5,289 research outputs found
Quantum Mutual Information Capacity for High Dimensional Entangled States
High dimensional Hilbert spaces used for quantum communication channels offer
the possibility of large data transmission capabilities. We propose a method of
characterizing the channel capacity of an entangled photonic state in high
dimensional position and momentum bases. We use this method to measure the
channel capacity of a parametric downconversion state, achieving a channel
capacity over 7 bits/photon in either the position or momentum basis, by
measuring in up to 576 dimensions per detector. The channel violated an
entropic separability bound, suggesting the performance cannot be replicated
classically.Comment: 5 pages, 2 figure
Anomalous decay of a prepared state due to non-Ohmic coupling to the continuum
We study the decay of a prepared state into a continuum {E_k} in the
case of non-Ohmic models. This means that the coupling is with . We find that irrespective of model details
there is a universal generalized Wigner time that characterizes the
evolution of the survival probability . The generic decay behavior
which is implied by rate equation phenomenology is a slowing down stretched
exponential, reflecting the gradual resolution of the bandprofile. But
depending on non-universal features of the model a power-law decay might take
over: it is only for an Ohmic coupling to the continuum that we get a robust
exponential decay that is insensitive to the nature of the intra-continuum
couplings. The analysis highlights the co-existence of perturbative and
non-perturbative features in the dynamics. It turns out that there are special
circumstances in which is reflected in the spreading process and not only
in the survival probability, contrary to the naive linear response theory
expectation.Comment: 13 pages, 11 figure
Generalized pulse equations for through-transmission evaluation of arbitrary multilayered structures
Generalized transit time and pulse amplitude equations were derived for modelling the ultrasonic through-transmission wave propagation of an arbitrary n-layered structure. The equations can be programmed into an expert system and used to identify and predict the through-transmission pulse signals from the critical interfaces of a multilayered structure. To test the formulas, the through transmission was measured from one- and three-layered configurations in the laboratory. The experimental measurements were compared with computer-generated data determined using the derived equations. The results verify the validity of the formulas
Generation of decoherence-free displaced squeezed states of radiation fields and a squeezed reservoir for atoms in cavity QED
We present a way to engineer an effective anti-Jaynes-Cumming and a
Jaynes-Cumming interaction between an atomic system and a single cavity mode
and show how to employ it in reservoir engineering processes. To construct the
effective Hamiltonian, we analyse considered the interaction of an atomic
system in a \{Lambda} configuration, driven by classical fields, with a single
cavity mode. With this interaction, we firstly show how to generate a
decoherence-free displaced squeezed state for the cavity field. In our scheme,
an atomic beam works as a reservoir for the radiation field trapped inside the
cavity, as employed recently by S. Pielawa et al. [Phys. Rev. Lett. 98, 240401
(2007)] to generate an Einstein-Podolsky-Rosen entangled radiation state in
high-Q resonators. In our scheme, all the atoms have to be prepared in the
ground state and, as in the cited article, neither atomic detection nor precise
interaction times between the atoms and the cavity mode are required. From this
same interaction, we can also generate an ideal squeezed reservoir for atomic
systems. For this purpose we have to assume, besides the engineered atom-field
interaction, a strong decay of the cavity field (i.e., the cavity decay must be
much stronger than the effective atom-field coupling). With this scheme, some
interesting effects in the dynamics of an atom in a squeezed reservoir could be
tested
The Relation Between Galaxy ISM and Circumgalactic OVI Gas Kinematics Derived from Observations and CDM Simulations
We present the first galaxy-OVI absorption kinematic study for 20 absorption
systems (EW>0.1~{\AA}) associated with isolated galaxies (0.150.55) that
have accurate redshifts and rotation curves obtained using Keck/ESI. Our sample
is split into two azimuthal angle bins: major axis () and
minor axis (). OVI absorption along the galaxy major axis is
not correlated with galaxy rotation kinematics, with only 1/10 systems that
could be explained with rotation/accretion models. This is in contrast to
co-rotation commonly observed for MgII absorption. OVI along the minor axis
could be modeled by accelerating outflows but only for small opening angles,
while the majority of the OVI is decelerating. Along both axes, stacked OVI
profiles reside at the galaxy systemic velocity with the absorption kinematics
spanning the entire dynamical range of their galaxies. The OVI found in AMR
cosmological simulations exists within filaments and in halos of ~50 kpc
surrounding galaxies. Simulations show that major axis OVI gas inflows along
filaments and decelerates as it approaches the galaxy while increasing in its
level of co-rotation. Minor axis outflows in the simulations are effective
within 50-75 kpc beyond that they decelerate and fall back onto the galaxy.
Although the simulations show clear OVI kinematic signatures they are not
directly comparable to observations. When we compare kinematic signatures
integrated through the entire simulated galaxy halo we find that these
signatures are washed out due to full velocity distribution of OVI throughout
the halo. We conclude that OVI alone does not serve as a useful kinematic
indicator of gas accretion, outflows or star-formation and likely best probes
the halo virial temperature.Comment: 24 pages, 21 figures, 4 tables. Accepted to ApJ on November 14, 201
The Gibbs-Thomson formula at small island sizes - corrections for high vapour densities
In this paper we report simulation studies of equilibrium features, namely
circular islands on model surfaces, using Monte-Carlo methods. In particular,
we are interested in studying the relationship between the density of vapour
around a curved island and its curvature-the Gibbs-Thomson formula. Numerical
simulations of a lattice gas model, performed for various sizes of islands,
don't fit very well to the Gibbs-Thomson formula. We show how corrections to
this form arise at high vapour densities, wherein a knowledge of the exact
equation of state (as opposed to the ideal gas approximation) is necessary to
predict this relationship. Exploiting a mapping of the lattice gas to the Ising
model one can compute the corrections to the Gibbs-Thomson formula using high
field series expansions. We also investigate finite size effects on the
stability of the islands both theoretically and through simulations. Finally
the simulations are used to study the microscopic origins of the Gibbs-Thomson
formula. A heuristic argument is suggested in which it is partially attributed
to geometric constraints on the island edge.Comment: 27 pages including 7 figures, tarred, gzipped and uuencoded. Prepared
using revtex and espf.sty. To appear in Phys. Rev.
Design and testing of an MRI-compatible cycle ergometer for non-invasive cardiac assessments during exercise
<p>Abstract</p> <p>Background</p> <p>Magnetic resonance imaging (MRI) is an important tool for cardiac research, and it is frequently used for resting cardiac assessments. However, research into non-pharmacological stress cardiac evaluation is limited.</p> <p>Methods</p> <p>We aimed to design a portable and relatively inexpensive MRI cycle ergometer capable of continuously measuring pedalling workload while patients exercise to maintain target heart rates.</p> <p>Results</p> <p>We constructed and tested an MRI-compatible cycle ergometer for a 1.5 T MRI scanner. Resting and sub-maximal exercise images (at 110 beats per minute) were successfully obtained in 8 healthy adults.</p> <p>Conclusions</p> <p>The MRI-compatible cycle ergometer constructed by our research group enabled cardiac assessments at fixed heart rates, while continuously recording power output by directly measuring pedal force and crank rotation.</p
A novel assay for monitoring internalization of nanocarrier coupled antibodies
BACKGROUND: Discovery of tumor-selective antibodies or antibody fragments is a promising approach for delivering therapeutic agents to antigen over-expressing cancers. Therefore it is important to develop methods for the identification of target- and function specific antibodies for effective drug delivery. Here we describe a highly selective and sensitive method for characterizing the internalizing potential of multivalently displayed antibodies or ligands conjugated to liposomes into tumor cells. The assay requires minute amounts of histidine-tagged ligand and relies on the non-covalent coupling of these antibodies to fluorescent liposomes containing a metal ion-chelating lipid. Following incubation of cells with antibody-conjugated liposomes, surface bound liposomes are gently removed and the remaining internalized liposomes are quantitated based on fluorescence in a high throughput manner. We have termed this methodology "Chelated Ligand Internalization Assay", or CLIA. RESULTS: The specificity of the assay was demonstrated with different antibodies to the ErbB-2 and EGF receptors. Antibody-uptake correlated with receptor expression levels in tumor cell lines with a range of receptor expression. Furthermore, Ni-NTA liposomes containing doxorubicin were used to screen for the ability of antibodies to confer target-specific cytotoxicity. Using an anti-ErbB2 single chain Fv (scFv) (F5) antibody, cytotoxicity could be conferred to ErbB2-overexpressing cells; however, a poly(ethylene glycol)-linked lipid (DSPE-PEG-NTA-Ni) was necessary to allow for efficient loading of the drug and to reduce nonspecific drug leakage during the course of the assay. CONCLUSION: The CLIA method we describe here represents a rapid, sensitive and robust assay for the identification and characterization of tumor-specific antibodies capable of high drug-delivery efficiency when conjugated to liposomal nanocarriers
Scattering from Electroweak Strings
The scattering of a charged fermion from an electroweak string is studied.
Owing to an amplification of the wave function at the core radius, the cross
sections for helicity flip processes can be largely enhanced. For (where is the Weinberg angle), and , we show that the helicity flip differential cross section
for electrons is of the order and is independent of angle. We
compare our results with those obtained in calculations of rates for baryon
number violating processes in the core of a cosmic string. In that case, while
the enhancement is a general phenomenon, its actual magnitude is extremely
sensitive to the fractional flux carried by the string core. Apart from showing
the existence of a similar enhancement effect for non-topological strings, our
results indicate that in some models the magnitude of enhancement can be
rendered much less sensitive to the value of the parameters in the theories.
Scattering of particles off semi-local strings and axion strings are also
considered.Comment: Replaced with revised version "Tex with phyzzx, 18 pages,
CALT-68-1921 Non-trivial changes made: discussion on axion strings corrected.
Overlap with a recently revised version of hep-ph/9311202 note
Orbits for the Impatient: A Bayesian Rejection Sampling Method for Quickly Fitting the Orbits of Long-Period Exoplanets
We describe a Bayesian rejection sampling algorithm designed to efficiently
compute posterior distributions of orbital elements for data covering short
fractions of long-period exoplanet orbits. Our implementation of this method,
Orbits for the Impatient (OFTI), converges up to several orders of magnitude
faster than two implementations of MCMC in this regime. We illustrate the
efficiency of our approach by showing that OFTI calculates accurate posteriors
for all existing astrometry of the exoplanet 51 Eri b up to 100 times faster
than a Metropolis-Hastings MCMC. We demonstrate the accuracy of OFTI by
comparing our results for several orbiting systems with those of various MCMC
implementations, finding the output posteriors to be identical within shot
noise. We also describe how our algorithm was used to successfully predict the
location of 51 Eri b six months in the future based on less than three months
of astrometry. Finally, we apply OFTI to ten long-period exoplanets and brown
dwarfs, all but one of which have been monitored over less than 3% of their
orbits, producing fits to their orbits from astrometric records in the
literature.Comment: 32 pages, 28 figures, Accepted to A
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