Specific Intensity Distribution Research Articles

A Variable Eddington Factor Model for Thermal Radiative Transfer with Closure Based on Data-Driven Shape Function

A new variable Eddington factor (VEF) model is presented for nonlinear problems of thermal radiative transfer (TRT). The VEF model is data-driven and acts on known (a-priori) radiation-diffusion solutions for material temperatures in the TRT problem. A linear auxiliary problem is constructed for the radiative transfer equation (RTE) whose emission source and opacities are evaluated at these known material temperatures. The solution to this RTE approximates the specific intensity distribution in phase-space and time. It is applied as a shape function to define the Eddington tensor for the presented VEF model. The shape function computed via the auxiliary RTE problem will capture some degree of transport effects within the TRT problem. The VEF moment equations closed with this approximate Eddington tensor will thus carry with them these captured transport effects. In this study, the temperature data comes from multigroup P 1 , P 1 / 3 , and flux-limited diffusion radiative transfer models. The proposed VEF model can be interpreted as a transport-corrected diffusion reduced-order model. Numerical results are presented on the Fleck-Cummings test problem which models a supersonic wavefront of radiation. The VEF model is shown to improve accuracy by 1–2 orders of magnitude compared to the considered radiation-diffusion model solutions to the TRT problem.

Abnormally autofocusing vortex Swallowtail Gaussian vector beam with low spatial coherence

The precondition for the application of light beams is the ability to devise light distribution with high precision. Controlling more dimensions for structured light fields is an effective method to improve the ability to devise light distribution. The Swallowtail beam, due to its rich regulatory parameters, provides the possibility to design a light field with a specific intensity distribution. Utilizing the Swallowtail beam as a foundation, we design its initial phase, polarization, and coherent structure, and propose a partially coherent azimuthally polarized circular vortex Swallowtail Gaussian beam (PCAPCVSGB) in our paper. This beam exhibits an abnormal self-focusing ability and forms an easily adjustable optical potential well at the focal plane, providing another effective tool for achieving optical manipulation. In addition, the PCAPCVSGB also shows an interesting vector property. It possesses a stable polarization singularity even with changes in coherence and topological charges, which exhibits a potential application value in optical communication.

Abruptly Autofocusing Vortex Beams for Rapid Controllable Femtosecond Two-Photon Polymerization.

Micro-fabrication based on structured-beam-assisted Two-Photon Polymerization (2 PP) provides a rapid and flexible method for the manufacture of microstructures with complex morphologies. The tunable Abruptly Autofocusing Vortex (AAFV) beams were designed theoretically and generated experimentally based on a single-phase-only Spatial Light Modulator (SLM). Their specific spatial intensity distributions were further utilized to assist the fabrication of a bowl-shaped Three-Dimensional (3D) micro-trap array via 2 PP with a one-step exposure technique. Finally, the fabricated microstructures act as a novel tool for the trapping and spatial positioning of micro-particles with different diameters, which shows potential applications in fiber optics and cell study.

Efficient Face Spoofing Detection With Flash

In light of the rising demand for biometric-authentication systems, preventing face spoofing attacks is a critical issue for the safe deployment of face recognition systems. Here, we propose an efficient face presentation attack detection (PAD) algorithm that requires minimal hardware and only a small database, making it suitable for resource-constrained devices such as mobile phones. Utilizing one monocular visible-light camera, the proposed algorithm takes two facial photos, taken with and without a flash, respectively. The proposed SpecDiff descriptor is constructed by leveraging two types of reflection: (i) specular reflections from the iris region that have a specific intensity distribution depending on liveness, and (ii) diffuse reflections from the entire face region that represents the 3D structure of a subject’s face. Classifiers trained with the SpecDiff descriptor outperform other flash-based PAD algorithms on both an in-house database and four publicly available databases: NUAA, Replay-Attack, Spoofing in the Wild, and OULU-NPU. Furthermore, the proposed algorithm achieves statistically significantly better accuracy to that of an end-to-end, deep neural network classifier, while being approximately six-times faster execution speed. The limitation of the proposed algorithm is also quantified under various adversarial lighting conditions, to guide users for the safe deployment of the algorithm. The code is publicly available at https://github.com/Akinori-F-Ebihara/SpecDiff-spoofing-detector. Example images of in-house database are also available at https://github.com/Akinori-F-Ebihara/SpecDiff in house database sample.

Limb and Gravity-darkening Coefficients for the Space Mission CHEOPS

Abstract The goal of this Research Note is to provide the theoretical calculations of the limb-darkening coefficients and gravity-darkening coefficients (GDC) for the space mission CHEOPS. We use two stellar atmosphere models: ATLAS (plane-parallel) and PHOENIX with spherical symmetry covering a wide range of effective temperatures, local gravities, and hydrogen/metal. These grids cover 19 metallicities ranging from 10−5 up to 10+1 solar abundances, 0 ≤ log g ≤ 6.0 and 2300 K ≤ T eff ≤ 50,000 K. The specific intensity distribution was fitted using six approaches: linear, quadratic, square root, logarithmic, power-2, and a series with four terms. The calculations of the GDC were performed for both stellar atmosphere models adopting an improved formulation.

Experimental demonstration of controllable flat focusing mirror excited by surface plasmon polaritons

In this study, we investigate an optical modulation of the focusing mirror based on photonic jet effect working in the reflection mode The photonic jet effects excited by surface plasmon polariton (SPP) in the near-field on the front-side of different core–shell micro-cuboids positioned on a substrate are presented. The core–shell micro-cuboid consists of a metallic shell (silver or gold) and a dielectric core (polydimethylsiloxane). The specific localized intensity distributions of the generated photonic jet at different core–shell micro-cuboids are simulated by using finite-difference time-domain technique. The experimental observations of focusing modulation are performed by a scanning optical microscope with oblique illumination. Due to the nature of SPP, the highly focused electric field near the metal–dielectric interface of the gold-coating micro-cuboids is enhanced by about 4 times. The generation of the focusing mirror based on SPP photonic jet can be flexibly controlled by varying the metallic shell. The controllable focusing mirror is a great possibility for integrated plasmonic circuits, surface optical tweezers, and biosensing.

Generalization of intensity distribution of medical images using GANs

The performance of a CNN based medical-image classification network depends on the intensities of the trained images. Therefore, it is necessary to generalize medical images of various intensities against degradation of performance. For lesion classification, features of generalized images should be carefully maintained. To maintain the performance of the medical image classification network and minimize the loss of features, we propose a method using a generative adversarial network (GAN) as a generator to adapt the arbitrary intensity distribution to the specific intensity distribution of the training set. We also select CycleGAN and UNIT to train unpaired medical image data sets. The following was done to evaluate each method’s performance: the similarities between the generalized image and the original were measured via the structural similarity index (SSIM) and histogram, and the original domain data set was passed to a classifier that trained only the original domain images for accuracy comparisons. The results show that the performance evaluation of the generalized images is better than that of the originals, confirming that our proposed method is a simple but powerful solution to the performance degradation of a classification network.

Small scale optimization in crystalline silicon solar cell on efficiency enhancement of low-concentrating photovoltaic cell

Compared with conventional silicon solar cell, concentrating photovoltaic cell has a higher incident illumination intensity and non-uniform illumination intensity distribution. There is a close relationship between the illumination intensity and the resistance and shading losses of front metal fingers. In this paper, according to the non-uniformity of the illumination distribution formed by the concentrator, the effects of different finger numbers and spacing on the performance of low-concentrating photovoltaic cells were studied. First, low-concentrating photovoltaic cell modules with different finger numbers and spacing were established, and efficiency of these modules was compared to determine the optimal finger numbers and spacing of the front metal fingers. Then, effects of the shading losses, finger resistance and lateral spreading resistance on the performance of the low-concentrating photovoltaic cell were analyzed. Results show that for the specific illumination intensity distribution of the low-concentrating photovoltaic cell when the numbers and spacing of the front metal fingers are optimized, efficiency of the low-concentrating photovoltaic cell can be increased from 13.805% to 13.837%. Additionally, it can be concluded that the optimization of the number and spacing of the front metal fingers in the crystalline silicon solar cell is an efficient way to improve the electrical performance of the concentrating photovoltaic cell.

Gravity and limb-darkening coefficients for compact stars: DA, DB, and DBA eclipsing white dwarfs

Context. The distribution of the specific intensity over the stellar disk is an essential tool for modeling the light curves in eclipsing binaries, planetary transits, and stellar diameters through interferometric techniques, line profiles in rotating stars, gravitational microlensing, etc. However, the available theoretical calculations are mostly restricted to stars on the main sequence or the giant branch, and very few calculations are available for compact stars. Aims. The main objective of the present work is to extend these investigations by computing the gravity and limb-darkening coefficients for white dwarf atmosphere models with hydrogen, helium, or mixed compositions (types DA, DB, and DBA). Methods. We computed gravity and limb-darkening coefficients for DA, DB, and DBA white dwarfs atmosphere models, covering the transmission curves of the Sloan, UBVRI, Kepler, TESS, and Gaia photometric systems. Specific calculations for the HiPERCAM instrument were also carried out. For all calculations of the limb-darkening coefficients we used the least-squares method. Concerning the effects of tidal and rotational distortions, we also computed for the first time the gravity-darkening coefficients y(λ) for white dwarfs using the same models of stellar atmospheres as in the case of limb-darkening. A more general differential equation was introduced to derive these quantities, including the partial derivative (∂ln Io(λ)/∂ln g)Teff. Results. Six laws were adopted to describe the specific intensity distribution: linear, quadratic, square root, logarithmic, power-2, and a more general one with four coefficients. The computations are presented for the chemical compositions log[H/He] = −10.0 (DB), −2.0 (DBA) and He/H = 0 (DA), with log g varying between 5.0 and 9.5 and effective temperatures between 3750 and 100 000 K. For effective temperatures higher than 40 000 K, the models were also computed adopting nonlocal thermal equilibirum (DA). The adopted mixing-length parameters are ML2/α = 0.8 (DA case) and 1.25 (DB and DBA). The results are presented in the form of 112 tables. Additional calculations, such as for other photometric systems and/or different values of log[H/He], log g, and Teff can be performed upon request.

Rapid determination of fluorescent molecular orientation in leakage radiation microscopy

We demonstrate an efficient and convenient method to recognize the orientation of fluorescent molecules through back focus imaging technology in leakage radiation microscopy. In the common structure of this microscope, the resonant energy transfer from a fluorescent emitter will be modulated and coupled into various waveguide modes. The specific intensity and angular distribution of all modes can be obtained clearly from the back focal plane. This energy transfer is strongly distance-dependent and the axial distribution information can be uniquely determined through the intensity ratio of transverse electric modes. When using the intensity ratio between transverse magnetic modes simultaneity, we find that the three-dimensional spatial orientations of the fluorescent molecules can be obtained directly.

Design of multi-beam optics for high throughput parallel processing

The utilization of ultrashort pulsed laser radiation enables the precise generation of microstructures and the processing of a wide variety of materials. However, for massive parallel processing, the raw intensity distribution of the beam emitted by the laser source usually has to be transformed into an arrangement of multiple laser beams with specific intensity distributions. Here, sophisticated, application-adapted optical systems serve as a key technology. This paper gives an overview of the optical design fundamentals of multi-beam optics. It also investigates the causes for one of the main challenges in the use of multi-beam optical systems: the distortion of the spot-array on the work piece. The distortion leads to individual spot position errors and can heavily limit the processing accuracy. Finally, active and passive concepts and technologies to reduce or eliminate distortion in multi-beam systems are presented.

A Simple Guidance Template-Based Defect Detection Method for Strip Steel Surfaces

Automatic defect detection on strip steel surfaces is a challenging task in computer vision, owing to miscellaneous patterns of defects, disturbance of pseudodefects, and random arrangement of gray-level in background. In this paper, a novel template establishment is presented. Further, a simple guidance template-based algorithm for strip steel surface defect detection is proposed. First, a large number of defect-free images are collected to obtain the statistical characteristic of normal textures. Second, for each given test image, the initial template is built according to the statistical characteristic and the size of test image. Then, a sorting operation is applied to the given test image. Further, by updating the initial template, a unique guidance template is generated based on specific intensity distribution of the sorted test image. So far, the background of each test image is approximately reconstructed in the guidance template. Finally, based on pixel-wise detection, the defects can be located accurately by subtraction operation between the guidance template and sorted test image, reverse sorting operation, and adaptive threshold determination. Experimental results show that the proposed method is both efficient and effective. It achieves a better average detection rate of 96.2% on a data set including 1500 test images.

Spectral-band replication phenomenon in a single pair of hybrid metal-organic nanospheres and nanodisks caused by plexcitonic coupling.

We study an unusual effect of spectral-band replication in the optical spectra of dimers, consisting of spherical nanoparticles or nanodisks with a silver core and a J-aggregate shell of TDBC-dye. It consists in the emergence of a doubled number of plexcitonic spectral bands compared to the case of a plasmonic dimer and in narrow peaks associated with the resonances of the J-aggregate shell. The plexcitonic bands can be divided into two groups: the "original" bands, accurately reproducing plasmonic peaks, and their "replicas," with a specific mutual arrangement and intensity distributions. The effect is interpreted using the multi-state effective Hamiltonian model describing a strong coupling between the quasi-degenerate Frenkel excitonic modes in the organic shells and multiple plasmonic modes in the pair of Ag-cores. We quantitatively explain some available experimental data on the optical properties of nanodisks and suggest a way for the observation of the replication effect. Our results extend the understanding of the nature of plexcitonic coupling to more complex systems compared to individual metal/J-aggregate nanoparticles.

Adaptive tape placement process control at geometrically changing substrates

The laser-assisted tape placement process faces thermal challenges at geometrically changing substrates. Due to changing optical conditions and thereby varying local energy absorption, local differences of the process temperature occur. These temperature inhomogeneities become even more pronounced due to restrictions with regard to machine dynamics. In particular, strong directional changes, which are necessary e.g. for small machining radii, result in the relative speed between workpiece and laser beam not being constant. The use of vertical-cavity surface-emitting lasers (short: VCSEL) as adaptive heat sources could improve the temperature control especially by use of application adapted intensity distributions that can be calculated through inverse simulations.In this work, the optical and thermal effects during tape placement on geometrically changing substrates are described and analyzed. A possible solution to the described challenges is shown by using application adapted intensity distributions, which aim at a suitable, constant process temperature. The simulations will consider the three-dimensional part geometry, specific intensity distributions of the VCSEL as well as machine dynamics. By the use of tape placement equipment of the Fraunhofer IPT the occurring local temperature changes and the resulting degree of process optimization are experimentally validated.

Application specific intensity distributions for laser materials processing: Tailoring the induced temperature profile

In laser materials processing the intensity distribution of the laser beam strongly influences the spatial and temporal temperature profile that is induced within the treated material and therefore the shape of the heat influenced zone. As a consequence, the processing quality and efficiency can be increased by using adapted intensity distributions that explicitly tailor the generated temperature profile. In this work, an efficient numerical method to calculate application specific intensity distributions is presented that induce prescribed spatial and temporal temperature profiles in the material. To this end, this task is described as an inverse heat conduction problem which is solved with the conjugate gradient method with adjoint problem. As temperature-dependent thermo-physical material properties, volumetric beam absorption and quasi-stationary distributions can be accounted for, this approach proves to be very general. The performance of the algorithm is then shown by presenting two different test cases. While the first one is taken from the application of laser softening, the second one simulates a time-dependent intensity distribution for laser transmission welding. Furthermore, ideas how to implement the obtained intensity distributions, which are very inhomogeneous, are provided using specialized beam shaping techniques. The results for both test cases are validated using commercial FEM solvers.

Removal of anti-Stokes emission background in STED microscopy by FPGA-based synchronous detection.

In stimulated emission depletion (STED) microscopy, the role of the STED beam is to de-excite, via stimulated emission, the fluorophores that have been previously excited by the excitation beam. This condition, together with specific beam intensity distributions, allows obtaining true sub-diffraction spatial resolution images. However, if the STED beam has a non-negligible probability to excite the fluorophores, a strong fluorescent background signal (anti-Stokes emission) reduces the effective resolution. For STED scanning microscopy, different synchronous detection methods have been proposed to remove this anti-Stokes emission background and recover the resolution. However, every method works only for a specific STED microscopy implementation. Here we present a user-friendly synchronous detection method compatible with any STED scanning microscope. It exploits a data acquisition (DAQ) card based on a field-programmable gate array (FPGA), which is progressively used in STED microscopy. In essence, the FPGA-based DAQ card synchronizes the fluorescent signal registration, the beam deflection, and the excitation beam interruption, providing a fully automatic pixel-by-pixel synchronous detection method. We validate the proposed method in both continuous wave and pulsed STED microscope systems.

Limb and gravity-darkening coefficients for the TESS satellite at several metallicities, surface gravities, and microturbulent velocities

We present new gravity and limb-darkening coefficients for a wide range of effective temperatures, gravities, metallicities, and microturbulent velocities. These coefficients can be used in many different fields of stellar physics as synthetic light curves of eclipsing binaries and planetary transits, stellar diameters, line profiles in rotating stars, and others. The limb-darkening coefficients were computed specifically for the photometric system of the space mission TESS and were performed by adopting the least-square method. In addition, the linear and bi-parametric coefficients, by adopting the flux conservation method, are also available. On the other hand, to take into account the effects of tidal and rotational distortions, we computed the passband gravity-darkening coefficients $y(\lambda)$ using a general differential equation in which we consider the effects of convection and of the partial derivative $\left(\partial{\ln I(\lambda)}/{\partial{\ln g}}\right)_{T_{\rm eff}}$. To generate the limb-darkening coefficients we adopt two stellar atmosphere models: ATLAS (plane-parallel) and PHOENIX (spherical, quasi-spherical, and $r$-method). The specific intensity distribution was fitted using five approaches: linear, quadratic, square root, logarithmic, and a more general one with four terms. These grids cover together 19 metallicities ranging from 10$^{-5}$ up to 10$^{+1}$ solar abundances, 0 $\leq$ log g $\leq$ 6.0 and 1500 K $\leq$ T$_{\rm eff}$ $\leq$ 50000 K. The calculations of the gravity-darkening coefficients were performed for all plane-parallel ATLAS models.

Analysis of anticoagulants for blood-based quantitation of amyloid β oligomers in the sFIDA assay.

Early diagnostics at the preclinical stage of Alzheimer's disease is of utmost importance for drug development in clinical trials and prognostic guidance. Since soluble Aβ oligomers are considered to play a crucial role in the disease pathogenesis, several methods aim to quantify Aβ oligomers in body fluids such as cerebrospinal fluid (CSF) and blood plasma. The highly specific and sensitive method surface-based fluorescence intensity distribution analysis (sFIDA) has successfully been established for oligomer quantitation in CSF samples. In our study, we explored the sFIDA method for quantitative measurements of synthetic Aβ particles in blood plasma. For this purpose, EDTA-, citrate- and heparin-treated blood plasma samples from five individual donors were spiked with Aβ coated silica nanoparticles (Aβ-SiNaPs) and were applied to the sFIDA assay. Based on the assay parameters linearity, coefficient of variation and limit of detection, we found that EDTA plasma yields the most suitable parameter values for quantitation of Aβ oligomers in sFIDA assay with a limit of detection of 16 fM.

Przemiany narodowościowo-językowe ludności Białorusi na przełomie XX i XXI wieku

Ethnic and linguistic changes of the Belarusian population at the turn of the 21th centuryThe first part of the article presents historical background of the origin of the Belarusian nation, located in the area of a confrontation between Russia and Poland. This rivalry was won by Russia, and in effect Belarusian land was incorporated into the Russian Empire, and later into the Soviet state. The next part presents the 20th century ethnic structure as the consequence of the Bolshevik Revolution and World Wars I and II, resulting in some border changes, war loses and migration movements. The main part of the article deals with the ethnic and language changes which occurred in the last decade of the 20th and in the first decade of the 21st centuries. The statistical analysis and interpretation is based on data from three population censuses (1989, 1999, 2009). An ethnic structure and linguistic situation are presented with the emphasis placed on the status of the two languages commonly used in Belarus, i.e. Russian and Belarusian, as seen in two categories: of mother language and of the language used for communication at home. The conclusions prove the expansion of popularity of the Russian language and gradual decrease of the use of the Belarusian language, both in public and at home. The processes of Russification, which had begun in the Soviet period, are intensifying despite the fact that Belarus regained its political souverianity as a country. On the basis of quantitative data the author defines specific intensity and territorial distribution of the influence of the Russian language. The final part of the article shows political and geo-political consequences of these changes in Belarus.

From regular periodic micro-lens arrays to randomized continuous phase profiles

Abstract Illumination systems for various industrial applications, e.g., in semiconductor industries and medical treatment techniques, require a specific and well-adapted intensity distribution with maximum efficiency, best achievable accuracy, and highest flexibility in the selection of the target light field. Additionally, for particular applications, all these aspects have to be fulfilled simultaneously for different wavelengths. In most of these situations, the challenging optical specifications are accompanied by the requirement of a cost-efficient fabrication technique, suitable at least for batch or small series production. In the present contribution, we first retrace the development steps and performance progress of micro-optical-based beam shaping setups. Secondly, we discuss the possibilities resulting from a combination of both refractive and diffractive optical characteristics. Especially, we show that a well-adapted combination of refractive and diffractive properties in a single element allows us to create achromatic diffusers with exceptional flexibility and high conversion efficiency.