723 research outputs found
The X-ray nebula around the Seyfert 2 galaxy NGC4388
We report on X-ray emission from the Seyfert 2 galaxy NGC4388 observed with
the Chandra X-ray Observatory. A hard X-ray peak is found at the position of
the active nucleus suggested by optical and radio observations. Extended soft
X-ray emission correlates well with the ionization cone found in optical line
emission. A large soft X-ray extension is found up to 16 kpc to the north of
the galaxy. Photoionized gas with low ionization parameters (xi<3) appears to
be the likely explanation of this emission. The same ionized gas clouds could
be responsible for the optical [OIII] emission. Fe K line emission from cold
material is found to be extended by a few kpc.Comment: 12 pages, one colour figure included, MNRAS in pres
Report of the working group on the measurement of triple gauge boson couplings
The working group discussed several aspects of triple gauge coupling analysis viewed in the light of experiences with the first high energy data recorded at energies above the W pair threshold. Some analysis methods were reviewed briefly, and consideration given to better ways of characterising the data. The measurement of CP violating parameters was discussed. Results were prepared to further quantify the precision attainable on anaomalous couplings in the four-quark channel using jet-charge methods, and finally the trade off between maximum LEP energy-vs-luminosity was quantified.The working group discussed several aspects of triple gauge coupling analysis viewed in the light of experiences with the first high energy data recorded at energies above the W pair threshold. Some analysis methods were reviewed briefly, and consideration given to better ways of characterising the data. The measurement of CP violating parameters was discussed. Results were prepared to further quantify the precision attainable on anaomalous couplings in the four-quark channel using jet-charge methods, and finally the trade off between maximum LEP energy-vs-luminosity was quantified
Thixotropy in macroscopic suspensions of spheres
An experimental study of the viscosity of a macroscopic suspension, i.e. a
suspension for which Brownian motion can be neglected, under steady shear is
presented. The suspension is prepared with a high packing fraction and is
density-matched in a Newtonian carrier fluid. The viscosity of the suspension
depends on the shear rate and the time of shearing. It is shown for the first
time that a macroscopic suspension shows thixotropic viscosity, i.e.
shear-thinning with a long relaxation time as a unique function of shear. The
relaxation times show a systematic decrease with increasing shear rate. These
relaxation times are larger when decreasing the shear rates, compared to those
observed after increasing the shear. The time scales involved are about 10000
times larger than the viscous time scale and about 1000 times smaller than the
thermodynamic time scale. The structure of the suspension at the outer cylinder
of a viscometer is monitored with a camera, showing the formation of a
hexagonal structure. The temporal decrease of the viscosity under shear
coincides with the formation of this hexagonal pattern
Low-light-level nonlinear optics with slow light
Electromagnetically induced transparency in an optically thick, cold medium
creates a unique system where pulse-propagation velocities may be orders of
magnitude less than and optical nonlinearities become exceedingly large. As
a result, nonlinear processes may be efficient at low-light levels. Using an
atomic system with three, independent channels, we demonstrate a quantum
interference switch where a laser pulse with an energy density of
photons per causes a 1/e absorption of a second pulse.Comment: to be published in PR
Trends in population structure of Patagonian toothfish over 25 years of fishery exploitation at South Georgia
Patagonian toothfish (Dissostichus eleginoides) supports valuable fisheries across the Southern Ocean under the management of the Commission for the Conservation of Antarctic Marine Living Resources. The fishery at South Georgia accounts for 26 % of the catch of this species in the Southern Ocean in the last 25 years. This study assesses the effects of exploitation and changes in management of the fishery on long-term trends in biological traits of Patagonian toothfish at South Georgia. Our results show variability in the size of fish, but no evidence of a systematic decline during the 25-year period. The mean size of fish was linked to recruitment, with pulses of recruitment associated with a reduction in mean size of the fishery. The years when recruitment was highest were in 2000–2010, with >50 % of toothfish of length classes < 90 cm. Management measures implemented over the last 25 years, including depth restrictions and benthic closed areas, have resulted in a gradual stabilization of the population structure. Catch per unit effort (CPUE) dropped from 1997 to 2010, gradually increased until 2017 and since 2018 has returned to values typical of the mid-2010s. Monthly changes in fish length, depth of capture and CPUE confirm that the spawning peak is in July. Size at maturity has remained stable over the last 25 years, suggesting the fishery has not had a major impact on population size structure. These results illustrate the role of management regulations in limiting the impacts of commercial exploitation on the population structure of a long-lived fish species. Given the bigger-deeper size pattern in Patagonian toothfish, there may be a case for increasing the minimum depth of the fishery (currently 700 m) when strong recruitment pulses are detected
Renormalized Path Integral for the Two-Dimensional Delta-Function Interaction
A path-integral approach for delta-function potentials is presented.
Particular attention is paid to the two-dimensional case, which illustrates the
realization of a quantum anomaly for a scale invariant problem in quantum
mechanics. Our treatment is based on an infinite summation of perturbation
theory that captures the nonperturbative nature of the delta-function bound
state. The well-known singular character of the two-dimensional delta-function
potential is dealt with by considering the renormalized path integral resulting
from a variety of schemes: dimensional, momentum-cutoff, and real-space
regularization. Moreover, compatibility of the bound-state and scattering
sectors is shown.Comment: 26 pages. The paper was significantly expanded and numerous equations
were added for the sake of clarity; the main results and conclusions are
unchange
Noise induced transitions in semiclassical cosmology
A semiclassical cosmological model is considered which consists of a closed
Friedmann-Robertson-Walker in the presence of a cosmological constant, which
mimics the effect of an inflaton field, and a massless, non-conformally coupled
quantum scalar field. We show that the back-reaction of the quantum field,
which consists basically of a non local term due to gravitational particle
creation and a noise term induced by the quantum fluctuations of the field, are
able to drive the cosmological scale factor over the barrier of the classical
potential so that if the universe starts near zero scale factor (initial
singularity) it can make the transition to an exponentially expanding de Sitter
phase. We compute the probability of this transition and it turns out to be
comparable with the probability that the universe tunnels from "nothing" into
an inflationary stage in quantum cosmology. This suggests that in the presence
of matter fields the back-reaction on the spacetime should not be neglected in
quantum cosmology.Comment: LaTex, 33.tex pages, no figure
The influence of localised size reorganisation on short-duration bidispersed granular flows
We investigate experimentally the runout resulting from the collapse of a granular column containing two particle species that differ in size only. The experimental configuration is strictly twodimensional (only one particle per width of the experimental tank) and we explore both the role of the initial arrangement and proportion of the two particle sizes in the column, using high-speed videography, and by determining the centres of mass of the big and small particles in the initial column and the final deposit. The duration of the experiment is sufficiently short that large-scale segregation does not occur, however, we find a clear dependence of runout on both initial mixture arrangement and proportion for all conditions. We investigated this observation through detailed analysis of the flow front motion, and identify a characteristic "stopping" phase when dissipation dominates, and we apply a shallow layer model at the flow front to show how the initial mixture arrangement and proportion influence the effective coefficient of friction during emplacement. We find that a bidispersed mixture can induce a larger friction on emplacement than a monodispersed mixture, and the highest coefficient of friction was found for a well-mixed initial arrangement of particles at the proportion that shows maximum horizontal spreading of the flow. These observations suggest that downwards percolation of fine particles takes place at the front of the collapsing column, and so localised size segregation processes at the flow front can control flow mobility. This effect is likely to be important in controlling the mobility of large geophysical flows that occur on finite time scales, and whose deposits typically show granular segregation at the front and edges but not throughout the entire deposit
Effects of thermoregulation on human sleep patterns: A mathematical model of sleep-wake cycles with REM-NREM subcircuit
In this paper we construct a mathematical model of human sleep/wake regulation with thermoregulation and temperature e ects. Simulations of this model show features previously presented in experimental data such as elongation of duration and number of REM bouts across the night as well as the appearance of awakenings due to deviations in body temperature from thermoneutrality. This model helps to demonstrate the importance of temperature in the sleep cycle. Further modi cations of the model to include more temperature e ects on other aspects of sleep regulation such as sleep and REM latency are discussedPostprint (author's final draft
'To live and die [for] Dixie': Irish civilians and the Confederate States of America
Around 20,000 Irishmen served in the Confederate army in the Civil War. As a result, they left behind, in various Southern towns and cities, large numbers of friends, family, and community leaders. As with native-born Confederates, Irish civilian support was crucial to Irish participation in the Confederate military effort. Also, Irish civilians served in various supporting roles: in factories and hospitals, on railroads and diplomatic missions, and as boosters for the cause. They also, however, suffered in bombardments, sieges, and the blockade. Usually poorer than their native neighbours, they could not afford to become 'refugees' and move away from the centres of conflict. This essay, based on research from manuscript collections, contemporary newspapers, British Consular records, and Federal military records, will examine the role of Irish civilians in the Confederacy, and assess the role this activity had on their integration into Southern communities. It will also look at Irish civilians in the defeat of the Confederacy, particularly when they came under Union occupation. Initial research shows that Irish civilians were not as upset as other whites in the South about Union victory. They welcomed a return to normalcy, and often 'collaborated' with Union authorities. Also, Irish desertion rates in the Confederate army were particularly high, and I will attempt to gauge whether Irish civilians played a role in this. All of the research in this paper will thus be put in the context of the Drew Gilpin Faust/Gary Gallagher debate on the influence of the Confederate homefront on military performance. By studying the Irish civilian experience one can assess how strong the Confederate national experiment was. Was it a nation without a nationalism
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