1,050 research outputs found
The self-consistent gravitational self-force
I review the problem of motion for small bodies in General Relativity, with
an emphasis on developing a self-consistent treatment of the gravitational
self-force. An analysis of the various derivations extant in the literature
leads me to formulate an asymptotic expansion in which the metric is expanded
while a representative worldline is held fixed; I discuss the utility of this
expansion for both exact point particles and asymptotically small bodies,
contrasting it with a regular expansion in which both the metric and the
worldline are expanded. Based on these preliminary analyses, I present a
general method of deriving self-consistent equations of motion for arbitrarily
structured (sufficiently compact) small bodies. My method utilizes two
expansions: an inner expansion that keeps the size of the body fixed, and an
outer expansion that lets the body shrink while holding its worldline fixed. By
imposing the Lorenz gauge, I express the global solution to the Einstein
equation in the outer expansion in terms of an integral over a worldtube of
small radius surrounding the body. Appropriate boundary data on the tube are
determined from a local-in-space expansion in a buffer region where both the
inner and outer expansions are valid. This buffer-region expansion also results
in an expression for the self-force in terms of irreducible pieces of the
metric perturbation on the worldline. Based on the global solution, these
pieces of the perturbation can be written in terms of a tail integral over the
body's past history. This approach can be applied at any order to obtain a
self-consistent approximation that is valid on long timescales, both near and
far from the small body. I conclude by discussing possible extensions of my
method and comparing it to alternative approaches.Comment: 44 pages, 4 figure
Signatures of Young Star Formation Activity Within Two Parsecs of Sgr A*
We present radio and infrared observations indicating on-going star formation
activity inside the pc circumnuclear ring at the Galactic center.
Collectively these measurements suggest a continued disk-based mode of on-going
star formation has taken place near Sgr A* over the last few million years.
First, VLA observations with spatial resolution 2.17 reveal 13
water masers, several of which have multiple velocity components. The presence
of interstellar water masers suggests gas densities that are sufficient for
self-gravity to overcome the tidal shear of the 4 \msol\, black
hole. Second, SED modeling of stellar sources indicate massive YSO candidates
interior to the molecular ring, supporting in-situ star formation near Sgr A*
and appear to show a distribution similar to that of the counter-rotating disks
of 100 OB stars orbiting Sgr A*. Some YSO candidates (e.g., IRS~5) have
bow shock structures suggesting that they have have gaseous disks that are
phototoevaporated and photoionized by the strong radiation field. Third, we
detect clumps of SiO (2-1) and (5-4) line emission in the ring based on CARMA
and SMA observations. The FWHM and luminosity of the SiO emission is consistent
with shocked protostellar outflows. Fourth, two linear ionized features with an
extent of pc show blue and redshifted velocities between and
\kms, suggesting protostellar jet driven outflows with mass loss rates of
solar mass yr. Finally, we present the imprint of
radio dark clouds at 44 GHz, representing a reservoir of molecular gas that
feeds star formation activity close to Sgr A*.Comment: 38 pages, 10 figures, ApJ (in press
Waves on the surface of the Orion molecular cloud
Massive stars influence their parental molecular cloud, and it has long been
suspected that the development of hydrodynamical instabilities can compress or
fragment the cloud. Identifying such instabilities has proved difficult. It has
been suggested that elongated structures (such as the `pillars of creation')
and other shapes arise because of instabilities, but alternative explanations
are available. One key signature of an instability is a wave-like structure in
the gas, which has hitherto not been seen. Here we report the presence of
`waves' at the surface of the Orion molecular cloud near where massive stars
are forming. The waves seem to be a Kelvin-Helmholtz instability that arises
during the expansion of the nebula as gas heated and ionized by massive stars
is blown over pre-existing molecular gas.Comment: Preprint of publication in Natur
Gravitational redshift of galaxies in clusters as predicted by general relativity
The theoretical framework of cosmology is mainly defined by gravity, of which
general relativity is the current model. Recent tests of general relativity
within the \Lambda Cold Dark Matter (CDM) model have found a concordance
between predictions and the observations of the growth rate and clustering of
the cosmic web. General relativity has not hitherto been tested on cosmological
scales independent of the assumptions of the \Lambda CDM model. Here we report
observation of the gravitational redshift of light coming from galaxies in
clusters at the 99 per cent confidence level, based upon archival data. The
measurement agrees with the predictions of general relativity and its
modification created to explain cosmic acceleration without the need for dark
energy (f(R) theory), but is inconsistent with alternative models designed to
avoid the presence of dark matter.Comment: Published in Nature issued on 29 September 2011. This version
includes the Letter published there as well as the Supplementary Information.
23 pages, 7 figure
CARMA Large Area Star Formation Survey: Project Overview with Analysis of Dense Gas Structure and Kinematics in Barnard 1
We present details of the CARMA Large Area Star Formation Survey (CLASSy),
while focusing on observations of Barnard 1. CLASSy is a CARMA Key Project that
spectrally imaged N2H+, HCO+, and HCN (J=1-0 transitions) across over 800
square arcminutes of the Perseus and Serpens Molecular Clouds. The observations
have angular resolution near 7" and spectral resolution near 0.16 km/s. We
imaged ~150 square arcminutes of Barnard 1, focusing on the main core, and the
B1 Ridge and clumps to its southwest. N2H+ shows the strongest emission, with
morphology similar to cool dust in the region, while HCO+ and HCN trace several
molecular outflows from a collection of protostars in the main core. We
identify a range of kinematic complexity, with N2H+ velocity dispersions
ranging from ~0.05-0.50 km/s across the field. Simultaneous continuum mapping
at 3 mm reveals six compact object detections, three of which are new
detections. A new non-binary dendrogram algorithm is used to analyze dense gas
structures in the N2H+ position-position-velocity (PPV) cube. The projected
sizes of dendrogram-identified structures range from about 0.01-0.34 pc.
Size-linewidth relations using those structures show that non-thermal
line-of-sight velocity dispersion varies weakly with projected size, while rms
variation in the centroid velocity rises steeply with projected size. Comparing
these relations, we propose that all dense gas structures in Barnard 1 have
comparable depths into the sky, around 0.1-0.2 pc; this suggests that
over-dense, parsec-scale regions within molecular clouds are better described
as flattened structures rather than spherical collections of gas. Science-ready
PPV cubes for Barnard 1 molecular emission are available for download.Comment: Accepted to The Astrophysical Journal (ApJ), 51 pages, 27 figures
(some with reduced resolution in this preprint); Project website is at
http://carma.astro.umd.edu/class
Noise reduction in gravitational wave interferometers using feedback
We show that the quantum locking scheme recently proposed by Courty {\it et
al.} [Phys. Rev. Lett. {\bf 90}, 083601 (2003)] for the reduction of back
action noise is able to significantly improve the sensitivity of the next
generation of gravitational wave interferometers.Comment: 12 pages, 2 figures, in print in the Special Issue of J. Opt. B on
Fluctuations and Noise in Photonics and Quantum Optic
Retrospective harm benefit analysis of pre-clinical animal research for six treatment interventions
The harm benefit analysis (HBA) is the cornerstone of animal research regulation and is considered to be a key ethical safeguard for animals. The HBA involves weighing the anticipated benefits of animal research against its predicted harms to animals but there are doubts about how objective and accountable this process is.i. To explore the harms to animals involved in pre-clinical animal studies and to assess these against the benefits for humans accruing from these studies; ii. To test the feasibility of conducting this type of retrospective HBA.Data on harms were systematically extracted from a sample of pre-clinical animal studies whose clinical relevance had already been investigated by comparing systematic reviews of the animal studies with systematic reviews of human studies for the same interventions (antifibrinolytics for haemorrhage, bisphosphonates for osteoporosis, corticosteroids for brain injury, Tirilazad for stroke, antenatal corticosteroids for neonatal respiratory distress and thrombolytics for stroke). Clinical relevance was also explored in terms of current clinical practice. Harms were categorised for severity using an expert panel. The quality of the research and its impact were considered. Bateson's Cube was used to conduct the HBA.The most common assessment of animal harms by the expert panel was 'severe'. Reported use of analgesia was rare and some animals (including most neonates) endured significant procedures with no, or only light, anaesthesia reported. Some animals suffered iatrogenic harms. Many were kept alive for long periods post-experimentally but only 1% of studies reported post-operative care. A third of studies reported that some animals died prior to endpoints. All the studies were of poor quality. Having weighed the actual harms to animals against the actual clinical benefits accruing from these studies, and taking into account the quality of the research and its impact, less than 7% of the studies were permissible according to Bateson's Cube: only the moderate bisphosphonate studies appeared to minimise harms to animals whilst being associated with benefit for humans.This is the first time the accountability of the HBA has been systematically explored across a range of pre-clinical animal studies. The regulatory systems in place when these studies were conducted failed to safeguard animals from severe suffering or to ensure that only beneficial, scientifically rigorous research was conducted. Our findings indicate a pressing need to: i. review regulations, particularly those that permit animals to suffer severe harms; ii. reform the processes of prospectively assessing pre-clinical animal studies to make them fit for purpose; and iii. systematically evaluate the benefits of pre-clinical animal research to permit a more realistic assessment of its likely future benefits
Optical properties of the pseudogap state in underdoped cuprates
Recent optical measurements of deeply underdoped cuprates have revealed that
a coherent Drude response persists well below the end of the superconducting
dome. In addition, no large increase in optical effective mass has been
observed, even at dopings as low as 1%. We show that this behavior is
consistent with the resonating valence bond spin-liquid model proposed by Yang,
Rice, and Zhang. In this model, the overall reduction in optical conductivity
in the approach to the Mott insulating state is caused not by an increase in
effective mass, but by a Gutzwiller factor, which describes decreased coherence
due to correlations, and by a shrinking of the Fermi surface, which decreases
the number of available charge carriers. We also show that in this model, the
pseudogap does not modify the low-temperature, low-frequency behavior, though
the magnitude of the conductivity is greatly reduced by the Gutzwiller factor.
Similarly, the profile of the temperature dependence of the microwave
conductivity is largely unchanged in shape, but the Gutzwiller factor is
essential in understanding the observed difference in magnitude between ortho-I
and -II YBaCuO.Comment: 9 pages, 6 figures, submitted to Eur. Phys. J.
Issues potentially affecting quality of life arising from long-term medicines use: a qualitative study
Background Polypharmacy is increasing and managing large number of medicines may create a burden for patients. Many patients have negative views of medicines and their use can adversely affect quality of life. No studies have specifically explored the impact of general long-term medicines use on quality of life. Objective To determine the issues which patients taking long-term medicines consider affect their day-to-day lives, including quality of life. Setting Four primary care general practices in North West England Methods Face-to-face interviews with adults living at home, prescribed four or more regular medicines for at least 1 year. Interviewees were identified from primary care medical records and purposively selected to ensure different types of medicines use. Interviews were recorded, transcribed and analysed thematically. Results Twenty-one interviews were conducted and analysed. Patients used an average of 7.8 medicines, 51 % were preventive, 40 % for symptom relief and 9 % treatment. Eight themes emerged: relationships with health professionals, practicalities, information, efficacy, side effects, attitudes, impact and control. Ability to discuss medicines with health professionals varied and many views were coloured by negative experiences, mainly with doctors. All interviewees had developed routines for using multiple medicines, some requiring considerable effort. Few felt able to exert control over medicines routines specified by health professionals. Over half sought additional information about medicines whereas others avoided this, trusting in doctors to guide their medicines use. Patients recognised their inability to assess efficacy for many medicines, notably those used for prophylaxis. All were concerned about possible side effects and some had poor experiences of discussing concerns with doctors. Medicines led to restrictions on social activities and personal life to the extent that, for some, life can revolve around medicines. Conclusion There is a multiplicity and complexity of issues surrounding medicines use, which impact on day-to-day lives for patients with long-term conditions. While most patients adapt to long-term medicines use, others did so at some cost to their quality of life
Investigating the loss of recruitment potential in red grouse (Lagopus lagopus scoticus) : the relative importance of hen mortality, food supply, tick infestation and louping-ill
Ticks and their pathogens cause significant disease
and economic loss in many animal populations. Despite
this, experiments that test the impact of ticks and tickborne
diseases on wild animal populations are rare. Here,
we report on an experiment assessing the effect of ticks
on red grouse productivity and chick growth in relation to
other causes of poor recruitment at two sites in the
Scottish uplands during 2005. Treated hens received two
leg bands impregnated with the acaricide permethrin,
while controls hens were untreated. Chicks were captured
at c.2 weeks of age and fitted with a metal patagial tag,
and chicks from treated hens also received a permethrinimpregnated
strip. Mean tick burdens in treated chicks
were close to zero compared with a mean of around 12
in the control group. Although treatment reduced tick
infestations, it did not increase brood size. Growth rates in
chicks from control and treated hens were similar during the first 10 days and comparable with chicks fed an ad-lib
invertebrate-based diet. These results suggest that in this case,
neither ticks (and the tick transmitted louping-ill virus) nor
food shortages was the main cause of chick mortality.
However, mortality in the adult hens was around 35 %, and
predation accounted for 62 % of these losses before broods
fledged. Our results indicate that on our study sites, predation
may have a more important impact on grouse population
dynamics than ticks and tick-borne disease. We suggest that
it may be more cost effective to determine the causes of poor
grouse population performance before implementing popular
but expensive tick control measures such as the culling
of alternative hosts and running acaracide treated sheep
‘tick-mop’ flocks.http://link.springer.com/journal/10344hb201
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