127,344 research outputs found
On Vertically Global, Horizontally Local Models for Astrophysical Disks
Disks with a barotropic equilibrium structure, for which the pressure is only
a function of the density, rotate on cylinders in the presence of a
gravitational potential, so that the angular frequency of such a disk is
independent of height. Such disks with barotropic equilibria can be
approximately modeled using the shearing box framework, representing a small
disk volume with height-independent angular frequency. If the disk is in
baroclinic equilibrium, the angular frequency does generally depend on height,
and it is thus necessary to go beyond the standard shearing box approach. In
this paper, we show that given a global disk model, it is possible to develop
approximate models that are local in horizontal planes without an expansion in
height with shearing-periodic boundary conditions. We refer to the resulting
framework as the vertically global shearing box (VGSB). These models can be
non-axisymmetric for globally barotropic equilibria but should be axisymmetric
for globally baroclinic equilibria. We provide explicit equations for this VGSB
which can be implemented in standard magnetohydrodynamic codes by generalizing
the shearing-periodic boundary conditions to allow for a height-dependent
angular frequency and shear rate. We also discuss the limitations that result
from the radial approximations that are needed in order to impose
height-dependent shearing periodic boundary conditions. We illustrate the
potential of this framework by studying a vertical shear instability and
examining the modes associated with the magnetorotational instability.Comment: 24 pages, 8 figures, updated to match published versio
Unified life detection system: A concept
Systematic investigation of techniques and hardware which could be utilized in life detection system has resulted in identification of group of candidate concepts and selection of "unified system". Theme of concept permits greatest flexibility in procedural details for experiments which can be performed in individual ampules
Ejaculate allocation by male sand martins, Riparia riparia
Males of many species allocate sperm to ejaculates strategically in response to variation in the risk and intensity of sperm competition. The notable exception is passerine birds, in which evidence for strategic allocation is absent. Here we report the results of a study testing for strategic ejaculate allocation in a passerine bird, the sand martin (Riparia riparia). Natural ejaculates were collected from males copulating with a model female. Ejaculates transferred in the presence of a rival male contained significantly more sperm than ejaculates transferred in the absence of a rival male. There was no evidence that this difference was due to the confounding effects of the year of ejaculate collection, the identity of the model female, the colony, the stage of season or the period of the day in which ejaculates were collected. A more detailed examination of the ejaculate patterns of individual males, achieved by the DNA profiling of ejaculates, provided additional evidence for strategic allocation of sperm
Recommendation for consideration in the development of Nepal's Irrigation Master Plan. Part 1 - Management of irrigation systems for effective O & M and resource mobilization; Part 2 - Farmer managed irrigation systems. Occasional paper
Irrigation management / Farmer managed irrigation systems / Resource management / Agricultural production / Nepal
VSAERO analysis of tip planforms for the free-tip rotor
The results of a numerical analysis of two interacting lifting surfaces separated in the spanwise direction by a narrow gap are presented. The configuration consists of a semispan wing with the last 32 percent of the span structurally separated from the inboard section. The angle of attack of the outboard section is set independently from that of the inboard section. In the present study, the three-dimensional panel code VSAERO is used to perform the analysis. Computed values of tip surface lift and pitching moment coefficients are correlated with experimental data to determine the proper approach to model the gap region between the surfaces. Pitching moment data for various tip planforms are also presented to show how the variation of tip pitching moment with angle of attack may be increased easily in incompressible flow. Calculated three-dimensional characteristics in compressible flow at Mach numbers of 0.5 and 0.7 are presented for new tip planform designs. An analysis of sectional aerodynamic center shift as a function of Mach number is also included for a representative tip planform. It is also shown that the induced drag of the tip surface is reduced for negative incidence angles relative to the inboard section. The results indicate that this local drag reduction overcomes the associated increase in wing induced drag at high wing lift coefficients
Implications of gauge-mediated supersymmetry breaking with vector-like quarks and a ~125 GeV Higgs boson
We investigate the implications of models that achieve a Standard Model-like
Higgs boson of mass near 125 GeV by introducing additional TeV-scale
supermultiplets in the vector-like 10+\bar{10} representation of SU(5), within
the context of gauge-mediated supersymmetry breaking. We study the resulting
mass spectrum of superpartners, comparing and contrasting to the usual
gauge-mediated and CMSSM scenarios, and discuss implications for LHC
supersymmetry searches. This approach implies that exotic vector-like fermions
t'_{1,2}, b',and \tau' should be within the reach of the LHC. We discuss the
masses, the couplings to electroweak bosons, and the decay branching ratios of
the exotic fermions, with and without various unification assumptions for the
mass and mixing parameters. We comment on LHC prospects for discovery of the
exotic fermion states, both for decays that are prompt and non-prompt on
detector-crossing time scales.Comment: 32 pages. v2: references added, figure caption 5.3 correcte
- …