Temperature Dependence of Transport Coefficients in Liquid and Amorphous Metals

We apply the muffin-tin effective medium approximation to calculate the temperature dependence of the resistivity and of the thermopower of amorphous and liquid metals. The results show unambiguously that a large resistivity is accompanied by a negative temperature coefficient, in agreement with the experimental situation. This behavior is shown to result from a pseudo-gap which opens in the 1-particle spectrum due to strong scattering at the quasi zone boundary. In turn the thermopower is found to have non-trivial density and temperature dependences.Comment: 9 pages, 9 Postscript figure

Self tolerance in a minimal model of the idiotypic network

We consider the problem of self tolerance in the frame of a minimalistic model of the idiotypic network. A node of this network represents a population of B lymphocytes of the same idiotype which is encoded by a bit string. The links of the network connect nodes with (nearly) complementary strings. The population of a node survives if the number of occupied neighbours is not too small and not too large. There is an influx of lymphocytes with random idiotype from the bone marrow. Previous investigations have shown that this system evolves toward highly organized architectures, where the nodes can be classified into groups according to their statistical properties. The building principles of these architectures can be analytically described and the statistical results of simulations agree very well with results of a modular mean field theory. In this paper we present simulation results for the case that one or several nodes, playing the role of self, are permanently occupied. We observe that the group structure of the architecture is very similar to the case without self antigen, but organized such that the neighbours of the self are only weakly occupied, thus providing self tolerance. We also treat this situation in mean field theory which give results in good agreement with data from simulation.Comment: 7 pages, 6 figures, 1 tabl

Employment creation in less developed countries: A cross section analysis

Research in the field of economic development and respective discussions in the political sphere are presently focussing on two major issues: the social inequality within the third world and the continuously widening, economic gap between developing (LDCs) and developed (DCs) nations. The remedy for both problems suggested by UNIDO, the UN General Assembly and various other institutions is a new international economic order''. One aspect of this new order is the claim for a 20 per cent share of LDCs in total manufacturing production of the world by the year 2000. Given a 6.8 per cent share of LDCs manufacturing output at present (in 1973) a tremendous structural change will have to take place in third world economies and in the international division of labour in order to achieve the 20 per cent target. The purpose of this paper is to analyse the past structural change in LDCs and to outline some of the implications of the intended increase of their share in world industry. In particular, the paper seeks tentative answers to such questions as - whether the necessary structural change is feasable and under which conditions it is likely to occur; - what the prospective employment effects of such a strategy would be and - whether alternative strategies might offer better chances in reducing unemployment and poverty within the third world. To fulfill this task in the first part of the paper, a cross section analysis is applied to a sample of LDCs and DCs respectively. The focus is to identify major determinants of sectoral patterns of production, employment and productivity in both country groups and to find out whether there are differences among the various patterns or among country groups. Based on these estimates some projections of production and employment patterns are made in the final section of the paper and some consideration is given to the potential contribution to employment creation in various economic activities.

Critical Systemic Discourse

The first part presented a philosophical staircase that can guide IS practitioners in identifying the various validity claims raised by any project of information systems definition, design, and development (ISD). It was concluded that the discursive principle is constitutive of every step in this staircase but requires pragmatization. The present second part of the paper begins with a short review of the way in which the discursive principle has been considered in the ISD literature thus far. It then introduces the second main pillar of the suggested approach to reflective practice in ISD, critically systemic discourse. The methodological core concept of critically systemic discourse is boundary critique, a concept based in the author’s work on critical systems heuristics and critical systems thinking. Based on this core concept and a practical application, a three-stage model for reflective practice in ISD is suggested

Nestedness analysis as a tool to identify ecological gradients

Nestedness describes patterns of species composition within continental biotas and among isolated habitats such as islands and landscape fragments. In a nested pattern, the species composition of small assemblages is an ordered subset (a true sample) of the species composition of large assemblages. Nested subsets of species are generated by environmental and ecological gradients, such as habitat quality, carrying capacities of sites, isolation, or fragmentation, that cause ordered sequences of species extinctions and colonization. Therefore nestedness analysis can be used to identify gradients that influence species composition and richness among sites and to identify species that run counter to these gradients (idiosyncratic species). Here I review the use of nestedness analysis to identify such gradients. I also describe how to perform the analysis and which metrics and null models to use for statistical inference

A Philosophical Staircase for Information Systems Definition, Design and Development

The paper proposes a critical1 approach to information systems definition, design, and development (ISD) grounded in discourse theory, semiotics, practical philosophy and critical systems thinking. It aims to support IS researchers and practitioners in the difficult process of identifying and scrutinizing the diverse issues they face in any ISD project. Two main components of the approach are a hierarchic arrangement of these issues, and of the basic kinds of validity claims they imply, in the form of a philosophical staircase; and a practical framework for critical discourse on these claims called critically systemic discourse. The present first part introduces the staircase and discusses the relevance of the discursive principle for dealing with the various validity claims raised by each one of its steps. The second part will present a discursive framework for applying the staircase

Tillage intensity and herbicide application influence surface-active springtail (Collembola) communities in Romanian vineyards

Vineyards are important perennial, often intensively managed agroecosystems. In most vineyards, ground vegetation is controlled by tillage and/or the application of broadband herbicides with scarcely known effects on the soil fauna. We studied a total of 16 commercial vineyards in the Târnave wine region, a typical viticultural region in Transylvania, Central Romania. As a model organism for surface-dwelling arthropods we examined the response of springtail (Collembola) species richness and activity density to vineyard tillage practices, fertilization, and herbicide application. A total of 24 species in 10 families were found in the studied vineyards. Principal coordinates analysis (PCoA) identified three distinct springtail communities linked to tillage and fertilization practice. Springtail species richness was positively associated with high tillage intensity (frequency: once or twice a year). Springtail activity density in inter-rows was positively correlated with inter-row tillage and herbicide application under grapevines. For the first time we could show that springtail species assemblages in vineyards were characterized by high niche overlap regarding soil quality (organic matter, pH, CaCO3, P and K), indicating similar resource utilization. We conclude that the positive influence of vineyard management and disturbance on surface-dwelling springtail communities is possibly due to the exclusion of potential competitors and predators, the stimulation of microorganisms and/or an increased nutrient input

Rethinking Critically Reflective Research Practice: Beyond Popper’s Critical Rationalism

We all know that ships are safest in the harbor; but alas, that is not what ships are built for. They are destined to leave the harbor and to confront the challenges that are waiting beyond the harbor mole. A similar challenge confronts the practice of research. Research at work cannot play it safe and stay in whatever theoretical and methodological harbors in which it may have found shelter in the past. Still less can it examine and maintain its foundations in the dry dock. Research is more like a ship that must be repaired on the open sea. Yet foundationalist ideas persist in the practice of research. Counter to what is often assumed, today’s dominating model for research--the fallibilist model of critical rationalism--has not really overcome the empirical foundationalism of earlier, positivist research practices. This paper analyses two major foundationalist traps that are currently in the upswing and work against reflective research practice