3,738 research outputs found
Stellar turbulence and mode physics
An overview of selected topical problems on modelling oscillation properties
in solar-like stars is presented. High-quality oscillation data from both
space-borne intensity observations and ground-based spectroscopic measurements
provide first tests of the still-ill-understood, superficial layers in distant
stars. Emphasis will be given to modelling the pulsation dynamics of the
stellar surface layers, the stochastic excitation processes and the associated
dynamics of the turbulent fluxes of heat and momentum.Comment: Proc. HELAS Workshop on 'Synergies between solar and stellar
modelling', eds M. Marconi, D. Cardini, M. P. Di Mauro, Astrophys. Space
Sci., in the pres
Viewgraph preparation made easier
Rolls of color-reversal film permit exposure of over 200 viewgraphs on one film loading. Time is saved in film development as roll film lends itself readily to automatic processing
N-Photon wave packets interacting with an arbitrary quantum system
We present a theoretical framework that describes a wave packet of light
prepared in a state of definite photon number interacting with an arbitrary
quantum system (e.g. a quantum harmonic oscillator or a multi-level atom).
Within this framework we derive master equations for the system as well as for
output field quantities such as quadratures and photon flux. These results are
then generalized to wave packets with arbitrary spectral distribution
functions. Finally, we obtain master equations and output field quantities for
systems interacting with wave packets in multiple spatial and/or polarization
modes.Comment: 20 pages, 8 figures. Published versio
Light Quark Masses with Dynamical Wilson Fermions
We determine the masses of the light and the strange quarks in the
-scheme using our high-statistics lattice simulation of QCD with
dynamical Wilson fermions. For the light quark mass we find
, which is lower than in quenched
simulations. For the strange quark, in a sea of two dynamical light quarks, we
obtain .Comment: 10 pages (latex file, uses epsf-style
Observations of Giant Pulses from Pulsar PSR B0950+08 using LWA1
We report the detection of giant pulse emission from PSR B0950+08 in 24 hours
of observations made at 39.4 MHz, with a bandwidth of 16 MHz, using the first
station of the Long Wavelength Array, LWA1. We detected 119 giant pulses from
PSR B0950+08 (at its dispersion measure), which we define as having SNRs at
least 10 times larger than for the mean pulse in our data set. These 119 pulses
are 0.035% of the total number of pulse periods in the 24 hours of
observations. The rate of giant pulses is about 5.0 per hour. The cumulative
distribution of pulse strength is a steep power law, , but much less steep than would be expected if we were observing the
tail of a Gaussian distribution of normal pulses. We detected no other
transient pulses in a dispersion measure range from 1 to 90 pc cm, in
the beam tracking PSR B0950+08. The giant pulses have a narrower temporal width
than the mean pulse (17.8 ms, on average, vs. 30.5 ms). The pulse widths are
consistent with a previously observed weak dependence on observing frequency,
which may be indicative of a deviation from a Kolmogorov spectrum of electron
density irregularities along the line of sight. The rate and strength of these
giant pulses is less than has been observed at 100 MHz. Additionally, the
mean (normal) pulse flux density we observed is less than at 100 MHz.
These results suggest this pulsar is weaker and produces less frequent giant
pulses at 39 MHz than at 100 MHz.Comment: 27 pages, 12 figures, typos correcte
Characterisation of the Mopra Radio Telescope at 16--50 GHz
We present the results of a programme of scanning and mapping observations of
astronomical masers and Jupiter designed to characterise the performance of the
Mopra Radio Telescope at frequencies between 16-50 GHz using the 12-mm and 7-mm
receivers. We use these observations to determine the telescope beam size, beam
shape and overall telescope beam efficiency as a function of frequency. We find
that the beam size is well fit by / over the frequency range with a
correlation coefficient of ~90%. We determine the telescope main beam
efficiencies are between ~48-64% for the 12-mm receiver and reasonably flat at
~50% for the 7-mm receiver. Beam maps of strong HO (22 GHz) and SiO masers
(43 GHz) provide a means to examine the radial beam pattern of the telescope.
At both frequencies the radial beam pattern reveals the presence of three
components, a central `core', which is well fit by a Gaussian and constitutes
the telescopes main beam, and inner and outer error beams. At both frequencies
the inner and outer error beams extend out to approximately 2 and 3.4 times the
full-width half maximum of the main beam respectively. Sources with angular
sizes a factor of two or more larger than the telescope main beam will couple
to the main and error beams, and therefore the power contributed by the error
beams needs to be considered. From measurements of the radial beam power
pattern we estimate the amount of power contained in the inner and outer error
beams is of order one-fifth at 22 GHz rising slightly to one-third at 43 GHz.Comment: Accepted for publication in PAS
Differential physiological responses to environmental change promote woody shrub expansion
© The Author(s), 2013. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Ecology and Evolution 3 (2013): 1149–1162, doi:10.1002/ece3.525.Direct and indirect effects of warming are increasingly modifying the carbon-rich vegetation and soils of the Arctic tundra, with important implications for the terrestrial carbon cycle. Understanding the biological and environmental influences on the processes that regulate foliar carbon cycling in tundra species is essential for predicting the future terrestrial carbon balance in this region. To determine the effect of climate change impacts on gas exchange in tundra, we quantified foliar photosynthesis (Anet), respiration in the dark and light (RD and RL, determined using the Kok method), photorespiration (PR), carbon gain efficiency (CGE, the ratio of photosynthetic CO2 uptake to total CO2 exchange of photosynthesis, PR, and respiration), and leaf traits of three dominant species – Betula nana, a woody shrub; Eriophorum vaginatum, a graminoid; and Rubus chamaemorus, a forb – grown under long-term warming and fertilization treatments since 1989 at Toolik Lake, Alaska. Under warming, B. nana exhibited the highest rates of Anet and strongest light inhibition of respiration, increasing CGE nearly 50% compared with leaves grown in ambient conditions, which corresponded to a 52% increase in relative abundance. Gas exchange did not shift under fertilization in B. nana despite increases in leaf N and P and near-complete dominance at the community scale, suggesting a morphological rather than physiological response. Rubus chamaemorus, exhibited minimal shifts in foliar gas exchange, and responded similarly to B. nana under treatment conditions. By contrast, E. vaginatum, did not significantly alter its gas exchange physiology under treatments and exhibited dramatic decreases in relative cover (warming: −19.7%; fertilization: −79.7%; warming with fertilization: −91.1%). Our findings suggest a foliar physiological advantage in the woody shrub B. nana that is further mediated by warming and increased soil nutrient availability, which may facilitate shrub expansion and in turn alter the terrestrial carbon cycle in future tundra environments.This study was supported by the National
Science Foundation #0732664; Australian
Research Council DP0986823; and Marsden
Fund of the Royal Society of New Zealand
Dynamical q-deformation in quantum theory and the stochastic limit
A model of particle interacting with quantum field is considered. The model
includes as particular cases the polaron model and non-relativistic quantum
electrodynamics. We show that the field operators obey q-commutation relations
with q depending on time. After the stochastic (or van Hove) limit, due to the
nonlinearity, the atomic and field degrees of freedom become entangled in the
sense that the field and the atomic variables no longer commute but give rise
to a new algebra with new commutation relations replacing the Boson ones. This
new algebra allows to give a simple proof of the fact that the non crossing
half-planar diagrams give the dominating contribution in a weak coupling regime
and to calculate explicitly the correlations associated to the new algebra. The
above results depend crucially on the fact that we do not introduce any dipole
or multipole approximation.Comment: Latex, 11 page
Posthumanist Education
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