Marine Ice-Pushed Boulder Ridge, Beaufort Sea, Alaska

A steep-faced boulder ridge up to 4 m high by 300 m long was encountered along the arctic coast east of Prudhoe Bay, Alaska, in the summer of 1979. Marine occurrences of similar ridges are rare. Since ice-push sorts cobble- and boulder-sized material in the construction of a ridge, recent onshore excursions of ice due to wind stress on the fast ice are believed to be responsible for building the boulder ridge. Ice push is a mechanism that preferentially sorts cobble- and boulder-sized material from 1-2 water depths and that forms boulder ridges in areas of high boulder concentrations.Key words: marine ice-pushed boulder ridge, Beaufort Sea, Alask

A thermal plume in NGC 2024

We present 1-arcmin resolution radio images of the Galactic H II region NGC 2024 made at 0.33 and 10.55 GHz. These are the highest dynamic range images of the nebula to date. The peak brightness in the 0.33-GHz radio continuum image indicates that the electron temperature is 6800–7600 K. The images clarify the structure of a thermal plume that is directed north from the H II region and opposite to a unipolar molecular outflow found in the molecular cloud near the H II region. We report the detection of H91α recombination lines from the plume: these data confirm that the plume is blueshifted relative to the molecular cloud. Finally, we discuss the relative merits of three possible explanations for the plume: that the plume results from the blueshifted counterjet to the CO outflow; that the plume is the continuation of the champagne flow observed in the denser parts of the H II region; and that the plume is produced by the photoevaporation of molecular clumps apparent in a 13CO map of the region

“Is it a slow day or a go day?”: The perceptions and applications of velocity-based training within elite strength and conditioning

Velocity-based training (VBT) is a contemporary prescriptive, programming, and testing tool commonly utilised in strength and conditioning (S&C). Over recent years, there has been an influx of peer-reviewed literature investigating several different applications (e.g. load-velocity profiling, velocity loss, load manipulation, and reliability of technology) of VBT. The procedures implemented in research, however, do not always reflect the practices within applied environments. The aim of this study, therefore, was to investigate the perceptions and applications of VBT within elite S&C to enhance contextual understanding and develop appropriate avenues of practitioner-focused research. Fourteen high-performance S&C coaches participated in semi-structured interviews to discuss their experiences of implementing VBT into their practices. Reflexive thematic analysis was adopted, following an inductive and realist approach. Three central organising themes emerged: Technology, applications, and reflections. Within these central themes, higher order themes consisting of drivers for buying technology; programming, testing, monitoring, and feedback; and benefits, drawbacks, and future uses also emerged. Practitioners reported varied drivers and applications of VBT, often being dictated by simplicity, environmental context, and personal preferences. Coaches perceived VBT to be a beneficial tool yet were cognizant of the drawbacks and challenges in certain settings. VBT is a flexible tool that can support and aid several aspects of S&C planning and delivery, with coaches valuing the impact it can have on training environments, objective prescriptions, tracking player readiness, and programme success.publishedVersio

On the potential of a new generation of magnetometers for MEG: a beamformer simulation study

Magnetoencephalography (MEG) is a sophisticated tool which yields rich information on the spatial, spectral and temporal signatures of human brain function. Despite unique potential, MEG is limited by a low signal-to-noise ratio (SNR) which is caused by both the inherently small magnetic fields generated by the brain, and the scalp-to-sensor distance. The latter is limited in current systems due to a requirement for pickup coils to be cryogenically cooled. Recent work suggests that optically-pumped magnetometers (OPMs) might be a viable alternative to superconducting detectors for MEG measurement. They have the advantage that sensors can be brought to within ~4 mm of the scalp, thus offering increased sensitivity. Here, using simulations, we quantify the advantages of hypothetical OPM systems in terms of sensitivity, reconstruction accuracy and spatial resolution. Our results show that a multi-channel whole-head OPM system offers (on average) a fivefold improvement in sensitivity for an adult brain, as well as clear improvements in reconstruction accuracy and spatial resolution. However, we also show that such improvements depend critically on accurate forward models; indeed, the reconstruction accuracy of our simulated OPM system only outperformed that of a simulated superconducting system in cases where forward field error was less than 5%. Overall, our results imply that the realisation of a viable whole-head multi-channel OPM system could generate a step change in the utility of MEG as a means to assess brain electrophysiological activity in health and disease. However in practice, this will require both improved hardware and modelling algorithms

The elevated Curie temperature and half-metallicity in the ferromagnetic semiconductor Lax_{x}Eu1−x_{1-x}O

Here we study the effect of La doping in EuO thin films using SQUID magnetometry, muon spin rotation ($\mu$SR), polarized neutron reflectivity (PNR), and density functional theory (DFT). The $\mu$SR data shows that the La$_{0.15}$Eu$_{0.85}$O is homogeneously magnetically ordered up to its elevated $T_{\rm C}$. It is concluded that bound magnetic polaron behavior does not explain the increase in $T_{\rm C}$ and an RKKY-like interaction is consistent with the $\mu$SR data. The estimation of the magnetic moment by DFT simulations concurs with the results obtained by PNR, showing a reduction of the magnetic moment per La$_{x}$Eu$_{1-x}$O for increasing lanthanum doping. This reduction of the magnetic moment is explained by the reduction of the number of Eu-4$f$ electrons present in all the magnetic interactions in EuO films. Finally, we show that an upwards shift of the Fermi energy with La or Gd doping gives rise to half-metallicity for doping levels as high as 3.2 %.Comment: 7 pages, 11 figure

What is the relationship between photospheric flow fields and solar flares?

We estimated photospheric velocities by separately applying the Fourier Local Correlation Tracking (FLCT) and Differential Affine Velocity Estimator (DAVE) methods to 2708 co-registered pairs of SOHO/MDI magnetograms, with nominal 96-minute cadence and ~2" pixels, from 46 active regions (ARs) from 1996-1998 over the time interval t45 when each AR was within 45^o of disk center. For each magnetogram pair, we computed the average estimated radial magnetic field, B; and each tracking method produced an independently estimated flow field, u. We then quantitatively characterized these magnetic and flow fields by computing several extensive and intensive properties of each; extensive properties scale with AR size, while intensive properties do not depend directly on AR size. Intensive flow properties included moments of speeds, horizontal divergences, and radial curls; extensive flow properties included sums of these properties over each AR, and a crude proxy for the ideal Poynting flux, the total |u| B^2. Several magnetic quantities were also computed, including: total unsigned flux; a measure of the amount of unsigned flux near strong-field polarity inversion lines, R; and the total B^2. Next, using correlation and discriminant analysis, we investigated the associations between these properties and flares from the GOES flare catalog, when averaged over both t45 and shorter time windows, of 6 and 24 hours. We found R and total |u| B^2 to be most strongly associated with flares; no intensive flow properties were strongly associated with flares.Comment: 57 pages, 13 figures; revised content; added URL to manuscript with higher-quality image

A Hierarchical Array of Integrable Models

Motivated by Harish-Chandra theory, we construct, starting from a simple CDD\--pole $S$\--matrix, a hierarchy of new $S$\--matrices involving ever ``higher'' (in the sense of Barnes) gamma functions.These new $S$\--matrices correspond to scattering of excitations in ever more complex integrable models.From each of these models, new ones are obtained either by ``$q$\--deformation'', or by considering the Selberg-type Euler products of which they represent the ``infinite place''. A hierarchic array of integrable models is thus obtained. A remarkable diagonal link in this array is established.Though many entries in this array correspond to familiar integrable models, the array also leads to new models. In setting up this array we were led to new results on the $q$\--gamma function and on the $q$\--deformed Bloch\--Wigner function.Comment: 18 pages, EFI-92-2

Spin and Charge Structure Factor of the 2-d Hubbard Model

The spin and charge structure factors are calculated for the Hubbard model on the square lattice near half-filling using a spin-rotation invariant six-slave boson representation. The charge structure factor shows a broad maximum at the zone corner and is found to decrease monotonically with increasing interaction strength and electron density and increasing temperature. The spin structure factor develops with increasing interaction two incommensurate peaks at the zone boundary and along the zone diagonal. Comparison with results of Quantum Monte Carlo and variational calculations is carried out and the agreement is found to be good. The limitations of an RPA-type approach are pointed out.Comment: 18 pages, revtex, 13 postscript figures, submitted to Phys. Rev.