Basic ingredients of free energy calculations: A review

Methods to compute free energy differences between different states of a molecular system are reviewed with the aim of identifying their basic ingredients and their utility when applied in practice to biomolecular systems. A free energy calculation is comprised of three basic components: (i) a suitable model or Hamiltonian, (ii) a sampling protocol with which one can generate a representative ensemble of molecular configurations, and (iii) an estimator of the free energy difference itself. Alternative sampling protocols can be distinguished according to whether one or more states are to be sampled. In cases where only a single state is considered, six alternative techniques could be distinguished: (i) changing the dynamics, (ii) deforming the energy surface, (iii) extending the dimensionality, (iv) perturbing the forces, (v) reducing the number of degrees of freedom, and (vi) multi‐copy approaches. In cases where multiple states are to be sampled, the three primary techniques are staging, importance sampling, and adiabatic decoupling. Estimators of the free energy can be classified as global methods that either count the number of times a given state is sampled or use energy differences. Or, they can be classified as local methods that either make use of the force or are based on transition probabilities. Finally, this overview of the available techniques and how they can be best used in a practical context is aimed at helping the reader choose the most appropriate combination of approaches for the biomolecular system, Hamiltonian and free energy difference of interest. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

Analysis of amphetamine and methamphetamine as emerging pollutants in wastewater and wastewater-impacted streams

The identification and quantitation of the non-ecstasy amphetamine-type stimulants (ATSs) amphetamine and methamphetamine in lakes, rivers, wastewater treatment plant influents, effluents, and biosolids are reviewed. Neither monitoring nor reporting is required of these ATSs, which are considered emerging pollutants, but they have been identified in the environment. Amphetamine and methamphetamine enter our water supply by human excretion after legal or illegal consumption and via manufacturing in clandestine laboratories. Analytical methodology for sampling, sample preparation, separation, and detection of ATSs is discussed. Reported occurrences of ATSs in the environment and their use in municipal sewage epidemiology are noted. Future research needs that challenge applications of analytical techniques are discussed. The review focuses on research reported from 2004 to 2009.     

基于SOPC的SPWM脉冲发生器的实现

针对逆变控制领域的需求,采用自然采样法设计一个基于SOPC的SPWM脉冲发生器。在系统中,结合DDS数字频率合成技术产生正弦调制波。使用Verilog语言编程实现可逆计数器,利用可逆计数器形成一个完整的三角波。然后将同一时刻的正弦函数值与三角函数值相比较,形成一路脉冲调制波。最后为防止同相桥臂功率器件的同时导通,经过死区延时部分,形成最终的SPWM脉宽调制波。基于SOPC系统的SPWM脉冲发生器既简化电路设计,又提高系统的可靠性、精确性,并通过实验验证实该系统设计的有效性、稳定性。     

基于自偏置电流镜的CMOS红外焦平面读出电路

针对高精度红外焦平面阵列应用设计了一种具有高注入效率、大动态范围、稳定的探测器偏压、小面积和低功耗的自偏置电流镜注入CMOS读出电路.所设计的电路结构包括一种由自偏置的宽摆幅PMOS共源共栅电流镜和NMOS电流镜构成的反馈结构读出单元电路和相关双采样电路.对所设计电路采用Chartered 0.35 μm CMOS工艺进行了流片.测试结果显示:电路线性度达到了99%,探测器两端偏压小于1mV.电路输入阻抗近似为0,单元电路面积为10μm×15μm,功耗小于0.4μW.电量存储能力3108电子.测试结果表明:电路功能和性能都达到了设计要求.     

一种基于合成带宽技术提高SAR分辨率的新方法

近年来,一种多chirp脉冲合成大带宽的技术受到雷达界的关注,该方法可以在降低系统瞬时带宽和采样率的情况下提高距离分辨率.针对子脉冲信号的参数如采样率、带宽和频段间隔等可能各不相同的问题,本文提出了采用SINC捕值进行信号均匀化重建的方法,并通过前处理方式来实现合成带宽技术在SAR中的应用.最后的仿真实验验证了本文方法适应于参数各不相同的多频段子脉冲信号,能有效提高距离分辨率.     

35 W集成控制型HID镇流器的设计

设计了一种基于集成芯片控制的HID灯镇流器。该镇流器集成了对恒功率、电流采样、温度补偿、斜坡补偿部分的控制,同时改进了采样电路,有效提高了调制信号的占空比。镇流器电路拓扑结构简单,降低了成本,效率达到80.3%,可靠性高,无声谐振现象。     

具有多种输出模式微弧氧化电源的研制

基于对微弧氧化工艺和负载特性的研究,提出一种新的带放电回路脉冲模式。并在此基础上研制了一种以80C196KB单片机为控制系统核心,具有多种输出模式的微弧氧化电源。通过对主电路结构的拓扑及对可控硅触发和IGBT驱动的控制,该电源能够产生带放电回路脉冲、单极性脉冲和双极性脉;中3种输出模式,而且其脉冲幅值、频率、占空比具有很宽的调节范围。此外还实现了对微弧氧化过程中电流和电压的实时采集和显示。经实践表明,该电源能很好地应用于实验研究及工业化生产。     

简易数字存储示波器电子综合实验项目设计

设计了一个电子综合实验项目简易存储示波器,让学生利用低频,数字电路、单片机技术、EDA技术等相关专业技能,完成方案设计,电路制作、直到最后的调试验收整个项目开发过程。培养学生应用已学的专业基础知识,进行项目设计和开发的能力。     

带通采样在数字多通道中频接收机中的应用

论述了带通信号采样定理,在对带通采样后的频谱结构做了详细分析的基础上,提出中频频率、采样频率的选取方法。将带通欠采样技术运用到软件无线电中频接收机设计中,并给出了带通采样定理在的不同条件下Matlab仿真的结果,验证了带通采样技术在宽带数字多通道、多速率、多模式软件无线电中频接收机设计中的可行性和实用性,在工程应用中具有较大的参考意义。     

一种新的数模混合型解扩方法

针对QPSK调制的WCDMA扩频信号提出了一种新的数摸混合型解扩方法。实验表明这种数模混合型解扩方法可以实现QPSK调制的WCDMA扩频信号的解扩功能。与全数字解扩方法相比,该方法无需A/D转换器和正交变换器,具有电路结构简单的特点,而且由于直接在模拟域计算,因此具有模拟运算电路功耗低、高速等优点,同时由于模拟电路受数字电路控制,该方法又具有数字电路灵活,稳定等优点。