12,935 research outputs found
Adsorption hysteresis and capillary condensation in disordered porous solids: a density functional study
We present a theoretical study of capillary condensation of fluids adsorbed
in mesoporous disordered media. Combining mean-field density functional theory
with a coarse-grained description in terms of a lattice-gas model allows us to
investigate both the out-of-equilibrium (hysteresis) and the equilibrium
behavior. We show that the main features of capillary condensation in
disordered solids result from the appearance of a complex free-energy landscape
with a large number of metastable states. We detail the numerical procedures
for finding these states, and the presence or absence of transitions in the
thermodynamic limit is determined by careful finite-size studies.Comment: 30 pages, 18 figures. To appear in J. Phys.: Condens. Matte
Detailed study of the microwave emission of the supernova remnant 3C 396
We have observed the supernova remnant 3C~396 in the microwave region using
the Parkes 64-m telescope. Observations have been made at 8.4 GHz, 13.5 GHz,
and 18.6 GHz and in polarisation at 21.5 GHz. We have used data from several
other observatories, including previously unpublished observations performed by
the Green Bank Telescope at 31.2 GHz, to investigate the nature of the
microwave emission of 3C 396. Results show a spectral energy distribution
dominated by a single component power law emission with . Data do not favour the presence of anomalous microwave emission coming
from the source. Polarised emission at 21.5 GHz is consistent with
synchrotron-dominated emission. We present microwave maps and correlate them
with infrared (IR) maps in order to characterise the interplay between thermal
dust and microwave emission. IR vs. microwave TT plots reveal poor correlation
between mid-infrared and microwave emission from the core of the source. On the
other hand, a correlation is detected in the tail emission of the outer shell
of 3C 396, which could be ascribed to Galactic contamination.Comment: published in MNRA
Cascade fragmentation : deviation from power law in primary radiation damage
The sizes of defect clusters, produced in materials by energetic ion or neutron impacts, are critically important input for models describing microstructural evolution of irradiated materials. We propose a model for the distribution of sizes of vacancy and self-interstitial defect clusters formed by high-energy impacts in tungsten, and provide new data from in situ ion irradiation experiments to validate the model. The model predicts the statistics of sub-cascade splitting and the resulting distribution of primary defects extending over the entire range of cluster sizes, and is able to provide initial conditions for quantitative multi-scale simulations of microstructural evolution. [GRAPHICS] .Peer reviewe
Swift-UVOT Observations of the X-Ray Flash 050406
We present Swift-UVOT data on the optical afterglow of the X-ray flash of
2005 April 6 (XRF 050406) from 88s to \sim 10^5s after the initial prompt
gamma-ray emission. Our observations in the V, B and U bands are the earliest
that have been taken of an XRF optical counterpart. Combining the early -time
optical temporal and spectral properties with \gamma- and simultaneous X-ray
data taken with the BAT and XRT telescopes on-board Swift, we are able to
constrain possible origins of the XRF. The prompt emission had a FRED profile
(fast-rise, exponential decay) with a duration of T_90 = 5.7\pm 0.2s, putting
it at the short end of the long-burst duration distribution. The absence of
photoelectric absorption red-ward of 4000 \AA in the UV/optical spectrum
provides a firm upper limit of z\leq 3.1 on the redshift, thus excluding a high
redshift as the sole reason for the soft spectrum. The optical light curve is
consistent with a power-law decay with slope alpha = -0.75\pm 0.26
(F_{\nu}\propto t^{\alpha}), and a maximum occurring in the first 200s after
the initial gamma-ray emission. The softness of the prompt emission is well
described by an off-axis structured jet model, which is able to account for the
early peak flux and shallow decay observed in the optical and X-ray bands.Comment: 14 pages, 4 figures, accepted for publication in ApJ; typos corrected
and upper limits in table 1 changed from background subtracted count rate in
extraction region to the error associated with thi
New Measurements of Nucleon Structure Functions from the CCFR/NuTeV Collaboration
We report on the extraction of the structure functions F_2 and Delta xF_3 =
xF_3nu-xF_3nubar from CCFR neutrino-Fe and antineutrino-Fe differential cross
sections. The extraction is performed in a physics model independent (PMI) way.
This first measurement for Delta xF_3, which is useful in testing models of
heavy charm production, is higher than current theoretical predictions. The F_2
(PMI) values measured in neutrino and muon scattering are in good agreement
with the predictions of Next to Leading Order PDFs (using massive charm
production schemes), thus resolving the long-standing discrepancy between the
two sets of data.Comment: 5 pages. Presented by Arie Bodek at the CIPNAP2000 Conference, Quebec
City, May 200
Prompt optical observations of GRB050319 with the Swift UVOT
The UVOT telescope on the Swift observatory has detected optical afterglow
emission from GRB 050319. The flux declines with a power law slope of alpha =
-0.57 between the start of observations some 230 seconds after the burst onset
(90s after the burst trigger) until it faded below the sensitivity threshold of
the instrument after ~5 x 10^4s. There is no evidence for the rapidly declining
component in the early light curve that is seen at the same time in the X-ray
band. The afterglow is not detected in UVOT shortward of the B-band, suggesting
a redshift of about 3.5. The optical V-band emission lies on the extension of
the X-ray spectrum, with an optical to X-ray slope of beta = -0.8. The
relatively flat decay rate of the burst suggests that the central engine
continues to inject energy into the fireball for as long as a few x 10^4s after
the burst.Comment: 16 pages, 4 figures, accepted by Ap
Images of the Early Universe from the BOOMERanG experiment
The CMB is the fundamental tool to study the properties of the early universe and of the
universe at large scales. In the framework of the Hot Big Bang model, when we look to
the CMB we look back in time to the end of the plasma era, at a redshift ~ 1000, when
the universe was ~ 50000 times younger, ~ 1000 times hotter and ~ 10^9 times denser
than today. The image of the CMB can be used to study the physical processes there, to
infer what happened before, and also to study the background geometry of our Universe
Kicking the Rugby Ball: Perturbations of 6D Gauged Chiral Supergravity
We analyze the axially-symmetric scalar perturbations of 6D chiral gauged
supergravity compactified on the general warped geometries in the presence of
two source branes. We find all of the conical geometries are marginally stable
for normalizable perturbations (in disagreement with some recent calculations)
and the nonconical for regular perturbations, even though none of them are
supersymmetric (apart from the trivial Salam-Sezgin solution, for which there
are no source branes). The marginal direction is the one whose presence is
required by the classical scaling property of the field equations, and all
other modes have positive squared mass. In the special case of the conical
solutions, including (but not restricted to) the unwarped `rugby-ball'
solutions, we find closed-form expressions for the mode functions in terms of
Legendre and Hypergeometric functions. In so doing we show how to match the
asymptotic near-brane form for the solution to the physics of the source
branes, and thereby how to physically interpret perturbations which can be
singular at the brane positions.Comment: 21 pages + appendices, references adde
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