117 research outputs found
THREE-DIMENSIONAL KINEMATICS OF THE BATTED BALL IN BASEBALL: THE EFFECT OF SPIN ON THE BALL TRAJECTORY AND FLIGHT DISTANCE
The purpose of this study was to describe the three-dimensional kinematics of batted baseballs toward the same-field, center-field, and opposite-field, and estimate the effect of ball spin on trajectory and flight distance. Two collegiate baseball players performed free-batting, and they were instructed to hit a ball as far as possible in each direction. Twenty-seven trials were analyzed, and compared the ball kinematics among three hitting directions. The mean flight distance for the center-field was greater than that of the other fields. For the same-field and opposite-field, the amount of side spin components was larger than that of the center-field. Thus, it was indicated that the batted ball trajectories for the same-field and opposite-field were curved due to the Magnus force works horizontally, and flight distance tended to be shorter than that of the center-field
Ten milliparsec-scale structure of the nucleus region in Centaurus A
We present the results of a VLBI Space Observatory Programme (VSOP)
observation of the subparsec structure in Centaurus A at 4.9 GHz. Owing to its
proximity, our Centaurus A space-VLBI image is one of the highest spatial
resolution images of an AGN ever made -- 0.01 pc per beam. The elongated core
region is resolved into several components over 10 milli-arcseconds long (0.2
pc) including a compact component of brightness temperature 2.2x10^10K. We
analyze the jet geometry in terms of collimation. Assuming the strongest
component to be the core, the jet opening angle at ~ 5,000 r_s (Schwarzchild
radii) from the core is estimated to be ~ 12 degree, with collimation of the
jet to ~ 3 degree continuing out to ~ 20,000 r_s. This result is consistent
with previous studies of the jet in M87, which favor MHD disk outflow models.
Future space VLBI observations at higher frequencies will probably be able to
image the collimation region, within 1,000 r_s of the center of Centaurus A,
together with the accretion disk itself.Comment: 12 pages, 6 figures, accepted for publication in PASJ, Vol.57 No.6,
VSOP special issu
Pulse Morphology of the Galactic Center Magnetar PSR J1745-2900
We present results from observations of the Galactic Center magnetar, PSR
J1745-2900, at 2.3 and 8.4 GHz with the NASA Deep Space Network 70 m antenna,
DSS-43. We study the magnetar's radio profile shape, flux density, radio
spectrum, and single pulse behavior over a ~1 year period between MJDs 57233
and 57621. In particular, the magnetar exhibits a significantly negative
average spectral index of = -1.86 0.02 when the
8.4 GHz profile is single-peaked, which flattens considerably when the profile
is double-peaked. We have carried out an analysis of single pulses at 8.4 GHz
on MJD 57479 and find that giant pulses and pulses with multiple emission
components are emitted during a significant number of rotations. The resulting
single pulse flux density distribution is incompatible with a log-normal
distribution. The typical pulse width of the components is ~1.8 ms, and the
prevailing delay time between successive components is ~7.7 ms. Many of the
single pulse emission components show significant frequency structure over
bandwidths of ~100 MHz, which we believe is the first observation of such
behavior from a radio magnetar. We report a characteristic single pulse
broadening timescale of = 6.9 0.2 ms at 8.4 GHz.
We find that the pulse broadening is highly variable between emission
components and cannot be explained by a thin scattering screen at distances
1 kpc. We discuss possible intrinsic and extrinsic mechanisms for the
magnetar's emission and compare our results to other magnetars, high magnetic
field pulsars, and fast radio bursts.Comment: 18 pages, 12 figures, Accepted for publication in ApJ on 2018 August
30. v2: Updated to match published versio
A Broadband Digital Spectrometer for the Deep Space Network
The Deep Space Network (DSN) enables NASA to communicate with its spacecraft in deep space. By virtue of its large antennas, the DSN can also be used as a powerful instrument for radio astronomy. Specifically, the Deep Space Station (DSS)-43, the 70 m antenna at the Canberra Deep Space Communications Complex (CDSCC), has a K-band radio astronomy system covering a 10 GHz bandwidth at 17–27 GHz. This spectral range covers a number of atomic and molecular lines, produced in a rich variety of interstellar gas conditions. Lines include hydrogen radio recombination lines (RRLs), cyclopropenylidene (C₃H₂), water masers (H₂O), and ammonia (NH₃). A new high-resolution spectrometer was deployed at CDSCC in 2019 November and connected to the K-band down converter. The spectrometer has a total bandwidth of 16 GHz. Such a large total bandwidth enables, for example, the simultaneous observations of a large number of RRLs, which can be combined together to significantly improve the sensitivity of these observations. The system has two firmware modes: (1) a 65k-pt fast Fourier transform to provide 32,768 spectral channels at 30.5 kHz and (2) a 16k-pt polyphase filter bank to provide 8192 spectral channels with a 122 kHz resolution. The observation process is designed to maximize autonomy, from the principle investigator's inputs to the output data in FITS file format. We present preliminary mapping observations of hydrogen RRLs in Orion KL mapping taken using the new spectrometer
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