6,235 research outputs found
A dimension-breaking phenomenon for water waves with weak surface tension
It is well known that the water-wave problem with weak surface tension has
small-amplitude line solitary-wave solutions which to leading order are
described by the nonlinear Schr\"odinger equation. The present paper contains
an existence theory for three-dimensional periodically modulated solitary-wave
solutions which have a solitary-wave profile in the direction of propagation
and are periodic in the transverse direction; they emanate from the line
solitary waves in a dimension-breaking bifurcation. In addition, it is shown
that the line solitary waves are linearly unstable to long-wavelength
transverse perturbations. The key to these results is a formulation of the
water wave problem as an evolutionary system in which the transverse horizontal
variable plays the role of time, a careful study of the purely imaginary
spectrum of the operator obtained by linearising the evolutionary system at a
line solitary wave, and an application of an infinite-dimensional version of
the classical Lyapunov centre theorem.Comment: The final publication is available at Springer via
http://dx.doi.org/10.1007/s00205-015-0941-
Arkansas Cotton Variety Test 2003
The primary aim of the Arkansas Cotton Variety Test is to provide unbiased data regarding the agronomic performance of cotton varieties and advanced breeding lines in the major cotton-growing areas of Arkansas. This information helps seed dealers establish marketing strategies and assists producers in choosing varieties to plant. In this way, the annual test facilitates the inclusion of new, improved genetic material in Arkansas cotton production
Dusty, Radiation Pressure Dominated Photoionization. II. Multi-Wavelength Emission Line Diagnostics for Narrow Line Regions
Seyfert narrow line region (NLR) emission line ratios are remarkably uniform,
displaying only ~0.5 dex variation between galaxies, and even less within an
individual object. Previous photoionization and shock models of this region
were unable to explain this observation without the introduction of arbitrary
assumptions or additional parameters. Dusty, radiation pressure dominated
photoionization models provide a simple physical mechanism which can reproduce
this spectral uniformity between different objects. In the first paper of this
series we described this model and its implementation in detail, as well as
presenting grids of model emission lines and examining the model structures.
Here we explore these models further, demonstrating their ability to reproduce
the observed Seyfert line ratios on standard line diagnostic diagrams in both
the optical and UV. We also investigate the effects that the variation of
metallicity, density and ionizing spectrum have upon both the new paradigm and
the standard photoionization models used hitherto. Along with the standard
diagnostic diagrams we provide several new diagnostic diagrams in the UV,
Optical and IR. These new diagrams can provide further tests of the dusty,
radiation pressure photoionization paradigm as well as being used as
diagnostics of the metallicity, density and ionizing spectrum of the emission
line clouds.Comment: Accepted by ApJS, full pdf including figures can be obtained at
http://www.mso.anu.edu.au/~bgroves/Papers/ApJS2.pd
Arkansas Cotton Variety Test 2002
The primary aim of the Arkansas Cotton Variety Test is to provide unbiased data regarding the agronomic performance of cotton varieties and advanced breeding lines in the major cotton-growing areas of Arkansas. This information helps seed dealers establish marketing strategies and assists producers in choosing varieties to plant. In this way, the annual test facilitates the inclusion of new, improved genetic material into Arkansas cotton production. Variety adaptation is determined by evaluation of the varieties and lines at four University of Arkansas research stations located near Keiser, Clarkedale, Marianna, and Rohwer. Tests are duplicated in irrigated and non-irrigated culture at the Keiser and Marianna locations. In 2002, 37 entries were evaluated in the main test and 25 were evaluated in the first-year test. This report also includes the Mississippi County Cotton Variety Test (a large-plot, on-farm evaluation of 12 Round-up Ready varieties) and 12 other on-farm cotton variety tests conducted by the University of Arkansas Cooperative Extension Service
The mass-metallicity relation of local active galaxies
We systematically measure the gas-phase metallicities and the
mass-metallicity relation of a large sample of local active galaxies for the
first time. Observed emission-line fluxes from the Sloan Digital Sky Survey
(SDSS) are compared to a four-dimensional grid of photoionization models using
the Bayesian parameter estimation code NebulaBayes. For the first time we take
into account arbitrary mixing between HII region and narrow-line region (NLR)
emission, and the models are also varied with metallicity, ionization parameter
in the NLR, and the gas pressure. The active galactic nucleus (AGN) oxygen
abundance is found to increase by dex as a function
of host galaxy stellar mass over the range .
We also measure the metallicity and ionization parameter of 231000 star-forming
galaxies for comparison with the sample of 7670 Seyfert 2 galaxies. A
systematic offset in oxygen abundance of 0.09 dex is observed between the
mass-metallicity relations of the star-forming and active galaxies. We
investigate potential causes of the offset, including sample selection and the
treatment in the models of diffuse ionized gas, pressure, and ionization
parameter. We cannot identify the major cause(s), but suspect contributions due
to deficiencies in modeling the ionizing spectra and the treatment of dust
physics. Optical diagnostic diagrams are presented with the star-forming and
Seyfert data colored by the inferred oxygen abundance, ionization parameter and
gas pressure, clearly illustrating the trends in these quantities.Comment: 12 pages, 4 figures and 1 table; accepted for publication in Ap
Fermionic Zero Modes on Domain Walls
We study fermionic zero modes in the domain wall background. The fermions
have Dirac and left- and right-handed Majorana mass terms. The source of the
Dirac mass term is the coupling to a scalar field . The source of the
Majorana mass terms could also be the coupling to a scalar field or a
vacuum expectation value of some other field acquired in a phase transition
well above the phase transition of the field . We derive the fermionic
equations of motion and find the necessary and sufficient conditions for a zero
mode to exist. We also find the solutions numerically. In the absence of the
Majorana mass terms, the equations are solvable analytically. In the case of
massless fermions a zero energy solution exists and we show that although this
mode is not discretely normalizable it is Dirac delta function normalizable and
should be viewed as part of a continuum spectrum rather than as an isolated
zero mode.Comment: 6 pages, 3 figures, matches version published in PR
Informing decisions on the purchase of equipment used by health services in response to incidents involving hazardous materials
Accidents involving release of chemical, biological, radiological or nuclear substances may prompt the need to decontaminate exposed casualties prior to further medical treatment. Health service workers who carry out decontamination procedures wear protective suits to avoid direct contact with contaminants. We developed an analytical framework based on queueing theory to inform UK Department of Health's decisions on the stock of protective suits that ambulance services and hospitals with emergency departments in England should hold. Our aim was to ensure that such allocation gave an accepted degree of resilience to locally identified hazards. Here we give an overview of our work and describe how we incorporated information in the public domain about local hazards with expert opinion about the patterns of demand for decontamination associated with different types of incident. We also give an account of how we worked with decision makers to inform national guidance on this topic
Modelling the Pan-Spectral Energy Distributions of Starburst & Active Galaxies
We present results of a self-consistent model of the spectral energy
distribution (SED) of starburst galaxies. Two parameters control the IR SED,
the mean pressure in the ISM and the destruction timescale of molecular clouds.
Adding a simplified AGN spectrum provides mixing lines on IRAS color : color
diagrams. This reproduces the observed colors of both AGNs and starbursts.Comment: Poster Paper for IAU 222: The Interplay among Black Holes, Stars and
ISM in Galactic Nucle
Reflections of a âlate-careerâ early-career researcher: An account of practice
This account of practice describes the journey of an âaccidental academicâ through the Doctoral programme in Business Administration. It reflects on her experience of action learning and lessons learned to better embed action learning in future DBA teaching and assessment. The account is told from the perspective of a mature student straddling business and academic interests. DBA students represent a mature cohort with significant business experience and responsibility. As such, they have an implicit understanding of action learning. Action learning for these individuals should be re-activated rather than re-learned for their doctoral studies. Suggestions are made for improving the utility of action learning for DBA students and their willing engagement in the action learning process
Stress-Energy Tensor for the Massless Spin 1/2 Field in Static Black Hole Spacetimes
The stress-energy tensor for the massless spin 1/2 field is numerically
computed outside and on the event horizons of both charged and uncharged static
non-rotating black holes, corresponding to the Schwarzschild,
Reissner-Nordstrom and extreme Reissner-Nordstr\"om solutions of Einstein's
equations. The field is assumed to be in a thermal state at the black hole
temperature. Comparison is made between the numerical results and previous
analytic approximations for the stress-energy tensor in these spacetimes. For
the Schwarzschild (charge zero) solution, it is shown that the stress-energy
differs even in sign from the analytic approximation. For the
Reissner-Nordstrom and extreme Reissner-Nordstrom solutions, divergences
predicted by the analytic approximations are shown not to exist.Comment: 5 pages, 4 figures, additional discussio
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