The estimation of distributions and the minimum relative entropy principle

Estimation of Distribution Algorithms (EDA) have been proposed as an extension of genetic algorithms. In this paper we explain the relationship of EDA to algorithms developed in statistics, artificial intelligence, and statistical physics. The major design issues are discussed within a general interdisciplinary framework. It is shown that maximum entropy approximations play a crucial role. All proposed algorithms try to minimize the Kullback-Leibler divergence KLD between the unknown distribution p(x) and a class q(x) of approximations. However, the Kullback-Leibler divergence is not symmetric. Approximations which suppose that the function to be optimized is additively decomposed (ADF) minimize KLD(q||p), the methods which learn the approximate model from data minimize KLD(p||q). This minimization is identical to maximizing the log-likelihood. In the paper three classes of algorithms are discussed. FDA uses the ADF to compute an approximate factorization of the unknown distribution. The factors are marginal distributions, whose values are computed from samples. The second class is represented by the Bethe-Kikuchi approach which has recently been rediscovered in statistical physics. Here the values of the marginals are computed from a difficult constrained minimization problem. The third class learns the factorization from the data. We analyze our learning algorithm LFDA in detail. It is shown that learning is faced with two problems: first, to detect the important dependencies between the variables, and second, to create an acyclic Bayesian network of bounded clique size.     

User centred design for a digital welding machine

The design of the user interface of a digital welding machine based on a user centred design process is described in this paper. Due to the iterative design process and the involvement of end users, interaction techniques have been designed which are optimised for the mental work model of the target user groups.     

Neue Aspekte der Feldtheorie

Zusammenfassung Es werden Lagrange-Dichten betrachtet, die neben den Potentialen und deren Ableitungen auch noch Ströme enthalten. Mit Hilfe eines Hamilton-Prinzips werden die Feld- und Bewegungsgleichungen unabhängig voneinander gewonnen.

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New aspects in field theory

Summary In this paper Lagrangian Densities are considered containing fluxes as well as potentials and their derivatives. By means of a Hamilton Principle the field equations and the equations of motion are derived indepedently of each other.

     

Experimental set-up for time resolved small angle X-ray scattering studies of nanoparticles formation using a free-jet micromixer

Recently, we have designed, fabricated and tested a free-jet micromixer for time resolved small angle X-ray scattering (SAXS) studies of nanoparticles formation in the <100 μs time range. The microjet has a diameter of 25 μm and a time of first accessible measurement of 75 μs has been obtained. This result can still be improved. In this communication, we present a method to estimate whether a given chemical or biological reaction can be investigated with the micromixer, and to optimize the beam size for the measurement at the chosen SAXS beamline. Moreover, we describe a system based on stereoscopic imaging which allows the alignment of the jet with the X-ray beam with a precision of 20 μm. The proposed experimental procedures have been successfully employed to observe the formation of calcium carbonate (CaCO₃) nanoparticles from the reaction of sodium carbonate (Na₂CO₃) and calcium chloride (CaCl₂). The induction time has been estimated in the order of 200 μs and the determined radius of the particles is about 14 nm.     

Diversifikation von Separatoren mit Düsen-, selbstreinigenden und Vollmantel-Trommeln

Diversification of separators with nozzles, provision for selfcleaning, and solid bowls . The flow processes in most centrifuges, and thus also in disk separators, are still partly unknown. An empirical approach and experimentation are therefore of considerable importance for design and applications. Special designs are developed primarily for dealing with liquids having particular properties and the characteristics of various basic types are combined. Highly specialized machines usually result which are optimized for only very narrow fields of application. This development is illustrated for the combination of characteristics of separators having nozzles, provision for self-cleaning, and solid bowls.     

Metallurgical Development in Steel‐plant‐internal Multi‐injection Hot Metal Desulphurisation

The use of thermodynamic, statistical, and light and electron‐optical microscopic methods has made it possible to analyse the course of reactions during steel‐plant‐internal hot metal desulphurisation. The theoretical dependence between oxygen and sulphur activity has been used to develop an EMF‐measurement‐based technique for determining the sulphur content as the hot metal is desulphurised. The absence of magnesium sulphide from the collection of phases in the final slag because of the greater stability and secondary formation of calcium sulphide has been explained with the aid of thermo‐chemical calculations.