2,337 research outputs found
The 2000 Periastron Passage of PSR B1259-63
We report here on a sequence of 28 observations of the binary pulsar system
PSR B1259-63/SS2883 at four radio frequencies made with the Australia Telescope
Compact Array around the time of the 2000 periastron passage. Observations made
on 2000 Sep 1 show that the pulsar's apparent rotation measure (RM) reached a
maximum of rad m, some 700 times the value measured
away from periastron, and is the largest astrophysical RM measured. This value,
combined with the dispersion measure implies a magnetic field in the Be star's
wind of 6 mG. We find that the light curve of the unpulsed emission is similar
to that obtained during the 1997 periastron but that differences in detail
imply that the emission disc of the Be star is thicker and/or of higher
density. The behaviour of the light curve at late times is best modelled by the
adiabatic expansion of a synchrotron bubble formed in the pulsar/disc
interaction. The expansion rate of the bubble km s is
surprisingly low but the derived magnetic field of 1.6 G close to that
expected.Comment: 8 pages, 6 figures, 3 tables, LaTeX (mn.sty). Accepted for
publication in the Monthly Notices of the Royal Astronomical Society. Also
available at http://astronomy.swin.edu.au/staff/tconnors/publications.htm
Development of a low-maintenance measurement approach to continuously estimate methane emissions: a case study
The chemical breakdown of organic matter in landfills represents a significant source of methane gas (CH4). Current estimates suggest that landfills are responsible for between 3% and 19% of global anthropogenic emissions. The net CH4 emissions resulting from biogeochemical processes and their modulation by microbes in landfills are poorly constrained by imprecise knowledge of environmental constraints. The uncertainty in absolute CH4 emissions from landfills is therefore considerable. This study investigates a new method to estimate the temporal variability of CH4 emissions using meteorological and CH4 concentration measurements downwind of a landfill site in Suffolk, UK from July to September 2014, taking advantage of the statistics that such a measurement approach offers versus shorter-term, but more complex and instantaneously accurate, flux snapshots. Methane emissions were calculated from CH4 concentrations measured 700 m from the perimeter of the landfill with observed concentrations ranging from background to 46.4 ppm. Using an atmospheric dispersion model, we estimate a mean emission flux of 709 ÎŒg mâ2 sâ1 over this period, with a maximum value of 6.21 mg mâ2 sâ1, reflecting the wide natural variability in biogeochemical and other environmental controls on net site emission. The emissions calculated suggest that meteorological conditions have an influence on the magnitude of CH4 emissions. We also investigate the factors responsible for the large variability observed in the estimated CH4 emissions, and suggest that the largest component arises from uncertainty in the spatial distribution of CH4 emissions within the landfill area. The results determined using the low-maintenance approach discussed in this paper suggest that a network of cheaper, less precise CH4 sensors could be used to measure a continuous CH4 emission time series from a landfill site, something that is not practical using far-field approaches such as tracer release methods. Even though there are limitations to the approach described here, this easy, low-maintenance, low-cost method could be used by landfill operators to estimate time-averaged CH4 emissions and their impact downwind by simultaneously monitoring plume advection and CH4 concentrations
Characteristics of long-duration inhibitory postsynaptic potentials in rat neocortical neurons in vitro
1. The characteristics of long-duration inhibitory postsynaptic potentials (l-IPSPs) which are evoked in rat frontal neocortical neurons by local electrical stimulation were investigated with intracellular recordings from anin vitro slice preparation.
2. Stimulation with suprathreshold intensities evoked l-IPSPs with typical durations of 600â900 msec at resting membrane potential. Conductance increases of 15â60% were measured at the peak amplitude of l-IPSPs (150â250 msec poststimulus).
3. The duration of the conductance increases during l-IPSPs displayed a significant voltage dependence, decreasing as the membrance potential was depolarized and increasing with hyperpolarization.
4. The reversal potential of l-IPSPs is significantly altered by reductions in the extracellular potassium concentration. Therefore it is concluded that l-IPSPs in rat neocortical neurons are generated by the activation of a potassium conductance.
5. l-IPSPs exhibit stimulation fatigue. Stimulation with a frequency of 1 Hz produces a complete fatigue of the conductance increases during l-IPSPs after approximately 20 consecutive stimuli. Recovery from this fatigue requires minutes.
6. l-IPSPs are not blocked by bicuculline but are blocked by baclofen
Signatures of stirring and mixing near the Gulf Stream front
In October, 1986 the surface waters adjacent to the Gulf Stream front were surveyed with an undulating profiler to describe the finescale structure of the mixed layer. The profiler was a Seasoar equipped with a CTD and fluorometer. The survey first defined the structure of a cyclonic eddy which resembled frontal eddies of the South Atlantic Bight in sea surface temperature imagery. The Seasoar transects revealed, however, that the cyclonic eddy lacked a cold dome typically seen in frontal eddies. Farther downstream the Seasoar defined the structure of streamers of Gulf Stream and Shelf water wrapped about the southern edge of a warm-core ring. The streamers had lateral and along-axis dimensions on the order of â 10 km and 100 km, respectively, and were bordered by narrow intrusive features. The temporal history of the streamers was described from SST imagery, and the surface flow derived from ship\u27s drift vectors. CTD casts taken while following an isopycnal float provided a means to examine the structure of the intrusive features. Interleaving was evident at the boundaries of the streamers and intrusive features where high conductivity Cox numbers were concentrated, suggesting elevated microstructure activity. The Turner angle distribution, indicating either saltfingering or diffusive convection, did not correlate well with the Cox number distribution. This is interpreted as evidence that lateral, rather than diapycnal, mixing was the process mediating the exchange of properties at the boundaries of contrasting water types. In contrast to physical properties, the distribution of fluorescence showed relatively less structure in the surface layer between the ring and Gulf Stream front. In the surface layers of the two streamers the pigment and bacterial biomass, and the diatom species composition, were typical of Slope water communities. We hypothesize that small-scale mixing processes concentrated at the boundaries of the streamers were the mechanism by which Slope water plankton were seeded into streamers of different hydrographic origins. Presumably, high netplankton growth rates allowed the Slope water species to dominate the communities in the streamers
"There's nothingâ: unemployment, attitudes to work and punitive welfare reform in post-crash Salford
This article explores attitudes and barriers to work and the impact of punitive welfare reform in the city of Salford (Greater Manchester). Contextualising our discussion in relation to the contemporary landscape of inequality and social class in the UK, we draw attention to the trends towards the expansion of low paid work, precarity and stigmatisation, and highlight the need for more qualitative, geographically sensitive, studies of how these phenomena are being played out. Describing the economic context of the City of Salford and the current state of its labour market, we then present the findings from qualitative interviews with a sample of low income, mostly working-class participants, who describe their orientations towards employment, perceptions of the labour market, barriers to employment and interactions with punitive welfare reform. Ultimately, we conclude by noting that both strategies of neoliberal statecraft aimed at the reduction of the charitable state described by Wacquant are at play in Salford and that their result is a discouragement from claiming welfare and a recommodification of labour
Shaping bursting by electrical coupling and noise
Gap-junctional coupling is an important way of communication between neurons
and other excitable cells. Strong electrical coupling synchronizes activity
across cell ensembles. Surprisingly, in the presence of noise synchronous
oscillations generated by an electrically coupled network may differ
qualitatively from the oscillations produced by uncoupled individual cells
forming the network. A prominent example of such behavior is the synchronized
bursting in islets of Langerhans formed by pancreatic \beta-cells, which in
isolation are known to exhibit irregular spiking. At the heart of this
intriguing phenomenon lies denoising, a remarkable ability of electrical
coupling to diminish the effects of noise acting on individual cells.
In this paper, we derive quantitative estimates characterizing denoising in
electrically coupled networks of conductance-based models of square wave
bursting cells. Our analysis reveals the interplay of the intrinsic properties
of the individual cells and network topology and their respective contributions
to this important effect. In particular, we show that networks on graphs with
large algebraic connectivity or small total effective resistance are better
equipped for implementing denoising. As a by-product of the analysis of
denoising, we analytically estimate the rate with which trajectories converge
to the synchronization subspace and the stability of the latter to random
perturbations. These estimates reveal the role of the network topology in
synchronization. The analysis is complemented by numerical simulations of
electrically coupled conductance-based networks. Taken together, these results
explain the mechanisms underlying synchronization and denoising in an important
class of biological models
United classification of cosmic gamma-ray bursts and their counterparts
United classification of gamma-ray bursts and their counterparts is
established on the basis of measured characteristics: photon energy E and
emission duration T. The founded interrelation between the mentioned
characteristics of events consists in that, as the energy increases, the
duration decreases (and vice versa). The given interrelation reflects the
nature of the phenomenon and forms the E-T diagram, which represents a natural
classification of all observed events in the energy range from 10E9 to 10E-6 eV
and in the corresponding interval of durations from about 10E-2 up to 10E8 s.
The proposed classification results in the consequences, which are principal
for the theory and practical study of the phenomenon.Comment: Keywords Gamma rays: burst
Observational Constraints on the Modified Gravity Model (MOG) Proposed by Moffat: Using the Magellanic System
A simple model for the dynamics of the Magellanic Stream (MS), in the
framework of modified gravity models is investigated. We assume that the galaxy
is made up of baryonic matter out of context of dark matter scenario. The model
we used here is named Modified Gravity (MOG) proposed by Moffat (2005). In
order to examine the compatibility of the overall properties of the MS under
the MOG theory, the observational radial velocity profile of the MS is compared
with the numerical results using the fit method. In order to obtain
the best model parameters, a maximum likelihood analysis is performed. We also
compare the results of this model with the Cold Dark Matter (CDM) halo model
and the other alternative gravity model that proposed by Bekenstein (2004), so
called TeVeS. We show that by selecting the appropriate values for the free
parameters, the MOG theory seems to be plausible to explain the dynamics of the
MS as well as the CDM and the TeVeS models.Comment: 14 pages, 3 Figures, accepted in Int. J. Theor. Phy
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