813 research outputs found
Individual physiological responses to environmental hypoxia and organic enrichment: Implications for early soft-bottom community succession
Infaunal inhabitants of coastal marine sediments occupy environments along a continuum from extremely food-rich, low-oxygen regions to food-poor habitats with relatively high levels of available oxygen. In organic-rich sediments, efficient utilization of available organic matter by deposit-feeding macrofauna may often be limited by the supply of oxygen. Specific feeding rate, growth, and production efficiency were measured on single individuals of the polychaete Capitella species 1 to determine whether previously measured declines in growth rates in response to hypoxia were due to decreased feeding, decreased conversion efficiency, or both. Under otherwise constant conditions, feeding rate was determined by the nitrogen content of the sediment, with a greater nitrogen content generally leading to higher specific feeding rates in a manner consistent with recent interpretations of optimal foraging theory. However, the relationship between feeding rate and growth was influenced by oxygen concentration such that in relatively nitrogen-poor sediment, greater growth rates were observed at the lower oxygen level. Simultaneous measurement of growth and feeding rates indicated that the effect of oxygen was due to a decrease in the efficiency with which ingested sediment was converted to tissue under low nitrogen, high oxygen conditions. We suggest that the decreased conversion rate of ingested sediment to body volume under the higher oxygen regime reflected an aerobic metabolic system poised to rapidly exploit available oxygen supplies. The physiological responses measured in our experiments are consistent with the classical faunal successional sequence occurring in a deposit following organic enrichment. When viewed temporally, these faunal changes parallel geochemical changes such that high organic matter, low oxygen conditions give way to higher oxygen levels and decreased concentrations of organic matter. Thus environmental conditions typically change toward those under which Capitella sp. 1 would be expected to perform most poorly. We suggest that an underlying physiological mechanism in Capitella spp. may strongly influence the early successional changes observed following the organic enrichment of soft-bottom benthic environments
The Electrosphere of Macroscopic "Quark Nuclei": A Source for Diffuse MeV Emissions from Dark Matter
Using a Thomas-Fermi model, we calculate the structure of the electrosphere
of the quark antimatter nuggets postulated to comprise much of the dark matter.
This provides a single self-consistent density profile from ultrarelativistic
densities to the nonrelativistic Boltzmann regime that use to present
microscopically justified calculations of several properties of the nuggets,
including their net charge, and the ratio of MeV to 511 keV emissions from
electron annihilation. We find that the calculated parameters agree with
previous phenomenological estimates based on the observational supposition that
the nuggets are a source of several unexplained diffuse emissions from the
Galaxy. As no phenomenological parameters are required to describe these
observations, the calculation provides another nontrivial verification of the
dark-matter proposal. The structure of the electrosphere is quite general and
will also be valid at the surface of strange-quark stars, should they exist.Comment: 20 Pages, REVTeX4.
Minimax Current Density Coil Design
'Coil design' is an inverse problem in which arrangements of wire are
designed to generate a prescribed magnetic field when energized with electric
current. The design of gradient and shim coils for magnetic resonance imaging
(MRI) are important examples of coil design. The magnetic fields that these
coils generate are usually required to be both strong and accurate. Other
electromagnetic properties of the coils, such as inductance, may be considered
in the design process, which becomes an optimization problem. The maximum
current density is additionally optimized in this work and the resultant coils
are investigated for performance and practicality. Coils with minimax current
density were found to exhibit maximally spread wires and may help disperse
localized regions of Joule heating. They also produce the highest possible
magnetic field strength per unit current for any given surface and wire size.
Three different flavours of boundary element method that employ different basis
functions (triangular elements with uniform current, cylindrical elements with
sinusoidal current and conic section elements with sinusoidal-uniform current)
were used with this approach to illustrate its generality.Comment: 24 pages, 6 figures, 2 tables. To appear in Journal of Physics D:
Applied Physic
Induced P-wave Superfluidity in Asymmetric Fermi Gases
We show that two new intra-species P-wave superfluid phases appear in
two-component asymmetric Fermi systems with short-range S-wave interactions. In
the BEC limit, phonons of the molecular BEC induce P-wave superfluidity in the
excess fermions. In the BCS limit, density fluctuations induce P-wave
superfluidity in both the majority and the minority species. These phases may
be realized in experiments with spin-polarized Fermi gases.Comment: published versio
WMAP Haze: Directly Observing Dark Matter?
In this paper we show that dark matter in the form of dense matter/antimatter
nuggets could provide a natural and unified explanation for several distinct
bands of diffuse radiation from the core of the Galaxy spanning over 12 orders
of magnitude in frequency. We fix all of the phenomenological properties of
this model by matching to x-ray observations in the keV band, and then
calculate the unambiguously predicted thermal emission in the microwave band,
at frequencies smaller by 10 orders of magnitude. Remarkably, the intensity and
spectrum of the emitted thermal radiation are consistent with--and could
entirely explain--the so-called "WMAP haze": a diffuse microwave excess
observed from the core of our Galaxy by the Wilkinson Microwave Anisotropy
Probe (WMAP). This provides another strong constraint of our proposal, and a
remarkable nontrivial validation. If correct, our proposal identifies the
nature of the dark matter, explains baryogenesis, and provides a means to
directly probe the matter distribution in our Galaxy by analyzing several
different types of diffuse emissions.Comment: 16 pages, REVTeX4. Updated to correspond with published version:
includes additional appendices discussing finite-size effect
Time-resolved multi-mass ion imaging: femtosecond UV-VUV pump-probe spectroscopy with the PImMS camera
The Pixel-Imaging Mass Spectrometry (PImMS) camera allows for 3D charged
particle imaging measurements, in which the particle time-of-flight is recorded
along with position. Coupling the PImMS camera to an ultrafast
pump-probe velocity-map imaging spectroscopy apparatus therefore provides a
route to time-resolved multi-mass ion imaging, with both high count rates and
large dynamic range, thus allowing for rapid measurements of complex
photofragmentation dynamics. Furthermore, the use of vacuum ultraviolet
wavelengths for the probe pulse allows for an enhanced observation window for
the study of excited state molecular dynamics in small polyatomic molecules
having relatively high ionization potentials. Herein, preliminary time-resolved
multi-mass imaging results from CFI photolysis are presented. The
experiments utilized femtosecond UV and VUV (160.8~nm and 267~nm) pump and
probe laser pulses in order to demonstrate and explore this new time-resolved
experimental ion imaging configuration. The data indicates the depth and power
of this measurement modality, with a range of photofragments readily observed,
and many indications of complex underlying wavepacket dynamics on the excited
state(s) prepared
Simultaneous Modelling of the Stellar Halo and Globular Cluster System of NGC 5128
An important test for models of galaxy formation lies in the metallicity
distribution functions (MDFs) of spheroid stars and their globular clusters
(GCs).We have compared the MDFs obtained from spectroscopy of the GCs and the
star-by-star photometry of red giants in the nearby elliptical NGC 5128, with
the predictions of a semi-analytic galaxy formation model. We have selected
model ellipticals comparable in luminosity and environment to NGC 5128, and
derived their MDFs. A direct comparison between models and data shows that the
MDFs are qualitatively similar, both have stellar components which are
predominantly metal-rich (0.8Z), with a small fraction of metal-poor stars
extending down to 0.002Z. The model MDFs show only small variations, whether
they are brightest cluster galaxies or low luminosity group ellipticals. Our
comparison also reveals that these model MDFs harbour a greater fraction of
stars above solar metallicity than the observations, producing generally more
metal-rich (by 0.1 dex) MDFs. One possibility is that the outer-bulge
observations are missing some of the highest metallicity stars. We find good
agreement between the model and observed GC MDFs, provided that the metal-poor
GC formation is halted early in the model. Under this proviso, both the models
and data are bimodal with peaks at 0.1Z and Z, and cover similar metallicity
ranges. This broad agreement for the stars and GCs suggests that the bulk of
the stellar population in NGC 5128 may have been built up in a hierarchical
fashion, involving both quiescent and merger-induced star formation. The
existence of age structure amongst the metal-rich GCs needs to be tested
against high-quality data for this galaxy.Comment: 13 pages, 9 figures and a table, accepted by MNRA
A 2dF spectroscopic study of globular clusters in NGC 5128: Probing the formation history of the nearest giant Elliptical
We have performed a spectroscopic study of globular clusters (GCs) in the
giant elliptical NGC 5128 using the 2dF facility at the Anglo-Australian
telescope. We obtained integrated optical spectra for a total of 254 GCs, 79 of
which are newly confirmed on the basis of their radial velocities and spectra.
In addition, we obtained an integrated spectrum of the galaxy starlight along
the southern major axis. We derive an empirical metallicity distribution
function (MDF) for 207 GCs (~14 of the estimated total GC system) based upon
Milky Way GCs. This MDF is multimodal at high statistical significance with
peaks at [Z/H]~-1.3 and -0.5. A comparison between the GC MDF and that of the
stellar halo at 20 kpc (~4 Reff) reveals close coincidence at the metal-rich
ends of the distributions. However, an inner 8 kpc stellar MDF shows a clear
excess of metal-rich stars when compared to the GCs. We compare a higher S/N
subsample (147 GCs) with two stellar population models which include non-solar
abundance ratio corrections. The vast majority of our sample (~90%) appears
old, with ages similar to the Milky Way GC system. There is evidence for a
population of intermediate-age (~4-8 Gy) GCs (<15% of the sample) which are on
average more metal-rich than the old GCs. We also identify at least one younger
cluster (~1-2 Gy) in the central regions of the galaxy. Our observations are
consistent with a picture where NGC 5128 has undergone at least two mergers
and/or interactions involving star formation and limited GC formation since
z=1, however the effect of non-canonical hot stellar populations on the
integrated spectra of GCs remains an outstanding uncertainty in our GC age
estimates.Comment: 17 figures, some long table
Physical activity and nutrition interventions for older adults with cancer: a systematic review
Purpose: The aim of this review was to summarize the current literature for the effectiveness of activity and nutritional based interventions on health-related quality of life (HRQoL) in older adults living with and beyond cancer (LWBC). Methods: We conducted systematic structured searches of CINAHL, Embase, Medline, Cochrane CENTRAL databases, and bibliographic review. Two independent researchers selected against inclusion criteria: (1) lifestyle nutrition and/or activity intervention for people with any cancer diagnosis, (2) measured HRQoL, (3) all participants over 60years of age and (4) randomized controlled trials. Results: Searches identified 5179 titles; 114 articles had full text review, with 14 studies (participant n = 1660) included. Three had nutrition and activity components, one, nutrition only and ten, activity only. Duration ranged from 7days to 1year. Interventions varied from intensive daily prehabilitation to home-based gardening interventions. Studies investigated various HRQoL outcomes including fatigue, general and cancer-specific quality of life (QoL), distress, depression, global side-effect burden and physical functioning. Eight studies reported significant intervention improvements in one or more QoL measure. Seven studies reported using a psychosocial/theoretical framework. There is a gap in tailored nutrition advice. Conclusions: Among the few studies that targeted older adults with cancer, most were activity-based programmes with half reporting improvements in QoL. Future research should focus on or include tailored nutrition components and consider appropriate behaviour change techniques to maximize potential QoL improvement. Implications for Cancer Survivors: More research is needed to address the research gap regarding older adults as current recommendations are derived from younger populations
Learning curve analysis of thoracic endovascular aortic repair in relation to credentialing guidelines
ObjectiveRecently, practice guideline documents have recommended the completion of different levels of interventional experience and 5 or 10 thoracic endovascular aortic cases prior to surgeon credentialing. This study’s purpose was to determine whether these requirements are valid by reviewing three surgeons’ learning curves with thoracic aortic endovascular repairs.MethodsBetween 1998 and 2006, 67 patients underwent emergent or elective endovascular repair of thoracic aortic pathologies by one of three vascular surgeons with extensive experience with catheter manipulation and abdominal aortic endografts. Following standard retrospective review, each surgeon’s learning curve was analyzed using the cumulative sum failure method with a target success rate of 95% derived from the literature. The main outcome variable was primary technical success.ResultsThese 67 patients presented with several pathologies including elective (n = 31) and ruptured (n = 11) thoracic aortic aneurysms, acute dissections or aortic ulcers (n = 10), and acute blunt thoracic aortic trauma (n = 15). The mean age was 65 (range: 20 to 90) and the early (30 day) mortality rate was 19.4% in urgent cases (n = 36) and 0% in elective cases (n = 31). Paraplegia occurred in two patients (3%). Primary technical success was achieved in 62 cases (92.5%) and did not differ between surgeons (92.6%, 91.3%, 94.1%, respectively; P = .9). Each surgeon’s cases were plotted sequentially and the resulting learning curves were similar. Although acceptable outcomes were obtained throughout the study period, improved results, compared with the target success rate, were not achieved until each surgeon treated 5 to 10 patients.ConclusionThis study supports the case volume requirements of the Society for Vascular Surgery credentialing guidelines, which also requires extensive catheter and guidewire experience. With this background in catheter manipulation and endovascular abdominal aortic repair, surgeons can achieve optimal outcomes with thoracic aortic lesions following 5 to 10 cases
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