Thermal behaviour of 6H-SiC bipolar transistors: spice simulation and applications

As material quality improves and growth technology develops, SiC BJTs are regaining interest. They have the advantage of carrier modulation, high current capabilities and lower initial voltage drop. In this work, the thermal behaviour of 6H-SiC bipolar transistors is simulated. The examined figures of merit such as input resistance h₁₁, current gain β and transconductance g_m show superior performance of 6H-SiC BJTs, at high temperatures, when compared to similar silicon counterparts. In the range of temperatures −20 to 160 °C, drawbacks found in Si BJTs are attenuated or eliminated with the use of SiC BJTs. These advantages are transferred to 6H-SiC based circuits. The built current mirror shows quasi-ideal behaviour while the designed input stage of the amplifier has a voltage gain thermally stabilised up to 140 °C.     

Characterization of nonspecific crossover in split-flow thin channel fractionation

Split-flow thin channel (SPLITT) fractionation is a technique for continuous separation of particles or macromolecules in a fluid stream into fractions according to the lateral migration induced by application of a field perpendicular to the direction of flow. Typical applications have involved isolation of different fractions from a polydisperse sample. Some specialized applications involve the separation of the fraction influenced by the transverse field from the fraction that is not. For example, immunomagnetically labeled biological cells may be separated from nonlabeled cells with the application of a transverse magnetic field gradient. In such cases, it may be critically important to minimize contamination of the labeled cells with nonlabeled cells while at the same time maximizing the throughput. Such contamination is known as nonspecific crossover (NSC) and refers to the real or apparent migration of nonmobile particles or cells across stream lines with the mobile material. The possible mechanisms for NSC are discussed, and experimental results interpreted in terms of shear-induced diffusion (SID) caused by viscous interactions between particles in a sheared flow. It is concluded that SID may contribute to NSC, but that further experiments and mathematical modeling are necessary to more fully explore the phenomenon.     

Multicellular Alamouti scheme performance in Rayleigh and shadow fading

In this paper, we study the performance of two downlink multicellular systems: a multiple inputs single output (MISO) system using the Alamouti code and a multiple inputs multiple outputs (MIMO) system using the Alamouti code at the transmitter side and a maximum ratio combining (MRC) as a receiver, in terms of outage probability. The channel model includes path-loss, shadowing, and fast fading, and the system is considered interference-limited. Two cases are distinguished: constant shadowing and log-normally distributed shadowing. In the first case, closed form expressions of the outage probability are proposed. For a log-normally distributed shadowing, we derive easily computable expressions of the outage probability. The proposed expressions allow for fast and simple performance evaluation for the two multicellular wireless systems: MISO Alamouti and MIMO Alamouti with MRC receiver. We use a fluid model approach to provide simpler outage probability expressions depending only on the distance between the considered user and its serving base station.     

Fast and automatic city-scale environment modelling using hard and/or weak constrained bundle adjustments

To provide high-quality augmented reality service in a car navigation system, accurate 6 degrees of freedom (DoF) localization is required. To ensure such accuracy, most current vision-based solutions rely on an off-line large-scale modelling of the environment. Nevertheless, while existing solutions to model the environment require expensive equipments and/or a prohibitive computation time, we propose in this paper a complete framework that automatically builds an accurate large-scale database of landmarks using only a standard camera, a low-cost global positioning system (GPS) and a geographic information system (GIS). As illustrated in the experiments, only few minutes are required to model large-scale environments. The resulting databases can then be used by an on-line localization algorithm to ensure high-quality augmented reality experiences.     

The Design of a Generic Intrusion-Tolerant Architecture for Web Servers

Nowadays, more and more information systems are connected to the Internet and offer Web interfaces to the general public or to a restricted set of users. Such openness makes them likely targets for intruders, and conventional protection techniques have been shown insufficient to prevent all intrusions in such open systems. This paper proposes a generic architecture to implement intrusion-tolerant Web servers. This architecture is based on redundancy and diversification principles, in order to increase the system resilience to attacks: usually, an attack targets a particular software, running on a particular platform, and fails on others. The architecture is composed of redundant proxies that mediate client requests to a redundant bank of diversified COTSfootnote{Commercial Off The Shelf.} application servers. The redundancy is deployed here to increase system availability and integrity. To improve performance, adaptive redundancy is applied: the redundancy level is selected according to the current alert level. The architecture can be used for static servers, i.e., for Web distribution of stable information (updated off-line), as well as for fully dynamic systems where information updates are executed immediately on an on-line database. The feasibility of this architecture has been demonstrated by implementing an example of a travel agency Web server.     

Exergetic analysis of an absorption/compression refrigeration unit based on R124/DMAC mixture for solar cooling

This work presents an energetic and exergetic analysis of an upgraded frigorific production unit, operating with a novel organic mixture: DMAC/R124 (N, N′-dimethylacetamide/2-chloro-1,1,1,2-tetrafluoroethane). Investigated parameters are the COP (performance coefficient), the irreversibility and the exergetic efficiency. Performances of the proposed mixture system are compared with those relative to the classical water/ammonia system. Results show that the COP obtained with the new fluids is similar to that relative to the old one, it is about 64% for a compression ratio about 2, while the same optimum value is achieved with a compression ratio about 3.3 when working with ammonia/water. Furthermore, the system using the new proposed couple uses lower threshold temperatures, between 60 °C and 80 °C as optimum COP, which allows the use of low temperature energy sources.Results of the exergetic analysis indicate that irreversibility of the R124/DMAC system is lower than that of the ammonia/water system by about 5 kW and so is the exergetic efficiency. It is noted from this study that the major gain brought by this new couple is the diminution of the operating temperatures of this type of heat pumps from temperatures going to 120 °C–80 °C and even 60 °C. We retain the advantages of introducing this organic absorbent (DMAC) in the refrigeration production field.     

Reducing the sulfur-dioxide binding power of sweet white wines by solid-phase extraction

The high sulfur-dioxide binding power of sweet white wines may be reduced by extracting the naturally present carbonyl compounds from wine that are responsible for carbonyl bisulphites formation. The carbonyl compounds mainly responsible for trapping SO₂ are acetaldehyde, pyruvic acid, and 2-oxoglutaric acid. The method employed was selective solid phase extraction, using phenylsulfonylhydrazine as a scavenging agent. The scavenging function was grafted onto a support prepared from raw materials derived from lignin. This approach is more acceptable to winemakers than the polymer media previously reported, as it reduces the possible contamination of wine to molecules already present in the wine making process.     

Optimal Prediction with Conditionally Heteroskedastic Factor Analysed Hidden Markov Models

The deficiencies of stationary models applied to financial time series are well documented. A special form of non-stationarity, where the underlying generator switches between (approximately) stationary regimes, seems particularly appropriate for financial markets. We use a dynamic switching (modelled by a hidden Markov model) combined with a linear conditionally heteroskedastic latent factor model in a hybrid conditionally heteroskedastic factor analysed hidden Markov model (CHFAHMM) and discuss the practical details of training such models with a new approximated version of the Viterbi algorithm in conjunction with the expectation-maximization algorithm to iteratively estimate the model parameters in a maximum-likelihood sense. The performance of the CHFAHMM is evaluated on both simulated and financial data sets. On the basis of out-of-sample forecast encompassing tests as well as other measures for forecasting accuracy, our results indicate that the use of this new method yields overall better forecasts than those generated by competing models.     

Design and implementation of a 6-GHz array of four differential VCOs coupled through a resistive network

This paper presents the design and the implementation of a fully monolithic coupled-oscillator array, operating at 6 GHz with close to zero coupling phase, in 0.25 μm BICMOS silicon germanium process. This array is made of four LC-NMOS differential VCOs coupled through a resistor. The single LC-NMOS VCO structure is designed and optimized in terms of phase noise with a graphical optimization approach while satisfying design constraints. At 2.5 V power supply voltage, and a power dissipation of only 125 mW, the coupled oscillators array features a simulated phase noise of ?127.3 dBc/Hz at 1 MHz frequency offset from a 6 GHz carrier, giving a simulated phase progression that was continuously variable over the range ?64° < Δ? < 64° and ?116° < Δ? < 116°. This constant phase progression can be established by slightly detuning the peripheral array elements, while maintaining mutual synchronization.