3,543 research outputs found
GONG p-mode parameters through two solar cycles
We investigate the parameters of global solar p-mode oscillations, namely
damping width , amplitude , mean squared velocity , energy , and energy supply rate ,
derived from two solar cycles' worth (1996 - 2018) of Global Oscillation
Network Group (GONG) time series for harmonic degrees . We correct
for the effect of fill factor, apparent solar radius, and spurious jumps in the
mode amplitudes. We find that the amplitude of the activity related changes of
and depends on both frequency and harmonic degree of the modes,
with the largest variations of for modes with and with a min-to-max variation of
and of for modes with and with a min-to-max variation of
. The level of correlation between the solar radio flux
and mode parameters also depends on mode frequency and harmonic
degree. As a function of mode frequency, the mode amplitudes are found to
follow an asymmetric Voigt profile with
. From the mode parameters, we
calculate physical mode quantities and average them over specific mode
frequency ranges. This way, we find that the mean squared velocities and energies of p modes are anti-correlated with the level of
activity, varying by and , respectively, and that
the mode energy supply rates show no significant correlation with activity.
With this study we expand previously published results on the temporal
variation of solar p-mode parameters. Our results will be helpful to future
studies of the excitation and damping of p modes, i.e., the interplay between
convection, magnetic field, and resonant acoustic oscillations.Comment: Accepted for publication in Solar Physics. 33 pages, 16 figures, 5
table
Adaptive Sensor Data Acquisition for Gait Analysis
AbstractIn this paper a method is presented that uses one sensor configuration for both static and dynamic loading conditions to capture plantar pressure distribution values. In the gait analysis, different phases are from interest. The phases produces highly different signals and with conventional sensors and static data acquisition systems it is often difficult to achieve high precision measure- ments. An advanced programmable amplifier can be used to adapt the full resolution of the measurement system dynamically to the needs of the gait analyses. With the proposed system, it is possible to precisely measure the gait phases without changing any hardware. While the system is performing it is energy efficient as it only consumes power if needed. Furthermore, it is highly integrated and space saving. Thus, ideally suited for mobile outdoor applications. The technology used in this example can be applied to many different general sensor measurement questions in sports engineering
HELAS Local Helioseismology Activities
The main goals of the HELAS local helioseismology network activity are to
consolidate this field of research in Europe, to organise scientific workshops,
and to facilitate the distribution of observations and data analysis software.
Most of this is currently accomplished via a dedicated website at
http://www.mps.mpg.de/projects/seismo/NA4/ . In this paper we list the outreach
material, observational data, analysis tools and modelling tools currently
available from the website and describe the focus of the scientific workshops
and their proceedings.Comment: 14 pages, 5 figure
A Comparison of Stripe Modulations in LaBaCuO and LaNdSrCuO
We report combined soft and hard x-ray scattering studies of the electronic
and lattice modulations associated with stripe order in
LaBaCuO and LaNdSrCuO. We
find that the amplitude of both the electronic modulation of the hole density
and the strain modulation of the lattice is significantly larger in
LaBaCuO than in LaNdSrCuO
and is also better correlated. The in-plane correlation lengths are isotropic
in each case; for LaBaCuO, \AA\
whereas for LaNdSrCuOF,
\AA. We find that the modulations are temperature independent in
LaBaCuO in the low temperature tetragonal phase. In
contrast, in LaNdSrCuO, the amplitude grows
smoothly from zero, beginning 13 K below the LTT phase transition. We speculate
that the reduced average tilt angle in LaBaCuO results
in reduced charge localization and incoherent pinning, leading to the longer
correlation length and enhanced periodic modulation amplitude.Comment: 6 pages, 4 figure
Entanglement correlations, Bell inequalities, and the concurrence
Probabilities of measurement outcomes of two-particle entangled states give a
physically transparent interpretation of the concurrence and of the
I-concurrence as entanglement measures. The (I)-concurrence can thus be
measured experimentally. The tight connection between these measures and Bell
inequalities is highlighted.Comment: Updated version of quant-ph/0110139, with extension to mixed states.
To appear in Phys. Lett.
Squeezed light from a silicon micromechanical resonator
Monitoring a mechanical object’s motion, even with the gentle
touch of light, fundamentally alters its dynamics. The experimental
manifestation of this basic principle of quantum mechanics, its
link to the quantum nature of light and the extension of quantum
measurement to the macroscopic realm have all received extensive
attention over the past half-century. The use of squeezed light, with
quantum fluctuations below that of the vacuum field, was proposed
nearly three decades ago
as a means of reducing the optical read-out
noise in precision force measurements. Conversely, it has also been proposed that a continuous measurement of a mirror’s position with
light may itself give rise to squeezed light. Such squeezed-light generation has recently been demonstrated in a system of ultracold
gas-phase atoms whose centre-of-mass motion is analogous to the
motion of a mirror. Here we describe the continuous position measurement of a solid-state, optomechanical system fabricated from a
silicon microchip and comprising a micromechanical resonator
coupled to a nanophotonic cavity. Laser light sent into the cavity is
used to measure the fluctuations in the position of the mechanical
resonator at a measurement rate comparable to its resonance frequency and greater than its thermal decoherence rate. Despite the
mechanical resonator’s highly excited thermal state (10^4
phonons),
we observe, through homodyne detection, squeezing of the reflected
light’s fluctuation spectrum at a level 4.5 ± 0.2 percent below that of
vacuum noise over a bandwidth of a few megahertz around the
mechanical resonance frequency of 28megahertz. With further
device improvements, on-chip squeezing at significant levels should
be possible, making such integrated microscale devices well suited
for precision metrology applications
Characterization of the Positivity of the Density Matrix in Terms of the Coherence Vector Representation
A parameterization of the density operator, a coherence vector
representation, which uses a basis of orthogonal, traceless, Hermitian matrices
is discussed. Using this parameterization we find the region of permissible
vectors which represent a density operator. The inequalities which specify the
region are shown to involve the Casimir invariants of the group. In particular
cases, this allows the determination of degeneracies in the spectrum of the
operator. The identification of the Casimir invariants also provides a method
of constructing quantities which are invariant under {\it local} unitary
operations. Several examples are given which illustrate the constraints
provided by the positivity requirements and the utility of the coherence vector
parameterization.Comment: significantly rewritten and submitted for publicatio
Stakes are High: Essays on Brazil and the Future of the Global Internet
This workbook seeks to provide some background to the Global Meeting on the Future of Internet Governance (NETmundial) scheduled for April 23rd and 24th 2014 in São Paulo, Brazil. It is designed to help outline the internet policy issues that are at stake and will be discussed at NETmundial, as well as background on internet policy in Brazil. The workbook includes essays on the history of the NETmundial meeting and the Marco Civil process in Brazil; some background on the environment in Germany—with particular attention to the link between the meeting and the Snowden case; questions of legitimacy surrounding open processes for lawmaking; and comments on the material presented to the organizing committee by official and unofficial commenters.
This workbook was produced as a part of the Internet Policy Observatory, a program at the Center for Global Communication Studies, the Annenberg School for Communication at the University of Pennsylvania. It was edited and curated by a steering committee including Ellery Roberts Biddle of Global Voices, Ronaldo Lemos of the Rio Institute for Technology and Society, and Monroe Price of the Annenberg School for Communication. They were assisted by Alexandra Esenler, Laura Schwartz-Henderson, and Briar Smith
Near collapse of the meridional SST gradient in the eastern equatorial Pacific during Heinrich Stadial 1
Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 28 (2013): 663–674, doi:10.1002/2013PA002499.Sea surface temperatures (SST) and inorganic continental input over the last 25,000 years (25 ka) are reconstructed in the far eastern equatorial Pacific (EEP) based on three cores stretching from the equatorial front (~0.01°N, ME0005-24JC) into the cold tongue region (~3.6°S; TR163-31P and V19-30). We revisit previously published alkenone-derived SST records for these sites and present a revised chronology for V19-30. Inorganic continental input is quantified at all three sites based on 230Th-normalized fluxes of the long-lived continental isotope thorium-232 and interpreted to be largely dust. Our data show a very weak meridional (cross-equatorial) SST gradient during Heinrich Stadial 1 (HS1, 18–15 ka B.P.) and high dust input along with peak export production at and north of the equator. These findings are corroborated by an Earth system model experiment for HS1 that simulates intensified northeasterly trade winds in the EEP, stronger equatorial upwelling, and surface cooling. Furthermore, the related southward shift of the Intertropical Convergence Zone (ITCZ) during HS1 is also indicative of drier conditions in the typical source regions for dust.This work was
supported by grants from the Canadian Foundation for Climate and Atmospheric
Sciences (CFCAS), the Canadian Institute for Advanced Research (CIFAR),
the Natural Sciences and Engineering Research Council (NSERC), Canada
and the National Science Foundation (NSF), USA. A. Timmermann and
T. Friedrich were supported by NSF grant 1010869.2014-05-2
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