2,098 research outputs found
Stability of the Submillimeter Brightness of the Atmosphere Above Mauna Kea, Chajnantor and the South Pole
The summit of Mauna Kea in Hawaii, the area near Cerro Chajnantor in Chile,
and the South Pole are sites of large millimeter or submillimeter wavelength
telescopes. We have placed 860 GHz sky brightness monitors at all three sites
and present a comparative study of the measured submillimeter brightness due to
atmospheric thermal emission. We report the stability of that quantity at each
site.Comment: 6 figure
Finite difference time domain calculation of transients in antennas with nonlinear loads
In this paper transient fields for antennas with more general geometries are calculated directly using Finite Difference Time Domain methods. In each FDTD cell which contains a nonlinear load, a nonlinear equation is solved at each time step. As a test case the transient current in a long dipole antenna with a nonlinear load excited by a pulsed plane wave is computed using this approach. The results agree well with both calculated and measured results previously published. The approach given here extends the applicability of the FDTD method to problems involving scattering from targets including nonlinear loads and materials, and to coupling between antennas containing nonlinear loads. It may also be extended to propagation through nonlinear materials
Signatures of Spin Glass Freezing in NiO Nanoparticles
We present a detailed study of the magnetic properties of sol-gel prepared
nickel oxide nanoparticles of different sizes. We report various measurements
such as frequency, field and temperature dependence of ac susceptibility,
temperature and field dependence of dc magnetization and time decay of
thermoremanent magnetization. Our results and analysis show that the system
behaves as a spin glass.Comment: 8 pages, 9 figure
RDF Querying
Reactive Web systems, Web services, and Web-based publish/
subscribe systems communicate events as XML messages, and in
many cases require composite event detection: it is not sufficient to react
to single event messages, but events have to be considered in relation to
other events that are received over time.
Emphasizing language design and formal semantics, we describe the
rule-based query language XChangeEQ for detecting composite events.
XChangeEQ is designed to completely cover and integrate the four complementary
querying dimensions: event data, event composition, temporal
relationships, and event accumulation. Semantics are provided as
model and fixpoint theories; while this is an established approach for rule
languages, it has not been applied for event queries before
Theory of Thermodynamic Magnetic Oscillations in Quasi-One-Dimensional Conductors
The second order correction to free energy due to the interaction between
electrons is calculated for a quasi-one-dimensional conductor exposed to a
magnetic field perpendicular to the chains. It is found that specific heat,
magnetization and torque oscillate when the magnetic field is rotated in the
plane perpendicular to the chains or when the magnitude of magnetic filed is
changed. This new mechanism of thermodynamic magnetic oscillations in metals,
which is not related to the presence of any closed electron orbits, is applied
to explain behavior of the organic conductor (TMTSF)ClO.Comment: 11 pages + 5 figures (included
Studies of the limit order book around large price changes
We study the dynamics of the limit order book of liquid stocks after
experiencing large intra-day price changes. In the data we find large
variations in several microscopical measures, e.g., the volatility the bid-ask
spread, the bid-ask imbalance, the number of queuing limit orders, the activity
(number and volume) of limit orders placed and canceled, etc. The relaxation of
the quantities is generally very slow that can be described by a power law of
exponent . We introduce a numerical model in order to understand
the empirical results better. We find that with a zero intelligence deposition
model of the order flow the empirical results can be reproduced qualitatively.
This suggests that the slow relaxations might not be results of agents'
strategic behaviour. Studying the difference between the exponents found
empirically and numerically helps us to better identify the role of strategic
behaviour in the phenomena.Comment: 19 pages, 7 figure
The NANOGrav 11 Year Data Set: Pulsar-timing Constraints on the Stochastic Gravitational-wave Background
We search for an isotropic stochastic gravitational-wave background (GWB) in the newly released 11 year data set from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). While we find no evidence for a GWB, we place constraints on a population of inspiraling supermassive black hole (SMBH) binaries, a network of decaying cosmic strings, and a primordial GWB. For the first time, we find that the GWB constraints are sensitive to the solar system ephemeris (SSE) model used and that SSE errors can mimic a GWB signal. We developed an approach that bridges systematic SSE differences, producing the first pulsar-timing array (PTA) constraints that are robust against SSE errors. We thus place a 95% upper limit on the GW-strain amplitude of AGWB \u3c 1.45 × 10−15 at a frequency of f = 1 yr−1 for a fiducial f−2/3 power-law spectrum and with interpulsar correlations modeled. This is a factor of ~2 improvement over the NANOGrav nine-year limit calculated using the same procedure. Previous PTA upper limits on the GWB (as well as their astrophysical and cosmological interpretations) will need revision in light of SSE systematic errors. We use our constraints to characterize the combined influence on the GWB of the stellar mass density in galactic cores, the eccentricity of SMBH binaries, and SMBH–galactic-bulge scaling relationships. We constrain the cosmic-string tension using recent simulations, yielding an SSE-marginalized 95% upper limit of Gμ \u3c 5.3 × 10−11—a factor of ~2 better than the published NANOGrav nine-year constraints. Our SSE-marginalized 95% upper limit on the energy density of a primordial GWB (for a radiation-dominated post-inflation universe) is ΩGWB(f) h2 \u3c 3.4 × 10−10
Role of the dimerized gap due to anion ordering in spin-density wave phase of (TMTSF)ClO at high magnetic fields
Magnetoresistance measurements have been carried out along the highly
conducting a axis in the FISDW phase of hydrogened and deuterated
(TMTSF)ClO for various cooling rates through the anion ordering
temperature. With increasing the cooling rate, a) the high field phase boundary
, observed at 27 T in hydrogened samples for slowly cooled,
is shifted towards a lower field, b) the last semimetallic SDW phase below
is suppressed, and c) the FISDW insulating phase above
is enhanced in both salts. The cooling rate dependence of
the FISDW transition and of in both salts can be explained
by taking into account the peculiar SDW nesting vector stabilized by the
dimerized gap due to anion ordering.Comment: 6pages,6figures(EPS), accepted for publication in PR
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