6,285 research outputs found
Enabling Radiative Transfer on AMR grids in CRASH
We introduce CRASH-AMR, a new version of the cosmological Radiative Transfer
(RT) code CRASH, enabled to use refined grids. This new feature allows us to
attain higher resolution in our RT simulations and thus to describe more
accurately ionisation and temperature patterns in high density regions. We have
tested CRASH-AMR by simulating the evolution of an ionised region produced by a
single source embedded in gas at constant density, as well as by a more
realistic configuration of multiple sources in an inhomogeneous density field.
While we find an excellent agreement with the previous version of CRASH when
the AMR feature is disabled, showing that no numerical artifact has been
introduced in CRASH-AMR, when additional refinement levels are used the code
can simulate more accurately the physics of ionised gas in high density
regions. This result has been attained at no computational loss, as RT
simulations on AMR grids with maximum resolution equivalent to that of a
uniform cartesian grid can be run with a gain of up to 60% in computational
time.Comment: 19 pages, 17 figures. MNRAS, in pres
Optical and X-ray Observations of the Afterglow to XRF030723
The X-ray-flash XRF030723 was detected by the HETE satellite and rapidly
disseminated, allowing for an optical transient to be detected ~1 day after the
burst. We discuss observations in the optical with Magellan, which confirmed
the fade of the optical transient. In a 2-epoch ToO observation with Chandra,
we discovered a fading X-ray source spatially coincident with the optical
transient. We present spectral fits to the X-ray data. We also discuss the
possibility that the source underwent a rebrightening in the X-rays, as was
observed in the optical. We find that the significance of a possible
rebrightening is very low (~1 sigma).Comment: 4 pages, 2 figures, to appear in Santa Fe GRB Conference Proceedings,
200
Perfused Platforms to Mimic Bone Microenvironment at the Macro/Milli/Microscale: Pros and Cons
As life expectancy increases, the population experiences progressive ageing. Ageing, in turn, is connected to an increase in bone-related diseases (i.e., osteoporosis and increased risk of fractures). Hence, the search for new approaches to study the occurrence of bone-related diseases and to develop new drugs for their prevention and treatment becomes more pressing. However, to date, a reliable in vitro model that can fully recapitulate the characteristics of bone tissue, either in physiological or altered conditions, is not available. Indeed, current methods for modelling normal and pathological bone are poor predictors of treatment outcomes in humans, as they fail to mimic the in vivo cellular microenvironment and tissue complexity. Bone, in fact, is a dynamic network including differently specialized cells and the extracellular matrix, constantly subjected to external and internal stimuli. To this regard, perfused vascularized models are a novel field of investigation that can offer a new technological approach to overcome the limitations of traditional cell culture methods. It allows the combination of perfusion, mechanical and biochemical stimuli, biological cues, biomaterials (mimicking the extracellular matrix of bone), and multiple cell types. This review will discuss macro, milli, and microscale perfused devices designed to model bone structure and microenvironment, focusing on the role of perfusion and encompassing different degrees of complexity. These devices are a very first, though promising, step for the development of 3D in vitro platforms for preclinical screening of novel anabolic or anti-catabolic therapeutic approaches to improve bone health
STOCHASTIC DYNAMICS OF LARGE-SCALE INFLATION IN DE~SITTER SPACE
In this paper we derive exact quantum Langevin equations for stochastic
dynamics of large-scale inflation in de~Sitter space. These quantum Langevin
equations are the equivalent of the Wigner equation and are described by a
system of stochastic differential equations. We present a formula for the
calculation of the expectation value of a quantum operator whose Weyl symbol is
a function of the large-scale inflation scalar field and its time derivative.
The unique solution is obtained for the Cauchy problem for the Wigner equation
for large-scale inflation. The stationary solution for the Wigner equation is
found for an arbitrary potential. It is shown that the large-scale inflation
scalar field in de Sitter space behaves as a quantum one-dimensional
dissipative system, which supports the earlier results. But the analogy with a
one-dimensional model of the quantum linearly damped anharmonic oscillator is
not complete: the difference arises from the new time dependent commutation
relation for the large-scale field and its time derivative. It is found that,
for the large-scale inflation scalar field the large time asymptotics is equal
to the `classical limit'. For the large time limit the quantum Langevin
equations are just the classical stochastic Langevin equations (only the
stationary state is defined by the quantum field theory).Comment: 21 pages RevTex preprint styl
Unstable states in QED of strong magnetic fields
We question the use of stable asymptotic scattering states in QED of strong
magnetic fields. To correctly describe excited Landau states and photons above
the pair creation threshold the asymptotic fields are chosen as generalized
Licht fields. In this way the off-shell behavior of unstable particles is
automatically taken into account, and the resonant divergences that occur in
scattering cross sections in the presence of a strong external magnetic field
are avoided. While in a limiting case the conventional electron propagator with
Breit-Wigner form is obtained, in this formalism it is also possible to
calculate -matrix elements with external unstable particles.Comment: Revtex, 7 pages. To appear in Phys. Rev. D53(2
When a Politician Disappoints: The Role of Gender Stereotypical Expectations in Post-Scandal Judgment
This study examines how evaluations of male and female politicians are worsened by corruption scandals that disappoint expectations of honesty. Participants evaluated a fictitious politician before and after watching a video about a corruption scandal involving that politician. The manipulated variables were the politician’s sex and whether they shared participants’ political affiliations. Results showed that a female politician affiliated with the participants’ preferred party was the most damaged by the scandal because she had the highest expectations of honesty placed upon her
Activation of diacylglycerol kinase alpha is required for VEGF-induced angiogenic signaling in vitro.
Vascular endothelial growth factor-A (VEGF-A) promotes angiogenesis by stimulating migration, proliferation and organization of endothelium, through the activation of signaling pathways involving Src tyrosine kinase. As we had previously shown that Src-mediated activation of diacylglycerol kinase-alpha (Dgk-alpha) is required for hepatocytes growth factor-stimulated cell migration, we asked whether Dgk-alpha is involved in the transduction of angiogenic signaling. In PAE-KDR cells, an endothelial-derived cell line expressing VEGFR-2, VEGF-A165, stimulates the enzymatic activity of Dgk-alpha: activation is inhibited by R59949, an isoform-specific Dgk inhibitor, and is dependent on Src tyrosine kinase, with which Dgk-alpha forms a complex. Conversely in HUVEC, VEGF-A165-induced activation of Dgk is only partially sensitive to R59949, suggesting that also other isoforms may be activated, albeit still dependent on Src tyrosine kinase. Specific inhibition of Dgk-alpha, obtained in both cells by R59949 and in PAE-KDR by expression of Dgk-alpha dominant-negative mutant, impairs VEGF-A165-dependent chemotaxis, proliferation and in vitro angiogenesis. In addition, in HUVEC, specific downregulation of Dgk-alpha by siRNA impairs in vitro angiogenesis on matrigel, further suggesting the requirement for Dgk-alpha in angiogenic signaling in HUVEC. Thus, we propose that activation of Dgk-alpha generates a signal essential for both proliferative and migratory response to VEGF-A165, suggesting that it may constitute a novel pharmacological target for angiogenesis control.
- …