23,991 research outputs found
Rotation in the ZAMS: Be and Bn stars
We show that Be stars belong to a high velocity tail of a single B-type star
rotational velocity distribution in the MS. This implies that: 1) the number
fraction N(Be)/N(Be+B) is independent of the mass; 2) Bn stars having ZAMS
rotational velocities higher than a given limit might become Be stars.Comment: 3 pages ; to appear in the proceedings of the Sapporo meeting on
active OB stars ; ASP Conference Series ; eds: S. Stefl, S. Owocki and A.
Okazak
Raman response of Stage-1 graphite intercalation compounds revisited
We present a detailed in-situ Raman analysis of stage-1 KC8, CaC6, and LiC6
graphite intercalation compounds (GIC) to unravel their intrinsic finger print.
Four main components were found between 1200 cm-1 and 1700 cm-1, and each of
them were assigned to a corresponding vibrational mode. From a detailed line
shape analysis of the intrinsic Fano-lines of the G- and D-line response we
precisely determine the position ({\omega}ph), line width ({\Gamma}ph) and
asymmetry (q) from each component. The comparison to the theoretical calculated
line width and position of each component allow us to extract the
electron-phonon coupling constant of these compounds. A coupling constant
{\lambda}ph < 0.06 was obtained. This highlights that Raman active modes alone
are not sufficient to explain the superconductivity within the electron-phonon
coupling mechanism in CaC6 and KC8.Comment: 6 pages, 3 figures, 2 table
Probing the electron-phonon coupling in ozone-doped graphene by Raman spectroscopy
We have investigated the effects of ozone treatment on graphene by Raman
scattering. Sequential ozone short-exposure cycles resulted in increasing the
doping levels as inferred from the blue shift of the 2 and peak
frequencies, without introducing significant disorder. The two-phonon 2 and
2 Raman peak intensities show a significant decrease, while, on the
contrary, the one-phonon G Raman peak intensity remains constant for the whole
exposure process. The former reflects the dynamics of the photoexcited
electrons (holes) and, specifically, the increase of the electron-electron
scattering rate with doping. From the ratio of 2 to 2 intensities, which
remains constant with doping, we could extract the ratio of electron-phonon
coupling parameters. This ratio is found independent on the number of layers up
to ten layers. Moreover, the rate of decrease of 2 and 2 intensities
with doping was found to slowdown inversely proportional to the number of
graphene layers, revealing the increase of the electron-electron collision
probability
Interactions between nutrition and gastrointestinal infections with parasitic nematodes in goats
Parasitic nematodes of the digestive tract remain one of the main constraints to goat production both in temperate and tropical
countries. The usual mode of control of these gastrointestinal nematodes (GIN) based on the repeated use of anthelmintics
is now strongly questioned because of the increasing development of resistance to these molecules. Among the alternative
methods to anthelmintics currently available, the manipulation of host nutrition in order to improve the host resistance and/or
resilience to parasitic infections seems to represent one of the most promising options to reduce the dependence on conventional
chemotherapy and to favour the sustainable control of gastro intestinal nematode infections. This paper will review the available
information on the interactions between nutrition and nematode parasitism in dairy or meat goats both in temperate and tropical
conditions. It will refer to quantitative aspects of the diet (influence of the protein and/or energy parts) as well as to qualitative
components (effects of plant secondary metabolites on worm biology) and will discuss the specificities of goats in regard of
theses interactions
Optical properties of Si/Si0.87Ge0.13 multiple quantum well wires
Nanometer-scale wires cut into a Si/Si0.87Ge0.13 multiple quantum well structure were fabricated and characterized by using photoluminescence and photoreflectance at temperatures between 4 and 20 K. It was found that, in addition to a low-energy broadband emission at around 0.8 eV and other features normally observable in photoluminescence measurements, fabrication process induced strain relaxation and enhanced electron-hole droplets emission together with a new feature at 1.131 eV at 4 K were observed. The latter was further identified as a transition related to impurities located at the Si/Si0.87Ge0.13 heterointerfaces
Casimir torque
We develop a formalism for the calculation of the flow of angular momentum
carried by the fluctuating electromagnetic field within a cavity bounded by two
flat anisotropic materials. By generalizing a procedure employed recently for
the calculation of the Casimir force between arbitrary materials, we obtain an
expression for the torque between anisotropic plates in terms of their
reflection amplitude matrices. We evaluate the torque in 1D for ideal and
realistic model materials.Comment: 8 pages, 4 figs, Submitted to Proc. of QFEXT'05, to appear in J.
Phys.
Reentrant Metallic Behavior of Graphite in the Quantum Limit
Magnetotransport measurements performed on several well-characterized highly
oriented pyrolitic graphite and single crystalline Kish graphite samples reveal
a reentrant metallic behavior in the basal-plane resistance at high magnetic
fields, when only the lowest Landau levels are occupied. The results suggest
that the quantum Hall effect and Landau-level-quantization-induced
superconducting correlations are relevant to understand the metallic-like
state(s) in graphite in the quantum limit.Comment: 4 pages, 5 figure
The thermal state of molecular clouds in the Galactic Center: evidence for non-photon-driven heating
We used the Atacama Pathfinder Experiment (APEX) 12 m telescope to observe
the J_KaKc=3_03-2_02, 3_22-2_21, and 3_21-2_20 transitions of para-H_2CO at 218
GHz simultaneously to determine kinetic temperatures of the dense gas in the
central molecular zone (CMZ) of our Galaxy. The map extends over approximately
40 arcmin x 8 arcmin (~100x20 pc^2) along the Galactic plane with a linear
resolution of 1.2 pc. The strongest of the three lines, the H_2CO (3_03-2_02)
transition, is found to be widespread, and its emission shows a spatial
distribution similar to ammonia. The relative abundance of para-H_2CO is
0.5-1.2 10^{-9}, which is consistent with results from lower frequency H_2CO
absorption lines. Derived gas kinetic temperatures for individual molecular
clouds range from 50 K to values in excess of 100 K. While a systematic trend
toward (decreasing) kinetic temperature versus (increasing) angular distance
from the Galactic center (GC) is not found, the clouds with highest temperature
(T_kin > 100 K) are all located near the nucleus. For the molecular gas outside
the dense clouds, the average kinetic temperature is 65+/-10 K. The high
temperatures of molecular clouds on large scales in the GC region may be driven
by turbulent energy dissipation and/or cosmic-rays instead of photons. Such a
non-photon-driven thermal state of the molecular gas provides an excellent
template for the more distant vigorous starbursts found in ultraluminous
infrared galaxies (ULIRGs).Comment: 23 pages, 11 figures, A&A in pres
Population-specific signatures of intra-individual mitochondrial DNA heteroplasmy and their potential evolutionary advantages
Heteroplasmy is the existence of more than one mitochondrial DNA (mtDNA) variant within a cell. The evolutionary mechanisms of heteroplasmy are not fully understood, despite being a very common phenomenon. Here we combined heteroplasmy measurements using high throughput sequencing on green turtles (Chelonia mydas) with simulations to understand how heteroplasmy modulates population diversity across generations and under different demographic scenarios. We found heteroplasmy to be widespread in all individuals analysed, with consistent signal in individuals across time and tissue. Significant shifts in haplotype composition were found from mother to offspring, signalling the effect of the cellular bottleneck during oogenesis as included in the model. Our model of mtDNA inheritance indicated that heteroplasmy favoured the increase of population diversity through time and buffered against population bottlenecks, thus indicating the importance of this phenomenon in species with reduced population sizes and frequent population bottlenecks like marine turtles. Individuals with recent haplotypes showed higher levels of heteroplasmy than the individuals with ancient haplotypes, suggesting a potential advantage of maintaining established copies when new mutations arise. We recommend using heteroplasmy through high throughput sequencing in marine turtles, as well as other wildlife populations, for diversity assessment, population genetics, and mixed stock analysis
Boson stars in massive dilatonic gravity
We study equilibrium configurations of boson stars in the framework of a
class scalar-tensor theories of gravity with massive gravitational scalar
(dilaton). In particular we investigate the influence of the mass of the
dilaton on the boson star structure. We find that the masses of the boson stars
in presence of dilaton are close to those in general relativity and they are
sensitive to the ratio of the boson mass to the dilaton mass within a typical
few percent. It turns out also that the boson star structure is mainly
sensitive to the mass term of the dilaton potential rather to the exact form of
the potential.Comment: 9 pages, latex, 9 figures, one figure dropped, new comments added,
new references added, typos correcte
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