Angular Rotation Rate Research Articles

Robust MEMS Gyroscope Based on Thermal Principles

Two variants of a novel single-axis thermal gyroscope without seismic mass are designed, fabricated, and characterized in this paper. The operating principle of the device is differential temperature detection due to the Coriolis effect on an oscillatory gas stream created by alternating two resistive microheaters. The fabrication process is based on a bulk micromachining technology on a silicon substrate using platinum as the only conductor layer. The device structure consists of two resistive temperature detectors equally spaced from the two microheaters. The 170-nm-thick platinum heater and detector microstructures are freely suspended over a cavity etched into the substrate, with minimal structural support. A computer-controlled precision rotary stage is constructed to accurately measure the device performance. The devices demonstrate excellent linearity within the tested ±3.5 revolution per second angular rate of rotation and show sensitivities of 0.947 and 1.287 mV/ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> /s at 20 mW heater powers. The robustness of the devices has been validated by the drop shocks of 2,722 to 16,398g (9.81 m/s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ).

Geometrical nonlinearity stabilizes a wave solid-state gyro

It was recognized long ago that quasi-harmonic standing waves in a thin-walled axisymmetric resonator, mounted on a rotating platform, are subject to a precession. This significant phenomenon is naturally associated with a concept of a solid-state wave gyro, or an inertial instrument used to measure angular rotation rate, as if any wave may be interpreted as a material particle moving in a rotating frame of reference. Because there are no typical mechanical parts, these wave sensors can be utilized with a lot of advantages. To run such a gyro in vita, one should excite and keep on by certain means a standing wave in the thin-walled axisymmetric resonator. Up to now, there are known two ways how to do it, and namely, using either external or parametric resonant mechanisms of excitation. Although both cases necessarily require an additional feedback control device in order to stabilize instable or other parasite oscillations of the resonator. This paper, following the study of nonlinear waves in a thin circular ring, demonstrates that the solid-state wave gyro may be naturally stabilized just at the expense of the geometrical nonlinearity by combining advantages of both the positional resonant excitation and the parametric resonance.

Premixed Flames Excited by Helical Disturbances: Flame Wrinkling and Heat Release Oscillations

This paper describes an analysis of the response of swirling premixed flames to helical disturbances, i.e., where the flow fluctuations have an azimuthal dependence of the form and denotes the helical mode number. Results elaborate the nature of local flame wrinkling and heat release fluctuations. Significantly, these results show that these different induced fluctuations exhibit very different sensitivities to helical mode number , swirl strength, and dimensionless frequency. In addition, the degree of axisymmetry of the time averaged flame plays a crucial role in these interactions, particularly in how flow disturbances translate into heat release oscillations. Thus, the helical mode , with the dominant contribution to local flame wrinkling and heat release, , and spatially integrated heat release fluctuations, , is generally different. For example, helical mode , leading to the largest amplitude of local flame wrinkling and heat release in a solid body swirl flowfield, is given by , where is the ratio of swirl angular rotation rate to forcing frequency, is the component of mean tangential velocity resolved along the axial forcing direction, and is the phase speed of the convecting vortex. In contrast, only the axisymmetric mode, , leads to global surface area fluctuations in axisymmetric flames, which are also completely insensitive to swirl number. Because the maximum amplitude of local flame wrinkling is, in general, excited by helical modes with , care must be taken in interpreting the significance of large scale helical flame flapping, as often is captured from planar experimental data or visualized in computations.

Swirl effects on harmonically excited, premixed flame kinematics

This paper describes the response of a swirling premixed flame with constant burning velocity to non-axisymmetric harmonic excitation. This work extends prior studies of axisymmetric forcing, which have shown that wrinkles are excited on the flame that propagate downstream along the mean flame surface at a speed given by U o cos ψ, where U o is the mean flow velocity and ψ is the flame angle. The swirl component in the flow field introduces an azimuthal transport mechanism for disturbances on the flame. As such, the flame response at any given position is a superposition of flame wrinkles excited at earlier times, upstream axial locations, and different azimuthal positions. These swirl transport effects do not arise in problems where axisymmetric flames are subjected to axisymmetric excitation, but enter quite prominently in the presence of non-axisymmetries, such as when the flame is subjected to transverse excitation. The solution characteristics are strongly dependent upon the ratio of angular rotation rate to excitation frequency, denoted by σ = Ω/ ω, which describes the fraction of azimuthal rotation a disturbance makes in one acoustic period. When σ ≪ 1 and σ ≫ 1, the axial wavelength of flame wrinkles scales with the convective wavelength, λ c , but becomes much longer for σ ∼ O(1). The spatial variation in phase of flame wrinkling is also strongly dependent upon σ. Regardless of swirl number, flame wrinkles propagate in helical spirals along the solution characteristics at a phase speed equal to the local tangential velocity. The axial phase characteristics of flame wrinkling at a fixed azimuthal location, as would be measured by laser sheet imaging, are much more complex. For σ < 1, the wrinkles exhibit the familiar negative roll-off character for the phase with axial downstream distance, indicative of an axially convecting disturbance. The slope of this phase roll-off decreases with increasing σ, however, and becomes zero at σ = 1 for a compact flame. For σ > 1, the wrinkles actually have a positive roll-off character for the phase with axial downstream distance, indicating a flame wrinkle with a negative trace velocity, but whose actual propagation velocity is positive. Finally, these results show that while the flame response to transverse acoustic excitation is quite strong locally, its spatially integrated effect is much smaller for acoustically compact flames. This suggests that the dominant mechanism through which the flame responds globally to transverse excitation is the induced vortical and longitudinal acoustic fluctuations.

Granular segregation in a tilted-rotating drum

In this manuscript we present experimental results for the rotation of a bi-disperse mixture of granular material (glass beads) in a titled cylindrical drum. The system parameters are the tilt angle (35° ≤ α ≤ 65°) measured from the horizontal where α = 0 is a vertically oriented right circular cylindrical drum, concentration of smaller beads based on volume ( ϕ = 0.30, 0.40 or 0.50), and the constant angular rotation rate of a 66 mm diameter drum (0.25 Hz ≤ Ω ≤ 1.1 Hz) resulting in rotational Froude numbers in the range 0.0002 < Fr < 0.004. The rotation rate range is chosen so that the mixture undergoes a continuous avalanche process resulting in a cylindrical wedge shaped granular domain. A horizontally oriented rotating drum typically yields segregation of the smaller beads into multiple bands that can merge and split, but in a tilted system it is observed that the smaller particles form a single-segregated band at a fixed axial location. It is unclear though if this segregation is mostly axial or radial and which parameters influence the axial location of the band which is observed to form at both extremum depending on the tilt angle and Froude number. In order to estimate the segregation quality a semi-analytical solution for the steady shape of the flowing granular media based on assumptions made for the total volume of beads, and subsequently the apparent volume of smaller diameter beads based on the segregated band width, is proposed. The segregated band location appears to be driven by both the rotation rate and tilt angle in the range of parameter used in this study. Stronger data trends appear when the tilt angle is used as the discriminating parameter.

SPECTRAL ENERGY DISTRIBUTIONS OF YOUNG STARS IN IC 348: THE ROLE OF DISKS IN ANGULAR MOMENTUM EVOLUTION OF YOUNG, LOW-MASS STARS

Theoretical work suggests that a young star's angular momentum content and rotation rate may be strongly influenced by magnetic interactions with its circumstellar disk. A generic prediction of these "disk-locking" theories is that a disk-locked star will be forced to co-rotate with the Keplerian angular velocity of the inner edge of the disk; that is, the disk's inner-truncation radius should equal its co-rotation radius. These theories have also been interpreted to suggest a gross correlation between young stars' rotation periods and the structural properties of their circumstellar disks, such that slowly rotating stars possess close-in disks that enforce the star's slow rotation, whereas rapidly rotating stars possess anemic or evacuated inner disks that are unable to brake the stars and instead the stars spin up as they contract. To test these expectations, we model the spectral energy distributions (SEDs) of 33 young stars in IC 348 with known rotation periods and infrared excesses indicating the presence of circumstellar disks. For each star, we match the observed SED, typically sampling 0.6–8.0 μm, to a grid of 200,000 pre-computed star+disk radiative transfer models, from which we infer the disk's inner-truncation radius. We then compare this truncation radius to the disk's co-rotation radius, calculated from the star's measured rotation period. We do not find obvious differences in the disk truncation radii of slow rotators versus rapid rotators. This holds true both at the level of whether close-in disk material is present at all, and in analyzing the precise location of the inner disk edge relative to the co-rotation radius among the subset of stars with close-in disk material. One interpretation is that disk locking is unimportant for the IC 348 stars in our sample. Alternatively, if disk locking does operate, then it must operate on both the slow and rapid rotators, potentially producing both spin-up and spin-down torques, and the transition from the disk-locked state to the disk-released state must occur more rapidly than the stellar contraction timescale.

The various contributions in Venus rotation rate and LOD

% context heading (optional) {Thanks to the Venus Express Mission, new data on the properties of Venus could be obtained in particular concerning its rotation.} % aims heading (mandatory) {In view of these upcoming results, the purpose of this paper is to determine and compare the major physical processes influencing the rotation of Venus, and more particularly the angular rotation rate.} % methods heading (mandatory) {Applying models already used for the Earth, the effect of the triaxiality of a rigid Venus on its period of rotation are computed. Then the variations of Venus rotation caused by the elasticity, the atmosphere and the core of the planet are evaluated.} % results heading (mandatory) {Although the largest irregularities of the rotation rate of the Earth at short time scales are caused by its atmosphere and elastic deformations, we show that the Venus ones are dominated by the tidal torque exerted by the Sun on its solid body. Indeed, as Venus has a slow rotation, these effects have a large amplitude of 2 minutes of time (mn). These variations of the rotation rate are larger than the one induced by atmospheric wind variations that can reach 25-50 seconds of time (s), depending on the simulation used. The variations due to the core effects which vary with its size between 3 and 20s are smaller. Compared to these effects, the influence of the elastic deformation cause by the zonal tidal potential is negligible.} % conclusions heading (optional), leave it empty if necessary {As the variations of the rotation of Venus reported here are of the order 3mn peak to peak, they should influence past, present and future observations providing further constraints on the planet internal structure and atmosphere.}

The Twente turbulent Taylor–Couette (T3C) facility: Strongly turbulent (multiphase) flow between two independently rotating cylinders

A new turbulent Taylor-Couette system consisting of two independently rotating cylinders has been constructed. The gap between the cylinders has a height of 0.927 m, an inner radius of 0.200 m, and a variable outer radius (from 0.279 to 0.220 m). The maximum angular rotation rates of the inner and outer cylinder are 20 and 10 Hz, respectively, resulting in Reynolds numbers up to 3.4 × 10(6) with water as working fluid. With this Taylor-Couette system, the parameter space (Re(i), Re(o), η) extends to (2.0 × 10(6), ±1.4 × 10(6), 0.716-0.909). The system is equipped with bubble injectors, temperature control, skin-friction drag sensors, and several local sensors for studying turbulent single-phase and two-phase flows. Inner cylinder load cells detect skin-friction drag via torque measurements. The clear acrylic outer cylinder allows the dynamics of the liquid flow and the dispersed phase (bubbles, particles, fibers, etc.) inside the gap to be investigated with specialized local sensors and nonintrusive optical imaging techniques. The system allows study of both Taylor-Couette flow in a high-Reynolds-number regime, and the mechanisms behind skin-friction drag alterations due to bubble injection, polymer injection, and surface hydrophobicity and roughness.

О финальном движении скользящих и вращающихся дисков с однородным кулоновым трением

Abstract We review previous investigations concerning the terminal motion of disks sliding and spinning with uniform dry friction across a horizontal plane. Previous analyses show that a thin circular ring or uniform circular disk of radius R always stops sliding and spinning at the same instant. Moreover, under arbitrary nonzero initial values of translational speed v and angular rotation rate ω , the terminal value of the speed ratio ϵ 0 = v / R ω is always 1.0 for the ring and 0.653 for the uniform disk. In the current study we show that an annular disk of radius ratio η = R 1 / R 2 stops sliding and spinning at the same time, but with a terminal speed ratio dependent on η . For a two-tier disk with lower tier of thickness H 1 and radius R 1 and upper tier of thickness H 2 and radius R 2 , the motion depends on both η and the thickness ratio λ = H 1 / H 2 . While translation and rotation stop simultaneously, their terminal ratio ϵ 0 either vanishes when k > 2 / 3 , is a nonzero constant when 1 / 2 k 2 / 3 , or diverges when k 1 / 2 , where k is the normalized radius of gyration. These three regimes are in agreement with those found by Goyal et al. [S. Goyal, A. Ruina, J. Papadopoulos, Wear 143 (1991) 331] for generic axisymmetric bodies with varying radii of gyration using geometric methods. New experiments with PVC disks sliding on a nylon fabric stretched over a plexiglass plate only partially corroborate the three different types of terminal motions, suggesting more complexity in the description of friction.

System Identification of MEMS Vibratory Gyroscope Sensor

Fabrication defects and perturbations affect the behavior of a vibratory MEMS gyroscope sensor, which makes it difficult to measure the rotation angular rate. This paper presents a novel adaptive approach that can identify, in an online fashion, angular rate and other system parameters. The proposed approach develops an online identifier scheme, by rewriting the dynamic model of MEMS gyroscope sensor, that can update the estimator of angular rate adaptively and converge to its true value asymptotically. The feasibility of the proposed approach is analyzed and proved by Lyapunov′s direct method. Simulation results show the validity and effectiveness of the online identifier.

Axisymmetric simulations of libration-driven fluid dynamics in a spherical shell geometry

We report on axisymmetric numerical simulations of rapidly rotating spherical shells in which the axial rotation rate of the outer shell is modulated in time. This allows us to model planetary bodies undergoing forced longitudinal libration. In this study we systematically vary the Ekman number, 10−7≤E≲10−4, which characterizes the ratio of viscous to Coriolis forces in the fluid, and the libration amplitude, Δϕ. For libration amplitudes above a certain threshold, Taylor–Görtler vortices form near the outer librating boundary, in agreement with the previous laboratory experiments of Noir et al. [Phys. Earth Planet. Inter. 173, 141 (2009)]. At the lowest Ekman numbers investigated, we find that the instabilities remain spatially localized at onset in the equatorial region. In addition, nonzero time-averaged azimuthal (zonal) velocities are observed for all parameters studied. The zonal flow is characterized by predominantly retrograde flow in the interior, with a stronger prograde jet in the outer equatorial region. The magnitude of the zonal flow scales as the square of the librational forcing, ϵ2, where ϵ=Δϕf and f is the dimensionless libration frequency defined as the ratio between the libration frequency and the mean angular rotation rate. In addition, the zonal flow is primarily independent of the Ekman number, implying that the zonal flow does not depend on the viscosity of the fluid. The simulations show that the zonal flow is driven by nonlinearities in the Ekman boundary layer; it is not driven by Taylor–Görtler vortices or by inertial waves in the fluid interior. Application of our results suggests that many librating bodies in the solar system are above the onset for centrifugal instabilities, with values up to ∼30 times supercritical. However, the spatial localization of the instabilities at onset in our simulations suggests that their effects are limited on the global dynamics of librating bodies. We find that the zonal flows driven by libration in axisymmetric spherical shells are unlikely to produce significant planetary magnetic fields, but will likely generate nonzero mean torques on the bounding surfaces.

A slitless spectroscopic survey for Hαemission-line objects in SMC clusters

This paper checks on the roles of metallicity and evolutionary age in the appearance of the so-called Be phenomenon. Slitless CCD spectra were obtained covering the bulk of the Small Magellanic Cloud. For Halpha line emission twice as strong as the ambient continuum, the survey is complete to spectral type B2/B3 on the main sequence. About 8120 spectra of 4437 stars were searched for emission lines in 84 open clusters. 370 emission-line stars were found, among them at least 231 near the main sequence. For 176 of them, photometry could be found in the OGLE database. For comparison with a higher-metallicity environment, the Galactic sample of the photometric Halpha survey by McSwain & Gies (2005) was used. Among early spectral sub-types, Be stars are more frequent by a factor 3-5 in the SMC than in the Galaxy. The distribution with spectral type is similar in both galaxies, i.e. not strongly dependent on metallicity. The fraction of Be stars does not seem to vary with local star density. The Be phenomenon mainly sets in towards the end of the main-sequence evolution (this trend may be more pronounced in the SMC); but some Be stars already form with Be-star characteristics. In all probability, the fractional critical angular rotation rate, \omc, is one of the main parameters governing the occurrence of the Be phenomenon. If the Be character is only acquired during the course of evolution, the key circumstance is the evolution of \omc, which not only is dependent on metallicity but differently so for different mass ranges.

Blind Equalization and Carrier Phase Recovery in a 16-QAM Optical Coherent System

Blind equalization and carrier phase recovery in a simulated 14 Gbaud 16-QAM optical coherent system are investigated. Equalization techniques to compensate for linear transmission impairments are presented using the constant modulus algorithm (CMA), the recursive least-squares (RLS)-CMA, and the radius directed equalization (RDE). With 7 T/2-spaced taps, the RDE and the RLS-CMA can compensate up to 1000 ps/nm of CD in the 16-QAM coherent system with performances comparable to the decision-directed (DD) equalizer. We show that the RDE is a promising technique for blind equalization in a 16-QAM coherent system with lower complexity than the RLS-CMA. Blind carrier phase recovery is investigated in a decision-directed-mode. We show that the blind carrier phase recovery algorithm can recover the Square-16-QAM constellation for laser beat linewidths of DeltanuTs ~ 10-4 in a polarization-multiplexed (POLMUX) 16-QAM coherent system with the RDE algorithm giving better overall performance than the CMA when compensating for CD and differential group delay (DGD). Finally, the dynamical characteristics of the equalizers to track endless polarization rotations are discussed. With the adaptation parameters optimized, the equalizers can track angular rate of rotation ~ 105 rad/s.

STABILITY OF THE MAGNETOPAUSE OF DISK-ACCRETING ROTATING STARS

We discuss three modes of oscillation of accretion disks around rotating magnetized neutron stars which may explain the separations of the kilo-Hertz quasi periodic oscillations (QPO) seen in low mass X-ray binaries. The existence of these compressible, non-barotropic magnetohydrodynamic (MHD) modes requires that there be a maximum in the angular velocity $\Omega_\phi(r)$ of the accreting material larger than the angular velocity of the star $\Omega_*$, and that the fluid is in approximately circular motion near this maximum rather than moving rapidly towards the star or out of the disk plane into funnel flows. Our MHD simulations show this type of flow and $\Omega_\phi(r)$ profile. The first mode is a Rossby wave instability (RWI) mode which is radially trapped in the vicinity of the maximum of a key function $g(r){\cal F}(r)$ at $r_{R}$. The real part of the angular frequency of the mode is $\omega_r=m\Omega_\phi(r_{R})$, where $m=1,2...$ is the azimuthal mode number. The second mode, is a mode driven by the rotating, non-axisymmetric component of the star's magnetic field. It has an angular frequency equal to the star's angular rotation rate $\Omega_*$. This mode is strongly excited near the radius of the Lindblad resonance which is slightly outside of $r_R$. The third mode arises naturally from the interaction of flow perturbation with the rotating non-axisymmetric component of the star's magnetic field. It has an angular frequency $\Omega_*/2$. We suggest that the first mode with $m=1$ is associated with the upper QPO frequency, $\nu_u$; that the nonlinear interaction of the first and second modes gives the lower QPO frequency, $\nu_\ell =\nu_u-\nu_*$; and that the nonlinear interaction of the first and third modes gives the lower QPO frequency $\nu_\ell=\nu_u-\nu_*/2$, where $\nu_*=\Omega_*/2\pi$.

TRIGONOMETRIC PARALLAXES OF MASSIVE STAR-FORMING REGIONS. VI. GALACTIC STRUCTURE, FUNDAMENTAL PARAMETERS, AND NONCIRCULAR MOTIONS

We are using the Very Long Baseline Array and the Japanese VLBI Exploration of Radio Astronomy project to measure trigonometric parallaxes and proper motions of masers found in high-mass star-forming regions across the Milky Way. Early results from 18 sources locate several spiral arms. The Perseus spiral arm has a pitch angle of 16 degrees +/- 3 degrees, which favors four rather than two spiral arms for the Galaxy. Combining positions, distances, proper motions, and radial velocities yields complete three-dimensional kinematic information. We find that star-forming regions on average are orbiting the Galaxy approximate to 15 km s(-1) slower than expected for circular orbits. By fitting the measurements to a model of the Galaxy, we estimate the distance to the Galactic center R(0) = 8.4 +/- 0.6 kpc and a circular rotation speed Theta(0) = 254 +/- 16 km s(-1). The ratio Theta(0)/R(0) can be determined to higher accuracy than either parameter individually, and we find it to be 30.3 +/- 0.9 km s(-1) kpc(-1), in good agreement with the angular rotation rate determined from the proper motion of Sgr A*. The data favor a rotation curve for the Galaxy that is nearly flat or slightly rising with Galactocentric distance. Kinematic distances are generally too large, sometimes by factors greater than 2; they can be brought into better agreement with the trigonometric parallaxes by increasing Theta(0)/R(0) from the IAU recommended value of 25.9 km s(-1) kpc(-1) to a value near 30 km s(-1) kpc(-1). We offer a revised prescription for calculating kinematic distances and their uncertainties, as well as a new approach for defining Galactic coordinates. Finally, our estimates of Theta(0) and Theta(0)/R(0), when coupled with direct estimates of R(0), provide evidence that the rotation curve of the Milky Way is similar to that of the Andromeda galaxy, suggesting that the dark matter halos of these two dominant Local Group galaxy are comparably massive.

Tangential oscillations of a differentially rotating spherical fluid layer

The natural harmonic oscillations of a differentially rotating fluid layer under the action of a potential force are considered. The rise in the layer level is assumed to be negligible. The oscillations satisfy an ordinary second-order differential equation with singular coefficients that depend on the spatial coordinate. This equation is solved by the method of local separation of singularities based on the use of the properties of the Fuchs series for a bounded solution. Various laws for the latitude dependence of the angular rate of ocean rotation and the effect of these laws on the problem spectrum are considered. An equation is obtained for the streamlines of the oscillations investigated. Two cases in which the latitude dependence of the base flow velocity coincides with the real dependence for a celestial body are considered and the corresponding modes are found.

GAS PROPERTIES AND IMPLICATIONS FOR GALACTIC STAR FORMATION IN NUMERICAL MODELS OF THE TURBULENT, MULTIPHASE INTERSTELLAR MATTER

Using numerical simulations of galactic disks resolving scales from ~1 to several hundred pc, we investigate dynamical properties of the multiphase ISM with turbulence driven by star formation feedback. We focus on HII region effects by applying intense heating in dense, self-gravitating regions. Our models are two-dimensional radial-vertical slices through the disk, and include sheared background rotation, vertical stratification, heating and cooling to yield temperatures T~10-10^4K, and thermal conduction. We separately vary the gas surface density Sigma, the stellar volume density rho_*, and the local angular rotation rate Omega to explore environmental dependencies, and analyze the steady-state properties of each model. Among other statistics, we evaluate turbulent amplitudes, virial ratios, Toomre Q parameters including turbulence, and the mass fractions at different densities. We find that the dense gas (n>100 cm^-3) has turbulence levels similar to observed GMCs and virial ratios ~1-2. The Toomre Q parameter in dense gas reaches near unity, demonstrating self-regulation via turbulent feedback. We also test how the star formation rate Sigma_SFR depends on Sigma, rho_*, and Omega. Under the assumption that the star formation rate is proportional to the mass at densities above n_th divided by the free-fall time at that threshold, we find that Sigma_SFR varies as Sigma^(1+p) with 1+p ~ 1.2-1.4 when n_th=10^2 or 10^3 cm^-3, consistent with observations. Estimated star formation rates based on large-scale properties (the orbital time, the Jeans time, or the free-fall time at the vertically-averaged density) however depart from rates computed using the dense gas mass, indicating that resolving the ISM structure in galactic disks at scales <<H is necessary for accurate predictions of the star formation rate.

Active tectonics of the Adriatic region from GPS and earthquake slip vectors

To investigate the kinematics of the Adriatic region, we integrate continuous and episodic GPS measurements with Mw &gt; 4.5 earthquake slip vectors selected from the Regional Centroid Moment Tensor catalogue. Coherent motion of GPS sites in the Po Valley, in Apulia, and in the Hyblean Plateau allows us to estimate geodetically constrained angular velocities for these regions. The predictions of the GPS‐inferred angular velocities are compared with the earthquake slip vectors, showing that the seismically expressed deformation at the microplate boundaries is consistent with the observed geodetic motion. The remarkable consistency between geodetic, seismological, and geological evidence of active tectonics suggests that active deformation in the central Adriatic is controlled by the relative motion between the Adria and Apulia microplates. The microplates' angular rotation rates are then compared with the rotation rates calculated with a simple block model supporting the hypotheses (1) that Apulia forms a single microplate with the Ionian Sea and possibly with the Hyblean region and (2) that Adria and Apulia rotate in such a way as to accommodate the Eurasia‐Nubia relative motion. We suggest that the present‐day microplate configuration follows a recent fragmentation of the Adriatic promontory that during the Neogene rigidly transferred the Africa motion to the orogenic belts that now surround the Adriatic region.

Quaternion-Based Transformation for Extraction of Image-Generating Doppler for ISAR

Inverse synthetic aperture radar (ISAR) is an imaging technique that is dependent on an object's rotational motion over a coherent processing interval. Maritime vessels and aircraft possess 3-D rotational motion, whereas it is only their ISAR contributing motion that is useful to the ISAR imaging process; the contributing motion consists of the Doppler generating axis and the effective angle of rotation. This letter presents a quaternion-based transformation that converts measured attitude and position data into an object's Doppler generating axis and effective angular rotation rate. This transformation is significant since it isolates the component of the motion that directly influences the ISAR image. It provides an alternative approach that can be used to understand the causes of blurring of most ISAR images of sea vessels as well to identify good imaging intervals for applications such as cooperative ISAR for radar cross section measurement purposes.

On asymptotics of low-frequency oscillations of the liquid core: 1. Basic relations

Asymptotic analysis of low-frequency oscillations of a rotating liquid bounded by a solid surface is performed under the condition that the oscillation frequency is much smaller than the angular rate of rotation. Simple analytical relations describing comprehensively asymptotic modes of these oscillations are obtained.