35,645 research outputs found
A seemingly unrelated regression analysis of regulator selection and electricity prices
Includes bibliographical references (p. 21-22)
Control of Variable Watermilfoil in Bashan Lake, CT with 2,4-D: Monitoring of Lake and Well Water.
Variable watermilfoil (Myriophyllum heterophyllum Michx.)
has recently become a problem in Bashan Lake, East Haddam,
CT, USA. By 1998, approximately 4 ha of the 110 ha lake
was covered with variable watermilfoil. In 1999, the milfoil
was spot treated with Aquacide®, an 18% active ingredient of
the sodium salt of 2,4-D [(2,4-dichlorophenoxy) acetic acid],
applied at a rate of 114 kg/ha. Aquacide® was used because
labeling regarding domestic water intakes and irrigation limitations
prevented the use of Navigate® or AquaKleen®, a
19% active ingredient of the butoxyethyl ester of 2,4-D. Variable
watermilfoil was partially controlled in shallow protected
coves but little control occurred in deeper more exposed
locations. 2,4-D levels in the treatment sites were lower than
desired and offsite dilution was rapid. In 2000, the United
States Environmental Protection Agency (USEPA) issued a
special local need (SLN) registration to allow the use of Navigate
® or AquaKleen® in lakes with potable and irrigation
water intakes. Navigate® was applied at a rate of 227 kg/ha
to the same areas as treated in 1999. An additional 2 ha of
variable watermilfoil was treated with Navigate® in 2001, and
0.4 ha was treated in mid-September. Dilution of the 2,4-D ester
formulation to untreated areas was slower than with the
salt formulation. Concentrations of 2,4-D exceeded 1000 ÎĽg/
L in several lake water samples in 2000 but not 2001. Nearly
all of the treated variable watermilfoil was controlled in both
years. The mid-September treatment appeared as effective as
the spring and early summer treatments. Testing of homeowner
wells in all 3 years found no detectable levels of 2,4-D.(PDF contains 8 pages.
Results of TC-1 boost pump icing tests in the space power facility
A series of tests were conducted in the space power facility to investigate the failure of the Centaur oxidizer boost pump during the Titan/Centaur proof flight February 11, 1974. The three basic objectives of the tests were: (1) demonstrate if an evaporative freezing type failure mechanism could have prevented the pump from operating, (2) determine if steam from the exhaust of one of the attitude control engine could have entered a pump seal cavity and caused the failure, and (3) obtain data on the heating effects of the exhaust plume from a hydrogen peroxide attitude control engine
HI and Hot Gas in the Outskirts of the M81 Group
Results are presented from a wide area, high resolution HI synthesis survey
of the outer regions of the nearby M81 group, where internal (galactic) and
external (group-related) evolution processes can be studied simultaneously in
great detail. The survey encompasses the star forming dwarf galaxies M81dwA,
UGC4483, and HoII, where evidence of ram pressure stripping was recently
discovered. The data do not reveal any intergalactic HI, but the outer parts of
HoII are reminiscent of tidal tails. We argue however that those structures are
equally consistent with the latest ram pressure models including cooling. The
case for a hot intergalactic medium in this poor, spiral-only group is thus
still open. The survey also puts tight constraints on possible counterparts to
the local high velocity cloud population in an external group, reaching a 3
sigma column density of 10^19 atom/cm^2 and a 6 sigma limiting mass of 1.5x10^5
M_sun.Comment: 6 pages, 3 figures, to be published in "Recycling Intergalactic and
Interstellar Matter," eds. P.-A. Duc, J. Braine, & E. Brinks (ASP: San
Francisco
Error bounds on block Gauss Seidel solutions of coupled\ud multiphysics problems
Mathematical models in many fields often consist of coupled sub–models, each of which describe a different physical process. For many applications, the quantity of interest from these models may be written as a linear functional of the solution to the governing equations. Mature numerical solution techniques for the individual sub–models often exist. Rather than derive a numerical solution technique for the full coupled model, it is therefore natural to investigate whether these techniques may be used by coupling in a block Gauss–Seidel fashion. In this study, we derive two a posteriori bounds for such linear functionals. These bounds may be used on each Gauss–Seidel iteration to estimate the error in the linear functional computed using the single physics solvers, without actually solving the full, coupled problem. We demonstrate the use of the bound first by using a model problem from linear algebra, and then a linear ordinary differential equation example. We then investigate the effectiveness of the bound using a non–linear coupled fluid–temperature problem. One of the bounds derived is very sharp for most linear functionals considered, allowing us to predict very accurately when to terminate our block Gauss–Seidel iteration.\ud
\ud
Copyright c 2000 John Wiley & Sons, Ltd
Singular order parameter interaction at nematic quantum critical point in two dimensional electron systems
We analyze the infrared behavior of effective N-point interactions between
order parameter fluctuations for nematic and other quantum critical electron
systems with a scalar order parameter in two dimensions. The interactions
exhibit a singular momentum and energy dependence and thus cannot be
represented by local vertices. They diverge for all N greater or equal 4 in a
collinear static limit, where energy variables scale to zero faster than
momenta, and momenta become increasingly collinear. The degree of divergence is
not reduced by any cancellations and renders all N-point interactions marginal.
A truncation of the order parameter action at quartic or any other finite order
is therefore not justified. The same conclusion can be drawn for the effective
action describing fermions coupled to a U(1) gauge field in two dimensions.Comment: 18 pages, 1 figur
Competition of Fermi surface symmetry breaking and superconductivity
We analyze a mean-field model of electrons on a square lattice with two types
of interaction: forward scattering favoring a d-wave Pomeranchuk instability
and a BCS pairing interaction driving d-wave superconductivity. Tuning the
interaction parameters a rich variety of phase diagrams is obtained. If the BCS
interaction is not too strong, Fermi surface symmetry breaking is stabilized
around van Hove filling, and coexists with superconductivity at low
temperatures. For pure forward scattering Fermi surface symmetry breaking
occurs typically via a first order transition at low temperatures. The presence
of superconductivity reduces the first order character of this transition and,
if strong enough, can turn it into a continuous one. This gives rise to a
quantum critical point within the superconducting phase. The superconducting
gap tends to suppress Fermi surface symmetry breaking. For a relatively strong
BCS interaction, Fermi surface symmetry breaking can be limited to intermediate
temperatures, or can be suppressed completely by pairing.Comment: 14 pages, 10 figure
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