RFID多碰撞位联合锁位动态可调整算法研究

针对现有RFID多标签防碰撞算法无法兼顾减小传输开销与降低碰撞率的缺点,提出了一种基于多碰撞位联合锁位动态可调防碰撞算法的系统。系统工作流程包括空闲时隙检测和多标签动态识别,空闲时隙检测用于锁定空闲时隙,以避免阅读器访问增大时间开销;多标签识别采用动态可调整防碰撞算法,其由多碰撞位联合锁位防碰撞算法和动态二叉树算法构成,阅读器根据曼彻斯特译码结果检测碰撞,估算标签数量,从而调用不同的防碰撞算法,成功识别一个标签后返回到上一次发生碰撞的节点。仿真结果表明,通信速率125 Kbit/s条件下,系统在传输开销、寻呼指令开销、吞吐率性能方面有明显的提高。

一个阻止内部碰撞转状态碰撞的海绵建构变体

对海绵建构进行了洞察后,作者发觉海绵建构及其多数变体建构在对抗一些一般攻击(包过Joux的多碰撞攻击,Dean的固定点技术,Kelsey and Schneier的长消息次原像攻击,Kelsey and Kohno的集群攻击等)时,主要采取的方法是提高内部状态的容量,本文给出了一个基于海绵建构的新的密码建构(简称为ESC),作者证明了ESC在带有相同内部状态容量时一般情况下将比海绵建构更加抵抗上述的一般攻击。作者的设计思想来源于海绵建构与Merkle-Damgard?建构的差别,由于海绵建构是基于变换(或置换)函数的迭代建构,变换(或置换)函数所处理的中间链值即整体状态下还有所谓的内部状态。当攻击者在对海绵建构发动上述等一般攻击时,一般情况下最好的方法是先寻找内部碰撞,然后将其转化为状态碰撞。因此如果能增加内部碰撞向状态碰撞转换的工作量,则自然增加了对上述一般攻击的抵抗性。最后作者还讨论了ESC的安全和效率问题。

多次弹性正碰的全过程中速度交换的分析

动量、能量知识贯穿整个物理学的学习,也是分析、解决物理问题的一条重要途径和重要的思维方法,对思维能力要求比较高.从动量、能量角度出发,探讨了在弹性碰撞过程中的速度交换问题,建立了在多次弹性碰撞过程中的速度交换模型,并分析了该模型的局限性和适应性.

中央造山带早古生代地体构架与高压/超高压变质带的形成

位于北中国板块群与南中国板块群之间的中央造山带是中国大陆一条十分醒目而又极其重要的巨型(长达5000km)构造带。中央造山带是经历了大致600Ma的活动历史,和泥盆纪、三叠纪的两次主要碰撞造山以及白垩纪以来的陆内造山过程而构筑成的典型的“复合造山带”。特别是巨型中央超高压变质带及其两期超高压变质作用的发现,揭示了中央造山带的形成还经历了板块会聚边界洋壳/陆壳深俯冲的两次壮观地质事件。位于中央造山带北部的“北中央早古生代造山带”具有“多地体、多岛弧”的地体构架和“多俯冲和多碰撞造山”的动力学作用。研究认为北中央早古生代多地体/岛弧群是冈瓦纳超大陆西侧(或西北侧)陆块/岛弧群的组成部分,其主要的证据是:1北中央寒武系—志留系的过渡性动物群性质反映早古生代古生物区系与始特提斯洋盆海水相通的古地理环境;2北中央诸多蛇绿岩带形成时代>500~540Ma(新元古代-奥陶纪)可作为始特提斯洋盆扩张时限的印证;3多岛弧带为北中央早古生代地体的陆缘增生带,形成于540~450Ma,岛弧带形成自南(外)而北(里)渐新的趋势表明与始特提斯洋盆相连接的弧前小洋盆逐级俯冲的特征;4北中央早古生代多地体/岛弧群的“弧/陆碰撞”及早古生代...

基于不同年龄的自适应儿童乘员约束系统参数优化研究

针对单一碰撞工况匹配的儿童乘员约束系统不能保证在其他碰撞工况下儿童乘员的保护,而且极易造成更大的伤害。基于内置式自适应儿童约束系统的参数可调的特征,选取坐垫高度、坐垫长度、安全带限力值为优化变量,以儿童综合伤害评价值I及颈部损伤临界值Nkm为优化目标,采用多项式回归近似模型和非支配遗传优化算法(Non-dominated sorting genetic algorithm II,NSGA-Ⅱ)相结合的方法,分别对3、6、10岁儿童假人在法规GB 27887规定的正面碰撞和追尾碰撞工况下进行多目标优化计算。优化结果表明,在优化设计点,3个年龄段的儿童假人在两种碰撞工况下都能获得较好的保护。基于文中3个年龄段假人的优化设计点,拟合出优化变量与儿童身高和体重的相关关系模型,从而对不同身高和体重的儿童乘员都能达到很好的保护效果。

对强化MD结构杂凑函数的一个新的“牧群”攻击

该文构造了具有2k个起始点的变长"钻石树"结构的多碰撞,并据此提出了对强化MD结构杂凑函数的一个新的选择目标强制前缀且原像长度为2k+3块的原像攻击(即"牧群"攻击)。由于增大了攻击过程中可利用的中间链接值的数量,故当k≥n/4-1.05时,新的牧群攻击可将该攻击的计算复杂性由现有结果O(2n-2(k+1)+2n/2+k+5/2)降至O(2n-k/3+2n/2+k+2)。

广义生日攻击的改进

广义生日攻击算法是密码分析的一个常用工具。2015年亚密会,Ivica Nikolic针对列表数目为2<k<n的情况提出了多碰撞算法,该算法的复杂度优于经典的k-树算法。针对多碰撞算法中列表数目是2<k≠2~a<n情况,我们提出新的newtree算法,主要的改进有两点:首先在处理消极列表的最后加入k-树算法的处理;其次,在处理积极列表的最后加入部分多碰撞算法。newtree算法的时间渐进复杂度为?(k2~{(n-(2+k_P)logp))/(logk_A+3)},相比于多碰撞算法的渐进复杂度?(k2~{(n-k_Plogp)/(logk_A+1)})而言有所提高。

对联接杂凑函数的“特洛伊”消息攻击

"特洛伊"消息攻击是Andreeva等针对MD结构杂凑函数提出的一种攻击方法,首次将其应用于不同于MD结构的一类杂凑函数,即联接杂凑。结合联接杂凑的特点,综合利用Joux的多碰撞和深度为n-l的"钻石树"结构多碰撞,构造出了2n-bit联接杂凑函数的长度为n·2~k块的"特洛伊"消息,并据此首次提出了对其的固定前缀"特洛伊"消息攻击,其存储复杂性为2l+2^(n-l+1)+n·2^(k+1)块消息,时间复杂性为O(n·2^(n+k)+l·2~l)次压缩函数运算,远低于理想的时间复杂性O(n·2^(2n+k)。

可用于哈希函数的安全迭代结构

Merkle-Damgard(MD)迭代结构存在着不能保持压缩函数的第2原像稳固性、伪随机函数性等不安全性问题.为增强迭代哈希函数的安全性,从抵抗现有攻击的角度提出1个强化MD迭代结构,称为CMD结构.经证明,该结构可以保持压缩函数的抗碰撞性,能抵抗现有的对MD迭代结构的攻击,包括第2原像攻击和任意选定前缀的原像攻击.利用这些攻击方法对enveloped Merkle-Damgard结构进行了分析,并指出该结构不能提供比MD结构更高的安全性.

链接变量循环的Hash函数结构

现有的Hash函数基本上都是根据Merkle-Damg°ard结构设计的。基于Merkle-Damg°ard结构易受到长度扩展攻击、多碰撞攻击、Herding攻击等这些缺陷,设计了一种链接变量循环的Hash结构,该结构是基于宽管道Hash结构的,具有大的内部状态,可以有效抵抗上述针对Merkle-Damg°ard结构的攻击。结构具有可分析的安全性,可以提高Hash函数的性能,尤其是基于数学困难问题的Hash算法,增加了消息块对Hash值的作用。

Simulation of Restraint System Performance upon the Occupant's Response During Impact

Aim To study the influence of restraint system performance upon the occupant's response during impact, and provide a scientific base for occupant restraint system design. Methods \ In the light of basic theory of multibody system dynamics and impact dynamics on the basis of classical theory of impact, R W method is adopted to construct the vehicle occupant system model consisting of fourteen rigid bodies, thirty seven DOFs and slip joints for the simulation. A software named SVC3D(3 dimensional simulation of vehicle crash) is developed in the FORTRAN language. Results\ The results of simulation have a good coincidence with those of tests and the restraint system with low elongation webbing and equipped with pretensioner provides better restraint effect for the occupant. Conclusion\ The model of vehicle occupant multibody system and SVC3D are suitable for use. Occupant should be belted with low elongation webbing to a certain degree and occupant restraint system should be equipped with pretensioner.

Diffusion of Nanoparticles in Semidilute Polymer Solutions： A Multiparticle Collision Dynamics Study

The diffusion of nanoparticles immersed in semidilute polymer solutions is investigated by a hybrid mesoscopic multiparticle collision dynamics method. Effects of polymer concentration and hydrodynamic interactions among polymer monomers are focused. Extensive simulations show that the dependence of diffusion coefficient D on the polymer concentration c agrees with Phillies equation D-exp （-αc^δ） with a scaling exponent δ≈0.97 which coincides with the experimental one in literature. For increasing nanoparticle size, the scaling prefactor α increases monotonically while the scaling exponent always keeps fixed. Moreover, we also study the diffusion of nanoparticle without hydrodynamic interactions and find that mobility of the nanoparticle slows down, and the scaling exponent is obviously different from the one in experiments, implying that hydrodynamic interactions play a crucial role in the diffusion of a nanoparticle in semidilute polymer solutions.

Train driver protection under secondary impact

An EMU train with detailed cabin structural is established based on the finite element method.The secondary impact between train driver and control desk is fully analysed and two measures are proposed to reduce the driver injury severity,such as the multi-objective optimization of the driver seat position and equipping the train with three-point seat belt.Simulation results indicate that the driver seat position has a significant effect on the driver injury severity during a secondary impact.According to the multi-objective optimization,some Pareto solutions are suggested to design the driver seat position.Besides that,it is also indicated although the chest and leg are well protected when the driver wears a two-point seat belt,it increases the head injure during a secondary impact.On the other hand,the three-point seat belt can supply the train driver with an overall protection against the secondary impact.The injury criteria(HIC,VC,TI)of the driver with the three-point seat belt is significantly lower than those of the driver without seat belt.Moreover,according to the simulation analysis,the limited load of the three-point seat belt is suggested about 1.5 kN.

Simulation of Fragment Impact on Multi-Layer Targets Using Contact Method

Cased explosives generate highly energetic fragments as their casing breaks up. Due to the complexity of casing fragment related behavior such as embedment, perforation and ricochet, it may be insufficient to use equivalent triangular pressure loading in fragment impact simulations. This simplified method may over- or under-predict the target response. Recently, a procedure using contact techniques has been proposed to overcome such difficulties. It has been shown that the new method has the inherent capability in modeling the multi-piece and multi-hit fragment impact problems in a more realistic way. To investigate the applicability of the proposed method to simulations involving multi-layer penetration, the selected problems of fragment impact on multi-layer targets are described in this paper. It is demonstrated that this method is capable of predicting the complicated multi-layer structural response caused by fragment impact and penetration. Modeling procedures and some technical issues are also discussed.

Shock Tube Measurement of Ethylene Ignition Delay Time and Molecular Collision Theory Analysis

In this study, 75% and 96% argon diluent conditions were selected to determine the ig- nition delay time of stoichiometric mixture of C2Ha/O2/Ar within a range of pressures （1.3-：3.0 arm） and temperatures （1092-1743 K）. Results showed a logarithmic linear rela- tionship of the ignition delay time with the reciprocal of temperatures. Under both two diluent conditions, ignition delay time decreased with increased temperature. By multiple linear regression analysis, the ignition delay correlation was deduced. According to this correlation, the calculated ignition delay time in 96% diluent was found to be nearly five times that in 75% diluent. To explain this discrepancy, the hard-sphere collision theory was adopted, and the collision numbers of ethylene to oxygen were calculated. The total collision numbers of ethylene to oxygen were 5.99×10^30 s^-1cm^-3 in 75% diluent and 1.53×10^29 s^-1cm^-3 in 96% diluent （about 40 times that in 75% diluent）. According to the discrepancy between ignition delay time and collision numbers, viz. 5 times corresponds to 40 times, the steric factor can

Two episodes of subduction and collision events at the northern foot of Dabie Mountains: Evidence from petrology and structural geology of granitoid rocks

The intrusive bodies studied include Mafan diorites ((462.7±1.5)Ma, 40Ar/39Ar amphibole plateau age), Duhudian granites ((293±12) Ma, U-Ph zircon age) and Suxianshi granites ((146.2±0.9) Ma) in Beihuaiyang area at the northern foot of Dabie Mountains, central China. Petrological studies indicate that all of them belong to I-type granitoid rocks. Among them, the Mafan and Duhudian stocks were formed by arc magmatism, while the Suxianshi pluton is a post-collisional granitic body. Three intrusive bodies have distinctive characteristics of structural deformation. The Mafan stock has a rather complicated structure pattern resulting from polyphase deformation during the Caledonian and Mesozoic, the Duhudian stock has been pronouncedly deformed during the Hercynian-Yanshanian events, while regional foliation is not pronounced within the Yanshanian Suxianshi stock. Combination of regional stratigraphic, regional structural and geochronological data shows that the Yangtze plate has experienced two episodes of subduction northward beneath the North China plate during the Paleozoic and following collisional events. The first phase of collision at about 400 Ma resulted in the formation of the Beihuaiyang crystalline basement and the Caledonian high-pressure metamorphism in Dabie orogenic zone, and a late phase of continent-continent collision (~230 Ma) is responsible for the Triassic ultrahigh- and high-pressure metamorphism in Dabie Mountains and for orogenic uplift of the Dabie Mountains. It is suggested that the Beihuaiyang tectonic belt at the northern foot of the Dabie Mountains is a multicyclic suture.

Multistage exhumation and partial melting of high-T ultrahigh-pressure metamorphic rocks in continental subduction-collision zones

High-temperature(HT, >850℃) metamorphism in continental collision orogens, particularly for those ultrahigh-pressure(UHP) metamorphic rocks, has become one of the remarkable topics in Earth science. It has bearing on the element and isotope behaviors of UHP rocks, their partial melting and related geodynamic effects during exhumation. In this paper, five representative continental collision orogens with typical HT/UHP rocks, including the Dabie orogen in China, the Kokchetav in Kazakhstan, the Caledonides in Greenland, the Rhodope in Greece, and the Erzgebirge in Germany are introduced, and their HT/UHP metamorphism and evolution processes are summarized. In addition, metamorphic P-T-t paths, multistage exhumation processes, and partial melting and preservation and retrogression of UHP index minerals during exhumation and their possible mechanisms are discussed. On this basis, the forthcoming key fields and scientific subjects of HT/UHP rocks within continental subduction channel are proposed.

multi-solitons interaction multicomponent plasma extended Poincare–Lighthill–Kuo method head-on collision

The propagation and interaction between ion acoustic multi-solitons in an unmagnetized multicomponent plasma consisting of fluid hot ions, positrons and both hot and cold electrons, are investigated by employing the extended Poincare–Lighthill–Kuo（PLK） method. Two different Kortewege-de Vries（K-dV） equations are derived. The Hirota＇s method is applied to get the K-dV multi-solitons solution. The phase shift due to the overtaking and head- on collision of the multi-solitons is obtained.

The Clash of Solidarities in the European Union Rethinking Jiirgen Habermas＇ Conception of Solidarity in the Transnational Context

The term solidarity is used extensively in the current political debate in Europe. Many times, the European Union is accused of a ＂lack of solidarity＂. But is this really the case？ From the perspective of political theory, Jurgen Habermas convincingly argues that solidarity beyond the nation state is indeed possible - even without a European demos. Since solidarity was artificially constructed within the nation state, it could very well expand into a form of transnational solidarity. However, the European Union is a complex sui generis institution, characterized by its multi-level governance. This paper therefore complements Habermas＇ concep- tion by Andrea Sangiovanni＇s reciprocity-based internationalism which differenti- ates more detailed between national, member state and transnational solidarity. Moreover, the paper argues that the democratic deficiencies and the economic liberalization in the European Union led to a fourth form of solidarity： a revived solidarity with the nation state. The current situation within the European Union is thus not the result of a lack of solidarity. On the contrary, there is plenty of solidarity around. However, the parallel existence of these different forms of solidarity could not persist without conflicts under the given discourse where solidarity is framed as a zero-sum game. Hence, the European Union does not suffer from a lack of solidarity but rather from a clash of multiple solidarities.

Achieving anti-sintering of supported platinum nanoparticles using a thermal management strategy

Sintering inhibition of a catalyst at high temperatures is a challenge during heterogeneous catalysis. In this paper, we report that hexagonal boron nitride(h-BN) is an optimal material for anti-sintering γ-Al_(2)O_(3)-supported Pt nanoparticles(NPs) originating from the high thermal conductivity of h-BN. The high thermal conductivity of h-BN ensures maximal heat dissipation from Pt NPs to γ-Al_(2)O_(3),thereby causing both Ostwald ripening and particle coalescence of Pt NPs to be decelerated at elevated temperatures.Inhibition of Pt NP sintering is also shown in the reducible TiO^(2-)supported Pt NPs with the help of h-BN. The proposed anti-sintering strategy using thermal management is universal, providing new insight into the design of anti-sintering materials and structures for a wide range of applications in heterogeneous catalysis.