9,466 research outputs found
A Catalogue of Field Horizontal Branch Stars Aligned with High Velocity Clouds
We present a catalogue of 430 Field Horizontal Branch (FHB) stars, selected
from the Hamburg/ESO Survey (HES), which fortuitously align with high column
density neutral hydrogen (HI) High-Velocity Cloud (HVC) gas. These stars are
ideal candidates for absorption-line studies of HVCs, attempts at which have
been made for almost 40 years with little success. A parent sample of 8321 HES
FHB stars was used to extract HI spectra along each line-of-sight, using the HI
Parkes All-Sky Survey. All lines-of-sight aligned with high velocity HI
emission with peak brightness temperatures greater than 120mK were examined.
The HI spectra of these 430 probes were visually screened and cross-referenced
with several HVC catalogues. In a forthcoming paper, we report on the results
of high-resolution spectroscopic observations of a sample of stars drawn from
this catalogue.Comment: 7 pages, 4 figures. ApJS accepted. Full catalogue and all online-only
images available at
http://astronomy.swin.edu.au/staff/cthom/catalogue/index.htm
The Emerging QCD Frontier: The Electron Ion Collider
The self-interactions of gluons determine all the unique features of QCD and
lead to a dominant abundance of gluons inside matter already at moderate .
Despite their dominant role, the properties of gluons remain largely
unexplored. Tantalizing hints of saturated gluon densities have been found in
+p collisions at HERA, and in d+Au and Au+Au collisions at RHIC. Saturation
physics will have a profound influence on heavy-ion collisions at the LHC. But
unveiling the collective behavior of dense assemblies of gluons under
conditions where their self-interactions dominate will require an Electron-Ion
Collider (EIC): a new facility with capabilities well beyond those In this
paper I outline the compelling physics case for +A collisions at an EIC and
discuss briefly the status of machine design concepts. of any existing
accelerator.Comment: 11 pages, 9 figures, prepared for 20th International Conference on
Ultra-Relativistic Nucleus-Nucleus Collisions: Quark Matter 2008 (QM2008),
Jaipur, India, 4-10 Feb. 200
Optical, near-IR and sub-mm IFU Observations of the nearby dual AGN Mrk 463
We present optical and near-IR Integral Field Unit (IFU) and ALMA band 6
observations of the nearby dual Active Galactic Nuclei (AGN) Mrk 463. At a
distance of 210 Mpc, and a nuclear separation of 4 kpc, Mrk 463 is an
excellent laboratory to study the gas dynamics, star formation processes and
supermassive black hole (SMBH) accretion in a late-stage gas-rich major galaxy
merger. The IFU observations reveal a complex morphology, including tidal
tails, star-forming clumps, and emission line regions. The optical data, which
map the full extent of the merger, show evidence for a biconical outflow and
material outflowing at 600 km s, both associated with the Mrk 463E
nucleus, together with large scale gradients likely related to the ongoing
galaxy merger. We further find an emission line region 11 kpc south of
Mrk 463E that is consistent with being photoionized by an AGN. Compared to the
current AGN luminosity, the energy budget of the cloud implies a luminosity
drop in Mrk 463E by a factor 3-20 over the last 40,000 years. The ALMA
observations of CO(2-1) and adjacent 1mm continuum reveal the presence
of 10M in molecular gas in the system. The molecular gas
shows velocity gradients of 800 km/s and 400 km/s around the Mrk
463E and 463W nuclei, respectively. We conclude that in this system the infall
of 100s /yr of molecular gas is in rough balance with the
removal of ionized gas by a biconical outflow being fueled by a relatively
small, 0.01% of accretion onto each SMBH.Comment: Accepted by The Astrophysical Journal, 23 pages, 19 figure
Radion Stabilization in Compact Hyperbolic Extra Dimensions
We consider radion stabilization in hyperbolic brane-world scenarios. We
demonstrate that in the context of Einstein gravity, matter fields which
stabilize the extra dimensions must violate the null energy condition. This
result is shown to hold even allowing for FRW-like expansion on the brane. In
particular, we explicitly demonstrate how one putative source of stabilizing
matter fails to work, and how others violate the above condition. We speculate
on a number of ways in which we may bypass this result, including the effect of
Casimir energy in these spaces. A brief discussion of supersymmetry in these
backgrounds is also given.Comment: 16 pages, 1 figur
Connective neck evolution and conductance steps in hot point contacts
Dynamic evolution of the connective neck in Al and Pb mechanically
controllable break junctions was studied during continuous approach of
electrodes at bias voltages V_b up to a few hundred mV. A high level of power
dissipation (10^-4 - 10^-3 W) and high current density (j > 10^10 A/cm^2) in
the constriction lead to overheating of the contact area, electromigration and
current-enhanced diffusion of atoms out of the "hot spot". At a low electrode
approach rate (10 - 50 pm/s) the transverse dimension of the neck and the
conductance of the junction depend on V_b and remain nearly constant over the
approach distance of 10 - 30 nm. For V_b > 300 mV the connective neck consists
of a few atoms only and the quantum nature of conductance manifests itself in
abrupt steps and reversible jumps between two or more levels. These features
are related to an ever changing number of individual conductance channels due
to the continuous rearrangement in atomic configuration of the neck, the
recurring motion of atoms between metastable states, the formation and breaking
of isolated one-atom contacts and the switching between energetically
preferable neck geometries.Comment: 21 pages 10 figure
Free-electron Model for Mesoscopic Force Fluctuations in Nanowires
When two metal electrodes are separated, a nanometer sized wire (nanowire) is
formed just before the contact breaks. The electrical conduction measured
during this retraction process shows signs of quantized conductance in units of
G_0=2e^2/h. Recent experiments show that the force acting on the wire during
separation fluctuates, which has been interpreted as being due to atomic
rearrangements. In this report we use a simple free electron model, for two
simple geometries, and show that the electronic contribution to the force
fluctuations is comparable to the experimentally found values, about 2 nN.Comment: 4 pages, 3 figures, reference correcte
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