2,357 research outputs found
Nuclear quantum transport for barrier problems
A method is presented which allows one to introduce collective coordinates
self-consistently, in distinction to the Caldeira-Leggett model. It is
demonstrated how the partition function Z for the total nuclear system can be
calculated to deduce information both on its level density as well as on the
decay rate of unstable modes. For the evaluation of Z different approximations
are discussed. A recently developed variational approach turns out superior to
the conventional methods that include quantum effects on the level of local
RPA. Dissipation is taken into account by applying energy smearing, simulating
in this way the coupling to more complicated states. In principle, such a
coupling must depend on temperature. Previous calculations along another
microscopic approach show this fact to imply an intriguing variation of the
transport coefficients of collective motion with T. The relevance of this
feature is demonstrated for the thermal fission rate and for the formation
probability of super-heavy elements.Comment: 8 pages, 4 figures, presented at FUSION03, Matsushima, Miyagi, Japan,
Nov 12-15, 2003, to appear in Progress of Theoretical Physic
Dynamic Bonus Pools
We analyze a two-period agency problem with limited liability and nonverifiable information. The principal commits to a dynamic bonus pool comprising a fixed total payment that may be distributed over time to the agent and a third party. We find that the optimal two-period contract features memory. If the agent succeeds in the first-period, second-period incentives are weakened whereas higher-powered incentives are provided if he fails. The two-period bonus pool offers a complementary reason for why third-party payments are not commonly observed in practice
Influence of microscopic transport coefficients on the formation probabilities for super-heavy elements
The formation probability is shown to increase by a few orders of magnitude
if microscopic transport coefficients are used rather than those of the common
macroscopic pictures. Quantum effects in collective dynamics are taken into
account through the fluctuating force, as exhibited in diffusion coefficients
for a Gaussian process. In the range of temperatures considered here, they turn
out to be of lesser importance.Comment: 20 pages, 9 figures, replaced by revised version accepted for
publication in NP
Metamodel for Tracing Concerns across the Life Cycle
Several aspect-oriented approaches have been proposed to specify aspects at different phases in the software life cycle. Aspects can appear within a phase, be refined or mapped to other aspects in later phases, or even disappear.\ud
Tracing aspects is necessary to support understandability and maintainability of software systems. Although several approaches have been introduced to address traceability of aspects, two important limitations can be observed. First, tracing is not yet tackled for the entire life cycle. Second, the traceability model that is applied usually refers to elements of specific aspect languages, thereby limiting the reusability of the adopted traceability model.We propose the concern traceability metamodel (CTM) that enables traceability of concerns throughout the life cycle, and which is independent from the aspect languages that are used. CTM can be enhanced to provide additional properties for tracing, and be instantiated to define\ud
customized traceability models with respect to the required aspect languages. We have implemented CTM in the tool M-Trace, that uses XML-based representations of the models and XQuery queries to represent tracing information. CTM and M-Trace are illustrated for a Concurrent Versioning System to trace aspects from the requirements level to architecture design level and the implementation
Extracting the Temperature of Hot Carriers in Time- and Angle-Resolved Photoemission
The interaction of light with a material's electronic system creates an
out-of-equilibrium (non-thermal) distribution of optically excited electrons.
Non-equilibrium dynamics relaxes this distribution on an ultrafast timescale to
a hot Fermi-Dirac distribution with a well-defined temperature. The advent of
time- and angle-resolved photoemission spectroscopy (TR-ARPES) experiments has
made it possible to track the decay of the temperature of the excited hot
electrons in selected states in the Brillouin zone, and to reveal their cooling
in unprecedented detail in a variety of emerging materials. It is, however, not
a straightforward task to determine the temperature with high accuracy. This is
mainly attributable to an a priori unknown position of the Fermi level and the
fact that the shape of the Fermi edge can be severely perturbed when the state
in question is crossing the Fermi energy. Here, we introduce a method that
circumvents these difficulties and accurately extracts both the temperature and
the position of the Fermi level for a hot carrier distribution by tracking the
occupation statistics of the carriers measured in a TR-ARPES experiment.Comment: 17 pages, 5 figure
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