2,655 research outputs found
Beam Energy Considerations for Gold Nano-Particle Enhanced Radiation Treatment
Purpose: A novel approach using nano technology enhanced radiation modalities
is investigated. The proposed methodology uses antibodies labeled with
organically inert metals with a high atomic number. Irradiation using photons
with energies in the kilo--electron volt (keV) range show an increase in dose
due to a combination of an increase in photo-electric interactions and a
pronounced generation of Auger and/or Coster-Kronig (A-CK) electrons.
Methods: The dependency of the dose deposition on various factors is
investigated using Monte Carlo simulation models. The factors investigated
include: agent concentration, spectral dependency looking at mono--energetic
sources as well as classical bremsstrahlung sources. The optimization of the
energy spectrum is performed in terms of physical dose enhancement as well as
the dose deposited by Auger and/or Coster-Kronig electrons and their biological
effectiveness.
Results: A quasi-linear dependency on concentration and an exponential
decrease within the target medium is observed. The maximal dose enhancement is
dependent on the position of the target in the beam. Apart from irradiation
with low photon energies (10 - 20 keV) there is no added benefit from the
increase in generation of Auger electrons. Interestingly, a regular 110kVp
bremsstrahlung spectrum shows a comparable enhancement in comparison with the
optimized mono--energetic sources.
Conclusions: In conclusion we find that the use of nano-particle enhanced
shows promise to be implemented quite easily in regular clinic on a physical
level due to the advantageous properties in classical beams.Comment: Preprint submitted to Phys Med Bio
On the origin of the difference between the runaway velocities of the OB-supergiant X-ray Binaries and the Be/X-ray Binaries
The recent finding by Chevalier & Ilovaisky (1998) that OB-supergiant X-ray
binaries have relatively large runaway velocities whereas Be/X-ray binaries
have low runaway velocities, provides confirmation of the current models for
the formation of these two types of systems. These predict a difference in
runaway velocity of an order of magnitude. This difference basically results
from the variation of the fractional helium core mass as a function of stellar
mass, in combination with the conservation of orbital angular momentum during
the mass transfer phase that preceded the formation of the compact object in
the system. This combination results into: (i) Systematically narrower
pre-supernova orbits in the OB-supergiant systems than in the Be-systems, and
(ii) A larger fractional amount of mass ejected in the supernovae in high-mass
systems relative to systems of lower mass. Regardless of possible kick
velocities imparted to neutron stars at birth, this combination leads to a
considerable difference in average runaway velocity between these two groups.
The observed low runaway velocities of the Be/X-ray binaries confirm that in
most cases not more than 1 to 2Msun was ejected in the supernovae that produced
their neutron stars. This, in combination with the --on average-- large orbital
eccentricities of these systems, indicates that their neutron stars must have
received a velocity kick in the range 60 - 250 km/s at birth.Comment: reduced abstract, 13 pages, accepted by A&
Forming short-period Wolf-Rayet X-ray binaries and double black holes through stable mass transfer
We show that black-hole High-Mass X-ray Binaries (HMXBs) with O- or B-type
donor stars and relatively short orbital periods, of order one week to several
months may survive spiral in, to then form Wolf-Rayet (WR) X-ray binaries with
orbital periods of order a day to a few days; while in systems where the
compact star is a neutron star, HMXBs with these orbital periods never survive
spiral-in. We therefore predict that WR X-ray binaries can only harbor black
holes. The reason why black-hole HMXBs with these orbital periods may survive
spiral in is: the combination of a radiative envelope of the donor star, and a
high mass of the compact star. In this case, when the donor begins to overflow
its Roche lobe, the systems are able to spiral in slowly with stable Roche-lobe
overflow, as is shown by the system SS433. In this case the transferred mass is
ejected from the vicinity of the compact star (so-called "isotropic
re-emission" mass loss mode, or "SS433-like mass loss"), leading to gradual
spiral-in. If the mass ratio of donor and black hole is , these systems
will go into CE evolution and are less likely to survive. If they survive, they
produce WR X-ray binaries with orbital periods of a few hours to one day.
Several of the well-known WR+O binaries in our Galaxy and the Magellanic
Clouds, with orbital periods in the range between a week and several months,
are expected to evolve into close WR-Black-Hole binaries,which may later
produce close double black holes. The galactic formation rate of double black
holes resulting from such systems is still uncertain, as it depends on several
poorly known factors in this evolutionary picture. It might possibly be as high
as per year.Comment: MNRAS in pres
Probing Electron-Capture Supernovae: X-Ray Binaries in Starbursts
Presenting population models of high-mass X-ray binaries (HMXBs) formed after
bursts of star formation, we investigate the effect of electron-capture
supernovae (ECS) of massive ONeMg white dwarfs and the hypothesis that ECS
events are associated with typically low supernova kicks imparted to the
nascent neutron stars. We identify an interesting ECS bump in the time
evolution of HMXB numbers; this bump is caused by significantly increased
production of wind-fed HMXBs 20-60 Myr post starburst. The amplitude and age
extent of the ECS bump depend on the strength of ECS kicks and the mass range
of ECS progenitors. We also find that ECS-HMXBs form through a specific
evolutionary channel that is expected to lead to binaries with Be donors in
wide orbits. These characteristics, along with their sensitivity to ECS
properties, provide us with an intriguing opportunity to probe ECS physics and
progenitors through studies of starbursts of different ages. Specifically, the
case of the Small Magellanic Cloud, with a significant observed population of
Be HMXBs and starburst activity 30-60 Myr ago, arises as a promising laboratory
for understanding the role of electron-capture supernovae in neutron star
formation.Comment: 5 pages, 3 figures, Published by ApJ in 07/0
Evolution of Neutron-Star, Carbon-Oxygen White-Dwarf Binaries
At least one, but more likely two or more, eccentric neutron-star,
carbon-oxygen white-dwarf binaries with an unrecycled pulsar have been
observed. According to the standard scenario for evolving neutron stars which
are recycled in common envelope evolution we expect to observe \gsim 50 such
circular neutron star-carbon oxygen white dwarf binaries, since their formation
rate is roughly equal to that of the eccentric binaries and the time over which
they can be observed is two orders of magnitude longer, as we shall outline. We
observe at most one or two such circular binaries and from that we conclude
that the standard scenario must be revised. Introducing hypercritical accretion
into common envelope evolution removes the discrepancy by converting the
neutron star into a black hole which does not emit radio waves, and therefore
would not be observed.Comment: 25 pages, 1 figure, accepted in Ap
Moving toward a framework to compose intelligent web services
A framework for contract-based support to establish virtual collaboration is proposed using loosely coupled and heterogeneous intelligent Web services. A business process redesign scenario is also discussed for integrating shared business process between a PC manufacturer and a semiconductor manufacturer. Contracts encapsulate the control information for intelligent Web services (IWS) engaged in e-business transactions. IWS show promise as a means of supporting cross-organizational business transactions
Tackling ageing continence through theory, tools & technology (TACT3)
This is the author's accepted manuscript. The final published article is available from the link below. Copyright @ 2012 Common Ground.After dementia, nothing is more feared by older people than the loss of continence. It is often the reason many people enter care facilities and can contribute to the breakdown of caring relationships. This paper reports on a three-year research project funded by the UK New Dynamics of Aging programme, which has explored three key issues in the predicament of maintaining continence from the “user’s” perspective. Firstly, understanding how continence services operated by the UK National Health Service can be improved to offer cost effective benefits that encourage people to report this sometimes embarrassing condition with confidence. Secondly, working directly with the US Simon Foundation, the project has developed user-requested, assistive devices that target the most embarrassing aspects of the condition, namely issues of personal odor control and urine leakage from continence pads. Lastly, understanding the challenges of managing continence in daily living outside of the home, with particular reference to accessing publicly accessible toilet facilities. The paper will highlight the research that has provided the basis for innovative design solutions.ESRC, EPSRC, BBSRC, MRC, and AHRC
XMM-Newton discovery of 217 s pulsations in the brightest persistent supersoft X-ray source in M31
We report on the discovery of a periodic modulation in the bright supersoft
X-ray source XMMU J004252.5+411540 detected in the 2000-2004 XMM-Newton
observations of M31. The source exhibits X-ray pulsations with a period P~217.7
s and a quasi-sinusoidal pulse shape and pulsed fraction ~7-11%. We did not
detect statistically significant changes in the pulsation period on the time
scale of 4 years. The X-ray spectra of XMMU J004252.5+411540 are extremely soft
and can be approximated with an absorbed blackbody of temperature 62-77 eV and
a weak power law tail of photon index ~1.7-3.1 in the 0.2-3.0 keV energy band.
The X-ray properties of the source and the absence of an optical/UV counterpart
brighter than 19 mag suggest that it belongs to M31. The estimated bolometric
luminosity of the source varies between ~2e38 and ~8e38 ergs/s at 760 kpc,
depending on the choice of spectral model. The X-ray pulsations and supersoft
spectrum of XMMU J004252.5+411540 imply that it is almost certainly an
accreting white dwarf, steadily burning hydrogen-rich material on its surface.
We interpret X-ray pulsations as a signature of the strong magnetic field of
the rotating white dwarf. Assuming that the X-ray source is powered by disk
accretion, we estimate its surface field strength to be in the range 4e5 G
<B_{0}<8e6 G. XMMU J004252.5+411540 is the second supersoft X-ray source in M31
showing coherent pulsations, after the transient supersoft source XMMU
J004319.4+411758 with 865.5 s pulsation period.Comment: 11 pages, 4 figures, uses emulateapj style. Submitted to Ap
Neutron Star Masses and Radii as Inferred from kilo-Hertz QPOs
Kilo-Hertz (kHz) Quasi-periodic oscillations (QPOs) have been discovered in
the X-ray fluxes of 8 low-mass X-ray binaries (LMXBs) with the Rossi X-ray
Timing Explorer (RXTE). The characteristics of these QPOs are remarkably
similar from one source to another. In particular, the highest observed QPO
frequencies for 6 of the 8 sources fall in a very narrow range: 1,066 to 1,171
Hz. This is the more remarkable when one considers that these sources are
thought to have very different luminosities and magnetic fields, and produce
very different count rates in the RXTE detectors. Therefore it is highly
unlikely that this near constancy of the highest observed frequencies is due to
some unknown selection effect or instrumental bias. In this letter we propose
that the highest observed QPO frequency can be taken as the orbital frequency
of the marginally stable orbit. This leads to the conclusions that the neutron
stars in these LMXBs are inside their marginally stable orbits and have masses
in the vicinity of 2.0 solar masses. This mass is consistent with the
hypothesis that these neutron stars were born with about 1.4 solar masses and
have been accreting matter at a fraction of the Eddington limit for 100 million
years.Comment: 7 pages, uses aas2pp4.sty, Accepted by ApJ
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