Showing papers on "Rotation published in 2003"

Roll-pitch-roll surgical tool

Abstract: A robotic surgical tool includes an elongate shaft having a working end and a shaft axis, and a pair of linking arms each having a proximal end and a distal end. The proximal end is pivotally mounted on the working end of the shaft to rotate around a first pitch axis to produce rotation in first pitch. A wrist member has a proximal portion pivotally connected to the distal end of the linking arm to rotate around a second pitch axis to produce rotation in second pitch. An end effector is pivotally mounted on a distal portion of the wrist member to rotate around a wrist axis of the wrist member to produce rotation in distal roll. The wrist axis extends between the proximal portion and the distal portion of the wrist member. The elongate shaft is rotatable around the shaft axis to produce rotation in proximal roll. At about 90° pitch, the wrist axis is generally perpendicular to the shaft axis. The proximal roll around the shaft axis and the distal roll around the wrist axis do not overlap. The use of the linking arms allows the end effector to be bent back beyond 90° pitch. The ability to operate the end effector at about 90° pitch and to bend back the end effector renders the wrist mechanism more versatile and adaptable to accessing hard to reach locations, particularly with small entry points such as those involving spinal, neural, or rectal surgical sites.

The Internal Rotation of the Sun

Abstract: ▪ Abstract Helioseismology has transformed our knowledge of the Sun's rotation. Earlier studies revealed the Sun's surface rotation, but now a detailed observational picture has been built up of the internal rotation of our nearest star. Unlike the predictions of stellar-evolution models, the radiative interior is found to rotate roughly uniformly. The rotation within the convection zone is also very different from prior expectations, which had been that the rotation rate would depend primarily on the distance from the rotation axis. Layers of rotational shear have been discovered at the base of the convection zone and in the subphotospheric layers. Studies of the time variation of rotation have uncovered zonal-flow bands, extending through a substantial fraction of the convection zone, which migrate over the course of the solar cycle, and there are hints of other temporal variations and of a jet-like structure. At the same time, building on earlier work with mean-field models, researchers have made great...

Formation of omega Centauri from an ancient nucleated dwarf galaxy in the young Galactic disc

Abstract: We first present a self-consistent dynamical model in which $\omega$ Cen is formed from an ancient nucleated dwarf galaxy merging with the first generation of the Galactic thin disc in a retrograde manner with respect to the Galactic rotation. Our numerical simulations demonstrate that during merging between the Galaxy and the $\omega$ Cen's host dwarf with $M_{\rm B}$ $\simeq$ -14 mag and its nucleus mass of $10^7$ $M_{\odot}$, the outer stellar envelope of the dwarf is nearly completely stripped whereas the central nucleus can survive from the tidal stripping because of its compactness. The developed naked nucleus has a very bound retrograde orbit around the young Galactic disc, as observed for $\omega$ Cen, with its apocenter and pericenter distances of $\sim$ 8 kpc and $\sim$ 1 kpc, respectively. The Galactic tidal force can induce radial inflow of gas to the dwarf's center and consequently triggers moderately strong nuclear starbursts in a repetitive manner. This result implies that efficient nuclear chemical enrichment resulting from the later starbursts can be closely associated with the origin of the observed relatively young and metal-rich stars in $\omega$ Cen. Dynamical heating by the $\omega$ Cen's host can transform the young thin disc into the thick disc during merging.

Determining the Inclination of the Rotation Axis of a Sun-like Star

Abstract: Asteroseismology provides us with the possibility of determining the angle, i, between the direction of the rotation axis of a pulsating Sun-like star and the line of sight. A knowledge of i is important not just for obtaining improved stellar parameters, but also in order to determine the true masses of extrasolar planets detected from the radial velocity shifts of their central stars. By means of Monte Carlo simulations, we estimate the precision of the measurement of i and other stellar parameters. We find that the inclination angle can be retrieved accurately when ie30 � for stars that rotate at least twice as fast as the Sun. Subject headings: planetary systems — stars: fundamental parameters — stars: oscillations — stars: rotation

Be-star rotation: how close to critical?

Abstract: We argue that, in general, observational studies of Be-star rotation have paid insufficient attention to the effects of equatorial gravity darkening. We present new line-profile calculations that emphasize the insensitivity of line width to rotation for fast rotators. Coupled with a critical review of observational procedures, these calculations suggest that the observational parameter v sin(i) may systematically underestimate the true projected equatorial rotation velocity, ve sin(i), by some tens of per cent for rapid rotators. The crucial implication of this work is that Be stars may be rotating much closer to their critical velocities than is generally supposed, bringing a range of new processes into contention for the elusive physical mechanism responsible for the circumstellar disk thought to be central to the Be phenomenon.

Electronically controlled prosthetic system

Abstract: A prosthetic joint system for users comprising a housing having an interior cavity, a center axis in said interior cavity, and an attachment means for fixedly connecting said housing to said user; an inner cylinder disposed in said housing interior cavity wherein said inner cylinder rotates around said center axis of said housing; an appendage attached to said inner cylinder; a sensor system attached to said appendage; and a dampening system, having a power source, in communication with said sensor system, said inner cylinder, and said housing for controlling dampening of the rotation of said inner cylinder around said center axis of said housing.

Rotation and differential rotation in field F- and G-type stars

Abstract: We present a detailed study of rotation and differential rotation analyzing high resolution high spectra of 142 F-, G- and early K-type field stars. Using Least Squares Deconvolution we obtain broadening profiles for our sample stars and use the Fourier transform method to determine projected rotational velocities . Distributions of rotational velocities and periods are studied in the HR-diagram. For a subsample of 32 stars of spectral type F0–G0 we derive the amount of differential rotation in terms of . We find evidence for differential rotation in ten of the 32 stars. Differential rotation seems to be more common in slower rotators, but deviations from rigid rotation are also found in some fast rotators. We search for correlations between differential rotation and parameters relevant for stellar activity and show indications against strong differential rotation in very active stars. We derive values of and , which support a period dependence of differential rotation. Derived lap times are of the order of 20 d and contradict the assumption that constant lap times of the order of the solar one (∼ 130 d) are the rule in stars that are thought to harbour magnetic dynamos.

Optical application and measurement of torque on microparticles of isotropic nonabsorbing material

Abstract: We show how it is possible to controllably rotate or align microscopic particles of isotropic nonabsorbing material in a TEM00 Gaussian beam trap, with simultaneous measurement of the applied torque using purely optical means. This is a simple and general method of rotation, requiring only that the particle is elongated along one direction. Thus, this method can be used to rotate or align a wide range of naturally occurring particles. The ability to measure the applied torque enables the use of this method as a quantitative tool - the rotational equivalent of optical tweezers based force measurement. As well as being of particular value for the rotation of biological specimens, this method is also suitable for the development of optically-driven micromachines.

Carbon Nanotube Based Bearing for Rotational Motions

Abstract: We report the fabrication of a nanoelectromechanical system consisting of a plate rotating around a multiwalled nanotube bearing. The motion is possible thanks to the low intershell friction. Indeed, the nanotube has been engineered so that the sliding happens between different shells. The plate rotation is activated electrostatically with stator electrodes. The static friction force is estimated at $\approx 2\cdot10^{-15}$ N/\AA$^2$.

Mode selection in swirling jet experiments: a linear stability analysis

Abstract: The primary goal of the study is to identify the selection mechanism responsible for the appearance of a double-helix structure in the pre-breakdown stage of so-called screened swirling jets for which the circulation vanishes away from the jet. The family of basic flows under consideration combines the azimuthal velocity profiles of Carton & McWilliams (1989) and the axial velocity profiles of Monkewitz (1988). This model satisfactorily represents the nozzle exit velocity distributions measured in the swirling jet experiment of Billant et al. (1998). Temporal and absolute/convective instability properties are directly retrieved from numerical simulations of the linear impulse response for different swirl parameter settings. A large range of negative helical modes, winding with the basic flow, are destabilized as swirl is increased, and their characteristics for large azimuthal wavenumbers are shown to agree with the asymptotic analysis of Leibovich & Stewartson (1983). However, the temporal study fails to yield a clear selection principle. The absolute/convective instability regions are mapped out in the plane of the external axial flow and swirl parameters. The absolutely unstable domain is enhanced by rotation and it remains open for arbitrarily large swirl. The swirling jet with zero external axial flow is found to first become absolutely unstable to a mode of azimuthal wavenumber , winding with the jet. It is suggested that this selection mechanism accounts for the experimental observation of a double-helix structure.

Asymptotic expressions for the angular dependence of low‐frequency pulsation modes in rotating stars

Abstract: Through the solution of Laplace's tidal equations, approximated to describe equatorially trapped wave propagation, analytical expressions are obtained for the angular dependence of pulsation modes in uniformly rotating stars. As the ratio between rotation and pulsation frequencies becomes large, these expressions approach the exact solutions of the governing low-frequency pulsation equations. Four classes of asymptotic solution are found, corresponding to g (gravito-inertial), r (Rossby), Kelvin and Yanai modes. The Kelvin modes arise through the conservation of specific vorticity, much like the r modes, but propagate in the same sense as the rotation; they are found to be the equivalents of prograde sectoral modes. The prograde Yanai modes behave like g modes, as do the retrograde ones if the rotation is sufficiently rapid; otherwise, the latter exhibit the character of r modes. Comparison between asymptotic and numerical solutions to the tidal equations reveals that the former converge rapidly towards the latter, for g and Yanai modes. The convergence is slower for Kelvin and r modes, as these become equatorially trapped only when the rotation is very rapid. It is argued that the utility of the asymptotic solutions does not rest on their accuracy alone, but also on the valuable physical insights that they are capable of providing.

Vortex states of rapidly rotating dilute Bose-Einstein condensates

Abstract: We show that, in the Thomas-Fermi regime, the cores of vortices in rotating dilute Bose-Einstein condensates adjust in radius as the rotation velocity, Omega, grows, thus precluding a phase transition associated with core overlap at high vortex density. In both a harmonic trap and a rotating hard-walled bucket, the core size approaches a limiting fraction of the intervortex spacing. At large rotation speeds, a system confined in a bucket develops, within Thomas-Fermi, a hole along the rotation axis, and eventually makes a transition to a giant vortex state with all the vorticity contained in the hole.

A multiphase model with internal degrees of freedom: application to shock–bubble interaction

Abstract: The aim of this paper is the derivation of a multiphase model of compressible fluids. Each fluid has a different average translational velocity, density, pressure, internal energy as well as the energies related to rotation and vibration. The main difficulty is the description of these various translational, rotational and vibrational motions in the context of a one-dimensional model. The second difficulty is the determination of closure relations for such a system: the 'drag' force between inviscid fluids, pressure relaxation rate, vibration and rotation creation rates, etc. The rotation creation rate is particularly important for turbulent flows with shock waves. In order to derive the one-dimensional multiphase model, two different approaches are used. The first one is based on the Hamilton principle. We use the second approach, in which the pure fluid equations are discretized at the microscopic level and then averaged. In this context, the flow is considered to be the annular flow of two turbulent fluids. We also derive the continuous limit of this model which provides explicit formulae for the closure laws

Optically controlled three-dimensional rotation of microscopic objects

Abstract: We demonstrate that microscopic objects held in optical tweezers can be set into controlled rotation about any axis of choice. Our approach relies on the use of a spatial light modulator to create a pair of closely separated optical traps holding different parts of the same object. The pair of traps can be made to revolve around each other in any plane, rotating the trapped object with them. This technique overcomes the previous restriction on the orientation of the rotation axis to be parallel to the beam axis, and extends the versatility of optical tweezers as micromanipulation tools.

The Rotation of the Deep Solar Layers

Abstract: From the analysis of low-order GOLF+MDI sectoral modes (l ≤ 3, 6 ≤ n ≤ 15, |m| = l) and LOWL data (l > 3), we derive the radial rotation profile by assuming no latitudinal dependence in the solar core. These low-order acoustic modes contain the most statistically significant information about the rotation of the deepest solar layers and should be least influenced by internal variability associated with the solar dynamo. After the correction of the sectoral splittings for their contamination by the rotation of the higher latitudes, we obtain a flat rotation profile down to 0.2 R☉.

Antenna device and transmitting/receiving device

Abstract: Two circular waveguides (1,3) having a propagation mode of TM01 mode are coaxially arranged with a waveguide side choke (4) disposed therebetween. A rectangular waveguide (2) is connected to the fixed circular waveguide (1), while a primary radiator (5) is connected to the rotary circular waveguide (3). In this way, a high frequency signal supplied from the rectangular waveguide (2) to the fixed circular waveguide (1) can be radiated from the primary radiator (5). The circular waveguides (1,3) and waveguide side choke (4) can constitute a rotary joint, and a rotation of the primary radiator (5) together with the rotary circular waveguide (3) allows the high frequency signal radiated from the primary radiator (5) to be scanned.

Stellar rotation: Evidence for a large horizontal turbulence and its effects on evolution

Abstract: We derive a new expression for the coefficient Dh of diffusion by horizontal turbulence in rotating stars. This new estimate can be up to two orders of magnitude larger than that given by a previous expression. As a consequence the differential rotation on an equipotential is found to be very small, which reinforces Zahn's hypothesis of shellular rotation. The role of the so-called µ-currents, as well as the driving of circulation, are reduced by the large horizontal turbulence. Stellar evolutionary models for a 20 Mstar are calculated with the new coefficient. The new and large Dh tends to limit the size of the convective core and at the same time it largely favours the diffusion of helium and nitrogen to the surface of rotating OB stars, a feature supported by recent observations.

Rotation angle detector

Abstract: A rotation angle detector includes a rotor, first and second detecting elements which rotate according to a rotation of the rotor, first and second detecting units for detecting rotations of the first and second detecting elements, respectively, and a control unit for detecting a rotation angle of the rotor based on a first signal when a difference between the first and second signals output from the first and second detecting units ranges within a predetermined range. The rotation angle detector has a simple structure and detects the rotation angle of the rotor accurately

Simulations of core convection in rotating A-type stars: Differential rotation and overshooting

Abstract: We present the results of 3--D simulations of core convection within A-type stars of 2 solar masses, at a range of rotation rates. We consider the inner 30% by radius of such stars, thereby encompassing the convective core and some of the surrounding radiative envelope. We utilize our anelastic spherical harmonic (ASH) code, which solves the compressible Navier-Stokes equations in the anelastic approximation, to examine highly nonlinear flows that can span multiple scale heights. The cores of these stars are found to rotate differentially, with central cylindrical regions of strikingly slow rotation achieved in our simulations of stars whose convective Rossby number (R_{oc}) is less than unity. Such differential rotation results from the redistribution of angular momentum by the nonlinear convection that strongly senses the overall rotation of the star. Penetrative convective motions extend into the overlying radiative zone, yielding a prolate shape (aligned with the rotation axis) to the central region in which nearly adiabatic stratification is achieved. This is further surrounded by a region of overshooting motions, the extent of which is greater at the equator than at the poles, yielding an overall spherical shape to the domain experiencing at least some convective mixing. We assess the overshooting achieved as the stability of the radiative exterior is varied, and the weak circulations that result in that exterior. The convective plumes serve to excite gravity waves in the radiative envelope, ranging from localized ripples of many scales to some remarkable global resonances.

The Mean Electromotive Force for MHD Turbulence: The Case of a Weak Mean Magnetic Field and Slow Rotation

Abstract: The mean electromotive force that occurs in the framework of mean-field magnetohydrodynamics is studied for cases in which magnetic field fluctuations are not only due to the action of velocity fluctuations on the mean magnetic field. The possibility of magnetic field fluctuations independent of a mean magnetic field, as they may occur as a consequence of a small-scale dynamo, is taken into account. Particular attention is paid to the effect of a mean rotation of the fluid on the mean electromotive force, although only small rotation rates are considered. Anisotropies of the turbulence due to gradients of its intensity or its helicity are admitted. The mean magnetic field is considered to be weak enough to exclude quenching effects. A � -approximation is used in the equation describing the deviation of the cross-helicity tensor from that for zero mean magnetic field, which applies in the limit of large hydrodynamic Reynolds numbers. For the effects described by the mean electromotive force like � -effect, turbulent diffusion of magnetic fields etc in addition to the contributions determined by the velocity fluctuations also those determined by the magnetic field fluctuations independent of the mean magnetic field are derived. Several old results are confirmed, partially under more general assumptions, and quite a few new ones are given. Provided the kinematic helicity and the current helicity of the fluctuations have the same signs the � -effect is always diminished by the magnetic fluctuations. In the absence of rotation these have, however, no influence on the turbulent diffusion. Besides the diamagnetic effect due to a gradient of the intensity of the velocity fluctuations there is a paramagnetic effect due to a gradient of the intensity of the magnetic fluctuations. In the absence of rotation these two effects compensate each other in the case of equipartition of the kinetic and magnetic energies of the fluctuations of the original turbulence, i.e. that with zero mean magnetic field, but the rotation makes the situation more complex. The:TJ-effect works in the same way with velocity fluctuations and magnetic field fluctuations. A contribution to the electromotive force connected with the symmetric parts of the gradient tensor of the mean magnetic field, which does not occur in the absence of rotation, was found in the case of rotation, resulting from velocity or magnetic fluctuations. The implications of the results for the mean electromotive force for mean-field dynamo models are discussed with special emphasis to dynamos working without � -effect. The results for the coefficients defining the mean electromotive force which are determined by the velocity fluctuations in the case of vanishing mean motion agree formally with the results obtained in the kinematic approach, specified by second-order approximation and high-conductivity limit. However, their range of validity is clearly larger.

The Rotation of the Globular Cluster 47 Tucanae in the Plane of the Sky

Abstract: We have used the Hubble Space Telescope (HST) to measure the component of rotation of 47 Tuc in the plane of the sky, using background stars of the SMC as a reference. The rotation is comparable to that in the line of sight, showing that the axis of rotation of the cluster is considerably inclined. We also give an improved value of the absolute proper motion of 47 Tuc.

Rotational and orientational behaviour of three-dimensional spheroidal particles in Couette flows

Abstract: This paper reports the results of lattice Boltzmann simulations of the rotation behaviour of neutrally buoyant spheroidal particles in a three-dimensional Couette flow. We find several distinctive states depending on the Reynolds number range and particle shape. As the Reynolds number increases, rotation may change from one state to another. For a prolate spheroid, two rotation transitions are found. In the low Reynolds number range 0

Kinematics of the distal tibiofibular syndesmosis - Radiostereometry in 11 normal ankles

Abstract: In 11 healthy volunteers, the normal kinematics of the tibiofibular syndesmosis of the ankle during weight bearing and external rotation stress were compared to a nonweight-bearing neutral position by radiostereometry. We found very small rotations and displacements in this "normal" group, which indicated that the fibula is closely attached to the tibia, thereby preventing larger movements at the level of the ankle. We found no common kinematic pattern during weight bearing in the neutral position. Application of a 75 Nm external rotation moment on the foot caused external rotation of the fibula between 2 and 5 degrees, medial translation between 0 and 2.5 mm and posterior displacement between 1.0 and 3.1 mm. These data can be used as normal reference values for studies of patients with suspected syndesmotic injuries.

A semi‐analytical formula for the light variations due to low‐frequency g modes in rotating stars

Abstract: Through the adoption of the so-called ‘traditional approximation’, a new semi-analytical formula is derived for the light variations produced by low-frequency g modes in uniformly rotating stars The formula is used to examine the influence of rotation on the variability produced by a stellar model representative of the slowly pulsating B-type class It is found that, for all apart from prograde sectoral modes, the Coriolis force acts to trap pulsation within an equatorial waveguide Towards rapid rotation and/or low pulsation frequency, this waveguide becomes so narrow that only a thin band around the stellar equator makes any appreciable contribution toward flux changes As a result, unless viewed from near the poles, the variability exhibited by the star becomes very small, possibly explaining why recent photometric observations of rapidly rotating stars have failed to find much evidence for the presence of low-frequency modes It is further demonstrated that the ratio between the variability amplitude in pairs of passbands depends, with the introduction of rotation, both on the azimuthal order of a mode, and on the location of the observer in relation to the rotation axis of the star This means that the standard photometric techniques used to identify modes in non-rotating stars cannot easily be applied to systems where rotation is significant

Image pickup apparatus

Abstract: An electronic camera adopts an image pickup and optical system of a mirror scan type in which a mirror for scanning is disposed at a forward side of a taking lens. A line image sensor relatively scans an object while rotating the mirror to perform photographing. When controlling the exposure, the taking lens is moved synchronously along with rotation of the mirror to adjust the focal position thereof each time a slender sub-image of the object is picked up by the CCD. Driving the taking lens to focus the sub-image each time of scanning the sub-image enables picking up an entirety of the object image perfectly in a focused state.

Magnetic twist and writhe of active regions On the origin of deformed flux tubes

Abstract: We study the long term evolution of a set of 22 bipolar active regions (ARs) in which the main photospheric polarities are seen to rotate one around the other during several solar rotations. We first show that differential rotation is not at the origin of this large change in the tilt angle. A possible origin of this distortion is the nonlinear development of a kink-instability at the base of the convective zone; this would imply the formation of a non-planar flux tube which, while emerging across the photosphere, would show a rotation of its photospheric polarities as observed. A characteristic of the flux tubes deformed by this mechanism is that their magnetic twist and writhe should have the same sign. From the observed evolution of the tilt of the bipoles, we derive the sign of the writhe of the flux tube forming each AR; while we compute the sign of the twist from transverse field measurements. Comparing the handedness of the magnetic twist and writhe, we find that the presence of kink-unstable flux tubes is coherent with no more than 35% of the 20 cases for which the sign of the twist can be unambiguously determined. Since at most only a fraction of the tilt evolution can be explained by this process, we discuss the role that other mechanisms may play in the inferred deformation. We find that 36% of the 22 cases may result from the action of the Coriolis force as the flux tube travels through the convection zone. Furthermore, because several bipoles overpass in their rotation the mean toroidal (East-West) direction or rotate away from it, we propose that a possible explanation for the deformation of all these flux tubes may lie in the interaction with large-scale vortical motions of the plasma in the convection zone, including also photospheric or shallow sub-photospheric large scale flows.

Direct measurement of the size and shape of the present-day stellar wind of $\eta$ Carinae

Abstract: We present new high angular resolution observations at near-IR wavelengths of the core of the Luminous Blue Variable Carinae, using NAOS-CONICA at the VLT and VINCI at the VLT Interferometer (VLTI). The latter observations provide spatial information on a scale of 5 milli-arcsec or 11 AU at the distance of Carinae. The present-day stellar wind of Carinae is resolved on a scale of several stellar radii. Assuming spherical symmetry, we find a mass loss rate of 1:610 3 M/yr and a wind clumping factor of 0.26. The VLTI data taken at a baseline of 24 m show that the object is elongated with a de- projected axis ratio of approximately 1.5; the major axis is aligned with that of the large bi-polar nebula that was ejected in the 19th century. The most likely explanation for this observation is a counter-intuitive model in which stellar rotation near the critical velocity causes enhanced mass loss along the rotation axis. This results from the large temperature dierence between pole and equator in rapidly rotating stars. Carinae must rotate in excess of 90 percent of its critical velocity to account for the observed shape. The large outburst may have been shaped in a similar way. Our observations provide strong support for the existence of a theoretically predicted rotational instability, known as the limit.

Handedness and azimuthal energy flow of optical vortex beams

Abstract: The propagation of optical vortex beams obstructed by a knife edge is investigated. The intensity profile shows a characteristic rotation around the beam axis which can be used to determine the absolute handedness of the vortex. Evolution of the intensity profile directly visualizes the rotation of the beam's local Poynting vector.