9,391 research outputs found
Lovelock gravities from Born-Infeld gravity theory
We present a Born-Infeld gravity theory based on generalizations of Maxwell
symmetries denoted as . We analyze different configuration
limits allowing to recover diverse Lovelock gravity actions in six dimensions.
Further, the generalization to higher even dimensions is also considered.Comment: v3, 15 pages, two references added, published versio
Dynamical reduction of the dimensionality of exchange interactions and the "spin-liquid" phase of -(BEDT-TTF)
We show that the anisotropy of the effective spin model for the dimer Mott
insulator phase of -(BEDT-TTF) salts is dramatically different
from that of the underlying tight-binding model. Intra-dimer quantum
interference results in a model of coupled spin chains, where frustrated
interchain interactions suppress long-range magnetic order. Thus, we argue, the
"spin liquid" phase observed in some of these materials is a remnant of the
Tomonaga-Luttinger physics of a single chain. This is consistent with previous
experiments and resolves some outstanding puzzles. An erratum [Phys. Rev. Lett.
120, 199901 (2018).] is added as an appendix.Comment: Accepted by PRL, 6 pages, 5 figure
Effects of forage supplements on milk production and chemical properties, in vivo digestibility, rumen fermentation and N excretion in dairy cows offered red clover silage and corn silage or dry ground corn
peer-reviewedThis study concerned the effects of partial substitution of clover silage with high starch forages on milk production and chemical composition, in vivo digestibility, rumen
fermentation pattern and nitrogen excretion of dairy cows. Sixteen dairy cows were
separated into two groups and were assigned to treatments in a two-period crossover
design. Two forage supplements were used: corn silage (CS) and dry ground corn (DG).
All animals received 4.5 kg of concentrate dry matter per day. Results showed no significant
difference between the forage supplements for milk production, while significant
differences (P<0.01) were observed for milk fat, milk protein and nitrogen utilisation
efficiency (42 v. 4.0 g/kg, 3.5 v. 3.3 g/kg and 222 v. 188 g/kg, respectively, for DG and CS).
Faecal N excretion did not differ between forage supplements, but urinary N excretion
was higher for CS (P<0.05). No significant differences were observed between treatments
for rumen fluid pH or for rumen fluid concentrations of ammonium nitrogen
or of acetic, propionic or butyric acids. Dry matter intake and the in vivo digestibility
of dry matter, organic matter, acid detergent fibre and neutral detergent fibre were all
higher for CS compared with DG.The authors are grateful to the Environmental Office
of the Cantabrian Government for funding the project
05-640.02-2174
Jupiter as an exoplanet: UV to NIR transmission spectrum reveals hazes, a Na layer and possibly stratospheric H2O-ice clouds
Currently, the analysis of transmission spectra is the most successful
technique to probe the chemical composition of exoplanet atmospheres. But the
accuracy of these measurements is constrained by observational limitations and
the diversity of possible atmospheric compositions. Here we show the UV-VIS-IR
transmission spectrum of Jupiter, as if it were a transiting exoplanet,
obtained by observing one of its satellites, Ganymede, while passing through
Jupiter's shadow i.e., during a solar eclipse from Ganymede. The spectrum shows
strong extinction due to the presence of clouds (aerosols) and haze in the
atmosphere, and strong absorption features from CH4. More interestingly, the
comparison with radiative transfer models reveals a spectral signature, which
we attribute here to a Jupiter stratospheric layer of crystalline H2O ice. The
atomic transitions of Na are also present. These results are relevant for the
modeling and interpretation of giant transiting exoplanets. They also open a
new technique to explore the atmospheric composition of the upper layers of
Jupiter's atmosphere.Comment: Accepted for publication in ApJ Letter
Nematic alignment of self-propelled particles: from particle to macroscopic dynamics
Starting from a particle model describing self-propelled particles interacting through nematic alignment, we derive a macroscopic model for the particle density and mean direction of motion. We first propose a mean-field kinetic model of the particle dynamics. After diffusive rescaling of the kinetic equation, we formally show that the distribution function converges to an equilibrium distribution in particle direction, whose local density and mean direction satisfies a cross-diffusion system. We show that the system is consistent with symmetries typical of a nematic material. The derivation is carried over by means of a Hilbert expansion. It requires the inversion of the linearized collision operator for which we show that the generalized collision invariants, a concept introduced to overcome the lack of momentum conservation of the system, plays a central role. This cross-diffusion system poses many new challenging questions
Seeing Star Formation Regions with Gravitational Microlensing
We qualitatively study the effects of gravitational microlensing on our view
of unresolved extragalactic star formation regions. Using a general
gravitational microlensing configuration, we perform a number of simulations
that reveal that specific imprints of the star forming region are imprinted,
both photometrically and spectroscopically, upon observations. Such
observations have the potential to reveal the nature and size of these star
forming regions, through the degree of variability observed in a monitoring
campaign, and hence resolve the star formation regions in distant galaxies
which are too small to be probed via more standard techniques.Comment: 7 pages, 8 figures, ApJ accepte
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