Strong Dynamic Coupling Research Articles

Atmosphere‐Ionosphere coupling observed over the dip equatorial MLTI region through the quasi 16‐day wave

The present paper analyses the variations of daytime mesopause temperature and the Equatorial electrojet strength over the dip equator during December 2005–March 2006 period, indicating a possible strong dynamical coupling between the two region through the intensification of planetary wave activity. The wave signatures (quasi 16‐day period) are seen in the mesopause temperature and the electrojet‐induced surface magnetic field, measured from Trivandrum (8.5°N, 76.5°E, 0.5°N diplat.), a geomagnetic dip equatorial station in India. This investigation reveals (1) amplification of the quasi 16‐day wave in the equatorial mesopause temperature and the EEJ induced magnetic field (2) regular occurrence of Counter Electrojet (CEJ), with a periodicity of ∼16 days (3) diminishing CEJ strength concurrent with the damping of the amplitude of wave oscillation with time. These results are new and reveal some newer aspects of the Mesosphere Lower Thermosphere Ionosphere (MLTI) dynamics.

Decoupling joint and elastic accelerations in deformable mechanical systems using non‐linear recursive formulations

AbstractThe aim of this paper is to develop non‐linear recursive formulations for decoupling joint and elastic accelerations, while maintaining the non‐linear inertia coupling between rigid body motion and elastic deformation in deformable mechanical systems. The inertia projection schemes used in most existing recursive formulations for the dynamic analysis of deformable mechanisms lead to dense coefficient matrices in the equations of motion. Consequently, there are strong dynamic couplings between the joint and elastic coordinates. When the number of elastic degrees of freedom increases, the size of the coefficient matrix in the equations of motion becomes large. Consequently, the use of these recursive formulations for solving the joint and elastic accelerations becomes less efficient. In this paper, the non‐linear recursive formulations have been used to decouple the elastic and joint accelerations in deformable mechanical systems. The relationships between the absolute, elastic and joint variables and generalized Newton–Euler equations are used to develop systems of loosely coupled equations that have sparse matrix structure. By using the inertia matrix structure of deformable mechanical systems and the fact that joint reaction forces associated with elastic coordinates do represent independent variables, a reduced system of equations whose dimension is dependent of the number of elastic degrees of freedom is obtained. This system can be solved for the joint accelerations as well as for the joint reaction forces. The use of the approaches developed in this investigation is illustrated using deformable open‐loop serial robot and closed‐loop four‐bar mechanical systems. Copyright © 2007 John Wiley & Sons, Ltd.

Dynamics of amylopectin in semidilute aqueous solution

The dynamic behaviors of potato amylopectin and waxy corn amylopectin in semidilute solution were investigated by laser light scattering and viscometer. For potato amylopectin with relatively smaller molecular weight, only pure diffusion motion of amylopectin was found by LLS in dilute regime. When the concentration was above the critical overlapping concentration ( C ∗), three relaxation modes were found. The line-width of fast mode ( Γ f) had a q 2 dependence, where q is the scattering vector, and the correlative length (〈 ξ h〉) could be scaled to concentration ( C) as 〈 ξ h〉 ∼ C −0.79±0.1 when C > 2%. This mode was attributed to the cooperative relaxation motion of the “blobs” in the transient network. The line-width of slow relaxation mode ( Γ s) could be scaled with q as Γ s ∼ q α s , α s varying from 2.0 to 2.66 as the concentration increased. The relaxation time of slow relaxation mode ( τ s) had a C 1.8±0.1 dependence. This mode was originated from the association of the amylopectin. The medium mode was found when C > 4%. The line-width of medium relaxation mode ( Γ m) could be scaled to q as Γ m ∼ q α m , α m varying from 2.7 to 2.5 with the increasing concentration. The relaxation time of medium relaxation mode ( τ m) had C 0.7±0.1 dependence. The relative intensity contribution of the medium relaxation mode decreased with a rise in the concentration. This mode was attributed to the thermally agitated density fluctuation in semidilute solution induced by heterogeneities of the transient network. For waxy corn amylopectin with relatively huge molecular weight (∼10 8 g/mol), only the internal motion of the single amylopectin molecule was found in dilute regime when qR g ≥ 2, where R g is the gyration radius of amylopectin. It was also found that there were three relaxation modes in semidilute solution of waxy corn amylopectin. The fast relaxation mode was found to be caused first by the internal motion of the single amylopectin molecule, and then, with the increasing concentration, by the cooperative motion of the transient network. The medium and slow relaxations for waxy corn amylopectin have the same physical origin as those for potato amylopectin. However, the C dependence and the q dependence of the medium and slow relaxation times for waxy corn amylopectin were different from those for potato amylopectin. This was attributed to the strong dynamic coupling effect in semidilute solution of the waxy corn amylopectin. The concentration dependence of the viscosity of amylopectin in semidilute solution indicated that the topological entanglement of amylopectin was weak due to the highly branching.

Nonlinear recursive method to solid deformable structure dynamic problems

AbstractThe recursive projection schemes used in most existing recursive methods for solid deformable structure dynamic problems lead to dense coefficient matrices in the acceleration equations and consequently there is a strong dynamic coupling between the joint and elastic coordinates. When the number of elastic degrees of freedom increases, the size of the coefficient matrix in the acceleration equations becomes large and consequently the use of these recursive methods for solving for the joint and elastic accelerations becomes less efficient. This paper discusses the problems associated with the recursive projection schemes used in the existing recursive methods, and it is shown that decoupling the joint and elastic accelerations using the nonlinear recursive method requires the factorization of nonlinear matrices whose dimensions are independent of the number of elastic degrees of freedom of the open‐loop and closed‐loop system. An amalgamated formulation that can be used to decouple the elastic and joint accelerations is then proposed. The use of the nonlinear recursive method developed in this paper is demonstrated using an open‐loop free‐falling deformable double pendulum system and a closed‐loop four‐bar mechanism. Copyright © 2006 John Wiley & Sons, Ltd.

Indian Ocean Variability and Its Association with ENSO in a Global Coupled Model

Abstract The evolution of the Indian Ocean during El Niño–Southern Oscillation is investigated in a 100-yr integration of an Australian Bureau of Meteorology coupled seasonal forecast model. During El Niño, easterly anomalies are induced across the eastern equatorial Indian Ocean. These act to suppress the equatorial thermocline to the west and elevate it to the east and initially cool (warm) the sea surface temperature (SST) in the east (west). Subsequently, the entire Indian Ocean basin warms, mainly in response to the reduced latent heat flux and enhanced shortwave radiation that is associated with suppressed rainfall. This evolution can be partially explained by the excitation of an intrinsic coupled mode that involves a feedback between anomalous equatorial easterlies and zonal gradients in SST and rainfall. This positive feedback develops in the boreal summer and autumn seasons when the mean thermocline is shallow in the eastern equatorial Indian Ocean in response to trade southeasterlies. This positive feedback diminishes once the climatological surface winds become westerly at the onset of the Australian summer monsoon. ENSO is the leading mechanism that excites this coupled mode, but not all ENSO events are efficient at exciting it. During the typical El Niño (La Niña) event, easterly (westerly) anomalies are not induced until after boreal autumn, which is too late in the annual cycle to instigate strong dynamical coupling. Only those ENSO events that develop early (i.e., before boreal summer) instigate a strong coupled response in the Indian Ocean. The coupled mode can also be initiated in early boreal summer by an equatorward shift of the subtropical ridge in the southern Indian Ocean, which stems from uncoupled extratropical variability.

Thermal Conductivity of Geometrically Frustrated, FerroelectricYMnO3: Extraordinary Spin-Phonon Interactions

The thermal conductivity of the magnetically frustrated, ferroelectric YMnO3 exhibits an isotropic suppression in the cooperative paramagnetic state, followed by a sudden increase upon magnetic ordering. This unprecedented behavior without an associated static structural distortion probably originates from the strong dynamic coupling between acoustic phonons and low-energy spin fluctuations in geometrically frustrated magnets. The replacement of magnetic Ho for Y at the ferroelectrically active site results in an even larger effect, suggestive of the strong influence of multiferroicity.

Conformational Change in Azobenzene in Photoisomerization Process Studied with Chirp-Controlled sub-10-fs Pulses

Negatively and positively chirped pulses were used to selectively excite vibrationally coherent wave packets in the ground and the excited states, respectively, in an azobenzene derivative molecule in solution. Strong dynamic mode coupling between the N=N and C-N stretching modes is observed in real time at ∼1400 and 1150 cm - 1 in the excited state of the molecule, but it is relatively week in the ground state. Instantaneous frequencies of N=N and C-N stretching modes around 1400 and 1150 wavenumbers (corresponding to ∼24 and ∼29 fs vibrational periods, respectively, in both of the states) were found to be modulated on the basis of time-frequency analysis of transmittance-change traces with high time-resolution of a few femtoseconds. In the excited state, the modulation periods of N=N and C-N stretching modes are ∼510 and ∼390 fs, respectively, directly indicating the existence of at least one more mode other than the torsion mode coupled to either or two of these stretching modes during the photoisomerization.

Gasdynamics in NGC 5248: Fueling a Circumnuclear Starburst Ring of Super–Star Clusters

Through observations and modeling, we demonstrate how the recently discovered large-scale bar in NGC 5248 generates spiral structure that extends from 10 kpc down to 100 pc, fuels star formation on progressively smaller scales, and drives disk evolution. Deep inside the bar, two massive molecular spirals cover nearly 180° in azimuth, show streaming motions of 20-40 km s-1, and feed a starburst ring of super-star clusters at 375 pc. They also connect to two narrow K-band spirals that delineate the UV bright star clusters in the ring. The data suggest that the K-band spirals are young, and the starburst has been triggered by a bar-driven spiral density wave (SDW). The latter may even have propagated closer to the center where a second Hα ring and a dust spiral are found. The molecular and Hubble Space Telescope data support a scenario where stellar winds and supernovae efficiently clear out gas from dense star-forming regions on timescales less than a few Myr. We have investigated the properties of massive CO spirals within the framework of bar-driven SDWs, incorporating the effect of gas self-gravity. We find good agreement between the model predictions and the observed morphology, kinematics, and pitch angle of the spirals. This combination of observations and modeling provides the best evidence to date for a strong dynamical coupling between the nuclear region and the surrounding disk. It also confirms that a low central mass concentration, which may be common in late-type galaxies, is particularly favorable to the propagation of a bar-driven gaseous SDW deep into the central region of the galaxy, whereas a large central mass concentration favors other processes, such as the formation and decoupling of nuclear bars.

Brownian dynamics simulations of salt-free polyelectrolyte solutions

The static and dynamic properties of dilute and semidilute salt-free polyelectrolyte solutions are studied using Brownian dynamics simulations. The polymer molecules and counterions are modeled as charged bead–spring chains and charged spheres, respectively. Results are presented for the static properties, polymer rotational dynamics, self and collective diffusion coefficients, intermediate scattering functions, and dynamic structure factors of polyelectrolytes and counterions. The simulations reveal a strong dynamical coupling between counterions and polyions at low concentrations; this coupling becomes weaker as the concentration is increased. The polyion self-diffusion coefficient shows a nonmonotonic concentration dependence, but the counterion self diffusion coefficient decreases monotonically as the concentration is increased. In semidilute solutions, the collective density relaxation dynamics are slowed down at wave vectors where there is a peak in the corresponding static structure factor. This can be qualitatively, but not quantitatively understood via the concept of de Gennes narrowing. A comparison with relevant experiments and theories is also presented.

On the solar wind flow control of the polar cusp

The position of the polar cusp in the dayside magnetosphere is known to be controlled by the solar wind dynamics and the interplanetary magnetic field. Using plasma data from the Viking and IMP 8 satellites, we have done a statistical analysis of the influence of the solar wind azimuth flow component on the cusp position in magnetic local time (MLT). We show that the position of the cusp in MLT is strongly coupled to the azimuthal (east‐west) flow component of the solar wind. For instance, the cusp in the northern hemisphere moves toward prenoon when the unaberrated solar wind appears to come from the west of the Sun (as compared to the radial flow), and vice versa. This suggests, first of all, a strong dynamical coupling of the cusp to the solar wind flow. Second, the dawn‐dusk cusp displacement with respect to the azimuthal flow component indicates a transfer of angular momentum from the Sun, potentially by a J × B force in the solar wind as suggested in the “hetegonic nebulae” theory by Alfven and Arrhenius [1976]. This lateral deflection force plays, on the average, a more important role for the cusp location than the aberration effect of the Earth's prograde motion across the expanding solar wind. In previous studies similar displacements of the cusp have been mainly related to the IMF By component; for example, a positive By leads to a cusp displacement to the postnoon side and vice versa. We compare these results and discuss them in context with the dynamical solar wind flow control of the cusp.

Anion Rotation and Cation Diffusion in Low-Temperature Sodium Orthophosphate: Results from Solid-State NMR

Numerous ionic crystals are known in which both cations and anions possess considerable mobility in the solid state. During the past decade, there has been considerable controversy about the question of whether cationic and anionic motion can be dynamically coupled in such materials. This issue has been studied recently on the plastic crystalline material high-temperature (HT-) Na3PO4, which forms from the low-temperature modification in a first-order phase transition at a temperature near 600 K. In the present study, the dynamics of the low-temperature phase have been characterized comprehensively by complementary NMR methods. Temperature-dependent 17O NMR line shape analyses indicate that the phosphate ions undergo 3-fold rotation on the time scale of milliseconds. There appears to be one preferred axis of rotation, however. Variable-temperature 23Na and 31P NMR spectra reveal further that the sodium cations exhibit considerable mobility. Both anionic and cationic motion appear to be jointly thermally activated and are characterized by correlation times of comparable magnitude. At temperatures about 70 K below the phase transition, diffuse diffraction peaks observed in X-ray powder diffraction data indicate the appearance of local clusters possessing the symmetry of the high-temperature phase. The strongly increased thermal volume expansion coefficient and the observation of excess specific heat within this temperature range suggest that both the cations and the anions exhibit strongly accelerated dynamics within these domains. The number of nuclei contributing to these domains are quantified on the basis of 17O and 23Na NMR line shape and nutation analyses. The combined experimental evidence suggests strong dynamic coupling between anion and cation motion in low-temperature (LT-) Na3PO4.

Electronic structure and kinetics of K on graphite

The K/graphite adsorption system is studied in a cluster model using ab initio density-functional methods. From the investigation of the potential energy surface a lower bound for the potassium atom binding energy 1.5 eV is obtained, and a surface diffusion barrier of 0.2 eV. To simulate experimentally reported thermal desorption spectra, a two-phase kinetic model is investigated and a desorption energy of 1 eV is found. The thermally activated surface diffusion of K atoms leads to intercalation at defects or steps, which is followed by desorption when further heating the sample. A normal mode analysis yields a K-graphite in-phase and out-of-phase vibrational mode with an energy split of 8 meV, which indicates a relatively strong dynamical coupling between the adsorbed K atom and the graphite substrate. The calculated electron density distribution is verified by an accurate reproduction of the measured dipole moment. From a projected density of state analysis we find a K 4s and an antibonding K 4p resonance located slightly above and 2.6 eV above the Fermi level, respectively. The location of the K 4s resonance, with a lower occupied tail, is consistent with an incomplete charge transfer, and the location of the K 4p resonance is consistent with a proposed hot-electron model to explain recent photodesorption data. The new assignment of the K-induced states near the Fermi level resolves previous apparent discrepancies of the charge state of the dispersed K atom.

Geomorphic limits to climate-induced increases in topographic relief

Recognition of the potential for strong dynamic coupling between atmospheric and tectonic processes has sparked intense cross-disciplinary investigation and debate on the question of whether tectonics have driven long-term climate change or vice versa. It has been proposed that climate change might have driven the uplift of mountain summits through an isostatic response to valley incision. Because isostasy acts to compensate mean elevations, the debate hinges on the question of whether climate change can significantly increase topographic relief or, more precisely, increase the volume of ‘missing mass’ between summits and ridges. Here we show that, in tectonically active mountain ranges, geomorphic constraints allow only a relatively small increase in topographic relief in response to climate change. Thus, although climate change may cause significant increases in denudation rates, potentially establishing an important feedback between surficial and crustal processes, neither fluvial nor glacial erosion is likely to induce significant isostatic peak uplift.

A Compensated Acoustic Actuator for Systems with Strong Dynamic Pressure Coupling

This study improves the performance of a previously developed acoustic actuator in the presence of an acoustic duct system with strong pressure coupling. The speaker dynamics and the acoustic duct dynamics are first modeled separately. The two systems are then coupled, and the resulting system is modeled. A velocity sensor is developed and used in feedback compensation. The resulting speaker system has minimal magnitude and phase variation over a 20–200 Hz bandwidth. These conclusions are verified through experimental results.

High‐temperature deformation of dry diabase with application to tectonics on Venus

We have performed an experimental study to quantify the high‐temperature creep behavior of natural diabase rocks under dry deformation conditions. Samples of both Maryland diabase and Columbia diabase were investigated to measure the effects of temperature, oxygen fugacity, and plagioclase‐to‐pyroxene ratio on creep strength. Flow laws determined for creep of these diabases were characterized by an activation energy of Q = 485±30 kJ/mol and a stress exponent of n = 4.7±0.6, indicative of deformation dominated by dislocation creep processes. Although n and Q are the same for the two rocks within experimental error, the Maryland diabase, which has the lower plagioclase content, is significantly stronger than the Columbia diabase. Thus the modal abundance of the various minerals plays an important role in defining rock strength. Within the sample‐to‐sample variation, no clear influence of oxygen fugacity on creep strength could be discerned for either rock. The dry creep strengths of both rocks are significantly greater than values previously measured on diabase under “as‐received” or wet conditions [Shelton and Tullis, 1981; Caristan, 1982]. Application of these results to the present conditions in the lithosphere on Venus predicts a high viscosity crust with strong dynamic coupling between mantle convection and crustal deformation, consistent with measurements of topography and gravity for that planet.

Interplay between Anion Rotation and Cation Transport in the Plastic High-Temperature Phase of Sodium Ortho-Phosphate

ABSTRACTThe high-temperature phase of sodium ortho-phosphate, α-Na3PO4, belongs to the class of ion conducting plastic crystals, i.e., it is characterized by a dynamic rotational disorder of its poly-atomic anions and, at the same time, by a considerable translational mobility of its cations. During the past decade, the possibility, nature, and importance of a dynamic interplay between the two kinds of motion have been a subject of continued controversy. Proponents of a strong interplay coined the expression “paddle-wheel mechanism”. In our present contribution we report, for the first time, on the results ofdynamicexperiments probing the elementary steps of anionic and cationic motion individually. The techniques utilized in this study are coherent quasielastic neutron scattering and high-frequency conductivity spectroscopy, respectively. The data are complemented by anab-initiomolecular-dynamics simulation. Our results provide a view of the movement of anions and cations and of correlations between them. Strong dynamic coupling is detected between the octahedrally coordinated sodium ions and nearby oxygen ions. For translational sodium-ion transport, a chain mechanism appears to be operative.

Inelastic tunneling in long-distance biological electron transfer reactions

The effect of protein dynamics on the long-distance biological electron transfer reactions is discussed. Computer simulations reported recently by our group [Daizadeh, Medvedev, and Stuchebrukhov, Proc. Natl. Acad. Sci. USA 94, 3703 (1997)] have shown that in some cases a strong dynamic coupling of a tunneling electron to vibrational motions of the protein matrix can exist. This results in a modification of the conventional picture of electron transfer in proteins. The new element in the modified theory is that the tunneling electron is capable of emitting or absorbing vibrational energy (phonons) from the medium. As a result, some biological reactions may occur in an activationless fashion. In the present paper we study analytically the probabilities of such inelastic tunneling events and show how they affect the overall dependence of the reaction rate on the driving force, temperature, and the strength of electron–phonon coupling. Harmonic and anharmonic models are proposed for vibrational dynamics of the intervening medium.

Effect of protein dynamics on biological electron transfer.

Computer simulations of the effect of protein dynamics on the long distance tunneling mediated by the protein matrix have been carried out for a Ru-modified (His 126) azurin molecule. We find that the tunneling matrix element is a sensitive function of the atomic configuration of the part of the protein matrix in which tunneling currents (pathways) are localized. Molecular dynamics simulations show that fluctuations of the matrix element can occur on a time scale as short as 10 fs. These short time fluctuations are an indication of a strong dynamic coupling of a tunneling electron to vibrational motions of the protein nuclear coordinates. The latter results in a modification of the conventional Marcus picture of electron transfer in proteins. The new element in the modified theory is that the tunneling electron is capable of emitting or absorbing vibrational energy (phonons) from the medium. As a result, some biological reactions may occur in an activationless fashion. An analytical theoretical model is proposed to account for thermal fluctuations of the medium in long distance electron transfer reactions. The model shows that, at long distances, the phonon-modified inelastic tunneling always dominates over the conventional elastic tunneling.

Dynamical coupling between side and main chains of amorphous polystyrene near Tg

The dynamics of amorphous polystyrene (PS) near the glass transition temperature T g( = 373 K) have been studied by quasielastic neutron scattering in the energy range from 0.1 to 10 meV. In order to elucidate the role of the side-chain motion for the glass-transition dynamics, we observed the motion of the side chains (phenyl groups) separately from that of the main chain by measuring PS with deuterated side chains (PS-d 5), in addition to hydrogenated PS. The observed dynamic scattering laws were analyzed by a curve-fitting method, assuming a phenomenological model function consisting of three components: a δ-function, a Lorentzian and a flat background. It was found that the widths of the Lorentzian are identical for PS and PS-d 5 near T g, suggesting strong dynamical coupling between the side and main chains.

Strong dynamic coupling effects in the IR spectra of H-bonded 2-mercaptoquinoline

Abstract In this paper we attempt to reproduce quantitatively the IR spectra of 2-mercaptoquinoline in the ν NH and ν ND band frequency regions. The investigated spectra were quantitatively interpreted within the limits of the “strong-coupling” theory for the hydrogen bond vibrations in centrosymmetric H-bonded dimers, including the observed isotopic effect. The observed, very nonregular, spectral properties of 2-mercaptoquinoline were found to be connected with the “strong-coupling” mechanism as well as with the electronic properties of the H-bonds in the molecular associates.