8,424 research outputs found
Nanophotonic hybridization of narrow atomic cesium resonances and photonic stop gaps of opaline nanostructures
We study a hybrid system consisting of a narrowband atomic optical resonance
and the long-range periodic order of an opaline photonic nanostructure. To this
end, we have infiltrated atomic cesium vapor in a thin silica opal photonic
crystal. With increasing temperature, the frequencies of the opal's
reflectivity peaks shift down by >20% due to chemical reduction of the silica.
Simultaneously, the photonic bands and gaps shift relative to the fixed
near-infrared cesium D1 transitions. As a result the narrow atomic resonances
with high finesse (f/df=8E5) dramatically change shape from a usual dispersive
shape at the blue edge of a stop gap, to an inverted dispersion lineshape at
the red edge of a stop gap. The lineshape, amplitude, and off-resonance
reflectivity are well modeled with a transfer-matrix model that includes the
dispersion and absorption of Cs hyperfine transitions and the
chemically-reduced opal. An ensemble of atoms in a photonic crystal is an
intriguing hybrid system that features narrow defect-like resonances with a
strong dispersion, with potential applications in slow light, sensing and
optical memory.Comment: 8 pages, 6 figure
Constraints on the Growth and Spin of the Supermassive Black Hole in M32 From High Cadence Visible Light Observations
We present 1-second cadence observations of M32 (NGC221) with the CHIMERA
instrument at the Hale 200-inch telescope of the Palomar Observatory. Using
field stars as a baseline for relative photometry, we are able to construct a
light curve of the nucleus in the g-prime and r-prime band with 1sigma=36
milli-mag photometric stability. We derive a temporal power spectrum for the
nucleus and find no evidence for a time-variable signal above the noise as
would be expected if the nuclear black hole were accreting gas. Thus, we are
unable to constrain the spin of the black hole although future work will use
this powerful instrument to target more actively accreting black holes. Given
the black hole mass of (2.5+/-0.5)*10^6 Msun inferred from stellar kinematics,
the absence of a contribution from a nuclear time-variable signal places an
upper limit on the accretion rate which is 4.6*10^{-8} of the Eddington rate, a
factor of two more stringent than past upper limits from HST. The low mass of
the black hole despite the high stellar density suggests that the gas liberated
by stellar interactions was primarily at early cosmic times when the low-mass
black hole had a small Eddington luminosity. This is at least partly driven by
a top-heavy stellar initial mass function at early cosmic times which is an
efficient producer of stellar mass black holes. The implication is that
supermassive black holes likely arise from seeds formed through the coalescence
of 3-100 Msun mass black holes that then accrete gas produced through stellar
interaction processes.Comment: 8 pages, 3 figures, submitted to the Astrophysical Journal, comments
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Physical disruption of intervertebral disc promotes cell clustering and a degenerative phenotype
© 2019, The Author(s). To test the hypothesis that physical disruption of an intervertebral disc disturbs cell-matrix binding, leading to cell clustering and increased expression of matrix degrading enzymes that contribute towards degenerative disc cell phenotype. Lumbar disc tissue was removed at surgery from 21 patients with disc herniation, 11 with disc degeneration, and 8 with adolescent scoliosis. 5 μm sections were examined with histology, and 30-µm sections by confocal microscopy. Antibodies were used against integrin α5beta1, matrix metalloproteinases (MMP) 1, MMP-3, caspase 3, and denatured collagen types I and II. Spatial associations were sought between cell clustering and various degenerative features. An additional, 11 non-herniated human discs were used to examine causality: half of each specimen was cultured in a manner that allowed free ‘unconstrained’ swelling (similar to a herniated disc in vivo), while the other half was cultured within a perspex ring that allowed ‘constrained’ swelling. Changes were monitored over 36 h using live-cell imaging. 1,9-Di-methyl methylene blue (DMMB) assay for glycosaminoglycan loss was carried out from tissue medium. Partially constrained specimens showed little swelling or cell movement in vitro. In contrast, unconstrained swelling significantly increased matrix distortion, glycosaminoglycan loss, exposure of integrin binding sites, expression of MMPs 1 and 3, and collagen denaturation. In the association studies, herniated disc specimens showed changes that resembled unconstrained swelling in vitro. In addition, they exhibited increased cell clustering, apoptosis, MMP expression, and collagen denaturation compared to ‘control’ discs. Results support our hypothesis. Further confirmation will require longitudinal animal experiments
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Assessing children's swallowing: Parent and professional perceptions
Purpose-For infants and children who have difficulties with eating, drinking and swallowing (dysphagia), there are significant health risks that include aspiration (food and fluid entering the lungs) and poor growth. Videofluoroscopy is often the instrumental method of assessment used to exclude or confirm aspiration. The purpose of this paper is to investigate parental and referrer perceptions of the reasons for and the outcomes of videofluoroscopy.
Design/methodology/approach-Data were gathered through the use of structured telephone interviews before and after videofluoroscopy.
Findings-Four key themes emerged: first, the importance of identifying specifically the problems with swallowing; second, understanding the rationale for videofluoroscopy; third, preparing a child for videofluoroscopy; and fourth, using videofluoroscopy to inform management. Referrers used videofluoroscopy to confirm their concerns about a child's ability to swallow safely.
Practical implications-Parents understood that the purpose of videofluoroscopy was to identify specific swallowing difficulties. They reported anxieties with managing the child's positioning during the procedure and whether the child would eat. They also had concerns about outcomes from the study. Some of these issues raise questions about the true value and benefits of videofluoroscopy.
Originality/value-This is the first study that considers parent views of an instrumental assessment. For some parents of children with learning disabilities, mealtimes are an important social occasion. Further studies that focus on decision making about children with learning disabilities who find feeding difficult are warranted as parents feel loss and disempowerment when decisions are made about non-oral feeding
Compton Scattering in Ultra-Strong Magnetic Fields: Numerical and Analytical Behavior in the Relativistic Regime
This paper explores the effects of strong magnetic fields on the Compton
scattering of relativistic electrons. Recent studies of upscattering and energy
loss by relativistic electrons that have used the non-relativistic, magnetic
Thomson cross section for resonant scattering or the Klein-Nishina cross
section for non-resonant scattering do not account for the relativistic quantum
effects of strong fields ( G). We have derived a
simplified expression for the exact QED scattering cross section for the
broadly-applicable case where relativistic electrons move along the magnetic
field. To facilitate applications to astrophysical models, we have also
developed compact approximate expressions for both the differential and total
polarization-dependent cross sections, with the latter representing well the
exact total QED cross section even at the high fields believed to be present in
environments near the stellar surfaces of Soft Gamma-Ray Repeaters and
Anomalous X-Ray Pulsars. We find that strong magnetic fields significantly
lower the Compton scattering cross section below and at the resonance, when the
incident photon energy exceeds in the electron rest frame. The cross
section is strongly dependent on the polarization of the final scattered
photon. Below the cyclotron fundamental, mostly photons of perpendicular
polarization are produced in scatterings, a situation that also arises above
this resonance for sub-critical fields. However, an interesting discovery is
that for super-critical fields, a preponderance of photons of parallel
polarization results from scatterings above the cyclotron fundamental. This
characteristic is both a relativistic and magnetic effect not present in the
Thomson or Klein-Nishina limits.Comment: AASTeX format, 31 pages included 7 embedded figures, accepted for
publication in The Astrophysical Journa
Impacts of climate change on the body size of horse mackerel in the North Sea
Clear biogeographic trends persist in the body sizes of individuals in marine communities, with smaller species and individuals within species found in warmer waters. Based on this trend (Bergmann’s Rule), communities undergoing warming at a given location are likely to become more representative of body sizes seen in warmer waters. Using fisheries independent North Sea survey data with established catchability corrections, we investigated the effect of 30 years of warming on average size and species size distributions. We found, as an example, that horse mackerel (Trachurus trachurus) is consistent with Bergmann’s Rule, with larger average sizes seen at higher latitudes. Over 30 years a significant decline in average size has occurred at several latitudes. Using a Eulerian (grid based) approach and dividing the North Sea into 82 1° x 1° cells, 56% of cells displayed size distributions shifting towards populations with higher proportions of smaller individuals. Changing size distribution correlated significantly with warming over the study period. Horse mackerel’s northern range is in the northern North Sea, indicating populations at species range boundaries may be most affected by further warming. This finding warrants further work on a wider number of species. Changing body sizes and shifts in size distributions has implications for ecosystem functioning, trophic level dynamics and the value of fisheries
Remote-refocusing light-sheet fluorescence microscopy enables 3D imaging of electromechanical coupling of hiPSC-derived and adult cardiomyocytes in co-culture
Improving cardiac function through stem-cell regenerative therapy requires functional and structural integration of the transplanted cells with the host tissue. Visualizing the electromechanical interaction between native and graft cells necessitates 3D imaging with high spatio-temporal resolution and low photo-toxicity. A custom light-sheet fluorescence microscope was used for volumetric imaging of calcium dynamics in co-cultures of adult rat left ventricle cardiomyocytes and human induced pluripotent stem cell-derived cardiomyocytes. Aberration-free remote refocus of the detection plane synchronously to the scanning of the light sheet along the detection axis enabled fast dual-channel 3D imaging at subcellular resolution without mechanical sample disturbance at up to 8 Hz over a ∼300 µm × 40 µm × 50 µm volume. The two cell types were found to undergo electrically stimulated and spontaneous synchronized calcium transients and contraction. Electromechanical coupling improved with co-culture duration, with 50% of adult-CM coupled after 24 h of co-culture, compared to 19% after 4 h (p = 0.0305). Immobilization with para-nitroblebbistatin did not prevent calcium transient synchronization, with 35% and 36% adult-CM coupled in control and treated samples respectively (p = 0.91), indicating that electrical coupling can be maintained independently of mechanotransduction
Colloidal brazil nut effect in sediments of binary charged suspensions
Equilibrium sedimentation density profiles of charged binary colloidal
suspensions are calculated by computer simulations and density functional
theory. For deionized samples, we predict a colloidal ``brazil nut'' effect:
heavy colloidal particles sediment on top of the lighter ones provided that
their mass per charge is smaller than that of the lighter ones. This effect is
verifiable in settling experiments.Comment: 4 pages, 4 figure
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