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.     

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.     

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.     

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...     

Qualitative properties of optimum acoustic structures

Problems of optimum synthesis of layered structures exposed to acoustic waves are investigated. Qualitative laws governing the interrelationship between the parameters in structures that realize the limiting possibilities for control of the energy characteristics of acoustic waves are established. A numerical example is given. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 5, pp. 902–905, September–October, 1998.     

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.     

带线性不等式约束的线性模型中线性预测的可容许性

本文刻画了线性模型在线性不等式约束条件下的线性预测的可容许性。我们给出了条件线性可预测变量和线性不等式约束条件下可容许预测的定义,在二次损失函数下,讨论了齐次和非齐次线性预测可容许性的关系,得到了条件线性可预测变量的线性预测是可容许线性预测的充要条件。     

Behaviour of underwater enclosures of optimum design

Experiments are described which support the application of the membrane theory of shell analysis in determining optimum shapes for underwater structures of constant strength. A relationship between marine life and such structures is considered and design procedures for shape selection are given. Proposals for the investigation of the behaviour of such structures under loadings other than the initial design forces are outlined both from an analytical! numerical and an experimental approach.