Variations In Rotation Rate Research Articles

S.20.04 Lithium responsive behavioural models: a tool for understanding atypical antipsychotic action in bipolar depression and mania

This paper reports the estimation of angular velocity in micro gyroscopes with parametric excitation. The identification procedure is done into two consecutive steps: In the first step, the physical parameters of the gyroscope (stiffness, damping, and actuator parameters) are estimated via continuous time Extended and Unscented Kalman filter. In the second step, a separate Kalman filter is dedicated to estimate the time varying rotation rate, using the output of the first step. Using numerical simulations, it is found that by introducing an artificial noise in the observer equations and tuning its variance, arbitrary temporal variation of angular velocity can be well tracked by the proposed observer.

Studies on the kinetics of ascorbate oxidation at a ruthenium oxide hexacyanoferrate modified electrode towards the detection at microenvironments

The electrocatalytic oxidation of ascorbate on a ruthenium oxide hexacyanoferrate (RuOHCF) glassy carbon (GC) modified electrode was investigated at pH 6.9 by using rotating disc electrode (RDE) voltammetry. The influence of the systematic variation of rotation rate, film thickness, ascorbate concentration and the electrode potential indicated that the rate of cross-chemical reaction between Ru(III) centres immobilized into the film and ascorbate controls the overall process. The kinetic regime may be classified as a S k″ mechanism and the second order rate constant for the surface electrocatalytic reaction was found to be 1.56 × 10 −3 mol −1 L 1 s −1 cm. A carbon fibre microelectrode modified with the RuOHCF film was successfully used as an amperometric sensor to monitor the ascorbate diffusion in a simulated microenvironment experiment.

Analysis of the semi-geostrophic shallow water equations

The semi-geostrophic shallow water equations are an accurate approximation to the rotating shallow water equations on scales larger than the Rossby radius of deformation. The global existence of weak solutions of the Lagrangian form of the equations is known. However, uniqueness is not known except for short times for smooth initial data. Similarly, a rigorous proof of existence of solutions has not been achieved for variable rotation rate, which is important for atmospheric applications. The obstacle is the lack of regularity of solutions to the Monge–Ampere equation, which underlies the solution procedure. In this note, it is shown formally that the modified form of the Monge–Ampere equation that appears in the solution procedure for the semi-geostrophic shallow water equations is better controlled on large scales than that of the standard equation that is used in the incompressible case. This suggests that more progress should be possible with the rigorous theory, and in particular that it should be possible to prove uniqueness.

Tectonic patterns on reoriented and despun planetary bodies

Several processes may produce global tectonic patterns on the surface of a planetary body. The stresses associated with distortions of biaxial figures due to despinning or reorientation were first calculated by Vening Meinesz [Vening Meinesz, F.A., 1947. Trans. Am. Geophys. Union 28 (1), 1–23]. We adopt a mathematically equivalent, but physically more meaningful treatment for distortions associated with rotation. The new approach allows us to find analytic solutions for the general case of stresses associated with distortions of biaxial or triaxial planetary figures. Distortions of biaxial figures may be driven by variations in rotation rate, rotation axis orientation, or the combination of both. Distortions of triaxial figures may be driven by the same mechanisms and/or variations in tidal axis orientation for tidally deformed satellites. While the magnitude of the resulting stresses depends on the adopted elastic and physical parameters, the expected tectonic pattern is independent of these parameters for these mechanisms. Reorientation of the rotation/tidal axis alone is expected to produce normal/thrust faulting provinces enclosing the initial rotation/tidal poles, and thrust/normal faulting provinces enclosing the final rotation/tidal poles. Reorientation of both the rotation and tidal axis results in a wide variety of tectonic patterns for different reorientation geometries. On Europa, the tidal axis reorientation which generally accompanies rotation axis reorientations may provide an alternative explanation for tectonic features that have been interpreted as evidence for non-synchronous rotation. The observed tectonic pattern on Enceladus is more easily explained by a large reorientation (∼90°) of the rotation axis, than by rotation rate variations.

Electrocatalytic oxidation of deoxyguanosine on a glassy carbon electrode modified with a ruthenium oxide hexacyanoferrate film

The electrocatalytic oxidation of deoxyguanosine on a ruthenium hexacyanoferrate (RuOHCF) glassy carbon (GC) modified electrode was investigated in acid medium by using rotating disc electrode (RDE) voltammetry. Chronoamperometric experiments allowed information on the charge transport rate through the RuOHCF film and at a very short time window a diffusion-like behavior was observed with a D ct value of 2.7 × 10 −11 cm 2 s −1 for a film with Γ = 4.47 × 10 −9 mol cm −2. The influence of systematic variation of rotation rate, film thickness and the electrode potential indicates that the rate of cross-chemical reaction between Ru(IV) centers immobilized into the film and deoxyguanosine controls the overall electrodic process and the value of the rate constant was found to be 3.2 × 10 6 mol −1 L 1 s −1. The relatively high rate constant of the cross-reaction, the facile penetration of the substrate through the film and the fast transport of electrons suggest that the electrocatalytic process occurs throughout the film layer.

Supergranule Superrotation Identified as a Projection Effect

Previous measurements of the rotation rate of the supergranule Doppler velocity pattern revealed surprising characteristics: (1) the pattern rotates faster than the plasma at the surface, and, at each latitude, it rotates faster than the plasma at any level below the surface (superrotation), (2) larger cells rotate more rapidly than smaller cells, and (3) faster rotation rates are found when using cross-correlation techniques with larger time lags between Doppler images. We simulate the supergranulation velocity pattern using a spectrum for the cellular flows that matches the observed spectrum, but we keep the pattern unchanged and rotating rigidly. Our simulation shows that the superrotation and its dependence on cell size can be largely reproduced by projection effects on the line-of-sight Doppler velocity signal. The remaining variation in rotation rate with cell size can be attributed to cells smaller than supergranules extending through shallower layers that have slower rotation rates.

Solar activity, Earth’s rotation rate and climate variations in the secular and semi-secular time scales

By applying the wavelet formalism to sudden storm commencements and aa geomagnetic indices and solar total irradiation, as a proxy data for solar sources of climate-forcing, we have searched the signatures of those variables on the Northern Hemisphere surface temperature. We have found that cyclical behaviour in surface temperature is not clearly related to none of these variables, so we have suggested that besides them surface temperature might be related to Earth’s rotation rate variations. Also it has been suggested that in the long-term Earth’s rotation rate variations might be excited by geomagnetic storm time variations which, in turn, depends on solar activity. The study of these phenomena and its relationships is addressed in the present paper. With this purpose we perform an analysis of the evolution during the last 350 years of the signals that conform the 11-year sunspot cycle maxima envelope for different time scales. The result is applied to analyze the relationship between long-term variations in sunspot number and excess of length of day; and to unearth the signature in surface temperature of this last from that of sudden storm commencement and aa geomagnetic indices and total solar irradiation. As solar dynamo experiments transient processes in all the time scales from seconds to centuries, Fourier analysis and its requirement for the process to be stationary is likely to produce spurious periodicities. We resort instead to wavelet formalism. By this representation we found that sunspot maxima envelope for the last 350 years may be described by means of the superposition of two cycles – a decadal and a semi-secular one – and a secular trend. And that the changing amplitude and phase of the cycles are well reconstructed using the superposition of two wavelets with nearby periods. The strong temporal changes in amplitude of the cycles facilitate to detect its phase in a given time series. It is found that a strong semi-secular cycle in the sunspot maxima envelope that started during the 1705 chaotic transition having its maximum amplitude at the Dalton minimum, was mapped 94 years later in Earth’s rotation rate and simultaneously in surface temperature. Also, there was a decrease (increase) of 0.022 °C for each millisecond of decrease (increase) in the Earth’s rotation period for the semi-secular cycle as well as the secular trend.

Variations in the rotation rate of Venus due to orbital eccentricity modulation of solar tidal torques

The rotational state of Venus is presumably determined by a balance between two different solar tidal torques: an atmospheric thermal tide yields a torque which acts in the same direction as the retrograde rotation of Venus and a gravitational solid body tide yields a torque which opposes the current rotation. The strengths of these opposing torques both depend on the eccentricity of the orbit of Venus but with different sensitivities. Thus variations in the orbital eccentricity cause fluctuations in the rotation rate at which the tidal torques balance. If Venus is considered to be a single rigid body, the rotational velocity will change by amounts equivalent to ∼1 km/yr at the equator, over timescales of 106 years. Allowance for differential rotation between the core, mantle, and atmosphere increases the range over which the solid surface rotation rate varies. For plausible values of the strength of viscous coupling at the atmosphere‐mantle boundary and the core‐mantle boundary the variations in solid surface rotational velocity can be 2–3 times larger than in the rigid coupling case. When these long‐period forced variations in rotation rate are considered, the present rotation rate of Venus is seen to be close enough to a resonant spin‐orbit interaction with the Earth that it may occasionally pass through that resonance.

Concentration and velocity patterns in a horizontal rotating suspension of non-Brownian settling particles

We report a systematic experimental study of concentration and velocity patterns formed in a horizontal rotating cylinder filled completely with a monodisperse suspension of non-Brownian settling particles. The system shows a series of concentration and velocity patterns, or phases, with varying rotation rate and solvent viscosity. Individual phases are studied using both side and cross-sectional imaging to examine the detailed flow structures. The overall phase diagram of the system is mapped out as a function of the rotation rate and solvent viscosity. Attempts are made to analyze the functional form of the phase boundaries in order to understand the transition mechanism between different phases.

Wavelet coherence analysis of Length-Of-Day variations and El Niño-Southern Oscillation

Abstract Wavelet coherence analysis is defined and used to analyze the relationships between Length-Of-Day (LOD) variations and El Nino-Southern Oscillation (ENSO) on interannual scales. Using the newest observation data, this study quantitatively shows time-scale-dependent correlations and phase shifts between LOD variations and the ENSO. Good no-lag correlations (larger than 0.8) can be found on 3.0–4.9-year scales, while either obvious phase-shifts or low correlations are found on the other interannual scales. Around 2.5-year (biennial), 3.5-year and 5.0-year scales (i.e. around the time scales of ENSO's significant modes), the LOD variations with respect to the ENSO lag in phase by 4–5 months, lead by 3 months and lag by 3–5 months, respectively. Thus, there are obvious time-scale-dependent correlations and phase-shifts between the Earth rotation rate variations and the ENSO even within interannual scales.

Effects of zonal deformations and the Earth's rotation rate variations on precession-nutation

Because of their importance in the accurate modeling of the Earth's orientation in space, some non-negligible predictable effects on precession-nutation are investigated. This paper considers the coupling effects between the axial and the equatorial components of the Earth's rotation vector in the dynamical equations, and the effects of the second order lunisolar torque due to the Earth's zonal deformations. Firstly, the coupling effects are shown to contribute for less than 0.1 μ as and are therefore negligible. Secondly, we demonstrate that the 0.7 mas contribution of the rotation rate variations due to zonal tides to the nutation in obliquity deduced by Bretagnon et al. ([CITE], Proc. IAU Coll., 180, 230; [CITE], Celest. Mech. Dyn. Astr., 80, 177) is an artefact which comes from an incomplete way of taking into account the effect of the rotation rate variations. The net contribution is shown to be negligibly small. Thirdly, for an Earth model with an elastic mantle and decoupled liquid core, the contribution of the second-order lunisolar torque due to the Earth's zonal deformations is shown to be 207.9 μ as and –9.7 μ as on the 18.6-year nutation respectively in longitude and in obliquity, and a correction of –4925.9 μ as/century on the precession in longitude.

Joint estimation of Martian 20 and rotation variations from simultaneous geodetic measurements: Numerical simulations of a Network Science Experiment

The Martian global‐scale CO2 seasonal cycle implies temporal variations in both the zonal gravity coefficients, such as 20, and in the rotation rate. To estimate the ability to detect simultaneously these two main geodetic signatures, a new approach based on a Network Science Experiment is investigated. We have numerically simulated the two types of Doppler signals involved, accurate orbiter tracking from the Earth and Martian lander tracking from the orbiter, by using a model of both the rotation variations and the seasonal variations of 20. Then, through a least square process, we have jointly adjusted the rotation and 20 parameters from an a priori knowledge. Our results show that it is possible to decorrelate 20 from all rotation parameters. We obtain an accurate adjustment of the 20 variations and a precision at the level of a few milliarcseconds for the estimation of the rotation rate variations.

Analytical modeling of the Doppler tracking between a lander and a Mars orbiter in terms of rotational dynamics

Radio Doppler shifts between a lander on Mars' surface and an orbiter are modeled through a linearized analytical formulation. This simplified formulation allows us to understand the signature and interplay of the different geophysical parameters (nutations, polar motion, and rotation rate variations) on the lander‐orbiter observable. The frequency band of the investigated periodic phenomena goes from some months to about one Martian year in their respective frames. Long‐term effects like precession are taken into account but are not investigated. The satellite orbit is modeled as a precessing orbit because of the oblateness of Mars. We show that we are able to see the signature of a possible liquid core after less than 50 weeks of observation for a given precision of 0.1 mm/s for the Doppler tracking. We are also able to monitor the rotation rate variation and polar motion at a level of 5 mas over the same period. This study was done in the frame of the preparation of the Netlander Ionosphere and Geodesy Experiment (NEIGE).

The gyromagnetic ratio of rapidly rotating compact stars in general relativity

We numerically calculate equilibrium configurations of uniformly rotating and charged neutron stars, in the case of insulating material and neglecting the electromagnetic forces acting on the equilibrium of the fluid. This allows us to study the behaviour of the gyromagnetic ratio for those objects when varying rotation rate and equation of state for the matter. Under the assumption of low charge and incompressible fluid, we find that the gyromagnetic ratio is directly proportional to the compaction parameter M/R of the star, and very little dependent on its angular velocity. Nevertheless, it seems impossible to have g = 2 for these models with low charge-to-mass ratio, where matter consists of a perfect fluid and the collapse limit is never reached.

Characterizations of ball-milled nanocrystalline WC–Co composite powders and subsequently rapid hot pressing sintered cermets

Nanostructured WC–Co cemented carbides, combining high hardness and high toughness, are expected to be widely applicable. In this study, nanocrystalline WC–10Co–0.8VC–0.2Cr 3C 2 (wt.%) composite powders, whose average grain size is bout 25 nm, were fabricated by a unique ball milling technique with variable rotation rate and repetitious circulation in 32 min. The high energy ball milling process was optimized and the as-prepared nanocrystalline powders were characterized and analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential thermal analysis (DTA). Furthermore, a low temperature, high heating rate, short soaking time and pressure sintering technique, that is, rapid hot pressing sintering, was used in the sintering process, by which nanostructured WC–Co cemented carbides with mean grain size of 250 nm were produced. The material exhibits high hardness of 93.6 HRA and transverse rapture strength of 2746 MPa. In the sintered composites, the distribution of elements W, Co, V and Cr is homogeneous, and it is small quantity of miropores and extraordinary coarse tungsten carbide phase that negatively influence the transverse rapture strength of nanostructured WC–Co cemented carbides.

Measurement of Kodaikanal white-light images – VI. Variation of Rotation Rate with Age of Sunspot Groups

We find from an analysis of the Kodaikanal sunspot group data that the rotation rates of spot groups increase with their age when the rotation rates are computed after sorting the spot groups life-span-wise. We confirm these findings from an analysis of the Mt. Wilson sunspot data set too. We show that this trend is in good agreement with the internal rotation profiles from helioseismology (GONG) observations and is also consistent with the concept that the footpoints of the magnetic loops of spot groups are initially anchored in the deeper layers in the solar interior and rise to shallower layers as the spots age, and that the spots reflect the rotation rates at the respective depths at which their footpoints are temporally located. We project the `first-day rotation rates' and the `daily rotation rates' of spot groups on the rotation profiles from the GONG observations and derive the initial anchoring depths of the footpoints of the magnetic loops of the spot groups and their rates of rise as the spot groups age. Our results of the rotation rates are in antithesis to the results reported by investigators from the Greenwich spot group data that show a deceleration in rotation rates as the spot groups age which are also inconsistent with the rotation profiles from helioseismology observations.

The 1.3-year and 156-day periodicities in sunspot data: Wavelet analysis suggests a common origin

Helioseismic data have revealed a 1.3-year periodicity in the solar rotation rate near the bottom of the solar convection zone. In order to test whether these rotation rate variations have a significant impact on the solar dynamo, we search for such a periodicity in tracers of relatively freshly emerged flux at the solar surface, namely sunspots. Sunspot areas and sunspot number time series are studied with the help of the wavelet transform. Significant power at this period (1.28 years) is indeed found and is observed to vary strongly with time. This provides independent support for the presence of a 1.3 year periodicity in solar data. The power at the 154–158-day Rieger period of solar flares is seen to vary approximately in phase with the 1.28-year period. Based on this we propose that the Rieger period is the third harmonic ( years) of the 1.3-year period. If the rotation rate of the Sun does vary with 1.3 years then the enhanced flaring with the Rieger period may finally be driven by the 1.3 year periodicity. However, the power in both periods is also found to approximately follow the total number of sunspots. Therefore we cannot rule out that the 1.3-year and 156-day periods are harmonics of the solar activity cycle. Finally, our analysis of a calibrated sunspot area record reveals that the 156-day period continues into the most recent cycles, in contrast to earlier results.

Change of rotation rates of sunspot groups during their lifetimes: Clues to the sites of origin of different flux tubes

From 103 years of data of non-recurrent sunspot groups and for the two sets (area 100 millionths of hemisphere), irrespective of their life span, we compute rotation rates and rate of change of rotation rates during their lifetime. It is found that variation of rotation rates of sunspot groups with respect to their lifetime is approximately similar to the radial variation of internal rotation inferred by helioseismology and it is conrmed that all the spot groups decelerate as they evolve into later phases of their lifetime. After classication according to dierent life spans, for the same two data sets, we compute initial rotation rates and rate of change of initial rotation rates of sunspot groups. For the two data sets, variation of initial rotation rates of sunspot groups with respect to their life spans is similar to the radial variation of internal rotation of solar plasma inferred from helioseismology. We also obtain the rate of change of initial rotation rates for two sets of spot groups and the results are as follows: (i) for the area 100, acceleration for the life spans of 9{12 days and deceleration for the life spans of 3{9 days. Interpreting these results, an attempt is made to locate the sites of origin of spot groups of dierent sizes and life spans in the convection zone.

The calcium K-line profiles as function of latitude and solar cycle phase

We have monitored the Calcium K-line profiles on daily basis at all the latitudes while integrating the spectrum over the visible longitudes of the Sun by moving a ∼ 340 mm solar image at a uniform speed in the E-W direction. The spectra were recorded at a dispersion of 9.34 mm/Å on 35 mm Kodak 103-a0 film for the time interval of 1986–95. Now we obtain the spectra using 1K × 1K peltier cooled CCD Camera. We plan to use the data to study possible long term variation in chromospheric rotation rate, differential rotation rate, variation in background flux, and changes in polar regions with the phase of the solar cycle through various parameters of this line.

Enhancement of the electrochemical oxidation of formic acid. Effects of anion adsorption and variation of rotation rate

Results are presented from a study on the electrochemical oxidation of formic acid. Perturbing a HCOOH+HClO 4 solution by causing a small amount of any one of several different anions to be present dramatically changes observed nonlinear behavior in an apparently unique manner. Quantitative changes are also observed. In current-control experiments, the presence of fluoroborate ions causes a substantial increase in the value of the applied current density for which low valued stationary potentials remain stable. In potential-control experiments, the current density substantially increases at relevant potential values. Although most properties possessed by the fluoroborate anion exist among the other anions studied, the presence of any one of these other ions in solution yields inferior current–potential characteristics. Results from current-control experiments show that changes in rotation rates have no effect on the observed behavior regardless of anion composition or whether the limiting state is stationary or oscillating.