Diet, especially seafood, is the main source of arsenic exposure for humans. The total arsenic content of a diet offers inadequate information for assessment of the toxicological consequences of arsenic intake, which has impeded progress in the establishment of regulatory limits for arsenic in food. Toxicity assessments are mainly based on inorganic arsenic, a well-characterized carcinogen, and arsenobetaine, the main organoarsenical in seafood. Scarcity of toxicity data for organoarsenicals, and the predominance of arsenobetaine as an organic arsenic species in seafood, has led to the assumption of their nontoxicity. Recent toxicokinetic studies show that some organoarsenicals are bioaccessible and cytotoxic with demonstrated toxicities like that of pernicious trivalent inorganic arsenic, underpinning the need for speciation analysis. The need to investigate and compare the bioavailability, metabolic transformation, and elimination from the body of organoarsenicals to the well-established physiological consequences of inorganic arsenic and arsenobetaine exposure is apparent. This review provides an overview of the occurrence and assessment of human exposure to arsenic toxicity associated with the consumption of seafood.
We present computer-simulation results of self-avoiding walks (SAW's) on a percolation cluster for a square lattice performed very close to the percolation threshold. We specifically consider the disorder averages of SAW's on all clusters supporting one or more ¹tepwalks and those on a backbone of an infinite cluster and estimate the critical exponents v and y that characterize the disorder averages of the end-to-end distance and the number of SAW's, respectively. Our results for y indicate a behavior rather similar to SAW s on fully occupied lattices for both cases, while for v one of two cases shows diferent behavior.
The two scaling relations in absorbing phase transitions, nu_||=beta/theta and z=nu_||/nu_(perpendicular), are studied for a conserved lattice gas model. The critical indices calculated elaborately from the all-sample average density of active particles appear to satisfy both relations. However, the exponent nu_(perpendicular) calculated from the surviving samples does not appear to be consistent with the value in the thermodynamic limit. This is in contrast with earlier observations [M. Rossi, Phys. Rev. Lett. 85, 1803 (2000); S. Lübeck and P. C. Heger, Phys. Rev. E. 68, 056102 (2003)], in that the former scaling relation was claimed to be violated.
The two-point cluster function C2(r1,r2) is determined for a D-dimensional interpenetrable-sphere continuum model from Monte Carlo simulations. C2(r1,r2) gives the probability of finding two points, at positions r1 and r2, in the same cluster of particles, and thus provides a measure of clustering in continuum-percolation systems. A pair of particles are said to be ‘‘connected’’ when they overlap. Results are reported for D=1,2, and 3 at selected values of the sphere number density ρ and of the impenetrability index λ, 0≤λ≤1. The extreme limits λ=0 and 1 correspond, respectively, to the cases of fully penetrable spheres (‘‘Swiss-cheese’’ model) and totally impenetrable spheres.
We investigated the nonequilibrium phase transition of the conserved lattice gas model in one dimension using two update methods: i.e., the sequential update and the parallel update. We measured the critical indices of theta, beta, nu(parallel), and nu(perpendicular), and found that, for a parallel update, the exponents were delicately influenced by the hopping rule of active particles. When the hopping rule was designed to be symmetric, the results were found to be consistent with those of the sequential update. The exponents we obtained were precisely the same as the corresponding results of a recently presented lattice model of two species of particles with a conserved field in one dimension, in contrast with the authors' claim. We also found that one of the scaling relations known for absorbing phase transition is violated.
We study the correction to scaling of the rms displacements of random walks in disordered media consisted of connected networks of the lattice percolation in two, three, and four dimensions. The two types of ensemble averages, i.e. an infinite-network average of random walks starting from an infinite network and an all-cluster average starting from any occupied site, are investigated using both the myoptic ants and the blind ants models. We find that the rms displacements exhibit strong nonanalytic corrections in all dimensions. The correction exponent δ defined by the rms displacement of t-step random walks via Rt=At1/d w (1+Bt-δ+Ct-1+⋯) was found as δ≃0.39, 0.27, and 0.27 for, respectively, two, three, and four dimensions for an infinite-network average, and δ≃0.37, 0.28, and 0.24 for an all-cluster average.
We discuss the logarithmic scaling of the nucleation density for pulsed laser deposition, discovered recently by Hinnemann et al. [Phys. Rev. Lett. 87, 135701 (2001)] in two dimensions. The logarithmic scaling is often observed in the upper critical dimension. We find that the nucleation density in one dimension also exhibits logarithmic scaling, implying that it is not a prerequisite for the upper critical dimension. The normalized island density also scales similarly both in one and two dimensions when plotted against the normalized coverage.
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