2,521 research outputs found
Decay of the Maxwell field on the Schwarzschild manifold
We study solutions of the decoupled Maxwell equations in the exterior region
of a Schwarzschild black hole. In stationary regions, where the Schwarzschild
coordinate ranges over , we obtain a decay rate of
for all components of the Maxwell field. We use vector field methods
and do not require a spherical harmonic decomposition.
In outgoing regions, where the Regge-Wheeler tortoise coordinate is large,
, we obtain decay for the null components with rates of
, , and . Along the event horizon and in ingoing regions, where ,
and when , all components (normalized with respect to an ingoing null
basis) decay at a rate of C \uout^{-1} with \uout=t+r_* in the exterior
region.Comment: 37 pages, 5 figure
Spatial Patterns in Mass Balance of the Siple Coast and Amundsen Sea Sectors, West Antarctica
Local rates of change in ice-sheet thickness were calculated at IS sites in West Antarctica using the submergence velocity technique. This method entails a comparison of the vertical velocity of the ice sheet, measured using repeat global positioning system surveys of markers, and local long-term rates of snow accumulation obtained using firn-core stratigraphy. Any significant difference between these two quantities represents a thickness change with time. Measurements were conducted at sites located similar to 100-200 km apart along US ITASE traverse routes, and at several isolated locations. All but one of the sites are distributed in the Siple Coast and the Amundsen Sea basin along contours of constant elevation, along flowlines, across ice divides and close to regions of enhanced flow. Calculated rates of thickness change are different from site to site. Most of the large rates of change in ice thickness (similar to 10 cm a(-1) or larger) are observed in or close to regions of rapid flow, and are probably related to ice-dynamics effects. Near-steady-state conditions are calculated mostly at sites in the slow-moving ice-sheet interior and near the main West Antarctic ice divide. These results are consistent with regional estimates of ice-sheet change derived from remote-sensing measurements at similar locations in West Antarctica
Edge pixel response studies of edgeless silicon sensor technology for pixellated imaging detectors
Silicon sensor technologies with reduced dead area at the sensor's perimeter are under development at a number of institutes. Several fabrication methods for sensors which are sensitive close to the physical edge of the device are under investigation utilising techniques such as active-edges, passivated edges and current-terminating rings. Such technologies offer the goal of a seamlessly tiled detection surface with minimum dead space between the individual modules. In order to quantify the performance of different geometries and different bulk and implant types, characterisation of several sensors fabricated using active-edge technology were performed at the B16 beam line of the Diamond Light Source. The sensors were fabricated by VTT and bump-bonded to Timepix ROICs. They were 100 and 200 μ m thick sensors, with the last pixel-to-edge distance of either 50 or 100 μ m. The sensors were fabricated as either n-on-n or n-on-p type devices. Using 15 keV monochromatic X-rays with a beam spot of 2.5 μ m, the performance at the outer edge and corners pixels of the sensors was evaluated at three bias voltages. The results indicate a significant change in the charge collection properties between the edge and 5th (up to 275 μ m) from edge pixel for the 200 μ m thick n-on-n sensor. The edge pixel performance of the 100 μ m thick n-on-p sensors is affected only for the last two pixels (up to 110 μ m) subject to biasing conditions. Imaging characteristics of all sensor types investigated are stable over time and the non-uniformities can be minimised by flat-field corrections. The results from the synchrotron tests combined with lab measurements are presented along with an explanation of the observed effects
Island diffusion on metal fcc(100) surfaces
We present Monte Carlo simulations for the size and temperature dependence of
the diffusion coefficient of adatom islands on the Cu(100) surface. We show
that the scaling exponent for the size dependence is not a constant but a
decreasing function of the island size and approaches unity for very large
islands. This is due to a crossover from periphery dominated mass transport to
a regime where vacancies diffuse inside the island. The effective scaling
exponents are in good agreement with theory and experiments.Comment: 13 pages, 2 figures, to be published in Phys. Rev. Let
Erratum: Leakage current measurements of a pixelated polycrystalline CVD diamond detector
This is an erratum for the article 2013 JINST 8 C0105
A proof of the uniform boundedness of solutions to the wave equation on slowly rotating Kerr backgrounds
We consider Kerr spacetimes with parameters a and M such that |a|<< M,
Kerr-Newman spacetimes with parameters |Q|<< M, |a|<< M, and more generally,
stationary axisymmetric black hole exterior spacetimes which are sufficiently
close to a Schwarzschild metric with parameter M>0, with appropriate geometric
assumptions on the plane spanned by the Killing fields. We show uniform
boundedness on the exterior for sufficiently regular solutions to the scalar
homogeneous wave equation. In particular, the bound holds up to and including
the event horizon. No unphysical restrictions are imposed on the behaviour of
the solution near the bifurcation surface of the event horizon. The pointwise
estimate derives in fact from the uniform boundedness of a positive definite
energy flux. Note that in view of the very general assumptions, the
separability properties of the wave equation on the Kerr background are not
used.Comment: 71 pages, 3 figure
Post-traumatic stress disorder following childbirth: an update of current issues and recommendations for future research
Objective:
This paper aimed to report the current status of research in the field of post-traumatic stress disorder following childbirth (PTSD FC), and to update the findings of an earlier 2008 paper.
Background:
A group of international researchers, clinicians and service users met in 2006 to establish the state of clinical and academic knowledge relating to PTSD FC. A paper identified four key areas of research knowledge at that time.
Methods:
Fourteen clinicians and researchers met in Oxford, UK to update the previously published paper relating to PTSD FC. The first part of the meeting focused on updating the four key areas identified previously, and the second part on discussing new and emerging areas of research within the field.
Results:
A number of advances have been made in research within the area of PTSD FC. Prevalence is well established within mothers, several intervention studies have been published, and there is growing interest in new areas: staff and pathways; prevention and early intervention; impact on families and children; special populations; and post-traumatic growth.
Conclusion:
Despite progress, significant gaps remain within the PTSD FC knowledge base. Further research continues to be needed across all areas identified in 2006, and five areas were identified which can be seen as ‘new and emerging’. All of these new areas require further extensive research. Relatively little is still known about PTSD FC
Effects of electrical stimulation of dorsal raphe nucleus on neuronal response properties of barrel cortex layer IV neurons following long-term sensory deprivation
Abstract: Objective To evaluate the effect of electrical stimulation of dorsal raphe nucleus (DRN) on response properties of layer IV barrel cortex neurons following long-term sensory deprivation. Methods: Male Wistar rats were divided into sensory-deprived (SD) and control (unplucked) groups. In SD group, all vibrissae except the D2 vibrissa were plucked on postnatal day one, and kept plucked for a period of 60 d. After that, whisker regrowth was allowed for 8-10 d. The D2 principal whisker (PW) and the D1 adjacent whisker (AW) were either deflected singly or both deflected in a serial order that the AW was deflected 20 ms before PW deflection for assessing lateral inhibition, and neuronal responses were recorded from layer IV of the D2 barrel cortex. DRN was electrically stimulated at inter-stimulus intervals (ISIs) ranging from 0 to 800 ms before whisker deflection. Results: PW-evoked responses increased in the SD group with DRN electrical stimulation at ISIs of 50 ms and 100 ms, whereas AW-evoked responses increased at ISI of 800 ms in both groups. Whisker plucking before DRN stimulation could enhance the responsiveness of barrel cortex neurons to PW deflection and decrease the responsiveness to AW deflection. DRN electrical stimulation significantly reduced this difference only in PW-evoked responses between groups. Besides, no DRN stimulation-related changes in response latency were observed following PW or AW deflection in either group. Moreover, condition test (CT) ratio increased in SD rats, while DRN stimulation did not affect the CT ratio in either group. There was no obvious change in 5-HT2A receptor protein density in barrel cortex between SD and control groups. Conclusion: These results suggest that DRN electrical stimulation can modulate information processing in the SD barrel cortex
Experimental study of pedestrian flow through a bottleneck
In this work the results of a bottleneck experiment with pedestrians are
presented in the form of total times, fluxes, specific fluxes, and time gaps. A
main aim was to find the dependence of these values from the bottleneck width.
The results show a linear decline of the specific flux with increasing width as
long as only one person at a time can pass, and a constant value for larger
bottleneck widths. Differences between small (one person at a time) and wide
bottlenecks (two persons at a time) were also found in the distribution of time
gaps.Comment: accepted for publication in J. Stat. Mec
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