Laser Synthesis of Low-Agglomerated Submicrometer Silicon Nitride Powders from Chlorinated Silanes

The laser chemical vapor precipitation of Si₃N₄ powder from mixtures of SiH₂Cl₂ and NH₃ has been studied. The reactant gases were mixed at different heights with respect to the laser beam, thus preventing low-temperature reactions and agglomeration of the produced particles. The morphology and the size of the particles formed are dependent on the injection height of NH₃ into the silicon reactant gas stream. Particle diameters are typically between 15 and 110 nm.     

Production of antimicrobial metabolites by strains of Lactobacillus or Lactococcus co-cultured with Bacillus cereus in milk

During co-culture of Lactobacillus (five strains) or Lactococcus (two strains) with Bacillus cereus, organic acids and other potentially antimicrobial metabolites are produced. Lactic acid was produced at very different rates by the lactic acid bacteria (LAB) and the final concentrations varied much, however, the crucial point of rapid pH reduction during the initial hours of fermentation coincides with lactic acid production. Moderate amounts of acetic acid were produced during fermentation and the final concentrations were much smaller compared to lactic acid. According to these experiments, production of diacetyl, carbon dioxide and ethanol was considered too small to contribute to inhibition of B. cereus. The inhibitory substance produced by the LAB strains was not sensitive to proteinase K, trypsin or pepsin, so it was not likely that the LAB strains produced bacteriocins antagonistic against B. cereus. The strains that produced lactic acid fastest inhibited B. cereus best. Increased concentrations of lactic and acetic acid and carbon dioxide were also observed after co-culture with B. cereus compared to growth of the LAB strains alone, which indicates that B. cereus stimulates the biosynthetic capacities of the LAB strains.     

Is formative measurement really measurement? Reply to Bollen (2007) and Bagozzi (2007).

R. D. Howell, E. Breivik, and J. B. Wilcox (2007; see record 2007-07830-006) examined the use of formative measurement models in theory testing in the social sciences. K. A. Bollen (2007; see record 2007-07830-007) and R. P. Bagozzi (2007; see record 2007-07830-008) have provided comments on this work. In this article, the authors reply to the commentators and suggest that the conclusions reached in the original article and the basis for those conclusions remain sound. They address the issue of misspecification raised by Bollen (2007) and the alternative to their realist philosophy of measurement offered by Bagozzi (2007). They conclude that misspecification as construed by Bollen (2007) will typically be undetectable in practice and cannot be distinguished from interpretational confounding. This can result in substantively different constructs retaining the same name from study to study, hindering the accumulation of knowledge. They further conclude that traditional reflective measurement is a better option for researchers in theory testing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spectral element multigrid. I. Formulation and numerical results

A variational spectral element multigrid algorithm is proposed, and results are presented for a one-dimensional Poisson equation on a finite interval. The key features of the proposed algorithm are as follows: the nested spaces and associated hierarchical bases are intra-element, resulting in simple data structures and rapid tensor-product sum-factorization evaluations; smoothing is effected by readily constructed and efficiently inverted (diagonal) Jacobi preconditioners; the technique is readily parallelized within the context of a medium-grained paradigm; and the (work-deflated) multigrid convergence rate is bounded from above well below unity, and is only a weak function of the number of spectral elementsK, the (large) order of the polynomial approximation,N, and the number of multigrid levels,J. Preliminary tests indicate that these convergence properties persist in higher space dimensions.     

Change profiles of a reused class framework vs. two of its applications

Software reuse is expected to improve software productivity and quality. Although many empirical studies have investigated the benefits and challenges of software reuse from development viewpoints, few studies have explored reuse from the perspective of maintenance. This paper reports on a case study that compares software changes during the maintenance and evolution phases of a reused Java class framework with two applications that are reusing the framework. The results reveal that: (1) The reused framework is more stable, in terms of change density, than the two applications that are reusing it. (2) The reused framework has profiles for change types that are similar to those of the applications, where perfective changes dominate. (3) The maintenance and evolution lifecycle of both the reused framework and its applications is the same: initial development, followed by a stage with extending capabilities and functionality to meet user needs, then a stage in which only minor defect repairs are made, and finally, phase-out. However, the reused framework goes faster from the stage of extending capabilities to the stage in which only minor defect repairs are made than its applications. (4) We have validated that several factors, such as are functionalities, development practice, complexity, size, and age, have affected the change densities and change profiles of the framework and applications. Thus, all these factors must be considered to predict change profiles in the maintenance and evolution phase of software.     

Analytical sensitivities for statistically extrapolated extreme load constraints in structural optimization

For some applications in structural optimization, it is required to have constraints on the extreme loads that represent long term loading conditions. This usually involves a statistical extrapolation procedure that fits maxima from simulated load time series to short term extreme value distributions and then extrapolates to an n-year return value. Often such situations are highly simplified because of the apparent complexity involved in evaluating the sensitivity of such constraints. However, such simplification is not necessary. In this study, we present a method to evaluate the sensitivities of such extrapolated extreme load constraints in a semi-analytical way. The method uses the implicit function theorem to obtain local derivatives at the points defined by the solution of the maximum likelihood estimate that is used to calculate the parameters of the short term extreme value distributions. Comparing with high accuracy finite difference estimates, the method is shown to give reasonably accurate values. We also demonstrate how the method can be used to estimate the uncertainty of the estimated n-year return value caused by uncertainty in both the maximum likelihood estimate and inherent uncertainties in the data. The method then is applied to a simple optimization example and shown to perform very well compared with using finite difference estimates for the sensitivities. Finally, we note that the method is in principle fairly general and could be applied to similar problems that do not specifically involve statistical extrapolation.     

How good are ideas identified by an automatic idea detection system?

Online communities can be an attractive source of ideas for product and process innovations. However, innovative user‐contributed ideas may be few. From a perspective of harnessing “big data” for inbound open innovation, the detection of good ideas in online communities is a problem of detecting rare events. Recent advances in text analytics and machine learning have made it possible to screen vast amounts of online information and automatically detect user‐contributed ideas. However, it is still uncertain whether the ideas identified by such systems will also be regarded as sufficiently novel, feasible and valuable by firms who might decide to develop them further. A validation study is reported in which 200 posts from an online home brewing community were extracted by an automatic idea detection system. Two professionals from a brewing company evaluated the posts in terms of idea content, idea novelty, idea feasibility and idea value. The results suggest that the automatic idea detection system is sufficiently valid to be deployed for the harvesting and initial screening of ideas, and that the profile of the identified ideas (in terms of novelty, feasibility and value) follows the same pattern identified in studies of user ideation in general.     

Concentration polarization and fouling

Concentration polarization is often the reason for the serious limitation of the membrane processes due to its negative influence on the transmembrane flux. Many theoretical studies on this polarization phenomena have resulted in mathematical models for concentration polarization. In most of them, solutions are sought for the coupled nonlinear system of the equations of continuity and motion. Each of these solutions makes use of some assumptions in order to simplify the equations which represent the phenomenon.Different kinds of flow systems have been constructed in order to reduce the concentration polarization. The aim of these flow systems has mainly been to improve the mass transport from the membrane surface back to the bulk solution.Fouling often is a result of concentration polarization, but can also have other reasons.The attention that was drawn to fouling ten to fifteen years ago mostly consisted of recognizing the fact as such and to roughly identify the foulant. Later, efforts to avoid the negative effects have basically followed the paths of altering the composition of the feed solution by a pretreatment to change or get rid of the foulant, to change the hydrodynamics of the membrane module or to alter the membrane itself.However, unveiling the basic mechanisms of fouling attracted little attention until the late seventies when for example fouling of an RO sea water desalination membrane could be subdivided into four consecutive steps.Also, studies of the chemistry and physics of fouling have being performed on whey lately and revealed in closer detail some of the responsible phenomena.     

机载隐蔽式垂尾高频天线辐射场特性分析

根据飞机高频天线输入阻抗的测试数据,对机载垂尾隐蔽式高频天线进行较精确的电磁建模。结合飞机复杂形体的整机电磁模型,对高频天线进行矩量法数值仿真计算,分析飞机某些关键部件位置处的天线辐射场强特性,进而确认这些关键位置处的场强强度是否超出预期设计的安全阈值。仿真结果可作为飞机电磁兼容相关方面的分析与设计的参考依据。