4,104 research outputs found
Electrochemical intercalation and electrical conductivity of graphite fibers
Lamellar compounds of graphite fibers were prepared by electrochemical intercalation. The dependence of the electrical resistance on the intercalate concentration was determined by a quasi simultaneous method. A factor 30 decrease of the relative fiber resistance was obtained with fluorosulfuric acid
Ammonia-Labile Bonds in High- and Low-Digestibility Strains of Switchgrass
Improvement in the forage quality of switchgrass (Panicum virgatum L.) through phenotypic selection for increased in vitro dry matter digestibility (IVDMD) has been demonstrated. This study tested the hypothesis that genetic improvement of fiber digestibility in switchgrass has been achieved by selection for a strain with a decreased quantity of ammonia-labile bonds. Tissue samples of a high-digestibility (high-IVDMD) and a low-digestibility strain (low-IVDMD) of switchgrass were ammoniated at rates of 0, 10, 20, and 40 g kg-1 dry matter. Fiber composition and in vitro rate and extent of neutral-detergent fiber (NDF) digestion were determined on control and ammoniated samples. The high-IVDMD strain had lower (P \u3c 0.05) concentrations of NDF and acid-detergent lignin (ADL) than the low-IVDMD strain. Lignin concentrations averaged 53 and 71 g kg-1 for the high- and low-IVDMD strains, respectively. The high-IVDMD strain had a greater (P \u3c 0.05) extent of NDF digestion when compared with the low strain; however, the rate of NDF digestion did not differ (P \u3e 0.05) between strains. Increased digestibility of the high-IVDMD strain was primarily attributed to increased cell-wall (NDF) digestibility. Ammoniation at 20 and 40 g kg-1 resulted in small decreases (P \u3c 0.05) in NDF concentrations when compared with the control; however, ammoniation had no effect on hemicellulose, cellulose, or ADL concentrations. Ammoniation increased (P \u3c 0.05) both the rate and extent of NDF digestion. Extent of NDF digestion averaged 0.395 for the control and 0.465, 0.498, and 0.493 for the 10, 20, and 40-g kg-1 treatments, respectively. Strain X ammoniation rate interaction was not significant for rate and extent of digestion, suggesting that genetic improvement in digestibility of switchgrass was not related to the number of ammonia-labile bonds
The VIPERS Multi-Lambda Survey. II. Diving with massive galaxies in 22 square degrees since z = 1.5
We investigate the evolution of the galaxy stellar mass function (SMF) and
stellar mass density from redshift z=0.2 to z=1.5 of a <22-selected
sample with highly reliable photometric redshifts and over an unprecedentedly
large area. Our study is based on NIR observations carried out with WIRCam at
CFHT over the footprint of the VIPERS spectroscopic survey and benefits from
the high quality optical photometry from the CFHTLS and UV observations with
the GALEX satellite. The accuracy of our photometric redshifts is <
0.03 and 0.05 for the bright (22.5) samples,
respectively. The SMF is measured with ~760,000 galaxies down to =22 and
over an effective area of ~22.4 deg, the latter of which drastically
reduces the statistical uncertainties (i.e. Poissonian error & cosmic
variance). We point out the importance of a careful control of the photometric
calibration, whose impact becomes quickly dominant when statistical
uncertainties are reduced, which will be a major issue for future generation of
cosmological surveys with, e.g. EUCLID or LSST. By exploring the rest-frame
(NUV-r) vs (r-) color-color diagram separating star-forming and quiescent
galaxies, (1) we find that the density of very massive log() >
11.5 galaxies is largely dominated by quiescent galaxies and increases by a
factor 2 from z~1 to z~0.2, which allows for additional mass assembly via dry
mergers, (2) we confirm a scenario where star formation activity is impeded
above a stellar mass log() = 10.640.01, a value that
is found to be very stable at 0.2 < z < 1.5, (3) we discuss the existence of a
main quenching channel that is followed by massive star-forming galaxies, and
finally (4) we characterise another quenching mechanism required to explain the
clear excess of low-mass quiescent galaxies observed at low redshift.Comment: 22 pages, 20 figures. Accepted for publication in A&A. Version to be
publishe
Boron Fertilization Effects on Nutritive Parameters of Alfalfa
With early pre-plant incorporation of limestone to raise soil pH to 6.8 to 7.0, alfalfa (Medicago sativa L.) may be grown successfully on acid, Coastal Plain, sandy loam soils. Fertility and forage quality for hay and/or grazing require alternative management of alfalfa on these Coastal Plain soils. A two-year experiment evaluated alfalfa fertilized with three rates of boron to quantify effects on nutritive entities, especially fiber components. On a whole-plant basis in year 1, only crude protein was increased (P \u3c .05) at one of six harvest dates. In year 2, chemical analyses of leaf-stem components indicated consistent increases in crude protein of leaf fractions at each harvest (P \u3c .05), reduction in neutral detergent fiber at three harvest dates (P \u3c .06), and reduced lignin (P \u3c .07) at the final harvest. Stem sections were affected by rate of boron at only the June harvest with an increase in crude protein (P \u3c .05). Rate of boron fertilization had indirect effects on nutritive value (crude protein) by either delaying physiological maturity or enhancing nitrogen fixation in leaves, and had a direct negative effect on certain fiber components
The lesson of causal discovery algorithms for quantum correlations: Causal explanations of Bell-inequality violations require fine-tuning
An active area of research in the fields of machine learning and statistics
is the development of causal discovery algorithms, the purpose of which is to
infer the causal relations that hold among a set of variables from the
correlations that these exhibit. We apply some of these algorithms to the
correlations that arise for entangled quantum systems. We show that they cannot
distinguish correlations that satisfy Bell inequalities from correlations that
violate Bell inequalities, and consequently that they cannot do justice to the
challenges of explaining certain quantum correlations causally. Nonetheless, by
adapting the conceptual tools of causal inference, we can show that any attempt
to provide a causal explanation of nonsignalling correlations that violate a
Bell inequality must contradict a core principle of these algorithms, namely,
that an observed statistical independence between variables should not be
explained by fine-tuning of the causal parameters. In particular, we
demonstrate the need for such fine-tuning for most of the causal mechanisms
that have been proposed to underlie Bell correlations, including superluminal
causal influences, superdeterminism (that is, a denial of freedom of choice of
settings), and retrocausal influences which do not introduce causal cycles.Comment: 29 pages, 28 figs. New in v2: a section presenting in detail our
characterization of Bell's theorem as a contradiction arising from (i) the
framework of causal models, (ii) the principle of no fine-tuning, and (iii)
certain operational features of quantum theory; a section explaining why a
denial of hidden variables affords even fewer opportunities for causal
explanations of quantum correlation
Semiclassical Theory for Parametric Correlation of Energy Levels
Parametric energy-level correlation describes the response of the
energy-level statistics to an external parameter such as the magnetic field.
Using semiclassical periodic-orbit theory for a chaotic system, we evaluate the
parametric energy-level correlation depending on the magnetic field difference.
The small-time expansion of the spectral form factor is shown to be
in agreement with the prediction of parameter dependent random-matrix theory to
all orders in .Comment: 25 pages, no figur
The bolometric and UV attenuation in normal spiral galaxies of the Herschel Reference Survey
The dust in nearby galaxies absorbs a fraction of the
UV-optical-near-infrared radiation produced by stars. This energy is
consequently re-emitted in the infrared. We investigate the portion of the
stellar radiation absorbed by spiral galaxies from the HRS by modelling their
UV-to-submillimetre spectral energy distributions. Our models provide an
attenuated and intrinsic SED from which we find that on average 32 % of all
starlight is absorbed by dust. We define the UV heating fraction as the
percentage of dust luminosity that comes from absorbed UV photons and find that
this is 56 %, on average. This percentage varies with morphological type, with
later types having significantly higher UV heating fractions. We find a strong
correlation between the UV heating fraction and specific star formation rate
and provide a power-law fit. Our models allow us to revisit the IRX-AFUV
relations, and derive these quantities directly within a self-consistent
framework. We calibrate this relation for different bins of NUV-r colour and
provide simple relations to relate these parameters. We investigated the
robustness of our method and we conclude that the derived parameters are
reliable within the uncertainties which are inherent to the adopted SED model.
This calls for a deeper investigation on how well extinction and attenuation
can be determined through panchromatic SED modelling.Comment: 14 pages, 7 figures. Accepted for publication in Astronomy &
Astrophysic
Quantum measurements without macroscopic superpositions
We study a class of quantum measurement models. A microscopic object is
entangled with a macroscopic pointer such that each eigenvalue of the measured
object observable is tied up with a specific pointer deflection. Different
pointer positions mutually decohere under the influence of a bath.
Object-pointer entanglement and decoherence of distinct pointer readouts
proceed simultaneously. Mixtures of macroscopically distinct object-pointer
states may then arise without intervening macroscopic superpositions.
Initially, object and apparatus are statistically independent while the latter
has pointer and bath correlated according to a metastable local thermal
equilibrium. We obtain explicit results for the object-pointer dynamics with
temporal coherence decay in general neither exponential nor Gaussian. The
decoherence time does not depend on details of the pointer-bath coupling if it
is smaller than the bath correlation time, whereas in the opposite Markov
regime the decay depends strongly on whether that coupling is Ohmic or
super-Ohmic.Comment: 50 pages, 5 figures, changed conten
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