Classical solutions of drift-diffusion equations for semiconductor devices: the 2d case

We regard drift-diffusion equations for semiconductor devices in Lebesgue spaces. To that end we reformulate the (generalized) van Roosbroeck system as an evolution equation for the potentials to the driving forces of the currents of electrons and holes. This evolution equation falls into a class of quasi-linear parabolic systems which allow unique, local in time solution in certain Lebesgue spaces. In particular, it turns out that the divergence of the electron and hole current is an integrable function. Hence, Gauss' theorem applies, and gives the foundation for space discretization of the equations by means of finite volume schemes. Moreover, the strong differentiability of the electron and hole density in time is constitutive for the implicit time discretization scheme. Finite volume discretization of space, and implicit time discretization are accepted custom in engineering and scientific computing.--This investigation puts special emphasis on non-smooth spatial domains, mixed boundary conditions, and heterogeneous material compositions, as required in electronic device simulation

New Results on Ultrafast Coherent Excitation of Molecular Vibrations in Liquids

Coherent Raman probe scattering experiments are performed to study dynamical processes of polyatomic liquids at 300 K. For single homogeneous transitions the dephasing timeT 2 is readily obtained from time resolved investigations. Spectral studies show an interesting time dependent shift in scattered frequency. After the excitaiton the vibrating molecules are shown to relax freely with their resonance frequency. Multiple, equally spaced transitions exhibit a beating phenomenon which provides the dephasing time and the frequency interval between neighboring vibrational states. Inhomogeneously broadened systems do not allow a ready determination of the dephasing time by the present probing technique. Previous experiments on the subject have to be reconsidered

Fremdvergabe von IT-Dienstleistungen aus personalwirtschaftlicher Sicht

Die Nutzung von Informationstechnologie (IT) nimmt weiter zu. Gleichzeitig besteht ein Mangel an Fachkräften. Da spezialisierte IT-Unternehmen Vorteile bei der Akquisition dieser Mitarbeiter haben, wirkt sich der Mangel an Spezialisten positiv auf das Ausmaß des Outsourcing von IT-Dienstleistungen aus. Auch andere personalwirtschaftliche Aspekte sollten einen starken Einfluss zeigen. In diesem Artikel werden zuerst die personalwirtschaftlichen Bestimmungsfaktoren der IT-Outsourcing-Entscheidung systematisiert. Es folgt eine deskriptive Analyse von IT-Fremdvergabeentscheidungen und der IT-Nutzung des Wirtschaftszweigs "Unternehmensnahe Dienstleistungen". Schließlich werden im Rahmen eines ökonometrischen Modells die Bestimmungsfaktoren von IT-Outsourcing in dieser Branche untersucht. Es zeigt sich, dass personalwirtschaftliche Variablen einen hohen Erklärungsbeitrag liefern. Die Resultate lassen sich u.a. als Beleg für strategische Komplementarität zwischen verschiedenen Outsourcing-Entscheidungen interpretieren

Neue Möglichkeiten zur Nutzung vertraulicher amtlicher Personen- und Firmendaten

Reasearches in Germany have nowadays access to confidential micro data compiled from official statistics ina way that could have been dreamt of just few years ago. This paper describes the new institutions that grant data access - mots importantly the research data centers located inside the data producing agencies - and how to access the micor data, and presents information about selected recently released data sets with a high potential for scientific research and policy evaluation. Furthermore, we contrast the German situation with the Danish way of handling research access to confidential micro data. Finally, we take a look at ongoing projects that will further improve data access in Germany.

Energy transfer from retinal to amino acids — a time-resolved study of the ultraviolet emission of bacteriorhodopsin

Two-step excitation of retinal in bacteriorhodopsin by visible light is followed by an energy transfer to amino acids that is seen as fluorescent emission around 350 nm. The fluorescence spectrum obtained after two-step excitation (2 × 527 nm) differs from the fluorescence spectrum obtained after one-step ultraviolet excitation (263.5 nm) by a strongly quenched emission with a fluorescence lifetime of 10 ± 5 ps and a smaller spectral width. The two-step absorption process presumably selects tryptophan residues which strongly couple to the retinal chromophore

Fremdvergabe von IT-Dienstleistungen aus personalwirtschaftlicher Sicht

Dieser Beitrag untersucht die personalwirtschaftlichen Aspekte der Fremdvergabe von IT-Leistungen. Er bietet einen systematischen Überblick über bestehende theoretische und empirische Arbeiten zum Thema IT-Outsourcing und legt dabei einen besonderen Schwerpunkt auf die personalwirtschaftlichen Komponenten der ITFremdvergabeentscheidung. Aus dem Überblick werden Hypothesen hinsichtlich der Wirkungsrichtung verschiedener Determinanten des IT-Outsourcings abgeleitet. Diese Hypothesen werden einem empirischen Test unterzogen. Auf Grundlage eines großzahligen Datensatzes (N=679) wird die Fremdvergabeentscheidung von (i) Betreuung und Wartung von Hard- und Software, (ii) Programmierleistungen und (iii) EDV-Schulungen analysiert. Die Schätzergebnisse zeigen, dass personalwirtschaftliche Variablen wie Weiterbildung, Mangel an qualifizierten Mitarbeitern, Qualifikationsniveau der Mitarbeiter und Unternehmensgröße einen hohen Erklärungsbeitrag liefern. Unsere Resultate lassen sich u.a. als Beleg für strategische Komplementarität zwischen verschiedenen Outsourcing-Entscheidungen interpretieren. -- This paper analyzes those aspects of IT outsourcing decisions that are related to personnel economics. It offers a systematic overview of existing theoretical and empirical studies on that issue. We draw empirically testable hypotheses from our overview and take them to data. Based on a comparatively large data set that comprises of 679 obser-vations, we estimate the determinants of outsourcing (i) hardware and software admini-stration and maintenance, (ii) programming services and (iii) IT training. The estimation results indicate that variables such as training, lack of qualified employees, skill structure of employees, and firm size have significant effects on the decision to outsource IT services. Our results also suggest that strategic complementarities exist between the various outsourcing decisions.

Optimal elliptic regularity at the crossing of a material interface and a Neumann boundary edge

We investigate optimal elliptic regularity of anisotropic div-grad operators in three dimensions at the crossing of a material interface and an edge of the spatial domain on the Neumann boundary part within the scale of Sobolev spaces

About a Stationary Schrödinger-Poisson System with Kohn-Sham potential in Nanoelectronics

The stationary Schrödinger-Poisson system with a self-consistent effective Kohn-Sham potential is a system of PDEs for the electrostatic potential and the envelopes of wave functions defining the quantum mechanical carrier densities in a semiconductor nanostructure. We regard both Poisson's and Schrödinger's equation with mixed boundary conditions and discontinuous coefficients. Without an exchange-correlation potential the Schrödinger-Poisson system is a nonlinear Poisson equation in the dual of a Sobolev space which is determined by the boundary conditions imposed on the electrostatic potential. The nonlinear Poisson operator involved is strongly monotone and boundedly Lipschitz continuous, hence the operator equation has a unique solution. The proof rests upon the following property: the quantum mechanical carrier density operator depending on the potential of the defining Schrödinger operator is anti-monotone and boundedly Lipschitz continuous. The solution of the Schrödinger-Poisson system without an exchange-correlation potential depends boundedly Lipschitz continuous on the reference potential in Schrödinger's operator. By means of this relation a fixed point mapping for the vector of quantum mechanical carrier densities is set up which meets the conditions in Schauder's fixed point theorem. Hence, the Kohn-Sham system has at least one solution. If the exchange-correlation potential is sufficiently small, then the solution of the Kohn-Sham system is unique. Moreover, properties of the solution as bounds for its values and its oscillation can be expressed in terms of the data of the problem