Spin Order in Paired Quantum Hall States

We consider quantum Hall states at even-denominator filling fractions, especially $\nu=5/2$, in the limit of small Zeeman energy. Assuming that a paired quantum Hall state forms, we study spin ordering and its interplay with pairing. We give numerical evidence that at $\nu = 5/2$ an incompressible ground state will exhibit spontaneous ferromagnetism. The Ginzburg-Landau theory for the spin degrees of freedom of paired Hall states is a perturbed CP$^2$ model. We compute the coefficients in the Ginzburg-Landau theory by a BCS-Stoner mean field theory for coexisting order parameters, and show that even if repulsion is smaller than that required for a Stoner instability, ferromagnetic fluctuations can induce a partially or fully polarized superconducting state

PARALLEL COMPUTATIONS WITH LARGE-SCALE AIR\ud POLLUTION MODELS

Large-scale mathematical models are very powerful tools in the efforts to provide more\ud information and more detailed information about the pollution levels, especially about pollution\ud levels which exceed certain critical values.. However, the model used must satisfy at\ud least two conditions: (i) it must be verified that the model results are reliable and (ii) it\ud should be possible to carry out different study by using the model. It is clear that comprehensive\ud studies about relationships between different input parameters and the model results\ud can only be carried out (a) if the numerical methods used in the model are sufficiently\ud fast and (b) if the code runs efficiently on the available high-speed computers.\ud Some results obtained recently by a new unified version of the Danish Eulerian Model will\ud be presented in this paper

A Stochastic Approach for Investigation Ultrafast Phenomena in Semiconductors

2002 Mathematics Subject Classification: 65C05In this paper a stochastic approach is proposed for investigation the ultrafast evolution of electrons interacting with phonons in the presence of an applied electric field. The quantum-kinetic equation describing the above ultrafast phenomena contains polynomial non-linearity which allows to use the link between non-stationary iterative processes and the branching stochastic processes. The considered stochastic approach relies on the numerical Monte Carlo (MC) theory as applied to the integral form of the quantum-kinetic equation and estimates the electron energy distribution using statistical averages over long evolution times. The numerical tests were performed for GaAs material parameters. The numerical results for the electron energy distribution function in the case of a non-linear electron quantum transport is compared with the obtained results in the linear case.Supported by Center of Excellence BIS-21 grant ICA1-2000-70016 and by the NSF of Bulgaria under Grants # I 811/98 and # MM 902/99

Monte Carlo Study of Particle Transport Problem in Air Pollution

2002 Mathematics Subject Classification: 65C05.The actual transport of the air pollutants is due to the wind. This normally called “advection of the air pollutants”. Diffusion and deposition are other two major physical processes, which take place during the transport of pollutants in the atmosphere. In this paper we study two classes of grid-free Monte Carlo (MC) algorithms for solving an elliptic boundary value problem, where the partial differential equation contains advection, diffusion and deposition parts. The grid-free MC approach to solve the above equation uses a local integral representation and leads to a stochastic process called a random “Walk on balls” (WOB). In the first class of algorithms, the choice of a transition density function in the Markov chain depends on the radius of the maximal ball, lying inside the domain, in which the problem is defined, and on the parameters of the differential operator. While the choice of a transition density function in the second class of algorithms does not depend on the deposition part of the problem. The computational complexity of both classes of grid-free MC algorithms was investigated using varied numerical tests on a PowerPC (G4 w/AltiVec) 450 MHz running YDL 2.0.Supported by Center of Excellence BIS-21 grant ICA1-2000-70016 and by the NSF of Bulgaria under Grants #I 811/98 and #MM 902/9

Incidence of epulides in the dog: A retrospective histopathological study

The retrospective histopathological study of 468 samples of tumour material obtained from dogs, referred to the Faculty of Veterinary Medicine, Trakia University, Stara Zagora during the period 1991-2000 showed that 29 specimens (6.19%) were epulides. According to their histogenesis, the lesions were classified in two primary groups: reactive lesions – 37.94% and peripheral odontogenic tumours – 62.06%. Epulides were most commonly encountered in males (68.96%) compared to females (31.04%). The average age of affected dogs was 4 years for both genders. In 18 cases (62.06%), the lesions were mandibular whereas in 11 (37.94%) – maxillar. The highest predilection to epulides was observed in German Shepherds – 27.58%

An Analysis and Forecast of Software and Services Research in Bulgaria

In the last 40 years much has been achieved in Software Engineering research and still more is to be done. Although significant progress is being made on several fronts in Service-Oriented Architecture (SOA), there is still no set of clear, central themes to focus research activity on. A task within the EU FP7 Sister project aimed at defining research priorities for the Faculty of Mathematics and Informatics (Sofia University) in the area of Software and Services. A dedicated methodology was proposed and developed, based on various sources of information. The information accumulated was systematised and processed according to this methodology. The final results obtained are described and discussed here.* The work reported in this paper is partly supported by the SISTER project, funded by the European Commission in FP7-SP4 Capacities via agreement no. 205030