Showing papers by "Technical University of Berlin published in 1989"

Out of scandinavia: alternative approaches to software design and system development

Abstract: This study set out to delineate the Scandinavian Approach to the development of computer-based systems. We aimed to help derive new ideas for human-oriented technology design in other countries. The study is based on the relevant literature, scientific contacts, and two field trips, and covers work in Denmark, Norway, and Sweden. The study focuses on methodological questions and their theoretical foundations, on explicit strategies for social implementation, and on innovative design illustrated by reference to concrete projects. Though it makes no claim to present a sociopolitical analysis of Scandinavian technology design, the sociocultural background is given due consideration. There is no general agreement among Scandinavians as to whether or not there is a well-defined Scandinavian Approach. We have come to identify such an approach in certain common features shared by the different schools of thought. These include efforts toward humanization and democratization as overriding design goals, in keeping with the aim of building an egalitarian society.

A unique geochemical record at the Permian/Triassic boundary

Abstract: A 330-metre core drilled through the marine Permian/Triassic boundary in the Carnic Alps of Austria allows closely correlated studies of geochemistry, petrography and palaeontology across the boundary. The isotope shifts and metal concentrations are extended, multiple and complex, and do not resemble those seen at the Cretaceous/Tertiary boundary. Both the carbon isotope shifts and the chemical events (including an indium anomaly) may have causes related to a major regression of the sea.

Gramicidin S biosynthesis operon containing the structural genes grsA and grsB has an open reading frame encoding a protein homologous to fatty acid thioesterases.

Abstract: The DNA sequence of about 5.9 kilobase pairs (kbp) of the gramicidin S biosynthesis operon (grs) was determined. Three open reading frames were identified; the corresponding genes, called grsT, grsA, and grsB, were found to be organized in one transcriptional unit, not two as previously reported (M. Krause and M. A. Marahiel, J. Bacteriol. 170:4669-4674, 1988). The entire nucleotide sequence of grsA, coding for the 126.663-kilodalton gramicidin S synthetase 1, grsT, encoding a 29.191-kilodalton protein of unknown function, and 732 bp of the 5' end of grsB, encoding the gramicidin S synthetase 2, were determined. A single initiation site of transcription 81 bp upstream of the grsT initiation condon GTG was identified by high-resolution S1 mapping studies. The sequence of the grsA gene product showed a high degree of homology to the tyrocidine synthetase 1 (TycA protein), and that of grsT exhibited a significant degree of homology to vertebrate fatty acid thioesterases.

Molecular Beam Epitaxy

Abstract: MBE is a versatile technique for growing thin epitaxial structures made of semiconductors, metals or insulators [7.1] (see also the definition given in Sect. 6.1.3). What distinguishes MBE from previous vacuum deposition techniques is its significantly more precise control of the beam fluxes and growth conditions. Because of vacuum deposition, MBE is carried out under conditions far from thermodynamic equilibrium and is governed mainly by the kinetics of the surface processes occurring when the impinging beams react with the outermost atomic layers of the substrate crystal. This is in contrast to other epitaxial growth techniques, such as LPE or atmospheric pressure VPE, which proceed at conditions near thermodynamic equilibrium and are most frequently controlled by diffusion processes occurring in the crystallizing phase surrounding the substrate crystal.

Computationally Tractable Classes of Ordered Sets

Abstract: Ordered sets have recently gained much importance in many applied and theoretical problems in computer science and operations research ranging from project planning via processor scheduling to sorting and retrieval problems. These problems involve partial orders as their basic structure, e.g. as precedence constraints in scheduling problems, or as comparability relation among the objects to be sorted or retrieved.

A note on the diffusion of directed polymers in a random environment

Abstract: A simple martingale argument is presented which proves that directed polymers in random environments satisfy a central limit theorem ford≧3 and if the disorder is small enough. This simplifies and extends an approach by J. Imbrie and T. Spencer.

STEPS to Software Development with Users

Abstract: The paper reports on the methodical approach STEPS, developed at the Technical University of Berlin and tried successfully in participative software development with users. STEPS views software development in its connection to work design. It gives guidance to developers and users for carrying out their cooperation, establishing quality criteria pertaining to software in use and putting them into practice in system design. It embodies an evolutionary approach, portraying system development in cycles of version production, application and revision. It supports mutual learning by developers and users by carefully establishing and coordinating processes of cooperation, by using prototyping for experiments and by adapting methods and tools to the needs of cooperation and incremental work.

Incomplete data problems in X-ray computerized tomography

Abstract: In the present paper we study truncated projections for the fanbeam geometry in computerized tomography First we derive consistency conditions for the divergent beam transform Then we study a singular value decomposition for the case where only the interior rays in the fan are provided, as for example in region-of-interest tomography We show that the high angular frequency components of the searched-for densities are well determined and we present reconstructions from real data where the missing information is approximated based on the singular value decomposition

Subshell photoionization of Xe between 40 and 1000 eV

Abstract: Partial cross sections and angular-distribution asymmetry parameters were measured for subshell photoionization of xenon for photon energies between 40 and 1000 eV. These large-scale measurements show that the pronounced interchannel coupling between the valence and the 4d electrons persists beyond the 4d shape resonance in the subsequent Cooper-minimum region. Multielectron processes associated with 4d and 4p photoemission were measured directly for the first time over a broader energy range covering the near-threshold behavior up to the sudden limit. Comparing our experimental results with calculations based on the single-particle model shows that this theory, which fails to describe the intermediate energy range even qualitatively for the valence electrons, gives partial cross sections in reasonable agreement with experiment at higher photon energies, particularly beyond the 3d threshold. The same result is shown by the angular-distribution asymmetry parameter \ensuremath{\beta}, except for the photoionization of the ``4p'' subshell which resembles more the behavior of a 4d electron, corroborating the theoretical assumptions of core-hole fluctuations between these two subshells. In the shape resonance region the presented 4d partial cross sections are in reasonable agreement with theoretical results obtained recently by many-body perturbation theory.

Formal program construction by transformations-computer-aided, intuition-guided programming

Abstract: Formal program construction by transformations is a method of software development in which a program is derived from a formal problem specification by manageable, controlled transformation steps which guarantee that the final product meets the initial specification. This methodology has been investigated in the Munich project CIP (computer-aided intuition-guided programming). The research includes the design of a wide-spectrum language specifically tailored to the needs of transformational programming, the construction of a transformation system to support the methodology, and the study of transformation rules and other methodological issues. Particular emphasis has been laid on developing a sound theoretical basis for the overall approach. >

Termination proofs and the length of derivations

Abstract: The derivation height of a term t, relative to a set R of rewrite rules, dh R (t), is the length of a longest derivation from t. We investigate in which way certain termination proof methods impose bounds on dh R . In particular we show that, if termination of R can be proved by polynomial interpretation then dh R is bounded from above by a doubly exponential function, whereas termination proofs by Knuth-Bendix ordering are possible even for systems where dh R cannot be bounded by any primitive recursive functions. For both methods, conditions are given which guarantee a singly exponential upper bound on dh R . Moreover, all upper bounds are tight.

Evolution Strategy: Nature’s Way of Optimization

Abstract: Biological Evolution has done development work on animated matter for more than three billion years. The method used in this process is the equivalent of an astute optimization procedure which is proverable by the theory of Evolution Strategy.

Rheology of dense model fluids via nonequilibrium molecular dynamics: Shear thinning and ordering transition

Abstract: Nonequilibrium molecular dynamics computer simulations are employed to investigate the rheology of dense simple model fluids. Besides the non-Newtonian behavior of the viscosity functions a shear-induced ordering transition is an essential feature of this presentation. Its occurrence in the simulation is supported by a hydrodynamic stability analysis. To illustrate the scenario preceding the instability, density and velocity profiles of the flow are considered as well as the static structure factor which enables a comparison with recent experimental results for dense suspensions. Problems related to experimental evidence of the ordering transition into layers are discussed in light of the derived stability criterion.

Assessment of earthworm burrowing efficiency in compacted soil with a combination of morphological and soil physical measurements

Abstract: Column experiments were carried out to quantify the effect of earthworms on compacted soil. The earthworms (Lumbricus terrestris) were able to burrow into soil which was artificially compacted to a pore volume as low as 40%; they may also penetrate an artificial “plough pan” deep in the soil. The effect of the burrowing activity of Lumbricus terrestris was quantified by measuring hydraulic conductivities and infiltration rates through the whole soil column (19 cm wide, 40 cm long). Morphological parameters, mainly the vertically projected burrow depth, were correlated with the saturated hydraulic conductivity. The amount of casts deposited by Lumbricus terrestris on the soil surface increased with the degree of soil compaction. The bulk density of casts was always less than that of the original soil.

Correlation of microstructure and creep stages in the 〈100〉 oriented superalloy SRR 99 at 1253 K

Abstract: The microstructure of creep specimens tested at 1253 K is analyzed in the three stages of the creep curve by TEM investigations. Stage I is characterized by the glide of screw dislocations in the matrix, while the transition to stage II is the beginning of γ′ rafting. Throughout stage II, the γ′ phase is not cut by dislocations. From these and other metallographic results, the mechanism of creep in the single-crystal alloy can be deduced. The misfit stress at the γ/γ′ interfaces proved to be of special importance for this type of alloy containing a high volume fraction of γ′.

On the size of the hysteresis in pseudoelasticity

Abstract: Pseudoelasticity is a phenomenon that occurs in alloys with shape memory: In a loading-unloading cycle a body will return to its original configuration, but its path in a load-deformation diagram will run through a hysteresis loop.

Cell-free biosynthesis of new cyclosporins.

Abstract: An enzyme preparation, isolated from extracts of the fungus Beauveria nivea (previously designated Tolypocladium inflatum), is able to synthesize cyclosporins (Cy's) in vitro. At suboptimal temperature it was possible to yield about 50 μg of CyA per ml. The enzyme also produces several of the naturally occuring congeners of CyA, such as the Cy's B, C, D, G, M, O, Q, U and V and some of the analogues known to be produced by the fungus via precursor directed biosynthesis, like dihydro-CyA, [N-methyl-L-β-cyclohexylalanine1]CyA, [1-allylglycine2]CyA and [D-serine8]CyA. Furthermore, Cy's not obtainable by the fungus could be prepared by the enzyme system in the presence of the appropriate precursor amino acids; the synthesis of [N-methyl(+)-2-amino-3-hydroxy-4, 4-dimethyloctanoic acid1]CyA, [1-norvaline2, 5, N-methyl-L-norvaline11]CyA, [L-norvaline5, N-methyl-L-norvaline11]CyA, [L-allo-isoleucine5, N-methyl-L-allo-isoleucine11]CyA; [L-allo-isoleucine5, 11]CyA, [D-2-aminobutyric acid8]CyA and [β-chloro-D-alanine8]CyA could be established. The immunosuppressive effects of the new derivatives are discussed.

On the convergence of generalized Padé approximants

Abstract: Letf be an analytic function with all its singularities in a compact set\(E_f \subset \bar C\) of (logarithmic) capacity zero. The function may have branch points. The convergence of generalized (multipoint) Pade approximants to this type of function is investigated. For appropriately selected schemes of interpolation points, it is shown that close-to-diagonal sequences of generalized Pade approximants converge in capacity tof in a certain domain that can be characterized by the property of the minimal condenser capacity. Using a pole elimination procedure, another set of rational approximants tof is derived from the considered generalized Pade approximants. These new approximants converge uniformly on a given continuum\(V \subset \bar C\backslash E_f\) with a rate of convergence that has been conjectured to be best possible. The continuumV is assumed not to divide the complex plane.

Dislocation structures in γ-γ′ interfaces of the single-crystal superalloy SRR 99 after annealing and high temperature creep

Abstract: Dislocation networks in γ-γ′ interfaces of a single-crystal superalloy containing about 60 vol.% of ordered γ′ phase have been analyzed after annealing and after creep. In both experiments gliding screw dislocations are the cause of dislocation accumulation at the interfaces. During annealing 60° segments left in the interfaces climb into edge orientation under the influence of elastic strain and form flat low energy networks. After creep testing dislocation networks built in stage II at the interfaces are folded and have different dislocation contents for interfaces normal rather than parallel to the external stress. These dislocation networks at γ-γ′ interfaces are highly energetic. They are not misfit dislocations and contribute to the strength of the alloy. Close to the rupture surface additional low energy twist dislocation networks are formed at γ-γ′ interfaces.