4,584 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
Characterizing spiral arm and interarm star formation
Interarm star formation contributes significantly to a galaxy's star
formation budget, and provides an opportunity to study stellar birthplaces
unperturbed by spiral arm dynamics. Using optical integral field spectroscopy
of the nearby galaxy NGC 628 with VLT/MUSE, we construct Halpha maps including
detailed corrections for dust extinction and stellar absorption to identify 391
HII regions at 35pc resolution over 12 kpc^2. Using tracers sensitive to the
underlying gravitational potential, we associate HII regions with either arm
(271) or interarm (120) environments. Using our full spectral coverage of each
region, we find that most HII region physical properties (luminosity, size,
metallicity, ionization parameter) are independent of environment. We calculate
the fraction of Halpha luminosity due to the diffuse ionized gas (DIG)
background contaminating each HII region, and find the DIG surface brightness
to be higher within HII regions compared to the surroundings, and slightly
higher within arm HII regions. Use of the temperature sensitive [SII]/Halpha
line ratio map instead of the Halpha surface brightness to identify HII region
boundaries does not change this result. Using the dust attenuation as a tracer
of the gas, we find depletion times consistent with previous work (2 x 10^9 yr)
with no differences between the arm and interarm, however this is very
sensitive to the DIG correction. Unlike molecular clouds, which can be
dynamically affected by the galactic environment, we see fairly consistent HII
region properties in both arm and interarm environments. This suggests either a
difference in arm star formation and feedback, or a decoupling of dense star
forming clumps from the more extended surrounding molecular gas.Comment: 10 pages, 4 figures, 1 table, accepted for publication in Ap
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
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
Using zoo welfare assessments to identify common issues in developing country zoos
Zoo animal welfare is a high priority for many institutions worldwide, with modern zoos now ensuring that animals are housed and cared for to the highest standards. However, in countries where this knowledge is not as available or understood, standards may be lower. The aim of this research was to investigate if there were common zoo welfare concerns across developing country zoos. Wild Welfare is a charity working globally to improve welfare for zoo animals and has an independent welfare audit that is carried out before any intervention occurs. The Wild Welfare Audit, consisting of 110 questions, covering nine topics, was completed at 11 zoos in seven developing countries (Brazil, Egypt, Libya, Indonesia, Thailand, Malaysia and Vietnam) following a Likert scale score (1-3). A principal component analysis was also performed to evaluate the audit questions. The results suggest that common areas of concern were animal behaviour, positive animal mental states and human health and safety. These themes were likely due to the lack knowledge and understanding that may be linked to historical and cultural differences. This research has helped to revise the welfare audit as well as inform future intervention strategies for improving developing country zoo animal welfare
Automated mining of the ALMA archive in the COSMOS field (A3COSMOS): II. Cold molecular gas evolution out to Redshift 6
We present new measurements of the cosmic cold molecular gas evolution out to redshift 6 based on systematic mining of the ALMA public archive in the COSMOS deep field (A3COSMOS). Our A3COSMOS dataset contains ~700 galaxies (0.3 < z < 6) with high-confidence ALMA detections in the (sub-)millimeter continuum and multi-wavelength spectral energy distributions (SEDs). Multiple gas mass calibration methods are compared and biases in band conversions (from observed ALMA wavelength to rest-frame Rayleigh-Jeans(RJ)-tail continuum) have been tested. Combining our A3COSMOS sample with ~1,000 CO-observed galaxies at 0 < z < 4 (75% at z < 0.1), we parameterize galaxies' molecular gas depletion time and molecular gas to stellar mass ratio (gas fraction) each as a function of the stellar mass, offset from the star-forming main sequence (Delta MS) and cosmic age (or redshift). Our proposed functional form provides a statistically better fit to current data (than functional forms in the literature), and implies a "downsizing" effect (i.e., more-massive galaxies evolve earlier than less-massive ones) and "mass-quenching" (gas consumption slows down with cosmic time for massive galaxies but speeds up for low-mass ones). Adopting galaxy stellar mass functions and applying our function for gas mass calculation, we for the first time infer the cosmic cold molecular gas density evolution out to redshift 6 and find agreement with CO blind surveys as well as semi-analytic modeling. These together provide a coherent picture of cold molecular gas, SFR and stellar mass evolution in galaxies across cosmic time
Probing star formation and ISM properties using galaxy disk inclination II: testing typical FUV attenuation corrections out to z~0.7
We evaluate dust-corrected far ultraviolet (FUV) star formation rates (SFRs) for samples of star-forming galaxies at and and find significant differences between values obtained through corrections based on UV colour, from a hybrid mid-infrared (MIR) plus FUV relation, and from a radiative transfer based attenuation correction method. The performances of the attenuation correction methods are assessed by their ability to remove the dependency of the corrected SFR on inclination, as well as returning, on average, the expected population mean SFR. We find that combining MIR (rest-frame 13m) and FUV luminosities gives the most inclination independent SFRs and reduces the intrinsic SFR scatter out of the methods tested. However, applying the radiative transfer based method of Tuffs et al. gives corrections to the FUV SFR that are inclination independent and in agreement with the expected SFRs at both and . SFR corrections based on the UV-slope perform worse than the other two methods tested. For our local sample, the UV-slope method works on average but does not remove inclination biases. At 0.7 we find that the UV-slope correction used locally flattens the inclination dependence compared to the raw FUV measurements but was not sufficient to correct for the large attenuation observed at 0.7
Are the Narrow Line Regions in Active Galaxies Dusty and Radiation Pressure Dominated?
The remarkable similarity between emission spectra of narrow line regions
(NLR) in Seyfert Galaxies has long presented a mystery. In photoionization
models, this similarity implies that the ionization parameter is nearly always
the same, about U ~ 0.01. Here we present dusty, radiation-pressure dominated
photoionization models that can provide natural physical insight into this
problem. In these models, dust and the radiation pressure acting on it provide
the controlling factor in moderating the density, excitation and surface
brightness of photoionized NLR structures. Additionally, photoelectric heating
by the dust is important in determining the temperature structure of the
models. These models can also explain the coexistence of the low-,
intermediate- and coronal ionization zones within a single self-consistent
physical structure. The radiation pressure acting on dust may also be capable
of driving the fast (~3000 km/s) outflows such as are seen in the HST
observations of NGC 1068.Comment: 23 pages, 8 figures, Accepted by Ap
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