Onset Of Motions Research Articles

Deuteron Magnetic Resonance Studies of Anhydrous Caffeine

AbstractMethyl deuterated caffeine powder was studied using2H-NMR relaxometry and line shape analysis. In caffeine's low-temperature phase the spin-lattice relaxation times indicate a thermally activated CD3reorientation (activation energy ≈4 kJ/mol). Below theT1minimum near 35 K the quadrupolar echo spectra develop features indicative for quantum mechanical tunneling. Dielectric measurements indicate the presence of dipole moment fluctuations with times scales that follow an Arrhenius law (energy barrier ≈107 kJ/mol). It is argued that the underlying motion involves small-angle molecular excursions and therefore remains undetectedviastimulated-echo spectroscopy. The hysteresis accompanying the order/disorder transition taking place above 400 K was monitored using solid-echo line shapes as well asviaspin relaxation times. In the high-temperature phase indications for the onset of anisotropic large-angle motions were obtained.

Influence of molecular dynamics on the dielectric properties of poly(9,9-di-n-octylfluorene-altbenzothiadiazole) -based devices

This paper uses Nuclear Magnetic Resonance (NMR) and Differential Scanning Calorimetry (DSC) techniques to study the molecular relaxations and phase transitions in poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT), which has been extensively studied as the active thin film in organic devices. Besides the identification of the glass transition, Β relaxation and crystal-to-crystal phase transition, we correlate such phenomena with dielectric and transport mechanisms in diodes with F8BT as the active layer. The Β relaxation has been assigned to a transition at about 210 K measured by 1H and <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> C solid state NMR, and can be attributed to local motions in the side chains. The glass transition has been detected by DSC and <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> H NMR. Dielectric spectroscopy (DS) carried out at low frequencies on diodes made from F8BT show two peaks which are coincident with the above transitions. This allowed us to correlate the electrical changes in the film with the onset of specific molecular motions. In addition, DS indicates a third peak related with a crystal-to-crystal phase transition. Finally, these transitions were correlated with changes in the carrier mobility recorded in thin films and published recently.

Natural convection in a horizontal porous cavity filled with a non-Newtonian binary fluid of power-law type

This paper investigates the onset of motion and the resulting convective motion in a shallow porous cavity filled with a non-Newtonian binary fluid. The two horizontal walls of the system are subject to constant fluxes of heat and solute while the two vertical ones are impermeable and adiabatic. A power law model is used to characterize the non-Newtonian fluid behavior of the binary solution. The governing parameters for the problem are the thermal Rayleigh number R T , power-law index n, Lewis number Le, buoyancy ratio φ, aspect ratio of the cavity A, normalized porosity ξ, and parameter a defining double-diffusive convection ( a = 0) or Soret induced convection ( a = 1). An analytical solution, valid for shallow enclosures ( A >> 1), is derived on the basis of the parallel flow approximation. Criteria, for supercritical and subcritical onset of motions, are predicted. In the range of the governing parameters considered in this study, a good agreement is found between the analytical predictions and the numerical results obtained by solving the full governing equations.

TRANSITION TO CHAOS IN PLASMA DENSITY WITH ASYMMETRY DOUBLE-WELL POTENTIAL FOR PARAMETRIC AND EXTERNAL HARMONIC OSCILLATIONS

We study the chaotic dynamics of one-degree-of-freedom nonlinear oscillator representing a density perturbation in plasma device model excited by parametric and external driven forces. Critical parameters for the onset of chaotic motions are specified using Melnikov method. The analytical results are confirmed by numerical simulations. The global dynamical changes of the system have been examined by evaluating parametric changes of the bifurcation diagrams, maximum Lyapunov exponent, Poincaré map and the basin boundaries of attraction. The transitions to chaos caused by the cascade bifurcation and intermittency are clearly shown by graphical methods.

Redox-Promoting Protein Motions in Rubredoxin

Proteins are dynamic objects, constantly undergoing conformational fluctuations, yet the linkage between internal protein motion and function is widely debated. This study reports on the characterization of temperature-activated collective and individual atomic motions of oxidized rubredoxin, a small 53 residue protein from thermophilic Pyrococcus furiosus (RdPf). Computational modeling allows detailed investigations of protein motions as a function of temperature, and neutron scattering experiments are used to compare to computational results. Just above the dynamical transition temperature which marks the onset of significant anharmonic motions of the protein, the computational simulations show both a significant reorientation of the average electrostatic force experienced by the coordinated Fe(3+) ion and a dramatic rise in its strength. At higher temperatures, additional anharmonic modes become activated and dominate the electrostatic fluctuations experienced by the ion. At 360 K, close to the optimal growth temperature of P. furiosus, simulations show that three anharmonic modes including motions of two conserved residues located at the protein active site (Ile7 and Ile40) give rise to the majority of the electrostatic fluctuations experienced by the Fe(3+) ion. The motions of these residues undergo displacements which may facilitate solvent access to the ion.

Resonant chaotic motions of a buckled rectangular thin plate with parametrically and externally excitations

Resonant chaotic motions of a simply supported rectangular thin plate with parametrically and externally excitations are analyzed using exponential dichotomies and an averaging procedure for the first time. The formulas of the rectangular thin plate are derived by a von Karman type equation and the Galerkin’s approach. The critical condition to predict the onset of chaotic motions for the full system is obtained by developing a Melnikov function containing terms from the non-hyperbolic mode. We prove that the non-hyperbolic mode of the thin plate does not affect the critical condition for the occurrence of chaotic motions in the resonant case. Simulations also show that the chaotic motions of the hyperbolic subsystem are shadowed by the chaotic motions for the full system of the rectangular thin plate.

Dynamics of Caged Hydronium Ions and Super-protonic Conduction in (H3O)SbTeO6

Abstract The defect pyrochlores have become the focus of attention for the development and optimization of novel solid-state proton conductors as alternatives to costly polymer-based materials. A promising candidate is (H3O)SbTeO6, a super-proton conductor characterized by an outstanding conductivity of 10–1 S cm–1 at ambient conditions. The crystal structure of this compound has been known for some time yet, to date, the physical mechanism underpinning proton conduction has remained elusive. Structurally, (H3O)SbTeO6 consists of corner-shared (Sb/Te)O6 octahedra forming a cubic framework of three-dimensional interconnected cages partially occupied with hydronium H3O+ ions. These ions are connected to the inorganic framework by weak hydrogen bonds. In this work, we present the first characterization of this compound by means of quasielastic and inelastic neutron spectroscopy over a wide temperature range (T = 1.5–500 K), as well as by heat capacity measurements. Our results show that the onset of low-frequency stochastic motions of the hydronium moiety takes place around room temperature and persists up to the highest temperatures investigated. Unlike other inorganic proton conductors, these motions are effectively decoupled from vibrational motions at higher frequencies, as evidenced by the temperature dependence of the vibrational density of states. These findings have important implications for the exploitation of the defect pyrochlores as proton-conducting media for fuel-cell and gas-sensing applications.

Spin relaxation of fullerene C70 photoexcited triplet in molecular glasses: Evidence for onset of fast orientational motions of molecules in the matrix near 100 K

Electron spin echo (ESE) was applied to study transversal spin relaxation of photoexcited triplet state of fullerene C(70) molecules in glassy o-terphenyl and cis-/trans-decalin matrices (glass transition temperatures of 243 and 137 K, respectively). The relaxation rate T(2) (-1) was found to increase sharply above 110 K in o-terphenyl and above 100 K in decalin. It is suggested that this increase arises from interaction of (3)C(70) pseudorotation with fast molecular librations in the matrix. Both these types of motion involve atomic vibrations and are uniaxial in their nature, the known literature data on Raman light scattering and others indicate that molecular librations may be thermally activated in glasses just near 100 K. The increase in T(2) (-1) near 100 K is not observed for photoexcited triplet state of fullerene C(60), for which pseudorotation is not uniaxial. As the fullerene molecule has a size much larger than that for glass solvent molecules, it is likely that molecular librations in the matrix are of collective nature.

Rapid Source Parameter Estimations of Southern California Earthquakes Using PreSEIS

Earthquake early warning (EEW) systems provide real-time estimates of earthquake source and ground motion parameters to users before strong ground shaking occurs at sites of interest (Kanamori et al. 1997; Kanamori 2005). They make use of the fact that the most destructive ground shaking during an earthquake is caused by S- and surface waves, which travel much slower than P waves and also slower than electromagnetic signals carrying warnings to potential users. Real-time information systems can minimize loss of life and property damage and are therefore an important tool in short-term seismic hazard mitigation and disaster management (Wenzel et al. 2001). If an alarm can be issued seconds before the onset of the strong ground motions, automatic emergency actions can be initiated such as slowing down high speed trains or shutting down computers or gas distribution, for instance (Goltz 2002). EEW systems are of two main types, regional and on-site. The former uses a dense network of seismic stations to locate the earthquake, determine its magnitude, and estimate the ground motion at given sites of interest. The latter uses the observations at a single sensor to estimate the ensuing ground motion at the same site (Kanamori 2005). While regional systems work more accurately, they need more time to estimate earthquake source parameters.

Conformational Heterogeneity and Spin-Labeled −SH Groups: Pulsed EPR of Na,K-ATPase

Membranous Na,K-ATPase from shark salt gland and from pig kidney was spin-labeled on class I -SH groups in the presence of glycerol, or on class II -SH groups in the absence of glycerol. The class I-labeled preparations retain full enzymatic activity, whereas the class II-labeled preparations are at least partially inactivated. This provides an excellent testbed on which to demonstrate how advanced electron paramagnetic resonance (EPR) can provide novel information on specific residues in unique environments in a complex, membrane-bound transport system. The polarity of the environment, and the librational dynamics and conformational exchange, of the spin-labeled groups were studied with pulsed EPR by using electron spin echo envelope modulation (ESEEM) spectroscopy and spin-echo detected (ED) EPR spectroscopy, respectively. 2H-ESEEM spectra of membranes dispersed in D2O reveal that class I groups of the shark enzyme are more exposed to water than are those of the pig enzyme or class II groups of either species, consistent with the more superficial membrane location in the former case. Spin-echo decay curves indicate conformational heterogeneity at low temperatures (<150 K), but a more homogeneous conformational state at higher temperatures that is characterized by a single phase-memory T2M relaxation time. Conventional EPR lineshapes also demonstrate conformational microheterogeneity at low temperatures: the inhomogeneously broadened lines narrow progressively with increasing temperature reaching an almost pure Lorentzian line shape at temperatures of ca. 220 K and above. The inhomogeneous broadening at low temperature is well described by a Gaussian distribution of Lorentzian lines. ED spectra as a function of echo-delay time demonstrate the onset of rapid librational motions of appreciable amplitude, and slower conformational exchange, at temperatures above 220 K. These motions could drive transitions between the different conformational substates, which are frozen in at lower temperatures but contribute to the pathways between the principal enzymatic intermediates at higher temperatures.

Turbulent motions and shocks waves in galaxy clusters simulated with adaptive mesh refinement

We have implemented an Adaptive Mesh Refinement criterion explicitly designed to increase spatial resolution around discontinuities in the velocity field in ENZO cosmological simulations. With this technique, shocks and turbulent eddies developed during the hierarchical assembly of galaxy clusters are followed with unprecedented spatial resolution, even at large distances from the clusters center. By measuring the spectral properties of the gas velocity field, its time evolution and the properties of shocks for a reference galaxy cluster, we investigate the connection between accretion processes and the onset of chaotic motions in the simulated Inter Galactic Medium over a wide range of scales

MECHANISM OF IMPACTING CHATTER WITH STICK IN A GEAR TRANSMISSION SYSTEM

In this paper, an investigation on nonlinear dynamical behaviors of a transmission system with a gear pair is conducted. The transmission system is described through an impact model with a possible stick between the two gears. From the theory of discontinuous dynamical systems, the motion mechanism of impacting chatter with stick is investigated. The onset and vanishing conditions of stick motions are developed, and the condition for maintaining the stick motion is achieved as well. The corresponding physics interpretation is given for a better understanding of nonlinear behaviors of gear transmission systems. Furthermore, such an understanding may be very helpful to improve the efficiency of gear transmission systems.

Bifurcation of operation modes of small wind power stations and optimization of their characteristics

Wind stations of small power (small WPS) are intended to ensure the operation of a small number of electric devices. Under these conditions, the connection of even a single additional consumer may result in operation disturbances. In [1, 2], a mathematical model of a small WPS operation was proposed, which allowed a qualitative explanation of the energy output hysteresis phenomenon experimentally observed under variation in the external load. In the present paper, on the basis of this model, we study the problems of existence and stability of steady-state modes and describe their attraction domains. We show that there exist different types of bifurcations of these modes, which result, in particular, in the onset of finite-amplitude periodic motions. For the first time, the performance of a power plant is estimated by the maximal consumption power criterion. The results are compared with the results obtained by other criteria.

Solvation Dynamics of Model Peptides Probed by Terahertz Spectroscopy. Observation of the Onset of Collective Network Motions

We have studied the solvation of model peptides at low hydration levels by terahertz absorption spectroscopy. We have recorded the concentration-dependent terahertz absorption coefficients of N-acetyl-glycine-amide (NAGA), N-acetyl-glycine-methylamide (NAGMA), N-acetyl-leucine-amide (NALA), N-acetyl-leucine-methylamide (NALMA), and N-acetyl-tryptophan-amide (NATA) in aqueous solution. We find a dramatic decrease in the THz absorption, if the number of water molecules per solute is less than 18-20. This change is taken as a signature for the breakdown of peptide-water network motions, which supports the hypothesis that a minimum number of hydration waters is required to activate these motions. This is well below a monolayer coverage of the model peptides. It is interesting to note that the required hydration level corresponds to the number of water molecules which are required for biological functionality.

Solvent and lipid dynamics of hydrated lipid bilayers by incoherent quasielastic neutron scattering

The microscopic dynamics of the planar, multilamellar lipid bilayer system 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) has been investigated using quasielastic neutron scattering. The DMPC was hydrated to a level corresponding to approximately nine water molecules per lipid molecule. Selective deuteration has been used to separately extract the dynamics of the water, the acyl chains, and the polar head groups from the strong incoherent scattering of the remaining hydrogen atoms. Furthermore, the motions parallel and perpendicular to the bilayers were probed by using two different sample orientations relative to the incident neutron beam. For both sample orientations, the results showed an onset of water motions at 260 K on the experimental time scale of about 100 ps. From lack of wave-vector dependence of the onset temperature for water motions, it is evident that the observed water dynamics is of mainly rotational character at such low temperatures. At 290 K, i.e., slightly below the gel-to-liquid transition around 295 K, the nature of the water dynamics had changed to a more translational character, well described by a jump-diffusion model. On the limited experimental time and length (about 10 A) scales, this jump-diffusion process was isotropic, despite the very anisotropic system. The acyl chains exhibited a weak onset of anharmonic motions already at 120 K, probably due to conformational changes (trans-gauche and/or syn-anti) in the plane of the lipid bilayers. Other anharmonic motions were not observed on the experimental time scale until temperature had been reached above the gel-to-liquid transition around 295 K, where the acyl chains start to show more substantial motions.

Periodic motions in a simplified brake system with a periodic excitation

In this paper, periodic motions for a simplified brake system under a periodical excitation are investigated, and the motion switchability on the discontinuous boundary is discussed through the theory of discontinuous dynamical systems. The onset and vanishing of periodic motions are discussed through the bifurcation and grazing analyses. Based on the discontinuous boundary, the switching planes and the basic mappings are introduced, and the mapping structures for periodic motions are developed. From the mapping structures, the periodic motions are analytically predicted and the corresponding local stability and bifurcation analysis is completed. Periodic motions will be illustrated for verification of analytical predictions. In addition, the relative force distributions along the displacement are illustrated for illustrations of the analytical conditions of motion switchability on the discontinuous boundary.

Differences in Internal Dynamics of Actin under Different Structural States Detected by Neutron Scattering

F-actin, a helical polymer formed by polymerization of the monomers (G-actin), plays crucial roles in various aspects of cell motility. Flexibility of F-actin has been suggested to be important for such a variety of functions. Understanding the flexibility of F-actin requires characterization of a hierarchy of dynamical properties, from internal dynamics of the actin monomers through domain motions within the monomers and relative motions between the monomers within F-actin to large-scale motions of F-actin as a whole. As a first step toward this ultimate purpose, we carried out elastic incoherent neutron scattering experiments on powders of F-actin and G-actin hydrated with D2O and characterized the internal dynamics of F-actin and G-actin. Well established techniques and analysis enabled the extraction of mean-square displacements and their temperature dependence in F-actin and in G-actin. An effective force constant analysis with a model consisting of three energy states showed that two dynamical transitions occur at ∼150K and ∼245K, the former of which corresponds to the onset of anharmonic motions and the latter of which couples with the transition of hydration water. It is shown that behavior of the mean-square displacements is different between G-actin and F-actin, such that G-actin is “softer” than F-actin. The differences in the internal dynamics are detected for the first time between the different structural states (the monomeric state and the polymerized state). The different behavior observed is ascribed to the differences in dynamical heterogeneity between F-actin and G-actin. Based on structural data, the assignment of the differences observed in the two samples to dynamics of specific loop regions involved in the polymerization of G-actin into F-actin is proposed.

Dynamics of Cryogenic Jets: Non-Rayleigh Breakup and Onset of Nonaxisymmetric Motions

We report development of generators for periodic, satellite-free fluxes of monodisperse drops with diameters down to 10 microm from cryogenic liquids such as H2, N2, Ar, and Xe (and, as a reference fluid, water). While the break up of water jets can be described well by Rayleigh's linear theory, we find jet regimes for H2 and N2 which reveal deviations from this behavior. Thus, Rayleigh's theory is inappropriate for thin jets that exchange energy and/or mass with the surrounding medium. Moreover, at high evaporation rates, the axial symmetry of the dynamics is lost. When the drops pass into vacuum, frozen pellets form due to surface evaporation. The narrow width of the pellet flux paves the way towards various industrial and scientific applications.

On the estimation of seismic intensity in earthquake early warning systems

The infamous Tokai Earthquake, which by some accounts is overdue, is expected to be a magnitude ≥ 8 event that will cause unprecedented damage in regions of Japan. To mitigate hazards from large earthquakes in Japan, an earthquake early warning (EEW) system was developed that is able to determine hypocentral locations from P‐arrival data within a few seconds and then transmit this information before the onset of large ground motions from the later arrival of S‐waves. We introduced a new source parameter for seismic intensity magnitude that can be estimated from the real‐time P‐wave data during the early stages of fault rupture for most earthquakes M ≥ 6.5. The use of this parameter results in a significant improvement in the uncertainty in the estimated seismic intensity compared to estimates derived from earthquake magnitude. A pre‐established relation between the P‐ and S‐wave seismic intensity therefore enables an EEW system to issue a rapid and reasonably reliable prediction of the amount of ground shaking that may be expected from the damaging S‐waves.

Anisotropic Pseudorotation of the Photoexcited Triplet State of Fullerene C60 in Molecular Glasses Studied by Pulse EPR

Spin-polarized echo-detected electron paramagnetic resonance (EPR) spectra and the transversal relaxation rate T2(-1) of the photoexcited triplet state of fullerene C60 molecules were studied in o-terphenyl, 1-methylnaphthalene, and decalin glassy matrices. The model is composed of a fast (correlation time approximately 10(-12) s) pseudorotation of (3)C60 in a local anisotropic potential created by interaction of the fullerene molecule with the surrounding matrix molecules. In simulations, this potential is assumed to be axially symmetric around some axis of a preferable orientation in a matrix cage. The fitted value of the potential was found to depend on the type of glass and to decrease monotonically with a temperature increase. A sharp increase of the T2(-1) temperature dependence was found near 240 K in glassy o-terphenyl and near 100 K in glassy 1-methylnaphthalene and decalin. This increase probably is related to the influence on the pseudorotation of the onset of large-amplitude vibrational molecular motions (dynamical transition in glass) that are known for glasses from neutron scattering and molecular dynamics studies. The obtained results suggest that molecular and spin dynamics of the triplet fullerene are extremely sensitive to molecular motions in glassy materials.