5,738 research outputs found

    The Emergence of El-Ni\~{n}o as an Autonomous Component in the Climate Network

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    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

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    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

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    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

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    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

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    We study the return interval τ\tau between price volatilities that are above a certain threshold qq 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 qq, the probability density function Pq(τ)P_q(\tau) scales with the mean interval τˉ\bar{\tau} as Pq(τ)=τˉ−1f(τ/τˉ)P_q(\tau)={\bar{\tau}}^{-1}f(\tau/\bar{\tau}), 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 qq and still obtain good statistics. We find that the scaling function f(x)f(x) is consistent for all 31 intraday datasets in various time resolutions, and the function is well approximated by the stretched exponential, f(x)∼e−axγf(x)\sim e^{-a x^\gamma}, with γ=0.38±0.05\gamma=0.38\pm 0.05 and a=3.9±0.5a=3.9\pm 0.5, which indicates the existence of correlations. We analyze the conditional probability distribution Pq(τ∣τ0)P_q(\tau|\tau_0) for τ\tau following a certain interval τ0\tau_0, and find Pq(τ∣τ0)P_q(\tau|\tau_0) depends on τ0\tau_0, which demonstrates memory in intraday return intervals. Also, we find that the mean conditional interval increases with τ0\tau_0, consistent with the memory found for Pq(τ∣τ0)P_q(\tau|\tau_0). 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

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    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

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    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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