2,858 research outputs found
Integral Invariants of 3-Manifolds
This note describes an invariant of rational homology 3-spheres in terms of
configuration space integrals which in some sense lies between the invariants
of Axelrod and Singer and those of Kontsevich.Comment: 39 pages, AMS-LaTeX, to appear in J. Diff. Geo
Configuration spaces and Vassiliev classes in any dimension
The real cohomology of the space of imbeddings of S^1 into R^n, n>3, is
studied by using configuration space integrals. Nontrivial classes are
explicitly constructed. As a by-product, we prove the nontriviality of certain
cycles of imbeddings obtained by blowing up transversal double points in
immersions. These cohomology classes generalize in a nontrivial way the
Vassiliev knot invariants. Other nontrivial classes are constructed by
considering the restriction of classes defined on the corresponding spaces of
immersions.Comment: Published by Algebraic and Geometric Topology at
http://www.maths.warwick.ac.uk/agt/AGTVol2/agt-2-39.abs.htm
Wilson surfaces and higher dimensional knot invariants
An observable for nonabelian, higher-dimensional forms is introduced, its
properties are discussed and its expectation value in BF theory is described.
This is shown to produce potential and genuine invariants of higher-dimensional
knots.Comment: 31 pages, 9 figure
On the naturality of the Mathai-Quillen formula
We give an alternative proof for the Mathai-Quillen formula for a Thom form
using its natural behaviour with respect to fiberwise integration. We also
study this phenomenon in general context.Comment: 6 page
The social and gender context of HIV disclosure in sub-Saharan Africa: A review of policies and practices
This paper reviews the legal and policy context of HIV disclosure in sub-Saharan Africa, as well as what is known about rates, consequences and social context of disclosure, with special attention to gender issues and the role of health services. Persistent rates of nondisclosure by those diagnosed with HIV raise difficult ethical, public health and human rights questions about how to protect the medical confidentiality, health and well-being of people living with HIV on the one hand, and how to protect partners and children from HIV transmission on the other. Both globally and within the sub-Saharan African region, a spate of recent laws, policies and programmes have tried to encourage or – in some cases – mandate HIV disclosure. These policies have generated ethical and policy debates. While there is consensus that the criminalization of transmission and nondisclosure undermines rights while serving little public health benefit, there is less clarity about the ethics of third party notification, especially in resource-constrained settings. Despite initiatives to encourage voluntary HIV disclosure and to increase partner testing in sub-Saharan Africa, health workers continue to grapple with difficult challenges in the face of nondisclosure, and often express a need for more guidance and support in this area. A large body of research indicates that gender issues are key to HIV disclosure in the region, and must be considered within policies and programmes. Taken as a whole, this evidence suggests a need for more attention to the challenges and dilemmas faced by both clients and providers in relation to HIV disclosure in this region and for continued efforts to consider the perspectives and rights of all those affected.Keywords: HIV testing, disclosure, policies, health providers, gende
Complex Line Bundles over Simplicial Complexes and their Applications
Discrete vector bundles are important in Physics and recently found
remarkable applications in Computer Graphics. This article approaches discrete
bundles from the viewpoint of Discrete Differential Geometry, including a
complete classification of discrete vector bundles over finite simplicial
complexes. In particular, we obtain a discrete analogue of a theorem of Andr\'e
Weil on the classification of hermitian line bundles. Moreover, we associate to
each discrete hermitian line bundle with curvature a unique piecewise-smooth
hermitian line bundle of piecewise constant curvature. This is then used to
define a discrete Dirichlet energy which generalizes the well-known cotangent
Laplace operator to discrete hermitian line bundles over Euclidean simplicial
manifolds of arbitrary dimension
A Note on the Equality of Algebraic and Geometric D-Brane Charges in WZW Models
The algebraic definition of charges for symmetry-preserving D-branes in
Wess-Zumino-Witten models is shown to coincide with the geometric definition,
for all simple Lie groups. The charge group for such branes is computed from
the ambiguities inherent in the geometric definition.Comment: 12 pages, fixed typos, added references and a couple of remark
Romantic Partnerships and the Dispersion of Social Ties: A Network Analysis of Relationship Status on Facebook
A crucial task in the analysis of on-line social-networking systems is to
identify important people --- those linked by strong social ties --- within an
individual's network neighborhood. Here we investigate this question for a
particular category of strong ties, those involving spouses or romantic
partners. We organize our analysis around a basic question: given all the
connections among a person's friends, can you recognize his or her romantic
partner from the network structure alone? Using data from a large sample of
Facebook users, we find that this task can be accomplished with high accuracy,
but doing so requires the development of a new measure of tie strength that we
term `dispersion' --- the extent to which two people's mutual friends are not
themselves well-connected. The results offer methods for identifying types of
structurally significant people in on-line applications, and suggest a
potential expansion of existing theories of tie strength.Comment: Proc. 17th ACM Conference on Computer Supported Cooperative Work and
Social Computing (CSCW), 201
The polarization of the planet-hosting WASP-18 system
We report observations of the linear polarization of the WASP-18 system,
which harbors a very massive ( approx 10 M_J) planet orbiting very close to its
star with an orbital period of 0.94 days. We find the WASP-18 system is
polarized at about 200 parts-per-million (ppm), likely from the interstellar
medium predominantly, with no strong evidence for phase dependent modulation
from reflected light from the planet. We set an upper limit of 40 ppm (99%
confidence level) on the amplitude of a reflected polarized light planetary
signal. We compare the results with models for a number of processes that may
produce polarized light in a planetary system to determine if we can rule out
any phenomena with this limit. Models of reflected light from thick clouds can
approach or exceed this limit, but such clouds are unlikely at the high
temperature of the WASP-18b atmosphere. Additionally, we model the expected
polarization resulting from the transit of the planet across the star and find
this has an amplitude of about 1.6 ppm, which is well below our detection
limits. We also model the polarization due to the tidal distortion of the star
by the massive planet and find this is also too small to be measured currently.Comment: 23 pages, 10 Figures, 6 Tables, Accepted to A
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