1,475 research outputs found
Coherence lengths for superconductivity in the two-orbital negative-U Hubbard model
We study the peculiarities of coherency in the superconductivity of
two-orbital system. The superconducting phase transition is caused here by the
on-site intra-orbital attractions (negative-U Hubbard model) and inter-orbital
pair-transfer interaction. The dependencies of critical and noncritical
correlation lengths on interaction channels and band fillings are analyzed.Comment: 5 pages, 3 figures, Acta Physica Polonica (2012) in pres
Evidence for alignment of the rotation and velocity vectors in pulsars. II. Further data and emission heights
We have conducted observations of 22 pulsars at frequencies of 0.7, 1.4 and
3.1 GHz and present their polarization profiles. The observations were carried
out for two main purposes. First we compare the orientation of the spin and
velocity vectors to verify the proposed alignment of these vectors by Johnston
et al. (2005). We find, for the 14 pulsars for which we were able to determine
both vectors, that 7 are plausibly aligned, a fraction which is lower than, but
consistent with, earlier measurements. Secondly, we use profiles obtained
simultaneously at widely spaced frequencies to compute the radio emission
heights. We find, similar to other workers in the field, that radiation from
the centre of the profile originates from lower in the magnetosphere than the
radiation from the outer parts of the profile.Comment: Accepted by MNRAS. 14 page
Direction-Dependent Polarised Primary Beams in Wide-Field Synthesis Imaging
The process of wide-field synthesis imaging is explored, with the aim of
understanding the implications of variable, polarised primary beams for
forthcoming Epoch of Reionisation experiments. These experiments seek to detect
weak signatures from redshifted 21cm emission in deep residual datasets, after
suppression and subtraction of foreground emission. Many subtraction algorithms
benefit from low side-lobes and polarisation leakage at the outset, and both of
these are intimately linked to how the polarised primary beams are handled.
Building on previous contributions from a number of authors, in which
direction-dependent corrections are incorporated into visibility gridding
kernels, we consider the special characteristics of arrays of fixed dipole
antennas operating around 100-200 MHz, looking towards instruments such as the
Square Kilometre Array (SKA) and the Hydrogen Epoch of Reionization Arrays
(HERA). We show that integrating snapshots in the image domain can help to
produce compact gridding kernels, and also reduce the need to make complicated
polarised leakage corrections during gridding. We also investigate an
alternative form for the gridding kernel that can suppress variations in the
direction-dependent weighting of gridded visibilities by 10s of dB, while
maintaining compact support.Comment: 15 pages, 4 figures. Accepted for publication in JA
Paternal effects in a wild‐type zebrafish implicate a role of sperm‐derived small RNAs
While the importance of maternal effects has long been appreciated, a growing body of evidence now points to the paternal environment having an important influence on offspring phenotype. Indeed, research on rodent models suggests that paternal stress leaves an imprint on the behaviour and physiology of offspring via nongenetic information carried in the spermatozoa; however, fish have been understudied with regard to these sperm‐mediated effects. Here, we investigated whether the zebrafish was subjected to heritable influences of paternal stress by exposing males to stressors (conspecific‐derived alarm cue, chasing and bright light) before mating and assessing the behavioural and endocrine responses of their offspring, including their behavioural response to conspecific‐derived alarm cue. We found that after males are exposed to stress, their larval offspring show weakened responses to stressors. Small RNA sequencing subsequently revealed that the levels of several small noncoding RNAs, including microRNAs, PIWI‐interacting RNAs and tRNA‐derived small RNAs, were altered in the spermatozoa of stressed fathers, suggesting that stress‐induced alterations to the spermatozoal RNA landscape may contribute to shaping offspring phenotype. The work demonstrates that paternal stress should not be overlooked as a source of phenotypic variation and that spermatozoal small RNAs may be important intergenerational messengers in fish
Nonlinear Dirac and diffusion equations in 1 + 1 dimensions from stochastic considerations
We generalize the method of obtaining the fundamental linear partial
differential equations such as the diffusion and Schrodinger equation, Dirac
and telegrapher's equation from a simple stochastic consideration to arrive at
certain nonlinear form of these equations. The group classification through one
parameter group of transformation for two of these equations is also carried
out.Comment: 18 pages, Latex file, some equations corrected and group analysis in
one more case adde
Self-consistency of relativistic observables with general relativity in the white dwarf-neutron star binary pulsar PSR J1141-6545
Here we report timing measurements of the relativistic binary pulsar PSR
J1141-6545 that constrain the component masses and demonstrate that the orbital
period derivative \dot Pb = (-4+/-1)x10^-13 is consistent with gravitational
wave emission as described by the general theory of relativity. The mass of the
neutron star and its companion are 1.30+/-0.02 Mo and 0.986+/-0.020 Mo
respectively, suggesting a white dwarf companion, and extending the range of
systems for which general relativity provides a correct description. On
evolutionary grounds, the progenitor mass of PSR J1141-6545 should be near the
minimum for neutron star production. Its mass is two standard deviations below
the mean of the other neutron stars, suggesting a relationship between
progenitor and remnant masses.Comment: 10 pages, 2 figures, revised version to Ap J Letter
PSR J1909-3744, a Binary Millisecond Pulsar with a Very Small Duty Cycle
We report the discovery of PSR J1909-3744, a 2.95 millisecond pulsar in a
nearly circular 1.53 day orbit. Its narrow pulse width of 43 microseconds
allows pulse arrival times to be determined with great accuracy. We have
spectroscopically identified the companion as a moderately hot (T = 8500 K)
white dwarf with strong absorption lines. Radial velocity measurements of the
companion will yield the mass ratio of the system. Our timing data suggest the
presence of Shapiro delay; we expect that further timing observations, combined
with the mass ratio, will allow the first accurate determination of a
millisecond pulsar mass. We have measured the timing parallax and proper motion
for this pulsar which indicate a transverse velocity of 140 (+80/-40) km/s.
This pulsar's stunningly narrow pulse profile makes it an excellent candidate
for precision timing experiments that attempt to detect low frequency
gravitational waves from coalescing supermassive black hole binaries.Comment: 12 pages, 4 figures. Accepted for publication in ApJ
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