1,258 research outputs found
XMM-Newton observations of the Galactic Centre Region - II: The soft thermal emission
We have extended our earlier study (Heard & Warwick 2013, Paper I) of the
X-ray emission emanating from the central 100 pc x 100 pc region of our Galaxy
to an investigation of several features prominent in the soft X-ray (2-4.5 keV)
band. We focus on three specific structures: a putative bipolar outflow from
the vicinity of Sgr A*; a high surface brightness region located roughly 12
arcmin to the north-east of Sgr A*; and a lower surface-brightness extended
loop feature seen to the south of Sgr A*. We show that all three structures are
thermal in nature and have similar temperatures (kT ~ 1 keV). The inferred
X-ray luminosities lie in the range (2 - 10) x 10^34 erg s^-1. In the case of
the bipolar feature we suggest that the hot plasma is produced by the
shock-heating of the winds from massive stars within the Central Cluster,
possibly collimated by the Circumnuclear Disc. Alternatively the outflow may be
driven by outbursts on Sgr A*, which follow tidal disruption events occurring
at a rate of roughly 1 every 4000 yr. The north-east enhancement is centred on
a candidate PWN which has a relatively hard non-thermal X-ray spectrum. We
suggest that the coincident soft-thermal emission traces the core of a new
thermal-composite supernova remnant, designated as SNR G0.13-0.12. There is no
clear evidence for an associated radio shell but such a feature may be masked
by the bright emission of the nearby Radio Arc and other filamentary
structures. SNR G0.13-0.12 is very likely interacting with the nearby molecular
cloud, G0.11-0.11, and linked to the Fermi source, 2FGL J1746.4-2851c. Finally
we explore a previous suggestion that the elliptically-shaped X-ray loop to the
south of Sgr A*, of maximum extent ~45 pc, represents the shell of a
superbubble located in the GC region. Although plausible, the interpretation of
this feature in terms a coherent physical structure awaits confirmation.Comment: 17 pages, 6 figures, accepted for publication in MNRA
Testing mu-e universality with Kl2 decays
The ratio R_K=Gamma(Ke2)/Gamma(Kmu2) provides a very powerful probe for the
weak interactions structure. This ratio of decay rates is calculated with very
high precision within the Standard Model but the corrections due to the
presence of New Physics could be as high as 3%. The data obtained by the NA48
experiment at the CERN SPS accelerator during a 56 hours special run in 2004
has been analyzed.The precision of the preliminary result for R_K is two times
better than the world average but is still insufficient to probe the existence
of physics Beyond the Standard Model. Currently the experiment is taking data
dedicated to the sub-percent precision measurement of R_K.Comment: for the NA48/2 collaboration; talk given at Kaon International
Conference (KAON'07), Frascati, Italy, 21-25 May 200
Langevin Thermostat for Rigid Body Dynamics
We present a new method for isothermal rigid body simulations using the
quaternion representation and Langevin dynamics. It can be combined with the
traditional Langevin or gradient (Brownian) dynamics for the translational
degrees of freedom to correctly sample the NVT distribution in a simulation of
rigid molecules. We propose simple, quasi-symplectic second-order numerical
integrators and test their performance on the TIP4P model of water. We also
investigate the optimal choice of thermostat parameters.Comment: 15 pages, 13 figures, 1 tabl
New Langevin and Gradient Thermostats for Rigid Body Dynamics
We introduce two new thermostats, one of Langevin type and one of gradient
(Brownian) type, for rigid body dynamics. We formulate rotation using the
quaternion representation of angular coordinates; both thermostats preserve the
unit length of quaternions. The Langevin thermostat also ensures that the
conjugate angular momenta stay within the tangent space of the quaternion
coordinates, as required by the Hamiltonian dynamics of rigid bodies. We have
constructed three geometric numerical integrators for the Langevin thermostat
and one for the gradient thermostat. The numerical integrators reflect key
properties of the thermostats themselves. Namely, they all preserve the unit
length of quaternions, automatically, without the need of a projection onto the
unit sphere. The Langevin integrators also ensure that the angular momenta
remain within the tangent space of the quaternion coordinates. The Langevin
integrators are quasi-symplectic and of weak order two. The numerical method
for the gradient thermostat is of weak order one. Its construction exploits
ideas of Lie-group type integrators for differential equations on manifolds. We
numerically compare the discretization errors of the Langevin integrators, as
well as the efficiency of the gradient integrator compared to the Langevin ones
when used in the simulation of rigid TIP4P water model with smoothly truncated
electrostatic interactions. We observe that the gradient integrator is
computationally less efficient than the Langevin integrators. We also compare
the relative accuracy of the Langevin integrators in evaluating various static
quantities and give recommendations as to the choice of an appropriate
integrator.Comment: 16 pages, 4 figure
Two coupled feedback loops explain random mono-allelic Xist upregulation at the onset of X-chromosome inactivation
In female mammal s, dosage compensation for X-linked genes is ensured through random X-chromosome inactivation, which is initiated by mono-allelic up-regulation of Xist . We use mathematical modeling to identify the regulatory principles required to establish the mono-allelic and female-specific Xist expression pattern and test model predictions experimentally. A cis -acting positive feedback, which in mice is mediated by mutual repression of Xist and its antisense transcript Tsix , together with a trans -acting negative feedba ck are sufficient to explain mono-allelic Xist up-regulation. The model can reproduce data from several mutant, aneuploid and polyploid murine cell lines and explain s Xist expression patterns in other mammalian species. Furthermore, it predicts that transient , reversible bi-allelic Xist expression is not restricted to rabbits and humans but can also occur in mice, which we indeed confirm to occur in mouse embryos. Overall, our study provides a conceptual framework of the molecular mechanisms required to initiate random X-chromosome inactivation
The generalized non-conservative model of a 1-planet system - revisited
We study the long-term dynamics of a planetary system composed of a star and
a planet. Both bodies are considered as extended, non-spherical, rotating
objects. There are no assumptions made on the relative angles between the
orbital angular momentum and the spin vectors of the bodies. Thus, we analyze
full, spatial model of the planetary system. Both objects are assumed to be
deformed due to their own rotations, as well as due to the mutual tidal
interactions. The general relativity corrections are considered in terms of the
post-Newtonian approximation. Besides the conservative contributions to the
perturbing forces, there are also taken into account non-conservative effects,
i.e., the dissipation of the mechanical energy. This dissipation is a result of
the tidal perturbation on the velocity field in the internal zones with
non-zero turbulent viscosity (convective zones). Our main goal is to derive the
equations of the orbital motion as well as the equations governing
time-evolution of the spin vectors (angular velocities). We derive the
Lagrangian equations of the second kind for systems which do not conserve the
mechanical energy. Next, the equations of motion are averaged out over all fast
angles with respect to time-scales characteristic for conservative
perturbations. The final equations of motion are then used to study the
dynamics of the non-conservative model over time scales of the order of the age
of the star. We analyze the final state of the system as a function of the
initial conditions. Equilibria states of the averaged system are finally
discussed.Comment: 37 pages, 13 figures, accepted to Celestial Mechanics and Dynamical
Astronom
Exploring the role of nurses in after-hours telephone services in regional areas; A scoping review
Introduction
The management of patients who need chronic and complex care is a focus of attention internationally, brought about by an increase in chronic conditions, requiring significantly more care over longer periods of time. The increase in chronic conditions has placed pressure on health services, financially and physically, bringing about changes in the way care is delivered, with hospital avoidance and home-based care encouraged. In this environment, nurses play an important role in co-ordinating care across services. This review formed one part of a funded project that explored the nurse navigator role within a proposed 24-hour telephone-call service in one regional area that has a diverse population in terms of cultural identity and geographical location in relation to service access.
Aim
The review reports on the extant literature on the nurse’s role in the provision of afterhours telephone services for patients with chronic and complex conditions. The specific aim was to explore the effectiveness of services for patients in geographically isolated locations.
Methods
The methodological approach to the review followed the Preferred Reporting System for Meta-Analyses (PRISMA) guidelines. A thematic analysis was used to identify themes with chronic care models underpinning analysis.
Results
Three themes were identified; nurse-led decision making; consumer profile; and program outcomes. Each theme was divided into two sub-themes. The two sub-themes for decision making were: the experience of the staff who provided the service and the tool or protocol used. The two sub-themes for consumers profile were; the geographic/demographic identity of the consumers, and consumer satisfaction. The final theme of outcomes describes how the effectiveness of the service is measured, broken into two sub-themes: the economic/workforce outcomes and the consumer outcomes.
Discussion
The provision of an after-hours telephone service, in whatever model used should align with a Chronic Care Model. In this way, after-hours telephone services provided by experienced nurses, supported by ongoing professional development and relevant protocols, form part of the ongoing improvement for chronic and complex care management as a health priority
Cosmological Evolution of a Tachyon-Quintom Model of Dark Energy
In this work we study the cosmological evolution of a dark energy model with
two scalar fields, i.e. the tachyon and the phantom tachyon. This model enables
the equation of state to change from to in the evolution of
the universe. The phase-space analysis for such a system with inverse square
potentials shows that there exists a unique stable critical point, which has
power-law solutions. In this paper, we also study another form of
tachyon-quintom model with two fields, which voluntarily involves the
interactions between both fields.Comment: 17 pages, 10 figure
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