Non-audio–Video Gesture Recognition Systems

Wireless Personal Communications - Gesture recognition as a topic in computer science and language technology has the goal of interpreting human gestures via mathematical algorithms. Gestures can...     

Robust Control of Permanent Magnet Synchronous Machine Based on Passivity Theory

This paper presents a robust control strategy for a Permanent Magnet Synchronous Machine (PMSM) based on passivity theory. Pre‐control terms ensure robustness to variation of parameters. The nominal electrical and mechanical dynamics are treated separately and a cascade structure is obtained. A comparative analysis is done in Matlab‐Simulink with a Simple Adaptive Control (SAC) strategy in terms of settling time, stationary error, time response and energy efficiency. Improvements of the proposed Passivity Based Control (PBC) strategy are shown in comparison with some other PBC controllers.     

Improved Physico-chemical Properties of Mesoporous Carbon by Functionalization with Aminopropyl-polydimethylsiloxane (AP-PDMS)

The present research reports on the synthesis and properties of mesoporous carbon (MC) surface with functionalized aminopropyl-polydimethylsiloxane (AP-PDMS). The aim of MC surface modification was focused on the improvement of its electrical properties (EC electric conductivity), as well as its sorption capacity for cesium ions. In order to anchor AP-PDMS molecules, an intermediate functionalization step of the MC surface with carboxylic groups was carried out. In this respect, two different methods, namely: (i) sonication in the presence of the hydrogen peroxide (MC-COOH) and (ii) gas-plasma activation (MCA) have been considered for carbon surface oxidation. Further, AP-PDMS component was crosslinked to the COOH-reached carbon surface. Fourier transform infrared spectroscopy (FT-IR) and energy dispersion spectroscopy (EDX) were used to confirm the presence of AP-PDMS molecules on MC surface. Morphological and textural properties of the obtained composites have been investigated by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen adsorption–desorption measurements, as well as their electrical properties (EC). The obtained results reveal the grafting of silane-containing component onto MC surface, an improved electrical conductivity of the synthesized composites toward MC sample. Also, the functionalization proved to be efficient in the sorption process of the cesium ions from aqueous solutions, despite the fact that the materials surface became hydrophobic.     

Access to RF White Spaces in Romania: Present and Future

As the demand for frequency resources increases because of the great number of new wireless technologies, the frequency spectrum becomes overcrowded and solutions have to be found in order to solve this problem. One possible solution would be to take advantage of the so called white spaces (WS), frequency bands that are actually not used by the primary (licensed) radio communication systems, by using a dynamic spectrum access (DSA) approach. In order to take advantage of these spaces, secondary (unlicensed) users have to perform a spectrum sensing process in order to accurately detect the presence of a primary system and avoid unwanted interference with it. This paper provides an overview of the status of WS in Romania by analysing the current regulations and the analogue switch-off that is planned to take place in the near future (2015). The current state of the art regarding several standards that incorporate DSA elements is being made, emphasizing the high interest in using this WS in upcoming communication systems. In order to prove the low degree in which the RF spectrum is currently used, the results of a measurement campaign performed in both urban and rural locations of Romania are discussed. A comparison with the results of other similar measurement campaigns conducted in several locations worldwide is performed as well. Several frequency bands are identified as possible WS for future opportunistic use.     

Sensor deployment in wireless sensor networks with linear topology using virtual node concept

Wireless Networks - In a multi-hop wireless sensor network with a convergecast communication model, there is a high traffic accumulation in the neighborhood of the sink. This area constitutes the...     

TIME-DEPENDENT INTERACTION BETWEEN WATER AT SUPERCRITICAL PRESSURES AND A HOT SURFACE

This article presents a numerical study of the thermal and fluid flow interaction driven by the sudden contact between saturated liquid water (373 K) and a hot (2300 K) spherical or plane surface. It is shown that under these conditions the sudden contact is characterized initially by single-phase interfacial water and supercritical pressure that decays in time as the water is accelerated away from the interface. The sudden contact generates (high) temperature, pressure, and density waves that propagate away from the surface. The water is modeled as an inviscid single-phase fluid that behaves either as an ideal gas or a real gas with properties taken from steam tables. The ideal-gas results are in good qualitative and quantitative (within a factor of order 1) agreement with the results based on the real-gas model. When the hot object is large (radius ≥ 10 mm), the results are insensitive to the geometry of the model (i.e., spherical versus plane).     

The development of spatial structure in an ionic chemical system induced by applied electric fields

The spatio-temporal structures that can arise in an ionic chemical system with a cubic autocatalytic reaction step (Gray-Scott kinetics) in the presence of an applied electric field are described. A linear stability analysis of the resulting reaction-diffusion-advection system, with different diffusion coefficients and consequently different electrochemical migration rates for the reacting species, suggests the possibility of both convective structures ('DIFICI') and Turing patterns (as well as interaction between them). The detailed linear analysis determines the domain of existence of these features in parameter space, the predictions from which are confirmed by extensive numerical simulations. These reveal that a wide variety of propagating structures can be sustained by the system, depending on the electric field strength and whether the ratio of diffusion coefficients of autocatalyst and substrate is above or below the critical values for Turing bifurcations.     

Forced convective structures in a differential-flow reactor

A model of an autocatalytic reaction in a differential-flow reactor is considered in which the reactant is immobilized and the autocatalyst allowed to flow (with uniform velocity) and to diffuse. Consideration is given to the influence that a periodic external signal (fluctuations in the inflow concentration of the autocatalyst) can have upon the convective structures which exist in this model. It is shown that, depending on the frequency of the signal, there are two parameter regions giving distinct spatio-temporal responses. There is a region of high excitation waves (convected forced waves) which appear for a finite range of frequencies. Outside this range there are two domains of natural response waves. Close to the boundary of these regions there are irregular responses suggestive of an excitable system: packets of travelling waves of complex form develop which appear at non-regular intervals surrounded by small amplitude periodic waves.     

Phase-transitions in GeSb induced by customized ultrafast optical pulses

The use of ultrafast laser pulses to initiate solid-state phase-transitions in certain materials has shown promise in achieving sub-nanosecond phase changes with different optical properties. These phase changes have been well studied using pulse durations between femtoseconds and nanoseconds to determine the dynamics for the reversible phase changes on multiple time scales. In this study femtosecond pulse shaping techniques, driven by evolutionary algorithms, were used to obtain optimized temporally shaped ultrashort laser pulses to induce and control permanent phase changes in GeSb thin-films. Through monitoring the pulse effects it has been determined that the crystalline-to-amorphous phase transition is minimized using optical pulses with pulse widths less than the electron-phonon coupling time. It is maximized by using pulses longer than the time required for energy transfer from the excited carriers to the lattice.