Complexity, Collective Effects and Modelling of Ecosystems: formation, function and stability

We discuss the relevance of studying ecology within the framework of Complexity Science from a statistical mechanics approach. Ecology is concerned with understanding how systems level properties emerge out of the multitude of interactions amongst large numbers of components, leading to ecosystems that possess the prototypical characteristics of complex systems. We argue that statistical mechanics is at present the best methodology available to obtain a quantitative description of complex systems, and that ecology is in urgent need of ``integrative'' approaches that are quantitative and non-stationary. We describe examples where combining statistical mechanics and ecology has led to improved ecological modelling and, at the same time, broadened the scope of statistical mechanics.Comment: 11 pages and 1 figur

Agricultural Water Demands in the Silistra Region

This paper, the ninth in the IIASA water demand series, reports on the analysis of water demands of a large agroindustrial complex in the northeastern part of Bulgaria, covering a territory of about 2,700 sq. km, with a population of some 175,000. With the aid of SWIM (Silistra Water for Irrigation Model), which was developed at IIASA, several factors that both influence agricultural production and associated water demands have been analyzed. The major goal of the Silistra complex, to maximize the total crop and livestock production within the limited regional resources, has been taken into account in the analysis. The model allows analyses to be made of substitution possibilities in agricultural production (water for fertilizers, irrigated for nonirrigated crops, one sub-region for another, and so on). The work leads ultimately to determining an economically efficient level of irrigation development

Anatomy of Malicious Singularities

As well known, the b-boundaries of the closed Friedman world model and of Schwarzschild solution consist of a single point. We study this phenomenon in a broader context of differential and structured spaces. We show that it is an equivalence relation $\rho$, defined on the Cauchy completed total space $\bar{E}$ of the frame bundle over a given space-time, that is responsible for this pathology. A singularity is called malicious if the equivalence class $[p_0]$ related to the singularity remains in close contact with all other equivalence classes, i.e., if $p_0 \in \mathrm{cl}[p]$ for every $p \in E$. We formulate conditions for which such a situation occurs. The differential structure of any space-time with malicious singularities consists only of constant functions which means that, from the topological point of view, everything collapses to a single point. It was noncommutative geometry that was especially devised to deal with such situations. A noncommutative algebra on $\bar{E}$, which turns out to be a von Neumann algebra of random operators, allows us to study probabilistic properties (in a generalized sense) of malicious singularities. Our main result is that, in the noncommutative regime, even the strongest singularities are probabilistically irrelevant.Comment: 16 pages in LaTe

QUANTITATIVE CLINICAL NEUROLOGICAL TESTING. I. A STUDY OF A BATTERY OF TESTS DESIGNED TO EVALUATE IN PART THE NEUROLOGICAL FUNCTION OF PATIENTS WITH MULTIPLE SCLEROSIS AND ITS USE IN A THERAPEUTIC TRIAL *

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73100/1/j.1749-6632.1965.tb20231.x.pd

Diffraction behaviour of three-component fibonacci Ta/Al multilayer films

A class of quasiperiodic structure three-component Fibonacci (3CF) Ta/Al multilayer films is fabricated by dual-target magnetron sputtering. The microstructure of this film is investigated by transmission electron microscopy and electron and X-ray diffraction. Cross-section transmission electron microscopy demonstrates a well formed layer structure of 3CF Ta/Al superlattices. The electron-diffraction satellite spots, which can be indexed by three integers, correspond to the X-ray diffraction peaks in both position and intensity. The scattering vectors observed in electron and X-ray diffraction are in good agreement with the analytical treatment from the projection method

A Simple Shell Model for Quantum Dots in a Tilted Magnetic Field

A model for quantum dots is proposed, in which the motion of a few electrons in a three-dimensional harmonic oscillator potential under the influence of a homogeneous magnetic field of arbitrary direction is studied. The spectrum and the wave functions are obtained by solving the classical problem. The ground state of the Fermi-system is obtained by minimizing the total energy with regard to the confining frequencies. From this a dependence of the equilibrium shape of the quantum dot on the electron number, the magnetic field parameters and the slab thickness is found.Comment: 15 pages (Latex), 3 epsi figures, to appear in PhysRev B, 55 Nr. 20 (1997

Far-infrared edge modes in quantum dots

We have investigated edge modes of different multipolarity sustained by quantum dots submitted to external magnetic fields. We present a microscopic description based on a variational solution of the equation of motion for any axially symmetric confining potential and multipole mode. Numerical results for dots with different number of electrons whose ground-state is described within a local Current Density Functional Theory are discussed. Two sum rules, which are exact within this theory, are derived. In the limit of a large neutral dot at B=0, we have shown that the classical hydrodynamic dispersion law for edge waves \omega(q) \sim \sqrt{q \ln (q_0/q)} holds when quantum and finite size effects are taken into account.Comment: We have changed some figures as well as a part of the tex

Far-infrared edge modes in quantum dots

We have investigated edge modes of different multipolarity sustained by quantum dots submitted to external magnetic fields. We present a microscopic description based on a variational solution of the equation of motion for any axially symmetric confining potential and multipole mode. Numerical results for dots with different number of electrons whose ground-state is described within a local Current Density Functional Theory are discussed. Two sum rules, which are exact within this theory, are derived. In the limit of a large neutral dot at B=0, we have shown that the classical hydrodynamic dispersion law for edge waves \omega(q) \sim \sqrt{q \ln (q_0/q)} holds when quantum and finite size effects are taken into account.Comment: We have changed some figures as well as a part of the tex

Water Demand for Generating Electricity - A Mathematical Programming Approach with Application in Poland

This report documents a water demand study developed as a collaborative effort between the International Institute for Applied Systems Analysis (IIASA), Laxenburg, Austria; the Institute of Meteorology and Water Management (IMGW), Warsaw, Poland; and the Industry Studies Program of the University of Houston, Houston, Texas, USA. The study developed and applied a mathematical programming model of resource in an electric power plant. The model specifically represents a hypothetical, coal-fired plant located on the Vistula River in Poland. The modeling techniques, however, have very general applicability. The report emphasizes issues of water demand in the modeled plant and also discusses coal transportation, and combustion. Major design and operating options for the plant are described, including the cooling system, water treatment processes, choices of coal type, and mode of transport, railroad or slurry pipeline. These options are constrained by identified standards for air and water quality, and the model is constructed to minimize costs of generating specified loads of electricity in accordance with these constraints. The report provides a detailed description of the model's structure, relating each component to the identified options and constraints. Some general issues in modeling industrial operations are discussed. The report concludes with a presentation of illustrative water demand analyses performed with the model. The results are not definitive but highlight the power of the method and the importance of an integrated approach to studying water demand and other aspects of industrial resource use