Network Control in ATM-Based LEO Satellite Networks

Low Earth Orbiting (LEO) satellite networks with on-board asynchronous transfer mode (ATM) switches hold the promise of offering an economically viable extension of terrestrial ATM systems by providing connectivity to areas where existing terrestrial networks are either infeasible or impractical. Network management in ATM LEO satellite networks is typically performed by the Network Control Center (NCC). The main contribution of this paper is to propose a network management system configuration with a stand-by solution and to describe an experimental Satellite Management Information Base (SMIB) that we have developed for implementation in ATM LEO satellite networks.     

Assessment of mitigation options for the energy system in Bulgaria

The Bulgarian greenhouse gas (GHG) emission profile reveals the energy sector as the most significant emission source and also as an area where great potential for GHG emissions reduction exists. Mitigation options in energy supply were selected considering the potential of fossil fuel substitution and new energy technology implementation in the context of the existing structure of energy system and projects for mid- and long-term development. Basically three modules of ENPEP were used: BALANCE — to calculate the energy flows and energy cost from primary fuel resources and fuel import to energy end-use, IMPACT — to calculate GHG emissions, and ELECTRIC — to project the electric system long-term development. Different mitigation measures combined in four scenarios were developed. The integrated mitigation scenario incorporated a mix of mitigation measures in the energy demand and supply. Implementation of CO₂ mitigation measures both in energy demand and energy supply would reduce the 2020 emission level by 34.3 Tg (29.1%), and by 544.2 Tg (21.7%) for the entire study period 2000 – 2020, compared to the baseline scenario.     

Validation of an EEG-derived spectral frequency index (SFx) for continuous monitoring of sleep depth in humans

Sleep in humans is classically assessed by recording a multichannel electroencephalogram (EEG) in connection with an electrooculogram (EOG) and an electromyogram (EMG). In general, human sleep is manually staged into 6 categories (from awake through REM sleep to stage 4 reflecting deep sleep) on the basis of a visual inspection of EEG periods (epochs) of 20 - 30 s duration. This cumbersome methodology is still used in practice and for reference purposes. - The conversion of EEG-signals by means of Fast Fourier Transformation provides objective and reproducible information reflecting specific communicative features of the central nervous system. A special part of this information based on a specific algorithm is defined by the so-called spectral frequency index (SFx). This SFx-algorithm contains relationships among some particular EEG frequencies and provides objective percentage values about the state of consciousness of a person. In order to validate this new SFx-method, sleep as a physiological state of continuous alterations of consciousness and vigilance was chosen. A total of 36 nights of sleep from 18 healthy volunteers were staged manually by a scientist unaware of the protocol. The volunteers received either placebo or lormetazepam prior to commencement of the nocturnal recordings. The manually staged data were compared with the data obtained by the SFx-analysis. Both data sets SFx values and manually staged data were made comparable by averaging their values to a basic period length of 2 min duration giving 7960 pairs of data. The SFx data for sleep were found within a range from 35% to 100%. The SFx-medians of the manually staged data from "awake" to stage 4 were found in a decending order ("awake": 83% (lower and upper quartile 78% / 87%);"REM": 68% (63%/74%),"stage 1" :63% (57%/70%),"stage 2" :51% (47%/57%), "stage 3" :44% (42%/46%) and "stage 4" :42% (40%/44%). The rank correlation coefficient between the data pairs was calculated to be 0.79 indicating a substantial matching between the manually staged score and the SFx. We therefore conclude that the SFx is a suitable and objective indicator of sleep depth in humans.     

Antiviral activity of cholesteryl esters of cinnamic acid derivatives

Cholesteryl 3",4"-dimethoxycinnamate (7) and a new synthesized o-coumaroyl ester of 3 beta-(2'-hydroxyethoxy)-cholest-5-en (13) exhibited a marked activity against poliovirus type 1 (Mahoney). Compound 7 showed an approximately 20-fold greater selectivity in its antiviral activity than compound 13. These compounds were selected from thirteen steryl esters of cinnamic acid derivatives through an in vitro antiviral screening against viruses belonging to taxonomic groups with causative agents of important human infectious diseases to which chemotherapy is indicated, i.e. Picornaviridae, Orthomyxoviridae, Paramyxoviridae and Herpesviridae.     

Atomic force microscopy study of TiO2 sol–gel films thermally treated under NH3 atmosphere

Multilayered TiO₂ films were obtained by sol–gel and dipping deposition on quartz substrate followed by thermal treatment under NH₃ atmosphere. In an attempt to understand the close relationship between microstructural characteristics and the synthesis parameters, a systematic research of the structure and the morphology of NH₃ modified TiO₂ sol–gel films by XRD and Atomic Force Microscopy is reported. The surface morphology has been evaluated in terms of grains size, fractal dimension and surface roughness. For each surface, it was found a self-similar behavior (with mean fractal dimension in the range of 2.67–3.00) related to an optimum morphology favorable to maintain a nano-size distribution of the grains. The root mean square (RMS) roughness of the samples was found to be in the range of 0.72–6.02 nm.     

Hydrogen sorption properties of ball-milled Mg–C nanocomposites

MgH₂ 75 at.%–C 25 at.% composites are synthesized by ball milling using different kinds of carbon additives: carbon black (CB), nanodiamonds (ND) and amorphous carbon soot (AC). X-ray diffraction analysis showed that the MgH₂ phase in the as-obtained composite powders is nanocrystalline (80–100 nm). The SEM observations revealed that the samples consist of 5–15 μm MgH₂ particles, surrounded and in some cases coated by carbon flakes. The composite containing nanodiamonds revealed strong decrease of the MgH₂ decomposition temperature with more than 100 °C, compared to ball-milled pure MgH₂. Important issue of the present study is also the low temperature hydriding of the ball-milled Mg–C nanocomposites, investigated by high-pressure DSC. The process starts at about 200 °C for all materials studied, but the hydriding mechanism looks different for the composites with different kinds of carbon additives. Whereas for Mg–carbon black it takes place in a relatively narrow temperature range, expressed by a single exothermic peak (200–300 °C) for the other two composites the hydriding is a multi-step process, featured by two overlapped exothermic peaks for Mg-nanodiamonds and by two well separated exothermic effects (at about 300 °C and 400 °C) for Mg-amorphous carbon soot. The observed difference in the hydriding behavior of the Mg–C composites is attributed to the different kind of carbon component, which is supposed to play a catalytic role as well as protects magnesium from oxidation. The incorporation of carbon into the MgH₂ particles results in the formation of high density of defects (dislocations and grain boundaries), which is supposed to be among the most possible reasons for the decreased hydride decomposition temperature. The Mg–C nanocomposites show reproducible hydriding/dehydriding behavior (thermodynamics and kinetics) during multiple cycling. Among the composites in the present study “Mg–carbon black” reveals the best hydriding characteristics – low temperature of hydriding in a relatively narrow temperature range by a single-step reaction and relatively fast hydriding kinetics.     

Relationship between the strain constant and viscosity of glasses above the glass transition temperature

The relationship between the strain constant and viscosity of glasses above the glass transition temperature is established. The process variables of soft glass molding and pressing operations should be calculated using this constant.     

Molecular weight characteristics of 2-naphthyl methacrylate copolymers obtained by radical polymerization in different solvents

Summary The influence of the chemical nature of the polymerization medium on the molecular weight characteristics of the copolymers 2-naphthyl methacrylate/styrene and 2-naphthyl methacrylate/acrylonitrile was investigated by gel permeation chromatography. The results obtained show that the influence of the nature of the solvent used on the molecular weight characteristics could be attributed to the different chain transfer constants. The contribution of the monomer complexes which affects mainly the relative reactivity ratios of the comonomers may be neglected.Dedicated to Professor Ivan M. Panayotov to his 60. birthday with the best wishes