2002 Society for Design and Process Science Printed in the United States of America PETRI N
IEEE 1243 --1997
IEEE Std 1243-1997 IEEE Guide for Improving the Lightning Performance of Transmission LinesSponsorTransmission and Distribution Committeeof theIEEE Power Engineering SocietyApproved 26 June 1997IEEE Standards BoardAbstract: The effects of routing, structure type, insulation, shielding, and grounding on transmis-sion lines are discussed. The way these transmission-line choices will improve or degrade light-ning performance is also provided. An additional section discusses several special methods that may be used to improve lightning performance. Finally, a listing and description of the FLASH pro-gram is presented.Keywords: grounding, lightning protection, overhead electric power transmission, shieldingIEEE Standards documents are developed within the IEEE Societies and the Standards Coordinat-ing Committees of the IEEE Standards Board. Members of the committees serve voluntarily and without compensation. They are not necessarily members of the Institute. The standards developed within IEEE represent a consensus of the broad expertise on the subject within the Institute as well as those activities outside of IEEE that have expressed an interest in participating in the develop-ment of the standard.Use of an IEEE Standard is wholly voluntary. The existence of an IEEE Standard does not imply that there are no other ways to produce, test, measure, purchase, market, or provide other goods and services related to the scope of the IEEE Standard. Furthermore, the viewpoint expressed at the time a standard is approved and issued is subject to change brought about through developments in the state of the art and comments received from users of the standard. Every IEEE Standard is sub-jected to review at least every Þve years for revision or reafÞrmation. When a document is more than Þve years old and has not been reafÞrmed, it is reasonable to conclude that its contents, although still of some value, do not wholly reßect the present state of the art. Users are cautioned to check to determine that they have the latest edition of any IEEE Standard.Comments for revision of IEEE Standards are welcome from any interested party, regardless of membership afÞliation with IEEE. Suggestions for changes in documents should be in the form of a proposed change of text, together with appropriate supporting comments.Interpretations: Occasionally questions may arise regarding the meaning of portions of standards as they relate to speciÞc applications. When the need for interpretations is brought to the attention of IEEE, the Institute will initiate action to prepare appropriate responses. Since IEEE Standards rep-resent a consensus of all concerned interests, it is important to ensure that any interpretation has also received the concurrence of a balance of interests. For this reason, IEEE and the members of its societies and Standards Coordinating Committees are not able to provide an instant response to interpretation requests except in those cases where the matter has previously received formal consideration.Comments on standards and requests for interpretations should be addressed to:Secretary, IEEE Standards Board445 Hoes LaneP.O. Box 1331Piscataway, NJ 08855-1331USAAuthorization to photocopy portions of any individual standard for internal or personal use is granted by the Institute of Electrical and Electronics Engineers, Inc., provided that the appropriate fee is paid to Copyright Clearance Center. To arrange for payment of licensing fee, please contact Copyright Clearance Center, Customer Service, 222 Rosewood Drive, Danvers, MA 01923 USA; (508) 750-8400. Permission to photocopy portions of any individual standard for educational class-room use can also be obtained through the Copyright Clearance Center.Introduction(This introduction is not part of IEEE Std 1243-1997, IEEE Guide for Improving the Lightning Performance of Trans-mission Lines.)For most overhead power transmission lines, lightning is the primary cause of unscheduled interruptions.Several methods for estimating lightning-outage rates have been developed in the past, and many publica-tions have been written on how to design transmission lines that experience minimum interruptions.The methods for estimating the lightning performance of transmission lines show several approaches to a real-life engineering problem that is ill-deÞned. Precise constants are rarely known and are often not really con-stant, input data is difÞcult to describe mathematically except in idealized ways, and outputs may be depictable only by probabilities or average values. By its nature, lightning is difÞcult to study and model. Lightning tran-sients are so fast that air ionization time constants lead to a time- and waveshape-dependent insulation strength. Lightning peak currents may be ten times higher or lower than the median 31 kA value. Typical ground-ßash densities are between 1 and 10 ßashes/km 2 , so a typical 100 km long strip of width 20 m should receive 2Ð20 ßashes per year. A transmission line of normal height will receive ten times more ßashes because it is tall. Structure footing impedances vary with soil characteristics, ßash current, and time. Nonlinear corona and surge response effects change the waveshape and magnitude of stresses. As a further complication, light-ning ßash density varies widely from year to year and changes with location and season.Any method of judging the lightning performance of transmission lines must cope with these uncertainties.It is pointless, and indeed misleading, to promote a method that is more precise than the accuracy of the input data. The uncertainties of the problem do permit some simpliÞcation of the method; rough estimates are likely to be as correct as a much more detailed solution. It is in this spirit that this guide and the FLASH program have been prepared. If the transmission-line designer keeps these limitations in mind, the factors that most inßuence the lightning performance of a given transmission line may be evaluated.Knowledge has improved in recent years in such areas as shielding design, stroke characteristics, impulse current behavior of grounds, and lightning ground-ßash density. Work is continuing in these areas, as well as others. However, a simple design guide is needed now. It is the purpose of this publication to provide a sim-pliÞed guide that includes new advances in this Þeld, for use by transmission-line designers.The IEEE Working Group on Estimating the Lightning Performance of Overhead Transmission Lines had the following membership during the preparation of this guide:James T. Whitehead, Chair, 1985-1989William A. Chisholm, Chair, 1989-1997The Working Group would like to thank the many individuals who reviewed the text and provided comments in the review and balloting process.John G. AndersonJohn W. AndersonPhilip BarkerRalph BernsteinJames E. ChapmanPritindra ChowdhuriErnico CinieriRoger ClaytonLuigi DelleraHamid ElahiAndrew J. ErikssonGeorge GelaStanislaw Grzybowski Christopher Hickman Andrew R. Hileman Atsuyuki Inoue Marasu Ishii Wasyl Janischewskyj John Kappenman Robert C. Latham Duilio M. Leite Vito J. Longo Harry G. Mathews James McBride Thomas McDermott Hideki Motoyama Charles H. Moser Abdul M. Mousa Richard E. Orville Dee E. Parrish Charles Pencinger John B. Posey Joseph D. Renowden Farouk A. M. Rizk Thomas Short Mohamed H. Shwehdi Martin A. Uman Edward R. WhiteheadThis document is dedicated to the work and memory of Ed Whitehead:ÒLightning is the enemy,Trees are your friends,TheyÕll shield your linesHoweÕer the leader bends.ÓThe following persons were on the balloting committee:Hanna E. Abdallah Edward J. Adolphson Glenn AndersenJ. G. AndersonJames E. Applequist Edwin AverillMichael P. Baldwin Phil P. BarkerRon L. BarkerE. BetancourtJohn BoyleH. Steve Brewer Joseph F. BuchJames J. Burke Vernon L. Chartier Nisar ChaurdhryPrit ChowdhuriDon ChuEnrico CinieriSam ClutsThomas M. Compton F. Leonard Consalvo William T. CrokerPaul L. Dandeno Glenn A. DavidsonR. DeckerTom. Diamantis William K. DickDale A. Douglass Robert Engelken William E. FeeroJon M. Ferguson Harald FienJames FunkeGeorge GelaDonald A. Gillies Edwin J. Tip Goodwin I. S. GrantStan GrzybowskiAdel E. Hammad Jerome G. Hanson Donald G. Heald Roland Heinrichs Richard W. Hensel Steven P. Hensley Christopher W. Hickman Andrew Robert Hileman John Hunt Atsuyuki InoueWasyl JanischewskyjJohn G. KappenmanRichard KennonJeff J. KesterRobert O. KlugeEd KnappNestor KolcioAlan E. KollarDonald E. KoonceDavid J. KourySamy G. KrishnasamyBarin KumarStephen R. LambertRobert C. LathamBenny H. LeeGerald E. LeeAntonio L. LimJoseph MaK. T. MassoudaMike. McCaffertyJohn McDanielNigel P. McQuinRoss McTaggartJohn E. Merando Jr.Sam MichaelJ. David MitchellDaleep MohlaRichard K. MooreJ. H. MoranHideki MotoyamaAbdul M. MousaJay L. NichollsD. L. NickelGeorge B. NilesStig L. NilssonRonald J. OedemannRobert G. OswaldGerald A. PaivaBert ParsonsMohammad A. PashaJesse M. PattonDavid F. PeeloCarlos PeixotoThomas J. PekarekRobert C. PetersTrevor PfaffR. Leon PlasterPercy E. PoolSteven C. PowellPatrick D. QuinnParvez RashidJerry L. RedingJoseph RenowdenFrank RichensStephen J. RodickJohn R. RossettiG. W. RoweTim E. RoysterThomas J. RozekJohn S. RumbleAnne-Marie SahazizianMahesh P. SampatDonald SandellNeil P. SchmidtJohn SchneiderMinesh ShahDevki N. SharmaJohn SheaTom ShortMohamed H. ShwehdiHyeong Jin SimPritpal SinghTarkeshwar SinghRobert A. SmithStephen F. SmithBrian T. SteinbrecherGary E. StemlerL .R. StenslandRobert P. StewartMike F. StringfellowAndy SweetanaEva J. TarasiewiczSubhash C. TuliJ. G. TzimorangasJoseph J. VaschakJohn VithayathilReigh WallingDaniel J. WardJames T. WhiteheadJeffrey S. WilliamsFrank S. YoungLuciano E. ZaffanellaPeter ZhaoRich ZinserWilliam B. ZollarsWhen the IEEE Standards Board approved this guide on 26 June 1997, it had the following membership:Donald C. Loughry, Chair Richard J. Holleman, Vice ChairAndrew G. Salem, Secretary*Member EmeritusAlso included are the following nonvoting IEEE Standards Board liaisons:Satish K. AggarwalAlan H. CooksonErika H. MurphyIEEE Standards Project EditorNational Electrical Safety Code and NESC are registered trademarks and service marks of the Institute of Electrical and Electronics Engineers, Inc.Windows is a trademark of Microsoft Corporation.Clyde R. Camp Stephen L. Diamond Harold E. Epstein Donald C. Fleckenstein Jay Forster*Thomas F. Garrity Donald N. Heirman Jim Isaak Ben C. JohnsonLowell JohnsonRobert KennellyE. G. ÒAlÓ KienerJoseph L. KoepÞnger*Stephen R. LambertLawrence V . McCallL. Bruce McClungMarco W. Migliaro Louis-Fran•ois Pau Gerald H. Peterson John W. Pope Jose R. Ramos Ronald H. Reimer Ingo RŸsch John S. Ryan Chee Kiow TanHoward L. WolfmanContents1.Overview (1)1.1Scope (1)1.2Purpose (1)1.3Disclaimer (2)2.References (2)3.Definitions and Acronyms (2)3.1Definitions (2)3.2Acronyms (4)4.Route selection (4)4.1Lightning frequency of incidence (4)4.2Route effects (5)4.3Structure height (5)4.4Soil resistivity (6)4.5Adjacent environment (6)5.Shielding (6)5.1Shielding angle (7)5.2The final leader step (7)5.3Flashover from shielding failure (9)5.4Shielding and engineering (10)5.5Shielding of the center phase (12)5.6Overhead ground wire size and operating losses (12)6.Insulation (13)6.1Effect of voltage waveshapes (13)6.2Effect of insulation levels and insulation type (16)6.3Wood or fiberglass in series with insulators (17)6.4Effect of power-line voltage (17)7.Tower footing impedance (18)7.1Composite line performance (18)7.2Supplemental grounding (19)7.3Counterpoise (20)7.4Resistance of complex footings (21)7.5Special grounding effects (21)8.Special methods of improving lightning performance (22)8.1Additional shield wires (22)8.2Guy wires on transmission towers (23)8.3Ground wire on separate structures (23)8.4Line surge arresters (23)8.5Unbalanced insulation on double-circuit lines (24)8.6Active air terminals (24)Annex A (informative) Isolated bonding of wooden structures (26)Annex B (normative) The FLASH program (27)Annex C (informative) Bibliography (34)IEEE Guide for Improving the Lightning Performance of Transmission Lines1. Overview1.1 ScopeFor this guide, a transmission line is any overhead line with a phase-to-phase voltage exceeding 69 kV and an average conductor height of more than 10 m. The transmission line is usually shielded by one or more overhead ground wires (OHGWs), at least for a short distance from a substation. While reference is prima-rily made to ac transmission characteristics, the guide is also relevant for high-voltage direct-current (HVDC) overhead lines.The guide is written for the transmission-line designer. When given the problem of designing or redesigning a transmission line, the designer should consider certain limiting factors such as the voltage level, the begin-ning and ending points for the transmission line, and the desired ampacity of the line. Sometimes the exact route, and the type of conductor and structure have already been determined. Usually the designer may choose structural details, the geometry of the structure, the structure height, the exact placement of the OHGWs, the amount and type of insulation, the type of grounding, and other design features of a line. This guide is written to show the designer which choices will improve or degrade lightning performance. Sections of the guide discuss the effect of routing, structure type, insulation, shielding, and grounding. An additional section discusses several special methods, which may be used to improve lightning performance. Finally, in Annex B, a listing and description of the FLASH program is presented.The line designer should be aware that lightning performance is not of primary importance in the economics of line designing. Other factors, such as line length, right-of-way costs, construction costs, material costs, and losses affect the economics of a line design much more than lightning performance. The designer should always balance the costs of higher insulation levels, improved grounding, better shielding, or line relocation against the beneÞts of improved reliability.1.2 PurposeThis guide contains simple mathematical equations, tables, and graphs that provide the information needed to design an overhead power transmission line with minimum lightning interruptions. Versions 1.6 and 1.7 of the FLASH program are provided on the diskette included with this guide. Annex B includes a description of the program. The FLASH program uses the models in the design guide along with a description of transmission-line features to estimate the lightning outage rate that may be expected. These simpliÞed models may also be adapted to assess the beneÞts of novel methods for improving lightning performance.IEEEStd 1243-1997IEEE GUIDE FOR IMPROVING THE 1.3 DisclaimerThe FLASH program is included in this guide as a convenience to the user. Other numerical methods may be more appropriate in certain situations. The IEEE Working Group on Estimating the Lightning Performance of Overhead Transmission Lines of the Lightning and Insulator Subcommittee has made every effort to ensure that the program yields representative calculations under anticipated conditions. However, there may well be certain calculations for which the method is not appropriate. It is the responsibility of the user to check calculations against Þeld experience or other existing calculation methods.2. ReferencesThis guide shall be used in conjunction with the following standards. When the following standards are superseded by an approved revision, the revision shall apply.ANSI C2-1997, National Electrical Safety Code¨ (NESC¨).1ANSI C29.1-1988 (Reaff 1996), American National Standard for Electric Power InsulatorsÑTest Methods.2 ANSI C29.2-1992, American National Standard for InsulatorsÑWet Process Porcelain and Toughened GlassÑSuspension Type.ANSI C29.8-1985 (Reaff 1995), American National Standard for Wet-Process Porcelain Insulators (Appara-tus, Cap, and Pin Type).3. DeÞnitions and Acronyms3.1 DeÞnitions3.1.1 active air terminal: An air terminal which has been modiÞed to lower its corona inception gradient.3.1.2 air terminal (lightning protection): The combination of an elevation rod and brace, or footing placed on upper portions of structures, together with tip or point, if used.3.1.3 back ßashover (lightning): A ßashover of insulation resulting from a lightning stroke to part of a net-work or electric installation which is normally at ground potential. See also:direct-stroke protection.3.1.4 back-ßashover rate: The annual outage rate on a circuit or tower-line length basis caused by back ßashover on a transmission line.3.1.5 counterpoise: A conductor or system of conductors arranged beneath the line; located on, above, or most frequently below the surface of the earth; and connected to the grounding systems of the towers or poles supporting the transmission lines.3.1.6 critical current: The Þrst-stroke lightning current to a phase conductor which produces a critical impulse ßashover voltage wave.1The NESC is available from the Sales Department, American National Standards Institute, 11 West 42nd Street, 13th Floor, New York, NY 10036, USA. It is also available from the Institute of Electrical and Electronics Engineers, 445 Hoes Lane, P.O. Box 1331, Piscataway, NJ 08855-1331, USA.2ANSI publications are available from the Sales Department, American National Standards Institute, 11 West 42nd Street, 13th Floor, New York, NY 10036, USA.IEEE LIGHTNING PERFORMANCE OF TRANSMISSION LINES Std 1243-1997 3.1.7 critical impulse ßashover voltage (insulators) (CFO): The crest value of the impulse wave which, under speciÞed conditions, causes ßashover through the surrounding medium on 50% of the applications.3.1.8 direct stroke protection (lightning): Lightning protection designed to protect a network or electric installation against direct strokes.3.1.9 ßashover: A disruptive discharge through air around or over the surface of solid or liquid insulation, between parts of different potential or polarity, produced by the application of voltage wherein the break-down path becomes sufÞciently ionized to maintain an electric arc.3.1.10 ground electrode: A conductor or group of conductors in intimate contact with the ground for the purpose of providing a connection with the ground.3.1.11 ground ßash density (GFD): The average number of lightning strokes to ground per unit area per unit time at a particular location.3.1.12 lightning Þrst stroke: A lightning discharge to ground initiated when the tip of a downward stepped leader meets an upward leader from the earth.3.1.13 lightning ßash: The complete lightning discharge, most often composed of leaders from a cloud fol-lowed by one or more return strokes.3.1.14 lightning subsequent stroke: A lightning discharge that may follow a path already established by a Þrst stroke.3.1.15 lightning outage: A power outage following a lightning ßashover that results in system fault current, thereby necessitating the operation of a switching device to clear the fault.3.1.16 line lightning performance: The performance of a line expressed as the annual number of lightning ßashovers on a circuit mile or tower-line mile basis. See also:direct-stroke protection.3.1.17 line surge arrester: A protective device for limiting surge voltages on transmission-line insulation by discharging or bypassing surge current; it prevents continued ßow of follow-current to ground and is capable of repeating these functions.3.1.18 overhead ground wire (OHGW): Grounded wire or wires placed above the phase conductors for the purpose of intercepting direct strokes in order to prevent the phase conductors from the direct strokes. They may be grounded directly or indirectly through short gaps. See also:direct-stroke protection.3.1.19 shielding failure ßash-over rate (SFFOR): The annual number of ßashovers on a circuit or tower-line length basis caused by shielding failures.3.1.20 shielding failure rate (SFR): The annual number of lightning events on a circuit or tower-line length basis, which bypass the overhead ground/shield wire and terminate directly on the phase conductor. This event may or may not cause ßashover.3.2 shield wire: Grounded wire(s) placed near the phase conductors for the purposes ofa)Protecting phase conductors from direct lightning strokes,b)Reducing induced voltages from external electromagnetic Þelds,c)Lowering the self-surge impedance of an OHGW system, ord)Raising the mutual surge impedance of an OHGW system to the protected phase conductors.3.2.1 standard lightning impulse: A unidirectional surge having a 30Ð90% equivalent rise time of 1.2 m s and a time to half value of 50 m s.IEEEStd 1243-1997IEEE GUIDE FOR IMPROVING THE 3.2.2 transmission line: Any overhead line used for electric power transmission with a phase-to-phase volt-age exceeding 69 kV and an average conductor height of more than 10 m.3.2.3 underbuilt shield wires: Shield wires arranged among or below the average height of the protected phase conductors for the purposes of lowering the OHGW system impedance and improving coupling. Underbuilt shield wires may be bonded to the structure directly or indirectly through short gaps. Insulated earth return conductors on HVDC transmission lines, and/or faulted phases, both function as underbuilt shield wires.3.2 AcronymsACSR aluminum conductor, steel reinforcedAWG American Wire GageCFO critical ßashoverEGM electro-geometricEHV extra-high voltageGFD ground ßash densityHV high voltageHVDC high-voltage direct currentOHGW overhead ground wireRTS rated tensile strengthSFR shielding failure rateSFFOR shielding failure ßashover rate4. Route selectionMany factors play an important role in route selection. Power system considerations dictate where the trans-mission line should begin and end. Economic considerations require the line to be as short as possible, because construction costs and electrical losses are high. Certain environmental constraints dictate where and how a transmission line may be built. Even with these restrictions, there are still ways for the transmis-sion-line designer to make decisions that will affect the lightning performance of the line. It is the purpose of this clause to illustrate the ways that a designer may improve the lightning performance of a transmission line by selecting the proper route.4.1 Lightning frequency of incidenceLightning location systems and ßash-counter networks have been deployed in North America [B11], [B34]3 and elsewhere. With enough experience, these networks may provide detailed ground ßash-density (GDF) maps. Orographic and geographic features, such as proximity to large bodies of water or elevation changes, will affect the ßash density. Flash-density maps will provide much greater detail and accuracy than what was previously available with thunder data. A typical GDF map is shown in [B35]. Lightning severity maps may also be available to show where more damaging lightning strokes occur. When two routes with similar soil characteristics are being compared, the route through a region with lower density of severe ßashes will have fewer outages.With more detailed maps averaged over enough time, the designer may select a route with a minimum expo-sure to lightning. By way of guidance about the averaging time required, MacGorman et al. [B29] found that 3The numbers in brackets correspond to those of the bibliography in Annex C.IEEE LIGHTNING PERFORMANCE OF TRANSMISSION LINES Std 1243-1997 one-year average thunder data had roughly 35Ð40% standard deviations, Þve-year averages had 30% stan-dard deviations, and ten-year averages had 25% standard deviations. A similar variation would be expected for GFD. Thus, a minimum of 5Ð10 years of GFD observations are desirable. The natural scatter of lightning activity may make it impossible to estimate a mean value with more precision than the ten-year standard deviation.4.2 Route effectsThe transmission-line designer is often faced with the choice of routing a line through a valley, along the side of a mountain, or on the top of a mountain. This decision may affect the lightning performance of the line in two ways. First, the route may affect the exposure of the line to lightning. Second, soil resistivity may be different for alternate routes. The effects of soil resistivity are discussed in 4.4.Transmission line exposure is affected by both GFD and by the lineÕs physical relation to its environment. A structure that protrudes above the surrounding terrain is more likely to be struck by lightning than a structure shielded by natural features. Structures located along the top of mountains, ridges, or hills will be likely targets for lightning strikes. These locations should be avoided as much as possible. It is preferable to locate structures along mountain sides where the top of the structure does not appear higher than the top of the mountain or ridge. Locating lines in the ßoor of a narrow valley may provide the line with useful lightning protection.Detailed design of lines should consider the effects of different routes on structure height, soil, or overburden depth and the adjacent environment.4.3 Structure heightThe Þrst factor of a line route that affects lightning performance is structure height, especially if its towers are higher than the surrounding terrain. Increasing the tower height has two important effects: more ßashes are collected by the taller structure, and the shielding characteristics of overhead conductors change as height is increased, as explained in Clause 5.The ßash collection rate, N s , is given by the following equation [B18]:(1)wherehis the tower height (m); bis the OHGW separation distance (m); N gis the GFD (ßashes/km 2 /yr); N s is the ßashes/100 km/yr.From Equation (l), if the tower height is increased by 20%, the ßash rate to the line would increase by 12%.If a measured value of N g is not available, it may be estimated [B18], [B29] using(2)(3)whereT dis the number of thunderstorm days/yr (Keraunic Level);N S N g 28h 0.6b +10-----------------------èøæö=N g 0.04T d 1.25=N g 0.04T h1.1=IEEEStd 1243-1997IEEE GUIDE FOR IMPROVING THE T h is the number of thunderstorm hours/yr.Data for T d and T h may be obtained from several meteorological sources, (e.g., [B11], [B29]).4.4 Soil resistivityThe second factor of a line route that affects lightning performance is soil resistivity. Resistivity has a linear relationship to footing impedance, which is explained in Clause 7. Substantial voltages are generated on grounded members of the structure when either the OHGW or the structure are struck by lightning. High structure footing impedances cause increased voltages and more lightning outages for a given lightning exposure.A complete line design will specify the types and sizes of ground electrodes needed to achieve the required footing impedance. The electrode sizes and shapes will depend on the range of soil conductivities found on installation. In some geographic areas, surveys of apparent ground resistivity have been carried out for radio-frequency broadcast [B25] or geological purposes. In particular, airborne electromagnetic surveys [B36] at 10Ð50 kHz return a suitable conductivity-depth product which may be analyzed further or used directly for tower spotting.High footing impedances occur in rocky terrain, which should be avoided as much as possible. When rocky terrain may not be avoided, improved grounding methods should be used to lower footing impedances to acceptable values. These improved methods usually require large-ring or radial-crowfoot installation at con-siderable cost. Rocky terrain usually occurs on mountain tops and mountain sides, while river lowlands tend to have low soil resistivity. This is a second reason why transmission-line routes away from hill crests will tend to have better lightning performance.4.5 Adjacent environmentOne way to prevent structures from being a target for lightning is to take advantage of surrounding forestation. Tall trees located near the transmission line may intercept a lightning stroke which may have caused an outage if the tree had not been there. Most transmission lines have sufÞcient impulse strength to be immune to the resulting induced voltages. Reference [B31] provides additional information about the effects of forestation. When possible, lines may be routed through forestation and tall trees may be left in place near the line. Trees that may fall on the line or reduce operating clearances will require more frequent trimming, and forest Þres may degrade the line protection locally. However, the reduction in apparent line height and corresponding reduction in lightning outages may still be worthwhile.Tall structures located in ßat, open Þelds make excellent targets for lightning. In these conditions, the struc-ture height should be minimized, and the structure footing impedance should be reduced much as possible. Another way to use the surrounding environment to shield a transmission line from lightning is to route the line next to existing transmission line structures. Experience has shown that a line sharing right-of-way with another line having taller structures will have fewer lightning outages than if it were on a separate right-of-way. Two lines of identical design and on adjacent rights-of-way share lightning strikes resulting in lower than normal outage rates for both lines. This improvement should be balanced with the greater risk of multi-ple line outages.5. ShieldingWhen lightning strikes a phase conductor, no other object shares in carrying the lightning current. Most ßashes to an unprotected phase conductor are therefore capable of producing ßashovers. OHGWs may inter-cept the stroke and shunt the current to the ground through the tower impedance and footing resistance if they are properly located. The resultant voltages across the transmission-line insulation, and the likelihood。
F2389标准 (2)
Designation:F2389–07´1Designation:F2389–10AnAmericanNationalStandardStandardSpecificationforPressure-ratedPolypropylene(PP)PipingSystems1
ThisstandardisissuedunderthefixeddesignationF2389;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.
´1NOTE—9.1waseditoriallycorrectedinJuly2008.1.Scope1.1Thisspecificationestablishesrequirementsforpolypropylene(PP)pipingsystemcomponentsmadetometricsizesandIPSschedule80sizes,andpressureratedforwaterserviceanddistributionsupply(seeAppendixX1).Includedarecriteriaformaterials,workmanship,dimensionsandtolerances,producttests,andmarkingforpolypropylene(PP)pipingsystemcomponentssuchaspipe,fittings,valves,andmanifolds.1.2Thecomponentsgovernedbythisspecificationshallbepermittedforuseinwaterservicelines,hot-and-coldwaterdistribution,hydronicheating,andirrigationsystems.1.3Thepipeandfittingsproducedunderthisspecificationshallbepermittedtobeusedtotransportindustrialprocessfluids,effluents,slurries,municipalsewage,etc.Theusershallconsultthemanufacturertodeterminewhetherthematerialbeingtransportediscompatiblewiththepolypropylenepipingsystemandwillnotaffecttheservicelifebeyondlimitsacceptabletotheuser.1.4Units—Thevaluesstatedininch-poundunitsaretoberegardedasstandard.ThevaluesgiveninparenthesesaremathematicalconversionstoSIunitsthatareprovidedforinformationonlyandarenotconsideredstandard.1.5Thisstandarddoesnotpurporttoaddressallofthesafetyconcerns,ifany,associatedwithitsuse.Itistheresponsibilityoftheuserofthisstandardtoestablishappropriatesafetyandhealthpracticesanddeterminetheapplicabilityofregulatoryrequirementspriortouse.
美国的五个标志
Do you know America? what can be the symbols of the US?
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1 a brief introduction of statue of liberty 2 origins of statue of liberty 3 some amazing black history of statue of liberty
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The origin of the Statue of Liberty project is sometimes traced to a comment made by a French law professor and a politician in mid-1865. someone said: "If monument should rise in the United States, as a memorial to their independence, I should think it only natural if it were built by united effort—a common work of both our nations.Bartholdi took no immediate action on the idea except to discuss it with a friend.
NSF_ANSI 51-2012 Food Equipment testing
NSF International, an independent, not-for-profit, non-governmental organization, is dedicated to being the leading global provider of public health and safety-based risk management solutions while serving the interests of all stakeholders.This Standard is subject to revision.Contact NSF to confirm this revision is current.Users of this Standard may request clarifications andinterpretations, or propose revisions by contacting:Chair, Joint Committee on Food Equipmentc/o NSF International789 North Dixboro Road, P.O. Box 130140Ann Arbor, Michigan 48113-0140 USAPhone: (734) 769-8010 Telex: 753215 NSF INTLFAX: (734) 769-0109E-mail: info@Web: NSF/ANSI 51 – 2012NSF International Standard/American National Standardfor Food Equipment —Food equipment materialsStandard DeveloperNSF InternationalNSF InternationalDesignated as an ANSI StandardJanuary 4, 2012American National Standards InstitutePrepared byThe NSF Joint Committee on Food EquipmentRecommended for Adoption byThe NSF Council of Public Health ConsultantsAdopted byThe NSF Board of DirectorsMay 1978Revised November 1997Revised May 2002Revised July 2005Revised April 2007Revised April 2009Revised January 2012Published byNSF InternationalP. O. Box 130140, Ann Arbor, Michigan 48113-0140, USAFor ordering copies or for making inquiries with regard to this Standard, please reference the designation “NSF/ANSI 51-2012.”Copyright 2012 NSF InternationalPrevious editions © 2009, 2007, 2005, 2002. 1997, 1978Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from NSF International. Printed in the United States of America.Disclaimers1NSF, in performing its functions in accordance with its objectives, does not assume or undertake to dis-charge any responsibility of the manufacturer or any other party. The opinions and findings of NSF repre-sent its professional judgment. NSF shall not be responsible to anyone for the use of or reliance upon this Standard by anyone. NSF shall not incur any obligation or liability for damages, including consequential damages, arising out of or in connection with the use, interpretation of, or reliance upon this Standard. NSF Standards provide basic criteria to promote sanitation and protection of the public health. Provisions for mechanical and electrical safety have not been included in this Standard because governmental agencies or other national standards-setting organizations provide safety requirements.Participation in NSF Standards development activities by regulatory agency representatives (federal, lo-cal, state) shall not constitute their agency's endorsement of NSF or any of its Standards.Preference is given to the use of performance criteria measurable by examination or testing in NSF Standards development when such performance criteria may reasonably be used in lieu of design, mate-rials, or construction criteria.The illustrations, if provided, are intended to assist in understanding their adjacent standard requirements. However, the illustrations may not include all requirements for a specific product or unit, nor do they show the only method of fabricating such arrangements. Such partial drawings shall not be used to justify im-proper or incomplete design and construction.Unless otherwise referenced, the appendices are not considered an integral part of NSF Standards. The appendices are provided as general guidelines to the manufacturer, regulatory agency, user, or certifying organization.1 The information contained in this Disclaimer is not part of this American National Standard (ANS) and has not been processed in accordance with ANSI’s requirements for an ANS. Therefore, this Disclaimer may contain material that has not been subjected to public review or a consensus process. In addition, it does not contain requirements neces-sary for conformance to the Standard.This page is intentionally left blank.Contents1 General (1)1.1 Purpose (1)1.2 Scope (1)1.3 Measurement (1)2 Normative references (1)3 Definitions (2)4 Material formulation (2)4.1 General requirements (2)4.2 Requirements for specific types of materials (3)5 General materials requirements (5)6 Coatings (5)6.1 Metallic coatings (5)6.2 Organic coatings (6)6.3 Performance requirements for coatings (8)7 Surface cleanability (8)7.1 Test method (8)7.2 Acceptance criteria (9)8 Corrosion resistance (9)8.1 Test method (9)8.2 Acceptance criteria (9)9 Abrasion resistance (9)9.1 Method I (for organic coatings used on food zones direct food contact surfaces) (9)9.2 Method II (for organic coatings used on splash zones and food zone non-directfood contact surfaces) (10)9.3 Method III (for organic coatings used on serving and display wares) (10)10 Impact resistance (10)10.1 Method I (for organic coatings used on food zones direct food contact andnon-direct food contact surfaces) (10)10.2 Method II (for organic coatings used on splash zones, serving and displaywares, and specific internal machine surfaces) (11)10.3 Method III (for specific glass and glass-like coatings used on splash zonesurfaces) (11)10.4 Method IV (for glass and glass-like coatings intended for food zone direct foodcontact and food zone-serving and display ware) (11)11 Heat resistance (12)11.1 Test method (12)11.2 Acceptance criteria (12)12 Adhesion ability (12)12.1 Method I (for organic coatings used on food zone – direct food contact surfaces) (12)12.2 Method II (for organic coatings used on serving and display wares) (12)Annex A ................................................................................................................................................. A1 Table A.I – ASTM Standard Specifications for common metallic coating processes ........................... A1Annex B 1B.1 Purpose .......................................................................................................................................... B1B.2 Preparation of exposure water ....................................................................................................... B1B.3 Exposure protocol .......................................................................................................................... B1 Interpretations Annex .......................................................................................................... I nterpretations - 1Foreword2The purpose of this Standard is to establish minimum food protection and sanitation requirements for the materials used in the construction of commercial food equipment.By way of reference, this Standard will define the basic materials requirements for all equipment covered by NSF/ANSI Food Equipment Standards.This Standard establishes requirements intended to ensure that a material is not formulated such that it may impart deleterious substances to food in its intended end use application. This Standard does not define specific extraction test methods or acceptance criteria to be used to assess the extent of chemical migration from food contact surfaces to food. Instead, the appropriate United States Federal Regulations have been cited as references upon which conformance with this Standard is based. Other NSF/ANSI Standards may establish extraction tests and acceptance criteria, as needed, for specific types of equipment based on the materials used in their construction and the nature of the food contact (i.e., beverage dispensing equipment, ice making equipment).This Standard establishes cleanability, corrosion resistance, impact resistance, abrasion resistance, heat resistance, and coating adhesion ability requirements and testing methods for food equipment materials of construction, as applicable.This edition of the Standard contains the following revision:Issue 10The purpose of this revision was to update the Normative References and boilerplate language, clarify the requirements for brass and bronze, glass and glass-like materials, and storage shelving intended for wet environments, relocate the lead requirement and test method from NSF/ANSI 4 and the glass materials requirement to NSF/ANSI 51, and expand Fluoropolymer coatings.The Interpretations Annex contains responses to interpretation requests. The responses will be published in each version of the Standard until such time that the interpretation response is no longer applicable.This Standard was developed by the NSF Joint Committee on Food Equipment using the consensus process of the American National Standards Institute.Suggestions for improvement of this Standard are welcome. Comments should be sent to the Chairperson of the Joint Committee on Food Equipment at standards@ or c/o NSF International, P.O. Box 130140, Ann Arbor, Michigan 48113-0140, USA.2The information contained in this Foreword is not part of this American National Standard (ANS) and has not been processed in accordance with ANSI’s requirements for an ANS. Therefore, this Foreword may contain material that has not been subjected to public review or a consensus process. In addition, it does not contain requirements neces-sary for conformance to the Standard.This page is intentionally left blank.© NSF 2012 NSF/ANSI 51 – 2012 NSF/ANSI Standardfor Food Equipment –Food equipment materials1 General1.1 PurposeThis Standard establishes minimum public health and sanitation requirements for materials used in the construction of commercial food equipment. The requirements of this Standard are intended to ensure that the composition and surface finish of food equipment materials are such that a material will not adulterate food nor render food equipment difficult to clean and sanitize.1.2 ScopeThis Standard is applicable to the materials and finishes used in the manufacture of food equipment (e.g., broiler, beverage dispenser, cutting board, stock pot). The Standard is also applicable to components such as tubing, sealants, gaskets, valves, and other items intended for various food equipment applications.These components shall meet the relevant design and construction requirements of the NSF Standard applicable to the type of food equipment on which the component is used.The requirements of 4 of this Standard may also be applied separately to determine whether a material is suitable for use in a food zone based on its formulation alone. The other relevant requirements of this Standard, including those for cleanability and corrosion resistance, would apply to the finished product for which the material is used.Materials other than those specifically mentioned in this Standard may be used provided that such materials meet the minimum requirements described herein.1.3 MeasurementDecimal and SI conversions provided parenthetically shall be considered equivalent. Metric conversions and significant figure rounding have been made according to IEEE/ASTM SI 10.2 Normative referencesThe following documents contain provisions that, through reference, constitute provisions of this NSF/ANSI Standard. At the time of publication, the editions listed below were valid. All standards are subject to revision, and parties are encouraged to investigate the possibility of applying the recent editions of the documents indicated below. The most recent published edition of the document shall be used for undated references.21 C.F.R. §§170-199, Food and Drug 33 Superintendent of Documents, U. S. Government Printing Office, Washington, DC 20402-0001 <>.21 U.S.C. §321 Definitions– generally (Food and Drugs)321 U.S.C. §348 Unsafe Food Additives (Food and Drugs)3ANSI Z97.1 – 2009. Safety Performance Specifications and Methods of Test for Glazing Materials Used in Buildings4ANSI/UL 197 – 2010. Standard for Commercial Electrical Cooking Appliances5ASTM B117 – 2009 Standard Practice for Operating Salt Spray (Fog) Apparatus6ASTM B 916 – 01(2007). Standard Test Method for Adherence of Porcelain Enamel Coatings to Sheet Metal 6ASTM D2794 – 93(2010) Standard Method for Resistance of Organic Coatings to the Effects of Rapid Deformation (Impact)6ASTM D3359 – 09e2 Standard Test Methods for Measuring Adhesion by Tape Test 6BS857:1967. Specification for Safety Glass for Land Transport7IEEE/ASTM SI 10 – 2010 American National Standard for Metric Practice6NSF/ANSI 2. Food equipmentNSF/ANSI 170. Glossary of food equipment terminologySAE Steel Numbering System83 DefinitionsTerms used in this Standard that have special technical meaning are defined in NSF/ANSI 170.4 Material formulation4.1 General requirements4.1.1Food zone materials shall be manufactured from or composed of substances that:– may not reasonably be expected to result, directly or indirectly, in their becoming a component of food, or otherwise affecting the characteristics of food, including the imparting of a color, taste, or odor to food; or– are generally recognized as safe or have received prior sanction for their intended use, as defined in the FD&C Act, Section 201(s) [21 U. S. C. 321 (s)]; or4 American National Standards Institute, 25 West 43rd Street, New York, NY 10036 <>.5Underwriters Laboratories, Inc., 33 Pfingsten Road, Northbrook, IL 60062 <>.6 ASTM International, 100 Barr Harbor Dr., West Conshohocken, PA 19428 <>.7 British Standards, 389 Chiswick High Road, London W4 4AL, United Kingdom. <>.8 SAE International, 400 Commonwealth Drive, Warrendale, PA15096-001 <>.– can be demonstrated to be safe for the intended use, subject to the FD&C Act, Section 409(h)(1) [21 U. S. C. 348(h)(1)]; or– can be demonstrated to be safe for the intended use, subject to the FD&C Act, Section 409(h)(6) [21 U. S. C. 348(h)(6)]; or– are regulated as indirect food additives under the provisions of the U. S. Code of Federal Regulations, Title 21, Sections 174 through 189 (21 CFR 174-189); or– are exempt from regulation as food additives under the provisions of the U. S. Code of Federal Regulations, Title 21, Part 170.39 Threshold of regulation for substances used in food contact articles.4.1.2Food zone materials shall not contain lead, arsenic, cadmium, or mercury as intentional ingredients. Brass and bronze materials may contain lead as permitted under 4.2.3.2.4.1.3Coatings containing lead as an intentional ingredient shall not be used on food equipment surfaces, including splash zones and nonfood zones. Coatings with an unintentional lead content (lead impurity) greater than 0.06% shall not be used.4.2 Requirements for specific types of materialsThis section establishes limitations on the use of specific types of materials. All materials shall conform to the general requirements in 4 and 5 and to the additional material-specific requirements established in this section.steel4.2.1 Stainless4.2.1.1Stainless steel used in food equipment shall be of a type in the:– SAE 200 series alloys;– SAE 300 series alloys; or– SAE 400 series alloys. 94.2.1.2 When used in a food zone, stainless steel shall have a minimum chromium content of 16%. Stainless steel with a chromium content of less than 16% may be used for cutlery, blades, and similar applications requiring a sharp edge, provided that the alloy has been hardened or tempered by an appropriate post-heat treatment process.alloys4.2.2 AluminumWhen used in a food zone, aluminum alloys shall have one of the following Aluminum Association10 alloy designations or equivalent:4.2.2.1Wrought alloys (sheet and extrusion)1xxx series alloys 5xxx series alloys3xxx series alloys 6xxx series alloys4xxx series alloys9 Under the Unified Numbering System (UNS), these types are designated as S2xxxx, S3xxxx, and S4xxxx, respectively.10 Aluminum Association, 900 19th St. NW, Washington, DC 20006 <>.4.2.2.2Casting alloys218.x 356.0 514.0308.0 360.0 520.0319.0 413.0 713.0332.0 B443.04.2.3 Copper and copper alloys4.2.3.1 Copper and copper alloys shall not be used in a food zone or splash zone except where rendered corrosion resistant or where exposure to food is limited to potable, non-carbonated water under constant service pressure. Exceptions to this requirement are specified in 4.2.3.2 for brass and bronze and in 4.2.3.4 for copper-nickel alloys.4.2.3.2 Brass and bronze may be used in a food zone or splash zone only where rendered corrosion resistant or where exposure to food is clearly and specifically limited to tea, coffee, or water. When used, the lead content of brass and bronze components shall not exceed 8.0%.4.2.3.3Equipment having brass or bronze components in contact with tea, coffee, or water (as permitted in 4.2.3.2) shall not impart a lead (Pb) concentration greater than 15 µg/L when tested in accordance with Annex B.NOTE 1 – If a coating (organic or metallic) is applied to the brass or bronze components, testing in accord-ance with annex B is still applicable.NOTE 2 – Equipment such as but not limited to proofers, steamers, combination ovens and other systems with similar humidification and vaporization pathways shall be exempt from 4.2.3.3.4.2.3.4 Copper-nickel alloys may be used in a food zone or splash zone only where rendered corrosion resistant or where exposure to food is clearly and specifically limited to non-acidic foods and beverages(i.e., food and beverages with a pH of 6.0 or greater).4.2.4 Glass and glass-like materialsGlass and glass-like materials, including porcelain, porcelain enamels, and ceramic coatings, shall not be used on surfaces intended for direct food contact that are also subject to impact by hard objects during use (e.g., countertops, tabletops, cutting boards, cooking surfaces) except as permitted in 4.2.4.1.4.2.4.1 Glass and glass-like materials may be used on grated cooking surfaces.4.2.4.2 When used on splash zone and food zone non-direct food contact surfaces that may be subject to impact by hard objects during use, glass and glass-like coatings shall meet the impact resistance requirements in 10.3.4.2.4.3 When used on direct food contact surfaces that are not subject to impact, glass and glass-like coatings shall meet the impact resistance requirements in 10.4. Glass-like coatings shall yield an adherence rating of 3 or better when tested according to ASTM B 916.4.2.4.4Glass, other than light fixtures, that may be subject to contact during use and routine maintenance and cleaning shall conform:– to the impact test in ANSI Z97.1 for Class A glass, or– to the impact test within ANSI/UL 197, or– to the impact test within BS857:1967.4.2.5 Wood4.2.5.1 Wood shall not be used in a food zone, except in wood-top bakers tables and cutting boards conforming to NSF/ANSI 2.4.2.5.2When used for non-decorative purposes (i.e., structural), wood shall be totally encapsulated so as not to be exposed.4.2.5.3 When used for decorative purposes, wood shall be sanded smooth and sealed with a sealant meeting the requirements of the zone of intended use. Decorative wood shall not be used on surfaces exposed to moisture or wear.5 General materials requirements5.1Materials shall be smooth and easily cleanable.If a material is textured so that it may hinder the removal of soil during cleaning, the material shall meet the surface cleanability requirements in 7.5.2 Corrosion resistance5.2.1Materials shall be corrosion resistant in the intended end use environment. Coatings conforming to 6, as applied, may be used to render a material corrosion resistant.NOTE – Materials that are worked (e.g., bent, cut, sheared, extruded, drawn) during equipment manufacture may require additional treatment (i.e., passivation) following fabrication in order to render them corrosion resistant.5.2.2 Storage shelving intended for wet environmentsStorage shelving that is manufactured, in whole or in part, of metallic materials and is intended for use in refrigerator or freezer interiors or warewashing areas shall meet the corrosion resistance requirements in 8.NOTE – Shelving shall not include non-removable parts of the refrigerator interior liner.5.2.2.1 Shelving manufactured of stainless steel in the SAE 200 or 300 series or of aluminum of the alloy series/designations listed in 4.2.2.1 and 4.2.2.2 is exempt from corrosion resistance requirements5.2.2.2Other requirements in this Standard, including the coating requirements in 6, shall also apply to storage shelving.6 CoatingsCoatings that are a combination of metallic and organic coatings shall conform to the requirements for organic coatings.6.1 Metallic coatings6.1.1Metallic coatings shall be applied in accordance with the appropriate ASTM Standard Specification, or equivalent.Annex A identifies the appropriate ASTM Standard Specifications for metallic coating processes commonly used for food equipment materials. The coating thickness and designation shall be in accordance with the coating manufacturer’s specifications for the zone of intended use.NOTE – Annex A is not all-inclusive.6.1.2 ZinccoatingsZinc coatings shall not be used in a food zone.6.2 Organic coatingszones6.2.1 Food6.2.1.1Organic coatings may be used on food zone surfaces.6.2.1.1.1Organic coatings may not be used on food zone surfaces that are designed in purpose to be subject to cutting and chopping actions.6.2.1.2 Coated surfaces used in direct food contact shall have substrate materials that conform to the requirements of 4.6.2.1.3 Organic coatings used on food zone direct food contact surfaces shall meet the abrasion resistance requirements in 9.1.6.2.1.4Organic coatings used on food zone direct food contact surfaces shall meet the impact resistance requirements in 10.1.6.2.1.4.1The impact resistance requirements in 10.2 shall apply to organic coatings used on food zone direct food contact surfaces that are:–internal to a unit, machine, or component;– not subject to impact or wear by internal parts or mechanisms or by operators; and– not designed to be removed during routine cleaning or maintenance.6.2.1.5Organic coatings used on food zone direct food contact surfaces shall meet the heat resistance requirements in 11.6.2.1.6 Organic coatings used on food zone direct food contact surfaces shall meet the adhesion requirements in 12.1.6.2.1.7 Fluoropolymer coatings and other non-stick coatings used on heated food zones shall be exempt from impact resistance, abrasion resistance, adhesion ability, and heat resistance performance tests.6.2.1.8 Organic coatings used on food zone non-direct food contact surfaces shall meet the abrasion resistance requirements in 9.2.6.2.1.9 Organic coatings used on food zone non-direct food contact surfaces shall meet the impact resistance requirements in 10.1.6.2.1.10 Organic coatings used on heated food zone non-direct food contact surfaces shall meet the heat resistance requirements in 11.zones6.2.2 Splash6.2.2.1Organic coatings may be used on splash zone surfaces.6.2.2.2Organic coatings used on splash zone surfaces shall meet the abrasion resistance requirements in 9.2.6.2.2.3Organic coatings used on splash zone surfaces shall meet the impact resistance requirements in 10.2.6.2.2.4 Organic coatings used on heated splash zone surfaces shall meet the heat resistance requirements in 11.NOTE – Organic coatings used on corrosion resistant substrates in a splash zone shall be exempt from abrasion resistance testing.6.2.3 Serving and display ware6.2.3.1 Organic coatings may be used on serving and display ware surfaces.6.2.3.2Organic coatings used on serving and display ware shall meet the abrasion resistance requirements in 9.3.6.2.3.3Organic coatings used on serving and display ware shall meet the impact resistance requirements in 10.2.6.2.3.4 Organic coatings used on serving and display ware surfaces shall meet the adhesion requirements in 12.2.6.2.3.5 Product literature shall be supplied by the manufacturer of coated serving and display ware expressly stating that the ware shall immediately be taken out of service and repaired or replaced if a fault in the coating occurs. The literature shall also state that the ware are not to be used for food preparation and are only for serving and display. The literature shall describe appropriate use environments, use limitations, and maintenance or care instructions. The literature shall also expressly state which utensil types are approved by the manufacturer for use on the ware.6.2.3.6Serving and display ware shall be marked (engraved, embossed, stamped, or otherwise) with the symbol “S” on the base of the equipment or surface or elsewhere when functionally or structurally necessary or where necessary for inspection. The marking shall be discernible and shall not adversely affect the cleanability, corrosion resistance, abrasion resistance, impact resistance, or heat resistance of the coating, or the adhesion of the coating to its substrate.6.3 Performance requirements for coatingsCoating type Zone Applicable performance test metallic food zone – direct food contact nonemetallic food zone – serving and display ware nonemetallic splashzone none metallic non-foodzone noneorganic food zone – direct food contact9.1 abrasionresistance 10.1 impactresistance 11 heatresistance 12.1 adhesionabilityorganic food zone – serving and display ware9.3 abrasionresistance 10.2 impactresistance 12.2 adhesionabilityorganic food zone - non-direct food contact9.2 abrasionresistance 10.1 impactresistance 11heat resistance(heated food zonesurfaces only)organic splashzone9.2 abrasionresistance 10.2 impactresistance 11heat resistance(heated splash zonesurfaces only)organic non-foodzone noneglass and glass-like food zone – direct food contact 10.4 impact resistance glass and glass-like food zone – serving and display ware 10.4 impact resistance glass and glass-like food zone – non direct food contact 10.3 Impact resistance glass and glass-like splash zone 10.3 impact resistance glass and glass-like non-food zone none7 Surface cleanability7.1 Test methodWhen required by this Standard, the surface cleanability of a textured material shall be determined by quantification of the amount of applied soil that remains on a material sample after cleaning. Four material test plaques (5.0 x 5.0 in [130 x 130 mm]) shall be washed with a non-ionic, low foaming, powdered mechanical washer detergent and water at 162 ± 2 °F (72 ± 1 °C) and shall be air dried. A standardized synthetic lard comprised of glycerol trioleate (62.5%), glycerol tristearate (37.5%), and trace amounts of 14C-labeled glycerol trioleate (0.845 μCi per gram of synthetic lard) and 14C-labeled stearic acid (0.514 μCi per gram of synthetic lard), shall be applied to the test plaques. The lard shall be heated to a liquid state, and 200 μL shall be applied to each of four equal quadrants on each test plaque. The lard shall be spread in a uniform layer onto the quadrants while under an infrared heat source to maintain the lard in a liquid state. The mass of soil on each quadrant shall be quantified using a beta radiation counting system; each quadrant shall have 20 ± 5 mg applied to its surface. The soiled test plaques shall be washed in a single-temperature, total-dump dishwashing machine having the following characteristics: – no overhead spray;– no detergent added;– wash and rinse water temperature: 162 ± 2 °F (72 ± 1 °C);– wash cycle time: 120 ± 2 s;– total wash cycle volume: 2.3 ± 0.2 gal (8.7 ± 0.8 L);。
美国
PART TWO The United States of American1.Population, race and ethnic groups 人口和种族1)introduction 概要①the third most populous country in the world,with 255.5 million people.②a nation of immigrants.Immigration accounts for a major source of population growth.There are many racial and ethnic groups. Between 80% and 90% of immigration ot the United States now is from Asian and Hispanic counties.The first immigrants in American history came from England and Netherlands. Population movements are common in America.移移民是人口增长的一个主要原因。
到目前80%-90%的移民来自亚洲和西班牙语国家。
美国历史上最早的移民来自于英格兰和荷兰。
人口迁徙在美国很普遍。
2)Black people and the Civil Rights Movement①blacks and slaverythe largest of the racial and ethnic minorities in the U.S., which 12.1 per cent of the population; the first blacks were brought to North America as slaves in 1619. 美国最大的少数人种是黑人，占人口的12。
2022《全品高考第二轮专题》英语 新高考版(特色专项)电子
2022《全品高考第二轮专题》英语新高考版(特色专项)电子第一节（共15小题；每小题2分，满分30分）阅读下列短文，从每题所给的A、B、C和D四个选项中，选出最佳选项。
ADon’t know where to enjoy yourself? Here are some choices for you.Santa Cruz Mission State Historic ParkPopUp Picnics in the Park return for the fourth summer in a row, taking place on Thursdays. Take a break to enjoy tacos（墨西哥玉米薄饼）. Prices change from $ 2 to $ 10. Cash only.144 School StreetJune 13 — August 15Start at 11:30 am and end at 1:30 pmThe Crow’s NestEach summer on Thursday evenings the Crow’s Nest offers its Summer Beach Party series on the beach. The party starts at 5:30 pmeach week and goes until sunset. Families are welcome and there is no entrance fee. After the sun sets, the fun begins with dancing to the best live music of local bands.2218 East Cliff DriveMay 30 — August 29Start at 5:30 pm and end at 8:30 pmBargetto WineryJoin us for a beautiful weekend of art and wine. Bargetto Winery will be hosting their yearly gathering of artists and foodies（美食家）at their amazing Soquel winery. No entrance fee. Wine tasting with purchase of $ 15 festival glass.3535 North Main StreetJuly 20 — July 21Start at 11:00 am and end at 5:00 pmChaminade Resort & SpaChef Page takes guests on a journey showing the area rich fruits, vegetables and meats. Dinner begins at 6:30 pm with a five-course menu and good wines. Seating booked is not a choice, as all guests are seated at large, connecting, beautifully set tables designed toinvite open conversations among guests. Ticket price: $ 90 per person. Tickets can be gotten online.1 Chaminade LaneJuly 26Start at 6:00 pm and end at 9:00 pm21.What can we know about PopUp Picnics in the Park?A. It lasts two days.B. It is held on Thursdays.C. It has been held twice.D. It can be paid in credit card.22.What can people do in the Crow’s Nest?A. Enjoy tacos.B. Talk with artists and foodies.C. Watch the sunrise on the beach.D. Watch the performance of the bands.23. Which activity can be booked on the Internet?A. The Crow’s Nest.B. Bargetto Winery.C. Chaminade Resort & Spa.D. Santa Cruz Mission State Historic Park.BAt just 40 years old, hip-hop star Kasseem Dean, more popularly known as Swizz Beatz, has amassed （积累）a track record, lifestyle and nearly $ 70 million net worth that would inspire most of us to retire early. So why does Dean continue to both work extremely hard and try projects that come with the risk of rejection?During our interview for Uncommon Drive, a video series for USA & Main that seeks to find out the motivations and magic of world-class business people, Dean provided a memorable answer: “You only have so much time —once it’s gone you don’t get it back. Don’t focus on money; focus on building something great er than yourself. If you’re not making history, you’re wasting your time on Earth.”When you look at his answer, you will learn two important lessons. The first is in “making history”. Doing so requires awareness. You must fully understand what has and has not been achieved in the market you’ve entered. Dean makes every effort with the goal of creating something important that has not beendone before and will be remembered for its impact beyond his years.The second part of his statement is just as powerful. In this interview, he never once said he is “trying” to make history. Instead, he has told himself that no matter what difficulty there is, it’s just going to happen. “I’m going to make history.” Dean said.After talking to Dean for nearly 45 minutes, it was clear to me that he has removed all ego（自我）from a statement that might otherwise be misread as false pride. I believe it’s a brilliant hack —rather than focus on all the reasons why a project can’t be re alized, he has convinced himself of the possibility.24. What is the function of the first paragraph?A. To list an example.B. To offer an explanation.C. To lead to the main topic.D. To make a summary.25. What motivates Dean to continue to work hard?A. His desire to be famous.B. His wish to be wealthy.C. His life goal to leave his mark on history.D. His adventurous spirit and imagination.26. What can we learn about Dean in the interview?A. He takes a pride in his work.B. He always believes in himself.C. He can predict the possibility.D. He gets prepared for his career.27. What’s the title of the text?A. How does Kasseem Dean face rejection?B. Why doesn’t Kasseem Dean want to retire?C. How does Kasseem Dean make history?D. What makes Kasseem Dean work hard?CThe world’s top automakers（汽车制造商）are increasingly offering more electric car models. This growth is expected to continue, with more people choosing to hit the road with clean- running electric cars.Environmentalists have praised the automakers for taking major steps to limit harmful pollutants linked to worldwide climate change.But electric cars are also known for not producing another kind of pollution — noise. They run on batteries instead of fuels, and can operate in silence.While many people might consider this a good thing, quiet cars can also cause problems. The main danger is that people around electric vehicles face a greater risk of being hit if they cannot hear the cars coming.Governments in the United States and Europe have recognized this problem. So they have set requirements for automakers to add warning sounds to electric vehicles. The U.S. Department of Transportation finalized its rules a year ago. The rules require electric and hybrid （混合物）cars to be equipped with some warning sounds when moving at a speed of up to 30 kilometers per hour. The rules are aimed at preventing injuries among people walking or riding bicycles and protecting the blind.So what kind of sound can we expect to hear from the next generation of electric cars? One of the easiest solutions would be for carmakers to reproduce the sound of a traditional car running on fuels. But many industry officials believe this would be a mistake.They say this would not support electric cars’ true identity. Frank Welsch, the head of technical development at Volkswagen, said that finding the perfect sound mix is not an easy process. He said, “It cannot be too annoying. It cannot sound like anything we had in the past.” An official from Me rcedes-Benz said the sound was designed to provide a safe warning without annoying passengers inside the car. He said the goal was to create a car that remains completely quiet inside.It might seem strange to think that part of our automotive future is currently being developed in the same kinds of recording studios used by musicians. But that is exactly what is happening.28. What’s Paragraph 2 mainly about?A. The main advantages of electric cars.B. The useful ways to improve electric cars.C. The autom akers’ effort to limit pollutants.D. The effect of climate change on the car industry.29. Why are sounds required to be added to electric cars?A. To add functions.B. To increase sales.C. To prevent injuries.D. To make cars smarter.30. What kind of sound is suitable for electric cars?A. The sound similar to that of a traditional car.B. The sound not troubling people inside cars.C. The sound matching cars’ identity.D. The sound chosen from recorded ones.31. Where does the text probably come from?A. A newspaper.B. An advertisement.C. A science report.D. A research plan.DDid you ever wonder why you have no memory of when you were a baby or very young child? The question of why adults do not remember how they learned to walk or talk has long been a mystery. Researchers at Temple University in Philadelphia, Pennsylvania in the United States are looking into this question.The study contained computer-based tests. The tests weredesigned to work like games. They were given to 32 four-year-olds, 32 six-year-olds and 50 young adults. The tests measured the memory process that helps people recognize differences between experiences. For example: A walk with your dog when you saw a friend, and a different walk without your dog or when you did not see your friend.The second test was showing the children and young adults taking the test a number of photographs. They were asked to compare the first group of photos with a second set of pictures. Sometimes, the two sets of photos were the same. But other times, they were different.The results showed that in both tests, six-year-olds showed far better memory than four-year-olds. That might help explain why adults do not remember when they learned to walk or talk, but they do remember their third, fourth or fifth birthdays.“We don’t have any memories in the first two years of life, and al l of a sudden we’re able to form these memories for something going on in early childhood or middle childhood. That’s very interesting,” said Zoe Ngo.Researchers said doing some research on the memory is of great value as doctors are trying to develop a c ure for Alzheimer’s disease. People with the disease suffer memory loss. For some people, memory loss is just for recent events. People may not remember what they did that morning, but remember experiences from 50 years ago. But memory loss research is not limited to helping patients with Alzheimer’s disease. It could also help find ways to get better and more reliable information about how to improve people’s memory.32. What do the researchers draw their attention to?A. Why people fail to complete simple tasks.B. Why people find it hard to learn special memory skills.C. Why people cannot recall their first few years of life.D. Why people have trouble forgetting past painful experiences.33. What is the purpose of the second test?A. To check how people remember differences in objects.B. To explain why people have better memory than before.C. To prove when people show interest in beautiful pictures.D. To show where people would like to take different photos.34. What can we infer from what Zoe Ngo said?A. People are willing to share good old days.B. People are likely to remember past special events.C. People are afraid of getting unexpected bad results.D. People are more concerned about their happy childhood.35. What does the last paragraph mainly discuss?A. The way to deal with memory loss.B. The importance of memory research.C. The possibility of collecting information.D. The measures to prevent Alzheimer’s disease.第二节（共5小题；每小题2分，满分10分）根据短文内容，从短文后的选项中选出能填入空白处的最佳选项。
大学英语通识教程第二册Unit 6 Science and Technology
Байду номын сангаас
Armstrong and Aldrin then moved into the Lunar Module and landed in the Sea of Tranquility. They stayed a total of about 21½ hours on the lunar surface. After lifting off in the upper part of the Lunar Module and rejoining Collins in the Command Module, they returned to Earth and landed in the Pacific Ocean on July 24. Broadcast on live TV to a world-wide audience, Armstrong stepped onto the lunar surface and described the event as "one small step for [a] man, one giant leap for mankind." Apollo 11 effectively ended the Space Raceand fulfilled a national goal proposed in 1961 by the late US President John F. Kennedy in a speech before the United States Congress, "before this decade is out, of landing a man on the Moon and returning him safely to the Earth."
四级考试阅读匹配练习题答案讲解
四级考试阅读匹配练习题答案讲解导读：我根据大家的需要整理了一份关于《四级考试阅读匹配练习题答案讲解》的内容，具体内容：阅读匹配作为阅读理解的重要题型，所占总分的比重高，需要考生的重视练习。
下面我为大家带来四级考试阅读匹配练习题讲解，欢迎各位考生提升训练。
四级考试阅读匹配练习题原文：Un...阅读匹配作为阅读理解的重要题型，所占总分的比重高，需要考生的重视练习。
下面我为大家带来四级考试阅读匹配练习题讲解，欢迎各位考生提升训练。
四级考试阅读匹配练习题原文：Universities Branch Out[A] As never before in their long history, universities have become instruments of national competition as well as instruments of peace. They are the place of the scientific discoveries that move economies forward, and the primary means of educating the talent required to obtain and maintain competitive advantage. But at the same time, the opening of national borders to the flow of goods, services, information and especially people has made universities a powerful force for global integration, mutual understanding and geopolitical stability.[B] In response to the same forces that have driven the world economy, universities have become more self?consciously global:seeking students from around the world who represent the entire range of cultures and values, sending their own students abroad to prepare them for global careers, offering courses of study that address the challenges of an interconnected world and collaborative (合作的)research programs to advance science for the benefit of all humanity.[C] Of the forces shaping higher education none is more sweeping than the movement across borders. Over the past three decades the number of students leaving home each year to study abroad has grown at an annual rate of 3.9 percent, from 800,000 in 1975 to 2.5 million in 2004. Most travel from one developed nation to another, but the flow from developing to developed countries is growing rapidly. The reverse flow, from developed to developing countries, is on the rise, too. Today foreign students earn 30 percent of the doctoral degrees awarded in the United States and 38 percent of those in the United Kingdom. And the number crossing borders for undergraduate study is growing as well, to 8 percent of the undergraduates at Americas best institutions and 10 percent of all undergraduates in the U.K. In the United States, 20 percent of the newly hired professors in science and engineering are foreign-born, and in China many newly hired faculty members at the top research universities received their graduate education abroad.[D ] Universities are also encouraging students to spend some of their undergraduate years in another country. In Europe, more than 140,000 students participate in the Erasmus program each year, taking courses for credit in one of 2,200 participating institutions across the continent. And in the United States, institutions are helping place students in summer internships (实习)abroad to prepare them for global careers. Yale and Harvard have led the way, offering every undergraduate at least one international study or internship opportunity—and providing the financial resources to make it possible.[E] Globalization is also reshaping the way research is done. One new trend involves sourcing portions of a research program to another country. Yale professor and Howard Hughes Medical Institute investigator Tian Xu directs a my 14research center focused on the genetics of human disease at Shanghais Fudan University, in collaboration with faculty colleagues from both schools. The Shanghai center has 95 employees and graduate students working in a 4,300-square-meter laboratory facility. Yale faculty, postdoctors and graduate students visit regularly and attend videoconference seminars with scientists from both campuses. The arrangement benefits both countries; Xus Yale lab is more productive, thanks to the lower costs of conducting research in China, andChinese graduate students, postdoctors and faculty get on-the-job training from a world-class scientist and his U.S. team.[F ] As a result of its strength in science, the United States has consistently led the world in the commercialization of major new technologies, from the mainframe computer and integrated circuit of the 1960s to the Internet infrastructure (基石出设施)and applications software of the 1990s. The link betweenuniversity-based science and industrial application is often indirect but sometimes highly visible: Silicon Valley was intentionally created by Stanford University, and Route 128 outside Boston has long housed companies spun off from MIT and Harvard. Around the world, governments have encouraged copying of this model, perhaps most successfully in Cambridge, England, where Microsoft and scores of other leading software and biotechnology companies have set up shop around the university.[G] For all its success, the United States remains deeply hesitant about sustaining the research-university model. Most politicians recognize the link between investment in science and national economic strength, but support for research funding has been unsteady. The budget of the National Institutes of Health doubled between 1998 and 2003, but has risen more slowly than inflations since then. Support for the physical sciences and engineering barelykept pace with inflation during that same period. The attempt to make up lost ground is welcome, but the nation would be better served by steady, predictable increases in science funding at the rate of long-term GDP growth, which is on the order of inflation plus 3 percent per year.[H ] American politicians have great difficulty recognizing that admitting more foreign students can greatly promote the national interest by increasing international understanding. Adjusted for inflation, public funding for international exchanges and foreign-language study is well below the levels of 40 years ago. In the wake of September 11, changes in the visa process caused a dramatic decline in the number of foreign students seeking admission to U.S. universities, and a corresponding surge in enrollments in Australia, Singapore and the U.K. Objections from American university and business leaders led to improvements in the process and a reversal of the decline, but the United States is still seen by many as unwelcoming to international students.[I ] Most Americans recognize that universities contribute to the nations well-being through their scientific research, but many fear that foreign students threaten American competitiveness by taking their knowledge and skills back home. They fail to grasp that welcoming foreign students to the United States has two importantpositive effects: first, the very best of them stay in the States and—like immigrants throughout history—strengthen the nation; and second, foreign students who study in the United States become ambassadors for many of its most cherished (珍视)values when they return home. Or at least they understand them better. In America as elsewhere, few instruments of foreign policy are as effective in promoting peace and stability as welcoming international university students.四级考试阅读匹配练习题选项：1. American universities prepare their undergraduates for global careers by giving them chances for international study or internship.2. Since the mid-1970s, the enrollment of overseas students has increased at an annual rate of3.9 percent.3. The enrollment of international students will have a positive impact on America rather than threaten its competitiveness.4. The way research is carried out in universities has changed as a result of globalization.5. Of the newly hired professors in science and engineering in the United States, twenty percent come from foreign countries.?6. The number of foreign students applying to U.S. universities decreased sharply after September 11 due to changes in the visaprocess.7. The U.S. federal funding for research has been unsteady for years.8. Around the world, governments encourage the model of linking university-based science and industrial application.9. Present-day universities have become a powerful force for global integration.10. When foreign students leave America, they will bring American values back to their home countries.：1. [D]。
英语国家社会与文化入门(高清上册))
UNIT 6 1. In what way do you think that religious freedom was a historical necessity in the United States? 1. By the middle of the 18th century, many different kinds of Protestants lived in America. 2. The Great Awakening of the 1740s, a "revival" movement that sought to breathe new feeling and strength into religion, cut across the lines of Protestant religious groups, or denominations. 3. A few Americans were so influenced by the new science and new ideas of the Enlightenment in Europe that they became deists, believing that reason teaches that God exists but leaves man free to settle his own affairs. 4. The First Amendment to the Constitution of the United States forbade the new federal government to give special favors to any religion or to hinder the free practice, or exercise, of religion. 3 What promotes the diversity in American religion? 1. The United States has always been a fertile ground for the growth of new religious movements. Frontier America provided plenty of room to set up a new church or found a new community. 2. Many religious communities and secular utopias, or experiments in new forms of social living, were founded in 18th and 19th century America. 3. Americans with different religions live together under the same law. 4. The religious beliefs of Americans continue to be strong with social progress. 5. In the United States every church is a completely independent organization, and concerned with its own finance and its own building. 6. Continuous immigration.
2023届山东省济宁市高三二模考试英语试题含答案
济宁市2023年高考模拟考试(二)英语试题2023. 04 注意事项：1. 答卷前, 考生务必将自己的姓名、考生号等填写在答题卡和试卷指定位置上。
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第一部分阅读（共两节, 满分50分）第一节（共15小题；每小题2. 5分, 满分37. 5分）阅读下列短文, 从每题所给的A、B、C、D四个选项中选出最佳选项。
AWith two documentaries-All That Breathes and The Elephant Whisperers-making it to the Oscars, there＇s renewed interest in India＇s diverse wildlife. However, most popular wildlife parks are usually expensive. Here are four less-known reserves that are not so costly but equally worth exploring.Coringa Wildlife ReserveCoringa is the second largest mangrove forest in the country. It is a birder＇s paradise and also home to otters, jackals, fishing cats and estuarine crocodiles. Endangered Olive Ridley sea turtles nest here during January-March every year.COST OF RIDE: 400-2, 500 per person by boatBEST TIME TO VISIT: November to FebruaryNational Chambal ReserveThe 5, 400 sq km reserve is the only one in India with three keystone species-Ganges river dolphin, ghariyal and red-crowned roof turtle-along with eight rare turtle species and about 300 species of migratory and resident birds.COST OF RIDE: 1, 800 per person by boatBEST TIME TO VISIT: November to MarchGulf of Mannar Marine National ParkThe park has 21 small islands and three distinct coastal ecosystems-coral reef, seagrass bed and mangroves-with over 4, 200 species of plants and animals. It is the last reserve of the unique “living fossil”Balanoglossus that links vertebrates （脊椎动物）and invertebrates.COST OF RIDE: 200-400 per person in a glass-bottomed boatBEST TIME TO VISIT: October to MarchManas National ParkThis reserve is a UNESCO Natural World Heritage Site. It is home to the threatened Indian Rhinoceros and other rare species like the Red Panda, Golden Langur and Pygmy Hog, and is also a Project Tiger Reserve and an elephant reserve with around 55 species of mammals, 450 species of birds and 50 species of reptiles.COST OF RIDE: 1, 150 per head on elephant, 4, 400 for a jeep with fourpeople, 8, 200 per person to 10, 600 for six people in a boatBEST TIME TO VISIT: October to May1. What is probably the major concern of visitors choosing these less-known reserves?A. Season.B. Security.C. Price.D. Transportation.2. Which attracts tourists who hope to see different turtle species most?A. Coringa Wildlife Reserve.B. National Chambal Reserve.C. Gulf of Mannar Marine National Park.D. Manas National Park.3. How much does it cost for 4 people to explore Manas National Park on elephant?A. 4, 400.B. 4, 600.C. 8, 200.D. 10, 600.BWhen 76-year-old Antoinette-Marie Williams played 17-year-old Emmett Daniels in chess for the first time, she gave Daniels a run for his money. Paired through DOROT, a New York organization which was launched in 1976, they are a. perfect match. “I was a good opponent for him. I don't think he expected it. ”Williams told the CVS Health blog Fortune Well. Their weekly games have led Daniels and Williams to a cross-generational relationship that they both enjoy. Williams and Daniels＇relationship disproves the idea that people of different generations have little in common.Since its founding, DOROT has achieved a reputation of excellence and innovation in the fields of aging services. Volunteers of young ages offer critical resources to older adults, in services specific to the person's needs and interests, with the ultimate goal of lessening loneliness of the old.Loneliness has been recognized as a significant social issue for many years, but the classification of loneliness as an epidemic （流行病）has emerged only in recent years. In 2018, the UK government appointed a Minister for Loneliness, highlighting the increasing concern around the issue. This followed the publication of the 2017 report by the Jo Cox Loneliness Commission, which found that loneliness was a growing social epidemic and called for a national strategy to address the issue.Fortunately, there are ways to battle loneliness, including the intervention in the lives of isolated seniors by organizations like DOROT. It advocates building a support network by reaching out to family and friends, joining a community or social group, or volunteering to connect with like-minded people. The connection between Williams and Daniels shows that these inter-generational relationships play an important role in reducing loneliness and adding joy to the lives of all the participants, young and old.Another way to battle loneliness is to use technology to stay connected with loved ones which fosters meaning and purpose through online activities and conversations. Practicing self-care is also encouraged, as is being patient because strong relationships take time and effort to create.4. What does the underlined sentence in paragraph 1 probably mean?A. She had a running race with Daniels.B. Daniels felt disappointed.C. Daniels had a tough win.D. She gave Daniels money as a gift of greeting.5. What is the purpose of DOROT?A. To make technological innovation.B. To enhance the living standards of the elderly.C. To offer job opportunities for people of all ages.D. To provide seniors with inter-generational connection.6. What does the author try to stress in paragraph 3?A. The solution to loneliness.B. The root cause of loneliness.C. The classification of loneliness.D. The growing attention to loneliness.7. In which section of a newspaper does this passage probably come from?A. Society Watch.B. News Express.C. Page Turner.D. Science Study.CSeveral years ago, I was at a pre-season football practice at a high school where I was working with the team on. a concussion（脑震荡）research project. The players were lined up in two rows facing each other and with little more instruction from the coach than, “on the whistle, hit the man across from you”, great concern rushed through my mind.Professional sports get the lion's share of attention, but over three million children and teenagers in the United States play the same game. This directly places concussions as a significant public health concern for all.However, for decades, concussion has been considered a temporary injury with no long-term consequences. Many athletes will do just about anything to stay on the field and “play through the pain”as a sign of toughness. In 2005, with the release of the brain tissue pathology （病理学）report of Mike Webstera, a retired National Football League player, our thinking on concussion began to shift. Since then, public attention has focused on this link between brain injury and blows to the head. As our understanding of concussion progressed to understanding its significance as an injury, so too did the development of player equipment.In the early 1900s football was played without helmets （头盔）, but severe injuries, like skull fractures, led to the occasional use of leather helmets in the 1920s. The first face mask entered the game in the 1950s. Modern helmets use advanced shel1 materials, have moveable panels to absorb forces, and multi-layered padding that responds todifferent impacts. Companies will continue to improve helmets as new materials become available, guided by the newest science.Sports are an important part of a society's culture and they give millions of children much-needed exercise. Yet, participation in any sport carries injury risk, and concussion will always be part of that. As those children become adults and make sport their hobby or 'even career, ensuring them play safely at all levels is essential.8. What made the author feel concerned?A. The coach's inexperience.B. The physical conflicts among the players.C. Unawareness of the potential injuries.D. Unpredictable outcome of the project.9. What did athletes use to do when meeting with sports-related concussion?A. They tended to ignore it.B. They felt scared about it.C. They quit playing immediately.D. They refused medical assistance.10. What does paragraph 4 mainly talk about concerning the helmet?A. Its gradual improvement.B. Its widespread influence.C. The discovery of its new materials.D. The difficulty of its mass production.11. What can be inferred from the last paragraph?A. Exercise is vital for children.B. Sports safety can't be overemphasized.C. No participation in sports is without injuries.D. Concussion is the most common injury in sports.DPeople generally feel secure with certainty. To be certain is to have power and control. Certainty is often used as a metric（衡量标准）of value, shaping how people view themselves and others. For example, people tend to respect those who present themselves as certain while viewing those who express uncertainty as wishy-washy, anduntrustworthy. Young people growing up in a culture that identifies strongly with certainty are told that to be certain is to be secure, right, and good. It is the idea, more than uncertainty itself, that causes great anxiety.But the reality is that certainty is transient; it is more a feeling than a fact. Too often people act as if certainties are drawn in permanent marker: Thick, clear, definitive, and rigid. But they are not. They are actually drawn with pencil-ready for revision, editing, and change.Springtide's recent report, The State of Religion and Young People: Navigating Uncertainty, allows us to hear how young people are questioning certainty and increasingly rejecting the rules that isolate them from themselves and one another. Milly, a 25-year-old quoted in the report, described her experience in a group discussion where uncertainty was welcomed rather than criticized:“Like, struggling to know what or what not to believe. . . . That's something we talked about in the group. It actually makes me feel a little bit better. It's like, oh, like we can have doubts. We can struggle with these feelings and they're still, we're still accepted, you know? So that was actually kind of refreshing" （Springtide, 2021, p. 46）.Young people are not rejecting certainty, but they are not accepting prepackaged answers or one-dimensional solutions. They are reexamining pre-drawn labels, beliefs, and identities and daring to ask “Why?”Their courage to question is an invitation to all of us to reconsider and rediscover uncertainty. We can listen to and learn from young people, embracing（拥抱）this opportunity as a moment of critical self-reflection and growth. If we will accept uncertainties, we might discover the ways that multiple beliefs, practices, values, identities, and communities can coexist and develop together.12. What is the purpose of paragraph 1?A. To explain a concept.B. To advocate a culture.C. To introduce a different opinion.D. To confirm an assumption.13. What does the underlined word "transient”probably mean in paragraph 2?A. Changeable.B. Predictable.C. Popular.D. O bjective.14. What was Milly's attitude towards the group discussion?A. Intolerant.B. Doubtful.C. Unconcerned.D. Positive.15. Which of the following can be the best title of the passage?A. Unmask the Culture of CertaintyB. Embrace the Gift of UncertaintyC. Certainty: Should It Be Rejected by the Young?D. Uncertainty: Should It Be Blamed for Anxiety?第二节（共5小题；每小题2. 5分, 满分12. 5分）阅读下面短文, 从短文后的选项中选出可以填入空白处的最佳选项。
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2002SocietyforDesignandProcessSciencePrintedintheUnitedStatesofAmerica
PETRINETMODULESJuliaPadberg**TechnicalUniversityBerlinInstituteforSoftwareEngineeringandTheoreticalComputerScienceGermanyemail:padberg@cs.tu-berlin.de
Abstract:HerewepresentanewmoduleconceptforPetrinetsthatisbasedonthecomponentconceptsofContinuousSoftwareEngineering(CSE).Accordingtothatconcepttwodistinguishedinterfacesarerequired.Theseareimportandexportinterfaces.Theimportdescribestheassumptionsontheenvironment,e.g.intermsofusedcomponents.Theexportgivesanabstractionofthefunctionalityandpresentse.g.theofferedservices.ThemodulesforPetriweintroducehereconsistofthreenetsfortheimport,thebodyofthemoduleandtheexport.Theimportnetstatestheprerequisitesthemodulesassumes.Thebodynetrepresentstheinternalfunctionality.Theexportnetgivesanabstractionofthebodythatcanbeusedbytheenvironment.Weprovidemoduleoperationstocomposelargermodulesfrombasicones.OperationstocomposePetrinetmodulesarecrucialasthemainpurposeiscomposition.Inmostapproachesmoduleconceptscomealongwithjustoneoperation.Agreatadvantageisachievedhavingdifferentpossibilitiestocomposemodules,asitincreasestheconvenienceofmodelinglargesystems.Weproposethreedifferentoperations,composition,disjointunion,andunion.Ourmainresultinthiscontributionisthatthesemoduleoperationsarecompatiblewitheachother.
1.IntroductionThemainmotivationforPetrinetmodulesisthemodelingofcomponent-basedsystems.Softwarecom-ponentsareanusefulandwidelyacceptedabstractionmechanism.Componentsaredeployedduringtheentiresoftwarelifecycle,fromanalysistomaintenance.Thecomponentconceptassuggestedin(M¨ullerandWeber,1998;Weber,1999)forContinuousSoftwareEngineering(CSE)isthebasicconceptforourapproach.EspeciallyinearlysoftwaredevelopmentphasesmodelingwithPetrinetsisacommonapproach.Unfortu-natelyPetrinetsdonotyetsupportthiscomponentidea.InthispaperwepresentPetrinetmodulesasanabstractionmechanismthatcorrespondstothecomponentconceptofCSE.ThisconceptisrealizedforPetri
TransactionsoftheSDPSSEPTEMBER2002,Vol.6,No.3,pp.121-96netsusingthefollowingbasicideas:Componentsconsistofthreenets:theimportnet,theexportnet,andthebodynet.Theimportnetpresentsthosepartsofthenetthatneedtobeprovidedfromthe”outside”.Theexportnetisthatwhatthenetmodulepresentstothe”outside.Thebodyistherealizationoftheexportusingtheimport.
Therelationbetweenimportandbodyisgivenbyaplainmorphism.Exportandbodyarerelatedbyasubstitutionmorphism,thatallowsmappingonetransitiontoasubnet.
Differentmoduleoperationsarerequiredfortheflexiblecompositionofmodules.Atthemomentwehaveunionofmodulesandcompositionofmodules.
Compatibilitybetweentheoperationsneedstobeguaranteed.Providedsomeconditionsaresatisfiedtheresultoffirstunionandthencompositionorviceversaisthesameuptoisomorphism.
Theoriginalalgebraicmoduleconceptisbasedonaloosesemantics.Uptonowthereisnoloosese-manticsdefinedforPetrinetsorotherPetrinetclasses.Thisisfutureresearchandwillbeinvestigatedinforthcomingpapers.
IntheareaofPetrinetsvariousstructuringconceptshavebeenproposedduringthelast40years,someoftheseareevencalledmodulesormodularapproach.Ontheonehandtherearehierarchicalconcepts(e.g.(Jensen,1992;Buchholz,1994;He,1996;Fehling,1993)).Thesystemisdescribedinanabstractnet,whilespecialfunctionalitiesareencapsulatedintosubnetsandcalledlikeproceduresbymergingtransitionsorplacesandexchangeoftokens.Ontheotherhandthereisalargevarietyofconnectormechanismsbetweenmodules.Thecommunication,coordinationorcooperationamongcomponentsviasignalsisgivenbyarelationbetweeninputandoutput(e.g.(ChristinsenandHansen,1994;Sibertin-Blanc,1994;Deseletal.,2000;DeitersandGruhn,1994)).Inthiswaytheexchangeoftokensoronlyread-operationofmodulesisdescribedbyspecialfeatureslikereadarcs,inhibitorarcsetc.Inotherapproachesplacesandtransitionsofmodulesaremergedbywell-definedoperations(e.g.(Kindler,1995;Battistonetal.,1991b;Battistonetal.,1991a;BroyandStreicher,1992)).IncontrasttotheseourapproachisbasedonconceptsofContinuousSoftwareEngineering(CSE).Thead-vantageisthatwemustnotextendtheunderlyingformalismofPetrinets,butcomposemodulesbymeansofaconnectorcomponent.Moreover,therearenoapproachesthatprovidedifferentcompositionopera-tionswithexplicitcompatibilityresultsandcompositionoperationsareusuallyonlygivenimplicitly.TheapproachtoPetrinetmodulesaspresentedinthispaperiscloselyrelatedtoalgebraicspecificationmodules(EhrigandMahr,1990).Theirimpactforpracticalconceptsinsoftwareengineeringhasbeenrelevantfromthebeginning(WeberandEhrig,1988).Thetransferoftheseconceptstoprocessdescriptiontechniquesisarecentdevelopment.Ithasbeenstartedin(Simeoni,1999)wheremodulesforgraphtransformationsystemsandlocalactionsystemshavebeeninvestigated.AgeneralframeworkforcomponentconceptsbasedonHigh-LevelReplacementSystems(Ehrigetal.,1991)ispresentedin(EhrigandOrejas,2001).Tosumupdifferentprocessmodelingtechniqueslikegraphtransformationsystems,Petrinetsandmanyothersbesides,therelationbetweenexportandbodyishereformalizedinamoregeneralwaybytransformationrulesinsteadofmorphismsandourconceptforPetrinetsmodulesfitsinverywell.Moreover,thePetrinetmodulesweintroducecanbeconsideredaninstantiationofthegenericcomponentconceptpresentedin(Ehrigetal.,2002c)(alsointhisvolume).In3.4.wediscussthisrelation.Thispaperisorganizedasfollows:FirstweintroducePetrinetmodulesinSection2.ThemoduleoperationsarepresentedinSection3.Inbothsectionsweuseasmallexampletoillustratetheintroducednotions.AsummaryandfutureworkaregivenintheconclusioninSection4.