Functional Methods in Stochastic Systems

Field-theoretic construction of functional representations of solutions of stochastic differential equations and master equations is reviewed. A generic expression for the generating function of Green functions of stochastic systems is put forward. Relation of ambiguities in stochastic differential equations and in the functional representations is discussed. Ordinary differential equations for expectation values and correlation functions are inferred with the aid of a variational approach.Comment: Plenary talk presented at Mathematical Modeling and Computational Science. International Conference, MMCP 2011, Star\'a Lesn\'a, Slovakia, July 4-8, 201

Spin-1 Antiferromagnetic Heisenberg Chains in an External Staggered Field

We present in this paper a nonlinear sigma-model analysis of a spin-1 antiferromagnetic Heisenberg chain in an external commensurate staggered magnetic field. After rediscussing briefly and extending previous results for the staggered magnetization curve, the core of the paper is a novel calculation, at the tree level, of the Green functions of the model. We obtain precise results for the elementary excitation spectrum and in particular for the spin gaps in the transverse and longitudinal channels. It is shown that, while the spectral weight in the transverse channel is exhausted by a single magnon pole, in the longitudinal one, besides a magnon pole a two-magnon continuum appears as well whose weight is a stedily increasing function of the applied field, while the weight of the magnon decreases correspondingly. The balance between the two is governed by a sum rule that is derived and discussed. A detailed comparison with the present experimental and numerical (DMRG) status of the art as well as with previous analytical approaches is also made.Comment: 23 pages, 3 figures, LaTe

Critical Factors Affecting the Safety Communication of Ethnic Minority Construction Workers

Ethnic minority workers (EMWs) or migrant workers continue to be confronted with communication problems, which can have serious effects on safety outcomes. This study aims to help improve construction industry EMW safety communication by uncovering and analyzing the criticality, underlying constructs, and explanatory power of the influencing factors involved. A mixed research design was employed by combining a literature review, semistructured interviews, and a questionnaire survey. Following the identification of an initial set of safety communication factors (SCFs) and a questionnaire designed and administered to EMWs in the Hong Kong and Australian construction industry, a total of 134 valid responses were analyzed through mean scoring, factor analysis, and importance-explanation analysis. Eighteen critical EMW SCFs are identified and categorized into three groups of worker-related SCFs, manager-related SCFs, and organization-related SCFs. A set of 36 SCFs identified cannot only be used to examine the relative importance of EMW SCFs, but can also be adopted to capture the critical SCFs for both local and ethnic minority construction workers in other countries. Narrowing a wide range of SCFs for EMWs provides stakeholders with the insights needed to the key contributory factors of safety communication, which in turn has a positive impact on safety performance. Despite this study being conducted in Hong Kong and Australia, its findings can also be used as a reference for other countries where EMWs are employed (e.g., the US, the UK, Canada, the Middle East, Malaysia, Singapore, and South Africa). Practical Applications Safety communication is a major safety challenge for EMWs and effective safety communication leads to improved safety performance and decreased injuries and fatalities. This research provides extra information on the key issues of safety communication that associated stakeholders need to address for EMWs to help them understand and mitigate the main safety communication barriers. This study suggests that apart from some measures (e.g., language courses, understandable safety training and safety materials, and bilingual translators) that have been taken for improving EMW safety communication in many countries, governments and employers are recommended to adopt multifaceted strategies manipulating worker-, manager-, and organization-related SCFs that would be more effective than a single measure. The critical roles of managers and organizations in promoting EMW safety communication are also emphasized in this study. Future efforts to improve or develop programs or interventions for EMW safety communication can benefit from this study by referring to the critical SCFs to include each aspect of safety communication. Furthermore, the identified critical SCFs will also help industry practitioners diagnose deficiencies in EMW safety management practices.</p

Real time statistical field theory

We have written a {\it Mathematica} program that calculates the integrand corresponding to any amplitude in the closed-time-path formulation of real time statistical field theory. The program is designed so that it can be used by someone with no previous experience with {\it Mathematica}. It performs the contractions over the tensor indices that appear in real time statistical field theory and gives the result in the 1-2, Keldysh or RA basis. We have used the program to calculate the ward identity for the QED 3-point function, the QED 4-point function for two photons and two fermions, and the QED 5-point function for three photons and two fermions. In real time statistical field theory, there are seven 3-point functions, 15 4-point functions and 31 5-point functions. We produce a table that gives the results for all of these functions. In addition, we give a simple general expression for the KMS conditions between $n$-point green functions and vertex functions, in both the Keldysh and RA basesComment: 25 pages, 12 figure

Short-time scaling behavior of growing interfaces

The short-time evolution of a growing interface is studied within the framework of the dynamic renormalization group approach for the Kadar-Parisi-Zhang (KPZ) equation and for an idealized continuum model of molecular beam epitaxy (MBE). The scaling behavior of response and correlation functions is reminiscent of the ``initial slip'' behavior found in purely dissipative critical relaxation (model A) and critical relaxation with conserved order parameter (model B), respectively. Unlike model A the initial slip exponent for the KPZ equation can be expressed by the dynamical exponent z. In 1+1 dimensions, for which z is known exactly, the analytical theory for the KPZ equation is confirmed by a Monte-Carlo simulation of a simple ballistic deposition model. In 2+1 dimensions z is estimated from the short-time evolution of the correlation function.Comment: 27 pages LaTeX with epsf style, 4 figures in eps format, submitted to Phys. Rev.

Response Functions in Phase Ordering Kinetics

We discuss the behavior of response functions in phase ordering kinetics within the perturbation theory approach developed earlier. At zeroth order the results agree with previous gaussian theory calculations. At second order the nonequilibrium exponents \lambda and \lambda_{R} are changed but remain equal.Comment: 29 page

Vibrational Study of 13C-enriched C60 Crystals

The infrared (IR) spectrum of solid C60 exhibits many weak vibrational modes. Symmetry breaking due to 13C isotopes provides a possible route for optically activating IR-silent vibrational modes. Experimental spectra and a semi-empirical theory on natural abundance and 13C-enriched single crystals of C60 are presented. By comparing the experimental results with the theoretical results, we exclude this isotopic activation mechanism from the explanation for weakly active fundamentals in the spectra.Comment: Accepted for Phys. Rev. B, typeset in REVTEX v3.0 in LaTeX. Postscript file including figures is available at http://insti.physics.sunysb.edu/~mmartin/papers/c13twocol2.ps File with figures will be e-mailed by reques

Chiral Lagrangians at finite density

The effective SU(2) chiral Lagrangian with external sources is given in the presence of non-vanishing nucleon densities by calculating the in-medium contributions of the chiral pion-nucleon Lagrangian. As a by product, a relativistic quantum field theory for Fermi many-particle systems at zero temperature is directly derived from relativistic quantum field theory with functional methods.Comment: 6 Pages, 3 figures, REVTeX. Extended version. Explicit Feynman rules are give