1,712 research outputs found
PSR J1453+1902 and the radio luminosities of solitary versus binary millisecond pulsars
We present 3 yr of timing observations for PSR J1453+1902, a 5.79-ms pulsar
discovered during a 430-MHz drift-scan survey with the Arecibo telescope. Our
observations show that PSR J1453+1902 is solitary and has a proper motion of
8(2) mas/yr. At the nominal distance of 1.2 kpc estimated from the pulsar's
dispersion measure, this corresponds to a transverse speed of 46(11) km/s,
typical of the millisecond pulsar population. We analyse the current sample of
55 millisecond pulsars in the Galactic disk and revisit the question of whether
the luminosities of isolated millisecond pulsars are different from their
binary counterparts. We demonstrate that the apparent differences in the
luminosity distributions seen in samples selected from 430-MHz surveys can be
explained by small-number statistics and observational selection biases. An
examination of the sample from 1400-MHz surveys shows no differences in the
distributions. The simplest conclusion from the current data is that the spin,
kinematic, spatial and luminosity distributions of isolated and binary
millisecond pulsars are consistent with a single homogeneous population.Comment: 8 pages, 5 figures and 3 tables, accepted for publication by MNRA
In a positive light? Experiencing Seasonal Affective Disorder (SAD) and the promise of biosolidarity
This paper explores Seasonal Affective Disorder (SAD) as an idiopathic and idiographic phenomenon in a discussion about (low) light and social relations. Tracing a history of unsuccessful biosociality around SAD via archived and contemporary testimony, the paper uses narrative responses from a recent qualitative survey to explore how and why winter depression might be a difficult experience around which to form community. With brief reflections on a series of public workshops led by the research team in Scotland, we suggest that social and cultural geographies of creative practice are one vehicle for fostering new kinds of environmental biosolidarities, arguably rendered essential in the face of uncertain climatic futures that threaten increasingly disruptive light-mental health relations. More broadly, we discuss our contributions to human geographies of light-dark relations, SAD and biosociality. We conclude the paper with a call for more nuanced account of social, cultural, and emotional geographies of environmental illness
Pulsar motions in our Galaxy
Pulsar motions in our Galaxy from their birth until 2 Gyr are studied
statistically via Monte-Carlo simulation of pulsars with the
best available representation of the Galactic potential. We find that the
distribution of height above the Galactic plane for pulsars with characteristic
ages less than about 8 Myr could be well fitted by a Gaussian function. For
older pulsars, an extra exponential function is necessary to fit the
distribution. The scale-height of the Gaussian component increases linearly
with time until about 40 Myr. The height distribution becomes stabilized after
about 200 Myr. These results are not sensitive to initial height or radial
distributions. Taking the relationship between the initial velocity and height
distribution, we found from the latest pulsar catalog that the height
distribution of pulsars younger than 1 Myr directly implies the mean initial
velocity of km s. Comparison of simulated sample of pulsars
with the current available millisecond pulsars shows that their 1D initial
velocity dispersion should be most probably km s.Comment: 11 pages, 16 figures, accepted by MNRA
Accurate evolutions of inspiralling and magnetized neutron-stars: equal-mass binaries
By performing new, long and numerically accurate general-relativistic
simulations of magnetized, equal-mass neutron-star binaries, we investigate the
role that realistic magnetic fields may have in the evolution of these systems.
In particular, we study the evolution of the magnetic fields and show that they
can influence the survival of the hypermassive-neutron star produced at the
merger by accelerating its collapse to a black hole. We also provide evidence
that even if purely poloidal initially, the magnetic fields produced in the
tori surrounding the black hole have toroidal and poloidal components of
equivalent strength. When estimating the possibility that magnetic fields could
have an impact on the gravitational-wave signals emitted by these systems
either during the inspiral or after the merger we conclude that for realistic
magnetic-field strengths B<~1e12 G such effects could be detected, but only
marginally, by detectors such as advanced LIGO or advanced Virgo. However,
magnetically induced modifications could become detectable in the case of
small-mass binaries and with the development of gravitational-wave detectors,
such as the Einstein Telescope, with much higher sensitivities at frequencies
larger than ~2 kHz.Comment: 18 pages, 10 figures. Added two new figures (figures 1 and 7). Small
modifications to the text to match the version published on Phys. Rev.
Friends in need: how chaperonins recognize and remodel proteins that require folding assistance
Chaperonins are biological nanomachines that help newly translated proteins
to fold by rescuing them from kinetically trapped misfolded states. Protein
folding assistance by the chaperonin machinery is obligatory in vivo for a
subset of proteins in the bacterial proteome. Chaperonins are large oligomeric
complexes, with unusual seven fold symmetry (group I) or eight/nine fold
symmetry (group II), that form double-ring constructs, enclosing a central
folding chamber. Dramatic large-scale conformational changes, that take place
during ATP-driven cycles, allow chaperonins to bind misfolded proteins,
encapsulate them into the expanded cavity and release them back into the
cellular environment, regardless of whether they are folded or not. The theory
associated with the iterative annealing mechanism, which incorporated the
conformational free energy landscape description of protein folding,
\textit{quantitatively} explains most, if not all, the available data.
Misfolded conformations are associated with low energy minima in a rugged
energy landscape. Random disruptions of these low energy conformations result
in higher free energy, less folded, conformations that can stochastically
partition into the native state. Group I chaperonins (GroEL homologues in
eubacteria and endosymbiotic organelles), recognize a large number of misfolded
proteins non-specifically and operate through highly coordinated cooperative
motions. By contrast, the less well understood group II chaperonins (CCT in
Eukarya and thermosome/TF55 in Archaea), assist a selected set of substrate
proteins. Chaperonins are implicated in bacterial infection, autoimmune
disease, as well as protein aggregation and degradation diseases. Understanding
the chaperonin mechanism and their substrates is important not only for the
fundamental aspect of cellular protein folding, but also for effective
therapeutic strategies.Comment: 26 pages, 4 figures, to be published in Frontiers in Molecular
Bioscience
PSR J1829+2456: a relativistic binary pulsar
We report the discovery of a new binary pulsar, PSR J1829+2456, found during
a mid-latitude drift-scan survey with the Arecibo telescope. Our initial timing
observations show the 41-ms pulsar to be in a 28-hr, slightly eccentric, binary
orbit. The advance of periastron, omegadot = 0.28 +/- 0.01 deg/yr is derived
from our timing observations spanning 200 days. Assuming that the advance of
periastron is purely relativistic and a reasonable range of neutron star masses
for PSR J1829+2456 we constrain the companion mass to be between 1.22 Msun and
1.38 Msun, making it likely to be another neutron star. We also place a firm
upper limit on the pulsar mass of 1.38 Msun. The expected coalescence time due
to gravitational-wave emission is long (~60 Gyr) and this system will not
significantly impact upon calculations of merger rates that are relevant to
upcoming instruments such as LIGO.Comment: Accepted MNRAS, 5 pages, 3 figure
Pulsational Analysis of the Cores of Massive Stars and its Relevance to Pulsar Kicks
The mechanism responsible for the natal kicks of neutron stars continues to
be a challenging problem. Indeed, many mechanisms have been suggested, and one
hydrodynamic mechanism may require large initial asymmetries in the cores of
supernova progenitor stars. Goldreich, Lai, & Sahrling (1997) suggested that
unstable g-modes trapped in the iron (Fe) core by the convective burning layers
and excited by the -mechanism may provide the requisite asymmetries.
We perform a modal analysis of the last minutes before collapse of published
core structures and derive eigenfrequencies and eigenfunctions, including the
nonadiabatic effects of growth by nuclear burning and decay by both neutrino
and acoustic losses. In general, we find two types of g-modes: inner-core
g-modes, which are stabilized by neutrino losses and outer-core g-modes which
are trapped near the burning shells and can be unstable. Without exception, we
find at least one unstable g-mode for each progenitor in the entire mass range
we consider, 11 M_{\sun} to 40 M_{\sun}. More importantly, we find that the
timescales for growth and decay are an order of magnitude or more longer than
the time until the commencement of core collapse. We conclude that the
-mechanism may not have enough time to significantly amplify core
g-modes prior to collapse.Comment: 32 pages including 12 color figures and 2 tables, submitted to Ap
The SPORTSMART study: a pilot randomised controlled trial of sexually transmitted infection screening interventions targeting men in football club settings
Background:
Uptake of chlamydia screening by men in England has been substantially lower than by women. Non-traditional settings such as sports clubs offer opportunities to widen access. Involving people who are not medically trained to promote screening could optimise acceptability.
Methods:
We developed two interventions to explore the acceptability and feasibility of urine-based sexually transmitted infection (STI) screening interventions targeting men in football clubs. We tested these interventions in a pilot cluster randomised control trial. Six clubs were randomly allocated, two to each of three trial arms: team captain-led and poster STI screening promotion; sexual health adviser-led and poster STI screening promotion; and poster-only STI screening promotion (control/comparator). Primary outcome was test uptake.
Results:
Across the three arms, 153 men participated in the trial and 90 accepted the offer of screening (59%, 95% CI 35% to 79%). Acceptance rates were broadly comparable across the arms: captain-led: 28/56 (50%); health professional-led: 31/46 (67%); and control: 31/51 (61%). However, rates varied appreciably by club, precluding formal comparison of arms. No infections were identified. Process evaluation confirmed that interventions were delivered in a standardised way but the control arm was unintentionally âenhancedâ by some team captains actively publicising screening events.
Conclusions:
Compared with other UK-based community screening models, uptake was high but gaining access to clubs was not always easy. Use of sexual health advisers and team captains to promote screening did not appear to confer additional benefit over a poster-promoted approach. Although the interventions show potential, the broader implications of this strategy for UK male STI screening policy require further investigation
Radio Pulses along the Galactic Plane
We have surveyed 68 deg^2 along the Galactic Plane for single, dispersed
radio pulses. Each of 3027 independent pointings was observed for 68 s using
the Arecibo telescope at 430 MHz. Spectra were collected at intervals of 0.5 ms
and examined for pulses with duration 0.5 to 8 ms. Such single pulse analysis
is the most sensitive method of detecting highly scattered or highly dispersed
signals from pulsars with large pulse-to-pulse intensity variations. A total of
36 individual pulses from five previously known pulsars were detected, along
with a single pulse not associated with a previously known source. Follow-up
observations discovered a pulsar, PSR J1918+08, from which the pulse
originated. This pulsar has period 2.130 s and dispersion measure 30 pc cm^-3,
and has been seen to emit single pulses with strength up to 8 times the
average.Comment: 14 pages, 5 figures, AASTeX, accepted by the Astrophysical Journa
Arecibo Pulsar Survey Using ALFA. I. Survey Strategy and First Discoveries
We report results from the initial stage of a long-term pulsar survey of the
Galactic plane using the Arecibo L-band Feed Array (ALFA), a seven-beam
receiver operating at 1.4 GHz with 0.3 GHz bandwidth. The search targets
Galactic latitudes |b| < 5 deg in the longitude ranges 32 deg < l < 77 deg and
168 deg < l < 77 deg. Data discussed here were collected over a 100 MHz
passband centered on 1.42 GHz using a spectrometer that recorded 256 channels
every 64 microsec. In a preliminary, standard period-DM analysis, we have
detected 29 previously known pulsars and discovered 11 new ones. One of these,
with a period of 69 ms and a low characteristic age of 82 kyr, is a plausible
candidate for association with the unidentified EGRET source 3EG J1928+1733.
Another is a non-recycled pulsar in a relativistic binary with orbital period
of 3.98 hr. We also search the data for isolated dispersed pulses, a technique
that yielded discovery of an extremely sporadic radio emitter with a spin
period of 1.2 s. Simulations we have carried out indicate that about 1000 new
pulsars will be found in the ALFA survey. In addition to providing a large
sample for use in population analyses and for probing the magnetoionic
interstellar medium, the survey maximizes the chances of finding rapidly
spinning millisecond pulsars and pulsars in compact binary systems. Our search
algorithms will exploit the multiple data streams from ALFA to discriminate
between radio frequency interference and celestial signals, including pulsars
and possibly new classes of transient radio sources.Comment: 10 pp, 9 figures, accepted by the Astrophysical Journa
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