Linear and nonlinear optical refractions of CR39 composite with CdSe nanocrystals

Hybrid composites of CdSe nanocrystals embedded in allyl diglycol carbonate (CR39) matrices have been prepared and characterized. The measurements show that the linear refractive index of the composite decreases as the CdSe nanocrystal’s weight-percentage concentration increases at the laser wavelengths of 632.8 nm and 532 nm. The room temperature nonlinear optical properties of the hybrid composites were investigated using a single-beam Z-scan technique with femtosecond laser pulses at the wavelengths of 794 nm and 397 nm. The experimental data reveals that the Kerr nonlinear refractive index n₂ of the composite increase at these wavelengths when the CdSe nanocrystal’s weight-percentage concentration increases. Also, the nonlinear refractive index n₂ of the CdSe/CR39 hybrid composites exhibit dispersion from a positive value at 794 nm (below the band gap) to a positive value at 395 nm (above the band gap). The measured dispersion of n₂ is roughly consistent with the Sheik-Bahae’s theory for the bound electronic nonlinear refraction resulting from the two-photon resonance.     

Observation of the trapping of radioactive inert gas radon on oxide glass surfaces: Macroporous scintillating-glass-fiber bundler alpha detector

We report the observation of the trapping of radioactive inert gas radon (²²²Rn) on oxide glass under ambient air temperature and pressure of 300 K and 760 Torr, respectively. Radon diffuses from the source, through two macroporous scintillating-glass-fiber bundle alpha detectors in series, to the end of the linear closed system filled with ambient air. The strategy is to provide radon atoms and alphas emitted from radon and its progeny with large accessible scintillating glass surface areas for efficient trapping and detection, respectively. Diffusion-only transport mechanism could not explain the experimental observations, strongly suggesting the trapping of radioactive inert gas radon (²²²Rn) on oxide glass.     

Bayesian Approach to Assessing Uncertainty and Calculating a Reference Value in Key Comparison Experiments

International experiments called Key Comparisons pose an interesting statistical problem, the estimation of a quantity called a Reference Value. There are many possible forms that this estimator can take. Recently, this topic has received much international attention. In this paper, it is argued that a fully Bayesian approach to this problem is compatible with the current practice of metrology, and can easily be used to create statistical models which satisfy the varied properties and assumptions of these experiments.     

A theoretical approach to the deposition and clearance of fibers with variable size in the human respiratory tract

In the study presented here, a mathematical approach for the deposition and clearance of rigid and chemically stable fibers in the human respiratory tract (HRT) is described in detail. For the simulation of fiber transport and deposition in lung airways an advanced concept of the aerodynamic diameter is applied to a stochastic lung model with individual particle trajectories computed according to a random walk algorithm. Interception of fibrous material at airway bifurcations is considered by implementation of correction factors obtained from previously published numerical approaches to fiber deposition in short bronchial sequences. Fiber clearance is simulated on the basis of a multicompartment model, within which separate clearance scenarios are assumed for the alveolar, bronchiolar, and bronchial lung region and evacuation of fibrous material commonly takes place via the airway and extrathoracic path to the gastrointestinal tract (GIT) or via the transepithelial path to the lymph nodes and blood vessels.Deposition of fibrous particles in the HRT is controlled by the fiber aspect ratio β in as much as particles with diameters <0.1 μm deposit less effectively with increasing β, while larger particles exhibit a positive correlation between their deposition efficiencies and β. A change from sitting to light-work breathing conditions causes only insignificant modifications of total fiber deposition in the HRT, whereas alveolar and, above all, tubular deposition of fibrous particles with a diameter ≥0.1 μm are affected remarkably. For these particles enhancement of the inhalative flow rate results in an increase of the extrathoracic and bronchial deposition fractions. Concerning the clearance of fibers from the HRT, 24-h retention is noticeably influenced by β and, not less important, by the preferential deposition sites of the simulated particles. The significance of β with respect to particle size may be regarded as similar to that determined for the deposition scenarios, while breathing conditions do not have a valuable effect on clearance.     

Uncertainty quantification in non-linear dynamic response of functionally graded materials plate

This study deals with the stochastic non-linear dynamic response of functionally graded materials (FGMs) plate with uncertain system properties subjected to time-dependent uniformly distributed transverse load in thermal environments. System properties, such as material properties of each constituent's material, volume fraction index, and transverse load, are taken as uncorrelated random input variables. Material properties are assumed as temperature dependent (TD). The formulation is based on higher-order shear deformation theory (HSDT) with von-Karman non-linear strain kinematics using modified C° continuity. A Newton–Raphson-based non-linear finite element method along with a first-order perturbation technique (FOPT) and Monte Carlo sampling (MCS) is outlined to examine the second-order statistics (mean, standard deviation (SD), and probability density function (PDF)) of the non-linear dynamic response of the FGM plate. The governing dynamic equation is solved by Newmark's time integration scheme. The effects of volume fraction index, load parameters, plate thickness ratios, and temperature changes with random system properties are examined through parametric studies. The present outlined approach is validated with the results available in the literature and by MCS.     

Direct simulation Monte Carlo modeling of metal vapor flows in application to thin film deposition

Thin films of metal for electronics, nano/microelectromechanical systems and optical coatings are often prepared by various vacuum deposition techniques. Modeling such metal vapor flows using methods such as the direct simulation Monte Carlo (DSMC) can aid in the design and analysis of deposition systems and accelerate development of films with desired properties. The determination of suitable variable hard sphere (VHS) molecular model parameters for DSMC simulations using measured growth rate distribution is demonstrated with aluminum vapor as an example. Axisymmetric DSMC simulations using a VHS model corresponding to a reference diameter of 0.8 nm and a viscosity-temperature exponent of 1 are shown to agree well with available experimental data. The model is then used in two-dimensional DSMC simulations to study the interaction of plumes from multiple sources. An expression for substrate mass flux assuming no interaction between sources agrees well with DSMC simulations for a mass flow rate of 0.1 g/min corresponding to a Knudsen number (Kn) of about 0.1. The non-additive interaction of plumes at a higher flow rate of 1 g/min corresponding to a Kn of about 0.01 results in a higher mass flux non-uniformity in the DSMC simulations which is not captured by the simplified analytical expression.     

An Outline of Supplement 1 to the Guide to the Expression of Uncertainty in Measurement on Numerical Methods for the Propagation of Distributions

Supplement 1 to the Guide to the Expression of Uncertainty in Measurement (GUM), concerned with numerical methods for the propagation of distributions, embodies a generalization of the uncertainty framework of the GUM. This paper presents a number of aspects of that supplement.__________Published in Izmeritel’naya Tekhnika, No. 4, pp. 17– 24, April, 2005.     

Polymer solutions confined in slit-like pores with attractive walls: An off-lattice Monte Carlo study of static properties and chain dynamics

Summary Using a bead spring model of flexible polymer chains, the density profiles and chain configurational properties of polymer solutions confined between parallel plates were studied. A wide range of density , chain length N, and strength of a short-range attractive wall potential was investigated. Both a temperature T in the good solvent regime (T > , being the Theta temperature where a chain in unconfined bulk three-dimensional solution would behave ideally) and a temperature in the bad solvent regime (T < ) were considered. It is shown that phase separation in a polymer-rich and polymer-poor solution in the slit competes with polymer adsorption at the walls. A qualitative connection to the wetting behavior of semi-infinite polymer solutions is drawn. The acceptance rate for monomer motions was studied for various conditions, and profiles of monomer mobility across the slit were recorded. Also, average chain relaxation times were extracted from the time dependence of mean-square displacements. Although with increasing density the chain radii (at T > ) show a crossover from two-dimensional excluded volume behavior (R_g N² with = 3/4) to ideal random walk behavior ( = 1/2), the relaxation times show effective exponents Z_eff ( N^{Z eff}) that clearly deviate from the Rouse prediction in concentrated confined solutions.     

浅海环境不确定性对声场扰动的影响

探索海洋环境各水声参数的不确定性所引发的声场扰动,对提高水声场预报的准确性与科学性至关重要,极具理论意义与应用价值。基于Workshop’97浅海环境基准模型,以扰动声场与实际声场的相关性函数作为量化指标,通过Kraken波动理论数值模型与马尔科夫链蒙特卡罗随机统计思想,基于单因子变量原则模拟分析了浅海水平不变环境中各水声参数声场扰动敏感性大小及其相关性,结果表明:沉积层声速C_1、水深D_1敏感性最强,沉积层衰减系数αs、沉积层密度ρs、沉积层声速C_2、沉积层厚度D_2、基底声速C_3次之,基底衰减系数αb、基底密度ρb几乎无影响;αs、ρs、C_1、D_1敏感性随距离增加逐渐增强,C_2、D_2、C_3敏感性随距离增加逐渐减弱;D_2、C_2,D_2、C_3,C_1、C_3,C_2、C_3之间存在较强的正相关性,D_2、C_1,C_1、C_2之间为显著的负相关性。     

Enhancing piecewise-defined surrogate response surfaces with adjoints on sets of unstructured samples to solve stochastic inverse problems

Many approaches for solving stochastic inverse problems suffer from both stochastic and deterministic sources of error. The finite number of samples used to construct a solution is a common source of stochastic error. When computational models are expensive to evaluate, surrogate response surfaces are often employed to increase the number of samples available for approximating the solution. This leads to a reduction in finite sampling errors while the deterministic error in the evaluation of each sample is potentially increased. The pointwise accuracy of sampling the surrogate is primarily impacted by two sources of deterministic error: the local order of accuracy in the surrogate and the numerical error from the numerical solution of the model. In this work, we use adjoints to simultaneously give a posteriori error and derivative estimates in order to construct low-order, piecewise-defined surrogates on sets of unstructured samples. Several examples demonstrate the computational gains of this approach in obtaining accurate estimates of probabilities for events in the design space of model input parameters. This lays the groundwork for future studies on goal-oriented adaptive refinement of such surrogates.     

A Comparative Study of Tests for Homogeneity of Variances,with Applications to the Outer Continental Shelf Bidding Data

Many of the existing parametric and nonparametric tests for homogeneity of variances, and some variations of these tests, are examined in this paper. Comparisons are made under the null hypothesis (for robustness) and under the alternative (for power). Monte Carlo simulations of various symmetric and asymmetric distributions, for various sample sizes, reveal a few tests that are robust and have good power. These tests are further compared using data from outer continental shelf bidding on oil and gas leases.     

利用贝叶斯推理估计二维含源对流扩散方程参数

为了克服观测数据的不确定性给参数反演带来的困难,利用贝叶斯推理建立了二维含源对流扩散方程参数估计的数学模型。通过贝叶斯定理,获得了模型参数的后验分布,从而获得反问题的解。对于多参数反演问题,基于数值解计算得到的参数后验分布很难直观地表现出来,采用马尔科夫链蒙特卡罗方法对参数的后验分布进行采样,获得了扩散系数和降解系数的估计值。研究了观测点位置对计算结果的影响;同时研究了似然函数的形式对估计结果的影响,结果表明在异常值可能出现时采用Laplace分布型的似然函数可以获得稳健估计。对不同观测点数目下的估计值进行了对比,认为对于二维稳态对流扩散方程的双参数估计问题,至少需要两个观测点才有可能得到合理的解。     

Likelihood-based estimation of continuous-time epidemic models from time-series data: application to measles transmission in London

We present a new statistical approach to analyse epidemic time-series data. A major difficulty for inference is that (i) the latent transmission process is partially observed and (ii) observed quantities are further aggregated temporally. We develop a data augmentation strategy to tackle these problems and introduce a diffusion process that mimics the susceptible-infectious-removed (SIR) epidemic process, but that is more tractable analytically. While methods based on discrete-time models require epidemic and data collection processes to have similar time scales, our approach, based on a continuous-time model, is free of such constraint. Using simulated data, we found that all parameters of the SIR model, including the generation time, were estimated accurately if the observation interval was less than 2.5 times the generation time of the disease. Previous discrete-time TSIR models have been unable to estimate generation times, given that they assume the generation time is equal to the observation interval. However, we were unable to estimate the generation time of measles accurately from historical data. This indicates that simple models assuming homogenous mixing (even with age structure) of the type which are standard in mathematical epidemiology miss key features of epidemics in large populations.     

Kinetic process of phase separation in Co-SiO2 thin films and preparation of mesoporous SiO2 thin films with mesopore channels aligned perpendicularly to substrate surfaces

A physical co-sputter deposition process under a relevant working gas pressure condition was used to produce a multi-component thin film with a longitudinally self-organized microstructure. In this paper, Co-Si-O thin films were prepared by radio frequency (RF) magnetron sputtering, and their growth structures were studied by means of SEM, TEM, XRD and XPS. The microstructural changes in the Co-Si-O thin film and their dependence on Ar working gas pressure were investigated; the formation of Co-Si-O thin films, having a regular array of needle-like Co columns aligned perpendicularly to the substrate surfaces, was observed with appropriate Ar working gas pressure, and the diameter of the columns increased with increasing Ar pressure. Mesoporous silica thin films having perpendicular mesopore channels were obtained by chemical etching of the columnar Co parts in the Co-Si-O thin films. Through experimental observations, we propose that the phase separation and resultant microstructures in the thin films are determined by the surface mobility of the two components (Co and silica) on the film surface. A simple model, incorporating a diffusion process in the simultaneous deposition of two components, is presented. The model demonstrates the general trends of a kinetically self-organized microstructure in a two-component thin film.