1,821 research outputs found
Naked Singularity in a Modified Gravity Theory
The cosmological constant induced by quantum fluctuation of the graviton on a
given background is considered as a tool for building a spectrum of different
geometries. In particular, we apply the method to the Schwarzschild background
with positive and negative mass parameter. In this way, we put on the same
level of comparison the related naked singularity (-M) and the positive mass
wormhole. We discuss how to extract information in the context of a f(R)
theory. We use the Wheeler-De Witt equation as a basic equation to perform such
an analysis regarded as a Sturm-Liouville problem . The application of the same
procedure used for the ordinary theory, namely f(R)=R, reveals that to this
approximation level, it is not possible to classify the Schwarzschild and its
naked partner into a geometry spectrum.Comment: 8 Pages. Contribution given to DICE 2008. To appear in the
proceeding
Mediators of leukocyte yctivation play a role in disseminated intravascular coagulation during orthotopic liver transplantation
Leukocytes play an important role in the development of disseminated intravascular coagulation (DIC). In the reperfusion phase of OLT a DIC-like situation has been described and has been held responsible for the high blood loss during this phase.
We investigated the role of leukocytes in the pathogenesis of DIC in OLT by measuring the leukocytic mediators released upon activation (cathepsin B, elastase, TNF, neopterin) and the levels of thrombin-antithrombin III (TAT) complexes, seen as markers of prothrombin activation. Arterial blood samples were taken at 10 different time points during and after OLT. Samples were also taken of the perfusate released from the liver graft vein during the flushing procedure before the reperfusion phase. Aprotinin was given as a continuous infusion (0.2-0.4 Mill. KlU/hr) and its plasma levels were determined.
Significantly elevated levels of neopterin (15-fold; P<0.01), cathepsin B (440-fold; P<0.01) in the perfusate, as compared with the systemic circulation, as well as their significant increases in the early reperfusion phase suggested that they were released by the graft liver. This was paralleled by elevated levels of elastase (1.3-fold, P<0.05), TNF (1.5-fold, P=NS), and TAT complexes (1.4-fold; P<0.1) in the perfusate. Significant correlations could be identified between the parameters of leukocyte activation and TAT complexes, whereas no correlation was observed between any of the parameters investigated and the aprotinin levels.
Our results strongly indicate a release of leukocytic mediators from the graft liver during its reperfusion which seems to be related to the parallely increased prothrombin activation. No correlation could be seen between levels of aprotinin and levels of leukocytic mediators
Hubble parameter reconstruction from a principal component analysis: minimizing the bias
A model-independent reconstruction of the cosmic expansion rate is essential
to a robust analysis of cosmological observations. Our goal is to demonstrate
that current data are able to provide reasonable constraints on the behavior of
the Hubble parameter with redshift, independently of any cosmological model or
underlying gravity theory. Using type Ia supernova data, we show that it is
possible to analytically calculate the Fisher matrix components in a Hubble
parameter analysis without assumptions about the energy content of the
Universe. We used a principal component analysis to reconstruct the Hubble
parameter as a linear combination of the Fisher matrix eigenvectors (principal
components). To suppress the bias introduced by the high redshift behavior of
the components, we considered the value of the Hubble parameter at high
redshift as a free parameter. We first tested our procedure using a mock sample
of type Ia supernova observations, we then applied it to the real data compiled
by the Sloan Digital Sky Survey (SDSS) group. In the mock sample analysis, we
demonstrate that it is possible to drastically suppress the bias introduced by
the high redshift behavior of the principal components. Applying our procedure
to the real data, we show that it allows us to determine the behavior of the
Hubble parameter with reasonable uncertainty, without introducing any ad-hoc
parameterizations. Beyond that, our reconstruction agrees with completely
independent measurements of the Hubble parameter obtained from red-envelope
galaxies.Comment: Modified to match journal versio
Different aprotinin applications influencing hemostatic chances in orthotopic liver transplantation
The effect of different aprotinin applications on hemmtatic changes and blood product requirements in orthotopic liver transplantation was investigated in a prospective, open, and randomized study.
From November 1989 to June 1990, 13 patients received aprotinin as a bolus of 0.5 Mill, kallikrein inac-tivator units (KIU) on three occasions in the course of an OLT, whereas 10 other patients were treated with continuous aprotinin infusion of 0.1-0.4 Mill. KIU/hr. Before and after reperfusion of the graft liver, signs of hyperfibrinolysis, measured by thrombelastography, were significantly lower in the infusion group. Tissue-type plasminogen activator (t-PA) activity increased during the anhepatic phase but to a significantly lesser extent in the infusion group. Blood product requirements during OLT were tendentiously higher in the bolus group but not significantly so. However, the use of packed red blood cells was significantly lower in the postoperative period, whereas there was no significant difference in fresh frozen plasma requirements between the two groups.
All 23 patients have survived, and only one woman of each group required retransplantation due to severe host-versus-graft reactions.
Furthermore, we investigated the perfusate of the graft liver in both groups and detected signs of a decreased t-PA release in the infusion group.
Our results demonstrate an advantage of aprotinin given as continuous infusion over bolus application in OLT
The Rate of Type Ia Supernovae at High Redshift
We derive the rates of Type Ia supernovae (SNIa) over a wide range of
redshifts using a complete sample from the IfA Deep Survey. This sample of more
than 100 SNIa is the largest set ever collected from a single survey, and
therefore uniquely powerful for a detailed supernova rate (SNR) calculation.
Measurements of the SNR as a function of cosmological time offer a glimpse into
the relationship between the star formation rate (SFR) and Type Ia SNR, and may
provide evidence for the progenitor pathway. We observe a progressively
increasing Type Ia SNR between redshifts z~0.3-0.8. The Type Ia SNR
measurements are consistent with a short time delay (t~1 Gyr) with respect to
the SFR, indicating a fairly prompt evolution of SNIa progenitor systems. We
derive a best-fit value of SFR/SNR 580 h_70^(-2) M_solar/SNIa for the
conversion factor between star formation and SNIa rates, as determined for a
delay time of t~1 Gyr between the SFR and the Type Ia SNR. More complete
measurements of the Type Ia SNR at z>1 are necessary to conclusively determine
the SFR--SNR relationship and constrain SNIa evolutionary pathways.Comment: 37 pages, 9 figures, accepted for publication in Astrophysical
Journal. Figures 7-9 correcte
Modified Chaplygin Traversable Wormholes
The modified Chaplygin gas (MCG) is a strong candidate for the unified model
of dark matter and dark energy. The equation of state of this modified model is
valid from the radiation era to the CDM model. In early epoch (when
was large), dark matter had the dominant role while at later stages
(when is small), the MCG model behaves as dark energy. In this work, we
have found exact solution of static spherically symmetric Einstein equations
describing a wormhole for an inhomogeneous distribution of modified Chaplygin
gas. For existence of wormhole solution, there are some restrictions relating
the parameters in the equation of state for MCG and the throat radius of the
wormhole. Physical properties and characteristics of these modified Chaplygin
wormholes are analyzed in details.Comment: 9 pages, 1 figur
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