4,179 research outputs found
Numerical Evidence for the Observation of a Scalar Glueball
We compute from lattice QCD in the valence (quenched) approximation the
partial decay widths of the lightest scalar glueball to pairs of pseudoscalar
quark-antiquark states. These predictions and values obtained earlier for the
scalar glueball's mass are in good agreement with the observed properties of
and inconsistent with all other observed meson resonances.Comment: 12 pages of Latex, 3 PostsScript figures as separate uufil
Complex Probabilities on R^N as Real Probabilities on C^N and an Application to Path Integrals
We establish a necessary and sufficient condition for averages over complex
valued weight functions on R^N to be represented as statistical averages over
real, non-negative probability weights on C^N. Using this result, we show that
many path-integrals for time-ordered expectation values of bosonic degrees of
freedom in real-valued time can be expressed as statistical averages over
ensembles of paths with complex-valued coordinates, and then speculate on
possible consequences of this result for the relation between quantum and
classical mechanics.Comment: 4 pages, 0 figure
Finite element analysis of wrinkling membranes
The development of a nonlinear numerical algorithm for the analysis of stresses and displacements in partly wrinkled flat membranes, and its implementation on the SAP VII finite-element code are described. A comparison of numerical results with exact solutions of two benchmark problems reveals excellent agreement, with good convergence of the required iterative procedure. An exact solution of a problem involving axisymmetric deformations of a partly wrinkled shallow curved membrane is also reported
Finite element analysis of wrinkling membranes
The finite element analysis of wrinkling membranes was investigated. The determination of stresses and deformations within large partly wrinkled membrane surfaces is a problem of significant technical interest in such areas as conceptual design and analysis of ultra lightweight spacecraft structures. A closed-form solution to an axisymmetric problem involving partial wrinkling of an inflated shallow membrane was obtained. In particular, a membrane in the shape of a sperical annulus was considered. The outer edge of the annulus was assumed to be fixed so that no displacements occur along the outer perimeter. The inner edge is assumed to be clamped to a rigid movable plug. Solutions for the complete stress, strain, and displacement fields under the assumption of inextensional material behavior are presented for the case of pure torsional loads applied to the plug, and for the case of pure axial loads applied to the plug
Heralded state preparation in a superconducting qubit
We demonstrate high-fidelity, quantum nondemolition, single-shot readout of a
superconducting flux qubit in which the pointer state distributions can be
resolved to below one part in 1000. In the weak excitation regime, continuous
measurement permits the use of heralding to ensure initialization to a fiducial
state, such as the ground state. This procedure boosts readout fidelity to
93.9% by suppressing errors due to spurious thermal population. Furthermore,
heralding potentially enables a simple, fast qubit reset protocol without
changing the system parameters to induce Purcell relaxation.Comment: 5 pages, 5 figure
EKF-based 3D SLAM for Structured Environment Reconstruction
This paper presents the extension and experimental validation of the widely used EKF1-based SLAM2 algorithm to 3D space. It uses planar features extracted probabilistically from dense three-dimensional point clouds generated by a rotating 2D laser scanner. These features are represented in compliance with the Symmetries and Perturbation model (SPmodel) in a stochastic map. As the robot moves, this map is updated incrementally while its pose is tracked by using an Extended Kalman Filter. After showing how three-dimensional data can be generated, the probabilistic feature extraction method is described, capable of robustly extracting (infinite) planes from structured environments. The SLAM algorithm is then used to track a robot moving through an indoor environment and its capabilities in terms of 3D reconstruction are analyzed
Impossibility of spontaneously breaking local symmetries and the sign problem
Elitzur's theorem stating the impossibility of spontaneous breaking of local
symmetries in a gauge theory is reexamined. The existing proofs of this theorem
rely on gauge invariance as well as positivity of the weight in the Euclidean
partition function. We examine the validity of Elitzur's theorem in gauge
theories for which the Euclidean measure of the partition function is not
positive definite. We find that Elitzur's theorem does not follow from gauge
invariance alone. We formulate a general criterion under which spontaneous
breaking of local symmetries in a gauge theory is excluded. Finally we
illustrate the results in an exactly solvable two dimensional abelian gauge
theory.Comment: Latex 6 page
Probabilistic Plane Fitting in 3D and an Application to Robotic Mapping
This paper presents a method for probabilistic plane fitting and an application to robotic 3D mapping. The plane is fitted in an orthogonal least-square sense and the output complies with the conventions of the Symmetries and Perturbation model (SPmodel). In the second part of the paper, the presented plane fitting method is used within a 3D mapping application. It is shown that by using probabilistic information, high precision 3D maps can be generate
pion scattering amplitude with Wilson fermions
We present an exploratory calculation of the scattering
amplitude at threshold using Wilson fermions in the quenched approximation,
including all the required contractions. We find good agreement with the
predictions of chiral perturbation theory even for pions of mass 560-700 MeV.
Within the 10\% errors, we do not see the onset of the bad chiral behavior
expected for Wilson fermions. We also derive rigorous inequalities that apply
to 2-particle correlators and as a consequence show that the interaction in the
antisymmetric state of two pions has to be attractive.Comment: This PS file includes 4 tables and figures 1-8 on 25 pages. Los
Alamos Preprint Number LAUR-92-364
On the Response of an OST to a Point-like Heat Source
A new technique of superconducting cavity diagnostics has been introduced by
D. Hartrill at Cornell University, Ithaca, USA. Oscillating Superleak
Transducers (OST) detect the heat transferred from a cavity's quench point via
"Second Sound" through the superfluid He bath, needed to cool the
superconducting cavity. The observed response of an OST is a complex, but
reproducible pattern of oscillations. A small helium evaporation cryostat was
built which allows the investigation of the response of an OST in greater
detail. The distance between a point-like electrical heater and the OST can be
varied. The OST can be mounted either parallel or perpendicular to the plate,
housing the heat source. If the artificial quench-point releases an amount of
energy compatible to a real quench spot on a cavity's surface, the OST signal
starts with a negative pulse, which is usually strong enough to allow automatic
detection. Furthermore, the reflection of the Second Sound on the wall is
observed. A reflection coefficient R = 0.39 +- 0.05 of the glass wall is
measured. This excludes a strong influence of multiple reflections in the
complex OST response. Fourier analyses show three main frequencies, found in
all OST spectra. They can be interpreted as modes of an oscillating circular
membrane.Comment: 10 pages, 16 figure
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