Numerical design of experiment for sensitivity analysis--application to skin burn injury prediction.

Temperature evolution and skin burn process resulting from a laser radiation exposure are investigated in this paper. Transient temperature in skin is numerically estimated using a 1-D multilayered model based on Penne's equation. The degree of burn injury is numerically evaluated by using an Arrhenius-type function. Unfortunately, most of the mathematical model parameters are not well defined in literature. Thus, a sensitivity analysis has been performed in order to evaluate the effect of each parameters inaccuracy on temperature estimation and on burn injuries prediction (according to several authors' characterization). Investigated parameters uncertainties that crucially invalidate the thermal model are as follows: epidermis and dermis volumetric heat, extinction coefficient, and skin thickness of the affected area. Considering the damage prediction, the activation energy is a key parameter for the validation of an efficient predictive tool.     

New thermal wave aspects on burn evaluation of skin subjected to instantaneous heating

Comparative studies on the well-known Pennes' equation and the newly developed thermal wave model of bioheat transfer (TWMBT) were performed to investigate the wave like behaviors of bioheat transfer occurred in thermal injury of biological bodies. The one-dimensional TWMBT in a finite medium was solved using separation of variables and the analytical solution showed distinctive wave behaviors of bioheat transfer in skin subjected to instantaneous heating. The finite difference method was used to simulate and study practical problems involved in burn injuries in which skin was stratified as three layers with various thermal physical properties. Deviations between the TWMBT and the traditional Pennes' equation imply that, for high flux heating with extremely short duration (i.e., flash fire), the TWMBT which accounts for finite thermal wave propagation may provide realistic predictions on burn evaluation. A general heat flux criterion has been established to determine when the thermal wave propagation dominates the principal heat transfer process and the TWMBT can be used for tissue temperature prediction and burn evaluation. A preliminary interpretation on the mechanisms of the wave like behaviors of heat transfer in living tissues was conducted. The application of thermal wave theory can also be possibly extended to other medical problems which involve instantaneous heating or cooling.     

基于有限元的电力电缆缆芯温度预测方法研究

温度是反映电力电缆是否正常运行的重要参数,但是电力电缆受安装环境制约,往往致使其缆芯温度无法直接测量。针对上述问题,提出了一种基于有限元分析的缆芯温度预测方法,采用可直接测量的电缆外护套温度结合环境参数、负荷参数等对缆芯温度进行预测。首先利用有限元分析方法,结合电力电缆的结构参数、热参数以及边界条件等,建立了电缆温度场分析的有限元模型;然后求解出不同环境参数和负荷参数下的缆芯温度,得到样本数据;最后利用样本数据训练神经网络,建立缆芯温度预测模型。实验结果表明:通过提出的温度预测方法,可较准确的预测缆芯温度,为实现电网从传统预防性维护到主动预测性管理的转变提供了一种有效途径。     

基于热电制冷器温控系统数学建模和参量辨识

为了实现对半导体激光器温度的高精度控制,利用热电制冷器、温度传感器与相应的散热装置,设计了一套半导体激光器温度控制的实验系统.首先采用热力学分析方法,对实验系统进行了理论分析,建立了该温控实验系统数学模型与相应的传递函数;其次,在取得了半导体激光器温度数据的条件下,根据模型参量的特点,提出了一种结合阶跃响应的实验曲线,应用非线性曲线最小二乘拟合进行模型参量的辨识;最后利用该模型参量进行了系统仿真和实验验证.结果表明,仿真曲线、拟合曲线与实验曲线结果一致,拟合的模型参量具有较高的预测精度.这些结果对优化调整温度控制实验是有帮助的.     

A nonlinear electrical-thermal model of the skin

Presents a model for the skin which accounts for both the nonlinearities and the asymmetries in its voltage-current characteristic. This model consists of an electrical submodel and a heat transfer submodel. The electrical submodel uses nonlinear devices in which some parameters depend on skin temperature. The heat transfer submodel models the heat exchange between the skin, the surrounding tissues, and the ambient medium and calculates the temperature of the skin to update the necessary parameters of the electrical submodel. The model is based on experiments designed to determine: (1) the dry skin voltage-current characteristic; (2) the changes in the skin breakdown voltage with location; (3) the moist skin voltage-current characteristic; (4) the changes in the voltage-current characteristic of the skin with duration after the onset of stimulation; and (5) the effect of skin temperature on its voltage-current characteristic. During these experiments the authors used 84-mm² square Ag-AgCl electrodes to apply sinusoidal voltage of 0.2 and 20 Hz. The simulations were performed using the Advanced Continuous Simulation Language (ACSL), capable of solving differential and integral equations with variable coefficients. The model predicted the skin behavior satisfactorily for a large range of amplitudes and frequencies. The authors found that the breakdown occurred when the energy delivered to the skin exceeded a threshold. Above this threshold the voltage-current characteristic of the skin became nonlinear and asymmetric and, in a real situation, the subject would experience an uncomfortable sensation which could rapidly develop into pain     

A vision-based technique for objective assessment of burn scars

In this paper a method for the objective assessment of burn scars is proposed. The quantitative measures developed in this research provide an objective way to calculate elastic properties of burn scars relative to the surrounding areas. The approach combines range data and the mechanics and motion dynamics of human tissues. Active contours are employed to locate regions of interest and to find displacements of feature points using automatically established correspondences. Changes in strain distribution over time are evaluated. Given images at two time instances and their corresponding features, the finite element method is used to synthesize strain distributions of the underlying tissues. This results in a physically based framework for motion and strain analysis. Relative elasticity of the burn scar is then recovered using iterative descent search for the best nonlinear finite element model that approximates stretching behavior of the region containing the burn scar. The results from the skin elasticity experiments illustrate the ability to objectively detect differences in elasticity between normal and abnormal tissue. These estimated differences in elasticity are correlated against the subjective judgments of physicians that are presently the practice     

太赫兹成像技术用于皮肤烧伤检测的研究进展

随着太赫兹(0.1~10 THz)光谱技术的快速发展,太赫兹成像开始应用于生物医学等领域,尤其是应用于皮肤烧伤检测中,但如何将这一技术从实验室研究转向实际临床检测还面临着巨大挑战。太赫兹技术在皮肤烧伤程度评估领域已经得到了较为深入的研究,包括成像系统、离体实验和活体实验研究等,得到了较为清晰的太赫兹图像。首先概述了皮肤烧伤程度分类方法和现有诊断方法,然后介绍太赫兹成像应用于皮肤烧伤评估的研究进展,本文重点从成像系统、检测结果和烧伤程度评估方法三个方面进一步说明了其研究进展和不足,最后提出了面向皮肤烧伤临床检测的太赫兹成像发展趋势和需要解决的问题。     

A new iterative algorithm for extrapolation of data available in multiple restricted regions with application to radar imaging

A new iterative method for extrapolation of incomplete segmented data available in multiple separated bands is proposed and tested. The method uses the Burg algorithm to find the linear prediction parameters and an iterative procedure to improve the estimation of the linear prediction parameters and the extrapolation of the data. This method is especially effective when the spectra (Fourier transform of the observed data) are in discrete forms, in the context of radar imaging represented here, this means the objects consist of distinctly spaced scattering centers. The advantages of this algorithm are demonstrated using both numerically generated and realistic experimental data pertaining to high resolution radar imaging.     

Current density imaging and electrically induced skin burns under surface electrodes

The origin of electrical burns under gel-type surface electrodes is a controversial topic that is not well understood. To investigate the phenomenon, we have developed an excised porcine skin-gel model, and used low-frequency current density imaging (LFCDI) to determine the current density (CD) distribution through the skin before and after burns were induced by application of electrical current (200 Hz, 70% duty cycle, 20-35 mA monophasic square waveform applied to the electrodes for 30-135 min). The regions of increased CD correlate well with the gross morphological changes (burns) observed. The measurement is sensitive enough to show regions of high current densities in the pre-burn skin, that correlate with areas were burn welts were produced, thus predicting areas where burns are likely to occur. Statistics performed on 28 skin patches revealed a charge dependency of the burn areas and a relatively uniform distribution. The results do not support a thermal origin of the burns but rather electro-chemical mechanisms. We found a statistically significant difference between burn area coverage during anodic and cathodic experiments.     

Thermal parametric imaging in the evaluation of skin burn depth

The aim of this paper is to determine the extent to which infrared (IR) thermal imaging may be used for skin burn depth evaluation. The analysis can be made on the basis of the development of a thermal model of the burned skin. Different methods such as the traditional clinical visual approach and the IR imaging modalities of static IR thermal imaging, active IR thermal imaging and active-dynamic IR thermal imaging (ADT) are analyzed from the point of view of skin burn depth diagnostics. In ADT, a new approach is proposed on the basis of parametric image synthesis. Calculation software is implemented for single-node and distributed systems. The properties of all the methods are verified in experiments using phantoms and subsequently in vivo with animals with a reference histopathological examination. The results indicate that it is possible to distinguish objectively and quantitatively burns which will heal spontaneously within three weeks of infliction and which should be treated conservatively from those which need surgery because they will not heal within this period.     

W-band investigation of material parameters, SAR distribution, and thermal response in human tissue

This investigation is divided into three parts. First, the W-band dielectric properties of different biological tissues are determined. Then, the electromagnetic field in the human eye and skin is simulated for plane-wave exposure. An analytical method is used to investigate the specific absorption rate (SAR) inside a layered model of the human skin between 3-100 GHz. Furthermore, the SAR inside a detailed model of the human eye is investigated numerically by the finite-difference time-domain method for a frequency of 77 GHz. Maximum local SAR values of 27.2 W/kg in skin tissue and 45.1 W/kg in eye tissue are found for 77 GHz and an incident power density of 1 mW/cm/sup 2/. In the third part of the investigation, the temperature changes of superficial tissue caused by millimeter-wave irradiation are measured by a thermal infrared imaging system. The exposure setup is based on a horn antenna with a Gunn oscillator operating at 15.8-dBm output power. The measurements showed a maximum temperature increase of 0.7/spl deg/C for a power density of 10 mW/cm/sup 2/ and less than 0.1/spl deg/C for 1 mW/cm/sup 2/, both in human skin (in vivo), as well as in porcine eye (in vitro). The comparison of the temperature measurements with a thermal bio-heat-transfer simulation of a layered skin model showed a good agreement.     

Single-Shot, High-Speed, Thermal-Interface Characterization of Semiconductor Laser Arrays

Through a detailed characterization of thermally induced output power degradation it is possible to use junction heating as a tool to resolve thermal interfaces on mus timescales using a single-shot characterization technique. In this work, the deleterious effect junction heating has on the optical output power of a laser array is characterized and then used to infer the time-dependent junction temperature in response to current pulses of varying widths. The extracted parameters are also used numerically to model the laser as a temperature-dependent heat source for thermal simulations. This treatment allows realistic packaging and emitter-placement studies to be parametrically performed by incorporating the relationship between temperature and output power/efficiency for each emitter. In this respect, once the temperature behavior of a single emitter is quantified, the operating temperature and output power performance can be accurately predicted for any realistic physical arrangement of laser array and packaging. The experimental method presented in this work is also compared to other techniques and numerical simulations using the nonlinear heat source; this demonstrates the utility of this approach and the convenience of using easily measured parameters in thermal simulations.     

Fusion of physically-based registration and deformation modelingfor nonrigid motion analysis

In our previous work, we used finite element models to determine nonrigid motion parameters and recover unknown local properties of objects given correspondence data recovered with snakes or other tracking models. In this paper, we present a novel multiscale approach to recovery of nonrigid motion from sequences of registered intensity and range images. The main idea of our approach is that a finite element (FEM) model incorporating material properties of the object can naturally handle both registration and deformation modeling using a single model-driving strategy. The method includes a multiscale iterative algorithm based on analysis of the undirected Hausdorff distance to recover correspondences. The method is evaluated with respect to speed and accuracy. Noise sensitivity issues are addressed. Advantages of the proposed approach are demonstrated using man-made elastic materials and human skin motion. Experiments with regular grid features are used for performance comparison with a conventional approach (separate snakes and FEM models). It is shown, however, that the new method does not require a sampling/correspondence template and can adapt the model to available object features. Usefulness of the method is presented not only in the context of tracking and motion analysis, but also for a burn scar detection application.     

固液混合火箭发动机尾焰的红外特性研究

针对固液混合火箭发动机中Al2O3颗粒运动的影响,对喷管的内流场和外流场进行了一体化数值仿真,得到了温度、压力、组分浓度以及粒子浓度等参数的分布。利用以最新的分子光谱数据库HITRAN和HITEMP为基础编写的逐线积分法计算了气体光谱吸收系数,采用米氏散射模型计算了固体粒子的辐射特性参数。利用基于有限体积法离散辐射传输方程的模型计算出了尾焰的红外辐射亮度。通过进一步求解,得到了特定波段的光谱辐射强度。在8—14岬波段,利用红外热像仪进行了试验,并将试验结果与数值计算结果进行了比较。结果表明,该计算模型和方法能较好地模拟固液混合火箭发动机尾焰的红外辐射特性。     

A Three-Parameter Inferior Mirage Model for Optical Sensing of Surface Layer Temperature Profiles

Inferior mirages provide a sensitive and fairly accurate probe for determining vertical temperature distributions in the atmospheric surface layer. Optical measurements on the image can be used to calculate the parameters in a temperature profile model, in this case a function with three adjustable parameters. The function contains an exponential term (two parameters) and an additive linear term (one parameter). The optical observations, for which a known target is required, consist of the elevation angles of the apparent peak, caustic, and horizon. Analytic expressions that must be simultaneously satisfied are derived for all three conditions. The parameter values are extracted numerically by minimizing a positive definite function of the three conditions. The model is tested on a set of images for which nearly simultaneous photographs, theodolite readings, and temperature profiles were available. For each image the three calculated elevations matched the measured values very closely. The complete images also match well in most of the cases. The results, a distinct improvement over previous two-parameter models, also provide a more accurate reconstruction than is obtained from the thermodynamic model for unstable stratification.     

Artificial neural networks for temperature dependent noise modeling of microwave transistors

In this paper an automated procedure for prediction of microwave transistor noise parameters versus temperature is presented. It is based on an improved Pospieszalski's noise model. In order to avoid extraction of device noise model equivalent circuit parameters (ECP) from the measured scattering and noise parameters for each operating temperature, an artificial neural network is introduced for modeling of the ECP temperature dependence. Therefore, it is necessary to acquire the measured data and extract the ECP only for several operating temperatures used for the network training. Once the network is trained and assigned to the considered noise model, the device noise parameters are easily obtained for each temperature from the operating range. It is done without changes in the network structure and without the need for time consuming and complex measurements and optimiztions.     

一种基于热阻网络的叠层芯片结温预测模型

提出了一种基于热阻网络的叠层芯片结温预测模型,该模型根据芯片内各组件的尺寸和热导率计算出对应的热阻,同时考虑了接触热阻和热量耦合效应,从而得到每层芯片在不同功耗情况下的结温预测值。在一个三芯片堆叠结构中,使用提出的方法对芯片结温进行预测,并与ANSYS仿真软件结果作比较,发现结温预测值的相对误差均小于4.5%。因此,该模型仅需根据芯片结构和材料参数,便可快速精确地估算出芯片在不同工作环境下的结温值。     

基于在线更新LSTM网络的短期4D航迹预测算法

航班飞行过程中一些因素会对当前飞行轨迹产生影响,从而导致实时航迹与历史航迹相比有一定的差异,使得仅基于历史航迹数据的航迹预测模型的预测性能变差.为解决该问题,提出了一种基于在线更新长短期记忆(Long Short-Term Memory,LSTM)网络的短期4D航迹预测算法,该算法由基于历史航迹数据的预测模型初始化参数...     

Numerical modeling of electrostatic discharge generators

The discharge current and the transient fields of an electrostatic discharge (ESD) generator in the contact mode are numerically simulated using the finite-difference time-domain method. At first the static field is established. Then the conductivity of the relay contact is changed, which initiates the discharge process. The simulated data are used to study the effect of design choices on the current and fields. They are compared to measured field and current data using a multidecade broadband field and current sensors. The model allows accurate prediction of the fields and currents of ESD generators, thus it can be used to evaluate different design choices.     

Use of the three-dimensional TLM method in the thermal simulationand design of semiconductor devices

The thermal behavior of semiconductor devices fabricated with a variety of different materials has been analyzed using the three-dimensional transmission-line matrix (TLM) method. This method can easily incorporate the temperature dependence of thermal parameters, is numerically stable, and compares favorably with other numerical techniques in computational expenditure and convenience in modeling complex geometries. As an example, a three-dimensional thermal analysis of a typical microwave power device structure is presented. The model demonstrates the effects of overlay metal and conductivity of the substrate material in limiting the temperature rise. Both the transient and steady-state thermal operation are quantitatively studied. The study shows that the TLM method has considerable potential in the thermal analysis and design of semiconductor devices