Long-wavelength GaInNAs(Sb) lasers on GaAs

The boom in fiber-optic communications has caused a high demand for GaAs-based lasers in the 1.3-1.6-μm range. This has led to the introduction of small amounts of nitrogen into InGaAs to reduce the bandgap sufficiently, resulting in a new material that is lattice matched to GaAs. More recently, the addition of Sb has allowed further reduction of the bandgap, leading to the first demonstration of 1.5-μm GaAs-based lasers by the authors. Additional work has focused on the use of GaAs, GaNAs, and now GaNAsSb barriers as cladding for GaInNAsSb quantum wells. We present the results of photoluminescence, as well as in-plane lasers studies, made with these combinations of materials. With GaNAs or GaNAsSb barriers, the blue shift due to post-growth annealing is suppressed, and longer wavelength laser emission is achieved. Long wavelength luminescence out to 1.6 μm from GaInNAsSb quantum wells, with GaNAsSb barriers, was observed. In-plane lasers from these samples yielded lasers operating out to 1.49 μm, a minimum threshold current density of 500 A/cm² per quantum well, a maximum differential quantum efficiency of 75%, and pulsed power up to 350 mW at room temperature     

Inclined hot-wire response equations for a flow field having a dominant tangential velocity component

Modified sets of response equations have been derived for a single inclined hot-wire probe introduced in various orientations in a flow field having a dominant tangential velocity component. By means of these equations, the components of the three dimensional mean velocity vectors, the turbulence intensity and the Reynolds stresses can be easily determined at any location in a swirling flow which is stationary with time. This method is particularly applicable to the characterization of the flow field in chemical processing equipment where this type of swirling flow is increasingly being used. It has been successfully applied to a study of the flow field in a spray-drying chamber, in the course of which good reproducibility and consistency of results were obtained.     

在多元连接数据查询中最小生成树法的改进应用

本文对最小生成树法在分布式数据库多元连接中的应用进行了阐述和分析,并利用分布式数据库数据的分布性对最小生成树法进行了改进。提出了基于最小生成树法的连接图划分方法将连接图划分成多个子连接图,提高连接操作的并行性,从而使得响应时间得到减少。     

Simulation of crack growth in composite material shell structures

This paper implements a domain integral energy method for modelling crack growth in composite material shell structures using the finite element method. Volume integral expressions to evaluate the dynamic energy release rate in a through‐thickness three‐dimensional crack are derived. Using the domain integral, the energy release rate computation is implemented in the DYNA3D explicit non‐linear dynamic finite element analysis program wherein crack propagation is modelled by releasing the constraints between initially constrained node pairs. The implementation enables the program to either determine the energy resistance response for the material (provided experimental data is available) or predict the rate of crack propagation in shell structures. The numerical implementation was verified by simulating mode I and mode III slow crack growth problems in semi‐infinite transversely isotropic media, for which analytic solutions are available. Oscillations of energy following the release of nodal constraints as the crack propagates in discrete increments were suppressed using light mass proportional damping and a moving averaging scheme. Copyright © 2004 John Wiley & Sons, Ltd.     

关于公布国家重点支持水泥工业结构调整大型企业(集团)名单的通知

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A beam theory for thin-walled composite beams

A beam theory is presented that is formulated in terms of the in-plane elastic properties of the panels of the cross-section of a thin-walled composite beam. Shear deformation is accounted for by using a suitable form of the Timoshenko beam theory together with a modified form of the shear coefficient. The theory gives both the bending deflection and the shear deflection of a beam loaded by an applied transverse load. Numerical and graphical results obtained from a computer code show the effects of using different composite material systems and lay-ups in the panels of typical beams.     

Multiscale modeling in rodent ventricular myocytes

This paper indicates that in ventricular myocytes when the SR (sarcoplasmic reticulum) is pharmacologically inhibited, the intracellular Ca²⁺concentration rapidly increases during Ca²⁺ entrance (0-70 ms), whereas the decay of Ca²⁺ is slow; in the absence of fluorescent dye, large Ca²⁺ concentration gradients might develop near the cell membrane; intracellular Ca²⁺ distribution is tightly regulated by the localization of Ca²⁺transporter proteins along the sarcolemma and strongly relays on the presence of mobile and stationary Ca²⁺ buffers. These studies also imply that in ventricular cells with intact and functional SR, the Ca²⁺ signal most likely would spread faster along the t-tubular system, surface membrane than to the cell interior and that in the absence of Ca²⁺ dye high Ca²⁺ gradients under the surface membrane and more uniform Ca²⁺ distribution in the cell interior might be expected.     

On the temperature sensitivity of 1.5-/spl mu/m GaInNAsSb lasers

We analyze the temperature sensitivity of 1.5-/spl mu/m GaInNAsSb lasers grown on GaAs. Building on the method of Tansu and coworkers, we find evidence that the characteristic temperatures for the threshold current T/sub 0/ and external efficiency T/sub 1/ are balanced by a combination of monomolecular recombination and temperature destabilizing mechanism(s) near room temperature. At elevated temperatures, the destabilizing process(es) dominate, due to increased threshold current density J/sub th/. While it is difficult to definitively identify carrier leakage, Auger recombination, or a combination of the two as the responsible mechanism(s), results indicate that carrier leakage certainly plays a role. Evidence of intervalence band absorption was also found; T/sub 1/ was reduced, but J/sub th/ and T/sub 0/ were not significantly degraded. Conclusions are corroborated by supporting measurements of the Z-parameter with bias, spontaneous emission spectrum, and band-offsets. Spontaneous emission measurements show evidence of weak Fermi-level pinning within the active region at threshold, indicating a form of carrier leakage. This is consistent with the characteristic temperature analysis and a leakage mechanism is proposed. This process is partially responsible for the greater temperature sensitivity of device parameters and the poor internal efficiency. Methods for reducing the effects of each parasitic mechanism are also described.