13,547 research outputs found
The Equivalence Principle in the Non-baryonic Regime
We consider the empirical validity of the equivalence principle for
non-baryonic matter. Working in the context of the TH\epsilon\mu formalism, we
evaluate the constraints experiments place on parameters associated with
violation of the equivalence principle (EVPs) over as wide a sector of the
standard model as possible. Specific examples include new parameter constraints
which arise from torsion balance experiments, gravitational red shift,
variation of the fine structure constant, time-dilation measurements, and
matter/antimatter experiments. We find several new bounds on EVPs in the
leptonic and kaon sectors.Comment: 22 pages, late
Near-Infrared Molecular Hydrogen Emission from the Central Regions of Galaxies: Regulated Physical Conditions in the Interstellar Medium
The central regions of many interacting and early-type spiral galaxies are
actively forming stars. This process affects the physical and chemical
properties of the local interstellar medium as well as the evolution of the
galaxies. We observed near-infrared H2 emission lines: v=1-0 S(1), 3-2 S(3),
1-0 S(0), and 2-1 S(1) from the central ~1 kpc regions of the archetypical
starburst galaxies, M82 and NGC 253, and the less dramatic but still vigorously
star-forming galaxies, NGC 6946 and IC 342. Like the far-infrared continuum
luminosity, the near-infrared H2 emission luminosity can directly trace the
amount of star formation activity because the H2 emission lines arise from the
interaction between hot and young stars and nearby neutral clouds. The observed
H2 line ratios show that both thermal and non-thermal excitation are
responsible for the emission lines, but that the great majority of the
near-infrared H2 line emission in these galaxies arises from energy states
excited by ultraviolet fluorescence. The derived physical conditions, e.g.,
far-ultraviolet radiation field and gas density, from [C II] and [O I] lines
and far-infrared continuum observations when used as inputs to
photodissociation models, also explain the luminosity of the observed H2 v=1-0
S(1) line. The ratio of the H2 v=1-0 S(1) line to far-IR continuum luminosity
is remarkably constant over a broad range of galaxy luminosities; L_H2/L_FIR =
about 10^{-5}, in normal late-type galaxies (including the Galactic center), in
nearby starburst galaxies, and in luminous IR galaxies (LIRGs: L_FIR > 10^{11}
L_sun). Examining this constant ratio in the context of photodissociation
region models, we conclude that it implies that the strength of the incident UV
field on typical molecular clouds follows the gas density at the cloud surface.Comment: Accepted for ApJ, 24 pages, 17 figures, for complete PDF file, see
http://kao.re.kr/~soojong/mypaper/2004_pak_egh2.pd
A role for human leucocyte antigens in the susceptibility to SARSâCovâ2 infection observed in transplant patients
We analysed data from 80 patients who tested positive for SARSâCoVâ2 RNA who had previously been HLA typed to support transplantation. Data were combined from two adjacent centres in Manchester and Leeds to achieve a sufficient number for early analysis. HLA frequencies observed were compared against two control populations: first, against published frequencies in a UK deceased donor population (n = 10,000) representing the target population of the virus, and second, using a cohort of individuals from the combined transplant waiting lists of both centres (n = 308), representing a comparator group of unaffected individuals of the same demographic. We report a significant HLA association with HLAâ DQB1*06 (53% vs. 36%; p < .012; OR 1.96; 95% CI 1.94â3.22) and infection. A bias towards an increased representation of HLAâA*26, HLAâDRB1*15, HLAâDRB1*10 and DRB1*11 was also noted but these were either only significant using the UK donor controls, or did not remain significant after correction for multiple tests. Likewise, HLAâA*02, HLAâB*44 and HLAâC*05 may exert a protective effect, but these associations did not remain significant after correction for multiple tests. This is relevant information for the clinical management of patients in the setting of the current SARSâCoVâ2 pandemic and potentially in riskâassessing staff interactions with infected patients
A review of recent perspectives on biomechanical risk factors associated with anterior cruciate ligament injury
There is considerable evidence to support a number of biomechanical risk factors associated with non-contact anterior cruciate ligament (ACL) injury. This paper aimed to review these biomechanical risk factors and highlight future directions relating to them. Current perspectives investigating trunk position and relationships between strength, muscle activity and biomechanics during landing/cutting highlight the importance of increasing hamstring muscle force during dynamic movements through altering strength, muscle activity, muscle length and contraction velocity. In particular, increased trunk flexion during landing/cutting and greater hamstring strength are likely to increase hamstring muscle force during landing and cutting which have been associated with reduced ACL injury risk. Decision making has also been shown to influence landing biomechanics and should be considered when designing tasks to assess landing/cutting biomechanics. Coaches should therefore promote hamstring strength training and active trunk flexion during landing and cutting in an attempt to reduce ACL injury risk.Peer reviewe
AKARI and BLAST Observations of the Cassiopeia A Supernova Remnant and Surrounding Interstellar Medium
We use new large area far infrared maps ranging from 65 - 500 microns
obtained with the AKARI and the Balloon-borne Large Aperture Submillimeter
Telescope (BLAST) missions to characterize the dust emission toward the
Cassiopeia A supernova remnant (SNR). Using the AKARI high resolution data we
find a new "tepid" dust grain population at a temperature of ~35K and with an
estimated mass of 0.06 solar masses. This component is confined to the central
area of the SNR and may represent newly-formed dust in the unshocked supernova
ejecta. While the mass of tepid dust that we measure is insufficient by itself
to account for the dust observed at high redshift, it does constitute an
additional dust population to contribute to those previously reported. We fit
our maps at 65, 90, 140, 250, 350, and 500 microns to obtain maps of the column
density and temperature of "cold" dust (near 16 K) distributed throughout the
region. The large column density of cold dust associated with clouds seen in
molecular emission extends continuously from the surrounding interstellar
medium to project on the SNR, where the foreground component of the clouds is
also detectable through optical, X-ray, and molecular extinction. At the
resolution available here, there is no morphological signature to isolate any
cold dust associated only with the SNR from this confusing interstellar
emission. Our fit also recovers the previously detected "hot" dust in the
remnant, with characteristic temperature 100 K.Comment: Accepted for publication in the Astrophysical Journal. Maps and
related data are available at http://blastexperiment.info
A comparative HST imaging study of the host galaxies of radio-quiet quasars, radio-loud quasars and radio galaxies: Paper I
We present the first results from a major HST WFPC2 imaging study aimed at
providing the first statistically meaningful comparison of the morphologies,
luminosities, scalelengths and colours of the host galaxies of radio-quiet
quasars, radio-loud quasars, and radio galaxies. We describe the design of this
study and present the images which have been obtained for the first half of our
33-source sample. We find that the hosts of all three classes of luminous AGN
are massive elliptical galaxies, with scalelengths ~=10 kpc, and R-K colours
consistent with mature stellar populations. Most importantly this is the the
first unambiguous evidence that, just like radio-loud quasars, essentially all
radio-quiet quasars brighter than M_R = -24 reside in massive ellipticals. This
result removes the possibility that radio `loudness' is directly linked to host
galaxy morphology, but is however in excellent accord with the
black-hole/spheroid mass correlation recently highlighted by Magorrian et al.
(1998). We apply the relations given by Magorrian et al. to infer the expected
Eddington luminosity of the putative black hole at the centre of each of the
spheroidal host galaxies we have uncovered. Comparison with the actual nuclear
R-band luminosities suggests that the black holes in most of these galaxies are
radiating at a few percent of the Eddington luminosity; the brightest host
galaxies in our low-z sample are capable of hosting quasars with M_R = -28,
comparable to the most luminous quasars at z = 3. Finally we discuss our
host-derived black-hole masses in the context of the
radio-luminosity:black-hole mass correlation recently uncovered for nearby
galaxies by Franceschini et al. (1998), and the resulting implications for the
physical origin of radio loudness.Comment: Submitted for publication in the Astrophysical Journal, 55 pages of
latex, plus 12 postscript figures (Figures 1a-1s (greyscales of images and
model fits, and Figures 2a-2g (luminosity profiles and model fits) can be
downloaded from http://www.roe.ac.uk/astronomy/html/rjm1.shtml
Development of a strontium optical lattice clock for the SOC mission on the ISS
Ultra-precise optical clocks in space will allow new studies in fundamental
physics and astronomy. Within an European Space Agency (ESA) program, the Space
Optical Clocks (SOC) project aims to install and to operate an optical lattice
clock on the International Space Station (ISS) towards the end of this decade.
It would be a natural follow-on to the ACES mission, improving its performance
by at least one order of magnitude. The payload is planned to include an
optical lattice clock, as well as a frequency comb, a microwave link, and an
optical link for comparisons of the ISS clock with ground clocks located in
several countries and continents. Within the EU-FP7-SPACE-2010-1 project no.
263500, during the years 2011-2015 a compact, modular and robust strontium
lattice optical clock demonstrator has been developed. Goal performance is a
fractional frequency instability below 1x10^{-15}, tau^{-1/2} and a fractional
inaccuracy below 5x10^{-17}. Here we describe the current status of the
apparatus' development, including the laser subsystems. Robust preparation of
cold {88}^Sr atoms in a second stage magneto-optical trap (MOT) is achieved.Comment: 27 Pages, 15 figures, Comptes Rendus Physique 201
Development of a strontium optical lattice clock for the SOC mission on the ISS
The ESA mission "Space Optical Clock" project aims at operating an optical
lattice clock on the ISS in approximately 2023. The scientific goals of the
mission are to perform tests of fundamental physics, to enable space-assisted
relativistic geodesy and to intercompare optical clocks on the ground using
microwave and optical links. The performance goal of the space clock is less
than uncertainty and
instability. Within an EU-FP7-funded project, a strontium optical lattice clock
demonstrator has been developed. Goal performances are instability below and fractional inaccuracy .
For the design of the clock, techniques and approaches suitable for later space
application are used, such as modular design, diode lasers, low power
consumption subunits, and compact dimensions. The Sr clock apparatus is fully
operational, and the clock transition in Sr was observed with linewidth
as small as 9 Hz.Comment: 12 pages, 8 figures, SPIE Photonics Europe 201
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