611 research outputs found
Bioinspired low-frequency material characterisation
New-coded signals, transmitted by high-sensitivity broadband transducers in the 40–200 kHz range, allow subwavelength material discrimination and thickness determination of polypropylene, polyvinylchloride, and brass samples. Frequency domain spectra enable simultaneous measurement of material properties including longitudinal sound velocity and the attenuation constant as well as thickness measurements. Laboratory test measurements agree well with model results, with sound velocity prediction errors of less than 1%, and thickness discrimination of at least wavelength/15. The resolution of these measurements has only been matched in the past through methods that utilise higher frequencies. The ability to obtain the same resolution using low frequencies has many advantages, particularly when dealing with highly attenuating materials. This approach differs significantly from past biomimetic approaches where actual or simulated animal signals have been used and consequently has the potential for application in a range of fields where both improved penetration and high resolution are required, such as nondestructive testing and evaluation, geophysics, and medical physics
Third wave of asbestos-related disease from secondary use of asbestos: A case report from industry
An occupational health survey conducted in a workshop in which asbestos cement was used showed initial atmospheric asbestos levels ranging frm 1,9 to 27,5 fibres per millilitre of air. Radiological changes suggestive of asbestos-related pleural disease were found in 2 workers (2,5%), while 3 (3,8%) had borderline features of asbestosis. The survey confinned that uncontrolled and hazardous use of asbestos continues in industry despite public awareness of its dangers and the Asbestos Regulations of 1987
A low power photoemission source for electrons on liquid helium
Electrons on the surface of liquid helium are a widely studied system that
may also provide a promising method to implement a quantum computer. One
experimental challenge in these studies is to generate electrons on the helium
surface in a reliable manner without heating the cryo-system. An electron
source relying on photoemission from a zinc film has been previously described
using a high power continuous light source that heated the low temperature
system. This work has been reproduced more compactly by using a low power
pulsed lamp that avoids any heating. About 5e3 electrons are collected on 1
cm^2 of helium surface for every pulse of light. A time-resolved experiment
suggests that electrons are either emitted over or tunnel through the 1eV
barrier formed by the thin superfluid helium film on the zinc surface. No
evidence of trapping or bubble formation is seen.Comment: 9 pages, 3 figures, submitted to J. Low Temp. Phy
Rapid X-ray Variability of Seyfert 1 Galaxies
The rapid and seemingly random fluctuations in X-ray luminosity of Seyfert
galaxies provided early support for the standard model in which Seyferts are
powered by a supermassive black hole fed from an accretion disc. However, since
EXOSAT there has been little opportunity to advance our understanding of the
most rapid X-ray variability. Observations with XMM-Newton have changed this.
We discuss some recent results obtained from XMM-Newton observations of Seyfert
1 galaxies. Particular attention will be given to the remarkable similarity
found between the timing properties of Seyferts and black hole X-ray binaries,
including the power spectrum and the cross spectrum (time delays and
coherence), and their implications for the physical processes at work in
Seyferts.Comment: To appear in From X-ray Binaries to Quasars: Black Hole Accretion on
All Mass Scales, ed. T. J. Maccarone, R. P. Fender, and L. C. Ho (Dordrecht:
Kluwer
Numerical Solutions of ideal two-fluid equations very closed to the event horizon of Schwarzschild black hole
The 3+1 formalism of Thorne, Price and Macdonald has been used to derive the
linear two-fluid equations describing transverse and longitudinal waves
propagating in the two-fluid ideal collisionless plasmas surrounding a
Schwarzschild black hole. The plasma is assumed to be falling in radial
direction toward the event horizon. The relativistic two-fluid equations have
been reformulate, in analogy with the special relativistic formulation as
explained in an earlier paper, to take account of relativistic effects due to
the event horizon. Here a WKB approximation is used to derive the local
dispersion relation for these waves and solved numerically for the wave number
k.Comment: 16 pages, 15 figures. arXiv admin note: text overlap with
arXiv:0902.3766, arXiv:0807.459
Serum glial fibrillary acidic protein: a neuromyelitis optica spectrum disorder biomarker
OBJECTIVE: Blood tests to monitor disease activity, attack severity, or treatment impact in neuromyelitis optica spectrum disorder (NMOSD) have not been developed. This study investigated the relationship between serum glial fibrillary acidic protein (sGFAP) concentration and NMOSD activity and assessed the impact of inebilizumab treatment. METHODS: N-MOmentum was a prospective, multicenter, double-blind, placebo-controlled, randomized clinical trial in adults with NMOSD. sGFAP levels were measured by single-molecule arrays (SIMOA) in 1,260 serial and attack-related samples from 215 N-MOmentum participants (92% aquaporin 4-immunoglobulin G-seropositive) and in control samples (from healthy donors and patients with relapsing-remitting multiple sclerosis). RESULTS: At baseline, 62 participants (29%) exhibited high sGFAP concentrations (≥170 pg/ml; ≥2 standard deviations above healthy donor mean concentration) and were more likely to experience an adjudicated attack than participants with lower baseline concentrations (hazard ratio [95% confidence interval], 3.09 [1.6-6.1], p = 0.001). Median (interquartile range [IQR]) concentrations increased within 1 week of an attack (baseline: 168.4, IQR = 128.9-449.7 pg/ml; attack: 2,160.1, IQR = 302.7-9,455.0 pg/ml, p = 0.0015) and correlated with attack severity (median fold change from baseline [FC], minor attacks: 1.06, IQR = 0.9-7.4; major attacks: 34.32, IQR = 8.7-107.5, p = 0.023). This attack-related increase in sGFAP occurred primarily in placebo-treated participants (FC: 20.2, IQR = 4.4-98.3, p = 0.001) and was not observed in inebilizumab-treated participants (FC: 1.1, IQR = 0.8-24.6, p > 0.05). Five participants (28%) with elevated baseline sGFAP reported neurological symptoms leading to nonadjudicated attack assessments. INTERPRETATION: Serum GFAP may serve as a biomarker of NMOSD activity, attack risk, and treatment effects. ANN NEUROL 2021;89:895-910
Supersymmetric Unification Without Low Energy Supersymmetry And Signatures for Fine-Tuning at the LHC
The cosmological constant problem is a failure of naturalness and suggests
that a fine-tuning mechanism is at work, which may also address the hierarchy
problem. An example -- supported by Weinberg's successful prediction of the
cosmological constant -- is the potentially vast landscape of vacua in string
theory, where the existence of galaxies and atoms is promoted to a vacuum
selection criterion. Then, low energy SUSY becomes unnecessary, and
supersymmetry -- if present in the fundamental theory -- can be broken near the
unification scale. All the scalars of the supersymmetric standard model become
ultraheavy, except for a single finely tuned Higgs. Yet, the fermions of the
supersymmetric standard model can remain light, protected by chiral symmetry,
and account for the successful unification of gauge couplings. This framework
removes all the difficulties of the SSM: the absence of a light Higgs and
sparticles, dimension five proton decay, SUSY flavor and CP problems, and the
cosmological gravitino and moduli problems. High-scale SUSY breaking raises the
mass of the light Higgs to about 120-150 GeV. The gluino is strikingly long
lived, and a measurement of its lifetime can determine the ultraheavy scalar
mass scale. Measuring the four Yukawa couplings of the Higgs to the gauginos
and higgsinos precisely tests for high-scale SUSY. These ideas, if confirmed,
will demonstrate that supersymmetry is present but irrelevant for the hierarchy
problem -- just as it has been irrelevant for the cosmological constant problem
-- strongly suggesting the existence of a fine-tuning mechanism in nature.Comment: Typos and equations fixed, references adde
Low-Luminosity Accretion in Black Hole X-ray Binaries and Active Galactic Nuclei
At luminosities below a few percent of Eddington, accreting black holes
switch to a hard spectral state which is very different from the soft
blackbody-like spectral state that is found at higher luminosities. The hard
state is well-described by a two-temperature, optically thin, geometrically
thick, advection-dominated accretion flow (ADAF) in which the ions are
extremely hot (up to K near the black hole), the electrons are also
hot ( K), and thermal Comptonization dominates the X-ray
emission. The radiative efficiency of an ADAF decreases rapidly with decreasing
mass accretion rate, becoming extremely low when a source reaches quiescence.
ADAFs are expected to have strong outflows, which may explain why relativistic
jets are often inferred from the radio emission of these sources. It has been
suggested that most of the X-ray emission also comes from a jet, but this is
less well established.Comment: To appear in "From X-ray Binaries to Quasars: Black Hole Accretion on
All Mass Scales" edited by T. Maccarone, R. Fender, L. Ho, to be published as
a special edition of "Astrophysics and Space Science" by Kluwe
OC-040 A pre-endoscopy point of care test (iga/igg-deamidated gliadin peptide) as a case finding tool for coeliac diseasein secondary care
Coeliac disease (CD) is common yet underdiagnosed. 12.4% CD patients had a gastroscopy within 5 years without duodenal biopsies taken, and coeliac serology was performed in only 30% of patients with anaemia or suspected CD. A pre-endoscopy point of care test (POCT) could potentially fill this gap. We aimed to evaluate the diagnostic accuracy and acceptability of the POCT, Simtomax (IgA/IgG-deamidated gliadin peptide, Tillotts Pharma, Rheinfelden, Switzerland), in detecting CD
Relativistic Hydrodynamic Evolutions with Black Hole Excision
We present a numerical code designed to study astrophysical phenomena
involving dynamical spacetimes containing black holes in the presence of
relativistic hydrodynamic matter. We present evolutions of the collapse of a
fluid star from the onset of collapse to the settling of the resulting black
hole to a final stationary state. In order to evolve stably after the black
hole forms, we excise a region inside the hole before a singularity is
encountered. This excision region is introduced after the appearance of an
apparent horizon, but while a significant amount of matter remains outside the
hole. We test our code by evolving accurately a vacuum Schwarzschild black
hole, a relativistic Bondi accretion flow onto a black hole, Oppenheimer-Snyder
dust collapse, and the collapse of nonrotating and rotating stars. These
systems are tracked reliably for hundreds of M following excision, where M is
the mass of the black hole. We perform these tests both in axisymmetry and in
full 3+1 dimensions. We then apply our code to study the effect of the stellar
spin parameter J/M^2 on the final outcome of gravitational collapse of rapidly
rotating n = 1 polytropes. We find that a black hole forms only if J/M^2<1, in
agreement with previous simulations. When J/M^2>1, the collapsing star forms a
torus which fragments into nonaxisymmetric clumps, capable of generating
appreciable ``splash'' gravitational radiation.Comment: 17 pages, 14 figures, submitted to PR
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