Opto-Thermal Mathematical Modeling and Inverse Depth Profiling Using Genetic Algorithm

The use of opto-thermal transient emission radiometry (OTTER) for non-invasive measurements of water concentration depth profiles in human skin is important for developing an understanding of its barrier function. In this paper, a new inverse method for analyzing opto-thermal data to yield optical depth profiles, which is based on a new multilayer mathematical model designed for opto-thermal skin data analysis, is presented. This has been combined with a novel inverse analysis technique using a genetic algorithm. The performance of the new approach is tested on both simulated data and in vivo experimental skin data. The theoretical background is presented, and the analysis of typical measurements using the new approach is compared with conventional analyses.Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22--27, 2003, Boulder, Colorado, U.S.A.     

In Vivo Skin Solvent Penetration Measurements Using Opto-thermal Radiometry and Fingerprint Sensor

This latest study on in vivo transdermal drug delivery by using opto-thermal radiometry and a capacitance-based fingerprint sensor is presented. A small amount of solvent was applied on the test sites of a volar forearm for a few minutes; opto-thermal measurements and fingerprint sensor measurements were performed both before the solvent application and periodically after. The results showed that, by selecting different detection wavelengths, opto-thermal radiometry could give the information either on the water concentration within skin or the solvent concentration within skin. The capacitance-based fingerprint sensor could clearly visualize solvent penetration through in vivo human skin, as it generated dynamic two-dimensional (2D) images of solvent distribution within skin, and combining with tape stripping, it was also possible to get solvent 3D depth profiles within skin. The correlation between opto-thermal transient emission radiometry and fingerprint sensor measurements was also evaluated.     

Photothermal Depth Profiling by Thermal Wave Backscattering and Genetic Algorithms

Photothermal depth profiling is usually applied to inhomogeneous materials to localize the optical inhomogeneity or retrieve the thermal effusivity depth profile by simply monitoring the photothermal signal after the pump beam excitation. In this paper the different kinds of inverse problems related to photothermal depth profiling are discussed, and the solutions given by thermal wave backscattering (TWBS) and genetic algorithms (GAs) are compared. Finally, the different performances and limits of validity on known linear profiles are compared. Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22–27 2003, Boulder, Colorado, U.S.A.     

Stratum Corneum Hydration; Consequences for Skin Permeation Experiments

Abstract

Experimental approaches to the study of drug diffusion in skin in vitro generally fail to take due account of the effects of hydration on the stratum corneum. Attention is therefore drawn to neglect of this aspect of the problem in a recent article which describes an otherwise very sophisticated apparatus for the study of diffusion phenomena.

Chien and Valia¹, have recently described a carefully designed experimental apparatus for long term permeation studies of skin. Most experimental problems are successfully controlled by this technique, which will undoubtedly prove valuable for membrane permeation experiments in general. However, the approach as described neglects an aspect so fundamental to the barrier property of skin in particular, that re-emphasis of the point at issue seems eminently desirable.

The major barrier to diffusion in intact skin is the stratum corneum. As a working hypothesis, the mechanism by which the stratum corneum exerts its barrier effect appears to consist of two components. Firstly, the movement of foreign molecules through the stratum corneum is slow; that is, the activation energy for the diffusion process is generally high. Secondly, for some molecules at least, a fraction of the diffusing material is bound within the stratum corneum, and is effectively immobilised. This seems to be true for steroids, as one example, and was first reported by Vickers². The phenomenon was discussed in terms of the existence of a reservoir for such molecules in the stratum corneum, and has subsequently been demonstrated by in vitro studies³.

The point at issue in the present discussion is that it has long been known that the overall barrier effect of the skin is markedly dependent on the degree of stratum corneum hydration⁴. It has also been shown that both components of the barrier mechanism are separately dependent on the hydration level. The reservoir effect, for example, can be reduced by occlusion of the skin in vivo. This was elegantly demonstrated by Vickers in human volunteers, by re-occluding sites previously treated with a corticosteroid, after the initial corticosteroid induced blanching response had disappeared². Skin blanching was again observed shortly thereafter, which suggests that a fraction of the applied steroid had been retained within the stratum corneum, and that the increase in stratum corneum hydration resulting from the occlusion had released this material from the reservoir, allowing it once again to exhibit its pharmacological effect. Using an in vitro technique, a preliminary attempt has recently been made to assess the change in enthalpy associated with displacement of a representative steroid from stratum corneum reservoir sites by water in this way. A value of -60+11 kJ mole^-1 was obtained⁵ which is consistent with a chemisorption process. Likewise it has been shown that the diffusion constant for the diffusing (non-reservoir bound) fraction is also appreciably increased by stratum corneum hydration⁶.

Any experimental design such as that described by Chien and Valia¹, in which the skin has both faces in contact with aqueous donor and receptor solutions, will inevitably cause the skin sample to become extensively hydrated. Further, the degree of hydration attained will almost certainly be in excess of that achievable in vivo by skin occlusion, and the measurements will therefore relate only to skin under unphysiologically high levels of hydration, where the barrier property is impaired. Such measurements must therefore be of very dubious value. What is clearly required is an experimental situation where the degree of stratum corneum hydration is controllable at least over physiologically realistic limits. Such a situation can, in fact, be established experimentally, and the appropriate mathematical analysis for diffusion under such circumstances has already been described⁷.     

Auger Depth Profiling of Carbonized SiC/Si Samples

Silicon carbide (SiC) has been prepared by passing natural gas over (100) oriented hot Si substrate at different temperatures in the range 930~1000℃. Reaction times of 60 and 90 min are used.Depth profile, using Auger Electron Spectroscopy, shows the formation of SiC under a thin coating of carbon for the samples prepared at 930 and 950℃. Annealing, at 1050℃ for 12 h,results in a more pronounced formation of SiC. It is found that at the temperature of 1000℃and reaction times of 60 and 90 min, a hard diamond-like coating is formed.     

Neutron Depth Profiling: Overview and Description of NIST Facilities

The Cold Neutron Depth Profiling (CNDP) instrument at the NIST Cold Neutron Research Facility (CNRF) is now operational. The neutron beam originates from a 16 L D₂O ice cold source and passes through a filter of 135 mm of single crystal sapphire. The neutron energy spectrum may be described by a 65 K Maxwellian distribution. The sample chamber configuration allows for remote controlled scanning of 150 × 150 mm sample areas including the varying of both sample and detector angle. The improved sensitivity over the current thermal depth profiling instrument has permitted the first nondestructive measurements of ¹⁷O profiles. This paper describes the CNDP instrument, illustrates the neutron depth profiling (NDP) technique with examples, and gives a separate bibliography of NDP publications.     

Determination of the Superconducting Penetration Depth From Coplanar-Waveguide Measurements

We introduce a novel transmission-line method for determining the penetration depth in thin high-temperature superconducting (HTS) films. The method is based on the accurate measurement of the inductance per unit length of a superconducting coplanar-waveguide (CPW) transmission line fabricated on the HTS sample. Using the experimentally obtained inductance per unit length, we interpolate the penetration depth from a table of numerically determined values of inductance (per unit length) as a function of penetration depth, calculated from a coupled transmission-line model. A novelty of our procedure is the utilization of the multiline thru-reflect-line (TRL) method and the calibration-comparison method to accurately determine the inductance per unit length of the superconducting transmission line. By measuring different CPW geometries patterned onto the same thin-film sample, we can verify our penetration depth values. We demonstrate this technique by extracting the penetration depth for several different HTS films at 76 K. Estimated uncertainties in the extracted penetration depth are also provided. Contribution of an agency of the US government not subject to copyright.     

深入解析噪声系数测量的实现过程

工作中为了达到更好的应用噪声系数分析仪目的,为测试者及研究工作者清晰的认识噪声,以及如何测量噪声,本文从理论入手逐级深入探讨了噪声系数分析仪从理论到实际的实现过程,把此过程清晰的展示给了读者。     

Argon Cluster Ion Beams for Organic Depth Profiling: Results from a VAMAS Interlaboratory Study

The depth profiling of organic materials with argon cluster ion sputtering has recently become widely available with several manufacturers of surface analytical instrumentation producing sources suitable for surface analysis. In this work, we assess the performance of argon cluster sources in an interlaboratory study under the auspices of VAMAS (Versailles Project on Advanced Materials and Standards). The results are compared to a previous study that focused on C(60)(q+) cluster sources using similar reference materials. Four laboratories participated using time-of-flight secondary-ion mass spectrometry for analysis, three of them using argon cluster sputtering sources and one using a C(60)(+) cluster source. The samples used for the study were organic multilayer reference materials consisting of a ～400-nm-thick Irganox 1010 matrix with ～1 nm marker layers of Irganox 3114 at depths of ～50, 100, 200, and 300 nm. In accordance with a previous report, argon cluster sputtering is shown to provide effectively constant sputtering yields through these reference materials. The work additionally demonstrates that molecular secondary ions may be used to monitor the depth profile and depth resolutions approaching a full width at half maximum (fwhm) of 5 nm can be achieved. The participants employed energies of 2.5 and 5 keV for the argon clusters, and both the sputtering yields and depth resolutions are similar to those extrapolated from C(60)(+) cluster sputtering data. In contrast to C(60)(+) cluster sputtering, however, a negligible variation in sputtering yield with depth was observed and the repeatability of the sputtering yields obtained by two participants was better than 1%. We observe that, with argon cluster sputtering, the position of the marker layers may change by up to 3 nm, depending on which secondary ion is used to monitor the material in these layers, which is an effect not previously visible with C(60)(+) cluster sputtering. We also note that electron irradiation, used for charge compensation, can induce molecular damage to areas of the reference samples well beyond the analyzed region that significantly affects molecular secondary-ion intensities in the initial stages of a depth profile in these materials.     

求解Job-shop调度问题的遗传算法

在引入一种新的具有自适应性的杂交概率和变异概率的基础上，提出了一种构造染色体的新方法，进而提出了一种面向工作车间问题的新的遗传算法。同时给出了一个例子来说明算法的收敛性和收敛效率。仿真结果表明了该算法的有效性。     

表面粗糙度测量中的高斯滤波快速算法

应用高斯函数的逼近法和冲激响应不变法,设计出用于表面粗糙度测量的高斯数字滤波器,并给出了其零相移的递归滤波算法,算法简洁,易于实现。递归计算方法的计算量小,计算效率高。适当增加滤波器节数,在不增加很多计算量的情况下,可以达到很高的精度。文中给出的滤波器例子,传输偏差大约为2％和1％,处理一次表面测量轮廓数据,在当今最普通的计算机上,滤波时间小于1s。     

Hardware Implementation for a Genetic Algorithm

A genetic algorithm (GA) can find an optimal solution in many complex problems. GAs have been widely used in many applications. A flexible-very-large-scale integration intellectual property for the GA has been proposed in this paper. This algorithm can dynamically perform various population sizes, fitness lengths, individual lengths, fitness functions, crossover operations, and mutation-rate settings to meet the real-time requirements of various GA applications. It can be seen from the simulation results that our design works very well for the three examples running at an 83-MHz clock frequency.     

Non-destructive Case Depth Determination by Means of Low-Frequency Barkhausen Noise Measurements

The availability of a fast and reliable method for non-destructive case depth determination which can be used to directly monitor the quality of various heat treatment processes is of great interest. Conventionally hardened steel components are analyzed by means of depth-resolved microhardness measurements providing the case hardening depth (CHD) of the material. However, as a consequence of mechanical destruction, the investigated part cannot be used in its original state anymore and needs to be replaced by a twin part whose properties might be different. In this work, a new approach of non-destructive CHD determination based on Barkhausen noise analysis with an excitation frequency of 0.5 Hz is described. The use of a low frequency allows to enhance the penetration depth of the external magnetic field and to reduce the eddy current damping of the filtered Barkhausen (BN) signal at the same time. In this way, simultaneous information about the hard case and the soft base material core is experimentally accessible. Various measurands derived from the detected BN signals are sensitive to the different magnetic properties of the case and the core. The so-obtained correlations with the measured CHD can be used for non-destructive CHD determination by means of appropriate calibration data. The investigated sample set consists of cylindrical parts of 18CrNiMo7-6 which were case-hardened and ground in order to provide graded CHD values up to 3.6 mm. The sensitivity of the tested low-frequency method will be quantitatively demonstrated over the complete range of interest and its potential for industrial applications will be discussed.     

一种新的群时延测量曲线平滑算法

本文提出一种新的测量曲线平滑算法,较以往基于矩形窗的平滑算法,可以实现更高的平滑度,同时造成的失真更小,基于滤波器群时延测量曲线的试验证实了该方法的较优性能.