3,273 research outputs found
Cooperative use of non invasive sensing methodologies for the geophysical monitoring of the archaeological park of Paestum
No abstract availabl
Deep geophysical investigation in urban area: Ferrara city example
No abstract available
Using the Rosat Catalogue to find Counterparts for Unidentified Objects in the 1st Fermi/LAT Catalogue
There are a total of 1451 gamma-ray emitting objects in the Fermi Large Area
Telescope First Source Catalogue. The point source location accuracy of
typically a few arcminutes has allowed the counterparts for many of these
sources to be found at other wavelengths, but even so there are 630 which are
described as having no plausible counterpart at 80% confidence. In order to
help identify the unknown objects, we have cross-correlated the positions of
these sources with the Rosat All Sky Survey Bright Source Catalogue. In this
way, for Fermi sources which have a possible counterpart in soft X-rays, we can
use the, much smaller, Rosat error box to search for identifications. We find a
strong correlation between the two samples and calculate that there are about
60 sources with a Rosat counterpart. Using the Rosat error boxes we provide
tentative associations for half of them, demonstrate that the majority of these
are either blazars or blazar candidates and give evidence that most belong to
the BL Lac class. Given that they are X-ray selected and most are high
synchrotron peaked objects, which indicates the presence of high energy
electrons, these sources are also good candidates for TeV emission, and
therefore good probes of the extragalactic background light.Comment: 9 pages, 1 figure; Accepted for publication in MNRA
Groundwater seepage is a key driver of theater-headed valley formation in limestone
Groundwater seepage leads to the formation of theater-headed valleys (THVs) in unconsolidated sediments. In bedrock, the role of groundwater in THV development remains disputed. Here, we integrate field and remote-sensing observations from Gnejna Valley (Maltese Islands) with numerical modeling to demonstrate that groundwater seepage can be the main driver of THV formation in jointed limestone overlying clays. The inferred erosion mechanisms entail (1) widening of joints and fractures by fluid pressure and dissolution and (2) creeping of an underlying clay layer, which lead to slope failure at the valley head and its upslope retreat. The latter is slower than the removal of the talus by creep and sliding on the valley bed. The location and width of THVs are controlled by the location of the master fault and the extent of the damage zone, respectively. The variability of seepage across the fault zone determines the shape of the valley head, with an exponential decrease in seepage away from the fault giving rise to a theater-shaped head that best matches that of Gnejna Valley. Our model may explain the formation of THVs by groundwater in jointed, strong-over-weak chemical sedimentary lithologies, particularly in arid terrestrial settings
Cosmological Tests of Gravity
Modifications of general relativity provide an alternative explanation to
dark energy for the observed acceleration of the universe. We review recent
developments in modified gravity theories, focusing on higher dimensional
approaches and chameleon/f(R) theories. We classify these models in terms of
the screening mechanisms that enable such theories to approach general
relativity on small scales (and thus satisfy solar system constraints). We
describe general features of the modified Friedman equation in such theories.
The second half of this review describes experimental tests of gravity in
light of the new theoretical approaches. We summarize the high precision tests
of gravity on laboratory and solar system scales. We describe in some detail
tests on astrophysical scales ranging from ~kpc (galaxy scales) to ~Gpc
(large-scale structure). These tests rely on the growth and inter-relationship
of perturbations in the metric potentials, density and velocity fields which
can be measured using gravitational lensing, galaxy cluster abundances, galaxy
clustering and the Integrated Sachs-Wolfe effect. A robust way to interpret
observations is by constraining effective parameters, such as the ratio of the
two metric potentials. Currently tests of gravity on astrophysical scales are
in the early stages --- we summarize these tests and discuss the interesting
prospects for new tests in the coming decade.Comment: Invited review for Annals of Physics; 58 pages, 8 figures
Correspondence: Are Cognitive Functions Localizable? Colin Camerer et al. versus Marieke van Rooij and John G. Holden
The Fall 2011 issue of this journal published a
two-paper section on “Neuroeconomics.” One
paper, by Ernst Fehr and Antonio Rangel, clearly
and concisely summarized a small part of the fast-growing
literature. The second paper, “It’s about
Space, It’s about Time, Neuroeconomics, and the
Brain Sublime,” by Marieke van Rooij and Guy Van
Orden, is beautifully written and enjoyable to read,
but misleading in many critical ways. A number
of economists and neuroscientists working at the
intersection of the two fields shared our reaction
and have signed this letter, as shown below. Some of
the paper’s descriptions of empirical findings and
methods in neuroeconomics are incomplete, badly
out of date, or flatly wrong. In studies the authors
describe in detail, their skeptical interpretations
have often been refuted by published data, old and
new, that they overlook
Super-heavy fermion material as metallic refrigerant for adiabatic demagnetization cooling
Low-temperature refrigeration is of crucial importance in fundamental
research of condensed matter physics, as the investigations of fascinating
quantum phenomena, such as superconductivity, superfluidity and quantum
criticality, often require refrigeration down to very low temperatures.
Currently, cryogenic refrigerators with He gas are widely used for cooling
below 1 Kelvin. However, usage of the gas is being increasingly difficult due
to the current world-wide shortage. Therefore, it is important to consider
alternative methods of refrigeration. Here, we show that a new type of
refrigerant, super-heavy electron metal, YbCoZn, can be used for
adiabatic demagnetization refrigeration, which does not require 3He gas. A
number of advantages includes much better metallic thermal conductivity
compared to the conventional insulating refrigerants. We also demonstrate that
the cooling performance is optimized in YbScCoZn by
partial Sc substitution with 0.19. The substitution induces chemical
pressure which drives the materials close to a zero-field quantum critical
point. This leads to an additional enhancement of the magnetocaloric effect in
low fields and low temperatures enabling final temperatures well below 100 mK.
Such performance has up to now been restricted to insulators. Since nearly a
century the same principle of using local magnetic moments has been applied for
adiabatic demagnetization cooling. This study opens new possibilities of using
itinerant magnetic moments for the cryogen-free refrigeration
INTEGRAL survey of the Cassiopeia region in hard X rays
We report on the results of a deep 1.6 Ms INTEGRAL observation of the
Cassiopeia region performed from December 2003 to February 2004. Eleven sources
were detected with the imager IBIS-ISGRI at energies above 20 keV, including
three new hard X-ray sources. Most remarkable is the discovery of hard X-ray
emission from the anomalous X-ray pulsar 4U 0142+61, which shows emission up to
\~150 keV with a very hard power-law spectrum with photon index Gamma = 0.73
+/- 0.17. We derived flux upper limits for energies between 0.75 MeV and 30 MeV
using archival data from the Compton telescope COMPTEL. In order to reconcile
the very hard spectrum of 4U 0142+61 measured by INTEGRAL with the COMPTEL
upper limits, the spectrum has to bend or break between ~75 keV and ~750 keV.
1E 2259+586, another anomalous X-ray pulsar in this region, was not detected.
INTEGRAL and COMPTEL upper limits are provided. The new INTEGRAL sources are
IGR J00370+6122 and IGR J00234+6144. IGR J00370+6122 is a new supergiant X-ray
binary with an orbital period of 15.665 +/- 0.006 days, derived from RXTE
All-Sky Monitor data. Archival BeppoSAX Wide-Field Camera data yielded four
more detections. IGR J00234+6144 still requires a proper identification. Other
sources for which INTEGRAL results are presented are high-mass X-ray binaries
2S 0114+650, Gamma~Cas, RX J0146.9+6121 and 4U 2206+54, intermediate polar V709
Cas and 1ES 0033+595, an AGN of the BL-Lac type. For each of these sources the
hard X-ray spectra are fitted with different models and compared with earlier
published results.Comment: 16 pages, 13 figures, accepted for publication in A&
- …