Articoli di riviste: "Rotating"

1

Erasmus, N., D. Kramer, A. McNeill, D. E. Trilling, P. Janse van Rensburg, G. T. van Belle, J. L. Tonry, L. Denneau, A. Heinze e H. J. Weiland. "Discovery of superslow rotating asteroids with ATLAS and ZTF photometry". Monthly Notices of the Royal Astronomical Society 506, n. 3 (10 luglio 2021): 3872–81. http://dx.doi.org/10.1093/mnras/stab1888.

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ABSTRACT We present here the discovery of a new class of superslow rotating asteroids (Prot ≳1000 h) in data extracted from the Asteroid Terrestrial-impact Last Alert System (ATLAS) and Zwicky Transient Facility (ZTF) all-sky surveys. Of the 39 rotation periods we report here, 32 have periods longer than any previously reported unambiguous rotation periods currently in the Asteroid Light Curve Data base. In our sample, seven objects have a rotation period >4000 h and the longest period we report here is 4812 h (∼200 d). We do not observe any correlation between taxonomy, albedo, or orbital properties with superslow rotating status. The most plausible mechanism for the creation of these very slow rotators is if their rotations were slowed by YORP spin-down. Superslow rotating asteroids may be common, with at least 0.4 per cent of the main-belt asteroid population with a size range between 2 and 20 km in diameter rotating with periods longer than 1000 h.

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LOPEZ, J. M. "Characteristics of endwall and sidewall boundary layers in a rotating cylinder with a differentially rotating endwall". Journal of Fluid Mechanics 359 (25 marzo 1998): 49–79. http://dx.doi.org/10.1017/s002211209700829x.

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The flow in a rotating cylinder driven by the differential rotation of its top endwall is studied by numerically solving the time-dependent axisymmetric Navier–Stokes equations. When the differential rotation is small, the flow is well described in terms of similarity solutions of individual rotating disks of infinite radius. For larger differential rotations, whether the top is co-rotating or counter-rotating results in qualitatively distinct behaviour. For counter-rotation, the boundary layer on the top endwall separates, forming a free shear layer and this results in a global coupling between the boundary layer flows on the various walls and a global departure from the similarity flows. At large Reynolds numbers, this shear layer becomes unstable. For a co-rotating top, there is a qualitative change in the flow depending on whether the top rotates faster or slower than the rest of the cylinder. When the top rotates faster, so does the bulk of the interior fluid, and the sidewall boundary layer region where the fluid adjusts to the slower rotation rate of the cylinder is centrifugally unstable. The secondary induced meridional flow is also potentially unstable in this region. This is manifested by the inflectional radial profiles of the vertical velocity and azimuthal vorticity in this region. At large Reynolds numbers, the instability of the sidewall layer results in roll waves propagating downwards.

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Kazachkov, Ivan. "Modeling of the Flow due to Double Rotations Causing Phenomenon of Negative Pressure". WSEAS TRANSACTIONS ON FLUID MECHANICS 18 (31 dicembre 2023): 259–71. http://dx.doi.org/10.37394/232013.2023.18.25.

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This paper is devoted to mathematical modeling and computational experiments of a flow with negative pressure. A previously unknown class of fluid flow under the action of counter-current centrifugal forces is in focus. Volumetric forces in a non-conducting fluid can arise from gravity, vibrations, or rotations. In this paper, we consider controlled variable volumetric forces in a system with two rotations around the vertical axis and the tangential axis of a horizontal disk rotating around the vertical axis. The study of the coordinate system during double rotation showed that the double rotation about two perpendicular axes, one of which moves along a tangential direction to the rotating horizontal disk, is equal to the rotation around the oscillating axis inclined at some angle to the vertical axis.

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Fischer, Patrick, Charles-Henri Bruneau e Hamid Kellay. "Numerical Study of Rotating Thermal Convection on a Hemisphere". Fluids 5, n. 4 (20 ottobre 2020): 185. http://dx.doi.org/10.3390/fluids5040185.

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Numerical simulations of rotating two-dimensional turbulent thermal convection on a hemisphere are presented in this paper. Previous experiments on a half soap bubble located on a heated plate have been used for studying thermal convection as well as the effects of rotation on a curved surface. Here, two different methods have been used to produce the rotation of the hemisphere: the classical rotation term added to the velocity equation, and a non-zero azimuthal velocity boundary condition. This latter method is more adapted to the soap bubble experiments. These two methods of forcing the rotation of the hemisphere induce different fluid dynamics. While the first method is classically used for describing rotating Rayleigh–Bénard convection experiments, the second method seems to be more adapted for describing rotating flows where a shear layer may be dominant. This is particularly the case where the fluid is not contained in a closed container and the rotation is imposed on only one side of it. Four different diagnostics have been used to compare the two methods: the Nusselt number, the effective computation of the convective heat flux, the velocity and temperature fluctuations root mean square (RMS) generation of vertically aligned vortex tubes (to evaluate the boundary layers) and the energy/enstrophy/temperature spectra/fluxes. We observe that the dynamics of the convective heat flux is strongly inhibited by high rotations for the two different forcing methods. Also, and contrary to classical three-dimensional rotating Rayleigh–Bénard convection experiments, almost no significant improvement of the convective heat flux has been observed when adding a rotation term in the velocity equation. However, moderate rotations induced by non-zero velocity boundary conditions induce a significant enhancement of the convective heat flux. This enhancement is closely related to the presence of a shear layer and to the thermal boundary layer just above the equator.

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Shaymatov, Sanjar, Bobomurat Ahmedov e Eldor Karimbaev. "Can a Rotating Black Hole Be Overspun in Seven Dimensions?" Universe 9, n. 4 (17 aprile 2023): 190. http://dx.doi.org/10.3390/universe9040190.

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Five-dimensional rotating black holes with two rotations could be overspun except for a single rotation, whereas a black hole in six dimensions always obeys the weak cosmic censorship conjecture (WCCC) in the weak form even for linear particle accretion. In this paper, we investigate the overspinning of a seven-dimensional rotating black hole with three rotation parameters. It is shown that a black hole in the seven dimensions cannot be similarly overspun, thereby obeying the WCCC even under linear particle accretion. It turns out that a black hole always respects the weak cosmic censorship conjecture in seven dimensions.

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Boshkayev, K. "Non-rotating and slowly rotating stars in classical physics". International Journal of Mathematics and Physics 5, n. 1 (2014): 69–80. http://dx.doi.org/10.26577/2218-7987-2014-5-1-69-80.

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Li, Jingyuan, e Zifeng Li. "Applications of the Theory of Continuous Oil Film Lubrication of a Radial Sliding Bearing for Three Combined Conditions". Applied Physics Research 8, n. 2 (15 febbraio 2016): 22. http://dx.doi.org/10.5539/apr.v8n2p22.

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<p class="1Body">The theory of lubrication of a radial sliding bearing is extended to three cases: the shaft neck rotation and bush rotation bearing, the rotating load bearing, and the floating sleeve bearing. For the bearing with rotating shaft neck and rotating bush, fixing the observer at the bushing can enable the determination, in a simple and more accurate manner, of the bearing capacity of the bearing with the rotating load. As long as a rotating load exists, whirl exists; if the shaft rotation speed is 2 times the load rotation speed, then the eccentricity reaches the maximum.</p>

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8

Lim, C. C. "The Super- and Sub-Rotation of Barotropic Atmospheres on a Rotating Planet". Nelineinaya Dinamika 18, n. 1 (2022): 19–42. http://dx.doi.org/10.20537/nd220102.

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A statistical mechanics canonical spherical energy-enstrophy theory of the superrotation phenomenon in a quasi-2D barotropic fluid coupled by inviscid topographic torque to a rotating solid body is solved in closed form in Fourier space, with inputs on the value of the energy to enstrophy quotient of the fluid, and two planetary parameters — the radius of the planet and its rate and the axis of spin. This allows calculations that predict the following physical consequences: (A) two critical points associated with the condensation of high and low energy (resp.) states in the form of distinct superrotating and subrotating (resp.) solid-body flows, (B) only solid-body flows having wavenumbers $l=1$, $m=0$ — tiltless rotations — are excited in the ordered phases, (C) the asymmetry between the superrotating and subrotating ordered phases where the subrotation phase transition also requires that the planetary spin is sufficiently large, and thus, less commonly observed than the superrotating phase, (D) nonexcitation of spherical modes with wavenumber $l>1$ in barotropic fluids. Comparisons with other canonical, microcanonical and dynamical theories suggest that this theory complements and completes older theories by predicting the above specific outcomes.

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9

Jose, Sharath, e Rama Govindarajan. "Non-normal origin of modal instabilities in rotating plane shear flows". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 476, n. 2233 (gennaio 2020): 20190550. http://dx.doi.org/10.1098/rspa.2019.0550.

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Small variations introduced in shear flows are known to affect stability dramatically. Rotation of the flow system is one example, where the critical Reynolds number for exponential instabilities falls steeply with a small increase in rotation rate. We ask whether there is a fundamental reason for this sensitivity to rotation. We answer in the affirmative, showing that it is the non-normality of the stability operator in the absence of rotation which triggers this sensitivity. We treat the flow in the presence of rotation as a perturbation on the non-rotating case, and show that the rotating case is a special element of the pseudospectrum of the non-rotating case. Thus, while the non-rotating flow is always modally stable to streamwise-independent perturbations, rotating flows with the smallest rotation are unstable at zero streamwise wavenumber, with the spanwise wavenumbers close to that of disturbances with the highest transient growth in the non-rotating case. The instability critical rotation number scales inversely as the square of the Reynolds number, which we demonstrate is the same as the scaling obeyed by the minimum perturbation amplitude in non-rotating shear flow needed for the pseudospectrum to cross the neutral line. Plane Poiseuille flow and plane Couette flow are shown to behave similarly in this context.

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10

Collier Cameron, A. "Differential rotation on rapidly rotating stars". Astronomische Nachrichten 328, n. 10 (dicembre 2007): 1030–33. http://dx.doi.org/10.1002/asna.200710880.

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Boshkayev, K., J. A. Rueda, R. Ruffini, B. Zhami, Zh Kalymova e G. Balgimbekov. "Non-rotating and slowly rotating white dwarfs in classical physics". Physical Sciences and Technology 2, n. 1 (2015): 66–71. http://dx.doi.org/10.26577/2409-6121-2015-2-1-66-71.

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12

Soong, C. Y. "Thermal Buoyancy Effects in Rotating Non-Isothermal Flows". International Journal of Rotating Machinery 7, n. 6 (2001): 435–46. http://dx.doi.org/10.1155/s1023621x01000380.

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The present paper is concerned with the non-isothermal flow mechanisms in rotating systems with emphasis on the rotation-induced thermal buoyancy effects stemming from the coexistence of rotational body forces and the nonuniformity of the fluid temperature field. Non-isothermal flow in rotating ducts of radial and parallel modes and rotating cylindrical configurations, including rotating cylinders and disk systems, are considered. Previous investigations closely related to the rotational buoyancy are surveyed. The mechanisms of the rotation-induced buoyancy are manifested by the author's recent theoretical results and scaling analyses pertaining to the rotation-induced buoyancy in rotating ducts and two-disk systems. Finally, the open issues for future researches in this area are proposed.

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13

Bormashenko, Edward. "Rotating Minimal Thermodynamic Systems". Entropy 24, n. 2 (23 gennaio 2022): 168. http://dx.doi.org/10.3390/e24020168.

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Minimal rotating thermodynamic systems are addressed. Particle m placed into the rotating symmetrical double-well potential (bowl), providing binary logical system is considered. The condition providing the transfer of the particle from one frictionless half-well to another, and, in this way, the possibility to record 1 bit of information is derived. The procedure of recording turns out to be irreversible; it is impossible to return the particle to its initial state under rotation about the same axis. The same rotating double-well system exerted to the thermal noise is considered. A minimal rotating thermal engine built of the rotating chamber, movable partition, and the particle confined within the chamber is treated. Rotation of the system displaces the partition, thus enabling erasing of one bit information. Erasing of 1 bit of information is due to the inertia (centrifugal force) acting on the partition. Isothermal expansion of the “minimal gas” expectedly gives rise to the Landauer bound. Compression of the “gas” with the rotation around the same axis is impossible and demands the additional axis of rotation. The interrelation between the possibility of recording/erasing information and the symmetry of the system is considered.

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Zhang, Zi Cheng, Kenichi Manabe, Tsuyoshi Furushima e Kazuo Tada. "Development of Cyclic Rotating Bending Process for Microstructure Control of AZ31 Magnesium Alloy Tube". Advanced Materials Research 652-654 (gennaio 2013): 1956–60. http://dx.doi.org/10.4028/www.scientific.net/amr.652-654.1956.

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In this study a cyclic rotating bending process for microstructure control of metal tubes was newly proposed. The AZ31 magnesium alloy tube was conducted to investigate the effect of the rotating bending process on the microstructure and mechanical properties of metal tubes. The rotating bending process was carried out with rotation speed of 20r/min for 10min at the temperature of 150, 200, 250, 300 and 350°C. The rotating bending processes carried out with various conditions show that the grains in cross-section and longitudinal section of magnesium alloy tube were refined for all samples by the rotating bending process with rotation speed of 20r/min for different rotation numbers and temperatures. The rotating bending temperature shows a various effects on the mechanical properties. When the temperature was 200°C, the highest strength as well as ductility was obtained.

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Ekene, Ilechukwu Anthonia, Omenyi Sam, Abonyi Sylvester Emeka, Okafor Anthony Amaechi e Odeh Calistus Princewill. "Theoretical and Simulation Finite Element Modal Analysis of Rotating Cantilever Beam". International Journal of Research and Innovation in Applied Science IX, n. II (2024): 291–306. http://dx.doi.org/10.51584/ijrias.2024.90225.

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The finite element method is used to carry out modal analysis of rotating cantilever beam. The virtual work method is then used to derive the stiffness matrix of a rotating beam element. The stiffness matrix of a rotating beam element is simply seen to be sum of the stiffness matrix of the non-rotating beam and an incremental stiffness matrix induced by rotation. This work presents a novel generalized incremental stiffness matrix that takes care of any element at any distance from the rotation axis. The established rotational stiffness matrix is then used together with consistent mass matrix (not affected by rotation) to carry out modal analysis of rotating cantilever beam. Theoretical computations were validated by simulations from ANSYS. It is seen that the contribution to modal frequencies and shapes of the blade of rotation via incremental stiffness matrix is very marginal at low rotational speeds. For exampleit is seen for a numerical case study that five-element model computes slight increase in fundamental natural frequency due to rotation relative to that of the non-rotating blade as 0.000195% for rotational speed of 300rpm. It is also seen that ten times increase in speed leads to about hundred times increase in rotational contribution meaning that it becomes more imperative to model rotation as speed of the blade increases. Points are also made regarding application to avoiding resonance of rotating cantilever beam.

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Gulyaev, V. I., A. A. Kirichuk, P. P. Lizunov e A. V. Mirchevskii. "Vibrations of a rotating membrane with unsteady rotations of the axis of rotation". Strength of Materials 22, n. 2 (febbraio 1990): 223–29. http://dx.doi.org/10.1007/bf00773242.

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Kolsi, Lioua, Fatih Selimefendigil, Samia Larguech, Kaouther Ghachem, Hind Albalawi, Badr M. Alshammari e Taher Labidi. "Convective Heat Transfer and Entropy Generation for Nano-Jet Impingement Cooling of a Moving Hot Surface under the Effects of Multiple Rotating Cylinders and Magnetic Field". Mathematics 11, n. 8 (17 aprile 2023): 1891. http://dx.doi.org/10.3390/math11081891.

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In this study, confined slot nano-jet impingement cooling of a hot moving surface is investigated under the combined utilization multiple rotating cylinders and magnetic field. Both convective heat transfer and entropy generation analysis are conducted using a finite element method. Parametric variation of the rotational Reynolds number (Rew between −500 and 500), velocity ratio (VR between 0 and 0.25), Hartmann number (Ha between 0 and 20) and the horizontal location of cylinders (Mx between −8 and 8) are considered. Rotation of the cylinders generally resulted in the degradation of cooling performance while increasing the wall velocity, and the horizontal location of the cylinder was found to positively contribute to this. Heat transfer rate reductions of 20% and 12.5% are obtained using rotations at the highest Rew for the case of stationary (VR = 0) and moving wall (VR = 0.25). When magnetic field at the highest strength is imposed in the rotating cylinder case, the cooling performance is increased by about 18.6%, while it is reduced by about 28% for the non-rotating cylinder case. The hot wall movement contributes, by about 14%, to the overall cooling performance enhancement. Away from the inlet location of the rotating cylinders, thermal performance improvement of 12% is obtained. The entropy generation rises with higher hot wall velocity and higher horizontal distances of the rotating cylinders, while it is reduced with a higher magnetic field for non-rotating cylinders. The best configurations in terms of cooling performance provide 8.7% and 34.2% enhancements for non-rotating and rotating cylinders compared with the reference case of (Rew, VR, Ha, Mx) = (0, 0, 0, 0), while entropy generation becomes 1% and 15% higher.

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Jaekl, P., M. Jenkin e L. R. Harris. "Perceptual stability during active head movements orthogonal and parallel to gravity". Journal of Vestibular Research 13, n. 4-6 (28 dicembre 2003): 265–71. http://dx.doi.org/10.3233/ves-2003-134-611.

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We measured how much the visual world could be moved during various head rotations and translations and still be perceived as visually stable. Using this as a monitor of how well subjects know about their own movement, we compared performance in different directions relative to gravity. For head rotations, we compared the range of visual motion judged compatible with a stable environment while rotating around an axis orthogonal to gravity (where rotation created a rotating gravity vector across the otolith macula), with judgements made when rotation was around an earth-vertical axis. For translations, we compared the corresponding range of visual motion when translation was parallel to gravity (when imposed accelerations added to or subtracted from gravity), with translations orthogonal to gravity. Ten subjects wore a head-mounted display and made active head movements at 0.5 Hz that were monitored by a low-latency mechanical tracker. Subjects adjusted the ratio between head and image motion until the display appeared perceptually stable. For neither rotation nor translation were there any differences in judgements of perceptual stability that depended on the direction of the movement with respect to the direction of gravity.

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Geng, Xinge, Weiguo Wu, Erpeng Liu, Yongshui Lin, Wei Chen e Chang-Kyu Rheem. "Experimental Study on Vibration of a Rotating Pipe in Still Water and in Flow". Polish Maritime Research 30, n. 1 (1 marzo 2023): 65–77. http://dx.doi.org/10.2478/pomr-2023-0007.

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Abstract To illustrate the vibration characteristics of a rotating pipe in flow, experiments were conducted for a pipe in flow, a rotating pipe in still water and a rotating pipe in flow. For the pipe in flow without rotation, the trajectory diagram is ‘8’ shaped. For the rotating pipe in still water, a multiple frequency component was induced, and a ‘positive direction whirl’ was found. For the flow and rotation, at a flow velocity of 0.46 m/s, the vibration is dominated by the combination of flow and rotation. With an increase in rotating frequency, the trajectory of the rotating pipe varies from an ‘8’ shape to a circular shape and the ‘reverse direction whirl’ is induced, which is different from ‘positive direction’ in still water. The vibration frequency ratio increases uniformly with flow velocity. At a flow velocity of 1.02 m/s, at which the frequency is close to the theoretical natural frequency, the vibration frequency ratio is f*≈1. Predominantly governed by vortex-induced vibration (VIV), the vibration behavior of a rotating pipe subjected to fluid flow conditions has been found to exhibit complete vanishing of whirl. The vibration characteristics of a rotating pipe in flow are studied by the experiments which is benefit for structural drilling design.

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Hirschi, Raphael, Georges Meynet, André Maeder e Stéphane Goriely. "Pre-Supernova Evolution of Rotating Massive Stars". International Astronomical Union Colloquium 192 (2005): 209–13. http://dx.doi.org/10.1017/s0252921100009209.

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SummaryThe Geneva evolutionary code has been modified to study the advanced stages (Ne, O, Si burnings) of rotating massive stars. Here we present the results of four 20 M⊙ stars at solar metallicity with initial rotational velocities, vini, of 0, 100, 200 and 300 km/s in order to show the crucial role of rotation in stellar evolution. As already known, rotation increases mass loss and core masses [4]. A fast rotating 20 M⊙ star has the same central evolution as a non-rotating 26 M⊙. Rotation also increases strongly net total metal yields. Furthermore, rotation changes the SN type so that more SNIb are predicted (see [5] and [6]). Finally, SN1987A-like supernovae progenitor colors can be explained in a single rotating star scenario.

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Ren, Baoming, Jiadong Zhang, Zhida Yang, Guanghui Zhu, Haiyang Zhou, Jian Zheng e Xuan Sun. "Plasma rotation driven by rotating magnetic fields". Plasma Physics and Controlled Fusion 63, n. 3 (3 febbraio 2021): 035027. http://dx.doi.org/10.1088/1361-6587/abdcdd.

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Reiners, A., e J. H. M. M. Schmitt. "Differential rotation in rapidly rotating F-stars". Astronomy & Astrophysics 412, n. 3 (dicembre 2003): 813–19. http://dx.doi.org/10.1051/0004-6361:20034255.

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Fetterman, Abraham J., e Nathaniel J. Fisch. "Wave-Driven Rotation in Supersonically Rotating Mirrors". Fusion Science and Technology 57, n. 4 (maggio 2010): 343–50. http://dx.doi.org/10.13182/fst10-a9496.

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Welsh, Stephen S., e Johannes Courtial. "View rotation with parallel ray-rotating windows". Optics Communications 285, n. 24 (novembre 2012): 4802–6. http://dx.doi.org/10.1016/j.optcom.2012.07.060.

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Chan, Kwing L., e Hans G. Mayr. "Rotating convection and the solar differential rotation". Solar Physics 152, n. 1 (giugno 1994): 283–90. http://dx.doi.org/10.1007/bf01473216.

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Chan, K. L. "Rotating convection in f-boxes: Faster rotation". Astronomische Nachrichten 328, n. 10 (dicembre 2007): 1059–61. http://dx.doi.org/10.1002/asna.200710837.

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Yang, Wen-Jei, Shin Fann e John H. Kim. "Heat and Fluid Flow Inside Rotating Channels". Applied Mechanics Reviews 47, n. 8 (1 agosto 1994): 367–96. http://dx.doi.org/10.1115/1.3111084.

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Power generation and refrigeration accomplished by means of rotating or reciprocating machinery. One of the basic elements of rotating machinery is the rotating channel system. With the desire for ever increasing efficiency in power generation and refrigeration, higher or lower operating temperatures are achieved. It has provided motivation for the pursuit of knowledge on heat transfer and fluid flow characteristics. This paper reviews the literature pertinent to studies of fluid flow and/or heat transfer in channel flows subjected to radial rotation, parallel rotation, and coaxial revolution. Special problems unique to rotating systems are discussed and future study areas are suggested.

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Gürer, Derya, Douwe J. J. van Hinsbergen, Murat Özkaptan, Iverna Creton, Mathijs R. Koymans, Antonio Cascella e Cornelis G. Langereis. "Paleomagnetic constraints on the timing and distribution of Cenozoic rotations in Central and Eastern Anatolia". Solid Earth 9, n. 2 (21 marzo 2018): 295–322. http://dx.doi.org/10.5194/se-9-295-2018.

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Abstract. To quantitatively reconstruct the kinematic evolution of Central and Eastern Anatolia within the framework of Neotethyan subduction accommodating Africa–Eurasia convergence, we paleomagnetically assess the timing and amount of vertical axis rotations across the Ulukışla and Sivas regions. We show paleomagnetic results from ∼ 30 localities identifying a coherent rotation of a SE Anatolian rotating block comprised of the southern Kırşehir Block, the Ulukışla Basin, the Central and Eastern Taurides, and the southern part of the Sivas Basin. Using our new and published results, we compute an apparent polar wander path (APWP) for this block since the Late Cretaceous, showing that it experienced a ∼ 30–35° counterclockwise vertical axis rotation since the Oligocene time relative to Eurasia. Sediments in the northern Sivas region show clockwise rotations. We use the rotation patterns together with known fault zones to argue that the counterclockwise-rotating domain of south-central Anatolia was bounded by the Savcılı Thrust Zone and Deliler–Tecer Fault Zone in the north and by the African–Arabian trench in the south, the western boundary of which is poorly constrained and requires future study. Our new paleomagnetic constraints provide a key ingredient for future kinematic restorations of the Anatolian tectonic collage.

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Myung, Yun Soo, e De-Cheng Zou. "Scalarization of slowly rotating black holes". International Journal of Modern Physics D 30, n. 11 (9 luglio 2021): 2150082. http://dx.doi.org/10.1142/s0218271821500826.

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It is interesting to note that most black holes are born very slowly rotating. We investigate scalarization of slowly rotating black holes in the Einstein-scalar-Chern–Simons (EsCS) theory. In the slow rotation approximation, the CS term takes a linear form of rotation parameter [Formula: see text] which determines the tachyonic instability. The tachyonic instability for slowly rotating black holes represents the onset of spontaneous scalarization. It is shown that the slowly rotating black holes are unstable against a spherically symmetric scalar-mode perturbation for positive coupling [Formula: see text], whereas these black holes are unstable for negative coupling without any [Formula: see text]-bound.

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Kim, J. "Rotation Effects on Vibration of Structures Seen From a Rotating Beam Simply Supported off the Rotation Axis". Journal of Vibration and Acoustics 128, n. 3 (30 novembre 2005): 328–37. http://dx.doi.org/10.1115/1.2172261.

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In rotating beams, the Coriolis force acts through the mass and rotary inertias of the beam. A rotating beam simply supported off the axis of rotation is used as an example to study effects of this Coriolis force on vibration of structures. By adopting such a simple model, mass- and rotary inertia-induced terms in the free vibration responses can be obtained in separate, closed forms. The effect of each of these terms on vibration characteristics of the rotating beam is discussed in relation to parameters such as nonrotating natural frequencies, the rotation speed, and the slenderness ratio. Practical implications of these results in analyses of rotating structures of other types are discussed, for example estimating the significance of rotary inertias in relation to the slenderness ratio and the rotation speed.

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Mitra, Shiladitya. "The curious case of the spinning neuronal mass". F1000Research 4 (27 gennaio 2015): 27. http://dx.doi.org/10.12688/f1000research.6044.1.

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Rotating cells have been reported in past. Rotation of cells and cell clusters has been associated with migration and development. This observation reports for the first time a rotating cluster of cells isolated from the hippocampi of neonatal mouse pups. The speed of rotation in these clusters is immensely high. Further analysis of such rotating neurons can shed valuable clues on the origin of such cells, their electro-mechanical properties and their role in the development of the brain.

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Gondek-Rosińska, D., P. Haensel, J. L. Zdunik e E. Gourgoulhon. "Rapidly rotating strange stars". International Astronomical Union Colloquium 177 (2000): 661–62. http://dx.doi.org/10.1017/s0252921100060930.

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AbstractWe study effects of the strange quark mass,ms, and of the QCD interactions, calculated to lowest order inαc, on the rapid rotation of strange stars (SS). The influence of rotation on global parameters of SS is greater than in the case of the neutron stars (NS). We show that independently ofmsandαcthe ratio of the rotational kinetic energy to the absolute value of the gravitational potential energyT/Wfor a rotating SS is significantly higher than for an ordinary NS. This might indicate that rapidly rotating SS could be important sources of gravitational waves.

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33

Jain, Kiran, Rudolf Komm, Irene González Hernández, Sushant C. Tripathy e Frank Hill. "Subsurface flows associated with rotating sunspots". Proceedings of the International Astronomical Union 6, S273 (agosto 2010): 356–60. http://dx.doi.org/10.1017/s1743921311015547.

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AbstractIn this paper, we compare components of the horizontal flow below the solar surface in and around regions consisting of rotating and non-rotating sunspots. Our analysis suggests that there is a significant variation in both components of the horizontal flow at the beginning of sunspot rotation as compared to the non-rotating sunspot. The flows in surrounding areas are in most cases relatively small. However, there is a significant influence of the motion on flows in an area closest to the sunspot rotation.

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34

Wang, Fengbin, Yuhua Li, Guangqin Shi, Guozhu Li, Xupeng Li e Wei Wang. "Design and implementation of high-rigidity and high-precision satellite antenna rotating unit". Journal of Physics: Conference Series 2760, n. 1 (1 maggio 2024): 012015. http://dx.doi.org/10.1088/1742-6596/2760/1/012015.

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Abstract The satellite antenna rotating unit is an important component that drives the satellite antenna to rotate in orbit, mainly composed of a stepper motor, harmonic reducer, and rotating transformer. This type of rotating unit has the advantages of small size, lightweight, high-rated output torque, and long rotating life. The high-stiffness and high-precision satellite antenna rotation unit is based on the existing antenna rotation unit. Through comprehensive improvement design, the measured closed-loop control has a rotation accuracy of better than 0.005°, a torsional stiffness of better than 6.5 Nm/(Å), a rotation accuracy of 6 times higher than the existing antenna rotation unit, a torsional stiffness increase of 13 times, and a rated output torque increase of 2.4 times. The article introduces the development of components, measurement of torsional stiffness, and measurement of rotational accuracy for the high-stiffness and high-precision satellite antenna rotating unit. Finally, the development conclusion is given. The successful development of a high-stiffness and high-precision satellite-borne antenna rotation unit can not only meet the precise pointing control requirements of the mechanical movable antennas and terahertz antennas of the narrow beam with a width of 0.2° but also solve practical problems such as jitter in ground testing of data transmission or relay antennas and unstable pointing of point beam antennas in orbit.

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35

Torii, Shuichi, e Wen-Jei Yang. "Secondary Flow Phenomena in an Axially Rotating Flow Passage with Sudden Expansion or Contraction". International Journal of Rotating Machinery 5, n. 2 (1999): 117–22. http://dx.doi.org/10.1155/s1023621x9900010x.

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This paper investigates rotational effects on secondary flow in rotating flow passages with sudden expansion or contraction. Consideration is given to laminar flow. The governing boundary-layer equations are discretized by means of a finite-difference technique and numerically solved to determine the distributions of velocity vector under the appropriate boundary conditions. The Reynolds number (Re) and rotation rate are varied to determine their effects on the formation ofsecondary flows. It is disclosed from the study that: (i) when laminar flow is introduced into an axially rotating pipe with expansion, the stretch ofthe secondary flow zone is amplified with an increase in the rotation rate and Re, and (ii) in contrast, for axially rotating pipe flows with contraction, the secondary flow region is somewhat suppressed due to pipe rotation, and the change is slightly affected by the rotation rate and Re. Results may find applications in automotive and rotating hydraulic transmission lines.

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36

Sofia, S., J. M. Howard e P. Demarque. "The Evolution of Rotating 15 M⊙ Stars". Symposium - International Astronomical Union 162 (1994): 131–44. http://dx.doi.org/10.1017/s007418090021471x.

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Theoretical evolutionary sequences have been generated with the YREC code for a 15 M⊙ star from the ZAMS to core helium exhaustion with a variety of physical assumptions, covering both rotating and non-rotating cases. The non-rotating models agree qualitatively with other models found in the literature. The addition of only rotational distortion has little effect on the models, while the full treatment of rotation results in additional mixing and theoretical tracks that are similar to models with small amounts of convective overshoot. Models which include only rotation have fair agreement with the observed main sequence surface rotation velocities, but rotate too rapidly during the post-main sequence phases. The addition of mass loss at the given rates helps this problem somewhat but does not appear to completely resolve it. Neither the non-rotating models nor the rotating models provide full agreement with the terminal-age main sequence band used by Maeder & Meynet (1987); this may be indicative that additional mixing processes are necessary or that a more recent TAMS, such as that of Stothers (1991), should be used.

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37

Rüdiger, G., M. Küker, P. J. Käpylä e K. G. Strassmeier. "Antisolar differential rotation of slowly rotating cool stars". Astronomy & Astrophysics 630 (30 settembre 2019): A109. http://dx.doi.org/10.1051/0004-6361/201935280.

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Rotating stellar convection transports angular momentum towards the equator, generating the characteristic equatorial acceleration of the solar rotation while the radial flux of angular momentum is always inwards. New numerical box simulations for the meridional cross-correlation ⟨uθuϕ⟩, however, reveal the angular momentum transport towards the poles for slow rotation and towards the equator for fast rotation. The explanation is that for slow rotation a negative radial gradient of the angular velocity always appears, which in combination with a so-far neglected rotation-induced off-diagonal eddy viscosity term ν⊥ provides “antisolar rotation” laws with a decelerated equator. Similarly, the simulations provided positive values for the rotation-induced correlation ⟨uruθ⟩, which is relevant for the resulting latitudinal temperature profiles (cool or warm poles) for slow rotation and negative values for fast rotation. Observations of the differential rotation of slowly rotating stars will therefore lead to a better understanding of the actual stress-strain relation, the heat transport, and the underlying model of the rotating convection.

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38

Huang, F. Y., e C. D. Mote. "On the Instability Mechanisms of a Disk Rotating Close to a Rigid Surface". Journal of Applied Mechanics 62, n. 3 (1 settembre 1995): 764–71. http://dx.doi.org/10.1115/1.2897012.

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The instability mechanisms of a rotating disk, coupled to a rigid surface through a viscous fluid film at the interface, are investigated analytically. The fluid in the film is driven circumferentially by the viscous shear, and it flows outwards radially under centrifugal forces. The circumferential flow component creates an equivalent viscous damping rotating at one half the disk rotation speed. This film damping dissipates all backward traveling waves where the undamped wave speeds are greater than one half the disk rotation speed. The radial flow component creates a nonsymmetric stiffness in the disk-film system that energizes any wave mode at rotation speeds above its flutter speed. Instabilities in the disk-film system are of two types. A rotating damping instability is caused by the rotating film damping at rotation speeds above a critical value that is less than the flutter speed. A combination instability is caused by the combined effect of the film stiffness and damping at rotation speeds above a threshold that is greater than the flutter speed. The maximum rotation speed of stable disk vibration is bounded above by the lowest onset speed of rotating damping instability. This speed limit is predicted for two wall enclosure designs. The maximum stable rotation speed of a 5.25-inch diameter flexible, memory disk, separated from a rigid surface by a viscous air film, is shown to be more than 15 times greater than the maximum speed of the disk without the air film.

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39

Hanhan, O., D. Orhon, Kh Krauth e B. Günder. "Evaluation of denitrification potential of rotating biological contactors for treatment of municipal wastewater". Water Science and Technology 51, n. 11 (1 giugno 2005): 131–39. http://dx.doi.org/10.2166/wst.2005.0399.

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In this study the effect of retention time and rotation speed in the denitrification process in two full-scale rotating biological contactors (RBC) which were operated parallel and fed with municipal wastewater is evaluated. Each rotating biological contactor was covered to prevent oxygen input. The discs were 40% submerged. On the axle of one of the rotating biological contactors lamellas were placed (RBC1). During the experiments the nitrate removal performance of the rotating biological contactor with lamellas was observed to be less than the other (RBC2) since the lamellas caused oxygen diffusion through their movement. The highest nitrate removal observed was 2.06 g/m2.d achieved by a contact time of 28.84 minutes and a recycle flow of 1 l/s. The rotation speed during this set had the constant value of 0.8 min−1. Nitrate removal efficiency on RBC1 was decreasing with increasing rotation speed. On the rotating biological contactor without lamellas no effect on denitrification could be determined within a speed range from 0.67 to 2.1 min−1. If operated in proper conditions denitrification on RBC is a very suitable alternative for nitrogen removal that can easily fulfil the nutrient limitations in coastal areas due to the rotating biological contactors economical benefits and uncomplicated handling.

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40

Hansen, Niels Chr, e David Huron. "Twirling Triplets: The Qualia of Rotation and Musical Rhythm". Music & Science 2 (1 gennaio 2019): 205920431881224. http://dx.doi.org/10.1177/2059204318812243.

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While musicologists have long noted that triplet rhythms evoke sensations of rotation in listeners, no theory has been proposed to account for this apparent association. To investigate this phenomenon, 33 excerpts of “spinning, rotating, twirling, or swirling” music were crowd-sourced from an online discussion forum. Analysis revealed a prominence of fast, repeated, isochronous patterns using stepwise pitch movement, with significantly more compound meters than generally found in Western music. Inspired by ecological acoustics, an Ecological Theory of Rotating Sounds (ETRoS) is proposed to explain these associations. The theory maps patterns of loudness fluctuations to trajectories of rotating sound sources. Two experiments tested the theory. In Experiment A, listeners rated how much binary, ternary, quaternary, and quinary figures (of 2–5 notes) evoked sensations of rotation. Experiment B used a two-alternative forced-choice paradigm pitting ecological quaternary stimuli (strong-medium-weak-medium) against unecological stimuli with permuted stress values more typical of Western music (strong-weak-medium-weak). Results indicate that perceived rotation increases with tempo and is poorly evoked by binary rhythms. Loudness patterns consistent with rotating trajectories were perceived as more rotating than unecological patterns—but only when pitch was also moving. Altogether, moderate support is provided for an acoustic-ecological account of rotating sounds.

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41

Shibahashi, H., e M. Takata. "Pulsation of Rotating Magnetic Stars". International Astronomical Union Colloquium 139 (1993): 134. http://dx.doi.org/10.1017/s0252921100117117.

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Recently, one of the rapidly oscillating Ap stars, HR 3831, has been found to have an equally split frequency septuplet, though its oscillation seems to be essentially an axisymmetric dipole mode with respect to the magnetic axis which is oblique to the rotation axis (Kurtz et al. 1992; Kurtz 1992). In order to explain this fine structure, we investigate oscillations of obliquely rotating magnetic stars by taking account of the perturbations due to the magnetic fields and the rotation. We suppose that the star is rigidly rotating and that the magnetic field is a dipole field and its axis is oblique to the rotation axis. We treat the effects of the rotation and of the magnetic field as perturbations. In doing so, we suppose that the rotation of the star is slow enough so that the effect of the rotation on oscillations is smaller than that of the magnetic field.

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42

Choplin, Arthur, Raphael Hirschi, Georges Meynet, Sylvia Ekström, Cristina Chiappini e Alison Laird. "Non-standard s-process in massive rotating stars". Astronomy & Astrophysics 618 (ottobre 2018): A133. http://dx.doi.org/10.1051/0004-6361/201833283.

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Context. Recent studies show that rotation significantly affects the s-process in massive stars. Aims. We provide tables of yields for non-rotating and rotating massive stars between 10 and 150 M⊙ at Z = 10−3 ([Fe/H] = −1.8). Tables for different mass cuts are provided. The complete s-process is followed during the whole evolution with a network of 737 isotopes, from hydrogen to polonium. Methods. A grid of stellar models with initial masses of 10, 15, 20, 25, 40, 60, 85, 120, and 150 M⊙ and with an initial rotation rate of both 0% or 40% of the critical velocity was computed. Three extra models were computed in order to investigate the effect of faster rotation (70% of the critical velocity) and of a lower 17O(α, γ) reaction rate. Results. At the considered metallicity, rotation has a strong impact on the production of s-elements for initial masses between 20 and 60 M⊙. In this range, the first s-process peak is boosted by 2−3 dex if rotation is included. Above 60 M⊙, s-element yields of rotating and non-rotating models are similar. Increasing the initial rotation from 40% to 70% of the critical velocity enhances the production of 40 ≲ Z ≲ 60 elements by ∼0.5−1 dex. Adopting a reasonably lower 17O(α, γ) rate in the fast-rotating model (70% of the critical velocity) boosts again the yields of s-elements with 55 ≲ Z ≲ 82 by about 1 dex. In particular, a modest amount of Pb is produced. Together with s-elements, some light elements (particularly fluorine) are strongly overproduced in rotating models.

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43

PAN, Y. Y., C. M. ZHANG, Y. H. ZHAO e R. JUN. "A TETRAD DESCRIPTION ON THE DIRAC SPIN-ROTATION EFFECT". International Journal of Modern Physics D 20, n. 10 (settembre 2011): 1979–82. http://dx.doi.org/10.1142/s0218271811020044.

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Rotation and Dirac spin coupling is described by the tetrad field for a rotating system, where the rotation-spin effect is replaced by an axial torsion-spin. After constructing a rotating tetrad field, we derive the torsion quantities, by which we deal with the torsion-spin coupling.

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44

Liu, Xiaojuan, David S. Battisti e Gerard H. Roe. "The Effect of Cloud Cover on the Meridional Heat Transport: Lessons from Variable Rotation Experiments". Journal of Climate 30, n. 18 (22 agosto 2017): 7465–79. http://dx.doi.org/10.1175/jcli-d-16-0745.1.

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Abstract The question “What determines the meridional heat transport (MHT)?” is explored by performing a series of rotation-rate experiments with an aquaplanet GCM coupled to a slab ocean. The change of meridional heat transport with rotation rate falls into two regimes: in a “slow rotating” regime (rotation rate < 1/2 modern rotation) MHT decreases with increasing rotation rate, whereas in a “fast rotating” regime (rotation rate ≥ 1/2 modern rotation) MHT is nearly invariant. The two-regime feature of MHT is primarily related to the reduction in tropical clouds and increase in tropical temperature that are associated with the narrowing and weakening of the Hadley cell with increasing rotation rate. In the slow-rotating regime, the Hadley cell contracts and weakens as rotation rate is increased; the resulting warming causes a local increase in outgoing longwave radiation (OLR), which consequently decreases MHT. In the fast-rotating regime, the Hadley cell continues to contract as rotation rate is increased, resulting in a decrease in tropical and subtropical clouds that increases the local absorbed shortwave radiation (ASR) by an amount that almost exactly compensates the local increases in OLR. In the fast-rotating regime, the model heat transport is approximately diffusive, with an effective eddy diffusivity that is consistent with eddy mixing-length theory. The effective eddy diffusivity decreases with increasing rotation rate. However, this decrease is nearly offset by a strong increase in the meridional gradient of moist static energy and hence results in a near-constancy of MHT. The results herein extend previous work on the MHT by highlighting that the spatial patterns of clouds and the factors that influence them are leading controls on MHT.

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45

Xiahui Han, Xiahui Han, e and Jianlang Li and Jianlang Li. "Maglev rotating disk laser". Chinese Optics Letters 13, n. 12 (2015): 121403–6. http://dx.doi.org/10.3788/col201513.121403.

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46

Yin, Yanjie, Hui Chen, Xiaoyi Yang e Shuang He. "Investigation of porosity in rotating laser-MIG hybrid welding A6N01 aluminum alloy". International Journal of Modern Physics B 33, n. 01n03 (30 gennaio 2019): 1940029. http://dx.doi.org/10.1142/s0217979219400290.

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In this study, rotating laser was employed to reduce the porosity defect in laser-MIG hybrid welding A6N01 aluminum alloy. The influence of laser rotating frequency and rotating radius on the weld were researched respectively. The images of the molten pool were acquired by the high-speed camera, and X-ray images of the weld were calculated by binarization. The result shows that rotating laser-MIG hybrid welding has a dramatic effect on suppressing the generation of porosity, which indicates the possibility to obtain the A6N01 aluminum alloy weld with few pores. With proper parameters about rotation frequency (50 Hz) and rotation radius (2 mm), the porosity decreased obviously from 8.41% to 5.68%, and there was hardly distinct change in the weld penetration. The keyhole stability of rotating laser-MIG hybrid welding was improved, compared with the conventional laser-MIG hybrid welding. On account of laser beam stirring the metal molten pool, it was beneficial for the pores to escape from the molten pool. The rotating laser-MIG hybrid welding shows a good prospect.

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47

Chavanne, Cédric P., Eric Firing e François Ascani. "Inertial Oscillations in Geostrophic Flow: Is the Inertial Frequency Shifted by ζ/2 or by ζ?" Journal of Physical Oceanography 42, n. 5 (1 maggio 2012): 884–88. http://dx.doi.org/10.1175/jpo-d-12-031.1.

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Abstract The short answer to the question posed in the title is that it depends on the frame of reference chosen to describe the motions. In the inertial limit, the frequency in a rotating frame of reference corresponds to the rotation rate of the inertial current vectors relative to that frame. When described in a reference frame rotating with a geostrophic flow having a relative vertical vorticity ζ, inertial oscillations have a frequency f + ζ, equal to twice the fluid’s rotation rate around the local vertical axis. From a nonrotating frame of reference, one would measure only half this frequency; the other half arises from describing inertial motions in a reference frame rotating with the background flow. However, when described in a reference frame rotating with Earth, hence rotating at −ζ/2 relative to the geostrophic frame, inertial oscillations have a frequency reduced to f + ζ/2.

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48

Zhang, Qingqing, e Zhiqiang Wan. "Design of an Intelligent Lifting Display Cabinet". Highlights in Science, Engineering and Technology 35 (11 aprile 2023): 122–26. http://dx.doi.org/10.54097/hset.v35i.7043.

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An intelligent lifting display cabinet is designed, which includes an upper cabinet body, a lower cabinet body is connected under the upper cabinet body, a first motor is arranged on the side of the lower cabinet body, a taking groove is arranged on the upper cabinet body, a cavity is arranged in the lower cabinet body, the lower cabinet body includes a rotating transmission component, the first motor is connected with the rotating transmission component, a driving opening component is engaged on the rotating transmission component, and a rising rotation component is connected on the rotating transmission component, One end of the cover assembly is connected with the driving opening assembly, and the other end of the cover assembly is connected with the rotating transmission assembly. The display cabinet has the effect of displaying the display items in all aspects through rotation or lifting, with strong pertinence and intuition.

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49

SUN, CHAO, TOM MULLIN, LEEN VAN WIJNGAARDEN e DETLEF LOHSE. "Drag and lift forces on a counter-rotating cylinder in rotating flow". Journal of Fluid Mechanics 664 (12 ottobre 2010): 150–73. http://dx.doi.org/10.1017/s0022112010003666.

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Results are reported of an experimental investigation into the motion of a heavy cylinder free to move inside a water-filled drum rotating around its horizontal axis. The cylinder is observed to either co-rotate or, counter-intuitively, counter-rotate with respect to the rotating drum. The flow was measured with particle image velocimetry, and it was found that the inner cylinder significantly altered the bulk flow field from the solid-body rotation found for a fluid-filled drum. In the counter-rotation case, the generated lift force allowed the cylinder to freely rotate without contact with the drum wall. Drag and lift coefficients of the freely counter-rotating cylinder were measured over a wide range of Reynolds numbers, 2500 < Re < 25000, dimensionless rotation rates, 0.0 < α < 1.2, and gap to cylinder diameter ratios 0.003 < G/2a < 0.5. Drag coefficients were consistent with previous measurements on a cylinder in a uniform flow. However, for the lift coefficient, considerably larger values were observed in the present measurements. We found the enhancement of the lift force to be mainly caused by the vicinity of the wall.

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50

JULIEN, KEITH, SONYA LEGG, JAMES McWILLIAMS e JOSEPH WERNE. "Plumes in rotating convection. Part 1. Ensemble statistics and dynamical balances". Journal of Fluid Mechanics 391 (25 luglio 1999): 151–87. http://dx.doi.org/10.1017/s0022112099005236.

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Atmospheric and oceanic convection often occurs over areas occupied by many localized circulation elements known as plumes. The convective transports therefore may depend not only on the individual elements, but also on the interactions between plumes and the turbulent environment created by other plumes. However, many attempts to understand these plumes focus on individual isolated elements, and the behaviour of an ensemble is not understood. Geophysical convection may be influenced by rotation when the transit time of a convecting element is long compared to an inertial period (for example in deep oceanic convection). Much recent attention has been given to the effect of rotation on individual plumes, but the role of rotation in modifying the behaviour of an ensemble is not fully understood. Here we examine the behaviour of plumes within an ensemble, both with and without rotation, to identify the influence of rotation on ensemble plume dynamics.We identify the coherent structures (plumes) present in numerical solutions of turbulent Rayleigh–Bénard convection, a canonical example of a turbulent plume ensemble. We use a conditional sampling compositing technique to extract the typical structure in both non-rotating and rotating solutions. The dynamical balances of these composite plumes are evaluated and compared with entraining plume models. We find many differences between non-rotating and rotating plumes in their transports of mass, buoyancy and momentum. As shown in previous studies, the expansion of the turbulent plume by entrainment of exterior fluid is suppressed by strong rotation. Our most significant new result is quantification of the continuous mixing between the plume and ambient fluid which occurs at high rotation without any net changes in plume volume. This mixing is generated by the plume–plume interactions and acts to reduce the buoyancy anomaly of the plume. By contrast, in the non-rotating case, no such loss of buoyancy by mixing occurs. As a result, the total buoyancy transport by upwardly moving plumes diminishes across the layer in the rotating case, while remaining approximately constant in the non-rotating case. At high values of rotation, the net vertical acceleration is considerably reduced compared to the non-rotating case due to loss of momentum through entrainment and mixing and a decelerating pressure gradient which partially balances the buoyancy-driven acceleration of plumes. As a result of the dilution of buoyancy, the pressure-gradient deceleration and the loss of momentum due to mixing with the environment in the rotating solutions, the conversion of potential energy to kinetic energy is significantly less than that of non-rotating plumes.The combination of efficient lateral mixing and slow vertical movement by the plumes accounts for the unstable mean temperature gradient that occurs in rotating Rayleigh–Bénard convection, while the less penetrative convection found at low Rossby number is a consequence of the reduced kinetic energy transport. Within the ensemble of plumes identified by the conditional sampling algorithm, distributions of vertical velocity, buoyancy and vorticity mimic those of the volume as a whole. Plumes cover a small fraction of the total area, yet account for most of the vertical heat flux.

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