2,278 research outputs found
Temporal Evolution of the Vela Pulsar's Pulse Profile
The mechanisms of emission and changes in rotation frequency ('glitching') of
the Vela pulsar (J0835-4510) are not well understood. Further insight into
these mechanisms can be achieved by long-term studies of integrated pulse
width, timing residuals, and bright pulse rates. We have undertaken an
intensive observing campaign of Vela and collected over 6000 hours of single
pulse data. The data shows that the pulse width changes with time, including
marked jumps in width after micro-glitches (frequency changes). The abundance
of bright pulses also changes after some micro-glitches, but not all. The
secular changes in pulse width have three possible cyclic periods, that match
with X-ray periodicities of a helical jet that are interpreted as free
precession.Comment: 6 pages, 8 figures. Accepted for publication in The Astrophysical
Journa
Statistical analysis of general aviation VG-VGH data
To represent the loads spectra of general aviation aircraft operating in the Continental United States, VG and VGH data collected since 1963 in eight operational categories were processed and analyzed. Adequacy of data sample and current operational categories, and parameter distributions required for valid data extrapolation were studied along with envelopes of equal probability of exceeding the normal load factor (n sub z) versus airspeed for gust and maneuver loads and the probability of exceeding current design maneuver, gust, and landing impact n sub z limits. The significant findings are included
P17. P3b event-related potentials show changes in varsity football players due to accumulated sub-concussive head impacts
BACKGROUND: Concussion has been a focus in football at all levels of participation. However, there is a growing appreciation that repetitive sub-concussive impacts may have more significant effects on overall neurological health than the isolated diagnosed concussions that have been the focus of recent research. The purpose of this study was to evaluate the relationship between the number of head impacts that players experience throughout the season and their P300 evoked potential.
METHODS: Canadian university football players (n=45) were separated into three groups based on player mass and position/skill (small-skilled, big-skilled and big-unskilled). Groups were separated into low and high levels of impact exposure based on the total number of head impacts experienced in-season. Players completed baseline, midseason, postseason, and follow-up neurophysiological tests to measure P300 evoked potentials. Statistically significant differences between high versus low impact subgroups for each player group were assessed using independent-samples t-tests.
RESULTS: Small-skilled and big-skilled players showed statistically significant decreases in P300 amplitude at midseason and postseason for high impact players compared to low impact players. Follow-up measures revealed that all groups were not significantly different compared to baseline measures.
DISCUSSION & CONCLUSION: Players that experience a large number of head impacts in varsity football demonstrate significant decreases in specific EEG measures of cognitive function and information processing.
INTERDISCIPLINARY REFLECTION: The combination of biomechanical head impact exposure with neurophysiological outcomes yields insight into the processes behind head impacts and their effects on the human brain
A High Galactic Latitude HI 21cm-line Absorption Survey using the GMRT: I. Observations and Spectra
We have used the Giant Meterwave Radio Telescope (GMRT) to measure the
Galactic HI 21-cm line absorption towards 102 extragalactic radio continuum
sources, located at high (|b| >15deg.) Galactic latitudes. The Declination
coverage of the present survey is Decl. ~ -45deg.. With a mean rms optical
depth of ~0.003, this is the most sensitive Galactic HI 21-cm line absorption
survey to date. To supplement the absorption data, we have extracted the HI
21-cm line emission profiles towards these 102 lines of sight from the Leiden
Dwingeloo Survey of Galactic neutral hydrogen. We have carried out a Gaussian
fitting analysis to identify the discrete absorption and emission components in
these profiles. In this paper, we present the spectra and the components. A
subsequent paper will discuss the interpretation of these results.Comment: 46 pages, Accepted for publication in Journal of Astrophysics &
Astronom
A note on the third family of N=2 supersymmetric KdV hierarchies
We propose a hamiltonian formulation of the supersymmetric KP type
hierarchy recently studied by Krivonos and Sorin. We obtain a quadratic
hamiltonian structure which allows for several reductions of the KP type
hierarchy. In particular, the third family of KdV hierarchies is
recovered. We also give an easy construction of Wronskian solutions of the KP
and KdV type equations
The thermally-unstable warm neutral medium: key for modeling the interstellar medium
We present 21-cm absorption measurements towards 12 radio continuum sources
with previously identified thermally-unstable warm neutral medium (WNM). These
observations were obtained with the Expanded Very Large Array (EVLA) and were
complemented with the HI emission spectra obtained with the Arecibo
Observatory. Out of 12 sources, HI absorption was detected along 5 lines of
sight (seven new absorption features in total), resulting in a detection rate
of ~42%. While our observations are sensitive to the WNM with a spin
temperature T_s<3000 K, we detected only two wide absorption lines with
T_s=400-900 K. These temperatures lie above the range allowed for the cold
neutral medium (CNM) by the thermal equilbrium models and signify the thermally
unstable WNM. Several absorption features have an optical depth of only a few
x10^{-3}. While this is close or lower than what is theoretically expected for
the CNM, we show that these weak lines are important for constraining the
fraction of the thermally unstable WNM. Our observations demonstrate that, for
the first time, high bandpass stability can be achieved with the VLA, allowing
detection of absorption lines with a peak optical depth of ~10^{-3}.Comment: 10 pages. Accepted by Ap
Power-law random walks
We present some new results about the distribution of a random walk whose
independent steps follow a Gaussian distribution with exponent
. In the case we show that a stochastic
representation of the point reached after steps of the walk can be
expressed explicitly for all . In the case we show that the random
walk can be interpreted as a projection of an isotropic random walk, i.e. a
random walk with fixed length steps and uniformly distributed directions.Comment: 5 pages, 4 figure
Additional symmetries of constrained CKP and BKP hierarchies
The additional symmetries of the constrained CKP (cCKP) and BKP (cBKP)
hierarchies are given by their actions on the Lax operators, and their actions
on the eigenfunction and adjoint eigenfunction are
presented explicitly. Furthermore, we show that acting on the space of the wave
operator, forms new centerless and
-subalgebra of centerless respectively. In
order to define above symmetry flows of the cCKP and cBKP
hierarchies, two vital operators are introduced to revise the additional
symmetry flows of the CKP and BKP hierarchies.Comment: 14 pages, accepted by SCIENCE CHINA Mathematics(2010
A Class of Coupled KdV systems and Their Bi-Hamiltonian Formulations
A Hamiltonian pair with arbitrary constants is proposed and thus a sort of
hereditary operators is resulted. All the corresponding systems of evolution
equations possess local bi-Hamiltonian formulation and a special choice of the
systems leads to the KdV hierarchy. Illustrative examples are given.Comment: 8 pages, late
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