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Exact Persistence Exponent for One-dimensional Potts Models with Parallel Dynamics
We obtain \theta_p(q) = 2\theta_s(q) for one-dimensional q-state
ferromagnetic Potts models evolving under parallel dynamics at zero temperature
from an initially disordered state, where \theta_p(q) is the persistence
exponent for parallel dynamics and \theta_s(q) = -{1/8}+
\frac{2}{\pi^2}[cos^{-1}{(2-q)/q\sqrt{2}}]^2 [PRL, {\bf 75}, 751, (1995)], the
persistence exponent under serial dynamics. This result is a consequence of an
exact, albeit non-trivial, mapping of the evolution of configurations of Potts
spins under parallel dynamics to the dynamics of two decoupled reaction
diffusion systems.Comment: 13 pages Latex file, 5 postscript figure
Doping, density of states and conductivity in polypyrrole and poly(p-phenylene vinylene)
The evolution of the density of states (DOS) and conductivity as function of
well controlled doping levels in OC_1C_10-poly(p-phenylene vinylene)
[OC_1C_10-PPV] doped by FeCl_3 and PF_6, and PF_6 doped polypyrrole (PPy-PF_6
have been investigated. At a doping level as high as 0.2 holes per monomer, the
former one remains non-metallic, while the latter crosses the metal-insulator
transition. In both systems a similar almost linear increase in DOS as function
of charges per unit volume c* has been observed from the electrochemical gated
transistor data. In PPy-PF_6, when compared to doped OC_1C_10-PPV, the energy
states filled at low doping are closer to the vacuum level; by the higher c* at
high doping more energy states are available, which apparently enables the
conduction to change to metallic. Although both systems on the insulating side
show log(sigma) proportional to T^-1/4 as in variable range hopping, for highly
doped PPy-PF_6 the usual interpretation of the hopping parameters leads to
seemingly too high values for the density of states.Comment: 4 pages (incl. 6 figures) in Phys. Rev.
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Do arsenic levels in rice pose a health risk to the UK population?
Consumption of rice and rice products can be a significant exposure pathway to inorganic arsenic (iAs), which is a group 1 carcinogen to humans. The UK follows the current European Commission regulations so that iAs concentrations must be 0.1 mg kg-1 were selected for As speciation using HPLC-ICP-MS. Based on the average concentration of iAs of our samples, we calculated values for the Lifetime Cancer Risk (LCR), Target Hazard Quotient (THQ) and Margin of Exposure (MoE). We found a statistically significant difference between organically and non-organically grown rice. We also found that brown rice contained a significantly higher concentration of iAs compared to white or wild rice. Notably, 28 rice samples exceeded the iAs maximum limit stipulated by the EU (0.1 mg kg-1) with an average iAs concentration of 0.13 mg kg-1; therefore consumption of these rice types could be riskier for infants than adults. Based on the MoE, it was found that infants up to 1 year must be restricted to a maximum of 20 g per day for the 28 rice types to avoid carcinogenic risks. We believe that consumers could be better informed whether the marketed product is fit for infants and young children, via appropriate product labelling containing information about iAs concentration
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