Showing papers by "Karlsruhe Institute of Technology published in 1994"

Review of particle properties.

Abstract: This biennial Review summarizes much of Particle Physics. Using data from previous editions, plus 2205 new measurements from 667 papers, we list, evaluate, and average measured properties of gauge bosons, leptons, quarks, mesons, and baryons. We also summarize searches for hypothetical particles such as Higgs bosons, heavy neutrinos, and supersymmetric particles. All the particle properties and search limits are listed in Summary Tables. We also give numerous tables, figures, formulae, and reviews of topics such as the Standard Model, particle detectors, probability, and statistics. This edition features expanded coverage of CP violation in B mesons and of neutrino oscillations. For the first time we cover searches for evidence of extra dimensions (both in the particle listings and in a new review). Another new review is on Grand Unified Theories. A booklet is available containing the Summary Tables and abbreviated versions of some of the other sections of this full Review. All tables, listings, and reviews (and errata) are also available on the Particle Data Group website: http://pdg.lbl.gov.

Valuation of Trust in Open Networks

Abstract: Authentication in open networks usually requires participation of trusted entities. Many protocols allow trust to be obtained by recommendation of other entities whose recommendations are known to be reliable. To consider an entity as being trustworthy, especially if there have been several mediators or contradicting recommendations, it is necessary to have a means of estimating its trustworthiness. In this paper we present a method for the valuation of trustworthiness which can be used to accept or reject an entity as being suitable for sensitive tasks. It constitutes an extension of the work of Yahalom, Klein and Beth ([YKB93]).

Analytic energy derivatives for ionized states described by the equation‐of‐motion coupled cluster method

Abstract: The theory for analytic energy derivatives of excited electronic states described by the equation‐of‐motion coupled cluster (EOM‐CC) method has been generalized to treat cases in which reference and final states differ in the number of electrons. While this work specializes to the sector of Fock space that corresponds to ionization of the reference, the approach can be trivially modified for electron attached final states. Unlike traditional coupled cluster methods that are based on single determinant reference functions, several electronic configurations are treated in a balanced way by EOM‐CC. Therefore, this quantum chemical approach is appropriate for problems that involve important nondynamic electron correlation effects. Furthermore, a fully spin adapted treatment of doublet electronic states is guaranteed when a spin restricted closed shell reference state is used—a desirable feature that is not easily achieved in standard coupled cluster approaches. The efficient implementation of analytic gradien...

Degradation of polycyclic aromatic hydrocarbons in the presence of synthetic surfactants.

Abstract: The biodegradation of polycyclic aromatic hydrocarbons (PAH) often is limited by low water solubility and dissolution rate. Nonionic surfactants and sodium dodecyl sulfate increased the concentration of PAH in the water phase because of solubilization. The degradation of PAH was inhibited by sodium dodecyl sulfate because this surfactant was preferred as a growth substrate. Growth of mixed cultures with phenanthrene and fluoranthene solubilized by a nonionic surfactant prior to inoculation was exponential, indicating a high bioavailability of the solubilized hydrocarbons. Nonionic surfactants of the alkylethoxylate type and the alkylphenolethoxylate type with an average ethoxylate chain length of 9 to 12 monomers were toxic to a PAH-degrading Mycobacterium sp. and to several PAH-degrading mixed cultures. Toxicity of the surfactants decreased with increasing hydrophilicity, i.e., with increasing ethoxylate chain length. Nontoxic surfactants enhanced the degradation of fluorene, phenanthrene, anthracene, fluoranthene, and pyrene.

Non-Fermi-liquid behavior in a heavy-fermion alloy at a magnetic instability.

Abstract: The specific heat C and electrical resistivity \ensuremath{\rho} of the heavy-fermion alloy ${\mathrm{CeCu}}_{5.9}$${\mathrm{Au}}_{0.1}$ exhibit non-Fermi-liquid behavior well below 1 K, i.e., C/T\ensuremath{\propto}-ln(T/${\mathit{T}}_{0}$) and \ensuremath{\rho}=${\mathrm{\ensuremath{\rho}}}_{0}$+A'T, over more than a decade in temperature T. The magnetic susceptibility \ensuremath{\chi} measured in 0.1 T shows a cusp for T\ensuremath{\rightarrow}0. This behavior is attributed to the proximity to magnetic order: In contrast to ${\mathrm{CeCu}}_{6}$, ${\mathrm{CeCu}}_{6\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Au}}_{\mathit{x}}$ alloys show long-range antiferromagnetic order, with ${\mathit{T}}_{\mathit{N}}$\ensuremath{\rightarrow}0 for ${\mathit{x}}_{\mathit{c}}$=0.1. Hence ${\mathrm{CeCu}}_{5.9}$${\mathrm{Au}}_{0.1}$ is at the edge of a zero-temperature quantum phase transition. In a large magnetic field (B\ensuremath{\ge}3 T) Fermi-liquid behavior is recovered.

Mesoscopic quantum transport : resonant tunneling in the presence of a strong coulomb interaction

Abstract: Coulomb-blockade phenomena and quantum fluctuations are studied in mesoscopic metallic tunnel junctions with high charging energies. If the resistance of the barriers is large compared to the quantum resistance, transport can be described by sequential tunneling. Here we study the influence of quantum fluctuations. They are strong when the resistance is small or the temperature is very low. A real-time approach is developed that allows the diagrammatic classification of resonant tunneling processes where different electrons tunnel coherently back and forth between the leads and the metallic island. With the help of a nonperturbative resummation technique we evaluate the spectral density, which describes the charge excitations of the system. From it, physical quantities of interest such as current and average charge can be deduced. Our main conclusions are as follows: An energy renormalization leads to a logarithmic temperature dependence of the renormalized system parameters. A finite lifetime broadening can change the classical picture drastically. It gives rise to a strong flattening of the Coulomb oscillations for low resistances, but in the Coulomb-blockade regime inelastic electron cotunneling persists. The effects become important at temperatures that are accessible in experiments.

The flapping shear layer formed by flow separation from the forward corner of a square cylinder

Abstract: The turbulent shear layer and the associated recirculation region on the sidewall formed in flow separation from the forward corner of a square cylinder have been studied with one-component laser-Doppler velocimetry. Because of vortex shedding, the flow is approximately periodic, and is treated as a separated flow undergoing largeamplitude forcing at the shedding frequency. Phase (ensemble)-averaged velocities and turbulence intensities were obtained, and a close relationship in phase and amplitude between phase-averaged turbulence intensities and gradients of phase-averaged velocity is found in much of the flow region. The similarity behaviour of the phase-averaged profiles in the shear layer as well as the streamwise growth of the shear layer are investigated. While phase-averaged velocity profiles collapse well in similarity coordinates, normalized turbulence intensities exhibit systematic deviations from similarity. Shear-layer growth also departs markedly from the linear growth law of unforced plane mixing layers. The effect of the recirculation is suggested as a possible explanation for some of these deviations. Similarities to and differences from steady and forced mixing layers, steady separated flows with recirculation, and unsteady boundary layers are discussed.

Modeling of mineralogical composition, density and elastic wave velocities in anhydrous magmatic rocks

Abstract: We use the technique of direct minimization of the Gibbs free energy of the 8-component (K2O-Na2O-Fe2O3-FeO-CaO-MgO-Al2O3-SiO2) multiphase system in order to determine the equilibrium mineral assemblages of rocks of different bulk chemical compositions equilibrated at various P-T conditions. The calculated modal compositions of rocks and experimental data on elastic moduli of single crystals are then used to calculate densities and isotropic elastic wave velocities of rocks together with their pressure and temperature derivatives. Sufficient accuracy of the calculations is confirmed by comparison with experimental data on the gabbro-eclogite transformation and precise ultrasonic measurements of elastic wave velocities in a number of magmatic and metamorphic rocks. We present calculated phase diagrams with isolines of density, elastic wave velocities, and their pressure and temperature derivatives for several anhydrous magmatic rocks, from granite to lherzolite. Density and elastic properties of rocks are controlled by their chemical compositions, especially the SiO2 content, and by P-T of equilibration, and they increase with pressure due to mineral reactions changing mineral assemblages from plagioclase-bearing and garnet-free to garnetbearing and plagioclase-free. TheV p -density correlation is high, and shows two clear trends: one for iron-poor ultramafic rocks and another for all the other rocks considered. Mineral reactions, which occur at high pressures, changeV p and density of anhydrous magmatic rocks following the well-known Birch (or a similar) law. Felsic, intermediate and mafic rocks can be well distinguished in theV p -V p /V s - diagram, although their values ofV p can be close to one another. TheV p -V p /V s -density diagrams together with calculated phase diagrams can serve as efficient instruments for petrologic interpretation of seismic velocities.

ARXPS studies of SiO2-SiC interfaces and oxidation of 6H SiC single crystal Si-(001) and C-(001) surfaces

Abstract: The main puzzle in oxidation of hexagonal SiC is the slower rate of the Si-terminated surface as compared to the C-terminated surface, which is blamed on an unknown interface compound. ARXPS is a unique method to identify minor amounts of interface compounds, especially for smooth surfaces. Our ARXPS analysis of oxidized Si-(001) and C-(001) surfaces of 6H SiC reveals the interface oxide Si4C4−xO2 (x < 2), likely a reaction product of a peroxidic O2-bond to a SiC double layer. Si4C4−xO2 occurs in larger thickness (≃1 nm) at the slowly oxidizing Si-(001) surface, whereas the C-(001) surface shows smaller amounts, diminishing fast with oxidation above 1000 K. Evidence is presented that with increasing amount of Si4C4−xO2 the oxidation of SiC to SiO2 is reduced. ARXPS is consistent with a layer of SiO2 containing less than 3% Si4C4O4 being an oxidation product of Si4C4−xO2. At the surface of SiO2, graphite and some Si4C4O4 exist, aside from standard adsorbates.

Optical flow estimation: advances and comparisons

Abstract: This contribution investigates local differential techniques for estimating optical flow and its derivatives based on the brightness change constraint. By using the tensor calculus representation we build the Taylor expansion of the gray-value derivatives as well as of the optical flow in a spatiotemporal neighborhood. Such a formulation simplifies a unifying framework for all existing local differential approaches and allows to derive new systems of equations to estimate the optical flow and its derivatives. We also tested various optical flow estimation approaches on real image sequences recorded by a calibrated camera fixed on the arm of a robot. By moving the arm of the robot along a precisely defined trajectory we can determine the true displacement rate of scene surface elements projected into the image plane and compare it quantitatively with the results of different optical flow estimators.

The development of functional digestive and metabolic organs in turbot, Scophthalmus maximus

Abstract: The functional status of organ systems involved into the processing of exogenous food is critical for the survival and growth of fish early life stages. The present study on laboratory-reared larval turbot, Scophthalmus maximus, provides an overview on the ontogeny of structure and functions involved in digestion, absorption and metabolism of nutrients. At start of exogenous feeding the intestine of larval turbot is anatomically differentiated, with enterocytes displaying an adult-type ultrastructure and being able to process lipids. At the microvillous border of the enterocytes, enzymes of contact digestion such as aminopeptidase are found. The ultrastructure of the exocrine pancreatic cells is fully differentiated from hatching onwards. Likewise, substantial activities of trypsin-type proteases are present. A stomach anlage exists in first-feeding larvae; however, the stomach becomes functional (appearance of gastric glands and pepsin secretion) only during metamorphosis. Liver parenchymal cells already display a functional ultrastructure during the endotrophic phase; with onset of exogenous feeding they develop pronounced diet-related changes of their energy stores. Larval respiration is not executed by the gills since respiratory surface of these structures develops only towards metamorphosis. The energy generation of larval muscle tissue depends on aerobic metabolism, whereas glycolytic activities start to increase at metamorphosis. In conclusion, two important patterns can be recognized in the development of turbot larvae: (1) The structure/function is differentiated at hatching or at the onset of exogenous feeding (afterwards it experiences mainly quantitative but not qualitative growth, i.e., intestine, exocrine pancreas, liver); or (2) the structure/function is absent in larvae and develops only during metamorphosis (i.e., gills, glycolytic muscle metabolism, stomach).

On almost perfect nonlinear permutations

Abstract: In this paper basic properties of APN permutations, which can be used in an iterated secret-key block cipher as a round function to protect it from a differential cryptanalysis, are investigated. Several classes of almost perfect nonlinear permutations and other permutations in GF(2)n with good nonlinearity and high nonlinear order are presented. Included here are also three methods for constructing permutations with good nonlinearity.

The heme-copper oxidase family consists of three distinct types of terminal oxidases and is related to nitric oxide reductase.

Abstract: Among aerobic prokaryotes, many different terminal oxidase complexes have been described. Sequence comparison has revealed that the aa3-type cytochrome c oxidase and the bo3-type quinol oxidase are variations on the same theme: the heme-copper oxidase. A third member of this family has recently been recognized: the cbb3-type cytochrome c oxidase. Here we give an overview, and report that nitric oxide (NO) reductase, a bc-type cytochrome involved in denitrification, shares important features with these terminal oxidases as well. Tentative structural, functional and evolutionary implications are discussed.

The one-loop renormalization of the MSSM Higgs sector and its application to the neutral scalar Higgs masses

Abstract: The structure of the Higgs sector in the minimal supersymmetric standard model is reviewed at the one-loop level. An on-shell renormalization scheme of the MSSM Higgs sector is presented in detail together with the complete list of formulae for the neutral Higgs masses at the one-loop level. The results of a complete one- loop calculation for the mass spectrum of the neutral MSSM Higgs bosons and the quality of simpler Born-like approximations are discussed for sfermion and gaugino masses in the range of the electroweak scale.

Analytic energy gradients for the equation‐of‐motion coupled‐cluster method: Implementation and application to the HCN/HNC system

Abstract: A recently developed theory for calculating analytic first derivatives of the energy for excited states treated by the equation‐of‐motion coupled‐cluster (EOM‐CC) method has been implemented and applied to study potential energy surfaces in the HCN/HNC system. The EOM‐CC singles and doubles (EOM‐CCSD) approximation is used to predict equilibrium structures, energies, dipole moments, harmonic vibrational frequencies and infrared intensities of HCN and HNC isomers in both the A 1A‘ and B 1A’ excited states. In addition, the activated complex for HCN→HNC isomerization in these states is investigated theoretically for the first time.

Integrated lithospheric modeling combining thermal, gravity, and local isostasy analysis: Application to the NE Spanish Geotransect

Abstract: A two-dimensional algorithm to determine the steady state thermal structure of the lithosphere that integrates thermal, gravity, and local isostasy analyses is presented. Gravity analyses together with seismic data are used to constrain spatial variations in density and crustal structure, while absolute elevation is used to determine the lithospheric mantle thickness. The calculation is performed using a finite element technique that links the different physical equations. The program optionally calculates the temperature at any material boundary and, with given rheological parameters, the strength distribution and the total lithospheric strength in selected columns. We apply the algorithm to the Northeastern Spanish Geotransect which extends from the Pyrenees to the Balearic Promontory and along which a strong variation in crustal and lithospheric thickness is evident. We assess the use of two different inferred density models for the lithospheric mantle: The first assumes a linear decrease in density with increasing temperature using the asthenospheric density as a reference; the second model assumes a constant density for the whole lithospheric mantle. Although conceptually the two hypotheses differ substantially, the results obtained do not show significant differences. Lithospheric thicknesses of 120–130 km below the Pyrenees, 60–65 km in the Valencia Trough, and 65–75 km below the Balearic Promontory are deduced. In all cases the mean lithospheric mantle density has to be 40–60 kg m−3 higher than the asthenospheric density. The algorithm is shown to be a powerful tool in lithospheric thermal modeling especially in areas where surface heat flow is poorly constrained because of the temperature-density-elevation relationship.

The ESPRIT Project CAFE - High Security Digital Payment Systems

Abstract: CAFE (“Conditional Access for Europe”) is an ongoing project in the European Community's ESPRIT program. The goal of CAFE is to develop innovative systems for conditional access, and in particular, digital payment systems. An important aspect of CAFE is high security of all parties concerned, with the least possible requirements that they are forced to trust other parties (so-called multi-party security). This should give legal certainty to everybody at all times. Moreover, both the electronic money issuer and the individual users are less dependent on the tamper-resistance of devices than in usual digital payment systems. Since CAFE aims at the market of small everyday payments that is currently dominated by cash, payments are offline, and privacy is an important issue.

Charging effects in ultrasmall quantum dots in the presence of time-varing fields.

Abstract: The influence of charging effects on time-dependent transport in small semicondutor quantum dots with arbitrary level spectra is studied. Starting from an explicit time-dependent tunneling Hamiltonian, a non-Markovian master equation is derived which is also valid in the nonlinear response regime. The many-body nonequilibrium distribution functions of the dot are calculated and the I-V characteristic of the structure including the displacement currents is obtained. New resonant features show up in the Coulomb oscillations and in the Coulomb staircase, and a new possibility to realize electronic pumps is described.

Peak effect and scaling of irreversible properties in untwinned Y-Ba-Cu-O crystals.

Abstract: We measured the peak effect in the magnetic hysteresis loop of an untwinned ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ crystal in the vicinity of the critical temperature and studied its temperature, time, and angular dependence. The location of the peak is determined by the component of the field along the c direction. The pinning force density ${\mathit{F}}_{\mathit{p}}$(B) is scaled into a single curve for all measured isotherms (75--87 K) and time scales (4--1500 sec), and its functional form reflects the observed peak effect. The scaling field is related to the irreversibility field of oxygen-deficient regimes. The results indicate that pinning in this system is due to inhomogeneity of the oxygen deficiency and that the peak is related to the formation of a percolationlike network of reversible regimes.

Interfacial tension between water and non-polar fluids up to 473 K and 2800 bar

Abstract: The method of the Pendant Drop or Standing Bubble is applied to measure interfacial tensions between water and nonpolar fluids to high temperatures and pressures. The high pressure cell with two sapphire windows and the auxiliary equipment with several feed autoclaves is described. The shapes and sizes (about 2 mm) of drops and bubbles are recorded with microscope and video camera. A digital image processing procedure was developed which permits fast, objective and precise determination of the contour parameters. The six gases helium, neon, argon, nitrogen, methane, and propane have been investigated to 473 K (with nitrogen to 573 K) and (in part) to 2800 bar. Gas densities came close to liquid density values. For comparison, water plus liquid n-hexane, n-decane, and toluene was investigated to 473 K and 3000 bar. For these liquid hydrocarbons, the interfacial tension γ always increases with pressure. At 373 K for water-n-hexane γ is 41.8 mN/m at 100 bar and 47.3 mN/m at 2600 bar, respectively. In the water-gas systems γ decreases with pressure and passes through a flat minimum around 1000 bar. For water-nitrogen at 373 K γ = 52.5, 46.5 and 48.3 mN/m at 200, 1400 and 2800 bar. Only with water-helium γ increases continuously with pressure.

Nitric oxide reductase from Pseudomonas stutzeri. Primary structure and gene organization of a novel bacterial cytochrome bc complex.

Abstract: The oxidation-reduction and spectroscopic properties of various forms of nitrous oxide reductase from Pseudomonas stutzeri were investigated. The high-activity form I of the enzyme (purple, 8 Cu, Mr 140 000) was reduced by a large variety of cationic, anionic and photochemically generated agents. The blue form III was the only product found in these experiments under anaerobic conditions. Reductive (dithionite) and oxidative (ferricyanide) titrations showed that the conversion of the purple form I to the blue species III was fully reversible in the absence of dioxygen. Two kinetically different phases of the reaction of form I with a stoichiometric amount of dithionite (1e−-equivalent/Cu) were detected: in the fast phase (seconds), the purple chromophore with λ-max at 540 nm disappeared almost completely, whereas in the slower phase (minutes) the blue species with λmax around 650 nm was generated. Irrespective of the nature of the reductant the blue species did not react even at large excess of reductant. It was reoxidized by ferricyanide, hydrogen peroxide and nitric oxide. A new, catalytically inactive derivative of nitrous oxide reductase (form V, 2 Cu, Mr 140 000) was isolated from a transposon Tn5-induced mutant with defective chromophore biosynthesis. The pink color of the mutant protein faded almost completely after addition of 0.5e−-equivalent/Cu. In this case no blue species was found, similar to earlier observations for the regenerated, catalytically inactive protein. Varying with the sample and the pH, 50–80% of the total copper of form I was in an electron-paramagnetic-resonance-(EPR)-silent state as compared to 47% in the mutant protein. The broad, featureless EPR signal recorded at 9.32 GHz for the blue, reduced form III of nitrous oxide reductase represented approximately 20% of the total copper. For the blue species no resolution enhancement was achieved at 34 GHz. At this frequency both forms I and V showed similar EPR signals with apparent g-values at 2.16 and 1.99. At 9.32 GHz, form V had an EPR signal with gII at 2.18, AII= 3.55 mT (4 or 5 lines, in contrast to form I) and gI at 2.03. Above 100 K the splitting of the gII region into seven equidistant lines in the EPR signal of the high-activity form I and the hyperfine structure of the perpendicular transition disappeared. Carbon monoxide and nitric oxide, but not nitrous oxide, had marked effects on the spectroscopic properties of the purple form I. Marked effects were also obtained for the exogenous ligands nitrite, azide, cyanate and thiocyanate. The purple chromophore disappeared in the presence of these agents and the gII region of the corresponding EPR spectra at 9.32 GHz broadened. No superhyperfine structure originating from the interaction between the Cu(II) centers of nitrous oxide reductase and these ligands was detected. Nitric oxide also reacted with the reduced form III of the enzyme, giving a species with the spectroscopic properties of the pink form II. A considerable amount of nitrite was generated in the reaction of nitric oxide and the purple form I, depending on the partial pressure and the reaction time. When form I was mixed with hydrogen peroxide or potassium superoxide at 0°C, a blue intermediate with a broad shoulder around 640 nm was observed. The EPR spectrum of the reaction product showed the presence of type 2 Cu(II) centers with gII= 2.26, AII= 18.5 mT and gI= 2.06. The present results indicate that the coordination sphere of the purple Cu centers in nitrous oxide reductase are rather labile towards subtle changes in the environment such as pH and exogenous ligands. The spectroscopic properties of the blue species and its persistence in the presence of strong reductants point towards a catalytic site with Cu in a ‘reduced' state, stabilized by thiol or disulfide sulfur with substantial spin density delocalized onto sulfur.

Selectivity and mechanism of Fischer-Tropsch synthesis with iron and cobalt catalysts

Abstract: The Fischer-Tropsch CO-hydrogenation has been comparatively performed on iron and cobalt in a gradientless tank reactor. Kinetic coefficients of elementary reactions and their dependence on pH 2 , Pco' ph 20 and T were determined with the help of a model for chain growth-, branching- and termination reactions. Changes of reaction rates of CO consumption, of methane formation, of chain propagation and chain branching are presented and discussed in terms of elemental surface reactions and characteristics of the catalyst base metals.

Subgap conductivity of a superconductor-normal-metal tunnel interface.

Abstract: At low temperatures, the transport through a superconductor--normal-metal tunnel interface is due to tunneling of electrons in pairs. We show that the rate for this process is often determined by the interference of the electron waves on a space scale determined by the coherence length. Therefore, the subgap current strongly depends on the layout of the electrodes within this space scale. The approach developed allows us to evaluate the subgap current for different layouts of interest.

Heterogeneity spectrum and scale-anisotropy in the upper crust revealed by the German Continental Deep-Drilling (KTB) Holes

Abstract: Crustal heterogeneities and their statistical characteristics bear important information about the dynamic processes and evolution of the crust The velocity well-log data from the German Continental Deep Drilling Project (KTB) offer a rare opportunity to measure directly the properties of crustal heterogeneities In this study, we first estimated the power spectrum of crustal heterogeneities from the P-velocity well-logs of the two holes For the first time, a power-law spectrum of crustal heterogeneities was directly observed in the spatial wavelength range from a few meters to a few kilometers The slope of the vertical 1D power spectrum of the random velocity perturbations is about 11, corresponding to a flicker-noise random medium The scale-anisotropy ratio (aspect ratio) and the horizontal spectral slope of crustal heterogeneities were also estimated by cross-correlation analysis between these two holes to be about 18 and 20, respectively