光学相关论题 生物光学

Q63 2005032397 漫射近似在测量生物组织光学性质中的适用范围=Valid- ity of the diffusion approximation in determining the optical properties of biological tissus[刊,中]／李剑平(山东大学信 息科学与工程学院．山东,济南(250100)),陈冰泉∥应用 光学．-2005,26(1).-20-24 采用Monte Carlo模拟校验的方法,对漫射近似理论 和Monte Carlo模拟计算的结果进行了比较,给出了基于     

连续光在生物组织中能流率分布的漫射近似和模拟

分析了半无限大介质漫射近似不同边界条件的镜像光源结构,用镜像光源的方法给出了连续光入射时稳态能流率分布的漫射近似表达式,并用Monte Carlo方法对能流率分布进行模拟,分析了两种模型能流率分布的特点及其形成的机理;用Monte Carlo模拟结果检验了能流率分布漫射近似的精度,结果表明:漫射近似采用EBC边界条件的结果有较高的精度和计算较简单等优点,为能流率分布的快速准确计算提供了依据.     

基于检测光纤的漫射高光谱采集的Monte Carlo仿真

从漫射高光谱中可以获得被测物体成分、结构及其分布等信息。采用光纤光谱仪获取漫射高光谱是一种常用的方法。Monte Carlo方法在研究光在浑浊介质的传播方面得到了广泛的应用。然而,使用Monte Carlo方法研究漫射高光谱时,必须考虑实际的检测条件对信号采集的影响。将光纤参数引入到Monte Carlo模型中,研究了光纤参数对被检测光学信号的影响。仿真结果表明,孔径角和半径增大,检测的漫射高光谱随之增大,而光纤与被测物质表面的距离小于1 mm时对漫射高光谱的影响在一定程度上可以忽略。进一步研究发现存在固定的修正系数使不同孔径角的光纤所采集的漫射高光谱转化为孔径角为π/2的光纤对应的信号。同时,得到了实际光纤孔径角范围内的修正系数拟合曲线。不同半径的光纤通过面积归一化可以得到很好的一致性。研究检测光纤参数对漫射高光谱的影响对实际测量有重要的指导意义,而且不同光纤所对应的检测结果可以通过修正系数和面积归一化进行移植。     

烟尘中电磁波传输特性的Monte Carlo模拟

根据等效颗粒模型和分形理论,运用Mie理论和离散偶极子近似方法分别计算了烟尘簇团粒子在波长为06328?μm的电磁波入射情况下的单次散射特性.根据辐射输运理论,利用Monte Carlo方法对电磁波在烟尘中的传输特性进行数值计算,给出烟尘中反射率和透射率随入射角和烟尘厚度变化的数值结果,并分析了入射角、烟尘粒子的密度和厚度对反射率和透射率的影响.这为研究电磁波在密集分布介质中的传输特性提供了一种方法. 关键词： 烟尘粒子 离散偶极子近似 传输特性 Monte Carlo模拟     

两层生物组织光学特性参数无损测量的模拟研究

生物组织的光学特性参数是与疾病的无损光诊断有关的重要的光学参数，一般的测量所应用的模型是假设生物组织为半无限厚的均匀结构。为了更能反映生物组织的真实特性，本文应用两层结构模型，即假设第一层为有限厚的均匀组织，第二层为半无限厚，由漫射方程经过傅立叶变换得到传输方程的漫射解。为检验漫射解的准确性，将漫射解的表面漫射光分布与Monte Carlo模拟结果进行了比较，结果表明两者符合得很好。为了研究由漫射解是否可以获得两层组织的光学特性参数，将漫射解与Monte Carlo模拟数据进行了非线性拟合，反演获得组织的光学特性参数，结果表明，由漫射解可以获得两层组织的有效散射系数和吸收系数。     

基于有限元模拟的圆柱边界介质中的光传输

应用有限元模拟方法,在外推边界条件下研究圆柱介质中的光传输问题,讨论了不同光学参数条件下圆柱表面空间分辨反射率和穿透深度的规律,并且与有限元分析、Monte Carlo模拟和解析解方法的结果进行比较.结果表明:有限元模拟的结果与Monte Carlo模拟的结果吻合度很好,其空间反射率在光学参数满足漫射近似条件μ′s/μa≥5时误差小于10%,在非近源区甚至小于5%;穿透深度的值随μ′s/μa值增大而增大.但比Monte Carlo模拟的穿透深度略小,误差不超过7%,且μ′s/μa的值越大时该误差越小.有限元模拟结果比解析解方法的结果误差要更小,解析解方法在μ′s/μa≥5时,其误差在非近源区接近10%,在近源区会超过15%.此外比较了三种方法的计算速度.单次运算有限元模拟用时约385s,甚至比通常用于快速计算的解析解方法(单次运算耗时416s)更快,而Monte Carlo模拟单次运算耗时8~9h.考虑到有限元模拟方法的介质模型构建简便,计算速度快,且模拟结果有着不错的精度,该方法对圆柱边界乃至一般具有曲率的复杂介质中光子辐射传输问题具有非常好的应用前景.     

光在多层匹配生物组织中的时域传输模型

建立了匹配介质的n层半无限厚频域方程的解,并对频域进行傅里叶变换,计算出时域方程的时间分辨漫反射（Time-resolved Reflectance）.为检验漫射模型的准确性,将时间分辨漫反射与蒙特卡罗（Monte Carlo）模拟结果进行了比较,结果表明两者符合得很好.研究表明：该时域漫射模型可以判断生物组织和病变的光学特性.     

超声调制漫射光子自相关的Monte Carlo模拟

本文首次用Monte Carlo方法研究了超声调制生物介质中漫射光子的时间自相关性质,讨论了超声参量、运动参量和散射参量对自相关函数的影响.正常生物组织和病变生物组织的自相关函数有明显的差别,超声调制自相关函数为光学医学诊断提供一种新参考.     

复杂混合溶液成分高光谱分析的可行性

采用高光谱技术对复杂混合溶液进行检测分析,同时利用被测物质的吸光度和散射特性信息以提高光谱的信噪比。实验设计了高光谱采集装置,采集生物组织模拟液(Intralipid-10%)的漫反射高光谱图像,并用Monte Carlo方法和漫射近似理论对其进行了正向和反向推导,获得了632nm波长下,Intralipid-10%吸收系数为0.002 0cm-1,与标准参数相对误差为11.1%;约化散射系数为63.35cm-1,与标准参数相对误差为6.49%,基本符合标准参数的误差范围,验证了该高光谱检测系统的准确性。还利用该高光谱系统对不同厂家出品的牛奶、果汁等样本进行了高光谱采集,得到不同样本间差异较传统二维光谱更为明显的结果,充分证明了高光谱方法在复杂混合溶液成分分析中具有很强的可行性。     

Monte Carlo方法在B样条函数分频理论中的应用

针对弹道参数的B样条表示问题,运用Monte Carlo方法对B样条函数分频理论进行仿真论证,得到B样条延拓节点的补充方法,并验证B样条函数逼近空间相容性定理的正确性.比较Monte Carlo方法和B样条分频算法的计算结果,说明分频算法合理.将该算法应用于外弹道跟踪测量数据的处理中,可以确定出表示弹道所需要的样条节点个数及样条节点序列的排布,有效减少待估参数个数.     

Total backscattering of keV light ions from solid targets in single-collision approximation

The reflection of light ions from heavy random targets has been calculated within the single-collision approximation on the basis of essentially the same physical model as Schiøtt's adaptation of the LSS range theory to light ions. An accurate effectivepower approximation has been utilized to evaluate a number of physical quantities relating to reflected ions under the assumption of Thomas-Fermi scattering. Analytical results as well as universal curves are presented for reflected-energy spectra integrated over ejection angle, particle and energy reflection coefficients, and quantities derived from these. Good agreement with experimental results is obtained for ε?, where ε is Lindhard's energy parameter. The results are compared with those from previous calculations on the basis of transport theory and computer simulation. An estimate is given of the single-collision tail of the light-ion range profile. Qualitative corrections for beam attenuation and recoil energy loss are presented in appendices.     

Thermodynamic properties of the one-dimensional Hubbard model

We discuss the thermodynamic behaviour of the one-dimensional Hubbard model in the narrow-band regime, where the intra-atomic Coulomb-repulsion is large compared to the bandwidth. An approximation scheme on a perturbative basis is developed which applies for all temperatures. First order perturbation theory is performed for arbitrary electron densities; second order perturbation theory is discussed in the case of the half-filled band. Also the one-particle Green's function is calculated. Our approximation agrees excellently with numerical calculations. By comparison with exact results, which are available for some special limits, the range of validity of our approximation is estimated.     

Three dimensional analyses of scattering by pressure-release sinusoidal surfaces

Scattering by pressure-release sinusoidal surfaces in three dimensions is analyzed using the Fresnel phase approximation and realistic source and receiver directivity approximations. Geometrical shadowing and second-order scattering are explicitly included to explore the validity of the Kirchhoff approximation. No restrictions on the surface heights and slopes are made. The "goodness" of the resulting expressions is verified by requiring the pressure scattered by a sinusoidal surface to reduce to the image solution as the surface amplitude goes to zero. The first-order scattered pressure achieves a very good approximation to the image solution, and the second-order scattered pressure goes to zero, as expected, under this requirement. The theory is compared with available experimental scattering measurements, and the agreement is good. Because the slopes on the experimental surface are very steep, shadowing corrections are indispensible to achieving accurate first and second order scattering results. Shadowing has a greater impact on the scattering prediction than the second-order scattering contribution. This suggests that the Kirchhoff approximation may be more robust when incorporated into a theory including a detailed shadowing treatment as well as the Fresnel phase approximation and a good directivity approximation.     

The validity of the average t-matrix approximation for low-energy electron diffraction from random alloys

We explore the validity of the average t-matrix approximation for the calculation of low-energy electron diffraction IV spectra from substitutionally disordered alloy surfaces. The accuracy of this approximation is assessed by comparison with the results of calculations for Ni_xPt_100−x(100) surfaces obtained using the more accurate coherent-potential approximation. We find excellent agreement the two approaches, demonstrating the validity of the average t-matrix approximation for interpreting low-energy electron diffraction from alloys. The physical origin of this agreement is discussed by reference to the scattering properties of the electrons in alloy surfaces.     

Vibration of simply supported-clamped skew plates at large amplitudest

The large amplitude, free, flexural vibration of orthotropic skew plates simply supported along two opposite edges and clamped along the other two are investigated on the basis of an assumed mode shape. The relationship between the amplitude and period is studied for both isotropic and orthotropic skew plates for various aspect ratios and skew angles under two in-plane edge conditions. It is found that the modal equation reduces to the Dufling type equation from which the period of non-linear vibration is found to decrease with increasing amplitude, exhibiting hardening type of non-linearity. The validity of the Berger approximation is investigated for the problem under consideration and this approximation is shown to give reasonably good results.     

Scattering amplitude of absorbing and nonabsorbing spheroidal particles in the WKB approximation

This work is devoted to a theoretical study of scattering of light by absorbing and nonabsorbing oriented spheroidal particles in the Wentzel-Kramers-Brillouin (WKB) approximation. Within the framework of the scattering theory, we investigate the form factor and the scattering amplitude for this approximation. The Rayleigh-Gans-Debye theory (RGD), the diffraction approximation (DA), and the anomalous diffraction (AD) are treated as particular cases for nonabsorbing spheroids. To illustrate our formalism, we analyze some numerical examples.     

非均匀平板波导的色散方程

利用转移矩阵理论分析了任意折射率分布平板波导的传输特性，导出了非均匀平板波导的近似解析色散方程，并指出了ＷＫＢ近似的局限性，数值比较的结果表明，文中所得公式的精确度优于传统的ＷＫＢ方法和其它近似方法。