Microstructure control during severe plastic deformation of Al-Cu-Li and the influence on strength and ductility

The microstructure and mechanical behaviour of an Al-Cu-Li alloy has been examined after processing over a wide range of conditions involving severe deformation at elevated temperatures with prior or subsequent heat treatments. Dislocation cellular or subgrain structures are obtained, with varying degrees of precipitation. High strength, as well as poor ductility, can be correlated with the presence of a high density of fine T₁ phase precipitates, with the dislocation substructure playing a smaller role. Careful control of processing conditions allows a suitable combination of good strength with ductility to be obtained.     

Effect of flow field design on performances of high temperature PEM fuel cells: Experimental analysis

Among all types of fuel cells, attention is being drawn lately on high temperature Polybenzimidazole (PBI) PEM because their operative temperature range (120-180 °C) increases the tolerance to carbon monoxide. This feature allows working with low quality hydrogen produced by hydrocarbon reformation. Most of the literature on PBI PEM deals with membrane and MEA related issues, however, cell efficiency and specially, commercial feasibility are conditioned by other fuel cell components as bipolar plates. In the present study the focus is on the effect of the flow field geometry of high temperature PBI PEM composite bipolar plates on the overall performance of the cell. For this purpose, three different channel geometries are studied: two serpentine flow fields and parallel channels flow field. Results show that serpentine geometry yields higher performance though it introduces higher pressure drop along the cell as well.     

Multipath channel identification by using global optimization in ambiguity function domain

A new transform domain array signal processing technique is proposed for identification of multipath communication channels. The received array element outputs are transformed to delay-Doppler domain by using the cross-ambiguity function (CAF) for efficient exploitation of the delay-Doppler diversity of the multipath components. Clusters of multipath components can be identified by using a simple amplitude thresholding in the delay-Doppler domain. Particle swarm optimization (PSO) can be used to identify parameters of the multipath components in each cluster. The performance of the proposed PSO-CAF technique is compared with the space alternating generalized expectation maximization (SAGE) technique and with a recently proposed PSO based technique at various SNR levels. Simulation results clearly quantify the superior performance of the PSO-CAF technique over the alternative techniques at all practically significant SNR levels.     

From defects creation to circuit reliability - A bottom-up approach (invited)

This paper presents a theoretical framework about interface states creation rate from Si-H bonds at the Si/SiO₂ interface. It includes three mains ways of bond breaking. In the first case, the bond can be broken thanks to the bond ground state rising with an electrical field. In the two others cases, incident carriers will play the main role either if there are very energetic or very numerous but less energetic. This concept allows us physically modeling the reliability of MOSFET transistors, and particularly NBTI permanent part, and Channel Hot Carrier (CHC) to Cold Carrier (CCC) damage. Finally, the translation of these physical models into reliability spice models is discussed. These models pave the way to Design-in Reliability (DiR) approach which seeks to provide a quantitative assessment of reliability - CMOS device reliability in this case - at design stage thereby enabling judicious margins to be taken beforehand.     

AN IMPROVED EPON UPSTREAM TRANSMISSION SCHEME WITH ZERO INTER-PERIOD IDLE LOSS

Existing Ethernet Passive Optical Network (EPON) Dynamic Bandwidth Allocation (DBA) algorithms suffer from the disadvantage of idle time loss,which lower the upstream bandwidth utilization.This letter ...     

Reducing channel change delay in IPTV by predictive pre-joining of TV channels

One of the major concerns of IPTV network deployment is channel change delay (also known as zapping delay). This delay can add up to 2 s or more, and its main culprits are synchronisation and buffering of the media streams. Proving the importance of the problem is the already significant amount of literature addressing it. We start this paper with a survey of techniques proposed to reduce IPTV channel change delay.Then, by analysing an extensive dataset from an operational IPTV provider - comprising 255 thousand users, 150 TV channels, and covering a 6-month period - we have observed that most channel switching events are relatively predictable: users very frequently switch linearly, up or down to the next TV channel. This fact motivated us to use this dataset to analyse in detail a specific type of solutions to this problem, namely, predictive pre-joining of TV channels. In these schemes each set top box (STB) simultaneously joins additional multicast groups (TV channels) along with the one that is requested by the user. If the user switches to any of these channels the switching latency is virtually eliminated, not affecting therefore user's experience.We start by evaluating a simple scheme, where the neighbouring channels (i.e., channels adjacent to the requested one) are pre-joined by the STB during zapping periods. Notwithstanding the simplicity of this scheme, trace-driven simulations show that the zapping delay can be virtually eliminated for a significant percentage of channel switching requests. For example, when sending the previous and the next channel concurrently with the requested one, for only 1 min after a zapping event, switching delay is eliminated for close to half of all channel switching requests. Importantly, this result is achieved with a negligible increase of bandwidth utilisation in the access link. Other more complex schemes where user behaviour is tracked were also evaluated, but the improvement over the simple scheme was insignificant.     

DYNAMIC RESOURCE ALLOCATION SCHEME UNDER TRAFFIC CONDITION IN SATELLITE SYSTEMS

As the traffic distribution in China mainland is far from uniform, a new traffic model in China mainland is presented on the basis of per-capita Gross Domestic Product (GDP) and density of population. Based on this characteristic traffic model, a new Traffic Dependent Dynamic Channel Allocation and Reservation (TDDCAR) technique is proposed, the simulation model is built, and the strategies’ performance is evaluated through computer simulation. The simulation results show that, compared to the conventional Fixed Channel Allocation (FCA), TDDCAR estimates the traffic con-ditions in every spot beam and frequently adjusts the traffic according to current traffic conditions. It has achieved a significant improvement in new call blocking probability, handover blocking probability, and fair index, particularly, in heavy traffic conditions. The building of traffic model in China mainland and the analysis of the simulation results has been a key foundation for the study of resource allocation schemes in the future.     

嫦娥一号X射线谱仪定标

介绍了嫦娥一号X射线谱仪实验室定标,主要包括能量响应(能量与能道关系、能量分辨率)和角度响应,这些定标结果对于环月运行获得的X射线数据的反演与分析是必不可少的.     

Microstructural and mechanical properties of commercially pure aluminum subjected to Dual Equal Channel Lateral Extrusion

This paper aims to provide an introductory insight about “Dual Equal Channel Lateral Extrusion”, a counterpart of “Equal Channel Angular Extrusion”. The process is implemented to severely refine the microstructure of aluminum slabs. Comparisons of macroscopic parameters as average straining and large scale distribution of strain, as well as process loads reveal the supremacies and short comings of DECLE with respect to ECAE. DECLE shares a relatively similar geometry of deformation with that of ECAE. The advantages of this process with respect to ECAE are: (i) more intensive strains attainable per pass, and (ii) less extruding power needed for a given sample size. Nonetheless, less homogeneous strain per pass is seen in case of DECLE. TEM inspections revealed remarkable refinement of the microstructure through out the process and also some recrystallization at the final passes. Hardness tends to increase through successive passes to a limiting value beyond which there appeared a decline associated with intense recovery and the recrystallization observed. Compression tests exhibit the same trend, viz. a general rise in strength followed by a decrease in work hardening with increasing number of passes, leading to uniform microstructure and hardness after 9 passes.     

Field Properties in Surface Irrigation Management and Design

Field properties—topography, hydraulic resistance, and infiltration—play an important role in the performance of surface irrigation systems, and appropriate characterizations of these are required as data input to simulation or design software. The EWRI/ASCE Task Committee on Soil and Crop Hydraulic Properties has been charged with preparing a guide for practitioners faced with such data entry. The result is this special section of the Journal of Irrigation and Drainage Engineering in which this paper is the first in the series presented. It describes the characteristics of these field properties and notes a series of caveats to be considered when dealing with them in the course of analyses or designs of surface irrigation systems.