Estimating the depth and lifetime of a fluorescent inclusion in a turbid medium using a simple time-domain optical method

A simple time-domain optical method for estimating the depth (d) and lifetime (tau) of fluorescent inclusions in a turbid medium is described. We demonstrate the method for depth and lifetime estimation of a fluorescent inclusion directly by fitting a monoexponential decay (tau(eff)) of the temporal position of the temporal point-spread function and the measurement of its maximum temporal position (t(max)). Since both of these measurements are intensity independent, this method provides a robust and efficient approach. This method is validated with experimental data.     

Simple time-domain optical method for estimating the depth and concentration of a fluorescent inclusion in a turbid medium

A simple time-domain optical method for estimating the depth and concentration of fluorescent inclusions in turbid media is described. We demonstrate direct depth estimation of a localized fluorescent object from the temporal position of the temporal point-spread function maximum. The depth estimation permits recovery of the fluorophore concentration, both of which are essential quantities for optical molecular imaging studies. Since the maximum is independent of the fluorophore concentration, excitation laser power, detector gain, and other system-dependent factors, this method ensures a robust and efficient approach.     

Fundamental studies of molecular depth profiling and 3D imaging using Langmuir-Blodgett films as a model

Molecular depth profiling and three-dimensional imaging using cluster projectiles and SIMS have become a prominent tool for organic and biological materials characterization. To further explore the fundamental features of cluster bombardment of organic materials, especially depth resolution and differential sputtering, we have developed a reproducible and robust model system consisting of Langmuir-Blodgett (LB) multilayer films. Molecular depth profiles were acquired, using a 40-keV C₆₀⁺ probe, with LB films chemically alternating between barium arachidate and barium dimyristoyl phosphatidate. The chemical structures were successfully resolved as a function of depth. The molecular ion signals were better preserved when the experiment was performed under cryogenic conditions than at room temperature. A novel method was used to convert the scale of fluence into depth which facilitated quantitative measurement of the interface width. Furthermore, the LB films were imaged as a function of depth. The reconstruction of the SIMS images correctly represented the original chemical structure of the film. It also provided useful information about interface mixing and edge effects during sputtering.     

Monte Carlo simulation of spectral reflectance using a multilayered skin tissue model

A nine-layered skin tissue model is newly developed for the Monte Carlo simulation of spectral reflectance. The derivation of the necessary parameters for each of the nine layers in the simulation is presented, in which the parameters used in the conventional three-layered model are modified on the basis of some histological findings on skin and reported examples. Using appropriate optical and geometrical parameters, simulated spectra can be produced that agree well with measured spectra. This approach provides a flexible means of spectral fitting to measured results and of estimating changes in the parameters of skin tissue.     

Improvement of mobility edge model by using new density of states with exponential tail for organic diode

The mobility edge(ME) model with single Gaussian density of states(DOS) is simplified based on the recent experimental results about the Einstein relationship. The free holes are treated as being non-degenerate, and the trapped holes are dealt with as being degenerate. This enables the integral for the trapped holes to be easily realized in a program. The J–V curves are obtained through solving drift-diffusion equations. When this model is applied to four organic diodes, an obvious deviation between theoretical curves and experimental data is observed. In order to solve this problem, a new DOS with exponential tail is proposed. The results show that the consistence between J–V curves and experimental data based on a new DOS is far better than that based on the Gaussian DOS. The variation of extracted mobility with temperature can be well described by the Arrhenius relationship.     

Tailoring the depth of focus for optical imaging systems using a Fourier transform approach

We show how to tailor the depth of focus for an optical system using pupil functions obtained from a Fourier transform approach. These complex amplitude and phase pupil functions are encoded onto a single liquid-crystal spatial light modulator. Experimental results show excellent agreement with theory and indicate the power of this approach.     

Location and depth profiling of Ne atoms implanted in a Nb crystal using a resonant nuclear reaction

Trapping of Ne by radiation induced defects is shown through the depth-profiling of Ne implanted into Nb crystals using the ²⁰Ne(p, γ)²¹ Na reaction. A channeling study shows that implanted atoms occupy octahedral interstices in niobium. The change of the Ne profile with further irradiation by other ions is attributed to radiation enhanced diffusion of Ne.     

Analytical approximation of the thermal and caloric equations of state for real gases over a wide density and temperature range

The thermal and caloric equations of state of the main components of gas mixtures normally used in calculations of gas dynamic processes, including combustion and detonation, as well as in problems of internal ballistics, are presented in an analytical form. The formulas obtained for the equations of state contain a relatively small number of parameters and provide an average error of approximation of less than 1% at temperatures from 500 to 2000–2500 K and densities up to the critical.     

Depth visualization of a local blood region in skin tissue by use of diffuse reflectance images

A simple method is proposed for visualizing the depth distribution of a local blood region in skin tissue by using diffuse reflectance images at two isosbestic wavelengths of hemoglobin, 420 and 585 nm. Monte Carlo simulation of light transport specifies a relation between optical densities and the depth of the region under given concentrations of melanin in the epidermis and blood in the dermis. Phantom and in vivo experiments were performed to show the usefulness of the method.     

Reliability improvement of a sound quality index for a vehicle HVAC system using a regression and neural network model

The reduction of vehicle interior noise has long been the main interest of noise and vibration harshness (NVH) engineers. A driver’s perception of vehicle noise is largely affected by psychoacoustic noise characteristics and SPL. Among the various types of vehicle interior noise, the sound of the heating, ventilation, and air conditioning (HVAC) systems is a source of distraction for drivers. HVAC noise is not as loud as the overall noise level; however, it affects a driver’s subjective perception and may lead to feelings of nervousness or annoyance. Therefore, vehicle engineers work not only to reduce noise, but also to improve sound quality. In this paper, HVAC noise samples were taken from many types of vehicles. Objective and subjective sound quality (SQ) evaluations were obtained, simple and multiple regression models were generated, and these were used with the Semantic Differential Method (SDM) to determine what characteristics trigger a “pleasant” response from listeners. The regression analysis produced diagnostic statistics and regression estimates. In addition, neural network (NN) models were created using three objective numerical inputs (loudness, sharpness, and roughness) of the SQ metrics and one subjective output (“pleasant”). The NN model was used primarily because human perceptions are very complex and often hard to estimate. The estimation models were compared via correlations between SQ output indices and hearing test results. Results demonstrated that the NN model is most highly correlated with SQ indices, which led to determination of suggested methods for SQ metrics prediction.     

Kinetic equations for the density matrix of two-level particles in a strong field

On the basis of the Green’s function method for nonequilibrium systems, the kinetic equation for two-level particles in a strong field is derived. In the binary approximation, all diagrams are expressed in terms of the reducible vertex part, whose calculation is reduced to the problem of two-channel scattering and finding the corresponding scattering amplitudes.     

Thermodynamic properties of noble-metal alloys using the cell approximation in the method of a model electron-density functional

The thermodynamic properties of the main ordered and disordered phases of copper, silver, and gold alloys are investigated theoretically using the cell approximation in the method of a model electron-density functional. Theoretical and experimental data for the energy of alloy formation, equilibrium volume, omnidirectional compression modulus, and order—disorder transition temperature are in satisfactory agreement.Institute of Strength Physics and Materials Science, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 30–36, December, 1993.     

Allowing for matrix effects in local electron-probe analysis using a new model of the distribution function for the depth of characteristic X-ray radiation

The results from using a new distribution function for the depth of characteristic X-ray radiation ??(??z) to calculate the allowance for absorption f(??) in quantitative electron-probe microanalysis are presented. The integral ??(??z) over ??z in the region of generation is proportional to the normalized absorbed energy value of the electron beam in a sample. This is used to calculate the backscattering factor R.     

Theoretical model for the transverse interference pattern of GRIN optical fiber using a laser sheet of light

A new technique (El-Ghandoor et al., Opt. Laser Technol. 31(7) (1999) 481–488) has been applied to study the shape of transverse interference fringes, instead of multiple beam Fizeau fringes (Marhic, Stein, Appl. Phys. Lett. 35 (1975) 1678–1682), from a GRIN optical fiber. In this technique, a laser light sheet is used to illuminate and pass directly through the optical fiber. Theoretical expressions are derived for the optical path differences of three groups of interference beams. The first one passes through the cladding, the core, and then the cladding once again; the second passes through the cladding only, and the third passes through the surrounding air. Theoretical expressions for the shape of transverse interference fringes formed across isotropic non-absorbing optical fibers are also calculated.     

Mean-field approximation for the potts model of a diluted magnet in the external field

The Potts model of a diluted magnet with an arbitrary number of states placed in the external field has been considered. Phase transitions of this model have been studied in the mean-field approximation, the dependence of the critical temperature on the external field and the density of magnetic atoms has been found, and the magnetic susceptibility has been calculated. An improved mean-field technique has been proposed, which provides more accurate account of the effects associated with nonmagnetic dilution. The influence of dilution on the first-order phase transition curve and the magnetization jump at the phase transition has been studied by this technique.     

Reconstructing in vivo spatially offset Raman spectroscopy of human skin tissue using a GPU-accelerated Monte Carlo platform

As one type of spatially offset Raman spectroscopy(SORS), inverse SORS is particularly suited to in vivo biomedical measurements due to its ring-shaped illumination scheme. To explain inhomogeneous Raman scattering during in vivo inverse SORS measurements, the light–tissue interactions when excitation and regenerated Raman photons propagate in skin tissue were studied using Monte Carlo simulation. An eight-layered skin model was first built based on the latest transmission parameters. Then, an o...     

Analytic solution of the mean spherical approximation for ion-dipole model in a neutralizing background

The analytic solution of the mean spherical approximation (MSA) for a multicomponent mixture of hard ions and hard dipoles with arbitrary valences and sizes of particles in a uniform neutralizing background is found. Expressions for the pair correlation functions and thermodynamics in the MSA are obtained.     

Analytical solution of a system of magnetohydrodynamic equations in a quasi-one-dimensional approximation for the monotonic variation of the flow velocity along a channel

An analytical solution is obtained for the system of magnetohydrodynamic (MHD) equations in a quasi-one-dimensional approximation for flow regimes with a monotonic variation of the velocity along a MHD channel. The problem of optimal choice of the parameters of an MHD generator for the given ratio of the areas of the outlet and inlet MHD channel cross sections is considered using the resultant analytic solution.     

Removal of a mirror image and enhancement of the signal-to-noise ratio in Fourier-domain optical coherence tomography using an electro-optic phase modulator

A novel swept-laser-based Fourier-domain optical coherence tomography system using an electro-optic phase modulator was demonstrated. The imaging range was doubled by cancellation of the mirror image. The elimination of low-frequency noises resulting from dc and autocorrelation terms increased the sensitivity by 20 dB.