3,585 research outputs found
Positive solutions of nonlinear fourth-order boundary-value problems with local and non-local boundary conditions
We establish new existence results for multiple positive solutions of fourth-order nonlinear equations which model deflections of an elastic beam. We consider the widely studied boundary conditions corresponding to clamped and hinged ends and many non-local boundary conditions, with a unified approach. Our method is to show that each boundary-value problem can be written as the same type of perturbed integral equation, in the space , involving a linear functional but, although we seek positive solutions, the functional is not assumed to be positive for all positive . The results are new even for the classic boundary conditions of clamped or hinged ends when , because we obtain sharp results for the existence of one positive solution; for multiple solutions we seek optimal values of some of the constants that occur in the theory, which allows us to impose weaker assumptions on the nonlinear term than in previous works. Our non-local boundary conditions contain multi-point problems as special cases and, for the first time in fourth-order problems, we allow coefficients of both signs
The central region of the Fornax cluster -- II. Spectroscopy and radial velocities of member and background galaxies
Radial velocities of 94 galaxies brighter than about V_tot = 20 mag in the
direction of the central Fornax cluster have been measured. Except for 8 Fornax
members, all galaxies lie in the background. Among the 8 members, there are 5
nucleated dwarf ellipticals that are already listed in the FCC (Ferguson 1989,
AJ 98, 367). Two of the 3 ``new'' members are very compact and have surface
brightnesses comparable to globular clusters, however their luminosities are in
the range of dwarf elliptical nuclei. The measured line indices (especially
Mg2, H beta, and iron) of the brighter of the compact objects suggest a solar
metallicity, whereas the fainter compact object as well as the dE,Ns have line
indices that are similar to those of old metal-poor globular clusters (GCs).
However, with these data it is not possible to clearly classify the compact
objects either as very bright globular clusters, isolated nuclei of dE,Ns, or
even compact ellipticals. A background galaxy cluster at z = 0.11 has been
found just behind the center of the Fornax cluster. This explains the excess
population of galaxies reported in Paper I. The brightest galaxy of the
background cluster lies only 1.1 arcmin south of NGC 1399 and is comparable in
absolute luminosity with the central Fornax galaxy itself.Comment: 12 pages, LaTeX2e, uses aa.cls, including 9 PostScript figures;
accepted for publication in A&AS, also available at
http://www.astro.puc.cl/~mhilker/publication.htm
Nonzero solutions of Hammerstein integral equations with discontinuous kernels
AbstractUsing the theory of fixed point index, we establish new results for the existence of nonzero solutions of integral equations of the form u(t)=â«Gk(t,s)f(s,u(s))ds, where G is a compact set in Rn and k changes sign, so positive solutions may not exist, f satisfies CarathĂ©odory conditions and k may be discontinuous. We apply our results to prove the existence of nontrivial solutions of some nonlocal boundary value problems
New results related to a conjecture of Manickam and Singhi
In 1998 Manickam and Singhi conjectured that for every positive integer
and every , every set of real numbers whose sum is nonnegative
contains at least subsets of size whose sums are
nonnegative. In this paper we establish new results related to this conjecture.
We also prove that the conjecture of Manickam and Singhi does not hold for
Wide Field Imaging. I. Applications of Neural Networks to object detection and star/galaxy classification
[Abriged] Astronomical Wide Field Imaging performed with new large format CCD
detectors poses data reduction problems of unprecedented scale which are
difficult to deal with traditional interactive tools. We present here NExt
(Neural Extractor): a new Neural Network (NN) based package capable to detect
objects and to perform both deblending and star/galaxy classification in an
automatic way. Traditionally, in astronomical images, objects are first
discriminated from the noisy background by searching for sets of connected
pixels having brightnesses above a given threshold and then they are classified
as stars or as galaxies through diagnostic diagrams having variables choosen
accordingly to the astronomer's taste and experience. In the extraction step,
assuming that images are well sampled, NExt requires only the simplest a priori
definition of "what an object is" (id est, it keeps all structures composed by
more than one pixels) and performs the detection via an unsupervised NN
approaching detection as a clustering problem which has been thoroughly studied
in the artificial intelligence literature. In order to obtain an objective and
reliable classification, instead of using an arbitrarily defined set of
features, we use a NN to select the most significant features among the large
number of measured ones, and then we use their selected features to perform the
classification task. In order to optimise the performances of the system we
implemented and tested several different models of NN. The comparison of the
NExt performances with those of the best detection and classification package
known to the authors (SExtractor) shows that NExt is at least as effective as
the best traditional packages.Comment: MNRAS, in press. Paper with higher resolution images is available at
http://www.na.astro.it/~andreon/listapub.htm
Photometric observations of Southern Abell Cluster Redshifts Survey Clusters: Structure of galaxies in the inner region of clusters of galaxies
We analyze photometric properties of 1384 cluster galaxies as a function of
the normalized distance to cluster center. These galaxies were selected in the
central region ( 0.8) of 14 southern Abell clusters chosen from
the Southern Abell Cluster Redshifts Survey (SARS). For 507 of these galaxies
we also obtained their luminosity profiles. We have studied the
morphology-clustercentric distance relation on the basis of the shape parameter
of the S\'ersic's law. We also have analyzed the presence of a possible
segregation in magnitude for both, the galaxy total luminosity and that of
their components (i.e. the bulge and the disk).
Results show a marginal ( level) decrease of the total luminosity as
a function of normalized radius. However, when bulges are analyzed separately,
a significant luminosity segregation is found ( and for
galaxies in projection and member galaxies respectively). The fraction of
bulges brighter than is three times larger in the core of
clusters than in the outer region. Our analysis of the disk component suggests
that disks are, on average, less luminous in the cluster core than at
. In addition, we found that the magnitude-size relation as
a function of indicates (at level) that disks are smaller
and centrally brighter in the core of clusters. However, the Kormendy relation
(the bulge magnitude-size relation) appears to be independent of environment.Comment: To appear in the A
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