Road Ditch Spraying can Contaminate Shallow Ground Water

Herbicides are the most often detected pesticides in shallow aquifers in eastern South Dakota. Since most of the people in this part of the state obtain drinking water from these shallow aquifers, there is increasing concern for aquifer water purity. In the Oakwood Lakes-Poinsett project area, Lasso was the herbicide most often detected in the aquifer, followed by 2,4-D. Tordon 22k (picloram) was second to Lasso in 1991 data from Turner County and Bowdle aquifer studies. The road ditch over the aquifer is one of the most sensitive environments to ground water pollution. This is particularly true for naturally shallow soils with only 1 to 3 feet of soil over the gravel aquifer material. In the process of building up the road, an average of 1 foot of soil is taken from the road ditch. This leaves the ditch with O to 2 feet of soil over the gravel. Thus, these road ditches are extremely sensitive to the leaching of herbicides into ground water

Ten simple rules for interpreting and evaluating a meta-analysis

A systematic review with meta-analysis is often considered the highest level of evidence in ranking the literature. The term “systematic review” refers to the overall publication, while the term “meta-analysis” indicates that the review includes a statistical synthesis of results from at least 2 of the included studies. Not all systematic reviews include a meta-analysis, but meta-analyses are always within a systematic review. There are different types of metaanalyses in which statistical analysis can be performed, including network meta-analysis and Bayesian meta-analysis. While these meta-analysis methods can vary, the majority are “variations on a weighted average of the effect estimates from the different studies.

Dynamics of earthquake nucleation process represented by the Burridge-Knopoff model

Dynamics of earthquake nucleation process is studied on the basis of the one-dimensional Burridge-Knopoff (BK) model obeying the rate- and state-dependent friction (RSF) law. We investigate the properties of the model at each stage of the nucleation process, including the quasi-static initial phase, the unstable acceleration phase and the high-speed rupture phase or a mainshock. Two kinds of nucleation lengths L_sc and L_c are identified and investigated. The nucleation length L_sc and the initial phase exist only for a weak frictional instability regime, while the nucleation length L_c and the acceleration phase exist for both weak and strong instability regimes. Both L_sc and L_c are found to be determined by the model parameters, the frictional weakening parameter and the elastic stiffness parameter, hardly dependent on the size of an ensuing mainshock. The sliding velocity is extremely slow in the initial phase up to L_sc, of order the pulling speed of the plate, while it reaches a detectable level at a certain stage of the acceleration phase. The continuum limits of the results are discussed. The continuum limit of the BK model lies in the weak frictional instability regime so that a mature homogeneous fault under the RSF law always accompanies the quasi-static nucleation process. Duration times of each stage of the nucleation process are examined. The relation to the elastic continuum model and implications to real seismicity are discussed.Comment: Title changed. Changes mainly in abstract and in section 1. To appear in European Physical Journal

Mapping the Two-Component Atomic Fermi Gas to the Nuclear Shell-Model

The physics of a two-component cold fermi gas is now frequently addressed in laboratories. Usually this is done for large samples of tens to hundreds of thousands of particles. However, it is now possible to produce few-body systems (1-100 particles) in very tight traps where the shell structure of the external potential becomes important. A system of two-species fermionic cold atoms with an attractive zero-range interaction is analogous to a simple model of nucleus in which neutrons and protons interact only through a residual pairing interaction. In this article, we discuss how the problem of a two-component atomic fermi gas in a tight external trap can be mapped to the nuclear shell model so that readily available many-body techniques in nuclear physics, such as the Shell Model Monte Carlo (SMMC) method, can be directly applied to the study of these systems. We demonstrate an application of the SMMC method by estimating the pairing correlations in a small two-component Fermi system with moderate-to-strong short-range two-body interactions in a three-dimensional harmonic external trapping potential.Comment: 13 pages, 3 figures. Final versio

Models for Enhanced Absorption in Inhomogeneous Superconductors

We discuss the low-frequency absorption arising from quenched inhomogeneity in the superfluid density rho_s of a model superconductor. Such inhomogeneities may arise in a high-T_c superconductor from a wide variety of sources, including quenched random disorder and static charge density waves such as stripes. Using standard classical methods for treating randomly inhomogeneous media, we show that both mechanisms produce additional absorption at finite frequencies. For a two-fluid model with weak mean-square fluctuations <(d rho_s)^2 > in rho_s and a frequency-independent quasiparticle conductivity, the extra absorption has oscillator strength proportional to the quantity <(d rho_s)^2>/rho_s, as observed in some experiments. Similar behavior is found in a two-fluid model with anticorrelated fluctuations in the superfluid and normal fluid densities. The extra absorption typically occurs as a Lorentzian centered at zero frequency. We present simple model calculations for this extra absorption under conditions of both weak and strong fluctuations. The relation between our results and other model calculations is briefly discussed

Low energy collective modes, Ginzburg-Landau theory, and pseudogap behavior in superconductors with long-range pairing interactions

We study the superconducting instability in systems with long but finite ranged, attractive, pairing interactions. We show that such long-ranged superconductors exhibit a new class of fluctuations in which the internal structure of the Cooper pair wave function is soft, and thus lead to "pseudogap" behavior in which the actual transition temperature is greatly depressed from its mean field value. These fluctuations are {\it not} phase fluctuations of the standard superconducting order parameter, and lead to a highly unusual Ginzburg-Landau description. We suggest that the crossover between the BCS limit of a short-ranged attraction and our problem is of interest in the context of superconductivity in the underdoped cuprates.Comment: 20 pages with one embedded ps figure. Minor revisions to the text and references. Final version to appear in PRB on Nov. 1st, 200

On slip pulses at a sheared frictional viscoelastic/ non deformable interface

We study the possibility for a semi-infinite block of linear viscoelastic material, in homogeneous frictional contact with a non-deformable one, to slide under shear via a periodic set of ``self-healing pulses'', i.e. a set of drifting slip regions separated by stick ones. We show that, contrary to existing experimental indications, such a mode of frictional sliding is impossible for an interface obeying a simple local Coulomb law of solid friction. We then discuss possible physical improvements of the friction model which might open the possibility of such dynamics, among which slip weakening of the friction coefficient, and stress the interest of developing systematic experimental investigations of this question.Comment: 23 pages, 3 figures. submitted to PR

Anharmonicities of giant dipole excitations

The role of anharmonic effects on the excitation of the double giant dipole resonance is investigated in a simple macroscopic model.Perturbation theory is used to find energies and wave functions of the anharmonic ascillator.The cross sections for the electromagnetic excitation of the one- and two-phonon giant dipole resonances in energetic heavy-ion collisions are then evaluated through a semiclassical coupled-channel calculation.It is argued that the variations of the strength of the anharmonic potential should be combined with appropriate changes in the oscillator frequency,in order to keep the giant dipole resonance energy consistent with the experimental value.When this is taken into account,the effects of anharmonicities on the double giant dipole resonance excitation probabilities are small and cannot account for the well-known discrepancy between theory and experiment

Keith County, Nebraska, Map Series

KEITH COUNTY--LIST OF MAPS AND THEIR AUTHORS Topography--U. S. Geological Survey Index of 7.5\u27 Topographic Quadrangles and Township Boundaries--R. F. Diffendal, Jr. Generalized Soils Map--M. Kuzila and J. Culver Approximate Loess Thickness--R. F. Diffendal, Jr. Bedrock Geologic Map--R. F. Diffendal, Jr. Volcanic Ash Localities--R. F. Diffendal, Jr. Ogallala Vertebrate Faunal Sites--R. F. Diffendal, Jr. Ogallala Group Outcrops--R. F. Diffendal, Jr. White River Group Outcrops--R. F. Diffendal, Jr. Conservation and Survey Division Test Hole Locations--R. F. Diffendal, Jr. Oil and/or Gas Test Hole Locations--R. F. Diffendal, Jr. Mineral Resources Localities--R. F. Diffendal, Jr. Locations of Registered Irrigation Wells--R. F. Diffendal, Jr. Configuration of Top of Bedrock--R. F. Diffendal, Jr. Configuration of Top of White River Group (= Brule Fm.)--R. F. Diffendal, Jr. Configuration of Top of Cretaceous--H. M. DeGraw Configuration of Top of Niobrara Fm.--H. M. DeGraw Configuration of Base of Greenhorn Limestone--H. M. DeGraw Configuration of Top of Permian System--R. R. Burchett Structural Contours on Top of Stone Corral--R. R. Burchett Structural Contours on Top of Pennsylvanian System--R. R. Burchett Depth to Precambrian Surface--M. P. Carlson Configuration of Top of Precambrian--R. R. Burchett and M. P. Carlson Geothermal Projected Temperatures on Top of Dakota Group--D. Eversoll and W. Gosnold Bouguer Gravity Anomaly Map--R. R. Burchett and T. Eversol

Momentum distribution of a trapped Fermi gas with large scattering length

Using a scattering length parametrization of the BCS-BEC crossover as well as the local density approximation for the density profile, we calculate the momentum distribution of a harmonically trapped atomic Fermi gas at zero temperature. Various interaction regimes are considered, including the BCS phase, the unitarity limit and the molecular regime. We show that the relevant parameter which characterizes the crossover is given by the dimensionless combination $N^{1/6}a/a_{ho}$, where $N$ is the number of atoms, $a$ is the scattering length and $a_{ho}$ is the oscillator length. The width of the momentum distribution is shown to depend in a crucial way on the value and sign of this parameter. Our predictions can be relevant for experiments on ultracold atomic Fermi gases near a Feshbach resonance.Comment: 6 pages, 2 figures. Submitted to Phys. Rev. A. Added reference