267 research outputs found
Relaxation of a Collisionless System and the Transition to a New Equilibrium Velocity Distribution
In this paper, we present our conclusions from the numerical study of the
collapse of a destabilized collisionless stellar system. We use both direct
integration of the Vlasov-Poisson equations and an N-body tree code to obtain
our results, which are mutually confirmed. We find that spherical and
moderately nonspherical collapse configurations evolve to new equilibrium
configurations in which the velocity distribution approaches a Gaussian form,
at least in the central regions. The evolution to this state has long been an
open question, and in this work we are able to clarify the process responsible
and to support predictions made from statistical considerations (Lynden-Bell
1967; Nakamura 2000). The simulations of merging N-body systems show a
transition to a Gaussian velocity distribution that is increasingly suppressed
as the initial separation of centres is increased. Possible reasons for this
are discussed.Comment: 25 pages, LaTeX. Accepted for publication in Ap
S(C)ENTINEL - monitoring automated vehicles with olfactory reliability displays
Overreliance in technology is safety-critical and it is assumed that this could have been a main cause of severe accidents with automated vehicles. To ease the complex task of per- manently monitoring vehicle behavior in the driving en- vironment, researchers have proposed to implement relia- bility/uncertainty displays. Such displays allow to estimate whether or not an upcoming intervention is likely. However, presenting uncertainty just adds more visual workload on drivers, who might also be engaged in secondary tasks. We suggest to use olfactory displays as a potential solution to communicate system uncertainty and conducted a user study (N=25) in a high-fidelity driving simulator. Results of the ex- periment (conditions: no reliability display, purely visual reliability display, and visual-olfactory reliability display) comping both objective (task performance) and subjective (technology acceptance model, trust scales, semi-structured interviews) measures suggest that olfactory notifications could become a valuable extension for calibrating trust in automated vehicles
Quasi-equilibria in one-dimensional self-gravitating many body systems
The microscopic dynamics of one-dimensional self-gravitating many-body
systems is studied. We examine two courses of the evolution which has the
isothermal and stationary water-bag distribution as initial conditions. We
investigate the evolution of the systems toward thermal equilibrium. It is
found that when the number of degrees of freedom of the system is increased,
the water-bag distribution becomes a quasi-equilibrium, and also the
stochasticity of the system reduces. This results suggest that the phase space
of the system is effectively not ergodic and the system with large degreees of
freedom approaches to the near-integrable one.Comment: 21pages + 7 figures (available upon request), revtex, submitted to
Physical Review
Hubble Space Telescope Observations of cD Galaxies and their Globular Cluster Systems
We have used WFPC2 on the Hubble Space Telescope to obtain F450W and F814W
images of four cD galaxies (NGC 541 in Abell 194, NGC 2832 in Abell 779, NGC
4839 in Abell 1656 and NGC 7768 in Abell 2666) in the range 5400 < cz < 8100 km
s^{-1}. For NGC 541, the HST data are supplemented by ground-based B and I
images obtained with the FORS1 on the VLT. We present surface brightness and
color profiles for each of the four galaxies, confirming their classification
as cD galaxies. Isophotal analyses reveal the presence of subarcsecond-scale
dust disks in the nuclei of NGC 541 and NGC 7768. Despite the extreme nature of
these galaxies in terms of spatial extent and luminosity, our analysis of their
globular cluster systems reveals no anomalies in terms of specific frequencies,
metallicity gradients, average metallicities, or the metallicity offset between
the globulars and the host galaxy. We show that the latter offset appears
roughly constant at \Delta [Fe/H] ~ 0.8 dex for early-type galaxies spanning a
luminosity range of roughly four orders of magnitude. We combine the globular
cluster metallicity distributions with an empirical technique described in a
series of earlier papers to investigate the form of the protogalactic mass
spectrum in these cD galaxies. We find that the observed GC metallicity
distributions are consistent with those expected if cD galaxies form through
the cannibalism of numerous galaxies and protogalactic fragments which formed
their stars and globular clusters before capture and disruption. However, the
properties of their GC systems suggest that dynamical friction is not the
primary mechanism by which these galaxies are assembled. We argue that cDs
instead form rapidly, via hierarchical merging, prior to cluster virialization.Comment: 36 pages, 20 postscript figures, uses emulateapj. Accepted for
publication in the Astronomical Journa
Optical polarization properties of (11–22) semi-polar InGaN LEDs with a wide spectral range
Electroluminescence polarization measurements have been performed on a series of semi-polar InGaN light emitting diodes (LEDs) grown on semi-polar (11–22) templates with a high crystal quality. The emission wavelengths of these LEDs cover a wide spectral region from 443 to 555 nm. A systematic study has been carried out in order to investigate the influence of both indium content and injection current on polarization properties, where a clear polarization switching at approximately 470 nm has been observed. The shortest wavelength LED (443 nm) exhibits a positive 0.15 polarization degree, while the longest wavelength LED (555 nm) shows a negative −0.33 polarization degree. All the longer wavelength LEDs with an emission wavelength above 470 nm exhibit negative polarization degrees, and they further demonstrate that the dependence of polarization degree on injection current enhances with increasing emission wavelength. Moreover, the absolute value of the polarization degree decreases with increasing injection current. In contrast, the polarization degree of the 443 nm blue LED remains constant with changing injection current. This discrepancy can be attributed to a significant difference in the density of states (DOS) of the valence subbands
Fasting and High-Fat Diet Alter Histone Deacetylase Expression in the Medial Hypothalamus
Increasing attention is now being given to the epigenetic regulation of animal and human behaviors including the stress response and drug addiction. Epigenetic factors also influence feeding behavior and metabolic phenotypes, such as obesity and insulin sensitivity. In response to fasting and high-fat diets, the medial hypothalamus changes the expression of neuropeptides regulating feeding, metabolism, and reproductive behaviors. Histone deacetylases (HDACs) are involved in the epigenetic control of gene expression and alter behavior in response to a variety of environmental factors. Here, we examined the expression of HDAC family members in the medial hypothalamus of mice in response to either fasting or a high-fat diet. In response to fasting, HDAC3 and −4 expression levels increased while HDAC10 and −11 levels decreased. Four weeks on a high-fat diet resulted in the increased expression of HDAC5 and −8. Moreover, fasting decreased the number of acetylated histone H3- and acetylated histone H4-positive cells in the ventrolateral subdivision of the ventromedial hypothalamus. Therefore, HDACs may be implicated in altered gene expression profiles in the medial hypothalamus under different metabolic states
Topical Review: Development of overgrown semi-polar GaN for high efficiency green/yellow emission
The most successful example of large lattice-mismatched epitaxial growth of semiconductors is
the growth of III-nitrides on sapphire, leading to the award of the Nobel Prize in 2014 and great
success in developing InGaN-based blue emitters. However, the majority of achievements in the
field of III-nitride optoelectronics are mainly limited to polar GaN grown on c-plane (0001)
sapphire. This polar orientation poses a number of fundamental issues, such as reduced quantum
efficiency, efficiency droop, green and yellow gap in wavelength coverage, etc. To date, it is still
a great challenge to develop longer wavelength devices such as green and yellow emitters. One
clear way forward would be to grow III-nitride device structures along a semi-/non-polar
direction, in particular, a semi-polar orientation, which potentially leads to both enhanced indium
incorporation into GaN and reduced quantum confined Stark effects. This review presents recent
progress on developing semi-polar GaN overgrowth technologies on sapphire or Si substrates,
the two kinds of major substrates which are cost-effective and thus industry-compatible, and also
demonstrates the latest achievements on electrically injected InGaN emitters with long emission
wavelengths up to and including amber on overgrown semi-polar GaN. Finally, this review
presents a summary and outlook on further developments for semi-polar GaN based
optoelectronics
Significance of Twist expression and its association with E-cadherin in esophageal squamous cell carcinoma
in esophageal squamous cell carcinom
NGC 1399: a complex dynamical case
Evidence for a disturbed velocity structure in the outer regions of the
galaxy NGC1399 comes from a re-analysis of the planetary nebulae data from
Arnaboldi et al. (1994). We find a strong rotation along a P.A.=140 degrees for
R<=140'' which is followed by a rapid drop off at larger radii, where the
velocity dispersion starts to increase. This kinematical behavior can be
interpreted as an indication for an interaction scenario. Interaction is
advocated in previous analysis of the halo regions of this system, based on
different dynamical tracers such as globular clusters and X-rays, but in all
these studies the mass distribution is derived under the equilibrium
hypothesis, which is not appropriate when an interaction takes place. Here we
attempt a non-equilibrium dynamical analysis of NGC1399: with a simple model
and under the impulse approximation, we show that the observed kinematics is
consistent with an energy injection caused by a flyby encounter of NGC 1399
with the nearby system NGC 1404. In this approach, we find a mass-to-light
ratio, M/L_B=26 within R=400'', which is about half of that requested when
equilibrium is assumed, i.e. M/L_B=56.Comment: 10 pages, 15 figures, accepted for pubblication in A&
The Cell Signaling Adaptor Protein EPS-8 Is Essential for C. elegans Epidermal Elongation and Interacts with the Ankyrin Repeat Protein VAB-19
The epidermal cells of the C. elegans embryo undergo coordinated cell shape changes that result in the morphogenetic process of elongation. The cytoskeletal ankyrin repeat protein VAB-19 is required for cell shape changes and localizes to cell-matrix attachment structures. The molecular functions of VAB-19 in this process are obscure, as no previous interactors for VAB-19 have been described.In screens for VAB-19 binding proteins we identified the signaling adaptor EPS-8. Within C. elegans epidermal cells, EPS-8 and VAB-19 colocalize at cell-matrix attachment structures. The central domain of EPS-8 is necessary and sufficient for its interaction with VAB-19. eps-8 null mutants, like vab-19 mutants, are defective in epidermal elongation and in epidermal-muscle attachment. The eps-8 locus encodes two isoforms, EPS-8A and EPS-8B, that appear to act redundantly in epidermal elongation. The function of EPS-8 in epidermal development involves its N-terminal PTB and central domains, and is independent of its C-terminal SH3 and actin-binding domains. VAB-19 appears to act earlier in the biogenesis of attachment structures and may recruit EPS-8 to these structures.EPS-8 and VAB-19 define a novel pathway acting at cell-matrix attachments to regulate epithelial cell shape. This is the first report of a role for EPS-8 proteins in cell-matrix attachments. The existence of EPS-8B-like isoforms in Drosophila suggests this function of EPS-8 proteins could be conserved among other organisms
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