Electrokinetic and Flotation Investigations of Surface Properties Modification of Magnesit

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National Institutes of Health

NIEHS REPORT onHealth Effects from Exposure to Power-Line Frequency Electric and Magnetic FieldsPrepared in Response to the 1992 Energy Policy Act(PL 102-486, Section 2118)National Institute of Environmental Health SciencesNational Institutes of HealthDr. Kenneth Olden, DirectorPrepared by theNIEHS EMF-RAPID Program StaffNIH Publication No. 99-4493Supported by the NIEHS/DOEDEPARTMENT OF HEALTH & HUMAN SERVICES Public Health ServiceNational Institutes of HealthNational Institute ofEnvironmental Health SciencesP. O. Box 12233Research Triangle Park, NC 27709 May 4, 1999Dear Reader:In 1992, the U.S. Congress authorized the Electric and Magnetic Fields Research and Public Information Dissemination Program (EMF-RAPID Program) in the Energy Policy Act. The Congress instructed the National Institute of Environmental Health Sciences (NIEHS), National Institutes of Health and the U.S. Department of Energy (DOE) to direct and manage a program of research and analysis aimed at providing scientific evidence to clarify the potential for health risks from exposure to extremely low frequency electric and magnetic fields (ELF-EMF). The EMF-RAPID Program had three basic components: 1) a research program focusing on health effects research, 2) information compilation and public outreach and 3) a health assessment for evaluation of any potential hazards arising from exposure to ELF-EMF. The NIEHS was directed to oversee the health effects research and evaluation, and the DOE was given the responsibility for overall administration of funding and engineering research aimed at characterizing and mitigating these fields. The Director of the NIEHS was mandated upon completion of the Program to provide this report outlining the possible human health risks associated with exposure to ELF-EMF. The scientific evidence used in preparation of this report has undergone extensive scientific and public review. The entire process was open and transparent. Anyone who wanted “to have a say” was provided the opportunity.The scientific evidence suggesting that ELF-EMF exposures pose any health risk is weak. The strongest evidence for health effects comes from associations observed in human populations with two forms of cancer: childhood leukemia and chronic lymphocytic leukemia in occupationally exposed adults. While the support from individual studies is weak, the epidemiological studies demonstrate, for some methods of measuring exposure, a fairly consistent pattern of a small, increased risk with increasing exposure that is somewhat weaker for chronic lymphocytic leukemia than for childhood leukemia. In contrast, the mechanistic studies and the animal toxicology literature fail to demonstrate any consistent pattern across studies although sporadic findings of biological effects have been reported. No indication of increased leukemias in experimental animals has been observed.The lack of connection between the human data and the experimental data (animal and mechanistic) severely complicates the interpretation of these results. The human data are in the "right" species, are tied to "real life" exposures and show some consistency that is difficult to ignore. This assessment is tempered by the observation that given the weak magnitude of these increased risks, some other factor or common source of error could explain these findings. However, no consistent explanation other than exposure to ELF-EMF has been identified.Page 2Epidemiological studies have serious limitations in their ability to demonstrate a cause and effect relationship whereas laboratory studies, by design, can clearly show that cause and effect are possible. Virtually all of the laboratory evidence in animals and humans and most of the mechanistic work done in cells fail to support a causal relationship between exposure to ELF-EMF at environmental levels and changes in biological function or disease status. The lack of consistent, positive findings in animal or mechanistic studies weakens the belief that this association is actually due to ELF-EMF, but it cannot completely discount the epidemiological findings.The NIEHS concludes that ELF-EMF exposure cannot be recognized at this time as entirely safe because of weak scientific evidence that exposure may pose a leukemia hazard. In my opinion, the conclusion of this report is insufficient to warrant aggressive regulatory concern. However, because virtually everyone in the United States uses electricity and therefore is routinely exposed to ELF-EMF, passive regulatory action is warranted such as a continued emphasis on educating both the public and the regulated community on means aimed at reducing exposures. The NIEHS does not believe that other cancers or non-cancer health outcomes provide sufficient evidence of a risk to currently warrant concern. The interaction of humans with ELF-EMF is complicated and will undoubtedly continue to be an area of public concern. The EMF-RAPID Program successfully contributed to the scientific knowledge on ELF-EMF through its support of high quality, hypothesis-based research. While some questions were answered, others remain. Building upon the knowledge base developed under the EMF-RAPID Program, meritorious research on ELF-EMF through carefully designed, hypothesis-driven studies should continue for areas warranting fundamental study including leukemia. Recent research in two areas, neurodegenerative diseases and cardiac diseases associated with heart rate variability, have identified some interesting and novel findings for which further study is ongoing. Advocacy groups have opposing views concerning the health effects of ELF-EMF. Some advocacy groups want complete exoneration and others want a more serious indictment. Our conclusions are prudent and consistent with the scientific data. I am satisfied with the report and believe it provides a pragmatic, scientifically-driven basis for any further regulatory review.I am pleased to transmit this report to the U.S. Congress.Sincerely,Kenneth Olden, Ph.D.DirectorNIEHS EMF-RAPID P ROGRAM S TAFF Gary A. Boorman, D.V.M., Ph.D., Associate Director for Special Programs, Environmental Toxicology Program and Director, EMF-RAPID ProgramNaomi J. Bernheim, M.S., Biologist, Office of Special Programs, Environmental Toxicology Program and Program Assistant, EMF-RAPID ProgramMichael J. Galvin, Ph.D., Health Scientist Administrator, Division of Extramural Research and Training and Extramural Program Administrator, EMF-RAPIDProgramSheila A. Newton, Ph.D., Director, Office of Policy, Planning and EvaluationFred M. Parham, Ph.D., Staff Scientist, Laboratory of Computational Biology and Risk AnalysisChristopher J. Portier, Ph.D., Associate Director for Risk Assessment, Environmental Toxicology Program; Chief, Laboratory of Computational Biology and RiskAnalysis; and Coordinator, EMF Hazard EvaluationMary S. Wolfe, Ph.D., Associate Coordinator, EMF Hazard Evaluation, Environmental Toxicology ProgramA CKNOWLEDGEMENTSThis report would not have been possible without the concerted and generous help of literally hundreds of research scientists. Many of the scientists who wrote the articles, which are cited in this report, attended our science review symposia where their research was carefully evaluated and critiqued. Their patience with our questions and their professional attitude in evaluating their own work was extraordinary and is greatly appreciated. We are also indebted to the many scientists from outside of the electric and magnetic fields (EMF) research community who participated in our symposia and spent time and effort evaluating these data on our behalf; this provides a clear example of the dedication of scientists concerned about health issues.Special thanks are extended to the 30 scientists who attended the Working Group Meeting in June 1998. Their hard work and conscientious effort led to one of the most concise and clear reviews of the extremely low frequency (ELF) EMF literature ever developed. The thousands of man-hours extended by this group in such a short period of time provided us with a background document on ELF-EMF health risks that made this report a much simpler task. We wish especially to thank Dr. Arnold Brown for attending our public meetings on the Working Group Report; his extensive experience and insightful comments helped to make these meetings a great success. We would also like to thank Dr. Brown and Dr. Paul Gailey for reviewing this report prior to its release and Mr. Fred Dietrich for advising us on exposure issues during the preparation of this document. Finally we would like to acknowledge the U.S. Department of Energy as our partner in the EMF-RAPID Program and its EMF program officer, Dr. Imre Gyuk.T ABLE OF C ONTENTSEXECUTIVE SUMMARY (i)I NTRODUCTION (i)NIEHS C ONCLUSION (ii)B ACKGROUND (iii)Program Oversight and Management (iii)ELF-EMF Health Effects Research (iv)Information Dissemination and Public Outreach (iv)Health Risk Assessment of ELF-EMF Exposure (v)INTRODUCTION (1)Funding (2)Oversight and Program Management (3)ELF-EMF Health Effects Research (3)Information Dissemination and Public Outreach (4)Literature Review and Health Risk Assessment (6)DO ELECTRIC AND MAGNETIC FIELDS POSE A HEALTH RISK? (9)S CIENTIFIC E VIDENCE S UPPORTING T HIS C ONCLUSION (10)Background on the Limitations of Epidemiology Studies (10)Childhood Cancers (12)Adult Cancers (15)Non-Cancer Findings in Humans (16)Animal Cancer Data (19)Non-Cancer Health Effects in Experimental Animals (23)Studies of Cellular Effects of ELF-EMF (25)Biophysical Theory (29)HOW HIGH ARE EXPOSURES IN THE U.S. POPULATION? (31)CONCLUSIONS AND RECOMMENDATIONS (35)Previous Panel Reviews (35)NIEHS Conclusion (35)Recommended Actions (37)Future Research (38)REFERENCES (41)E XECUTIVE S UMMARYIntroductionElectrical energy has been used to great advantage for over 100 years. Associated with the generation, transmission, and use of electrical energy is the production of weak electric and magnetic fields (EMF). In the United States, electricity isusually delivered as alternating current that oscillates at 60 cycles per second(Hertz, Hz) putting fields generated by this electrical energy in the extremely low frequency (ELF) range.Prior to 1979 there was limited awareness of any potential adverse effects fromthe use of electricity aside from possible electrocution associated with directcontact or fire from faulty wiring. Interest in this area was catalyzed with thereport of a possible association between childhood cancer mortality and proximity of homes to power distribution lines. Over the next dozen years, the U.S.Department of Energy (DOE) and others conducted numerous studies on theeffects of ELF-EMF on biological systems that helped to clarify the risks andprovide increased understanding. Despite much study in this area, considerabledebate remained over what, if any, health effects could be attributed to ELF-EMF exposure.In 1992, the U.S. Congress authorized the Electric and Magnetic Fields Research and Public Information Dissemination Program (EMF-RAPID Program) in theEnergy Policy Act (PL 102-486, Section 2118). The Congress instructed theNational Institute of Environmental Health Sciences (NIEHS), National Institutes of Health and the DOE to direct and manage a program of research and analysisaimed at providing scientific evidence to clarify the potential for health risks from exposure to ELF-EMF. The EMF-RAPID Program had three basic components:1) a research program focusing on health effects research, 2) informationcompilation and public outreach and 3) a health assessment for evaluation of any potential hazards arising from exposure to ELF-EMF. The NIEHS was directedto oversee the health effects research and evaluation and the DOE was given theresponsibility for overall administration of funding and engineering researchaimed at characterizing and mitigating these fields. The Director of the NIEHSwas mandated upon completion of the Program to provide a report outlining thepossible human health risks associated with exposure to ELF-EMF. Thisdocument responds to this requirement of the law.This five-year effort was signed into law in October 1992 and provisions of thisAct were extended for one year in 1997. The Program ended December 31, 1998.The EMF-RAPID Program was funded jointly by Federal and matching privatefunds and has been an extremely successful Federal/private partnership withsubstantial financial support from the utility industry. The NIEHS received$30.1 million from this program for research, public outreach, administration and the health assessment evaluation of ELF-EMF. In addition to EMF-RAPIDProgram funds from the DOE, the NIEHS contributed $14.5 million for support of extramural and intramural research including long-term toxicity studies conducted by the National Toxicology Program.NIEHS ConclusionThe scientific evidence suggesting that ELF-EMF exposures pose any health risk is weak. The strongest evidence for health effects comes from associationsobserved in human populations with two forms of cancer: childhood leukemia and chronic lymphocytic leukemia in occupationally exposed adults. While thesupport from individual studies is weak, the epidemiological studies demonstrate, for some methods of measuring exposure, a fairly consistent pattern of a small,increased risk with increasing exposure that is somewhat weaker for chroniclymphocytic leukemia than for childhood leukemia. In contrast, the mechanisticstudies and the animal toxicology literature fail to demonstrate any consistentpattern across studies although sporadic findings of biological effects (includingincreased cancers in animals) have been reported. No indication of increasedleukemias in experimental animals has been observed.The lack of connection between the human data and the experimental data (animal and mechanistic) severely complicates the interpretation of these results. Thehuman data are in the “right” species, are tied to “real-life” exposures and showsome consistency that is difficult to ignore. This assessment is tempered by theobservation that given the weak magnitude of these increased risks, some otherfactor or common source of error could explain these findings. However, noconsistent explanation other than exposure to ELF-EMF has been identified.Epidemiological studies have serious limitations in their ability to demonstrate acause and effect relationship whereas laboratory studies, by design, can clearlyshow that cause and effect are possible. Virtually all of the laboratory evidence in animals and humans and most of the mechanistic work done in cells fail tosupport a causal relationship between exposure to ELF-EMF at environmentallevels and changes in biological function or disease status. The lack of consistent, positive findings in animal or mechanistic studies weakens the belief that thisassociation is actually due to ELF-EMF, but it cannot completely discount theepidemiological findings.The NIEHS concludes that ELF-EMF exposure cannot be recognized as entirelysafe because of weak scientific evidence that exposure may pose a leukemiahazard. In our opinion, this finding is insufficient to warrant aggressiveregulatory concern. However, because virtually everyone in the United Statesuses electricity and therefore is routinely exposed to ELF-EMF, passiveregulatory action is warranted such as a continued emphasis on educating both the public and the regulated community on means aimed at reducing exposures. The NIEHS does not believe that other cancers or non-cancer health outcomes provide sufficient evidence of a risk to currently warrant concern.The interaction of humans with ELF-EMF is complicated and will undoubtedlycontinue to be an area of public concern. The EMF-RAPID Program successfully contributed to the scientific knowledge on ELF-EMF through its support of highquality, hypothesis-based research. While some questions were answered, others remain. Building upon the knowledge base developed under the EMF-RAPIDProgram, meritorious research on ELF-EMF through carefully designed,hypothesis-driven studies should continue for areas warranting fundamental study including leukemia. Recent research in two areas, neurodegenerative diseases and cardiac diseases associated with heart rate variability, have identified someinteresting and novel findings for which further study is ongoing.BackgroundProgram Oversight and ManagementThe 1992 Energy Policy Act created two committees to provide guidance anddirection to this program. The first, the Interagency Committee (IAC), wasestablished by the President of the United States and composed of representatives from the NIEHS, the DOE and seven other Federal agencies with responsibilities related to ELF-EMF. This group receives the report from the NIEHS Directorand must prepare its own report for Congress. The IAC had responsibility fordeveloping a strategic research agenda for the EMF-RAPID Program, facilitating interagency coordination of Federal research activities and communication to the public and monitoring and evaluating the Program.The second committee, the National EMF Advisory Committee (NEMFAC),consisted of representatives from public interest groups, organized labor, stategovernments and industry. This group was involved in all aspects of theEMF-RAPID Program providing advice and critical review to the DOE and theNIEHS on the design and implementation of the EMF-RAPID Program’sactivities.ELF-EMF Health Effects ResearchThe EMF-RAPID Program’s health effects research initiative relied upon accepted principles of hazard identification and risk assessment to establish priorities. All studies supported by the NIEHS and the DOE under this program were selected for their potential to provide solid, scientific data on whetherELF-EMF exposure represents a human health hazard, and if so, whether risks are increased under exposure conditions in the general population. Research efforts did not focus on epidemiological studies (i.e. those in the human population) because of time constraints and the number of ongoing, well-conducted studies. The NIEHS health effects research program focused on mechanistic, cellular and laboratory studies in the areas of neurophysiology, behavior, reproduction, development, cellular research, genetic research, cancer and melatonin. Mechanistic, cellular and laboratory studies are part of the overall criteria used to determine causality in interpreting epidemiological studies. In this situation, the most cost-effective and efficient use of the EMF-RAPID Program’s research funds was clearly for trying to clarify existing associations identified from population studies. The DOE research initiatives focused on assessment of exposure and techniques of mitigation.The EMF-RAPID Program through the combined efforts of the NIEHS and the DOE radically changed and markedly improved the quality of ELF-EMF research. This was accomplished by providing biological and engineering expertise to investigators and emphasizing hypothesis-driven, peer-reviewed research. Four regional facilities were also set-up where state-of-the-art magnetic field exposure systems were available for in-house and outside investigators to conduct mechanistic research. The EMF-RAPID Program through rigorous review and use of multi-disciplinary research teams greatly enhanced the understanding of the interaction of biological systems with ELF-EMF. Information Dissemination and Public OutreachThe EMF-RAPID Program provided the public, regulated industry and scientists with useful, targeted information that addressed the issue of uncertainty regarding ELF-EMF health effects. Two booklets, a question and answer booklet onELF-EMF and a layman’s booklet addressing ELF-EMF in the workplace, were published. A telephone information line for ELF-EMF was available where callers could request copies of ELF-EMF documents and receive answers to standard questions from operators. The NIEHS also developed a web-site for the EMF-RAPID Program where all of the Program’s documents are on-line and links are available to other useful sites on ELF-EMF. Efforts were made to include the public in EMF-RAPID Program activities through sponsorship of scholarships to meetings; holding open, scientific workshops; and setting aside a two-month period for public comment and review on ELF-EMF and the workshop reports. In addition, the NIEHS sponsored attendance of NEMFACmembers at relevant scientific meetings and at each of the public comment meetings.Health Risk Assessment of ELF-EMF ExposureIn preparation of the NIEHS Director’s Report, the NIEHS developed a process to evaluate the potential health hazards of ELF-EMF exposure that was designed to be open, transparent, objective, scholarly and timely under the mandate of the 1992 Energy Policy Act. The NIEHS used a three-tiered strategy for collection and evaluation of the scientific information on ELF-EMF that included: 1) three science review symposia for targeted ELF-EMF research areas, 2) a working group meeting and 3) a period of public review and comment. Each of the three symposia focused on a different, broad area of ELF-EMF research: mechanistic and cellular research (24-27 March 1997, Durham, NC), human population studies (12-14 January 1998, San Antonio, TX) and laboratory human and clinical work (6-9 April 1998, Phoenix, AZ). These meetings were aimed at including a broad spectrum of the research community and the public in the evaluation of ELF-EMF health hazards, identifying key research findings and providing opinion on the quality of this research. Discussion reports from small discussion groups held for specific topics were prepared for each meeting.Following the symposia, a working group meeting (16-24 June 1998, Brooklyn Park, MN) was held where a scientific panel reviewed historical and novel evidence on ELF-EMF and determined the strength of the evidence for human health and biological effects. Stakeholders and the public attended this meeting and were given the opportunity to comment during the process. The Working Group conducted a formal, comprehensive review of the literature for research areas identified from the symposia as being important to the assessment ofELF-EMF-related biological or health effects. Separate draft documents covering areas of animal carcinogenicity, animal non-cancer findings, physiological effects, cellular effects, theories and human population studies (epidemiology studies) in children and adults for both occupational and residential ELF-EMF exposures were rewritten into a single book. The Working Group characterized the strength of the evidence for a causative link between ELF-EMF exposure and disease in each category of research using the criteria developed by the International Agency for Research on Cancer (IARC).The IARC criteria fall into four basic categories: sufficient, limited, inadequate and evidence suggesting the lack of an effect. After critical review and discussion, members of the Working Group were asked to determine the categorization for each research area; the range of responses reflected the scientific uncertainty in each area. A majority of the Working Group members concluded that childhood leukemia and adult chronic lymphocytic leukemia from occupational exposure were areas of concern. For other cancers and for non-cancer health endpoints, the Working Group categorized the experimental data asproviding much weaker evidence or no support for effects from exposure to ELF-EMF.Following the Working Group Meeting, the NIEHS established a formal review period for solicitation of comments on the symposia and Working Group reports. The NIEHS hosted four public meetings (14-15 September 1998, Tucson, AZ;28 September, Washington, DC; 1 October 1998, San Francisco, CA; and5 October 1998, Chicago, IL) where individuals and groups could voice their opinions; the meetings were recorded and transcripts prepared. In addition, the NIEHS received 178 written comments that were also reviewed in preparation of this report. The remarks that NIEHS received covered many areas related to ELF-EMF and provided insight about areas of concern on behalf of the public, researchers, regulatory agencies and industry.I NTRODUCTIONElectricity is used to the benefit of people all over the world. Wherever electricity is generated, transmitted or used, electric fields and magnetic fields are created. These fields are a direct consequence of the presence and/or motion of electric charges. It is impossible to generate and use electrical energy without creating these fields; hence they are an inevitable consequence of our reliance on this form of energy. Electrical energy is generally supplied as alternating current where the electricity flows in one direction and then in the other to complete a cycle. The number of cycles completed in a fixed period of time (such as a second) is known as the frequency and is generally measured in units of Hertz (Hz), which are cycles per second. In the United States, electricity is usually delivered as 60 Hz alternating current; 50 to 60 Hz cycles are generally referred to as the power-line frequency of alternating current electricity. Just as alternating current electricity has a frequency, so do the associated electric and magnetic fields (EMF). Thus, 60 Hz alternating current electricity will generate a 60 Hz electric field and a60 Hz magnetic field. EMF with cycle frequencies of greater than 3 Hz and less that 3000 Hz is generally referred to as extremely low frequency (ELF) EMF. In addition to magnetic fields associated with electricity, the earth also has a static magnetic field (frequency of 0 Hz) that varies by location from approximately 30 to 50 µT.Electricity has been used, to great advantage, for 100 years and with this widespread use, there has been limited awareness of any potential adverse health effects other than effects caused by direct contact such as electrocution or by faulty wiring such as fire. Research into potential health effects caused by the ELF-EMF resulting from indirect exposure to electrical energy has been underway for several decades. The catalyst that sparked increased study in this area of research was the 1979 report by Wertheimer and Leeper (1) that children living near power lines had an increased risk for developing cancer. Since that initial finding, there have been numerous studies of human populations, animals and isolated cells aimed at clarification of the observations of Wertheimer and Leeper and others. Despite this multitude of research, considerable debate remains over what, if any, health effects can be attributed to ELF-EMF exposure. In 1992, under the Energy Policy Act (PL 102-486, Section 2118), the U.S. Congress instructed the National Institute of Environmental Health Sciences(NIEHS), National Institutes of Health and the U.S. Department of Energy (DOE) to direct and manage a program of research and analysis aimed at providing scientific evidence to clarify the potential for health risks from exposure toELF-EMF. This resulted in formation of the EMF Research and Public Information Dissemination Program (EMF-RAPID Program). The EMF-RAPID Program had three basic components: 1) a research program focusing on health effects research primarily through mechanistic studies of ELF-EMF and engineering research targeting measurement, characterization and management of ELF-EMF; 2) information compilation and dissemination through brochures, public outreach and an ELF-EMF information line for communicating with the public; and 3) a health assessment including an analysis of the research data aimed at summarizing the strength of the evidence for evaluation of any hazard possibly arising from exposure to ELF-EMF. The NIEHS was directed to oversee the health effects research and evaluation and the DOE was given responsibility for engineering research aimed at characterizing and mitigating these fields. Under the Energy Policy Act, the Director of the NIEHS is mandated upon completion of the EMF-RAPID Program to provide a report outlining the possible human health risks associated with exposure to ELF-EMF. This document responds to this requirement of the law.FundingThe EMF-RAPID Program was funded jointly by Federal and matching private funds; through fiscal year 1998, authorized funding for this program was approximately $46 million. Administration of funding for the EMF-RAPID Program was the responsibility of the DOE with funds for NIEHS-sponsored program activities transferred from the DOE to the NIEHS. The EMF-RAPID Program has been an extremely successful Federal/private partnership with substantial financial support from the utility industry. The NIEHS received $30.1 million from this program for research, public outreach, administration and the health assessment evaluation of ELF-EMF. Of the funds received, the NIEHS spent the majority (89%) for research through grants and contracts. The remainder was used for public outreach/administration (2%) and the health risk evaluation (9%). In addition to EMF-RAPID Program funds from the DOE, the NIEHS contributed $14.5 million for support of extramural grants and contracts and intramural research as well as long-term toxicity studies conducted by the National Toxicology Program.。

Electrochemical Detection of Neurotransmitters

Electrochemical Detection ofNeurotransmitters神经递质是神经系统中非常重要的分子，负责提供神经元交流所需的化学信号。

这些分子包括多巴胺、去甲肾上腺素和血清素等，都是生命活动中不可或缺的一部分。

探测这些神经递质的浓度和变化对神经科学的研究有着非常重要的意义。

现代科技提供了一个高效、灵敏的方法，即通过电化学检测神经递质的存在和变化。

电化学检测是一种测量电化学反应的变化的方法。

基本原理是，在电化学反应中产生或消耗电子，形成电势的变化。

电化学检测器可以通过电极来检测这些变化，进而确定溶液中的化合物的浓度和转化率。

比如在神经科学中，利用电化学检测技术可以测量神经递质在神经元间的转移和释放，从而更好地理解神经元之间的沟通方式。

一种常用的电化学检测技术是循环伏安法（Cyclic Voltammetry, CV）。

这种方法通过电势扫描电极表面，在电化学反应发生的过程中测量电流。

神经递质专用的电极可以打磨成微小斜面，以提高检测的精度。

此外，还可以对电极表面添加化学物质以提高选择性。

一个成功电化学检测神经递质的电极需要经过多次测试和修饰。

首先进行的是电极表面的表征，以确定电极的峰电位和氧化还原峰电位。

然后根据实验需要选择最佳扫描速度和电解质。

最后，可以对电极进行化学修饰，以增加电极与目标分子之间的亲和力。

需要注意的是，电化学检测神经递质并不是一项便宜的技术，需要专门的电极和设备。

但是，这种技术具有高灵敏度、良好的选择性和反应速度，比其他测量方法更为优越。

通过电化学检测，我们可以更好地理解神经递质的动态变化过程，从而为神经系统相关疾病的治疗提供新的思路。

总之，电化学检测神经递质是神经科学领域中非常重要的技术。

虽然这种技术需要一定的投入和学习，但其高灵敏度和优越的选择性使得其在神经递质研究及治疗方面有着广泛的应用前景。

2024届山东中学联盟高三下学期5月预测热身卷英语试题+详细解析

2024届山东中学联盟高三下学期5月预测热身卷英语试题+详细解析注意事项: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。

2. 选择题的作答：选出每小题答案后，用2B铅笔把答题卡上对应题目的答案标号涂黑。

如需改动，用橡皮擦干净后，再选涂其他答案标号。

回答非选择题时，将答案写在答题卡上。

3. 考试结束后，将本试卷和答题卡一并交回。

第一部分：阅读理解（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，从每题所给的四个选项（A、B、C和D）中，选出最佳选项。

ASmall Ways You Can Donate Money To CharityThere are plenty of innovative ways that you can help people in need, even when money is tight. Here are just a few unique ways to give.Food Angel, Hong KongFood insecurity has become a global problem for families. In Hong Kong, the people behind the Food Angel program collect 45 tonnes of edible surplus food each week that grocery stores, restaurants and individuals would otherwise dispose of. That includes fresh fruits and vegetables and other perishables (易腐烂的食物) that aren’t normally accepted in food-donation boxes.The impact is significant: Volunteers make and serve around 20,000 meals and distribute more than 11,000 other meals and food packs every day.Frigos Solidaires, FranceImagine if those in need could help themselves to food with anonymity (匿名) and dignity. Frigos Solidaires, or Solidarity Fridges, was started with that aim by Dounia Mebtoul, a young restaurateur in Paris. Now, 130 fridges installed in front of places such as shops and schools offer free food to the hungry across France.Stuff A Bus, CanadaIn Edmonton, the transit service parks vehicles in front of supermarkets for its annual “Stuff a Bus” campaign each November. Volunteers collect food and cash donations from shoppers to fill buses bound for food banks. Since its start in 1995, the campaign has collected 553,000 kilograms of food and roughly half a million dollars.Rice Bucket Challenge, IndiaHeard of the Ice Bucket Challenge? You take a video of yourself dumping a bucket of ice water over your head, then nominate (指定) three more people to do the same. In some versions, the participant donates $100 if they don’t complete the challenge.“I thought it was an amazing way to raise awareness of ALS and raise funds,” recall s Manju Kalanidhi, a journalist in Hyderabad, India. But it didn’t make sense in her country, where water is too precious to waste, even for a good cause. Then in 2014, it hit her: Why not make it a Rice Bucket Challenge to fight hunger? “I gave a bucket o f rice to someone in need and clicked a photo. I shared it on Facebook and said, ‘This is a Rice Bucket Challenge.Why don’t you do it, too?’” Participants donate a bucket of rice to an individual or family —no, it’s not dumped — take a photo and post it on social media with a message encouraging others to do the same.1. Which one can help people in need get food without hurting their pride?A. Food Angel, Hong KongB. Frigos Solidaires, FranceC. Stuff A Bus, CanadaD. Rice Bucket Challenge, India2. What do you know about Rice Bucket Challenge in India?A. It is an amazing way to raise awareness of ALS.B. It was inspired by the Ice Bucket Challenge.C. A bucket of rice is given and dumped.D. A bucket of water is donated for a good cause.3. What’s the p urpose of the text?A. To explain how important to help people in need.B. To inspire readers to start a non-profit organization.C. To introduce some creative ways to give away.D. To appeal to readers to donate money to charity.【答案】1. B 2. B 3. C【解析】【导语】本文是一篇说明文。

电针对坐骨神经损伤大鼠脑源性神经营养因子的影响

·60·Chinese Journal of Information on TCMJun.2017 Vol.24 No.6电针对坐骨神经损伤大鼠脑源性神经营养因子的影响叶晓春，邵水金，国海东，韩小晶，刘玉璞，陆萍萍上海中医药大学基础医学院，上海 201203 摘要：目的观察电针对坐骨神经损伤（SNI）大鼠脑源性神经营养因子（BDNF）的影响，探讨其治疗SNI 的生物学机制。

方法选取成年雄性 Wistar 大鼠 50 只，分离并切断大鼠坐骨神经后于体式显微镜下将两侧断端拉入神经再生室内造模。

大鼠随机分为正常组、假手术组、模型组和电针组。

电针组进行电针治疗，连续 28 d。

治疗结束后，HE 染色观察神经再生，免疫荧光检测神经组织和脊髓 BDNF 的表达，ELISA 检测血清 BDNF 的表达。

结果电针组轴突再生数量明显多于模型组，且大体轮廓较清晰；与模型组比较，电针组可促进大鼠神经组织、脊髓和血清 BDNF 的表达（P＜0.01）。

结论电针可能通过上调神经损伤后 BDNF 的表达，促进大鼠 SNI 的再生修复。

关键词：电针；坐骨神经损伤；脑源性神经营养因子；轴突；大鼠 DOI：10.3969/j.issn.1005-5304.2017.06.015 中图分类号：R245 文献标识码：A 文章编号：1005-5304(2017)06-0060-04Effects of Electroacupuncture on Brain Derived Neurotrophic Factor of Rats with Sciatic Nerve Injury YE Xiao-chun, SHAO Shui-jin, GUO Hai-dong, HAN Xiao-jing, LIU Yu-pu, LU Ping-ping(School of Basic Medicine, Shanghai University of TCM, Shanghai 201203, China) Abstract: Objective To explore the effects of electroacupuncture on brain derived neurotrophic factor (BDNF) of rats with sciatic nerve injury (SNI); To discuss its biological mechanism for treatment of SNI. Methods Fifty adult male Wistar rats were chosen, and the sciatic nerves of rats were cut off and pulled on both sides of the cut ends into nerve regeneration chamber. The rats were randomly divided into normal group, sham-operation group, model group, and electroacupuncture group. In the electroacupuncture group, the rats were treated by electroacupuncture for 28 days. After the treatment, the nerve regeneration was observed through HE staining. Immunofluorescence was used to analyze the expression changes of BDNF in the nerve tissue and spinal cord. ELISA was used to observe the changes of expression of serum BDNF. Results The amount of axon regeneration in the electroacupuncture group was obviously more than that in the model group, and the outline of the tissue more clear. Electroacupuncture could promote the expression of BDNF in the nerve, spinal cord and serum of SNI of rats compared with model group (P<0.01). Conclusion Electroacupuncture can promote the repairment and regeneration of SNI in rats by upregulating the expression of BDNF. Key words: electroacupuncture; sciatic nerve; brain derived neurotrophic factor; axon; rats周围神经损伤（PNI）属中医学“伤筋” “痿证” 范畴。

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神经元的电生理学研究方法

神经元的电生理学研究方法一、前言神经元是神经系统的基本单位，它具有高度的可塑性和复杂的传递功能。

在神经科学领域，如何了解神经元的电生理学特性是非常基础而又重要的问题。

神经元的电生理学研究方法主要包括膜片钳技术、全细胞记录技术、离子探针技术等。

这些技术的研究进展不仅为神经科学提供了丰富的理论基础和实验研究手段，也为疾病的治疗提供了基础。

二、膜片钳技术膜片钳技术最早是由Hodgkin和Huxley在20世纪50年代提出的，它是一种使用玻璃微针贴附在细胞膜上的电极，在细胞的微小电位变化时对细胞进行记录的技术。

该技术可以记录到细胞膜电位的变化，包括静息电位和动作电位等重要指标。

此外，膜片钳技术还可以记录到神经递质的转运和释放等信息。

膜片钳技术具有高时间分辨率和高灵敏度的特点，可以研究单个离子通道或电流，同时对细胞进行电刺激，获得反应性质。

三、全细胞记录技术全细胞记录技术是膜片钳技术的改进，它是在细胞膜上形成孔洞，加入内液后记录细胞内信号。

与膜片钳技术相比，全细胞记录技术的灵敏度更高，可以记录到较小电流和离子通道功能的研究信息，同时可以进行长时间的稳态记录。

通过切换不同内液和药物，可以研究神经元各项电生理参数的变化和互相影响，深入解析调节机制。

四、离子探针技术离子探针技术是近年来发展的一种全新的神经元电生理学研究方法，它主要借助一种特殊设计的微纳米设备，即离子通道探针，在神经元膜表面监测离子流动情况。

与膜片钳技术和全细胞记录技术不同，离子探针技术可以实时记录化学分子灵敏度的离子流量和离子通道的即时带宽。

离子探针技术具有空间分辨率高、时间分辨率高等优点，可以建立神经元电生理信息的三维分布图，对神经元的细胞外域内离子流动研究提供了全新的方法。

五、总结神经元的电生理学研究是神经科学的核心领域之一，不同的电生理学技术提供了不同的研究层面。

膜片钳技术、全细胞记录技术和离子探针技术都是在微小尺度下研究神经元电信号的有效方法。

小学上册第十一次英语第3单元真题试卷

小学上册英语第3单元真题试卷英语试题一、综合题(本题有100小题，每小题1分，共100分.每小题不选、错误，均不给分)1.I enjoy ______ (riding) horses.2.I drink __________ in the morning.3.The __________ (美国宪法) was adopted in 1787.4. A saturated solution does not change when more solute is ______.5.The _____ (carrot) grows underground.6.What do we call a person who studies the stars and planets?A. AstronomerB. GeologistC. MeteorologistD. Biologist7.I enjoy playing with my ________ (拼搭玩具) to create new designs.8.The country known for its festivals is ________ (印度).9. A ______ (种子收藏) can preserve different varieties.10.The _____ is a large area of stars, gas, and dust.11.What do we call the process of water turning into vapor?A. EvaporationB. CondensationC. PrecipitationD. FiltrationA12.What do we call the study of insects?A. EntomologyB. ZoologyC. BotanyD. AnthropologyA Entomology13.The fall of the Roman Empire happened in the ______ (五世纪).14.What is the name of the famous Canadian landmark?A. Sydney Opera HouseB. CN TowerC. Empire State BuildingD. Burj KhalifaB15.I like to draw ______ (漫画) characters in my free time. It’s fun to create my own stories.16.What is the opposite of "big"?A. HugeB. SmallC. TallD. Large17.The element with atomic number is ______.18._____ (生态保护) is necessary for future generations.19.We have a ________ (field trip) scheduled.20. A ________ (猫) likes to chase after mice and can be very playful.21.What is 7 2?A. 4B. 5C. 6D. 3B22.ower brought the first Pilgrims to ________ (美洲). The Medi23.What do you call the process of a liquid turning into a gas?A. EvaporationB. CondensationC. FreezingD. MeltingA24.What is 7 + 5?A. 10B. 12C. 13D. 14C25.What do we call the path that a planet takes around the Sun?A. OrbitB. RotationC. RevolutionD. Cycle26.The process of ionization involves the formation of ______.27.What is the name of the largest organ inside the human body?A. HeartB. LiverC. BrainD. LungsB Liver28.The city of Apia is the capital of _______.29. A _____ is a body of water that moves continuously.30.The ________ is often called "man's best friend."31.I love to ___ (cook/eat) with my family.32.What is the capital of Lithuania?A. VilniusB. KaunasC. KlaipedaD. PanevezysA33.What is the name of the imaginary line that divides the Earth into the Eastern and Western Hemispheres?A. EquatorB. Prime MeridianC. International Date LineD. Tropic of CancerB34. A reaction that requires energy is called an ______ reaction.35.The process of combustion produces ______ and heat.36.What do you call a young male alligator?A. HatchlingB. PupC. KitD. Calf37.We have ______ at the picnic. (sandwiches)38.I enjoy ________ (走路) in the park.39. A chemical reaction that involves the exchange of ions is called a _____.40.What do we call the effect of the Earth's rotation on weather patterns?A. Coriolis EffectB. Trade WindsC. Jet StreamD. Ocean Currents41.The boy has a new ________.42.An indicator is a substance that changes color in response to _____.43.The _______ (猫) climbs the tree.44.The park is ___. (fun)45.The ________ is a small but mighty creature.46.The city of Yerevan is the capital of _______.47.My friend enjoys helping __________ (他人).48.What do you call a collection of stories?A. AnthologyB. CompilationC. CollectionD. All of the above49.We have a ______ (精彩的) program for students at school.50.He is a firefighter, ______ (他是一名消防员), who bravely goes into danger.51._____ (thyme) is a common herb used in cooking.52.What is the name of the famous lake in Africa?A. Lake VictoriaB. Lake BaikalC. Lake SuperiorD. Lake Michigan53.The _____ (violet) grows low to the ground.54.I can ______ (开发) my talents through practice.55.Which insect can produce honey?A. AntB. ButterflyC. BeeD. FlyC56.Which of these is a common household pet?A. SnakeB. ParrotC. CatD. HamsterC57.The capital of Portugal is ________.58.I like to explore the ________ (森林) near my house.59.My sister loves to _______ (动词) in her spare time. 她觉得很 _______ (形容词).60.We have _____ (English/math) class today.61.What is the name of the telescope that observes ultraviolet light?A. Hubble Space TelescopeB. Chandra X-ray ObservatoryC. Kepler Space TelescopeD. Spitzer Space Telescope62.Sediments can be carried away by wind and __________.63.What is the name of the famous detective created by Arthur Conan Doyle?A. Hercule PoirotB. Sherlock HolmesC. Miss MarpleD. Philip MarloweB64. A dolphin is a playful _______ that loves to swim and splash around.65.We enjoy ________ (cooking) together.66.Her _____ (阿姨) is very kind.67.The _____ (根系) of a plant can be very extensive.68.The ______ (狐狸) is very clever.69.The process of evaporation involves heat and ______.70.I like to help my parents with ________.71.What is the term for a scientist who studies plants?A. BotanistB. ZoologistC. MicrobiologistD. EcologistA72.The _____ (花蜜) attracts many pollinators.73.The trees in the _______ provide shade and a place to relax.74.The part of the atom that has a positive charge is called a _______.75.How many players are on a field hockey team?A. 10B. 11C. 12D. 1376.The chemical formula for sodium fluoride is _____.77.What is the primary function of the heart?A. To breatheB. To pump bloodC. To digest foodD. To filter wasteB78.What is the capital of Afghanistan?A. KabulB. IslamabadC. TehranD. DohaA79.The capital of Aruba is __________.80.What is the capital of the United States?A. New YorkB. Washington,C. Los AngelesD. ChicagoB81.What is the name of the famous American author known for his adventure novels?A. Mark TwainB. Ernest HemingwayC. F. Scott FitzgeraldD. John SteinbeckA82.I like to _______ my family.83.The ______ is known for her supportive nature.84.I have a toy ________ that can sing.85.The sheep says _______ (咩) in the pasture.86.Which of these is a musical instrument?A. ViolinB. PaintbrushC. PencilD. CameraA87.Planets can be terrestrial or _______ gas giants.88.I share secrets with my __________. (朋友)89.The chemical formula for sodium sulfate is _____.90.The capital of Tonga is _______.91.The Earth's surface is shaped by natural ______.92.The element with atomic number is _______.93.What is 5 x 2?A. 7B. 8C. 9D. 10D94.What is the capital of Norway?A. OsloB. BergenC. TrondheimD. StavangerA95.The formula for table salt is _______.96. A butterfly floats gently in the _______.97.In ______, the days are longer, which means we have more time to play. I love watching the ______ change colors, painting the landscape in shades of ______. It makes everything look magical.98.I brush my teeth _______ (every day/once a week).99.I have a toy _______ that glows in the dark and lights up my whole room.100.I enjoy going to the ________ (游乐场) during summer.。

CFD modelling of bubble–particle attachments in flotation cells

CFD modelling of bubble–particle attachments in ﬂotation cellsP.T.L.Koh *,M.P.SchwarzCSIRO Division of Minerals,Bayview Avenue,Box 312,Clayton South,Victoria 3169,AustraliaReceived 12July 2005;accepted 6September 2005Available online 19October 2005AbstractIn recent years,computational ﬂuid dynamic (CFD)modelling of mechanically stirred ﬂotation cells has been used to study the com-plexity of the ﬂow within the cells.In CFD modelling,the ﬂotation cell is discretized into individual ﬁnite volumes where local values of ﬂow properties are calculated.The ﬂotation eﬀect is studied as three sub-processes including collision,attachment and detachment.In the present work,these sub-processes are modelled in a laboratory ﬂotation cell.The ﬂotation kinetics involving a population balance for particles in a semi-batch process has been developed.From turbulent collision models,the local rates of bubble–particle encounters have been estimated from the local turbulent velocities.The probabilities of collision,adhesion and stabilization have been calculated at each location in the ﬂotation cell.The net rate of attach-ment,after accounting for detachments,has been used in the kinetic model involving transient CFD simulations with removal of bubble–particle aggregates to the froth layer.Comparison of the predicted fraction of particles remaining in the cell and the fraction of free particles to the total number of particles remaining in the cell indicates that the particle recovery rate to the pulp–froth interface is much slower than the net attachment rates.For the case studied,the results indicate that the bubbles are loaded with particles quite quickly,and that the bubble surface area ﬂux is the limiting factor in the recovery rate at the froth interface.This explains why the relationship between ﬂotation rate and bubble surface area ﬂux is generally used as a criterion for designing ﬂotation cells.The predicted ﬂotation rate constants also indicate that ﬁne and large particles do not ﬂoat as well as intermediate sized particles of 120–240l m range.This is consistent with the ﬂotation recovery generally observed in ﬂotation practice.The magnitude of the ﬂotation rate constants obtained by CFD modelling indicates that transport rates of the bubble–particle aggregates to the froth layer contribute quite signiﬁcantly to the overall ﬂotation rate and this is likely to be the case especially in plant-scale equipment.Ó2005Elsevier Ltd.All rights reserved.Keywords:Flotation bubbles;Flotation kinetics;Flotation machines;Modelling1.IntroductionResearchers have recently started to use computational ﬂuid dynamics (CFD)for modelling mechanically stirred ﬂotation cells to study the complexity of three-phase (air–water–solids)ﬂows within the cells (Koh and Schwarz,2003).Flotation cells are conventionally designed using empirically derived relations.In CFD modelling,the ﬂota-tion cell is discretized into individual ﬁnite volumes wherelocal values of ﬂow properties are calculated.The detailed understanding of ﬂow gained using this approach allows modiﬁcation to existing equipment and operation to im-prove ﬂotation performance.The ﬂotation eﬀect is modelled as three sub-processes involving collision,attachment and detachment.A turbu-lent collision model is used to estimate the rate of bub-ble–particle encounters,employing the local turbulent velocity,and the size and number concentrations of bub-bles and particles in diﬀerent parts of the cell.The proba-bilities of collision,adhesion and stabilization are also calculated such that attachment rates can now be esti-mated.The detachment rates are also estimated from the0892-6875/$-see front matter Ó2005Elsevier Ltd.All rights reserved.doi:10.1016/j.mineng.2005.09.013*Corresponding author.E-mail address:Peter.Koh@csiro.au (P.T.L.Koh).This article is also available online at:/locate/minengMinerals Engineering 19(2006)619–626ﬂuid turbulence.The net rate of attachment,after account-ing for detachments,is used in the combined CFD kinetic model involving transient population-balance simulations with removal of bubble–particle aggregates to the froth layer.In this paper,the local turbulent energy dissipation rates used in the kinetic model are obtained by CFD modelling of the cell.This is a signiﬁcant improvement over other models where assumptions based on an average dissipation rate or an assumed Gaussian distribution for turbulent velocities for the whole cell(e.g.Bloom and Heindel, 2003)have been used.CFD modelling provides a realistic approach toﬂotation models without the additional assumptions on turbulent energy dissipation rates.Flotation in a cylindrical tankﬁtted with a Rushton turbine impeller is studied in this paper since commercial ﬂotation equipment are mostly of this typeﬁtted with ro-tor–stator system.For comparison,a laboratoryﬂotation cell designed by CSIRO Minerals is also modelled.2.Flotation kineticsFlotation is generally modelled as aﬁrst-order rate pro-cess with respect to the number of particles and number of bubbles in the attachment step,and a detachment process with respect to the number of bubble–particle aggregates. The kinetic equation for the bubble–particle encounters is described by the rate of removal of the number of particles in a given volume as follows:d N p1d t¼Àk1N p1N bþk2N að1Þwhere N p1is the number concentration(mÀ3)of free parti-cles,N b is the number concentration of bubbles available for attachment,N a is the number concentration of bub-ble–particle aggregates,k1is the particle–bubble attach-ment rate constant,and k2is the particle–bubble detachment rate constant.In a given volume within theﬂo-tation cell,the total number of particles consists of free particles(N p1)and particles that are attached to bubbles (N p2),both as functions of timeN pT¼N p1þN p2ð2Þwith N pTo as the initial particle concentration.In general, bubbles will have any number of particles attached as they move up toward the froth layer,with the number of parti-cles per bubble varying with time and position,as well as from bubble to bubble.To simplify the situation,it is as-sumed in this paper that certain bubbles are fully loaded with particles while the remaining bubbles are clean.The number of bubble–particle aggregates(N a)is then related to the total number of bubbles(N bT)by an average loading parameter(b)as follows:N a¼b N bTð3ÞThe average loading parameter(b)in a given volume varies with time and position in the cell.The number of bubbles that are available for attachment(N b)is also related to the total number of bubbles as follows:N b¼ð1ÀbÞN bTð4ÞSo,the attachment–detachment kinetics in Eq.(1)can be re-written as follows:d N p1d t¼Àk1N p1N bTð1ÀbÞþk2N bT bð5ÞAn interpretation of the new equation is that the kinetics is now based on the free surface area available for particle attachment with a bubble loading parameter b such that b=0for clean bubbles and b=1for fully loaded bubbles. The number of particles that can be attached to a single bubble is given by S which is the ratio of the total surface area of the bubble to the particle projected area as follows:S¼4d bd p2ð6Þwhere d p is the particle diameter and d b is the bubble diam-eter.Realistically,it is not possible for the particles to cov-er the whole bubble surface due to packing,shape and other factors.As aﬁrst approximation,it is assumed that the attached particles occupy about half of the total bubble surfaces when the bubbles are fully loaded.The maximum number of particles per bubble ratio(S max)is then de-scribed byS max¼0:5S¼2d bd p2¼N p2b N bTð7ÞBy rearranging the above equation,the bubble loading parameter b can be obtained fromb¼N p2S max N bTð8ÞThe present method is a signiﬁcant improvement over pre-vious models in modelling the number of particles that can be attached to a bubble.Theﬁrst model proposed by Bloom and Heindel(1997)had assumed that only bubbles which do not already have a particle attached to them are capable of picking up a particle,and that the average num-ber of particles on a bubble was equal to1.0.This assump-tion was replaced in their latest model(Bloom and Heindel, 2003)by an average loading based on total numbers of par-ticles and bubbles in theﬂotation cell.In the kinetic equation,the particle–bubble attachment rate constant k1(m3/s)is deﬁned byk1¼Z1P c P a P sð9Þand the particle–bubble detachment rate constant k2(1/s)is deﬁned byk2¼Z2P d¼Z2ð1ÀP sÞð10Þwhere P c,P a and P s are the probabilities of particle–bubble collision,adhesion and stabilisation against external forces. P d is the probability a bubble–particle aggregate will be-come unstable and is assumed to be equal to(1ÀP s).P s620P.T.L.Koh,M.P.Schwarz/Minerals Engineering19(2006)619–626is included in both the particle–bubble attachment rate constant k1and in the detachment rate constant k2because the processes involve diﬀerent turbulent eddies acting inde-pendently of each other.The eddy that facilitates attach-ment can also cause detachment of the aggregate during the attachment process.Z1is related to the particle–bubble collision frequency dependent on the size of the particles and bubbles,and hydrodynamics of theﬂotation pulp.Z2 is the detachment frequency of particles from bubbles.Based on work of Abrahamson(1975),Schubert and Bischofberger(1979)applied the following equation for the number of particle–bubble collisions per unit time and volume inﬂotation cells.The equation is valid only in turbulentﬂows where inertial eﬀects are the primary cause of collisionsZ1¼5:0d pþd b22U2pþU2b1=2ð11Þwhere U p is the turbulent(rms)ﬂuctuating velocity of the particle relative to theﬂuid,and U b is the turbulent(rms)ﬂuctuating velocity of the bubble relative to theﬂuid.In typicalﬂotation processes,these velocities(U i=U p or U b)are a function of the local turbulent energy dissipation rate as follows(Leipe and Mo¨ckel,1976):U i¼0:4e4=9d7=9im1=3q iÀq fqf2=3ð12Þwhere e is the turbulent energy dissipation rate per unit mass,m is the kinematic viscosity,q f is theﬂuid density, and q i is the density of the particle(p)or bubble(b).The condition for use of the above model with independent bubble or particle velocities is that the diameter of the par-ticle or bubble must be greater than the critical diameter, d crit in the following equation:d2 i >d2crit¼15l f U2fqieð13Þwhere l f is theﬂuid viscosity and U f is the meanﬂuid veloc-ity deviation.In applying the case to bubbles,the critical diameter is based on the virtual mass which is estimated by q i=0.5q f using theﬂuid density.The criterion is used to determine the applicability in terms of particle and bub-ble diameters in various turbulent regimes within theﬂota-tion cell.In regions where velocities for the particle and bubbles are not independent,the collision equation by Saﬀman and Turner(1956)is applicable forﬁne particles and bub-bles conﬁned within eddies in low turbulent dissipation re-gions as follows:Z1¼ﬃﬃﬃﬃﬃﬃ8p15rd pþd b23em1=2ð14ÞThe bubble–particle detachment frequency Z2is depen-dent on the relative velocity between the particle–bubble aggregate and the surroundingﬂuid,and is estimated by Z2¼ﬃﬃﬃﬃﬃﬃC1pe1=3ðd pþd bÞ2=3ð15Þwhere C1is an empirical constant with a value of2as sug-gested by Bloom and Heindel(2003).The collision eﬃciency P c accounts for the tendency of particles to follow theﬂuid streamlines around the bubble and avoid actual contact,which is especially true for parti-cles that are much smaller than the bubble.The equation for the collision probability proposed by Yoon and Luttrell (1989)for intermediate bubble Reynolds number in the range of0.2<Re b<100is applied:P c¼1:5þ415Re0:72bd2pd2bð16Þwhere the bubble Reynolds number based on Re b=d b U b/m is used.The equation is valid for particles smaller than 100l m and bubbles smaller than1mm with immobile sur-faces due to adsorbed surfactants.The probability of adhesion P a is determined by the slid-ing time of the particles on bubble surfaces and the induc-tion time for rupture of the disjoiningﬁlm between the particle and bubble.If the sliding time is longer than the induction time,adhesion is likely.Yoon and Luttrell (1989)derived an expression for the adhesion probability dependent on the particle and bubble sizes,the bubble Rey-nolds number and the induction time as follows:P a¼sin22arctan expÀð45þ8Re0:72bÞU b t ind15d bðd b=d pþ1Þ!ð17Þwhere t ind is the induction time and U b is the bubble rela-tive velocity.The induction time is a function of the parti-cle size and contact angle which can be determined by experiment and correlated in the formt ind¼Ad Bpð18Þwhere parameters A and B are independent of particle size. From measurements with particles and bubbles of various sizes in solutions of varying ionic strength,Dai et al.(1999) found that parameter B is constant with a value of0.6,and parameter A is inversely proportional to the particle con-tact angle h.Based on theseﬁndings,the following equa-tion was constructed by the present authors and applied in the CFD model:t ind¼75hd0:6pð19Þwhere t ind is given in s,h in degrees and d p in m.The prob-ability of adhesion can now be calculated for given values of bubble size,particle size and contact angle.The probability of stability P s accounts for the stabiliza-tion or destabilization of the bubble–particle aggregate. Schulze(1993)proposed a form as follows:P s¼1Àexp1À1BoÃð20ÞP.T.L.Koh,M.P.Schwarz/Minerals Engineering19(2006)619–626621where the modiﬁed Bond number(Bo*)is deﬁned as the ra-tio of detachment to attachment forces,and is given by where g is the acceleration due to gravity,r is the surface tension,and D q p=(q pÀq f).In the derivation by Schulze, the acceleration(force)that determines the detachment of a particle from the bubble is dependent on the intensity of turbulence in theﬂow.It is assumed that turbulent vortices of dimensions corresponding to those of the bubble–parti-cle aggregate cause the detachment.From their validation experiments,Bloom and Heindel(2003)suggested a modi-ﬁed form as follows:P s¼1Àexp A s1À1 BoÃ!ð22Þwhere A s is an empirical constant with a value of0.5.3.Model descriptionMulti-phaseﬂow equations for the conservation of mass,momentum and turbulence quantities have been solved using an Eulerian–Eulerian approach in which the pulp(liquid–solid)and the gas phases are treated as inter-penetrating continua.Two mesh blocks have been gener-ated for modelling the rotating impeller and the stationary stator within the tank.Transport equations have been solved using the multiple frames of reference tech-nique in the CFX-4.4(2001)computer code.Source terms include buoyancy for the gas phase.The froth layer is not included in the computational domain;only the pulp zone is simulated.At the froth–pulp interface,gas bubbles with attached particles are transferred from the pulp zone to the froth layer at the rate bubbles arrive at the interface.For theﬂotation kinetics,the transfer of particles between the pulp and bubbles is achieved by applying source/sink terms in the population-balance equation in Eq.(1).The tran-sient simulation uses adjustable/variable time steps such that the mass error is less than0.1%for each time step.A stirred tank cell used inﬂotation experiments has been simulated.Aﬂat-bottomed cylindrical tank of diameter T=0.195m wasﬁtted with a standard Rushton turbine with a diameter D=T/3stirring at840rpm(Hui and Ahmed,1999).The tank includes four baﬄes of width T/ 10.An average bubble diameter of1mm,and monosized particles of density2600kg/m3in a pulp of32%by weight have been applied in the model.This is equivalent to a par-ticle volume fraction of0.153.For comparison,a laboratoryﬂotation cell designed by CSIRO Minerals has also been modelled.The CSIROﬂo-tation cell,with a volume of3.78l,has an eight-bladed72-mm diameter impeller driven from below and enclosed in a conical shroud similar to a Denver-type mechanism.Air isinjected at a rate of8l/min through a nozzle located within the stator and directed downwards at the impeller which isstirring at1200rpm.4.Results and discussionCFD predictions indicate a complexﬂowﬁeld within the ﬂotation cell and much of the action occurs in the impeller region.Theﬂow around the cell is important as it deter-mines the paths taken by the bubble–particle aggregates to-wards the froth layer.Proﬁles of theﬂowﬁeld obtained include turbulent energy dissipation,volumetric fraction of air phase and particle–bubble collision rate.The cumulative distribution of the turbulent energy dis-sipation rates in the stirred cell have been reported(Koh et al.,2000)from which two regions in theﬂotation cell are represented:the impeller region having higher values of the turbulent energy dissipation rate and the remainder of the cell having lower dissipation values.In the popula-tion balance,the bubble number concentration is obtained by dividing the local gas holdup by the bubble volume.The probabilities of collision,adhesion and stabilization have been calculated using values of turbulent energy dissi-pation rates found in theﬂotation cell.Two contact angles have been used in the calculation for comparison.The attachment rate,(Z1P c P a P s N bT)is plotted as a function of particle diameter in Fig.1.This rate represents the initial rate of contact between particles and clean bubbles.BoÃ¼d2pD qpgþ1:9qpe2=3d p2þd b2À1=3!þ1:5d p4rd bÀd b q f gsin2pÀh2ÀÁ6r sin pÀh2ÀÁsin pþh2ÀÁð21ÞFig.1.Attachment rate(Z1P c P a P s N bT)for a bubble of diameter1.0mmplotted as a function of particle diameter at four turbulent energydissipation rates and two contact angles.622P.T.L.Koh,M.P.Schwarz/Minerals Engineering19(2006)619–626To obtain ﬂotation rates,the mass transfer of particles between the pulp and the bubbles in the ﬂotation cell has been simulated for a contact angle 38°.The total number of particles remaining in the batch cell is determined by summing particles in all the ﬁnite volumes.The results for the case of 60l m particles are shown in Fig.2where the predicted fractions of free,attached and ﬂoated parti-cles are plotted as a function of time.These results may be interpreted as produced by a ‘‘reaction in series’’mech-anism.The sum of free and attached particles remaining in the cell is plotted against time in Fig.3(semi-log)for var-ious particle sizes.This plot is similar to results usually ob-tained from ﬂotation tests.A more interesting plot is the ratio of free particles to the total number of particles remaining in the cell (free and attached)shown in Fig.4.A global ‘‘equilibrium’’between free and attached particles is observed in some of the cases in Fig.4due to attachmentand detachment processes occurring in diﬀerent parts of the cell.Assuming a ﬁrst-order rate process,ﬂotation rate constants can be obtained from the half times t 0.5using the following equation:k ¼ln 2:0t 0:5ð23ÞThe predicted rate constants are plotted as a function of particle diameters in Fig.5showing that ﬁne and large par-ticles do not ﬂoat as well as intermediate sized particles of 120–240l m.This trend is generally observed with ﬂotation recovery (Trahar,1981).Experimental data reported by Pyke et al.(2003),Duan et al.(2003)and Ahmed and Jameson (1985)are also consistent with this observation.An initial comparison against experimental rate constant for quartz at 600rpm by Ahmed and Jameson in Fig.5Fig.2.CFD prediction of the fractions of free,attached and ﬂoated particles plotted as a function of time for particles of 60l mdiameter.Fig. 3.CFD prediction of the sum of free and attached particles remaining in the cell plotted as a function of time for various particlediameters.Fig.4.CFD prediction of the ratio of free particles to the sum of free and attached particles remaining in the cell plotted as a function of time for various particlediameters.Fig.5.CFD predicted ﬂotation rate constant plotted as a function of particle diameter and comparison against experimental rate constant for quartz by Ahmed and Jameson.P.T.L.Koh,M.P.Schwarz /Minerals Engineering 19(2006)619–626623shows that the CFD predicted values are of the same order of magnitude.Detailed comparison against experiment is planned in further work.In practice,the rate constants are usually correlated with the bubble surface areaﬂux S b which can be obtained fromS b¼6J gd bð24Þwhere J g is the superﬁcial gas velocity.Plant data indicate that S b is dependent on the impeller speed and airﬂow rate. Gorain et al.(1999)found that theﬂotation rate constant k has a strong correlation with S b as follows:k¼P kÁS bÁR fð25Þwhere P k is theﬂotation probability representing theﬂoat-ability of the ore,and R f is the froth recovery factor.The ﬂotation probability for various particle sizes have been calculated from CFD predicted k values,with R f=1.0 and J g=0.0106m/s(or S b of63.4sÀ1)in the cell.The cal-culated values of P k of the order of10À4are shown in Ta-ble1.P k is calculated using Eq.(25)based on the rate constant k predicted by CFD simulation.The relationship between P k and P c P a P s is not obvious since they are de-ﬁned diﬀerently.The probabilities P c P a P s are involved dur-ing a single particle–bubble encounter,while P k is obtained from the rate of decrease of the total number of particles in theﬂotation cell as a result of multiple encounters over time.The attachment rates from previous simulations in a laboratoryﬂotation cell designed by CSIRO Minerals (Koh and Schwarz,2003)are for bubble–particle attach-ments only,without the recovery of particles through the froth interface.In the previous work,the attached particles were removed from the pulp phase as soon as a bubble–particle aggregate was formed.The attachment rate con-stant of the order of300sÀ1for60l m particles was ob-tained and is much larger in comparison to theﬂotation rate of0.02sÀ1(or1.13minÀ1)in Table1as obtained in the present work which includes transport to the froth interface.In Fig.2,the fraction of free particles to the total num-ber of particles remaining in the cell decreases quite rapidly initially with the rate of decrease abating at longer times. The reason for slower decrease in free particles at longer times is because the removal of attached particles from the pulp is limiting the process.The distribution of bubble loading in the cell is plotted in Fig.6showing that the bub-bles are almost fully loaded in the top part of the cell with b values closer to1.0.The initial attachment rate is found to be very fast in comparison to the recovery rates of attached particles from the froth interface.Since the bubbles are loaded with particles quite quickly,the bubble surface area ﬂux is the limiting factor in the recovery rate from the froth interface.This explains why the relationship in Eq.(25)be-tweenﬂotation rate and bubble surface areaﬂux is gener-ally observed in batch or plant-scale cells and why this relationship has been used as a criterion for designingﬂo-tation cells.The recovery rate is slower than the net attachment rate because of transport times for bubble–particle aggregates to move through the pulp to the froth interface.The pre-dicted recovery rates are still quite large in comparison with the observed rates in the plant because the overall rates include transport within the froth layer.For example, measuredﬂotation rates of0.1–0.25minÀ1have been re-ported by Gorain et al.(1998)in3m3commercial cells. The transport times are quite signiﬁcant in plant-scaleﬂo-tation cells as the bubble–particle aggregates have to move over large distances.This is one reason whyﬂotation rates are much faster in laboratory batch cells where the bubble–particle aggregates have shorter distances to reach the froth layer.The distribution of attachment rates in the stirred cell is plotted in Fig.7where negative values represent detach-ment.The plot shows that detachment rates are large near the impeller tip.The maximum attachment rates are not far from the impeller.The two zones are quite close.The netTable1CFD predictedﬂotation rate constant andﬂotation probability for various particle diametersd p(l m)t0.5(s)k(sÀ1)k(minÀ1)P k7.5205.90.00340.202 5.3·10À5 15113.00.00610.3689.7·10À5 3061.30.01130.678 1.8·10À4 6036.80.0188 1.130 3.0·10À4 12019.90.0348 2.090 5.5·10À4 24011.70.0592 3.5559.3·10À4 48016.70.0416 2.496 6.6·10À4Fig.6.CFD prediction of the bubble loading parameter b afterﬂotation time of320s for particles of60l m diameter in the stirred cell.624P.T.L.Koh,M.P.Schwarz/Minerals Engineering19(2006)619–626eﬀects of the attachment rates are shown in the predicted distribution of free particles remaining in the cell plotted in Fig.8,and in the distribution of attached particles plot-ted in Fig.9.For comparison,the distribution of net attachment rates in the CSIRO Denver cell is shown in Fig.10.The plot shows that detachment rates (with negative values)are also large near the impeller tip,but the maximum attachment rates are outside the impeller zone.The two zones are sep-arated by the stator shroud.The negative regions are inev-itable because of the need to use a high impeller speed to generate ﬁne bubbles for the necessary bubble surface area ﬂux to operate.Flotation cell design should ideally mini-mize the negative regions while maximizing the attachment rates available in the cell.5.ConclusionsCFD modelling of a batch ﬂotation cell has been per-formed.Bubble–particle collision rates,detachment rates and the probabilities of collision,adhesion and stabiliza-tion have been calculated in diﬀerent parts of the -parison of the predicted fraction of particles remaining in the cell and the fraction of free particles to the totalnumberFig.7.CFD predicted net attachment rates (108m À3s À1)after ﬂotation time of 320s for particles of 60l m diameter in the stirred cell.Negative values indicate netdetachment.Fig.8.CFD predicted volume fraction of free particles after ﬂotation time of 320s for particles of 60l mdiameter.Fig.9.CFD predicted volume fraction of attached particles after ﬂotation time of 320s for particles of 60l m diameter in the stirredcell.Fig.10.CFD predicted net attachment rates (108m À3s À1)after ﬂotation time of 228s for particles of 60l m diameter in the CSIRO Denver cell.P.T.L.Koh,M.P.Schwarz /Minerals Engineering 19(2006)619–626625。

大脑活动的电生理学研究方法

大脑活动的电生理学研究方法大脑活动的电生理学研究方法主要包括脑电图（EEG）、脑磁图（MEG）、脑皮层电图（ECoG）和多单元记录等。

这些方法可以帮助研究者了解大脑在不同状态下的电活动特征，揭示不同脑区之间的相互作用，进而推进对大脑结构和功能的理解。

脑电图（EEG）是一种最常用的电生理学方法，通过在头皮上放置电极来记录大脑的电活动。

EEG可以提供具有较高时间分辨率（毫秒级）的大脑电活动信息。

研究者可以利用EEG来研究大脑在不同任务和刺激条件下的电生理变化，如注意力、认知过程和情绪等。

此外，EEG还可以应用于疾病诊断和脑机接口领域。

脑磁图（MEG）是一种记录大脑磁场的电生理学方法。

MEG可以测量大脑中神经元的磁场活动，提供具有较高时间分辨率和空间分辨率的信息。

与EEG相比，MEG在记录脑活动时更加敏感，并且不受头皮和颅骨的干扰。

因此，MEG能够提供更准确的脑活动信号，为研究大脑结构和功能提供了有力的工具。

脑皮层电图（ECoG）是一种记录大脑皮层电活动的方法。

与EEG相比，ECoG的电极直接放置在大脑皮层上，能够提供更高分辨率的电活动信号。

ECoG广泛应用于癫痫手术前定位、脑机接口和认知神经科学等领域的研究。

由于ECoG信号的高时空分辨率，它在理解大脑的局部电活动和功能连接方面具有独特的优势。

多单元记录是一种记录单个神经元电活动的方法。

通过将微电极放置在大脑区域中，研究者可以记录到不同神经元的电活动。

多单元记录可以提供最高的时空分辨率，可以更详细地了解神经元网络的活动。

多单元记录广泛应用于认知神经科学、运动控制和药物研发等领域。

除了以上几种主要的电生理学方法，还有其他一些相关的技术和方法，如功能磁共振成像（fMRI）、脑干听觉诱发电位（ABR）和视觉诱发电位（VEP）等。

这些方法在研究大脑活动时具有独特的优势和应用价值。

总之，电生理学研究方法在研究大脑结构和功能中起着重要的作用。

通过这些技术和方法，研究者可以了解大脑在不同活动状态下的电活动特征，并进一步探索大脑的组织和功能连接。

基于团簇微观结构分析的离子电活性聚合物驱动特性

第 55 卷第 1 期2024 年 1 月中南大学学报(自然科学版)Journal of Central South University (Science and Technology)V ol.55 No.1Jan. 2024基于团簇微观结构分析的离子电活性聚合物驱动特性王红，杨亮，杨延宁(延安大学物理与电子信息学院，陕西延安，716000)摘要：首先，对离子交换膜吸附水分子微观过程进行分析，并结合团簇结构揭示离子电活性聚合物的传质动力学特性；其次，基于溶胀理论研究团簇受力情况，依据几何变形特点和变形传质机理建立物理模型；最后，对得到的驱动模型进行验证和分析讨论。

研究结果表明：本文模型所得结果和实验结果较吻合。

含水量对离子交换膜团簇通道的形成有重要影响，阳离子的迁移以及水分子运动是离子交换膜驱动的主控因素。

随着阳离子浓度和水分子浓度增加，静水压力、渗透压力以及静电压力均逐渐增大，渗透压力对离子电活性聚合物弯曲变形起主导作用。

关键词：离子聚合物金属复合材料；团簇微观结构；软体机器人；驱动特性中图分类号：TB381 文献标志码：A 文章编号：1672-7207（2024）01-0106-10Actuation characteristics of ionic electroactive polymers based oncluster microstructure analysisWANG Hong, YANG Liang, YANG Yanning(School of Physics and Electronic Information, Yan'an University, Yan'an 716000, China)Abstract: Firstly, analysis of the microscopic process of water molecule adsorption by ion-exchange membranes was carried out and the mass transfer kinetics of ion-electrically active polymers in the context of cluster structure was revealed. Secondly, physical model based on the geometrical deformation characteristics and deformation mass transfer mechanism was established, and the force on the clusters was studied based on the dissolution theory. Finally, the obtained model was experimentally validated and analytically discussed. The results show that the proposed actuation model result matches well with the experimental result. The water content has an important influence on the formation of cluster channels in ion exchange membranes, and the migration of cations and the收稿日期： 2023 −06 −18；修回日期： 2023 −10 −08基金项目(Foundation item)：国家自然科学基金资助项目(52365069)；陕西省教育厅科学研究计划项目(23JK0730)；延安大学博士科研启动基金资助项目(YDBK2021-09，YDBK2023-09) (Project(52365069) supported by the National Natural Science Foundation of China; Project(23JK0730) supported by Scientific Research Program of Department of Education of Shaanxi Province; Projects(YDBK2021-09, YDBK2023-09) supported by the PhD Research Startup Foundation of Yan'an University)通信作者：杨亮，博士，副教授，从事微纳机械系统、柔性智能材料、仿生人工肌肉以及机器人技术研究；E-mail ：*************************.DOI: 10.11817/j.issn.1672-7207.2024.01.009引用格式：王红, 杨亮, 杨延宁. 基于团簇微观结构分析的离子电活性聚合物驱动特性[J]. 中南大学学报(自然科学版), 2024, 55(1): 106−115.Citation: WANG Hong, YANG Liang, YANG Yanning. Actuation characteristics of ionic electroactive polymers based on cluster microstructure analysis[J]. Journal of Central South University(Science and Technology), 2024, 55(1): 106−115.第 1 期王红，等：基于团簇微观结构分析的离子电活性聚合物驱动特性movement of water molecules are the main controlling factors leading to the actuation of ion exchange membranes. The hydrostatic, osmotic and electrostatic pressures increase with the increase of the cation and water molecule concentrations, and the osmotic pressure plays dominant role in the bending and deformation of ion-electrically active polymers.Key words: ionic polymer-metal composites; cluster microstructures; soft robotics; actuation characteristics大力发展机器人产业对于促进国民经济具有重要意义。

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