Determination of thermal conductivity of magnesium-alloys

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二氧化碳喷射器运行效率的实验研究

本文针对一个新型二氧化碳喷射器进行相关实验研究。通过对一个两相二氧化碳喷射器制冷系统进行不同试验工况的实验:主喷嘴入口温度从19~31℃,气冷器出口压力从6~8 MPa,从而得出喷射器效率最优时各个参数的范围。实验结果显示,引射比为0.4~0.8、喷射器出口压力和喷射器引射端压力的比值为1.09~1.20时,喷射器的工作效率较高。而在压比为1.132时,喷射器可以达到最高效率为0.389。文中还对针对质量流量进行了数学拟合,拟合结果与实验结果较为吻合,实验结果为喷射器的设计和应用提供了实验基础。     

Superconvergent Patch Recovery for plate problems using statically admissible stress resultant fields

In this paper, we study an approach for recovery of an improved stress resultant field for plate bending problems, which then is used for a posteriori error estimation of the finite element solution. The new recovery procedure can be classified as Superconvergent Patch Recovery (SPR) enhanced with approximate satisfaction of interior equilibrium and natural boundary conditions. The interior equilibrium is satisfied a priori over each nodal patch by selecting polynomial basis functions that fulfil the point‐wise equilibrium equations. The natural boundary conditions are accounted for in a discrete least‐squares manner. The performance of the developed recovery procedure is illustrated by analysing two plate bending problems with known analytical solutions. Compared to the original SPR‐method, which usually underestimates the true error, the present approach gives a more conservative error estimate. Copyright © 1999 John Wiley & Sons, Ltd.     

Identification of more risks can lead to increased over-optimism of and over-confidence in software development effort estimates

Software professionals are, on average, over-optimistic about the required effort usage and over-confident about the accuracy of their effort estimates. A better understanding of the mechanisms leading to the over-optimism and over-confidence may enable better estimation processes and, as a consequence, better managed software development projects. We hypothesize that there are situations where more work on risk identification leads to increased over-optimism and over-confidence in software development effort estimates, instead of the intended improvement of realism. Four experiments with software professionals are conducted to test the hypothesis. All four experiments provide results in support of the hypothesis. Possible explanations of the counter-intuitive finding relate to results from cognitive science on “illusion-of-control”, “cognitive accessibility”, “the peak-end rule” and “risk as feeling.” Thorough work on risk identification is essential for many purposes and our results should not lead to less emphasis on this activity. Our results do, however, suggest that it matters how risk identification and judgment-based effort estimation processes are combined. A simple approach for better combination of risk identification work and effort estimation is suggested.     

Simulation of 3D flow with gravity forces in a porous medium

Recently an operator splitting technique for convection diffusion equations, originating in porous medium flow, has been developed and analysed for one and two space dimensional models. The method is based on a solution of a modified hyperbolic problem which is used to approximate the original equation in a second step. The main objective of this paper is to investigate these algorithms for three dimensional porous media models, where handling of the gravity term is a main issue. The balance between the external pressure and the gravity may give a velocity field which is vanishing and may change sign in parts of the computational domain. This type of problem is dificult to solve accurately. Two different solution approaches are tested for accuracy, stability and computational costs. Received: 29 June 1998 / Accepted: 11 February 2000     

Free radical addition of thiolacetic acid to esters and amides of unsaturated acids and screening of the products for antimicrobial activity

Free radical addition of thiolacetic acid to terminal and internal double bonds of mono-and diunsaturated amides, as well as to unsaturated esters, was achieved by irradiation with Cobalt-60. Screening for antimicrobial activity againstStaphylococcus aureus, Escherichia coli, Aspergillus species,Torula species, andCandida albicans indicated that terminal addition products may be more active than internal addition products.     

Implicit treatment of molar mass equations in secondary oil migration

The hydrocarbon migration can be described by a coupled set of partial differential equations describing the dynamics of the temperature, component flow, pressure and velocity. A sequential solution procedure where the component flow is solved explicitly, gives severe restrictions on the time step given by the CFL condition. In this paper an implicit solution procedure is given and results from numerical tests are presented. The results are compared with the explicit solutions. As expected the implicit algorithm allows for substantially larger time steps. Received: 31 January 2001 / Accepted: 30 September 2001     

Collecting Feedback during Software Engineering Experiments

Objective: To improve the qualitative data obtained from software engineering experiments by gathering feedback during experiments. Rationale: Existing techniques for collecting quantitative and qualitative data from software engineering experiments do not provide sufficient information to validate or explain all our results. Therefore, we would like a cost-effective and unobtrusive method of collecting feedback from subjects during an experiment to augment other sources of data. Design of study: We formulated a set of qualitative questions that might be answered by collecting feedback during software engineering experiments. We then developed a tool to collect such feedback from experimental subjects. This feedback-collection tool was used in four different experiments and we evaluated the usefulness of the feedback obtained in the context of each experiment. The feedback data was triangulated with other sources of quantitative and qualitative data collected for the experiments. Results: We have demonstrated that the collection of feedback during experiments provides useful additional data to: validate the data obtained from other sources about solution times and quality of solutions; check process conformance; understand problem solving processes; identify problems with experiments; and understand subjects perception of experiments. Conclusions: Feedback collection has proved useful in four experiments and we intend to use the feedback-collection tool in a range of other experiments to further explore the cost-effectiveness and limitations of this technique. It is also necessary to carry out a systematic study to more fully understand the impact of the feedback-collecting tool on subjects performance in experiments.     

Amide plasticizers from safflower and tall oil derived fatty acids

Fatty acids derived from a high oleic strain of safflower seeds are eminently suited for the preparation of compatible and efficient N,N-disubstituted fatty acid amide polyvinyl chloride plasticizers with low temperature properties in the adipate-azelate range. N,N-disubstituted amides of tall oil-derived acids, Westvaco Type 1480, give comparable plasticizing performance. Polyvinyl chloride compositions plasticized with the hexachlorocyclopentadiene adduct of N,N-dibutyloleamide show no soapy water extraction loss. So. Market. Nutr. Res. Div., ARS, USDA.