1,226 research outputs found
On the essential constants in Riemannian geometries
In the present work the problem of distinguishing between essential and
spurious (i.e., absorbable) constants contained in a metric tensor field in a
Riemannian geometry is considered. The contribution of the study is the
presentation of a sufficient and necessary criterion, in terms of a covariant
statement, which enables one to determine whether a constant is essential or
not. It turns out that the problem of characterization is reduced to that of
solving a system of partial differential equations of the first order. In any
case, the metric tensor field is assumed to be smooth with respect to the
constant to be tested. It should be stressed that the entire analysis is purely
of local character.Comment: 10 pages, LaTeX2e typesetting system, no tables or figures, J. Math.
Phys. 47, 092502 (2006) [still open issue
An experimental study of permeability development as a function of crystal-free melt viscosity
Concerted changes in tropical forest structure and dynamics: evidence from 50 South American long-term plots
Several widespread changes in the ecology of old-growth tropical forests have recently been documented for the late twentieth century, in particular an increase in stem turnover (pan-tropical), and an increase in above-ground biomass (neotropical). Whether these changes are synchronous and whether changes in growth are also occurring is not known. We analysed stand-level changes within 50 long-term. monitoring plots from across South America spanning 1971-2002. We show that: (i) basal area (BA: sum of the cross-sectional areas of all trees in a plot) increased significantly over time (by 0.10 +/- 0.04 m(2) ha(-1) yr(-1), mean +/- 95% CI); as did both (ii) stand-level BA growth rates (sum of the increments of BA of surviving trees and BA of new trees that recruited into a plot); and (iii) stand-level BA mortality rates (sum of the cross-sectional areas of all trees that died in a plot). Similar patterns were observed on a per-stem basis: (i) stem density (number of stems per hectare; 1 hectare is 10(4) m(2)) increased significantly over time (0.94 +/- 0.63 stems ha(-1) yr(-1)); as did both (ii) stem recruitment rates; and (iii) stem mortality rates. In relative terms, the pools of BA and stem density increased by 0.38 +/- 0.15% and 0.18 +/- 0.12% yr(-1), respectively. The fluxes into and out of these pools-stand-level BA growth, stand-level BA mortality, stem recruitment and stem mortality rates-increased, in relative terms, by an order of magnitude more. The gain terms (BA growth, stem recruitment) consistently exceeded the loss terms (BA loss, stem mortality) throughout the period, suggesting that whatever process is driving these changes was already acting before the plot network was established. Large long-term increases in stand-level BA growth and simultaneous increases in stand BA and stem density imply a continent-wide increase in resource availability which is increasing net primary productivity and altering forest dynamics. Continent-wide changes in incoming solar radiation, and increases in atmospheric concentrations of CO2 and air temperatures may have increased resource supply over recent decades, thus causing accelerated growth and increased dynamism across the world's largest tract of tropical forest
Precision measurements of large scale structure with future type Ia supernova surveys
Type Ia supernovae are currently the best known standard candles at
cosmological distances. In addition to providing a powerful probe of dark
energy they are an ideal source of information about the peculiar velocity
field of the local universe. Even with the very small number of supernovae
presently available it has been possible to measure the dipole and quadrupole
of the local velocity field out to z~0.025. With future continuous all-sky
surveys like the LSST project the luminosity distances of tens of thousands of
nearby supernovae will be measured accurately. This will allow for a
determination of the local velocity structure of the universe as a function of
redshift with unprecedented accuracy, provided the redshifts of the host
galaxies are known. Using catalogues of mock surveys we estimate that future
low redshift supernova surveys will be able to probe sigma-8 to a precision of
roughly 5% at 95% C.L. This is comparable to the precision in future galaxy and
weak lensing surveys and with a relatively modest observational effort it will
provide a crucial cross-check on future measurements of the matter power
spectrum.Comment: 18 pages, 9 figures, submitted to JCA
Correlations in Two-Dimensional Vortex Liquids
We report on a high temperature perturbation expansion study of the
superfluid-density spatial correlation function of a Ginzburg-Landau-model
superconducting film in a magnetic field. We have derived a closed form which
expresses the contribution to the correlation function from each graph of the
perturbation theory in terms of the number of Euler paths around appropriate
subgraphs. We have enumerated all graphs appearing out to 10-th order in the
expansion and have evaluated their contributions to the correlation function.
Low temperature correlation functions, obtained using Pad\'{e} approximants,
are in good agreement with Monte Carlo simulation results and show that the
vortex-liquid becomes strongly correlated at temperatures well above the vortex
solidification temperature.Comment: 18 pages (RevTeX 3.0) and 4 figures, available upon request,
IUCM93-01
The Use of a Pressure-Indicating Sensor Film to Provide Feedback upon Hydrogel-Forming Microneedle Array Self-Application In Vivo
PURPOSE: To evaluate the combination of a pressure-indicating sensor film with hydrogel-forming microneedle arrays, as a method of feedback to confirm MN insertion in vivo. METHODS: Pilot in vitro insertion studies were conducted using a Texture Analyser to insert MN arrays, coupled with a pressure-indicating sensor film, at varying forces into excised neonatal porcine skin. In vivo studies involved twenty human volunteers, who self-applied two hydrogel-forming MN arrays, one with a pressure-indicating sensor film incorporated and one without. Optical coherence tomography was employed to measure the resulting penetration depth and colorimetric analysis to investigate the associated colour change of the pressure-indicating sensor film. RESULTS: Microneedle insertion was achieved in vitro at three different forces, demonstrating the colour change of the pressure-indicating sensor film upon application of increasing pressure. When self-applied in vivo, there was no significant difference in the microneedle penetration depth resulting from each type of array, with a mean depth of 237 μm recorded. When the pressure-indicating sensor film was present, a colour change occurred upon each application, providing evidence of insertion. CONCLUSIONS: For the first time, this study shows how the incorporation of a simple, low-cost pressure-indicating sensor film can indicate microneedle insertion in vitro and in vivo, providing visual feedback to assure the user of correct application. Such a strategy may enhance usability of a microneedle device and, hence, assist in the future translation of the technology to widespread clinical use
Identifying runoff sources across scales in Amazon watersheds: an LBA synthesis effort.
Abstract ID: 54
Increasing biomass in Amazonian forest plots
A previous study by Phillips et al. of changes in the biomass of permanent sample plots in Amazonian forests was used to infer the presence of a regional carbon sink. However, these results generated a vigorous debate about sampling and methodological issues. Therefore we present a new analysis of biomass change in old-growth Amazonian forest plots using updated inventory data. We find that across 59 sites, the above-ground dry biomass in trees that are more than 10 cm in diameter (AGB) has increased since plot establishment by 1.22 ± 0.43 Mg per hectare per year (ha-1 yr-1), where 1 ha = 104 m2), or 0.98 ± 0.38 Mg ha-1 yr-1 if individual plot values are weighted by the number of hectare years of monitoring. This significant increase is neither confounded by spatial or temporal variation in wood specific gravity, nor dependent on the allometric equation used to estimate AGB. The conclusion is also robust to uncertainty about diameter measurements for problematic trees: for 34 plots in western Amazon forests a significant increase in AGB is found even with a conservative assumption of zero growth for all trees where diameter measurements were made using optical methods and/or growth rates needed to be estimated following fieldwork. Overall, our results suggest a slightly greater rate of net stand-level change than was reported by Phillips et al. Considering the spatial and temporal scale of sampling and associated studies showing increases in forest growth and stem turnover, the results presented here suggest that the total biomass of these plots has on average increased and that there has been a regional-scale carbon sink in old-growth Amazonian forests during the previous two decades
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Measured energy savings from using night temperature setback
The measured energy savings resulting from using night temperature setback in typical light-construction wooden office buildings was determined. Researchers installed monitoring equipment in a six-building sample of two-story wooden buildings at Fort Devens, Massachusetts. Data obtained during both single-setting and night-setback operating modes were used to develop models of each building`s heat consumption as a function of the difference between inside and outside temperature. These models were used to estimate seasonal savings that could be obtained from the use of night-setback thermostat control. The measured savings in heating energy from using night temperature setback for the six Fort Devens buildings ranged from 14% to 25%; the mean savings was 19.2%. Based on an energy cost of 780 per year per building
iPTF16geu: A multiply imaged, gravitationally lensed type Ia supernova
We report the discovery of a multiply-imaged gravitationally lensed Type Ia
supernova, iPTF16geu (SN 2016geu), at redshift . This phenomenon could
be identified because the light from the stellar explosion was magnified more
than fifty times by the curvature of space around matter in an intervening
galaxy. We used high spatial resolution observations to resolve four images of
the lensed supernova, approximately 0.3" from the center of the foreground
galaxy. The observations probe a physical scale of 1 kiloparsec, smaller
than what is typical in other studies of extragalactic gravitational lensing.
The large magnification and symmetric image configuration implies close
alignment between the line-of-sight to the supernova and the lens. The relative
magnifications of the four images provide evidence for sub-structures in the
lensing galaxy.Comment: Matches published versio
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