348 research outputs found
Two chemically similar stellar overdensities on opposite sides of the plane of the Galaxy
Our Galaxy is thought to have undergone an active evolutionary history
dominated by star formation, the accretion of cold gas, and, in particular,
mergers up to 10 gigayear ago. The stellar halo reveals rich fossil evidence of
these interactions in the form of stellar streams, substructures, and
chemically distinct stellar components. The impact of dwarf galaxy mergers on
the content and morphology of the Galactic disk is still being explored. Recent
studies have identified kinematically distinct stellar substructures and moving
groups, which may have extragalactic origin. However, there is mounting
evidence that stellar overdensities at the outer disk/halo interface could have
been caused by the interaction of a dwarf galaxy with the disk. Here we report
detailed spectroscopic analysis of 14 stars drawn from two stellar
overdensities, each lying about 5 kiloparsecs above and below the Galactic
plane - locations suggestive of association with the stellar halo. However, we
find that the chemical compositions of these stars are almost identical, both
within and between these groups, and closely match the abundance patterns of
the Milky Way disk stars. This study hence provides compelling evidence that
these stars originate from the disk and the overdensities they are part of were
created by tidal interactions of the disk with passing or merging dwarf
galaxies.Comment: accepted for publication in Natur
Experimental simulation of quantum tunneling in small systems
It is well known that quantum computers are superior to classical computers
in efficiently simulating quantum systems. Here we report the first
experimental simulation of quantum tunneling through potential barriers, a
widespread phenomenon of a unique quantum nature, via NMR techniques. Our
experiment is based on a digital particle simulation algorithm and requires
very few spin-1/2 nuclei without the need of ancillary qubits. The occurrence
of quantum tunneling through a barrier, together with the oscillation of the
state in potential wells, are clearly observed through the experimental
results. This experiment has clearly demonstrated the possibility to observe
and study profound physical phenomena within even the reach of small quantum
computers.Comment: 17 pages and 8 figure
Lost & Found Dark Matter in Elliptical Galaxies
There is strong evidence that the mass in the Universe is dominated by dark
matter, which exerts gravitational attraction but whose exact nature is
unknown. In particular, all galaxies are believed to be embedded in massive
haloes of dark matter. This view has recently been challenged by surprisingly
low random stellar velocities in the outskirts of ordinary elliptical galaxies,
which were interpreted as indicating a lack of dark matter (Mendez et al. 2001;
Romanowsky et al. 2003). Here we show that the low velocities are in fact
compatible with galaxy formation in dark-matter haloes. Using numerical
simulations of disc-galaxy mergers, we find that the stellar orbits in the
outer regions of the resulting ellipticals are very elongated. These stars were
torn by tidal forces from their original galaxies during the first close
passage and put on outgoing trajectories. The elongated orbits, combined with
the steeply falling density profile of the observed tracers, explain the
observed low velocities even in the presence of large amounts of dark matter.
Projection effects when viewing a triaxial elliptical can lead to even lower
observed velocities along certain lines of sight.Comment: Letter to Nature, 13+15 pages, 2+11 figures, improved text, extended
Supplementary Information adde
Clumps and streams in the local dark matter distribution
In cold dark matter cosmological models, structures form and grow by merging
of smaller units. Numerical simulations have shown that such merging is
incomplete; the inner cores of halos survive and orbit as "subhalos" within
their hosts. Here we report a simulation that resolves such substructure even
in the very inner regions of the Galactic halo. We find hundreds of very
concentrated dark matter clumps surviving near the solar circle, as well as
numerous cold streams. The simulation reveals the fractal nature of dark matter
clustering: Isolated halos and subhalos contain the same relative amount of
substructure and both have cuspy inner density profiles. The inner mass and
phase-space densities of subhalos match those of recently discovered faint,
dark matter-dominated dwarf satellite galaxies and the overall amount of
substructure can explain the anomalous flux ratios seen in strong gravitational
lenses. Subhalos boost gamma-ray production from dark matter annihilation, by
factors of 4-15, relative to smooth galactic models. Local cosmic ray
production is also enhanced, typically by a factor 1.4, but by more than a
factor of ten in one percent of locations lying sufficiently close to a large
subhalo. These estimates assume that gravitational effects of baryons on dark
matter substructure are small.Comment: 14 pages, 5 figures, to appear in Nature, includes supplementary
information. Full version of Figure 1 available at
http://www.ucolick.org/~diemand/vl2/fig1.pn
The use of CAM and conventional treatments among primary care consulters with chronic musculoskeletal pain
Chronic musculoskeletal pain is the single most cited reason for use of complementary and alternative medicine (CAM). Primary care is the most frequent conventional medical service used by patients with pain in the UK. We are unaware, however, of a direct evidence of the extent of CAM use by primary care patients, and how successful they perceive it to be.
Methods Aims and objectives
To determine CAM use among patients with chronic musculoskeletal pain who have consulted about their pain in primary care.
Study design
Face-to-face interview-based survey.
Setting
Three general practices in North Staffordshire.
Participants
Respondents to a population pain survey who had reported having musculoskeletal pain in the survey and who had consulted about their pain in primary care in the previous 12 months as well as consenting to further research and agreeing to an interview. Information was gathered about their pain and the use of all treatments for pain, including CAM, in the previous year.
Results
138 interviews were completed. 116 participants (84%) had used at least one CAM treatment for pain in the previous year. 65% were current users of CAM. The ratio of over-the-counter CAM use to care from a CAM provider was 3:2. 111 participants (80%) had used conventional treatment. 95 (69%) were using a combination of CAM and conventional treatment. Glucosamine and fish oil were the most commonly used CAM treatments (38%, 35% respectively). Most CAM treatments were scored on average as being helpful, and users indicated that they intended to use again 87% of the CAM treatments they had already used.
Conclusion
We provide direct evidence that most primary care consulters with chronic musculoskeletal pain have used CAM in the previous year, usually in combination with conventional treatments. The high prevalence and wide range of users experiences of benefit and harm from CAM strengthen the argument for more research into this type of medicine to quantify benefit and assess safety. The observation that most users of conventional medicine also used CAM suggests a continuing need for more investigation of effective pain management in primary care
Management of hydrocele in adolescent patients
Hydrocele is defined as an abnormal collection of serous fluid in the potential space between the parietal and visceral layers of the tunica vaginalis. In the majority of affected adolescents, hydrocele is acquired and is idiopathic in origin. The pathogenesis of idiopathic hydrocele is thought to be an imbalance in the normal process of fluid production and reabsorption. The diagnosis is usually clinical. Taking a thorough history is essential to rule out any fluctuation in size, which is an indication of a patent processus vaginalis. Scrotal ultrasonography is mandatory in nonpalpable testicles to rule out a subtending testicular solid mass requiring inguinal exploration. Otherwise, open hydrocelectomy via a scrotal incision is the standard treatment of idiopathic hydroceles. The second most common cause of hydrocele in adolescents is varicocelectomy. The risk of hydrocele formation is higher with non-artery-sparing procedures or those performed without microsurgical aid, and in surgery requiring cord dissection. If hydrocele occurs after varicocelectomy, initial management should include observation with or without hydrocele aspiration. Large persistent hydroceles are best served by open hydrocelectomy
Differential hypoglycaemic, anorectic, autonomic and emetic effects of the glucagon-like peptide receptor agonist, exendin-4, in the conscious telemetered ferret.
Background: Rodents are incapable of emesis and consequently the emetic potential of glucagon-like peptide-1 receptor (GLP-1R) agonists in studies designed to assess a potential blood glucose lowering action of the compound was missed. Therefore, we investigated if the ferret, a carnivore with demonstrated translation capability in emesis research, would identify the emetic potential of the GLP-1R agonist, exendin-4, and any associated effects on gastric motor function, appetite and cardiovascular homeostasis.
Methods: The biological activity of the GLP-1R ligands was investigated in vivo using a glucose tolerance test in pentobarbitone-anesthetised ferrets and in vitro using organ bath studies. Radiotelemetry was used to investigate the effect of exendin-4 on gastric myoelectric activity (GMA) and cardiovascular function in conscious ferrets; behaviour was also simultaneously assessed. Western blot was used to characterize GLP-1R distribution in the gastrointestinal and brain tissues.
Results: In anesthetised ferrets, exendin-4 (30 nmol/kg, s.c.) reduced experimentally elevated blood glucose levels by 36.3%, whereas the GLP-1R antagonist, exendin (9–39) (300 nmol/kg, s.c.) antagonised the effect and increased AUC0–120 by 31.0% when injected alone (P < 0.05). In animals with radiotelemetry devices, exendin-4 (100 nmol/kg, s.c.) induced emesis in 1/9 ferrets, but inhibited food intake and decreased heart rate variability (HRV) in all animals (P < 0.05). In the animals not exhibiting emesis, there was no effect on GMA, mean arterial blood pressure, heart rate, or core body temperature. In the ferret exhibiting emesis, there was a shift in the GMA towards bradygastria with a decrease in power, and a concomitant decrease in HRV. Western blot revealed GLP-1R throughout the gastrointestinal tract but exendin-4 (up to 300 nM) and exendin (9–39), failed to contract or relax isolated ferret gut tissues. GLP-1R were found in all major brain regions and the levels were comparable those in the vagus nerve.
Conclusions: Peripherally administered exendin-4 reduced blood glucose and inhibited feeding with a low emetic potential similar to that in humans (11% vs 12.8%). A disrupted GMA only occurred in the animal exhibiting emesis raising the possibility that disruption of the GMA may influence the probability of emesis occurring in response to treatment with GLP-1R agonists
Nociceptors: a phylogenetic view
The ability to react to environmental change is crucial for the survival of an organism and an essential prerequisite is the capacity to detect and respond to aversive stimuli. The importance of having an inbuilt “detect and protect” system is illustrated by the fact that most animals have dedicated sensory afferents which respond to noxious stimuli called nociceptors. Should injury occur there is often sensitization, whereby increased nociceptor sensitivity and/or plasticity of nociceptor-related neural circuits acts as a protection mechanism for the afflicted body part. Studying nociception and nociceptors in different model organisms has demonstrated that there are similarities from invertebrates right through to humans. The development of technology to genetically manipulate organisms, especially mice, has led to an understanding of some of the key molecular players in nociceptor function. This review will focus on what is known about nociceptors throughout the Animalia kingdom and what similarities exist across phyla; especially at the molecular level of ion channels
Surgical trial in traumatic intracerebral hemorrhage (STITCH(Trauma)): study protocol for a randomized controlled trial
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