Oxyhemoglobin photodissociation efficiency in biological tissue exposed to laser radiation

We have obtained quantitative data on the differential (with respect to depth) and the integrated oxyhemoglobin photodissociation efficiency in the dermis when the skin surface is exposed to a light beam in the wavelength range 300–650 nm. With this aim, we have used our own previously developed optical model for skin tissue and analytical procedure for calculating the characteristics of optical fields in a medium. We have estimated the number of oxygen molecules formed at different depths in the medium, and also their integrated number over the entire thickness of the dermis as a function of the irradiation wavelength. We consider models for a dermis that is homogeneous with respect to depth and a dermis that has a layered structure. We show that the spectral photodissociation efficiency has a number of maxima associated with the absorption spectrum of oxyhemoglobin and the optical properties of all the layers of skin tissue. We discuss the effect of the epidermis on these maxima.     

Laser heating of biological tissue with blood vessels: Modeling and clinical trials

The spatial distribution of the energy absorbed by a unit volume of a laser-irradiated biological tissue is calculated by the Monte Carlo method. Based on these calculations, the temperature fields in biological tissues subjected to laser radiation at 810 nm are modeled. The temperature fields in subcutaneous blood vessels are modeled separately taking into account the inhomogeneous volumetric distribution of heat sources inside the vessels. The results of the modeling showed that laser heating can be efficiently used both for small-diameter and large vessels. Experimental clinical trials of therapy of vascular skin changes by pulsed diode laser radiation (at 810 nm) confirmed these results.     

Simulation and improvement of temperature distributions of a framed mould during the autoclave composite curing process

It is recognized that the uniformity of mould temperature fields during the composite curing process has a vital important effect on the component and, thereby, the product quality. Previous studies mainly considered the temperature along the thickness direction of the mould or composite component, or under a rather simple external environment, leading to some deviations from the actual composite autoclave curing process. In this paper, taking into consideration some factors such as auxiliaries, framed mould and forced convection phenomenon inside an autoclave, a simulation model has been established on the mould curing temperature field in an autoclave. On this basis, simulation and thermal analysis of the framed mould temperature fields with regard to composite structure and material system in the aviation industry have been performed. Besides, the influences of the time of heat preservation, heating rate have been also investigated, and two nondimensional factors are introduced for evaluating temperature uniformity and heating quality. It is found that increasing the time of heat preservation and the number of periods could improve the uniformity significantly, and, thus, the improvements of heating efficiency and uniformity of temperature field are achieved, and that a smaller heating rate would give much better heating quality.     

Wavelet analysis of the polarization structure of biospeckle fields of statistical and multifractal phase-inhomogeneous layers

The mechanisms of formation of the polarization structure of biospeckle fields of statistical and multifractal phase-inhomogeneous layers are studied. Polarization maps of images are determined for biological tissues of various structures, namely, epidermis, muscular tissue, and myometrium. A relation between the polarization structure of biospeckles and the physiological conditions of phase-inhomogeneous layers is found. The distributions of wavelet coefficients of the polarization images of statistical and multifractal biological tissues are obtained. Criteria for the determination of the coordinate localization and scale of optical inhomogeneities of the architectonics of biological tissues are ascertained.     

Nonlinear dynamical modelling of chaotic electrostatic ion cyclotron oscillations by jerk equations

Plasma being a nonlinear and complex system, is capable of sustaining a wide spectrum of waves, oscillations and instabilities. These fluctuations interact nonlinearly amongst themselves and also with particles: electrons/ions and thus lead to nonlinear wave-wave or wave-particle interaction. In the presence of coherent waves the particles are accelerated whereas irregular oscillations can give rise to particle heating which is also called stochastic heating. Particle orbits are known to be randomized by the wave fields such that their motion can also become stochastic. For fusion to be sustained one needs a very high temperature plasma for an extended duration. It quite common to deploy external waves like electron cyclotron waves or ion cyclotron waves for plasma heating and current drive. These external waves also work only in certain regimes. Conventional plasma techniques have been able to answer several of the observations of the above processes related to heating transport etc, but nonlinear dynamics as a tool has helped in comprehending the plasma oscillations better. We have for the first time obtained a Third Order nonlinear ordinary differential equation (TONLODE) also known as jerk equation to describe the electrostatic ion cyclotron plasma oscillations in a magnetic field. The interesting feature of this equation is that it does not require an external forcing term to obtain chaotic behaviour.     

Effect of acoustic nonlinearity on heating of biological tissue by high-intensity focused ultrasound

Effect of strong acoustic nonlinearity on the efficiency of heating of a biological tissue by high-intensity focused ultrasound in the modes of operation used in real clinical setups is studied. The spatial distributions of thermal sources and the corresponding temperature increments caused by ultrasonic absorption are analyzed. Numerical algorithms are developed for simulating the nonlinear focusing of ultrasound in the calculations of both the heat sources on the basis of the Khokhlov-Zabolotskaya-Kuznetsov-type equations and the temperature field in a tissue on the basis of an inhomogeneous thermal conduction equation with a relaxation term. It is demonstrated that in the mode of operation typical of acoustic surgery, the nonlinearity improves the locality of heating and leads to an increase in the power of thermal sources in the focus by approximately an order of magnitude. The diffusion phenomena in the tissue lead to a smoothing of the spatial temperature distributions, as compared to the distributions of thermal sources. In the case of one-second exposure in the nonlinear mode of focusing, the maximal temperature in the focus exceeds the values obtained in the approximation of linear wave propagation by a factor of three.     

托卡马克氘氚聚变堆中氚的二倍频ICRF加热物理分析

本文从准线性理论出发，导出了ＩＣＲＦ二倍频加热时对磁面平均的吸收功率密度的近似解析表达式，并指出了这一近似的适用范围。采用冷等离子体近似计算波的色散关系，利用ＥＰＰＡＣ程序求解二维时间相关Ｆｏｋｋｅｒ－Ｐｌａｎｃｋ方程，分析了氚的二倍频加热。对于典型的氘氚聚变反应堆参数，计算了等离子体各组分温度随时间的变化及氚的分布函数随时间的演化，并分析了氚的非麦氏分布及相关的氘氚聚变反应率。结果表明，对于反应堆规模的等离子体来说，ＩＣＲＦ加热只在温度不太高时才导致明显的非麦氏分布及氘氚聚变反应率提高；在等离子体温度提高到约１０ｋｅＶ后，反应率不再有明显的提高     

The Challenge of Spectroscopy in the Microanalysis of Biological Surfaces

Abstract

Chemical interactions between solids and their environments are initially characterized by the chemical composition of the surfaces. This is especially true for biochemical processes, such as ionic transport through biological membranes, the maintenance of mineral ion homeostasis which is critically dependent on the activity of the “bone membrane,” the biocompatibility of surgical implants which appears to be only a surface problem, etc. This is because biological surfaces have shown an increased interest for different fields of science. However, biological surfaces are heterogeneous and generally more complex than inorganic ones, and biological subsurfaces (internal surfaces) are not usually identical with the external surfaces. Taking into account that much of the functional significance of biological surfaces is related to the internal surfaces and these are normally hidden, we must expose them for analysis without introducing artifacts during the preparative procedures. As a result, the specimen preparation techniques are to a large extent the first limiting factor. Preparation of fully mineralized tissues such as teeth, bone, and kidney stones consisting of embedding in resin, sectioning, and fine polishing have been successfully accomplished. However, soft biological materials are prepared by cryogenic methods to preserve the original elemental distributions (but altering the tissue morphology) or by chemical fixation and water replacement by embedding media to preserve the morphology (but increasing diffusion and translocation of elements).     

Morphological characterization of the anuran integument of the Proceratophrys and Odontophrynus genera (Amphibia, Anuran, Leptodactylidae)

The morphological characteristics of the leptodactylid integument of Proceratophrys and Odontophrynus genera were investigated by means of stereoscopic, low vacuum scanning electron and light microscopy. The integument surface of Proceratophrys boiei, Proceratophrys laticeps and Proceratophrys appendiculata exhibited several projections, while the integument of Odontophrynus americanus had rounded elevations with smooth profile. Light microscopic observations showed the basic integument morphology for all anurans, i.e., an epidermis and a dermis, which is subdivided into a spongious layer and a compact layer. The epidermis is formed by basal, intermediary and cornified layers. However, in Proceratophrys genus the cornified layer had an irregular outline, while in O. americanus the external surface was smooth. In the spongious dermis, mucous and venom exocrine glands were observed, but in O. americanus an exclusive glandular type with apocrine secretory pattern was identified. The integument morphology showed peculiar characteristics that may be helpful for genus distinction. Thus, morphological methods may be considered as an efficient means to characterize and to differentiate anuran genera.     

Comparing Diffusion Approximation with Radiation Transfer Analysis for Light Transport in Tissues

The diffusion model that is an approximation of the equation of radiation transfer is typically used to describe photon migration in scattering-dominant media. In general biological tissue is highly scattering and very weakly absorbing against near-infrared light, yet it is heterogeneous and may contain relatively highly absorbing or low-scattering regions. Here applicability of the diffusion approximation over the radiative transfer theory for describing ultrafast laser transport in biological tissues is numerically studied and investigated over different kinds of tissue conditions and geometries. Tissues having tumors of different sizes, locations and nature as well as dual-tumor and low-scattering conditions are considered. Radiation transfer analysis is taken as a comparison objective and it is initially proved to be accurate in benchmark comparisons with Monte Carlo simulation. The results predict systematically about the compatible conditions where and when we can use the diffusion approximation and the conditions in which the diffusion approximation may provide misleading results.     

Heating of the phantom of a biological tissue by a phase conjugate ultrasonic beam

The local heating of an absorbing medium by an ultrasonic beam with a conjugate wave front has been experimentally demonstrated. Plastisol, which is a polymeric material close in acoustic properties to biological tissue, is used as the medium. An ultrasonic heating of 7.2°C has been obtained in a time of about 100 s when the sample equipped with a thermocouple is placed between a focused piezoelectric transducer emitting a “probe wave” with a frequency of 5.0 MHz and a system that reverses the ultrasonic wave front with amplification. The characteristic features of heating by ultrasonic beams with the conjugate front, as well as the prospects of applications of this effect in medicine and other fields, have been discussed.     

The effect of temperature and viscoelasticity on cavitation dynamics during ultrasonic ablation

Inertial cavitation has been shown to enhance heating rates during high intensity focused ultrasound treatments. Cavitation dynamics will be affected by heating and by the changes in mechanical properties of tissue resultant from thermal denaturation; however, the nature of the change is not known and forms the focus of the current study. A Keller-Miksis equation is used to find the variation in inertial cavitation threshold with temperature in water and, when coupled with a Kelvin-Voigt viscoelastic model, in biological tissue. Simulated thermal ablation treatments in liver and muscle are used to explore the changes in cavitation dynamics, and the resultant frequency spectra of secondary acoustic emissions, due to tissue denaturation. Results indicate that viscosity is the key parameter controlling cavitation dynamics in biological tissues. The increase in viscosity during denaturation is predicted to increase inertial cavitation thresholds, leading to a substantial decrease in the higher harmonic content of the emitted pressure signal across a wide range of bubble radii. Experimental validation of these observations could offer improved methods to monitor therapeutic ultrasound treatments.     

Calculation of the thermal effect of an electron probe on a sample of GaN

Stationary temperature fields due to the interaction of an electron probe with a GaN sample are examined. In order to calculate the density of generated heat, the process of electron energy loss is modeled by the Monte Carlo method. The heat generation region is assumed to have the shape of a half-ellipsoid. In the case of uniform heat generation in the ellipsoid, an analytical solution to the heat conduction problem is found and expressed in terms of elementary functions. It is shown that the maximum heating temperature and the temperature field distribution depend only slightly on the shape of the heat generation region. An approximation of the density of heat sources by a uniform distribution over a hemisphere of radius equal to the ultimate range of electrons leads to a considerably underestimated maximum heating temperature. An expression is derived for determining the characteristic size of the heat generation region in GaN; this expression allows one to calculate the maximum heat temperature with an accuracy of 3% in a wide range of electron beam energies.     

Tissue self-affinity and polarized light scattering in the born approximation: a new model for precancer detection

Light scattered from biological tissues can exhibit an inverse power law spectral component. We develop a model based on the Born approximation and von Karman (self-affine) spatial correlation of submicron tissue refractive index to account for this. The model is applied to light scattering spectra obtained from excised esophagi of normal and carcinogen-treated rats. Power law exponents used to fit dysplastic tissue site spectra are significantly smaller than those from normal sites, indicating that changes in tissue self-affinity can serve as a potential biomarker for precancer.     

Laser polarimetry of the orientation structure of bone tissue osteons

A matrix method is proposed for describing polarization properties of biological tissues as an aggregate of uniaxial crystal structures. We investigated 25 μm-thick histological sections of compact bone tissue which provided single light scattering. It is shown that in this case there exists a unique relationship between the polarization parameters of the boundary laser field and the parameters of anisotropy and orientation of the structural elements of biological tissue. On this basis, contactless methods of laser polarimetry of histological sections of bone tissue have been proposed. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 52–55, January–February, 2000.     

论无创血糖监测的红外光谱方法(特邀)

介绍了无创血糖监测的几种光学方法以及红外光谱法用于无创血糖监测的优势。分析了无创血糖监测红外光谱法的主要问题,包括光在人体组织中的复杂传播;葡萄糖吸收信号微弱,且与人体中其它生化成分吸收光谱重叠;人体组织背景吸收干扰严重等。总结了无创血糖监测红外光谱法的最新进展,给出抑制人体组织背景吸收干扰的方法,并认为组织液可代替血液用于血糖水平的测量。展望了该领域未来研究趋势,主要涉及精确描述光子在组织中的传输、测量皮肤表皮内或表皮与真皮浅层光谱信息,以及提高光谱仪器信噪比,建立葡萄糖吸收带定标模型。     

Supercurrent and Its Quantum Statistical Properkies in Mesoscopic Josephson Junction in the Presence of Nonclassical Light Fields

In this paper, we study the supercurrent in a mesoscopic Josephson junction (MJJ) and its quantum statistical properties in the presence of nonclassical light fields. We investigate in detail the influence of external nonclassical light fields on current-voltage step structures of the MJJ. We also study in detail quantum statistical properties of the supercurrent when the external quantum electromagnetic fields are even and odd coherent-sta!e light fields. It is shown that the supercurrent in the MJJ exhibits both squeezing effect and quantum coherence. It is demonstrated that the MJJ can feel the difference not only between classical light fields and nonclassical light fields but also between different nonclassical light fields.     

Effects of an electric field on the electronic and optical properties of zigzag boron nitride nanotubes

We have investigated the electro-optical properties of zigzag BNNTs, under an external electric field, using the tight binding approximation. It is found that an electric field modifies the band structure and splits the band degeneracy. Also the large electric strength leads to coupling the neighbor subbands which these effects reflect in the DOS and JDOS spectrum. It has been shown that, unlike CNTs, the band gap of BNNTs can be reduced linearly by applying a transverse external electric field. Also we show that the larger diameter tubes are more sensitive than small ones. The semiconducting metallic transition can be achieved through increasing the applied fields. The number and position of peaks in the JDOS spectrum are dependent on electric field strength. It is found that at a high electric field, the two lowest subbands are oscillatory with multiple nodes at the Fermi level.     

The effect of acoustically-induced cavitation on the permeance of a bullfrog urinary bladder

It is well known that ultrasound enhances drug delivery to tissues, although there is not a general consensus about the responsible mechanisms. However, it is known that the most important factor associated with ultrasonically-enhanced drug permeance through tissues is cavitation. Here we report results from research conducted using a experimental approach adapted from single bubble sonoluminescence experiments which generates very well defined acoustic fields and allows controlled activation and location of cavitation. The experimental design requires that a biological tissue be immersed inside a highly degassed liquid media to avoid random bubble nucleation. Therefore, live frog bladders were used as the living tissue due to their high resistance to hypoxia. Tissue membrane permeance was measured using radiolabeled urea. The results show that an increase in tissue permeance only occurs when cavitation is present near the tissue membrane. Moreover, confocal microscopy shows a direct correlation between permeance increases and physical damage to the tissue.     

Nonresonant photocreation of electron-positron pair on a nucleus in the field of a pulsed light wave

The nonresonant Coulomb photocreation of electron-positron pair on a nucleus in the field of a pulsed light wave is theoretically investigated. The approximation is examined when pulsewidth is considerably greater than the characteristic time of wave oscillations. The interaction of an electron and a positron with a Coulomb potential of a nucleus is considered in the first order of perturbation theory (the Born approximation). An analytic expression for the nonresonant differential cross section was obtained for the range of moderately strong fields in the case relativistic and nonrelativistic energies. It is shown, that the nonresonant cross section of Coulomb photocreation of nonrelativistic pair in the field of a pulsed light wave is two times larger than the cross section of Coulomb photocreation in the absence of an external field.