4,728 research outputs found
Compton reflection and iron fluorescence in BeppoSAX observations of Seyfert type 1 galaxies
A sample of nine bright Seyfert 1 and NELG type galaxies, observed with
BeppoSAX, is analyzed to assess on a truly broad band basis (0.1-200 keV) the
issue of the spectral contributions of Compton reflection and iron line
fluorescence from circumnuclear gas. The empirical description adopted for the
direct continuum is the commonly used power law with an exponential cut-off.
The most direct test of the theoretical predictions, namely that the equivalent
width of the line, Walpha, and the strength R of the reflection relative to the
direct continuum are closely related to each other, gives a substantially
positive result, that is their mean ratio is very close to expectation, and
only a modest spread in the iron abundance seems implied. The existence of a
steep correlation between R and the slope Gamma of the power law is not
confirmed. A weak evidence is found that the existence of a very shallow trend
to increase on average with Gamma cannot be altogether excluded in both R and
Walpha, but needs to be tested with a larger sample. The energy Ef in the
exponential cut-off spans a range from about 80 to more than 300 keV. A
possible correlation is found, with Ef increasing on average with Gamma: if
ignored, for instance by keeping Ef at a fixed value in a sample study, it
could be cause of artificial steepening in a correlation between R and Gamma.Comment: accepted for publication in A&
Investigation of pulsed laser induced dewetting in nanoscopic metal films
Hydrodynamic pattern formation (PF) and dewetting resulting from pulsed laser
induced melting of nanoscopic metal films have been used to create spatially
ordered metal nanoparticle arrays with monomodal size distribution on
SiO_{\text{2}}/Si substrates. PF was investigated for film thickness h\leq7 nm
< laser absorption depth \sim11 nm and different sets of laser parameters,
including energy density E and the irradiation time, as measured by the number
of pulses n. PF was only observed to occur for E\geq E_{m}, where E_{m} denotes
the h-dependent threshold energy required to melt the film. Even at such small
length scales, theoretical predictions for E_{m} obtained from a
continuum-level lumped parameter heat transfer model for the film temperature,
coupled with the 1-D transient heat equation for the substrate phase, were
consistent with experimental observations provided that the thickness
dependence of the reflectivity of the metal-substrate bilayer was incorporated
into the analysis. The spacing between the nanoparticles and the particle
diameter were found to increase as h^{2} and h^{5/3} respectively, which is
consistent with the predictions of the thin film hydrodynamic (TFH) dewetting
theory. These results suggest that fast thermal processing can lead to novel
pattern formation, including quenching of a wide range of length scales and
morphologies.Comment: 36 pages, 11 figures, 1 tabl
Strongly nonlinear dynamics of electrolytes in large ac voltages
We study the response of a model micro-electrochemical cell to a large ac
voltage of frequency comparable to the inverse cell relaxation time. To bring
out the basic physics, we consider the simplest possible model of a symmetric
binary electrolyte confined between parallel-plate blocking electrodes,
ignoring any transverse instability or fluid flow. We analyze the resulting
one-dimensional problem by matched asymptotic expansions in the limit of thin
double layers and extend previous work into the strongly nonlinear regime,
which is characterized by two novel features - significant salt depletion in
the electrolyte near the electrodes and, at very large voltage, the breakdown
of the quasi-equilibrium structure of the double layers. The former leads to
the prediction of "ac capacitive desalination", since there is a time-averaged
transfer of salt from the bulk to the double layers, via oscillating diffusion
layers. The latter is associated with transient diffusion limitation, which
drives the formation and collapse of space-charge layers, even in the absence
of any net Faradaic current through the cell. We also predict that steric
effects of finite ion sizes (going beyond dilute solution theory) act to
suppress the strongly nonlinear regime in the limit of concentrated
electrolytes, ionic liquids and molten salts. Beyond the model problem, our
reduced equations for thin double layers, based on uniformly valid matched
asymptotic expansions, provide a useful mathematical framework to describe
additional nonlinear responses to large ac voltages, such as Faradaic
reactions, electro-osmotic instabilities, and induced-charge electrokinetic
phenomena.Comment: 30 pages, 17 eps-figures, RevTe
Understanding the evolution and spread of chikungunya virus in the Americas using complete genome sequences
Local transmission of chikungunya virus (CHIKV) was first
detected in the Americas in December 2013, after which it spread
rapidly throughout the Caribbean islands and American mainland,
causing a major chikungunya fever epidemic. Previous
phylogenetic analysis of CHIKV from a limited number of
countries in the Americas suggests that an Asian genotype strain
was responsible, except in Brazil where both Asian and
East/Central/South African (ECSA) lineage strains were detected.
In this study, we sequenced thirty-three complete CHIKV genomes
from viruses isolated in 2014 from fourteen Caribbean islands,
the Bahamas and two mainland countries in the Americas.
Phylogenetic analyses confirmed that they all belonged to the
Asian genotype and clustered together with other Caribbean and
mainland sequences isolated during the American outbreak,
forming an 'Asian/American' lineage defined by two amino acid
substitutions, E2 V368A and 6K L20M, and divided into two
well-supported clades. This lineage is estimated to be evolving
at a mean rate of 5 x 10-4 substitutions per site per year (95%
higher probability density, 2.9-7.9 x 10-4) and to have arisen
from an ancestor introduced to the Caribbean (most likely from
Oceania) in about March 2013, 9 months prior to the first report
of CHIKV in the Americas. Estimation of evolutionary rates for
individual gene regions and selection analyses indicate that (in
contrast to the Indian Ocean Lineage that emerged from the ECSA
genotype followed by adaptive evolution and with a significantly
higher substitution rate) the evolutionary dynamics of the
Asian/American lineage are very similar to the rest of the Asian
genotype and natural selection does not appear to have played a
major role in its emergence. However, several codon sites with
evidence of positive selection were identified within the
non-structural regions of Asian genotype sequences outside of
the Asian/American lineage
A Chandra Survey of the Nearest ULIRGs: Obscured AGN or Super-Starbursts?
We present initial results from a Chandra survey of a complete sample of the
8 nearest (z <= 0.04) ultraluminous IR galaxies (ULIRGs), and also include the
IR-luminous galaxy NGC 6240 for comparison. In this paper we use the hard
X-rays (2-8 kev) to search for the possible presence of an obscured AGN. In
every case, a hard X-ray source is detected in the nuclear region. If we divide
the sample according to the optical/IR spectroscopic classification (starburst
vs. AGN), we find that the 5 ``starburst'' ULIRGs have hard X-ray luminosities
about an order-of-magnitude smaller than the 3 ``AGN'' ULIRGs. NGC 6240 has an
anomalously high hard X-ray luminosity compared to the ``starburst'' ULIRGs.
The Fe Kalpha line is convincingly detected in only two ULIRGs. The weakness of
the Fe-K emission in these ULIRGs generally suggests that the hard X-ray
spectrum is not dominated by reflection from high N_H neutral material. The
hard X-ray continuum flux ranges from a few X 10^3 to a few X 10^-5 of the
far-IR flux, similar to values in pure starbursts, and several
orders-of-magnitude smaller than in Compton-thin AGN. The upper limits on the
ratio of the Fe Kalpha to far-IR flux are below the values measured in
Compton-thick type 2 Seyfert galaxies. While very large column densities of
molecular gas are observed in the nuclei of these galaxies, we find no evidence
that the observed X-ray sources are obscured by Compton-thick material. Thus,
our new hard X-ray data do not provide direct evidence that powerful ``buried
quasars'' dominate the overall energetics of most ultraluminous infrared
galaxies.Comment: 22 pages, 8 figures, formatted with emulateapj.sty, accepted for
publication in August 2003 Ap
HSC-CLAUDS survey: The star formation rate functions since z ~ 2 and comparison with hydrodynamical simulations
Star formation rate functions (SFRFs) give an instantaneous view of the
distribution of star formation rates (SFRs) in galaxies at different epochs.
They are a complementary and more stringent test for models than the galaxy
stellar mass function, which gives an integrated view of the past star
formation activity. However, the exploration of SFRFs has been limited thus far
due to difficulties in assessing the SFR from observed quantities and probing
the SFRF over a wide range of SFRs. We overcome these limitations thanks to an
original method that predicts the infrared luminosity from the rest-frame
UV/optical color of a galaxy and then its SFR over a wide range of stellar
masses and redshifts. We applied this technique to the deep imaging survey
HSC-CLAUDS combined with near-infrared and UV photometry. We provide the first
SFR functions with reliable measurements in the high- and low-SFR regimes up to
and compare our results with previous observations and four
state-of-the-art hydrodynamical simulations.Comment: 29 pages, 19 figure
Stromal integrin α11 regulates PDGFR-β signaling and promotes breast cancer progression
Cancer-associated fibroblasts (CAFs) are key actors in modulating the progression of many solid tumors, such as breast cancer (BC). Herein, we identify an integrin α11/PDGFRβ–positive CAF subset displaying tumor-promoting features in BC. In the preclinical MMTV-PyMT mouse model, integrin α11 deficiency led to a drastic reduction of tumor progression and metastasis. A clear association between integrin α11 and PDGFRβ was found at both transcriptional and histological levels in BC specimens. High stromal integrin α11/PDGFRβ expression was associated with high grades and poorer clinical outcome in human BC patients. Functional assays using 5 CAF subpopulations (1 murine, 4 human) revealed that integrin α11 promotes CAF invasion and CAF-induced tumor cell invasion upon PDGF-BB stimulation. Mechanistically, the proinvasive activity of integrin α11 relies on its ability to interact with PDGFRβ in a ligand-dependent manner and to promote its downstream JNK activation, leading to the production of tenascin C, a proinvasive matricellular protein. Pharmacological inhibition of PDGFRβ and JNK impaired tumor cell invasion induced by integrin α11+ CAFs. Collectively, our study uncovers an integrin α11+ subset of protumoral CAFs that exploits the PDGFRβ/JNK signaling axis to promote tumor invasiveness in BC.publishedVersio
A Region of Violent Star Formation in the Irr Galaxy IC 10: Structure and Kinematics of Ionized and Neutral Gas
We have used observations of the galaxy IC 10 at the 6-m telescope of the
Special Astrophysical Observatory with the SCORPIO focal reducer in the
Fabry-Perot interferometer mode and with the MPFS spectrograph to study the
structure and kinematics of ionized gas in the central region of current
intense star formation. Archive VLA 21-cm observations are used to analyze the
structure and kinematics of neutral gas in this region. High-velocity wings of
the H-alpha and [SII] emission lines were revealed in the inner cavity of the
nebula HL 111 and in other parts of the complex of violent star formation. We
have discovered local expanding neutral-gas shells around the nebulae HL 111
and HL 106.Comment: 22 pages, 10 figures; accepted in Astronomy Report
Light emission from a scanning tunneling microscope: Fully retarded calculation
The light emission rate from a scanning tunneling microscope (STM) scanning a
noble metal surface is calculated taking retardation effects into account. As
in our previous, non-retarded theory [Johansson, Monreal, and Apell, Phys. Rev.
B 42, 9210 (1990)], the STM tip is modeled by a sphere, and the dielectric
properties of tip and sample are described by experimentally measured
dielectric functions. The calculations are based on exact diffraction theory
through the vector equivalent of the Kirchoff integral. The present results are
qualitatively similar to those of the non-retarded calculations. The light
emission spectra have pronounced resonance peaks due to the formation of a
tip-induced plasmon mode localized to the cavity between the tip and the
sample. At a quantitative level, the effects of retardation are rather small as
long as the sample material is Au or Cu, and the tip consists of W or Ir.
However, for Ag samples, in which the resistive losses are smaller, the
inclusion of retardation effects in the calculation leads to larger changes:
the resonance energy decreases by 0.2-0.3 eV, and the resonance broadens. These
changes improve the agreement with experiment. For a Ag sample and an Ir tip,
the quantum efficiency is 10 emitted photons in the visible
frequency range per tunneling electron. A study of the energy dissipation into
the tip and sample shows that in total about 1 % of the electrons undergo
inelastic processes while tunneling.Comment: 16 pages, 10 figures (1 ps, 9 tex, automatically included); To appear
in Phys. Rev. B (15 October 1998
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