4,424 research outputs found
Cancer therapeutic potential of combinatorial immuno- and vaso-modulatory interventions
Currently, most of the basic mechanisms governing tumor-immune system
interactions, in combination with modulations of tumor-associated vasculature,
are far from being completely understood. Here, we propose a mathematical model
of vascularized tumor growth, where the main novelty is the modeling of the
interplay between functional tumor vasculature and effector cell recruitment
dynamics. Parameters are calibrated on the basis of different in vivo
immunocompromised Rag1-/- and wild-type (WT) BALB/c murine tumor growth
experiments. The model analysis supports that tumor vasculature normalization
can be a plausible and effective strategy to treat cancer when combined with
appropriate immuno-stimulations. We find that improved levels of functional
tumor vasculature, potentially mediated by normalization or stress alleviation
strategies, can provide beneficial outcomes in terms of tumor burden reduction
and growth control. Normalization of tumor blood vessels opens a therapeutic
window of opportunity to augment the antitumor immune responses, as well as to
reduce the intratumoral immunosuppression and induced-hypoxia due to vascular
abnormalities. The potential success of normalizing tumor-associated
vasculature closely depends on the effector cell recruitment dynamics and tumor
sizes. Furthermore, an arbitrary increase of initial effector cell
concentration does not necessarily imply a better tumor control. We evidence
the existence of an optimal concentration range of effector cells for tumor
shrinkage. Based on these findings, we suggest a theory-driven therapeutic
proposal that optimally combines immuno- and vaso-modulatory interventions
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
A dose-volume histogram based decision-support system for dosimetric comparison of radiotherapy treatment plans
Background: The choice of any radiotherapy treatment plan is usually made after the evaluation of a few preliminary isodose distributions obtained from different beam configurations. Despite considerable advances in planning techniques, such final decision remains a challenging task that would greatly benefit from efficient and reliable assessment tools. Methods: For any dosimetric plan considered, data on dose-volume histograms supplied by treatment planning systems are used to provide estimates on planning target coverage as well as on sparing of organs at risk and the remaining healthy tissue. These partial metrics are then combined into a dose distribution index (DDI), which provides a unified, easy-to-read score for each competing radiotherapy plan. To assess the performance of the proposed scoring system, DDI figures for fifty brain cancer patients were retrospectively evaluated. Patients were divided in three groups depending on tumor location and malignancy. For each patient, three tentative plans were designed and recorded during planning, one of which was eventually selected for treatment. We thus were able to compare the plans with better DDI scores and those actually delivered. Results: When planning target coverage and organs at risk sparing are considered as equally important, the tentative plan with the highest DDI score is shown to coincide with that actually delivered in 32 of the 50 patients considered. In 15 (respectively 3) of the remaining 18 cases, the plan with highest DDI value still coincides with that actually selected, provided that organs at risk sparing is given higher priority (respectively, lower priority) than target coverage. Conclusions: DDI provides a straightforward and non-subjective tool for dosimetric comparison of tentative radiotherapy plans. In particular, DDI readily quantifies differences among competing plans with similar-looking dose-volume histograms and can be easily implemented for any tumor type and localization, irrespective of the planning system and irradiation technique considered. Moreover, DDI permits to estimate the dosimetry impact of different priorities being assigned to sparing of organs at risk or to better target coverag
The edge of the M87 halo and the kinematics of the diffuse light in the Virgo cluster core
We present high resolution FLAMES/VLT spectroscopy of intracluster planetary
nebula (ICPN) candidates, targeting three new fields in the Virgo cluster core
with surface brightness down to mu_B = 28.5. Based on the projected phase space
information we separate the old and 12 newly-confirmed PNs into galaxy and
intracluster components. The M87 PNs are confined to the extended stellar
envelope of M87, within a projected radius of ~ 160 kpc, while the ICPNs are
scattered across the whole surveyed region between M87 and M86. The velocity
dispersions determined from the M87 PNs at projected radii of 60 kpc and 144
kpc show that the galaxy's velocity dispersion profile decreases in the outer
halo, down to 78 +/- 25 km/s. A Jeans model for the M87 halo stars in the
gravitational potential traced by the X-ray emission fits the observed velocity
dispersion profile only if the stellar orbits are strongly radially anisotropic
(beta ~= 0.4 at r ~= 10 kpc increasing to 0.8 at the outer edge), and if
additionally the stellar halo is truncated at ~= 150 kpc average elliptical
radius. From the spatial and velocity distribution of the ICPNs we infer that
M87 and M86 are falling towards each other and that we may be observing them
just before the first close pass. The inferred luminosity-specific PN numbers
for the M87 halo and the ICL are in the range of values observed for old (> 10
Gyr) stellar populations (abridged).Comment: Accepted for publication in Astronomy and Astrophysics. 16 pages, 14
figures and 4 table
The Second INTEGRAL AGN Catalogue
The INTEGRAL mission provides a large data set for studying the hard X-ray
properties of AGN and allows testing of the unified scheme for AGN. We present
analysis of INTEGRAL IBIS/ISGRI, JEM-X, and OMC data for 199 AGN supposedly
detected by INTEGRAL above 20 keV. The data analysed here allow a significant
spectral extraction on 148 objects and an optical variability study of 57 AGN.
The slopes of the hard X-ray spectra of Seyfert 1 and Seyfert~2 galaxies are
found to be consistent within the uncertainties, whereas higher cut-off
energies and lower luminosities are measured for the more absorbed / type 2
AGN. The intermediate Seyfert 1.5 objects exhibit hard X-ray spectra consistent
with those of Seyfert 1. When applying a Compton reflection model, the
underlying continua appear the same in Seyfert 1 and 2 with photon index 2, and
the reflection strength is about R = 1, when assuming different inclination
angles. A significant correlation is found between the hard X-ray and optical
luminosity and the mass of the central black hole in the sense that the more
luminous objects appear to be more massive. There is also a general trend
toward the absorbed sources and type 2 AGN having lower Eddington ratios. The
black holemass appears to form a fundamental plane together with the optical
and X-ray luminosity of the form Lv being proportional to Lx^0.6 M^0.2, similar
to that found between radio luminosity Lr, Lx, and M. The unified model for
Seyfert galaxies seems to hold, showing in hard X-rays that the central engine
is the same in Seyfert 1 and 2, but seen under different inclination angles and
absorption. (Abridged)Comment: 26 pages, 16 figures, accepted for publication in A&A. Corrections by
language editor included in version
Electron transport properties of sub-3-nm diameter copper nanowires
Density functional theory and density functional tight-binding are applied to
model electron transport in copper nanowires of approximately 1 nm and 3 nm
diameters with varying crystal orientation and surface termination. The copper
nanowires studied are found to be metallic irrespective of diameter, crystal
orientation and/or surface termination. Electron transmission is highly
dependent on crystal orientation and surface termination. Nanowires oriented
along the [110] crystallographic axis consistently exhibit the highest electron
transmission while surface oxidized nanowires show significantly reduced
electron transmission compared to unterminated nanowires. Transmission per unit
area is calculated in each case, for a given crystal orientation we find that
this value decreases with diameter for unterminated nanowires but is largely
unaffected by diameter in surface oxidized nanowires for the size regime
considered. Transmission pathway plots show that transmission is larger at the
surface of unterminated nanowires than inside the nanowire and that
transmission at the nanowire surface is significantly reduced by surface
oxidation. Finally, we present a simple model which explains the transport per
unit area dependence on diameter based on transmission pathways results
Maser emission from SiO isotopologues traces the innermost 100 AU around Radio Source I in Orion BN/KL
We have used the Very Large Array (VLA) at 7 mm wavelength to image five
rotational transitions (J=1-0) from three SiO isotopologues towards Orion
BN/KL: 28SiO v=0,1,2; and 29SiO and 30SiO v=0. For the first time, we have
mapped the 29SiO and 30SiO J=1-0 emission, established the maser nature of the
emission, and confirmed association with the deeply embedded high-mass young
stellar object commonly denoted radio Source I. The 28SiO v=0 maser emission
shows a bipolar structure that extends over ~700 AU along a northeast-southwest
axis, and we propose that it traces a bipolar outflow driven by Source I. The
high-brightness isotopic SiO maser emission imaged with a ~0.2 arcsec
resolution has a more compact distribution, generally similar to that of the
28SiO v=1,2 emission, and it probably traces bulk gas flows in a region of
diameter <100 AU centered on Source I. On small scales of <10 AU, however,
compact 29SiO/30SiO v=0 and 28SiO v=1,2 emission features may be offset from
one another in position and line-of-sight velocity.
From a radiative transfer analysis based on a large velocity gradient (LVG)
pumping model, we derive similar temperatures and densities for the optimum
excitation of both 29SiO/30SiO v=0 and 28SiO v=1,2 masers, significantly higher
than required for 28SiO v=0 maser excitation. In order to account for the
small-scale differences among the isotopologues (v=0) and the main species
(v=1,2), follow-up radiative transfer modeling that incorporates non-local line
overlap among transitions of all SiO isotopic species may be required.Comment: 10 pages, 3 figures, accepted for publication by Ap
High-excitation OH and H_2O lines in Markarian 231: the molecular signatures of compact far-infrared continuum sources
The ISO/LWS far-infrared spectrum of the ultraluminous galaxy Mkn 231 shows
OH and H_2O lines in absorption from energy levels up to 300 K above the ground
state, and emission in the [O I] 63 micron and [C II] 158 micron lines. Our
analysis shows that OH and H_2O are radiatively pumped by the far-infrared
continuum emission of the galaxy. The absorptions in the high-excitation lines
require high far-infrared radiation densities, allowing us to constrain the
properties of the underlying continuum source. The bulk of the far-infrared
continuum arises from a warm (T_dust=70-100 K), optically thick
(tau_100micron=1-2) medium of effective diameter 200-400 pc. In our best-fit
model of total luminosity L_IR, the observed OH and H2O high-lying lines arise
from a luminous (L/L_IR~0.56) region with radius ~100 pc. The high surface
brightness of this component suggests that its infrared emission is dominated
by the AGN. The derived column densities N(OH)>~10^{17} cm^{-2} and
N(H_2O)>~6x10^{16} cm^{-2} may indicate XDR chemistry, although significant
starburst chemistry cannot be ruled out. The lower-lying OH, [C II] 158 micron,
and [O I] 63 micron lines arise from a more extended (~350 pc) starburst
region. We show that the [C II] deficit in Mkn 231 is compatible with a high
average abundance of C+ because of an extreme overall luminosity to gas mass
ratio. Therefore, a [C II] deficit may indicate a significant contribution to
the luminosity by an AGN, and/or by extremely efficient star formation.Comment: 16 pages, 6 figures, accepted for publication in The Astrophysical
Journa
Constraints on the H2O formation mechanism in the wind of carbon-rich AGB stars
Context. The recent detection of warm HO vapor emission from the outflows
of carbon-rich asymptotic giant branch (AGB) stars challenges the current
understanding of circumstellar chemistry. Two mechanisms have been invoked to
explain warm HO vapor formation. In the first, periodic shocks passing
through the medium immediately above the stellar surface lead to HO
formation. In the second, penetration of ultraviolet interstellar radiation
through a clumpy circumstellar medium leads to the formation of HO
molecules in the intermediate wind.
Aims. We aim to determine the properties of HO emission for a sample of
18 carbon-rich AGB stars and subsequently constrain which of the above
mechanisms provides the most likely warm HO formation pathway.
Methods, Results, and Conclusions. See paper
- âŠ