High dynamic range streak camera for subpicosecond time-resolved x-ray spectroscopy

The full characterization of a time resolved x-ray spectrometer is presented. It is based on the coupling of a conical crystal with a subpicosecond x-ray streak camera. The detector is designed to operate in accumulation mode at high repetition rate (up to 1 kHz) allowing signal to noise ratio as high as 10(4):1. Optical switches have been used to limit the jitter induced in the subpicosecond range, demonstrating the very long term stability (a few hours) of the entire device. The data analysis have been developed to get the spectral and temporal resolution of an ultrashort laser-plasma-based x-ray source.     

(4R)-5,6,7,9-四-O-乙酰基-4,8-脱水-4-氯-2,3-二脱氧-D-葡糖壬腈的合成

以乙酰基保护的葡萄糖为原料 ,经氯化 ,溴化反应 ,再与丙烯腈在中压汞灯( 4 50 W)下发生自由基反应 ,高选择性地合成了 ( 4 R) - 5,6,7,9-四 - O-乙酰基 - 4,8-脱水 - 4-氯 - 2 ,3-二脱氧 - D-葡糖壬腈。     

Occurrence of sessile Pseudomonas oryzihabitans from a karstified chalk aquifer

Pseudomonas oryzihabitans is an uncommon pathogen that may cause opportunistic infections. Although it has been previously isolated from the environment, the source of human infection has not been well documented. In this study, we describe the presence of P. oryzihabitans adhering on suspended particulate matters recovered from karst groundwaters. The isolated pathogen was capable of forming biofilms on silicon supports and clay beads. Adherent P. oryzihabitans cells displayed a high resistance to chlorine as compared with the same organisms cultured in the planktonic mode. These results demonstrate that aquifer biofilms are potential environmental sources for water-born P. oryzihabitans infections and that bacterial attachment might affect drinking water purification.     

Oxford ion-trap quantum computing project

We describe recent progress in the development of an ion-trap quantum information processor. We discuss the choice of ion species and describe recent experiments on read-out for a ground-state qubit and photoionization trap loading.     

3rdgeneration mobile systems umts/imt-2000

When International Telecommunication Union (itu) identified in 1992 new frequency bands for third generation mobile systems, few people were really convinced that there was a need for such systems because the first second generation systems (like gsm in Europe) were recently launched and nobody could imagine at that time that 8 years later penetrations rates for voice will exceed 50% in several countries. The development of multimedia services in fixed networks was the key factor to trigger standardisation activities in different organisations (ITU, etsi ) involved in mobile systems. But rapidly, the globalisation of this activity led to the birth of different standardisation forums with the objective to develop specifications for multimedia mobile systems called imt 2000 (International Mobile Telecommunication 2000). One of this system is UMTS (Universal Mobile Telecommunication System) which is supported by different Japanese and European companies; the first commercial launch of such a network is foreseen in October 2001 in Japan and at the beginning of 2002 in Europe, umts will offer higher data rates (up to 384 kbit/s in a first phase) and better spectral efficiency than existing mobile systems;     

The impact of etched trenches geometry and dielectric material on the electrical behaviour of silicon-on-insulator self-switching diodes

Hole electrical transport in a p-doped nanochannel defined between two L-shape etched trenches made on a silicon-on-insulator substrate is investigated using a TCAD-Medici simulator. We study the impact of the etched trenches' geometry and dielectric filling materials on the current-voltage characteristics of the device. Carrier accumulation on frontiers defined by the trenches causes a modulation of the hole density inside the conduction channel as the bias voltage varies and this gives rise to a diode-like characteristic. For a 1.2?μm-long channel, plots of the electric field distribution show that a nonlinear transport regime is reached at a moderate reverse and forward bias of ± 2?V. Plots of the carrier velocity along the conduction channel show that holes remain hot for a few hundreds of nm outside the nanometre-wide channel, at a bias of ± 10?V. Filling the etched trenches with a high-κ dielectric material gives rise to a lower threshold voltage, V(th). A similar decrease of V(th) is also achieved by reducing the longitudinal and/or the transverse trench width. Our simulation results provide useful design guidelines for future integrated self-switching-diode-based circuits.     

An evaluation of the role of particle size in the flotation of coal using different cell technologies

A large variety of new flotation cells has been introduced in the last few years, probably as a result of the successful introduction of column flotation in the minerals processing industry. In common with the column cell, a number of these new cells employ an essentially quiescent separation zone. However, a number of novel cell designs have been introduced that use agitation mechanisms similar to those employed on conventional flotation cells. The aim of this investigation was to evaluate flotation behaviour in both an agitated and non-agitated environment, particularly with respect to particle size. A hybrid ‘agitated’ column cell was designed for the investigation, and the operation of this unit was compared to that of a column cell, and to a batch flotation cell, on a laboratory scale. The testwork was conducted on coal fines, as problems with the flotation of coarse coal particles in a column cell had previously been identified. It was demonstrated that the addition of an agitated stage to a column cell can significantly improve the coarse particle recovery in comparison to the conventional column cell, while maintaining good selectivity in the fine sizes.     

The conducting behavior and stability of conducting polymer composites

Results of measurements of the electrical conductivity of low density polyethylene/polypyrrole and polystyrene/polypyrrole composites are reported. It is observed that the electrical conductivity of the composite vs. concentration follows the power law predicted by the percolation theory. The manufacturing process influences the homogeneity of the composite at microscopic scale and thus the percolation threshold. Annealing studies show that the stability of the electrical conductivity of the composite is related to the thermal expansion of the polymers and the relaxation of the polymer chains. The decrease of the electrical conductivity of the composite is attributed to the interruption of the percolation path.     

STUDY OF THE AIR FLOW IN A WOOD DRIER

As the main condition of good wood drying is the uniformity of air velocity on the pieces, we focus in this paper on the problem of air flow in a wood drier loaded with stacks of planks. The case of the upper ventilation is mainly considerad A numerical study, based on the. resolution of movement equations for a turbulent flow, concerns the inlet and outer part of the stack. The result helped us to understand the part played by the space on each side of the stack, which differs for large or narrow distances from the wall. An experimental study gave us values for velocity distribution in the stack for given geometrical ratio of the drier and led us to recommend some rules for good loading.