471 research outputs found
Terrestrial Effects of Nearby Supernovae: Updated Modeling
We have re-evaluated recent studies of effects on Earth by cosmic rays (CRs)
from nearby supernovae (SNe) at 100 pc and 50 pc, in the diffusive transport CR
case, here including an early time suppression at lower CR energies neglected
in the previous work. Inclusion of this suppression leads to lower overall CR
flux at early times, lower atmospheric ionization, smaller resulting ozone
depletion, and lower sea-level muon radiation dose. Differences in atmospheric
impacts are most pronounced for the 100 pc case with less significant
differences in the 50 pc case. We find a greater discrepancy in the modeled
sea-level muon radiation dose, with significantly smaller dose values in the 50
pc case; our results indicate it is unlikely that muon radiation is a
significant threat to the biosphere for SNe beyond at least 20 pc. We have also
performed new modeling of effects by SNe at 20 pc and 10 pc. Overall, our
results indicate that, considering only effects of SN CRs, the "lethal" SN
distance may be closer to 20 pc rather than the typically quoted 8-10 pc.Comment: 21 pages, 6 figures; submitted to Ap
Quantum Oscillations in the Underdoped Cuprate YBa2Cu4O8
We report the observation of quantum oscillations in the underdoped cuprate
superconductor YBa2Cu4O8 using a tunnel-diode oscillator technique in pulsed
magnetic fields up to 85T. There is a clear signal, periodic in inverse field,
with frequency 660+/-15T and possible evidence for the presence of two
components of slightly different frequency. The quasiparticle mass is
m*=3.0+/-0.3m_e. In conjunction with the results of Doiron-Leyraud et al. for
YBa2Cu3O6.5, the present measurements suggest that Fermi surface pockets are a
general feature of underdoped copper oxide planes and provide information about
the doping dependence of the Fermi surface.Comment: Contains revisions addressing referees' comments including a
different Fig 1b. 4 pages, 4 figure
Dirac Surface States and Nature of Superconductivity in Noncentrosymmetric BiPd
In non-magnetic bulk materials, inversion symmetry protects the spin
degeneracy. If the bulk crystal structure lacks a centre of inversion, however,
spin-orbit interactions lift the spin degeneracy, leading to a Rashba metal
whose Fermi surfaces exhibit an intricate spin texture. In superconducting
Rashba metals a pairing wavefunction constructed from these complex spin
structures will generally contain both singlet and triplet character. Here we
examine the possible triplet components of the order parameter in
noncentrosymmetric BiPd, combining for the first time in a noncentrosymmetric
superconductor macroscopic characterization, atomic-scale ultra-low-temperature
scanning tunnelling spectroscopy, and relativistic first-principles
calculations. While the superconducting state of BiPd appears topologically
trivial, consistent with Bardeen-Cooper-Schrieffer theory with an order
parameter governed by a single isotropic s-wave gap, we show that the material
exhibits Dirac-cone surface states with a helical spin polarization.Comment: replaced by published versio
Managing shoulder pain in general practice: The value of academic detailing
Copyright © Royal Australian College of General Practitioners Copyright to Australian Family Physician. Reproduced with permission. Permission to reproduce must be sought from the publisher, The Royal Australian College of General Practitioners.After low back pain and neck pain, shoulder pain is the third musculoskeletal reason for presentation to general practice, with a self reported prevalence of 16-26%. Approximately 1% of the adult population is expected to visit a general practitioner annually for shoulder pain. Shoulder complaints are more common in women and despite the fact that 50% of acute shoulder pain resolves in 8-10 weeks, many patients present with the anticipation of being referred for imaging.Norman A. Broadhurst, Christopher A. Barton, Lisa N. Yelland, David K. Martin and Justin J. Beilb
Superconductivity induced by spark erosion in ZrZn2
We show that the superconductivity observed recently in the weak itinerant
ferromagnet ZrZn2 [C. Pfleiderer et al., Nature (London) 412, 58 (2001)] is due
to remnants of a superconducting layer induced by spark erosion. Results of
resistivity, susceptibility, specific heat and surface analysis measurements on
high-quality ZrZn2 crystals show that cutting by spark erosion leaves a
superconducting surface layer. The resistive superconducting transition is
destroyed by chemically etching a layer of 5 microns from the sample. No
signature of superconductivity is observed in rho(T) of etched samples at the
lowest current density measured, J=675 Am-2, and at T < 45 mK. EDX analysis
shows that spark-eroded surfaces are strongly Zn depleted. The simplest
explanation of our results is that the superconductivity results from an alloy
with higher Zr content than ZrZn2.Comment: Final published versio
VEGFA, B, C: Implications of the C-Terminal Sequence Variations for the Interaction with Neuropilins
Vascular endothelial growth factors (VEGFs) are the key regulators of blood and lymphatic vessels’ formation and function. Each of the proteins from the homologous family VEGFA, VEGFB, VEGFC and VEGFD employs a core cysteine-knot structural domain for the specific interaction with one or more of the cognate tyrosine kinase receptors. Additional diversity is exhibited by the involvement of neuropilins–transmembrane co-receptors, whose b1 domain contains the binding site for the C-terminal sequence of VEGFs. Although all relevant isoforms of VEGFs that interact with neuropilins contain the required C-terminal Arg residue, there is selectivity of neuropilins and VEGF receptors for the VEGF proteins, which is reflected in the physiological roles that they mediate. To decipher the contribution made by the C-terminal sequences of the individual VEGF proteins to that functional differentiation, we determined structures of molecular complexes of neuropilins and VEGFderived peptides and examined binding interactions for all neuropilin-VEGF pairs experimentally and computationally. While X-ray crystal structures and ligand-binding experiments highlighted similarities between the ligands, the molecular dynamics simulations uncovered conformational preferences of VEGF-derived peptides beyond the C-terminal arginine that contribute to the ligand selectivity of neuropilins. The implications for the design of the selective antagonists of neuropilins’ functions are discussed
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MP3 - A meteorology and physical properties package to explore air-sea interaction on Titan
The exchange of mass, heat and momentum at the air:sea interface are profound influences on the terrestrial environment, affecting the intensity of hurricanes, the size of waves and lake-effect precipitation. Titan presents us with an opportunity to study these processes in a novel physical context, with a different sea, atmosphere and gravity. The MP3 instrument, under development for the proposed Discovery mission TiME (Titan Mare Explorer [1,2]) is an integrated suite of small, simple sensors that combines the function of traditional meteorology packages with liquid physical properties and depth-sounding : these latter functions follow the concept of - and indeed use spare elements from - the Huygens Surface Science Package (SSP,[3]). However, unlike Huygens’ brief and dynamic 3 hours of measurement, in TiME’s 6-Titan-day (96 Earth day) nominal mission enabled by radioisotope power, MP3 will have an unprecedented long-term measurement opportunity in one of the most evocative environments in the solar system, Titan’s sea Ligeia Mare
Handling misclassified stratification variables in the analysis of randomised trials with continuous outcomes
Many trials use stratified randomisation, where participants are randomised within strata defined by one or more baseline covariates. While it is important to adjust for stratification variables in the analysis, the appropriate method of adjustment is unclear when stratification variables are affected by misclassification and hence some participants are randomised in the incorrect stratum. We conducted a simulation study to compare methods of adjusting for stratification variables affected by misclassification in the analysis of continuous outcomes when all or only some stratification errors are discovered, and when the treatment effect or treatment-by-covariate interaction effect is of interest. The data were analysed using linear regression with no adjustment, adjustment for the strata used to perform the randomisation (randomisation strata), adjustment for the strata if all errors are corrected (true strata), and adjustment for the strata after some errors are discovered and corrected (updated strata). The unadjusted model performed poorly in all settings. Adjusting for the true strata was optimal, while the relative performance of adjusting for the randomisation strata or the updated strata varied depending on the setting. As the true strata are unlikely to be known with certainty in practice, we recommend using the updated strata for adjustment and performing subgroup analyses, provided the discovery of errors is unlikely to depend on treatment group, as expected in blinded trials. Greater transparency is needed in the reporting of stratification errors and how they were addressed in the analysis
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