16,856 research outputs found
Differential Astrometry of Sub-arcsecond Scale Binaries at the Palomar Testbed Interferometer
We have used the Palomar Testbed Interferometer to perform very high
precision differential astrometry on the 0.25 arcsecond separation binary star
HD 171779. In 70 minutes of observation we achieve a measurement uncertainty of
approximately 9 micro-arcseconds in one axis, consistent with theoretical
expectations. Night-to-night repeatability over four nights is at the level of
16 micro-arcseconds. This method of very-narrow-angle astrometry may be
extremely useful for searching for planets with masses as small as 0.5 Jupiter
Masses around a previously neglected class of stars -- so-called ``speckle
binaries.'' It will also provide measurements of stellar parameters such as
masses and distances, useful for constraining stellar models at the 10^-3
level.Comment: 19 pages including 6 figures. Submitted to ApJ. Typos corrected,
several parts reworded for clarificatio
Initial Scientific Results from Phase-Referenced Astrometry of Sub-Arcsecond Binaries
The Palomar Testbed Interferometer has observed several binary star systems
whose separations fall between the interferometric coherence length (a few
hundredths of an arcsecond) and the typical atmospheric seeing limit of one
arcsecond. Using phase-referencing techniques we measure the relative
separations of the systems to precisions of a few tens of micro-arcseconds. We
present the first scientific results of these observations, including the
astrometric detection of the faint third stellar component of the kappa Pegasi
system.Comment: 8 pages, 5 figures. To appear in SPIE conference proceedings volume
5491, "New Frontiers in Stellar Interferometery
Introduction to Categories and Categorical Logic
The aim of these notes is to provide a succinct, accessible introduction to
some of the basic ideas of category theory and categorical logic. The notes are
based on a lecture course given at Oxford over the past few years. They contain
numerous exercises, and hopefully will prove useful for self-study by those
seeking a first introduction to the subject, with fairly minimal prerequisites.
The coverage is by no means comprehensive, but should provide a good basis for
further study; a guide to further reading is included. The main prerequisite is
a basic familiarity with the elements of discrete mathematics: sets, relations
and functions. An Appendix contains a summary of what we will need, and it may
be useful to review this first. In addition, some prior exposure to abstract
algebra - vector spaces and linear maps, or groups and group homomorphisms -
would be helpful.Comment: 96 page
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
Vacuum Alignment in Technicolor Theories-I. The Technifermion Sector
We have carried out numerical studies of vacuum alignment in technicolor
models of electroweak and flavor symmetry breaking. The goal is to understand
alignment's implications for strong and weak CP nonconservation in quark
interactions. In this first part, we restrict our attention to the
technifermion sector of simple models. We find several interesting phenomena,
including (1) the possibility that all observable phases in the technifermions'
unitary vacuum-alignment matrix are integer multiples of \pi/N' where N' \le N,
the number of technifermion doublets, and (2) the possibility of exceptionally
light pseudoGoldstone technipions.Comment: 19 pages, Latex with one postscript figur
Dynamical symmetry of isobaric analog 0+ states in medium mass nuclei
An algebraic sp(4) shell model is introduced to achieve a deeper
understanding and interpretation of the properties of pairing-governed 0+
states in medium mass atomic nuclei. The theory, which embodies the simplicity
of a dynamical symmetry approach to nuclear structure, is shown to reproduce
the excitation spectra and fine structure effects driven by proton-neutron
interactions and isovector pairing correlations across a broad range of nuclei.Comment: 7 pages, 5 figure
HeadScan: A Wearable System for Radio-Based Sensing of Head and Mouth-Related Activities
The popularity of wearables continues to rise. However, possible applications, and even their raw functionality are constrained by the types of sensors that are currently available. Accelerometers and gyroscopes struggle to capture complex user activities. Microphones and image sensors are more powerful but capture privacy sensitive information. Physiological sensors are obtrusive to users as they often require skin contact and must be placed at certain body positions to function. In contrast, radio-based sensing uses wireless radio signals to capture movements of different parts of the body, and therefore provides a contactless and privacy-preserving approach to detect and monitor human activities. In this paper, we contribute to the search for new sensing modalities for the next generation of wearable devices by exploring the feasibility of mobile radiobased human activity recognition. We believe radio-based sensing has the potential to fundamentally transform wearables as we currently know them. As the first step to achieve our vision, we have designed and developed HeadScan, a first-of-its-kind wearable for radio-based sensing of a number of human activities that involve head and mouth movements. HeadScan only requires a pair of small antennas placed on the shoulder and collar and one wearable unit worn on the arm or the belt of the user. Head- Scan uses the fine-grained CSI measurements extracted from radio signals and incorporates a novel signal processing pipeline that converts the raw CSI measurements into the targeted human activities. To examine the feasibility and performance of HeadScan, we have collected approximate 50.5 hours data from seven users. Our wide-ranging experiments include comparisons to a conventional skin-contact audio-based sensing approach to tracking the same set of head and mouth-related activities. Our experimental results highlight the enormous potential of our radio-based mobile sensing approach and provide guidance to future explorations
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