9,893 research outputs found
Effects of Mosquito Control Chemicals on Aquatic Fauna
No mosquito abatement districts have ever been organized in Arkansas. Mosquito control efforts have been largely adulticiding operations by either aerial application or ground thermal fogging machines. Practically no chemical applications have been directed at the larval stage in residual water in ditches and depressions from which adult populations arise. Some larviciding with ethyl parathion has been done in ricefields. Although the treatment is very effective in mosquito reduction, voluntary treatment has not been completely successful. Because relatively little insecticide has been used as a larvicide in Arkansas, it was possible to evaluate the effect of recommended larvicides on non-target organisms in the aquatic environment. A developing mosquito control demonstration program in the rice-producing area provided the study site
Sudakov Logarithm Resummation for Vector Boson Production at Hadron Colliders
A complete description of W and Z boson production at high-energy colliders
requires the resummation of large Sudakov logarithms which dominate the
production at small transverse momentum. Currently there are two techniques for
performing this resummation: impact parameter space and transverse momentum
space. We argue that the latter can be formulated in a way which retains the
advantages of the former, while at the same time allowing a smooth transition
to finite order dominance at high transverse momentum.Comment: 5 pages, LaTeX, 2 figures, epsfig, contribution to the proceedings of
the UK Phenomenology Workshop on Collider Physics, 19-24 September 1999,
Durham, to be published in J. Phys.
Energy-level ordering and ground-state quantum numbers for frustrated two-leg spin-1/2 ladder model
The Lieb-Mattis theorem about antiferromagnetic ordering of energy levels on
bipartite lattices is generalized to finite-size two-leg spin-1/2 ladder model
frustrated by diagonal interactions. For reflection-symmetric model with
site-dependent interactions we prove exactly that the lowest energies in
sectors with fixed total spin and reflection quantum numbers are monotone
increasing functions of total spin. The nondegeneracy of most levels is proved
also. We also establish the uniqueness and obtain the spin value of the
lowest-level multiplet in the whole sector formed by reflection-symmetric
(antisymmetric) states. For a wide range of coupling constants, we prove that
the ground state is a unique spin singlet. For other values of couplings, it
may be also a unique spin triplet or may consist of both multiplets. Similar
results have been obtained for the ladder with arbitrary boundary impurity
spin. Some partial results have also been obtained in the case of periodical
boundary conditions.Comment: 17 page
Shaped nozzles for cryogenic buffer gas beam sources
Cryogenic buffer gas beams are important sources of cold molecules. In this
work we explore the use of a converging-diverging nozzle with a buffer-gas
beam. We find that, under appropriate circumstances, the use of a nozzle can
produce a beam with improved collimation, lower transverse temperatures, and
higher fluxes per solid angle
Numerical study of the transition of the four dimensional Random Field Ising Model
We study numerically the region above the critical temperature of the four
dimensional Random Field Ising Model. Using a cluster dynamic we measure the
connected and disconnected magnetic susceptibility and the connected and
disconnected overlap susceptibility. We use a bimodal distribution of the field
with for all temperatures and a lattice size L=16. Through a
least-square fit we determine the critical exponents and . We find the magnetic susceptibility and the overlap
susceptibility diverge at two different temperatures. This is coherent with the
existence of a glassy phase above . Accordingly with other simulations
we find . In this case we have a scaling theory with
two indipendet critical exponentsComment: 10 pages, 2 figures, Late
Large-volume lava flow fields on Venus: Dimensions and morphology
Of all the volcanic features identified in Magellan images, by far the most extensive and really important are lava flow fields. Neglecting the widespread lava plains themselves, practically every C1-MIDR produced so far contains several or many discrete lava flow fields. These range in size from a few hundred square kilometers in area (like those fields associated with small volcanic edifices for example), through all sizes up to several hundred thousand square kilometers in extent (such as many rift related fields). Most of these are related to small, intermediate, or large-scale volcanic edifices, coronae, arachnoids, calderas, fields of small shields, and rift zones. An initial survey of 40 well-defined flow fields with areas greater than 50,000 sq km (an arbitrary bound) has been undertaken. Following Columbia River Basalt terminology, these have been termed great flow fields. This represents a working set of flow fields, chosen to cover a variety of morphologies, sources, locations, and characteristics. The initial survey is intended to highlight representative flow fields, and does not represent a statistical set. For each flow field, the location, total area, flow length, flow widths, estimated flow thicknesses, estimated volumes, topographic slope, altitude, backscatter, emissivity, morphology, and source has been noted. The flow fields range from about 50,000 sq km to over 2,500,000 sq km in area, with most being several hundred square kilometers in extent. Flow lengths measure between 140 and 2840 km, with the majority of flows being several hundred kilometers long. A few basic morphological types have been identified
An assessment of internal blankets for gas-cooled fast reactors
Originally presented as first author's thesis (Ph. D.--Massachusetts Institute of Technology), 1980Includes bibliographical references (pages 338-346)Sponsored by General Atomic Compan
Muon-fluorine entangled states in molecular magnets
The information accessible from a muon-spin relaxation experiment is often
limited since we lack knowledge of the precise muon stopping site. We
demonstrate here the possibility of localizing a spin polarized muon in a known
stopping state in a molecular material containing fluorine. The muon-spin
precession that results from the entangled nature of the muon-spin and
surrounding nuclear spins is sensitive to the nature of the stopping site and
we use this property to identify three classes of site. We are also able to
describe the extent to which the muon distorts its surroundings.Comment: 4 pages, 3 figure
Thermodynamic and magnetic properties of the layered triangular magnet NaNiO2
We report muon-spin rotation, heat capacity, magnetization, and ac magnetic
susceptibility measurements of the layered spin-1/2 antiferromagnet NaNiO2.
These show the onset of long-range magnetic order below T_N = 19.5K. Rapid muon
depolarization persisting to about 5K above T_N is consistent with the presence
of short-range magnetic order. The temperature and frequency dependence of the
ac susceptibility suggests that magnetic clusters persist above 25K in the
paramagnetic state and that their volume fraction decreases with increasing
temperature. A frequency dependent peak in the ac magnetic susceptibility at
T_sf = 3K is observed, consistent with a slowing of spin fluctuations at this
temperature. A partial magnetic phase diagram is deduced.Comment: 4 pages, 4 figure
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