662 research outputs found
Loop Quantum Cosmology II: Volume Operators
Volume operators measuring the total volume of space in a loop quantum theory
of cosmological models are constructed. In the case of models with rotational
symmetry an investigation of the Higgs constraint imposed on the reduced
connection variables is necessary, a complete solution of which is given for
isotropic models; in this case the volume spectrum can be calculated
explicitly. It is observed that the stronger the symmetry conditions are the
smaller is the volume spectrum, which can be interpreted as level splitting due
to broken symmetries. Some implications for quantum cosmology are presented.Comment: 21 page
Independent Loop Invariants for 2+1 Gravity
We identify an explicit set of complete and independent Wilson loop
invariants for 2+1 gravity on a three-manifold , with
a compact oriented Riemann surface of arbitrary genus . In the
derivation we make use of a global cross section of the -principal
bundle over Teichm\"uller space given in terms of Fenchel-Nielsen coordinates.Comment: 11pp, 2 figures (postscript, compressed and uu-encoded), TeX,
Pennsylvania State University, CGPG-94/7-
New Loop Representations for 2+1 Gravity
Since the gauge group underlying 2+1-dimensional general relativity is
non-compact, certain difficulties arise in the passage from the connection to
the loop representations. It is shown that these problems can be handled by
appropriately choosing the measure that features in the definition of the loop
transform. Thus, ``old-fashioned'' loop representations - based on ordinary
loops - do exist. In the case when the spatial topology is that of a two-torus,
these can be constructed explicitly; {\it all} quantum states can be
represented as functions of (homotopy classes of) loops and the scalar product
and the action of the basic observables can be given directly in terms of
loops.Comment: 28pp, 1 figure (postscript, compressed and uuencoded), TeX,
Pennsylvania State University, CGPG-94/5-
Loop Quantum Cosmology I: Kinematics
The framework of quantum symmetry reduction is applied to loop quantum
gravity with respect to transitively acting symmetry groups. This allows to
test loop quantum gravity in a large class of minisuperspaces and to
investigate its features - e.g. the discrete volume spectrum - in certain
cosmological regimes. Contrary to previous studies of quantum cosmology
(minisuperspace quantizations) the symmetry reduction is carried out not at the
classical level but on an auxiliary Hilbert space of the quantum theory before
solving the constraints. Therefore, kinematical properties like volume
quantization survive the symmetry reduction. In this first part the kinematical
framework, i.e. implementation of the quantum symmetry reduction and
quantization of Gauss and diffeomorphism constraints, is presented for Bianchi
class A models as well as locally rotationally symmetric and spatially
isotropic closed and flat models.Comment: 24 page
On-instrument wavefront sensor design for the TMT infrared imaging spectrograph (IRIS) update
The first light instrument on the Thirty Meter Telescope (TMT) project will
be the InfraRed Imaging Spectrograph (IRIS). IRIS will be mounted on a bottom
port of the facility AO instrument NFIRAOS. IRIS will report guiding
information to the NFIRAOS through the On-Instrument Wavefront Sensor (OIWFS)
that is part of IRIS. This will be in a self-contained compartment of IRIS and
will provide three deployable wavefront sensor probe arms. This entire unit
will be rotated to provide field de-rotation. Currently in our preliminary
design stage our efforts have included: prototyping of the probe arm to
determine the accuracy of this critical component, handling cart design and
reviewing different types of glass for the atmospheric dispersion.Comment: Proceedings of the SPIE, 9147-35
Surgical treatment of prosthetic valve endocarditis
AbstractFrom 1975 through 1992, we reoperated on 146 patients for the treatment of prosthetic valve endocarditis. Prosthetic valve endocarditis was considered to be early (<1 year after operation) in 46 cases and active in 103 cases. The extent of the infection was prosthesis only in 66 patients, anulus in 46, and cardiac invasion in 34. Surgical techniques evolved in the direction of increasingly radical débridement of infected tissue and reconstruction with biologic materials. All patients were treated with prolonged postoperative antibiotic therapy. There were 19 (13%) in-hospital deaths. Univariate analyses demonstrated trends toward increasing risk for patients with active endocarditis and extension of infection beyond the prosthesis; however, the only variables with a significant (p < 0.05) association with increased in-hospital mortality confirmed with multivariate testing were impaired left ventricular function, preoperative heart block, coronary artery disease, and culture of organisms from the surgical specimen. During the study period, mortality decreased from 20% (1975 to 1984) to 10% (1984 to 1992). For hospital survivors the mean length of stay was 25 days. Follow-up (mean interval 62 months) documented a late survival of 82% at 5 postoperative years and 60% at 10 years. Older age was the only factor associated (p = 0.006) with late death. Nineteen patients needed at least one further operation; reoperation-free survival was 75% at 5 and 50% at 10 postoperative years. Fever in the immediate preoperative period was the only factor associated with decreased late reoperation-free survival (p = 0.032). Prosthetic valve endocarditis remains a serious complication of valve replacement, but the in-hospital mortality of reoperations for prosthetic valve endocarditis has declined. With extensive débridement of infected tissue and postoperative antibiotic therapy, the extent and activity of prosthetic valve endocarditis does not appear to have a major impact on late outcome, and the majority of patients with this complication survive for 10 years after the operation. (J THORAC CARDIOVASC SURG 1996;111:198-210
Neutrino Mass from R-parity Violation in Split Supersymmetry
We investigate how the observed neutrino data can be accommodated by R-parity
violation in Split Supersymmetry. The atmospheric neutrino mass and mixing are
explained by the bilinear parameters inducing the neutrino-neutralino
mixing as in the usual low-energy supersymmetry. Among various one-loop
corrections, only the quark-squark exchanging diagrams involving the order-one
trilinear couplings can generate the solar neutrino mass
and mixing if the scalar mass is not larger than GeV. This scheme
requires an unpleasant hierarchical structure of the couplings, e.g.,
, and . On the other hand, the model has a distinct collider
signature of the lightest neutralino which can decay only to the final states,
and , arising from the bilinear mixing. Thus, the
measurement of the ratio; would provide a clean probe of the small reactor and
large atmospheric neutrino mixing angles as far as the neutralino mass is
larger than 62 GeV.Comment: 10 pages, 3 figures, version submitted to JHE
The internal thoracic artery skeletonization study: A paired, within-patient comparison [NCT00265499]
BACKGROUND: Traditional harvesting of the internal thoracic artery (ITA) for use as a conduit in coronary bypass surgery involves the dissection of a rim of tissue surrounding the artery on either side. Recent studies, primarily observational, have suggested that skeletonization of the ITA can improve conduit flow, increase length, and reduce the risk of deep sternal infection in high risk patients. Furthermore, skeletonization of the ITA can potentially preserve intercostal nerves and reduce post-operative pain and dysesthesias associated with ITA harvesting. In order to assess the effects of ITA skeletonization, we report a prospective, randomized, within-patient study design that shares many features of a cross-over study. METHODS: Patients undergoing bilateral internal thoracic artery harvest will be randomized to having one side skeletonized and the other harvested in a non-skeletonized manner. Outcome measures include ITA flow and length measured intra-operatively, post-operative pain and dysesthesia, evaluated at discharge, four weeks, and three months post-operatively, and sternal perfusion assessed using single photon emission computed tomography. Harvest times as well as safety endpoints of ITA injury will be recorded. DISCUSSION: This study design, using within-patient comparisons and paired analyses, minimizes the variability of the outcome measures, which is seldom possible in the evaluation of surgical techniques, with minimal chance of carryover effects that can hamper the interpretation of traditional cross-over studies. This study will provide a valid evaluation of clinically relevant effects of internal thoracic artery skeletonization in improving outcomes following coronary artery bypass surgery
The complete spectrum of the area from recoupling theory in loop quantum gravity
We compute the complete spectrum of the area operator in the loop
representation of quantum gravity, using recoupling theory. This result extends
previous derivations, which did not include the ``degenerate'' sector, and
agrees with the recently computed spectrum of the connection-representation
area operator.Comment: typos corrected in eqn.(21). Latex with IOP and epsf styles, 1 figure
(eps postscript file), 12 pages. To appear in Class. Quantum Gra
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