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For transferring existing knowledge into new projects, reuse has become an important factor in today's software industry. However, to set reuse into practice, reusable artifacts have to be stored somewhere, and must be offered to (re-)users on demand. For this purpose, advanced reuse repository systems like, for instance, instantiations of the Experience Base concept, are quite frequently used. Many people, from different projects, have to access such a repository at various phases of software development processes to retrieve or store reusable data. In order to fulfill the given tasks, each of these user has specific needs. Taking this into account, a reuse repository has to offer tailored user interfaces and functions for different user groups. Furthermore, since the contents of such a repository usually represent the state of the art of an organization's (core) competencies, not everyone should be allowed to freely access each and every repository entry. This isespecially true for persons that are not part of the organization. This report discusses role concepts that can be applied to reuse repository systems to overcome some of the stated access problems. Commonly used roles for software development and reuse repository management are listed. Based on these roles, a basic set of roles, as implemented in the SFB 501 Experience Base, is introduced.
In this paper we construct a multiscale solution method for the gravimetry problem, which is concerned with the determination of the earth's density distribution from gravitational measurements. For this purpose isotropic scale continuous wavelets for harmonic functions on a ball and on a bounded outer space of a ball, respectively, are constructed. The scales are discretized and the results of numerical calculations based on regularization wavelets are presented. The obtained solutions yield topographical structures of the earth's surface at different levels of localization ranging from continental boundaries to local structures such as Ayer's Rock and the Amazonas area.
Spherical Tikhonov Regularization Wavelets in Satellite Gravity Gradiometry with Random Noise
(2000)
This paper considers a special class of regularization methods for satellite gravity gradiometry based on Tikhonov spherical regularization wavelets with particular emphasis on the case of data blurred by random noise. A convergence rate is proved for the regularized solution, and a method is discussed for choosing the regularization level a posteriori from the gradiometer data.
Linear viscoelastic properties for a dilute polymer solution are predicted by modeling the solution as a suspension of non-interacting bead-spring chains. The present model, unline the Rouse model, can describe the solution's rheological behavior even when the solvent quality is good, since excluded volume effects are explicitly taken into account through a narrow Gaussian repulsive potential between pairs of beads in a bead-spring chain. The use of the narrow Gaussian potential, which tends to the more commonly used delta-function repulsive potential in the limit of a width parameter d going to zero, enables the performance of Brownian dynamics simulations. The simulations results, which describe the exact behavior of the model, indicate that for chains of arbitrary but finite length, a delta-function potential leads to equilibrium and zero shear rate properties which are identical to the predictions of the Rouse model. On the other hand, a non-zero value of d gives rise to a predictionof swelling at equilibrium, and an increase in zero shear rate properties relative to their Rouse model values. The use of a delta-function potential appears to be justified in the limit of infinite chain length. The exact simulation results are compared with those obtained with an approximate solution, which is based on the assumption that the non-equilibrium configurational distribution function is Gaussian. The Gaussian approximation is shown to be exact to first order in the strength of excluded volume interaction, and is used to explore long chain rheological properties by extrapolating results obtained numerically for finite chains, to the limit of infinite chain length.
Einer der Schwerpunkte dieser Arbeit ist die Reaktivitätsstudie von Mesitylphosphaalkin gegnüber 1,3-Butadien. Durch diese Umsetzung gelingt erstmals die Synthese eines 1-Phosphacyclohexa-1,4-diens und somit ein Beweis für die Gültigkeit des postulierten Reaktionsmechanismus zum Aufbau von Diphosphatricyclooctenen. Die Isolierung dieses Phosphacyclohexadiens ermöglicht auch erstmals die Darstellung von in 2- und 8-Position sterisch aufwendig gemischt substituierter Tricyclooctene aus je einem Äquivalent zweier verschiedener Phosphaalkine und einem Molekül eines offenkettigen 1,3-Diens. Ein weiteres Hauptaugenmerk lag auf dem Reaktionsverhalten von kinetisch stabilisierten Phosphaalkinen gegenüber Vinylallenen. Diese reagieren, obwohl sie auch die konstitutionelle Voraussetzung für En-Reaktionen mit sich bringen, fast ausnahmslos im Sinne offenkettiger 1,3-Diene. Je nach Wahl des Substitutionsmusters der Reaktanden sind so Tricyclooctene, Phosphinine, Phosphacyclohexadiene, Tetrahydrophosphinolizine und auch ein hochsubstituiertes Phosphan zugänglich. Trotz sterischer Abschirmung eignen sich die neuen Phosphine und Tricyclooctene als Liganden in Übergangsmetallcarbonylkomplexen. Im zweiten Teil der Arbeit steht die Synthese neuer auch perfluorierter Phosphaalkene des Becker-Typs im Vordergrund. Sie lassen sich als Syntheseäquivalente der entsprechenden Phosphaalkine einsetzen, auch wenn deren Darstellung nur in einem einzigen Fall gelingt. Das neu synthetisierte Phosphaalkin entzieht sich aufgrund seines hohen Dampfdrucks einer Isolierung. Seine Existenz steht jedoch außer Frage, da es in 1,3-dipolaren Cycloadditionen die erwarteten Heterophosphole liefert. Im letzten Abschnitt der Arbeit wurden Untersuchungen bezüglich der En-Reaktivität eines perfluorierten Phosphaalkens angestellt. Umsetzungen mit kinetisch nicht stabilisierten Phosphaalkenen ermöglichen hier den Zugang zu sehr hydrolyseempfindlichen Diphosphanen. Eine Dimerisierung der Reaktionspartner wird unterdrückt.
The paper studies the effect of a weak periodic driving on metastable Wannier-Stark states. The decay rate of the ground Wannier-Stark states as a continuous function of the driving frequency is calculated numerically. The theoretical results are compared with experimental data of Wilkinson et at. [Phys.Rev.Lett.76, 4512 (1996)] obtained for cold sodium atoms in an accelerated optical lattice.
The statistics of the resonance widths and the behavior of the survival probability is studied in a particular model of quantum chaotic scattering (a particle in a periodic potential subject to static and time-periodic forces) introduced earlier in Ref. [5,6]. The coarse-grained distribution of the resonance widths is shown to be in good agreement with the prediction of Random Matrix Theory (RMT). The behavior of the survival probability shows, however, some deviation from RMT.
We study the transitions between the ground and excited Wannier states induced by a weak ac field. Because the upper Wannier states are several order of magnitude less stable than the ground states, these transitions decrease the global stability of the system characterized by the rate of probability leakage or decay rate. Using nonhermitian resonant perturbation theory we obtain an analytical expression for this induced decay rate. The analytical results are compared with exact numerical calculations of the system decay rate.
The quasienergy spectrum of a Bloch electron affected by dc-ac fields is known to have a fractal structure as function of the so-called electric matching ratio, which is the ratio of the ac field frequency and the Bloch frequency. This paper studies a manifestation of the fractal nature of the spectrum in the system "atom in a standing laser wave", which is a quantum optical realization of a Bloch electron. It is shown that for an appropriate choice of the system parameters the atomic survival probability (a quantity measured in laboratory experiments) also develops a fractal structure as a function of the electric matching ratio. Numerical simulations under classically chaotic scattering conditions show good agreement with theoretical predictions based on random matrix theory.