Showing papers by "Technical University of Dortmund published in 1994"

Convergence analysis of canonical genetic algorithms

Abstract: This paper analyzes the convergence properties of the canonical genetic algorithm (CGA) with mutation, crossover and proportional reproduction applied to static optimization problems. It is proved by means of homogeneous finite Markov chain analysis that a CGA will never converge to the global optimum regardless of the initialization, crossover, operator and objective function. But variants of CGA's that always maintain the best solution in the population, either before or after selection, are shown to converge to the global optimum due to the irreducibility property of the underlying original nonconvergent CGA. These results are discussed with respect to the schema theorem. >

Human glutathione S-transferase theta (GSTT1): cDNA cloning and the characterization of a genetic polymorphism.

Abstract: In humans, glutathione-dependent conjugation of halomethanes is polymorphic, with 60% of the population classed as conjugators and 40% as non-conjugators. We report the characterization of the genetic polymorphism causing the phenotypic difference. We have isolated a cDNA that encodes a human class Theta GST (GSTT1) and which shares 82% sequence identity with rat class Theta GST5-5. From PCR and Southern blot analyses, it is shown that the GSTT1 gene is absent from 38% of the population. The presence or absence of the GSTT1 gene is coincident with the conjugator (GSST1+) and non-conjugator (GSTT1-) phenotypes respectively. The GSTT1+ phenotype can catalyse the glutathione conjugation of dichloromethane, a metabolic pathway which has been shown to be mutagenic in Salmonella typhimurium mutagenicity tester strains and is believed to be responsible for carcinogenicity of dichloromethane in the mouse. In humans, the enzyme is found in the erythrocyte and this may act as a detoxification sink. Characterization of the GSTT1 polymorphism will thus enable a more accurate assessment of human health risk from synthetic halomethanes and other industrial chemicals.

Selective pressure in evolutionary algorithms: a characterization of selection mechanisms

Abstract: Due to its independence of the actual search space and its impact on the exploration-exploitation tradeoff, selection is an important operator in any kind of evolutionary algorithm. All important selection operators are discussed and quantitatively compared with respect to their selective pressure. The comparison clarifies that only a few really different and useful selection operators exist: proportional selection (in combination with a scaling method), linear ranking, tournament selection, and (/spl mu/,/spl lambda/)-selection (respectively (/spl mu/+/spl lambda/)-selection). Their selective pressure increases in the order as they are listed here. The theoretical results are confirmed by an experimental investigation using a genetic algorithm with different selection methods on a simple unimodal objective function. >

Second harmonic generation and magnetic-dipole-electric-dipole interference in antiferromagnetic Cr2O3.

Abstract: The second harmonic spectrum of ${\mathrm{Cr}}_{2}$${\mathrm{O}}_{3}$ is studied in the 1.7-2.9 eV spectral range as a function of temperature. Below the N\'eel temperature ${T}_{N}=307.5$ K a nonlinear electric susceptibility ${\ensuremath{\chi}}_{\mathrm{ijk}}^{e}(c)$ appears, which changes sign under the time-reversal operation. The interference of this susceptibility with the time-invariant magnetic susceptibility ${\ensuremath{\chi}}_{\mathrm{ijk}}^{m}(i)$ leads to a pronounced polarization dependence for circularly polarized light propagating along the optical axis. This gives a novel tool to study antiferromagnetic domains with opposite orientation of the order parameter.

A multiresolution framework for volume rendering

Abstract: In dieser Arbeit wurde ein genereller hierarchischer Ansatz zur Visualisierung skalarer Volumendaten entwickelt. Dieser ermoglicht die direkte Visualisierung komprimierter Daten, die Beschleunigung des Darstellungsvorgangs und die Extraktion und Hervorhebung der wesentlichen Strukturen. Grundlegende Konzepte der Multiskalenanalyse mittels hierarchischer Basisfunktionen wurden hierzu verwendet und entsprechend den Anforderungen erweitert. Insbesondere resultierte die Arbeit in speziellen Verfahren zur Vorverarbeitung und Darstellung zeitvarianter Datensequenzen. Sowohl fur die Datenanalyse als auch fur die Bildsynthese wurden Parallelisierungskonzepte entworfen und implementiert. Die integrierte Analyse und Darstellung komplexer skalarer Volumendaten wurde durch diese Entwicklungen ermoglicht.

Reverse annealing of the effective impurity concentration and long term operational scenario for silicon detectors in future collider experiments

Abstract: Systematic investigations of the reverse annealing effect after radiation damage have been performed in particular for the change of the effective impurity concentration. The pronounced long term anneal observed at room temperature was further investigated by isochronal and isothermal studies. In order to demonstrate the radiation hardness of silicon detectors during 10 years of LHC operation an experiment was started at a higher temperature which compressed the real operational scenario to about 10 months.

The shape of the Shape Lemma

Abstract: The Shape Lemma was originally introduced in [3] and so christened by Lakshman ([5]). It is an easy generalization of the Primitive Element Theorem and it states that a Odimensional radical ideal in a polynomial ring k[X1, . . . . Xn], after most changes of coordinates, has a basis {91(X1),X2 -92(X1 ),. ~.,xn -gn(xl)} Notwithstanding its triviality, it has proved ubiquitous in recent papers on polynomial system solving ([1, 2, 4, 6, 7]). The obvious example (X2, XY, Y2) is sufficient to show that some assumption is needed on a O-dimensional ideal in order that it holds; the obvious example (X2, Y) is sufficient to show that radicality is too strong an assumption. Since most of the results making use of the Shape Lemma are valid whenever the Shape Lemma holds and are of interest also for non radical ideals, it is worthwhile to exactly characterize those O-dimensional ideals to which the Shape Lemma applies. It turns out that this exact characterization is as trivial as the original Shape Lemma itself. In fact both this characterization and the generalization of it we give are easy specializations of a classical result in algebraic geometry on the minimum dimension of a generic biregular projection of a variety as a function of its dimension and of the dimension of its tangent bundle. We give a direct, elementary, self-contained proof of this specialization.

Polarized and unpolarized isolated prompt photon production beyond the leading order.

Abstract: We present a simple and accurate analytical method for calculating the cross section for polarized and unpolarized [ital isolated] prompt photon production in next-to-leading order, taking into account also the next-to-leading-order fragmentation contribution in the unpolarized case. We demonstrate the good accuracy of our method over a wide range of the isolation parameters and study the effects the isolation cuts have on the cross section at colliders.

New perspectives of NMR in ultrahigh static magnetic field gradients

Abstract: The magnetic field gradient nuclear magnetic resonance (NMR) stimulated echo experiment measures the incoherent (or self) part of the intermediate scattering function S( Q ,t) ∼ 〈 exp [ − i Qr (O)] exp [ i Qr (t)]〉 with a ‘generalized’ scattering vector Q = γ· g ·τ (γ is the gyromagnetic ratio, g is the magnetic field gradient, τ is the evolution time). With ultrahigh static field gradients up to ≈ 180 T/m, a prototype of which has recently been installed in Mainz, Q-values up to > 10−2 A−1 become accessible. The first part of the paper focusses on details of this technical development and points out the close analogy with incoherent neutron scattering. In the second part, the enormous new possibilities of this kind of gradient NMR are demonstrated through a collection of most recent applications: the measurement of small self-diffusion coefficients down to about 10−15 m2s−1 in supercooled liquids and in molecular crystals, long chain polymer dynamics, restricted diffusion in systems of confined mesocopic geometries and anomalous diffusion on fractal structures.

Metabolism of dichloromethane (methylene chloride) to formaldehyde in human erythrocytes: influence of polymorphism of glutathione transferase Theta (GST T1-1)

Abstract: Human hemolysate was incubated in vitro with different concentrations of dichloromethane (methylene chloride). The resulting enzymatically mediated production of formaldehyde was determined by two independent analytical methods (Nash-reaction/colorimetry or HPLC). The formation of formaldehyde from dichloromethane is influenced by the polymorphism of glutathione-S-transferase (GST) Theta, in the same way as the metabolism of methyl bromide, methyl chloride, methyl iodide and ethylene oxide. Three quarters of the population (“conjugators”) possess, whereas one quarter (“non-conjugators”) lack this enzyme activity in human erythrocytes. The metabolism of dichloromethane in hemolysate in vitro can be described by Michaelis-Menten kinetics; for an individual with high GST T1-1 enzyme activity, the maximum velocity of formaldehyde production was calculated to be approximately 180 pmol/min per mg Hb, the k M being approximately 60 mM dichloromethane. Carcinogenicity of dichloromethane in long-term inhalation exposure of rodents has been attributed to metabolism of the compound via the GST-dependent pathway. Extrapolation of the results to humans for risk assessment should consider the newly discovered polymorphic enzyme activity of GST Theta. Furthermore, the possible existence of a “high-risk” population among humans should be considered in epidemiological research.

An evolutionary heuristic for the maximum independent set problem

Abstract: The results obtained from the application of a genetic algorithm, GENEsYs, to the NP-complete maximum independent set problem are reported. In contrast to many other genetic algorithm-based approaches that use domain-specific knowledge, the approach presented in this paper relies on a graded penalty term component of the fitness function to penalize infeasible solutions. The method is applied to several large problem instances of the maximum independent set problem. The results clearly indicate that genetic algorithms can be successfully used as heuristics for finding good approximative solutions for this highly constrained optimization problem. >

Polarization dependence of dephasing processes: A probe for many-body effects.

Abstract: The spectra of the diffracted wave in femtosecond-four-wave mixing and their dependence on the polarization of the driving fields are shown to be a very sensitive probe for the fundamental scattering processes that govern the coherent dynamics in a semiconductor. We demonstrate that the total dephasing rate is the result of a delicate balance between self-energies and vertex corrections. Particle interactions of the polarization scattering type are shown to be important contributions to the nonlinear optical response in the coherent regime.

Multiorganyltin Compounds. Designing a novel phosphate‐selective carrier

Abstract: A series of distannyl derivatives, 1–9, were studied for their application as phosphate-selective carriers in polymer-based liquid membranes. A drastically different potentiometric behavior was observed depending on the distance between the tin(IV) coordinating centers and the ligands attached to them. Some of the compounds examined, i.e. (PhSnBr2)2CH2(1) and (Me3SiCH2SnCl2CH2)2 (3) showed very high potentiometric selectivity towards phosphate over other lipophilic anions such as perchlorate and thiocyanate. Results indicate that (1) the optimal number of CH2 groups between the Sn-centers are either one or three, (2) the electron-withdrawing power of the organic ligands attached to Sn-centers strongly influences the overall response towards phosphate, and (3) the steric effect of the organic substituents is important in the potentiometric selectivity observed.

On the computational power of depth 2 circuits with threshold and modulo gates

Abstract: We investigate the computational power of depth two circuits consisting of MODr--gates at the bottom and a threshold gate at the top (for short, threshold--MODr circuits) and circuits with two levels of MOD gates (MODp-MODq circuits.) In particular, we will show the following results (i) For all prime numbers p and integers qr it holds that if p divides r but not q then all threshold--MODq circuits for MODr have exponentially many nodes. (ii) For all integers r all problems computable by depth two ANDORNOT --circuits of (quasi) polynomial size can be represented by threshold--MODr circuits with (quasi)poly\-no\-mially many edges. (iii) There is a problem computable by depth three ANDORNOT --circuits of linear size and constant bottom fan--in which for all r needs threshold--MODr circuits with exponentially many nodes. (iv) For pr different primes, and q2 k positive integers, where p does not divide q every MODpk-MODq circuit for MODr has exponentially many nodes...

Quantum fluctuations around the electroweak sphaleron.

Abstract: We present an analysis of the quantum fluctuations around the electroweak sphaleron and calculate the associated determinant which gives the one-loop correction to the sphaleron transition rate. The calculation differs in various technical aspects from a previous analysis by Carson and co-workers so that it can be considered as independent. The numerical results differ also, by several orders of magnitude, from those of this previous analysis; we find that the sphaleron transition rate is much less suppressed than found previously.

Objects and Databases

Abstract: Part 1 Introduction: shortcomings of the relational model extensions of the relational model object oriented database systems. Part 2 Concepts of OOP: concepts of OOP in LISP and AutoLISP concepts of OOP in SmallTalk and OPAL. Part 3 Analysis and design methodology: developing an application. Part 4 Implementation techniques: indexing techniques transaction management perspective for OODBMSs.

Evolution strategies applied to perturbed objective functions

Abstract: We investigate the behavior of evolution strategies on noisy objective functions. We show for the simple sphere model that convergence velocity is not reduced as long as the noise level is small compared to the function value. If the noise level reaches a certain threshold, a size of the parent population greater than 1 improves the convergence precision significantly. Convergence reliability is tested for two nonconvex functions. Again the search process seems to be not influenced by low level noise. Interpreting the impact of noise purely as a modification of the selection process gives new insight into the role of selection in evolution strategies. >

On T-quantifiers and S-quantifiers

Abstract: We show how the "classical" theory of T-norms and S-norms of fuzzy logic can be generalized to a theory of T-quantifiers and S-quantifiers, respectively. The key idea leading to this generalization is the fact that the (infinite) iteration of the two-valued conjunction and disjunction gives the two-valued all-quantifier and ex-quantifier, respectively. In the framework of fuzzy logic the same holds for min with respect to Inf and for max with respect to Sup. As a T-norm (S-norm) is commutative and associative, we can construct an all-/spl tau/-quantifier (an ex-/spl sigma/-quantifier) from a given T-norm /spl tau/ (S-norm /spl sigma/). These quantifiers are characterized by axioms (T-quantifiers and S-quantifiers). Furthermore we show that the generating procedure is "complete" with respect to arbitrary T-quantifiers (S-quantifiers) and uniquely reversible. >

Synthesis and characterization of diorganotin(IV) derivatives of 2-mercaptopyridine and crystal structure of diphenyl pyridine-2-thiolatochlorotin(IV)

Abstract: Diorganotin(IV) derivatives of 2-mercaptopyridine (HSPy), R2Sn(SPy)2, R2SnCl(SPy) (R = Me, iPr, nBu, tBu, Cy, Ph) and Cy2SnBr(SPy), were obtained from R2SnX2 (X = Cl, Br) and NaSPy. Ph2SnCl(SPy) crystals, as determined by singlecrystal X–ray diffraction, are monoclinic in the space group P21/n. Tin forms with the bidentate SPy ligand a four–membered chelate ring with a short NSnS bite angle of 64.8(1)° leading to a heavily distorted trigonal–bipyramidal environment about tin. Apical Cl–Sn–N angle = 156.1(1)° equatorial C–Sn–C angle = 121.9(2)°. From 119Sn Mossbauer and IR data, analogous structures are inferred for the other solid compounds R2SnX(SPy), and distorted octahedral molecular structures for the solid compounds R2Sn(SPy)2 with R in the trans position, and sulfur atoms and nitrogen–donor atoms each in cis positions. According to IR and 1H, 13C and 119Sn NMR data, the solid–state molecular structures are retained in chloroform solution.