3,921 research outputs found
17Beta-estradiol modulates gastroduodenal preneoplastic alterations in rats exposed to the carcinogen N-methyl-N'-nitro-nitrosoguanidine
Goldstone Bosons in Josephson Junctions
For a microscopic model of a Josephson junction the normal coordinates of the
two junction Goldstone bosons are constructed and their dynamical spectrum is
computed. The explicit dependence on the phase difference of the two
superconductors is calculated
A microscopic model for Josephson currents
A microscopic model of a Josephson junction between two superconducting
plates is proposed and analysed. For this model, the nonequilibrium steady
state of the total system is explicitly constructed and its properties are
analysed. In particular, the Josephson current is rigorously computed as a
function of the phase difference of the two plates and the typical properties
of the Josephson current are recovered
Bogolyubov approximation for diagonal model of an interacting Bose gas
We study, using the Bogolyubov approximation, the thermodynamic behaviour of
a superstable Bose system whose energy operator in the second-quantized form
contains a nonlinear expression in the occupation numbers operators. We prove
that for all values of the chemical potential satisfying ,
where is the lowest energy value, the system undergoes
Bose--Einstein condensation
Self-consistent equation for an interacting Bose gas
We consider interacting Bose gas in thermal equilibrium assuming a positive
and bounded pair potential such that 0<\int d\br V(r) = a<\infty.
Expressing the partition function by the Feynman-Kac functional integral yields
a classical-like polymer representation of the quantum gas. With Mayer graph
summation techniques, we demonstrate the existence of a self-consistent
relation between the density and the
chemical potential , valid in the range of convergence of Mayer series.
The function is equal to the sum of all rooted multiply connected graphs.
Using Kac's scaling V_{\gamma}(\br)=\gamma^{3}V(\gamma r) we prove that in
the mean-field limit only tree diagrams contribute and function
reduces to the free gas density.
We also investigate how to extend the validity of the self-consistent
relation beyond the convergence radius of Mayer series (vicinity of
Bose-Einstein condensation) and study dominant corrections to mean field. At
lowest order, the form of function is shown to depend on single polymer
partition function for which we derive lower and upper bounds and on the
resummation of ring diagrams which can be analytically performed.Comment: 33 pages, 6 figures, submitted to Phys.Rev.
Metastability in the BCS model
We discuss metastable states in the mean-field version of the strong coupling
BCS-model and study the evolution of a superconducting equilibrium state
subjected to a dynamical semi-group with Lindblad generator in detailed balance
w.r.t. another equilibrium state. The intermediate states are explicitly
constructed and their stability properties are derived. The notion of
metastability in this genuine quantum system, is expressed by means of
energy-entropy balance inequalities and canonical coordinates of observables
Shopping centre siting and modal choice in Belgium: a destination based analysis
Although modal split is only one of the elements considered in decision-making on new shopping malls, it remarkably often arises in arguments of both proponents and opponents. Today, this is also the case in the debate on the planned development of three major shopping malls in Belgium. Inspired by such debates, the present study focuses on the impact of the location of shopping centres on the travel mode choice of the customers. Our hypothesis is that destination-based variables such as embeddedness in the urban fabric, accessibility and mall size influence the travel mode choice of the visitors. Based on modal split data and location characteristics of seventeen existing shopping centres in Belgium, we develop a model for a more sustainable siting policy. The results show a major influence of the location of the shopping centre in relation to the urban form, and of the size of the mall. Shopping centres that are part of a dense urban fabric, measured through population density, are less car dependent. Smaller sites will attract more cyclists and pedestrians. Interestingly, our results deviate significantly from the figures that have been put forward in public debates on the shopping mall issue in Belgium
Cognitive mapping of organic vegetable production in Flanders to support farmers strategy design
Organic farmers inherently have to cope with complex agricultural production system processes. Next to pursuing economic performance, farm management also encompasses optimization of the farm's ecological and social performance. The question arises how to maintain a certain balance between the multiple purposes. For this consideration, farmers as well as researchers need to have a good understanding of the whole farm functioning. Therefore this study aims to model the factors and their inter-relations influencing an organic farmers' decision-making process. These factors and inter-relations were modelled by using the qualitative cognitive mapping technique. Cognitive mapping can be used to develop maps of socio-ecological systems based on people's knowledge of ecosystems. Different stakeholders (farmers and experts) were interviewed in order to represent and visualize their tacit knowledge. Through in-depth interviews, stakeholders were questioned on the critical success factors of organic farm management and how these factors relate to each other. Based on these interviews, individual cognitive maps were constructed which were subsequently merged to build a social cognitive map. The social cognitive map represents the stakeholders' perception of the agricultural production system. It covers a broad range of factors (economic, agro-technical and biophysical factors, next to a few social factors), of which the most central ones are crop choice, crop rotation, marketing and technology and mechanization
Spectrum of the Dirac Operator and Multigrid Algorithm with Dynamical Staggered Fermions
Complete spectra of the staggered Dirac operator \Dirac are determined in
quenched four-dimensional gauge fields, and also in the presence of
dynamical fermions.
Periodic as well as antiperiodic boundary conditions are used.
An attempt is made to relate the performance of multigrid (MG) and conjugate
gradient (CG) algorithms for propagators with the distribution of the
eigenvalues of~\Dirac.
The convergence of the CG algorithm is determined only by the condition
number~ and by the lattice size.
Since~'s do not vary significantly when quarks become dynamic,
CG convergence in unquenched fields can be predicted from quenched
simulations.
On the other hand, MG convergence is not affected by~ but depends on
the spectrum in a more subtle way.Comment: 19 pages, 8 figures, HUB-IEP-94/12 and KL-TH 19/94; comes as a
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