8,455 research outputs found
Nonlocal hydrodynamic influence on the dynamic contact angle: Slip models versus experiment
Experiments reported by Blake et al. [Phys. Fluids. 11, 1995 (1999)] suggest that the dynamic contact angle formed between the free surface of a liquid and a moving solid boundary at a fixed contact-line speed depends on the flow field/geometry near the moving contact line. The present paper examines quantitatively whether or not it is possible to attribute this effect to bending of the free surface due to hydrodynamic stresses acting upon it and hence interpret the results in terms of the so-called ``apparent'' contact angle. It is shown that this is not the case. Numerical analysis of the problem demonstrates that, at the spatial
resolution reported in the experiments, the variations of the ``apparent'' contact angle (defined in two different ways) caused by variations in the flow field, at a fixed contact-line speed, are too small to account for the observed effect. The results clearly indicate that the actual (macroscopic) dynamic contact angle, i.e.\ the one used in fluid mechanics as a boundary condition for the equation determining the free surface shape, must be regarded as dependent not only on the contact-line speed but also on the flow field/geometry in the vicinity of the moving contact line
On-chip electrically controlled routing of photons from a single quantum dot
Electrical control of on-chip routing of photons emitted by a single InAs/GaAs self-assembled quantum dot (SAQD) is demonstrated in a photonic crystal cavity-waveguide system. The SAQD is located inside an H1 cavity, which is coupled to two photonic crystal waveguides. The SAQD emission wavelength is electrically tunable by the quantum-confined Stark effect. When the SAQD emission is brought into resonance with one of two H1 cavity modes, it is preferentially routed to the waveguide to which that mode is selectively coupled. This proof of concept provides the basis for scalable, low-power, high-speed operation of single-photon routers for use in integrated quantum photonic circuits
Brain asymmetry is encoded at the level of axon terminal morphology
Background: Functional lateralization is a conserved feature of the central nervous system (CNS). However, underlying left-right asymmetries within neural circuitry and the mechanisms by which they develop are poorly described.Results: In this study, we use focal electroporation to examine the morphology and connectivity of individual neurons of the lateralized habenular nuclei. Habenular projection neurons on both sides of the brain share a stereotypical unipolar morphology and elaborate remarkable spiraling terminal arbors in their target interpeduncular nucleus, a morphology unlike that of any other class of neuron described to date. There are two quite distinct sub-types of axon arbor that differ both in branching morphology and in their localization within the target nucleus. Critically, both arbor morphologies are elaborated by both left and right-sided neurons, but at greatly differing frequencies. We show that these differences in cell type composition account for the gross connectional asymmetry displayed by the left and right habenulae. Analysis of the morphology and projections of individual post-synaptic neurons suggests that the target nucleus has the capacity to either integrate left and right inputs or to handle them independently, potentially relaying information from the left and right habenulae within distinct downstream pathways, thus preserving left-right coding. Furthermore, we find that signaling from the unilateral, left-sided parapineal nucleus is necessary for both left and right axons to develop arbors with appropriate morphology and targeting. However, following parapineal ablation, left and right habenular neurons continue to elaborate arbors with distinct, lateralized morphologies.Conclusion: By taking the analysis of asymmetric neural circuitry to the level of single cells, we have resolved left-right differences in circuit microarchitecture and show that lateralization can be recognized at the level of the morphology and connectivity of single projection neuron axons. Crucially, the same circuitry components are specified on both sides of the brain, but differences in the ratios of different neuronal sub-types results in a lateralized neural architecture and gross connectional asymmetry. Although signaling from the parapineal is essential for the development of normal lateralization, additional factors clearly act during development to confer left-right identity upon neurons in this highly conserved circuit
Dynamical extensions for shell-crossing singularities
We derive global weak solutions of Einstein's equations for spherically
symmetric dust-filled space-times which admit shell-crossing singularities. In
the marginally bound case, the solutions are weak solutions of a conservation
law. In the non-marginally bound case, the equations are solved in a
generalized sense involving metric functions of bounded variation. The
solutions are not unique to the future of the shell-crossing singularity, which
is replaced by a shock wave in the present treatment; the metric is bounded but
not continuous.Comment: 14 pages, 1 figur
The GALEX View of "Boyajian's Star" (KIC 8462852)
The enigmatic star KIC 8462852, informally known as "Boyajian's Star", has
exhibited unexplained variability from both short timescale (days) dimming
events, and years-long fading in the Kepler mission. No single physical
mechanism has successfully explained these observations to date. Here we
investigate the ultraviolet variability of KIC 8462852 on a range of timescales
using data from the GALEX mission that occurred contemporaneously with the
Kepler mission. The wide wavelength baseline between the Kepler and GALEX data
provides a unique constraint on the nature of the variability. Using 1600
seconds of photon-counting data from four GALEX visits spread over 70 days in
2011, we find no coherent NUV variability in the system on 10-100 second or
months timescales. Comparing the integrated flux from these 2011 visits to the
2012 NUV flux published in the GALEX-CAUSE Kepler survey, we find a 3% decrease
in brightness for KIC 8462852. We find this level of variability is
significant, but not necessarily unusual for stars of similar spectral type in
the GALEX data. This decrease coincides with the secular optical fading
reported by Montet & Simon (2016). We find the multi-wavelength variability is
somewhat inconsistent with typical interstellar dust absorption, but instead
favors a R = 5.0 0.9 reddening law potentially from circumstellar
dust.Comment: 8 pages, 4 figures, ApJ Accepte
2D Monte-Carlo Radiative transfer modeling of the disk shaped secondary of Epsilon Aurigae
We present two dimensional Monte-Carlo radiative transfer models for the disk
of the eclipsing binary Aur by fitting its spectral energy
distribution from optical to the far-IR wavelengths. We also report new
observations of Aur made by AKARI in its five mid and far-IR
photometric bands and were used to construct our SED. The disk is optically
thick and has flared disk geometry containing gas and dust with a gas to dust
mass ratio of 100. We have taken the primary of the binary to be a F0Iae-type
post-AGB star and the disk is heated by a B5V hot star with a temperature of
15,000 K at the center of the disk. We take the radius of the disk to be 3.8 AU
for our models as constrained from the IR interferometric imaging observations
of the eclipsing disk. Our models imply that the disk contains grains which are
much bigger than the ISM grains (grain sizes 10 to 100). The grain
chemistry of the disk is carbonaceous and our models show that silicate and ISM
dust chemistry do not reproduce the slope of the observed SED in the mid-IR to
far-IR regions. This implies that the formation of the disk shaped secondary in
Aur system could be the result of accretion of matter and or mass
transfer from the primary which is now a F0Iae post-AGB star. It is not a
proto-planetary disk. The disk is seen nearly edge on with an inclination angle
larger than 85. We propose from our radiative transfer modeling that the
disk is not solid and have a void of 2AU radius at the center within which no
grains are present making the region nearly transparent. The disk is not
massive, its mass is derived to be less than 0.005M.Comment: 27 pages, 5 figures, 2 table
Curvature singularity of the distributional BTZ black hole geometry
For the non-rotating BTZ black hole, the distributional curvature tensor
field is found. It is shown to have singular parts proportional to a
-distribution with support at the origin. This singularity is related,
through Einstein field equations, to a point source. Coordinate invariance and
independence on the choice of differentiable structure of the results are
addressed.Comment: Latex, 7 page
High redshift X-ray cooling-core cluster associated with the luminous radio loud quasar 3C186
We present the first results from a new, deep (200ks) Chandra observation of
the X-ray luminous galaxy cluster surrounding the powerful (L ~10^47 erg/s),
high-redshift (z=1.067), compact-steep-spectrum radio-loud quasar 3C186. The
diffuse X-ray emission from the cluster has a roughly ellipsoidal shape and
extends out to radii of at least ~60 arcsec (~500 kpc). The centroid of the
diffuse X-ray emission is offset by 0.68(+/-0.11) arcsec (5.5+/-0.9 kpc) from
the position of the quasar. We measure a cluster mass within the radius at
which the mean enclosed density is 2500 times the critical density,
r_2500=283(+18/-13)kpc, of 1.02 (+0.21/-0.14)x10^14 M_sun. The gas mass
fraction within this radius is f_gas=0.129(+0.015/-0.016). This value is
consistent with measurements at lower redshifts and implies minimal evolution
in the f_gas(z) relation for hot, massive clusters at 0<z<1.1. The measured
metal abundance of 0.42(+0.08/-0.07) Solar is consistent with the abundance
observed in other massive, high redshift clusters. The spatially-resolved
temperature profile for the cluster shows a drop in temperature, from kT~8 keV
to kT~3 keV, in its central regions that is characteristic of cooling core
clusters. This is the first spectroscopic identification of a cooling core
cluster at z>1. We measure cooling times for the X-ray emitting gas at radii of
50 kpc and 25 kpc of 1.7(+/-0.2)x10^9 years and 7.5(+/-2.6)x 10^8 years, as
well as a nominal cooling rate (in the absence of heating) of
400(+/-190)M_sun/year within the central 100 kpc. In principle, the cooling gas
can supply enough fuel to support the growth of the supermassive black hole and
to power the luminous quasar. The radiative power of the quasar exceeds by a
factor of 10 the kinematic power of the central radio source, suggesting that
radiative heating may be important at intermittent intervals in cluster cores.Comment: 15 pages, 9 figures, ApJ in pres
Single-photon electroluminescence for on-chip quantum networks
An electrically driven single-photon source has been monolithically integrated with nano-photonic circuitry. Electroluminescent emission from a single InAs/GaAs quantum dot (QD) is channelled through a suspended nanobeam waveguide. The emission line has a linewidth of below 6 μeV, demonstrating the ability to have a high coherence, electrically driven, waveguide coupled QD source. The single-photon nature of the emission is verified by g(2) (τ) correlation measurements. Moreover, in a cross-correlation experiment, with emission collected from the two ends of the waveguide, the emission and propagation of single photons from the same QD is confirmed. This work provides the basis for the development of electrically driven on-chip single-photon sources, which can be readily coupled to waveguide filters, directional couplers, phase shifters, and other elements of quantum photonic networks
Activated c-SRC in ductal carcinoma in situ correlates with high tumour grade, high proliferation and HER2 positivity
Overexpression and/or activity of c-Src non-receptor tyrosine kinase is associated with progression of several human epithelial cancers including breast cancer. c-Src activity in ‘pure' ductal carcinoma in situ (DCIS) was measured to assess whether this predicts recurrence and/or correlates with HER2 expression and other clinical parameters. Activated c-Src levels were evaluated in DCIS biopsies from 129 women, with median follow-up at 60 months. High levels of activated c-Src correlated with HER2 positivity, high tumour grade, comedo necrosis and elevated epithelial proliferation. In univariate analysis, high activated c-Src level associated with lower recurrence-free survival at 5 years (P=0.011). Thus, high c-Src activity may identify a subset of DCIS with high risk of recurrence or progression to invasive cancer where therapeutics targeting c-Src may benefit this patient subset
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