面光源照射下生物组织中光传输规律的计算机模拟

本文利用基于脉冲响应函数的MonteCarlo方法,模拟了了不同分布的面光源照射条件下,生物组织中不同层面上的二维光场分布,分析了透射深度与入射光源分布对组织中光分布特点的影响,说明该模拟方法计算效率高且统计稳定性好,同时讲座了不同情况下,脉冲响应函数模拟量与光源离散量的选取原则。     

用Monte Carlo方法重建OCT图像

采用MonteCarlo模拟成像过程的方法对图像进行恢复，成像所需点扩散函数通过Monte Carlo模拟光在生物组织中的传播获得，对获得的原始猪肉组织图像进行了恢复处理，重建后图像的横向分辨率有显著提高。     

微气体流量计的模拟与优化

温差法测流量是一种新型气体流量计的基本原理 ,温度传感器的布置对流量计的性能影响很大。本文使用基于分子运动理论的直接模拟MonteCarlo法对这种微气体流量计通道内的气体流动进行了数值模拟 ,对比了有无传感器时速度场和温度场的分布 ,指出传感器的布置对温度场的影响很小 ,并根据温差分布规律提出了传感器布置的优化方案。     

表面照射下激光与生物组织的光热作用分析

建立了表面照射下激光与生物组织光热作用的二维变物性数学模型,采用Monte Carlo模拟方法数值求解了表面照射下组织内激光能量的分布,进而采用有限差分方法数值求解Pennes生物传热方程得到了组织内的温度分布。计算结果表明：假设组织热物性为常数,将高估组织的温升;假设激光能量在组织内按指数规律衰减,计算得到的光束范围内的组织温升高于采用Monte Carlo方法的模拟结果;在功率相同的情况下,光束半径越大,光束范围内组织的温升越小,径向温升区域越大。     

移动无线信道脉冲响应的计算机模拟

根据移动通信多径传播的一般化模型,模拟产生了移动无线信道的复值脉冲响应函数,模拟结果自然地反映了信道的衰落相关性,通过调整四个参数,可描述瑞利、Rice或其它形式的衰落信道,利用模拟结果分折数字通信中由于多径衰落引起的突发误码分布已取得成效。     

声场脉冲响应的分段模拟方法

计算脉冲响应是封闭空间声场模拟技术的重要工作。针对脉冲响应各部分的特点，改变仅利用某一种模型模拟整个脉冲响应的传统做法，把声线跟踪法、虚源法和统计学方法结合起来，对脉冲响应进行分段模拟研究。算法设计过程中，对扩散反射和镜面反射都作了考虑，并研究了“混响尾巴”的计算方法以及提高计算效率的具体途径。仿真实践表明，所棕方法能在保证一定精度的前提下使计算效率得到有效提高。     

漫射光自相关测组织微循环血流模型

提出了一种用漫射光自相关方法无损测量组织微循环血流速度的模型 ,理论分析了散射粒子的布朗运动和微循环血流对漫射光自相关函数的影响。理论计算和蒙特卡罗 (MonteCarlo)法模拟结果表明 ,随着微循环血流均方速率的增大 ,特征相关时间呈负指数规律减小     

线形宽带超声相控阵换能器的声场分析

讨论了一种计算矩形活塞阵元声场脉冲响应函数的简便算法,通过对不同延时量的矩形活塞阵元声场脉冲响应函数进行叠加,得到线形换能器阵列的脉冲响应函数;再施以宽带脉冲激励函数,得到线形换能器阵列的声场分布。比较了3种不同换能器的脉冲响应及声场分布,该法对工业无损检测领域超声成像用换能器参数优化具有重要意义。     

半无限大生物组织中光子分布规律的研究

光子在生物组织中的传播和分布问题, 是影响光动力疗法治疗结果的重要因素之一。本文给出了蒙特卡罗方法模拟半无限大均匀生物组织中光子分布的计算方法和模拟结果, 分析了半无限大生物组织中光子分布规律。结果表明, 生物组织的光学性质强烈影响光在组织中的分布情况。具有低散射系数, 低吸收系数和高各项异性因子的生物组织, 有利于光子深入均匀地分布其中。力图为光动力疗法的临床应用提供了有效的诊断和治疗依据。     

小功率LED光源封装光学结构的Monte Carlo模拟及实验分析

采用MonteCarlo方法对不同光学封装结构的LED进行模拟,建立了小功率LED的仿真模型,应用空间二次曲面方程描述LED的封装结构,对其光强分布进行模拟和统计.通过测量实际样品,并与模拟结果进行比较和分析,表明计算机模拟值与实验测量值比较吻合.     

面光源在皮肤组织中传输的蒙特卡罗模拟计算

光在生物组织中的传输可用蒙特卡罗模拟来计算,但多数局限于对线光源垂直入射的模拟。在实际的使用中,入射光源的形状、大小、光强分布和会聚情况对生物组织内的光传输均有影响。本文以最简单的强度均匀分布的圆形面光源（平圆光源）和实际使用中最具代表性的强度成高斯分布的面光源（高斯光源）为例,讨论光束的大小,强度分布和聚焦情况对生物组织内光能量分布的影响。     

柱弥散光源内部辐照组织的Monte-Carlo模拟和实验研究

为无损获取组织中光剂量分布信息,本文构建 了弥散光源内部辐照柱状组织的光学模型,利用Monte-Carlo模拟方法实现了 组织内光分布信息的无损预测, 有关模拟结果与实验测量结果基本一致。提出的模型模拟方法对于由弥散光源在组织内部实 施光辐照的临床医用中光剂量的无损确定和治疗方案的优化设计有实际价值。     

Near‐Infrared Light Propagation in an Adult Head Model with Refractive Index Mismatch

We investigate near‐infrared light (NIR) propagation in a model of an adult head using an extensive Monte Carlo (MC) simulation. The adult head model is a four‐layered slab which consists of a surface layer, a cerebrospinal fluid layer, a gray‐matter layer, and a white‐matter layer. We study the effects of a refractive index mismatch on the model, calculating the intensity of detected light, mean flight time, and partial mean flight time of each layer for various refractive indices of the cerebrospinal fluid layer as functions of source‐detector spacing. The Monte Carlo simulation shows that the refractive index mismatch presents very rich results including rapidly decaying intensity of detected light and a peak and cross‐over in the partial mean flight time with source‐detector spacing. We also investigate spatial sensitivity profiles at various source‐detector spacings, discussing the index mismatch effect on the model.     

Coupled Monte Carlo-drift diffusion analysis of hot-electroneffects in MOSFETs

A general method of calculating the substrate current for n-MOSFETs, using a two-dimensional conventional device simulator coupled with a full-band-structure Monte Carlo simulation, has been enhanced through the use of efficient estimators and statistical weighting of the high-energy electrons. The detailed physics of hot-electron effects in MOSFETs is explained on the basis of the energy distribution as a function of the spatial variables. Monte Carlo results show that the distribution function in the region of the device that makes the largest contribution to the substrate current does not fit a Maxwell-Boltzmann function. The effective cooling of the distribution, due in part to energy loss to impact ionization, is shown clearly. The results of the Monte Carlo calculation are used to evaluate the validity of the assumption of a constant mean path for inelastic scattering used in various analytic treatments. The calculated values of substrate current are compared to experimental results     

Modeling of non-line-of-sight ultraviolet scattering channels for communication

A stochastic non-line-of-sight (NLOS) ultraviolet (UV) communication channel model is developed using a Monte Carlo simulation method based on photon tracing. The expected channel impulse response is obtained by computing photon arrival probabilities and associated propagation delay at the receiver. This method captures the multiple scattering effects of UV signal propagation in the atmosphere, and relaxes the assumptions of single scattering theory. The proposed model has a clear advantage in reliable prediction of NLOS path loss, as validated by outdoor experiments at small to medium elevation angles. A Gamma function is shown to agree well with the predicted impulse response, and this provides a simple means to determine the channel bandwidth. The developed model is employed to study the characteristics of NLOS UV scattering channels, including path loss and channel bandwidth, for a variety of scattering conditions, source wavelength, transmitter and receiver optical pointing geometries, and range.     

红外光源辐射特性的蒙特卡洛模拟

为满足红外跟踪仿真的高精度、高稳定性设计要求,本文基于蒙特卡洛算法针对红外光源的辐射特性进行了模拟仿真研究。首先,介绍了系统结构和工作原理。接着,以蒙特卡洛方法为基础,对钨丝灯圆柱体光源进行建模,给出光阑处的辐照度精确分布,为建立光阑通光口径的非线性控制函数提供依据。然后,分析了不同条件下蒙特卡洛算法的准确度,并研究了装配位置对系统光能利用率的影响。仿真结果表明:在旋转抛物面反射镜的焦点外存在一个最佳的光源装配位置;在装配过程中,允许的轴向偏移为0.1 mm,垂轴偏移为0.1 mm,角度偏移为2°。该系统满足了红外跟踪仿真的稳定可靠、高精度要求。同时,本文所采用的分析方法对其他红外光源的优化设计也有借鉴作用。     

Estimation of Multipath Channels With Long Impulse Response at Low SNR via an MCMC Method

This paper addresses the estimation of multipath channels with long impulse response at low signal-to-noise ratio (SNR). The channel sparseness impulse response is modeled by means of a Bernoulli-Gaussian process. Then, the optimization of the resulting posterior distribution resorts to Monte Carlo Markov chain (MCMC) simulation techniques. Special attention is devoted to noise correlation involved by matched filtering: Taking this correlation into account in the algorithm derivation leads to significantly improved performance for both amplitude and time-delay estimation. The method is also extended to cope with Doppler frequency offsets. In particular, simultaneous paths with different Doppler offsets can be estimated. Crameacuter-Rao lower bounds (CRLBs) are derived and presented together with simulation results     

Light absorption distribution of prostate tissue irradiated by diffusing light source

Nitric oxide(NO)and nitric oxide synthase(NOS)have an important role in pain signaling transmission in animal models.Low-level laser therapy(LLLT)is known to have an analgesic effect,but the mechanism is unclear.The aim of the study is to investigate the influence of LLLT on NO release and NOS synthesis in dorsal root ganglion(DRG)neurons,in order to find whether LLLI can ameliorate pain through modulating NO production at the cellular level.The results show that in stress conditions,the laser irradiation at 658 nm can modulate NO production in DRG neurons with soma diameter of about 20μm in a short time after illumination,and affect NOS synthesis in a dose-dependent manner.It is demonstrated that LLLT might treat pain by altering NO release directly and indirectly in DRG neurons.     

生物组织光学特性参数无损测量的模拟研究

生物组织的吸收系数和散射系数决定了组织表面的漫射光分布,但其理论关系式由于推导过程的近似及假设的边界条件不同,有几种不同的表示形式。为确定哪种表达形式更能精确地描述实际问题,本文给出了一种通过 Monte Carlo模拟进行校验的方法,确定了不同表达式的精确度,为进一步进行生物组织光学特性参数的无损测量打好基础。