40,598 research outputs found
Ionisation-induced star formation II: External irradiation of a turbulent molecular cloud
In this paper, we examine numerically the difference between triggered and
revealed star formation. We present Smoothed Particle Hydrodynamics (SPH)
simulations of the impact on a turbulent 10^4 solar-mass molecular cloud of
irradiation by an external source of ionising photons. In particular, using a
control model, we investigate the triggering of star formation within the
cloud. We find that, although feedback has a dramatic effect on the morphology
of our model cloud, its impact on star formation is relatively minor. We show
that external irradiation has both positive and negative effects, accelerating
the formation of some objects, delaying the formation of others, and inducing
the formation of some that would not otherwise have formed. Overall, the
calculation in which feedback is included forms nearly twice as many objects
over a period of \sim0.5 freefall times (\sim2.4 Myr), resulting in a
star--formation efficiency approximately one third higher (\sim4% as opposed to
\sim3% at this epoch) as in the control run in which feedback is absent.
Unfortunately, there appear to be no observable characteristics which could be
used to differentiate objects whose formation was triggered from those which
were forming anyway and which were simply revealed by the effects of radiation,
although this could be an effect of poor statistics.Comment: 12 pages, 9 figures, accepted by MNRA
Condition matters: pupil voices on the design and condition of secondary schools
This research was produced by Sheffield Hallam University. The project aimed to inform the creation of a national schools Facilities Management network and an ongoing programme to research and benchmark the impact of school condition and design on pupils
Metal-Insulator Transition Revisited for Cold Atoms in Non-Abelian Gauge Potentials
We discuss the possibility of realizing metal-insulator transitions with
ultracold atoms in two-dimensional optical lattices in the presence of
artificial gauge potentials. Such transitions have been extensively studied for
magnetic fields corresponding to Abelian gauges; they occur when the magnetic
flux penetrating the lattice plaquette is an irrational multiple of the
magnetic flux quantum. Here we present the first study of these transitions for
non-Abelian U(2) gauge fields, which can be realized with atoms with two pairs
of degenerate internal states. In contrast to the Abelian case, the spectrum
and localization transition in the non-Abelian case is strongly influenced by
atomic momenta. In addition to determining the localization boundary, the
momentum fragments the spectrum and the minimum energy viewed as a function of
momentum exhibits a step structure. Other key characteristics of the
non-Abelian case include the absence of localization for certain states and
satellite fringes around the Bragg peaks in the momentum distribution and an
interesting possibility that the transition can be tuned by the atomic momenta.Comment: 4 pages, 4 figures, see http://physics.gmu.edu/~isatija/recentpub.htm
for high resolution figure
Studies of Martian polar regions
The flow law determined experimentally for solid CO2 establishes that an hypothesis of glacial flow of CO2 at the Martian poles is not physically unrealistic. Compression experiments carried out under 1 atmosphere pressure and constant strain rate conditions demonstrate that the strength of CO2 near its sublimation point is considerably less than the strength of water ice near its melting point. A plausible glacial model for the Martian polar caps was constructed. The CO2 deposited near the pole would have flowed outward laterally to relieve high internal shear stresses. The topography of the polar caps, and the uniform layering and general extent of the layered deposits were explained using this model
Hypersonic test facility Patent
Hypersonic test facility for studying ablation in models under high pressure and high temperatur
Using food intake records to estimate compliance with the Eatwell plate dietary guidelines
This work was supported by the Scottish Government's Rural and Environment Science and Analytical Services (RESAS) Division. The original studies, from which the current data were taken, were funded by the Food Standards Agency, UK, and the Biscuit, Cake, Chocolate and Confectionery Association, London, UK.Peer reviewedPostprin
Colliders and Brane Vector Phenomenology
Brane world oscillations manifest themselves as massive vector gauge fields.
Their coupling to the Standard Model is deduced using the method of nonlinear
realizations of the spontaneously broken higher dimensional space-time
symmetries. Brane vectors are stable and weakly interacting, and therefore
escape particle detectors unnoticed. LEP and Tevatron data on the production of
a single photon in conjunction with missing energy are used to delineate
experimentally excluded regions of brane vector parameter space. The additional
region of parameter space accessible to the LHC as well as a future lepton
linear collider is also determined by means of this process.Comment: 12 pages, 13 figure
Behavioral ontogeny in larvae and early juveniles of the giant trevally (Caranx ignobilis) (Pisces: Carangidae)
Behavior of young (8−18 mm SL) giant trevally (Caranx ignobilis), a large coral-reef−associated predator, was observed in the laboratory and the ocean. Size was a better predictor of swimming speed and endurance than was age. Critical speed increased with size from 12 to 40 cm/s at 2.7 cm/s for each mm increase in size. Mean scaled critical speed was 19 body lengths/s and was not size related. Swimming speed in the ocean was 4 to 20 cm/s (about half of critical speed) and varied among areas, but within each area, it increased at 2 cm/s for each mm increase in size. Swimming endurance in the laboratory increased from 5 to 40 km at 5 km for each mm increase in size. Vertical distribution changed ontogenetically: larvae swam shallower, but more variably, and then deeper with growth. Two-thirds of individuals swam directionally with no ontogenetic increase in orientation precision. Larvae swam offshore off open coasts, but not in a bay. In situ observations of C. ignobilis feeding, interacting with pelagic animals, and reacting to reefs are reported.
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