5,418 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
The Excitation of NH in Interstellar Molecular Clouds. I - Models
We present LVG and non-local radiative transfer calculations involving the
rotational and hyperfine structure of the spectrum of NH with
collisional rate coefficients recently derived by us. The goal of this study is
to check the validity of the assumptions made to treat the hyperfine structure
and to study the physical mechanisms leading to the observed hyperfine
anomalies.
We find that the usual hypothesis of identical excitation temperatures for
all hyperfine components of the =1-0 transition is not correct within the
range of densities existing in cold dense cores, i.e., a few 10 \textless
n(H) \textless a few 10 cm. This is due to different radiative
trapping effects in the hyperfine components. Moreover, within this range of
densities and considering the typical abundance of NH, the total
opacity of rotational lines has to be derived taking into account the hyperfine
structure. The error made when only considering the rotational energy structure
can be as large as 100%. Using non-local models we find that, due to
saturation, hyperfine anomalies appear as soon as the total opacity of the
=1-0 transition becomes larger than 20. Radiative scattering in
less dense regions enhance these anomalies, and particularly, induce a
differential increase of the excitation temperatures of the hyperfine
components. This process is more effective for the transitions with the highest
opacities for which emerging intensities are also reduced by self-absorption
effects. These effects are not as critical as in HCO or HCN, but should be
taken into account when interpreting the spatial extent of the NH
emission in dark clouds.Comment: 13 pages, 12 figure
Windows through the Dusty Disks Surrounding the Youngest Low Mass Protostellar Objects
The formation and evolution of young low mass stars are characterized by
important processes of mass loss and accretion ocurring in the innermost
regions of their placentary circumstellar disks. Because of the large
obscuration of these disks at optical and infrared wavelengths in the early
protostellar stages (Class 0 Sources), they were previously detected only at
radio wavelengths using interferometric techniques. We have detected with the
Infrared Space Observatory (ISO) the mid-infrared emission associated with the
Class 0 protostar VLA1 in the HH1-2 region located in the Orion nebula. The
emission arises in the three wavelength windows at 5.3, 6.6 and 7.5 micras
where the absorption due to ices and silicates has a local minimum that exposes
the central parts of the youngest protostellar systems to mid-infrared
investigations. The mid-infrared emission arises from a central source with 4
AU diameter at an averaged temperature of 700 K, deeply embedded in a dense
region with a visual extinction of Av=80-100mag.Comment: The article is here and on pres
Yacimientos de estaño del Oeste de España
[Resumen] En este trabajo se realiza una clasificación de los. yacimientos de estaño del oeste español basada, fundamentalmente, en consideraciones económicas. Tras una introducción explicativa de los objetivos y metodología empleados, así como una breve exposición del significado de las explotaciones de estaño españolas en el contexto mundial, se describen y clasifican los indicios y yacimientos más importantes, aportándose además un listado de la bibliografía específica más destacable[Abstract] This work presents a classification of the tin deposits in the westof Spain, based, mainly, on economic reasons. After an explaining introduction of the objetives and the method used, and a short exposition of the importance of spanish tin exploitations in the world context, the most important mines and occurrences are described and classified; in addition a list of the most relevant specific bibliography is given
Contribución al estudio de las mineralizaciones Pb-Zn en el entorno macizo granítico de las Peñas de Haya (Guipúzcoa-Navarra)
Se presenta un primer estudio de las mineralizaciones filonianas PbZn asociadas a pizarras oscuras v granito tardihercínico. Las menas y gangas aparecen fuertemente deformadas y brechificadas y es frecuente la removilización de los sulfuros. En el proceso de formación de estas mineralizaciones se distinguen varias fases: una fase hidrotermal de edad hercínica post-intrusiva y una última fase de removilización. Las paragénesis principales permiten clasificar estos yacimientos como mesotermales. Se discuten los modelos genéticos más probables
Tungsten deposits in the west of Spain
[Resumen] En este trabajo se realiza una clasificación de los yacimientos de volframio del oeste español basada, fundamentalmente, en consideraciones económicas. Tras una introducción en la que se comenta la reciente historia del volframio, así como una breve exposición del significado de las explotaciones de volframioespañolas en el contexto mundial, se describen y clasifican los indicios y yacimientos más importantes, aportándose también un listado de la bibliografía específica más destacable.[Abstract] This work presents a classification of the tungsten deposits en the west of Spain, based, mainly, on economic reasons. Mter an explaining introduction of the recent history of the tungsten, and a short exposition of the importance of spanish exploitations in the world context, the most important mines and occurrences are described and c1assified; in addition a list of the most relevant specific bibliography is given
A Search for H2O in the Strongly Lensed QSO MG 0751+2716 at z=3.2
We present a search for 183 GHz H_2O(3_13-2_20) emission in the
infrared-luminous quasar MG 0751+2716 with the NRAO Very Large Array (VLA). At
z=3.200+/-0.001, this water emission feature is redshifted to 43.6 GHz. As
opposed to the faint rotational transitions of HCN (the standard high-density
tracer at high-z), H_2O(3_13-2_20) is observed with high maser amplification
factors in Galactic star-forming regions. It therefore holds the potential to
trace high-density star-forming regions in the distant universe. If indeed all
star-forming regions in massively star-forming galaxies at z>3 have similar
physical properties as e.g. the Orion or W49N molecular cloud cores, the flux
ratio between the maser-amplified H_2O(3_13-2_20) and the thermally excited
CO(1-0) transitions may be as high as factor of 20 (but has to be corrected by
their relative filling factor). MG 0751+2716 is a strong CO(4-3) emitter, and
therefore one of the most suitable targets to search for H_2O(3_13-2_20) at
cosmological redshifts. Our search resulted in an upper limit in line
luminosity of L'(H_2O) < 0.6 x 10^9 K km/s pc^2. Assuming a brightness
temperature of T_b(H_2O) ~= 500 K for the maser emission and CO properties from
the literature, this translates to a H_2O(3_13-2_20)/CO(4-3) area filling
factor of less than 1%. However, this limit is not valid if the H_2O(3_13-2_20)
maser emission is quenched, i.e. if the line is only thermally excited. We
conclude that, if our results were to hold for other high-z sources, H_2O does
not appear to be a more luminous alternative to HCN to detect high-density gas
in star-forming environments at high redshift.Comment: 6 pages, 1 figure, to appear in ApJ (accepted May 19, 2006
Quasar Feedback in the Ultraluminous Infrared Galaxy F11119+3257: Connecting the Accretion Disk Wind with the Large-Scale Molecular Outflow
In Tombesi et al. (2015), we reported the first direct evidence for a quasar
accretion disk wind driving a massive molecular outflow. The target was
F11119+3257, an ultraluminous infrared galaxy (ULIRG) with unambiguous type-1
quasar optical broad emission lines. The energetics of the accretion disk wind
and molecular outflow were found to be consistent with the predictions of
quasar feedback models where the molecular outflow is driven by a hot
energy-conserving bubble inflated by the inner quasar accretion disk wind.
However, this conclusion was uncertain because the energetics were estimated
from the optically thick OH 119 um transition profile observed with Herschel.
Here, we independently confirm the presence of the molecular outflow in
F11119+3257, based on the detection of broad wings in the CO(1-0) profile
derived from ALMA observations. The broad CO(1-0) line emission appears to be
spatially extended on a scale of at least ~7 kpc from the center. Mass outflow
rate, momentum flux, and mechanical power of (80-200) R_7^{-1} M_sun/yr,
(1.5-3.0) R_7^{-1} L_AGN/c, and (0.15-0.40)% R_7^{-1} L_AGN are inferred from
these data, assuming a CO-to-H_2 conversion factor appropriate for a ULIRG (R_7
is the radius of the outflow normalized to 7 kpc and L_AGN is the AGN
luminosity). These rates are time-averaged over a flow time scale of 7x10^6
yrs. They are similar to the OH-based rates time-averaged over a flow time
scale of 4x10^5 yrs, but about a factor 4 smaller than the local
("instantaneous"; <10^5 yrs) OH-based estimates cited in Tombesi et al. The
implications of these new results are discussed in the context of time-variable
quasar-mode feedback and galaxy evolution. The need for an energy-conserving
bubble to explain the molecular outflow is also re-examined.Comment: 15 pages, 6 figures, 4 tables, accepted for publication in Ap
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