17,722 research outputs found
Explosion of white dwarfs harboring hybrid CONe cores
Recently, it has been found that off-centre carbon burning in a subset of
intermediate-mass stars does not propagate all the way to the center, resulting
in a class of hybrid CONe cores. Here, we consider the possibility that stars
hosting these hybrid CONe cores might belong to a close binary system and,
eventually, become white dwarfs accreting from a non-degenerate companion at
rates leading to a supernova explosion. We have computed the hydrodynamical
phase of the explosion of Chandrasekhar-mass white dwarfs harboring hybrid
cores, assuming that the explosion starts at the center, either as a detonation
(as may be expected in some degenerate merging scenarios) or as a deflagration
(that afterwards transitions into a delayed detonation). We assume these hybrid
cores are made of a central CO volume, of mass M(CO), surrounded by an ONe
shell. We show that, in case of a pure detonation, a medium-sized CO-rich
region, M(CO)<0.4 Msun, results in the ejection of a small fraction of the
mantle while leaving a massive bound remnant. Part of this remnant is made of
the products of the detonation, Fe-group nuclei, but they are buried in its
inner regions, unless convection is activated during the ensuing cooling and
shrinking phase of the remnant. In contrast, and somehow paradoxically, delayed
detonations do not leave remnants but for the minimum M(CO) we have explored,
M(CO)=0.2 Msun, and even in this case the remnant is as small as 0.13 Msun. The
ejecta produced by these delayed detonations are characterized by slightly
smaller masses of 56Ni and substantially smaller kinetic energies than obtained
for a delayed detonation of a 'normal' CO white dwarf. The optical emission
expected from these explosions would hardly match the observational properties
of typical Type Ia supernovae, although they make interesting candidates for
the subluminous class of SN2002cx-like or SNIax.Comment: Accepted for Astronomy and Astrophysics, 11 pages, 4 figure
Super-AGB Stars and their role as Electron Capture Supernova progenitors
We review the lives, deaths and nucleosynthetic signatures of intermediate
mass stars in the range approximately 6.5-12 Msun, which form super-AGB stars
near the end of their lives. We examine the critical mass boundaries both
between different types of massive white dwarfs (CO, CO-Ne, ONe) and between
white dwarfs and supernovae and discuss the relative fraction of super-AGB
stars that end life as either an ONe white dwarf or as a neutron star (or an
ONeFe white dwarf), after undergoing an electron capture supernova. We also
discuss the contribution of the other potential single-star channels to
electron-capture supernovae, that of the failed massive stars. We describe the
factors that influence these different final fates and mass limits, such as
composition, the efficiency of convection, rotation, nuclear reaction rates,
mass loss rates, and third dredge-up efficiency. We stress the importance of
the binary evolution channels for producing electron-capture supernovae. We
discuss recent nucleosynthesis calculations and elemental yield results and
present a new set of s-process heavy element yield predictions. We assess the
contribution from super-AGB star nucleosynthesis in a Galactic perspective, and
consider the (super-)AGB scenario in the context of the multiple stellar
populations seen in globular clusters. A brief summary of recent works on dust
production is included. Lastly we conclude with a discussion of the
observational constraints and potential future advances for study into these
stars on the low mass/high mass star boundary.Comment: 28 pages, 11 figures. Invited review for Publications of the
Astronomical Society of Australia, to be published in special issue on
"Electron Capture Supernovae". Submitte
Reducing sample variance: halo biasing, non-linearity and stochasticity
Comparing clustering of differently biased tracers of the dark matter
distribution offers the opportunity to reduce the cosmic variance error in the
measurement of certain cosmological parameters. We develop a formalism that
includes bias non-linearities and stochasticity. Our formalism is general
enough that can be used to optimise survey design and tracers selection and
optimally split (or combine) tracers to minimise the error on the
cosmologically interesting quantities. Our approach generalises the one
presented by McDonald & Seljak (2009) of circumventing sample variance in the
measurement of . We analyse how the bias, the noise,
the non-linearity and stochasticity affect the measurements of and explore
in which signal-to-noise regime it is significantly advantageous to split a
galaxy sample in two differently-biased tracers. We use N-body simulations to
find realistic values for the parameters describing the bias properties of dark
matter haloes of different masses and their number density.
We find that, even if dark matter haloes could be used as tracers and
selected in an idealised way, for realistic haloes, the sample variance limit
can be reduced only by up to a factor .
This would still correspond to the gain from a three times larger survey volume
if the two tracers were not to be split. Before any practical application one
should bear in mind that these findings apply to dark matter haloes as tracers,
while realistic surveys would select galaxies: the galaxy-host halo relation is
likely to introduce extra stochasticity, which may reduce the gain further.Comment: 21 pages, 13 figures. Published version in MNRA
Physician-Patient Communication Among Southern European Cancer Physicians: the Influence of Psychosocial Orientation and Burnout
Physician-patient communication is a critical factor for comprehensive care in oncology. Although a number of studies have been carried out in Northern Europe and the US on this subject, no data are available in Southern European countries. As a part of a multicenter Southern European Psycho-Oncology study (SEPOS), the present investigation was conducted to examine communication skills and related variables (i.e. psychosocial orientation, and burnout) among 125 physicians from Italy, Portugal, and Spain. The Self-Confidence in Communication Skills (SCCS) scale was given to assess physicians' perception of their communication skills and the Expected Outcome of Communication (EOC) scale was administered to examine the physicians' expectations about the effects of communicating with their patients. Doctors' psychosocial orientation was measured by using the Physician Belief Scale (PBS) and burnout was measured by using the Maslach Burnout Inventory (MBI). Although the physicians reported receiving minimal training in communication during their education, they tended to perceive themselves as skilled in patient communication, apart from some areas (e.g. dealing with denial, managing uncertainty, assessing anxiety and depression, and promoting patient-family openness). Low psychosocial orientation and burnout symptoms (i.e. emotional exhaustion, depersonalization, and poor personal accomplishment in their job) were associated with lower confidence in communication skills and higher expectations of a negative outcome, following physician-patient communication. The results suggest that there is a need for training cancer physicians in communication and for increasing a more definite psychosocially oriented approach in cancer care in Mediterranean countries.info:eu-repo/semantics/publishedVersio
GCRT J1745-3009 as a Transient White Dwarf Pulsar
A transient radio source in the direction of the Galactic Center, GCRT
J1745-3009, exhibited 5 peculiar consecutive outbursts at 0.33 GHz with a
period of 77.13 minutes and a duration of ~10 minutes for each outburst. It has
been claimed to be the prototype of a hitherto unknown class of transient radio
sources. We interpret it as a transient white dwarf pulsar with a period of
77.13 minutes. The ~10-minute flaring duration corresponds to the epoch when
the radio beam sweeps our line of sight. The bursting epoch corresponds to the
episodes when stronger sunspot-like magnetic fields emerge into the white dwarf
polar cap region during which the pair production condition is satisfied and
the white dwarf behaves like a radio pulsar. It switches off as the pair
production condition breaks down.Comment: minor changes, ApJL, in pres
Determining the regimes of cold and warm inflation in the susy hybrid model
The SUSY hybrid inflation model is found to dissipate radiation during the
inflationary period. Analysis is made of parameter regimes in which these
dissipative effects are significant. The scalar spectral index, its running,
and the tensor-scalar ratio are computed in the entire parameter range of the
model. A clear prediction for strong dissipative warm inflation is found for
n_S-1 \simeq 0.98 and a low tensor-scalar ratio much below 10^{-6}. The strong
dissipative warm inflation regime also is found to have no \eta-problem and
with the field amplitude much below the Planck scale. As will be discussed,
this has important theoretical implications in permitting a much wider variety
of SUGRA extensions to the basic model.Comment: paragraph added at the end of section V; references added; accepted
for publication in Phys. Rev.
WKB formalism and a lower limit for the energy eigenstates of bound states for some potentials
In the present work the conditions appearing in the WKB approximation
formalism of quantum mechanics are analyzed. It is shown that, in general, a
careful definition of an approximation method requires the introduction of two
length parameters, one of them always considered in the text books on quantum
mechanics, whereas the second one is usually neglected. Afterwards we define a
particular family of potentials and prove, resorting to the aforementioned
length parameters, that we may find an energy which is a lower bound to the
ground energy of the system. The idea is applied to the case of a harmonic
oscillator and also to a particle freely falling in a homogeneous gravitational
field, and in both cases the consistency of our method is corroborated. This
approach, together with the Rayleigh--Ritz formalism, allows us to define an
energy interval in which the ground energy of any potential, belonging to our
family, must lie.Comment: Accepted in Modern Physics Letters
Separation of bacteriochlorophyll c and chlorophil a from mixed extracts by reversed-phase high performance liquid chromatography
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