Fiber-optical analogue of the event horizon

The physics at the event horizon resembles the behavior of waves in moving media. Horizons are formed where the local speed of the medium exceeds the wave velocity. We use ultrashort pulses in microstructured optical fibers to demonstrate the formation of an artificial event horizon in optics. We observed a classical optical effect, the blue-shifting of light at a white-hole horizon. We also show by theoretical calculations that such a system is capable of probing the quantum effects of horizons, in particular Hawking radiation.Comment: MEDIA EMBARGO. This paper is subject to the media embargo of Scienc

Understanding the influence of the head coach on soccer training drills—an 8 season analysis

Soccer players perform a variety of training drills to develop the physical, technical and tactical qualities required for match-play. The role of coaches in prescribing training suggests that players may not always meet physical targets set by conditioning staff. To quantify the physical outputs elicited by different training drill types, 183 professional soccer players were monitored over 8 seasons using Microelectromechanical Systems during normal training, yielding 65,825 drill observations [362 ± 341 observations·player−1]. Linear mixed models assessed the influence of drill type, head coach and playing position on physical output. Drills lasted ~14 min, eliciting total distances and high speed running of ~1000 m and 40 m, respectively. Conditioning drills elicited substantially greater relative high-speed running [18.8 ± 27.2 m.min−1] and Sprint [3.5 ± 9.4 m.min−1] distances than all other drill types. The proportion of training drill types used and external outputs elicited per drill were affected by the head coach. Midfielders recorded the highest total distance [77.3 ± 36.1 m.min] and PlayerLoad™ [8.29 ± 3.54] of any playing position, whilst the lowest outputs were recorded by goalkeepers. This study provides reference data for practitioners when seeking to manipulate training prescription to achieve physical output targets whilst also meeting the team’s technical and tactical objectives

Evaluating Psychometric Properties of the International Knee Documentation Committee Subjective Knee Form in a Heterogeneous Sample of Post-Operative Patients

# Background The International Knee Document Committee Subjective Knee Form (IKDC-SKF) is a patient-reported outcome measure used in orthopedics and sports medicine. Further psychometric assessment is necessary to confirm measurement properties in a large, heterogenous sample. # Purpose The purpose of the study was to assess the psychometric properties of the IKDC-SKF in a large, heterogenous sample. # Study Design Cross-Sectional Study # Methods An exploratory factor analysis (EFA) was conducted to identify a sound latent structure and to assess internal consistency in a large sample of patients who underwent knee arthroscopy. A confirmatory factor analysis (CFA) was conducted to confirm structural validity. Multi-group invariance was conducted to assess factorial stability across sex and age groups, while longitudinal invariance procedures were performed to assess stability over time. # Results A 3-factor, 9-item IKDC-SKF short form was identified with EFA procedures. The model was confirmed with CFA (CFI = 0.983; TLI = 0.975; IFI = 0.983; RMSEA = 0.057), while a sound 2-factor, 6-item model was also identified (CFI = 1.0; TLI = 0.999; IFI = 1.0; RMSEA = 0.11). The 9-item IKDC-SKF short form was invariant across groups but not time; removal of a single item (i.e., 8-item IKDC-SKF short form) resulted in longitudinal invariance. The 6-item IKDC-SKF short form was invariant across groups and time. # Conclusion The 6-item, 8-item, and 9-item short form versions of the IKDC-SKF exceed contemporary fit recommendations and present as plausible alternatives to the IKDC-SKF with improved measurement properties, reduced scale response burden, and evidence of multi-group and longitudinal invariance. Further, the 6- and 8-item IKDC-SKF short forms may be used to assess group differences or change across time. # Level of evidence here Level 3 ©The Author(s

Plasmatrough exohiss waves observed by Van Allen Probes: Evidence for leakage from plasmasphere and resonant scattering of radiation belt electrons

Abstract Exohiss waves are whistler mode hiss observed in the plasmatrough region. We present a case study of exohiss waves and the corresponding background plasma distributions observed by the Van Allen Probes in the dayside low-latitude region. The analysis of wave Poynting fluxes, suprathermal electron fluxes, and cold electron densities supports the scenario that exohiss leaks from the plasmasphere into the plasmatrough. Quasilinear calculations further reveal that exohiss can potentially cause the resonant scattering loss of radiation belt electrons

The X-ray luminous cluster underlying the bright radio-quiet quasar H1821+643

We present a Chandra observation of the only low redshift, z=0.299, galaxy cluster to contain a highly luminous radio-quiet quasar, H1821+643. By simulating the quasar PSF, we subtract the quasar contribution from the cluster core and determine the physical properties of the cluster gas down to 3 arcsec (15 kpc) from the point source. The temperature of the cluster gas decreases from 9.0\pm0.5 keV down to 1.3\pm0.2 keV in the centre, with a short central radiative cooling time of 1.0\pm0.1 Gyr, typical of a strong cool-core cluster. The X-ray morphology in the central 100 kpc shows extended spurs of emission from the core, a small radio cavity and a weak shock or cold front forming a semi-circular edge at 15 arcsec radius. The quasar bolometric luminosity was estimated to be 2 x 10^{47} erg per sec, requiring a mass accretion rate of 40 Msolar per yr, which corresponds to half the Eddington accretion rate. We explore possible accretion mechanisms for this object and determine that Bondi accretion, when boosted by Compton cooling of the accretion material, could provide a significant source of the fuel for this outburst. We consider H1821+643 in the context of a unified AGN accretion model and, by comparing H1821+643 with a sample of galaxy clusters, we show that the quasar has not significantly affected the large-scale cluster gas properties.Comment: 20 pages, 19 figures, accepted by MNRA

Disappearance of plasmaspheric hiss following interplanetary shock

Abstract Plasmaspheric hiss is one of the important plasma waves controlling radiation belt dynamics. Its spatiotemporal distribution and generation mechanism are presently the object of active research. We here give the first report on the shock-induced disappearance of plasmaspheric hiss observed by the Van Allen Probes on 8 October 2013. This special event exhibits the dramatic variability of plasmaspheric hiss and provides a good opportunity to test its generation mechanisms. The origination of plasmaspheric hiss from plasmatrough chorus is suggested to be an appropriate prerequisite to explain this event. The shock increased the suprathermal electron fluxes, and then the enhanced Landau damping promptly prevented chorus waves from entering the plasmasphere. Subsequently, the shrinking magnetopause removed the source electrons for chorus, contributing significantly to the several-hours-long disappearance of plasmaspheric hiss

A statistical study of BRIs (SMCs), isolated substorms, and individual sawtooth injections

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95420/1/jgra19762.pd

On the Origin of Cosmic Magnetic Fields

We review the literature concerning how the cosmic magnetic fields pervading nearly all galaxies actually got started. some observational evidence involves the chemical abundance of the light elements Be and B, while another one is based on strong magnetic fields seen in high red shift galaxies. Seed fields, whose strength is of order 10^{-20} gauss, easily sprung up in the era preceding galaxy formation. Several mechanisms are proposed to amplify these seed fields to microgauss strengths. The standard mechanism is the Alpha-Omega dynamo theory. It has a major difficulty that makes unlikely to provide the sole origin. The difficulty is rooted in the fact that the total flux is constant. This implies that flux must be removed from the galactic discs. This requires that the field and flux be separated, for otherwise interstellar mass must be removed from the deep galactic gravitational and then their strength increased by the alpha omega theory.Comment: 90 pages and 6 figures; accepted for publication in Reports of Progress in Physics as an invited revie

A Search for Jet Handedness in Hadronic Z0Z^0 Decays

We have searched for signatures of polarization in hadronic jets from $Z^0 \to q \bar{q}$ decays using the ``jet handedness'' method. The polar angle asymmetry induced by the high SLC electron-beam polarization was used to separate quark jets from antiquark jets, expected to be left- and right-polarized, respectively. We find no evidence for jet handedness in our global sample or in a sample of light quark jets and we set upper limits at the 95% C.L. of 0.063 and 0.099 respectively on the magnitude of the analyzing power of the method proposed by Efremov {\it et al.}Comment: Revtex, 8 pages, 2 figure

Generation of unusually low frequency plasmaspheric hiss

It has been reported from Van Allen Probe observations that plasmaspheric hiss intensification in the outer plasmasphere, associated with a substorm injection on 30 September 2012, occurred with a peak frequency near 100 Hz, well below the typical plasmaspheric hiss frequency range, extending down to ∼20 Hz. We examine this event of unusually low frequency plasmaspheric hiss to understand its generation mechanism. Quantitative analysis is performed by simulating wave raypaths via the HOTRAY ray tracing code with measured plasma density and calculating raypath-integrated wave gain evaluated using the measured energetic electron distribution. We demonstrate that the growth rate due to substorm-injected electrons is positive but rather weak, leading to small wave gain (∼10 dB) during a single equatorial crossing. Propagation characteristics aided by the sharp density gradient associated with the plasmapause, however, can enable these low-frequency waves to undergo cyclic raypaths, which return to the unstable region leading to repeated amplification to yield sufficient net wave gain (>40 dB) to allow waves to grow from the thermal noise