378 research outputs found
Transverse Chromatic Aberrations in Virtual Reality Devices
We demonstrate a method for measuring the transverse chromatic aberration (TCA) in a virtual reality head-mounted display (VR HMD). This procedure was used to characterize the optical performance of the Oculus Go VR HMD. Results show a measurable TCA for angles larger than approximately 6⊠from the center of the field of view. TCA can be thought of as a wavelength dependent magnification, and as a result, the relative size of objects vary based on the rendering color. In addition, this leads to color changes in the image due to mixing with neighboring pixels, which impacts image quality. The test results for the Oculus Go show promise for characterizing TCA across different HMDs
Ultracold collisions in tight harmonic traps: Quantum defect model and application to metastable helium atoms
We analyze a system of two colliding ultracold atoms under strong harmonic
confinement from the viewpoint of quantum defect theory and formulate a
generalized self-consistent method for determining the allowed energies. We
also present two highly efficient computational methods for determining the
bound state energies and eigenfunctions of such systems. The perturbed harmonic
oscillator problem is characterized by a long asymptotic region beyond the
effective range of the interatomic potential. The first method, which is based
on quantum defect theory and is an adaptation of a technique developed by one
of the authors (GP) for highly excited states in a modified Coulomb potential,
is very efficient for integrating through this outer region. The second method
is a direct numerical solution of the radial Schr\"{o}dinger equation using a
discrete variable representation of the kinetic energy operator and a scaled
radial coordinate grid. The methods are applied to the case of trapped
spin-polarized metastable helium atoms. The calculated eigenvalues agree very
closely for the two methods, and with those computed self-consistently using
the generalized self-consistent method.Comment: 11 pages,REVTEX, text substantially revised, title modifie
Clone flow analysis for a theory inspired Neutrino Experiment planning
The presence of several clone solutions in the simultaneous measurement of
() has been widely discussed in literature. In this letter
we write the analytical formulae of the clones location in the
() plane as a function of the physical input pair
(). We show how the clones move with changing
. The "clone flow" can be significantly different if computed
(naively) from the oscillation probabilities or (exactly) from the
probabilities integrated over the neutrino flux and cross-section.
Using our complete computation we compare the clone flow of a set of possible
future neutrino experiments: the CERN SuperBeam, BetaBeam and Neutrino Factory
proposals. We show that the combination of these specific BetaBeam and
SuperBeam does not help in solving the degeneracies. On the contrary, the
combination of one of them with the Neutrino Factory Golden and Silver channel
can be used, from a theoretical point of view, to solve completely the
eightfold degeneracy.Comment: 23 pages, using epsfi
Spatial variations in lead isotopes, Tasman Element, eastern Australia
Lead isotope data from ore deposits and mineral occurrences in the Tasman Element of eastern Australia have been used to construct isotopic maps of this region. These maps exhibit systematic patterns in parameters derived from isotope ratios. The parameters include ÎŒ (238U/204Pb), as calculated using the Cumming and Richards (1975) lead evolution model, and the difference between true age of mineralisation and the Cumming and Richards lead isotope model age of mineralisation (Ît).
Variations in Ό coincide with boundaries at the orogen, subprovince and zone scales. The boundary between the Lachlan and New England orogens is accompanied by a decrease in Ό, and within the Lachlan Orogen, the Central Subprovince is characterised by Ό that is significantly higher than in the adjacent Eastern and Western subprovinces. Within the Eastern Subprovince, the Cu-Au-rich Macquarie Arc is characterised by significantly lower Ό relative to adjacent rocks.
The Macquarie Arc is also characterised by very high Ît (generally above 200 Myr). Other regions characterised by very high Ît include western Tasmania, the southeastern New England Orogen, and the Hodgkinson Province in northern Queensland. These anomalies are within a broad pattern of decreasing Ît from east to west, with Paleozoic deposits within or adjacent to Proterozoic crust characterised by Ît values of 50 Myr or below.
The patterns in Ît are interpreted to reflect the presence of the two major tectonic components involved in the Paleozoic Tasman margin in Australia (cf., MĂŒnker, 2000): subducting proto-Pacific crust (Ît >150 Myr), and Proterozoic Australia crust (Ît < 50 Myr) on the over-riding plate. Proterozoic Australia crustal sources are interpreted to dominate the western parts of the Tasman Element and Proterozoic crust further to the west, whereas Pacific crustal sources are inferred to characterise western Tasmania and much of the eastern part of the Tasman Element. Contrasts in Ît between the Cambrian Mount Read Volcanics in western Tasmania and similar aged rocks in western Victoria and New South Wales make direct tectonic correlation between these rocks problematic
Unity of CP and T Violation in Neutrino Oscillations
In a previous work a simultaneous P- CP[P] and P- T[P] bi-probability plot
was proposed as a useful tool for unified graphical description of CP and T
violation in neutrino oscillation. The ``baseball diamond'' structure of the
plot is understood as a consequence of the approximate CP-CP and the T-CP
relations obeyed by the oscillation probabilities. In this paper, we make a
step forward toward deeper understanding of the unified graphical
representation by showing that these two relations are identical in its
content, suggesting a truly unifying view of CP and T violation in neutrino
oscillations. We suspect that the unity reflects the underlying CPT theorem. We
also present calculation of corrections to the CP-CP and the T-CP relations to
leading order in Delta m^2_{21} / Delta m^2_{31} and s^2_{13}.Comment: 20 references added, version to appear in "Focus Issue on Neutrino
Physics" of New Journal of Physic
Observation of the nonlinear Hall effect under time reversal symmetric conditions
The electrical Hall effect is the production of a transverse voltage under an
out-of-plane magnetic field. Historically, studies of the Hall effect have led
to major breakthroughs including the discoveries of Berry curvature and the
topological Chern invariants. In magnets, the internal magnetization allows
Hall conductivity in the absence of external magnetic field. This anomalous
Hall effect (AHE) has become an important tool to study quantum magnets. In
nonmagnetic materials without external magnetic fields, the electrical Hall
effect is rarely explored because of the constraint by time-reversal symmetry.
However, strictly speaking, only the Hall effect in the linear response regime,
i.e., the Hall voltage linearly proportional to the external electric field,
identically vanishes due to time-reversal symmetry. The Hall effect in the
nonlinear response regime, on the other hand, may not be subject to such
symmetry constraints. Here, we report the observation of the nonlinear Hall
effect (NLHE) in the electrical transport of the nonmagnetic 2D quantum
material, bilayer WTe2. Specifically, flowing an electrical current in bilayer
WTe2 leads to a nonlinear Hall voltage in the absence of magnetic field. The
NLHE exhibits unusual properties sharply distinct from the AHE in metals: The
NLHE shows a quadratic I-V characteristic; It strongly dominates the nonlinear
longitudinal response, leading to a Hall angle of about 90 degree. We further
show that the NLHE directly measures the "dipole moment" of the Berry
curvature, which arises from layer-polarized Dirac fermions in bilayer WTe2.
Our results demonstrate a new Hall effect and provide a powerful methodology to
detect Berry curvature in a wide range of nonmagnetic quantum materials in an
energy-resolved way
Graphene plasmonics: A platform for strong light-matter interaction
Graphene plasmons provide a suitable alternative to noble-metal plasmons
because they exhibit much larger confinement and relatively long propagation
distances, with the advantage of being highly tunable via electrostatic gating.
We report strong light- matter interaction assisted by graphene plasmons, and
in particular, we predict unprecedented high decay rates of quantum emitters in
the proximity of a carbon sheet, large vacuum Rabi splitting and Purcell
factors, and extinction cross sections exceeding the geometrical area in
graphene ribbons and nanometer-sized disks. Our results provide the basis for
the emerging and potentially far-reaching field of graphene plasmonics,
offering an ideal platform for cavity quantum electrodynamics and supporting
the possibility of single-molecule, single-plasmon devices.Comment: 39 pages, 15 figure
Neutral currents and tests of three-neutrino unitarity in long-baseline experiments
We examine a strategy for using neutral current measurements in long-baseline
neutrino oscillation experiments to put limits on the existence of more than
three light, active neutrinos. We determine the relative contributions of
statistics, cross section uncertainties, event misidentification and other
systematic errors to the overall uncertainty of these measurements. As specific
case studies, we make simulations of beams and detectors that are like the K2K,
T2K, and MINOS experiments. We find that the neutral current cross section
uncertainty and contamination of the neutral current signal by charge current
events allow a sensitivity for determining the presence of sterile neutinos at
the 0.10--0.15 level in probablility.Comment: 24 pages, Latex2e, uses graphicx.sty, 2 postscript figures. Submitted
to the Neutrino Focus Issue of New Journal Physics at http://www.njp.or
Abstracts
Abstracts of papers about Giuseppe Verdi and his works, presented at joint meetings of the AIVS and Greater NY Chapter of the American Musicological Society, 1979-81 (Hepokoski, Lawton, Chusid, Hornick, NĂĄdas, Tomlinson, Garrison, Powers), at the 1982 national meeting of the American Musicological Society (Harwood), and at an NEH-sponsored summer seminar at NYU in 1980 (Beams, Cole, Cordell, Davis, Fry, King, Mason, McCauley, Town)
Coordinated strategy for a model-based decision support tool for coronavirus disease, Utah, USA
The coronavirus disease pandemic has highlighted the key role epidemiologic models play in supporting public health decision-making. In particular, these models provide estimates of outbreak potential when data are scarce and decision-making is critical and urgent. We document the integrated modeling response used in the US state of Utah early in the coronavirus disease pandemic, which brought together a diverse set of technical experts and public health and healthcare officials and led to an evidence-based response to the pandemic. We describe how we adapted a standard epidemiologic model; harmonized the outputs across modeling groups; and maintained a constant dialogue with policymakers at multiple levels of government to produce timely, evidence-based, and coordinated public health recommendations and interventions during the first wave of the pandemic. This framework continues to support the state's response to ongoing outbreaks and can be applied in other settings to address unique public health challenges
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