93 research outputs found
Hubble Space Telescope NICMOS Imaging of W3 IRS 5: A Trapezium in the Making?
We present Hubble Space Telescope NICMOS imaging of W3 IRS 5, a binary
high-mass protostar. In addition to the two protostars, NICMOS images taken in
the F222M and F160W filters show three new 2.22 micron sources with very red
colors; these sources fall within a region 5600 AU in diameter, and are
coincident with a 100 solar mass dense molecular clump. Two additional point
sources are found within 0.4'' (800 AU) of one of the high-mass protostars;
these may be stellar companions or unresolved emission knots from an outflow.
We propose that these sources constitute a nascent Trapezium system in the
center of the W3 IRS 5 cluster containing as many as five proto OB stars. This
would be the first identification of a Trapezium still deeply embedded in its
natal gas.Comment: accepted to ApJ letter
Diameters of Open Star Clusters
The present paper presents a tabulation of data on all 600 Galactic open
clusters for which it is presently possible to calculate linear diameters. As
expected, the youngest `clusters' with ages < 15 Myr, contain a significant
(greater than or equal to 20%) admixture of associations. Among
intermediate-age clusters, with ages in the range 15 Myr to 1.5 Gyr, the median
cluster diameter is found to increase with age. Small compact clusters are rare
among objects with ages > 1.5 Gyr. Open clusters with ages > 1 Gyr appear to
form what might be termed a `cluster thick disk', part of which consistst of
objects that were probably captured gravitationally by the main body of the
Galaxy.Comment: Astronomical Journal, in pres
Geometrical Ambiguity of Pair Statistics. I. Point Configurations
Point configurations have been widely used as model systems in condensed
matter physics, materials science and biology. Statistical descriptors such as
the -body distribution function is usually employed to characterize
the point configurations, among which the most extensively used is the pair
distribution function . An intriguing inverse problem of practical
importance that has been receiving considerable attention is the degree to
which a point configuration can be reconstructed from the pair distribution
function of a target configuration. Although it is known that the pair-distance
information contained in is in general insufficient to uniquely determine
a point configuration, this concept does not seem to be widely appreciated and
general claims of uniqueness of the reconstructions using pair information have
been made based on numerical studies. In this paper, we introduce the idea of
the distance space, called the space. The pair distances of a
specific point configuration are then represented by a single point in the
space. We derive the conditions on the pair distances that can be
associated with a point configuration, which are equivalent to the
realizability conditions of the pair distribution function . Moreover, we
derive the conditions on the pair distances that can be assembled into distinct
configurations. These conditions define a bounded region in the
space. By explicitly constructing a variety of degenerate point configurations
using the space, we show that pair information is indeed
insufficient to uniquely determine the configuration in general. We also
discuss several important problems in statistical physics based on the
space.Comment: 28 pages, 8 figure
Deficit of wide binaries in the eta Chamaeleontis young cluster
We have carried out a sensitive high-resolution imaging survey of stars in
the young (6-8 Myr), nearby (97 pc) compact cluster around eta Chamaeleontis to
search for stellar and sub-stellar companions. Given its youth and proximity,
any sub-stellar companions are expected to be luminous, especially in the near
infrared, and thus easier to detect next to their parent stars. Here, we
present VLT/NACO adaptive optics imaging with companion detection limits for 17
eta Cha cluster members, and follow-up VLT/ISAAC near-infrared spectroscopy for
companion candidates. The widest binary detected is ~0.2", corresponding to the
projected separation 20 AU, despite our survey being sensitive down to
sub-stellar companions outside 0.3", and planetary mass objects outside 0.5".
This implies that the stellar companion probability outside 0.3" and the brown
dwarf companion probability outside 0.5" are less than 0.16 with 95%
confidence. We compare the wide binary frequency of eta Cha to that of the
similarly aged TW Hydrae association, and estimate the statistical likelihood
that the wide binary probability is equal in both groups to be < 2e-4. Even
though the eta Cha cluster is relatively dense, stellar encounters in its
present configuration cannot account for the relative deficit of wide binaries.
We thus conclude that the difference in wide binary probability in these two
groups provides strong evidence for multiplicity properties being dependent on
environment. In two appendices we derive the projected separation probability
distribution for binaries, used to constrain physical separations from observed
projected separations, and summarize statistical tools useful for multiplicity
studies.Comment: Accepted by ApJ. 13 pages, 10 figure
A catalog of Kazarian galaxies
The entire Kazarian galaxies (KG) catalog is presented which combines
extensive new measurements of their optical parameters with a literature and
database search. The measurements were made using images extracted from the
STScI Digitized Sky Survey (DSS) of Jpg(blue), Fpg(red) and Ipg(NIR) band
photographic sky survey plates obtained by the Palomar and UK Schmidt
telescopes. We provide accurate coordinates, morphological type, spectral and
activity classes, blue apparent diameters, axial ratios, position angles, red,
blue and NIR apparent magnitudes, as well as counts of neighboring objects in a
circle of radius 50 kpc from centers of KG. Special attention was paid to the
individual descriptions of the galaxies in the original Kazarian lists, which
clarified many cases of misidentifications of the objects, particularly among
interacting systems. The total number of individual Kazarian objects in the
database is now 706. We also include the redshifts which are now available for
404 galaxies and the 2MASS infrared magnitudes for 598 KG. The database also
includes extensive notes, which summarize information about the membership of
KG in different systems of galaxies, and about revised activity classes and
redshifts. An atlas of several interesting subclasses of KG is also presented.Comment: 15 pages, 5 figures, 1 table, Accepted in Astrophysics, Vol. 53, No.
1, 2010 (English translation of Astrofizika
The metastasis associated protein S100A4: role in tumour progression and metastasis
The metastasis associated protein S100A4 is a small calcium binding protein that is associated with metastatic tumors and appears to be a molecular marker for clinical prognosis. Below we discuss its biochemical properties and possible cellular functions in metastasis including cell motility, invasion, apoptosis, angiogenesis and differentiation
Guidelines and Recommendations on the Use of Higher OrderFinite Elements for Bending Analysis of Plates
This paper compares and evaluates various plate finite elements to analyse the static response of thick and thin plates subjected to different loading and boundary conditions. Plate elements are based on different assumptions for the displacement distribution along the thickness direction. Classical (Kirchhoff and Reissner-Mindlin), refined (Reddy and Kant), and other higher-order displacement fields are implemented up to fourth-order expansion. The Unified Formulation UF by the first author is used to derive finite element matrices in terms of fundamental nuclei which consist of 3 × 3 arrays. The MITC4 shear-locking free type formulation is used for the FE approximation. Accuracy of a given plate element is established in terms of the error vs. thickness-to-length parameter. A significant number of finite elements for plates are implemented and compared using displacement and stress variables for various plate problems. Reduced models that are able to detect the 3D solution are built and a Best Plate Diagram (BPD) is introduced to give guidelines for the construction of plate theories based on a given accuracy and number of terms. It is concluded that the UF is a valuable tool to establish, for a given plate problem, the most accurate FE able to furnish results within a certain accuracy range. This allows us to obtain guidelines and recommendations in building refined elements in the bending analysis of plates for various geometries, loadings, and boundary conditions
Cosmology and Cosmogony in a Cyclic Universe
In this paper we discuss the properties of the quasi-steady state
cosmological model (QSSC) developed in 1993 in its role as a cyclic model of
the universe driven by a negative energy scalar field. We discuss the origin of
such a scalar field in the primary creation process first described by F. Hoyle
and J. V. Narlikar forty years ago. It is shown that the creation processes
which takes place in the nuclei of galaxies are closely linked to the high
energy and explosive phenomena, which are commonly observed in galaxies at all
redshifts.
The cyclic nature of the universe provides a natural link between the places
of origin of the microwave background radiation (arising in hydrogen burning in
stars), and the origin of the lightest nuclei (H, D, He and He). It
also allows us to relate the large scale cyclic properties of the universe to
events taking place in the nuclei of galaxies. Observational evidence shows
that ejection of matter and energy from these centers in the form of compact
objects, gas and relativistic particles is responsible for the population of
quasi-stellar objects (QSOs) and gamma-ray burst sources in the universe.
In the later parts of the paper we briefly discuss the major unsolved
problems of this integrated cosmological and cosmogonical scheme. These are the
understanding of the origin of the intrinsic redshifts, and the periodicities
in the redshift distribution of the QSOs.Comment: 51 pages including 1 figur
Sensitization of interferon-γ induced apoptosis in human osteosarcoma cells by extracellular S100A4
BACKGROUND: S100A4 is a small Ca(2+)-binding protein of the S100 family with metastasis-promoting properties. Recently, secreted S100A4 protein has been shown to possess a number of functions, including induction of angiogenesis, stimulation of cell motility and neurite extension. METHODS: Cell cultures from two human osteosarcoma cell lines, OHS and its anti-S100A4 ribozyme transfected counterpart II-11b, was treated with IFN-γ and recombinant S100A4 in order to study the sensitizing effects of extracellular S100A4 on IFN-γ mediated apoptosis. Induction of apoptosis was demonstrated by DNA fragmentation, cleavage of poly (ADP-ribose) polymerase and Lamin B. RESULTS: In the present work, we found that the S100A4-expressing human osteosarcoma cell line OHS was more sensitive to IFN-γ-mediated apoptosis than the II-11b cells. S100A4 protein was detected in conditioned medium from OHS cells, but not from II-11b cells, and addition of recombinant S100A4 to the cell medium sensitized II-11b cells to apoptosis induced by IFN-γ. The S100A4/IFN-γ-mediated induction of apoptosis was shown to be independent of caspase activation, but dependent on the formation of reactive oxygen species. Furthermore, addition of extracellular S100A4 was demonstrated to activate nuclear factor-κB (NF-κB). CONCLUSION: In conclusion, we have shown that S100A4 sensitizes osteosarcoma cells to IFN-γ-mediated induction of apoptosis. Additionally, extracellular S100A4 activates NF-κB, but whether these events are causally related remains unknown
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