72,406 research outputs found
PROJECTED USE OF GROUNDWATER FOR IRRIGATION IN THE TEXAS HIGH PLAINS
Projections of groundwater irrigation under alternative price conditions are computed for representative resource situations in the Texas High Plains. The rate of groundwater depletion and pumping costs are related to the level of irrigation pumpage over the period 1976-2026. The projected economic life of irrigation in this region is responsive to changing economic conditions; in particular, the rate of increase in energy prices for pumping.Resource /Energy Economics and Policy,
Establishing laboratory standards for biological flight experiments
The general objective of this research was to assess the effects of exposure to simulated microgravity on ultrastructural aspects of the contractile system in chicken skeletal muscle cells. This general objective had two specific experimental components: (1) the progression of changes in cell morphology, fusion, and patterns of contractile filament organization in muscle cell cultures grown in hollow fibers in the Clinostat were evaluated, with appropriate controls; (2) to initiate experiments in which muscle cells were grown on the surface of microcarrier beads. The ultimate objective of this second portion of the work is to determine if these beads can be rotated in a bioreactor and thereby obtain a more accurate approximation of the effects of simulated microgravity on differentiated muscle cells
Chiral effective field theory beyond the power-counting regime
Novel techniques are presented, which identify the chiral power-counting
regime (PCR), and realize the existence of an intrinsic energy scale embedded
in lattice QCD results that extend outside the PCR. The nucleon mass is
considered as a benchmark for illustrating this new approach. Using
finite-range regularization, an optimal regularization scale can be extracted
from lattice simulation results by analyzing the renormalization of the low
energy coefficients. The optimal scale allows a description of lattice
simulation results that extend beyond the PCR by quantifying and thus handling
any scheme-dependence. Preliminary results for the nucleon magnetic moment are
also examined, and a consistent optimal regularization scale is obtained. This
indicates the existence of an intrinsic scale corresponding to the finite size
of the source of the pion cloud.Comment: 6 pages, 4 figures, conferenc
Chiral extrapolations for nucleon magnetic moments
Lattice QCD simulations have made significant progress in the calculation of
nucleon electromagnetic form factors in the chiral regime in recent years. With
simulation results achieving pion masses of order ~180 MeV, there is an
apparent challenge as to how the physical regime is approached. By using
contemporary methods in chiral effective field theory, both the quark-mass and
finite-volume dependence of the isovector nucleon magnetic moment are carefully
examined. The extrapolation to the physical point yields a result that is
compatible with experiment, albeit with a combined statistical and systematic
uncertainty of 10%. The extrapolation shows a strong finite-volume dependence;
lattice sizes of L > 5 fm must be used to simulate results within 2% of the
infinite-volume result for the magnetic moment at the physical pion mass.Comment: 7 pages, 12 figures, 1 tabl
Power Counting Regime of Chiral Effective Field Theory and Beyond
Chiral effective field theory complements numerical simulations of quantum
chromodynamics (QCD) on a space-time lattice. It provides a model-independent
formalism for connecting lattice simulation results at finite volume and a
variety of quark masses to the physical world. The asymptotic nature of the
chiral expansion places the focus on the first few terms of the expansion.
Thus, knowledge of the power-counting regime (PCR) of chiral effective field
theory, where higher-order terms of the expansion may be regarded as
negligible, is as important as knowledge of the expansion itself. Through the
consideration of a variety of renormalization schemes and associated
parameters, techniques to identify the PCR where results are independent of the
renormalization scheme are established. The nucleon mass is considered as a
benchmark for illustrating this general approach. Because the PCR is small, the
numerical simulation results are also examined to search for the possible
presence of an intrinsic scale which may be used in a nonperturbative manner to
describe lattice simulation results outside of the PCR. Positive results that
improve on the current optimistic application of chiral perturbation theory
beyond the PCR are reported.Comment: 18 pages, 55 figure
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