Das Auszugsverhalten junger Menschen

In dieser Arbeit wird untersucht, welche individuellen Faktoren einen Einfluß auf das Auszugsverhalten junger Menschen in der Bundesrepublik (West) haben. Die Untersuchung wird auf der Basis von Daten des Sozioökonomischen Panels f�r die Geburtenjahrgänge von 1968-1982 durchgeführt. Es wird ein semiparametrisches Hazardratenmodell geschätzt, in dem die Zielzustände "Single-Haushalt" und "Wohnung mit Partner" unterschieden werden. Variablen wie das eigene Einkommen und das Elterneinkommen werden nonparametrisch im Modell berücksichtigt. Es zeigt sich, daß Arbeitslosigkeit keinen negativen Effekt auf die Auszugswahrscheinlichkeit hat. Die Institution Familie fungiert also für junge Menschen nur in geringem Maße als Versicherung gegen Arbeitslosigkeit. Ein höheres eigenes Einkommen führt hingegen ebenso wie ein hüheres Elterneinkommen zu einer höheren Auszugswahrscheinlichkeit

Polarons in semiconductor quantum-dots and their role in the quantum kinetics of carrier relaxation

While time-dependent perturbation theory shows inefficient carrier-phonon scattering in semiconductor quantum dots, we demonstrate that a quantum kinetic description of carrier-phonon interaction predicts fast carrier capture and relaxation. The considered processes do not fulfill energy conservation in terms of free-carrier energies because polar coupling of localized quantum-dot states strongly modifies this picture.Comment: 6 pages, 6 figures, accepted for publication in Phys.Rev.

Influence of carrier-carrier and carrier-phonon correlations on optical absorption and gain in quantum-dot systems

A microscopic theory is used to study the optical properties of semiconductor quantum dots. The dephasing of a coherent excitation and line-shifts of the interband transitions due to carrier-carrier Coulomb interaction and carrier-phonon interaction are determined from a quantum kinetic treatment of correlation processes. We investigate the density dependence of both mechanisms and clarify the importance of various dephasing channels involving the localized and delocalized states of the system.Comment: 12 pages, 10 figure

Modeling and Optimization for Transportation Systems Planning and Operations

In this paper, we focus on a number of applications of network optimization techniques to transportation systems analysis. In particular, network analysis problems, network design problems, and network management problems are discussed in some detail. The intent is to survey important application areas.*To be presented at the International Symposium on Large Engineering Systems, University of Manitoba, Winnipeg, Manitoba, Canada, August 9-12, 197

Influence of symmetry and Coulomb-correlation effects on the optical properties of nitride quantum dots

The electronic and optical properties of self-assembled InN/GaN quantum dots (QDs) are investigated by means of a tight-binding model combined with configuration interaction calculations. Tight-binding single particle wave functions are used as a basis for computing Coulomb and dipole matrix elements. Within this framework, we analyze multi-exciton emission spectra for two different sizes of a lens-shaped InN/GaN QD with wurtzite crystal structure. The impact of the symmetry of the involved electron and hole one-particle states on the optical spectra is discussed in detail. Furthermore we show how the characteristic features of the spectra can be interpreted using a simplified Hamiltonian which provides analytical results for the interacting multi-exciton complexes. We predict a vanishing exciton and biexciton ground state emission for small lens-shaped InN/GaN QDs. For larger systems we report a bright ground state emission but with drastically reduced oscillator strengths caused by the quantum confined Stark effect.Comment: 15 pages, 17 figure

Infrared spectra of the water-CO2 complex in the 4.3-3.6 micron region and determination of the ground state tunneling splitting for HDO-CO2

Spectra of water-CO2 dimers are studied using a tunable mid-infrared source to probe a pulsed slit jet supersonic expansion. H2O-CO2 and D2O-CO2 are observed in the CO2 nu3 fundamental region (~2350 cm-1), D2O-CO2 is also observed in the D2O nu3 fundamental region (~2790 cm-1), and HDO-CO2 is observed in the HDO O-D stretch fundamental region (~2720 cm-1), all for the first time in these regions. Analysis of the spectra yields excited state rotational parameters and vibrational shifts. They also yield the first experimental values of the ground state internal rotation tunneling splittings for D2O-CO2 (0.003 cm-1) and HDO-CO2 (0.0234 cm-1). The latter value is a direct determination made possible by the reduced symmetry of HDO-CO2. These results provide stringent and easily interpreted tests for theoretical water - CO2 potential energy surface calculations.Comment: 19 pages, 6 figure and 5 table

Traffic Network Optimum Principle - Minimum Probability of Congestion Occurrence

We introduce an optimum principle for a vehicular traffic network with road bottlenecks. This network breakdown minimization (BM) principle states that the network optimum is reached, when link flow rates are assigned in the network in such a way that the probability for spontaneous occurrence of traffic breakdown at one of the network bottlenecks during a given observation time reaches the minimum possible value. Based on numerical simulations with a stochastic three-phase traffic flow model, we show that in comparison to the well-known Wardrop's principles the application of the BM principle permits considerably greater network inflow rates at which no traffic breakdown occurs and, therefore, free flow remains in the whole network.Comment: 22 pages, 6 figure