758 research outputs found
Levy model of cancer
A small portion of a tissue defines a microstate in gene expression space.
Mutations, epigenetic events or external factors cause microstate displacements
which are modeled by combining small independent gene expression variations and
large Levy jumps, resulting from the collective variations of a set of genes.
The risk of cancer in a tissue is estimated as the microstate probability to
transit from the normal to the tumor region in gene expression space. The
formula coming from the contribution of large Levy jumps seems to provide a
qualitatively correct description of the lifetime risk of cancer, and reveals
an interesting connection between the risk and the way the tissue is protected
against infections.Comment: arXiv admin note: text overlap with arXiv:1507.0692
The silicate absorption profile in the ISM towards the heavily obscured nucleus of NGC 4418
The 9.7-micron silicate absorption profile in the interstellar medium
provides important information on the physical and chemical composition of
interstellar dust grains. Measurements in the Milky Way have shown that the
profile in the diffuse interstellar medium is very similar to the amorphous
silicate profiles found in circumstellar dust shells around late M stars, and
narrower than the silicate profile in denser star-forming regions. Here, we
investigate the silicate absorption profile towards the very heavily obscured
nucleus of NGC 4418, the galaxy with the deepest known silicate absorption
feature, and compare it to the profiles seen in the Milky Way. Comparison
between the 8-13 micron spectrum obtained with TReCS on Gemini and the larger
aperture spectrum obtained from the Spitzer archive indicates that the former
isolates the nuclear emission, while Spitzer detects low surface brightness
circumnuclear diffuse emission in addition. The silicate absorption profile
towards the nucleus is very similar to that in the diffuse ISM in the Milky Way
with no evidence of spectral structure from crystalline silicates or silicon
carbide grains.Comment: 7 Pages, 3 figures. MNRAS in pres
Spatially Resolved [FeII] 1.64 \mu m Emission in NGC 5135. Clues for Understanding the Origin of the Hard X-rays in Luminous Infrared Galaxies
Spatially resolved near-IR and X-ray imaging of the central region of the
Luminous Infrared Galaxy NGC 5135 is presented. The kinematical signatures of
strong outflows are detected in the [FeII]1.64 \mu m emission line in a compact
region at 0.9 kpc from the nucleus. The derived mechanical energy release is
consistent with a supernova rate of 0.05-0.1 yr. The apex of the
outflowing gas spatially coincides with the strongest [FeII] emission peak and
with the dominant component of the extranuclear hard X-ray emission. All these
features provide evidence for a plausible direct physical link between
supernova-driven outflows and the hard X-ray emitting gas in a LIRG. This
result is consistent with model predictions of starbursts concentrated in small
volumes and with high thermalization efficiencies. A single high-mass X-ray
binary (HMXB) as the major source of the hard X-ray emission although not
favoured, cannot be ruled out. Outside the AGN, the hard X-ray emission in NGC
5135 appears to be dominated by the hot ISM produced by supernova explosions in
a compact star-forming region, and not by the emission due to HMXB. If this
scenario is common to U/LIRGs, the hard X-rays would only trace the most
compact (< 100 pc) regions with high supernova and star formation densities,
therefore a lower limit to their integrated star formation. The SFR derived in
NGC 5135 based on its hard X-ray luminosity is a factor of two and four lower
than the values obtained from the 24 \mu m and soft X-ray luminosities,
respectively.Comment: Accepted for Publication in ApJ, 18 pages, 2 figure
Synthetic spectra of H Balmer and HeI absorption lines. I: Stellar library
We present a grid of synthetic profiles of stellar H Balmer and HeI lines at
optical wavelengths with a sampling of 0.3 A. The grid spans a range of
effective temperature 4000 K < Teff < 50000 K, and gravity 0.0 < log g < 5.0 at
solar metallicity. For Teff > 25000 K, NLTE stellar atmosphere models are
computed using the code TLUSTY (Hubeny 1988). For cooler stars, Kurucz (1993)
LTE models are used to compute thesynthetic spectra. The grid includes the
profiles of the high-order hydrogen Balmer series and HeI lines for effective
temperatures and gravities that have not been previously synthesized. The
behavior of H8 to H13 and HeI 3819 with effective temperature and gravity is
very similar to that of the lower terms of the series (e.g. Hb) and the other
HeI lines at longer wavelengths; therefore, they are suited for the
determination of the atmospheric parameters of stars. These lines are
potentially important to make predictions for these stellar absorption features
in galaxies with active star formation. Evolutionary synthesis models of these
lines for starburst and post-starburst galaxies are presented in a companion
paper. The full set of the synthetic stellar spectra is available for retrieval
at our website http://www.iaa.es/ae/e2.html and
http://www.stsci.edu/science/starburst/ or on request from the authors at
[email protected]: To be published in ApJS. 28 pages and 12 figure
The Multitude of Unresolved Continuum Sources at 1.6 microns in Hubble Space Telescope images of Seyfert Galaxies
We examine 112 Seyfert galaxies observed by the Hubble Space Telescope (HST)
at 1.6 microns. We find that ~50% of the Seyfert 2.0 galaxies which are part of
the Revised Shapeley-Ames (RSA) Catalog or the CfA redshift sample contain
unresolved continuum sources at 1.6 microns. All but a couple of the Seyfert
1.0-1.9 galaxies display unresolved continuum sources. The unresolved sources
have fluxes of order a mJy, near-infrared luminosities of order 10^41 erg/s and
absolute magnitudes M_H ~-16. Comparison non-Seyfert galaxies from the RSA
Catalog display significantly fewer (~20%), somewhat lower luminosity nuclear
sources, which could be due to compact star clusters. We find that the
luminosities of the unresolved Seyfert 1.0-1.9 sources at 1.6 microns are
correlated with [OIII] 5007A and hard X-ray luminosities, implying that these
sources are non-stellar. Assuming a spectral energy distribution similar to
that of a Seyfert 2 galaxy, we estimate that a few percent of local spiral
galaxies contain black holes emitting as Seyferts at a moderate fraction, 10^-1
to 10^-4, of their Eddington luminosities. With increasing Seyfert type the
fraction of unresolved sources detected at 1.6 microns and the ratio of 1.6
microns to [OIII] fluxes tend to decrease. These trends are consistent with the
unification model for Seyfert 1 and 2 galaxies.Comment: accepted by Ap
Techno-economic feasibility of photovoltaic solar electrodialysis with bipolar membranes
Electrodialysis with bipolar membranes (EDBM) can transform concentrated brines into acids and bases through the application of an electric field. Nevertheless, the widespread use of EDBM is limited by its high energy consumption, typically based on fossil fuels. Yet, the integration of EDBM with renewable energy sources, like solar photovoltaic (PV), remains unexplored. This study presents a techno-economic analysis of PV-EDBM to produce NaOH and HCl from seawater reverse osmosis (SWRO) brines. An integrated PV-EDBM model was developed and applied to a hypothetical PV-EDBM plant located in the SWRO facility of Lampedusa (Italy). Results revealed that PV has no negative impact on the performance in terms of product concentration, specific energy consumption and current efficiency. Meanwhile, the levelized cost of NaOH for PV-EDBM was reduced by 20 % in comparison to the electrical grid mix, achieving 210 €·ton−1 NaOH on an annual average for PV-EDBM. Therefore, the investment associated with PV is offset by the benefits of reduced electricity costs from the grid. Consequently, EDBM emerges as a feasible solution to address resource scarcity, representing a significant step towards integrating renewable energies with advanced wastewater treatment technologies, thus paving the path to a greener future
The Variability of Seyfert 1.8 and 1.9 Galaxies at 1.6 microns
We present a study of Seyfert 1.5-2.0 galaxies observed at two epochs with
the Hubble Space Telescope (HST) at 1.6 microns. We find that unresolved
nuclear emission from 9 of 14 nuclei varies at the level of 10-40% on
timescales of 0.7-14 months, depending upon the galaxy. A control sample of
Seyfert galaxies lacking unresolved sources and galaxies lacking Seyfert nuclei
show less than 3% instrumental variation in equivalent aperture measurements.
This proves that the unresolved sources are non-stellar and associated with the
central pc of active galactic nuclei. Unresolved sources in Seyfert 1.8 and 1.9
galaxies are not usually detected in HST optical surveys, however high angular
resolution infrared observations will provide a way to measure time delays in
these galaxies.Comment: accepted by ApJLetters (emulateapj latex
Upholding the unified model for Active Galactic Nuclei: VLT/FORS2 spectropolarimetry of Seyfert 2 galaxies
The origin of the unification model for Active Galactic Nuclei (AGN) was the detection of broad hydrogen recombination lines in the optical polarized spectrum of the Seyfert 2 galaxy (Sy2) NGC 1068. Since then, a search for the hidden broad-line region (HBLR) of nearby Sy2s started, but polarized broad lines have only been detected in ?30–40% of the nearby Sy2s observed to date. Here we present new VLT/FORS2 optical spectropolarimetry of a sample of 15 Sy2s, including Compton-thin and Compton-thick sources. The sample includes six galaxies without previously published spectropolarimetry, some of them normally treated as non-hidden BLR (NHBLR) objects in the literature, four classified as NHBLR, and five as HBLR based on previous data. We report ?4? detections of a HBLR in 11 of these galaxies (73% of the sample) and a tentative detection in NGC 5793, which is Compton-thick according to the analysis of X-ray data performed here. Our results confirm that at least some NHBLRs are misclassified, bringing previous publications reporting differences between HBLR and NHBLR objects into question. We detect broad H? and H? components in polarized light for 10 targets, and just broad H? for NGC 5793 and NGC 6300, with line widths ranging between 2100 and 9600 km s?1. High bolometric luminosities and low column densities are associated with higher polarization degrees, but not necessarily with the detection of the scattered broad components
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