# Search articles

## Complex Dynamics and Chaos in the Rabinovich – Fabrikant Model

**Background and Objectives:** In the work we consider a finitedimensional three-mode model of the nonlinear parabolic equation. It was proposed in 1979 by M. I. Rabinovich and A. L. Fabrikant. It describes the stochasticity arising from the modulation instability in a non-equilibrium dissipative medium with a spectrally narrow amplification increment. The Rabinovich – Fabrikant system presents some extremely rich dynamics die to the third-order nonlinearities presented in the equations. The considered system is universal.

## On the Theory of Synchronization of a Two-Mode Electron Maser with a Hard Excitation

**Background and Objectives: **Medium-power (10–100 W) THz continuous-wave electron cyclotron masers (gyrotrons) are of great interest for many applications, such as spectroscopy with dynamic nuclear polarization, plasma diagnostics, non-destructive testing, remote detection of radioactive materials, biomedical applications, etc. For these applications, a high frequency stability is required, with the possibility of frequency tuning within 1–2 GHz.

## Linear Model of Surface Terahertz Plasmons Amplification in Two Parallel Graphene Sheets

Amplification of terahertz plasmons in a pair of parallel active graphene monolayers is studied theoretically. It is shown that the antisymmetric mode increment of plasmons in the two parallel graphene monolayers may be several times greater than that in a single graphene layer due to deceleration of the antisymmetric plasmon mode as compared to the plasmon mode in a single graphene monolayer.

## Methods of Digital Holography in Interference Microscopy of Reflective Object in Partially Coherent Light

The theoretical foundation of the possibility of using the interference microscopes with extended and frequency broadband light source for recording digital holograms of microscopic objects, reconstruction and visualization of phase images is presented. Numerical procedure for processing of spatially localized digital holograms of the focused image in a partially coherent light are considered. Results of experiments on digital holographic microscopy of biological objects in a partially coherent light with Linnik interference microscope are shown.

## Optical Soliton Inelastic Interacitons in Nonlinear Schrödinger Equation with Variable Coefficients Model

It is shown that in systems described by nonlinear Schrödinger equation with variable coefficients, interaction of two solitons can carry an inelastic character. Inelastic collision solitons can lead to changes in their group velocities, amplitudes and durations. We consider some particular cases related to the separation of the soliton pair and formation of a bound state of two solitons. In the applied aspect these phenomena can be used to control the soliton interaction in optical fiber communications.

## Dynamic Light Scattering Method in Studies of Silica and Gold Nanoparticles

**Background and Objectives:** It is well known, that uncritical use of the dynamic light scattering (DLS) method may give unacceptable results for the volume or number distributions of particles as compared with transmission electron microscopy (TEM) data. The purpose of this study is to investigate application of the DLS method for determining the size of colloidal silica and gold nanoparticles and to compare results of three methods: DLS, TEM, and absorption spectroscopy (see next paper).

## Application of Dynamic Light Scattering and Absorption Spectroscopy to Studies of Systems with Colloidal Gold Nanoparticles + DNA

**Background and Objectives:** The dynamic light scattering (DLS) method is widely used to evaluate the particle size distributions. However, DLS is not free of serious drawbacks. For a fast approximate estimation of the average size of colloidal gold nanoparticles (AuNPs) within the range of 15–100 nm reasonable results can be obtained with using the absorption spectroscopy. We discuss the advantages and drawbacks of DLS, transmission electron microscope (TEM), and absorption spectroscopy in gold nanoparticle sizing.

## Mathematical Modeling of Lihgt Transfer in Low-Coherence Reflectometry of Random Media

**Background and Objectives: **The mathematical model of stochastic interference of spectrally selected fluorescence radiation in multiple scattering random media is considered. The expressions for the normalized second- and third-order moments of spatial intensity fluctuations of detected probe light are derived.

## Discrete-Eigenvalue Multiplexing for Soliton Fiber-Optic Communication Links

**Background and Objectives:** The nonlinear Fourier transform gives a powerful tool to analyze fiber-optics solitons. The solitons are described by a discrete set of eigenvalues of two coupled differential equations, which gives the nonlinear Fourier transform. Using the discrete eigenvalues for optical signal coding can increase the signal-to-noise ratio and reduce the effect of fiber nonlinearity. In the present paper an all-fiber-optics method is proposed to modulate the discrete eigenvalues.

## Optical Absorption and Raman Scattering in Doped Crystals TlGaSe2 and TlInS2

**Background and Objectives. **The TlGaSe2 and TlInS2 monocrystals are the А3В3С6 2 type ternary semiconductor compounds. Studies of TlGaSe2 and TlInS2 materials are carried out quite intensively due to the uniqueness of their optical and electrophysical properties and significant prospects for their practical use. At the same time, information about the effect of specific doping impurities on the properties of such materials is insufficient and often contradictory.

## Intermolecular Interaction in Two-component Compounds of Nanodiamonds and Doxorubicin

**Background and Objectives:** Detonation nanodiamond (ND) is one of the most promising materials for targeted drug delivery – one of rapidly developing areas of modern chemistry, pharmacology and medicine. Wide possibilities of surface modification and advantageous dimensions make nanodiamonds very attractive objects for using in the drug delivery process. A number of studies have shown that therapeutic efficacy of drugs is enhanced and their toxicities may be attenuated with immobilization on the enriched ND. There are a lot of drug immobilization methods on ND surfacy.

## Methods of Autodyne Interferometry of the Distance by Injected Current Modulation of a Semiconductor Laser

**Background and Objectives: **Two methods of distance interferometry for two types of wave modulation of laser radiation have been presented. The methods of triangular and harmonic wave modulation of a signal have been described. The advantages of the triangular wave modulation method in combination with the use of the frequency of the self-mixing signal spectrum, as well as the advantages of the harmonic wave modulation method in combination with the use of the amplitudes of the self-mixing signal spectrum have been shown.

## A Hybrid Approach in Modeling of Statistical Characteristics of Multiple Scattered Light

**Background and Objectives:** A hybrid approach to modeling of the statistical characteristics of multiple scattered light in application to optical probes of random media is considered. The approach is based on recovery of the probability density of path lengths for partial components of a scattered light field in a probed medium using approximate analytical methods or the numerical simulation.

## Difference-Frequency Generator and Optical Parametric Oscillator Pumped by a Semiconductor Disk Laser: Comparative Study with a Time Delay Model

**Background and Objectives:** High-resolution spectroscopy is known to need sources of coherent radiation in the mid- and farinfrared spectral bands. Sources based on optical nonlinear interaction (a difference-frequency generator and an optical parametric oscillator) are known to be almost ideally suitable for an application. Intracavity realizations of the devices with a nonlinear crystal located in the cavity, can likely be made simple, compact and easy to use.

## Interpretation of IR and Raman Spectra of Albumin

**Object and purpose of work: **The subject of the study is bovine serum albumin (BSA). The aim of the work is to give an interpretation of the vibrational spectra of BSA aqueous solution in the region of ~1700–600 cm– 1. **Methods: **In this regard the experimental measurement of the IR and Raman spectra of BSA and the calculation of vibrational spectra of zwitterionic ion forms 20 amino acids and their dipeptides were carried out. The effect of anharmonicity and intermolecular interaction (IMI) on the vibrational spectra of amino acids was considered.

## Influence of Sm Impurity Atoms on the Switching Effect in Thin Films of GeS

**Background and Objectives:** Nowadays interest has grown considerably to AivBvi type semiconductor media. Among them there is a special interest to the thin photosensitive films of germanium mono-sulfide. So, GeS thin layers have the ability to contain a large number of lithium ions. Therefore, it is possible to prepare the items: solar cells and super condenser. There are no limitations for practical applications of GeS crystal. Prospects of such semiconductor films are determined by the possibility of holographic recording and effects of switching and memory.

## Phase Changes of Multiferroic Magnetic Materials, Used in External Memory Systems

**Background and Objectives:** A review of studies on technological bases of multiferroic materials for their possible use in devices for the urgent destruction of information is presented. The analysis of characteristics of materials allows one to specify their phase changes caused by external influences and to investigate the magnetic properties.

## Electric and Magnetic-Field-Induced Formation of Macrostructures in Ferroelectric Liquid Crystals

**Background and Objectives: **The study of ferroelectric liquid crystals in smectic C* phase fits together several most relevant research areas, including electro-optic devices with response time in the range of 10 μs. A distinguishing feature of smectic C* liquid crystals is its chiral layered structure, which is formed due to the center of masses orientational ordering along the preferred orientation [called the director].

## Rotational Isomeric and Vibrational Spectra of Monomers and Dimers for Acrylic Acid

In frame of method DFT/b3LYP modelling calculation of geometrical structure and vibrational spectra for monomers and dimmers of trans- and cis- isomers of acrylic acid are carried out. The influence of anharmonic resonance effects and intermolecular interection on state and intensities of bands in IR and Raman spectra are researched.

## Application of Atomic Force Microscopy for Detection of Influence of Antibiotic Upon the Microbial Cell (on the Model of E.coli and I Generation Cephalosporins)

Alteration of E.coli cell wall caused by Cefazolin-AKOS was observed atomic force microscopy (AFM).Using semi-contact and contact modes the damaging effect of the Cefazolin-AKOS antibiotic was shown after a 30 minutes exposure. The assessment of physical parameters of cell allow to get more detailed information on the effect of antibiotics on microorganisms.

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