3,283 research outputs found
Frustration driven structural distortion in VOMoO4
Nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR),
magnetization measurements and electronic structure calculations in VOMoO4 are
presented. It is found that VOMoO4 is a frustrated two-dimensional
antiferromagnet on a square lattice with competing exchange interactions along
the side J1 and the diagonal J2 of the square. From magnetization measurements
J1+J2 is estimated around 155 K, in satisfactory agreement with the values
derived from electronic structure calculations. Around 100 K a structural
distortion, possibly driven by the frustration, is evidenced. This distortion
induces significant modifications in the NMR and EPR spectra which can be
accounted for by valence fluctuations. The analysis of the spectra suggests
that the size of the domains where the lattice is distorted progressively grows
as the temperature approaches the transition to the magnetic ground state at
Tc=42 K
Loop algorithm for Heisenberg models with biquadratic interaction and phase transitions in two dimensions
We present a new algorithm for quantum Monte Carlo simulation based on global
updating with loops. While various theoretical predictions are confirmed in one
dimension, we find, for S=1 systems on a square lattice with an
antiferromagnetic biquadratic interaction, that the intermediate phase between
the antiferromagnetic and the ferromagnetic phases is disordered and that the
two phase transitions are both of the first order in contrast to the
one-dimensional case. It is strongly suggested that the transition points
coincide those at which the algorithm changes qualitatively.Comment: 4 pages including 4 figures, to appear in JPS
ELVIS: Entertainment-led video summaries
© ACM, 2010. This is the author's version of the work. It is posted here by permission of ACM for your personal use. Not for redistribution. The definitive version was published in ACM Transactions on Multimedia Computing, Communications, and Applications, 6(3): Article no. 17 (2010) http://doi.acm.org/10.1145/1823746.1823751Video summaries present the user with a condensed and succinct representation of the content of a video stream. Usually this is achieved by attaching degrees of importance to low-level image, audio and text features. However, video content elicits strong and measurable physiological responses in the user, which are potentially rich indicators of what video content is memorable to or emotionally engaging for an individual user. This article proposes a technique that exploits such physiological responses to a given video stream by a given user to produce Entertainment-Led VIdeo Summaries (ELVIS). ELVIS is made up of five analysis phases which correspond to the analyses of five physiological response measures: electro-dermal response (EDR), heart rate (HR), blood volume pulse (BVP), respiration rate (RR), and respiration amplitude (RA). Through these analyses, the temporal locations of the most entertaining video subsegments, as they occur within the video stream as a whole, are automatically identified. The effectiveness of the ELVIS technique is verified through a statistical analysis of data collected during a set of user trials. Our results show that ELVIS is more consistent than RANDOM, EDR, HR, BVP, RR and RA selections in identifying the most entertaining video subsegments for content in the comedy, horror/comedy, and horror genres. Subjective user reports also reveal that ELVIS video summaries are comparatively easy to understand, enjoyable, and informative
Kinetics of neuropeptide Y, catecholamines, and physiological responses during moderate and heavy intensity exercises.
Neuropeptide Y 1-36 (NPY1-36) is a vasoconstrictor peptide co-secreted with norepinephrine (NE) by nerve endings during sympathetic activation. NPY1-36 potentiates NE action post-synaptically through the stimulation of the Y1 receptor, whereas its metabolite NPY3-36 resulting from DPP4 action activates Y2 presynaptic receptors, inhibiting NE and acetylcholine secretion. The secretions of NPY1-36 and NPY3-36 in response to sympathetic nervous system activation have not been studied due to the lack of analytical techniques available to distinguish them. We determined in healthy volunteers NPY1-36, NPY3-36 and catecholamine kinetics and how these neurotransmitters modulate the physiological stress response during and after moderate- and heavy-intensity exercises. Six healthy males participated in this randomized, double-blind, saxagliptin vs placebo crossover study. The volunteers performed an orthostatic test, a 30-min exercise at moderate intensity and a 15-min exercise at heavy intensity each followed by 50 min of recovery in two separate sessions with saxagliptin or placebo. Oxygen consumption (V̇O <sub>2</sub> ), ventilation and heart rate were continuously recorded. NE, epinephrine, NPY1-36 and NPY3-36 were quantified by tandem mass spectrometry. We found that exercise triggers NPY1-36 and NE secretion in an intensity-dependent manner and that NE returns faster to the baseline concentration than NPY1-36 after exercise. NPY3-36 rises during recovery parallel to the decline of NPY1-36. Saxagliptin reverses the NPY1-36/NPY3-36 ratio but does not affect hemodynamics, nor NPY1-36 and catecholamine concentrations. We found that NPY1-36 half-life is considerably shorter than previously established with immunoassays. NPY1-36 and NE secretions are finely regulated to prevent an excessive physiological Y1 stimulating response to submaximal exercise
Magnetic properties of NaV2O5, a one-dimensional spin 1/2 antiferromagnet with finite chains
We have performed measurements of the magnetic susceptibility of NaVO
between 2 and 400 K. The high temperature part is typical of spin 1/2 chains
with a nearest--neighbour antiferromagnetic exchange integral of 529 K. We
develop a model for the susceptibility of a system with finite chains to
account for the low temperature part of the data, which cannot be fitted by a
standard Curie-Weiss term. These results suggest that the next
nearest--neighbour exchange integral in CaVO should be of the
order of 500 K because, like in NaVO, it corresponds to corner
sharing VO square pyramids.Comment: An early version of the manuscript was mistakenly submitted. Although
relatively minor, the changes concern the list of authors, the main text, the
references and the figure captions. 10 pages of latex, 2 figure
Deterministic assembly of a charged quantum dot-micropillar cavity device
Developing future quantum communication may rely on the ability to engineer
cavity-mediated interactions between photons and solid-state artificial atoms,
in a deterministic way. Here, we report a set of technological and experimental
developments for the deterministic coupling between the optical mode of a
micropillar cavity and a quantum dot trion transition. We first identify a
charged transition through in-plane magnetic field spectroscopy, and then tune
the optical cavity mode to its energy via in-situ lithography. In addition, we
design an asymmetric tunneling barrier to allow the optical trapping of the
charge, assisted by a quasi-resonant pumping scheme, in order to control its
occupation probability. We evaluate the generation of a positively-charged
quantum dot through second order auto-correlation measurements of its resonance
fluorescence, and the quality of light-matter interaction for these spin-photon
interfaces is assessed by measuring the performance of the device as a
single-photon source.Comment: 9 pages, 7 figure
Global atmospheric budget of acetaldehyde: 3-D model analysis and constraints from in-situ and satellite observations
We construct a global atmospheric budget for acetaldehyde using a 3-D model of atmospheric chemistry (GEOS-Chem), and use an ensemble of observations to evaluate present understanding of its sources and sinks. Hydrocarbon oxidation provides the largest acetaldehyde source in the model (128 Tg a<sup>&minus;1</sup>, a factor of 4 greater than the previous estimate), with alkanes, alkenes, and ethanol the main precursors. There is also a minor source from isoprene oxidation. We use an updated chemical mechanism for GEOS-Chem, and photochemical acetaldehyde yields are consistent with the Master Chemical Mechanism. We present a new approach to quantifying the acetaldehyde air-sea flux based on the global distribution of light absorption due to colored dissolved organic matter (CDOM) derived from satellite ocean color observations. The resulting net ocean emission is 57 Tg a<sup>&minus;1</sup>, the second largest global source of acetaldehyde. A key uncertainty is the acetaldehyde turnover time in the ocean mixed layer, with quantitative model evaluation over the ocean complicated by known measurement artifacts in clean air. Simulated concentrations in surface air over the ocean generally agree well with aircraft measurements, though the model tends to overestimate the vertical gradient. PAN:NO<sub>x</sub> ratios are well-simulated in the marine boundary layer, providing some support for the modeled ocean source. We introduce the Model of Emissions of Gases and Aerosols from Nature (MEGANv2.1) for acetaldehyde and ethanol and use it to quantify their net flux from living terrestrial plants. Including emissions from decaying plants the total direct acetaldehyde source from the land biosphere is 23 Tg a<sup>&minus;1</sup>. Other terrestrial acetaldehyde sources include biomass burning (3 Tg a<sup>&minus;1</sup>) and anthropogenic emissions (2 Tg a<sup>&minus;1</sup>). Simulated concentrations in the continental boundary layer are generally unbiased and capture the spatial gradients seen in observations over North America, Europe, and tropical South America. However, the model underestimates acetaldehyde levels in urban outflow, suggesting a missing source in polluted air. Ubiquitous high measured concentrations in the free troposphere are not captured by the model, and based on present understanding are not consistent with concurrent measurements of PAN and NO<sub>x</sub>: we find no compelling evidence for a widespread missing acetaldehyde source in the free troposphere. We estimate the current US source of ethanol and acetaldehyde (primary + secondary) at 1.3 Tg a<sup>&minus;1</sup> and 7.8 Tg a<sup>&minus;1</sup>, approximately 60{%} and 480% of the corresponding increases expected for a national transition from gasoline to ethanol fuel
The control of catalytic performance of rutile-type Sn/V/Nb/Sb mixed oxides, catalysts for propane ammoxidation to acrylonitrile
This paper describes the effect of the composition of rutile-type Sn/V/Nb/Sb mixed oxides catalysts on the
catalytic performance in the gas-phase ammoxidation of propane to acrylonitrile. The variation in the
atomic ratio between components in catalysts is the key for the control of activity and selectivity. In
samples with atomic composition Sn/V/Nb/Sb 1/0.2/1/x (0 x 5) and 1/0.2/y/3 (0 y 3) several
compounds formed, i.e., SnO2, Sb/Nbmixed oxide, Sb6O13 and non-stoichiometric rutile-type V/Nb/Sb/O;
the latter segregated preferentially at the surface of the catalyst. Tin oxide provided the rutile matrix for
the dispersion of the mixed oxides. The main role of Sb was shown to generate mixed oxides containing
specific sites for the allylic ammoxidation of propylene intermediately formed. The presence of Nb
enhanced the activity and selectivity of these sites
- …