Showing papers by "Technical University of Dortmund published in 1990"

Determination of new ASOG parameters.

Abstract: To extend the applicable systems and improve the accuracy of ASOG (Analytical Solution of Groups), which is a predictive method for activity coefficients, the group interaction parameters have been newly determined and some of those reported are revised. The group interaction parameters are increased to 341 group pairs consisting of 43 groups against the previous 31 groups and 138 group pairs. Twelve groups are newly added: pyridine, furfural, ACRY, Cl (C=C), DMSO, NMP, C≡C, SH, DMF, ethanediol, DEG, and sulfolane. The parameters for the previous 31 groups are revised for 10 of those groups: C=C, ArOH, GOH, O, CHO, CON, CN, ArNH2, Cl, and ArCl. The parameters are then extended by providing missing values for others among the 31 previous groups. The temperature range of experimental data used for parameter determination is 293 K to 423 K.

Radiatively generated parton distributions for high-energy collisions

Abstract: The gluon and antiquark distributions of the nucleon are generated radiatively using the assumption that at some low resolution scale the nucleon consists entirely of valence quarks and valence-like gluons. The agreement between the uniquely predicted gluon and sea distributions and the available data on deep inelastic structure functions (including also recent low-Q2 measurements) and direct-photon production is demonstrated and discussed in detail. Simple parametrizations of the resulting (positive definite!) parton distributions are presented in the range 10−4≲x≦1 and 0.2≲Q2≲106 GeV2 as obtained according to the leading- and higher-order renormalization group evolution equations.

R‐Curve Behavior of Long Cracks in Alumina

Abstract: Coarse-grained alumina is among those monolithic ceramics which can exhibit an increase in crack resistance with crack extension. This R-curve behavior is most pronounced for intergranular fracture and does not depend exclusively on material properties. Crack and specimen geometries also influence the shape of the R-curves. The magnitude of the effect increases with increasing crack surface roughness, which is microstructure-dependent, and with crack-opening displacement, which is geometry-dependent. Based on experimental observations, a “dynamic”R-curve model is presented which relates the increasing resistance to an increasing crack tip shielding caused by crack surface bridging. Applying a J-integral approach, R-curves are calculated for two specimen geometries (short double cantilever beam and single-edged notched beam) and different grain sizes. The good agreement between calculation and experiment indicates that the R-curve behavior of long cracks in alumina can be predicted by a simple wake model.

On Restrictions of Ordered Paramodulation with Simplification

Abstract: We consider a restricted version of ordered paramodulation, called strict superposition. We show that strict superposition (together with equality resolution) is refutationally complete for Horn clauses, but not for general first-order clauses. Two moderate enrichments of the strict superposition calculus are, however, sufficient to establish refutation completeness. This strictly improves previous results. We also propose a simple semantic notion of redundancy for clauses which covers most simplification and elimination techniques used in practice yet preserves completeness of the proposed calculi. The paper introduces a new and comparatively simple technique for completeness proofs based on the use of canonical rewrite systems to represent equality interpretations.

Global jet properties at 14–44 GeV center of mass energy in e + e − annihilation

Abstract: Jet properties ine + e − annihilation at center of mass energies of 14, 22, 35 and 43.7 GeV were studied with the data collected in the TASSO detector at PETRA, using the same evaluation procedures for all the energies. The total hadronic cross section ratio for the center of mass energy interval 39–47 GeV was determined to be ℛ=4.11±0.05 (stat)±0.18(syst.) at $$\langle \sqrt s \rangle = 43 - 7$$ GeV. Corrected distributions of global shape variables are presented as well as the inclusive charged particle distributions for scaled momentum and transverse momentum. The center of mass energy evolution of the average sphericity, thrust, aplanarity and particle momentum is shown.

Thermodynamics of the Falicov-Kimball model in large dimensions II

Abstract: In a former paper we presented the exact solution of the Falicov-Kimball-model in large dimensions and showed the existence of phase transitions for certain parameter combinations, especially for the symmetric case. In this contribution we investigate the conditions for transitions apart from the symmetric case and show that the phase following the homogeneous high temperature phase will have chessboard symmetry if the transition is a continuous charge density transition. The corresponding phase diagrams are shown as well as results on the order parameter of the chessboard phase.

Exclusive hadronic decays of B mesons

Abstract: Using the ARGUS detector at thee + e − storage ring DORIS II, we have measuredB decays into exclusive final states containing aD orD * meson plus several pions, or containing aJ/ψ or ψ′ meson plus a strange particle. Some of these channels have not been seen before, while others represent updated measurements of previous results. The branching ratios are compared with the predictions of the model of Bauer, Stech and Wirbel. Using the cleanest decay channels, the mass of the charged and neutralB meson are found to bem B −=(5280.5±1.0±2.0) MeV/c2 andm B 0=(5279.6±0.7±2.0) MeV/c2 respectively, yielding a mass differencem B 0−m B − =(−0.9±1.2±0.5) MeV/c2.

Ammonothermalsynthese von kupfernitrid, Cu3N

Abstract: Zusammenfassung Tetraamminkupfer(II)-nitrat komproportioniert bei Raumtemperatur in flussigem Ammoniak mit Kupfer zu Tri- bzw. Diamminkupfer(I)-nitrat (f(T) und p(NH3)). [Cu(NH3)x]NO3 mit 2 ⩽ x ⩽ 3 geht ab 350 °C bis 580 °C und p(NH3) = 6 kbar im Temperaturgefalle von Autoklaven in Cu3N, N2 und H2O uber; das Nitrid kristallisiert in der heiβen Zone. Rontgenographische Einkristallstrukturbestimmungen bei Raumtemperatur und −143 °C bestatigen den ReO3-typ: a = 3,819(1) A , Z = 1 , Pm3m, R R w = 0,010/0,014 bei Z(F0)2)⩾3σ(F0)2) = 108. Die kovalente NCuNBindung ist mit 173 ° bei 21 °C und 176 ° bei − 143 °C leicht gewinkelt. Modelle dynamischer und statischer Verkippung von NCu6-Oktaedern werden diskutiert. Cu3N sieht dunkel glanzend aus mit einem Grunschimmer. Es kann ohne Zersetzung an der Luft gehandhabt werden. Die Verbindung ist ein diamagnetischer Nichtleiter. Sie ist bei Raumtemperatur metastabil und zerfallt bei 470°C mit einer Enthalpie von 83,7 kJ mol−1 zu Cu und N2.

Electroweak Parameters From a High Statistics Neutrino Nucleon Scattering Experiment

Abstract: The final results from the WA 1/2 neutrino experiment in the 1984 CERN 160 GeV narrow band beam are presented. The ratiosR ν and\(R_{\bar v} \) of neutral to charged current interaction rates of neutrinos and antineutrinos in iron are measured to beR ν=0.3072±0.0033 and\(R_{\bar v} \)=0.382±0.016. A value of the electroweak parameter sin2 θ w = 1 −m W 2 /m Z 2 is extracted fromR ν. The result is sin2 θ w =0.228+0.013(m c −1.5)±0.0003 (theor.) wherem c is the mass of the charmed quark in GeV form t =60 GeV,M H =100 GeV, ρ=1. CombiningR ν and\(R_{\bar v} \) one obtains a value for ρ=0.991+0.023(m c −1.5)±0.020(exp.). Alternatively,R ν and\(R_{\bar v} \) yield a precise value of the ratio of intermediate vector boson massesm W /m Z =0.880−0.007(m c −1.5)±0.002(exp.)±0.002(theor.). Comparison of these results with those from direct measurements of the vector boson masses are presented. In a model-independent analysis the left- and right-handed neutral current coupling constants,g L 2 andg R 2 , are determined.

Compiling Logic Programs with Equality

Abstract: Horn clause logic with equality is an amalgamation of functional and logic programming languages. A sound and complete operational semantics for logic programs with equality is based on resolution to solve literals, and rewriting and narrowing to evaluate functional expressions. This paper proposes a technique for compiling programs with these inference rules into programs of a low-level abstract machine which can be efficiently executed on conventional architectures. The presented approach is based on an extension of the Warren abstract machine (WAM). In our approach pure logic programs without function definitions are compiled in the same way as in the WAM-approach, and for logic programs with function definitions particular instructions are generated for occurrences of functions inside clause bodies. In order to obtain an efficient implementation of functional computations, a stack of occurrences of function symbols in goals is managed by the abstract machine. The compiler generates the necessary instructions for the efficient manipulation of the occurrence stack from the given equational logic programs.

A comparative investigation of the metabolism of methyl bromide and methyl iodide in human erythrocytes

Abstract: Human erythrocyte cytoplasm was incubated in head space vials with either methyl bromide or methyl iodide. The decline in concentration of the two methyl halides was monitored by gas chromatography. Simultaneously, the production of S-methylglutathione was determined by thin layer chromatography. In parallel experiments, boiled erythrocyte cytoplasm was used in order to determine non-enzymatic conjugation. Furthermore, inhibition experiments with sulfobromophthalein were performed. The results were compared with previous findings on the metabolism of methyl chloride. In contrast to methyl chloride, both methyl bromide and methyl iodide showed a significant non-enzymatic conjugation with glutathione. In addition, an enzymatic conjugation could be observed in the erythrocyte cytoplasm of the majority of the population, whereas a minority lacks this enzymatic activity. This is consistent with findings on methyl chloride. Inhibition experiments show that a minor form of the erythrocyte glutathione transferase may be responsible for the enzymatic conjugation. Of the three monohalogenated methanes, methyl bromide is the substrate with the highest affinity for the conjugating enzyme(s). In the case of methyl iodide, non-enzymatic reaction overweighs the enzymatic process. There are possible implications of the results for occupational health and the toxicity of the substances.

The reaction Pomeron-Pomeron → π + π - and an unusual production mechanism for the f 2 (1270)

Abstract: Data are presented on Pomeron-Pomeron interactions which produce a centralπ+π− system in proton-proton collisions at\(\sqrt s = 62 GeV\) at the CERN Intersecting Storage Rings. This process may favor the production of gluonic bound states. A partial-wave analysis of theπ+π− system shows evidence for the production of the statesf0(975),f0(1400), andf2(1270). The fitted mass for thef2(1270) is about 50 MeV below the world average. In addition, the production mechanism for thef2(1270) is uniquely different from that for the other final states in that there is a correlation between the outgoing protons. this is consistent with a picture of two-gluon exchange with thef2(1270) produced by gluon fusion, and could indicate that thef2(1270) has a glueball component.

Secondary school students’ strategies in stoichiometry

Abstract: This study was designed (1) to analyse the relationship between the answer profile from multiple‐choice questions on stoichiometric problems and the students’ reasoning patterns and (2) to examine the effect for certain variables on the facility values of test items. The instruments used were mainly paper‐and‐pencil tests. The subjects were 6262 grammar school students from all parts of the Federal Republic of Germany. They were randomly assigned to the test items. The results indicated that many students arrived at their answers by mixing up amount and reacting mass, or molar mass and reacting mass. It was also found that the variables ‘easy/hard calculations’, and ‘formula given/to be developed’ determined the facility values of test items. From the results, it was possible to make recommendations to practising teachers as well as to examiners. Knowing students’ ideas, the teacher can think of how to make use of them before entering the classroom. A teaching unit may start off with easy problems leaving...

Acoustic emission: A probe into dislocation dynamics in plasticity

Abstract: Acoustic emission (AE) from deforming copper and its dilute alloys was recorded at varied frequencies at room temperature and up to 500°C. All results proved to be compatible with the spurt-like dislocation movement between two bounds being the AE generating event. AE presents a maximum in the beginning of stage II deformation when event lifetimes in the range of microseconds correspond to the recording frequency. Furthermore, AE decreases rapidly with decreasing event size (by work-hardening) resp. decreasing dislocation mobility (by elevated temperature or solute content). In copper viscous dislocation movement achieves some m/s. As event bounds dislocation or cell walls should act. Solution hardening increases the stress exponent in dislocation mobility, but it is demonstrated, that doubt is advisable in some of such results. So AE proves to serve as probe into dislocation dynamics inside the bulk of a work-hardening metal.