416 research outputs found
Hyperons and massive neutron stars: vector repulsion and SU(3) symmetry
With the discovery of massive neutron stars such as PSR J1614-2230, the
question has arisen whether exotic matter such as hyperons can exist in the
neutron star core. We examine the conditions under which hyperons can exist in
massive neutron stars. We consistently investigate the vector meson-hyperon
coupling, going from SU(6) quark model to a broader SU(3) symmetry. We propose
that the maximum neutron star mass decreases linearly with the strangeness
content f_s of the neutron star core as M_max(f_s) = M_max(0) - 0.6 M_solar
(f_s/0.1), which seems to be independent of the underlying nuclear equation of
state and the vector baryon-meson coupling scheme. Thus, pulsar mass
measurements can be used to constrain the hyperon fraction in neutron stars.Comment: 13 pages, 10 figure
Formation of carbohydrate-functionalised polystyrene and glass slides and their analysis by MALDI-TOF MS
Glycans functionalised with hydrophobic trityl groups were synthesised and adsorbed onto polystyrene and glass slides in an array format. The adsorbed glycans could be analysed directly on these minimally conducting surfaces by MALDI-TOF mass spectrometry analysis after aluminium tape was attached to the underside of the slides. Furthermore, the trityl group appeared to act as an internal matrix and no additional matrix was necessary for the MS analysis. Thus, trityl groups can be used as simple hydrophobic, noncovalently linked anchors for ligands on surfaces and at the same time facilitate the in situ mass spectrometric analysis of such ligands
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
Cortical networks are disturbed in people with cirrhosis even in the absence of neuropsychometric impairment
OBJECTIVE: Hepatic encephalopathy is a common complication of cirrhosis; it is characterised by neuropsychometric/neurophysiological abnormalities. Its pathophysiology is complex but glial neuronal communication is likely to be disrupted and to impact on oscillatory networks and cortical connectivity. The aim of this study was to use multichannel electroencephalography (EEG) to investigate functional connectivity, as a surrogate for cortical networks, in patients with cirrhosis. METHODS: Resting EEGs were recorded in 98 healthy controls and in 264 patients with cirrhosis characterised psychometrically using the Psychometric Hepatic Encephalopathy Score (PHES). Functional connectivity was calculated using the phase-lag index with stratification into standard EEG frequency bands. The findings were validated in a further cohort of 39 healthy controls and 106 patients with cirrhosis. RESULTS: Widespread disruption in functional connectivity was observed in the patients compared with the controls; connectivity was increased in the theta (4-8 Hz) band and decreased in the delta (1-3.5 Hz), alpha (8.5-13 Hz) and beta (13.5-26.5 Hz) bands. Changes were apparent even in patients who were psychometrically unimpaired compared with healthy controls viz mean ± SEM theta 0.107 ± 0.001 vs. 0.103 ± 0.002 (p < 0.05) and alpha 0.139 ± 0.003 vs. 0.154 ± 0.003 (p < 0.01); more pronounced changes were observed with increasing neuropsychometric impairment. The findings were replicated in the second cohort. CONCLUSIONS: Cortical networks are disturbed in patients with cirrhosis even in the absence of psychometric impairment. SIGNIFICANCE: These findings will facilitate further exploration of the pathophysiology of this condition and provide a robust means for assessing treatment effects in research settings
Addressing the ‘hypoxia paradox’ in severe COVID-19: literature review and report of four cases treated with erythropoietin analogues
Background: Since fall 2019, SARS-CoV-2 spread world-wide, causing a major pandemic with estimated ~ 220 million subjects affected as of September 2021. Severe COVID-19 is associated with multiple organ failure, particularly of lung and kidney, but also grave neuropsychiatric manifestations. Overall mortality reaches > 2%. Vaccine development has thrived in thus far unreached dimensions and will be one prerequisite to terminate the pandemic. Despite intensive research, however, few treatment options for modifying COVID-19 course/outcome have emerged since the pandemic outbreak. Additionally, the substantial threat of serious downstream sequelae, called ‘long COVID’ and ‘neuroCOVID’, becomes increasingly evident. Main body of the abstract: Among candidates that were suggested but did not yet receive appropriate funding for clinical trials is recombinant human erythropoietin. Based on accumulating experimental and clinical evidence, erythropoietin is expected to (1) improve respiration/organ function, (2) counteract overshooting inflammation, (3) act sustainably neuroprotective/neuroregenerative. Recent counterintuitive findings of decreased serum erythropoietin levels in severe COVID-19 not only support a relative deficiency of erythropoietin in this condition, which can be therapeutically addressed, but also made us coin the term ‘hypoxia paradox’. As we review here, this paradox is likely due to uncoupling of physiological hypoxia signaling circuits, mediated by detrimental gene products of SARS-CoV-2 or unfavorable host responses, including microRNAs or dysfunctional mitochondria. Substitution of erythropoietin might overcome this ‘hypoxia paradox’ caused by deranged signaling and improve survival/functional status of COVID-19 patients and their long-term outcome. As supporting hints, embedded in this review, we present 4 male patients with severe COVID-19 and unfavorable prognosis, including predicted high lethality, who all profoundly improved upon treatment which included erythropoietin analogues. Short conclusion: Substitution of EPO may—among other beneficial EPO effects in severe COVID-19—circumvent downstream consequences of the ‘hypoxia paradox’. A double-blind, placebo-controlled, randomized clinical trial for proof-of-concept is warrante
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
Autoantibodies against NMDAR subunit NR1 disappear from blood upon anesthesia
Anesthetics penetrate the blood-brain-barrier (BBB) and - as confirmed preclinically – transiently disrupt it. An analogous consequence in humans has remained unproven. In mice, we previously reported that upon BBB dysfunction, the brain acts as ‘immunoprecipitator’ of autoantibodies against N-methyl-D-aspartate-receptor subunit-NR1 (NMDAR1-AB). We thus hypothesized that during human anesthesia, pre-existing NMDAR1-AB will specifically bind to brain. Screening of N = 270 subjects undergoing general anesthesia during cardiac surgery for serum NMDAR1-AB revealed N = 25 NMDAR1-AB seropositives. Only N = 14 remained positive post-surgery. No changes in albumin, thyroglobulin or CRP were associated with reduction of serum NMDAR1-AB. Thus, upon anesthesia, BBB opening likely occurs also in humans
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
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