Showing papers by "University of Stuttgart published in 1995"

Social Force Model for Pedestrian Dynamics

Abstract: It is suggested that the motion of pedestrians can be described as if they would be subject to ``social forces.'' These ``forces'' are not directly exerted by the pedestrians' personal environment, but they are a measure for the internal motivations of the individuals to perform certain actions (movements). The corresponding force concept is discussed in more detail and can also be applied to the description of other behaviors. In the presented model of pedestrian behavior several force terms are essential: first, a term describing the acceleration towards the desired velocity of motion; second, terms reflecting that a pedestrian keeps a certain distance from other pedestrians and borders; and third, a term modeling attractive effects. The resulting equations of motion of nonlinearly coupled Langevin equations. Computer simulations of crowds of interacting pedestrians show that the social force model is capable of describing the self-organization of several observed collective effects of pedestrian behavior very realistically.

PKC zeta is a molecular switch in signal transduction of TNF-alpha, bifunctionally regulated by ceramide and arachidonic acid.

Abstract: Tumor necrosis factor (TNF-alpha) stimulates a number of signal transduction pathways in which phospholipases produce lipid second messengers. However, the immediate molecular targets of these messengers, in particular those of ceramide and arachidonic acid (AA) and their role in TNF signaling are not well defined. In this study we investigated the relationship of ceramide and AA in regulating an atypical PKC isozyme, PKC zeta. U937 cells responding to TNF-alpha treatment with NF kappa B activation displayed enhanced phosphorylation of PKC zeta, which is already detectable 30 s after stimulation. [14C]ceramide specifically binds to and regulates kinase activity of PKC zeta in a biphasic manner. Binding studies indicate high and low affinity binding with bmax values of 60 and 600 nM and Kd values of 7.5 and 320 nM respectively. At ceramide concentrations as low as 0.5 nM an up to 4-fold increase in autophosphorylation is obtained, which, at concentrations > 60 nM, again declines to basal levels. Interestingly, AA competes for ceramide binding and inhibits basal and ceramide-stimulated PKC zeta kinase activity at < 100 nM. Metabolism of [14C]ceramide in cells is slow and is inhibited in the presence of equimolar concentrations of lyso-phosphatidylcholine. Based on the bifunctional modulation of PKC zeta by the lipid messengers ceramide and AA, a model of TNF signal pathways is suggested in which PKC zeta takes a central position, acting as a molecular switch between mitogenic and growth inhibitory signals of TNF-alpha.

Isolation and characterization of Dehalospirillum multivorans gen. nov., sp. nov., a tetrachloroethene-utilizing, strictly anaerobic bacterium

Abstract: A strictly anaerobic bacterium dechlorinating tetrachloroethene (perchloroethylene, PCE) via trichloroethene (TCE) to cis-1,2-dichloroethene (DCE) was isolated from activated sludge with pyruvate plus PCE as energy substrates. The organism, called Dehalospirillum multivorans, is a gram-negative spirillum that does not form spores. The G+C content of the DNA was 41.5 mol%. According to 16S rRNA gene sequence analysis, D. multivorans represents a new genus and a new species belonging to the epsilon subdivision of Proteobacteria. Quinones, cytochromes b and c, and corrinoids were extracted from the cells. D. multivorans grew in defined medium with PCE and H2 as sole energy sources and acetate as carbon source; the growth yield under these conditions was 1.4g of cell protein per mol chloride released. Alternatively to PCE, fumarate and nitrate could serve as electron acceptors; sulfate could not replace fumarate, nitrate, or PCE in this respect. In addition to H2, the organism utilized a variety of electron donors for dechlorination (pyruvate, lactate, ethanol, formate, glycerol). Upon growth on pyruvate plus PCE, the main fermentation products formed were acetatc, lactate, DCE, and H2. At optimal pH (7.3–7.6) and temperature (30°C), and in the presence of pyruvate (20mM) and PCE (160μM), a dechlorination rate of about 50 nmol min-1 (mg cell protein)-1 and a doubling time of about 2.5h were obtained with growing cultures. The ability to reduce PCE to DCE appears to be constitutive under the experimental conditions applied since cultures growing in the absence of PCE for several generations immediately started dechlorination when transferred to a medium containing PCE. The organism may be useful for bioremediation of environments polluted with tetrachloroethene.

A continuum-based shell theory for non-linear applications

Abstract: The paper introduces a non-linear shell theory, which provides a complete three-dimensional state of stress. Since the theory is derived from simple three-dimensional continuum mechanics, it is very easy to understand. As an example, the theory is applied to quadrilateral shell elements, which provide only displacement degrees of freedom located at nodes on the outer surfaces and one degree of freedom at the middle surface. It is proposed to eliminate this degree of freedom on element level, so that the elements have the same layout as the equivalent brick elements, but have a better behaviour in bending, have stress resultants and are cheaper with respect to computational effort. The advantages with respect to implementation in a finite element program, as well as in special applications, are obvious. However, well-known conditioning problems in thin shell applications must be expected. Therefore emphasis is put on this issue in the example problems. It is shown that the elements can give acceptable answers in engineering applications and offer a potential for material non-linear applications, which will be considered in a forthcoming paper.

Density functionals for the Yukawa electron-electron interaction

Abstract: mShort-range nonclassical electron-electron interaction is described by a density functional in a scheme that allows multideterminant wave functions. The parameter that determines the coupling with the configuration-interaction-type calculations can be chosen in a controlled manner. Results are presented for the He and the Be series using a Yukawa-type interaction. 0 1995 John Wiley & Sons, Inc.

Basic knowledge and perspectives on biodegradation of 2,4,6-trinitrotoluene and related nitroaromatic compounds in contaminated soil

Abstract: Although a few aromatic compounds bearing one nitro group as a substituent are produced as secondary metabolites by microorganisms (31, 44, 45, 49) the majority of nitroaromatic compounds in the environment are due to anthropogenic activities. Nitrations are important reactions for the large-scale production of aminoaromatic structures that are synthons for pesticides, dyes, polymers, and pharmaceuticals. Nitroaromatic compounds such as nitrobenzene are used as solvents, whereas polynitroaromatic compounds serve as explosives. According to Hartter (16) 2,4,6-trinitrotoluene (TNT) is produced in amounts of 2 million pounds per year. Nitroaromatic compounds are therefore abundantly present in industrial waste streams and surface waters. 2,4,6-Trinitrotoluene is commonly found as the main contaminant of soil and ground water originating from facilities for manufacturing, processing, and disposing of explosives. Often these contaminants have leached from disposal lagoons into the surrounding soil, and in the case of military burdens of World War I and II, have contaminated the groundwater (13). Consequently, in Germany large areas of highly contaminated soils at former production plants must be remediated. TNT, its metabolites, and related compounds represent an environmental hazard because they exhibit considerable toxicity to humans, fish, algae, and microorganisms (39, 43, 50). Since incineration, the only proven technology for the destruction of explosives, is prohibitively costly, bioremediation represents an important alternative approach, which deserves to be considered.

Improved PO-MM hybrid formulation for scattering from three-dimensional perfectly conducting bodies of arbitrary shape

Abstract: The method of moments (MM) represents a suitable procedure for dealing with electromagnetic scattering problems of arbitrary geometrical shape in the lower frequency range. However, with increasing frequency both computation time and memory requirement often exceed available computer capacities. Therefore a current based hybrid method combining the MM with the physical optics (PO) approximation suitable for three-dimensional perfectly conducting bodies is proposed in this paper. The hybrid formulation allows a substantial reduction of computation time and memory requirement, while the results are in reasonable agreement with those based on an application of the MM alone. Further improvement can be achieved for flat polygonal parts of the scattering body by a heuristic modification of the PO current density taking into account the effects of edges. As opposed to the physical theory of diffraction (PTD), no additional electric and magnetic line currents along the edges are necessary. >

Direct numerical simulation of controlled transition in a flat-plate boundary layer

Abstract: The three-dimensional development of controlled transition in a flat-plate boundary layer is investigated by direct numerical simulation (DNS) using the complete Navier-Stokes equations. The numerical investigations are based on the so-called spatial model, thus allowing realistic simulations of spatially developing transition phenomena as observed in laboratory experiments. For solving the Navier-Stokes equations, an efficient and accurate numerical method was developed employing fourth-order finite differences in the downstream and wall-normal directions and treating the spanwise direction pseudo-spectrally. The present paper focuses on direct simulations of the wind-tunnel experiments by Kachanov et al. (1984, 1985) of fundamental breakdown in controlled transition. The numerical results agreed very well with the experimental measurements up to the second spike stage, in spite of relatively coarse spanwise resolution. Detailed analysis of the numerical data allowed identification of the essential breakdown mechanisms. In particular, from our numerical data, we could identify the dominant shear layers and vortical structures that are associated with this breakdown process.

An introduction to synergetics

Abstract: We introduce basic concepts and principles of synergetics in an elementary way and work out the interdisciplinary aims of this young scientific discipline. To some detail the laser as a system of physics and an application of synergetics to a problem from economics will be presented. A generalization of the methods to a class of functional differential equations will be outlined.

The PMR2 gene cluster encodes functionally distinct isoforms of a putative Na+ pump in the yeast plasma membrane.

Abstract: We report a structural and functional analysis of the PMR2 gene cluster in yeast. We found that several strains of Saccharomyces cerevisiae contain multiple PMR2 genes repeated in tandem, whereas most phylogenetically related yeasts appear to possess only a single PMR2 gene. This unusual tandem array of nearly identical genes encodes putative ion pumps involved in Na+ tolerance. Pmr2a and Pmr2b, the proteins encoded by the first two repeats, differ by only 13 amino acid exchanges. Both proteins share localization to the plasma membrane, but represent distinct isoforms of a putative Na+ pump. When expressed under identical conditions in vivo, Pmr2a and Pmr2b cause different tolerances to Na+ and Li+. Finally, we show that the Na+ tolerance mediated through these pumps is regulated by calmodulin via a calcineurin-independent mechanism which activates the Pmr2 ion pumps post-transcriptionally.

Improved fluid-dynamic model for vehicular traffic.

Abstract: The fluid-dynamic traffic model of Kerner and Konh\"auser [Phys. Rev. E 48, 2335 (1993); 50, 54 (1994)] is extended by an equation for the vehicles' velocity variance. It is able to describe the observed increase of velocity variance immediately before a traffic jam develops. Another modification takes into account the finite amount of space that each vehicle needs. As a consequence, the improved traffic model does not produce densities that exceed the maximum vehicle density or negative velocities, like former models did.

An Adaptive Stream Synchronization Protocol

Abstract: Protocols for synchronizing data streams should be highly adaptive with regard to both changing network conditions as well as to individual user needs. The Adaptive Synchronization Protocol we are going to describe in this paper supports any type of distribution of the stream group to be synchronized. It incorporates buffer level control mechanisms allowing an immediate reaction on overflow or underflow situations. Moreover, the proposed mechanism is flexible enough to support a variety of synchronization policies and allows to switch them dynamically during presentation. Since control messages are only exchanged when the network conditions actually change, the message overhead of the protocol is very low.

Adaptive topology optimization

Abstract: Topology optimization of continuum structures is often reduced to a material distribution problem. Up to now this optimization problem has been solved following a rigid scheme. A design space is parametrized by design patches, which are fixed during the optimization process and are identical to the finite element discretization. The structural layout is determined, whether or not there is material in the design patches. Since many design patches are necessary to describe approximately the structural layout, this procedure leads to a large number of optimization variables. Furthermore, due to a lack of clearness and smoothness, the results obtained can often only be used as a conceptual design idea. To overcome these shortcomings adaptive techniques, which decrease the number of optimization variables and generate smooth results, are introduced. First, the use of pure mesh refinement in topology optimization is discussed. Since this technique still leads to unsatisfactory results, a new method is proposed that adapts the effective design space of each design cycle to the present material distribution. Since the effective design space is approximated by cubic or Bezier splines, this procedure does not only decrease the number of design variables and lead to smooth results, but can be directly joined to conventional shape optimization. With examples for maximum stiffness problems of elastic structures the quality of the proposed techniques is demonstrated.

Symmetry breaking and structural changes at the neutral-to-ionic transition in tetrathiafulvalene-p-chloranil.

Abstract: The structural aspect of the temperature-induced neutral-to-ionic transition in the mixed-stack charge-transfer complex TTF-p-chloranil is directly analyzed using results obtained from neutron-scattering experiments. The symmetry breaking of the structural order parameter is determined together with the complete structural change. It is shown that the ionic phase is characterized by a dimerization along the stacking direction into weakly bond donor-acceptor dimers, which adopt a ferroelectric arrangement. Values of both dipole moment and dipolar energy in the unit cell are evaluated and commented. The evolution of the three-dimensional contacts which interconnect the chains, and in particular of the hydrogen interaction network, is discussed. Moreover, the associated intramolecular deformations are related in a satisfying way with the change of the ionicity and with the loss of centrosymmetry at the transition. Phenomena of metastability are also briefly discussed.

Multiwatt diode-pumped Yb:YAG thin disk laser continuously tunable between 1018 and 1053 nm.

Abstract: A new powerful source of broadly (35-nm) tunable laser radiation in the near-infrared (near 1030 nm) wavelength range is presented. Inserting a birefringent filter into a 10-W diode-pumped Yb:YAG thin disk laser resonator gives several watts of narrow-linewidth (0.07-nm) continuously tunable cw output power. By taking advantage of the power scalability of the thin disk concept, even hundreds of watts of tunable power with near-diffraction-limited beam quality and high efficiency are feasible. Generation and amplification of subpicosecond pulses with high average and peak powers are also promising applications of the Yb:YAG thin disk laser.

Fuzzy rule-based classification of atmospheric circulation patterns

Abstract: A fuzzy rule-based methodology is applied to the problem of classifying daily atmospheric circulation patterns (CP). The purpose of the approach is to produce a semi-automated classification that combines the expert knowledge of the meteorologist and the speed and objectivity of the computer. Rules are defined corresponding to the geographical location of pressure anomalies. A CP is described by the location of four different possible pressure anomalies. The rules are formulated with fuzzy sets, allowing a certain flexibility because slightly different pressure maps may correspond to a given CP. Accordingly the degree of fulfilment of a rule is defined in order to measure the extent to which a pressure map may indeed belong to a CP type. As an output of the analysis, the CP on any given day is assigned to one, and only one, CP type to a varying degree of credibility. The methodology is applied to a European case study. The subjective classification of European CPs given by Hess and Brezowsky provides a basis for constructing the rules. The classification obtained can be used, for example, to simulate local precipitation conditioned on the 700 hPa pressure field. The information content of the fuzzy classification as measured by precipitation-related indices is similar to that of existing subjective classifications. The fuzzy rule-based approach thus has potential to be applicable to the classification of GCM produced daily CPs for the purpose of predicting the effect of climate change on space-time precipitation over areas where only a rudimentary classification exists or where none at all exists.

Ab initio force-constant method for phonon dispersions in alkali metals.

Abstract: The force-constant matrix and the phonon dispersion curves are calculated for metals (Li, Na, K) by the fully self-consistent direct ab initio supercell approach based on the local-density approximation and on norm-conserving pseudopotentials. Apart from a constant scale factor for each material there is a very good agreement between theoretical and experimental data for the dispersion curves.

Mud mounds: A polygenetic spectrum of fine-grained carbonate buildups

Abstract: This research report contains nine case studies (part II to X) dealing with Palaeozoic and Mesozoic mud mounds, microbial reefs, and modern zones of active micrite production, and two parts (I and XI) summarizing the major questions and results. The formation of different types ofin situ formed micrites (automicrites) in close association with siliceous sponges is documented in Devonian, Carboniferous, Triassic, Jurassic and Cretaceous mounds and suggests a common origin with a modern facies found within reef caves. Processes involved in the formation of autochthonous micrites comprise: (i) calcifying mucus enriched in Asp and Glu, this type presumably is linked to the formation of stromatolites, thrombolites and massive fabrics; (ii) protein-rich substances within confined spaces (e.g. microcavities) result in peloidal pockets, peloidal coatings and peloidal stromatolites, and (iii) decay of sponge soft tissues, presumably enriched with symbiotic bacteria, lead to the micropeloidal preservation of parts of former sponge bodies. As a consequence, there is strong evidence that the primary production of micrite in place represents the initial cause for buildup development. The mode of precipitation corresponds to biologically-induced, matrix-mediated mineralization which results in high-Mg-calcites, isotopically balanced with inorganic cements or equilibrium skeletal carbonates, respectively. If distinct automicritic fabrics are absent, the source or origin of micrite remains questionable. However, the co-occurring identifiable components are inadequate, by quantity and physiology, to explain the enhanced accumulation of fine-grained calcium carbonate. The stromatolite reefs from the Permian Zechstein Basin are regarded as reminiscent of ancestral (Precambrian) reef facies, considered the precursor of automicrite/sponge buildups. Automicrite/sponge buildups represent the basic Phanerozoic reef type. Analogous facies are still present within modern cryptic reef habitats, where the biocalcifying carbonate factory is restricted in space.

Photochemistry of dibenzoyl methane UVA filters Part 1

Abstract: Two dibenzoyl methane derivatives, 4-isopropyldibenzoyl methane (I-DBM) and 4-t-butyl-3′-methoxydibenzoyl methand (BM-DBM), have been found to be photolabile towards UVA light in non-polar solvents, whereas in polar solvents photodegradation was very low. In each case about a dozen photoproducts were identified: their formation involves primary α bond cleavages of carbonyl groups, followed by hydrogen abstraction and/or oxidation or radical recombination. These photoproducts can be classified as substituted benzaldehydes, benzoic acids, acetophenones, phenglglyoxals, benzils, dibenzoyl methanes or dibenzoyl ethanes.

Simultaneous study of vacancy formation and migration at high temperatures in B2-type Fe aluminides.

Abstract: In order to study the vacancy formation and migration the temperature variation and the equilibration process of the thermal vacancy concentration in $B$2-type Fe aluminides ( ${\mathrm{Fe}}_{63}{\mathrm{Al}}_{37}$, ${\mathrm{Fe}}_{61}{\mathrm{Al}}_{39}$) were measured by means of the positron lifetime technique using a diffused ${}^{58}$Co positron emitter. The equilibration process occurs rather slowly, indicating a low vacancy mobility. The present values for the enthalpies of vacancy formation ${H}_{\mathrm{V}}^{\mathrm{F}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.04\mathrm{eV}$ ( ${\mathrm{Fe}}_{63}{\mathrm{Al}}_{37}$) or 0.98 eV ( ${\mathrm{Fe}}_{61}{\mathrm{Al}}_{39}$) and migration ${H}_{\mathrm{V}}^{\mathrm{M}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.7\mathrm{eV}$ are discussed with respect to the self-diffusion mechanisms.

Femtosecond Yb:YAG laser using semiconductor saturable absorbers

Abstract: We demonstrate a passively mode-locked femtosecond Yb:YAG laser using different semiconductor saturable absorber devices, a high-finesse and a low-finesse antiresonant Fabry–Perot saturable absorber. We achieved pulses as short as 540 fs with dispersion compensation and 1.7-ps pulses without dispersion compensation. We also mode locked the laser at either 1.03 or 1.05 μm by adjusting the band gap and antiresonance wavelength design of the antiresonant Fabry–Perot saturable absorber.