536 research outputs found
The Scintillation Velocity of the Relativistic Binary Pulsar PSR J1141-6545
We report a dramatic orbital modulation in the scintillation timescale of the
relativistic binary pulsar J1141--6545 that both confirms the validity of the
scintillation speed methodology and enables us to derive important physical
parameters. We have determined the space velocity, the orbital inclination and
even the longitude of periastron of the binary system, which we find to be in
good agreement with that obtained from pulse timing measurements. Our data
permit two equally-significant physical interpretations of the system. The
system is either an edge-on binary with a high space velocity ( km
s) or is more face-on with a much slower velocity ( km
s). We favor the former, as it is more consistent with pulse timing and
the distribution of known neutron star masses. Under this assumption, the
runaway velocity of 115 km s is much greater than is expected if pulsars
do not receive a natal kick at birth. The derived inclination of the binary
system is (76\pm 2.5^{\circ}) degrees, implying a companion mass of 1.01 (\pm
)~0.02 M(_{\odot}) and a pulsar mass of 1.29 (\pm)~0.02 M(_{\odot}). Our
derived physical parameters indicate that this pulsar should prove to be an
excellent laboratory for tests of gravitational wave emission.Comment: Minor text and figure changes and corrections following referee's
Comments. 14 pages, 3 figures, accepted for publication in Ap
Challenges in the development of the orbiter atmosphere revitalization subsystem
The space shuttle orbiter atmospheric revitalization subsystem provides thermal and contaminant control as well as total- and oxygen partial-pressure control of the environment within the orbiter crew cabin. Challenges that occurred during the development of this subsystem for the space shuttle orbiter are described. The design of the rotating hardware elements of the system (pumps, fans, etc.) required significant development to meet the requirements of long service life, maintainability, and high cycle-fatigue life. As a result, a stringent development program, particularly in the areas of bearing life and heat dissipation, was required. Another area requiring significant development was cabin humidity control and condensate collection
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Development of an Under-Sodium Ultrasonic Scanner for in-Reactor Surveillance.
Quantum-classical transition in Scale Relativity
The theory of scale relativity provides a new insight into the origin of
fundamental laws in physics. Its application to microphysics allows us to
recover quantum mechanics as mechanics on a non-differentiable (fractal)
spacetime. The Schrodinger and Klein-Gordon equations are demonstrated as
geodesic equations in this framework. A development of the intrinsic properties
of this theory, using the mathematical tool of Hamilton's bi-quaternions, leads
us to a derivation of the Dirac equation within the scale-relativity paradigm.
The complex form of the wavefunction in the Schrodinger and Klein-Gordon
equations follows from the non-differentiability of the geometry, since it
involves a breaking of the invariance under the reflection symmetry on the
(proper) time differential element (ds - ds). This mechanism is generalized
for obtaining the bi-quaternionic nature of the Dirac spinor by adding a
further symmetry breaking due to non-differentiability, namely the differential
coordinate reflection symmetry (dx^mu - dx^mu) and by requiring invariance
under parity and time inversion. The Pauli equation is recovered as a
non-relativistic-motion approximation of the Dirac equation.Comment: 28 pages, no figur
Discovery of Five Recycled Pulsars in a High Galactic Latitude Survey
We present five recycled pulsars discovered during a 21-cm survey of
approximately 4,150 deg^2 between 15 deg and 30 deg from the galactic plane
using the Parkes radio telescope. One new pulsar, PSR J1528-3146, has a 61 ms
spin period and a massive white dwarf companion. Like many recycled pulsars
with heavy companions, the orbital eccentricity is relatively high (~0.0002),
consistent with evolutionary models that predict less time for circularization.
The four remaining pulsars have short spin periods (3 ms < P < 6 ms); three of
these have probable white dwarf binary companions and one (PSR J2010-1323) is
isolated. PSR J1600-3053 is relatively bright for its dispersion measure of
52.3 pc cm^-3 and promises good timing precision thanks to an intrinsically
narrow feature in its pulse profile, resolvable through coherent dedispersion.
In this survey, the recycled pulsar discovery rate was one per four days of
telescope time or one per 600 deg^2 of sky. The variability of these sources
implies that there are more millisecond pulsars that might be found by
repeating this survey.Comment: 15 pages, 3 figures, accepted for publication in Ap
ZOBOV: a parameter-free void-finding algorithm
ZOBOV (ZOnes Bordering On Voidness) is an algorithm that finds density
depressions in a set of points, without any free parameters, or assumptions
about shape. It uses the Voronoi tessellation to estimate densities, which it
uses to find both voids and subvoids. It also measures probabilities that each
void or subvoid arises from Poisson fluctuations. This paper describes the
ZOBOV algorithm, and the results from its application to the dark-matter
particles in a region of the Millennium Simulation. Additionally, the paper
points out an interesting high-density peak in the probability distribution of
dark-matter particle densities.Comment: 10 pages, 8 figures, MNRAS, accepted. Added explanatory figures, and
better edge-detection methods. ZOBOV code available at
http://www.ifa.hawaii.edu/~neyrinck/vobo
The emission and scintillation properties of RRAT J2325-0530 at 154 MHz and 1.4 GHz
Rotating Radio Transients (RRATs) represent a relatively new class of pulsar,
primarily characterised by their sporadic bursting emission of single pulses on
time scales of minutes to hours. In addition to the difficulty involved in
detecting these objects, low-frequency (300 MHz) observations of RRATs are
sparse, which makes understanding their broadband emission properties in the
context of the normal pulsar population problematic. Here, we present the
simultaneous detection of RRAT J2325-0530 using the Murchison Widefield Array
(154 MHz) and Parkes radio telescope (1.4 GHz). On a single-pulse basis, we
produce the first polarimetric profile of this pulsar, measure the spectral
index (), pulse energy distributions, and present the pulse
rates in the context of detections in previous epochs. We find that the
distribution of time between subsequent pulses is consistent with a Poisson
process and find no evidence of clustering over the 1.5 hr observations.
Finally, we are able to quantify the scintillation properties of RRAT
J2325-0530 at 1.4 GHz, where the single pulses are modulated substantially
across the observing bandwidth, and show that this characterisation is feasible
even with irregular time sampling as a consequence of the sporadic emission
behaviour.Comment: 18 pages, 8 figures, 5 tables, accepted for publication in PAS
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