287 research outputs found
On chains in -closed topological pospaces
We study chains in an -closed topological partially ordered space. We give
sufficient conditions for a maximal chain in an -closed topological
partially ordered space such that contains a maximal (minimal) element.
Also we give sufficient conditions for a linearly ordered topological partially
ordered space to be -closed. We prove that any -closed topological
semilattice contains a zero. We show that a linearly ordered -closed
topological semilattice is an -closed topological pospace and show that in
the general case this is not true. We construct an example an -closed
topological pospace with a non--closed maximal chain and give sufficient
conditions that a maximal chain of an -closed topological pospace is an
-closed topological pospace.Comment: We have rewritten and substantially expanded the manuscrip
Near Infrared Spectra and Intrinsic Luminosities of Candidate Type II Quasars at 2 < z < 3.4
We present JHK near-infrared (NIR) spectroscopy of 25 candidate Type II
quasars selected from the Sloan Digital Sky Survey, using Triplespec on the
Apache Point Observatory 3.5m telescope, FIRE at the Magellan/Baade 6.5m
telescope, and GNIRS on Gemini. At redshifts of 2 < z < 3.4, our NIR spectra
probe the rest-frame optical region of these targets, which were initially
selected to have strong lines of CIV and Ly alpha, with FWHM<2000 km/s from the
SDSS pipeline. We use the [OIII]5007 line shape as a model for the narrow line
region emission, and find that \halpha\ consistently requires a broad component
with FWHMs ranging from 1000 to 7500 km/s. Interestingly, the CIV lines also
require broad bases, but with considerably narrower widths of 1000 to 4500
km/s. Estimating the extinction using the Balmer decrement and also the
relationship in lower-z quasars between rest equivalent width and luminosity in
the [OIII] line, we find typical A_V values of 0-2 mag, which naturally explain
the attenuated CIV lines relative to Halpha. We propose that our targets are
moderately obscured quasars. We also describe one unusual object with three
distinct velocity peaks in its [OIII] spectrum.Comment: Accepted for publication in ApJ, 18 pages, 14 figure
On the flux phase conjecture at half-filling: an improved proof
We present a simplification of Lieb's proof of the flux phase conjecture for
interacting fermion systems -- such as the Hubbard model --, at half filling on
a general class of graphs. The main ingredient is a procedure which transforms
a class of fermionic Hamiltonians into reflection positive form. The method can
also be applied to other problems, which we briefly illustrate with two
examples concerning the model and an extended Falicov-Kimball model.Comment: 23 pages, Latex, uses epsf.sty to include 3 eps figures, to appear in
J. Stat. Phys., Dec. 199
On the equivalence between hierarchical segmentations and ultrametric watersheds
We study hierarchical segmentation in the framework of edge-weighted graphs.
We define ultrametric watersheds as topological watersheds null on the minima.
We prove that there exists a bijection between the set of ultrametric
watersheds and the set of hierarchical segmentations. We end this paper by
showing how to use the proposed framework in practice in the example of
constrained connectivity; in particular it allows to compute such a hierarchy
following a classical watershed-based morphological scheme, which provides an
efficient algorithm to compute the whole hierarchy.Comment: 19 pages, double-colum
Candidate Type II Quasars at 2 < z < 4.3 in the Sloan Digital Sky Survey III
At low redshifts, dust-obscured quasars often have strong yet narrow
permitted lines in the rest-frame optical and ultraviolet, excited by the
central active nucleus, earning the designation Type II quasars. We present a
sample of 145 candidate Type II quasars at redshifts between 2 and 4.3,
encompassing the epoch at which quasar activity peaked in the universe. These
objects, selected from the quasar sample of the Baryon Oscillation
Spectroscopic Survey of the Sloan Digital Sky Survey III, are characterized by
weak continuum in the rest-frame ultraviolet (typical continuum magnitude of i
\approx 22) and strong lines of CIV and Ly \alpha, with Full Width at Half
Maximum less than 2000 kms-1. The continuum magnitudes correspond to an
absolute magnitude of -23 or brighter at redshift 3, too bright to be due
exclusively to the host galaxies of these objects. Roughly one third of the
objects are detected in the shorter-wavelength bands of the WISE survey; the
spectral energy distributions (SEDs) of these objects appear to be intermediate
between classic Type I and Type II quasars seen at lower redshift. Five objects
are detected at rest frame 6\mu m by Spitzer, implying bolometric luminosities
of several times 10^46 erg s-1. We have obtained polarization measurements for
two objects; they are roughly 3% polarized. We suggest that these objects are
luminous quasars, with modest dust extinction (A_V ~ 0.5 mag), whose
ultraviolet continuum also includes a substantial scattering contribution.
Alternatively, the line of sight to the central engines of these objects may be
partially obscured by optically thick material.Comment: 26 pages, 13 figures, 10 tables, 4 machine readable tables. Accepted
for publication in MNRA
Chain Homotopies for Object Topological Representations
This paper presents a set of tools to compute topological information of
simplicial complexes, tools that are applicable to extract topological
information from digital pictures. A simplicial complex is encoded in a
(non-unique) algebraic-topological format called AM-model. An AM-model for a
given object K is determined by a concrete chain homotopy and it provides, in
particular, integer (co)homology generators of K and representative (co)cycles
of these generators. An algorithm for computing an AM-model and the
cohomological invariant HB1 (derived from the rank of the cohomology ring) with
integer coefficients for a finite simplicial complex in any dimension is
designed here. A concept of generators which are "nicely" representative cycles
is also presented. Moreover, we extend the definition of AM-models to 3D binary
digital images and we design algorithms to update the AM-model information
after voxel set operations (union, intersection, difference and inverse)
Stability and convergence in discrete convex monotone dynamical systems
We study the stable behaviour of discrete dynamical systems where the map is
convex and monotone with respect to the standard positive cone. The notion of
tangential stability for fixed points and periodic points is introduced, which
is weaker than Lyapunov stability. Among others we show that the set of
tangentially stable fixed points is isomorphic to a convex inf-semilattice, and
a criterion is given for the existence of a unique tangentially stable fixed
point. We also show that periods of tangentially stable periodic points are
orders of permutations on letters, where is the dimension of the
underlying space, and a sufficient condition for global convergence to periodic
orbits is presented.Comment: 36 pages, 1 fugur
A Class of Topological Actions
We review definitions of generalized parallel transports in terms of
Cheeger-Simons differential characters. Integration formulae are given in terms
of Deligne-Beilinson cohomology classes. These representations of parallel
transport can be extended to situations involving distributions as is
appropriate in the context of quantized fields.Comment: 41 pages, no figure
Supernatants from lymphocytes stimulated with Bacillus Calmette-Guerin can modify the antigenicity of tumours and stimulate allogeneic T-cell responses
BACKGROUND: Reduced expression of class 1 human leucocyte antigens (HLA1) is often a mechanism by which tumours evade surveillance by the host immune system. This is often associated with an immune function that is unable to mount appropriate responses against disease, which can result in a state that favours carcinogenesis. METHODS: In the current study, we have explored the effects of Bacillus Calmette-Guerin (BCG) on the cytokine output of leucocytes, which is a key determinant in generating antitumour action, and have also assessed the effect of these cytokine cocktails on HLA1 expression in solid tumour cell lines. RESULTS: BCG potently activated a broad range of leucocytes, and also enhanced the production of cytokines that were Th(1)-predominant. Supernatants from BCG-treated leucocytes significantly increased the expression of HLA1 on the surface of cancer cell lines, which correlated with increased cytolytic T-cell activity. We also showed that the increased HLA1 expression was associated with activation of intracellular signalling pathways, which was triggered by the increases in the Th(1)-cytokines interferon-γ and tumour necrosis factor-α, as counteracting their effects negated the enhancement. CONCLUSION: These studies reaffirm the role of BCG as a putative immunotherapy through their cytokine-modifying effects on leucocytes and their capacity to enhance tumour visibility
Cambodian Higher Education Governance: The Politics of Global Summitry and Clientelism
This chapter uses the concepts of âglobal summitryâ and âclientelismâ to theorize higher education governance in Cambodia. After reviewing the history of higher education since the 1960s, the chapter analyzes the countryâs experiences amid regional attempts to harmonize standards, degree structures, quality assurance systems, and credit systems in Southeast Asia. Rather than explicit intervention into Cambodiaâs higher education sector as has been historically common, the contemporary order transmits policy and governance practices through various regional and international forums, creating a seemingly homogenous system of higher education. External influence through global summitry, however, must be paired with a recognition of the prevalence of clientelism. By exploring the case of the Accreditation Council of Cambodia, higher education governance is shown to reproduce the engrained system of clientelism, empowering elites and contributing further to systems of informal patronage. The chapter concludes with recent (up to April 2016) developments in higher education governance, offering some observations and obstacles for future development in the sector
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