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向东融合翻译"向东融合"的英文翻译可以是 "Eastward integration"。
以下是一些关于"向东融合"的用法和中英文对照例句：1. "向东融合"是指国家或地区在经济、文化、政治等方面向东方国家或地区发展和融合。
"Eastward integration" refers to the development and integration of countries or regions towards Eastern countries or regions in terms of economy, culture, politics, etc.2. 近年来，我国积极推动向东融合，加强与东盟国家的合作。
In recent years, China has actively promoted Eastward integration and strengthened cooperation with ASEAN countries.3. 东盟成员国之间的向东融合有助于实现区域经济的繁荣和发展。
Eastward integration among ASEAN member countries contributes to the prosperity and development of the regional economy.4. 向东融合可以促进不同国家之间的互利合作和共同发展。
Eastward integration can promote mutually beneficial cooperation and common development among differentcountries.5. 中国提出的"一带一路"倡议旨在推动向东融合，加强亚欧各国的合作。
八年级人工智能英语阅读理解20题1<背景文章>Artificial intelligence (AI) is making significant impacts in the field of healthcare. One of the major applications of AI in healthcare is disease diagnosis. AI algorithms can analyze large amounts of medical data and detect patterns that may be difficult for human doctors to identify. For example, AI can be used to analyze blood test results, medical images, and patient symptoms to diagnose diseases such as cancer, diabetes, and heart disease.Another area where AI is being used in healthcare is medical imaging analysis. AI can analyze medical images such as X-rays, CT scans, and MRIs to detect abnormalities and assist radiologists in making diagnoses. AI can also help in the early detection of diseases by identifying subtle changes in medical images that may not be visible to the human eye.AI is also being used to develop personalized treatment plans for patients. By analyzing a patient's medical history, genetic information, and other data, AI can recommend personalized treatment options that are tailored to the patient's specific needs.In addition to disease diagnosis and treatment planning, AI is also being used in healthcare for tasks such as patient monitoring and drugdiscovery. AI-powered devices can monitor patients' vital signs and detect early signs of deterioration, allowing for timely intervention. In drug discovery, AI can analyze large amounts of data to identify potential drug candidates and predict their efficacy and safety.Overall, AI has the potential to revolutionize healthcare by improving disease diagnosis, treatment planning, and patient outcomes. However, there are also concerns about the ethical and legal implications of using AI in healthcare, such as issues related to data privacy and the responsibility of AI in making medical decisions.1. What is one of the major applications of AI in healthcare?A. EducationB. Disease diagnosisC. EntertainmentD. Transportation答案：B。
中国对“一带一路”国家的贸易效率基于随机前沿引力模型作者：徐锦波来源：《商业经济研究》2017年第10期中图分类号：F352.8 文献标识码：A内容摘要：研究中国与“一带一路”沿线国家的贸易效率有重要的理论和现实意义。
本文采用随机前沿引力模型，利用2010-2014年的数据进行实证研究发现，非效率因素限制着贸易效率。
中国对“一带一路”沿线国家的贸易效率呈现两极分化，并有衰减趋势。
提高中国对“一带一路”沿线国家的贸易效率，需要进一步促进双方企业对对方市场的了解，完善“一带一路”沿线的运输通道以及相关基础设施建设，并加强与沿线国家的经贸合作，降低贸易壁垒。
关键词：一带一路贸易效率随机前沿引力模型引言本文研究的是中国与“一带一路”沿线国家的贸易效率问题。
贸易效率指实际贸易量和贸易潜力（即最大贸易水平）的比率，反映了既定的经济规模、地理距离等自然条件制约下，一国的贸易潜力得以实现的程度（Nilsson，2000）。
通过观察实际贸易水平与贸易潜力的比值及其变化可以评估现有政策的效果，对针对性地设计未来提升贸易效率的政策有重要参考价值（贺书锋等，2013）。
那么，中国对“一带一路”沿线国家或地区的贸易效率如何？是否存在非效率因素限制贸易效率？应当怎样挖掘中国在“一带一路”中的贸易潜力？这些问题的研究将丰富和完善“一带一路”的内涵，对推动和加快“一带一路”建设具有重要的理论价值和现实意义。
测算贸易效率的关键是确定贸易潜力的大小。
在贸易潜力的测算上，国内外学者主要采用贸易引力模型（Egger，2002；赵雨霖等，2008）。
传统引力模型认为贸易规模主要由贸易伙伴的经济规模和距离等决定。
但是，除了经济规模和距离之外，还存在不可观测因素显著地影响着贸易规模。
因此，基于传统引力模型采用OLS方法进行估计和测算，容易导致R平方较低，估计偏误很难纠正。
针对传统引力模型的缺陷，近年来越来越多的学者开始使用随机前沿引力模型来测算贸易潜力和贸易效率。
第 29 卷第 3 期分析测试技术与仪器Volume 29 Number 3 2023年9月ANALYSIS AND TESTING TECHNOLOGY AND INSTRUMENTS Sep. 2023综述(231 ~ 244)行波离子迁移谱技术及应用研究进展潘慢慢1, 2 ，李 杭2 ，徐一仟1, 2 ，杨其穆1, 2 ，蒋丹丹2 ，王卫国2 ，陈 创2, 3 ，李海洋2（1. 中国科学院大学，北京 100049；2. 中国科学院大连化学物理研究所，辽宁大连 116023；3. 国民核生化灾害防护国家重点实验室，北京 102205）摘要：离子迁移谱（ion mobility spectrometry，IMS）是利用离子迁移率K（离子碰撞截面）差异来实现不同离子的分离与测定，具有分析速度快、检测灵敏度高的优点，其与质谱联用在蛋白质组学、代谢组学、医药等领域已获得了广泛的应用. 随着分析对象复杂性的增加，对IMS的分辨能力也提出了更高要求. 行波离子迁移谱（travelling wave ion mobility spectrometry，TWIMS）采用时域连续的行波电场实现离子传输与分离，其分析通道的长度不受行波电压幅值的限制，理论上可以无限延长离子分析通道来提高分辨能力. 目前，TWIMS的分辨率最高可达1 860，对于分析存在多种同分异构体的复杂样品别具优势. 对TWIMS的原理及分辨能力的影响因素进行了介绍，进一步探讨了不同结构TWIMS仪器的特点、性能和应用，对TWIMS未来发展方向进行了展望.关键词：离子碰撞截面；行波离子迁移谱；循环式离子迁移谱；无损离子操纵结构；离子淌度质谱中图分类号：O657. 63 文献标志码：A 文章编号：1006-3757（2023）03-0231-14DOI：10.16495/j.1006-3757.2023.03.001Advancement of Traveling Wave Ion Mobility Spectrometry andIts ApplicationPAN Manman1, 2， LI Hang2， XU Yiqian1, 2， YANG Qimu1, 2， JIANG Dandan2，WANG Weiguo2， CHEN Chuang2, 3， LI Haiyang2（1. University of Chinese Academy of Sciences, Beijing 100049, China；2. Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, Liaoning China；3. State Key Laboratory of NBC Protection forCivilian, Beijing 102205, China）Abstract：Ion mobility spectrometry (IMS) utilizes the difference in ion mobility K (collision cross section) to realize the separation and determination of different ions, which has the advantages of fast analysis speed and high sensitivity. And it coupling with mass spectrometry (IM-MS) was widely used in the fields of proteomics, metabolomics, medicine, etc.With the increasing complexity of the analyzed objects, higher demands are put on the resolution of the IMS. Traveling wave ion mobility spectrometry (TWIMS) uses a time-domain continuous traveling wave electric field to realize ion transport and separation. The analytical path length of the TWIMS is not limited by the amplitude of the travelling wave收稿日期：2023−05−24； 修订日期：2023−07−13.基金项目：国家自然科学基金项目（Nos. 22027804, 21974141），国民核生化灾害防护国家重点实验室科研基金项目（SKLNBC2021-16），大连化物所创新研究基金项目（DICP I202141）[Natural Science Foundation of China (Nos.22027804, 21974141), State Key Laboratory of NBC Protection for Civilian (SKLNBC2021-16), Dalian Institute of Chemical Physics (DICP I202141)]作者简介：潘慢慢（1998−），女，博士研究生，主要从事质谱分析工作，E-mail：通信作者：陈创（1984−），男，博士，《分析测试技术与仪器》青年编委，主要从事质谱分析工作，E-mail：；李海洋（1964−），男，博士，《分析测试技术与仪器》编委，主要从事质谱分析工作，E-mail：.voltage, theoretically the path can be extended indefinitely to improve the resolution. Currently, the resolution of TWIMS can reach up to 1 860, which is advantageous for the analysis of complex samples with the multiple isomers. The principle of TWIMS and the influencing factors of resolution were introduced, the characteristics, performance and applications of TWIMS instruments with different structures were further discussed, and finally the future development directions of TWIMS were prospected.Key words：collision cross section；travelling wave ion mobility spectrometry；cyclic ion mobility spectrometry；structure for lossless ion manipulation；ion mobility-mass spectrometry离子迁移谱（ion mobility spectrometry，IMS）是利用电场驱动气相离子在中性气体中迁移从而实现不同迁移率离子分离和识别的一种技术[1]. IMS能够灵敏检测pg或ng/L量级的目标物，并且具有ms级单谱图分析速度、适用于发展便携式仪器等优点，被广泛应用于化学战剂监测、爆炸物检测等领域. IMS与质谱（mass spectrometry，MS）的联用结合了IMS灵敏、快速、能提供离子结构信息和MS提供精确质量信息的特点，在食品安全、医药和生物分析等领域得到了迅速发展[2-6].在低电场条件下（E/N<2 Td），离子在中性气体中的迁移速度V d与电场强度E成正比，比例系数即为离子迁移率K，其关系如式（1）：根据Revercomb等[7]对电场作用下气相离子的运动进行的研究，离子迁移率K与碰撞截面（collision cross section，CCS）满足式（2）：其中，z是电荷数，e是单位电荷，N是中性气体的分子数密度，µ是离子和中性气体分子的约化质量，k是玻尔兹曼常数，T eff是有效温度，α为修正因子，ΩD (Teff)是离子的碰撞截面（即CCS），与离子的大小和形状有关，直接反映离子的结构信息. 因此IMS 可以区分MS无法分辨的同分异构体，离子的CCS 差异越小，要求IMS的分辨率越高.根据分离方式的不同，IMS可以分为迁移时间离子迁移谱（DTIMS）、非对称场离子迁移谱（FAIMS/DMS）、行波离子迁移谱（TWIMS）、阱离子迁移谱（TIMS）等，通过提高电场强度或延长离子迁移路径，可以提高IMS的分辨率[8]. 对于DTIMS 而言，延长路径的同时需要提高电压，由于空气击穿电压的限制，依靠延长路径提高分辨率非常有限.而与DTIMS依靠直流电场驱动离子不同，TWIMS 依靠沿迁移区轴向移动的脉冲电压驱动离子，电压幅值不随迁移路径的延长而增大，理论上可以无限延长迁移路径而不受电压的限制. 正是由于这一特性，TWIMS的分辨率目前已经超过1 860，成为目前超高分辨IMS-MS技术的主流[9]. 不同类型IMS 技术对比如表1所列.本文首先介绍TWIMS的原理及分辨能力的影响因素，进一步探讨不同结构TWIMS仪器的特点、性能和应用，最后对TWIMS未来发展方向进行展望.1 TWIMS原理1.1 TWIMS分离原理2004年，Giles等[14]首次将行波应用于环形电极堆栈离子导向器，提出一种使用行波进行离子迁表 1 不同IMS技术对比Table 1 Comparison of different IMSIMS技术工作气压[10]分离场CCS测量最高分辨率/(Ω/ΔΩ)联用技术迁移时间离子迁移谱（DTIMS）266 Pa~大气压强直流电场直接测量250[11]IMS-MS, GC (gaschromatography)-IMS等非对称场离子迁移谱（FAIMS/DMS）大气压强非对称射频电场无法测量Null GC-DMS, DMS-MS等行波场离子迁移谱（TWIMS）~533 Pa方波直流电场需经校准 1 860[9]550[12]TWIMS-MS阱离子迁移谱（TIMS）~400 Pa气流场结合直流电场需经校准400[13]TIMS-MS232分析测试技术与仪器第 29 卷移率分离的新模式，如图1所示. 通过在相邻电极环依次施加脉冲电压产生行波电场，离子在波前位置时，电场驱动离子轴向前进，而离子处于波后位置时，电场驱使离子反向运动，造成运动轨迹折返，即翻滚事件[图1（a）（c）]. 迁移率K较大的离子随波迁移能力强，发生翻滚的次数少，所需总迁移时间较短. 而迁移率K较小的离子随波迁移能力弱，发生翻滚的次数多，所需总迁移时间较长. 如此，不同迁移率离子即可分离. 当离子迁移率K足够大时，离子可以随波作“冲浪”运动[图1（b）].ion trajectory ring electrode(d)stacked-ring ionguidetimeringelectrodeions travelling wavevoltage pulse(a)(b)(c)图1 行波场中离子（a）（c）翻滚事件和（b）“冲浪”行为的SIMION轨迹模拟，（d）行波场的产生[14] Fig. 1 SIMION simulation showing ions (a) (c) roll over wave and (b) surf wave, (d) generation of travelling wave[14]此后数年，尽管TWIMS仪器和相关应用快速发展，但对于其分离原理的认识仍停留在定性阶段，影响离子传输时间和分辨率的因素没有得到深入研究. 直到2008年，Shvartsburg等[15]构建了简化的TWIMS数值分析模型，不考虑离子的速度弛豫、扩散和射频产生的聚焦场，使用推导和离子动力学模拟对迁移时间和分辨率进行预测，并与实际结果进行比较.定义c为行波前最大场强处（E max）的离子漂移速度和波速（s）的比值，如式（3）所列：以波长为b的三角波为例，其任一位置的电场E都相同，即E=Emax . 当c≥1，即KEmax≥s时，离子在波前的运动速度与波速相同，因此离子表现为随着行波一起运动，迁移时间t即为迁移管长L除以行波波速s.当c<1，即KE max<s时，由于离子的翻滚事件，造成迁移率分离. 离子在波前和波后的运动时间分别为t F和t B，其公式如式（4）（5）所列：由于t F>t B，离子每被一个三角波超越，在轴向会产生向前的净位移d，如式（6）：v离子的平均运动速度为式（7）：对于长度为L的迁移管，离子迁移时间t为式（8）：对于形状更复杂的行波如半正弦波，在满足KEmax<<s时，有相似结论，即：从公式（9）可以看出，与DTIMS不同，TWIMS 中离子迁移速度与离子迁移率和电场强度并非线性关系，无法直接用迁移时间t计算CCS，需要使用结构相似的标准物进行校准方程的拟合，然后将待测物的迁移时间代入校准方程计算出CCS.2018年，Richardson等[16]进一步拓展了TWIMS 的理论，推导出平滑移动的正弦行波驱动下离子迁移时间的表达式，不经校准可直接测量CCS. 然而，动力学推导仍被限制在轴向，没有考虑高场下的离子加热，且实际设备中行波并非是平滑移动的，关于TWIMS的理论仍然需要科研工作者继续探索.第 3 期潘慢慢，等：行波离子迁移谱技术及应用研究进展2331.2 TWIMS分辨率的影响因素在离子迁移与扩散相互独立的前提下，不考虑库伦斥力，对于三角波而言，扩散控制分辨率R TW 为式（10）：其中，E与行波波幅U的关系为E=2U/b. 因此，在保证c<1适用于所有离子的前提下，可以通过提高行波波幅或减小波长以提高电场强度、延长路径来提高分辨率，这是TWIMS仪器设计改进的理论依据.而对于DTIMS，扩散控制分辨率R DT为式（11）：提高电场强度和延长路径，同样可以提高DTIMS的分辨率. 然而，DTIMS的电场是通过在迁移管两端施加电压差形成的，越长的迁移路径，意味着越大的电压差，过高的电压会引起放电. 不同与DTIMS，TWIMS的电场是在电极单元的单个或多个电极上循环施加脉冲电压形成的行波电场，脉冲电压幅值与迁移路径总长度无关. 因此，通过延长路径提高分辨率不受电压限制.2 TWIMS的仪器进展TWIMS于2004年出现后，经过近二十年的发展，目前的仪器按照结构主要分为三类：第一类是Waters公司早期开发的环形电极堆栈结构（stacked ring ion guide，SRIG）的TWIMS，第二类是Waters 公司于2019年推出的循环离子迁移谱（cyclic ion mobility， cIM），第三类是基于无损离子操纵结构（structures for lossless ion manipulations，SLIM）的TW-SLIM. 下面将介绍它们的结构特点、性能以及应用.2.1 环形电极堆栈结构2006年，Waters推出首款基于SRIG的TWIM-Q-ToF-MS（TWIM-quadrupole-time of flight-MS）系统，即Synapt HDMS[17].如图2（b）所示，Synapt HDMS包括三个施加行波和射频限制的SRIG（即TriWave结构），依次为trap、IM和transfer，其中IM的结构如图2（a）所示. trap用于离子积累，然后将离子团簇释放到IM离子导向器中进行迁移率分离，transfer用于将分离后的离子传送到ToF-MS中进行质荷比分析.(a)sideplategas inion transmission aperturering electrodesprintedcircuitboardsendplateanalyte spray(b)lockspraybafflelockmassreference sprayT-waveion guidequadrupoledre lenstrapgateIMS transfereinzellens transferlensespusherreflectronair-cooled turbomolecular pumpsoil-freescroll pumpisolation valveand removablesample conedetector2 mmdiameteraperture图2 （a）第一代行波离子迁移管[14]，（b）Synapt HDMS示意图[18]Fig. 2 (a) First generation TWIM separator[14], (b) schematic diagram of Synapt HDMS system[18]根据分辨率影响因素的理论基础，Waters公司于2009年对行波离子迁移管进行改进，推出了Synapt G2 HDMS. 相比第一代TWIM，Synapt G2的改进如图3所示，增加电极环的数目以延长迁移路径，脉冲电压施加到4个电极环上，比原来两个电极环时平均场强提高了约20%，行波幅值从30 V 提高到40 V，进一步提高了电场强度[19]. 由于低电场条件的限制，在提高行波幅值的同时，需要提高气压以避免离子热化. 因此，在IM前增加了一个充满氦气的腔室以平衡N2的压强，将工作气压从50 Pa提升到了300 Pa. 试验结果显示，Synapt G2将SDGRG和GRGDS两种反序小肽离子的分辨率提234分析测试技术与仪器第 29 卷高了近4倍，达到了45.在之后几年，Waters 公司又相继推出了Synapt G2-S 、Synapt G2-Si 和Vion 等产品，在分辨率、灵敏度和配套软件等方面均有所提升[20].由于技术成熟、商品化程度高， SRIG 的IMS-MS 系统在蛋白质组学[21-22]、脂质组学[23-24]、代谢组学[25-26]、医药[27-29]等领域得到了广泛应用. Hale等[21]使用液体萃取表面技术（LESA ）结合TWIM-MS 对小鼠肾脏组织切片的蛋白质进行质谱成像分析，将蛋白质结构与组织特征进行关联. 其中，TWIMS 提供内源蛋白质的空间、构象和质量信息，以及计算检测到的蛋白质或蛋白质复合物的碰撞截面. 此外，按到达时间过滤质荷比（m/z ）维度中的离子信号，增加低强度信号来提高信噪比，进一步提高离子图像的特异性. Zang 等[25]使用流动注射法（flow injection ，FI ）结合TWIM-MS 对61名前列腺癌患者和42名对照者的血清提取物进行非靶向代谢分析，将质量数、CCS 值和裂解模式与标准物或数据库进行匹配，鉴定出特征代谢物. 使用监督多元分类方法，将前列腺癌患者样本与对照样本区分开来，具有良好的准确性（88.3%~89.3%）、敏感性（88.5%~90.2%）和特异性（88.1%），展示了FI-TWIM-MS 作为用于代谢组学研究的高通量分析工具的潜力. 与超高效液相色谱（ultra-performance liquid chromatography ，UPLC ）联用后，UPLC-TWIM-MS 的多维分离能力在复杂中药成分中已知、未知化合物及其异构体的发现和鉴定上有巨大的应用前景，对中药的质量评价和解释作用机制有重要意义，已成功应用于龟龄集[27]、桔梗[28]、丹芝片[29]等中药.此外，TWIM 有助于在Q-ToF-MS 仪器上实现电子转移解离功能（electron transfer dissociation ，ETD ）[30]. ETD 是一种自由基驱动的裂解技术，与碰Synaptstacked ring ion guidenitrogenions in ionsin ions out ions out nitrogen out nitrogen outnitrogen outmax. field 25 V/cm (10 V applied)~90% of applied v oltagemax. field 21 V/cm (10 V applied)~60% of applied v oltage(b)(c)4 repeat pattern6 repeatpattern(a)helium outT-wave IMS cellT-wave IMS cellhelium cellheliumSynapt G2stacked ring ion guidenitrogen图3 Synapt HDMS 和Synapt G2 HDMS 的（a ）IM 腔室，行波电压（b ）施加方式和（c ）重复模式对比图[19]Fig. 3 Comparison of (a) IM cells, (b) applied voltage and (c) repeat pattern of travelling wave betweenSynapt HDMS and Synapt G2 HDMS[19]第 3 期潘慢慢，等：行波离子迁移谱技术及应用研究进展235撞诱导解离（collision induced dissociation，CID）互补，在N-Cα键裂解后产生一系列c和z离子，对于蛋白质翻译后修饰的识别和定位非常有价值[31]. 在Synapt系统中，trap用于捕获辉光放电产生的阴离子，从而实现与进入的阳离子的气相反应. 改变行波的速度，可以精细地控制阴离子/阳离子相互作用的水平，从而控制ETD碎片的水平[32]. 结合电喷雾电离，TWIM-MS成为肽和蛋白质的测序和结构分析的有力工具.2012年，Waters基于SRIG开发出了Stepwave 技术，用于大气压离子源（如ESI）的离子传输[33]. 通过缺口处相对平行排列且内径不同的两个SRIG之间的施加电势差，实现离子的离轴传输和聚焦，而通过去除气体分子和未电离的中性分子，提高信噪比和灵敏度.2.2 循环离子迁移谱结构尽管TWIMS通过延长路径提高分辨率不受电压限制，但仍受到仪器体积的制约. 为了解决上述问题，2014年Giles等[34]提出一种循环离子迁移谱，即Cyclic Ion Mobility（如图4所示）. cIM包括主体[图4（b]与MS系统的主离子光轴相交的接口区域[图4（c）]两个部分，路径长度共计98 cm，可以取代传统线性TWIM单元，嵌入到Synapt G2-Si系统中[图4（a）][12, 35]. 主体部分由印刷电路板支撑，电极结构如图4（d）所示. 相邻的cIM电极上同时施加反相的射频（2.5 MHz，300 V p-p）和行波脉冲（最大波幅45 V，波速300~1 000 m/s），射频形成的赝势阱提供z方向的限制，行波驱动离子进行迁移率分离.侧板上的repeller电极上施加高于行波波幅的直流电压（60 V），提供x方向的限制. cIM主体部分的电极形成了一个5 cm×0.5 cm的矩形离子通道，离子容量比孔径0.5 cm的线性TWIM高10倍[35]. z方向的窄电极间距，可以最大程度的减少“赛道效应”，即外圈的离子比内圈的离子迁移路径更长引起峰展宽. 接口区域是cIM的关键部分，需要在离子进入、射出和迁移率分离三种功能之间切换，且对离子传输率和分辨率不能有显著影响. Giles等[35]设计出阵列电极结构，将其分为两组，分别施加x方向[图4（e）]、y方向[图4（f）]的行波，从而实现功能切换. 此外，阵列电极结构允许cIM在多通道模式和旁道模式进行切换，在旁道模式下，离子不经过cIM的主体部分，不进行迁移率分离.cIM前后均连接传统线性TWIM，可以实现离子的注入、喷射、存储、激活. 将其与cIM的功能进行组合，可以实现IMS n（多级IMS）功能. IMS n可以选择将cIM中的特定迁移率范围的离子喷射出去，剩余的离子继续执行迁移率分离，重复这一过程将持续减小分析范围. 该功能可以避免在多通道试验中，较大迁移率离子超过较小迁移率离子产生的“套圈”现象. IMS n激活是指将特定迁移率的离子喷射回前级TWIM，其余离子被喷射到ToF中以去除，前级TWIM中的离子经过碰撞诱导激活/解离后重新注入cIM进行迁移率分离，再将分离后的离子喷射到ToF进行检测或者继续进行IMS n分析.√6初代cIM系统对松三糖和棉子糖的分析结果显示，6次循环后分辨率达到139，约为单次通过分辨率的倍，且相比于单次通过离子损失小于15%[34]. 2017年，第二代cIM系统问世，SDGRG和GRGDS两种反序肽离子经过50次循环后，分辨率超过500，实现了超高分辨离子迁移谱的一项巨大进步[12]. 2019年，Waters公司推出了商品化仪器Select Series cyclic IMS.Sisley等[36]使用LESA-QcIM-MS分析小鼠大脑和大鼠肾脏组织中的蛋白质，在cIM前通过四极杆隔离将m/z检测范围缩小到870~920（即QcIM）以避免“套圈”现象，1、2和3次通过后分别检测到24、37和54种蛋白质，充分体现了多通道cIM 的高分辨率在复杂生物样品检测上的优势.Eldrid等[37]研究了cIM中气相蛋白质离子的稳定性，并且利用IMS n结合碰撞诱导展开（CIU）探索了+7细胞色素C（CytC）离子的展开行为（如图5所示）. 结果显示在与迁移率分离兼容的时间尺度上（几百毫秒），蛋白质可以很大程度保留其天然和多聚体状态. 对已激活的+7 CytC离子的不同到达时间范围的切片分别进行IMS n激活，探索了不同构象之间的转化现象以及展开顺序，展现了cIM在研究蛋白质动力学、稳定性和展开行为的应用潜力. 2021年，Eilrid等[38]将此方法命名为slice-CA（碰撞激活，collision activation），并研究了一种由胰岛β细胞产生的与Ⅱ型糖尿病有关的激素hIAPP，揭示了hIAPP解离前构象之间的相互转换.除了生物样品，cIM在石油组学上也获得了应用[39-40]. 石油作为最复杂的混合物之一，存在大量的236分析测试技术与仪器第 29 卷同分异构体和同量异位素，对IM-MS 的分辨率要求很高. Ruger 等[40]证明，在多次通过后，QcIM-MS可以更深入地了解瓦斯油中异构体的分布，并且消除同量异位素的干扰，结合碰撞诱导解离技术，可以分离多环芳烃和杂环化合物.2.3 无损离子操纵结构2014年，Garimella 等人提出了无损离子操纵结构（SLIM ）[41-44]. SLIM 由一对蚀刻了条状电极的平行印刷线路板组成，通过在电极上施加电压产生静电场、射频电场和驱动电场，可以实现离子无损传输、迁移率分离、选择性离子捕获和积累等复杂操作[45-46]. SLIM 分为基于直流（DC ）的DC-SLIM 和基于行波（TW ）的TW-SLIM ，由于DC-SLIM 的分辨率有限，TW-SLIM 更受青睐.TW-SLIM 通常由6列射频电极和5列行波电极以及两边的保护电极组成（如图6所示），与cIM 相似，相邻两列射频电极上施加反相射频提供纵向限制，保护电极上施加直流电势提供横向限制，行波电极上施加行波驱动离子进行迁移率分离. 射频电极与行波电极间隔分布，既简化了电源，又保证离子束缚的有效性[47]. 由于印刷线路板工艺成熟，SLIM 具有加工方便、组装灵活、成本低廉的优点，结合TWIMS 电压不随迁移路径延长而增大的特点，目前TW-SLIM 已经实现了商品化[9].ESIstepwaveIGquadtrapIGHecyclic IMSpre-array store post-array store IG arrayreflectronrepellercIM electrode0.5 cm5 cmrepellerPCBs (d)yxPCBscIM electrodes(b)(c)(e)(f)array PCBentrancearray electrodescIM electrodesexitrepellerzx yzx yzx yentrancezxtransferWdetectorpusher(a)图4 cIM 的结构示意图[35]（a ）cIM 平台概览，（b ）cIM 设备，（c ）包含阵列电极结构的离子注入/喷射区域，（d ）cIM 电极结构，（e ）离子注入/喷射模式下行波方向为x 或-x ，（f ）分离模式下行波方向为yFig. 4 Schematic diagram of structure of cIM[35](a) overview of cIM plateform, (b) cIM device, (c) ion entry/exit region, consisting of array electrodes, (d) structure of cIMelectrodes, (e) ion injection/ejection mode, array TWs applied in x (or -x ) direction,(f) separation mode, array TWs applied in y -direction第 3 期潘慢慢，等：行波离子迁移谱技术及应用研究进展2372.3.1 多圈循环式TW-SLIM为了在相对紧凑的空间尽可能的实现路径的延长，Hamid 等[48]将90°转弯结构应用在TW-SLIM 上，在有16个90°转弯结构的TW-SLIM 模块上，离子传输效率接近100%且分辨率没有显著损失. 在此基础上，Deng 等[49]开发出了分析通道长13 m 的蛇形路径TW-SLIM[图7（a ）]，并且对气压、板间距、行波和射频等参数进行了优化，单峰分辨率达到46，峰容量和峰生成率分别为246和370 s −1，实现了异构糖LNFP i 和LNFP ii 的基线分离. 目前，MOBILion Systems 公司已经将其集成到MS 系统中，完成了仪器的商品化，即MOBIE. 2021年，Wormwood Moser 等[50]结合流动注射分析，使用MOBIE 原型机分析了野生型小鼠半脑的脑提取物，仅需2 min 即可实现神经节苷脂的定量和高选择性测量，比传统的LC-MS 更加快速、高通量，且无需色谱样品制备步骤.在13 m 蛇形路径的基础上，结合动态开关结构，Smith 等人提出了多圈循环式TW-SLIM [图7（b ）][9, 43]. 离子经过40次多圈飞行后，分析路径长度超过500 m ，分离能力达到1 860，并且可以实现基本无损的离子传输. 在初步应用中，9次通过后，低聚糖LNnH 新的构象特征首次被清楚地区分（如图8所示）. 与cIM 相似，多圈循环式TW-SLIM 也存在离子飞行“套圈”现象并导致迁移率分析窗口受限. TW-SLIM 可以利用出口处的动态开关结构，摒弃一部分离子，避免“套圈”现象，简化分析结果.异构体的存在使得分析生物样品和其他复杂混合物具有挑战性，多圈循环式TW-SLIM 的超高分辨率在分析结构差异极小的异构体上有巨大优势[51]. Nagy 等[52]将α-环糊精用作手性主体，通过对环糊精与氨基酸分子形成的主客体非共价复合物进行高分辨的迁移率分离，实现了D -和L -对映体氨基酸混合物的快速检测. 此外，多圈循环式TW-SLIM 在聚糖、蛋白质等生物分子的异构体的分离和鉴定都得到了应用[53-54].然而，超长飞行路径不可避免的伴随着离子团Relative intensityV oltage/V16~17 ms slicefull ATD(a)(b)A r r i v a l t i m e /m s 1.01520253035400.50020406080100V oltage/V19~20 ms slice(c)20406080100V oltage/V23~24 ms slice (d)20406080100V oltage/V26~27 ms slice (e)20406080100Int1.00.5αβγδαβγδεζ图5 激活的+7 CytC 离子的（a ）到达时间分布，（b ）16~17 ms 、（c ）19~20 ms 、（d ）23~24 ms 和（e ）26~27 ms 切片的CIU 指纹，α、β、γ、δ、ε和ζ表示离子种群[37]Fig. 5 (a) Arrival time distribution of activated +7 CytC ion, and CIU fingerprints for slices (b) 16~17 ms, (c) 19~20 ms,(d) 23~24 ms, (e) 26~27 ms, populations labeled as α, β, γ, δ, ε and ζ[37]RFguardguardTWTWTWTWTW1234567812345678图6 TW-SLIM 的电极结构[47]Fig. 6 Structure of electrodes in TW-SLIM[47](a)(b)TWRFguardswitch ONswitch OFFMSentranceg u a r d图7 （a ）13 m 长的蛇形TW-SLIM [49]，（b ）循环蛇形路径TW-SLIM 和动态离子开关[9]Fig. 7 (a) 13 m serpentine path length TW-SLIM [49],(b) serpentine ultralong path with extended routing TW-SLIM and dynamic ion switch[9]238分析测试技术与仪器第 29 卷扩散导致的峰展宽、信噪比低、灵敏度降低等缺陷.为了解决这一问题，Garimella 等[55]提出了一种时空操纵气相离子群的方法，即压缩比离子迁移率程序（compression ratio ion mobility programming ，CRIMP ），利用断续前进的行波，将迁移率分离中的离子分布折叠成更紧密的离子包. 与使用离子漏斗进行富集相比，CRIMP 显著提高了肽的检测限，灵敏度提高了100倍以上[56]. 具有高灵敏度、高分离能力的多通道蛇形TW-SLIM 与MS 的耦合，对于解决蛋白质组学、代谢组学等长期存在的低丰度、异构混合物的挑战具有重大意义[57].2.3.2 并行分析TW-SLIM长迁移率分离时间（秒级）与有限的离子积累时间（毫秒级）的结合导致长路径TW-SLIM 存在占空比低、离子利用率低的缺点. 为了提高离子利用率，增加离子捕获区域的大小、in-SLIM 离子积累、多路复用策略等方法被相继提出，然而这些方法受到空间电荷容量、检测器的饱和点等限制[58-59]. 2022年，Deng 等[60]开发出一种新的并行分析TW-SLIM ，占空比达100%，分辨率达到150，并和三重四极质谱仪（QQQ ）联用，用于靶向定量分析.并行分析TW-SLIM 由入口、开关板载积累区域（SOBA ）、两条平行离子路径和出口部分组成，每条离子路径包括一个30 cm 的预过滤区域、离子开关、离子检测器、板载积累区域（OBA ）和一条集成了多个迁移率过滤门的4.8 m 的蛇形路径SLIM （如图9所示）. SOBA 处积累的离子可以进入任一路径的预过滤区域，经过低分辨的迁移率分离后通过离子开关将无需检测的离子传输到离子检测器，目标离子进入OBA 区域进行富集，再通过离子门注入到后面的长蛇形路径中进行迁移率分离.通过将SOBA 积累的离子多次注入到同一路径以及在两条路径分别同时进行离子积累和迁移率分离，并行分析TW-SLIM 的占空比大大提高，8次注入后利血平离子的占空比达100%，多种标准分析物的实际离子利用效率约为80%. 预过滤对目标离子靶向富集，增加了OBA 区域的目标离子容量，提高灵敏度，结合蛇形路径中的多个过滤门进一步去除干扰离子，大大提高了信噪比. 在过滤模式下，SLIM-QQQ 比QQQ 对醛固酮和可的松的灵Drift time/s0.12900.1320.1350.1380.1410.1441LNnH(a)LNHLNHβ-D-Gal-(1→3)-β-D-GlcNAc-(1→3)-[β-D-Gal-(1→4)-β-D-GlcNAc-(1→6)]-β-D-Gal-(1→4)-D-Glcβ-D-Gal-(1→4)-β-D-GlcNAc-(1→3)-[β-D-Gal-(1→4)-β-D-GlcNAc-(1→6)]-β-D-Gal-(1→4)-D-GlcOH OH OH OHOHOHOHOHOHOHOH OHNHAcOH AcHNHOHOHOHOHOO O OOOO O O OO O OH OH OH OHOHOHOHOHOH OHOHOHNHAcOH AcHNHOHOHOHOHOO O OOOO OO OO ODrift time/s1.120 1.14 1.161.18 1.20 1.22 1.241LNnHLNnH(b)LNH图8 （a ）1次和（b ）9次通过后获得的乳-N -六糖和乳-N -新六糖的迁移率分离结果[9]Fig. 8 IM-MS separation of sugar isomers lacto-N -hexaose and lacto-N -neohexaose obtained at (a) 1 pass and (b) 9 passes[9]第 3 期潘慢慢，等：行波离子迁移谱技术及应用研究进展239。
Fast food has become an integral part of modern society,offering convenience and quick sustenance to busy individuals.The rise of fast food chains around the world has revolutionized the way people eat,particularly in urban areas where time is of the essence.The Origin and Growth of Fast Food:Fast food originated in the United States in the early20th century,with the advent of drivein restaurants and the first McDonalds franchise in1940.The concept quickly spread,and by the latter half of the century,fast food chains had become a global phenomenon.The growth of fast food is attributed to its affordability,speed of service, and standardized taste.Types of Fast Food:Fast food encompasses a wide variety of cuisines,from Americanstyle burgers and fries to Asianinspired dishes like sushi and noodles.Popular items include hamburgers,hot dogs,fried chicken,pizza,tacos,and subs.These foods are typically characterized by their high calorie content,use of processed ingredients,and minimal preparation time.Health Implications:One of the most significant concerns associated with fast food is its impact on health. Many fast food items are high in saturated fats,sugars,and sodium,which can contribute to obesity,heart disease,and diabetes.Despite these concerns,the industry has made efforts to introduce healthier options,such as salads,grilled items,and lowercalorie beverages.Cultural Impact:Fast food has had a profound cultural impact,influencing not only eating habits but also social behaviors.It has become synonymous with convenience and efficiency,often associated with the fastpaced lifestyle of urban living.Additionally,fast food chains have become cultural icons,with their logos and mascots recognized worldwide.Economic Influence:The fast food industry is a major economic force,providing employment opportunities and contributing to local economies.However,it has also been criticized for its labor practices,including low wages and limited benefits for employees. Environmental Considerations:The environmental impact of fast food is another area of concern.The industry is often linked to deforestation,pollution from packaging,and the excessive use of water and energy resources.Efforts to make fast food more sustainable include sourcing ingredients from local producers and reducing packaging waste.Future of Fast Food:The future of fast food is likely to involve a continued focus on convenience,but with a growing emphasis on health,sustainability,and ethical practices.There is a trend towards more diverse menus that cater to various dietary needs and preferences,including vegetarian,vegan,and glutenfree options.In conclusion,fast food is a complex and multifaceted aspect of contemporary society. While it offers undeniable benefits in terms of convenience and affordability,it also presents challenges related to health,culture,and the environment.As consumers become more aware and discerning,the industry will need to adapt to meet these evolving expectations.。
21专升本英语试题及答案一、阅读理解（共20分，每题4分）1. According to the passage, what is the main reason for the increase in obesity in the United States?A. The fast-food industry's aggressive marketing.B. The decrease in physical activities.C. The increase in the number of fast-food restaurants.D. The change in people's eating habits.Answer: A2. What does the author think about the fast-food industry's marketing strategy?A. It is effective.B. It is misleading.C. It is harmless.D. It is beneficial to the economy.Answer: B3. What is the author's attitude towards the fast-food industry?A. Supportive.B. Critical.C. Indifferent.D. Sympathetic.Answer: B4. What is the main purpose of the passage?A. To explain the causes of obesity.B. To criticize the fast-food industry.C. To suggest ways to reduce obesity.D. To discuss the effects of obesity on society.Answer: B5. What does the author suggest as a solution to the obesity problem?A. Banning fast-food advertisements.B. Encouraging people to eat more fruits and vegetables.C. Reducing the number of fast-food restaurants.D. Implementing stricter regulations on the fast-food industry.Answer: D二、词汇与语法（共20分，每题2分）6. The company has recently ________ a new policy to reduce employee turnover.A. implementedB. performedC. manufacturedD. demonstratedAnswer: A7. Despite the heavy rain, the construction of the new bridge is ________ on schedule.A. holdingB. proceedingC. occurringD. happeningAnswer: B8. The teacher asked the students to ________ their essays before submitting them.A. reviseB. reverseC. reviseD. reserveAnswer: A9. The new shopping mall is expected to ________ a significant number of jobs in the area.A. generateB. degradeC. eliminateD. duplicateAnswer: A10. The scientist's research has ________ a new understanding of the disease.A. contributed toB. subtracted fromC. added toD. removedAnswer: A三、完形填空（共20分，每题2分）11. The ________ of the old factory has caused a lot of controversy among the local residents.A. demolitionB. constructionC. renovationD. relocationAnswer: A12. The company's profits have ________ significantly since the introduction of the new product line.A. soaredB. plummetedC. stabilizedD. fluctuatedAnswer: A13. The government has taken measures to ________ the spread of the virus.A. containB. accelerateC. promoteD. ignoreAnswer: A14. The artist's work is characterized by a unique ________ of color and form.A. combinationB. separationC. divisionD. distinctionAnswer: A15. The team's ________ to the challenge was impressive, and they emerged victorious.A. responseB. reactionC. answerD. replyAnswer: A四、翻译（共20分，每题5分）16. 随着科技的发展，远程工作已经成为可能。
Vol. 43 No. 4April 2021第43卷第4期2021年4月文章编号：1001-506X(2021)04-1119-07系统工程与电子技术Systems Engineering and Electronics网址 :www. sys-ele. com高移动性Jakes 信道的学习与估计邵 凯123，**，陈连成1,2,3,刘 胤1,2,3收稿日期：2020 -04 - 20；修回日期：2020 - 05 - 27；网络优先出版日期：2020 - 08 - 06。
网络优先出版地址:https ： // kns. cnki. net/kcms/detail/11. 2422. TN. 20200806. 1705. 004. html基金项目：重庆市科委项目(stc2017shmsA130115)资助课题* 通讯作者. E-mail ：shaokai@cqupt. edu. cn引用格式：邵凯，陈连成，刘胤.高移动性Jakes 信道的学习与估计[J ].系统工程与电子技术，2021, 43():1119-1125.Reference format : SHAO K , CHEN L C , LIU Y. Learning and estimation of high mobility Jakes channel [J ]. Systems Engineering andElectronics, 2021, 43(4) ： 1119-1125.(1.重庆邮电大学通信与信息工程学院，重庆400065；2.移动通信技术重庆市重点实验室，重庆400065；3.移动通信教育部工程研究中心,重庆400065)摘要：在高移动场景下，信道具有快速时变性和非平稳特性，对信道的准确估计提出了新的挑战。
针对高移动性Jakes 信道，提出一种基于图像重建和恢复原理的信道学习估计网络。
首先，根据Jakes 信道矩阵中局部相关特性，构建快速超分辨卷积神经网络提取信道特征，并对信道插值完成信道图像建模。
Unit1The Evolution of Transport交通工具的演化The evolution of transport has been closely linked to the development of humankind throughout the earth’s history．Transport’s early function was to meet the basic need of hauling food supplies and building materials．But with the formation of tribes，then peoples，and finally nations，the societal and economic functions of transport became more and more complex. At first there was mobility required for individuals,clans,households，and animals to protect them against，and to escape from，the dangers of natural disasters and tribal aggressions,and in the search for the best places to settle．As tribal groups formed and gradually established their geographical identity，transport was increasingly needed to open up regions for development，to provide access to natural resources,to promote intercommunal trade,and to mobilize territorial defense．When the first nations came into being,transport played a major role in establishing national integrity．交通工具的演变紧密相连的人类在整个地球的历史发展。
Education is a fundamental aspect of human development and societal progress.It is not merely a process of acquiring knowledge but also a means of personal growth and social integration.In this essay,I will discuss the importance of education,the challenges faced in the educational system,and the role of education in shaping the future.The Importance of Education1.Personal Development:Education is crucial for the intellectual and emotional growth of an individual.It helps in developing critical thinking skills,problemsolving abilities, and creativity.It also fosters a sense of curiosity and a desire to learn,which are essential for personal development.2.Social Integration:Education plays a vital role in integrating individuals into society.It imparts values,norms,and social skills that are necessary for harmonious coexistence.It also helps in understanding and respecting cultural diversity,which is crucial in our increasingly globalized world.3.Economic Growth:A welleducated populace is a key driver of economic development. Education equips individuals with the skills needed for employment and entrepreneurship, contributing to a countrys economic prosperity.4.Civic Responsibility:Education instills a sense of civic responsibility and encourages active participation in democratic processes.It helps individuals understand their rights and responsibilities,fostering a more informed and engaged citizenry.Challenges in the Educational SystemDespite its importance,the educational system faces numerous challenges:1.Access to Education:Inequality in access to education is a significant issue, particularly in developing countries.Factors such as poverty,gender discrimination,and geographical isolation can limit educational opportunities for many.2.Quality of Education:Even where access is available,the quality of education can vary greatly.Overcrowded classrooms,outdated curricula,and a lack of qualified teachers are common problems that affect the educational experience.3.Technological Integration:With the rapid advancement of technology,integrating digital tools and resources into the educational process is becoming increasingly important.However,this presents challenges in terms of infrastructure,training,andensuring equitable access to technology.4.Lifelong Learning:The concept of lifelong learning is gaining prominence as the pace of change in the job market accelerates.The educational system must adapt to support continuous learning and skill development throughout an individuals life.The Role of Education in Shaping the FutureEducation is a cornerstone for building a better future.It is through education that we can:1.Promote Equality:By ensuring equal access to quality education,we can reduce social and economic disparities and promote a more equitable society.2.Encourage Innovation:Education fosters a culture of inquiry and experimentation, which is essential for driving innovation and addressing the complex challenges of the future.3.Prepare for the Future of Work:As the nature of work evolves,education must equip individuals with the skills needed for the jobs of tomorrow,including digital literacy, adaptability,and the ability to work in diverse and dynamic teams.4.Sustain Global Development:Education is a key factor in achieving the United Nations Sustainable Development Goals,contributing to poverty reduction,health improvement, and environmental sustainability.In conclusion,education is a powerful tool for personal and societal transformation.It is our collective responsibility to ensure that education is accessible,equitable,and of high quality,empowering individuals to contribute positively to the world around them.As we look to the future,the role of education in shaping a more just,prosperous,and sustainable world cannot be overstated.。
第41卷增刊2 2020年6月兵工学报ACTA ARMAMENTARIIVol.41Suppl.2Jun.2020基于VMware的Link11数据链半实物仿真技术李慧博，吴海乔，栗苹，龚鹏(北京理工大学机电学院，北京100081)摘要：针对战术数据链大规模网络半实物仿真中真实电台接入带来的硬件成本过高、资源受限等问题，采用虚拟机运行数字模型接入仿真网络的方法，提出融合VMware软件与QualNet软件的半实物网络仿真测试体系架构。
基于此架构设计一种面向VMware的Link11数据链动态仿真交互接口，以及Link11数字电台交互模型，实现仿真过程中虚拟机搭载的Link11数字电台交互模型与QualNet中Link11虚拟网络模型的实时数据交互，如动态工作参数获取与重配置等功能。
通过引入虚拟机运行数字模型替代真实设备，在保证网络仿真精度的前提下，有效地降低仿真测试成本。
测试结果证明了所提半实物仿真体系架构的可行性和高效性。
关键词：战术数据链；半实物网络仿真；虚拟机；动态交互接口；VMware软件中图分类号：TN919.25文献标志码：A文章编号：1000-1093(2020)S2-0224-10 DOI：10.3969/j.issn.1000-1093.2020.S2.030VMware-based Hardware-in-the-loop SimulationApproach for Link11Data LinkLI Huibo,WU Haiqiao,LI Ping,GONG Peng(School of Mechatronical Engineering,Beijing Institute of Technology,Beijing100081,China)Abstract:The high hardware cost and limited resources may be caused by real radio access in the large-scale network hardware-in-the-loop simulation of tactical data link.For the problems above,a novel hardware-in-the-loop simulation test architecture integrating VMware with QualNet was designed. Specifically,instead of using real radios,the multiple virtual machines running digital radio model, initiated on the VMware,are integrated with the simulation network.Based on this architecture,a dynamic simulation interface for Link11data link based on VMware and a digital radio model for Link11 radio are designed to implement the real-time data interactions between the Link11digital radio model running on virtual machines and the Link11virtual network model in QualNet,such as dynamic parameter acquisition,parameter reconfiguration and so on.The virtual machine running digital model, instead of real equipment,can be used to effectively reduce the required hardware cost while ensuring the accuracy of network simulation.The experimental results prove the feasibility and high efficiency of the proposed hardware-in-the-loop emulation architecture.Keywords:tactical data link；hardware-in-the-loop network simulation；virtual machine;dynamic interaction interface;VMware收稿日期：2020-03-17基金项目：国家科技部重点研发计划项目(2018YFC0823000)；国家自然科学基金项目(61671062)作者简介：李慧博(1995—),女,博士研究生。
Integrating fast mobility in the OLSR routing protocol Mounir B ENZAID1,2,Pascale M INET1and Khaldoun A L A GHA1,21INRIA,Domaine de V oluceau-B.P.105,78153Le Chesnay Cedex,FRANCEmounir.benzaid,pascale.minet@inria.fr2LRI,Bˆa t490Universit´e Paris Sud,91405Orsay Cedex,FRANCEalagha@lri.frAbstract-With the current increase in ad-hoc mobile networks in public domains(e.g.airports,cities,etc.),and the widespread use of IEEE802.11wireless LAN,there is a growing need to handle and manage fast mobility.Extending the coverage area of ad-hoc networks and taking into account fast mobility in routing proto-cols could offer a complementary solution to the UMTS for fourth generation(4G)mobile networks.In this paper we present an extension of the Optimized Link State Routing protocol(OLSR), denoted Fast-OLSR,which is designed to meet the need for fast mobility in Mobile Ad-hoc NETworks(MANETs).Performance evaluation of Fast-OLSR is done by simulation,and the results show that the loss rate can be minimized while maintaining a rea-sonable overhead traffic.Keywords:mobile ad-hoc networks,wireless networks,fast mobil-ity,routing protocol,proactive protocol,OLSR.I.I NTRODUCTIONWith recent technological advances in laptop computers and wireless data communication devices,wireless communica-tions represent one of the fastest growing segments of the com-munications industry today.Wireless networks bring a new dimension to mobility;indeed they enable a user to access the Internet anywhere and at any time.At present,mobile wireless networks can be classified according to two main types:infras-tructure and infrastructureless mobile networks;this last type of network is called an ad-hoc network[1],[2],[3].A Mobile Ad-Hoc NETwork(MANET)[4]is a collection of mobile nodes that communicate using a wireless medium, forming an autonomous network.There is no centralized ac-cess point or pre-existing infrastructure.Such networks have dynamic,random,sometimes rapidly changing topologies,lim-ited bandwidth,variable throughput links,and limited power (e.g.battery operated devices).When a node needs to com-municate with another node,it uses either a direct wireless link or a multi-hop route to reach the destination.This means that all the nodes must incorporate routing capability to ensure that packets are delivered to the designated destination.Moreover ad-hoc routing protocols must minimize the induced control traffic.With the increasing appearance of ad-hoc mobile networks in public domains(e.g.highways,cities,etc.),there is an in-creasing need to handle and manage fast mobility.Extending the coverage area of ad-hoc networks and taking into account fast mobility in routing protocols could offer a complementary solution to the UMTS in fourth generation(4G)mobile net-works.The design of a fast and efficient routing protocol is necessary for the performance of an ad-hoc network in partic-ular in the case of large and dense networks with fast moving nodes.This paper focuses on how to deal with fast moving nodes in the OLSR routing protocol.OLSR[1]is one of the protocols discussed in the MANET working group.The protocol as described in this paper inherits the stability of a Link-State routing protocol and the availabil-ity of routes when needed due to its proactive nature.How-ever,when a node is moving fast,the links with its neighbors are valid only during a short time interval.If packets are for-warded on an invalid link,not yet detected as broken,they are lost.Hence to minimize packet loss,broken links between the node and its neighbors must be quickly detected.In this paper, we propose the Fast-OLSR extension to account for fast nodes in routing while keeping the routing overhead as low as possi-ble.This extension is based on the initial study[5].A tradeoff is found between the routing overhead and the loss rate.The remainder of this paper is organized as follows:in Section2,we describe the two families of routing protocols (i.e.reactive and proactive protocols)discussed in the MANET working group.In Section3,we briefly present OLSR,a proac-tive protocol.In Section4,we show how this protocol can be extended to take into account fast mobility.In Section5,we evaluate the performance of the Fast-OLSR extension in terms of message loss and induced overhead.II.MANET R OUTING PROTOCOLSDifferent routing protocols are proposed in the MANET working group of the IETF[4].They address the problem of unicast routing,while taking into account the features of wireless,multi-hop,mobile ad-hoc networks.All these proto-cols generally deal with low mobility environment conditions. Such protocols can be divided into two categories:proactive and reactive,depending on the route discovery mechanism that is used.With reactive protocols,a node discovers routes on-demand and maintains only active routes.Thus,a route is discoveredwhenever a source node needs to communicate with a destina-tion node for which a route is not available.This discovery is based on pureflooding in the network.The source node broad-casts a route request message to all its neighbors.The neigh-bors in turn rebroadcast the route request to their neighbors if they do not have a route to the destination.When the route re-quest reaches either the destination or a node that has a valid route to the destination,a route reply message is generated and transmitted back to the source.Therefore as soon as the source receives the route reply,a route is created from the source to the destination.The advantage of reactive protocols is that no control message is needed for non-active routes.The drawback is the latency when establishing a route.Examples of reactive protocols include AODV[6]and DSR[7].With proactive protocols,each node continuously maintains the routes to all other nodes in the network by the periodic exchange of control messages.When a node needs to send a packet to any other node in the network,the route is immedi-ately available.The main advantage of proactive protocols is that they do not introduce a delay before sending data.Fur-thermore,these types of protocols are useful for traffic patterns where a large subset of nodes is communicating with another large subset of nodes,and where the[source,destination]pairs are changing over time.Examples of proactive protocols in-clude DSDV[8](an adaptation of Routing Information Proto-col[9]),OLSR[1](an optimization of the Link-State algorithm OSPF[10])and TBRPF[11].III.O PTIMIZED L INK S TATE R OUTING P ROTOCOL(OLSR)OLSR[1]is a proactive routing protocol,providing the ad-vantage of having routes immediately available in each node for all destinations in the network.It is an optimization of a pure Link State routing protocol.This optimization is based on the concept of multipoint relays(MPRs)[12].First,using mul-tipoint relays reduces the size of the control messages:rather than declaring all links,a node declares only the set of links with its neighbors that are its“multipoint relays”.The use of multipoint relays also minimizesflooding of control traffic.In-deed only MPRs forward control messages.This technique sig-nificantly reduces the number of retransmissions of broadcast control messages[13].OLSR is characterized by two types of control messages: neighborhood and topology messages,called respectively Hello messages and Topology Control(TC)messages.OLSR provides two main functionalities:thefirst is Neighbor Discov-ery,and the second is Topology Dissemination.These will be detailed in the following.A.Neighbor DiscoveryEach node must detect the neighbor nodes with which it has a direct link.Due to the uncertainties in radio propagation,a link between neighboring nodes may enable the transmission of data in either one or both directions over the link.For this, each node periodically broadcasts Hello messages,containing the list of neighbors known to the node and their link status. The link status can be either symmetric(if communication is possible in both directions),asymmetric(if communication is only possible in one direction),multipoint relay(if the link is symmetric and the sender node of the Hello message has se-lected this node as a multipoint relay),or lost(if the link has been lost).The Hello messages are received by all one-hop neighbors,but are not forwarded.They are broadcast at a low frequency determined by the refreshing period“Hello-interval”(the default value is2seconds).Thus,Hello messages enable each node to discover its one-hop neighbors,as well as it two-hop neighbors(the neighbors of its neighbors).This neighborhood and two-hop neighbor-hood information has an associated holding time“Neighbor-hold-time”,after which it is no longer valid.On the basis of this information,each node m of the network independently selects its own set of MPRs among its one-hop neighbors.The multipoint relay set of m,denoted MP R(m)is computed as follows:it is a minimum subset of one-hop neighbors with a symmetric link,such that all two-hop neighbors of m have sym-metric links with MP R(m).This means that the MPRs cover (in terms of radio range)all the two-hop neighbors.Figure1 shows the MPRs selection by node m.A possible algorithm to select these MPRs is described in[12].The MPR set is com-puted whenever a change in the one-hop neighborhood or two-hop neighborhood isdetected.mFig.1.Multipoint relays of node m.Each node m maintains the set of its“multipoint relay se-lectors”(MPR selectors).This set contains the nodes which have selected m as a multipoint relay.Node m only forwards broadcast messages received from one of its MPR selectors. B.Topology DisseminationEach node of the network maintains topological information about the network obtained by means of TC messages.Each node m selected as a MPR,broadcasts a TC message at least ev-ery“TC-interval”(the default value is6seconds).If a change occurs in the MPR selector set,the next TC can be sent ear-lier(e.g.after some pre-specified minimum interval).The TCmessages areflooded to all nodes in the network and take ad-vantage of MPRs to reduce the number of retransmissions.The TC message originated from node m declares the MPR selec-tors of m.Thus,a node is reachable either directly or via its MPRs.This topological information collected in each node has an associated holding time“Top-hold-time”,after which it is no longer valid.The neighbor information and the topology information are refreshed periodically,and they enable each node to compute the routes to all known destinations.These routes are com-puted with Dijkstra’s shortest path algorithm.Hence,they are optimal as concerns the number of hops.Moreover,for any route,any intermediate node on this route is a MPR of the next node.The routing table is computed whenever there is a change in neighborhood information or a change in topology informa-tion.IV.F AST-OLSRIn an OLSR ad-hoc network,when a node is moving fast, its neighborhood changes quickly and the default Hello fre-quency in OLSR is not sufficient to track the nodes’motion. Therefore,routes to this node become inactive and messages sent to this node may be lost.A higher Hello frequency would overcome this problem,but at the cost of an additional control overhead.We propose an extension of OLSR to address the is-sues for fast mobility nodes.This“Fast-OLSR”extension has two main objectives:first,The induced control traffic is tuned to node mobility,in such a way that it allows a fast node’s mo-tion to be tracked,i.e.there is very low overhead when there is no mobility and an appropriate overhead as mobility increases. Second,the bandwidth consumed must remain reasonable(i.e. maintained below a certain threshold).Fast-OLSR has been designed as an extension of the OLSR protocol such that:(i)not all nodes are required to implement Fast-OLSR;OLSR and Fast-OLSR can coexist in the same mo-bile ad-hoc network.(ii)Fast-OLSR is based on the same basic principles as OLSR.It only differs in the Neighbor Discovery functionality,which is adapted to deal with fast mobility. Moreover,to stay general and completely independent of the underlying link layer(e.g.IEEE802.11,Bluetooth,etc.),Fast-OLSR does not make any assumptions concerning the informa-tion provided by the chosen link layer.This means for instance that Fast-OLSR must work even when neither information on signal attenuation nor link layer notification of broken links are available.In such conditions,the only way that Fast-OLSR can detect node mobility is to observe the neighborhood changes. The basic idea of neighbor discovery in Fast-OLSR is to en-able a fast moving node,m,to quickly discover a small num-ber of neighbors.Among these,a small number of multipoint relays are selected to maintain connectivity with other nodes in the network.To achieve this,a fast moving node estab-lishes a small number of symmetric links refreshed at a high frequency by means of Fast-Hellos.Such links are called Fast links and this high frequency is determined by the refreshing period“Fast-hello-interval”.There are three main mechanisms in Fast-OLSR:–Switching to the Fast-Moving/Default mode:when a node detects that it is moving fast(e.g.a high number of changes in its neighborhood),it switches to the Fast-Moving mode and starts sending Fast-Hellos.On the other hand,when a node in Fast-Moving mode detects that it is no longer moving fast(e.g.a small number of changes in its neighborhood),it switches back to the Default mode,which is the initial one.–Establishing Fast links:a node in Fast-Moving mode sends Fast-Hello messages at high frequency.A Fast-Hello is similar to a Hello,however its size is smaller because it contains a reduced number of neighbor addresses.Fast-Hello messages are used to establish Fast links.When a node in De-fault mode receives a Fast-Hello from a node m in Fast-Moving Mode,it replies with a Fast-Hello.Among the received replies, node m selects a small number of MPRs.These are declared in the next Fast-Hello.“The declared nodes”will then broadcast TC messages to all the nodes in the network declaring that they are MPRs of m.Only nodes in Default mode can be selected as MPRs.This simplified selection of MPRs is used because the node m,which is moving fast,only partially knows its two-hop neighborhood.–Refreshing Fast links and Detecting new/broken links: a node m in Fast-Moving mode sends Fast-Hellos contain-ing the addresses of its MPRs and its MPRs reply with empty Fast-Hellos.Empty Fast-Hello save bandwidth usage,and they are sufficient to enable node m to know that it can always be reached by these MPRs.If a MPR of m has not received the Fast-Hello of m,it sends a TC message to inform all nodes in the network that it is no longer a MPR for m.By means of Fast-Hellos,Fast-OLSR enables a broken link to be detected quickly.Hence the computation of a new route is made earlier,and message loss is reduced.Moreover,as the number of Fast links refreshed by a node in Fast-Moving mode is reduced,the additional overhead remains reasonable. As soon as a node in Default mode no longer has any Fast links, it stops sending Fast-Hellos and returns to normal OLSR be-havior,by sending only Hello and TC messages.V.S IMULATIONIn this section,we study the behavior of Fast-OLSR in worst-case conditions.We conduct a performance evaluation by sim-ulation.The velocity of mobile nodes ranges from a cyclist’s speed up to a car’s speed on a highway.Two parameters are measured:the packet loss and the overhead produced by Fast-OLSR.A.Simulation modelThe considered simulation model is depicted in Figure2.A fixed node C is located in a central position.It communicates by symmetric links with6nodes denoted m1to m6.These nodes arefixed.One node m,moving at high speed,is alsoconsidered.It moves continually around m1to m6in a circu-lar way.The velocity of m is constant,and its value depends on the simulation.This model can,for instance,represent the effective architecture where C is a gateway and m i,i∈[1,6] are base stations that connect a fast moving wireless node m to another wired/wireless network via the gateway.We con-sider that there is no overlapping between the radio coverage areas of two adjacent nodes m i and m i+1.This means that it is impossible for m to be in a soft handoff situation where it can receive or send packets from both m i and m i+1.Thus, node m loses connectivity with m i before having connectiv-ity with m i+1.We make this assumption in order to study the behavior of Fast-OLSR in worst-case conditions.Indeed,over-lapping areas would enable a mobile node to maintain connec-tivity while a new route is being established.Moreover,we assume that neither link layer notification,nor information on signal attenuation are available.In each simulation,there is an initialization time in which there is an exchange of Hello and TC messages to establish the links between node C and nodes m1to m6.Then,m switches to Fast-Moving mode.Fast-OLSR performances are evaluated while m is moving9times around m1to m6.The signal at-tenuation distance isfixed to60meters(mean value of the at-tenuation distance in IEEE802.11).This model can be applied with IEEE802.11.In such a case,collisions could occur,they result from simultaneous transmissions of C and m i.As in all considered scenarios,they are reduced to a minimum,and are not considered in ourmodel.Fig.2.Simulation model.B.Simulation Measurements and ParametersLet us assume that a Constant Bit Rate(CBR)stream of packets is being transmitted from node C to mobile m.With our model,C is always two hops from m but the next hop to reach m changes when m moves.We are interested in evaluat-ing the number of lost packets due to hard handoffs,assuming the worst conditions(no buffering and no retransmission).-Packet Loss:This number is computed as follows.Wefirst compute the number of lost packets during a handoff between nodes m i and m i+1.Packets are lost during the time interval [t1,t2)where t1is the time when m loses connectivity with m i and t2is the time when m can be reached through m i+1.The total number of lost packets is obtained by adding the number of packets lost in each handoff generated during the simulation.-Induced overhead:We compute the overhead induced by Fast-OLSR due to fast mobility of node m.This overhead is equal to the total number of(i)Fast-Hello messages generated in the network and(ii)the TC messages sent each time a Fast link is established or broken.-Parameters:We have measured the packet loss and the overhead induced in various simulations,each simulation being characterized by two parameters:first,the refreshing period of Fast links(i.e.,Fast-hello-interval),secondly the velocity of m in kilometers per hour.C.Simulation resultsFigures3and4highlight the performance of Fast-OLSR in terms of loss rate and overhead,when node C sends CBR traf-fic to mobile m.Mobility ranges from20km/h to150km/h. Figure3depicts the packet loss rate versus mobility.Several curves are drawn with regard to the value of the Fast-hello-interval(from100ms to300ms).As Figure3shows,the greater the Fast-hello-interval is,the greater the loss rate is, and,of course,the packet loss becomes greater as the speed increases.Our simulation results show that the packet loss rate can be maintained smaller than10.6%for a velocity up to90km/h. Recall that these results are obtained in a worst-case where is no overlapping radio coverage area of two adjacent nodes m i,m i+1(see Figure2)and no buffering or retransmission are considered.The routing overhead produced for the smallest Fast-hello-interval(i.e.100ms)is kept below7.7kbit/s.To establish a comparison,this interval is equivalent to the120ms Slow Associated Control CHannel(SACCH)in GSM radio in-terface.The SACCH channel is used to report received signal strength and thus triggers the handoff between cells.For a given maximum acceptable loss rate and the maxi-mum reachable speed,we can determine the largest Fast-hello-interval that produces the least routing overhead.First we draw the vertical line indicating the maximum speed,and the hori-zontal line representing the acceptable loss rate.The acceptable region is then delimited by the x-axis,the y-axis,the speed line and the loss rate line.The most appropriate Fast-hello-interval is the one given by the intersection of the highest curve in the acceptable region with the speed line.For example,for a maxi-mum speed of125km/h and a loss rate of15%,the only possi-ble Fast-hello-interval is100ms.However,for a speed limited to40km/h with a loss rate of10%,there are several possibil-ities for the Fast-hello-interval:100ms,140ms,200ms.We select the highest curve,which gives us a Fast-hello-interval of 200ms.Indeed this value incurs the smallest overhead in the acceptable region.Figure4depicts the routing overhead induced by Fast-OLSR versus mobility.Several curves are drawn with regard to the value of the Fast-hello-interval(from100ms to300ms). As Figure4shows,the smaller the Fast-hello-interval is,the greater the routing overhead is.The routing overhead becomes slightly greater as the speed increases.510152025303540455055L o s s r a t e (%)Mobility Km/hO v e r h e a d t r a f f i c b y t e /s e cMobility Km/hFig.3.Loss rate versus mobility.Fig.4.Overhead traffic versus mobility.Table I.Mobility classes and associated results.ClassSpeed Loss rate ≤10%10%<Loss rate ≤15%15%<Loss rate ≤20%Fast-hello Overhead Fast-hello Overhead Fast-hello Overhead km per hour ms kbps ms kbps ms kbps Cyclist 20≤S <45140 5.4240 3.7>300 2.7Urban 45≤S <901007.7140 5.7140 5.7Road 90≤S <120××1007.8140 6.2Highway120≤S <150××××1008.1Figure 4also shows the additional overhead resulting from a decrease in the Fast-hello-interval .The choice of a smaller Fast-hello-interval is justified only when the resulting gain in loss rate is significant.For example,for a maximum speed of 50km/h and a loss rate of 10%,a Fast-hello-interval of 140ms is chosen.A Fast-hello-interval of 100ms would improve the loss rate (it would be 7%)but at the cost of an additional over-head of 1kByte/s.On the other hand,for a maximum speed of 90km/h and a loss rate of 25%,a Fast-hello-interval of 240ms is chosen.This improves the loss rate (it would be 30%with a Fast-hello-interval of 300ms)at the cost of an additional over-head of only 30Byte/s.Results of our simulations are summarized in Table I.Four classes of mobile node are defined.Each class is defined by its maximum speed.For each class,we determine the best Fast-hello-interval and associated maximum routing overhead in terms of kbit per second,compliant with the acceptable loss rate.VI.C ONCLUSIONWith the deployment of mobile ad-hoc networks in public domains (e.g.highways,cities,etc.),routing protocols must support fast mobility.In this paper,we have proposed a Fast-OLSR,an extension of OLSR dealing with fast mobility.Fast-OLSR maintains connectivity with fast moving nodes,while maintaining a reasonable overhead.The performances of Fast-OLSR are evaluated by simulation in worst-case conditions (no buffering,no retransmission,no overlap in coverage areas and no link layer notification).Simulation results show how to tune the value of the refreshing period (Fast-hello-interval )for different classes of mobile and different acceptable loss rates.Thus,in the considered configuration,ad-hoc network nodes can move as fast as cellular network nodes with a velocity that can reach 150km/h and the loss rate is maintained below 15%with an acceptable overhead (the refreshing period being equal to 100ms).In further work,we will study how to dynamically adjust the value of the refreshing period as a function of the mobile speed and the acceptable loss rate.R EFERENCES[1]P.Jacquet,P.Muhlethaler, A.Qayyum, ouiti,L.Viennot,T.Clausen,“Optimized Link State Routing Protocol,”draft-ietf-manet-olsr-06.txt,IETF,,September 2001.[2]J.Broch,D.Maltz,D.Johnson,Y .Hu,J.Jetcheva,“A performance com-parison of multi-hop wireless ad hoc network routing protocols,”in ACM Mobicom’98,(Dallas,USA),October 1998.[3] C.Perkins,Ad Hoc Networking .Addison Wesley,2000.[4]Mobile Ad-hoc Networks (MANET),manet-charter ./html.charters/manet-charter.html,2002.[5]P.Jacquet,P.Muhlethaler,P.Minet,A.Qayyum,ouiti,L.Viennot,T.Clausen,“OLSR Extensions,”draft-ietf-manet-olsr-extensions-00.txt,IETF,,August 2001.[6] C.Perkins,E.Royer,S.Das,“Ad hoc On-Demand Distance Vector Rout-ing,”draft-ietf-manet-aodv-08.txt,IETF,March 2001.[7]J.Broch,D.Johnson,D.Maltz,“The Dynamic Source Routing Protocolfor Mobile Ad Hoc Networks,”draft-ietf-manet-dsr-01.txt,Dec 1998.[8] C.Perkins,P.Bhagwat,“Highly Dynamic Destination-SequencedDistance-Vector Routing for Mobile Computers,”in ACM SIG-COMM’94,(London,UK),August 1994.[9]J.Malkin,“RIP Version 2,”RFC 1388,IETF,Jan 1993.[10]J.Moy,“OSPF version 2,”RFC 2328,IETF,Jan 1998.[11]R.G.Ogier,F.L.Templin,B.Bellur,M.G.Lewis,“Topology BroadcastBased on Reverse-Path Forwarding,”draft-ietf-manet-tbrpf-05.txt,IETF,March 2002.[12] A.Qayyum,L.Viennot,ouiti,“Multipoint Relaying:An EfficientTechnique for flooding in Mobile Wireless Networks,”Tech.Rep.RR-3898,INRIA,http://www.inria.fr,Feb 2000.[13]P.Jacquet,P.Muhletaler,A.Qayyum,ouiti,T.Clausen,L.Viennot,“Optimized Link State Routing Protocol,”in IEEE INMIC ,(Pakistan),Dec 2001.。
