A hydrodynamic transport model and its applications in semiconductor device simulation

In this paper, a generalized hydrodynamic model that includes four conservation equations for a general, position-dependent energy band structure and effective mass is presented. An analytical mobility model is extended to simulate two-valley semiconductor devices. A semiconductor device simulation package, DYNA, is introduced. Simulation results for both bulk materials and submicron-gate GaAs MESFETs show good agreement with experimental data and Monte Carlo device simulation results.     

QoS provisioning in micro-cellular networks supporting multiple classes of traffic

We introduce an adaptive call admission control mechanism for wireless/mobile networks supporting multiple classes of traffic, and discuss a number of resource sharing schemes which can be used to allocate wireless bandwidth to different classes of traffic. The adaptive call admission control reacts to changing new call arrival rates, and the resource sharing mechanism reacts to rapidly changing traffic conditions in every radio cell due to mobility of mobile users. In addition, we have provided an analytical methodology which shows that the combination of the call admission control and the resource sharing schemes guarantees a predefined quality-of-service to each class of traffic. One major advantage of our approach is that it can be performed in a distributed fashion removing any bottlenecks that might arise due to frequent invocation of network call control functions.     

Field-Assisted Ion Exchange in Type III Silica

Field-assisted ion exchange of protons in type III silica for Cs or Nu ions from a molten salt was investigated. Although electrolysis occurred, infrared measurements showed no change in hydroxyl content after ion exchange for extended periods. Scanning electron microprobe studies of cesium-exchanged specimens revealed a high-cesium-content layer =2,μm thick; this layer is believed to result from surface reaction with the molten salt.     

Axial resistance and energy absorption of externally reinforced metal tubes

A simplified analytical model for the static crushing of externally reinforced metal tubes is presented. The classical Alexander's solution is modified to take into account the contribution of the compound metal/ composite wall. The mean crushing force and the length of the local folding wave derived from this model are found to be in good agreement with the experimental data.     

Grafting of 2-(dimethlamino) ethyl methacrylate onto gamma irradiated polypropylene fabric

Polypropylene fabric was gamma pre-irradiated at doses of 1,2 and 3 Mrads. The irradiated fabric was grafted with an aqueous solution of 2-(dimethylamino) ethyl methacrylate. The graft yield was studied as a function of the different variable conditions such as storage time, monomer concentration (10–40%), reaction time, and temperature (50, 70, 100°C). The grafted polypropylene was further quaternized with dimethyl sulphate or monochloroacetic acid. The grafted and quarternized fabrics were dyed with an acid dye. The fixation properties of the dyed samples were determined by DMF extraction. The moisture regain and mechanical properties were also measured.     

The nucleation of iron on dense wustite: A morphological study

Dense wustite was reduced at temperatures from 430 to 1100 °C in CO-A, CO-CO₂, H₂-A, and H₂-H₂O mixtures. Most of the experiments were conducted on a hot stage microscope, providing a clear record of the sequence of events. The morphology of phases was further studied on the optical and the scanning electron microscopes. Two types of nuclei were identified: (1) dense nuclei, ranging from regular whiskers to simple protrusions, around which flat bases develop to form a protective film, and (2) porous nuclei with lenticular shapes, which remain level with the sample surface as they grow (both radially and into the wustite) to form a porous layer. Mild gases and moderate temperatures favor dense iron, whereas strong gases and extreme temperatures (either low or high) favor porous iron. The domains of the two types are represented in morphology maps. They overlap in transition zones where mixed nuclei are found; in this case the porous nuclei appear later than the dense ones but they grow much faster. The morphology maps support the view that sponge iron in iron ore reduction does not originate from porous iron nuclei but develops as a maze of dense iron growths. Experiments with cold-worked and annealed samples indicate that dislocations are essential to the growth of whiskers. Formerly at the Ecole Centrale des Arts et Manufactures, Chatenay-Malabry, France     

Photoacoustic study of thermal degradation of polyurethane

Polyurethane rigid foam shows substantial changes in its photoacoustic absorption spectra (PAS) on heating in the presence of air. These spectral changes are due to conjugated structures and quinone–imide formation, formed during degradation. The mechanism of degradation appears to be free radical in nature.     

The influence of Cd(ZnO) on the structure,optical and thermal stabilities of polyvinyl chloride nanocomposites

The doping of nanomaterials into polymers creates novel nanocomposite materials with desired properties. The influence of these nanoscale fillers on the structure and optical and thermal stabilities of polymer are the crucial clue to introduce these novel nanocomposites to service life applications. In this work, cadmium doped zinc oxide (Cd_0.5Zn_0.5O) nanopowders with a uniform particle size of around 10 nm have been synthesized, purified, and blended with polyvinyl chloride (PVC) by solution mixing to prepare PVC/Cd_0.5Zn_0.5O nanocomposite films. The structure and morphology of PVC/Cd_0.5Zn_0.5O nanocomposite films have been characterized using transmission electron microscopy. The results showed that as the amount of nanoscale fillers increases the nanocrystals tend to aggregates and the size of these aggregates increases from 25 to 100 nm. The UV–vis spectra showed that the prepared PVC/Cd_0.5Zn_0.5O nanocomposite films are highly transparent. The transparency at higher concentrations slightly decreased as a consequence of light scattering due to large aggregates. The thermogravimetric results showed that a small amount of Cd_0.5Zn_0.5O nanopowders (<0.6 wt%) without further surface modification can greatly improve the thermal stability of PVC. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers