4,535 research outputs found
Kinetic Theory of Collisionless Self-Gravitating Gases: Post-Newtonian Polytropes
In this paper we study the kinetic theory of many-particle astrophysical
systems and we present a consistent version of the collisionless Boltzmann
equation in the 1PN approximation. We argue that the equation presented by
Rezania and Sobouti in A&A 354 1110 (2000) is not the correct expression to
describe the evolution of a collisionless self-gravitating gas. One of the
reasons that account for the previous statement is that the energy of a
free-falling test particle, obeying the 1PN equations of motion for static
gravitational fields, is not a static solution of the mentioned equation. The
same statement holds for the angular momentum, in the case of spherical
systems. We provide the necessary corrections and obtain an equation that is
consistent with the corresponding equations of motion and the 1PN conserved
quantities. We suggest some potential relevance for the study of high density
astrophysical systems and as an application we construct the corrected version
of the post-Newtonian polytropes.Comment: 23 pages, 24 figures. Accepted for publication in PR
pPKCα mediated-HIF-1α activation related to the morphological modifications occurring in neonatal myocardial tissue in response to severe and mild hyperoxia
In premature babies birth an high oxygen level exposure can occur and newborn hyperoxia exposure can be associated with free radical oxygen release with impairment of myocardial function, while in adult animal models short exposure to hyperoxia seems to protect heart against ischemic injury. Thus, the mechanisms and consequences which take place after hyperoxia exposure are different and related to animals age. The aim of our work has been to analyze the role played by HIF-1α in the occurrence of the morphological modifications upon hyperoxia exposure in neonatal rat heart. Hyperoxia exposure induces connective compartment increase which seems to allow enhanced blood vessels growth. An increased hypoxia inducible factor-1α (HIF-1α) translocation and vascular endothelial growth factor (VEGF) expression has been found upon 95% oxygen exposure to induce morphological modifications. Upstream pPKC-α expression increase in newborn rats exposed to 95% oxygen can suggest PKC involvement in HIF-1α activation. Since nitric oxide synthase (NOS) are involved in heart vascular regulation, endothelial NOS (e-NOS) and inducible NOS (i-NOS) expression has been investigated: a lower eNOS and an higher iNOS expression has been found in newborn rats exposed to 95% oxygen related to the evidence that hyperoxia provokes a systemic vasoconstriction and to the iNOS pro-apoptotic action, respectively. The occurrence of apoptotic events, evaluated by TUNEL and Bax expression analyses, seems more evident in sample exposed to severe hyperoxia. All in all such results suggest that in newborn rats hyperoxia can trigger oxygen free radical mediated membrane injury through a pPKCα mediated HIF-1α signalling system, even though specificity of such response could be obtained by in vivo administration to the rats of specific inhibitors of PKCα. This intracellular signalling can switch molecular events leading to blood vessels development in parallel to pro-apoptotic events due to an immature anti-oxidant defensive system in newborn rat hearts
Chiral corrections to kaon-nucleon scattering lengths
We calculate the threshold T-matrices of kaon-nucleon and antikaon-nucleon
scattering to one loop order in SU(3) heavy baryon chiral perturbation theory.
To that order the complex-valued isospin-1 threshold T-matrix can be
successfully predicted from the isospin-0 and 1 threshold T-matrices. As
expected perturbation theory fails to explain the isospin-0 threshold
T-matrix which is completely dominated by the nearby subthreshold
-resonance. Cancelations of large terms of second and third
chiral order are observed as they seem to be typical for SU(3) baryon chiral
perturbation theory calculations. We also give the kaon and eta loop
corrections to the scattering lengths and we investigate
scattering to one-loop order. The second order s-wave low-energy constants are
all of natural size and do not exceed 1 GeV in magnitude.Comment: 8 pages, 2 figures, published in Phys. Rev. C64, 045204 (2001),
corrections of numerical prefactors in Eqs.(10,11,12
Theory of Room Temperature Ferromagnet V(TCNE)_x (1.5 < x < 2): Role of Hidden Flat Bands
Theoretical studies on the possible origin of room temperature ferromagnetism
(ferromagnetic once crystallized) in the molecular transition metal complex,
V(TCNE)_x (1.5<x<2) have been carried out. For this family, there have been no
definite understanding of crystal structure so far because of sample quality,
though the effective valence of V is known to be close to +2. Proposing a new
crystal structure for the stoichiometric case of x=2, where the valence of each
TCNE molecule is -1 and resistivity shows insulating behavior, exchange
interaction among d-electrons on adjacent V atoms has been estimated based on
the cluster with 3 vanadium atoms and one TCNE molecule. It turns out that
Hund's coupling among d orbitals within the same V atoms and antiferromagnetic
coupling between d oribitals and LUMO of TCNE (bridging V atoms) due to
hybridization result in overall ferromagnetism (to be precise, ferrimagnetism).
This view based on localized electrons is supplemented by the band picture,
which indicates the existence of a flat band expected to lead to ferromagnetism
as well consistent with the localized view. The off-stoichiometric cases (x<2),
which still show ferromagnetism but semiconducting transport properties, have
been analyzed as due to Anderson localization.Comment: Accepted for publication in J. Phys. Soc. Jpn. Vol.79 (2010), No. 3
(March issue), in press; 6 pages, 8 figure
Impediments to mixing classical and quantum dynamics
The dynamics of systems composed of a classical sector plus a quantum sector
is studied. We show that, even in the simplest cases, (i) the existence of a
consistent canonical description for such mixed systems is incompatible with
very basic requirements related to the time evolution of the two sectors when
they are decoupled. (ii) The classical sector cannot inherit quantum
fluctuations from the quantum sector. And, (iii) a coupling among the two
sectors is incompatible with the requirement of physical positivity of the
theory, i.e., there would be positive observables with a non positive
expectation value.Comment: RevTex, 21 pages. Title slightly modified and summary section adde
Femtosecond-laser nanostructuring of black diamond films under different gas environments
Irradiation of diamond with femtosecond (fs) laser pulses in ultra-high vacuum (UHV) conditions results in the formation of surface periodic nanostructures able to strongly interact with visible and infrared light. As a result, native transparent diamond turns into a completely different material, namely âblackâ diamond, with outstanding absorptance properties in the solar radiation wavelength range, which can be efficiently exploited in innovative solar energy converters. Of course, even if extremely effective, the use of UHV strongly complicates the fabrication process. In this work, in order to pave the way to an easier and more cost-effective manufacturing workflow of black diamond, we demonstrate that it is possible to ensure the same optical properties as those of UHV-fabricated films by performing an fs-laser nanostructuring at ambient conditions (i.e., room temperature and atmospheric pressure) under a constant He flow, as inferred from the combined use of scanning electron microscopy, Raman spectroscopy, and spectrophotometry analysis. Conversely, if the laser treatment is performed under a compressed air flow, or a N2 flow, the optical properties of black diamond films are not comparable to those of their UHV-fabricated counterparts
Hypophosphataemia after intravenous iron therapy with ferric carboxymaltoseâReal world experience from a tertiary centre in the UK
Background:
Iron deficiency is the most common global cause of anaemia. Intravenous (IV) iron is used to correct iron deficiency anaemia (IDA) where oral iron cannot be used. Despite being effective, certain IV iron formulations cause significant hypophosphataemia. However, current knowledge on the clinical consequences of IV ironâinduced hypophosphataemia is broadly anecdotal or limited to isolated case reports.
/
Aims:
To retrospectively examine the incidence and potential clinical consequences of hypophosphataemia postâIV ferric carboxymaltose (FCM) in hospitalised patients with IDA (mixed aetiology). /
Methods:
Data were collected for 162 patients, who received a total of 169 FCM courses during a 2âyear audit period. Outcomes included incidence of moderate/severe hypophosphataemia (serum phosphate <0.65 mmol/L) â€90 days postâFCM, changes in alkaline phosphatase, need for phosphate replacement, and length of hospital stay. /
Results:
The incidence of moderate/severe hypophosphataemia postâFCM was 33.7%; within this group the rate of severe hypophosphataemia (serum phosphate â€0.32 mmol/L) was 8.8%. Moderate/severe hypophosphataemia persisted, with 35% of patients having a serum phosphate of <0.65 mmol/L for â€90 days at the last measurement after IV FCM. Intervention with IV phosphateâan average of 4.4 infusions per personâwas required in 29.8% of cases with moderate/severe hypophosphataemia. FCMâinduced moderate/severe hypophosphataemia was associated with a significantly longer hospital stay (P < 0.0035). /
Conclusions:
Moderate/severe hypophosphataemia is a frequent adverse drug reaction with FCM. In our study, FCMâinduced moderate/severe hypophosphataemia was also persistent, often required treatment, and was associated with longer hospital stay
Molecular diagnostic and genetic characterization of highly pathogenic viruses: application during CrimeanâCongo haemorrhagic fever virus outbreaks in Eastern Europe and the Middle East
AbstractSeveral haemorrhagic fevers are caused by highly pathogenic viruses that must be handled in Biosafety level 4 (BSLâ4) containment. These zoonotic infections have an important impact on public health and the development of a rapid and differential diagnosis in case of outbreak in risk areas represents a critical priority. We have demonstrated the potential of a DNA resequencing microarray (PathogenID v2.0) for this purpose. The microarray was first validated in vitro using supernatants of cells infected with prototype strains from five different families of BSL-4 viruses (e.g. families Arenaviridae, Bunyaviridae, Filoviridae, Flaviviridae and Paramyxoviridae). RNA was amplified based on isothermal amplification by Phi29 polymerase before hybridization. We were able to detect and characterize Nipah virus and CrimeanâCongo haemorrhagic fever virus (CCHFV) in the brains of experimentally infected animals. CCHFV was finally used as a paradigm for epidemics because of recent outbreaks in Turkey, Kosovo and Iran. Viral variants present in human sera were characterized by BLASTN analysis. Sensitivity was estimated to be 105â106 PFU/mL of hybridized cDNA. Detection specificity was limited to viral sequences having Ë13â14% of global divergence with the tiled sequence, or stretches of Ë20 identical nucleotides. These results highlight the benefits of using the PathogenID v2.0 resequencing microarray to characterize geographical variants in the follow-up of haemorrhagic fever epidemics; to manage patients and protect communities; and in cases of bioterrorism
Demystifying Governance and its Role for Transitions in Urban SocialâEcological Systems
Governance is key to sustainable urban transitions. Governance is a system of social, power, and decisionâmaking processes that acts as a key driver of resource allocation and use, yet ecologistsâeven urban ecologistsâseldom consider governance concepts in their work. Transitions to more sustainable futures are becoming increasingly important to the management of many ecosystems and landscapes, and particularly so for urban systems. We briefly identify and synthesize important governance dimensions of urban sustainability transitions, using illustrations from cities in which longâterm socialâecological governance research is underway. This article concludes with a call to ecologists who are interested in environmental stewardship, and to urban ecologists in particular, to consider the role of governance as a driver in the dynamics of the systems they study
Mixing quantum and classical mechanics and uniqueness of Planck's constant
Observables of quantum or classical mechanics form algebras called quantum or
classical Hamilton algebras respectively (Grgin E and Petersen A (1974) {\it J
Math Phys} {\bf 15} 764\cite{grginpetersen}, Sahoo D (1977) {\it Pramana} {\bf
8} 545\cite{sahoo}). We show that the tensor-product of two quantum Hamilton
algebras, each characterized by a different Planck's constant is an algebra of
the same type characterized by yet another Planck's constant. The algebraic
structure of mixed quantum and classical systems is then analyzed by taking the
limit of vanishing Planck's constant in one of the component algebras. This
approach provides new insight into failures of various formalisms dealing with
mixed quantum-classical systems. It shows that in the interacting mixed
quantum-classical description, there can be no back-reaction of the quantum
system on the classical. A natural algebraic requirement involving restriction
of the tensor product of two quantum Hamilton algebras to their components
proves that Planck's constant is unique.Comment: revised version accepted for publication in J.Phys.A:Math.Phy
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