，让你的研究问题在一个当前热门或者仍旧可以讨论的旧领域的上下文中。
翻译Mg3N2的高压结构理论研究
NMg7（绿色）原子组成的多面体 NMg6（黄色）原子组成的八面体
MgN4（绿和橙色）原子组成的四面体 MgN5（紫色）原子组成的角锥体
03
PART THREE
力学性能
Mechanical Properties
Mechanical Properties--力学性能
表7：在新发现的结构中弹性常数的计算值06源自PART SIX总结
Conclusions
总 结
总的来说，除了先前研究的已经报道过的三个结构， Mg3N2的五种新的高压下的结构被首次提出，通过使用进化 的方法展示了与压力有关的多个相图。基于第一性原理，发 现ɛ-，ω-，λ-，Γ-和μ-Mg3N2在某些压力值下低于ɑ-Mg3N2. 除此之外，ɑ-Mg3N2首先在20GPa下转化为β-Mg3N2，又在 65GPa下转化为ϒ-Mg3N2。弹性常数和声子特性曲线表明 所有的结构都是动态稳定的。更重要的是通过维氏硬度的计 算这些新的结构比ɑ-，β-，ϒ-Mg3N2硬度更大。电子能带计 算表明除了ω-Mg3N2，其他的结构都是直接能带半导体，随 着压力增加带隙增大。有趣的是，ω-Mg3N2是间接能带半导 体。Mg3N2的这些卓越高压下结构性能，在机械和光学应用 上将有很大的潜力。
根据胡克定律，晶体对称性，不同的组采用不同的计算方法。如表7所示。 因为这些结构都属于三方晶系或是正交晶系，所以有6或9种独立的弹性常数。 对于三方晶系的力学稳定态判断如下： (C11+C12)C33-2C132>0; (C11-C12)C44-2C142>0. 对于斜方晶系的力学稳定态判断如下： Cii>0(i=1,2,3,4,5,6); C11+C22+C33+2(C12+C13+C23)>0 C11+C22-2C12>0;C11+C33-2C13>0; C22+C33-2C23>0 从表7中可以得出，所有结构都是稳定的。