Showing papers on "Rotation published in 2001"

Wing rotation and the aerodynamic basis of insect flight

Abstract: The enhanced aerodynamic performance of insects results from an interaction of three distinct yet interactive mechanisms: delayed stall, rotational circulation, and wake capture. Delayed stall functions during the translational portions of the stroke, when the wings sweep through the air with a large angle of attack. In contrast, rotational circulation and wake capture generate aerodynamic forces during stroke reversals, when the wings rapidly rotate and change direction. In addition to contributing to the lift required to keep an insect aloft, these two rotational mechanisms provide a potent means by which the animal can modulate the direction and magnitude of flight forces during steering maneuvers. A comprehensive theory incorporating both translational and rotational mechanisms may explain the diverse patterns of wing motion displayed by different species of insects.

Controlled rotation of optically trapped microscopic particles.

Abstract: We demonstrate controlled rotation of optically trapped objects in a spiral interference pattern. This pattern is generated by interfering an annular shaped laser beam with a reference beam. Objects are trapped in the spiral arms of the pattern. Changing the optical path length causes this pattern, and thus the trapped objects, to rotate. Structures of silica microspheres, microscopic glass rods, and chromosomes are set into rotation at rates in excess of 5 hertz. This technique does not depend on intrinsic properties of the trapped particle and thus offers important applications in optical and biological micromachines.

Driving Bose-Einstein-Condensate Vorticity with a Rotating Normal Cloud

Abstract: We have developed an evaporative cooling technique that accelerates the rotation of an ultracold 87Rb gas, confined in a static harmonic potential. As a normal gas is evaporatively spun up and cooled below quantum degeneracy, it is found to nucleate vorticity in a Bose-Einstein condensate. Measurements of the condensate's aspect ratio and surface-wave excitations are consistent with effective rigid-body rotation. Rotation rates of up to 94% of the centrifugal limit are inferred. A threshold in the normal cloud's rotation is observed for the intrinsic nucleation of the first vortex. The threshold value lies below the prediction for a nucleation mechanism involving the excitation of surface waves of the condensate.

Collocated rotating flexure microactuator for dual-stage servo in disk drives

Abstract: A head gimbal assembly ( 10 ) for a disk drive ( 1 ), having a flexure ( 30 ) with a stationary portion ( 40 ) and at least one movable portion ( 42 ), a portion of the flexure ( 30 ) being attached to a load beam ( 28 ). A slider ( 20 ) containing a read/write head ( 22 ) is attached to one of the movable portions ( 40 ) of the flexure ( 30 ). The load beam ( 28 ) provides a center of rotation ( 54 ) for the slider ( 20 ) and one or more microactuators ( 24 ) connect between the stationary portion ( 40 ) of the flexure ( 30 ) and one of the movable portions ( 42, 44 ) for applying a moment which causes pure or nearly pure rotation of the slider ( 20 ) about the center of rotation ( 54 ). A disk drive ( 1 ) and an actuator arm ( 2 ) including the head gimbal assembly ( 10 ) are also disclosed.

Error field amplification and rotation damping in tokamak plasmas.

Abstract: Toroidal rotation is normally very weakly damped in plasmas that are magnetically confined in the nominally toroidally symmetric tokamak. However, a strong damping of toroidal rotation is observed as such plasmas approach marginal stability for perturbations that produce a kinklike distortion of the plasma. It is shown that the damping of toroidal rotation by very small departures of the magnetic field from toroidal symmetry is greatly enhanced as marginal stability is approached. The response of a plasma to perturbations is studied using a set of electrical circuit elements, which provide an equation for the rotational damping that requires minimal information about the plasma.

Polyethylene contact stresses, articular congruity, and knee alignment.

Abstract: Increased conformity at the tibiofemoral articulation increases contact area and reduces contact stresses in total knee arthroplasty. Malalignment, however, can increase polyethylene contact stresses. The effect of knee alignment and articular conformity on contact stresses was evaluated in a finite element model. The polyethylene insert and femoral component were modeled in high- and low-conformity conditions. An axial tibial load of 3000 N was applied across the tibiofemoral articulation at different knee positions ranging from 0° to 90° flexion, 0 to 10 mm anteroposterior translation, 0° to 10° axial rotation, and coronal plane angulation (liftoff). Increased conformity significantly reduced contact stresses in neutral alignment (by 44% at 0° flexion and 36% at 60° and 90° flexion). Liftoff significantly increased contact stresses in low- and high-conformity conditions, but to a lesser degree in the high-conformity condition. Malalignment in rotation was most detrimental especially with the high-conformity insert design. Overall, increasing articular conformity reduced stresses when the knee was well-aligned. However, malalignment in axial rotation was detrimental. Mobile-bearing knee designs with increased articular congruity may result in lower contact stresses, especially the rotating-bearing designs that theoretically minimize rotational malalignment.

Large-scale velocity structures in turbulent thermal convection.

Abstract: A systematic study of large-scale velocity structures in turbulent thermal convection is carried out in three different aspect-ratio cells filled with water. Laser Doppler velocimetry is used to measure the velocity profiles and statistics over varying Rayleigh numbers Ra and at various spatial positions across the whole convection cell. Large velocity fluctuations are found both in the central region and near the cell boundary. Despite the large velocity fluctuations, the flow field still maintains a large-scale quasi-two-dimensional structure, which rotates in a coherent manner. This coherent single-roll structure scales with Ra and can be divided into three regions in the rotation plane: (1) a thin viscous boundary layer, (2) a fully mixed central core region with a constant mean velocity gradient, and (3) an intermediate plume-dominated buffer region. The experiment reveals a unique driving mechanism for the large-scale coherent rotation in turbulent convection.

Coordinate input device and portable information apparatus equipped with coordinate input device

Abstract: A coordinate input device has a keyboard; a rotary dial annular in shape and mounted in substantially the same plane as the keyboard, the rotary dial being rotatable within the plane; and a rotation detector for detecting the amount and direction of rotation of the rotary dial, and wherein: the rotary dial is disposed below the keyboard

Directional inertial tactile feedback using rotating masses

Abstract: Directional haptic feedback for a haptic feedback interface device. A haptic feedback interface device, in communication with a host computer, includes a housing physically contacted by a user operating the interface device, and a plurality of actuators producing inertial forces when the actuators are driven by control signals. Each of the actuators includes a rotatable eccentric mass positioned offset on a rotating shaft of the actuator, where the actuators are rotated simultaneously such that centrifugal forces from the rotation of masses combine to output the inertial forces substantially only along a single axis having a desired direction approximately in a plane of rotation of the masses.

Dynamics of fine particles in magnetized plasmas

Abstract: Here are presented experiments on fine particles levitating in low-pressure weakly ionized plasmas under a vertical magnetic field. The magnetic field is useful to provide a vertically long cylindrical column of fine-particle clouds, yielding even string-shaped vertically aligned fine particles, under the double-plasma configuration. Measurements show that fine-particle clouds rotate in the azimuthal direction on the horizontal plane even in such a weak magnetic field that positive ions are slightly magnetized. With an increase of the magnetic field, the rotation speed increases, being followed by subsequent saturation. The rotation speed and direction can be controlled by varying radial plasma potential and/or density profiles. The rotation is induced under the condition that the interparticle distance is small enough for the strong Coulomb coupling among fine particles. A mechanism of the rotation could be explained by effects of ion motions on fine particles, which are modified in the presence of the vertical magnetic field.

The four final rotation states of Venus

Abstract: Venus rotates very slowly on its axis in a retrograde direction, opposite to that of most other bodies in the Solar System1. To explain this peculiar observation, it has been generally believed2,3,4,5,6 that in the past its rotational axis was itself rotated to 180° as a result of core–mantle friction inside the planet, together with atmospheric tides. But such a change has to assume a high initial obliquity (the angle between the planet's equator and the plane of the orbital motion). Chaotic evolution7, however, allows the spin axis to flip for a large set of initial conditions6,8. Here we show that independent of uncertainties in the models, terrestrial planets with dense atmosphere like Venus can evolve into one of only four possible rotation states. Moreover, we find that most initial conditions will drive the planet towards the configuration at present seen at Venus, albeit through two very different evolutionary paths. The first is the generally accepted view whereby the spin axis flips direction2,3,4,5,6. But we have also found that it is possible for Venus to begin with prograde rotation (the same direction as the other planets) yet then develop retrograde rotation while the obliquity goes towards zero9: a rotation of the spin axis is not necessary in this case.

Dynamics of blue compact galaxies, as revealed by their H alpha velocity fields - II. Mass models and the starburst triggering mechanism

Abstract: The Hα velocity fields of a sample of six luminous blue compact galaxies (BCGs) and two companions have been obtained by observations with a scanning Fabry-Perot interferometer. The Fabry-Perot images, velocity fields and rotations curves have been presented in a previous paper (Paper I). In general, the velocity fields are irregular and often contain secondary dynamical components, but display overall rotation. The two companions have more regular velocity fields and rotation curves. In this article we analyse the velocity fields and dynamics together with the morphology of the studied BCGs, and present detailed mass models. In addition, we model the stellar mass content by means of multicolour surface photometry and spectral evolutionary synthesis analysis. By comparison of the masses of stars and those derived from the rotation curve, we show that about half of the galaxies cannot be supported by rotation alone. The morphology and dynamics of the BCGs suggest that the starburst activity in these galaxies are most likely triggered by mergers involving gas-rich dwarf galaxies and/or massive gas clouds.

Intervertebral linking device

Abstract: The invention concerns a device comprising at least a fixed element (2) designed to be secured to a vertebra or sacrum, at least a mobile linking element (10) and at least an intermediate element (20), articulating the mobile element relative to the fixed element, the intermediate element being received, in use, in an internal volume (16) of the mobile element (10). Said intermediate element (20) is deformable, so as to be introduced by impingement into said inner volume (16), and the fixed element (2) is received at least partly, in use, in an internal volume (30) of the intermediate element (20). Said fixed element (2) has, with the intermediate element, a position for use, wherein said fixed element has three degrees of freedom in rotation, but is linked in translation, relative to the intermediate element and a position for insertion, wherein said fixed element has three degrees of freedom in rotation and in translation relative to the intermediate element.

Physically realistic computer simulation of medical procedures

Abstract: An apparatus for interfacing the movement of a shaft with a computer includes a support, a gimbal mechanism having two degrees of freedom, and three electromechanical transducers. When a shaft is engaged with the gimbal mechanism, it can move with three degrees of freedom in a spherical coordinate space, where each degree of freedom is sensed by one of the three transducers. A fourth transducer can be used to sense rotation of the shaft around an axis. The method includes the steps of defining an origin in 3-dimensional space, physically constraining a shaft in the 3-dimensional space such that a portion of the shaft always intersects the origin and such that a portion of the shaft extending beyond the origin defines a radius in a spherical coordinate system, transducing a first electrical signal related to a first angular coordinate of the radius with a first transducer, transducing a second electrical signal related to a second angular coordinate with a second transducer, transducing a third electrical signal related to the length of the radius with a third transducer, and coupling the transducers to a computer.

Roll-pitch-roll-yaw surgical tool

Abstract: A robotic surgical tool includes an elongate shaft having a working end and a shaft axis. A wrist member has a proximal portion pivotally connected to the working end to rotate relative to the working end around a pitch axis which is nonparallel to the shaft axis. An end effector is pivotally mounted on a distal portion of the wrist member to rotate around a wrist roll axis of the wrist member. The wrist roll axis extends between the proximal portion and the distal portion of the wrist member. The end effector is pivotally mounted to rotate relative to the wrist member around a yaw axis which is nonparallel to the wrist roll axis. A torsion tube is coupled with the end effector base and is rotatable to turn the end effector base around the wrist roll axis of the wrist member. The torsion tube extends through an interior of the elongate shaft to a proximal end opposite from the working end of the elongate shaft. The torsion tube is bendable around the pitch axis with rotation of the wrist member around the pitch axis relative to the working end.

Direct Measurement of the Preferred Sense of NO Rotation After Collision with Argon

Abstract: The preferred sense of product molecule rotation (clockwise or counterclockwise) in a bimolecular collision system has been measured. Rotationally inelastic collisions of nitric oxide (NO) molecules with Ar atoms were studied by combining crossed molecular beams, circularly polarized resonant multiphoton ionization probing, and velocity-mapped ion imaging detection. The observed sense of NO product rotation varies with deflection angle and is a strong function of the NO final rotational state. The largest preferences for sense of rotation are observed at the highest kinematically allowed product rotational states; for lower rotational states, the variation with deflection angle becomes oscillatory. Quantum calculations on the most recently reported NO-Ar potential give good agreement with the observed oscillation patterns in the sense of rotation.

Anisotropic spectra in two-dimensional turbulence on the surface of a rotating sphere

Abstract: The anisotropic characteristics of small-scale forced 2D turbulence on the surface of a rotating sphere are investigated. In the absence of rotation, the Kolmogorov k−5/3 spectrum is recovered with the Kolmogorov constant CK≈6, close to previous estimates in plane geometry. Under strong rotation, in long-term simulations without a large-scale drag, a −5 slope emerges in the vicinity of the zonal axis (kx→0), while a −5/3 slope prevails in other sectors far away from the zonal axis in the wave number plane. This picture is consistent with the new flow regime recently simulated by Chekhlov et al. [Physica D 98, 321–334 (1995)] and Smith and Waleffe [Phys. Fluids 11, 1608–1622 (1999)] on the beta plane. The concentration of energy in the zonal components and breaking of isotropy are caused by the strongly anisotropic spectral energy transfer and the stabilization of zonal mean flow by the meridional gradient of the planetary vorticity. The sharp tilt-up of the spectrum along the zonal axis was qualitatively ...

Annular and spiral patterns in flows between rotating and stationary discs

Abstract: Different instabilities of the boundary layer flows that appear in the cavity between stationary and rotating discs are investigated using three-dimensional direct numerical simulations. The influence of curvature and confinement is studied using two geometrical configurations: (i) a cylindrical cavity including the rotation axis and (ii) an annular cavity radially confined by a shaft and a shroud. The numerical computations are based on a pseudo-spectral Chebyshev{Fourier method for solving the incompressible Navier{Stokes equations written in primitive variables. The high level accuracy of the spectral methods is imperative for the investigation of such instability structures. The basic flow is steady and of the Batchelor type. At a critical rotation rate, stationary axisymmetric and/or three-dimensional structures appear in the B¨odewadt and Ekman layers while at higher rotation rates a second transition to unsteady flow is observed. All features of the transitions are documented. A comparison of the wavenumbers, frequencies, and phase velocities of the instabilities with available theoretical and experimental results shows that both type II (or A) and type I (or B) instabilities appear, depending on flow and geometric control parameters. Interesting patterns exhibiting the coexistence of circular and spiral waves are found under certain conditions.

Overcritical rotation of a trapped Bose-Einstein condensate.

Abstract: The rotational motion of an interacting Bose-Einstein condensate confined by a harmonic trap is investigated by solving the hydrodynamic equations of superfluids, with the irrotationality constraint for the velocity field. We point out the occurrence of an overcritical branch where the system can rotate with angular velocity larger than the oscillator frequencies. We show that in the case of isotropic trapping the system exhibits a bifurcation from an axisymmetric to a triaxial configuration, as a consequence of the interatomic forces. The dynamical stability of the rotational motion with respect to the dipole and quadrupole oscillations is explicitly discussed.

Fluid instabilities in precessing spheroidal cavities

Abstract: We study by direct numerical simulation the motion of incompressible fluid contained in an ellipsoid of revolution with ellipticity 0.1 or less which rotates about its axis of symmetry and whose rotation axis is executing precessional motion. A solution to this problem for an inviscid fluid given by Poincare (1910) predicts motion of uniform vorticity. The simulations show how the orientation of the average vorticity of a real fluid is influenced by both pressure and viscous torques exerted by the boundaries. Axisymmetric shear layers appear which agree well with those observed experimentally by Malkus (1968). Shear caused by deviations from a velocity field with uniform vorticity triggers an instability consisting of waves propagating around the average rotation axis of the fluid. The Ekman layers at the boundaries may also become unstable.

Neural processing of gravito-inertial cues in humans. II. Influence of the semicircular canals during eccentric rotation.

Abstract: All linear accelerometers, including the otolith organs, respond equivalently to gravity and linear acceleration. To investigate how the nervous system resolves this ambiguity, we measured perceived roll tilt and reflexive eye movements in humans in the dark using two different centrifugation motion paradigms (fixed radius and variable radius) combined with two different subject orientations (facing-motion and back-to-motion). In the fixed radius trials, the radius at which the subject was seated was held constant while the rotation speed was changed to yield changes in the centrifugal force. In variable radius trials, the rotation speed was held constant while the radius was varied to yield a centrifugal force that nearly duplicated that measured during the fixed radius condition. The total gravito-inertial force (GIF) measured by the otolith organs was nearly identical in the two paradigms; the primary difference was the presence (fixed radius) or absence (variable radius) of yaw rotational cues. We found that the yaw rotational cues had a large statistically significant effect on the time course of perceived tilt, demonstrating that yaw rotational cues contribute substantially to the neural processing of roll tilt. We also found that the orientation of the subject relative to the centripetal acceleration had a dramatic influence on the eye movements measured during fixed radius centrifugation. Specifically, the horizontal vestibuloocular reflex (VOR) measured in our human subjects was always greater when the subject faced the direction of motion than when the subjects had their backs toward the motion during fixed radius rotation. This difference was consistent with the presence of a horizontal translational VOR response induced by the centripetal acceleration. Most importantly, by comparing the perceptual tilt responses to the eye movement responses, we found that the translational VOR component decayed as the subjective tilt indication aligned with the tilt of the GIF. This was true for both the fixed radius and variable radius conditions even though the time course of the responses was significantly different for these two conditions. These findings are consistent with the hypothesis that the nervous system resolves the ambiguous measurements of GIF into neural estimates of gravity and linear acceleration. More generally, these findings are consistent with the hypothesis that the nervous system uses internal models to process and interpret sensory motor cues.

FALCON gravity gradiometer technology

Abstract: BHP Billiton's FALCON airborne gravity gradiometer is a derivative of the Gravity Gradient Instrument (GGI) developed by Bell Aerospace (now Lockheed Martin) between 1975 and 1990. The basis of the GGI design is an accelerometer complement consisting of four accelerometers equi-spaced on a circle with their sensitive axes tangential to the circle. This configuration rejects both common mode acceleration and rotations about the axis perpendicular to the plane of the complement. The complement remains intrinsically sensitive to rotation rates about axes in the plane of the complement and is sensitive to the acceleration environment to the extent that there is imbalance in the accelerometer sensitivities. Rotation of the complement about the perpendicular axis moves the gradient signal to twice the rotation frequency, away from the effects of low frequency accelerometer bias changes. The GGI is mounted in a high-performance inertial stabilised platform to reduce rotation of the instrument so that its sensitivity to this motion does not represent a significant noise source. The GGI accelerometers are designed for very low noise, requiring hard evacuation, high pendulosity, low spring constant and attention to the constrainment loop. Accelerometer pairs are aligned with precision and their sensitivities and frequency responses are matched. The scale factor (sensitivity) and alignment of the sensitive axis of each accelerometer are adjusted by compensation feedback loops to minimise accelerometer imbalance by monitoring the response of the system to specific stimuli. The requirements of survey operations were taken into account during development of the system and the result is an instrument which requires limited preparation, is largely automated during surveys, places few restrictions on flight planning and has been operated in harsh ambient conditions. Data processing is streamlined and data quality can be checked immediately after a flight.

Mental object rotation and the planning of hand movements

Abstract: Recently, we showed that the simultaneous execution of rotational hand movements interferes with mental object rotation, provided that the axes of rotation coincide in space We hypothesized that mental object rotation and the programming of rotational hand movements share a common process presumably involved in action planning Two experiments are reported here that show that the mere planning of a rotational hand movement is sufficient to cause interference with mental object rotation Subjects had to plan different spatially directed hand movements that they were asked to execute only after they had solved a mental object rotation task Experiment 1 showed that mental object rotation was slower if hand movements were planned in a direction opposite to the presumed mental rotation direction, but only if the axes of hand rotation and mental object rotation were parallel in space Experiment 2 showed that this interference occurred independent of the preparatory hand movements observed in Experiment 1 Thus, it is the planning of hand movements and not their preparation or execution that interferes with mental object rotation This finding underlines the idea that mental object rotation is an imagined (covert) action, rather than a pure visual-spatial imagery task, and that the interference between mental object rotation and rotational hand movements is an interference between goals of actions

Three-dimensional magneto-optic trap for micro-object manipulation.

Abstract: A magneto-optic trap for micro-objects is described. Magnetic beads were trapped by optical tweezers while being rotated by a new integrated magnetic manipulator. Rotation was achieved with eight electromagnets with tip-pole geometry. The time orbital potential technique was used to achieve rotation of magnetic beads. Trapping in three dimensions and rotation of magnetic beads on three axes are demonstrated with forces up to 230 pN and force momenta of up to 10-16 N m. A position-detection apparatus based on an interferometric scheme provides nanometer sensitivities in a few milliseconds.

A unified equation of state of dense matter and neutron star structure

Abstract: An equation of state (EOS) of neutron star matter, describing both the neutron star crust and the liquid core, is calculated. It is based on the effective nuclear interaction SLy of the Skyrme type, which is particularly suitable for the application to the calculation of the properties of very neutron rich matter (Chabanat et al. 1997, 1998). The structure of the crust, and its EOS, is calculated in the T=0 approximation, and under the assumption of the ground state composition. The crust-core transition is a very weakly first-order phase transition, with relative density jump of about one percent. The EOS of the liquid core is calculated assuming (minimal) n-p-e-mu composition. Parameters of static neutron stars are calculated and compared with existing observational data on neutron stars. The minimum and maximum masses of static neutron stars are 0.094 M_sun and 2.05 M_sun, respectively. Effects of rotation on the minimum and the maximum mass of neutron stars are briefly discussed.