46,457 research outputs found
Zero dimensional area law in a gapless fermion system
The entanglement entropy of a gapless fermion subsystem coupled to a gapless
bulk by a "weak link" is considered. It is demonstrated numerically that each
independent weak link contributes an entropy proportional to lnL, where L is
linear dimension of the subsystem.Comment: 6 pages, 11 figures; added 3d computatio
Isomorphic classical molecular dynamics model for an excess electron in a supercritical fluid
Ring polymer molecular dynamics (RPMD) is used to directly simulate the
dynamics of an excess electron in a supercritical fluid over a broad range of
densities. The accuracy of the RPMD model is tested against numerically exact
path integral statistics through the use of analytical continuation techniques.
At low fluid densities, the RPMD model substantially underestimates the
contribution of delocalized states to the dynamics of the excess electron.
However, with increasing solvent density, the RPMD model improves, nearly
satisfying analytical continuation constraints at densities approaching those
of typical liquids. In the high density regime, quantum dispersion
substantially decreases the self-diffusion of the solvated electron.
In this regime where the dynamics of the electron is strongly coupled to the
dynamics of the atoms in the fluid, trajectories that can reveal diffusive
motion of the electron are long in comparison to .Comment: 24 pages, 4 figure
Anomalous cooling of the parallel velocity in seeded beams
We have measured the parallel velocity distribution of a lithium supersonic
beam produced by seeding lithium in argon. The parallel temperature for lithium
is considerably lower than the calculated parallel temperature of the argon
carrier gas. We have extended the theory of supersonic cooling to calculate the
parallel temperature of the seeded gas, in the limit of high dilution. The
theoretical result thus obtained is in good agreement with ourobservations.Comment: 01 june 200
A new data analysis framework for the search of continuous gravitational wave signals
Continuous gravitational wave signals, like those expected by asymmetric
spinning neutron stars, are among the most promising targets for LIGO and Virgo
detectors. The development of fast and robust data analysis methods is crucial
to increase the chances of a detection. We have developed a new and flexible
general data analysis framework for the search of this kind of signals, which
allows to reduce the computational cost of the analysis by about two orders of
magnitude with respect to current procedures. This can correspond, at fixed
computing cost, to a sensitivity gain of up to 10%-20%, depending on the search
parameter space. Some possible applications are discussed, with a particular
focus on a directed search for sources in the Galactic center. Validation
through the injection of artificial signals in the data of Advanced LIGO first
observational science run is also shown.Comment: 21 pages, 8 figure
An improved algorithm for narrow-band searches of continuous gravitational waves
Continuous gravitational waves signals, emitted by asymmetric spinning
neutron stars, are among the main targets of current detectors like Advanced
LIGO and Virgo. In the case of sources, like pulsars, which rotational
parameters are measured through electromagnetic observations, typical searches
assume that the gravitational wave frequency is at a given known fixed ratio
with respect to the star rotational frequency. For instance, for a neutron star
rotating around one of its principal axis of inertia the gravitational signal
frequency would be exactly two times the rotational frequency of the star. It
is possible, however, that this assumption is wrong. This is why search
algorithms able to take into account a possible small mismatch between the
gravitational waves frequency and the frequency inferred from electromagnetic
observations have been developed. In this paper we present an improved pipeline
to perform such narrow-band searches for continuous gravitational waves from
neutron stars, about three orders of magnitude faster than previous
implementations. The algorithm that we have developed is based on the {\it
5-vectors} framework and is able to perform a fully coherent search over a
frequency band of width (Hertz) and for hundreds of spin-down
values running a few hours on a standard workstation. This new algorithm opens
the possibility of long coherence time searches for objects which rotational
parameters are highly uncertain.Comment: 19 pages, 8 figures, 6 tables, submitted to CQ
Dislodged But Not Dead: Survivorship of a High Intertidal Snail Following Wave Dislodgement
Waves breaking on rocky shorelines impart large forces on intertidal organisms, sometimes dislodging individuals. Dislodged individuals may be deposited in habitats that have a greater risk of predation or that prevent return to preferred regions on the shore. Thus, dislodgement is often assumed to be lethal. We experimentally dislodged Littorina keenae snails from high in the intertidal zone to test the likelihood of survival. Under a variety of wave conditions, we measured return rates to the high shore of 54–90%, so in this species, dislodgement is not equal to death. Snails showed a strong preference for returning to the approximate tidal height from which they were dislodged, but we found no evidence of widespread homing behaviour back to the original site of dislodgement
Lymphocyte reactivity in patients with carcinoma of the breast and large bowel.
The reactivity of lymphocytes from patients with either carcinoma of the breast or large bowel has been studied using the human to mouse normal lymphocyte transfer (NLT) reaction. It was found that, in the case of breast cancer, there was a direct correlation between the clinical stage and a reduced NLT reaction. Only patients with regional lymph node or generalized metastases showed significantly reduced lymphocyte reactivity. However, in the case of large bowel cancer there was a generalized reduction in NLT reactivity which was independent of the clinical stage. Incubation of lymphocytes from individuals without neoplastic disease in serum or plasma from breast cancer patients, showing reduced NLT reactivity, resulted in a reduced NLT reaction. This appears to be indicative of the presence of circulating "blocking factor" in such patients
A DMRG Study of Low-Energy Excitations and Low-Temperature Properties of Alternating Spin Systems
We use the density matrix renormalization group (DMRG) method to study the
ground and low-lying excited states of three kinds of uniform and dimerized
alternating spin chains. The DMRG procedure is also employed to obtain
low-temperature thermodynamic properties of these systems. We consider a 2N
site system with spins and alternating from site to site and
interacting via a Heisenberg antiferromagnetic exchange. The three systems
studied correspond to being equal to and
; all of them have very similar properties. The ground state is found
to be ferrimagnetic with total spin . We find that there is
a gapless excitation to a state with spin , and a gapped excitation to
a state with spin . Surprisingly, the correlation length in the ground
state is found to be very small for this gapless system. The DMRG analysis
shows that the chain is susceptible to a conditional spin-Peierls instability.
Furthermore, our studies of the magnetization, magnetic susceptibility
and specific heat show strong magnetic-field dependences. The product
shows a minimum as a function of temperature T at low magnetic fields; the
minimum vanishes at high magnetic fields. This low-field behavior is in
agreement with earlier experimental observations. The specific heat shows a
maximum as a function of temperature, and the height of the maximum increases
sharply at high magnetic fields. Although all the three systems show
qualitatively similar behavior, there are some notable quantitative differences
between the systems in which the site spin difference, , is large
and small respectively.Comment: 16 LaTeX pages, 13 postscript figure
A semi-coherent analysis method to search for continuous gravitational waves emitted by ultra-light boson clouds around spinning black holes
As a consequence of superradiant instability induced in Kerr black holes,
ultra-light boson clouds can be a source of persistent gravitational waves,
potentially detectable by current and future gravitational-wave detectors.
These signals have been predicted to be nearly monochromatic, with a small
steady frequency increase (spin-up), but given the several assumptions and
simplifications done at theoretical level, it is wise to consider, from the
data analysis point of view, a broader class of gravitational signals in which
the phase (or the frequency) slightly wander in time. Also other types of
sources, e.g. neutron stars in which a torque balance equilibrium exists
between matter accretion and emission of persistent gravitational waves, would
fit in this category. In this paper we present a robust and computationally
cheap analysis pipeline devoted to the search of such kind of signals. We
provide a full characterization of the method, through both a theoretical
sensitivity estimation and through the analysis of syntethic data in which
simulated signals have been injected. The search setup for both all-sky
searches and higher sensitivity directed searches is discussed.Comment: 13 pages, 13 figure
Thermo-elasticity for anisotropic media in higher dimensions
In this note we develop tools to study the Cauchy problem for the system of
thermo-elasticity in higher dimensions. The theory is developed for general
homogeneous anisotropic media under non-degeneracy conditions.
For degenerate cases a method of treatment is sketched and for the cases of
cubic media and hexagonal media detailed studies are provided.Comment: 33 pages, 5 figure
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