1,633 research outputs found
Finite temperature phase diagram of a polarised Fermi condensate
The two-component Fermi gas is the simplest fermion system displaying
superfluidity, and as such finds applications ranging from the theory of
superconductivity to QCD. Ultracold atomic gases provide an exceptionally clean
realization of this system, where the interatomic interaction and the atom
species population are both independent, tuneable parameters. This allows one
to investigate the Fermi gas with imbalanced spin populations, which had
previously been experimentally elusive, and this prospect has stimulated much
theoretical activity. Here we show that the finite temperature phase diagram
contains a region of phase separation between the superfluid and normal states
that touches the boundary of second-order superfluid transitions at a
tricritical point, reminiscent of the phase diagram of He-He mixtures.
A variation of interaction strength then results in a line of tricritical
points that terminates at zero temperature on the molecular Bose-Einstein
condensate (BEC) side. On this basis, we argue that tricritical points will
play an important role in the recent experiments on polarised atomic Fermi
gases.Comment: 6 pages, 4 figures. Manuscript extended and figures modified. For
final version, see Nature Physic
Directional memory arises from long-lived cytoskeletal asymmetries in polarized chemotactic cells
Chemotaxis, the directional migration of cells in a chemical gradient, is robust to fluctuations associated with low chemical concentrations and dynamically changing gradients as well as high saturating chemical concentrations. Although a number of reports have identified cellular behavior consistent with a directional memory that could account for behavior in these complex environments, the quantitative and molecular details of such a memory process remain unknown. Using microfluidics to confine cellular motion to a 1D channel and control chemoattractant exposure, we observed directional memory in chemotactic neutrophil-like cells. We modeled this directional memory as a long-lived intracellular asymmetry that decays slower than observed membrane phospholipid signaling. Measurements of intracellular dynamics revealed that moesin at the cell rear is a long-lived element that when inhibited, results in a reduction of memory. Inhibition of ROCK (Rho-associated protein kinase), downstream of RhoA (Ras homolog gene family, member A), stabilized moesin and directional memory while depolymerization of microtubules (MTs) disoriented moesin deposition and also reduced directional memory. Our study reveals that long-lived polarized cytoskeletal structures, specifically moesin, actomyosin, and MTs, provide a directional memory in neutrophil-like cells even as they respond on short time scales to external chemical cues
Determination of the Fermion Pair Size in a Resonantly Interacting Superfluid
Fermionic superfluidity requires the formation of pairs. The actual size of
these fermion pairs varies by orders of magnitude from the femtometer scale in
neutron stars and nuclei to the micrometer range in conventional
superconductors. Many properties of the superfluid depend on the pair size
relative to the interparticle spacing. This is expressed in BCS-BEC crossover
theories, describing the crossover from a Bardeen-Cooper-Schrieffer (BCS) type
superfluid of loosely bound and large Cooper pairs to Bose-Einstein
condensation (BEC) of tightly bound molecules. Such a crossover superfluid has
been realized in ultracold atomic gases where high temperature superfluidity
has been observed. The microscopic properties of the fermion pairs can be
probed with radio-frequency (rf) spectroscopy. Previous work was difficult to
interpret due to strong and not well understood final state interactions. Here
we realize a new superfluid spin mixture where such interactions have
negligible influence and present fermion-pair dissociation spectra that reveal
the underlying pairing correlations. This allows us to determine the
spectroscopic pair size in the resonantly interacting gas to be 2.6(2)/kF (kF
is the Fermi wave number). The pairs are therefore smaller than the
interparticle spacing and the smallest pairs observed in fermionic superfluids.
This finding highlights the importance of small fermion pairs for superfluidity
at high critical temperatures. We have also identified transitions from fermion
pairs into bound molecular states and into many-body bound states in the case
of strong final state interactions.Comment: 8 pages, 7 figures; Figures updated; New Figures added; Updated
discussion of fit function
Precise measurement of positronium hyperfine splitting using the Zeeman effect
Positronium is an ideal system for the research of the quantum
electrodynamics (QED) in bound state. The hyperfine splitting (HFS) of
positronium, , gives a good test of the bound state
calculations and probes new physics beyond the Standard Model. A new method of
QED calculations has revealed the discrepancy by 15\,ppm (3.9) of
between the QED prediction and the experimental
average. There would be possibility of new physics or common systematic
uncertainties in the previous all experiments. We describe a new experiment to
reduce possible systematic uncertainties and will provide an independent check
of the discrepancy. We are now taking data and the current result of
has been obtained so far. A measurement with a precision of (ppm) is
expected within a year.Comment: 8 pages, 8 figures, 2 tables, proceeding of LEAP2011, accepted by
Hyperfine Interaction
Automated data analysis to rapidly derive and communicate ecological insights from satellite-tag data: A case study of reintroduced red kites
Analysis of satellite-telemetry data mostly occurs long after it has been collected, due to the time and effort needed to collate and interpret such material. Such delayed reporting does reduce the usefulness of such data for nature conservation when timely information about animal movements is required. To counter this problem we present a novel approach which combines automated analysis of satellite-telemetry data with rapid communication of insights derived from such data. A relatively simple algorithm (comprising speed of movement and turning angle calculated from fixes), allowed instantaneous detection of excursions away from settlement areas and automated calculation of home ranges on the remaining data Automating the detection of both excursions and home range calculations enabled us to disseminate ecological insights from satellite-tag data instantaneously through a dedicated web portal to inform conservationists and wider audiences. We recommend automated analysis, interpretation and communication of satellite tag and other ecological data to advance nature conservation research and practice
High Post-Capture Survival for Sharks, Rays and Chimaeras Discarded in the Main Shark Fishery of Australia?
Most sharks, rays and chimaeras (chondrichthyans) taken in commercial fisheries are discarded (i.e. returned to the ocean either dead or alive). Quantifying the post-capture survival (PCS) of discarded species is therefore essential for the improved management and conservation of this group. For all chondrichthyans taken in the main shark fishery of Australia, we quantified the immediate PCS of individuals reaching the deck of commercial shark gillnet fishing vessels and applied a risk-based method to semi-quantitatively determine delayed and total PCS. Estimates of immediate, delayed and total PCS were consistent, being very high for the most commonly discarded species (Port Jackson shark, Australian swellshark, and spikey dogfish) and low for the most important commercial species (gummy and school sharks). Increasing gillnet soak time or water temperature significantly decreased PCS. Chondrichthyans with bottom-dwelling habits had the highest PCS whereas those with pelagic habits had the lowest PCS. The risk-based approach can be easily implemented as a standard practice of on-board observing programs, providing a convenient first-step assessment of the PCS of all species taken in commercial fisheries
The extraordinary evolutionary history of the reticuloendotheliosis viruses
The reticuloendotheliosis viruses (REVs) comprise several closely related amphotropic retroviruses isolated from birds. These viruses exhibit several highly unusual characteristics that have not so far been adequately explained, including their extremely close relationship to mammalian retroviruses, and their presence as endogenous sequences within the genomes of certain large DNA viruses. We present evidence for an iatrogenic origin of REVs that accounts for these phenomena. Firstly, we identify endogenous retroviral fossils in mammalian genomes that share a unique recombinant structure with REVs—unequivocally demonstrating that REVs derive directly from mammalian retroviruses. Secondly, through sequencing of archived REV isolates, we confirm that contaminated Plasmodium lophurae stocks have been the source of multiple REV outbreaks in experimentally infected birds. Finally, we show that both phylogenetic and historical evidence support a scenario wherein REVs originated as mammalian retroviruses that were accidentally introduced into avian hosts in the late 1930s, during experimental studies of P. lophurae, and subsequently integrated into the fowlpox virus (FWPV) and gallid herpesvirus type 2 (GHV-2) genomes, generating recombinant DNA viruses that now circulate in wild birds and poultry. Our findings provide a novel perspective on the origin and evolution of REV, and indicate that horizontal gene transfer between virus families can expand the impact of iatrogenic transmission events
ARPES: A probe of electronic correlations
Angle-resolved photoemission spectroscopy (ARPES) is one of the most direct
methods of studying the electronic structure of solids. By measuring the
kinetic energy and angular distribution of the electrons photoemitted from a
sample illuminated with sufficiently high-energy radiation, one can gain
information on both the energy and momentum of the electrons propagating inside
a material. This is of vital importance in elucidating the connection between
electronic, magnetic, and chemical structure of solids, in particular for those
complex systems which cannot be appropriately described within the
independent-particle picture. Among the various classes of complex systems, of
great interest are the transition metal oxides, which have been at the center
stage in condensed matter physics for the last four decades. Following a
general introduction to the topic, we will lay the theoretical basis needed to
understand the pivotal role of ARPES in the study of such systems. After a
brief overview on the state-of-the-art capabilities of the technique, we will
review some of the most interesting and relevant case studies of the novel
physics revealed by ARPES in 3d-, 4d- and 5d-based oxides.Comment: Chapter to appear in "Strongly Correlated Systems: Experimental
Techniques", edited by A. Avella and F. Mancini, Springer Series in
Solid-State Sciences (2013). A high-resolution version can be found at:
http://www.phas.ubc.ca/~quantmat/ARPES/PUBLICATIONS/Reviews/ARPES_Springer.pdf.
arXiv admin note: text overlap with arXiv:cond-mat/0307085,
arXiv:cond-mat/020850
Differential Response of High-Elevation Planktonic Bacterial Community Structure and Metabolism to Experimental Nutrient Enrichment
Nutrient enrichment of high-elevation freshwater ecosystems by atmospheric deposition is increasing worldwide, and bacteria are a key conduit for the metabolism of organic matter in these oligotrophic environments. We conducted two distinct in situ microcosm experiments in a high-elevation lake (Emerald Lake, Sierra Nevada, California, USA) to evaluate responses in bacterioplankton growth, carbon utilization, and community structure to short-term enrichment by nitrate and phosphate. The first experiment, conducted just following ice-off, employed dark dilution culture to directly assess the impact of nutrients on bacterioplankton growth and consumption of terrigenous dissolved organic matter during snowmelt. The second experiment, conducted in transparent microcosms during autumn overturn, examined how bacterioplankton in unmanipulated microbial communities responded to nutrients concomitant with increasing phytoplankton-derived organic matter. In both experiments, phosphate enrichment (but not nitrate) caused significant increases in bacterioplankton growth, changed particulate organic stoichiometry, and induced shifts in bacterial community composition, including consistent declines in the relative abundance of Actinobacteria. The dark dilution culture showed a significant increase in dissolved organic carbon removal in response to phosphate enrichment. In transparent microcosms nutrient enrichment had no effect on concentrations of chlorophyll, carbon, or the fluorescence characteristics of dissolved organic matter, suggesting that bacterioplankton responses were independent of phytoplankton responses. These results demonstrate that bacterioplankton communities in unproductive high-elevation habitats can rapidly alter their taxonomic composition and metabolism in response to short-term phosphate enrichment. Our results reinforce the key role that phosphorus plays in oligotrophic lake ecosystems, clarify the nature of bacterioplankton nutrient limitation, and emphasize that evaluation of eutrophication in these habitats should incorporate heterotrophic microbial communities and processes
2019 international consensus on cardiopulmonary resuscitation and emergency cardiovascular care science with treatment recommendations : summary from the basic life support; advanced life support; pediatric life support; neonatal life support; education, implementation, and teams; and first aid task forces
The International Liaison Committee on Resuscitation has initiated a continuous review of new, peer-reviewed, published cardiopulmonary resuscitation science. This is the third annual summary of the International Liaison Committee on Resuscitation International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science With Treatment Recommendations. It addresses the most recent published resuscitation evidence reviewed by International Liaison Committee on Resuscitation Task Force science experts. This summary addresses the role of cardiac arrest centers and dispatcher-assisted cardiopulmonary resuscitation, the role of extracorporeal cardiopulmonary resuscitation in adults and children, vasopressors in adults, advanced airway interventions in adults and children, targeted temperature management in children after cardiac arrest, initial oxygen concentration during resuscitation of newborns, and interventions for presyncope by first aid providers. Members from 6 International Liaison Committee on Resuscitation task forces have assessed, discussed, and debated the certainty of the evidence on the basis of the Grading of Recommendations, Assessment, Development, and Evaluation criteria, and their statements include consensus treatment recommendations. Insights into the deliberations of the task forces are provided in the Justification and Evidence to Decision Framework Highlights sections. The task forces also listed priority knowledge gaps for further research
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