4,438 research outputs found
Solitary vortex couples in viscoelastic Couette flow
We report experimental observation of a localized structure, which is of a
new type for dissipative systems. It appears as a solitary vortex couple
("diwhirl") in Couette flow with highly elastic polymer solutions. A unique
property of the diwhirls is that they are stationary, in contrast to the usual
localized wave structures in both Hamiltonian and dissipative systems which are
stabilized by wave dispersion. It is also a new object in fluid dynamics - a
couple of vortices that build a single entity somewhat similar to a magnetic
dipole. The diwhirls arise as a result of a purely elastic instability through
a hysteretic transition at negligible Reynolds numbers. It is suggested that
the vortex flow is driven by the same forces that cause the Weissenberg effect.
The diwhirls have a striking asymmetry between the inflow and outflow, which is
also an essential feature of the suggested elastic instability mechanism.Comment: 9 pages (LaTeX), 5 Postscript figures, submitte
Obscured Activity: AGN, Quasars, Starbursts and ULIGs observed by the Infrared Space Observatory
Some of the most active galaxies in the Universe are obscured by large
quantities of dust and emit a substantial fraction of their bolometric
luminosity in the infrared. Observations of these infrared luminous galaxies
with the Infrared Space Observatory (ISO) have provided a relatively unabsorbed
view to the sources fuelling this active emission. The improved sensitivity,
spatial resolution and spectroscopic capability of ISO over its predecessor
Infrared Astronomical Satellite (IRAS), has enabled significant advances in the
understanding of the infrared properties of active galaxies. ISO surveyed a
wide range of active galaxies which, in the context of this review, includes
those powered by intense bursts of star-formation as well as those containing a
dominant active galactic nucleus (AGN). Mid infrared imaging resolved for the
first time the dust enshrouded nuclei in many nearby galaxies, while a new era
in infrared spectroscopy was opened by probing a wealth of atomic, ionic and
molecular lines as well as broad band features in the mid and far infrared.
This was particularly useful since it resulted in the understanding of the
power production, excitation and fuelling mechanisms in the nuclei of active
galaxies including the intriguing but so far elusive ultraluminous infrared
galaxies. Detailed studies of various classes of AGN and quasars greatly
improved our understanding of the unification scenario. Far-infrared imaging
and photometry also revealed the presence of a new very cold dust component in
galaxies and furthered our knowledge of the far-infrared properties of faint
starbursts, ULIGs and quasars. We summarise almost nine years of key results
based upon ISO data spanning the full range of luminosity and type of active
galaxies.Comment: Accepted for publication in 'ISO science legacy - a compact review of
ISO major achievements', Space Science Reviews - dedicated ISO issue. To be
published by Springer in 2005. 62 pages (low resolution figures version).
Higher resolution PDFs available from
http://users.physics.uoc.gr/~vassilis/papers/VermaA.pdf or
http://www.iso.vilspa.esa.es/science/SSR/Verma.pd
Clinical Outcomes of Intraoperative Radiation Therapy for Extremity Sarcomas
Purpose. Radiation of extremity lesions, a key component of limb-sparing therapy, presents particular challenges, with significant risks of toxicities. We sought to explore the efficacy of intraoperative radiation therapy (IORT) in the treatment of soft tissue sarcomas of the extremities. Patients. Between 1995 and 2001, 17 patients received IORT for soft tissue sarcomas of the extremities. Indications for IORT included recurrent tumors in a previously radiated field or tumors adjacent to critical structures. Results. Gross total resections were achieved in all 17 patients. Two patients experienced locoregional relapses, six patients recurred at metastatic sites, and one patient died without recurrence. Thirty-six month estimates for locoregional control, disease free survival, and overall survival were 86%, 50%, and 78%, respectively. IORT was extremely well tolerated, with no toxicities referable to IORT. Conclusions. For patients with soft tissue sarcomas of the extremities, IORT used as a boost to EBRT provides excellent local control, with limited acute toxicities
Hole Doping Evolution of the Quasiparticle Band in Models of Strongly Correlated Electrons for the High-T_c Cuprates
Quantum Monte Carlo (QMC) and Maximum Entropy (ME) techniques are used to
study the spectral function of the one band Hubbard model
in strong coupling including a next-nearest-neighbor electronic hopping with
amplitude . These values of parameters are chosen to improve the
comparison of the Hubbard model with angle-resolved photoemission (ARPES) data
for . A narrow quasiparticle (q.p.) band is observed in the
QMC analysis at the temperature of the simulation , both at and away
from half-filling. Such a narrow band produces a large accumulation of weight
in the density of states at the top of the valence band. As the electronic
density decreases further away from half-filling, the chemical
potential travels through this energy window with a large number of states, and
by it has crossed it entirely. The region near momentum
and in the spectral function is more sensitive to doping
than momenta along the diagonal from to . The evolution with
hole density of the quasiparticle dispersion contains some of the features
observed in recent ARPES data in the underdoped regime. For sufficiently large
hole densities the ``flat'' bands at cross the Fermi energy, a
prediction that could be tested with ARPES techniques applied to overdoped
cuprates. The population of the q.p. band introduces a {\it hidden} density in
the system which produces interesting consequences when the quasiparticles are
assumed to interact through antiferromagnetic fluctuations and studied with the
BCS gap equation formalism. In particular, a region of extended s-wave is found
to compete with d-wave in the overdoped regime, i.e. when the chemical
potential has almost entirely crossed the q.p.Comment: 14 pages, Revtex, with 13 embedded ps figures, submitted to Phys.
Rev. B., minor modifications in the text and in figures 1b, 2b, 3b, 4b, and
6
Ecological and environmental factors affecting the risk of tick-borne encephalitis in Europe, 2017 to 2021
Background: Tick-borne encephalitis (TBE) is a disease which can lead to severe neurological symptoms, caused by the TBE virus (TBEV). The natural transmission cycle occurs in foci and involves ticks as vectors and several key hosts that act as reservoirs and amplifiers of the infection spread. Recently, the incidence of TBE in Europe has been rising in both endemic and new regions. Aim: In this study we want to provide comprehensive understanding of the main ecological and environmental factors that affect TBE spread across Europe. Methods: We searched available literature on covariates linked with the circulation of TBEV in Europe. We then assessed the best predictors for TBE incidence in 11 European countries by means of statistical regression, using data on human infections provided by the European Surveillance System (TESSy), averaged between 2017 and 2021. Results: We retrieved data from 62 full-text articles and identified 31 different covariates associated with TBE occurrence. Finally, we selected eight variables from the best model, including factors linked to vegetation cover, climate, and the presence of tick hosts. Discussion: The existing literature is heterogeneous, both in study design and covariate types. Here, we summarised and statistically validated the covariates affecting the variability of TBEV across Europe. The analysis of the factors enhancing disease emergence is a fundamental step towards the identification of potential hotspots of viral circulation. Hence, our results can support modelling efforts to estimate the risk of TBEV infections and help decision-makers implement surveillance and prevention campaigns
VISIR/VLT mid-infrared imaging of Seyfert nuclei: Nuclear dust emission and the Seyfert-2 dichotomy
Half of the Seyfert-2 galaxies escaped detection of broad lines in their
polarised spectra observed so far. Some authors have suspected that these
non-HBLRs contain real Sy2 nuclei without intrinsic broad line region hidden
behind a dust torus. If this were true, then their nuclear structure would
fundamentally differ from that of Sy2s with polarised broad lines: in
particular, they would not be explained by orientation-based AGN unification.
Further arguments for two physically different Sy2 populations have been
derived from the warm and cool IRAS F25/F60 ratios. These ratios, however,
refer to the entire host galaxies and are unsuitable to conclusively establish
the absence of a nuclear dust torus. Instead, a study of the Seyfert-2
dichotomy should be performed on the basis of nuclear properties only. Here we
present the first comparison between [OIII] 5007A and mid-infrared imaging at
matching spatial resolution. Exploring the Seyfert-2 dichotomy we find that the
distributions of nuclear mid-infrared/[OIII] luminosity ratios are
indistinguishable for Sy1s and Sy2s with and without detected polarised broad
lines and irrespective of having warm or cool IRAS F25/F60 ratios. We find no
evidence for the existence of a population of real Sy2s with a deficit of
nuclear dust emission. Our results suggest 1) that all Seyfert nuclei possess
the same physical structure including the putative dust torus and 2) that the
cool IRAS colours are caused by a low contrast of AGN to host galaxy. Then the
Seyfert-2 dichotomy is explained in part by unification of non-HBLRs with
narrow-line Sy1s and to a larger rate by observational biases caused by a low
AGN/host contrast and/or an unfavourable scattering geometry.Comment: 11 pages, 6 figures, accepted by A&
Improved annotation of 3' untranslated regions and complex loci by combination of strand-specific direct RNA sequencing, RNA-seq and ESTs
The reference annotations made for a genome sequence provide the framework
for all subsequent analyses of the genome. Correct annotation is particularly
important when interpreting the results of RNA-seq experiments where short
sequence reads are mapped against the genome and assigned to genes according to
the annotation. Inconsistencies in annotations between the reference and the
experimental system can lead to incorrect interpretation of the effect on RNA
expression of an experimental treatment or mutation in the system under study.
Until recently, the genome-wide annotation of 3-prime untranslated regions
received less attention than coding regions and the delineation of intron/exon
boundaries. In this paper, data produced for samples in Human, Chicken and A.
thaliana by the novel single-molecule, strand-specific, Direct RNA Sequencing
technology from Helicos Biosciences which locates 3-prime polyadenylation sites
to within +/- 2 nt, were combined with archival EST and RNA-Seq data. Nine
examples are illustrated where this combination of data allowed: (1) gene and
3-prime UTR re-annotation (including extension of one 3-prime UTR by 5.9 kb);
(2) disentangling of gene expression in complex regions; (3) clearer
interpretation of small RNA expression and (4) identification of novel genes.
While the specific examples displayed here may become obsolete as genome
sequences and their annotations are refined, the principles laid out in this
paper will be of general use both to those annotating genomes and those seeking
to interpret existing publically available annotations in the context of their
own experimental dataComment: 44 pages, 9 figure
On the origin of [Ne II] emission in young stars: mid-infrared and optical observations with the Very Large Telescope
{Abridged version for ArXiv}. We provide direct constraints on the origin of
the [Ne II] emission in 15 young stars using high-spatial and spectral
resolution observations with VISIR at the VLT that allow us to study the
kinematics of the emitting gas. In addition we compare the [Ne II] line with
optical forbidden lines observed for three stars with UVES. The [Ne II] line
was detected in 7 stars, among them the first confirmed detection of [Ne II] in
a Herbig Be star, V892 Tau. In four cases, the large blueshifted lines indicate
an origin in a jet. In two stars, the small shifts and asymmetric profiles
indicate an origin in a photo-evaporative wind. CoKu Tau 1, seen close to
edge-on, shows a spatially unresolved line centered at the stellar rest
velocity, although cross-dispersion centroids move within 10 AU from one side
of the star to the other as a function of wavelength. The line profile is
symmetric with wings extending up to about +-80 km/s. The origin of the [Ne II]
line could either be due to the bipolar jet or to the disk. For the stars with
VLT-UVES observations, in several cases, the optical forbidden line profiles
and shifts are very similar to the profile of the [Ne II] line, suggesting that
the lines are emitted in the same region. A general trend observed with VISIR
is a lower line flux when compared with the fluxes obtained with Spitzer. We
found no correlation between the line full-width at half maximum and the line
peak velocity. The [Ne II] line remains undetected in a large part of the
sample, an indication that the emission detected with Spitzer in those stars is
likely extended.Comment: Accepted for publication in Astronomy & Astrophysics; revised
version: corrected minor typos, corrected center values (col 3) for CoKuTau1
in Table
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