Low‐Temperature Growth of SiO2 Films by Plasma‐Enhanced Atomic Layer Deposition

Silicon dioxide (SiO₂) films prepared by plasma‐enhanced atomic‐layer deposition were successfully grown at temperatures of 100 to 250 °C, showing self‐limiting characteristics. The growth rate decreases with an increasing deposition temperature. The relative dielectric constants of SiO₂ films are ranged from 4.5 to 7.7 with the decrease of growth temperature. A SiO₂ film grown at 250 °C exhibits a much lower leakage current than that grown at 100°C due to its high film density and the fact that it contains deeper electron traps.     

High performance AlyGa1−yAs-GaAs-lrxGa1−xAs quantum well lasers defined by silicon-oxygen impurity-induced layer disordering

In these experiments impurity-induced layer disordering (IILD) utilizing chemical reduction of SiO₂ by Al (from Al_0.8Ga_0.2As) is employed to generate Si and O to effect layer disordering. The SiO₂-Al_0.8Ga_0.2As reaction is studied with respect to annealing ambient. By controlling the extent of disordering via As₄ overpressure, closely spaced (∼1μm) Si-O IILD buried heterostructure lasers can be optically coupled or uncoupled. Direct observation of O incorporation into the buried layers is shown using secondary ion mass spectroscopy (SIMS). The thermal stability of separate-confinement Al_yGa_1−yAs-GaAs-In_xGa_1−xAs quantum well heterostructure (QWH) laser crystals is investigated using SIMS, transmission electron microscopy (TEM), and photoluminescence (PL) measurements. The data show that the thermal stability of a strained-layer In_0.1Ga_0.9As quantum well (QW) is strongly dependent upon: (1) the layer thickness and heterointerfaces of the Al_yGa_1−yAs-GaAs waveguide layers located directly above and below the QW, (2) the type of surface encapsulant employed, and (3) the annealing ambient. Narrow single-stripe (<2μm) lasers fabricated via Si-O diffusion and layer disordering exhibit low threshold currents (I_th ∼ 4 mA) and differential quantum efficiencies,η, of 22% per facet under continuous (cw) room-temperature operation.     

A Cross Layer Scheduling Framework for Supporting Bursty Data Applications in WCDMA Networks

In future wireless networks multimedia applications are expected to finally dominate the overall traffic volume. Shared channels are more suitable for the transmission of this type of traffic, as they are able to periodically adjust their transmission rate. In this paper, we introduce a cross-layer framework for WCDMA based networks which aims to make the packet scheduling procedure more efficient. In addition to that, we further propose a traffic scheduling scheme which serves the connections not only according to their delay sensitivity, but also according to the predicted state of their wireless channel. The efficiency of the proposed scheme, in terms of average packet delay and channel utilization is verified via simulations.     

Asymptotics for steady‐state voltage potentials in a bidimensional highly contrasted medium with thin layer

We study the behaviour of steady‐state voltage potentials in two kinds of bidimensional media composed of material of complex permittivity equal to 1 (respectively, α) surrounded by a thin membrane of thickness h and of complex permittivity α (respectively, 1). We provide in both cases a rigorous derivation of the asymptotic expansion of steady‐state voltage potentials at any order as h tends to zero, when Neumann boundary condition is imposed on the exterior boundary of the thin layer. Our complex parameter α is bounded but may be very small compared to 1, hence our results describe the asymptotics of steady‐state voltage potentials in all heterogeneous and highly heterogeneous media with thin layer. The asymptotic terms of the potential in the membrane are given explicitly in local coordinates in terms of the boundary data and of the curvature of the domain, while these of the inner potential are the solutions to the so‐called dielectric formulation with appropriate boundary conditions. The error estimates are given explicitly in terms of h and α with appropriate Sobolev norm of the boundary data. We show that the two situations described above lead to completely different asymptotic behaviours of the potentials. Copyright © 2007 John Wiley & Sons, Ltd.     

费用非对称通信网络上的群播路由算法

文中考虑了费用非对称通信网络上的群播路由问题,提出了一种接近最小成本的启发式算法--NEW-GM算法.该算法以FMPH(Fast Minimum Path Cost HouriStic)为基础,可以有效的降低成本.数值实验表明:这种算法是有效的,且所获得问题解的总费用几乎总是小于或等于由GTM算法所获得的解的总费用.NEW-GM算法的时间复杂度与GTM算法的相同,为O(p3n2).     

Effect of amino and polysiloxane groups on the chemical adsorption of polymers containing thiophosphate at the oil/metal interface under extreme pressure

Copolymers that separately contained thiophosphate–polysiloxane, thiophosphate–amino, and thiophosphate–polysiloxane–amino groups were synthesized and characterized. The performances of these synthesized copolymers on metal surfaces under a high load and rotary velocity were examined by the measurement of the oil temperature, frictional coefficient, and electrical contact resistance between two metal surfaces. The configuration of the adsorption layer was studied with energy‐dispersive spectrometry (EDS) and scanning electron microscopy (SEM). Copolymers that contained amino–thiophosphate groups reduced the frictional coefficient between two metal surfaces and markedly limit the increase in the oil temperature. Notably, a higher content of polysiloxane groups in the copolymer corresponded to an increased operating time to establish the adsorption layer on the metal surface. However, a higher content of amino groups reduced the time required for the layer to form. The adsorption layers that formed on the metal surfaces were investigated by EDS as phosphides produced by a chemical reaction of the thiophosphate‐containing copolymer with the metal surface. These adsorption layers on the metal surface were directly observed with SEM. The layer that formed on the metal surface of copolymers containing less polysiloxane and more amino groups was the thickest layer for all the synthesized copolymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1795–1803, 2002     

Ultrasonic cavitation at liquid/solid interface in a thin Ga–In liquid layer with free surface

Cavitation in thin layer of liquid metal has potential applications in chemical reaction, soldering, extraction, and therapeutic equipment. In this work, the cavitation characteristics and acoustic pressure of a thin liquid Ga–In alloy were studied by high speed photography, numerical simulation, and bubble dynamics calculation. A self-made ultrasonic system with a TC4 sonotrode, was operated at a frequency of 20 kHz and a max output power of 1000 W during the cavitation recording experiment. The pressure field characteristic inside the thin liquid layer and its influence on the intensity, types, dimensions, and life cycles of cavitation bubbles and on the cavitation evolution process against experimental parameters were systematically studied. The results showed that acoustic pressure inside the thin liquid layer presented alternating positive and negative characteristics within 1 acoustic period (T). Cavitation bubbles nucleated and grew during the negative-pressure stage and shrank and collapsed during the positive-pressure stage. A high bubble growth speed of 16.8 m/s was obtained and evidenced by bubble dynamics calculation. The maximum absolute pressure was obtained at the bottom of the thin liquid layer and resulted in the strongest cavitation. Cavitation was divided into violent and weak stages. The violent cavitation stage lasted several hundreds of acoustic periods and had higher bubble intensity than the weak cavitation stage. Cavitation cloud preferentially appeared during the violent cavitation stage and had a life of several acoustic periods. Tiny cavitation bubbles with life cycles shorter than 1 T dominated the cavitation field. High cavitation intensities were observed at high ultrasonication power and when Q235B alloy was used because such conditions lead to high amplitudes on the substrate and further high acoustic pressure inside the liquid.     

The BER analysis of OFDMA and SC‐FDMA under pilot‐assisted channel estimation and pilot jamming in rayleigh slow‐fading channel

In this paper, the authors derived the analytical bit error rate expressions for orthogonal frequency division multiple access and single‐carrier frequency‐division multiple access (SC‐FDMA) in Rayleigh slow‐fading channel for binary phase‐shift keying/quadrature phase‐shift keying/16‐quadrature amplitude modulations under pilot jamming and pilot symbol‐assisted channel estimation. Beginning with the bit error rate analysis from the general case of pilot symbol‐assisted channel estimation technique in Rayleigh slow‐fading channel, the expressions are first modified for different modulations and then further customized to account for the Zero‐Forcing equalization in frequency or time direction with application respectively to orthogonal frequency division multiple access or SC‐FDMA without and with pilot jamming. Piecewise‐linear interpolation is used for its simplicity. The simulation results match perfectly with the theoretical predictions except for some discrepancies with SC‐FDMA, which imply that the generalized equations developed here have to be further modified to account for system‐specific features like discrete Fourier transform precoding for SC‐FDMA. Copyright © 2016 John Wiley & Sons, Ltd.     

Context‐aware Android applications through transportation mode detection techniques

In this paper, we study the problem of how to detect the current transportation mode of the user from the smartphone sensors data, because this issue is considered crucial for the deployment of a multitude of mobility‐aware systems, ranging from trace collectors to health monitoring and urban sensing systems. Although some feasibility studies have been performed in the literature, most of the proposed systems rely on the utilization of the GPS and on computational expensive algorithms that do not take into account the limited resources of mobile phones. On the opposite, this paper focuses on the design and implementation of a feasible and efficient detection system that takes into account both the issues of accuracy of classification and of energy consumption. To this purpose, we propose the utilization of embedded sensor data (accelerometer/gyroscope) with a novel meta‐classifier based on a cascading technique, and we show that our combined approach can provide similar performance than a GPS‐based classifier, but introducing also the possibility to control the computational load based on requested confidence. We describe the implementation of the proposed system into an Android framework that can be leveraged by third‐part mobile applications to access context‐aware information in a transparent way. Copyright © 2016 John Wiley & Sons, Ltd.