Lean body mass associated with upper body strength in healthy older adults while higher body fat limits lower extremity performance and endurance

Impaired strength adversely influences an older person\u27s ability to perform activities of daily living. A cross-sectional study of 117 independently living men and women (age = 73.4 9.4 year; body mass index (BMI) = 27.6 4.8 kg/m2) aimed to assess the association between body composition and: (1) upper body strength (handgrip strength, HGS); (2) lower extremity performance (timed up and go (TUG) and sit to stand test (STS)); and (3) endurance (6-minute walk (SMWT). Body composition (% fat; lean body mass (LBM)) was assessed using bioelectrical impedance. Habitual physical activity was measured using the Minnesota Leisure Time Physical Activity Questionnaire (MLTPA) and dietary macronutrient intake, assessed using 24 h recalls and 3-day food records. Regression analyses included the covariates, protein intake (g/kg), MLTPA, age and sex. For natural logarithm (Ln) of right HGS, LBM (p \u3c 0.001) and % body fat (p \u3c 0.005) were significant (r2 = 46.5%; p \u3c 0.000). For left LnHGS, LBM (p \u3c 0.000), age (p = 0.036), protein intake (p = 0.015) and LnMLTPA (p = 0.015) were significant (r2 = 0.535; p \u3c 0.000). For SMW, % body fat, age and LnMLTPA were significant (r2 = 0.346; p \u3c 0.000). For STS, % body fat and age were significant (r2 = 0.251; p \u3c 0.000). LBM is a strong predictor of upper body strength while higher % body fat and lower physical activity are associated with poorer outcomes on tests of lower extremity performance

Time Dependent Models of Flares from Sagittarius A*

The emission from Sgr A*, the supermassive black hole in the Galactic Center, shows order of magnitude variability ("flares") a few times a day that is particularly prominent in the near-infrared (NIR) and X-rays. We present a time-dependent model for these flares motivated by the hypothesis that dissipation of magnetic energy powers the flares. We show that episodic magnetic reconnection can occur near the last stable circular orbit in time-dependent magnetohydrodynamic simulations of black hole accretion - the timescales and energetics of these events are broadly consistent with the flares from Sgr A*. Motivated by these results, we present a spatially one-zone time-dependent model for the electron distribution function in flares, including energy loss due to synchrotron cooling and adiabatic expansion. Synchrotron emission from transiently accelerated particles can explain the NIR/X-ray lightcurves and spectra of a luminous flare observed 4 April 2007. A significant decrease in the magnetic field strength during the flare (coincident with the electron acceleration) is required to explain the simultaneity and symmetry of the simultaneous lightcurves. Our models predict that the NIR and X-ray spectral indices differ by 0.5 and that there is only modest variation in the spectral index during flares. We also explore implications of this model for longer wavelength (radio-submm) emission seemingly associated with X-ray and NIR flares; we argue that a few hour decrease in the submm emission is a more generic consequence of large-scale magnetic reconnection than delayed radio emission from adiabatic expansion.Comment: 18 pages, 10 figures, ApJ accepte

An Extremely Top-Heavy IMF in the Galactic Center Stellar Disks

ArXiv e-prints. 2009. vol. 0908

An Extremely Top-Heavy IMF in the Galactic Center Stellar Disks

ArXiv e-prints. 2009. vol. 0908

An Extremely Top-Heavy IMF in the Galactic Center Stellar Disks

ArXiv e-prints. 2009. vol. 0908

Massive Young Stars in the Galactic Center

International audienc

Massive Young Stars in the Galactic Center

International audienc

Massive Young Stars in the Galactic Center

International audienc

GRAVITY: Astrometry on the galactic center and beyond

International audienceWe present the second-generation VLTI instrument GRAVITY, which currently is in the preliminary design phase. GRAVITY is specifically designed to observe highly relativistic motions of matter close to the event horizon of Sgr A*, the massive black hole at the center of the Milky Way. We have identified the key design features needed to achieve this goal and present the resulting instrument concept. It includes an integrated optics, four-telescope, dual feed beam combiner operated in a cryogenic vessel, near-infrared wavefront sensing adaptive optics, fringe tracking on secondary sources within the field of view of the VLTI and a novel metrology concept. Simulations show that the planned design matches the scientific needs; in particular that 10 muas astrometry is feasible for a source with a magnitude of mK = 15 like Sgr A*, given the availability of suitable phase reference sources