11,573 research outputs found
Twisted equivariant K-theory, groupoids and proper actions
In this paper we define twisted equivariant K-theory for actions of Lie
groupoids. For a Bredon-compatible Lie groupoid, this defines a periodic
cohomology theory on the category of finite CW-complexes with equivariant
stable projective bundles. A classification of these bundles is shown. We also
obtain a completion theorem and apply these results to proper actions of
groups.Comment: 26 page
A Geometric Model of Arbitrary Spin Massive Particle
A new model of relativistic massive particle with arbitrary spin
(()-particle) is suggested. Configuration space of the model is a product
of Minkowski space and two-dimensional sphere, . The system describes Zitterbewegung at the classical level.
Together with explicitly realized Poincar\'e symmetry, the action functional
turns out to be invariant under two types of gauge transformations having their
origin in the presence of two Abelian first-class constraints in the Hamilton
formalism. These constraints correspond to strong conservation for the
phase-space counterparts of the Casimir operators of the Poincar\'e group.
Canonical quantization of the model leads to equations on the wave functions
which prove to be equivalent to the relativistic wave equations for the massive
spin- field.Comment: 25 pages; v2: eq. (45.b) correcte
The body in the library: adventures in realism
This essay looks at two aspects of the virtual ‘material world’ of realist fiction: objects encountered by the protagonist and the latter’s body. Taking from Sartre two angles on the realist pact by which readers agree to lend
their bodies, feelings, and experiences to the otherwise ‘languishing signs’ of the text, it goes on to examine two sets of first-person fictions published between 1902 and 1956 — first, four modernist texts in which banal objects defy and then gratify the protagonist, who ends up ready and almost able to write; and, second, three novels in which the body of the protagonist is indeterminate in its sex, gender, or sexuality. In each of these cases, how do we as readers make texts work for us as ‘an adventure of the body’
Massive spinning particle on anti-de Sitter space
To describe a massive particle with fixed, but arbitrary, spin on
anti-de Sitter space , we propose the point-particle model with
configuration space , where the sphere
corresponds to the spin degrees of freedom. The model possesses two gauge
symmetries expressing strong conservation of the phase-space counterparts of
the second- and fourth-order Casimir operators for . We prove that the
requirement of energy to have a global positive minimum over the
configuration space is equivalent to the relation , being the
particle's spin, what presents the classical counterpart of the quantum massive
condition. States with the minimal energy are studied in detail. The model is
shown to be exactly solvable. It can be straightforwardly generalized to
describe a spinning particle on -dimensional anti-de Sitter space ,
with the corresponding configuration
space.Comment: 23 pages, LaTe
Liver Adiposity and Metabolic Profile in Individuals with Chronic Spinal Cord Injury
Purpose. To quantify liver adiposity using magnetic resonance imaging (MRI) and to determine its association with metabolic profile in men with spinal cord injury (SCI). Materials and Methods. MRI analysis of liver adiposity by fat signal fraction (FSF) and visceral adipose tissue (VAT) was completed on twenty participants. Intravenous glucose tolerance test was conducted to measure glucose effectiveness (g) and insulin sensitivity (i ). Lipid panel, fasting glucose, glycated hemoglobin (HbA1c), and inflammatory cytokines were also analyzed. Results. Average hepatic FSF was 3.7% ± 2.1. FSF was positively related to TG, non-HDL-C, fasting glucose, HbA1c, VAT, and tumor necrosis factor alpha (TNF-). FSF was negatively related to i and testosterone. FSF was positively related to VAT ( = 0.48, = 0.032) and TNF- ( = 0.51, = 0.016) independent of age, level of injury (LOI), and time since injury (TSI). The associations between FSF and metabolic profile were independent of VAT. Conclusions. MRI noninvasively estimated hepatic adiposity in men with chronic SCI. FSF was associated with dysfunction in metabolic profile, central adiposity, and inflammation. Importantly, liver adiposity influenced metabolic profile independently of VAT. These findings highlight the significance of quantifying liver adiposity after SCI to attenuate the development of metabolic disorders
Testing the Hubble Law with the IRAS 1.2 Jy Redshift Survey
We test and reject the claim of Segal et al. (1993) that the correlation of
redshifts and flux densities in a complete sample of IRAS galaxies favors a
quadratic redshift-distance relation over the linear Hubble law. This is done,
in effect, by treating the entire galaxy luminosity function as derived from
the 60 micron 1.2 Jy IRAS redshift survey of Fisher et al. (1995) as a distance
indicator; equivalently, we compare the flux density distribution of galaxies
as a function of redshift with predictions under different redshift-distance
cosmologies, under the assumption of a universal luminosity function. This
method does not assume a uniform distribution of galaxies in space. We find
that this test has rather weak discriminatory power, as argued by Petrosian
(1993), and the differences between models are not as stark as one might expect
a priori. Even so, we find that the Hubble law is indeed more strongly
supported by the analysis than is the quadratic redshift-distance relation. We
identify a bias in the the Segal et al. determination of the luminosity
function, which could lead one to mistakenly favor the quadratic
redshift-distance law. We also present several complementary analyses of the
density field of the sample; the galaxy density field is found to be close to
homogeneous on large scales if the Hubble law is assumed, while this is not the
case with the quadratic redshift-distance relation.Comment: 27 pages Latex (w/figures), ApJ, in press. Uses AAS macros,
postscript also available at
http://www.astro.princeton.edu/~library/preprints/pop682.ps.g
Large-scale structure and the redshift-distance relation
In efforts to demonstrate the linear Hubble law v = Hr from galaxy
observations, the underlying simplicity is often obscured by complexities
arising from magnitude-limited data. In this paper we point out a simple but
previously unremarked fact: that the shapes and orientations of structures in
redshift space contain in themselves independent information about the
cosmological redshift-distance relation.
The orientations of voids in the CfA slice support the Hubble law, giving a
redshift-distance power index p = 0.83 +/- 0.36 (void data from Slezak, de
Lapparent, & Bijoui 1993) or p = 0.99 +/- 0.38 (void data from Malik &
Subramanian 1997).Comment: 11 pages (AASTeX), 4 figures, to appear in the Astrophysical Journal
Letter
On a notion of maps between orbifolds, I. function spaces
This is the first of a series of papers which are devoted to a comprehensive
theory of maps between orbifolds. In this paper, we define the maps in the more
general context of orbispaces, and establish several basic results concerning
the topological structure of the space of such maps. In particular, we show
that the space of such maps of C^r-class between smooth orbifolds has a natural
Banach orbifold structure if the domain of the map is compact, generalizing the
corresponding result in the manifold case. Motivations and applications of the
theory come from string theory and the theory of pseudoholomorphic curves in
symplectic orbifolds.Comment: Final version, 46 pages. Accepted for publication in Communications
in Contemporary Mathematics. A preliminary version of this work is under a
different title "A homotopy theory of orbispaces", arXiv: math. AT/010202
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