72,826 research outputs found
The velocity field of a system of unsteady cycloidal vorticies
An essential difference between two-dimensional and three-dimensional models of cycloidal rotors, the presence of unsteady trailing cycloidal vorticies in the wake, was studied. The velocity induced by these vorticies is the primary mechanism producing flow retardation for low span/radius ratio, finite blade number rotors. Results of using idealized rigid wake model of finite blade cycloidal rotors to investigate some cycloidal rotor problems are presented
Searching for an anomalous coupling via single top quark production at a collider
We investigate the potential of a high-energy collider to
detect an anomalous coupling from observation of the reaction
, , where or . We find that with
-tagging and suitable kinematic cuts this process should be observable if
the anomalous coupling is no less than about 0.05/TeV, where
is the scale of new physics associated with the anomalous
interaction. This improves upon the bound possible from observation of top
decays at the Tevatron.Comment: 13 pages, RevTeX, 1 PS figur
Polyimides with pendant alkyl groups
The effect on selected polyimide properties when pendant alkyl groups were attached to the polymer backbone was investigated. A series of polymers were prepared using benzophenone tetracarboxylic acid dianhydride (BTDA) and seven different p-alkyl-m,p'-diaminobenzophenone monomers. The alkyl groups varied in length from C(1) (methyl) to C(9) (nonyl). The polyimide prepared from BTDA and m,p'-diaminobenzophenone was included as a control. All polymers were characterized by various chromatographic, spectroscopic, thermal, and mechanical techniques. Increasing the length of the pendant alkyl group resulted in a systematic decrease in glass transition temperature (Tg) for vacuum cured films. A 70 C decrease in Tg to 193 C was observed for the nonyl polymer compared to the Tg for the control. A corresponding systematic increase in Tg indicative of crosslinking, was observed for air cured films. Thermogravimetric analysis revealed a slight sacrifice in thermal stability with increasing alkyl length. No improvement in film toughness was observed
Generalized contact process with two symmetric absorbing states in two dimensions
We explore the two-dimensional generalized contact process with two absorbing
states by means of large-scale Monte-Carlo simulations. In part of the phase
diagram, an infinitesimal creation rate of active sites between inactive
domains is sufficient to take the system from the inactive phase to the active
phase. The system therefore displays two different nonequilibrium phase
transitions. The critical behavior of the generic transition is compatible with
the generalized voter (GV) universality class, implying that the
symmetry-breaking and absorbing transitions coincide. In contrast, the
transition at zero domain-boundary activation rate is not critical.Comment: 7 pages, 7 eps figures included, final version as publishe
An Economic Assessment of the Myanmar Rice Sector: Current Developments and Prospects
In this study, the Myanmar rice economy is described in the context of the current political situation and state of national economic development. The forces that are changing rice production and exports are identified; however, the rate of development involves a complex integration of government intervention and politics, as well as availability of resources. Probable scenarios for rice production and export are projected based on recent growth trends and expected infrastructure development. The Arkansas Global Rice Model is used to integrate the Myanmar rice sector with the global rice market in developing projections
A List of Wisconsin Springtails With New Records and Annotations (Hexapoda: Parainsecta: Collembola)
Twenty Collembola species new to Wisconsin were collected from soil at two agricultural sites in southern Wisconsin, including an undescribed species of Isotomidae. The state faunal list now contains 52 species representing seven families
Generating entanglement with low Q-factor microcavities
We propose a method of generating entanglement using single photons and
electron spins in the regime of resonance scattering. The technique involves
matching the spontaneous emission rate of the spin dipole transition in bulk
dielectric to the modified rate of spontaneous emission of the dipole coupled
to the fundamental mode of an optical microcavity. We call this regime
resonance scattering where interference between the input photons and those
scattered by the resonantly coupled dipole transition result in a reflectivity
of zero. The contrast between this and the unit reflectivity when the cavity is
empty allow us to perform a non demolition measurement of the spin and to non
deterministically generate entanglement between photons and spins. The chief
advantage of working in the regime of resonance scattering is that the required
cavity quality factors are orders of magnitude lower than is required for
strong coupling, or Purcell enhancement. This makes engineering a suitable
cavity much easier particularly in materials such as diamond where etching high
quality factor cavities remains a significant challenge
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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