How to manipulate the electrospinning jet with controlled properties to obtain uniform fibers with the smallest diameter?—a brief discussion of solution electrospinning process

Solutions of five different polymers, namely, polystyrene (PS), polyacrylonitrile (PAN), polyhydroxybutrate (PHB), poly(D-L-lactic acid) (PLA), and Nylon6, were used to investigate their rheological properties on the electrospinnability. In order to effectively reduce the diameter of electrospun fibers, polymers with higher molecular weights (MW) were needed to develop entangled solutions at much lower concentrations and with viscosities as low as that of a pure solvent. A minimum polymer concentration 1.0–2.0 times larger than the entanglement concentration was required to prepare the bead-free fibers. Using this strategy, uniform PS fibers with the lowest ever diameter of ∼15 nm were successfully obtained using an MW of 3 × 10⁷ g/mol at a concentration of 0.1 vol.%. For a given electrospinning solution, processing variables of low flow-rate (Q) and high voltage (V) were desirable in obtaining fibers with small diameters. However, Q and V were correlated by a power law relation: V∼Q ^a, wherein the exponent a had a value of 0.1–0.4, which was relevant with the solution types. Based on the finite element analysis (FEA), a significant measure of electric field (E) occurred around the needle tip used in the experiment, and its magnitude decayed with increasing distance from the needle end (z): E∼z ⁻ⁿ. The exponent n was 1.0–2.0, depending on the needle–plate geometry, i.e., needle length, needle diameter (D _o ), plate diameter, and tip-to-plate distance (H). According to FEA results, H exhibited negligible effects on the electric field in the region of interest, i.e., z/D _o ∼1 to 10. Due to the presence of high measures of E at the needle end, approaches to render a shorter and thinner straight jet issuing from the Taylor cone to yield thinner fibers were sought because a more significant jet stretching in the “jet whipping region” can take place. A feasible route to predict the as-spun fiber diameter produced by the manipulation of the electrified jet is provided by experimentally measuring the jet diameter and numerically calculating the electric field for the jet whipping process.     

The Parallel Image Processing Environment (PIPE): automated parallelization of satellite data analyses

A Beowulf‐type cluster can: (1) mitigate many issues associated with the analysis of large, complex remotely sensed data sets; (2) shorten the response time of operational agencies to crisis‐management situations; and (3) expedite the reanalysis of large archives of satellite data. Whereas most Beowulf‐type designs support modeling applications, the Parallel Image Processing Environment (PIPE) addresses the unique requirements of remote sensing applications. PIPE has four hierarchical layers: hardware, operating system, middleware and applications. Rocks, a middleware sublayer, manages the cluster. DIAL‐developed interprocess communication and control daemons form the second middleware sublayer. They encapsulate user‐defined applications and thereby support automated, user‐transparent parallelization of satellite data analyses, implemented in the applications layer using generalized constructs. The daemons also monitor resource (computational and I/O) utilization on a node/thread basis, a feature not supported by other generally available monitoring utilities. The application support libraries are fully extensible, facilitate the reuse of modular and commonly used software functions in new applications and thereby reduce both the cost and time to implement new applications. Two applications (signal analysis, image classification) show PIPE's versatility and performance characteristics. PIPE is intrinsically scalable, reliable and can be incrementally implemented. A comparison with other embarrassingly parallel systems is also provided. Copyright © 2006 John Wiley & Sons, Ltd.     

A packing algorithm for three-dimensional convex particles

Simulation of granular particles is an important tool in many fields. However, simulation of particles of complex shapes remains largely out of reach even in two-dimension. One of the major hurdles is the difficulty in representing particles in an efficient, flexible, and accurate manner. By representing particles as convex polyhedrons which are themselves the intersection of a set of half spaces, we develop a method that allows one to efficiently carry out key operations, including particle–particle and particle–container wall overlapping detection, precise identification of the overlapping region, particle shifting, particle rotation, and others. The simulation of packing 1,000 particles into a container takes only a few minutes with this approach. We further demonstrate the potential of this approach with a simulation that re-generates the “Brazil nut” phenomenon by mixing and shaking particles of two different sizes.     

利用汉字二元语法关系解决汉语自动分词中的交集型歧义

本文提出了一种利用句内相邻之间的互信息及ｔ－测试差这两个统计量解决汉语自动分词中交集型歧义切分字段的方法。初步的实验结果显示，可以正确处理９０．３％的交集字段。     

A unified lubrication approach for the design of a coat-hanger die

A simple unified lubrication approach has been proposed to design a coat-hanger die that can deliver wide and uniform liquid sheets. This approach requires that the wall stress in the manifold be constant. With this constraint, any inelastic non-Newtonian fluid model can be used to describe the liquid motion inside the die. Fluid models that can represent the pseudoplastic or viscoplastic behavior of polymeric liquids have been selected for illustration. A general equation that can be solved to determine the effect of production variations on flow uniformity inside the die has also been derived.     

Improving InAs double heterostructure lasers with betterconfinement

The authors have conducted a theoretical study of InAs double heterostructure lasers. Carrier leakage due to drift current is shown to be the main mechanism of the injected carriers in lasers fabricated to date. Reduction of carrier leakage is shown to be possible by using wider bandgap lattice-matched material as the cladding layers. Increased optical confinement is also required to achieve the lowest possible threshold current, which strongly affects the highest lasing temperature achievable. An InAs double heterostructure employing AlAs_0.16Sb_0.84 as the cladding material is proposed. Simulation on this structure indicates that its threshold current density will be dominated by Auger recombination for most of the temperature range below 300 K, the estimated highest lasing temperature     

Fiber-Matrix interactions in brittle matrix composites

Brittle matrix composites, including carbon-carbon (C-C) and ceramic matrix, offer a new dimension in the area of high-temperature structural materials. Fiber-matrix interactions determine the mechanism of the load transfer between the fiber and matrix and resulting mechanical properties. Composites studied in this work include a C-C composite densified with a chemical vapor infiltration (CVI) pyrolytic carbon, silicon carbide fiber-silicon carbide matrix composite, and carbon fiber-silicon carbide matrix composites densified by the CVI technique. The type of the interfacial carbon in C-C composites was found to control their mechanical properties. The presence of the compressive stress exerted by the matrix on the carbon fibers was attributed to an increase in flexural strength. The transverse matrix cracking in C/SiC composites was believed to cause a lowering in the flexural strength value. Brittle fracture behavior of SiC/SiC composites was correlated with the presence of an amorphous silica layer at the fiber-matrix interface. This invited paper is based on a presentation made in the symposium “Structure and Properties of Fine and Ultrafine Particles, Surfaces and Interfaces” presented as part of the 1989 Fall Meeting of TMS, October 1–5, 1989, in Indianapolis, IN, under the auspices of the Structures Committee of ASM/MSD.     

DETECTING SINUSOIDS IN NON-GAUSSIAN NOISE

Abstract. Spectral analysis is a well-established procedure for detecting harmonic signals in a noisy environment. Much research has been done on methods that use second-order statistics (i.e. the autocovariance function and power spectrum) such as Whittle's test, Bartlett's test, Hannan's test and the Priestley P ( Λ ) test. When the noise is non-Gaussian, statistics of order greater than two can provide more information to detect the periodicities in noisy data. We direct our main attention to the third (fourth) order cumulant and bispectral (trispectral) methods. New test statistics are derived and are shown to be more powerful than other methods based on second-order statistics under a mixed spectrum condition. The asymptotic power functions of the new test statistics and other tests are studied. Some Monte Carlo simulations are used to evaluate the performance of the new methods with moderate sample sizes.     

A 150-MHz graphics rendering processor with 256-Mb embedded DRAM

A 150-MHz graphics rendering processor with an integrated 256-Mb embedded DRAM, delivering a rendering rate of 75 M polygons/s, is presented, 287.5 M transistors are integrated on a 21.3×21.7 mm ² die in a 0.18-μm embedded DRAM CMOS process with six layers of metal. Design methodologies for hierarchical electrical and physical design of this very large-scale IC, including power distribution, fully hierarchical timing design, and verification utilizing a newly developed nonlinear model, clock design, propagation delay, and crosstalk noise management in multi-millimeter RC transmission lines, are presented     

The compatible and mechanical properties of biodegradable poly(Lactic Acid)/ethylene glycidyl methacrylate copolymer blends

The Fourier transform infrared results suggest that the carboxylic acid groups of poly(lactic acid) (PLA) molecules react with the epoxy groups of molecules of Ethylene Glycidyl Methacrylate Copolymer (EGMC) during the reactive extrusion processes of PLA_xEGMC_y specimens. The tensile and tear strength values of PLA_xEGMC_y blown-film specimens in machine and transverse directions improve significantly, and reach their maximal values as their EGMC contents approach an optimum value of 6 wt.%. The melt shear viscosity values of PLA_xEGMC_y resins, measured at varying shear rates, are significantly higher than those of the PLA resin, and increase consistently with their EGMC contents. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) of PLA and PLA_xEGMC_y specimens reveal that the percentage crystallinity, peak melting temperature, and onset re-crystallization temperature values of PLA_xEGMC_y specimens reduce gradually as their EGMC contents increase. In contrast, the glass transition temperatures of PLA_xEGMC_y specimens increase gradually in conjunction with their EGMC contents. Demarcated porous morphology with several connected fungi-decomposed cavities was found on the surfaces of the PLA_xEGMC_y specimens after being buried for specific amounts of time, in which the sizes of the fungi-decomposed cavities found on the surfaces of buried PLA_xEGMC_y specimens reduce significantly as their EGMC contents increase. Further DMA and morphological analysis of PLA_xEGMC_y specimens reveal that the EGMC molecules are compatible with PLA molecules at EGMC contents equal to or less than 2 wt.% because no phase-separated EGMC droplets and tan δ transitions were found on fracture surfaces and tan δ curves of PLA_xEGMC_y specimens, respectively. The possible reasons for these remarkable properties of the PLA/EGMC specimens are proposed in this study.