8,422 research outputs found
Time delay and integration detectors using charge transfer devices
An imaging system comprises a multi-channel matrix array of CCD devices wherein a number of sensor cells (pixels) in each channel are subdivided and operated in discrete intercoupled groups of subarrays with a readout CCD shift register terminating each end of the channels. Clock voltages, applied to the subarrays, selectively cause charge signal flow in each subarray in either direction independent of the other subarrays. By selective application of four phase clock voltages, either one, two or all three of the sections subarray sections cause charge signal flow in one direction, while the remainder cause charge signal flow in the opposite direction. This creates a form of selective electronic exposure control which provides an effective variable time delay and integration of three, six or nine sensor cells or integration stages. The device is constructed on a semiconductor sustrate with a buried channel and is adapted for front surface imaging through transparent doped tin oxide gates
An LED-based Flasher System for VERITAS
We describe a flasher system designed for use in monitoring the gains of the
photomultiplier tubes used in the VERITAS gamma-ray telescopes. This system
uses blue light-emitting diodes (LEDs) so it can be operated at much higher
rates than a traditional laser-based system. Calibration information can be
obtained with better statistical precision with reduced loss of observing time.
The LEDs are also much less expensive than a laser. The design features of the
new system are presented, along with measurements made with a prototype mounted
on one of the VERITAS telescopes.Comment: Accepted for publication in Nuclear Instruments and Methods in
Physics Research
Universality in escape from a modulated potential well
We show that the rate of activated escape from a periodically modulated
potential displays scaling behavior versus modulation amplitude . For
adiabatic modulation of an optically trapped Brownian particle, measurements
yield with . The theory gives
in the adiabatic limit and predicts a crossover to scaling as
approaches the bifurcation point where the metastable state disappears.Comment: 4 pages, 3 figure
Ultracold, radiative charge transfer in hybrid Yb ion - Rb atom traps
Ultracold hybrid ion-atom traps offer the possibility of microscopic
manipulation of quantum coherences in the gas using the ion as a probe.
However, inelastic processes, particularly charge transfer can be a significant
process of ion loss and has been measured experimentally for the Yb ion
immersed in a Rb vapour. We use first-principles quantum chemistry codes to
obtain the potential energy curves and dipole moments for the lowest-lying
energy states of this complex. Calculations for the radiative decay processes
cross sections and rate coefficients are presented for the total decay
processes. Comparing the semi-classical Langevin approximation with the quantum
approach, we find it provides a very good estimate of the background at higher
energies. The results demonstrate that radiative decay mechanisms are important
over the energy and temperature region considered. In fact, the Langevin
process of ion-atom collisions dominates cold ion-atom collisions. For spin
dependent processes \cite{kohl13} the anisotropic magnetic dipole-dipole
interaction and the second-order spin-orbit coupling can play important roles,
inducing couplingbetween the spin and the orbital motion. They measured the
spin-relaxing collision rate to be approximately 5 orders of magnitude higher
than the charge-exchange collision rate \cite{kohl13}. Regarding the measured
radiative charge transfer collision rate, we find that our calculation is in
very good agreement with experiment and with previous calculations.
Nonetheless, we find no broad resonances features that might underly a strong
isotope effect. In conclusion, we find, in agreement with previous theory that
the isotope anomaly observed in experiment remains an open question.Comment: 7 figures, 1 table accepted for publication in J. Phys. B: At. Mol.
Opt. Phys. arXiv admin note: text overlap with arXiv:1107.114
Computational Morphology: Three-Dimensional Computer Graphics for Electron Microscopy
This paper describes a method for the computer reconstruction of surfaces from a sequence of electron micrographs, and a data structuring approach to the problem of representing and analyzing objects of physiological importance. The reconstruction technique involves the following stages: 1) object outlines are traced from each section, 2) the computer chain encodes these outlines, 3) the chain codes are reduced to the minimum number of boundary points which satisfactorily define the boundary, 4) polygons are mapped onto the boundary points between sections to approximate the surface, and 4) color coded, shaded surface views are computed of any subset of objects viewed and illuminated from arbitrary locations
Infrared spectroscopy of hole doped ABA-stacked trilayer graphene
Using infrared spectroscopy, we investigate bottom gated ABA-stacked trilayer
graphene subject to an additional environment-induced p-type doping. We find
that the Slonczewski-Weiss-McClure tight-binding model and the Kubo formula
reproduce the gate voltage-modulated reflectivity spectra very accurately. This
allows us to determine the charge densities and the potentials of the
{\pi}-band electrons on all graphene layers separately and to extract the
interlayer permittivity due to higher energy bands.Comment: 6 pages, 6 figures Corrected sign of fig 3 and visibilty of fig
Politics in the Classroom
Nursing and midwifery is, in the UK, regulated by the Nursing and Midwifery Council (NMC). Regulatory duties include establishing standards for education, and from January 2019, new educational programmes will be approved against standards detailed in the document Future nurse: Standards of proficiency for registered nurses (NMC, 2019 â hereafter âthe standardsâ). This publication lists âthe knowledge and skills that registered nurses must demonstrate when caring for peopleâ (ibid, p.3); and from September 2020, registration (licence) will require the successful completion of programmes that have been ratified against these standards. The importance of this document in a UK context cannot be understated. However, less parochially, learning outcomes contained in section 7 of the standards raise questions that require educator attention whenever politically sensitive topics (broadly conceived) are discussed. This study explores these questions insofar as they relate to the stance (neutrality or partisanship) that educators adopt in politicised discussion, and the management of student speech/expression. Pratt, Boll and Collinsâ (2007) paper Towards a plurality of perspectives for nurse educators is recruited to structure argument
Raised Shoreline Phenomena and Postglacial Emergence in South-Central Newfoundland
Two types of raised marine shoreline features occur in the Burin-Hermitage area of southern Newfoundland marine benches cut in bedrock, and terraces and beaches developed in unconsolidated materials. Most of the benches are older than Late Wisconsinan, and a horizontal rock shoreline at 4.5 ± 1.5 m, which occurs throughout the region, was probably formed in the last interglacial period. Raised deltas and coastal outwash deposits graded to former sea level positions, which define the Late Wisconsinan marine limit across the northern part of the study area, are correlated with terraces and raised beaches further south on the Burin Peninsula. The elevations of these features are used to define the regional pattern of postglacial emergence. More than 30 m of emergence has occurred in the northwest, but the extreme southern part of the region is undergoing submergence.Dans la rĂ©gion de Burin-Hermitage, au sud de Terre-Neuve, on retrouve deux types de lignes de rivage marines soulevĂ©es: des plates-formes marines entaillĂ©es dans la roche en place ainsi que des terrasses et des plages dĂ©veloppĂ©es dans des matĂ©riaux meubles. La plupart des plates-formes datent d'avant le Wisconsinien infĂ©rieur. Une ligne de rivage rocheuse horizontale situĂ©e Ă 4,5 ± 1,5 m, qu'on retrouve Ă travers la rĂ©gion, fut probablement formĂ©e au cours du dernier interglaciaire. Des deltas soulevĂ©s et des Ă©pandages fluvioglaciaires cĂŽtiers, associĂ©s Ă des plans d'eau marins qui marquent la limite marine du Wisconsinien infĂ©rieur dans la partie nord de la zone d'Ă©tude, sont mis en relation avec des terrasses et des plages soulevĂ©es existant plus au sud dans la pĂ©ninsule de Burin. L'altitude de ces formes sert Ă Ă©tablir le mode rĂ©gional d'Ă©mersion post-glaciaire. Il s'est produit une emersion de plus de 30 m dans le nord-ouest, alors que l'extrĂȘme-sud de la rĂ©gion est en phase de submersion
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