Narrow Results

The parallelization of a structurally inhomogeneous Metropolis Monte Carlo particle/ potential problem was studied in an application to solvent clusters. The program was ported to a small parallel-processor system consisting of five T800–20 transputers. Different topologies are discussed. The optimum topology depends on the size of the computational problem; for our problem size it is a modified tree structure. Benchmarks are given for a transputer farm, and compared with results obtained on various scalar and vector processors.

We have studied the chain length dependence of folding time for proteins by implementing a novel Monte Carlo (MC) method. The physical parameters in our model are derived from the statistics for bending and torsion angles and distances between the centers of the monomers up to the fourth neighborhood. By assigning potential wells to each of the physical parameters, we are able to use a modified Metropolis algorithm to efficiently trace the later conformations of the proteins as time evolves. Our prescription for microscopic dynamics of the protein "Crambin" results in an increase of folding times with increasing chain length. The folding times are determined via Debye relaxation process.

We review Monte Carlo computer simulations of spin models — both discrete and continuous. We explain the phenomenon of critical slowing which seriously degrades the efficiency of standard local Monte Carlo algorithms such as the Metropolis algorithm near phase transitions. We then go onto describe in detail the new algorithms which ameliorate the problem of critical slowing down, and give their dynamical critical exponent values.

The electron propagator in the Aharonov-Bohm effect is investigated using the Feynman path integral formalism. The calculation of the propagator is effected using a variation of the Metropolis Monte Carlo algorithm. Unlike “exact” calculations, our approach permits us to include a nonvanishing solenoid radius. We investigate the dependence of the resulting interference pattern on the magnetic field as well as the solenoid radius. Our results agree with the exact case in the limit of an infinitesimally small solenoid radius.

This paper makes an attempt to deal with the description, and possibly the explanation, of the profound transformation of the city, and of the changes in urban experience and practices, connected with the shape of contemporary urbanization. I stress the term description, because as it occurs in all periods of fast social changes, our conceptual tools tend to become blunt before we realize that normal science keeps failing us. The city is a complex and ambiguous object, as it is constituted by two parts, or orders of facts, inextricably bound. One is visible, i.e. observable through physical wavelengths: the other is not physically visible and can be grasped only by intellectual tools. Arrangements in the second order of facts, though, are responsible for arrangements in the first one, in the sense of producing them, and these in turn affect the former ones, although in ways and in degrees that are far from being clear. In general, decoding between the two order of facts is hazardous and has not produced a set of rules widely consented upon. This is why I remain very skeptical and in some cases outright critical of models stressing continuities in the concepts of civic organization, by referring to traditional urban forms. Reminiscent of Anthony Gidden's sharp statement that the city is one of those social forms that display "a specious continuity with pre-existing social orders" (Giddens, (1990) The Consequences of Modernity, Stanford University Press, Stanford, p. 6) I will try to etch analytical tools capable to clarify at least a few processes that are shaping civic life in contemporary metropolis.