154 research outputs found
A Comparison of Lower Extremity Joint Work and Initial Loading Rates among Four Different Running Styles
The annual injury incidence rate among the 36 million runners in the United States is approximately 50%. The majority of those injuries occur at the knee joint. The purpose of this study was to measure lower extremity eccentric work and average vertical loading rates among four groups of runners. Seventy-four healthy runners volunteered for this study. The four groups of runners consisted of traditional shoe wearing rearfoot strikers (TSR), minimalist shoe wearing anterior footstrikers (MSA), certified Chi runners (Chi), and minimalist shoe wearing rearfoot strikers (MSR). Study variables were ankle dorsiflexion eccentric work (ADEW), ankle plantarflexion eccentric work (APEW), knee extension eccentric work (KEEW), and average vertical ground reaction force loading rates (VALR). Volunteers ran for five minutes at a self-selected speed on a Bertec instrumented treadmill with Vicon Nexus 3D motion capture. Eccentric joint work was obtained by integrating the negative portion of the joint power curves. VALR was defined as the slope of the vertical ground reaction force curve. TSR runners demonstrated greater ADEW, greater KEEW, and greater VALR than anterior footstriking runners. MSA runners demonstrated the greatest APEW with reduced ADEW, reduced VALR, and reduced KEEW compared to TSR runners. Chi runners demonstrated the least VALR, no ADEW, no significant additional APEW, and reduced KEEW compared to TSR runners. MSR runners demonstrated the greatest and potentially injurious VALR. The mere existence of the group of 17 MSR runners was an unexpected development. The prevailing thinking has been that runners who wore minimalist running shoes would automatically transition to using an anterior footstrike pattern. To our knowledge, this is the first biomechanical evaluation of Chi runners. These findings suggest Chi running may be a desirable alternative running style for a runner with a history of lower extremity overuse injuries or someone who desires to reduce potentially injurious forces on the lower extremity. Running with a rearfoot strike pattern in minimalist shoes may produce vertical ground reaction force loading rates that have been associated with injury. Clinicians should not assume that a runner who wears minimalist shoes uses an anterior footstrike pattern. Clinical evaluation and runner education are imperative.Doctor of Philosoph
The Linear Polarization of Sagittarius A* I. VLA Spectro-polarimetry at 4.8 and 8.4 GHz
Synchrotron radiation from active galactic nuclei (AGN) is often highly
polarized. We present a search for linear polarization with the Very Large
Array (VLA) at 4.8 GHz and 8.4 GHz from the nearest AGN, Sagittarius A*. As a
part of this study we used spectro-polarimetric data that were sensitive to a
rotation measure (RM) as large as 3.5 x 10^6 rad m^-2 at 4.8 GHz and 1.5 x 10^7
rad m^-2 at 8.4 GHz. The upper limit to the linear polarization of Sgr A* over
a broad range of RM is 0.2% at both frequencies. We also present continuum
observations with the VLA at 4.8 GHz which give an upper limit of 0.1% for RMs
less than 10^4 rad m^-2. We conclude that depolarization is unlikely to occur
in the Galacter Center scattering medium. However, it is possible for
depolarization to occur in the accretion region of Sgr A* if the outer scale of
turbulence is small enough. We also consider the implications of a very low
intrinsic polarization for Sgr A*.Comment: 16 pages, 3 figures, accepted for publication in the Astrophysical
Journal, August 20, 1999, Vol 521 #
A Radio Transient 0.1 pc from Sagittarius A*
We report the discovery of a transient radio source 2.7 arcsec (0.1 pc
projected distance) South of the Galactic Center massive black hole,
Sagittarius A*. The source flared with a peak of at least 80 mJy in March 2004.
The source was resolved by the Very Large Array into two components with a
separation of ~0.7 arcsec and characteristic sizes of ~0.2 arcsec. The two
components of the source faded with a power-law index of 1.1 +/- 0.1. We detect
an upper limit to the proper motion of the Eastern component of ~3 x 10^3 km
s^-1 relative to Sgr A*. We detect a proper motion of ~10^4 km s^-1 for the
Western component relative to Sgr A*. The transient was also detected at X-ray
wavelengths with the Chandra X-ray Observatory and the XMM-Newton telescope and
given the designation CXOGC J174540.0-290031. The X-ray source falls in between
the two radio components. The maximum luminosity of the X-ray source is ~10^36
erg s^-1, significantly sub-Eddington. The radio jet flux density predicted by
the X-ray/radio correlation for X-ray binaries is orders of magnitude less than
the measured flux density. We conclude that the radio transient is the result
of a bipolar jet originating in a single impulsive event from the X-ray source
and interacting with the dense interstellar medium of the Galactic Center.Comment: accepted in ApJ; 24 pages; 8 figure
The Intrinsic Size of Sagittarius A* from 0.35 cm to 6 cm
We present new high-resolution observations of Sagittarius A* at wavelengths
of 17.4 to 23.8 cm with the Very Large Array in A configuration with the Pie
Town Very Long Baseline Array antenna. We use the measured sizes to calibrate
the interstellar scattering law and find that the major axis size of the
scattering law is smaller by ~6% than previous estimates. Using the new
scattering law, we are able to determine the intrinsic size of Sgr A* at
wavelengths from 0.35 cm to 6 cm using existing results from the VLBA. The new
law increases the intrinsic size at 0.7 cm by ~20% and <5% at 0.35 cm. The
intrinsic size is 13^{+7}_{-3} Schwarzschild radii at 0.35 cm and is
proportional to lambda^gamma, where gamma is in the range 1.3 to 1.7.Comment: ApJL, in pres
Radio astronomy
The following subject areas are covered: (1) scientific opportunities (millimeter and sub-millimeter wavelength astronomy; meter to hectometer astronomy; the Sun, stars, pulsars, interstellar masers, and extrasolar planets; the planets, asteroids, and comets; radio galaxies, quasars, and cosmology; and challenges for radio astronomy in the 1990's); (2) recommendations for new facilities (the millimeter arrays, medium scale instruments, and small-scale projects); (3) continuing activities and maintenance, upgrading of telescopes and instrumentation; (4) long range programs and technology development; and (5) social, political, and organizational considerations
Detection of the Intrinsic Size of Sagittarius A* through Closure Amplitude Imaging (includes Online Supporting Material)
We have detected the intrinsic size of Sagittarius A*, the Galactic Center
radio source associated with a supermassive black hole, showing that the
short-wavelength radio emission arises from very near the event horizon of the
black hole. Radio observations with the Very Long Baseline Array show that the
source has a size of Schwarzschild radii at 7 mm wavelength. In one
of eight 7-mm epochs we also detect an increase in the intrinsic size of
%. These observations place a lower limit to the mass density
of Sgr A* of solar masses per cubic astronomical unit.Comment: Accepted for publication in Science. Includes the supporting online
material that accompanies the main article, which describe further details of
the analysis of this experimen
Study design considerations for the Standardized Treatment of Pulmonary Exacerbations 2 (STOP2): A trial to compare intravenous antibiotic treatment durations in CF
BACKGROUND:
Pulmonary exacerbations (PEx) in cystic fibrosis (CF) are common and contribute to morbidity and mortality. Duration of IV antibiotic therapy to treat PEx varies widely in the US, and there are few data to guide treatment decisions.
METHODS:
We combined a survey of CF stakeholders with retrospective analyses of a recent observational study of CF PEx to design a multicenter, randomized, prospective study comparing the efficacy and safety of different durations of IV antibiotics for PEx to meet the needs of people with CF and their caregivers.
RESULTS:
IV antibiotic duration was cited as the most important PEx research question by responding CF physicians and top concern among surveyed CF patients/caregivers. During PEx, forced expiratory volume in 1s (FEV1% predicted) and symptom responses at 7-10days of IV antibiotics identified two distinct groups: early robust responders (ERR) who subsequently experienced greater FEV1 improvements compared to non-ERR (NERR). In addition to greater FEV1 and symptom responses, only 14% of ERR patients were treated with IV antibiotics for >15days, compared with 45% of NERR patients.
CONCLUSIONS:
A divergent trial design that evaluates subjects' interim improvement in FEV1 and symptoms to tailor randomization to IV treatment duration (10 vs. 14days for ERR, 14 vs. 21days for NERR) may alleviate physician and patient concerns about excess or inadequate treatment. Such a study has the potential to provide evidence necessary to standardize IV antibiotic duration in CF PEx care -a first step to conducting PEx research of other treatment features
Massive stars in the Cl 1813-178 Cluster. An episode of massive star formation in the W33 complex
Young massive (M >10^4 Msun) stellar clusters are a good laboratory to study
the evolution of massive stars. Only a dozen of such clusters are known in the
Galaxy. Here we report about a new young massive stellar cluster in the Milky
Way. Near-infrared medium-resolution spectroscopy with UIST on the UKIRT
telescope and NIRSPEC on the Keck telescope, and X-ray observations with the
Chandra and XMM satellites, of the Cl 1813-178 cluster confirm a large number
of massive stars. We detected 1 red supergiant, 2 Wolf-Rayet stars, 1 candidate
luminous blue variable, 2 OIf, and 19 OB stars. Among the latter, twelve are
likely supergiants, four giants, and the faintest three dwarf stars. We
detected post-main sequence stars with masses between 25 and 100 Msun. A
population with age of 4-4.5 Myr and a mass of ~10000 Msun can reproduce such a
mixture of massive evolved stars. This massive stellar cluster is the first
detection of a cluster in the W33 complex. Six supernova remnants and several
other candidate clusters are found in the direction of the same complex.Comment: 11 Figures. Accepted for publication in Ap
Lower Extremity Biomechanics and Self-Reported Foot-Strike Patterns Among Runners in Traditional and Minimalist Shoes
The injury incidence rate among runners is approximately 50%. Some individuals have advocated using an anteriorâfoot-strike pattern to reduce ground reaction forces and injury rates that they attribute to a rearâfoot-strike pattern. The proportion of minimalist shoe wearers who adopt an anteriorâfoot-strike pattern remains unclear
American Academy of Periodontology best evidence consensus statement on modifying periodontal phenotype in preparation for orthodontic and restorative treatment
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154649/1/jper10498.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154649/2/jper10498_am.pd
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