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M Krech

Publications and source records attributed to M Krech.

12 recordsLinked to original sources
PubMed2004

Phase diagram of a model for 3He-4He mixtures in three dimensions.

A lattice model of 3He-4He mixtures which takes into account the continuous rotational symmetry O(2) of the superfluid degrees of freedom of 4He is studied in the molecular-field approximation and by Monte Carlo simulations in three dimensions. In contrast to its two-dimensional version, for reasonable values of the interaction parameters the resulting phase diagram resembles that observed experimentally for 3He-4He mixtures, for which phase separation occurs as a consequence of the superfluid transition. The corresponding continuum Ginzburg-Landau model with two order parameters describing 3He-4He mixtures near tricriticality is derived from the considered lattice model. All coupling constants appearing in the continuum model are explicitly expressed in terms of the mean concentration of 4He, the temperature, and the microscopic interaction parameters characterizing the lattice system.

Journal Article↗
PubMed2000

Optimized energy calculation in lattice systems with long-range interactions

We discuss an efficient approach to the calculation of the internal energy in numerical simulations of spin systems with long-range interactions. Although, since the introduction of the Luijten-Blote algorithm, Monte Carlo simulations of these systems no longer pose a fundamental problem, the energy calculation is still an O(N2) problem for systems of size N. We show how this can be reduced to an O(N log N) problem, with a break-even point that is already reached for very small systems. This allows the study of a variety of, until now hardly accessible, physical aspects of these systems. In particular, we combine the optimized energy calculation with histogram interpolation methods to investigate the specific heat of the Ising model and the first-order regime of the three-state Potts model with long-range interactions.

Journal Article↗
PubMed1999

Critical adsorption near edges.

Symmetry breaking surface fields give rise to nontrivial and long-ranged order parameter profiles for critical systems such as fluids, alloys, or magnets confined to wedges. We discuss the properties of the corresponding universal scaling functions of the order parameter profile and the two-point correlation function, and determine the critical exponents eta(parallel) and eta( perpendicular) for the so-called normal transition.

Journal Article↗
PubMed1998

[Social intelligence deficits in autistic children and adolescents--subjective theories of psychosocial health care professionals].

The paper is concerned with personal theories of health care professionals about deficiencies in social intelligence of autistic persons. In the component-model of social intelligence means the ability of individuals or groups, to interact with each other in social situations. This contains social perception, social behavior as well as social conceptions and refers to emotional, cognitive and normative aspects. 33 interviewees, working as psychologists or teachers in kindergartens, schools or therapy institutions, are questioned by a half-standardized single interview concerning their beliefs about nonverbal social abilities, social perspective taking, and construction of a theory of mind in autistic persons. The major finding is: The impairments can be found in all aspects of social intelligence. Especially emotional handicaps, which are quoted by more than 80% of the interviewees, and low cognitive preconditions of mastering social stimuli, which are quoted by nearly all interviewees, are relevant. The subjective theories of the interviewees are in accordance to the models of parents as well as the models of the leading experts. The professional relationship to autistic persons and the practical experiences of the health care professionals lead to their specific personal theories of deficiencies in social intelligence of autistic people with wide consequences in respect to the professional contact with the autistic children and young adults.

Adolescent↗