6,903 research outputs found
Maximum relative excitation of a specific vibrational mode via optimum laser pulse duration
For molecules and materials responding to femtosecond-scale optical laser
pulses, we predict maximum relative excitation of a Raman-active vibrational
mode with period T when the pulse has an FWHM duration of 0.42 T. This result
follows from a general analytical model, and is precisely confirmed by detailed
density-functional-based dynamical simulations for C60 and a carbon nanotube,
which include anharmonicity, nonlinearity, no assumptions about the
polarizability tensor, and no averaging over rapid oscillations within the
pulse. The mode specificity is, of course, best at low temperature and for
pulses that are electronically off-resonance, and the energy deposited in any
mode is proportional to the fourth power of the electric field.Comment: 5 pages, 4 figure
Sphingomyelin and GM1 Influence Huntingtin Binding to, Disruption of, and Aggregation on Lipid Membranes
Huntington disease (HD) is an inherited neurodegenerative disease caused by the expansion beyond a critical threshold of a polyglutamine (polyQ) tract near the N-terminus of the huntingtin (htt) protein. Expanded polyQ promotes the formation of a variety of oligomeric and fibrillar aggregates of htt that accumulate into the hallmark proteinaceous inclusion bodies associated with HD. htt is also highly associated with numerous cellular and subcellular membranes that contain a variety of lipids. As lipid homeostasis and metabolism abnormalities are observed in HD patients, we investigated how varying both the sphingomyelin (SM) and ganglioside (GM1) contents modifies the interactions between htt and lipid membranes. SM composition is altered in HD, and GM1 has been shown to have protective effects in animal models of HD. A combination of Langmuir trough monolayer techniques, vesicle permeability and binding assays, and in situ atomic force microscopy (AFM) were used to directly monitor the interaction of a model, synthetic htt peptide and a full-length htt-exon1 recombinant protein with model membranes comprised of total brain lipid extract (TBLE) and varying amounts of exogenously added SM or GM1. The addition of either SM or GM1 decreased htt insertion into the lipid monolayers. However, TBLE vesicles with an increased SM content were more susceptible to htt-induced permeabilization, whereas GM1 had no effect on permeablization. Pure TBLE bilayers and TBLE bilayers enriched with GM1 developed regions of roughened, granular morphologies upon exposure to htt-exon1, but plateau-like domains with a smoother appearance formed in bilayers enriched with SM. Oligomeric aggregates were observed on all bilayer systems regardless of induced morphology. Collectively, these observations suggest that the lipid composition and its subsequent effects on membrane material properties strongly influence htt binding and aggregation on lipid membranes
First-order coherence versus entanglement in a nano-mechanical cavity
The coherence and correlation properties of effective bosonic modes of a
nano-mechanical cavity composed of an oscillating mirror and containing an
optical lattice of regularly trapped atoms are studied. The system is modeled
as a three-mode system, two orthogonal polariton modes representing the coupled
optical lattice and the cavity mode, and one mechanical mode representing the
oscillating mirror. We examine separately the cases of two-mode and three-mode
interactions which are distinguished by a suitable tuning of the mechanical
mode to the polariton mode frequencies. In the two-mode case, we find that the
occurrence of entanglement between one of the polariton modes and the
mechanical mode is highly sensitive to the presence of the first-order
coherence between the modes. In particular, the creation of the first-order
coherence among the modes is achieved at the expense of entanglement between
the modes. In the three-mode case, we show that no entanglement is created
between the independent polariton modes if both modes are coupled to the
mechanical mode by the parametric interaction. There is no entanglement between
the polaritons even if the oscillating mirror is damped by a squeezed vacuum
field. The interaction creates the first-order coherence between the polaritons
and the degree of coherence can, in principle, be as large as unity. This
demonstrates that the oscillating mirror can establish the first-order
coherence between two independent thermal modes. A further analysis shows that
two independent thermal modes can be made entangled in the system only when one
of the modes is coupled to the intermediate mode by a parametric interaction
and the other is coupled by a linear-mixing interaction.Comment: Published versio
Entangling two distant nanocavities via a waveguide
In this paper, we investigate the generation of continuous variable
entanglement between two spatially-separate nanocavities mediated by a coupled
resonator optical waveguide in photonic crystals. By solving the exact dynamics
of the cavity system coupled to the waveguide, the entanglement and purity of
the two-mode cavity state are discussed in detail for the initially separated
squeezing inputs. It is found that the stable and pure entangled state of the
two distant nanocavities can be achieved with the requirement of only a weak
cavity-waveguide coupling when the cavities are resonant with the band center
of the waveguide. The strong couplings between the cavities and the waveguide
lead to the entanglement sudden death and sudden birth. When the frequencies of
the cavities lie outside the band of the waveguide, the waveguide-induced cross
frequency shift between the cavities can optimize the achievable entanglement.
It is also shown that the entanglement can be easily manipulated through the
changes of the cavity frequencies within the waveguide band.Comment: 8 pages, 8 figure
Location Privacy and Its Applications: A Systematic Study
© 2013 IEEE. This paper surveys the current research status of location privacy issues in mobile applications. The survey spans five aspects of study: the definition of location privacy, attacks and adversaries, mechanisms to preserve the privacy of locations, location privacy metrics, and the current status of location-based applications. Through this comprehensive review, all the interrelated aspects of location privacy are integrated into a unified framework. Additionally, the current research progress in each area is reviewed individually, and the links between existing academic research and its practical applications are identified. This in-depth analysis of the current state-of-play in location privacy is designed to provide a solid foundation for future studies in the field
Learning from Weak and Noisy Labels for Semantic Segmentation
This work was partially supported by National Natural Science Foundation of China (61573363 and 61573026), 973 Program of China (2014CB340403 and 2015CB352502), the Fundamental Research Funds for the Central Universities
and the Research Funds of Renmin University of China (15XNLQ01), IBM Global SUR Award Program, European
Research Council FP7 Project SUNNY (313243), and the funding from KAUST
The K giant stars from the LAMOST survey data I: identification, metallicity, and distance
We present a support vector machine classifier to identify the K giant stars
from the LAMOST survey directly using their spectral line features. The
completeness of the identification is about 75% for tests based on LAMOST
stellar parameters. The contamination in the identified K giant sample is lower
than 2.5%. Applying the classification method to about 2 million LAMOST spectra
observed during the pilot survey and the first year survey, we select 298,036 K
giant candidates. The metallicities of the sample are also estimated with
uncertainty of \,dex based on the equivalent widths of Mg and iron lines. A Bayesian method is then developed to estimate the
posterior probability of the distance for the K giant stars, based on the
estimated metallicity and 2MASS photometry. The synthetic isochrone-based
distance estimates have been calibrated using 7 globular clusters with a wide
range of metallicities. The uncertainty of the estimated distance modulus at
\,mag, which is the median brightness of the K giant sample, is about
0.6\,mag, corresponding to % in distance. As a scientific verification
case, the trailing arm of the Sagittarius stream is clearly identified with the
selected K giant sample. Moreover, at about 80\,kpc from the Sun, we use our K
giant stars to confirm a detection of stream members near the apo-center of the
trailing tail. These rediscoveries of the features of the Sagittarius stream
illustrate the potential of the LAMOST survey for detecting substructures in
the halo of the Milky Way.Comment: 24 pages, 20 figures, submitted to Ap
Neutron Scattering Measurements of Spatially Anisotropic Magnetic Exchange Interactions in Semiconducting K0.85Fe1.54Se2 (TN=280 K)
We use neutron scattering to study the spin excitations associated with the
stripe antiferromagnetic (AFM) order in semiconducting
KFeSe (= K). We show that the spin wave spectra
can be accurately described by an effective Heisenberg Hamiltonian with highly
anisotropic in-plane couplings at = K. At high temperature (=
K) above , short range magnetic correlation with anisotropic correlation
lengths are observed. Our results suggest that, despite the dramatic difference
in the Fermi surface topology, the in-plane anisotropic magnetic couplings are
a fundamental property of the iron based compounds; this implies that their
antiferromagnetism may originate from local strong correlation effects rather
than weak coupling Fermi surface nesting.Comment: 5 pages, 4 figure
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