Numerical computations of the flow in a finite diverging channel     

Zhao-sheng Yu  Xue-ming Shao  Jian-zhong Lin 《浙江大学学报(A卷英文版)》2010,11(1):50-60

The flow in a finite diverging channel opening into a large space and resembling the experimental prototype of Putkaradze and Vorobieff （2006） was numerically investigated. The effects of the Reynolds number, initial condition, intersection angle, length of the wedge edges, and the outer boundary condition were examined. The numerical results showed that the flow in the wedge undergoes a change from symmetrical flow to unsymmetrical flow with a weak backflow, then a vortical （circulation） flow and finally an unsteady jet flow as the Reynolds number is increased for an intersection angle of 32° and a wedge edge of length 30 times the width of the inlet slit. For the unsteady flow, the jet attached to one side of the wedge constantly loses stability and rolls up into a mushroom-shaped vortex-pair near the outlet of the wedge. As the intersection angle is increased to 50°, a stable jet flow is observed as a new regime between the vortex and unsteady regimes. Both the intersection angle and the wedge length have negative effects on the stability of the flow, although the effect of the wedge length on the critical Reynolds number for the symmetry-breaking instability is not pronounced. The outer boundary condition was found not to affect the flow patterns inside the wedge significantly. At a certain Re regime above the onset of symmetry-breaking instability, the flows evolve into steady state very slowly except for the initial stage in the case of decreasing flow flux. Two different solutions can be observed within the normal observation time for the experiment, providing a possible explanation for the hysteresis phenomenon in the experiment.  相似文献   

Effect of a semi electro-mechanical engine valve on performance and emissions in a single cylinder spark ignited engine     

Bülent 《浙江大学学报(A卷英文版)》2010,11(2):106-114

In this study, an electro-mechanical valve （EMV） system for the intake valve ofa fottr stroke, single cylinder, overhead valve and spark ignition （SI） engine was designed and constructed. An engine with the EMV system and a standard engine were tested to observe the effects of the EMV on engine performance and emissions at different speeds under full load. The EMV engine showed improved engine power, engine torque and break specific fuel consumption （BSFC）. A 66% decrease in CO emissions was also obtained with the EMV system, but hydrocarbons （HC） and NOx emissions increased by 12% and 13% respectively.  相似文献   

Temporal variation in modal properties of a base-isolated building during an earthquake     

Izuru TAKEWAKI  Mitsuru NAKAMURA 《浙江大学学报(A卷英文版)》2010,11(1):1-8

Temporal variation of dynamical modal properties of a base-isolated building is investigated using earthquake records in the building. A batch processing least-squares estimation method is applied to segment-wise time-series data. To construct an input-output system, an auto-regressive model with exogenous input （ARX） of second-order including a forgetting coefficient as a weighting coefficient is used for the estimation of modal parameters. The fundamental and second natural frequencies and the damping ratios of the fundamental and second natural modes of the base-isolated building are identified in the time domain. The identified results are consistent with the results obtained from the micro-tremor vibration data, forced-vibration test data and earthquake records in the present base-isolated building in the case of taking into account the amplitude-dependency of the iso- lators and viscous dampers. It is finally pointed out that several factors, e.g., amplitude dependency of the isolator and damper system and special characteristics of the series-type viscous damper system, may be related complicatedly with the temporal variation in modal properties of the above-mentioned system.  相似文献   

Improved response surface method for anti-slide reliability analysis of gravity dam based on weighted regression   总被引：1，自引：0，他引：1  

Jian-yun Chen  Qiang Xu  Jing Li  Shu-li Fan 《浙江大学学报(A卷英文版)》2010,11(6):432-439

The aim of this study was to design and construct an improved response surface method （RSM） based on weighted regression for the anti-slide reliability analysis of concrete gravity dam. The limitation and lacuna of the traditional RSM were briefly analyzed. Firstly, based on small experimental points, research was devoted to an improved RSM with singular value decomposition techniques. Then, the method was used on the basis of weighted regression and deviation coefficient correction to reduce iteration times and experimental points and improve the calculation method of checking point. Finally, a test example was given to verify this method. Compared with other conventional algorithms, this method has some strong advantages： this algorithm not only saves the arithmetic operations but also greatly enhances the calculation efficiency and the storage efficiency.  相似文献   

<Emphasis Type="Italic">Minerva</Emphasis> and the Development of Science (Policy) Studies     

Niels C. Taubert 《Minerva》2012,50(3):261-275

This article analyzes the transformation of Minerva from an intellectual towards a scholarly journal by making use of bibliometric methods. The aim is to provide some empirical insights that help to understand what properties of the journal changed in the course of this transformation process. Minerva was one of the first journals that reflected on science and its role in society and science policy in particular. Analyzing the development of the journal sheds light on the emergence of science (policy) studies and on Minerva’s role as a forerunner in this field. In a first step, the methods will be described. The second section provides some empirical results of the publication output of Minerva and its relations to other journals in the field. The empirical findings are put into a broader perspective in the concluding third section.  相似文献   

The Congress for Cultural Freedom, <Emphasis Type="Italic">Minerva</Emphasis>, and the Quest for Instituting “Science Studies” in the Age of Cold War     

Elena Aronova 《Minerva》2012,50(3):307-337

The Congress for Cultural Freedom is remembered as a paramount example of the “cultural cold wars.” In this paper, I discuss the ways in which this powerful transnational organization sought to promote “science studies” as a distinct – and politically relevant – area of expertise, and part of the CCF broader agenda to offer a renewed framework for liberalism. By means of its Study Groups, international conferences and its periodicals, such as Minerva, the Congress developed into an influential forum for examining the ways Big Science impacted the relations between science, society, and politics, thus constituting a semi-institutional niche for Science Studies before its professionalization within academia during the 1970s. I argue that the Congress contributed to the construction of public space in which the relations between science, society and politics were debated, and science was reconceptualized as a social activity. The vision of “science studies” the CCF-associated intellectuals promulgated was different from the science studies we know today. Yet, this alternative vision, in which the issues of science politics appeared inseparable from those of science policy, science organization, and science governance, constituted the “pre-history” of science studies today.  相似文献   

<Emphasis Type="Italic">Minerva</Emphasis> - 50 Years Reflecting on Science in Society     

Peter Weingart 《Minerva》2012,50(3):255-259

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The Middle East Books Market: a Personal Overview     

Bill Kennedy 《Publishing Research Quarterly》2010,26(3):187-192

A concise review is presented of the essential elements of the book publishing and bookselling business in a complex and diverse market. Demographics create the diversity while Arabic is the one language spoken across a multitude of different countries. Three features are common to all of these countries and they are: the dominance of English as the second language, education has and will remain to be a priority, and economic pressures cause price sensitivity to be a major challenge especially in the educational market segments. It is the price sensitivity as a key factor for the lack of respect for intellectual property and copyright regulations. A review of distribution and retail stores is a very important topic in relation to this complex collection of countries. The emergence of e-books is discussed especially in the educational, professional and reference market segments. Finally, there is a review of the Arabic language publishers and local book fairs to bring this article to closure.  相似文献   

Robert McCrum: GLOBISH: How the English Language Became the World’s Language     

Claire Wyckoff 《Publishing Research Quarterly》2010,26(4):299-300

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Finding related sentence pairs in MEDLINE     

Smith LH  Wilbur WJ 《Information Retrieval》2010,13(6):601-617

We explore the feasibility of automatically identifying sentences in different MEDLINE abstracts that are related in meaning. We compared traditional vector space models with machine learning methods for detecting relatedness, and found that machine learning was superior. The Huber method, a variant of Support Vector Machines which minimizes the modified Huber loss function, achieves 73% precision when the score cutoff is set high enough to identify about one related sentence per abstract on average. We illustrate how an abstract viewed in PubMed might be modified to present the related sentences found in other abstracts by this automatic procedure.  相似文献