7,821 research outputs found
Boundary Terms and Junction Conditions for the DGP Pi-Lagrangian and Galileon
In the decoupling limit of DGP, Pi describes the brane-bending degree of
freedom. It obeys second order equations of motion, yet it is governed by a
higher derivative Lagrangian. We show that, analogously to the Einstein-Hilbert
action for GR, the Pi-Lagrangian requires Gibbons-Hawking-York type boundary
terms to render the variational principle well-posed. These terms are important
if there are other boundaries present besides the DGP brane, such as in higher
dimensional cascading DGP models. We derive the necessary boundary terms in two
ways. First, we derive them directly from the brane-localized Pi-Lagrangian by
demanding well-posedness of the action. Second, we calculate them directly from
the bulk, taking into account the Gibbons-Hawking-York terms in the bulk
Einstein-Hilbert action. As an application, we use the new boundary terms to
derive Israel junction conditions for Pi across a sheet-like source. In
addition, we calculate boundary terms and junction conditions for the galileons
which generalize the DGP Pi-lagrangian, showing that the boundary term for the
n-th order galileon is the (n-1)-th order galileon.Comment: 23 pages, 1 figure. Extended the analysis to the general galileon
field. Version to appear in JHE
X-Ray Synchrotron Emitting Fe-Rich Ejecta in SNR RCW 86
Supernova remnants may exhibit both thermal and nonthermal X-ray emission. We
present Chandra observations of RCW 86. Striking differences in the morphology
of X-rays below 1 keV and above 2 keV point to a different physical origin.
Hard X-ray emission is correlated fairly well with the edges of regions of
radio emission, suggesting that these are the locations of shock waves at which
both short-lived X-ray emitting electrons, and longer-lived radio-emitting
electrons, are accelerated. Soft X-rays are spatially well-correlated with
optical emission from nonradiative shocks, which are almost certainly portions
of the outer blast wave. These soft X-rays are well fit with simple thermal
plane-shock models. Harder X-rays show Fe K alpha emission and are well
described with a similar soft thermal component, but a much stronger
synchrotron continuum dominating above 2 keV, and a strong Fe K alpha line.
Quantitative analysis of this line and the surrounding continuum shows that it
cannot be produced by thermal emission from a cosmic-abundance plasma; the
ionization time is too short, as shown both by the low centroid energy (6.4
keV) and the absence of oxygen lines below 1 keV. Instead, a model of a plane
shock into Fe-rich ejecta, with a synchrotron continuum, provides a natural
explanation. This requires that reverse shocks into ejecta be accelerating
electrons to energies of order 50 TeV. We show that maximum energies of this
order can be produced by radiation-limited diffusive shock acceleration at the
reverse shocks.Comment: ApJ, accepted; full resolution images in
http://spider.ipac.caltech.edu/staff/rho/rcw86chandra.p
Technical management techniques for identification and control of industrial safety and pollution hazards
Constructive recommendations are suggested for pollution problems from offshore energy resources industries on outer continental shelf. Technical management techniques for pollution identification and control offer possible applications to space engineering and management
Meta-research: justifying career disruption in funding applications, a survey of Australian researchers.
Background: When researchers' careers are disrupted by life events - such as illness or childbirth - they often need to take extended time off. This creates a gap in their research output that can reduce their chances of winning funding. In Australia, applicants can disclose their career disruptions and peer reviewers are instructed to make appropriate adjustments. However, it is not clear if and how applicants use career disruption sections or how reviewers adjust and if they do it consistently. Methods: To examine career disruption, we used surveys of the Australian health and medical research community. We used both a random sample of Australian authors on PubMed and a non-random convenience sample. Results: Respondents expressed concerns that sharing information on career disruption would harm their chances of being funded, with 13% saying they have medical or social circumstances but would not include it in their application, with concerns about appearing 'weak'. Women were more reluctant to include disruption. There was inconsistency in how disruption was adjusted for, with less time given for those with depression compared with caring responsibilities, and less time given for those who did not provide medical details of their disruption. Conclusions: The current system is likely not adequately adjusting for career disruption and this may help explain the ongoing funding gap for senior women in Australia. Funding: National Health and Medical Research Council Senior Research Fellowship (Barnett)
Diffuse Hard X-ray Sources Discovered with the ASCA Galactic Plane Survey
We found diffuse hard X-ray sources, G11.0+0.0, G25.5+0.0, and G26.6-0.1 in
the ASCA Galactic plane survey data. The X-ray spectra are featureless with no
emission line, and are fitted with both models of a thin thermal plasma in
non-equilibrium ionization and a power-law function. The source distances are
estimated to be 1-8 kpc, using the best-fit NH values on the assumption that
the mean density in the line of sight is 1 H cm^-3. The source sizes and
luminosities are then 4.5-27 pc and (0.8-23)x10^33 ergs/s. Although the source
sizes are typical to supernova remnants (SNR) with young to intermediate ages,
the X-ray luminosity, plasma temperature, and weak emission lines in the
spectra are all unusual. This suggests that these objects are either shell-like
SNRs dominated by X-ray synchrotron emission, like SN 1006, or, alternatively,
plerionic SNRs. The total number of these classes of SNRs in our Galaxy is also
estimated.Comment: 17 pages, 9 figures; to appear in Ap
Fine Structures of Shock of SN 1006 with the Chandra Observation
The north east shell of SN 1006 is the most probable acceleration site of
high energy electrons (up to ~ 100 TeV) with the Fermi acceleration mechanism
at the shock front. We resolved non-thermal filaments from thermal emission in
the shell with the excellent spatial resolution of Chandra. The thermal
component is extended widely over about ~ 100 arcsec (about 1 pc at 1.8 kpc
distance) in width, consistent with the shock width derived from the Sedov
solution. The spectrum is fitted with a thin thermal plasma of kT = 0.24 keV in
non-equilibrium ionization (NEI), typical for a young SNR. The non-thermal
filaments are likely thin sheets with the scale widths of ~ 4 arcsec (0.04 pc)
and ~ 20 arcsec (0.2 pc) at upstream and downstream, respectively. The spectra
of the filaments are fitted with a power-law function of index 2.1--2.3, with
no significant variation from position to position. In a standard diffusive
shock acceleration (DSA) model, the extremely small scale length in upstream
requires the magnetic field nearly perpendicular to the shock normal. The
injection efficiency (eta) from thermal to non-thermal electrons around the
shock front is estimated to be ~ 1e-3 under the assumption that the magnetic
field in upstream is 10 micro G. In the filaments, the energy densities of the
magnetic field and non-thermal electrons are similar to each other, and both
are slightly smaller than that of thermal electrons. in the same order for each
other. These results suggest that the acceleration occur in more compact region
with larger efficiency than previous studies.Comment: 24 pages, 11 figures, Accepted for publication in ApJ, the paper with
full resolution images in
http://www-cr.scphys.kyoto-u.ac.jp/member/bamba/Paper/SN1006.pd
Genomic features of the Helicobacter pylori strain PMSS1 and its virulence attributes as deduced from its in vivo colonisation patterns
The influence of lower-limb prostheses technology on Paracanoeing time-trial performance
Within the Paracanoeing discipline, it is important to ensure appropriate control is achieved by a paddler with a disability. However, this Paralympic Games discipline has seen very little attention to date. The aims of this study were to understand the kinematic impact to a paracanoeist when not utilising the use of a prosthetic lowerlimb. A kayaker with a uni-lateral transfemoral amputation completed several 200m maximal efforts both with and without their prosthesis. When the prosthetic limb was removed, there were significant differences found in stroke rate, stroke speed, stroke length and overall power output. Sagittal and frontal video analysis demonstrated the residual limb movements when paddling and indicated where support would be required to improve the kayak’s control. It is recommended that those with lower-limb absence wishing to paddle a kayak competitively utilise the use of a prostheses designed for the kayaking environment that supports the residual limb at both the upper and inner thigh and the distal end
A microfluidic chip based model for the study of full thickness human intestinal tissue using dual flow
© 2016 Author(s). The study of inflammatory bowel disease, including Ulcerative Colitis and Crohn's Disease, has relied largely upon the use of animal or cell culture models; neither of which can represent all aspects of the human pathophysiology. Presented herein is a dual flow microfluidic device which holds full thickness human intestinal tissue in a known orientation. The luminal and serosal sides are independently perfused ex vivo with nutrients with simultaneous waste removal for up to 72 h. The microfluidic device maintains the viability and integrity of the tissue as demonstrated through Haematoxylin & Eosin staining, immunohistochemistry and release of lactate dehydrogenase. In addition, the inflammatory state remains in the tissue after perfusion on the device as determined by measuring calprotectin levels. It is anticipated that this human model will be extremely useful for studying the biology and tes ting novel interventions in diseased tissue
Distributed Community Detection in Dynamic Graphs
Inspired by the increasing interest in self-organizing social opportunistic
networks, we investigate the problem of distributed detection of unknown
communities in dynamic random graphs. As a formal framework, we consider the
dynamic version of the well-studied \emph{Planted Bisection Model}
\sdG(n,p,q) where the node set of the network is partitioned into two
unknown communities and, at every time step, each possible edge is
active with probability if both nodes belong to the same community, while
it is active with probability (with ) otherwise. We also consider a
time-Markovian generalization of this model.
We propose a distributed protocol based on the popular \emph{Label
Propagation Algorithm} and prove that, when the ratio is larger than
(for an arbitrarily small constant ), the protocol finds the right
"planted" partition in time even when the snapshots of the dynamic
graph are sparse and disconnected (i.e. in the case ).Comment: Version I
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