5,937 research outputs found
Large Top Mass and Non-Linear Representation of Flavour Symmetry
We consider an effective theory (ET) approach to flavour-violating processes
beyond the Standard Model (SM), where the breaking of flavour symmetry is
described by spurion fields whose low-energy vacuum expectation values are
identified with the SM Yukawa couplings. Insisting on canonical mass dimensions
for the spurion fields, the large top-quark Yukawa coupling also implies a
large expectation value for the associated spurion, which breaks part of the
flavour symmetry already at the UV scale Lambda of the ET. Below that scale,
flavour symmetry in the ET is represented in a non-linear way by introducing
Goldstone modes for the partly broken flavour symmetry and spurion fields
transforming under the residual symmetry. As a result, the dominance of certain
flavour structures in rare quark decays can be understood in terms of the
1/Lambda expansion in the ET. We also discuss the generalization to
2-Higgs-doublet models with large tan(beta).Comment: 4 pages, no figures, uses revtex
Suppression of vortex channeling in meandered YBa2Cu3O7-d grain boundaries
We report on the in-plane magnetic field (H) dependence of the critical
current density (Jc) in meandered and planar single grain boundaries (GBs)
isolated in YBa2Cu3O7-d (YBCO) coated conductors. The Jc(H)properties of the
planar GB are consistent with those previously seen in single GBs of YBCO films
grown on SrTiO3 bi-crystals. In the straight boundary a characteristic flux
channeling regime when H is oriented near the GB plane, associated with a
reduced Jc, is seen. The meandered GB does not show vortex channeling since it
is not possible for a sufficient length of vortex line to lie within it.Comment: Submitted to AP
Geochemistry and metallogeny of Neoproterozoic pyrite in oxic and anoxic sediments
The Neoproterozoic Dalradian Supergroup contains widespread diagenetic sulphides present as pyrite. The sulphides occur in both carbonaceous shales and glacial diamictites, that were deposited in relatively reducing and oxidising conditions respectively. The trace element compositions of the pyrite, and consequently the whole rock compositions, contrast between the two lithologies. The highest concentrations of selenium, tellurium and gold are all found in diamictite-hosted pyrite. The data suggest that increased mobility of these elements in oxidising conditions led to greater uptake when pyrite was precipitated. As one model for the formation of orogenic gold ore deposits assumes a sulphide-rich protolith, pyrite ultimately formed during relatively oxidising conditions could make a contribution, including the widespread pyrite precipitated during the Neoproterozoic ‘Snowball Earth’ glaciations
Bloch oscillations of Bose-Einstein condensates: Breakdown and revival
We investigate the dynamics of Bose-Einstein condensates (BEC) in a tilted
one-dimensional periodic lattice within the mean-field (Gross-Pitaevskii)
description. Unlike in the linear case the Bloch oscillations decay because of
nonlinear dephasing. Pronounced revival phenomena are observed. These are
analyzed in detail in terms of a simple integrable model constructed by an
expansion in Wannier-Stark resonance states. We also briefly discuss the pulsed
output of such systems for stronger static fields.Comment: RevTeX4, 9 pages, 14 figure
A black shale protolith for gold-tellurium mineralisation in the Dalradian Supergroup (Neoproterozoic) of Britain and Ireland
The Dalradian Supergroup of Britain and Ireland is mineralised by gold-tellurium vein deposits. The host succession includes carbonaceous, pyritic shales (pelites) which were a source of trace elements, including gold and tellurium. LA-ICP-MS mapping of pyrite crystals shows that late stages are enriched in gold, tellurium and lead, representing concentration of these elements during metamorphism and related hydrothermal activity. The sulphur isotope composition of the pyrite varies with stratigraphic position, reflecting an origin for the pyrite in the depositional environment through microbial sulphate reduction. Where pyrite was converted to pyrrhotite, trace element contents are much lower, indicating element liberation during metamorphism. These observations are consistent with a model of black shale protoliths for orogenic gold deposits
A Discrete Four Stroke Quantum Heat Engine Exploring the Origin of Friction
The optimal power performance of a first principle quantum heat engine model
shows friction-like phenomena when the internal fluid Hamiltonian does not
commute with the external control field. The model is based on interacting
two-level-systems where the external magnetic field serves as a control
variable.Comment: 4 pages 3 figure
Calibration of Asynchronous Camera Networks: CALICO
Camera network and multi-camera calibration for external parameters is a
necessary step for a variety of contexts in computer vision and robotics,
ranging from three-dimensional reconstruction to human activity tracking. This
paper describes CALICO, a method for camera network and/or multi-camera
calibration suitable for challenging contexts: the cameras may not share a
common field of view and the network may be asynchronous. The calibration
object required is one or more rigidly attached planar calibration patterns,
which are distinguishable from one another, such as aruco or charuco patterns.
We formulate the camera network and/or multi-camera calibration problem using
rigidity constraints, represented as a system of equations, and an approximate
solution is found through a two-step process. Simulated and real experiments,
including an asynchronous camera network, multicamera system, and rotating
imaging system, demonstrate the method in a variety of settings. Median
reconstruction accuracy error was less than mm for all datasets.
This method is suitable for novice users to calibrate a camera network, and the
modularity of the calibration object also allows for disassembly, shipping, and
the use of this method in a variety of large and small spaces.Comment: 11 page
Vector meson - mixing and their form factors in light-cone quark model
The vector meson - mixing is studied in two alternative
scenarios with different numbers of mixing angles, i.e., the one-mixing-angle
scenario and the two-mixing-angle scenario, in both the octect-singlet mixing
scheme and the quark flavor mixing scheme. Concerning the reproduction of
experimental data and the behavior of transition form factors,
one-mixing-angle scenario in the quark flavor scheme performs better than that
in the octet-singlet scheme, while the two-mixing-angle scenario works well for
both mixing schemes. The difference between the two mixing angles in the
octet-singlet scheme is bigger than that in the quark flavor scheme.Comment: 16 pages, 7 figures, final version to appear in PR
Changes in vegetation spectra with deterioration of leaves under two methods of preservation
An experiment to measure changes in leaf spectra under different methods of preservation over time was conducted. The spectral measurements were made by a three band hand held radiometer which simulated three Thematic Mapper (TM) bands: TM3, TM4, and TM5. Daily spectral measurements of white oak leaves under three preservation treatments were made. The spectral readings over three treatments (fresh, bottled, and bagged vegetation) were indistinguishable in bands TM3 and TM5 for up to 4 days after collection. After that time bagged and bottled samples showed significant increases in reflected energy caused by loss of chlorophyll from and dehydration of the vegetation. No significant variation in the reflectance values from TM4 over preservation type for the experimental period was observed
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