Showing papers by "Technical University of Berlin published in 1993"
TL;DR: A new algorithm to compute stable discrete minimal surfaces bounded by a number of fixed or free boundary curves in R 3, S 3 and H 3 is presented and an algorithm that, starting from a discrete harmonic map, gives a conjugate harmonic map is presented.
Abstract: We present a new algorithm to compute stable discrete minimal surfaces bounded by a number of fixed or free boundary curves in R 3, S 3 and H 3. The algorithm makes no restr iction on the genus and can handl e singular triangulations. Additionally, we present an algorithm that, starting from a discrete harmonic map, gives a conjugate harmonic map. This can be applied to the identity map on a minimal surface to produce its conjugate minimal surface, a procedure that often yields unstable solutions to a free boundary value problem for minimal surfaces. Symmetry properties of boundary curves are respected during conjugation.
1,339 citations
TL;DR: In this article, the first observation of cholesteric blue phases in chiral anisotropic polymer networks was reported, in which two-component mixtures of a chiral and a non-chiral diacrylate were photopolymerized at constant temperature.
Abstract: We report the first observation of cholesteric blue phases in chiral anisotropic polymer networks. In two-component mixtures of a chiral and a non-chiral diacrylate, we observed typical textures of BPI, BPII and BPIII phases. By photopolymerization of these materials at constant temperature we obtained blue phase networks. After polymerization, the blue phases were stored, which enabled us to further study them without any temperature control.
1,008 citations
TL;DR: Experimental results clearly indicate a definite superiority of even non-optimized magnetic fluids over MDP ferrites regarding their specific absorption rate (SAR), and inductive heating by magnetic fluids can improve temperature distributions in critical regions.
Abstract: The potential of colloidal subdomain ferrite particle suspensions (SDP) (‘magnetic fluids’), exposed to an alternating magnetic field, is evaluated for hyperthermia. Power absorption measurements o...
653 citations
TL;DR: In this article, the electrical conductivity of mixtures of conductive and insulating materials is reviewed and different models have been proposed aimed at the prediction of the conductivity or the percolation concentration.
Abstract: The electrical conductivity of mixtures of conductive and insulating materials is reviewed In general, the conductivity of such mixtures increases drastically at a certain concentration of the conductive component, the so-called percolation concentration Among the parameters influencing the percolation concentration, the filler distribution, filler shape, filler/matrix interactions and the processing technique are the most important ones On the basis of these parameters, different models have been proposed aimed at the prediction of the conductivity or the percolation concentration It will be shown here that statistical, geometric or thermodynamic models explain the conductivity behaviour of specific mixtures on the basis of insufficient assumptions However, the conductivity seems to be predictable with the help of structure-oriented models
651 citations
TL;DR: A review of dynamic modelling of railway track and of the interaction of vehicle and track at frequencies which are sufficiently high for the track's dynamic behaviour to be significant is presented in this paper.
Abstract: A review is presented of dynamic modelling of railway track and of the interaction of vehicle and track at frequencies which are sufficiently high for the track's dynamic behaviour to be significant. Since noise is one of the most important consequences of wheel/rail interaction at high frequencies, the maximum frequency of interest is about 5kHz: the limit of human hearing. The topic is reviewed both historically and in particular with reference to the application of modelling to the solution of practical problems. Good models of the rail, the sleeper and the wheelset are now available for the whole frequency range of interest. However, it is at present impossible to predict either the dynamic behaviour of the railpad and ballast or their long term behaviour. This is regarded as the most promising area for future research.
615 citations
TL;DR: In this paper, a simple but comprehensive survey of the stability behavior of a rotating shaft with a crack, and of the forced vibrations due to imbalance and to the crack, is provided, restricted to that of the Laval rotor.
414 citations
TL;DR: X-ray structure analysis showed that the trimeric photosystem I (PS I) of Synechococcus sp. as mentioned in this paper consists of a catalytic domain and a smaller domain that connects the monomers.
Abstract: X-ray structure analysis shows that the monomer of trimeric photosystem I (PS I) of Synechococcus sp. consists of a catalytic domain and a smaller domain that connects the monomers. The 4Fe–4S clusters FX,FA and FB, 28 α-helices and 45 chlorophyll a molecules were located. The two large subunits of PS I are represented by nine a-helices each; they are related by a local 2-fold rotation axis passing through Fx. Electron densities close to this axis are interpreted as carriers of the electron transfer chain.
350 citations
TL;DR: In this paper, a review of heat propagation in dielectric solids at low temperatures where the phenomenon of second sound occurs is presented, which views them as special cases of a unified theory which is formulated within the framework of extended thermodynamics of phonos.
Abstract: This is a review of heat propagation — theory and experiment — in dielectric solids at low temperatures where the phenomenon of second sound occurs. The review does not merely present a list of the various explanations of the observed phenomena. Rather it views them as special cases of a unified theory which is formulated within the framework of extended thermodynamics of phonos. Field equations are derived by averaging over the phonon-Boltzmann equation and initial and boundary value problems are solved. Thus it became possible to achieve a full explanation of the observations of the heat-pulse experiments in which ballistic phonons, second sound and ordinary heat conduction compete.
318 citations
TL;DR: This deformation of particle image patterns by strong velocity gradients and out-of-pattern motions is investigated and its effect on conventional PIV techniques is quantified for 2D flows.
Abstract: In this second part of the paper, the Particle Image Distortion (PID) technique is described. It is proposed to overcome the limitations of conventional PIV due to the local deformations ∂u/∂x, ∂u/∂y, ∂v/∂x and ∂v/∂y in two-dimensional flows. Both simulation and experiment demonstrate that high accuracy and high spatial resolution are possible with this technique. The large time required to compute the cross-correlations, however, limits its wide applications at present.
267 citations
01 Jan 1993
TL;DR: A comprehensive overview of measures that have been employed to assess burnout can be found in this paper, where several psychometric criteria are used for assessing the various measures, such as inter-item reliability, test-retest consistency, and complexity of the factor structure.
Abstract: The importance of reliable and valid instruments to measure burnout is evident not only for the purpose of empirical research but ultimately for individual assessment. This chapter presents a comprehensive overview of measures that have been employed to assess burnout. Several psychometric criteria are used for assessing the various measures, such as inter-item reliability, test-retest consistency, and complexity of the factor structure. Self-report burnout measures can be distinguished according to the amount of psychometric research on which they are based. Two self-report instruments have been intensively studied psychometrically: Burnout Measure (BM) and Maslach Burnout Inventory (MBI). The psychometric qualities of the MBI are encouraging but not completely beyond question. In particular, its discriminant validity is rather poor. In most self-report inventories the individual's depletion of emotional resources is included in one way or another. The chapter also discusses the directions for future research.
245 citations
TL;DR: In this article, the authors present an overview of disassembly research at universities, research centers and industrial companies, pointing out ongoing topics and trends for future activities, including technological development, product design, process design, and system design.
30 Aug 1993
TL;DR: A class of graph partitioning problems whose two extreme representatives are the well-known Min Cut and Graph Bisection problems is investigated, finding the more balanced the partition the authors look for has to be, the harder the problem.
Abstract: We investigate a class of graph partitioning problems whose two extreme representatives are the well-known Min Cut and Graph Bisection problems. The former is known to be efficiently solvable by flow techniques, the latter to be NP-complete. The results presented in this paper are
a monotony result of the type“ The more balanced the partition we look for has to be, the harder the problem”.
a complexity result clarifying the status of a large part of intermediate problems in the class.
TL;DR: In this article, the authors generalized the Hartree-Fock variational principle to include quasi-free states and showed that these are in one-to-one correspondence with the one-particle density matrices and these, in turn, provide a convenient formulation of the BCS theory as a special case.
Abstract: The familiar unrestricted Hartree-Fock variational principle is generalized to include quasi-free states. As we show, these are in one-to-one correspondence with the one-particle density matrices and these, in turn provide a convenient formulation of a generalized Hartree-Fock variational principle, which includes the BCS theory as a special case. While this generalization is not new, it is not well known and we begin by elucidating it. The Hubbard model, with its particle-hole symmetry, is well suited to exploring this theory because BCS states for the attractive model turn into usual HF states for the repulsive model. We rigorously determine the true, unrestricted minimizers for zero and for nonzero temperature in several cases, notably the half-filled band. For the cases treated here, we can exactly determine all broken and unbroken spatial and gauge symmetries of the Hamiltonian.
TL;DR: The gene encoding the multifunctional enzyme enniatin synthetase from Fusarium scirpi (esyn1) was isolated and characterized by transcriptional mapping and expression studies in Escherichia coli and seems to harbour the N‐methyl‐transferase function of the multienzyme.
Abstract: The gene encoding the multifunctional enzyme enniatin synthetase from Fusarium scirpi (esyn1) was isolated and characterized by transcriptional mapping and expression studies in Escherichia coli. This is the first example of a gene encoding an N-methyl peptide synthetase. The nucleotide sequence revealed an open reading frame of 9393 bp encoding a protein of 3131 amino acids (M(r) 346,900). Two domains designated EA and EB within the protein were identified which share similarity to each other and to microbial peptide synthetase domains. In contrast to the N-terminal domain EA, the carboxyl terminal domain EB is interrupted by a 434-amino-acid portion which shows local similarity to a motif apparently conserved within adenine and cytosine RNA and DNA methyltransferases and therefore seems to harbour the N-methyl-transferase function of the multienzyme.
TL;DR: In this paper, the nucleation and crystallization kinetics of three glasses with stoichiometric composition Li2O·2SiO2, Na2O2CaO·3SiO 2 and 2Na2OµCaOÔµµ 3SiO µ have been investigated by determining the nucleations and crystal growth rates and corresponding induction times.
Abstract: The nucleation and crystallization kinetics in three glasses with stoichiometric composition Li2O·2SiO2, Na2O·2CaO·3SiO2 and 2Na2O·CaO·3SiO2 are investigated by determining the nucleation and crystal growth rates and the corresponding induction times. An analysis of the induction times for crystal growth and nucleation indicates that in the two soda-lime metasilicate glasses nucleation and crystallisation of the crystals occur subsequently, i.e., no time lag exists between the two experimentally determined induction times. By contrast with this absence of a time lag, a considerable time lag appears in the case of lithium disilicate, indicating a metastable phase formation and probably compositional changes during crystallisation in this early stage. Transmission electron microscopy shows that a metastable phase (denoted by transient-phase) occurs in the early stage which is totally dissimilar to lithium disilicate and which acts as a precursor to the equilibrium crystallisation of lithium disilicate. This two-stage process leads to the conclusion that the theory of homogeneous nucleation cannot be applied to the Li-disilicate melt.
TL;DR: Inactivation of the yeast at low aw could be achieved by pressure treatment at increased temperature, and at atmospheric pressure, processing temperatures of 70 to 80°C were required to accomplish the same effects.
Abstract: High hydrostatic pressure (200 to 400 MPa) treatment of Rhodotorula rubra suspended in solutions of sucrose, glucose, fructose or sodium chloride resulted in water activity (aw) dependent barotolerance. The protective effect started at values below aw = 0.92 to 0.88. Increase in time of treatment over 15 min had a small influence. In sucrose, the effect was independent of pH between pH 3.0 and 8.0. Inactivation of the yeast at low aw could be achieved by pressure treatment at increased temperature (45°C). At atmospheric pressure, processing temperatures of 70 to 80°C were required to accomplish the same effects.
TL;DR: In this article, Pseudoelasticity refers to a hysteretic loading-unloading characteristic observed in the stress-induced martensitic transformation of shape memory alloys.
Abstract: Solid-solid phase transitions often exhibit hystereses, and a hysteresis indicates energy dissipation. Pseudoelasticity refers to a hysteretic loadingunloading characteristic observed in the stress-induced martensitic transformation of shape memory alloys.
TL;DR: The electron spin density distribution of the cation radical of the primary donor, D+, a bacteriochlorophyll a dimer was determined by endor and TRIPLE resonance experiments performed on single crystals of reaction centers (RCs) of Rhodobacter sphaeroides R-26 as mentioned in this paper.
TL;DR: In this article, Chenopodium rubrum and Morinda citrifolia cells were subjected to high electric field pulses (0 to 1.6 kV ∗ cm−1, 0 to 30 pulses) or high hydrostatic pressure (0.1 to 350 MPa, 10 min, RT) to examine their role in cell permeabilization.
Abstract: Chenopodium rubrum and Morinda citrifolia cells were subjected to high electric field pulses (0 to 1.6 kV ∗ cm−1, 0 to 30 pulses) or high hydrostatic pressure (0.1 to 350 MPa, 10 min, RT) to examine their role in cell permeabilization. A maximum amount of 85 % of the total amaranthin content and 5.7 % of total amount of anthraguinones of the cells could be released after treatment with electric field pulses. However, cell viability was lost at release values higher than 16 % and 2 % respectively. Pressure treatment at 350 MPa resulted in pigment release of 99 % and 9.4 %. Viability was lost at pressures of 110 MPa and of 75 MPa respectively. Although the methods applied have limited potential for cell permeabilization while preserving cell viability we are proposing them as useful processes for metabolite recovery.
TL;DR: In this paper, it was shown that accumulation points (as the scaled Planck constant tends to zero) of solutions of a corresponding slightly regularized Wigner-Poisson system are distributional solutions of the classical Vlasov Poisson system.
Abstract: Under natural assumptions on the initial density matrix of a mixed quantum state (Hermitian, non-negative definite, uniformly bounded trace, Hilbert-Schmidt norm and kinetic energy) we prove that accumulation points (as the scaled Planck constant tends to zero) of solutions of a corresponding slightly regularized Wigner-Poisson system are distributional solutions of the classical Vlasov-Poisson system. The result holds for the gravitational and repulsive cases. Also, for every phase-space density in (with bounded kinetic energy) we prepare a sequence of density matrices satisfying the above assumptions, such that the given density is the limit of the Wigner transforms of these density matrices.
TL;DR: The biogenic amines serotonin (5HT) and octopamine (OA) exist in the bee and can modulate neuronal activity and behaviour and binds to neuropils which are not directly innervated by 5HT-like or OA-like immunoreactive neurons.
Abstract: The biogenic amines serotonin (5HT) and octopamine (OA) exist in the bee and can modulate neuronal activity and behaviour. 5HT-like and OA-like immunoreactivities can be found in most neuropils of the brain. Binding sites for the two amines are also present in most brain neuropils. The highest density of binding sites for [3H]serotonin and [3H]octopamine was found in the mushroom bodies. In some brain areas, especially the mushroom bodies, mismatches exist between binding sites and immunoreactivities, suggesting that the two amines also bind to neuropils which are not directly innervated by 5HT-like or OA-like immunoreactive neurons. The action of the two amines on behaviour in the bee is antagonistic. In the antennal pathway, proboscis and antennal responses to olfactory and gustatory stimuli are enhanced by OA and reduced by 5HT. In olfactory conditioning experiments, storage and retrieval of the learned signal can be enhanced by OA and reduced by 5HT. The specificity of these effects depends on the site of amine application in the neuropil. In the visual system the direction specificity of the visual antennal response is enhanced by OA and reduced by 5HT after topical application or injection into the lobula, the third optic ganglion. Correlates for the behavioural modulation can be found in higher-order visual interneurons. While OA application can mimic the stimulation of the bee with sugar water, the behavioural conditions leading to the release of 5HT are not yet known.
TL;DR: The Gay-Berne potential is proving to be of considerable value in computer simulation studies of liquid crystals as mentioned in this paper, however, the parameters employed in the potential were chosen by comparison with that for a line of four Lennard-Jones centres; they may not, therefore, be appropriate for mesogenic molecules.
Abstract: The Gay-Berne potential is proving to be of considerable value in computer simulation studies of liquid crystals. However, the parameters employed in the potential were chosen by comparison with that for a line of four Lennard-Jones centres; they may not, therefore, be appropriate for mesogenic molecules. To see if this is the case we have estimated the parameters in the Gay-Berne potential by comparison with the site-site potential constructed for p-terphenyl, which has a molecular structure typical of many mesogens. Unlike the Gay-Berne potential the site-site potential is biaxial, and a method for projecting out this biaxiality is proposed. The resultant uniaxial model has then been used to obtain values for the parameters occurring in the Gay-Berne potential. These are found to differ significantly from those proposed originally; they are, we believe, more appropriate for investigations of the behaviour of liquid crystals. Our own molecular dynamics simulations, based on the new parametrization, revea...
TL;DR: In this paper, the photophysical behavior of para-nitro, para-cyano, and meta-nibro-4′-dimethylaminostilbenes is compared and explained.
TL;DR: In this article, a three-dimensional steady state irrotational flow model for semiconductors based on the hydrodynamic equations is presented, where the authors prove existence and local uniqueness of smooth solutions under a smallness assumption on the data.
Abstract: We present a three-dimensional steady state irrotational flow model for semiconductors which is based on the hydrodynamic equations. We prove existence and local uniqueness of smooth solutions under a smallness assumptions on the data. This assumption implies subsonic flow of electrons in the semiconductors device.
TL;DR: It is shown that the pathwidth problem for chordal graphs is NP-hard, and polynomial algorithms for subclasses are given – a generalization of split graphs and a class of graphs where the intersection behavior of maximal cliques is strongly restricted.
TL;DR: There is no mincut-model in general if only positive weights are allowed, and such models are constructed using positive and negative weights.
TL;DR: In this article, high hydrostatic pressure treatment (400 MPa, 15 min, 5-50°C) of potato cubes (2 × 2 × 2 cm) was compared with hot water blanching (100°C, 30-180 set).
Abstract: High hydrostatic pressure treatment (400 MPa, 15 min, 5–50°C) of potato cubes (2 × 2 × 2 cm) was compared with hot water blanching (100°C, 30–180 set). Inactivation of microorganisms and polyphenoloxidase, texture and density change, leaching of potassium and loss of ascorbic acid were monitored. Reduction of microbial counts was comparable for both methods and polyphenoloxidase was completely inactivated at 20°C, when dilute citric acid solutions (0.5 or 1.0%) were used as “immersion” medium. Hot water blanching and high pressure treatment resulted in samples of similar softness. Leaching of potassium was reduced 20% after pressure treatment on vacuum-packaged samples. Retention of ascorbic acid in pressure-treated samples was temperature dependent ranging from = 90% at 5°C to = 35% at 50°C.
TL;DR: By gel filtration of a crude extract of Bacillus subtilis ATCC 21332 and OKB 105, the multienzyme system that forms the lipoheptapeptide surfactin was separated into three enzyme fractions, E1, E2, and E3, with high rates of lipopeptide formation.
TL;DR: In this article, two simple cellular automata (CA) models which exhibit the essential attributes of soliton systems are described. But neither of these models is soliton-like.
Abstract: We describe two simple cellular automata (CA) models which exhibit the essential attributes of soliton systems. The first one is an invertible, 2-state, 1-dimensional CA or, in other words, a nonlinearZ
2-valued dynamical system with discrete space and time. Against a vacuum state of 0, the system exhibits light cone particles in both spatial directions, which interact in a soliton-like fashion. A complete solution of this system is obtained. We also consider another CA, which is described by the Hirota equation over a finite field, and present a Lax representation for it.