Multicanonical Simulations Step by Step

The purpose of this article is to provide a starter kit for multicanonical simulations in statistical physics. Fortran code for the $q$-state Potts model in $d=2, 3,...$ dimensions can be downloaded from the Web and this paper describes simulation results, which are in all details reproducible by running prepared programs. To allow for comparison with exact results, the internal energy, the specific heat, the free energy and the entropy are calculated for the $d=2$ Ising ($q=2$) and the $q=10$ Potts model. % in a temperature range from $T=\infty$ down to sufficiently low % temperatures, such that the groundstates are included in the sampling. Analysis programs, relying on an all-log jackknife technique, which is suitable for handling sums of very large numbers, are introduced to calculate our final estimators

An ERTS-1 study of coastal features on the North Carolina coast

There are no author-identified significant results in this report

Stepping into the Intersection: The Unintended Consequences of Presenting a ‘Latina Educational’ at a Feminist Health Organisation

An intersectional approach is typically applied to individuals, but this lens is also needed at the level of systems. Similar to large institutions, human service agencies may maintain racism due to established patterns of Eurocentricity. Agencies also function as entities where change can be affected. The following case study is about the process of decentering whiteness at a feminist health organisation located in an urban centre in the United States. The author, a white, non-binary woman, serving on the board of directors, offered to present a graduate paper at an agency-wide meeting. Preparations for this presentation evolved into a year-long process, during which time the agency began to grapple with the limitations of a cultural competence framework in its services for women’s and trans health.Feminist intersectionality theory is used to examine the organisation’s steps towards facing its Eurocentricity. This case study provides examples from organisational practice, during a year of racial turbulence, to explore three strategies that human service agencies commonly use to avoid confronting internal issues of race. It deconstructs past events in which staff maintained systemic racism through (1) disowning past harm, (2) suppression of criticism, and (3) deflection of responsibility through white feminine fragility.A narrative of events is analysed with the support of scholarship to explore how an intersectional approach can address gaps in the flawed implementation of a cultural competence framework. Intersectionality theory can transform ways of thinking among human service providers to promote critical analysis of racism within agency settings. This framework also shows the connection between systemic racism and the delegitimisation of individuals, an essential concept to the task of decentering whiteness within human service organisations

The Problem of the "Prebiotic and Never Born Proteins"

It has been argued that the limited set of proteins used by life as we know it could not have arisen by the process of Darwinian selection from all possible proteins. This probabilistic argument has a number of implicit assumptions that may not be warranted. A variety of considerations are presented to show that the number of amino-acid sequences that need have been sampled during the evolution of proteins is far smaller than assumed by the argument.Comment: 14 Pages; International Journal of Astrobiology / FirstView Article / October 2012, pp 1

On the null-controllability of the heat equation in unbounded domains

We make two remarks about the null-controllability of the heat equation with Dirichlet condition in unbounded domains. Firstly, we give a geometric necessary condition (for interior null-controllability in the Euclidean setting)which implies that one can not go infinitely far away from the control region without tending to the boundary (if any), but also applies when the distance to the control region is bounded. The proof builds on heat kernel estimates. Secondly, we describe a class of null-controllable heat equations on unbounded product domains. Elementary examples include an infinite strip in the plane controlled from one boundary and an infinite rod controlled from an internal infinite rod. The proof combines earlier results on compact manifolds with a new lemma saying that the null-controllability of an abstract control system and its null-controllability cost are not changed by taking its tensor product with a system generated by a non-positive self-adjoint operator.Comment: References [CdMZ01, dTZ00] added, abstract modifie

Magnetic Spectrometer for the IUCF Cooler

This research was sponsored by the National Science Foundation Grant NSF PHY-931478

Probability of graphs with large spectral gap by multicanonical Monte Carlo

Graphs with large spectral gap are important in various fields such as biology, sociology and computer science. In designing such graphs, an important question is how the probability of graphs with large spectral gap behaves. A method based on multicanonical Monte Carlo is introduced to quantify the behavior of this probability, which enables us to calculate extreme tails of the distribution. The proposed method is successfully applied to random 3-regular graphs and large deviation probability is estimated.Comment: 3pages 4figure

Surface effects in the crystallization process of elastic flexible polymers

Investigating thermodynamic properties of liquid-solid transitions of flexible homopolymers with elastic bonds by means of multicanonical Monte Carlo simulations, we find crystalline conformations that resemble ground-state structures of Lennard-Jones clusters. This allows us to set up a structural classification scheme for finite-length flexible polymers and their freezing mechanism in analogy to atomic cluster formation. Crystals of polymers with "magic length" turn out to be perfectly icosahedral

Effective Sampling in the Configurational Space by the Multicanonical-Multioverlap Algorithm

We propose a new generalized-ensemble algorithm, which we refer to as the multicanonical-multioverlap algorithm. By utilizing a non-Boltzmann weight factor, this method realizes a random walk in the multi-dimensional, energy-overlap space and explores widely in the configurational space including specific configurations, where the overlap of a configuration with respect to a reference state is a measure for structural similarity. We apply the multicanonical-multioverlap molecular dynamics method to a penta peptide, Met-enkephalin, in vacuum as a test system. We also apply the multicanonical and multioverlap molecular dynamics methods to this system for the purpose of comparisons. We see that the multicanonical-multioverlap molecular dynamics method realizes effective sampling in the configurational space including specific configurations more than the other two methods. From the results of the multicanonical-multioverlap molecular dynamics simulation, furthermore, we obtain a new local-minimum state of the Met-enkephalin system.Comment: 15 pages, (Revtex4), 9 figure

The non-zero baryon number formulation of QCD

We discuss the non-zero baryon number formulation of QCD in the quenched limit at finite temperature. This describes the thermodynamics of gluons in the background of static quark sources. Although a sign problem remains in this theory, our simulation results show that it can be handled quite well numerically. The transition region gets shifted to smaller temperatures and the transition region broadens with increasing baryon number. Although the action is in our formulation explicitly Z(3) symmetric the Polyakov loop expectation value becomes non-zero already in the low temperature phase and the heavy quark potential gets screened at non-vanishing number density already this phase.Comment: LATTICE99(Finite Temperature and Density), Latex2e using espcrc2.sty, 3 pages, 7 figure