An improved mixing model providing joint statistics of scalar and scalar dissipation

For the calculation of nonpremixed turbulent flames with thin reaction zones the joint probability density function (PDF) of the mixture fraction and its dissipation rate plays an important role. The corresponding PDF transport equation involves a mixing model for the closure of the molecular mixing term. Here, the parameterized scalar profile (PSP) mixing model is extended to provide the required joint statistics. Model predictions are validated using direct numerical simulation (DNS) data of a passive scalar mixing in a statistically homogeneous turbulent flow. Comparisons between the DNS and the model predictions are provided, which involve different initial scalar-field lengthscales.     

Uncertainties in the SPRT Subranges of ITS-90: Topics for Further Research

The CCT has completed the guide summarizing the uncertainties in the realization of the SPRT subranges of ITS-90 between the triple point of neon (24.5561 K) and the freezing point of silver (961.78 °C). This article identifies aspects of standard platinum resistance thermometry where either data or models are lacking and further research is required. In the calibration of SPRTs, the two main concerns are the need for data on liquidus slopes for the different impurities in the fixed points and improved understanding of the impact of the thermal environment of the fixed point on the realized temperature. In the use of SPRTs, the two largest sources of uncertainty are Types 1 and 3 non-uniqueness and oxidation. The causes of Type 3 non-uniqueness are not yet understood, especially at low temperatures, and there is a paucity of data for the high-temperature subranges. In respect of oxidation, there is a need for validation of the models developed in the 1980s, especially in light of the reduced partial pressure of oxygen used in modern SPRTs. A range of other effects including vacancy effects in SPRTs, isotopic effects in fixed points, and improved statistical methods are discussed.     

High-temperature performance of InGaAs-InGaAlAs-InP 1.79-μmdiode lasers grown in solid-source molecular-beam epitaxy

1.79-μm InGaAs-InGaAlAs strained-layer quantum-well diode lasers have been fabricated. A characteristic temperature of 72 K has been achieved. At a temperature as high as 100°C, a continuous-wave output power of more than 6.5 mW per facet has been demonstrated with lasers using as-cleaved facets as mirrors     

An Integrated Model for an Industrial Production–Distribution Problem

In this paper, we are interested in a multi-facility, multi-product and multi-period industrial problem. In this problem, both production and distribution costs are significant and they are inter-related. Therefore they should be considered simultaneously in a cost optimization problem. We model this combined production-distribution problem in the form of a network flow problem with relatively few additional 0-1 variables describing the linking constraints between periods. Computational experiments show that the real size problems we encountered can be solved in reasonable time using commercial linear programming codes like CPLEX     

Modeling the high strain rate behavior of titanium undergoing ballistic impact and penetration

Titanium is an important candidate in the search for lighter weight armors. Increasingly, it is being considered as a replacement for steel components. It is also an important component in the application of ceramics to armor systems, especially in armor modules that are capable of defeating kinetic energy penetrators while sustaining little or no penetration of the ceramic element. The best alloy available today for ballistic applications is Ti-6Al-4V, an aerospace grade titanium alloy. The principal deterrent to widespread use of this alloy as an armor material is cost, and a significant portion of the cost is in processing. Consequently, the U.S. Army Research Laboratory undertook a program to study a particular lower cost processing technique [1].

The objectives of this work are to characterize the low-cost titanium alloy by generating constants for the Johnson-Cook (JC) and Zerilli-Armstrong (ZA) strength models, and to use and compare these two models in simulations of ballistic experiments. High strain rate strength data for the low-cost titanium alloy are used to generate parameters for the two models. The approach to fitting the JC parameters follows one previously used successfully to model 2-in thick rolled homogeneous armor (RHA) [2]. The approach to fitting the ZA parameters is based on a method described by Gray et al. [3]. The resulting model parameters are used in the shock physics code CTH [4] to model a Ti-6Al-4V penetrator penetrating a Ti-6Al-4V semi-infinite block at impact velocities up to 2,000 m/s. Similar experiments are performed, and the predictions of the two models are compared to each other and to the experimental results.     

Executive control of cognitive processes in task switching.

In 4 experiments, participants alternated between different tasks or performed the same task repeatedly. The tasks for 2 of the experiments required responding to geometric objects in terms of alternative classification rules, and the tasks for the other 2 experiments required solving arithmetic problems in terms of alternative numerical operations. Performance was measured as a function of whether the tasks were familiar or unfamiliar, the rules were simple or complex, and visual cues were present or absent about which tasks should be performed. Task alternation yielded switching-time costs that increased with rule complexity but decreased with task cuing. These factor effects were additive, supporting a model of executive control that has goal-shifting and rule-activation stages for task switching. It appears that rule activation takes more time for switching from familiar to unfamiliar tasks than for switching in the opposite direction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Processing and properties of 15–70 MHz 1–3 PZT fiber/polymer composites

This paper reports on the fabrication and characterization of fine scale piezoelectric composites with 1–3 connectivity using fibers derived from a metal alkoxide sol-gel process. Using this technique, pure thickness mode resonance for this type of composite has been increased from 15 MHz up to 70 MHz by maintaining pillar aspect ratio requirements. Piezoceramic fibers of Nb or La modified lead zirconate titanate (PZT) were produced with final diameters ranging from 15 to 50 μm. Composites having 1–3 connectivity were produced using the fibers as pillars. Composites could be fabricated with volume fractions from 10 to 45% allowing tailoring of both the dielectric constant and acoustic impedance without degrading coupling. Dielectric constant, polarization and coercive field values varied slightly from bulk values due to clamping by the polymer matrix, increasing as the fiber diameter decreased. Composites with resonance frequencies ranging from 15 to 70 MHz were studied. The thickness dependence of the properties gave indications to radial mode/thickness mode interactions at pillar aspect ratios near 1.7 to 1 thickness to diameter. Coupling coefficients (k_t) from 58% to 73% with mechanical quality factors <15 were detected. Received: 4 April 2000 / Reviewed and accepted: 8 June 2000     

Dispersoid-free zones in the heat-affected zone of aluminum alloy welds

The local microstructure in the heat-affected zone 1 (HAZ1) of a laser beam-welded Al-Mg-Si-Cu aluminum alloy is investigated closely. Dispersoid-free zones (DFZs), where the dispersoids of the base material (BM) are dissolved, are found in the vicinity of the fusion line (FL). They are not uniformly surrounding a grain, but oriented toward the FL. Their width can be as large as 10 μm. Detailed analysis has revealed a decreased silicon concentration as well as a decreased hardness of the oriented dispersoid-free zones (ODFZs). Two mechanisms for the formation of this welding metallurgical feature are discussed.     

Assessment of Spirit Yield in Barley Breeding Lines

A number of random inbred lines of barley, grown at two sites, were assessed for high gravity spirit yield. A range of values was obtained and there was good agreement, for nearly all samples, between high gravity spirit yield and spirit yield predicted from extracts and fermentabilities measured by Institute of Brewing recommended methods. One sample, which gave a low predicted spirit yield but good high gravity spirit yield, was shown to have modified poorly and unevenly. Over both sites, high gravity spirit yield appeared to correlate negatively with grain nitrogen content, but this reflected large differences between sites in grain nitrogen. High gravity spirit yield did not correlate with soluble nitrogen, but did with fermentability, so samples with low levels of fermentability had either low or moderate levels of high gravity spirit yield. It was concluded that identification of genetic factors, influencing extract and fermentability, would enhance breeding of barley cultivars suitable for malt whisky distilling.     

What is Special about Patent Citations? Differences between Scientific and Patent Citations

The emergence of pattent bibliometrics as a new branch of scientometrics necessitates a deeper understanding of the relationship between patents and papers. As this connection is established through the linkage between patents and research papers, one must have a clear idea of similarities and differences between patent and paper citations. This paper will investigate to what extent one can not only apply bibliometric methods to patents but also extend the existing interpretative framework for citations in research papers to the field of patent citations. After pointing out some parallels in the debates about the nature of citations in patents and scientific articles, the paper outlines those parts of bibliometric theory covering scientific citations that could be relevant to patent citations too. Then it highlights the specialties and peculiarities of patent citations. One major conclusion is that the general nature of a common framework for both scientific and patent citations would severely limit its usefulness, but research on academic citations might still be a great source of inspiration to the study of patent citations.