5,832 research outputs found
Magnetic-Field Amplification in the Thin X-ray Rims of SN1006
Several young supernova remnants (SNRs), including SN1006, emit synchrotron
X-rays in narrow filaments, hereafter thin rims, along their periphery. The
widths of these rims imply 50 to 100 G fields in the region immediately
behind the shock, far larger than expected for the interstellar medium
compressed by unmodified shocks, assuming electron radiative losses limit rim
widths. However, magnetic-field damping could also produce thin rims. Here we
review the literature on rim width calculations, summarizing the case for
magnetic-field amplification. We extend these calculations to include an
arbitrary power-law dependence of the diffusion coefficient on energy, . Loss-limited rim widths should shrink with increasing photon
energy, while magnetic-damping models predict widths almost independent of
photon energy. We use these results to analyze Chandra observations of SN 1006,
in particular the southwest limb. We parameterize the full widths at half
maximum (FWHM) in terms of energy as FWHM . Filament
widths in SN1006 decrease with energy; to , implying
magnetic field amplification by factors of 10 to 50, above the factor of 4
expected in strong unmodified shocks. For SN 1006, the rapid shrinkage rules
out magnetic damping models. It also favors short mean free paths (small
diffusion coefficients) and strong dependence of on energy ().Comment: Accepted by ApJ, 49 pages, 10 figure
Hubble space telescope STIS spectroscopy of the peculiar nova-like variables BK Lyn, V751 Cygni, and V380 Oph
We obtained Hubble STIS spectra of three nova-like variables: V751 Cygni, V380 Oph, andâthe only confirmed nova-like variable known to be below the period gapâBK Lyn. In all three systems, the spectra were taken during high optical brightness state, and a luminous accretion disk dominates their far-ultraviolet (FUV) light. We assessed a lower limit of the distances by applying the infrared photometric method of Knigge. Within the limitations imposed by the poorly known system parameters (such as the inclination, white dwarf mass, and the applicability of steady state accretion disks) we obtained satisfactory fits to BK Lyn using optically thick accretion disk models with an accretion rate of for a white dwarf mass of Mwd = 1.2M and for Mwd = 0.4M. However, for the VY Scl-type nova-like variable V751 Cygni and for the SW Sex star V380 Oph, we are unable to obtain satisfactory synthetic spectral fits to the high state FUV spectra using optically thick steady state accretion disk models. The lack of FUV spectra information down to the Lyman limit hinders the extraction of information about the accreting white dwarf during the high states of these nova-like systems
Photogrammetry and ballistic analysis of a high-flying projectile in the STS-124 space shuttle launch
A method combining photogrammetry with ballistic analysis is demonstrated to
identify flying debris in a rocket launch environment. Debris traveling near
the STS-124 Space Shuttle was captured on cameras viewing the launch pad within
the first few seconds after launch. One particular piece of debris caught the
attention of investigators studying the release of flame trench fire bricks
because its high trajectory could indicate a flight risk to the Space Shuttle.
Digitized images from two pad perimeter high-speed 16-mm film cameras were
processed using photogrammetry software based on a multi-parameter optimization
technique. Reference points in the image were found from 3D CAD models of the
launch pad and from surveyed points on the pad. The three-dimensional reference
points were matched to the equivalent two-dimensional camera projections by
optimizing the camera model parameters using a gradient search optimization
technique. Using this method of solving the triangulation problem, the xyz
position of the object's path relative to the reference point coordinate system
was found for every set of synchronized images. This trajectory was then
compared to a predicted trajectory while performing regression analysis on the
ballistic coefficient and other parameters. This identified, with a high degree
of confidence, the object's material density and thus its probable origin
within the launch pad environment. Future extensions of this methodology may
make it possible to diagnose the underlying causes of debris-releasing events
in near-real time, thus improving flight safety.Comment: 26 pages, 11 figures, 3 table
The State Correction Officer as Keeper and Counselor: An Empirical Investigation of the Role
This paper addresses two essential research needs in criminal justice literature: (1) the need for an assessment of the content of the role of block officer; and (2) the need for an empirical test of the presumed irreconcilable goals of custody and treatment as these are embedded in the role of state correction officer. A Task Inventory approach was adapted and a random sample of 100 correction officers in four heterogeneous state institutions were interviewed. Results of the study reveal that custodial staff spend at least sixty-percent of their on-job time performing duties not classified as security in nature. Results of the study challenge many of the existing stereotypes of correction officers in the literature. *Th
An unusual new fossil shark (Pisces: Chondrichthyes) from the Late Devonian of South Africa
A new stem-group chondrichthyan fish, PlesioselacJllIs macracanthlls gen. et sp. nov., is described from the Late Devonian Witpoort Formation, representing an estuarine lagoon site, near Grahamstown, South Africa. Based on a single, fairly complete specimen, it is distinctive in its a single dorsal fin braced by a large, stout spine with numerous ribs and posterior denticles, apparently no second dorsal or anal fin, an amphistylic jaw suspension, and a distinctive triangular palatoquadrate. It is suggested that the species may represent a high-latitude, Late Devonian relict taxon
External Workloads Vary by Position and Game Result in US-based Professional Soccer Players
International Journal of Exercise Science 16(6): 688-699, 2023. Professional soccer is a physically demanding sport that requires players to be highly trained. Advances using GPS allow the tracking of external workloads for individual players in practice and competition, however, there is a lack of evidence on how these measures impact match results. Therefore, we analyzed external workloads by player position and determined if they vary depending on the result of competitive matches. External workloads were analyzed in professional soccer players (n = 25) across 28 competitive games. One-way ANOVA determined if workloads varied by position (striker â ST, wide midfielder - WM, central midfielder â CM, wide defender - WD, central defender â CD) or across games won (n = 8), lost (n = 13) or tied (n = 7). Repeated-measures ANOVA assessed differences in workloads specific to each position in each of the result categories. Statistical significance was set at p \u3c 0.05. Across all games, more high-speed and very-high speed running was done by ST and WD compared to CD (p \u3c 0.001) and CM (p \u3c 0.001 - 0.02). Whole-team data showed no differences in any external workload variable with respect to match result (p \u3e 0.05), however, in games won ST did more very high-speed running than in losing games (p = 0.03) and defending players did more high and very high-speed running in games tied vs. those won or lost (p \u3c 0.05). Whole-team external workloads do not vary depending on the match result; however, high speed running may be a differentiating factor at the positional level. Coaches should consider position-specific analysis when examining player workloads
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