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In this paper we apply an inverse method that estimates parameters of deterministic mathematical models to an HIV model. We consider the case where experimental data concerning the values of some variables is incomplete or unknown. The objective is to estimate the parameters and to restore the information concerning the behaviour of the incomplete data. The method is based on integrating both sides of equations of a dynamic system, and applying some minimization methods (for example least square method). Such an approach was first suggested in [7] and [8]. Analysis of the HIV model and a corresponding numerical example is presented. [ABSTRACT FROM AUTHOR]

Spectral broadening in the regime of normal dispersion in a large-mode-area all-silica photonic band-gap fiber (PBGF) is shown to enable compression of an optical parametric amplifier output with a peak power of 3 MW, a central wavelength of 1140 nm, and an initial pulse width of about 200 fs to a minimum pulse width of 20 fs, corresponding to a maximum peak power of 20 MW. The spectral bandwidth of the PBGF output generated in our experiments is sufficient to support compression to a two-cycle pulse width. [ABSTRACT FROM AUTHOR]

Highly efficient collection of the fluorescent response of silicon nanoparticles loaded in micro- and nanowaveguide fiber structures is experimentally demonstrated. Micro- and nanowaveguide channels of a fiber structure are used to optically excite nanoparticles, capture their fluorescent response, and deliver the fluorescence signal to the detector. Enhancement of the evanescent field in the modes of nanowaveguide channels improves the efficiency of optical excitation of an analyte. [ABSTRACT FROM AUTHOR]

The problem of construction of an active dynamic damper for a wide frequency band of external perturbations is considered. The problem is formulated as an H ∞ optimal control problem with the use of a degenerate integral functional not containing control explicitly. The problem is solved by applying the approach based on linear matrix inequalities. [ABSTRACT FROM AUTHOR]

We report direct spectral and temporal characterization of ultrashort ultraviolet (UV) pulses resulting from third-harmonic generation by high-intensity Ti: sapphire laser radiation in the atmosphere. The experimental technique implemented in this work enables the measurement of the pulse width and the chirp of the UV field, as well as the electron density of the plasma produced by laser pulses. The bandwidth of the third harmonic generated in our experiments by laser pulses with an initial pulse width of 45 fs supports transform-limited UV pulses as short as 30 fs. [ABSTRACT FROM AUTHOR]

The complex study of the polarization-controlled supercontinuum generation in a dual-core square lattice photonic crystal fiber made of multicomponent glass was accomplished. The fiber was excited by 100-fs pulses at a 1250-nm wavelength in the anomalous dispersion region and the registered spectra exhibited soliton fission and Raman-induced self-frequency shift processes. The study also involved a detailed analysis of the infrared-to-visible light conversion exhibiting a dispersive wave origin. The special dual-core properties were investigated by separate spectral analysis of each of the two cores and the near-field profile registration. The emphasis was on the visible part of the spectrum where the input energy and polarization direction dependences were studied. The increase in the input energy allowed for the tuning of the wavelength of the visible spectral features, a further rotation of the polarization direction had an effect on the spectral dependence of the light distribution between the cores. The dual-core fiber exhibited a significant coupling performance and the spectral dependence of the visible light distribution is in good agreement with the simulated coupling length spectral characteristics. Single-core excitation in the linear regime revealed the possibility of coupling 50% of the energy to the other core and the same polarization-controlled redirection possibilities as that at the nonlinear experiments. Dual-core excitation of the fiber enhances the light redirection effect with the application potential for the polarization-controlled directional coupler accompanied by nonlinear frequency conversion. [ABSTRACT FROM AUTHOR]

Photonic-crystal fibers are shown to allow efficient spectral transformation of nanosecond laser pulses through parametric four-wave mixing and stimulated Raman scattering. Regimes providing highly efficient transformation of nanosecond laser pulses into white-light broadband radiation (supercontinuum) are identified. A strong parametric coupling between Stokes and anti-Stokes Raman sidebands around the wavelength of zero group-velocity dispersion is shown to increase the bandwidth and to improve the spectral quality of supercontinuum radiation. [ABSTRACT FROM AUTHOR]

The article discusses the study which examines the longitudinal vibrations of a rigid rod with a nonuniform cross-section with the use of the Rayleigh theory. It applies the characteristic equation of motion and the boundary conditions which is derived form Hamilton's variational principle to calculate the eigenvalues for the harmonic vibrations of the rod. Moreover, it employs the method of the separation of variables based on the exact solutions of the equations of the Rayleigh rod's motion.

A one-dimensional model is developed to describe atomic diffusion in a graphite tube atomizer for electrothermal atomic adsorption spectrometry. The underlying idea of the model is the solution of an inhomogeneous one-dimensional diffusion equation, with the diffusion coefficient being a function of temperature over the entire inhomogeneous region. An analytical solution of the problem is obtained in the form of a Green’s function. [ABSTRACT FROM AUTHOR]

The first part of the paper focuses on a detailed description of strictly pseudohyperbolic polynomials. The classes of homogeneous and nonhomogeneous polynomials are considered separately. Based on this description, a priori estimates for pseudohyperbolic PDOs with constant coefficients are obtained and the solvability of the Cauchy problem is developed. [ABSTRACT FROM AUTHOR]

Presents a research on Schwartz alternating method for elliptic boundary-value problems satisfying the maximum principle by A. S. Demidov, J. Mwambakana and A. Fedotov. Support of the Russian Federation for Basic Research on the study; Construction of solutions of the elliptic boundary problems; Application of Schwartz's idea to the problem; Theorems used in the construction of proofs for the solution of the problem.

The main results of the 12-year radiation-genetic monitoring of radiobiological, cytogenetic, and genetic parameters in Pinus sylvestrisforest plantation from the Chernobyl meltdown area are presented. The acute ionizing irradiation at doses > 1 Gy was shown to induce formation of morphoses and depressed growth; at doses >2 Gy, the reproductive ability of the trees declined. The radiobiological parameters showed a linear or close to linear dose-dependence relationship. The acute irradiation at a dose of 0.5 Gy induced cytogenetic and genetic effects that were significantly higher than the corresponding control values. The relationship between the cytogenetic effects and the absorbed dose was exponential. The dependence of the mutation frequency at specific loci on the absorbed dose was described by a nonlinear curve. The results of cytogenetic analysis of seedlings obtained from seeds annually collected in zones of slight, moderate, and strong damage of Pinus sylvestrisL. are presented. [ABSTRACT FROM AUTHOR]

Abstract. Time-resolved dependence of the transient current through a ns laser pulse illuminated scanning tunneling microscope (STM) tip/sample gap in tunneling mode and out of tunneling range is presented. A self-designed fast STM-preamplifier (bandwidth 35 MHz) allows one to resolve the fine structure of the transient signal as well as the observation of some effects that are undetectable by using conventional low-band preamplifiers. The dependence of the threshold laser pulse intensity, which corresponds to the beginning of electron emission from tip (in non-tunneling mode), as a function of the tip/sample distance was investigated. At tip/sample distances from tunnel contact up to approximately 1 micro m a linear dependence is found. This behavior is in good agreement with the theory for field enhancement in a STM tip/sample system. In tunneling mode a ns (fast component) as well as a micro s (slow component) current response was found as a result of the laser pulse illumination. These data suggest the tip bending to be an important factor in clarifying the thermal/mechanical mechanism of laser-assisted surface nanomodification. [ABSTRACT FROM AUTHOR]

A resonant method was used to determine the ultrasonic velocity in circular plates of a ferroelectric niobate ceramic having the composition (PbBa)NbO, over the frequency range 3-9 MHz at 19 °C. The average values of the elastic constants are calculated for unpolarized samples. A study is made of the Young's modulus (the ΔE effect) and of the polarization vector P as functions of the polarizing field ℰ and the time for which this field is applied. The ΔE effect and P, which increase monotonically but nonlinearly with increasing ℰ, approach limiting values as functions of the polarization time in different manners. A comparative analysis of the ΔE and polarization curves shows that the domain structure can be thought of as slightly different from that found from a scheme proposed for its behavior during the polarization process. [ABSTRACT FROM AUTHOR]

The cascaded nonlinear-optical transformation of high-power ultrashort light pulses in an ionizing gas medium involving supercontinuum generation, followed by a frequency conversion of this radiation in the field of femtosecond laser pulses with an intensity of 1014–1015 W/cm2 has been demonstrated. Parametric four-wave mixing is shown to allow a highly efficient spectral transformation and shaping of supercontinuum radiation. The maximum efficiency of a parametric frequency conversion of femtosecond laser pulses in an ionizing gas medium achieved under the conditions of our experiments is estimated as 1%. [ABSTRACT FROM AUTHOR]