6,960 research outputs found
Why one-size-fits-all vaso-modulatory interventions fail to control glioma invasion: in silico insights
There is an ongoing debate on the therapeutic potential of vaso-modulatory
interventions against glioma invasion. Prominent vasculature-targeting
therapies involve functional tumour-associated blood vessel deterioration and
normalisation. The former aims at tumour infarction and nutrient deprivation
medi- ated by vascular targeting agents that induce occlusion/collapse of
tumour blood vessels. In contrast, the therapeutic intention of normalising the
abnormal structure and function of tumour vascular net- works, e.g. via
alleviating stress-induced vaso-occlusion, is to improve chemo-, immuno- and
radiation therapy efficacy. Although both strategies have shown therapeutic
potential, it remains unclear why they often fail to control glioma invasion
into the surrounding healthy brain tissue. To shed light on this issue, we
propose a mathematical model of glioma invasion focusing on the interplay
between the mi- gration/proliferation dichotomy (Go-or-Grow) of glioma cells
and modulations of the functional tumour vasculature. Vaso-modulatory
interventions are modelled by varying the degree of vaso-occlusion. We
discovered the existence of a critical cell proliferation/diffusion ratio that
separates glioma invasion re- sponses to vaso-modulatory interventions into two
distinct regimes. While for tumours, belonging to one regime, vascular
modulations reduce the tumour front speed and increase the infiltration width,
for those in the other regime the invasion speed increases and infiltration
width decreases. We show how these in silico findings can be used to guide
individualised approaches of vaso-modulatory treatment strategies and thereby
improve success rates
Critical Point Theory and the Number of Solutions of a Nonlinear Dirichlet Problem
No abstract provided
Organizaciones populares, construcción de identidad y acción política
El artículo analiza la experiencia de algunas organizaciones populares urbanas en Bogotá durante las últimas décadas del Siglo XX. La hipótesis principal es que estas asociaciones contribuyen a la conformación de los pobladores populares como sujetos sociales, al fortalecer su tejido social y asociativo, al afirmar identidades culturales y al crear nuevas prácticas y subjetividades políticas democráticas. La metodología empleada fue participativa y combinó investigación documental y siete estudios de caso.En primer lugar, se presenta el contexto histórico en el que surgen las organizaciones estudiadas, así como las dinámicas generadas por ellas y que han influido en el tejido social y asociativo en los barrios. También presenta las estrategias culturales que desarrollan las organizaciones, así como las concepciones y prácticas políticas que contribuyen a la constitución de nuevas identidades sociales y ciudadanías críticas.-1. Presentación. 2. Surgimiento y trayectoria de las organizaciones. 3. Las organizaciones y el tejido social local. 4. La identidad de las organizaciones. 5. La política de las organizaciones. Bibliografía
Estimating the Effects of Lenght of Exposure to Traning Program: The Case of Job Corps
Length of exposure to a training program is important in determining the labor market outcomes of participants. Employing methods to estimate the causal effects from continuous treatments, we provide insights regarding the effects of different lengths of enrollment to Job Corps (JC)— America’s largest and most comprehensive job training program for disadvantaged youth. We semiparametrically estimate average causal effects (on the treated) of different lengths of exposure to JC, using the “generalized propensity score” under the assumption that selection into different lengths is based on a rich set of observed covariates. “Placebo tests” are performed to gauge the plausibility of this assumption. We find that the estimated effects are increasing in the length of training, and that the marginal effects of additional training are decreasing with length of enrollment. We also document differences in the estimated effects of length of exposure across different demographic groups, which are particularly large between males and females. Finally, our results suggest an important “lock-in” effect in JC training.Training Programs, Continuous Treatments, Generalized Propensity Score, Dose-Response Function
Some Unique Constants Associated with Extremal Black Holes
In recent papers we had developed a unified picture of black hole entropy and
curvature which was shown to lead to Hawking radiation. It was shown that for
any black hole mass, holography implies a phase space of just one quantum
associated with the interior of the black hole. Here we study extremal rotating
and charged black holes and obtain unique values for ratios of angular momentum
to entropy, charge to entropy, etc. It turns out that these ratios can be
expressed in terms of fundamental constants in nature, having analogies with
other physical systems, like in condensed matter physics.Comment: "Accepted for publication in Astrophysics & Space Science" 4 pages,
10 equation
Water vapor emission from IRC+10216 and other carbon-rich stars: model predictions and prospects for multitransition observations
We have modeled the emission of H2O rotational lines from the extreme C-rich
star IRC+10216. Our treatment of the excitation of H2O emissions takes into
account the excitation of H2O both through collisions, and through the pumping
of the nu2 and nu3 vibrational states by dust emission and subsequent decay to
the ground state. Regardless of the spatial distribution of the water
molecules, the H2O 1_{10}-1_{01} line at 557 GHz observed by the Submillimeter
Wave Astronomy Satellite (SWAS) is found to be pumped primarily through the
absorption of dust-emitted photons at 6 m in the nu2 band. As noted by
previous authors, the inclusion of radiative pumping lowers the ortho-H2O
abundance required to account for the 557 GHz emission, which is found to be
(0.5-1)x10^{-7} if the presence of H2O is a consequence of vaporization of
orbiting comets or Fischer-Tropsch catalysis. Predictions for other
submillimeter H2O lines that can be observed by the Herschel Space Observatory
(HSO) are reported. Multitransition HSO observations promise to reveal the
spatial distribution of the circumstellar water vapor, discriminating among the
several hypotheses that have been proposed for the origin of the H2O vapor in
the envelope of IRC+10216. We also show that, for observations with HSO, the
H2O 1_{10}-1_{01} 557 GHz line affords the greatest sensitivity in searching
for H2O in other C-rich AGB stars.Comment: 35 pages, 12 figures, to be published in The Astrophysical Journa
Resonating bipolarons
Electrons coupled to local lattice deformations end up in selftrapped
localized molecular states involving their binding into bipolarons when the
coupling is stronger than a certain critical value. Below that value they exist
as essentially itinerant electrons. We propose that the abrupt crossover
between the two regimes can be described by resonant pairing similar to the
Feshbach resonance in binary atomic collision processes. Given the
intrinsically local nature of the exchange of pairs of itinerant electrons and
localized bipolarons, we demonstrate the occurrence of such a resonance on a
finite-size cluster made out of metallic atoms surrounding a polaronic ligand
center.Comment: 7 pages, 4 figures, to be published in Europhysics Letter
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