Intrinsic second-order nonlinearity in chalcogenide glasses containing HgI2

Frequency conversion using nonlinear optical (NLO) crystals is widely used in advanced photonic technologies to produce coherent light in the spectral regions where the available laser sources are missing. Isotropic glasses usually do not show second order nonlinear processes like second harmonic or difference frequency generation (SHG, DFG) except for temporarily induced anisotropy under external stimuli. Here, we show that a HgI₂–Ga₂S₃–GeS₂ homogeneous glass exhibits a strong intrinsic SHG response comparable with that of the well-known NLO single crystal LiNbO₃. The origin of this extremely rare phenomenon seems to be noncentrosymmetric bent HgI₂ molecules embedded in a sulfide glassy host. Taking into account the unique properties of chalcogenide glasses (wide IR transmission, low phonon density, unlimited ability to be modified changing the appropriate glass properties, fiber drawing and thin layer design), the observed phenomenon opens up the possibility of creating fundamentally new devices for mid-IR photonics.     

Characterization of functionalized multiwalled carbon nanotubes and application as an effective filter for heavy metal removal from aqueous solutions☆

Filtration efficiency of Ni(II) from aqueous solution using pristine and modified MWCNTs filters was investigated as a function of Ni(II) ion concentration, pH, and filter mass. MWCNTs were synthesized by CVD method and modified using two complementary treatments, purification (using a mixture of hydrochloric acid and hydrogen peroxide) and functionalization (using nitric acid). The effect and mechanism of each treatment on the structural integrity of pristine MWCNTs has been studied. Morphology of the pristine and modified filters was investigated by Raman Spectrometry (RS), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), Fourier Transform Infrared (FTIR) spectrometry and Thermogravimetric analysis. It was found from Raman spec-tra that the ratio of the intensity of D-band to that of G-band decreased by purification process, and increased by functionalization process. The adsorption mechanism of Ni(II) onto the surface functional groups of modified MWCNTs was confirmed by FTIR spectrum. The filtration results showed that the removal efficiency of Ni(II) is strongly dependent on pH and could reach 85%at pH=8. Also, modified MWCNT filters can be reused through many cycles of regeneration with high performance. Functionalized MWCNTs filters may be a promising adsor-bent candidate for heavy metal removal from wastewater.     

Temperature hysteresis of AgI phase transition in AgI–chalcogenide glass nanolayered films

Using a method of laser ablation, a number of AgI–chalcogenide glass nanolayered films has been obtained with different thicknesses of the layers (10, 25, 50, and 100 nm). In order to study α ? β phase transition in AgI, X-ray phase analysis has been carried out in the temperature range from 30 to 200°C. A correlation between the layer thickness and the temperature of the α → β phase transition during the lowering of the temperature is found. An explanation of the correlation is proposed.     

Backward representation of Markov jump processes and related problems. I. Optimal linear estimation

Abstrat The Martingale representation for a class of special Markov jump processes in reverse time is derived and applied to study optimal linear filtering and smoothing of states of nonlinear observation systems. Original Russian Text ? A.V. Borisov, 2006, published in Avtomatika i Telemekhanika, 2006, No. 8, pp. 51–76. This work was supported in part by the Russian Foundation for Basic Research, project no. 05-01-00508a, and OITVS Project “Fundamental Algorithms for Information Technologies,” Russian Academy of Sciences, project no. 1.5. This paper was recommended for publication by A.I. Kibzun, a member of the Editorial Board     

Evidence for a central substructure in a Lumbricus terrestris hemoglobin obtained with STEM low-dose and digital processing techniques

Applications of scanning transmission electron microscope (STEM) low-dose and digital image processing techniques to the annelid extracellular hemoglobin of Lumbricus terrestris have shown the existence of a central substructure. The techniques involve low-dose STEM images of less than 2 e/A2 irradiation. Many such low-dose images were then aligned in their symmetry, N-fold averaged, and summed. The central substructure appears to be supported by spokes which are connected to a surrounding hexagonal bilayer of 12 subunits. In comparison to the summed image of Nephtys hombergii hemoglobin which is known to possess a central substructure, the morphology of both central mass and spokes were very similar. This finding of a central substructure is consistent with the report of a small angle X-ray scattering study (Pilz et al., 1980, Int. J. Biol. Macromol. 2, 279-283) which predicted the possible existence of substructure in the center of the molecule.     

The Conditionally Minimax Nonlinear Filtering Method and Modern Approaches to State Estimation in Nonlinear Stochastic Systems

We consider, in chronological order, the main results that have defined the concept of conditionally minimax nonlinear filtering. This would let us to follow all the evolution stages of this universal method, from a particular application, through basic mathematical concepts, to an advanced theory able to solve a wide class of robust estimation problems in linear and nonlinear stochastic systems.     

Optimal estimates for the operating parameters of an information web portal

We consider the problems of state estimation and Bayesian parameter identification for a stochastic model of an observation system that describes the evolution of one parameter of a web portal. Based on the thread pool control process analysis, we offer a mathematical model for the oscillations of the operating parameters for the portal’s information sources as a nonlinear stochastic observation system of a special kind. We obtain solutions of the optimal estimation problem and give numerical results.     

Abnormal action detection based on Markov models

The task of using Markov chains to develop a statistical behavioral model of a DS user to detect abnormal activity is described. In order to verify the assumption about the possibility of using this method in electronic health records, a program system was developed. The experiments with the system showed that the approach in question could be efficiently applied in abnormal action detection, for example, in data systems handling sensitive information.