93 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
Rings, modules, and algebras in infinite loop space theory
We give a new construction of the algebraic -theory of small permutative
categories that preserves multiplicative structure, and therefore allows us to
give a unified treatment of rings, modules, and algebras in both the input and
output. This requires us to define multiplicative structure on the category of
small permutative categories. The framework we use is the concept of
multicategory, a generalization of symmetric monoidal category that precisely
captures the multiplicative structure we have present at all stages of the
construction. Our method ends up in Smith's category of symmetric spectra, with
an intermediate stop at a new category that may be of interest in its own
right, whose objects we call symmetric functors.Comment: 59 pages, 1 figur
Supersymmetric Gauge Theories in Twistor Space
We construct a twistor space action for N=4 super Yang-Mills theory and show
that it is equivalent to its four dimensional spacetime counterpart at the
level of perturbation theory. We compare our partition function to the original
twistor-string proposal, showing that although our theory is closely related to
string theory, it is free from conformal supergravity. We also provide twistor
actions for gauge theories with N<4 supersymmetry, and show how matter
multiplets may be coupled to the gauge sector.Comment: 23 pages, no figure
Noncommutative resolutions of ADE fibered Calabi-Yau threefolds
In this paper we construct noncommutative resolutions of a certain class of Calabi-Yau threefolds studied by F. Cachazo, S. Katz and C. Vafa. The threefolds under consideration are fibered over a complex plane with the fibers being deformed Kleinian singularities. The construction is in terms of a noncommutative algebra introduced by V. Ginzburg, which we call the "N=1 ADE quiver algebra"
On Darboux-Treibich-Verdier potentials
It is shown that the four-parameter family of elliptic functions
introduced
by Darboux and rediscovered a hundred years later by Treibich and Verdier, is
the most general meromorphic family containing infinitely many finite-gap
potentials.Comment: 8 page
Analysis technique for exceptional points in open quantum systems and QPT analogy for the appearance of irreversibility
We propose an analysis technique for the exceptional points (EPs) occurring
in the discrete spectrum of open quantum systems (OQS), using a semi-infinite
chain coupled to an endpoint impurity as a prototype. We outline our method to
locate the EPs in OQS, further obtaining an eigenvalue expansion in the
vicinity of the EPs that gives rise to characteristic exponents. We also report
the precise number of EPs occurring in an OQS with a continuum described by a
quadratic dispersion curve. In particular, the number of EPs occurring in a
bare discrete Hamiltonian of dimension is given by ; if this discrete Hamiltonian is then coupled to continuum
(or continua) to form an OQS, the interaction with the continuum generally
produces an enlarged discrete solution space that includes a greater number of
EPs, specifically , in which
is the number of (non-degenerate) continua to which the discrete sector is
attached. Finally, we offer a heuristic quantum phase transition analogy for
the emergence of the resonance (giving rise to irreversibility via exponential
decay) in which the decay width plays the role of the order parameter; the
associated critical exponent is then determined by the above eigenvalue
expansion.Comment: 16 pages, 7 figure
Translation to practice: a randomised controlled study of an evidenced based booklet targeted at breast care nurses in the United Kingdom
BACKGROUND: In the United Kingdom (UK), it was documented that a problem of knowledge transfer existed within the speciality of breast-cancer care, thus depriving patients of receiving optimal care. Despite increasingly robust research evidence indicating recommendation of whole body exercise for people affected by breast cancer, commensurate changes to practice were not noted amongst breast-care nurses (BCNs).
AIM: To evaluate the effect of a targeted booklet, Exercise and Breast Cancer: A Booklet for Breast-Care Nurses, on changes in knowledge, reported practice, and attitudes of BCNs in the UK.
METHOD: A prospective, experimental approach was used for designing a pre- and post-test randomised controlled study. Comparisons of knowledge, reported practice, and attitudes based on responses to a questionnaire were made at two time-points in two groups of BCNs (control and experimental). The unit of randomisation and analysis was hospital clusters of BCNs. The sample comprised 92 nurses from 62 hospitals. Analysis consisted of descriptive statistics and clustered regression techniques: clustered logistic regression for knowledge items, clustered linear regression for knowledge scores, ologit for attitude and reported practice items, and clustered multiple regression for paired and multiple variable analysis.
RESULTS: A statistically significant increase in knowledge and changes in reported practice and attitudes were found. Robust variables affecting knowledge acquisition were: promotion of health, promotion of exercise, and understanding how exercise can reduce cancer-related fatigue.
DISCUSSION: The study has shown that evidence-based printed material, such as an information booklet, can be used as an effective research dissemination method when developed for needs, values, and context of a target audience.
CONCLUSIONS: This practical approach to research dissemination could be replicated and applied to other groups of nurses.</p
Abundances of the elements in the solar system
A review of the abundances and condensation temperatures of the elements and
their nuclides in the solar nebula and in chondritic meteorites. Abundances of
the elements in some neighboring stars are also discussed.Comment: 42 pages, 11 tables, 8 figures, chapter, In Landolt- B\"ornstein, New
Series, Vol. VI/4B, Chap. 4.4, J.E. Tr\"umper (ed.), Berlin, Heidelberg, New
York: Springer-Verlag, p. 560-63
Setting and analysis of the multi-configuration time-dependent Hartree-Fock equations
In this paper we motivate, formulate and analyze the Multi-Configuration
Time-Dependent Hartree-Fock (MCTDHF) equations for molecular systems under
Coulomb interaction. They consist in approximating the N-particle Schrodinger
wavefunction by a (time-dependent) linear combination of (time-dependent)
Slater determinants. The equations of motion express as a system of ordinary
differential equations for the expansion coefficients coupled to nonlinear
Schrodinger-type equations for mono-electronic wavefunctions. The invertibility
of the one-body density matrix (full-rank hypothesis) plays a crucial role in
the analysis. Under the full-rank assumption a fiber bundle structure shows up
and produces unitary equivalence between convenient representations of the
equations. We discuss and establish existence and uniqueness of maximal
solutions to the Cauchy problem in the energy space as long as the density
matrix is not singular. A sufficient condition in terms of the energy of the
initial data ensuring the global-in-time invertibility is provided (first
result in this direction). Regularizing the density matrix breaks down energy
conservation, however a global well-posedness for this system in L^2 is
obtained with Strichartz estimates. Eventually solutions to this regularized
system are shown to converge to the original one on the time interval when the
density matrix is invertible.Comment: 48 pages, 1 figur
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