4,431 research outputs found
Effect of spatial dimension on a model of fluid turbulence
A numerical study of the -dimensional Eddy Damped Quasi-Normal Markovian
equations is performed to investigate the dependence on spatial dimension of
homogeneous isotropic fluid turbulence. Relationships between structure
functions and energy and transfer spectra are derived for the -dimensional
case. Additionally, an equation for the -dimensional enstrophy analogue is
derived and related to the velocity derivative skewness. Comparisons are made
to recent four dimensional direct numerical simulation results. Measured energy
spectra show a magnified bottleneck effect which grows with dimension whilst
transfer spectra show a varying peak in the non-linear energy transfer as the
dimension is increased. These results are consistent with an increased forward
energy transfer at higher dimensions, further evidenced by measurements of a
larger asymptotic dissipation rate with growing dimension. The enstrophy
production term, related to the velocity derivative skewness, is seen to reach
a maximum at around five dimensions and may reach zero in the limit of infinite
dimensions, raising interesting questions about the nature of turbulence in
this limit.Comment: 29 pages, 9 figures. In press Journal of Fluid Mechanics, 202
Cohomology of quantum groups: An analog of Kostant's Theorem
We prove the analog of Kostant's Theorem on Lie algebra cohomology in the
context of quantum groups. We prove that Kostant's cohomology formula holds for
quantum groups at a generic parameter , recovering an earlier result of
Malikov in the case where the underlying semisimple Lie algebra . We also show that Kostant's formula holds when is
specialized to an -th root of unity for odd (where is
the Coxeter number of ) when the highest weight of the
coefficient module lies in the lowest alcove. This can be regarded as an
extension of results of Friedlander-Parshall and Polo-Tilouine on the
cohomology of Lie algebras of reductive algebraic groups in prime
characteristic.Comment: 12 page
Overcoming the roadblocks to cardiac cell therapy using tissue engineering
Transplantations of various stem cells or their progeny have repeatedly improved cardiac performance in animal models of myocardial injury; however, the benefits observed in clinical trials have been generally less consistent. Some of the recognized challenges are poor engraftment of implanted cells and, in the case of human cardiomyocytes, functional immaturity and lack of electrical integration, leading to limited contribution to the heart’s contractile activity and increased arrhythmogenic risks. Advances in tissue and genetic engineering techniques are expected to improve the survival and integration of transplanted cells, and to support structural, functional, and bioenergetic recovery of the recipient hearts. Specifically, application of a prefabricated cardiac tissue patch to prevent dilation and to improve pumping efficiency of the infarcted heart offers a promising strategy for making stem cell therapy a clinical reality.
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Validity of self-measured waist and hip circumferences: results from a community study in Malaysia
Background: Measures of central adiposity are better predictors of adverse health events than BMI. Nonetheless, BMI is more widely used in health research. One reason for this may be the limited research supporting the self-measurement of waist and hip circumference. The lack of validity studies is particularly acute in Asia. The main objective was to establish the validity of self-measurement of waist and hip circumference in a community setting and the correlation of those measures with BMI, blood pressure, and blood glucose levels. Methods. A community based, cross-sectional survey. A "healthy living expo" at a shopping mall in a rural town on peninsular Malaysia One hundred and thirty six (136) individuals volunteered to participate in the study, 125 of whom met the inclusion criteria. The ethnic distribution of the participants was 80% Chinese, 17% Malay and 3% Indian. Most participants were female (60%), with participants' ages ranging from 18 to 78 years (mean, 47.2). Self and assisted measurements of waist and hip were taken. Blood pressure, non-fasting blood glucose, height, and weight were also measured. Bland Altman plots and Lin's concordance coefficient were used to measure agreement between self and assisted measures. Pearson's correlation was used to examine the association of self and assisted measures with blood pressure, blood glucose, and BMI. Results: There was a downwards bias in self measured waist (-0.81 cm) and hip (-1 cm) circumferences compared with assisted measures. The concordance for the self and assisted measures of waist, hip and the ratio of the two were, respectively,.96,.93, and.84. The correlation between measures of central adiposity and BMI, blood pressure and blood glucose were similar for self and assisted measures. Conclusion: The results provide additional support for the use of self-measurement of waist and hip circumference studies of central adiposity, but is limited by the specificity of the setting. © 2013 Reidpath et al.; licensee BioMed Central Ltd
Device-independent certification of entangled measurements
We present a device-independent protocol to test if a given black-box
measurement device is entangled, that is, has entangled eigenstates. Our scheme
involves three parties and is inspired by entanglement swapping; the test uses
the Clauser-Horne-Shimony-Holt (CHSH) Bell inequality, checked between each
pair of parties. Also, focusing on the case where all particles are qubits, we
characterize quantitatively the deviation of the measurement device from a
perfect Bell state measurement.Comment: 5 pages, 2 figure
A millimeter-wave kinetic inductance detector camera for long-range imaging through optical obscurants
Millimeter-wave imaging provides a promising option for long-range target detection through optical obscurants such as fog, which often occur in marine environments. Given this motivation, we are currently developing a 150 GHz polarization-sensitive imager using a relatively new type of superconducting pair-breaking detector, the kinetic inductance detector (KID). This imager will be paired with a 1.5 m telescope to obtain an angular resolution of 0.09° over a 3.5° field of view using 3,840 KIDs. We have fully characterized a prototype KID array, which shows excellent performance with noise strongly limited by the irreducible fluctuations from the ambient temperature background. Full-scale KID arrays are now being fabricated and characterized for a planned demonstration in a maritime environment later this year
The Sloan Digital Sky Survey Reverberation Mapping Project: Ensemble Spectroscopic Variability of Quasar Broad Emission Lines
We explore the variability of quasars in the MgII and Hbeta broad emission
lines and UV/optical continuum emission using the Sloan Digital Sky Survey
Reverberation Mapping project (SDSS-RM). This is the largest spectroscopic
study of quasar variability to date: our study includes 29 spectroscopic epochs
from SDSS-RM over months, containing 357 quasars with MgII and 41 quasars
with Hbeta . On longer timescales, the study is also supplemented with
two-epoch data from SDSS-I/II. The SDSS-I/II data include an additional
quasars with MgII and 572 quasars with Hbeta. The MgII emission line is
significantly variable ( 10% on 100-day timescales), a necessary
prerequisite for its use for reverberation mapping studies. The data also
confirm that continuum variability increases with timescale and decreases with
luminosity, and the continuum light curves are consistent with a damped
random-walk model on rest-frame timescales of days. We compare the
emission-line and continuum variability to investigate the structure of the
broad-line region. Broad-line variability shows a shallower increase with
timescale compared to the continuum emission, demonstrating that the broad-line
transfer function is not a -function. Hbeta is more variable than MgII
(roughly by a factor of ), suggesting different excitation mechanisms,
optical depths and/or geometrical configuration for each emission line. The
ensemble spectroscopic variability measurements enabled by the SDSS-RM project
have important consequences for future studies of reverberation mapping and
black hole mass estimation of quasars.Comment: 20 pages, 25 figures. ApJ accepted: minor revisions following referee
repor
Characterizing unknown systematics in large scale structure surveys
Photometric large scale structure (LSS) surveys probe the largest volumes in
the Universe, but are inevitably limited by systematic uncertainties. Imperfect
photometric calibration leads to biases in our measurements of the density
fields of LSS tracers such as galaxies and quasars, and as a result in
cosmological parameter estimation. Earlier studies have proposed using
cross-correlations between different redshift slices or cross-correlations
between different surveys to reduce the effects of such systematics. In this
paper we develop a method to characterize unknown systematics. We demonstrate
that while we do not have sufficient information to correct for unknown
systematics in the data, we can obtain an estimate of their magnitude. We
define a parameter to estimate contamination from unknown systematics using
cross-correlations between different redshift slices and propose discarding
bins in the angular power spectrum that lie outside a certain contamination
tolerance level. We show that this method improves estimates of the bias using
simulated data and further apply it to photometric luminous red galaxies in the
Sloan Digital Sky Survey as a case study.Comment: 24 pages, 6 figures; Expanded discussion of results, added figure 2;
Version to be published in JCA
Pressure-induced alpha-to-omega transition in titanium metal: A systematic study of the effects of uniaxial stress
We investigated the effects of uniaxial stress on the pressure-induced
alpha-to-omega transition in pure titanium (Ti) by means of angle dispersive
x-ray diffraction in a diamond-anvil cell. Experiments under four different
pressure environments reveal that: (1) the onset of the transition depends on
the pressure medium used, going from 4.9 GPa (no pressure medium) to 10.5 GPa
(argon pressure medium); (2) the a and w phases coexist over a rather large
pressure range, which depends on the pressure medium employed; (3) the
hysteresis and quenchability of the w phase is affected by differences in the
sample pressure environment; and (4) a short term laser-heating of Ti lowers
the alpha-to-omega transition pressure. Possible transition mechanisms are
discussed in the light of the present results, which clearly demonstrated the
influence of uniaxial stress in the alpha-to-omega transition.Comment: 16 pages, 6 figures, 1 tabl
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