Synthesis and Characterization of Some Nonionic Bolaamphiphiles

A series of nonionic bolaamphiphiles were synthesized from the reaction of fluoroalkylene (dimercaptoacetates) with maleate crown ethers. Surface activity of the new surfactants was evaluated on the basis of surface tension measurements. The new fluorinated bolamphiphiles exhibit a remarkable lowering of surface tension in comparison with nonfluorinated analogues.     

Numerical study of elliptical cracks in cylinders with a thickness transition

The paper deals with elliptical cracks in a cylinder with a thickness transition. This structure is an assembly of two cylinders of thickness t and t₂ (t<t₂). In the transition zone, the thickness varies linearly. The purpose is to check whether tabulated data used for SIF calculations in a cylinder of uniform thickness t can be used for the cylinder with a thickness transition. A comparative study is made on the effect of a crack in a cylinder with a thickness transition and in a uniform thickness cylinder. Loads considered are pure tensile stress and bending moment. A numerical analysis was performed considering elastic behaviour at the crack tip. A crack mesh was designed and validated for 3D models. The results show that SIF calculations in the transition assuming a uniform thickness cylinder are conservative but not precise. The comparative study shows that the cylinder with a thickness transition is more vulnerable to a defect.     

Numerical analysis of the behaviour of mechanically stabilized earth walls reinforced with different types of strips

A mechanically stabilized earth (MSE) wall behaves as a flexible coherent block able to sustain significant loading and deformation due to the interaction between the backfill material and the reinforcement elements. The internal behaviour of a reinforced soil mass depends on a number of factors, including the soil, the reinforcement and the soil/structure interaction and represents a complex interaction sol/structure problem. The use of parameters determined from experimental studies should allow more accurate modelling of the behaviour of the MSE structures.In this article, a reference MSE wall is modelled from two points of view: serviceability limit state “SLS” and ultimate limit state “ULS”. The construction of the wall is simulated in several stages and the soil/interface parameters are back analysed from pullout tests. An extensive parametric study is set up and permits to highlight the influence of the soil, the reinforcement and the soil/structure parameters. The behaviour of MSE walls with several geosynthetic straps is compared with the metallic one. Several constitutive models with an increasing complexity have been used and compared.The results obtained from stress-deformation analyses are presented and compared. The use of geosynthetic straps induces more deformation of the wall but a higher safety factor. To design theses walls the important parameters are: the soil friction, the cohesion, the interface shear stiffness and the strip elastic modulus.It is shown that for wall construction that involves static loading conditions, the modified Duncan-Chang model is a good compromise but induces slightly lower strip tensile forces due to the fact that it do not take into account of dilatancy before failure.     

Using microchannels to cool microprocessors: a transmission-line-matrix study

As microprocessors components density and clock frequency increase, so do heat dissipation. The heat results from Joule effect due to leakage currents in the components area or active region. This region is only few microns thick and can quickly reach destructing temperatures if heat is not quickly removed. On this critical issue depends the system reliability. The active region is separated from the ventilated heat sink by a silicon substrate and a metal integrated heat spreader, both hundreds of microns thick. This interface region is the microprocessor's heat transfer plate where heat exchange is achieved by conduction. Because of the localized heat source, the thermal spreading resistance of the interface region can be high. A novel way of spreading heat in that region is the use of microchannel arrays where an appropriate thermal compound or a phase change liquid can be trapped to increase heat transfer by conduction or to create micro-heat-pipes. Traditional cooling methods, with conventional and well optimised heat sinks, can then be used with less burden.In this paper, the Transmission-Line-Matrix (TLM) technique is used to simulate the effect of microchannels on the temperature distribution in the active region. To minimize the interface heat resistance various microchannel and patterns are examined. In this part of the work, the microchannels are filled with the heat spreader material copper or aluminium. The results show an improved thermal transient behaviour and a reduced active region temperature in steady state.     

Transition metal-isolant dans l'oxyde V6O11: Etude structurale,magnetique et calorimetrique

Structural, magnetic and thermal properties have been carried out on V₆O₁₁ mixed valence oxide. It has been shown that the metal-insulator transition which occurs at 163 K is associated to a crystallographic modification. On the basis of the already known low temperature structure of V₄O₇ a scheme is proposed in order to describe the M-I transition. It involves both electron localization and pair formation, and agrees well with the magnetic susceptibility data in the paramagnetic region.     

Thermal behavior Spice study of 6H-SiC NMOS transistors

Silicon carbide is a material that is undergoing major advances associated with a broad scope in the field of electronics. The main properties of silicon carbide such as its high thermal conductivity and high band gap make it a material suitable for use in high-temperature and high-power applications. In this Spice study, the thermal behavior of 6H-SiC NMOS transistors is analyzed through their conductance and transconductance changes with temperature in the range −200 to 700 °C. The performances in two basic applications, current mirrors and differential amplifiers, are compared to similar circuits with silicon transistors. The results show that the 6H-SiC NMOS transistors can be used up to 700 °C, while those based on silicon transistors are limited to around 160 °C.     

Benchmarking of lightweight cryptographic algorithms for wireless IoT networks

Wireless Networks - Cryptographic algorithms that can provide both encryption and authentication are increasingly required in modern security architectures and protocols (e.g. TLS v1.3). Many...     

A Novel Speech Enhancement Method Using Fourier Series Decomposition and Spectral Subtraction for Robust Speaker Identification

Wireless Personal Communications - This paper presents a novel speech enhancement approach by combining Fourier series expansion and spectral subtraction. This approach is implemented in speaker...