Mercury Content of Waters in the Midcontinent Region

Two major areas of the midcontinent region were investigated for their aqueous mercury concentrations. Sixteen surface water and 17 ground water samples were collected in an eleven county area of N.W. Arkansas, S.W. Missouri and N.E. Oklahoma (Ozark area) and analyzed for total dissolved mercury by the flameless atomic absorption spectrophotometric method. The range (\u3c0.2 to 0.8 ppb), the mean (0.4 ppb) and the median (0.4 ppb) are the same for both ground water and surface water. Values obtained for the Ozark area are slightly greater than those reported for surface water by others (about 0.1 ppb), but are well within the range reported for surface waters (0.1 to 17.0 ppb). The range for 102 ground water samples from the Ouachita Mountain area is \u3c0.1 to 2.3 ppb, the mean 0.3 ppb and the median 0.1 ppb. Thus, the mercury values for this area are similar to those of the Ozark area except fora higher upper range. The mercury mineralization (cinnabar) in the southern part of the Ouachita Mountain area, in part, is the cause of the higher values. Only two samples (2.1 and 2.3 ppb), both from the Ouachita Mountain area, exceed the EPA drinking water limits of 2 ppb mercury in the western Arkansas region

Solving the puzzle of an unconventional phase transition for a 2d dimerized quantum Heisenberg model

Motivated by the indication of a new critical theory for the spin-1/2 Heisenberg model with a spatially staggered anisotropy on the square lattice as suggested in \cite{Wenzel08}, we re-investigate the phase transition of this model induced by dimerization using first principle Monte Carlo simulations. We focus on studying the finite-size scaling of $\rho_{s1} 2L$ and $\rho_{s2} 2L$, where $L$ stands for the spatial box size used in the simulations and $\rho_{si}$ with $i \in \{1,2\}$ is the spin-stiffness in the $i$-direction. Remarkably, while we do observe a large correction to scaling for the observable $\rho_{s1}2L$ as proposed in \cite{Fritz11}, the data for $\rho_{s2}2L$ exhibit a good scaling behavior without any indication of a large correction. As a consequence, we are able to obtain a numerical value for the critical exponent $\nu$ which is consistent with the known O(3) result with moderate computational effort. Specifically, the numerical value of $\nu$ we determine by fitting the data points of $\rho_{s2}2L$ to their expected scaling form is given by $\nu=0.7120(16)$, which agrees quantitatively with the most accurate known Monte Carlo O(3) result $\nu = 0.7112(5)$. Finally, while we can also obtain a result of $\nu$ from the observable second Binder ratio $Q_2$ which is consistent with $\nu=0.7112(5)$, the uncertainty of $\nu$ calculated from $Q_2$ is more than twice as large as that of $\nu$ determined from $\rho_{s2}2L$.Comment: 7 figures, 1 table; brief repor

Multiple Thresholds in a Model System of Noisy Ion Channels

Voltage-activated ion channels vary randomly between open and closed states, influenced by the membrane potential and other factors. Signal transduction is enhanced by noise in a simple ion channel model. The enhancement occurs in a finite range of signals; the range can be extended using populations of channels. The range increases more rapidly in multiple-threshold channel populations than in single-threshold populations. The diversity of ion channels may thus be present as a strategy to reduce the metabolic costs of handling a broad class of electrochemical signals.Comment: REVTeX 4, 5 pages, 4 figures; added paragrap

The Sound of Sonoluminescence

We consider an air bubble in water under conditions of single bubble sonoluminescence (SBSL) and evaluate the emitted sound field nonperturbatively for subsonic gas-liquid interface motion. Sound emission being the dominant damping mechanism, we also implement the nonperturbative sound damping in the Rayleigh-Plesset equation for the interface motion. We evaluate numerically the sound pulse emitted during bubble collapse and compare the nonperturbative and perturbative results, showing that the usual perturbative description leads to an overestimate of the maximal surface velocity and maximal sound pressure. The radius vs. time relation for a full SBSL cycle remains deceptively unaffected.Comment: 25 pages; LaTex and 6 attached ps figure files. Accepted for publication in Physical Review

Nanointerfacial strength between non-collagenous protein and collagen fibrils in antler bone

This research was supported by the Engineering and Physical Science Research Council, UK (grant award EP/E039928/1)