249 research outputs found
On a functional satisfying a weak Palais-Smale condition
In this paper we study a quasilinear elliptic problem whose functional
satisfies a weak version of the well known Palais-Smale condition. An existence
result is proved under general assumptions on the nonlinearities.Comment: 18 page
Nonlinear Klein-Gordon-Maxwell systems with Neumann boundary conditions on a Riemannian manifold with boundary
Let (M,g) be a smooth compact, n dimensional Riemannian manifold, n=3,4 with
smooth n-1 dimensional boundary. We search the positive solutions of the
singularly perturbed Klein Gordon Maxwell Proca system with homogeneous Neumann
boundary conditions or for the singularly perturbed Klein Gordon Maxwell system
with mixed Dirichlet Neumann homogeneous boundary conditions. We prove that
stable critical points of the mean curvature of the boundary generates
solutions when the perturbation parameter is sufficiently small.Comment: arXiv admin note: text overlap with arXiv:1410.884
Cosmic Evolution of Stellar Disk Truncations: From z~1 to the Local Universe
We have conducted the largest systematic search so far for stellar disk
truncations in disk-like galaxies at intermediate redshift (z<1.1), using the
Great Observatories Origins Deep Survey South (GOODS-S) data from the Hubble
Space Telescope - ACS. Focusing on Type II galaxies (i.e. downbending profiles)
we explore whether the position of the break in the rest-frame B-band radial
surface brightness profile (a direct estimator of the extent of the disk where
most of the massive star formation is taking place), evolves with time. The
number of galaxies under analysis (238 of a total of 505) is an order of
magnitude larger than in previous studies. For the first time, we probe the
evolution of the break radius for a given stellar mass (a parameter well suited
to address evolutionary studies). Our results suggest that, for a given stellar
mass, the radial position of the break has increased with cosmic time by a
factor 1.3+/-0.1 between z~1 and z~0. This is in agreement with a moderate
inside-out growth of the disk galaxies in the last ~8 Gyr. In the same period
of time, the surface brightness level in the rest-frame B-band at which the
break takes place has increased by 3.3+/-0.2 mag/arcsec^2 (a decrease in
brightness by a factor of 20.9+/-4.2). We have explored the distribution of the
scale lengths of the disks in the region inside the break, and how this
parameter relates to the break radius. We also present results of the
statistical analysis of profiles of artificial galaxies, to assess the
reliability of our results.Comment: 22 pages, 14 figures, accepted for publication in ApJ. Figures 1, 3
and 6 have somehow downgraded resolution to match uploading requirement
Radial Distribution of Near-UV Flux in Disc Galaxies in the range 0<z<1
(Abridged) The goal of this paper is to quantify the changes on the SF
distribution within the disc galaxies in the last ~8 Gyr. We use as a proxy for
the SF radial profile the Near-UV surface brightness distributions, allowing
suitably for extinction. We compare the effective radii (R_eff) and
concentration of the flux distribution in the rest-frame Near-UV for a sample
of 270 galaxies in the range 0<z<1. This radial distribution is compared to
that measured in the rest-frame B-band, which traces older stellar populations.
The analysis is performed using deep, high resolution, multi-band images from
GALEX, SDSS, and HST/ACS - GOODS-South. The relation R_eff(NUV)- M* suffers a
moderate change between z~1 and z~0: at a fixed stellar mass of 1E10 M_sun,
galaxies increase their effective radii by a factor 1.18+/-0.06. Median
profiles in NUV show signs of truncation at R~R_eff, and median colour profiles
(NUV-B) show a minimum (a "bluest" point) also around R~1-1.5 R_eff. The
distributions of NUV flux are more compact at z~1 than nowadays, in terms of
the fraction of flux enclosed in a specific radius (in kpc). Our results
indicate that the SF surface density has decreased dramatically in discs since
z~1, and this decline has been more intense in the central parts (<~R_eff) of
the galaxies. In addition, our data suggest that the bulges/pseudo-bulges have
grown in surface brightness with regard to the discs since z~1.Comment: 26 pages, 21 figures, accepted for publication in Astronomy &
Astrophysics on March 21s
Anti-truncated stellar light profiles in the outer regions of STAGES spiral galaxies: bulge or disc related?
We present a comparison of azimuthally averaged radial surface brightness
mu(r) profiles and analytical bulge-disc decompositions (de Vaucouleurs,
r^(1/4) bulge plus exponential disc) for spiral galaxies using Hubble Space
Telescope/Advanced Camera for Surveys V-band imaging from the Space Telescope
A901/2 Galaxy Evolution Survey (STAGES). In the established classification
scheme, antitruncated mu(r) profiles (Type III) have a broken exponential disc
with a shallower region beyond the break radius r_brk. The excess light at
large radii (r > r_brk) can either be caused by an outer exponential disc (Type
III-d) or an extended spheroidal component (Type III-s). Using our comparisons,
we determine the contribution of bulge light at r > r_brk for a large sample of
78 (barred/unbarred, Sa-Sd) spiral galaxies with outer disc antitruncations
(mu_brk > 24 mag arcsec^-2). In the majority of cases (~85 per cent), evidence
indicates that excess light at r > r_brk is related to an outer shallow disc
(Type III-d). Here, the contribution of bulge light at r > r_brk is either
negligible (~70 per cent) or too little to explain the antitruncation (~15 per
cent). However in the latter cases, bulge light can affect the measured disc
properties (e.g. mu_brk, outer scalelength). In the remaining cases (~15 per
cent), light at r > r_brk is dominated by the bulge (Type III-s). Here, for
most cases the bulge profile dominates at all radii and only occasionally (3
galaxies, ~5 per cent) extends beyond that of a dominant disc and explains the
excess light at r > r_brk. We thus conclude that in the vast majority of cases
antitruncated outer discs cannot be explained by bulge light and thus remain a
pure disc phenomenon.Comment: Accepted to MNRA
Hybrid fibroin/polyurethane small-diameter vascular grafts: from fabrication to in vivo preliminary assessment
To address the need of alternatives to autologous vessels for small-calibre vascular applications (e.g. cardiac surgery), a bio-hybrid semi-degradable material composed of silk fibroin (SF) and polyurethane (Silkothane (R)) was herein used to fabricate very small-calibre grafts (o(in) = 1.5 mm) via electrospinning. Bio-hybrid grafts were in vitro characterized in terms of morphology and mechanical behaviour, and compared to similar grafts of pure SF. Similarly, two native vessels from a rodent model (abdominal aorta and vena cava) were harvested and characterized. Preliminary implants were performed on Lewis rats to confirm the suitability of Silkothane (R) grafts for small-calibre applications, specifically as aortic insertion and femoral shunt. The manufacturing process generated pliable grafts consisting of a randomized fibrous mesh and exhibiting similar geometrical features to rat aortas. Both Silkothane (R) and pure SF grafts showed radial compliances in the range from 1.37 +/- 0.86 to 1.88 +/- 1.01% 10(-2) mmHg(-1), lower than that of native vessels. The Silkothane (R) small-calibre devices were also implanted in rats demonstrating to be adequate for vascular applications; all the treated rats survived the surgery for three months after implantation, and 16 rats out of 17 (94%) still showed blood flow inside the graft at sacrifice. The obtained results lay the basis for a deeper investigation of the interaction between the Silkothane (R) graft and the implant site, which may deal with further analysis on the potentialities in terms of degradability and tissue formation, on longer time-points
On the stability of standing waves of Klein-Gordon equations in a semiclassical regime
We investigate the orbital stability and instability of standing waves for
two classes of Klein-Gordon equations in the semi-classical regime.Comment: 9 page
The environmental dependence of the structure of outer galactic discs in STAGES spiral galaxies
We present an analysis of V-band radial surface brightness profiles for
spiral galaxies from the field and cluster environments using Hubble Space
Telescope/Advanced Camera for Surveys imaging and data from the Space Telescope
A901/2 Galaxy Evolution Survey (STAGES). We use a large sample of ~330 face-on
to intermediately inclined spiral galaxies and assess the effect of the galaxy
environment on the azimuthally averaged radial surface brightness mu profiles
for each galaxy in the outer stellar disc (24 < mu < 26.5 mag per sq arcsec).
For galaxies with a purely exponential outer disc (~50 per cent), we determine
the significance of an environmental dependence on the outer disc scalelength
h_out. For galaxies with a broken exponential in their outer disc, either
down-bending (truncation, ~10 per cent) or up-bending (anti-truncation, ~40 per
cent), we measure the strength T (outer-to-inner scalelength ratio,
log_10(h_out/h_in) of the mu breaks and determine the significance of an
environmental dependence on break strength T. Surprisingly, we find no evidence
to suggest any such environmental dependence on either outer disc scalelength
h_out or break strength T, implying that the galaxy environment is not
affecting the stellar distribution in the outer stellar disc. We also find that
for galaxies with small effective radii (r_e < 3 kpc) there is a lack of outer
disc truncations in both the field and cluster environments. Our results
suggest that the stellar distribution in the outer disc of spiral galaxies is
not significantly affected by the galaxy environment.Comment: Accepted to MNRAS. Appendix A available at
http://www.nottingham.ac.uk/~ppxdtm/STAGES_profiles_appendix.pd
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