40,274 research outputs found
Wave Equations for Classical Two-Component Proca Fields in Curved Spacetimes with Torsionless Affinities
The world formulation of the full theory of classical Proca fields in
generally relativistic spacetimes is concisely reviewed and the entire set of
pertinent field equations is transcribed in a straightforward way into the
framework of one of the Infeld-van der Waerden formalisms. Some well-known
calculational techniques are then utilized for deriving the wave equations that
control the propagation of the fields allowed for. It appears that no
interaction couplings between such fields and electromagnetic curvatures are
carried by the wave equations at issue. What results is, in effect, that the
only interactions which ultimately occur in the theoretical context under
consideration involve strictly Proca fields and wave functions for gravitons.Comment: Many improvements on the paper have still been made. In particular,
its title has been modified so as to conform further to one of its main aim
New family of potentials with analytical twiston-like solutions
In this letter we present a new approach to find analytical twiston models.
The effective two-field model was constructed by a non-trivial combination of
two one field systems. In such an approach we successfully build analytical
models which are satisfied by a combination of two defect-like solutions, where
one is responsible to twist the molecular chain by , while the other
implies in a longitudinal movement. Such a longitudinal movement can be fitted
to have the size of the distance between adjacent molecular groups. The
procedure works nicely and can be used to describe the dynamics of several
other molecular chains.Comment: 7 pages, 3 figure
Light elements in stars with exoplanets
It is well known that stars orbited by giant planets have higher abundances
of heavy elements when compared with average field dwarfs. A number of studies
have also addressed the possibility that light element abundances are different
in these stars. In this paper we will review the present status of these
studies. The most significant trends will be discussed.Comment: 10 pages, 6 figures. Submitted to the proceedings of IAU symposium
268: Light elements in the universe
New XMM-Newton observation of the Phoenix cluster: properties of the cool core
(Abridged) We present a spectral analysis of a deep (220 ks) XMM-Newton
observation of the Phoenix cluster (SPT-CL J2344-4243), which we also combine
with Chandra archival ACIS-I data. We extract CCD and RGS X-ray spectra from
the core region to search for the signature of cold gas, and constrain the mass
deposition rate in the cooling flow which is thought to be responsible of the
massive star formation episode observed in the BCG. We find an average mass
deposition rate of /yr in the temperature range 0.3-3.0 keV from MOS data. A
temperature-resolved analysis shows that a significant amount of gas is
deposited only above 1.8 keV, while upper limits of the order of hundreds of
/yr can be put in the 0.3-1.8 keV temperature range. From pn data we
obtain /yr, and the
upper limits from the temperature-resolved analysis are typically a factor of 3
lower than MOS data. In the RGS spectrum, no line emission from ionization
states below Fe XXIII is seen above , and the amount of gas cooling
below keV has a best-fit value
/yr. In addition, our analysis of the FIR SED of the BCG based on
Herschel data provides /yr, significantly lower
than previous estimates by a factor 1.5. Current data are able to firmly
identify substantial amount of cooling gas only above 1.8 keV in the core of
the Phoenix cluster. While MOS data analysis is consistent with values as high
as within , pn data provide
yr at c.l. at temperature below 1.8 keV. At present, this
discrepancy cannot be explained on the basis of known calibration uncertainties
or other sources of statistical noise.Comment: A&A in press, typos corrected, revised text according to published
versio
Entanglement and Bell's inequality violation above room temperature in metal carboxylates
In the present work we show that a special family of materials, the metal
carboxylates, may have entangled states up to very high temperatures. From
magnetic susceptibility measurements, we have estimated the critical
temperature below which entanglement exists in the cooper carboxylate
\{Cu(OCH)\}\{Cu(OCH)(2-methylpyridine)\}, and we have
found this to be above room temperature ( K). Furthermore, the
results show that the system remains maximally entangled until close to K and the Bell's inequality is violated up to nearly room temperature
( K)
Regulação da produção da eritropoietina e perspectivas terapêuticas na anemia
About 30 years ago, the treatment of chronic renal disease anaemia was revolutionized by the introduction of recombinant human erythropoietin, which reduced the need for blood transfusions. In spite of this huge advance, the first recombinant human erythropoietin has a relatively short half-life and needs to be administered two to three times per week. Subsequently, other molecules were developed, such as darbepoetin alfa, continuous erythropoietin receptor activator (CERA) and peginesatide, with longer half-life, but the route of administration still remains a problem. Erythropoietin has an action that exceeds erythropoiesis and plays an important role in cell protection. Based on knowledge of the molecular mechanisms that control erythropoiesis, namely the regulation of EPO gene expression, through HIF system, GATA-2 and NF-kB, several upcoming therapeutic agents and strategies for stimulating and treating anaemia emerged.
The main effort in developing these treatments is to achieve other routes of administration, more convenient for the patient, such as oral therapy, not disregarding an easier production, storage and frequency of administration. Some of them are still in laboratory phase and others already in clinical trials phase II or III. In this work, based on a literature search of studies using MEDLINE, our objective is to review the regulation of erythropoietin production and its functions, as well as treatment approach for anaemia of chronic kidney disease, with particular focus on new therapiesHá cerca de 30 anos atrás, o tratamento da anemia da doença renal crónica foi revolucionado pela introdução da eritropoietina (EPO) humana recombinante que permitiu reduzir drasticamente a necessidade de transfusões sanguÃneas. Apesar deste grande avanço, a primeira EPO humana recombinante tem uma semivida relativamente curta e tem de ser administrada duas a três vezes por semana. Subsequentemente, foram desenvolvidas outras moléculas, como a darbepoetina alfa, o ativador contÃnuo do EPO-R (CERA) e o peginesatide, com uma semivida mais longa, mas a via de administração continua a ser exclusivamente parenteral. A eritropoietina desempenha várias funções além da eritropoiética. Tendo por base os mecanismos moleculares que controlam a eritropoiese, nomeadamente a regulação da expressão do gene da EPO, através do sistema do HIF, GATA-2 e NF-kB, surgiram vários fármacos e estratégias terapêuticas para o tratamento da anemia. O principal objetivo destes novos tratamentos passa por desenvolver outras vias de administração, mais cómodas para o doente, como a terapia oral, e facilitar a produção, armazenamento e frequência de administração dos fármacos. Alguns destes ainda se encontram em fase laboratorial, enquanto outros já estão em ensaios clÃnicos fase II ou III. Neste trabalho, baseado na revisão bibliográfica de artigos cientÃficos publicados na MEDLINE, procuramos rever a regulação da produção da EPO e respetivas funções, bem como abordar o tratamento da anemia da doença renal crónica, com especial enfoque nas novas terapêutica
Nonlinear viscosity and velocity distribution function in a simple longitudinal flow
A compressible flow characterized by a velocity field is
analyzed by means of the Boltzmann equation and the Bhatnagar-Gross-Krook
kinetic model. The sign of the control parameter (the longitudinal deformation
rate ) distinguishes between an expansion () and a condensation ()
phenomenon. The temperature is a decreasing function of time in the former
case, while it is an increasing function in the latter. The non-Newtonian
behavior of the gas is described by a dimensionless nonlinear viscosity
, that depends on the dimensionless longitudinal rate . The
Chapman-Enskog expansion of in powers of is seen to be only
asymptotic (except in the case of Maxwell molecules). The velocity distribution
function is also studied. At any value of , it exhibits an algebraic
high-velocity tail that is responsible for the divergence of velocity moments.
For sufficiently negative , moments of degree four and higher may diverge,
while for positive the divergence occurs in moments of degree equal to or
larger than eight.Comment: 18 pages (Revtex), including 5 figures (eps). Analysis of the heat
flux plus other minor changes added. Revised version accepted for publication
in PR
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