Quantitative modeling of laser speckle imaging

We have analyzed the image formation and dynamic properties in laser speckle imaging (LSI) both experimentally and with Monte-Carlo simulation. We show for the case of a liquid inclusion that the spatial resolution and the signal itself are both significantly affected by scattering from the turbid environment. Multiple scattering leads to blurring of the dynamic inhomogeneity as detected by LSI. The presence of a non-fluctuating component of scattered light results in the significant increase in the measured image contrast and complicates the estimation of the relaxation time. We present a refined processing scheme that allows a correct estimation of the relaxation time from LSI data.Comment: submitted to Optics Letter

Optical coherence tomography of the epidermal sulfakrilate surface strippings

Method of the epidermal surface biopsy (ESB) with the adhesive compositions is the alter-native to the classic his-tological examination. Materials and Methods. In this study medical adhesive "Sulfacrylate" was used, small portions of which had been spread on an object glass, and then on different skin areas. To study the structural organization of the samples ESB the technique of optical coherence tomography (ОСТ) was used. Results. We obtained the pictures that visualize the structural organization of the different layers of the epidermis in lichen planus, hyperkeratosis, scabies and other skin diseases. Conclusion. This technique allows non-invasive measurement of high-precision structure of different layers of the epidermis, which can be useful both for research and for the practical dermatology

Computer simulation of conductivity fluctuations in a dynamic percolation model based on resistive networks

Background and Objectives: Percolation models are widely used in the analysis of electrical, thermophysical and other properties of various systems with disordered structure, which causes their wide application in the theoretical consideration of near-critical behavior of such systems in various fields of modern science and technology. Studies of noise processes, in particular noise, in the context of percolation networks have significantly extended the understanding of how fluctuations can arise in this kind of systems. An important aspect that has often received less attention in classical approaches is the fact that local conductivity processes in a number of disordered materials occur in a dynamic environment. In this paper, we present results from computer simulations of fluctuations in the conductivity of a time-evolving random resistor network. The model calculates the conductance of a three-dimensional rectangular lattice in which about 70% of the total number of nodes is empty, corresponding to a percolation threshold. Materials and Methods: The modeled percolation network consists of 160000 nodes, connected in a three-dimensional rectangular lattice. A potential difference is applied to the opposite edges of the lattice along the long side containing each node, providing charge transfer in the system. The value of bond conductivity in the lattice could take either zero or finite value (two-phase system). The numerical value of the potential for each node and the current at each site are calculated by solving Kirchhoff’s equations. Dynamics was introduced into the system by assuming that a small fraction of the whole nodes are able to diffuse through the lattice, thus changing the conduction paths, but keeping on the other hand the total fraction of the conducting phase unchanged. Results: The process of exchange between neighboring conducting and non-conducting nodes between each other in space has been simulated, after which the conductivity of the network has been recalculated. After repeating this process many times, temporal realizations of the conductivity fluctuations have been obtained, which allows a systematic analysis of the system dynamics. The characteristic lifetime τ reflects the reconfiguration time of the conductive part of the grid. In the limit of high exchange rate υ → 1 it is expected that the power spectral density of the conductivity fluctuations will be white noise. Conclusion: The results are of particular interest for advancing fundamental understanding of charge transfer mechanisms in dispersed semiconductor materials, which are relevant to chemoresistive sensing and catalytic chemistry

Оптическая когерентная томография и поляриметрический анализ поверхностных биопсий кожи

The goal. Of this study was to develop and assess the efficacy of polarization probing of biotissues in vitro. The method is based on the determination of polarization parameters of scattered radiation. Materials and methods. The well-known superficial epidermis stripping method was applied using the Sulfacrylate self-sterile medical adhesive. Small portions of thin layers of the adhesive were applied to slide plates and then to different skin sites. The corneous layer in the normal condition and in case of skin diseases (psoriasis, lichen acuminatus, discoid lupus erythematosus, alopecia, itching and demodectic mange) was examined based on the optical coherence tomography (OCT) method using the 0CS1300SS device (Thorlabs Inc, USA). Results. The authors obtained pictures visualizing the structural organization of different layers of the epidermis using the superficial epidermis biopsy method in case of lichen acuminatus, hyperkeratosis, itching and other skin diseases. Conclusion. This method ensures non-invasive high-precision measurement of the structure of different layers of the epidermis, which may be useful both for research purposes and practical dermatology.Цель исследования. Разработка и оценка эффективности поляризационного зондирования биотканей in vitro. Метод основан на определении параметров поляризации рассеянного излучения. Материал и методы. Использовали общепризнанный метод поверхностных отрывов эпидермиса с помощью медицинского аутостерильного клея «Сульфакрилат», небольшие порции которого тонким слоем наносились на предметное стекло, а затем на различные участки кожного покрова. Роговой слой в норме и при кожных заболеваниях (псориаз, красный плоский лишай, дискоидная красная волчанка, алопеция, чесотка, демодекоз) изучали с помощью методики оптической когерентной томографии на аппарате ОСТ OCS1300SS (производство Thorlabs Inc, США). Результаты. Приведены картины, визуализирующие структурную организацию различных слоев эпидермиса, полученных с помощью методики поверхностной биопсии эпидермиса при красном плоском лишае, гиперкератозе, чесотке и других кожных заболеваниях. Заключение. Данная методика позволяет проводить неинвазивные высокоточные измерения структуры различных слоев эпидермиса, что может оказаться полезным как для научных исследований, так и для практической дерматологии

PHOTON MIGRATION IN PULP AND PAPER

Abstract The thesis clearly demonstrates that photon migration measurements allow characterization of pulp and paper properties, especially the fines and filler content of pulp, and the basis weight, thickness and porosity of paper. Pulp and paper are materials with a worldwide significance. Their properties strongly depend on the manufacturing process used. For efficient process control, the employed monitoring and measuring has to be fast. Therefore it is worthwhile to try to develop new approaches and techniques for such measurements. Recent advancements in optics offer new possibilities for such development. If two samples have different optical properties their photon migration distributions are different. The measurement of a photon migration distribution allows some features between two optically slightly dissimilar samples to be distinguished. Some simple measurements, which only yielded the photons' average time of flight, were made with an oscilloscope and a time-of-flight lidar. More precise measurements yielding photon pathway distribution or some selected characteristics like light pulse rise time, broadening, or fall time were measured with a streak camera. Two methods to assess photon path length distribution were introduced: particle determination with simulation, and streak camera with deconvolution. The basic properties for pulp are consistency and fines content and for paper the basic properties are thickness, basis weight and porosity. The influence on photon migration caused by changes in these basic properties was determined. As pulp and paper are rarely very basic, an additional property was demonstrated for both materials. For pulp it was the content of filler talc, and for paper it was the use of beaten pulp as a raw material. These additional properties were also distinguishable

Specific features of charge transfer fluctuations in disperse structures based on anatase nanoparticles near the percolation threshold

Background and Objectives: Nanostructured dispersed semiconductor structures are of some interest as functional materials for modern chemoresistive sensing and photocatalytic chemistry. Among the promising semiconductor materials for such applications is, in particular, titanium dioxide in the modification of anatase. Despite a significant number of experimental and theoretical works devoted to the consideration of electrophysical properties of anatase nanophase and various structures based on it, the features of degradation of electrical conductivity of such systems with time are not fully investigated. The aim of this work was to analyze the behavior of the fluctuation component of the voltage drop on partially conducting systems of interelectrode bridges made of anatase nanoparticles under conditions of direct current flow in the quasi-stationary regime (with a slow increase in the voltage drop) and as it approaches the threshold of flow, characterized by a rapid increase in the voltage drop. Materials and Methods: Experimental studies of the charge transfer fluctuations in disperse structures near the percolation threshold were carried out using specially prepared samples consisting of densely packed titanium oxide nanoparticles (TiO2). The technique is based on the registration of time dependences of the voltage drop across the structures when a constant current flows through the system of anatase bridges. The behavior of fluctuation components during the measurement cycles was analyzed using moving estimates of the Hurst exponent of sample structural functions of intensity fluctuations. In addition to the sample values of the Hurst exponent, the sample normalized autocorrelation functions of the fluctuation component were calculated. To interpret the observed features, we propose a qualitative phenomenologicalmodel that considers the influence of random sequences of acts of blocking and soft breakdown of local conduction channels in the studied structures on the degradation of the effective ohmic conductivity of the structures. Results: It has been established that when approaching the threshold of percolation due to the depletion of the ensemble of free charge carriers (electrons) in bridges, there are qualitative changes in the dynamics of voltage drop fluctuations on bridge systems (in particular, a significant increase in the Hurst exponent of structural functions of voltage drop fluctuations, correlating with a sharp decline in the effective ohmic conductivity of the structures under study). “Soft” breakdowns of previously blocked local conduction channels may be due to the Poole – Frenkel effect, leading to the escape of trapped electrons into the conduction zone due to thermal fluctuations when the depth of traps decreases under the influence of an external electric field. Conclusion: The results obtained are of some interest from the point of view of further development of fundamental ideas about charge transfer mechanisms in dispersed semiconductor materials used in chemoresistive sensing and catalytic chemistry

Speckle correlometry as a method for evaluating the dynamics of the liquids foam

Background and Objectives: The two-phase gas-liquid foams have been an active object of research over the past few decades. Usually, during the coarsening of the foam such physical processes as a foam syneresis (the liquid drainage along the Plateau channel and the bubble walls under the gravity), an Oswald ripening of the gas bubbles, and their coalescence are investigated. Another process that accompanies the aging of gas-liquid foams is the evaporation of the liquid component of the foam that is insufficiently described in the literature. Each of these processes is characterized by its own kinetics. The major factors that determine the dynamic and kinematic characteristics of the foams are the volume fraction of the liquid in the foam, the rheological properties of foam films, the average thickness of films between the gas bubbles, and the dispersion of the system. The modern methods for the diagnostic of the structural rearrangements and the foam aging do not allow studying the evolution of the three-dimensional foams in the real time. In this work, a comparative analysis of the behavior of the time correlations of the intensity fluctuations of the scattered by the liquid foam laser radiation on long time scales is carried out for the case of the system with mass transfer of the liquid component due to its partial evaporation and the isolated system. Such studies play an important role in the development of the coherent-optical methods for the morphofunctional diagnostic of the micro- and nanostructured multiphase systems in the real time. Materials and Methods: The analysis of the evolution of the isolated and “open” liquid foams during their aging is carried out by use of the speckle correlometry method. Two series of the experiments were performed with an isolated system and an “open” system at a temperature of 24°C. Results: The correlation time of the intensity fluctuations of the radiation scattered by the medium was calculated from the normalized correlation function, based on the criterion of its decay by a factor of e. The dependences of the correlation time of the intensity fluctuations on the aging time for isolated and “open” systems are obtained. A phenomenological model to describe the increase in the correlation time of intensity fluctuations is proposed. Within the framework of the model, the experimental data agree with the model data for an isolated foam and correlates with a power law with an exponent equal to 1.5. Conclusion: A speckle-correlation analysis as method for the analysis of the local instabilities caused by the structural rearrangements in the foams under the coarsening was considered. The phenomenological model, that establishes the relationship between the correlation time of the intensity fluctuations of the laser radiation scattered by the foam and the aging time of the foam, is proposed. The obtained results may be useful for the further development of laser methods for the diagnostic of nonstationary multiphase systems with a complex structure and dynamics.&nbsp

Statistical properties of GB speckle patterns: Influence of the phase modulation depth of the synthesized GB apertures

Background and Objectives: Results of theoretical studies of the statistical properties of gene-based speckle patterns are presented. These gene-based (GB) speckle patterns visualize digital versions of genetic structures of biological objects under investigation. The reported study was the focused on influence of the depth of phase modulation of a collimated coherent beam used to read information from a synthesized GB phase screen. Materials and Methods: In the modeling, the nucleotide sequence of the target gene B602L of the causative agent of African swine fever (the HuB20 strain) was used to synthesize a model GB phase screen. The procedure was based on establishing a correspondence between the unique number of each codon (triplet) in the sequence, which is in the range between 0 and 63, and the depth of phase modulation of the readout beam by the related pixel in the synthesized GB-aperture. After that, the random spatial distribution of the speckle intensity in the Fraunhofer diffraction zone was calculated. The obtained model data were compared to similar data for phase screens with Gaussian and uniform distributions of local phase shifts. Results: It has been found that the synthesized GB speckle pattern, in contrast to the simulated speckle patterns for Gaussian and uniform distributions of local phase shifts in speckle-generating phase screens, is characterized by significant oscillations of the coherent component of the speckle field with the increasing phase modulation depth. This is caused by featured statistical properties of the codon ensemble in the processed nucleotide sequence of the target gene of the HuB20 strain. The original model data on the sensitivity of the synthesized GB fields to mutation-driven codon substitutions in the original sequence for the target gene of the HuB20 strain are presented. Conclusion: As the result, the original model data on the sensitivity of synthesized GB speckle patterns to mutation-induced codon substitutions in the initial sequence for the target gene of the HuB20 strain have been presented.&nbsp

Small-angle polarimetry as a technique for identification of nucleotide sequences in bioinformatics

Background and Objectives: The method of identification of symbolic sequences associated with the genetic structure of biological objects using the principles of small-angle polarimetry is considered. This method of analyzing and visualizing symbolic sequences obtained by sequencing DNA fragments can be defined as small-angle polarimetry of phase-modulating structures associated with genetic information. Materials and Methods: The analyzed symbolic sequence is represented by a two-dimensional phase-modulating matrix, each element of which corresponds to one of the four basic nucleotides (adenine, cytosine, thymine, guanine), and the depth of modulation of the phase of the reading coherent linearly polarized beam is determined by the content of this nucleotide in the corresponding triplet in the nucleotide sequence. As a result of the diffraction of a reading coherent beam with a polarization plane oriented at an angle of 45° to the sides of the phase-modulating matrix, a spatial distribution of local polarization states of the reading field diffracted on the matrix is formed in the paraxial region of the far diffraction zone. Discrimination of local polarization states in accordance with the proposed algorithm makes it possible to synthesize a binary spatial distribution, which is a unique identifier of the analyzed symbol sequence. Results: Modeling of the processes of phase coding and subsequent analysis of local polarization states in the near-axial region using sequencing results for the strains “Wuhan”, “Delta” and “Omicron” of the SARS-CoV-2 virus has shown a high sensitivity of the method to local changes in the structure of nucleotide sequences. Conclusion: The results of the simulation allow us to conclude that binary distributions of local polarization states of light fields diffracted on DNA-associated phase-modulating structures recorded in the axial region are characterized by high sensitivity to local mutational changes in the structure of nucleotide sequences. The results obtained can be used as a basis for creating effective hybrid methods for analyzing genetic information using the principles of polarization coding and small-angle polarimetry