Second law based modeling to optimum design of high capacity pulse tube refrigerators

The optimum design of a high capacity double inlet pulse tube refrigerator based on second law of thermodynamics has been presented in this paper. Second law is applied to calculate the work loss in the regenerator and to optimize the cryocooler performance. To investigate the behavior of the pulse tube refrigerator, mass and energy balance equations are applied to several control volumes of the cryocooler cycle. A complete system of conservation equations is employed to solve the regenerator analytically. The proposed model reports the cooling capacity of 110 W at 80 K cold end temperature at frequency of 50 Hz, orifice conductance of 0.4 and double inlet coefficient of 0.6, with 2.4 kW net power delivered to the gas. In this case, the entropy generation in the gas phase is dominant which is contributing more than 85% of the total lost work in the regenerator. The optimum thermal efficiency of 99.1% was achieved at a proper mesh number. However, the second law efficiency is reported to have an inverse behavior at this mesh number.     

Art and law in the age of digital production

Abstract

‘We might adopt for the artist the joke about there being nothing more dangerous than implements of war in the hands of generals. In the same way, there is nothing more dangerous than justice in the hands of judges, and a paintbrush in the hands of a painter. Just think of the danger to society!’ (Pablo Picasso)¹     

A few special cases: scientific creativity and network dynamics in the field of rare diseases

We develop a model of scientific creativity and test it in the field of rare diseases. Our model is based on the results of an in-depth case study of the Rett Syndrome. Archival analysis, bibliometric techniques and expert surveys are combined with network analysis to identify the most creative scientists. First, we compare alternative measures of generative and combinatorial creativity. Then, we generalize our results in a stochastic model of socio-semantic network evolution. The model predictions are tested with an extended set of rare diseases. We find that new scientific collaborations among experts in a field enhance combinatorial creativity. Instead, high entry rates of novices are negatively related to generative creativity. By expanding the set of useful concepts, creative scientists gain in centrality. At the same time, by increasing their centrality in the scientific community, scientists can replicate and generalize their results, thus contributing to a scientific paradigm.     

Size,age and productivity of scientific and technical research groups

Varied empirical studies show that the average output (measured in various ways) of a scientific or technical research group is directly proportional to its size (also measured in various ways), when the size and output are measured independently. Hence groups of different sizes have the same average output per unit of size. There is no reliable evidence for the existence of a size or a range of sizes for a research group that maximizes output per unit of size. Present theoretical explanations for the proportionality between size and output are largely inadequate or untested. Similarly, among reported results on group age and output, the only consistency so far is that age, measured as years since the founding or first functioning of the group, is uncorrelated with output per capita. Again, there is no evidence for the existence of an age or a range of ages for a research group that is optimal.This paper was prepared for the conference on Generational Dynamics and Innovation in Basic Science, June 1–2, 1989, organized byKarl Urlich Mayer, and held at the Max-Planck-Gesellschaft zur Förderung der Wissenschaften, Schloß Ringberg, Tegernsee, B. R. D. (West Germany). A German translation of this article has been published in theMitteilungen der Max-Planck-Gesellschaft, Heft 3/90.     

Gaining scientific recognition by position: Does editorship increase citation rates?

We investigated three rival hypotheses concerning scientific communication and recognition: the performance hypothesis and two alternative assumptions, the reputation hypothesis and the resource hypothesis. The performance hypothesis reflects the norm of universalism in the sense given byMerton, the reputation hypothesis predicts a Matthew Effect (scientists receive communications and recognition on the basis of their reputation), and the resource hypothesis assumes that communication with other scientitis is used as a form of asset to defend one's own research results. Using bibliometric methods, we assessed whether assuming an important scientific position enhances scientific impact and prestige. Specifically, we explored whether a person's assumption of editorship responsibilities of a psychology journal increases the frequency with which that person is cited in theSocial Sciences Citation Index. The data base consisted of ten psychology journals, seven premier American and three German journals, covering the years 1981 to 1995. Citation rates for the years prior to, during, and following periods of editorship were compared for three groups: editors cited in the journal they edited, editors cited in a journal they did not edit, and non-editors. The results showed that during their editorship, editors showed an increased citation rate in the journal edited; this result was found for American journals, but not for German journals. These findings indicate that, for American journals, assuming editorship responsibilities for a major psychology journal increases one's scientific impact, at least as reflected by a measure of citation rate. A careful examination of ages of the non-editors' citations reveals that the post-editorship citation rates of editors and comparable non-editors do not differ significantly. The reputation hypothesis (Matthew Effect) is therefore preferred for interpreting the results, because it shows the cumulative nature of prestige-oriented citations. The results contradict the convention of using citation rates as pure performance measures.     

Lotka's law reconsidered: The evolution of publication and citation distributions in scientific fields

This paper reports early steps in research that seeks to clarify how publications of scientists interact dynamically with citations and reputation in shaping the evolution of scientific fields. We assume that Lotka's modified law holds for scientific fields. A primary approach to model publication productivity was published by Yablonsky. In contrast to Yablonsky's unfinished mathematical approach, our simulation approach is not predominantly driven by insight into the formal generation mechanisms of certain processes but more theory driven. It considers the evolution of publication and citation distributions over the histories of scientific fields using both simulated and real historical data.     

Effect of mechanical characteristics of a unidirection composite on the law of optimum reinforcement of fibrous composite materials

The authors examined the problem of the effect of the mechanical characteristics of a unidirectional composite material and of winding methods on the position of the optimum reinforcement trajectories. The conditions are determined which the method of reinforcement of the material in designing a structure on the basis of the equal strength criterion with an allowance made for the elasticity of the binder taken into account should be satisfied. For a network glass-plastic cylindrical shell the optimum reinforcement angle is equal to approximately 56° and the deviation from this value results in a small increase of the shell thickness.Translated from Problemy Prochnosti, No. 12, pp. 78–85, December, 1993.     

The relationships between age,mobility and scientific productivity. Part I

The main aim of this study is to estimate to what extent the productivity of researchers is influenced by their mobility. Based on emperical data of Dutch scientists it is shown that job mobility is a characteristic of productive scientists rather than a means to enhance productivity. Field mobility appears to stimulate productivity in the long run.     

The relationships between age,mobility and scientific productivity. Part II

In this paper we show that it is theoretically impossible to draw empirically founded conclusions about the relation between age and productivity. Only the relation between age and productivityincrease can be verified empirically. With this limitation in mind, a subsequent analysis of productivity data of Dutch physicists, chemists en economists, indicates that thegrowth rate of productivity is higher at ages under 35 than at ages over 35.     

Distribution of major scientific and technological achievements in terms of age group — Welbull distribution

A statistical analysis is made of two data sets and it is found that the distribution of major scientific and technological achievements in terms of the age of those achievement makers is Weibull distribution. Pearson'sx ² test results are satisfactory. This finding holds for different centuries, different nations and different disciplines.     

How old is the Web? Characterizing the age and the currency of the European scientific Web

The aim of this paper is to model and study the age of the Web using a sample of about four million of web pages from the 16 European Research Area countries obtained during 2004 and 2005. Web page time-stamp (date when the web pages were created or last changed for last time), format and size in bytes data have been analysed. Several indicators are introduced to measure longitudinal aspects of the Web. Half-age is proposed as a measure of the age distribution because this is found to be exponential. “Web Update Index” and “Lifespan Index” are introduced to measure the changing rate of a small sample over time. Results show that the British Web space has the youngest Web pages while the Greek and Belgian ones have the oldest. The study also compared Web pages topics and found that Biology pages are more stable than Physics pages.     

Effect of intercommunication between various elements of a material on its crack extension resistance: Linear intercommunication force law

A material's resistance to failure by crack extension is influenced by the characteristics of the intercommunication between the various elements that comprise the material's structure. This paper investigates in detail the case where the material consists of linear elements with the crack being transverse to these elements. Various simulation models are analysed, with consideration being focused on the case where the shear intercommunication between the elements is linearly related to the shear strain. It is shown that there is a correlation between weak intercommunication and a high crack extension resistance but that, for a wide range of situations, the strength of the shear intercommunication has relatively little effect on the crack extension resistance. This means that when seeking explanations for large differences in the crack extension resistances of various types of material, it is appropriate to look for such explanations beyond the confines of a simple linear intercommunication law.     

Linear thermodynamic systems with memory. II. Necessary and sufficient conditions for applicability of the second law of thermodynamics

The paper is the second work in a series devoted to nonequilibrium thermodynamics of linear systems with memory. A theorem is proved that contains necessary and sufficient conditions which should be satisfied by constitutive equations for such systems in order to meet the second law of thermodynamics.Academic Scientific Complex A. V. Luikov Institute of Heat and Mass Transfer of the Academy of Sciences of Belarus, Minsk, Belarus. Translated from Inzhenerno-Fizicheskii Zhurnal Vol. 68, No. 5, September–October 1995, pp. 724–738.     

创造力支持系统的体系结构研究

介绍了创造力支持系统发展历程、创造力与创造性思维,综合研究了各类创造力支持系统,给出了创造力支持系统的构成要素、体系结构,并以构建系统用于电力系统故障分析实例研究,阐述了创造力支持系统对专家思维的支持过程。为创造力支持系统开发实现与应用提供参考。     

Exploring the influence of scientific journal ranking on publication performance in the Hungarian social sciences: the case of law and economics

Scientometrics - Using a case study of the Economic and Law Department of the Hungarian Academy of Sciences, we find that domestic rankings greatly distort researchers’ publication...     

Black bear femoral porosity decreases and mechanical properties increase with age despite annual periods of disuse (hibernation)

Inactivity causes bone loss, and a remobilization period that is 2-3 times longer than the disuse period is required to recover lost bone. Black bears (Ursus americanus), however, experience annual disuse (hibernation) and active periods that are approximately equal in length, but maintain bone material properties with age. Here, the effects of annual hibernation periods on whole bone properties were investigated. This study shows that mineral, geometrical and whole bone mechanical properties increase with age in black bear femurs, whereas porosity decreases with age. These results provide further support that black bears possess a biological mechanism to avoid disuse osteoporosis.