1,269 research outputs found
A STEADY PSEUDO-COMPRESSIBILITY APPROACH BASED ON UNSTRUCTURED HYBRID FINITE VOLUME TECHNIQUES APPLIED TO TURBULENT PREMIXED FLAME PROPAGATION
A pseudo-compressibility method for zero Mach number turbulent reactive
flows with heat release is combined with an unstructured finite volume
hybrid grid scheme. The spatial discretization is based on an overlapped cell
vertex approach. An infinite freely planar flame propagating into a turbulent
medium of premixed reactants is considered as a test case. The recourse to a
flamelet combustion modeling for which the reaction rate is quenched in a
continuous way ensures the uniqueness of the turbulent flame propagation
velocity. To integrate the final form of discretized governing equations, a
three-stage hybrid time-stepping scheme is used and artificial dissipation
terms are added to stabilize the convergence path towards the final steady
solution. The results obtained with such a numerical procedure prove to be
in good agreement with those reported in the literature on the very same
flow geometry. Indeed, the flame structure as well as its propagation
velocity are accurately predicted thus confirming the validity of the
approach followed and demonstrating that such a numerical procedure will
be a valuable tool to deal with complex reactive flow geometries
Great Balls of FIRE III: Modeling Black Hole Mergers from Massive Star Clusters in Simulations of Galaxies
After the nearly hundred gravitational-wave detections reported by the
LIGO-Virgo-KAGRA Collaboration, the question of the cosmological origin of
merging binary black holes (BBHs) remains open. The two main formation channels
generally considered are from isolated field binaries or via dynamical assembly
in dense star clusters. Here, we focus on understanding the dynamical formation
of merging BBHs within massive clusters in galaxies of different masses. To
this end, we apply a new framework to consistently model the formation and
evolution of massive star clusters in zoom-in cosmological simulations of
galaxies. Each simulation, taken from the FIRE project, provides a realistic
star formation environment with a unique star formation history and hosts
realistic giant molecular clouds that constitute the birthplace of star
clusters. Combined with the code for star cluster evolution CMC, we are able to
produce populations of dynamically formed merging BBHs across cosmic time in
different environments. As the most massive star clusters preferentially form
in dense massive clouds of gas, we find that, despite their low metallicities
favourable to the creation of black holes, low-mass galaxies contain few
massive clusters and therefore have a limited contribution to the global
production of dynamically formed merging BBHs. Furthermore, we find that
massive clusters can host hierarchical BBH mergers with clear identifiable
physical properties. Looking at the evolution of the BBH merger rate in
different galaxies, we find strong correlations between BBH mergers and the
most extreme episodes of star formation. Finally, we discuss the implications
for future LIGO-Virgo-KAGRA gravitational wave observations.Comment: 14 pages, 9 figures, 3 table
Is the black-widow pulsar PSR J1555-2908 in a hierarchical triple system?
The 559 Hz black-widow pulsar PSR J1555-2908, originally discovered in radio, is also a bright gamma-ray pulsar. Timing its pulsations using 12 yr of Fermi-LAT gamma-ray data reveals long-term variations in its spin frequency that are much larger than is observed from other millisecond pulsars. While this variability in the pulsar rotation rate could be intrinsic "timing noise", here we consider an alternative explanation: the variations arise from the presence of a very-low-mass third object in a wide multi-year orbit around the neutron star and its low-mass companion. With current data, this hierarchical-triple-system model describes the pulsar's rotation slightly more accurately than the best-fitting timing-noise model. Future observations will show if this alternative explanation is correct
Is the Black-widow Pulsar PSR J1555-2908 in a Hierarchical Triple System?
The 559 Hz black-widow pulsar PSR J1555-2908, originally discovered in radio, is also a bright gamma-ray pulsar. Timing its pulsations using 12 yr of Fermi-Large Area Telescope gamma-ray data reveals long-term variations in its spin frequency that are much larger than is observed from other millisecond pulsars. While this variability in the pulsar rotation rate could be intrinsic "timing noise,"here we consider an alternative explanation: the variations arise from the presence of a very-low-mass third object in a wide multiyear orbit around the neutron star and its low-mass companion. With current data, this hierarchical-triple-system model describes the pulsar's rotation slightly more accurately than the best-fitting timing noise model. Future observations will show if this alternative explanation is correct. © 2022. The Author(s). Published by the American Astronomical Society
The effects of graded levels of calorie restriction : I. impact of short term calorie and protein restriction on body composition in the C57BL/6 mouse
We acknowledge the BSU staff for their invaluable help with caring for the animals and anonymous referees for their inputs. The work was supported by the Biotechnology and Biological Sciences Research Council (BBSRC) of the UK (Standard grant BB/G009953/1 and China partnering award BB/JO20028/1). The authors declare no competing interests.Peer reviewedPublisher PD
Impact of extreme weather events frequency and intensity in shaping phytoplankton communities
Lake habitats and communities can often be correlated with general morphometric and geographic
characteristics such as depth, latitude, altitude, or watershed area. Further, communities are typically
correlated with average environmental conditions such as seasonal temperature and nutrient levels. The
frequency and intensity of extreme weather events (rain and wind) are typically not encompassed by average
environmental descriptors, yet, can modify the physical habitats of lakes, significantly influencing
phytoplankton growth and survival. We tested the hypothesis that lakes with a higher frequency and intensity
of extreme weather events have a functionally different phytoplankton assemblage from lakes with a lower
frequency of extreme weather events. We compiled long-term (mean = 20±13 years, range 0.6-44 years)
phytoplankton datasets for 22 lakes across a wide gradient of altitude, latitude, depth, and trophic state. We
classified the phytoplankton genera into morpho-functional groups and C-S-R strategists, and compared
among lake phytoplankton assemblagesâ characteristics across the gradient of wind and rain conditions
experienced by the lakes. We discuss how the frequency of extreme weather events can affect phytoplankton
functional groups, the dominance of differing life history strategies and ultimately community structure. The
frequency and intensity of extreme events is expected to increase with climate change, with the potential to
drive shifts in phytoplankton composition
A global dataset on weather, lake physics, and phytoplankton dynamics
We compiled data from over 30 lakes across the globe to address how storms influence thermal structure
and phytoplankton community dynamics mediated by lake conditions and functional traits. In addition to
(generally) fortnightly phytoplankton samples (mean ± SD temporal coverage across all lakes = 20 ± 13 years),
the dataset includes limnological variables from standard long-term monitoring programs (24 ± 15 years
coverage), daily weather observations (16 ± 10 years coverage) and, when available, high-frequency lake
water temperature and water chemistry profiles (12 ± 7 years coverage). All data have been standardized to
similar formats and include complete metadata. We used the dataset to develop an R-package
(âalgaeClassifyâ), which assigns phytoplankton genus/species information to multiple functional trait groups,
and here we provide a summary of ongoing research using the dataset to investigate: 1) the influence of storm
events on seasonal phytoplankton succession, 2) the impact of storms on lake thermal structure, and 3)
whether lake phytoplankton communities are shaped by long-term patterns in disturbance frequency and
intensity. We give an overview on how to access these data, and we further highlight the opportunities the
dataset provides for asking both basic and applied questions in limnology, ecology, climate change, and lake
management
GPs' reasons for referral of patients with chest pain: a qualitative study
<p>Abstract</p> <p>Background</p> <p>Prompt diagnosis of an acute coronary syndrome is very important and urgent referral to a hospital is imperative because fast treatment can be life-saving and increase the patient's life expectancy and quality of life. The aim of our study was to identify GPs' reasons for referring or not referring patients presenting with chest pain.</p> <p>Methods</p> <p>In a semi-structured interview, 21 GPs were asked to describe why they do or do not refer a patient presenting with chest pain. Interviews were taped, transcribed and qualitatively analysed.</p> <p>Results</p> <p>Histories of 21 patients were studied. Six were not referred, seven were referred to a cardiologist and eight to the emergency department. GPs' reasons for referral were background knowledge about the patient, patient's age and cost-benefit estimation, the perception of a negative attitude from the medical rescue team, recent patient contact with a cardiologist without detection of a coronary disease and the actual presentation of signs and symptoms, gut feeling, clinical examination and ECG results.</p> <p>Conclusion</p> <p>This study suggests that GPs believe they do not exclusively use the 'classical' signs and symptoms in their decision-making process for patients presenting with chest pain. Background knowledge about the patient, GPs' personal ideas and gut feeling are also important.</p
The pregnane X receptor drives sexually dimorphic hepatic changes in lipid and xenobiotic metabolism in response to gut microbiota in mice.
The gut microbiota-intestine-liver relationship is emerging as an important factor in multiple hepatic pathologies, but the hepatic sensors and effectors of microbial signals are not well defined.
By comparing publicly available liver transcriptomics data from conventional vs. germ-free mice, we identified pregnane X receptor (PXR, NR1I2) transcriptional activity as strongly affected by the absence of gut microbes. Microbiota depletion using antibiotics in Pxr <sup>+/+</sup> vs Pxr <sup>-/-</sup> C57BL/6J littermate mice followed by hepatic transcriptomics revealed that most microbiota-sensitive genes were PXR-dependent in the liver in males, but not in females. Pathway enrichment analysis suggested that microbiota-PXR interaction controlled fatty acid and xenobiotic metabolism. We confirmed that antibiotic treatment reduced liver triglyceride content and hampered xenobiotic metabolism in the liver from Pxr <sup>+/+</sup> but not Pxr <sup>-/-</sup> male mice.
These findings identify PXR as a hepatic effector of microbiota-derived signals that regulate the host's sexually dimorphic lipid and xenobiotic metabolisms in the liver. Thus, our results reveal a potential new mechanism for unexpected drug-drug or food-drug interactions. Video abstract
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