Showing papers by "Technical University of Dortmund published in 1985"

Micromechanism for metallic-glass formation by solid-state reactions.

Abstract: Metallic-glass formation by solid-state reactions has been observed in multilayer Zr-Co diffusion couples and studied by cross-sectional transmission electron microscopy. Planar growth of a Corich amorphous phase proceeds from each interface of the unreacted sample, thus consuming the Co layers at a higher rate. Further annealing results eventually in a reaction of the Co-rich glassy phase with remaining Zr. Because of the high diffusivity of the Co in the amorphous phase, Kirkendall voids are formed during this homogenizing process and are lined up with the periodicity of the original layered structure.

Polybaric differentiation of alkali basaltic magmas: evidence from green-core clinopyroxenes (Eifel, FRG)

Abstract: The Quaternary foidites and basanites of the West Eifel (Germany) contain optically and chemically heterogeneous clinopyroxenes, some of which occur as discrete zones within individual crystals: Most clinopyroxene phenocrysts are made up of a core and a normally zoned comagmatic titanaugite mantle Most cores are greenish pleochroic and moderately resorbed (fassaitic augite) Some are pale green and strongly resorbed (acmitic augite) Cores of Al-augite composition and of Cr-diopside derived from peridotite xenoliths are rare The fassaitic augites are similar in trace element distribution pattern to the titanaugites, but are more enriched in incompatible elements The acmitic augites, in contrast, are clearly different in their trace element composition and are enriched in Na, Mn, Fe and depleted in Al, Ti, Sr, Zr A model for polybaric magma evolution in the West Eifel is proposed: Primitive alkali basaltic magma rises through the upper mantle precipitating Al-augite en route It stagnates and differentiates near the crust/mantle boundary crystallizing Fe-rich fassaitic augites The magma differentiated at high pressure is subsequently mixed with new pulses of primitive magma from which the rims of pyroxene are crystallized Sporadic alkali pyroxenite xenoliths are interpreted to represent cumulates of cognate phases formed within the crust and not metasomatized upper mantle material (Lloyd and Bailey 1975)

Model of the local structure of random ternary alloys: Experiment versus theory.

Abstract: We have performed an extended x-ray-absorption fine-structure (EXAFS) measurement of ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Te solid solutions for various concentrations x in the single-phase range 0\ensuremath{\le}x\ensuremath{\le}0.7. Data have been collected on the Mn K, Cd ${L}_{\mathrm{III}}$, and Te ${L}_{\mathrm{III}}$ edges. We have found well-defined different nearest-neighbor Cd-Te and Mn-Te distances almost independent of x. A model of the microscopic structure of the zinc-blende-type ${A}_{1\mathrm{\ensuremath{-}}x}$${B}_{x}$C ternary alloys based on a random distribution of cations has been developed. The model describes the bimodal distribution of near-neighbor distances in terms of distortion of the anion sublattice (the cation sublattice is assumed to remain fixed) with use only of the lattice constants of the alloy and the bond-stretching constants of each binary component. Its application to ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Te and ${\mathrm{In}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Ga}}_{\mathrm{x}}$As alloys is proved to be in good agreement with the EXAFS results. Within the framework of this model we also consider the problem of the structural stability of ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Te.

Observation of the resonant optical Stark effect in a semiconductor.

Abstract: This Letter presents for the first time the observation of the resonant optical Stark effect in a semiconductor. The excitonic system of ${\mathrm{Cu}}_{2}$O is well suited to the investigation of this effect because of its rather large binding energy and well-resolved resonances at low temperatures. The mixing between the $1S$ and $2P$ excitons by the electric field of a tunable high-power C${\mathrm{O}}_{2}$ laser leads to drastic changes in the one-photon spectrum around the $2P$ absorption line. Even details of the line shape are consistently described in terms of the frequency-dependent nonlinear susceptibility.

Parametrizations of the photon structure and applications to supersymmetric particle production at HERA

Abstract: We presentQ2-dependent parametrizations for the parton distributions within real photons obtained from full solutions of the corresponding leading order evolution equations. We show that our results differ appreciably from fits of the “asymptotic” solutions. Furthermore we discuss the production of heavy quarks as well as squarks and gluinos at the HERA collider using our parametrizations. The production rates are very promising especially in the case of gluino production.

Boundary elements and symmetry

Abstract: This paper discusses the deficiencies of boundary element stiffness matrices, gives an account of the methods proposed to circumvent these defects and proposes a new procedure to obtain symmetric stiffness matrices.

Fast uptake kinetics in vitro of 51Cr (VI) by red blood cells of man and rat.

Abstract: Fast transport kinetics of 51Cr (VI) into red blood cells (RBCs) in vitro were studied. No significant species differences were found between RBCs of man and rat. The uptake of 51Cr (VI) by RBCs in whole blood was composed of two different first order processes of different velocities (apparent t1/2 of 22.7 s and 10.4 min for man and 6.9 s and 10.1 min for rat, respectively). However, even after longer time periods a fixed portion of approximately 15% of the administered dose remained in the plasma and did not penetrate into RBCs Over the entire concentration range studied (10 μM–50 mM), the fast initial uptake followed Michaelis-Menten kinetics. The maximal capacity of this Cr(VI) transport into RBCs of man and rat was 3.1×108 CrO42− ions × cell−1 × min−1 and 2.5×108 CrO4−2 ions × cell−1 × min−1, respectively. It is likely that Cr(VI) is transported into RBCs via a physiological anion carrier (“band-3-protein”).

The language of pain.

Abstract: The expression ‘pain’ refers to a phenomenon intrinsic to individuals. The object of the language of pain is restricted to an individual experience which excludes any form of direct access by others. Speaking about pain is thus one of the most difficult forms of linguistic activities, as has been repeatedly pointed out by Wittgenstein. The difficulties involved in this type of communication are not only dependent upon individual linguistic ability but are also clearly reflected in the state and structure of the linguistic means which are at the disposal of the speakers of a language. Linguistic means vary in status and complexity with respect to the ends which they can be used for.

Metabolism and pharmacokinetics of vinyl acetate.

Abstract: The hydrolysis of vinyl acetate (formation of acetic acid) has been studied in vitro with rat liver and lung microsomes, rat and human plasma and purified esterases (such as acetylcholine esterase, butyrylcholine esterase, carboxyl esterase). Characterization of the kinetic parameters revealed that rat liver microsomes and purified carboxyl esterase (from porcine liver) displayed the highest activity. In order to establish the rate of metabolism of vinyl acetate in vivo, rats were exposed in closed desiccator jar chambers, and gas uptake kinetics were studied. The decay of vinyl acetate was dose-dependent, indicating possible saturation of metabolic pathway(s). The maximal clearance (at lower concentrations) of vinyl acetate from the system (30 000 ml/h per kg body weight) was similar to the maximal ventilation rate in this species. This indicated that under conditions when metabolic enzymes are not saturated the metabolic rate is mainly determined by pulmonary uptake. The exposure of rats to vinyl acetate resulted in a transient exhalation of significant amounts of acetaldehyde into the closed exposure system. This indicates the presence of this metabolic intermediate of vinyl acetate in the organism in vivo.

Ternäre Palladiumpnictide der Erdalkali- und Seltenen Erdmetalle mit ThCr2Si2- und CaBe2Ge2-Struktur

Abstract: Fifteen compounds of compositionMPd2 Pn 2 (M = alkaline earth or rare earth metal,Pn = As, Sb, Bi) were prepared. TheirGuinier powder patterns show that the arsenides crystallize with the ThCr2Si2 type structure, the bismuthides with the closely related CaBe2Ge2 type structure. The antimonides most likely also have the CaBe2Ge2 structure as is demonstrated by a structure refinement of EuPd2Sb2 from single crystal X ray data (R = 0.039 for 366 independent structure factors and 15 variable parameters). The structure of SrPd2As2 (ThCr2Si2 type) was refined to a residual ofR = 0.020 for 182F values and 9 variables. EuPd2Sb2 is paramagnetic and a metallic conductor. A comparison of the cell volumes suggests intermediate valency for Eu in EuPd2As2. Chemical bonding and especially the reasons for the adoption of the ThCr2Si2 or CaBe2Ge2 type structures by these compounds are discussed. It is suggested that in going from the phosphides to the bismuthides the ThCr2Si2 structure is loosing and the CaBe2Ge2 structure is gaining stability due to decreasing Pd-Pd bonding and increasing Pd-pnictogen bonding. This trend is caused by the increasing size of the pnictogen component.

Supersymmetric-particle production at pp-bar collider energies.

Abstract: The recently observed hadronic single- and multijet events accompanied by large missing ${p}_{T}$ can be consistently explained by gluinos (g\ifmmode \tilde{}\else \~{}\fi{}), produced via qq\ifmmode\bar\else\textasciimacron\fi{},gg\ensuremath{\rightarrow}g\ifmmode \tilde{}\else \~{}\fi{} g\ifmmode \tilde{}\else \~{}\fi{} with an optimal mass of ${m}_{g\ifmmode \tilde{}\else \~{}\fi{}}$=35 to 45 GeV. This result agrees surprisingly well with theoretical predictions of the minimal N=1 supergravity model. Adopting the theoretically somewhat less appealing alternative where scalar quarks (q\ifmmode \tilde{}\else \~{}\fi{}) are lighter than gluinos such that they are dominantly produced via qq\ifmmode\bar\else\textasciimacron\fi{},gg\ensuremath{\rightarrow}q\ifmmode \tilde{}\else \~{}\fi{} q\ifmmode \tilde{}\else \~{}\fi{}, the events can also be explained by scalar quarks in a similar mass range. Currently available data, including the observed jet properties, cannot meaningfully distinguish between these two mechanisms. In addition we present detailed predictions for cross sections and distributions in 〈${E}_{T}$〉, ${p}_{T}^{\mathrm{miss}}$, ${p}_{T}^{\mathrm{jet}}$, and invariant observed jet masses for gluino as well as scalar-quark production at present and forthcoming CERN pp\ifmmode\bar\else\textasciimacron\fi{} collider energies (\ensuremath{\surd}s =540 and 620 GeV). Realistic tests are suggested which would allow discrimination between gluinos and scalar quarks in the near future.

Ternäre Palladiumpnictide der Erdalkali‐ und Seltenerdmetalle mit ThCr2Si2 ‐ und CaBe2Ge2 ‐Struktur.

Abstract: Fifteen compounds of compositionMPd2Pn2 (M = alkaline earth or rare earth metal,Pn = As, Sb, Bi) were prepared. TheirGuinier powder patterns show that the arsenides crystallize with the ThCr2Si2 type structure, the bismuthides with the closely related CaBe2Ge2 type structure. The antimonides most likely also have the CaBe2Ge2 structure as is demonstrated by a structure refinement of EuPd2Sb2 from single crystal X ray data (R = 0.039 for 366 independent structure factors and 15 variable parameters). The structure of SrPd2As2 (ThCr2Si2 type) was refined to a residual ofR = 0.020 for 182F values and 9 variables. EuPd2Sb2 is paramagnetic and a metallic conductor. A comparison of the cell volumes suggests intermediate valency for Eu in EuPd2As2.

M2Ta9S6 (M ≡ Fe, Co, Ni): A metal-rich channel structure with condensed tetrakaidecahedral tantalum clusters

Abstract: Fe2Ta9S6, Co2Ta9S6, and Ni2Ta9S6 have been prepared by high temperature techniques. The crystal structure has been determined from single crystal X-ray diffraction data for Fe2Ta9S6 (R = 0.042) and Ni2Ta9S6 (R = 0.031). The hexagonal cell contains one formula unit. The tantalum substructure can be viewed as condensed clusters consisting of tetrakaidecahedra sharing faces along the c axis and vertices in the hexagonal plane. The tantalum clusters are additionally bridged by low coordinated sulfur atoms sheathing channels of about 400 pm diameter which run along the c axis. The iron-group metal occupies centers of the tricapped trigonal tantalum prisms. Anomalies in the lattice parameters of Ni2Ta9S6 are discussed.

The argus electron-photon calorimeter III. Electron-hadron separation

Abstract: The high granularity of the ARGUS shower counter system allows one to determine the lateral energy deposition. An algorithm based on the number of shower counters set by an incoming particle, the amount of energy deposited in the shower counters and the lateral distribution of the energy allows to separate electrons from muons and hadrons. For electrons with momenta larger than 0.7 GeV/c the hadron rejection rate is of the order of 50 at an electron detection efficiency of 80%.