23,389 research outputs found
A Presheaf Interpretation of the Generalized Freyd Conjecture
We give a generalized version of the Freyd conjecture and a way to think
about a possible proof. The essential point is to describe an elementary formal
reduction of the question that holds in any triangulated category. There are no
new results, but at least one known example drops out quite trivially.Comment: 8 pages; formerly titled "Thinking about the Freyd conjecture
Splitting between Bright and Dark excitons in Transition Metal Dichalcogenide Monolayers
The optical properties of transition metal dichalcogenide monolayers such as
the two-dimensional semiconductors MoS and WSe are dominated by
excitons, Coulomb bound electron-hole pairs. The light emission yield depends
on whether the electron-hole transitions are optically allowed (bright) or
forbidden (dark). By solving the Bethe Salpeter Equation on top of wave
functions in density functional theory calculations, we determine the sign and
amplitude of the splitting between bright and dark exciton states. We evaluate
the influence of the spin-orbit coupling on the optical spectra and clearly
demonstrate the strong impact of the intra-valley Coulomb exchange term on the
dark-bright exciton fine structure splitting.Comment: 6 pages, 2 figure
Time resolved spectroscopy of dust and gas from extrasolar planetesimals orbiting WD 1145+017
Multiple long and variable transits caused by dust from possibly
disintegrating asteroids were detected in light curves of WD 1145+017. We
present time-resolved spectroscopic observations of this target with QUCAM CCDs
mounted in the Intermediate dispersion Spectrograph and Imaging System at the
4.2-m William Herschel Telescope in two different spectral arms: the blue arm
covering 3800-4025 {\AA} and the red arm covering 7000-7430 {\AA}. When
comparing individual transits in both arms, our observations show with 20
{\sigma} significance an evident colour difference between the in- and
out-of-transit data of the order of 0.05-0.1 mag, where transits are deeper in
the red arm. We also show with > 6 {\sigma} significance that spectral lines in
the blue arm are shallower during transits than out-of-transit. For the
circumstellar lines it also appears that during transits the reduction in
absorption is larger on the red side of the spectral profiles. Our results
confirm previous findings showing the u'-band excess and a decrease in line
absorption during transits. Both can be explained by an opaque body blocking a
fraction of the gas disc causing the absorption, implying that the absorbing
gas is between the white dwarf and the transiting objects. Our results also
demonstrate the capability of EMCCDs to perform high-quality time resolved
spectroscopy of relatively faint targets.Comment: 9 pages, 5 figures. Accepted to MNRA
PPAR Gamma Activity and Control of Bone Mass in Skeletal Unloading
Bone loss occuring with unloading is associated with decreased osteoblastogenesis and increased bone marrow adipogenesis, resulting in bone loss and decreased bone formation. Here, we review the present knowledge on the role of PPARγ in the control of osteoblastogenesis and bone mass in skeletal unloading. We showed that PPARγ positively promotes adipogenesis and negatively regulates osteoblast differentiation of bone marrow stromal cells in unloading, resulting in bone loss. Manipulation of PPARγ2 expression by exogenous TGF-β2 inhibits the exaggerated adipogenesis and corrects the balance between osteoblastogenesis and adipogenesis induced by unloading, leading to prevention of bone loss. This shows that PPARγ plays an important role in the control of bone mass in unloaded bone. Moreover, this opens the possibility that manipulation of PPARγ may correct the balance between osteoblastogenesis and adipogenesis and prevent bone loss, which may have potential implications in the treatment of bone loss in clinical conditions
Anomalous dispersion of optical phonons at the neutral-ionic transition: Evidence from diffuse X-ray scattering
Diffuse X-ray data for mixed stack organic charge-transfer crystals
approaching the neutral-ionic phase transition can be quantitatively explained
as due to the softening of the optical phonon branch. The interpretation is
fully consistent with vibrational spectra, and underlines the importance of
electron-phonon coupling in low-dimensional systems with delocalized electrons.Comment: 4 pages, 4 figure
A COMPARISON OF SELECTED MILK INDICATORS IN ORGANIC HERDS WITH CONVENTIONAL HERD AS REFERENCE
In a historical sense, current organic farming is an old-new
alternative under changed world conditions. Organic dairying
(O) is an alternative of friendly use of the environment in
time of presupposed global climate changes. Potential impact
of organic farming on raw cow-milk quality, composition and
properties, as conpared to conventional milk production (C),
were evaluatedin this paper on the basis of selectedm ilk indicators
(MIs). Total solids, whey volume, pH of milk fermentation
ability (FAM-pH), FAM streptococci, FAM noble lactic acid
bacteria, I and Cu were higher in C milk (P0.05) were observed in pH, rennet coagulation time, curd quality, FAM lactobacilli and streptococci/lactobacilli, Na, Mn and Zn. In general, the differences were a little more advantageous for O milk from both technological and nutritional point of view, particularly because of AS (0.461 .81m m), FAM-T (27.3 4.6 ) , Ca (1172 < l257 mg.kg-1)P, ( 950 < l004 mg. kg-1) and Mg 107.4<ll2.0mg.kg{) results. Organic milk can also produce better environment for yoghurt fermentation. Nevertheless, the results obtained should not be overestimated as both sources produced milk of good quality. Additional results are
needed to prove organic milk benefits
Aggregation of frictional particles due to capillary attraction
Capillary attraction between identical millimeter sized spheres floating at a
liquid-air interface and the resulting aggregation is investigated at low
Reynolds number. We show that the measured capillary forces between two spheres
as a function of distance can be described by expressions obtained using the
Nicolson approximation at low Bond numbers for far greater particle sizes than
previously assumed. We find that viscous hydrodynamics interactions between the
spheres needs to be included to describe the dynamics close to contact. We then
consider the aggregates formed when a third sphere is added after the initial
two spheres are already in contact. In this case, we find that linear
superposition of capillary forces describes the observed approach qualitatively
but not quantitatively. Further, we observe an angular dependence of the
structure due to a rapid decrease of capillary force with distance of
separation which has a tendency to align the particles before contact. When the
three particles come in contact, they may preserve their shape or rearrange to
form an equilateral triangle cluster - the lowest energy state - depending on
the competition between attraction between particles and friction. Using these
observations, we demonstrate that a linear particle chain can be built from
frictional particles with capillary attraction.Comment: accepted for Physical Review
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