350 research outputs found
Hybrid stars in the light of the massive pulsar PSR J1614-2230
We perform a systematic study of hybrid star configurations using several
parametrizations of a relativistic mean-field hadronic EoS and the NJL model
for three-flavor quark matter. For the hadronic phase we use the stiff GM1 and
TM1 parametrizations, as well as the very stiff NL3 model. In the NJL
Lagrangian we include scalar, vector and 't Hooft interactions. The vector
coupling constant is treated as a free parameter. We also consider that
there is a split between the deconfinement and the chiral phase transitions
which is controlled by changing the conventional value of the vacuum pressure
in the NJL thermodynamic potential by , being a free parameter. We find that, as we
increase the value of , hybrid stars have a larger maximum
mass but are less stable, i.e. hybrid configurations are stable within a
smaller range of central densities. For large enough , stable
hybrid configurations are not possible at all. The effect of increasing the
coupling constant is very similar. We show that stable hybrid
configurations with a maximum mass larger than the observed mass of the pulsar
PSR J1614-2230 are possible for a large region of the parameter space of
and provided the hadronic equation of state contains nucleons
only. When the baryon octet is included in the hadronic phase, only a very
small region of the parameter space allows to explain the mass of PSR
J1614-2230. We compare our results with previous calculations of hybrid stars
within the NJL model. We show that it is possible to obtain stable hybrid
configurations also in the case that corresponds to the
conventional NJL model for which the pressure and density vanish at zero
temperature and chemical potential.Comment: 7 pages, 5 figures; typos in Table 1 have been correcte
Structural properties of InAlN single layers nearly latice-matched to GaN grown by plasma assisted molecular beal epitaxy
The high lattice mismatch between III-nitride binaries (InN, GaN and AlN) remains a key problem to grow high quality III-nitride heterostructures. Recent interest has been focused on the growth of high-quality InAlN layers, with approximately 18% of indium incorporation, in-plane lattice-matched (LM) to GaN. While a lot of work has been done by metal-organic vapour phase epitaxy (MOVPE) by Carlin and co-workers, its growth by molecular beam epitaxy (MBE) is still in infanc
Solving relativistic hydrodynamic equation in presence of magnetic field for phase transition in a neutron star
Hadronic to quark matter phase transition may occur inside neutron stars (NS)
having central densities of the order of 3-10 times normal nuclear matter
saturation density (). The transition is expected to be a two-step
process; transition from hadronic to 2-flavour matter and two-flavour to
equilibrated charge neutral three-flavour matter. In this paper we
concentrate on the first step process and solve the relativistic hydrodynamic
equations for the conversion front in presence of high magnetic field. Lorentz
force due to magnetic field is included in the energy momentum tensor by
averaging over the polar angles. We find that for an initial dipole
configuration of the magnetic field with a sufficiently high value at the
surface, velocity of the front increases considerably.Comment: 16 pages, 4 figures, same as published version of JPG, J. Phys. G:
Nucl. Part. Phys. 39 (2012) 09520
Core-collapse supernova explosions triggered by a quark-hadron phase transition during the early post-bounce phase
We explore explosions of massive stars, which are triggered via the
quark-hadron phase transition during the early post bounce phase of
core-collapse supernovae. We construct a quark equation of state, based on the
bag model for strange quark matter. The transition between the hadronic and the
quark phases is constructed applying Gibbs conditions. The resulting
quark-hadron hybrid equations of state are used in core-collapse supernova
simulations, based on general relativistic radiation hydrodynamics and three
flavor Boltzmann neutrino transport in spherical symmetry. The formation of a
mixed phase reduces the adiabatic index, which induces the gravitational
collapse of the central protoneutron star. The collapse halts in the pure quark
phase, where the adiabatic index increases. A strong accretion shock forms,
which propagates towards the protoneutron star surface. Due to the density
decrease of several orders of magnitude, the accretion shock turns into a
dynamic shock with matter outflow. This moment defines the onset of the
explosion in supernova models that allow for a quark-hadron phase transition,
where otherwise no explosions could be obtained. The shock propagation across
the neutrinospheres releases a burst of neutrinos. This serves as a strong
observable identification for the structural reconfiguration of the stellar
core. The ejected matter expands on a short timescale and remains neutron-rich.
These conditions might be suitable for the production of heavy elements via the
r-process. The neutron-rich material is followed by proton-rich neutrino-driven
ejecta in the later cooling phase of the protoneutron star where the vp-process
might occur.Comment: 29 pages, 24 figures, submitted to Ap
Nanofiber fabrication in a temperature and humidity controlled environment for improved fibre consistency
To fabricate nanofibers with reproducible characteristics, an important demand for many applications, the effect of controlled atmospheric conditions on resulting electrospun cellulose acetate (CA) nanofibers was evaluated for temperature ranging 17.5 - 35°C and relative humidity ranging 20% - 70%. With the potential application of nanofibers in many industries, especially membrane and filter fabrication, their reproducible production must be established to ensure commercially viability.
Cellulose acetate (CA) solution (0.2 g/ml) in a solvent mixture of acetone/DMF/ethanol (2:2:1) was electrospun into nonwoven fibre mesh with the fibre diameter ranging from 150nm to 1µm.
The resulting nanofibers were observed and analyzed by scanning electron microscopy (SEM), showing a correlation of reducing average fibre diameter with increasing atmospheric temperature. A less pronounced correlation was seen with changes in relative humidity regarding fibre diameter, though it was shown that increased humidity reduced the effect of fibre beading yielding a more consistent, and therefore better quality of fibre fabrication.
Differential scanning calorimetry (DSC) studies observed lower melt enthalpies for finer CA nanofibers in the first heating cycle confirming the results gained from SEM analysis. From the conditions that were explored in this study the temperature and humidity that gave the most suitable fibre mats for a membrane purpose were 25.0°C and 50%RH due to the highest level of fibre diameter uniformity, the lowest level of beading while maintaining a low fibre diameter for increased surface area and increased pore size homogeneity. This study has highlighted the requirement to control the atmospheric conditions during the electrospinning process in order to fabricate reproducible fibre mats
Core collapse supernovae in the QCD phase diagram
We compare two classes of hybrid equations of state with a hadron-to-quark
matter phase transition in their application to core collapse supernova
simulations. The first one uses the quark bag model and describes the
transition to three-flavor quark matter at low critical densities. The second
one employs a Polyakov-loop extended Nambu-Jona-Lasinio (PNJL) model with
parameters describing a phase transition to two-flavor quark matter at higher
critical densities. These models possess a distinctly different temperature
dependence of their transition densities which turns out to be crucial for the
possible appearance of quark matter in supernova cores. During the early post
bounce accretion phase quark matter is found only if the phase transition takes
place at sufficiently low densities as in the study based on the bag model. The
increase critical density with increasing temperature, as obtained for our PNJL
parametrization, prevents the formation of quark matter. The further evolution
of the core collapse supernova as obtained applying the quark bag model leads
to a structural reconfiguration of the central proto-neutron star where, in
addition to a massive pure quark matter core, a strong hydrodynamic shock wave
forms and a second neutrino burst is released during the shock propagation
across the neutrinospheres. We discuss the severe constraints in the freedom of
choice of quark matter models and their parametrization due to the recently
observed 2 solar mass pulsar and their implications for further studies of core
collapse supernovae in the QCD phase diagram.Comment: 19 pages, 4 figures, CPOD2010 conference proceedin
Human 13N-ammonia PET studies: the importance of measuring 13N-ammonia metabolites in blood
Dynamic 13N-ammonia PET is used to assess ammonia metabolism in brain, liver and muscle based on kinetic modeling of metabolic pathways, using arterial blood 13N-ammonia as input function. Rosenspire et al. (1990) introduced a solid phase extraction procedure for fractionation of 13N-content in blood into 13N-ammonia, 13N-urea, 13N-glutamine and 13N-glutamate. Due to a radioactive half-life for 13N of 10 min, the procedure is not suitable for blood samples taken beyond 5–7 min after tracer injection. By modifying Rosenspire’s method, we established a method enabling analysis of up to 10 blood samples in the course of 30 min. The modified procedure was validated by HPLC and by 30-min reproducibility studies in humans examined by duplicate 13N-ammonia injections with a 60-min interval. Blood data from a 13N-ammonia brain PET study (from Keiding et al. 2006) showed: (1) time courses of 13N-ammonia fractions could be described adequately by double exponential functions; (2) metabolic conversion of 13N-ammonia to 13N-metabolites were in the order: healthy subjects > cirrhotic patients without HE > cirrhotic patients with HE; (3) kinetics of initial tracer distribution in tissue can be assessed by using total 13N-concentration in blood as input function, whereas assessment of metabolic processes requires 13N-ammonia measurements
The effects of alcohol intoxication on accuracy and the confidence-accuracy relationship in photographic simultaneous lineups
(Summary) Acute alcohol intoxication during encoding can impair subsequent identification accuracy, but results across studies have been inconsistent, with studies often finding no effect. Little is also known about how alcohol intoxication affects the identification confidence-accuracy relationship. We randomly assigned women (N = 153) to consume alcohol (dosed to achieve a 0.08% blood alcohol content) or tonic water, controlling for alcohol expectancy. Women then participated in an interactive hypothetical sexual assault scenario and, 24 hours or 7 days later, attempted to identify the assailant from a perpetrator present or a perpetrator absent simultaneous line-up and reported their decision confidence. Overall, levels of identification accuracy were similar across the alcohol and tonic water groups. However, women who had consumed tonic water as opposed to alcohol identified the assailant with higher confidence on average. Further, calibration analyses suggested that confidence is predictive of accuracy regardless of alcohol consumption. The theoretical and applied implications of our results are discussed
A Novel Mechanism of Transposon-Mediated Gene Activation
Transposable Insertion Sequences (IS elements) have been shown to provide various benefits to their hosts via gene activation or inactivation under stress conditions by appropriately inserting into specific chromosomal sites. Activation is usually due to derepression or introduction of a complete or partial promoter located within the element. Here we define a novel mechanism of gene activation by the transposon IS5 in Escherichia coli. The glycerol utilization operon, glpFK, that is silent in the absence of the cAMP-Crp complex, is activated by IS5 when inserted upstream of its promoter. High-level expression is nearly constitutive, only mildly dependent on glycerol, glucose, GlpR, and Crp, and allows growth at a rate similar to or more rapid than that of wild-type cells. Expression is from the glpFK promoter and dependent on (1) the DNA phase, (2) integration host factor (IHF), and (3) a short region at the 3′ end of IS5 harboring a permanent bend and an IHF binding site. The lacZYA operon is also subject to such activation in the absence of Crp. Thus, we have defined a novel mechanism of gene activation involving transposon insertion that may be generally applicable to many organisms
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