228 research outputs found
Invaded cluster algorithm for a tricritical point in a diluted Potts model
The invaded cluster approach is extended to 2D Potts model with annealed
vacancies by using the random-cluster representation. Geometrical arguments are
used to propose the algorithm which converges to the tricritical point in the
two-dimensional parameter space spanned by temperature and the chemical
potential of vacancies. The tricritical point is identified as a simultaneous
onset of the percolation of a Fortuin-Kasteleyn cluster and of a percolation of
"geometrical disorder cluster". The location of the tricritical point and the
concentration of vacancies for q = 1, 2, 3 are found to be in good agreement
with the best known results. Scaling properties of the percolating scaling
cluster and related critical exponents are also presented.Comment: 8 pages, 5 figure
The Quantitative X-Ray Analysis of Bauxite. I. The System Hydrargillite-Boehmite-Goehtite-Haematite
A photographic X-Ray method for quantitative analysis of
the main four- component system in bauxites is described. The
required standard straigp.t lines are given. The use of the overl apping
haematite- goehtite line (d = 2.69 A a nd d = 2.67 A resp.) is
shown theoretically to be possible and is experimentally verified
Critical behaviour of the 1D q-state Potts model with long-range interactions
The critical behaviour of the one-dimensional q-state Potts model with
long-range interactions decaying with distance r as has been
studied in the wide range of parameters and . A transfer matrix has been constructed for a truncated range of
interactions for integer and continuous q, and finite range scaling has been
applied. Results for the phase diagram and the correlation length critical
exponent are presented.Comment: 20 pages plus 4 figures, Late
Bioindicative values of microfungi in starch and possible deficiencies of the new Serbian regulation on food hygiene
The results of tests on the presence of yeasts and molds in cornstarch [AD ‘IPOK’ Zrenjanin, 2007-2008, made at the time when previous Regulations were valid] were analyzed in terms of bioindicative values of microfungi as indicators of quality and safety of raw material or final food products. Microbiological analysis was used to detect the presence of a number of microorganisms MMI-0001, and a questionnaire was designed at the Department of Public Health in Zrenjanin town (Republic of Serbia), where the analyses were done, regarding the microbiological tests on starch. In order to rationalize the analyses and make them more economical, several areas of product quality control (water, food, raw materials, space) were recommended either to be excluded or regarded as optional. Thus, analysis of presence of microfungi as indicators of product quality was categorized as optional. The results obtained from this research suggest a different conclusion because the bacteria in the samples indicated ˮmicrobiologically“, namely bacteriologically, safe samples of food, while, on the contrary, the presence of some microfungi as distinct xerophilous or xerotolerant microorganisms, indicated that the food was mycologically non-safe. The obtained data are crucial for questioning the decision to exclude the earlier required (mycological) analysis of the samples (in the production of starch, or end products, etc.) and categorize such analyses in new Regulations as optional, depending on the manufacturer’s preference. Bioindicative values of microfungi as indicators of the quality of starch, clearly point to the shortsightedness of the new Regulations on food hygiene and safety, where tests on certain microorganisms (in this case, yeasts and molds) are not legally defined as mandatory, but the Law leaves manufacturers a possibility to choose (or not to choose) the testing and frequency of testing on the presence (absence) of microorganisms, which can be risky, both in the production and marketing of the finial products. [Projekat Ministarstva nauke Republike Srbije, br. OI-179079
First-order transition in the one-dimensional three-state Potts model with long-range interactions
The first-order phase transition in the three-state Potts model with
long-range interactions decaying as has been examined by
numerical simulations using recently proposed Luijten-Bl\"ote algorithm. By
applying scaling arguments to the interface free energy, the Binder's
fourth-order cumulant, and the specific heat maximum, the change in the
character of the transition through variation of parameter was
studied.Comment: 6 pages (containing 5 figures), to appear in Phys. Rev.
Absence of phase coexistence in disordered exclusion processes with bypassing
Adding quenched disorder to the one-dimensional asymmetric exclusion process
is known to always induce phase separation. To test the robustness of this
result, we introduce two modifications of the process that allow particles to
bypass defect sites. In the first case, particles are allowed to jump l sites
ahead with the probability p_l ~ l^-(1+sigma), where sigma>1. By using Monte
Carlo simulations and the mean-field approach, we show that phase coexistence
may be absent up to enormously large system sizes, e.g. lnL~50, but is present
in the thermodynamic limit, as in the short-range case. In the second case, we
consider the exclusion process on a quadratic lattice with symmetric and
totally asymmetric hopping perpendicular to and along the direction of driving,
respectively. We show that in an anisotropic limit of this model a regime may
be found where phase coexistence is absent.Comment: 18 pages, 10 figures, to appear in JSTA
Correlations in Ising chains with non-integrable interactions
Two-spin correlations generated by interactions which decay with distance r
as r^{-1-sigma} with -1 <sigma <0 are calculated for periodic Ising chains of
length L. Mean-field theory indicates that the correlations, C(r,L), diminish
in the thermodynamic limit L -> \infty, but they contain a singular structure
for r/L -> 0 which can be observed by introducing magnified correlations,
LC(r,L)-\sum_r C(r,L). The magnified correlations are shown to have a scaling
form F(r/L) and the singular structure of F(x) for x->0 is found to be the same
at all temperatures including the critical point. These conclusions are
supported by the results of Monte Carlo simulations for systems with sigma
=-0.50 and -0.25 both at the critical temperature T=Tc and at T=2Tc.Comment: 13 pages, latex, 5 eps figures in a separate uuencoded file, to
appear in Phys.Rev.
Evidence of exactness of the mean field theory in the nonextensive regime of long-range spin models
The q-state Potts model with long-range interactions that decay as 1/r^alpha
subjected to an uniform magnetic field on d-dimensional lattices is analized
for different values of q in the nonextensive regime (alpha between 0 and d).
We also consider the two dimensional antiferromagnetic Ising model with the
same type of interactions. The mean field solution and Monte Carlo calculations
for the equations of state for these models are compared. We show that, using a
derived scaling which properly describes the nonextensive thermodynamic
behaviour, both types of calculations show an excellent agreement in all the
cases here considered, except for alpha=d. These results allow us to extend to
nonextensive magnetic models a previous conjecture which states that the mean
field theory is exact for the Ising one.Comment: 10 pages, 4 figure
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