3,927 research outputs found
The constrained modified KP hierarchy and the generalized Miura transformations
In this letter, we consider the second Hamiltonian structure of the
constrained modified KP hierarchy. After mapping the Lax operator to a pure
differential operator the second structure becomes the sum of the second and
the third Gelfand-Dickey brackets defined by this differential operator. We
simplify this Hamiltonian structure by factorizing the Lax operator into linear
terms.Comment: 8 pages, latex, no figure
Neutral hydrogen in the starburst galaxy NGC3690/IC694
Researchers made observations of the neutral hydrogen (HI) emission structure surrounding the very deep absorption peak (observed earlier by Dickey (1986)) in the galaxy pair NGC3690/IC694. This galaxy pair is highly luminous in the far infrared, and known to exhibit extensive star formation as well as nuclear activity. Knowledge of the spatial distribution and velocity structure of the HI emission is of great importance to the understanding of the dynamics of the interaction and the resulting environmental effects on the galaxies
High-Resolution Images of Diffuse Neutral Clouds in the Milky Way. I. Observations, Imaging, and Basic Cloud Properties
A set of diffuse interstellar clouds in the inner Galaxy within a few hundred
pc of the Galactic plane has been observed at an angular resolution of ~1
arcmin combining data from the NRAO Green Bank Telescope and the Very Large
Array. At the distance of the clouds the linear resolution ranges from ~1.9 pc
to ~2.8 pc. These clouds have been selected to be somewhat out of the Galactic
plane and are thus not confused with unrelated emission, but in other respects
they are a Galactic population. They are located near the tangent points in the
inner Galaxy, and thus at a quantifiable distance: kpc
from the Galactic Center, and pc from the Galactic
plane. These are the first images of the diffuse neutral HI clouds that may
constitute a considerable fraction of the ISM. Peak HI column densities range
from cm. Cloud diameters vary between
about 10 and 100 pc, and their HI mass spans the range from less than a hundred
to a few thousands Msun. The clouds show no morphological consistency of any
kind except that their shapes are highly irregular. One cloud may lie within
the hot wind from the nucleus of the Galaxy, and some clouds show evidence of
two distinct thermal phases as would be expected from equilibrium models of the
interstellar medium.Comment: 81 pages, 42 figures, accepted for publication in the Astrophysical
Journal Supplement Serie
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
Courant-like brackets and loop spaces
We study the algebra of local functionals equipped with a Poisson bracket. We
discuss the underlying algebraic structures related to a version of the
Courant-Dorfman algebra. As a main illustration, we consider the functionals
over the cotangent bundle of the superloop space over a smooth manifold. We
present a number of examples of the Courant-like brackets arising from this
analysis.Comment: 20 pages, the version published in JHE
P18. Backstroke Start Performance: The Impact of Using the Omega Backstroke Ledge
Background: FINA recently approved use of the “backstroke ledge” (Omega OBL2) to improve backstroke start performance in competition, but its performance has not been thoroughly evaluated. The purpose of this study was to compare starts performed on a flat wall to those performed with the OBL2, and to identify factors that contribute to better start performance. Methods: Ten elite backstroke swimmers performed three flat-wall and three OBL2 starts. Horizontal impulse, vertical impulse, takeoff velocity and takeoff angle were calculated from the force plate data. Entry distance, time to 10 m and start of hip and knee extension were recorded using digital video cameras. Results: We determined that starts performed with the OBL2 had a faster time to 10 m, less variability in vertical impulse and greater entry distance. Time to 10 m and head entry distance had a significant negative correlation. Starts with the OBL2 also had a trend toward lower resultant takeoff velocity, lower horizontal impulse and greater COM takeoff angle. Discussion and Conclusions: The OBL2 appears to provide a performance advantage by allowing an increased head entry distance, rather than larger impulse on the wall. Additional studies are needed to evaluate the factors that contribute to improved performance when using the OBL2. Coaches may consider head entry distance as a training target. Athletes should use the OBL2 in training and competition to ensure optimal start performance. Interdisciplinary Reflection: Concepts from physical and biological sciences are combined to explain the factors which affect backstroke start performance
Detection of Cold Atomic Clouds in the Magellanic Bridge
We report a detection of cold atomic hydrogen in the Magellanic Bridge using
21-cm absorption spectroscopy toward the radio source B0312-770. With a column
density of N_HI=1.2E20 cm^-2, a maximum absorption optical depth of tau=0.10
and a maximum 21-cm emission brightness temperature of 1.4 K, this line of
sight yields a spin temperature, T_s, between 20 K and 40 K. H I 21-cm
absorption and emission spectroscopy toward 7 other low column density
sightlines on the periphery of the LMC and SMC reveal absorption toward one
additional background radio source behind the SMC with tau=0.03. The data have
typical sensitivities of sigma_tau=0.005 to 0.070 in absorption and
sigma_{T_B}=0.03 K in emission. These data demonstrate the presence of a cold
atomic phase which is probably accompanied by molecular condensations in the
tenuous interstellar medium of the Bridge region. Young OB stars observed in
the Magellanic Bridge could form "in situ" from these cold condensations rather
than migrate from regions of active star formation in the main body of the SMC.
The existence of cold condensations and star formation in the Magellanic Bridge
might be understood as a small scale version of the mechanism that produces
star formation in the tidal tails of interacting galaxies.Comment: 25 pages, uses AASTeX and psfig; Accepted for Publication in the
Astronomical Journa
Soliton solutions of the Kadomtsev-Petviashvili II equation
We study a general class of line-soliton solutions of the
Kadomtsev-Petviashvili II (KPII) equation by investigating the Wronskian form
of its tau-function. We show that, in addition to previously known line-soliton
solutions, this class also contains a large variety of new multi-soliton
solutions, many of which exhibit nontrivial spatial interaction patterns. We
also show that, in general, such solutions consist of unequal numbers of
incoming and outgoing line solitons. From the asymptotic analysis of the
tau-function, we explicitly characterize the incoming and outgoing
line-solitons of this class of solutions. We illustrate these results by
discussing several examples.Comment: 28 pages, 4 figure
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
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
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