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Coupling Strength (coupling + strength)
Selected AbstractsA comparison of Granger causality and coherency in fMRI-based analysis of the motor systemHUMAN BRAIN MAPPING, Issue 11 2009Andrew S. Kayser Abstract The ability of functional MRI to acquire data from multiple brain areas has spurred developments not only in voxel-by-voxel analyses, but also in multivariate techniques critical to quantifying the interactions between brain areas. As the number of multivariate techniques multiplies, however, few studies in any modality have directly compared different connectivity measures, and fewer still have done so in the context of well-characterized neural systems. To focus specifically on the temporal dimension of interactions between brain regions, we compared Granger causality and coherency (Sun et al., 2004, 2005: Neuroimage 21:647,658, Neuroimage 28:227,237) in a well-studied motor system (1) to gain further insight into the convergent and divergent results expected from each technique, and (2) to investigate the leading and lagging influences between motor areas as subjects performed a motor task in which they produced different learned series of eight button presses. We found that these analyses gave convergent but not identical results: both techniques, for example, suggested an anterior-to-posterior temporal gradient of activity from supplemental motor area through premotor and motor cortices to the posterior parietal cortex, but the techniques were differentially sensitive to the coupling strength between areas. We also found practical reasons that might argue for the use of one technique over another in different experimental situations. Ultimately, the ideal approach to fMRI data analysis is likely to involve a complementary combination of methods, possibly including both Granger causality and coherency. Hum Brain Mapp, 2009. © 2009 Wiley-Liss, Inc. [source] Hyperchaotic behaviour of two bi-directionally coupled Chua's circuitsINTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS, Issue 6 2002Barbara Cannas Abstract In this paper, a non-linear bi-directional coupling of two Chua's circuits is presented. The coupling is obtained by using polynomial functions that are symmetric with respect to the state variables of the two Chua's circuits. Both a transverse and a tangent system are studied to ensure a global validity of the results in the state space. First, it is shown that the transverse system is an autonomous Chua's circuit, which directly allows the evaluation of the conditions on its chaotic behaviour, i.e. the absence of synchronization between the coupled circuits. Moreover, it is demonstrated that the tangent system is also a Chua's circuit, forced by the transverse system; therefore, its dynamics is ruled by a time-dependent equation. Thus, the calculus of conditional Lyapunov exponents is necessary in order to exclude antisynchronization along the tangent manifold. The properties of the transverse and tangent systems simplify the study of the coupled Chua's circuits and the determination of the conditions on their hyperchaotic behaviour. In particular, it is shown that hyperchaotic behaviour occurs for proper values of the coupling strength between the two Chua's circuits. Finally, numerical examples are given and discussed. Copyright © 2002 John Wiley & Sons, Ltd. [source] Revealing the Electron,Phonon Coupling in a Conjugated Polymer by Single-Molecule Spectroscopy,ADVANCED MATERIALS, Issue 15 2007R. Hildner Electron,phonon coupling in a ,-conjugated polymer is revealed by single-molecule spectroscopy in combination with statistical pattern recognition techniques. The technique allows to reveal the phonon-side band in the spectra of methyl-substituted ladder-type poly(para-phenylene) (see figure). For this polymer a weak electron,phonon coupling strength is found at low temperatures. The distribution of the phonon frequencies provides strong evidence that the low-energy vibrational modes, which couple to the electronic transitions, stem from vibrations of the host matrix. [source] A bandpass filter with adjustable bandwidth and predictable transmission zerosINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 2 2010Li Zhu Abstract In this article, a microstrip bandpass filter with an adjustable bandwidth and predictable transmission zeros is proposed. The proposed filter is implemented by combining two hairpin edge-coupled resonators with interdigital capacitors. Compared to typical edge-coupled filters, the proposed filter provides a wider bandwidth resulting from a higher coupling strength between its resonators. To further increase the coupling and consequently the bandwidth, a pair of etched slots in the ground plane is used. By adjusting the geometrical parameters of the interdigital capacitors and etched slots, the bandwidth can be easily adjusted. The filter features two transmission zeros, which are determined by means of the semi-analytical model developed as part of this work. Furthermore, the proposed filters can be cascaded to obtain a sharper cutoff frequency response. Frequency responses of the filters from measurements are in good agreement with those simulated using IE3D in the 5,9 GHz range. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010. [source] Spectroscopic Properties and Local Structure of Eu3+ in Ge,Ga,S,CsBr (or CsCl) GlassesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2003Woon Jin Chung Spectroscopic properties and local structure of Eu3+ in Ge,Ga,S,CsBr (or CsCl) glasses were investigated using fluorescence measurements and several spectroscopic methods. Fluorescence from Eu3+:5D0,7F2 was observed only from glasses with CsBr/Ga ratios greater than unity and disappeared at temperatures above 140 K. Phonon sideband (PSB) spectra revealed that Eu3+ ions are located next to halogen ions, which form part of well-structured complexes such as EuCl3, tetrahedral [GaS3/2Cl],, subunits and/or Ga2Cl6. These new bonds showed reduced coupling strength compared with Eu3+,S bonds in Ge,Ga,S glass. Fluorescence line narrowing experiments showed little site-to-site variation of Eu3+ ions. [source] A multi-mode model of a non-classical atom laser produced by outcoupling from a Bose-Einstein condensate with squeezed lightLASER PHYSICS LETTERS, Issue 12 2005S. A. Haine Abstract We examine the properties of an atom laser produced by outcoupling from a Bose-Einstein condensate with squeezed light. We introduce a method which allows us to model the full multimode dynamics of the squeezed optical field and the outcoupled atoms. We show that for experimentally reasonable parameters that the quantum statistics of the optical field are almost completely transferred to the outcoupled atoms, and investigate the robustness to the coupling strength and the two-photon detuning. [source] Microstrip-CPW bandpass filter for antenna applicationMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 1 2008Atallah Balalem Abstract This article presents a quasi-lumped bandpass filter with CPW-microstrip ports. The structure serves as CPW-microstrip transmission in addition to its filtering function. The filter was integrated with a microstrip patch antenna. To enable the filter design, the characteristic impedance of the slotted microstrip line and the coupling strength of microstrip to microstrip, CPW to CPW and microstrip to CPW transitions were calculated. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 51,55, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23001 [source] Behaviour of torsional Alfvén waves and field line resonance on rotating magnetarsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2005Taishi Okita ABSTRACT Torsional Alfvén waves are likely excited with bursts in rotating magnetars. These waves are probably propagated through corotating atmospheres toward a vacuum exterior. We have studied the physical effects of the azimuthal wavenumber and the characteristic height of the plasma medium on wave transmission. In this work, explicit calculations were carried out based on the three-layered cylindrical model. We found that the coupling strength between the internal shear and the external Alfvén modes is drastically enhanced, when resonance occurs in the corotating plasma cavity. The spatial structure of the electromagnetic fields in the resonance cavity is also investigated when Alfvén waves exhibit resonance. [source] Crayfish Procambarus clarkii Retina and Nervous System Exhibit Antioxidant Circadian Rhythms Coupled with Metabolic and Luminous Daily CyclesPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2009María Luisa Fanjul-Moles Based on previous work in which we proposed midgut as a putative peripheral oscillator responsible for circadian reduced glutathione (GSH) crayfish status, herein we investigated the retina and optic lobe-brain (OL-B) circadian GSH system and its ability to deal with reactive oxygen species (ROS) produced as a consequence of metabolic rhythms and light variations. We characterized daily and antioxidant circadian variations of the different parameters of the glutathione system, including GSH, oxidized glutathione (GSSG), glutathione reductase (GR) and glutathione peroxidase (GPx), as well as metabolic and lipoperoxidative circadian oscillations in retina and OL-B, determining internal and external GSH-system synchrony. The results demonstrate statistically significant bi- and unimodal daily and circadian rhythms in all GSH-cycle parameters, substrates and enzymes in OL-B and retina, as well as an apparent direct effect of light on these rhythms, especially in the retina. The luminous condition appears to stimulate the GSH system to antagonize ROS and lipid peroxidation (LPO) daily and circadian rhythms occurring in both structures, oscillating with higher LPO under dark conditions. We suggest that the difference in the effect of light on GSH rhythmic mechanisms of both structures for antagonizing ROS could be due to differences in glutathione-system coupling strength with the circadian clock. [source] Thickness dependence of magnetic coupling strength and thermal stability in a spin-dependent tunnel junctionPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2004C. H. Nam Abstract The change of magnetic coupling strength between two ferromagnetic layers, separated by an insulating barrier, was investigated as a function of the barrier thickness (TB) and thermal annealing temperatures. The magnetic junctions consist of Ta/CoFe/AlOx/NiFe/Ta layers with three different nominal thickness of TB = 1.3, 1.6, and 2.0 nm. Isothermal magnetization at room temperature revealed that, while the junction with a lower TB showed a higher magnetic coupling strength, thermal annealing at T = 225 °C increased (and diminished) the coupling strength of the junctions with TB = 1.3 and 1.6 nm (and 2.0 nm), respectively. This observation was utilized to understand consistently the magneto-resistance behavior and specific junction resistance of the junctions as a function of thermal annealing temperature. This study demonstrated that the physical properties of a magnetic tunnel junction, such as magneto-resistance ratio, specific junction resistance and their thermal stability, were substantially influenced by the insulating barrier structure as well as the interface quality between the layers. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Phase-coupled oscillator models can predict hippocampal inhibitory synaptic connectionsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2001F. K. Skinner Abstract What factors are responsible for propagating electrical activity in the hippocampus? Using an intact, isolated hippocampus preparation, it is possible to observe spontaneous delta (, 4 Hz) waves of rhythmic field potentials. These rhythmic potentials are inhibitory in nature, mediated by GABAergic inhibitory potentials originating from a population of principal neurons. They start in the ventro-temporal region and move longitudinally towards the dorso-septal region with a phase lag of , 10% between the extracellular recordings. We use the mathematical framework of phase-coupled oscillators (PCO) to gain some insight into the underlying network system. A chain of 15 nearest-neighbour bidirectionally coupled PCOs is used where each oscillator refers to a segment of the CA1 region of the hippocampus that can generate these slow field potentials. We find that ventro-dorsal delta waves exist if there is a dominance in coupling strength in one direction. Without a one-way coupling dominance, ventro-dorsal waves can still exist, but then the coupling strengths need to be much larger. The relationship between entrained and intrinsic frequencies and the variation of propagation speeds along the longitudinal axis can be used to determine which case applies. Currently available experimental data supports one of the cases, predicting that there is a stronger ventral to dorsal inhibitory effect. [source] Computational study of titanium (IV) complexes with organic chromophoresINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2006Ivan Kondov Abstract A computational study of small titanium complexes with the chromophores catechol, alizarin, and coumarin 343 is presented. Employing density functional theory (DFT), the ground-state geometries, energies, and harmonic frequencies of the different compounds are calculated. Furthermore, time-dependent DFT and the configuration interaction singles (CIS) method are used to determine excitation energies and excited-state gradients. Based on these results, the character of the excited states as well as electronic-vibrational coupling strengths are analyzed, and the implications for electron-transfer reactions at dye,semiconductor interfaces are discussed. © 2005 Wiley Periodicals, Inc. 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