光电耦合器电流传输比的噪声表征

光电耦合器中可俘获载流子的陷阱密度是影响其电流传输比(CTR)的重要因素,并与器件可靠性有密切关系.在器件内部的多种噪声中,1/f噪声可有效地表征器件陷阱密度.本文在研究光电耦合器工作原理以及1/f噪声理论的基础上,建立了光电耦合器的CTR表征模型和1/f噪声模型.在输入电流宽范围变化的条件下,测量了器件的电学噪声和CTR变化,实验结果验证了以上模型的正确性.将CTR模型与噪声模型相结合,得到了CTR与1/f噪声之间的关系.此关系应用于对光电耦合器辐照实验结果的分析,实验结果与理论得到的结论一致.理论与实验结果表明,噪声幅值越大,电流指数越接近于2,则器件的可靠性越差,相同工作条件下CTR的老化衰减量越大,其失效率显著增大.从而证明噪声可表征光电耦合器的CTR并能准确地反映器件的可靠性.     

高灵敏度CMOS光电集成接收机设计

设计了一个由调节型级联跨阻抗放大器(TIA)和双光电二极管(DPD)构成的CMOS光电集成(OEIC)接收机.具体分析了这个光电集成接收机的噪声和灵敏度及其相互关系.接收机中的噪声主要是电路中电阻的热噪声和MOS器件的闪烁噪声.提出了优化接收机灵敏度的方法.通过低成本的CSMC 0.6μm CMOS工艺流片并对芯片进行了测试.从测试眼图可知,该CMOS光电集成接收机可工作在1.25GB/s的传输速率下,灵敏度为-12dBm.     

一种声发射传感器的研制

设计了一种接触式声发射传感器,详细介绍了压电晶片、背衬、声匹配层以及前置放大器对声发射传感器灵敏度、分辨率、信噪比等指标的影响。利用阻抗分析仪对声发射传感器的输入电导进行了测定,结果表明声发射传感器设计方法可行。     

一种多路微波功率及温度数据采集系统的实现

实现了一套微波化学实验数据的自动采集系统,该系统的硬件结构基于MAX197和AT89C51单片机分别实现模数转换和数据采集的控制;采集控制软件使用计算机高级语言编写。在波导系统微波加热去离子水的实验中,使用该系统对实验数据电压反射系数和水中不同位置的温度进行自动采集,获得它们随时间变化的数据。该系统结构简单,使用方便,提供多种数据处理方式,比昂贵的数据采集卡节约成本,又能实现实时长时间采集,方便了微波化学实验的开展。     

电化学还原法制备氧化铅纳米棒

用电化学还原法制备出氧化铅纳米棒，用SEM、TEM、EDS和XRD研究其微观形貌和晶体结构。实验过程中发现电流密度是影响氧化铅纳米棒生成质量的主要因素。研究结果表明，用电化学还原法制备氧化铅纳米棒的最佳电流密度是30mA/cm^2，所制备的氧化铅纳米棒是单晶结构。     

活细胞内单个大分子的行为

以往细胞内大分子活动的研究,多数是许多分子活动的一个平均结果,即一种集群平均（ensemble averaging）的结果,随着各种技术,特别是光学及荧光检测技术的成熟,实时视见活细胞内单个大分子的时代已经到来.在现时条件下,有许多方法可供选择,如荧光共振能量转移、原子力显微镜、全内反射显微技术、荧光相关光谱法等等.“活细胞内单个大分子的行为”的研究有可能为了解活细胞内单个分子的活动带来完全新的认识,但目前还存在不少方法学上的局限性,有待进一步提高,如有效的特异标记物、细胞深部荧光的检测、新型显微镜的开发等.     

Approximate importance sampling Monte Carlo for data assimilation

Importance sampling Monte Carlo offers powerful approaches to approximating Bayesian updating in sequential problems. Specific classes of such approaches are known as particle filters. These procedures rely on the simulation of samples or ensembles of the unknown quantities and the calculation of associated weights for the ensemble members. As time evolves and/or when applied in high-dimensional settings, such as those of interest in many data assimilation problems, these weights typically display undesirable features. The key difficulty involves a collapse toward approximate distributions concentrating virtually all of their probability on an implausibly few ensemble members.

After reviewing ensembling, Monte Carlo, importance sampling and particle filters, we present some approximations intended to moderate the problem of collapsing weights. The motivations for these suggestions are combinations of (i) the idea that key dynamical behavior in many systems actually takes place on a low dimensional manifold, and (ii) notions of statistical dimension reduction. We illustrate our suggestions in a problem of inference for ocean surface winds and atmospheric pressure. Real observational data are used.     

Statistical equilibrium in simple exchange games I

This erratum corrects a mistake in reference [E. Scalas, U. Garibaldi, S. Donadio, Eur. Phys. J. B 53, 267 (2006)]. In that paper, we needed an aperiodic version of the BDY game, but, in formula (1), we incorrectly presented a periodic transition matrix of period 2 in the special case of g = 2 agents. Here, we present the right aperiodic version.     

Emergence of bimodality in noisy systems with single-well potential

We study the stationary probability density of a Brownian particle in a potential with a single-well subject to the purely additive thermal and dichotomous noise sources. We find situations where bimodality of stationary densities emerges due to presence of dichotomous noise. The solutions are constructed using stochastic dynamics (Langevin equation) or by discretization of the corresponding Fokker-Planck equations. We find that in models with both noises being additive the potential has to grow faster than |x| in order to obtain bimodality. For potentials ∝|x| stationary solutions are always of the double exponential form.     

Spontaneously generated coherence in a Doppler broadened atomic system

We investigate the spontaneously generated coherence (SGC) in a Doppler broadened four-level atomic system driven by two coherent fields. We plot the spontaneous emission spectra with different parameters and discuss how the initial atomic conditions and parameters of both fields change the number of peaks and dark lines of spontaneous emission spectra. Furthermore, we also show how the spontaneous emission spectrum is modified by Doppler effects in the viewed direction. Our results have important references to the experimental observation of SGC in hot atomic vapors.