Optimisation de la quantification vectorielle codée par treillis: application au codage des paramètres LSF

Speech coders operating at low bit rates necessitate efficient encoding of the linear predictive coding (Lpc) coefficients. Line spectral Frequencies (Lsf) parameters are currently one of the most efficient choices of transmission parameters for theLpc coefficients. In this paper, an optimized trellis coded vector quantization (Tcvq) scheme for encoding theLsf parameters is presented. When the selection of a proper distortion measure is the most important issue in the design and operation of the encoder, an appropriate weighted distance measure has been used during theTcvq construction process. We further applied the optimizedTcvq system for encoding theLsf parameters of the us Federal Standard (Fs1016) 4.8 kbps speech coder. At lower bit rates, objective and subjective evaluation results show that the incorporatedLsf tcvq encoder performs better than the 34 bits/frameLsf scalar quantizer used originally in the fs1016 coder. The subjective tests reveal also that the 27 bit/frame scheme produces equivalent perceptual quality to that when theLsf parameters are unquantized.     

An approach for detecting and preventing DDoS attacks in campus

Nowadays, Denial of Service (DoS) attacks have become a major security threat to networks and the Internet. Therefore, even a naive hacker can launch a large-scale DoS attack to the victim from providing Internet services. This article deals with the evaluation of the Snort IDS in terms of packet processing performance and detection. This work describes the aspect involved in building campus network security system and then evaluates the campus network security risks and threats, mainly analyses the attacks DoS and DDoS, and puts forward new approach for Snort campus network security solutions. The objective is to analyze the functional advantages of the solution, deployment and configuration of the open source based on Snort intrusion detection system. The evaluation metrics are defined using Snort namely comparison between basic rules with new ones, available bandwidth, CPU loading and memory usage.     

Electrical properties of Cu4ZnSnS2/ZnS heterojunction prepared by ultrasonic spray pyrolysis

Cu₂ZnSnS₄ (CZTS)/ZnS heterojunctions have been prepared by a successive deposition of ZnS and CZTS thin films by ultrasonic spray pyrolysis technique on glass substrates. The cupric chloride concentration has been varied in the starting solution in order to investigate its influence on device properties. CZTS/ZnS heterojunctions were characterized by recording their current-voltage characteristics at different temperatures. The obtained results exhibit a good rectifying behavior of the realized heterojunction. Analysis of these results yields saturation current, series resistance and ideality factor determination. From the activation energy of saturation current we inferred that the thermal emission through the barrier height is the dominant mechanism of the reverse current rather than the defects contribution.     

Codage conjoint source-canal des paramètres lsf du codeur FS1016: application de la quantification vectorielle par treillis optimisée pour un canal bruité

In this paper, we present an optimized trellis coded vector quantization (tcvq) coding system designed for the effective and robust coding of lsf spectral parameters at low bit rate. The aim of this system, called at the beginning « lsf-otcvq Encoder », is to achieve a low bit rate transparent quantization of lsf parameters of the us Federal Standard (fs1016) speech coder. Once the effectiveness of our lsf-otcvq encoders (with weighted distance) was proven in the case of ideal transmissions over noiseless channel, we were interested after in the improvement of their robustnesses for real transmissions over noisy channel. To implicitly protect the transmission indices of our lsf-otcvq coders incorporated in the Fsl016, we used a joint source-channel coding carried out by the channel optimized vector quantization (covq) method. In the case of transmissions over noisy channel, we will show that our new encoding system, called “covq-lsf-otcvq Encoder”, would be able to contribute significantly in the improvement of the fs1016 performances by ensuring a good coding robustness of its lsf spectral parameters.     

Thermal and mechanical behavior of Al-Si alloy cast using magnetic molding and lost foam processes

Magnetic molding technology is an original alternative process aimed at improving the metallurgical quality and dimensional tolerances of the final components that are currently produced using the lost foam process. The initial development of the magnetic molding process took place at the same time as the lost foam process, more than 30 years ago, but the magnetic moldin process has never achieved the same level of industrial development. The purposes of this study are to introduce the magnetic molding process and to define its advantages and characteristics. The comparative results obtained with both the lost foam and the magnetic molding processes for aluminum casting are given. The main factors involved in the magnetic molding process are also discussed.     

Conical filtering centrifuge for separation of solvent-diluted bitumen from oil sand mineral particles

The development of a continuous process for the separation of solvent-diluted bitumen from mineral particles is an important step for the development of solvent-based extraction technology of bitumen from mined oil sands. In this work, a custom-made conical filtering centrifuge is used to separate toluene-diluted bitumen from oil sand mineral particles. Compositions of wet granular samples are analyzed before and after centrifugation for three different oil sand ores. Results suggest that conical filtering centrifuges could be used for continuous separation of solvent-diluted bitumen from oil sand ores with relatively coarse particles.     

Phase behaviour and phase separation kinetics measurement using acoustic arrays

Speed of sound and acoustic wave attenuation are sensitive to fluid phase composition and to the presence of liquid-liquid interfaces. In this work, the use of an acoustic array comprising 64 elements as a non-intrusive sensor for liquid-liquid interface, phase separation kinetics measurement in bulk fluids, and local composition measurement in porous media is illustrated. Three benchmark examples: the phase behaviour of methanol + mixed hexanes and methanol + heptane mixtures at 25.0 °C and 1 bar, and Athabasca bitumen + heptane in a synthetic silica porous medium at 22.5 °C and 1 bar, illustrate the accuracy of liquid-liquid interface and potential research and industrial applications of the technique. Liquid-liquid interfaces can be detected independently using both speed of sound and acoustic wave attenuation measurements. The precision of the interface location measurement is 300 μm. As complete scans can be performed at a rate of 1 Hz, phase separation kinetics and diffusion of liquids within porous media are readily tracked. The technique is expected to find application where the fluids or porous media are opaque to visible light and where other imaging techniques are not readily applied, or are too costly. A current limitation is that the acoustic probes must be cooled to less than 315 K in order for them to operate.     

Parallel QRD-M encoder for multi-user MIMO systems

In the context of multi-user precoding, the idea behind vector perturbation (VP) lies in adding an integer vector to the data vector such that the overall transmit power is reduced, where the performance at the users end is consequently improved. In the literature, several techniques have been proposed to find a quasi-optimum perturbing vector, where this process was represented as an integer lattice search problem. In this paper, we propose a parallel QRD-M encoder (PQRDME) that, besides attaining a quasi-optimum diversity order, leads to tremendous reduction in the latency of the vector perturbation stage. Based on the set grouping, the proposed encoder transforms the full tree-search of the conventional QRDME into partial trees that can be pipelined to increase the encoding throughput. We evaluate the proposed algorithm under several scenarios with both perfect channel state information (PCSI) and imperfect CSI (ICSI) at the transmitter side, where simulation results show robust performance when compared to the optimum encoder.