Self-seeded Ti: Sapphire laser with an active feedback mirror

Abstract

A single-longitudinal mode (SLM) dual-cavity pulsed Ti:sapphire laser is presented. It is self-seeded by means of an active feedback mirror (AFM) consisting of a partially reflecting mirror and additional active medium. The use of AFM results in an increase of both the laser output energy and overall conversion efficiency by a factor of about 1.4 compared to results achieved with a passive feedback mirror, under equivalent conditions. A reliable, temporally stable SLM regime of operation is achieved in the 740–820 nm spectral range.     

Interaction of Counter-propagating Elliptically Polarized Light Waves in Isotropic Nonlinear Media

Abstract

The nonlinear interaction of elliptically polarized counter-propagating waves in an isotropic transparent medium is analysed. Self-induced changes in the polarization of the counter-propagating light waves, are described. Using these results, a new type of modulator giving self-induced rotation of the polarization ellipse (SIRPE) is studied. The transmission of counter-propagating waves in the SIRPE modulator is shown to exhibit saturation with increase in light intensity and to be a multiple-valued function of the light intensity.     

A Simple Optical Procedure for Characterizing Uniaxial Media

Abstract

Angle-dependent reflectivities, at the interface between an isotropic medium and a uniaxial crystal, have been analysed for the situation where the index of the isotropic medium lies between the ordinary and extraordinary indices of the uniaxial crystal. The analytic results reveal simple relationships between the parameters specifying the optical tensor of the uniaxial medium and the angles of incidence for which a suitable combination of the input and output polarization angles gives zero reflected signal. As a consequence, by using a prism together with a matching fluid of the same index and determining these incidence angles, a procedure for complete optical characterization of a single crystal of calcite with one polished face has been demonstrated. The experimental results are in good agreement with the analytic predictions.     

Experimental Validation of a Monte Carlo Procedure for the Evaluation of the Effect of a Turbid Medium on the Point Spread Function of an Optical System

Abstract

The presence of particulate matter interposed between the object and the receiver affects the quality of the image produced by an optical system. This paper presents the results of measurements pertaining to the effect of a turbid medium on the point spread function of an optical system. The results refer to transmitted received power measurements obtained in controlled laboratory experiments. A random distribution of polystyrene microspheres suspended in water constituted the investigated turbid medium. Measurements were carried out for particulate with diameters of 0·33 μm, 0·995 μm, 15·7 μm at a wavelength of 0·6328 μm and for different values of sphere concentration in water. The measured data are favourably compared with results obtained by means of a Monte Carlo based numerical method. This numerical procedure allows us to obtain the point spread function and the modulation transfer function (MTF) of an optical system when a turbid medium is present. Examples of calculated MTFs that refer to the three kinds of spheres used in the measurements are presented.     

Preparation and characterization of self nano-emulsifying drug delivery system (SNEDDS) for oral delivery of heparin using hydrophobic complexation by cationic polymer of β-cyclodextrin

Objective: The aim of this study was the preparation of a self nano-emulsifying drug delivery system (SNEDDS) for oral delivery of heparin.

Significance: Preparation of hydrophobic complexes between heparin as the hydrophilic macromolecule and cationic polymer of β-cyclodextrin (CPβCD) was considered for preparation of orally administered SNEDDS in which the drug incorporated in internal oil phase of O/W nano-droplets.

Methods: Hydrophobic complexes of heparin-CPβCD were prepared by electrostatic interaction. The lipophilic feature of complexes was characterized by determining their partition co-efficients. SNEDDS prototypes were prepared by mixing liquid paraffin, Tween 80, propylene glycol and ethanol, diluted 1:100 in an aqueous medium. Central composite response surface methodology was applied for statistical optimization. Independent variables were the amount of liquid paraffin and the amount of Tween 80, while responses were size and poly dispersity index (PdI). Optimized SNEDDS were studied morphologically using transmission electron microscopy (TEM). In vitro release of heparin was studied in the simulated gastric and simulated intestinal media.

Results: The data revealed that in molar ratio 1:3 (heparin:CPβCD), the n-octanol recovery was maximized and reached 67.6?±?11.86%. Size, PdI, zeta potential, EE% in gastric medium and EE% in intestinal medium for optimized nano-droplets were reported as 307?±?30.51?nm, 0.236?±?0.02,?+2.1?±?0.66?mV, 90.2?±?0.04 and 96.1?±?0.73%, respectively. Microscopic images revealed spherical nano-droplets. The obtained data revealed no burst release of heparin from nano-droplets.

Conclusions: The obtained results indicate that SNEDDS could be regarded as a good candidate for oral delivery of heparin as the hydrophilic macromolecule.     

Degenerate two-photon propagation and the oscillating two-stream instability: The general solution for amplitude-modulated pulses

Abstract

Coherent propagation of an optical pulse in a medium with a second-order resonance is investigated when we include both the dynamical Stark effect and a population-dependent refraction index. We show how to obtain the general solution when the incident pulse has no phase-modulation. The amplitude-modulation of the incident pulse can be arbitrary as can be the initial state of the medium. This general solution is reduced to obtaining the solution of an ordinary differential equation and quadratures. For an initially de-excited medium, the solution reduces to that given by Poluektov et al. {I. A. Poluektov, Yu. M. Popov and V. S. Roitberg, 1975, Kvant. Elektron. (Moscow), 2, 1147 [1975, Sov. J. Quant. Electron., 5, 620]}. We give some illustrative examples of solutions for various initial profiles. It is also shown that the oscillating two-stream instability (OTSI) from plasma physics is equivalent to the Maxwell-Bloch equations for degenerate two-photon propagation. We give a solution for the OTSI which contains five arbitrary real functions.     

Self-action of Counterpropagating Axially Symmetric Light Beams in a Transparent Cubic-nonlinearity Medium

Abstract

The stationary effect of self-action of counterpropagating axially symmetric light beams in a medium with cubic nonlinearity is discussed. Self-similar solutions for initial radiation parameters and nonlinear medium characteristics in the case of slowly varying amplitudes of beams are found. The analysis of approximate solutions obtained on the basis of motion constants is carried out and results are compared with numerical experimental data.     

Multidimensional calculation of ray path in a twisted nematic liquid crystal cell

In general, light propagating an inhomogeneous liquid crystal (LC) cell can be modeled as ‘bundle rays’ because the LC cell consists of many birefringence layers. In order to calculate the optical path of the propagating light in the inhomogeneous LC cell, we multidimensionally calculated the wavevector, k, and the Poynting vector, S, of an ordinary and an extraordinary ray at LC grid interfaces, which are isotropic to a uniaxial medium and a uniaxial-to-uniaxial medium, by using the phase matching method. Furthermore, we also investigated the transmission coefficients and transmittance of the ordinary and the extraordinary rays as a function of difference of the optical axes of the facing birefringence medium at the interface to obtain the significant rays in the LC cell. Finally, we could calculate the exact path of the significant rays in the inhomogeneous LC cell, and compared the ray path in an electrically controlled birefringence (ECB) mode and a twisted nematic (TN) LC mode.     

Transformation of a Gaussian Beam into a Uniform Beam by a Lenslike Medium with Gain or Loss

Abstract

The propagation of Gaussian beams through lenslike media with gain or loss is analysed in order to discuss the transformation of these beams into uniform beams. The results obtained are applied to a lenslike medium with gain increasing along the radial direction.     

Nonlinear stage of instability evolution in a monostable active medium

A theoretical analysis is made of the nonlinear stage of instability evolution in a monostable active medium described by a “reaction-diffusion” type equation. The boundary of that region of the medium in which instability develops propagates at constant velocity. Group-theoretical analysis of the problem yields an analytic expression for the propagation velocity of this boundary. The results may be important for the analysis of instability evolution in a wide range of active media. Pis’ma Zh. Tekh. Fiz. 24, 10–15 (July 26, 1998)     

Fresnel Coefficients for Anisotropic Media with Gain or Loss

Abstract

The Fresnel coefficients describing reflection and refraction at an interface are derived in terms of the elements of the characteristic admittance matrix of an anisotropic medium. The cases considered include the general gyroelectromagnetic medium under normal incidence and the polar and longitudinal orientations under inclined incidence. The characteristic equation of surface polaritons associated with linear anisotropic media is also given.     

About Faraday rotation in bulk media,in a magneto-active layer and in a magneto-photonic crystal layer

ABSTRACT

In this paper, we studied the influence of medium parameters and the wavelength of incident light on Faraday’s rotation and on the ellipticity of polarization. The results of comparison of these dependencies for bulk (unbounded) media, for a layer of a magnetically active medium of finite thickness and, finally, for a magneto-photonic crystal layer are investigated. The dependences of the reflection on the same parameters are investigated too.     

Critical perturbations in a monostable active medium

An analysis is made of critical perturbations which initiate the evolution of instability in a monostable active medium described by a reaction-diffusion equation. A group-theoretical analysis of the problem yields an analytic expression for the energy of the critical perturbations. The results may be important for analyses of stability with respect to external perturbations of a wide range of active media. Pis’ma Zh. Tekh. Fiz. 24, 76–80 (November 26, 1998)     

Boundary integral equation analysis for radiation and scattering of elastic waves in three dimensions

Abstract

In this paper, the boundary integral equation (BIE) method is employed to investigate the radiation and scattering of time‐harmonic elastic waves by obstacles of arbitrary shape embedded in an infinite medium. Based on the vector BIE, entirely free of Cauchy principal value integrals, an efficient numerical scheme using quadratic isoparametric boundary elements is proposed. Furthermore, the difficulty of non‐uniquess of a solution inherent with BIE formulations for exterior elastodynamic problems is studied numerically and analytically. The counterparts of the combined Helmholtz integral formulation method for elastodynamics together with the least‐square or Lagrange‐multiplier technique are derived and applied to overcome this difficulty successfully. In addition, the elastic‐wave fields radiated or scattered by either a spherical cavity or a rigid sphere in an infinite medium are calculated and the results are compared with the analytical solutions to demonstrate the accuracy and versatility of the proposed numerical scheme.     

Numerical simulation of chainlike cluster movement of feeble magnetic particles by induced magnetic dipole moment under high magnetic fields

Abstract

In this paper, the motion of a chainlike cluster of feeble magnetic particles induced by high magnetic field is discussed on the basis of the results of numerical simulations. The simulations were performed on glass particles with a diameter of 0.8 mm; and the viscosity, applied magnetic field and magnetic properties of the surrounding medium were changed. In addition to the magnetic field and the difference in magnetic susceptibility between the particles and the surrounding medium, the obtained results indicate that the viscosity is an essential factor for the formation of the chainlike alignment of feeble magnetic particles. We also carried out simulations using glass particles with a smaller diameter of 0.1 mm. Chainlike clusters were produced similar to those of ferromagnetic particles formed in a ferromagnetic fluid.     

The In-Vitro Uptake of a Low Dose Drug (Riboflavine) by Some Adsorbents

Abstract

An investigation was carried out of the in-vitro adsorption of a low-dose model drug (riboflavine) by three typzs of kaolin, attapulgite, magnesium trisilicate and a grade of magnesium aluminium silicate (veegum^R. The adsorption experiments were designed under conditions simulating in-vivo with respect to variations in pH values, volume of the adsorption medium, and the presence of electrolytes, a hydrophilic colloid and a surfactant. Under all conditions examined, riboflavine adsorption followed the sequence veegum attapulgite kaolin magnesium trisilicate

The presence of either veegum^R (1 g) or kaolin (4 g) in the medium reduced the level of drug in solution during dissolution rate testing of capsules. Desorption results suggest only partial release of the adsorbed drug. The results obtained emphasiz,e the strong uptake of a potent ionic drug by the various silicates commonly used in pharmacy.     

Call for Papers

Abstract

We obtain expressions for the third-order nonlinearities responsible for degenerate four-wave mixing (DFWM) with folded boxcar geometry in an isotropic medium. The effects of various combinations of polarizations of the three input beams are also discussed.     

Scheduling flexible manufacturing cells using Tabu Search

Scheduling is an important aspect in the overall control of a flexible manufacturing system. The research presented focuses on production scheduling of jobs within a flexible manufacturing cell (FMC)–one type of flexible manufacturing system. Due to the complexity of the FMC scheduling problem, a 0–1 mixed-integer linear programming (MILP) model is formulated for M machines and N jobs with alternative routings. Although small instances of the problem can be solved optimally with MILP models, a two-stage Tabu Search (TS² ) algorithm that minimises the manufacturing makespan (MS) is proposed to solve medium-to-large-scale problems more efficiently. During Stage I (construction phase), two heuristics are utilised to generate an initial feasible sequence and an initial MS solution. In Stage II (improvement phase), the acquired initial solutions from Stage I are combined with a Tabu Search meta-heuristic procedure that provides improved MS solutions. The TS² algorithm provides tremendous savings in computational time for medium/large-sized multi-machine FMC problems.     

Supervisory control on the cooking time for a batch pulping digester

Abstract

Acidic ferric ion, an effective and important oxidizing agent for mineral leaching, is usually produced by direct dissolution of the corresponding salts into the solution or can be prepared in‐situ or in separate aerated batch reactors by chemical oxidation of iron sulfide through a number of different processes. The purpose of this paper is to present the idea and the results of generating the useful ferric leaching medium by bacterial oxidation of pyrite under the commercial leaching conditions in an underground copper mine. The information presented deals mainly with factors promoting the continuous oxidation of pyrite by iron‐oxidizing bacteria and the related factors influencing the extraction of copper from the enargite. This is the first attempt to produce a ferric leaching medium in an underground mine by a microbiological process. The generation technology and engineering layout are also discussed.     

Theory of multiple scattering in a fractal medium

An analysis is made of multiple scattering of particles whose ranges have a power-law distribution corresponding to a fractal medium. The small-angle approximation is used to derive an expression for the angular distribution of particles which have traversed a specific path. The results of numerical calculations are presented. Pis’ma Zh. Tekh. Fiz. 25, 34–40 (June 12, 1999)