Observations of Fallout from the Fukushima Reactor Accident in San Francisco Bay Area Rainwater

We have observed fallout from the recent Fukushima Dai-ichi reactor accident in samples of rainwater collected in the San Francisco Bay area. Gamma ray spectra measured from these samples show clear evidence of fission products - 131,132I, 132Te, and 134,137Cs. The activity levels we have measured for these isotopes are very low and pose no health risk to the public.Comment: 5 pages, 2 figure

Potential energy landscape-based extended van der Waals equation

The inherent structures ({\it IS}) are the local minima of the potential energy surface or landscape, $U({\bf r})$, of an {\it N} atom system. Stillinger has given an exact {\it IS} formulation of thermodynamics. Here the implications for the equation of state are investigated. It is shown that the van der Waals ({\it vdW}) equation, with density-dependent $a$ and $b$ coefficients, holds on the high-temperature plateau of the averaged {\it IS} energy. However, an additional ``landscape'' contribution to the pressure is found at lower $T$. The resulting extended {\it vdW} equation, unlike the original, is capable of yielding a water-like density anomaly, flat isotherms in the coexistence region {\it vs} {\it vdW} loops, and several other desirable features. The plateau energy, the width of the distribution of {\it IS}, and the ``top of the landscape'' temperature are simulated over a broad reduced density range, $2.0 \ge \rho \ge 0.20$, in the Lennard-Jones fluid. Fits to the data yield an explicit equation of state, which is argued to be useful at high density; it nevertheless reproduces the known values of $a$ and $b$ at the critical point

Microscopic theory of network glasses

A molecular theory of the glass transition of network forming liquids is developed using a combination of self-consistent phonon and liquid state approaches. Both the dynamical transition and the entropy crisis characteristic of random first order transitions are mapped out as a function of the degree of bonding and the density. Using a scaling relation for a soft-core model to crudely translate the densities into temperatures, the theory predicts that the ratio of the dynamical transition temperature to the laboratory transition temperature rises as the degree of bonding increases, while the Kauzmann temperature falls relative to the laboratory transition. These results indicate why highly coordinated liquids should be "strong" while van der Waals liquids without coordination are "fragile".Comment: slightly revised version that has been accepted for publication in Phys. Rev. Let

Book Reviews

Book Reviews of: John H. Dryfhout, The Works of Augustus Saint-Gaudens (University Press of New England) Alan Dershowitz, The Best Defense (Random House, 1982) John LeCarré, The Little Drummer Girl (Alfred A. Knopf

The Potential Energy Landscape and Mechanisms of Diffusion in Liquids

The mechanism of diffusion in supercooled liquids is investigated from the potential energy landscape point of view, with emphasis on the crossover from high- to low-T dynamics. Molecular dynamics simulations with a time dependent mapping to the associated local mininum or inherent structure (IS) are performed on unit-density Lennard-Jones (LJ). New dynamical quantities introduced include r2_{is}(t), the mean-square displacement (MSD) within a basin of attraction of an IS, R2(t), the MSD of the IS itself, and g_{loc}(t) the mean waiting time in a cooperative region. At intermediate T, r2_{is}(t) posesses an interval of linear t-dependence allowing calculation of an intrabasin diffusion constant D_{is}. Near T_{c} diffusion is intrabasin dominated with D = D_{is}. Below T_{c} the local waiting time tau_{loc} exceeds the time, tau_{pl}, needed for the system to explore the basin, indicating the action of barriers. The distinction between motion among the IS below T_{c} and saddle, or border dynamics above T_{c} is discussed.Comment: submitted to pr

Cooling rate, heating rate and aging effects in glassy water

We report a molecular dynamics simulation study of the properties of the potential energy landscape sampled by a system of water molecules during the process of generating a glass by cooling, and during the process of regenerating the equilibrium liquid by heating the glass. We study the dependence of these processes on the cooling/heating rates as well as on the role of aging (the time elapsed in the glass state). We compare the properties of the potential energy landscape sampled during these processes with the corresponding properties sampled in the liquid equilibrium state to elucidate under which conditions glass configurations can be associated with equilibrium liquid configurations.Comment: to be published in Phys. Rev. E (rapid comunication

The effect of pygmy resonances on p-process nucleosynthesis

The γ-ray strength function (γSF) is a key component for calculating photodisintegration reaction rates used for the simulation of the p-process. During the p-process, the nucleus can be thermally excited lowering the threshold for photodisintegration, thus significantly enhancing the reaction rate for neutron photodisintegration. To calculate the (γ, n) reaction rates for excited states the γSF needs to be known below the neutron separation energy. The presence of a pygmy dipole resonance (PDR) near the neutron separation energy could further enhance the reaction rate. To study the low energy γSF, particularly the PDR, and its dependence on the neutron number, measurements to determine the γSF both above and below the neutron separation energy were done on 142Nd and 150Nd. To determine the γSF above the neutron separation energy the (γ, n) cross sections were measured near threshold for 142Nd, and, for the first time, for 150Nd. The (γ, n) measurements were made using the monoenergetic γ-ray beam at the AIST TERAS facility in Tsukuba, Japan. To determine the γSF below the neutron separation energy a new technique using nuclear resonance fluorescence was developed, and measurements were taken for 142Nd at Eγ= 3.4 – 9.7 MeV, and 150Nd at Eγ= 5.6 – 7.2 MeV. The experiment was performed using a polarimeter consisting of four Clover detectors at the mono-energetic γ-ray beam facility, HIγS, at the DFELL in Durham, NC. The results will be compared to theoretical calculations using the quasi-particle random phase approximation(QRPA), and the neutron number dependence of the low-energy E1 γSF, and the potential effects of the results on the p-process will be discussed

The Ising M-p-spin mean-field model for the structural glass: continuous vs. discontinuous transition

The critical behavior of a family of fully connected mean-field models with quenched disorder, the $M-p$ Ising spin glass, is analyzed, displaying a crossover between a continuous and a random first order phase transition as a control parameter is tuned. Due to its microscopic properties the model is straightforwardly extendable to finite dimensions in any geometry.Comment: 10 pages, 1 figure, 1 tabl

Saddles in the energy landscape: extensivity and thermodynamic formalism

We formally extend the energy landscape approach for the thermodynamics of liquids to account for saddle points. By considering the extensive nature of macroscopic potential energies, we derive the scaling behavior of saddles with system size, as well as several approximations for the properties of low-order saddles (i.e., those with only a few unstable directions). We then cast the canonical partition function in a saddle-explicit form and develop, for the first time, a rigorous energy landscape approach capable of reproducing trends observed in simulations, in particular the temperature dependence of the energy and fractional order of sampled saddles.Comment: 4 pages, 1 figur