5,762 research outputs found
The Emergence of El-Ni\~{n}o as an Autonomous Component in the Climate Network
We construct and analyze a climate network which represents the
interdependent structure of the climate in different geographical zones and
find that the network responds in a unique way to El-Ni\~{n}o events. Analyzing
the dynamics of the climate network shows that when El-Ni\~{n}o events begin,
the El-Ni\~{n}o basin partially loses its influence on its surroundings. After
typically three months, this influence is restored while the basin loses almost
all dependence on its surroundings and becomes \textit{autonomous}. The
formation of an autonomous basin is the missing link to understand the
seemingly contradicting phenomena of the afore--noticed weakening of the
interdependencies in the climate network during El-Ni\~{n}o and the known
impact of the anomalies inside the El-Ni\~{n}o basin on the global climate
system.Comment: 5 pages,10 figure
Ranking the economic importance of countries and industries
In the current era of worldwide market interdependencies, the global financial village has become increasingly vulnerable to systemic collapse. The global financial crisis has highlighted the necessity of understanding and quantifying the interdependencies among the world’s economies; developing new, effective approaches for risk evaluation; and providing mitigating solutions. We present a methodological framework for quantifying interdependencies in the global market and for evaluating risk levels in the worldwide financial network. The resulting information will enable policy and decision makers to better measure, understand and maintain financial stability. We use this methodology to rank the economic importance of each industry and country according to the global damage that would result from its failure. Our quantitative results shed new light on China’s increasing economic dominance over other economies, including that of the United States, as well as the global economy
Quantification of propagation modes in an astronomical instrument from its radiation pattern
Context. Understanding complex phenomena and unsolved problems in modern
astronomy requires wider-bandwidth observations. The current technique for
designing and fabricating an astronomical instrument potentially provides such
observations with higher efficiency and precision than in the past.
Higher-order modes in an instrument associated with wider bandwidths have been
reported, which may degrade observation precision. Aims. To reduce the
unfavorable degradation, we need to quantify the higher-order propagation
modes, though their power is too difficult to measure directly. Instead of the
direct mode measurement, we aim at developing a method based on measurable
radiation patterns from an instrument of interest. Method. Assuming a linear
system, whose radiated field is determined as a superposition of the mode
coefficients in an instrument, we obtain a coefficient matrix connecting the
inside modes and the outside radiated field and calculate the pseudo-inverse
matrix. To understand the estimation accuracy of the proposed method, we
demonstrate two cases with numerical simulations, axially-corrugated horn case
and offset Cassegrain antenna case, and investigate the effect of random errors
on the accuracy. Results. Both cases showed the estimated mode coefficients
with a precision of 10e-6 with respect to the maximum mode amplitude and 10e-3
degrees in phase, respectively. The calculation errors were observed when the
random errors were smaller than 0.01 percent of the maximum radiated field
amplitude. The demonstrated method works independently of the details of a
system. Conclusions. The method can quantify the propagation modes inside an
instrument and will be applicable to most of linear components and antennas.
This method can be employed for a general purpose, such as diagnosis of feed
alignment and higher-performance feed design.Comment: 7 pages, 11 figure
Ka-band Ga-As FET noise receiver/device development
The development of technology for a 30 GHz low noise receiver utilizing GaAs FET devices exclusively is discussed. This program required single and dual-gate FET devices, low noise FET amplifiers, dual-gate FET mixers, and FET oscillators operating at Ka-band frequencies. A 0.25 micrometer gate FET device, developed with a minimum noise figure of 3.3 dB at 29 GHz and an associated gain of 7.4 dB, was used to fabricate a 3-stage amplifier with a minimum noise figure and associated gain of 4.4 dB and 17 dB, respectively. The 1-dB gain bandwidth of this amplifier extended from below 26.5 GHz to 30.5 GHz. A dual-gate mixer with a 2 dB conversion loss and a minimum noise figure of 10 dB at 29 GHz as well as a dielectric resonator stabilized FET oscillator at 25 GHz for the receiver L0. From these components, a hybrid microwave integrated circuit receiver was constructed which demonstrates a minimum single-side band noise figure of 4.6 dB at 29 GHz with a conversion gain of 17 dB. The output power at the 1-dB gain compression point was -5 dBm
Scaling and memory of intraday volatility return intervals in stock market
We study the return interval between price volatilities that are above
a certain threshold for 31 intraday datasets, including the Standard &
Poor's 500 index and the 30 stocks that form the Dow Jones Industrial index.
For different threshold , the probability density function
scales with the mean interval as
, similar to that found in daily
volatilities. Since the intraday records have significantly more data points
compared to the daily records, we could probe for much higher thresholds
and still obtain good statistics. We find that the scaling function is
consistent for all 31 intraday datasets in various time resolutions, and the
function is well approximated by the stretched exponential, , with and , which indicates the
existence of correlations. We analyze the conditional probability distribution
for following a certain interval , and find
depends on , which demonstrates memory in intraday
return intervals. Also, we find that the mean conditional interval
increases with , consistent with the memory found for
. Moreover, we find that return interval records have long
term correlations with correlation exponents similar to that of volatility
records.Comment: 19 pages, 8 figure
Electric Control of Spin Helicity in a Magnetic Ferroelectric
Magnetic ferroelectrics or multiferroics, which are currently extensively
explored, may provide a good arena to realize a novel magnetoelectric function.
Here we demonstrate the genuine electric control of the spiral magnetic
structure in one of such magnetic ferroelectrics, TbMnO3. A spin-polarized
neutron scattering experiment clearly shows that the spin helicity, clockwise
or counter-clockwise, is controlled by the direction of spontaneous
polarization and hence by the polarity of the small cooling electric field.Comment: 4 pages, 3 figure
Possible Kondo resonance in PrFe4P12 studied by bulk-sensitive photoemission
Pr 4f electronic states in Pr-based filled skutterudites PrT4X12(T=Fe and Ru;
X=P and Sb) have been studied by high-resolution bulk-sensitive Pr 3d-4f
resonance photoemission. A very strong spectral intensity is observed just
below the Fermi level in the heavy-fermion system PrFe4P12. The increase of its
intensity at lower temperatures is observed. We speculate that this is the
Kondo resonance of Pr, the origin of which is attributed to the strong
hybridization between the Pr 4f and the conduction electrons.Comment: 4 pages(camera ready format), 4 figures, ReVTeX
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