Search

Artificial neural networks (ANNs) experience catastrophic forgetting (CF) during sequential learning. In contrast, the brain can learn continuously without any signs of catastrophic forgetting. Spiking neural networks (SNNs) are the next generation of ANNs with many features borrowed from biological neural networks. Thus, SNNs potentially promise better resilience to CF. In this paper, we study the susceptibility of SNNs to CF and test several biologically inspired methods for mitigating catastrophic forgetting. SNNs are trained with biologically plausible local training rules based on spike-timing-dependent plasticity (STDP). Local training prohibits the direct use of CF prevention methods based on gradients of a global loss function. We developed and tested the method to determine the importance of synapses (weights) based on stochastic Langevin dynamics without the need for the gradients. Several other methods of catastrophic forgetting prevention adapted from analog neural networks were tested as well. The experiments were performed on freely available datasets in the SpykeTorch environment., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

When direct vision is obstructed, detecting an object usually involves either using mirrors or actively controlling some of the properties of light used for illumination. In our paradigm, we show that a highly scattering wall can transfer certain statistical properties of light, which, in turn, can assist in detecting objects even in non-line-of-sight conditions. We experimentally demonstrate that the transformation of spatial coherence during the reflection of light from a diffusing wall can be used to retrieve geometric information about objects hidden around a corner and assess their location. This sensing approach is completely passive, assumes no control over the source of light, and relies solely on natural broadband illumination.

Spatial coherence function (SCF) is a complex function of two spatial coordinates that, in general, carries more information than the bare intensity distribution. A fast and quantitatively accurate measurement of the SCF is extremely important for a range of applications in optical sensing and imaging. Here, we demonstrate an efficient two-step procedure for measuring the full-field complex coherence function. The measurement relies on an optimized design of a wavefront shearing interferometer capable of characterizing spatially inhomogeneous fields over an extended angular domain. The measurement precision is confirmed by the excellent agreement with a numerical estimation based on Fresnel calculations. We demonstrate that the sensitivity and the measurement range afforded by our instrument permits us to reliably describe the differences in the complex coherence functions that are due to subtle modifications in the shape, position, and orientation of radiation sources.

The traditional Monte Carlo technique of photon transport in random media describes only single point properties of light, such as its intensity. Here we demonstrate an approach that extends these capabilities to simulations involving properties of spatial coherence, a two-point characteristic of light. Numerical experiments illustrate the use of this Monte Carlo technique for describing the propagation of partially spatially coherent light through random multiply scattering media.

Undoubtedly, laser tweezers are the most recognized application of optically induced mechanical action. Their operation is usually described in terms of conservative forces originating from intensity gradients. However, the fundamental optical action on matter is non-conservative. We will review different manifestations of non-conservative optical forces (NCF) and discuss their dependence on the specific spatial properties of optical fields that generate them. New developments relevant to the NCF such as tractor beams and transversal forces are also discussed.

In classical diffraction theory, Babinet's principle relates the electromagnetic fields produced by complementary sources. This theorem was always formulated for single-point quantities, both intensities or field amplitudes, in conditions where the full spatial coherence is implicitly assumed. However, electromagnetic fields are, in general, partially coherent, and their spatial properties are described in terms of two-point field-field correlation functions. In this case, a generalized Babinet's principle can be derived that applies to the spatial coherence functions. We present both the derivation and the experimental demonstration of this generalized Babinet theorem.

In dense multiple scattering media, optical fields evolve through both homogeneous and evanescent waves. New regimes of light transport emerge because of the near-field coupling between individual scattering centers at mesoscopic scales. We present a novel propagation model that is developed in terms of measurable far- and near-field scattering cross sections. Our quantitative description explains the increase of total transmission in dense scattering media and its accuracy is established through both full-scale numerical calculations and enhanced backscattering experiments.

Advection is critical for efficient mass transport. For instance, bare diffusion cannot explain the spatial and temporal scales of some of the cellular processes. The regulation of intracellular functions is strongly influenced by the transport of mass at low Reynolds numbers where viscous drag dominates inertia. Mimicking the efficacy and specificity of the cellular machinery has been a long time pursuit and, due to inherent flexibility, optical manipulation is of particular interest. However, optical forces are relatively small and cannot significantly modify diffusion properties. Here we show that the effectiveness of microparticle transport can be dramatically enhanced by recycling the optical energy through an effective optical advection process. We demonstrate theoretically and experimentally that this new advection mechanism permits an efficient control of collective and directional mass transport in colloidal systems. The cooperative long-range interaction between large numbers of particles can be optically manipulated to create complex flow patterns, enabling efficient and tunable transport in microfluidic lab-on-chip platforms.

The optical size and intrinsic material properties of scattering particles introduce inherent restrictions on their scattering patterns. We show that large size, core-shell dielectric structures with spherical symmetry provide the necessary flexibility for exciting higher-order spherical modes and, consequently, allow us to control the directivity of the scattered radiation. Significant scattering can be generated over angular domains that were formerly believed to be accessible only to dipolar scattering.

The symmetry in action and reaction between interacting particulate matter breaks down when the interaction is mediated by an out-of-equilibrium environment. Nevertheless, even in this case, the space translational invariance still imposes the conservation of canonical momentum. Here we show that optical binding of an asymmetric material system can result in non-reciprocal interactions between constituents. We demonstrate that a non-conservative force applies to the center of mass of an optically bound dimer of dissimilar particles, which leads to an unexpected action in the transversal direction. The sign and the magnitude of this positional force depend on the abrupt phase transitions in the properties of the asymmetric dimer.

We demonstrate a new multi-frequency approach for mapping near-field optically induced forces with subwavelength spatial resolution. The concept relies on oscillating a scanning probe at two different frequencies. Oscillations at one frequency are driven electrically to provide positional feedback regulation. Modulations at another frequency are induced optically and are used to measure the mechanical action of the optical field on the probe. Because the measurement is based on locally detecting the force of the electromagnetic radiation acting on the probe, the new method does not require a photodetector to map the radiation distribution and, therefore, can provide true broadband detection of light with a single probe.

We demonstrate that a nonvanishing interaction force exists between pairs of induced dipoles in a random, statistically stationary electromagnetic field. This new type of optical binding force leads to long-range interaction between dipolar particles even when placed in spatially incoherent fields. We also discuss several unique features of the dipole-dipole interaction in spatially incoherent Gaussian fields.

We demonstrate that the conventional optical signal in near-field scanning optical microscopy and the optical force induced topography contain complementary information about the complex three-dimensional field distribution. Crucially, the additional information about the field distribution can be retrieved without increasing the measurement complexity.

We show that optical anisotropy can exist in composite materials even when they consist of components that are isotropic in shape, spatial distribution, and optical properties. We demonstrate that the simple presence of a surface on a metal-dielectric composite induces an optical anisotropy that manifests itself in an unusual change of the state of polarization and spin Hall effect of reflected light.

The properties of light scattered from material systems depend on the characteristics of input optical fields. We study numerically the effect of the state of spatial coherence on the properties of scattered fields. Using a customized coupled dipole technique, we demonstrate that this influence manifests in changes of the statistics of intensities scattered at different angles.

In the practice of near-field scanning probe microscopy, it is typically assumed that the distance regulation is independent of the optical signal. However, we demonstrate that these two signals are entangled due to the inherent action of optically induced force. This coupling leads to artifacts in both estimating the magnitude of optical fields and recording topographic maps.

Based on the conservation of linear momentum on scattering from arbitrary objects, we demonstrate the generation of nonconservative optical forces that act in a direction opposite to the propagation of the incident beam. The concept can be applied to tailor the force fields produced on nonabsorbing bodies regardless of their sizes and shapes.

We demonstrate the existence of a class of optical beams where the nonconservative forces can be locally oriented in a direction opposite to the propagation wave vector. Objects placed in the vicinity of these locations will move toward the source of light. The behavior of these negative forces is discussed for the particular case of nondiffracting rotating scale-invariant vector electromagnetic waves.

We show that the interferometric interaction between the tip and the sample is inherently measured by a near-field scanning optical microscope (NSOM) operating in reflection mode. This is demonstrated by measuring the phase of the sample reflectivity on a standard multilayer system with variable thickness. The demonstrated intrinsic sensitivity to the phase has implications in the interpretation of images collected by using reflection mode NSOM.

By solving a linear stochastic equation, we demonstrate how probability density functions of scattered intensities and order statistics can be used for reconstructing the statistical properties of fluctuating anisotropic polarizabilities. Depending on the statistical relationship between the elements of the polarizability tensor, we show how task optimized measurements can be conducted to reduce the number of necessary measurements. This approach is directly applicable to polarimetric measurements with limited control over the experimental conditions.

Optical properties of inhomogeneous materials are, in general, scale dependent. We show that, when observed at mesoscopic scales, the local anisotropic polarizabilities depend on the volume of interaction, which may be limited by either the excitation field or material dimensions. We demonstrate the existence of a specific interaction length scale corresponding to the maximum degree of local anisotropy and discuss its relation to the detailed morphology of a disordered medium. Probing these mesoscopic scales provides information about the local structure and allows characterizing material systems that otherwise may appear similar.

We show that in the canonical case of two lossless spheres that are electromagnetically coupled there is interplay between conservative and nonconservative forces, which is controlled by the polarization of the bounding field. We demonstrate that this phenomenon leads to new mechanisms to induce torques on spherically symmetric, optically isotropic, and lossless objects. The electromagnetic interaction can be exploited to apply orbital torque about the mutual center of mass of the bounded spheres as well as spin around the individual axes. When the incident field is linearly polarized, the torques are mostly conservative and affect only transient behaviors while for circularly polarized fields, the torques are entirely nonconservative, resulting in steady rotations. Means to control the magnitudes of orbital and spin torques are presented and applications to nanorotator machines are discussed.

Electromagnetic waves carry angular momenta, and, due to spin-orbit interaction, an encounter with a gradient of refractive index leads to transport of spin similar to the electronic spin Hall effect. We show here that transversal spin transport is possible even when the symmetry of optical interaction is of higher dimensionality. We demonstrate that for a wave in a pure state of polarization, the spin-orbit interaction results in a spiraling power flow that is determined by the extent of the interaction. As a result, the spin transport can be resonantly enhanced in a spherical geometry. Our results open the possibility for developing new functionalities for photonic devices.

A taking of the biologically active supplements by judoists had made a positive influence on the functional status, physical efficiency and oxygen-transporting function of these athletes. An improvement in muscle-strengthening exercises and special endurance has been registered by the athletes, which have taken these biologically active supplements.

We present an extension of the coupled dipole approximation technique to model optical properties of large-scale slabs of homogeneous and inhomogeneous materials. This method is based on a modification of the Green's function to take into account the interaction between dipoles located at arbitrary distances within the slab. This method allows modeling of various aspects of the structural morphology of composite materials, including component size and spatial distribution as well as surface roughness effects. Our procedure provides an adequate description of far-field optical properties such as the specular and diffuse reflection of light.

We introduce the general concept of stochastic scattering polarimetry and demonstrate that the anisotropic polarizability of a scattering object can be obtained by analyzing the statistical moments of polarimetrically measured intensity distributions. This general procedure is valid even in situations where the state of polarization of the incident field is not known. The efficiency of recovering different scattering polarizabilities is demonstrated numerically for several particular cases pertaining to both far- and near-field optics.

The model of apertureless near-field optical microscope is developed taking into account the multipole moment of probe. In the case of samples with small dielectric absorption, the multipole moments are shown to be responsible for the appearance of additional resonances in the spectrum of scattered signal. The influence of multipole moments is especially pronounced in the near-field microscopy with modulation of tip-sample distance. A good agreement of the theoretical results with experimental data in the case of resonant interaction of the probe and sample is demonstrated.

The microflora of the small and large intestines was studied in 105 patients with chronic enteritis. Significant amounts of various microorganisms were detected in the small intestine. The content of E. coli, bacteroids, bifidobacteria in feces diminished, while that of staphylococcus, enterococcus and fungi rose. The patients were given diet N 4 (intended for enteritis patients) containing lactic acid products (200 ml, 5 times/day, during 24 days); 38 patients received shubat, 30--koumiss and 37--kefir. Koumiss proved to be most effective in the treatment of intestinal dysbacteriosis. Shubat possessed a lower antibiotic activity. Kefir administration did not produce significant shifts in the intestinal microflora. Lactic acid products were ineffective in fungous and Proteus dysbacteriosis. Koumiss and shubat could be recommended for the therapy of certain types of intestinal dysbacteriosis, thus restricting the use of antibacterial drugs.

A total of 156 patients with chronic enteritis have been examined for the bile lipid and bile acid composition, the small and large intestine proximal portions microflora, membranous digestion and absorption of the lipids, blood serum lipid composition; morphometry of the small intestine proximal portion mucosa has been carried out. The findings have been processed in correlation and regression analysis, that has revealed a number of relationships between these parameters. This helped specify some aspects in the pathogenesis of lipid metabolism disorders associated with the small intestine abnormalities and select the tests most valuable for the diagnosis and prognosis of the condition. The authors recommend a wider application of such analysis to clinical studies.