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1
Klimov, Alexandr V., i Akop V. Antonyan. "Research of features of oscillating process’ behavior in the nonlinear system of individual traction drive of an electrobus". Izvestiya MGTU MAMI 17, nr 1 (24.06.2023): 87–96. http://dx.doi.org/10.17816/2074-0530-115233.
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BACKGROUND: When a vehicle is in motion, self-oscillations which properties are dependent on slip rate in a contact patch may occur in the area of tire interaction with ground surface. Oscillations frequency will vary in dependence with value of wheel slip relative to ground surface. Soft self-oscillations are excited by variable set of initial conditions at full slip in traction and driven wheel rolling modes as well as in mixed braking mode with partial slip. Hard mode of self-oscillations occurs at full wheel slip in braking mode. These processes have a negative impact on the processes in electric drive and mechanical drivetrain reducing their efficiency and may cause damage of components. Oscillations in the system are excited by interaction forces of an elastic tire with ground surface featuring vertical oscillations due to elastic behavior of its interaction with road unevenness.
AIMS: Research of features of oscillating process behavior in the nonlinear system of individual traction drive of an electrobus.
METHODS: Simulation of self-oscillation excitation processes in the area of contact interaction of a wheel and road was carried out in the MATLAB/Simulink software package.
RESULTS: The article features the results of simulation and experimental studies of self-oscillation excitation processes of the KAMAZ 6282 electrobus moving on asphalt-concrete surface. It was found that vertical wheel displacement when moving through unevenness lead to oscillating behavior of vertical reaction forces in contact patches and, as a consequence, to oscillating behavior of longitudinal reaction forces, torque and rotation velocity of the shaft of the traction electric motor of the individual drive. It was defined that tire oscillation frequency is 67 Hz that coincides with electric motor shaft rotation oscillation frequency and this value is the same for both experiment and simulation.
CONCLUSIONS: Practical value of the study lies in ability of using the study results at development of self-oscillation processes exclusion algorithms as a part of vehicle control system.
2
Zhileykin, Mikhail M., Pavel V. Sirotin, Sergey S. Nosikov i Nikolay N. Pulyaev. "Method for detecting the loss of stability of the movement of tractors when towing a trailer or a coupled unit". Tractors and Agricultural Machinery 90, nr 1 (23.05.2023): 39–48. http://dx.doi.org/10.17816/0321-4443-321266.
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BACKGROUND:Currently, combines and tractors, being the most energy-intensive transport and technological machines for agricultural purposes, largely determine the possibility of transition to an efficient and environmentally friendly agricultural economy, and also provide the technical aspect of the transformation of the agro-industrial complex into the leading sector of the countrys industry. One of the sources of dynamic loads in the units and subsystems of tractor equipment are self-oscillating modes.
AIMS:Study of the conditions for the occurrence of self-oscillating processes in the design of wheeled tractor trains and development of methods to increase the handling and safety of their movement by means of reducing the galloping and yawing of the tractor-tractor when towing heavy loads.
METHODS:It has been established that due to the coupling of oscillations along the longitudinal displacement of a truck tractor and a trailer with oscillations along the vertical displacement of the center of mass and with pitch angle oscillations of the truck tractor, when an auto-oscillatory mode occurs in the interaction zone of an elastic wheel with a solid surface, the same mode of self-oscillation will occur along the mentioned degrees of freedom. Moreover, it is possible to specify the sequence of occurrence of self-oscillating modes in different zones of the tractor train design.
RESULTS:First, self-oscillations are excited in the contact patch of a wheel with a solid surface when a complete slip occurs, then self-oscillations along the pitch angle of a truck tractor body begin and after that self-oscillations along the vertical displacement of the center of mass of a truck tractor occur. Folding angle oscillations of a tractor train are associated with oscillations of the translational motion of wheel centers, which lead to the emergence of an self-oscillating mode, both with partial and full slip in the interaction zone of an elastic tire with a solid surface. Since the self-oscillations of each of the wheels occur at random times, the self-oscillations of a truck tractor along the folding angle will be chaotic.
CONCLUSIONS:The practical value of the study lies in the possibility of using the proposed methods to identify the danger of self-oscillating processes in the design of promising types of agricultural machinery.
3
H Thomas, John. "Oscillations in Sunspots". Australian Journal of Physics 38, nr 6 (1985): 811. http://dx.doi.org/10.1071/ph850811.
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Recent observational and theoretical work on oscillations in sunspots is reviewed. The characteristic 3-minute umbral oscillations and flashes are reSonant modes of the sunspot itself, whereas the 5-minute oscillations in the umbra are a passive response to forcing by p modes in the surrounding convection zone. The observational evidence suggests that the fundamental cause of the 3-minute oscillations is the photospheric fast-mode resonance, with chromospheric slow-mode resonances perhaps producing additional oscillation frequencies in the chromosphere. Observations and theoretical models of the interaction of 5-minute p-mode oscillations with a sunspot offer a means of probing the structure of a sunspot magnetic flux tube beneath the solar surface. The observed differences between running penumbral waves in the chromosphere and in the photosphere may be explained by the effect of the Evershed flow on trapped magneto-atmospheric waves in the penumbra.
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Mitura, Z., S. L. Dudarev i M. J. Whelan. "Theoretical Investigations of RHEED Oscillations". Microscopy and Microanalysis 5, S2 (sierpień 1999): 710–11. http://dx.doi.org/10.1017/s1431927600016871.
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Nowadays there is great interest in the application of reflection high energy electron diffraction (RHEED) to monitor the growth of ultra thin films. This popularity of RHEED arose from the discovery of RHEED intensity oscillations in the early eighties. Namely, it was experimentally found that if the growth of a material follows a layer-by-layer mode then regular oscillating changes in the intensity of the specular beam occur, and the period of the oscillations corresponds to the deposition of one atomic layer of the material. These findings are of great practical importance and consequently RHEED is an important experimental technique used in nanoscale engineering. Nevertheless, the basic question of why RHEED oscillation are observed still remains open. In the past the Philips group suggested that intensity oscillations are a consequence of periodic changes in the roughness of the surface. About the same time, the University of Minnesota group claimed that during the growth the electron wave is reflected by two terraces (in an idealised case) and periodic changes of the interference conditions imply RHEED oscillation.
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Liu, Yunqiao, i Benlong Wang. "Dynamics and surface stability of a cylindrical cavitation bubble in a rectilinear vortex". Journal of Fluid Mechanics 865 (1.03.2019): 963–92. http://dx.doi.org/10.1017/jfm.2019.103.
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In this paper, we formulate the dynamic equations of radial and surface modes for a cylindrical cavitation bubble subject to a prescribed uniform rectilinear vortex flow. The potential flow in the bulk volume of the external flow is modelled using the general mode decomposition approach. The stability of surface modes is investigated under linear analysis. The effects of confinement due to a limited flow domain in a water tunnel and viscosity at the bubble surface are evaluated, which can be fairly neglected for the cylindrical cavitation bubbles discussed. Our model is capable of predicting the developments of surface modes, which agrees well with experimental observations reported in the literature. We derive the Mathieu structure in the dynamic equation of the surface oscillation and the associated instability condition of the surface mode oscillations. The numerical results confirm that the Mathieu-type instability controls the stability diagrams and the emergence of surface modes under specific radial oscillation.
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Strohmayer, T. E. "Oscillations of Rotating Neutron Stars". International Astronomical Union Colloquium 128 (1992): 299–304. http://dx.doi.org/10.1017/s0002731600155386.
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AbstractWe use a perturbation technique to compute the rotational corrections to the non-radial oscillation spectrum of a realistic neutron-star model. We compute, to first order in the rotation rate, the corrections to the normal mode eigenfrequencies and eigenfunctions. We find that l = l0 oscillations are coupled to l = l0 ± 1 oscillations by the Coriolis force. For the toroidal modes, this coupling introduces a non-zero radial component to the velocity field. We have used this result to compute the neutrino damping rates for several corrected toroidal modes. This damping mechanism is inoperative for toroidal modes in a non-rotating star because these modes produce no density nor temperature perturbations. The neutrino damping time can approach the gravitational radiation damping time in rotating neutron stars if the central temperature is high enough, (Tc ≥ 108 K). The rotationally induced coupling of spheroidal oscillations to toroidal modes can also produce significant displacements at the stellar surface. This may have interesting implications for channeling energy, e.g., that associated with a glitch, to the surface of the star. Perhaps this might produce observable effects in the pulsar emission process or a γ-ray burst event.
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Ignatyev, Alexander Anatolevich, Irina Pavlovna Nasad i Tat'yana Gennadievna Nasad. "Modeling lathe dynamic system in terms of estimated dampening coefficient of autocorrelation function of oscillations". Vestnik of Astrakhan State Technical University. Series: Management, computer science and informatics 2023, nr 2 (28.04.2023): 17–22. http://dx.doi.org/10.24143/2072-9502-2023-2-17-22.
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Part machining on the lathes with automated tools is a complex process that depends on the properties
of the lathe dynamic system. Oscillations in processing the main parts determine the dynamic quality of the lathes, quality of the surface layer and resistance of the cutting tool, therefore, it is necessary to identify the methods to control the operation mode. Increased efficiency of the process is provided by the forced cutting modes, which can lead to the deterioration of processing quality and premature wear of a cutting tool. Theoretical definition of rational cutting modes causes certain difficulties, so the experimental search for a solution to the problem is most urgent. In order to select rational cutting modes on the lathes and grinding machines, it is proposed to use the stability margin of the lathe dynamic system (DS), which should be determined from the transfer function of DS using the autocorrelation function (ACF) of oscillations. A condition for identification of the lathe DS is a preliminary identification of ACF, which can be implemented using oscillation records during cutting. Pre-filtering of oscillations is carried out to exclude low-frequency range containing frequencies caused by oscillations of lathe system elements and to save frequencies associated with the cutting process. Cut modes are assigned to the highest stability margin, which ensures high surface quality. There is an unambiguous ana-lytical relationship between the oscillation index and the damping coefficient of the ACF, which makes it possible to calculate the α coefficient, by the value of which it is possible to estimate the stability margin of the ET in different cutting modes and select the most appropriate one. Studying the lathe oscillations in processing high-precision parts makes it possible to control the technological mode, using the oscillation level as one of the indicators of its quality.
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Wang, Minyang, Shang-Ping Xie, Samuel S. P. Shen i Yan Du. "Rossby and Yanai Modes of Tropical Instability Waves in the Equatorial Pacific Ocean and a Diagnostic Model for Surface Currents". Journal of Physical Oceanography 50, nr 10 (1.10.2020): 3009–24. http://dx.doi.org/10.1175/jpo-d-20-0063.1.
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AbstractMesoscale activities over the equatorial Pacific Ocean are dominated by the Rossby and Yanai modes of tropical instability waves (TIWs). The TIW-induced surface velocity has not been accurately estimated in previous diagnostic models, especially for the meridional component across the equator. This study develops a diagnostic model that retains the acceleration terms to estimate the TIW surface velocity from the satellite-observed sea surface height. Validated against moored observations, the velocity across the equator is accurately estimated for the first time, much improved from existing products. The results identify the Rossby- and Yanai-mode TIWs as the northwest–southeastward (NW–SE) velocity oscillations north of the equator and the northeast–southwestward (NE–SW) velocity oscillations on the equator, respectively. Barotropic instability is the dominant energy source of the two TIW modes. The NE–SW velocity oscillation of the Yanai mode is associated with the counterclockwise shear of the South Equatorial Current on the equator. The two TIW modes induce different sea surface temperature patterns and vertical motions. Accurate estimates of TIW velocity are important for studying equatorial ocean dynamics and climate variability in the tropical Pacific Ocean.
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Szentirmay, Zs. "Slow-mode surface plasma oscillations in layered structures". Physical Review B 36, nr 5 (15.08.1987): 2607–13. http://dx.doi.org/10.1103/physrevb.36.2607.
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MacLeod, Morgan, Michelle Vick i Abraham Loeb. "Tidal Wave Breaking in the Eccentric Lead-in to Mass Transfer and Common Envelope Phases". Astrophysical Journal 937, nr 1 (1.09.2022): 37. http://dx.doi.org/10.3847/1538-4357/ac8aff.
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Abstract The evolution of many close binary and multiple star systems is defined by phases of mass exchange and interaction. As these systems evolve into contact, tidal dissipation is not always sufficient to bring them into circular, synchronous orbits. In these cases, encounters of increasing strength occur while the orbit remains eccentric. This paper focuses on the outcomes of close tidal passages in eccentric orbits. Close eccentric passages excite dynamical oscillations about the stars’ equilibrium configurations. These tidal oscillations arise from the transfer of orbital energy into oscillation mode energy. When these oscillations reach sufficient amplitude, they break near the stellar surface. The surface wave-breaking layer forms a shock-heated atmosphere that surrounds the object. The continuing oscillations in the star’s interior launch shocks that dissipate into the atmosphere, damping the tidal oscillations. We show that the rapid, nonlinear dissipation associated with the wave breaking of fundamental oscillation modes therefore comes with coupled mass loss to the wave-breaking atmosphere. The mass ratio is an important characteristic that defines the relative importance of mass loss and energy dissipation and therefore determines the fate of systems evolving under the influence of nonlinear dissipation. The outcome can be rapid tidal circularization (q ≪ 1) or runaway mass exchange (q ≫ 1).
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Fahrbach, Michael, Min Xu, Wilson Ombati Nyang’au, Oleg Domanov, Christian H. Schwalb, Zhi Li, Christian Kuhlmann, Uwe Brand i Erwin Peiner. "Damped Cantilever Microprobes for High-Speed Contact Metrology with 3D Surface Topography". Sensors 23, nr 4 (10.02.2023): 2003. http://dx.doi.org/10.3390/s23042003.
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We addressed the coating 5 mm-long cantilever microprobes with a viscoelastic material, which was intended to considerably extend the range of the traverse speed during the measurements of the 3D surface topography by damping contact-induced oscillations. The damping material was composed of epoxy glue, isopropyl alcohol, and glycerol, and its deposition onto the cantilever is described, as well as the tests of the completed cantilevers under free-oscillating conditions and in contact during scanning on a rough surface. The amplitude and phase of the cantilever’s fundamental out-of-plane oscillation mode was investigated vs. the damping layer thickness, which was set via repeated coating steps. The resonance frequency and quality factor decreased with the increasing thickness of the damping layer for both the free-oscillating and in-contact scanning operation mode, as expected from viscoelastic theory. A very low storage modulus of E′≈100kPa, a loss modulus of E″≈434kPa, and a density of ρ≈1.2gcm−3 were yielded for the damping composite. Almost critical damping was observed with an approximately 130 µm-thick damping layer in the free-oscillating case, which was effective at suppressing the ringing behavior during the high-speed in-contact probing of the rough surface topography.
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Cocciaro, Bruno, Sandro Faetti i Maurizio Nobili. "Capillarity effects on surface gravity waves in a cylindrical container: wetting boundary conditions". Journal of Fluid Mechanics 231 (październik 1991): 325–43. http://dx.doi.org/10.1017/s0022112091003415.
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Surface capillary–gravity waves are experimentally investigated in a cylindrical basin subjected to a horizontal oscillation by using a high-sensitivity optical method. We study the low-oscillation-amplitude regimes for a fluid which wets the vertical walls and we show that the presence of the capillary meniscus can effect greatly the main properties of the system. Both the free decay and the forced oscillations of surface oscillations are investigated. The amplitude, the phase and the damping of gravity waves are investigated in detail. The damping of the fundamental surface mode is found to exhibit nonlinear behaviour which is in qualitative agreement with the predictions of the Miles (1967) theory of capillary damping. The amplitude and the phase of gravity waves with respect to the oscillation of the container exhibit unusual behaviour which is strictly connected with the presence of the wetting boundary condition for the fluid at the vertical walls.
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Saio, Hideyuki. "Pulsation of magnetic stars". Proceedings of the International Astronomical Union 9, S301 (sierpień 2013): 197–204. http://dx.doi.org/10.1017/s1743921313014324.
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AbstractSome Ap stars with strong magnetic fields pulsate in high-order p modes; they are called roAp (rapidly oscillating Ap) stars. The p-mode frequencies are modified by the magnetic fields. Although the large frequency separation is hardly affected, small separations are modified considerably. The magnetic field also affects the latitudinal amplitude distribution on the surface. We discuss the properties of axisymmetric p-mode oscillations in roAp stars.
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Persinger, Michael A. "Potential Gravitational - Solar Electromagnetic Spectral Radiance Interaction as the Source of the Earth’s Background Free Oscillations". International Letters of Chemistry, Physics and Astronomy 21 (listopad 2013): 11–14. http://dx.doi.org/10.18052/www.scipress.com/ilcpa.21.11.
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The origins of the continuous free oscillations of the whole earth have been attributed to coupling between the solid earth and atmosphere primarily through the fundamental spheroidal mode 0S29 oscillation of ~3.7 mHz. The origins of these interference patterns have been attributed to an excitation source just above the Earth’s surface. However, comparable surface oscillations have been measured in the Sun’s photosphere. The cube root of the product of the gravitational constant, the spectral radiance of the sun, and the square of the frequency produced an acceleration value that was identical to the measured amplitude of the free Earth oscillations (~0.4∙10-11 m∙s-2). The quantitative convergence suggests these narrow-band accelerations may emerge within the Sun-Earth system as it moves through galactic space.
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Persinger, Michael A. "Potential Gravitational - Solar Electromagnetic Spectral Radiance Interaction as the Source of the Earth’s Background Free Oscillations". International Letters of Chemistry, Physics and Astronomy 21 (4.11.2013): 11–14. http://dx.doi.org/10.56431/p-scxfvs.
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The origins of the continuous free oscillations of the whole earth have been attributed to coupling between the solid earth and atmosphere primarily through the fundamental spheroidal mode 0S29 oscillation of ~3.7 mHz. The origins of these interference patterns have been attributed to an excitation source just above the Earth’s surface. However, comparable surface oscillations have been measured in the Sun’s photosphere. The cube root of the product of the gravitational constant, the spectral radiance of the sun, and the square of the frequency produced an acceleration value that was identical to the measured amplitude of the free Earth oscillations (~0.4∙10-11 m∙s-2). The quantitative convergence suggests these narrow-band accelerations may emerge within the Sun-Earth system as it moves through galactic space.
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Dyadya, S., О. Kozlova i Ye Kushnir. "Investigation of the formation of a machined surface profile during end milling with a tool with a long overhang". Innovative Materials and Technologies in Metallurgy and Mechanical Engineering, nr 2 (7.12.2021): 50–54. http://dx.doi.org/10.15588/1607-6885-2021-3-8.
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Purpose. Investigate the mechanism of forming the profile of the machined surface when milling with a tool with a long overhang.
Methodology. Experimental method was used with a special stand, which makes it possible to simulate an elastic system of a part with different dynamic properties, record oscillograms of oscillations of a part and a tool during the cutting process. Milling was performed with a milling cutter with cutting modes in which self-oscillations occur. To determine the patterns of movement of the part and the tool, the method of aligning the fragments of oscillograms was used.
Results. The scheme of the formation of the profile of the machined surface under the conditions of milling with self-oscillations by a tool with a long overhang has been investigated. It was found that the free vibrations of the tool after the tooth leaves the cutting zone have a higher intensity than that of the part. This affects the position of the infeed point on the cutting surface. To determine the period and range of self-oscillations of the cutter and the part, the section of the oscillogram with self-oscillations was straightened using the Savitsky-Galei filter. Comparison with the cutting surface of the sections of the oscillogram of the part and the tool during milling showed an identical vibration mode of the cutter. Based on the results of experimental studies, the deviation from the line of elastic equilibrium of the first wave of self-oscillation of the cutter was determined and a graph of its change was plotted. The studies performed have confirmed the previously established effect of deviation from the elastic equilibrium position of the first self-oscillation wave during counter milling on the shaping of the treated surface.
Originality. It has been established that the profile of the machined surface when milling with long overhang end mills is directly related to the deviation of the tool from the elastic equilibrium position during self-oscillation.
Practical value. The obtained results show the effect of a tool with a long overhang on the formation of a machined surface during milling with self-oscillation.
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Williams, J. E. Ffowcs, i Y. P. Guo. "On resonant nonlinear bubble oscillations". Journal of Fluid Mechanics 224 (marzec 1991): 507–29. http://dx.doi.org/10.1017/s0022112091001854.
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If a bubble were produced with an initial surface distortion, the energy carried by surface modes could be converted to other modes by nonlinear interaction, a conversion that provides a possible mechanism of second generation by bubbles. Longuet-Higgins (1989a,b) has argued that volume pulsation would be excited at twice the frequency of the distortion mode and that the response to such excitation is ‘surprisingly large’ when its frequency is close to the natural resonance frequency of the volumetrical mode. It is shown in this paper that this is feasible only if the driving system is sufficiently energetic to supply the energy involved in those volume pulsations, and that this is not generally the case. In the absence of external sources, the sum of energies in the interacting modes cannot exceed the initial bubble energy; an increase in one mode is always accompanied by a decrease in another. In contrast to any expectation of significant pulsations near resonance, we find that, once modal coupling is admitted, the volumetrical pulsation has very small amplitude in comparison with that of the initial surface distortion. This is because of the constraint of energy, a constraint that becomes more severe once damping is admitted. Our conclusion therefore is that the distortion modes of a bubble are unlikely to be the origin of an acoustically significant bubble response.
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Abi Chebel, Nicolas, Jiří Vejražka, Olivier Masbernat i Frédéric Risso. "Shape oscillations of an oil drop rising in water: effect of surface contamination". Journal of Fluid Mechanics 702 (30.05.2012): 533–42. http://dx.doi.org/10.1017/jfm.2012.205.
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AbstractInertial shape oscillations of heptane drops rising in water are investigated experimentally. Diameters from 0.59 to 3.52 mm are considered, corresponding to a regime where the rising motion should not affect shape oscillations for pure immiscible fluids. The interface, however, turns out to be contaminated. The drag coefficient is considerably increased compared to that of a clean drop due to the well-known Marangoni effect resulting from a gradient of surfactant concentration generated by the fluid motion along the interface. Thanks to the decomposition of the shape into spherical harmonics, the eigenfrequencies and the damping rates of oscillation modes $n= 2$, 3, 4 and 5 have been measured. Frequencies are not affected by contamination, while damping rates are increased by a considerable amount that depends neither on drop instantaneous velocity nor on diameter. This augmentation, however, depends on the mode number: it is maximum for mode two (multiplied by 2.4) and then relaxes towards the value of a clean drop as $n$ increases. A previous similar investigation of a drop attached to a capillary has not revealed such an increase of the damping rates, indicating that the coupling between rising motion and surface contamination is responsible for this effect.
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Qin, Z., X. Zou i F. Weng. "Arctic and Antarctic four-month oscillations detected from Advanced Microwave Sounding Unit-A measurements". Antarctic Science 24, nr 5 (17.05.2012): 507–13. http://dx.doi.org/10.1017/s0954102012000417.
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AbstractSatellite microwave measurements can penetrate through clouds and therefore provide unique information of surface and near-surface temperatures and surface emissivity. In this study, the brightness temperatures from NOAA-15 Advanced Microwave Sounding Unit-A (AMSU-A) are used to analyse the surface temperature variation in the Arctic and Antarctic regions during the past 13 years from 1998–2010. The data from four AMSU-A channels sensitive to surface are analysed with wavelet and Fourier spectrum techniques. A very pronounced maximum is noticed in the period range centred around four months. Application of a statistical significance test confirms that it is a dominant mode of variability over polar regions besides the annual and semi-annual oscillations in the data. No evidence of this feature could be found in middle and low latitudes. The four-month oscillation is 90° out of phase at the Arctic and Antarctic, with the Arctic four-month oscillation reaching its maximum in the beginning of March, July and November and the Antarctic four-month oscillation in the middle of April, August and December. The intensity of the four-month oscillation varies interannually. The years with pronounced four-month oscillation were 2002–03, 2005–06 and 2008–09. The strongest year for the Arctic and Antarctic four-month oscillations occurred in 2005–06 and 2008–09, respectively. The sign of four-month oscillation is also found in the surface skin temperatures and two-metre air temperatures from ERA-Interim reanalysis, with strongest signal in 2005–06 when this oscillation is strongest in the data. It is hypothesized that the Arctic and Antarctic four-month oscillations are a combined result of unique features of solar radiative forcing and snow/sea ice formation and metamorphosis.
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Musoke, Elle, Bernd Krauskopf i Hinke M. Osinga. "A Surface of Heteroclinic Connections Between Two Saddle Slow Manifolds in the Olsen Model". International Journal of Bifurcation and Chaos 30, nr 16 (28.12.2020): 2030048. http://dx.doi.org/10.1142/s0218127420300487.
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The Olsen model for the biochemical peroxidase-oxidase reaction has a parameter regime where one of its four variables evolves much slower than the other three. It is characterized by the existence of periodic orbits along which a large oscillation is followed by many much smaller oscillations before the process repeats. We are concerned here with a crucial ingredient for such mixed-mode oscillations (MMOs) in the Olsen model: a surface of connecting orbits that is followed closely by the MMO periodic orbit during its global, large-amplitude transition back to another onset of small oscillations. Importantly, orbits on this surface connect two one-dimensional saddle slow manifolds, which exist near curves of equilibria of the limit where the slow variable is frozen and acts as a parameter of the so-called fast subsystem. We present a numerical method, based on formulating suitable boundary value problems, to compute such a surface of connecting orbits. It involves a number of steps to compute the slow manifolds, certain submanifolds of their stable and unstable manifolds and, finally, a first connecting orbit that is then used to sweep out the surface by continuation. If it exists, such a surface of connecting orbits between two one-dimensional saddle slow manifolds is robust under parameter variations. We compute and visualize it in the Olsen model and show how this surface organizes the global return mechanism of MMO periodic orbits from the end of small oscillations back to a region of phase space where they start again.
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Zrnić, D., P. Berglez i G. Brenn. "Weakly nonlinear shape oscillations of a Newtonian drop". Physics of Fluids 34, nr 4 (kwiecień 2022): 043103. http://dx.doi.org/10.1063/5.0085070.
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Nonlinear axisymmetric shape oscillations of a Newtonian drop in a vacuum are investigated theoretically, for fundamental interest and for their relevance in transport processes across the drop surface. The weakly nonlinear analysis is carried out for, but not limited to, the modes of initial drop deformation up to m = 4. The drop Ohnesorge number covers the range between 0.01 and 1. The weakly nonlinear approach, which is carried to third order, accounts for the coupling of different oscillation modes. With increasing surface deformation, the oscillations develop an asymmetry of the times during one period the drop spends in different states of deformation, a frequency decrease below the linear value, and quasi-periodicity of the motion. In contrast to the inviscid case [D. Zrnić and G. Brenn, “Weakly nonlinear shape oscillations of inviscid drops,” J. Fluid Mech. 923, A9 (2021)], the present analysis reveals the frequency decrease and the quasi-periodicity already in the second-order approximation. The results are positively validated against relevant literature. The theory quantifies the effects of viscosity, measured by the drop Ohnesorge number, dampening the nonlinear behavior and enhancing the coupling of different oscillation modes [E. Becker et al., “Nonlinear dynamics of viscous droplets,” J. Fluid Mech. 258, 191 (1994)]. The present theory reveals the quasi-periodicity of nonlinear viscous drop shape oscillations at strong deformation. The resultant drop motion, starting from a higher-order mode of initial deformation, for which the drop exhibits aperiodic linear behavior, may turn into damped oscillatory with ongoing time due to the coupling to lower-order modes.
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Volina, T., S. Pylypaka i V. Babka. "THE MOTION OF A PARTICLE ON A WAVY SURFACE DURING ITS TRANSLATIONAL CIRCULAR OSCILLATIONS IN HORIZONTAL PLANES". Odes’kyi Politechnichnyi Universytet Pratsi 1, nr 63 (2021): 44–52. http://dx.doi.org/10.15276/opu.1.63.2021.05.
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The rough plane is a universal structural element of many machines and devices for sifting and separation of parts of technological material. The motion of particles on the horizontal plane, which performs oscillating rectilinear or circular motion, is the most studied. A wavy surface with a sinusoidal cross-sectional line as a working surface will significantly change the trajectories of their motion. The mathematical description of such a motion will change accordingly. The sliding of a particle in a plane will be a partial case of sliding on a wavy surface when the amplitude of the sinusoid is equal to zero. When the wavy surface oscillates and all its points describe circles, the motion of the technological material changes significantly. The regularities of the motion of material particles on such a surface during its circular translational oscillations in the horizontal planes are investigated in the article. Differential equations of relative particle displacement are compiled and solved by numerical methods. The trajectories of the particle sliding on the surface and the graphs of its reaction are constructed. A partial case of a surface is a plane, and the sliding trajectory of a particle is a circle. An analytical expression to determine its radius is found. During circular oscillations of a wavy linear surface with a cross section in the form of a sinusoid relative trajectory of a particle after stabilization of the motion can be closed or periodic spatial curves. To avoid the breakaway of the particle from the surface, the oscillation mode should be set, which takes into account the shape of the surface and the kinematic parameters of oscillations. With the diameter of the circle, which is described by all points of the surface during its oscillation, is equal to the period of the sinusoid, the trajectory of the relative motion of the particle can be a periodic curve. In this case, the particle moves in a direction close to the transverse, overcoming depressions and ridges. In other cases, the trajectory is a closed spatial curve, the horizontal projection of which is close to a circle. The found analytical dependencies allow determining the influence of structural and technological parameters of the surface on the trajectory of the particle.
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Weijer, Wilbert, Ernesto Muñoz, Niklas Schneider i François Primeau. "Pacific Decadal Variability: Paced by Rossby Basin Modes?" Journal of Climate 26, nr 4 (15.02.2013): 1445–56. http://dx.doi.org/10.1175/jcli-d-12-00316.1.
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Abstract A systematic study is presented of decadal climate variability in the North Pacific. In particular, the hypothesis is addressed that oceanic Rossby basin modes are responsible for enhanced energy at decadal and bidecadal time scales. To this end, a series of statistical analyses are performed on a 500-yr control integration of the Community Climate System Model, version 3 (CCSM3). In particular, a principal oscillation pattern (POP) analysis is performed to identify modal behavior in the subsurface pressure field. It is found that the dominant energy of sea surface temperature (SST) variability at 25 yr (the model equivalent of the Pacific decadal oscillation) cannot be explained by the resonant excitation of an oceanic basin mode. However, significant energy in the subsurface pressure field at time scales of 17 and 10 yr appears to be related to internal ocean oscillations. However, these oscillations lack the characteristics of the classical basin modes, and must either be deformed beyond recognition by the background circulation and inhomogeneous stratification or have another dynamical origin altogether. The 17-yr oscillation projects onto the Pacific decadal oscillation and, if present in the real ocean, has the potential to enhance the predictability of low-frequency climate variability in the North Pacific.
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Kumar, Praphull, i Dean M. Townsley. "Gravity Modes on Rapidly Rotating Accreting White Dwarfs and Their Variation after Dwarf Novae". Astrophysical Journal 951, nr 2 (1.07.2023): 122. http://dx.doi.org/10.3847/1538-4357/acd1df.
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Abstract Accreting white dwarfs (WDs) in cataclysmic variables (CVs) show short-period (tens of minutes) brightness variations that are consistent with nonradial oscillations similar to gravity (g) modes observed in isolated WDs. The dwarf nova GW Librae was the first CV in which nonradial oscillations were observed and continues to be the best-studied accreting WD displaying these pulsations. Unlike isolated WDs, accreting WDs rotate rapidly, with spin periods comparable to or shorter than typical low-order oscillation periods. Accreting WDs also have a different relationship between their interior and surface temperatures. The surface temperature of an accreting WD varies on a months-to-year timescale between dwarf nova accretion events, allowing study of how this temperature change affects g-mode behavior. Here we show results from adiabatic seismological calculations for accreting WDs, focusing on low-order (ℓ = 1) modes. We demonstrate how g-modes vary in response to temperature changes in the subsurface layers due to a dwarf nova accretion event. These calculations include rotation nonperturbatively, required by the high spin rate. We discuss the thermal history of these accreting WDs and compare the seismological properties with and without rotation. Comparison of g-mode frequencies to observed objects may allow inference of features of the structure of the WD such as mass, surface abundance, accretion history, and more. The variation of mode frequencies during cooling after an outburst provides a novel method of identifying modes.
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Serykh, Ilya V., i Dmitry M. Sonechkin. "El Niño–Global Atmospheric Oscillation as the Main Mode of Interannual Climate Variability". Atmosphere 12, nr 11 (1.11.2021): 1443. http://dx.doi.org/10.3390/atmos12111443.
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The interannual variability of the global mean monthly anomalies of near-surface air temperature, sea-level pressure, wind speed near the surface, amount of precipitation and total cloudiness was investigated. The amplitudes of the anomalies of these hydrometeorological characteristics between opposite phases of the Global Atmospheric Oscillation (GAO) were calculated. The regional element of the GAO in the tropics of the Indian and Pacific Oceans is the Southern Oscillation. The results show that the oscillations of these characteristics are associated with the GAO not only in the tropical belt of the Earth but also in the middle and high latitudes, especially in the Arctic and northern Eurasia. The physical mechanism by which the transition of the GAO from the negative to the positive phase influences the weakening of the Pacific trade winds, and, as a consequence, the onset of El Niño is described.
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Cummings, D. L., i D. A. Blackburn. "Oscillations of magnetically levitated aspherical droplets". Journal of Fluid Mechanics 224 (marzec 1991): 395–416. http://dx.doi.org/10.1017/s0022112091001817.
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In experiments to measure the surface energy of a magnetically levitated molten metal droplet by observation of its oscillation frequencies, Rayleigh's equation is usually used. This assumes that the equilibrium shape is a sphere, and the surface restoring force is due only to surface tension. This work investigates how the vibrations of a non-rotating liquid droplet are affected by the asphericity and additional restoring forces that the levitating field introduces. The calculations show that the expected single frequency of the fundamental mode is split into either three, when there is an axis of rotational symmetry, or five unequally spaced bands. Frequencies, on average, are higher than those of an unconstrained droplet; the surface tension appears to be increased over its normal value. This requires a small correction to be made in all analyses of surface energy. A frequency sum rule is derived from a simplified model of the magnetic field which allows the corresponding Rayleigh frequency to be evaluated from the observed frequencies of the fundamental and translational modes. A more detailed analysis shows a similar correction but one that is also sensitive to the position of the droplet in the field.
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Limarchenko, O., O. Klimenkov, O. Nefedov i O. Konstantinov. "CHARACTER OF MANIFESTATION OF NONLINEARITIES FOR VIBRATION DISTURBANCE OF MOTION OF ELLIPSOIDAL RESERVOIR WITH LIQUID WITH A FREE SURFACE". Bulletin Taras Shevchenko National University of Kyiv. Mathematics Mechanics, nr 1 (41) (2020): 47–50. http://dx.doi.org/10.17721/1684-1565.2020.01-41.11.47-50.
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The problem with vibration disturbance of the reservoir of ellipsoidal shape, partially filled with a liquid, is under consideration. For the construction of the model, we use the before developed method, based on the use of non-Cartesian parametrization of the domain, occupied by a liquid. And the method of the auxiliary domain for satisfying boundary conditions on tank walls above the unperturbed free surface of a liquid, where the liquid can pass in its perturbed motion. The liquid is considered as ideal incompressible. The mathematical model of the system is constructed based on the variational formulation of the problem in the form of the Hamilton–Ostrogradskiy principle. The motion of a liquid free surface is given in the form of decomposition with respect to normal modes of oscillations. Amplitude parameters of oscillations of a liquid free surface together with parameters of the translational motion of the reservoir form a complete independent system of parameters, for which the resolving system of ordinary differential equations is constructed. The constructed model includes nonlinear properties of the system and corresponds to the model of the combined motion of the liquid with the reservoir. According to its structure, the model has considerable similarities with the case of the cylindrical reservoir. The practical implementation of the method is done for vibration disturbance of the system motion in the horizontal plane for the case of extended and compressed ellipsoidal reservoirs. The analysis of the character of manifestation of the dynamical behavior of the system in different ranges of frequencies of motion disturbance shows that mainly this system behaves as a system with the soft type of nonlinearities. The system output to the steady mode of oscillations is not observed. Modulation of oscillations of a liquid free surface is considerably manifested for most modes. Increased attention is paid to the study of regularities of variation of a period of the oscillation modulation. It was ascertained that due to compression of the spectrum of liquid oscillations with the increase of the wavenumber, the simultaneous considerable effect of several frequencies is manifested in the system reservoir–liquid, which leads to complex modulation envelope lines.
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Buffum, D. H., i S. Fleeter. "The Aerodynamics of an Oscillating Cascade in a Compressible Flow Field". Journal of Turbomachinery 112, nr 4 (1.10.1990): 759–67. http://dx.doi.org/10.1115/1.2927719.
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Fundamental experiments are performed in the NASA Lewis Research Center Transonic Oscillating Cascade Facility to investigate and quantify the aerodynamics of a cascade of bioconvex airfoils executing torsion mode oscillations at realistic reduced frequency values. Both steady and unsteady airfoil surface pressures are measured at two inlet Mach numbers, 0.65 and 0.80. and two incidence angles, 0 and 7 deg, with the harmonic torsional airfoil cascade oscillations at realistic high reduced frequency and unsteady data obtained at several interbladephase angle values. The time-variant pressures are analyzed by means of discrete Fourier transform techniques, with these unique data compared with predictions from a linearized unsteady cascade model. The experimental results indicate that the interblade phase angle has a major effect on the chordwise distributions of the airfoil surface unsteady pressure, with the effects of reduced frequency, incidence angle, and Mach number somewhat less significant.
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Kjeldsen, Hans, i Timothy R. Bedding. "Observations of Solar-Like Oscillations". Highlights of Astronomy 13 (2005): 407–10. http://dx.doi.org/10.1017/s1539299600016051.
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AbstractThe solar-like oscillations are oscillations that are expected to be excited by near-surface convection. Apart from the Sun itself, we now have a number of stars where p-mode solar-like oscillations have been detected. In this paper we present a short presentation of those recently discovered oscillations.
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Nguyen, Duc Ngoc, i Tuan Anh Nguyen. "The Dynamic Model and Control Algorithm for the Active Suspension System". Mathematical Problems in Engineering 2023 (7.02.2023): 1–9. http://dx.doi.org/10.1155/2023/2889435.
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Road surface roughness is the leading cause of vehicle oscillation. The suspension system is used to dampen these oscillations. The active suspension system equipped with a hydraulic actuator is more efficient than the passive one. Therefore, it is used to replace the passive suspension system. The article reviews and analyses models and control algorithms for active suspension systems. In this article, the author mentioned three dynamic models commonly used to simulate vehicle oscillations: a quarter-dynamic model, a half-dynamic model, and a fully dynamic model. Each hydraulic actuator can be considered a state variable in the dynamic model. Besides, the control algorithm for the suspension system is significant. Algorithms like PID (proportional–integral–derivative) and LQR (linear quadratic regulator) will fit the linear model. In contrast, the nonlinear model’s algorithms, such as SMC (sliding mode control), fuzzy, and ANN (artificial neural network), will perform better. Overall, vehicle oscillation can be significantly improved once an active suspension system is used. The contents analysed in this article will be the database for selecting control models and algorithms by other researchers in the future.
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Omelyanov, Oleg. "EXPERIMENTAL EVALUATION OF ENERGY PARAMETERS OF BULK VIBROSEPARATION OF BULK PRODUCTS". Vibrations in engineering and technology, nr 4(103) (24.12.2021): 61–67. http://dx.doi.org/10.37128/2306-8744-2021-4-7.
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The article presents the results of experiments to evaluate vibration parameters when using spatial oscillation excitation drive. Among the main directions of the intensification of the vibration technological action during separation of bulk agricultural products, not only the adjustment of amplitude-frequency characteristics can be noted, but also the improvement of the geometric and structural parameters of the drive mechanisms. Currently, in the processes of separation or classification of bulk masses by the method of siting separation, fixed sieves are displaced by sieves receiving an additional power pulse in order to intensify this processing process. The developed scheme of the drained vibration process involves the oblique location of the working body, which allows to implement the creation of spatial oscillations of the sieve surface. The developed experimental model of the spatial oscillation screen and the studies carried out to obtain graphic dependence of the energy consumption on the process of treating crushed grain material from changes in mass, geometric and structural parameters of the oscillating system. When choosing a rational mode of vibration cutting of bulk products as the evaluation criteria used the eccentricity of the drive shaft, the angle of the tilt surface, the value of the energy consumption and the pattern of its change in the conditions of variation of the power pulse when the eccentricity of the drive shaft, the trajectory of the movement of the sieve elements and the, bulk mass by changing the angle the inclination of the working container, the measurability of the oscillatory movement from the flat to the spatial parameters of the developed vibro-industry, corresponding to the configuration of the structural parameters. Experimental studies have shown the effectiveness of the use of spatial oscillations of the sieve surface during separation of bulk masses, made it possible to substantiate the structural parameters of the vibratory screen.
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Kumar, Pawan. "Excitation of solar acoustic oscillations". Symposium - International Astronomical Union 181 (1997): 287–305. http://dx.doi.org/10.1017/s0074180900061222.
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The stochastic excitation of solar oscillations due to turbulent convection is reviewed. A number of different observational results that provide test for solar p-mode excitation theories are described. I discuss how well the stochastic excitation theory does in explaining these observations. The location and properties of sources that excite solar p-modes are also described. Finally, I discuss why solar g-modes should be linearly stable, and estimate the surface velocity amplitudes of low degree g-modes assuming that they are stochastically excited by the turbulent convection in the sun.
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Schoof, C., C. A. Rada, N. J. Wilson, G. E. Flowers i M. Haseloff. "Oscillatory subglacial drainage in the absence of surface melt". Cryosphere 8, nr 3 (22.05.2014): 959–76. http://dx.doi.org/10.5194/tc-8-959-2014.
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Abstract. The presence of strong diurnal cycling in basal water pressure records obtained during the melt season is well established for many glaciers. The behaviour of the drainage system outside the melt season is less well understood. Here we present borehole observations from a surge-type valley glacier in the St Elias Mountains, Yukon Territory, Canada. Our data indicate the onset of strongly correlated multi-day oscillations in water pressure in multiple boreholes straddling a main drainage axis, starting several weeks after the disappearance of a dominant diurnal mode in August 2011 and persisting until at least January 2012, when multiple data loggers suffered power failure. Jökulhlaups provide a template for understanding spontaneous water pressure oscillations not driven by external supply variability. Using a subglacial drainage model, we show that water pressure oscillations can also be driven on a much smaller scale by the interaction between conduit growth and distributed water storage in smaller water pockets, basal crevasses and moulins, and that oscillations can be triggered when water supply drops below a critical value. We suggest this in combination with a steady background supply of water from ground water or englacial drainage as a possible explanation for the observed wintertime pressure oscillations.
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Schoof, C., C. A. Rada, N. J. Wilson, G. E. Flowers i M. Haseloff. "Oscillatory subglacial drainage in the absence of surface melt". Cryosphere Discussions 7, nr 6 (20.11.2013): 5613–57. http://dx.doi.org/10.5194/tcd-7-5613-2013.
Pełny tekst źródłaStreszczenie:
Abstract. The presence of strong diurnal cycling in basal water pressure records obtained during the melt season is well-established for many glaciers. The behaviour of the drainage system outside the melt season is less well understood. Here we present borehole observations from a surge-type valley glacier in the St Elias Mountains, Yukon Territory, Canada. These indicate the onset of strongly correlated multi-day oscillations in water pressure in multiple boreholes straddling a main drainage axis, starting several weeks after the disappearance of a dominant diurnal mode in August 2011 and persisting until at least January 2012, when multiple data loggers suffered power failure. Jökulhlaups provide a template for understanding spontaneous water pressure oscillations not driven by external supply variability. Using a subglacial drainage model, we show that water pressure oscillations can also be driven on a much smaller scale by the interaction between conduit growth and distributed water storage in smaller water pockets, basal crevasses and moulins, and that oscillations can be triggered when water supply drops below a critical value. We suggest this in combination with a steady background supply of water from groundwater or englacial drainage as a possible explanation for the observed wintertime pressure oscillations.
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Li, Liang, Shenhao Chena, Hongtai Wu i Haitao Cui. "Chaotic, mixed-mode and periodic oscillations during the electro-oxidation of copper in trichloroacetic acid". Journal of the Serbian Chemical Society 69, nr 1 (2004): 33–42. http://dx.doi.org/10.2298/jsc0401033l.
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The current oscillations of a copper electrode in trichloroacetic acid solutions were studied in this paper. The Cu/CCl3COOH system is a new electrochemical oscillator, showing rich dynamic behaviour on two controllable parameters: the trichloroacetic acid concentration (CCCl3COOH) and the imposed potential (E). Phase trajectories were reconstructed from time series using time delaymethods in order that the complex oscillations could be analyzed. Five kinds of oscillations, periodic and quasiperiodic mixed-mode, aperiodic, small amplitude and chaotic current oscillations, were observed. The EDS (energy dispersive spectroscopy) technique was used to analyze the elemental composition of the film formed on the surface of the copper electrode after the current oscillations.
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Boztepe, Tuğba, Ersin Göğüş, Tolga Güver i Kai Schwenzer. "Strengthening the bounds on the r-mode amplitude with X-ray observations of millisecond pulsars". Monthly Notices of the Royal Astronomical Society 498, nr 2 (19.08.2020): 2734–49. http://dx.doi.org/10.1093/mnras/staa2503.
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ABSTRACT R-mode oscillations have been shown to have a significant potential to constrain the composition of fast spinning neutron stars. Due to their high rotation rates, millisecond pulsars (MSPs) provide a unique platform to constrain the properties of such oscillations, if their surface temperatures can be inferred. We present the results of our investigations of archival X-ray data of a number of MSPs, as well as recent XMM–Newton observations of PSR J1810+1744 and PSR J2241−5236. Using the neutron star atmosphere model and taking into account various uncertainties, we present new bounds on the surface temperature of these sources. Thereby, we significantly strengthen previous bounds on the amplitude of the r-mode oscillations in MSPs and find rigorous values as low as α ≲ 3 × 10−9. This is by now about three orders of magnitude below what standard saturation mechanisms in neutron stars could provide, which requires very strong dissipation in the interior, strongly pointing towards a structurally complex or exotic composition of these sources. At such low temperatures, sources could even be outside of the instability region, and taking into account the various uncertainties, we obtain for an observed surface temperature a simple frequency bound below which r-modes are excluded in slower spinning pulsars.
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Hindman, Bradley W., Rekha Jain i Ellen G. Zweibel. "The Surface Amplitudes and Frequencies ofp‐Mode Oscillations in Active Regions". Astrophysical Journal 476, nr 1 (10.02.1997): 392–402. http://dx.doi.org/10.1086/303615.
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Libbrecht, K. G. "Comparison of solar p-mode oscillations in surface brightness and velocity". Astrophysical Journal 359 (sierpień 1990): 232. http://dx.doi.org/10.1086/169054.
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Latković, Olivera, i Attila Cséki. "Modeling non-radial oscillations on components of close binaries". Proceedings of the International Astronomical Union 9, S301 (sierpień 2013): 447–48. http://dx.doi.org/10.1017/s1743921313014981.
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AbstractWe developed an advanced binary system model that includes stellar oscillations on one or both stars, with the goal of mode identification by fitting of the photometric light curves. The oscillations are modeled as perturbations of the local surface temperature and the local gravitational potential. In the case of tidally distorted stars, it is assumed that the pulsation axis coincides with the direction connecting the centers of the components rather than with the rotation axis. The mode identification method, originally devised by B. Bíró, is similar to eclipse mapping in that it utilizes the amplitude, phase and frequency modulation of oscillations during the eclipse; but the identification is achieved by grid-fitting of the observed light curve rather than by image reconstruction. The proposed model and the mode identification method have so far been tested on synthetic data with encouraging results.
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Hill, F. "Helioseismic Data Reduction". Symposium - International Astronomical Union 185 (1998): 13–20. http://dx.doi.org/10.1017/s0074180900238187.
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Helioseismology seeks to infer the properties of the solar interior using measurements of the global normal mode oscillations as a function of spherical harmonic degree l, azimuthal order m, and radial order n as observed on the solar surface. The frequencies, v0(l, m, n), of the modes are influenced by the physical conditions of the solar plasma through which the p-mode (pressure) waves propagate, while the power, P(l, m, n), and line widths, Γ(l, m, n), provide clues about the excitation and damping of the oscillations. These mode parameters are extracted from observations of the solar surface using a long and complex data reduction procedure. It is thus important to precisely describe the steps in the reduction and to assess the influence of the choices on the resulting inferred physical conditions.
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Karachevtseva, L. A., M. T. Kartel, Yu I. Sementsov, O. O. Lytvynenko i O. Yu Sapelnikova. "Hong-Ou-Mandel quantum effect on “expanded graphite - cnts” composites". Himia, Fizika ta Tehnologia Poverhni 14, nr 3 (30.09.2023): 387–92. http://dx.doi.org/10.15407/hftp14.03.387.
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We investigated influence of multiwalled carbon nanotubes (CNTs) on spectral characteristics of composites “thermo-expanded graphite – carbon nanotubes (TEG–CNTs)”. The introduction of CNTs in an amount of 0-3% by weight of TEG composites results in a significant increase in the strength characteristics and thermal stability of the composites. This result indicates that CNTs is ideal filler for composites based on TEG compositions and structures. Measurements the giant two-polar oscillations with very small half-width 0.5 cm–1 testify the strong interaction of surface polaritons with photons. When frequencies of local oscillations of surface bonds of carbon nanotubes and modes along “nanotube-TEG” boundaries matches, then the light absorption increases 102–105 times. Thus, IR absorption with two-polar oscillations was measured at 0% of nanotubes in TEG at frequency of 2750 cm–1. It is own optical mode in the thermally expanded graphite. 5 peaks with two-polar oscillations were measured in the IR absorption spectra at 1% of carbon nanotubes. And 8 peaks with two-polar oscillations were measured at 3 % of carbon nanotubes at optical mode frequencies along the boundaries of thermally expanded graphite - carbon nanotubes. When frequencies of local oscillations of carbon nanotubes and composite’s modes matches, then the light absorption extremely increases (in 102–105 times), and two-polar IR absorption oscillations with negative components are formed. In general, two-photon interference is a result of quantum entanglement of dipole-active oscillations and splitting of photons according to the Hong-Ou-Mendel (HOM) quantum effect. Two-photon entanglement is built on the basis of the most entanglement states, also known as Bell's states. The HOM–quantum effect on composites “expanded graphite-carbon nanotubes” is promising for the development of highly coherent optical quantum computers.
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Enisherlova, Kira L., Lev A. Seidman, Ella M. Temper i Yuliy A. Kontsevoy. "Effect of PECVD SiNx deposition process parameters on electrical properties of SiNx/AlGaN/GaN structures". Modern Electronic Materials 7, nr 2 (30.06.2021): 63–71. http://dx.doi.org/10.3897/j.moem.7.2.73293.
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The effect of parameters of plasma enhanced chemical vapor deposition (PECVD) processes for SiNx film fabrication on the electrical parameters of dielectric/АlGaN/GaN structures has been studied. The effect of growing film composition, additional heterostructure surface treatment with nitrogen plasma before dielectric deposition and HF biasing during treatment on the parameters of the С–V and I–V curves of SiNx/АlGaN/GaN structures has been analyzed. We show that films with nitrogen to silicon concentration ratios of 60 and 40% and a high oxygen content exhibit a decrease in the positive fixed charge in the structures although the I–V curves of the structures exhibit current oscillations. Information has been reported on the effect of PECVD process mode on current oscillation parameters, e.g. period and amplitude, and length of I–V curve section in which oscillations occur. Possible explanation of these oscillations has been suggested. Additional nitrogen plasma treatment of heterostructure surface before monosilane supply to the chamber changes the magnitude and sign of fixed charge and reduces the free carrier concentration in the 2D gas channel of SiNx/АlGaN/GaN heterostructures. Experimental evidence has been provided for the effect of PECVD process parameters and surface preparation on the electrical parameters of the heterostructures grown.
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Misra, Sambit, Harry Dankowicz i Mark R. Paul. "Event-driven feedback tracking and control of tapping-mode atomic force microscopy". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 464, nr 2096 (15.04.2008): 2113–33. http://dx.doi.org/10.1098/rspa.2007.0016.
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This paper presents an event-driven, discrete-in-time feedback strategy for tracking and stabilizing naturally occurring periodic oscillations in the probe-tip dynamics of atomic force microscope (AFM) cantilevers in tapping-mode operation. Specifically, robust dynamic tracking and stabilization is achieved by the imposition of discrete changes in the vertical offset between the cantilever support and the sample surface based on an estimated linearization of the system dynamics about a dynamically generated reference trajectory. Here, use is made not only of the oscillation amplitude, as is typical in commercial control implementations for AFMs, but also of the instantaneous phase information. It is shown that stabilization and desirable performance during surface scanning is possible, even in the presence of uncertainty and limited state access. In particular, the methodology enables robust tracking and use of low-contact-velocity periodic system responses that are unstable in the absence of control.
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Zhang, Baiyi, Guobiao Cai, Bijiao He, Kai Zhang, Hongru Zheng i Weizong Wang. "Plume neutralization of an ionic liquid electrospray thruster: better insights from particle-in-cell modelling". Plasma Sources Science and Technology 30, nr 12 (1.12.2021): 125009. http://dx.doi.org/10.1088/1361-6595/ac3e7f.
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Abstract Ionic liquid electrospray thrusters with high specific impulse, high thrust accuracy and low thrust noise are very promising for space gravitational wave detection missions. The plume, which may lead to surface charging of solar panels and sensitive spacecraft components is a great concern for the applications of electrospray thruster. Therefore, this paper investigates the plume neutralization process of the ionic liquid electrospray thruster through fully kinetic particle-in-cell simulations. The unipolarity operation mode is firstly simulated and compared with the experimental measurements. The bipolar operation mode is analyzed by considering the premixing and the separation of positive and negative ion beams. At the same time, the effect of beam spacing on the plume characteristics is investigated. The results show that the plume neutralization of the ionic liquid electrospray thruster is achieved by the spatial and temporal oscillations of the ion beams. In the horizontal direction, the spatial oscillations are caused by the different mass and hence velocities of positive and negative ions. In the vertical direction, the spatial oscillations are mainly because of the non-zero beam spacing. The temporal oscillations may be related to the tradition plasma oscillation. As the beam spacing increases, the oscillation amplitude of the horizontal electric potential curve changes scarcely; however, in the vertical direction, the oscillation amplitude of the curve increases. The ion temperature goes up with the beam spacing and the deviation of the temperature of beam ions does not exceed 15 eV in the horizontal direction but exceeds 100 eV in the vertical direction. Moreover, the plume divergence half angle and the beam spacing are positively correlated, suggesting that the ionic electrospray thrusters with positive and negative polarity need to be placed as close as possible in the spacecraft.
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Miyama, Toru, Julian P. McCreary, Debasis Sengupta i Retish Senan. "Dynamics of Biweekly Oscillations in the Equatorial Indian Ocean*". Journal of Physical Oceanography 36, nr 5 (1.05.2006): 827–46. http://dx.doi.org/10.1175/jpo2897.1.
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Abstract Variability of the wind field over the equatorial Indian Ocean is spread throughout the intraseasonal (10–60 day) band. In contrast, variability of the near-surface υ field in the eastern, equatorial ocean is concentrated at biweekly frequencies and is largely composed of Yanai waves. The excitation of this biweekly variability is investigated using an oceanic GCM and both analytic and numerical versions of a linear, continuously stratified (LCS) model in which solutions are represented as expansions in baroclinic modes. Solutions are forced by Quick Scatterometer (QuikSCAT) winds (the model control runs) and by idealized winds having the form of a propagating wave with frequency σ and wavenumber kw. The GCM and LCS control runs are remarkably similar in the biweekly band, indicating that the dynamics of biweekly variability are fundamentally linear and wind driven. The biweekly response is composed of local (nonradiating) and remote (Yanai wave) parts, with the former spread roughly uniformly along the equator and the latter strengthening to the east. Test runs to the numerical models separately forced by the τx and τy components of the QuikSCAT winds demonstrate that both forcings contribute to the biweekly signal, the response forced by τy being somewhat stronger. Without mixing, the analytic spectrum for Yanai waves forced by idealized winds has a narrowband (resonant) response for each baroclinic mode: Spectral peaks occur whenever the wavenumber of the Yanai wave for mode n is sufficiently close to kw and they shift from biweekly to lower frequencies with increasing modenumber n. With mixing, the higher-order modes are damped so that the largest ocean response is restricted to Yanai waves in the biweekly band. Thus, in the LCS model, resonance and mixing act together to account for the ocean's favoring the biweekly band. Because of the GCM's complexity, it cannot be confirmed that vertical mixing also damps its higher-order modes; other possible processes are nonlinear interactions with near-surface currents, and the model's low vertical resolution below the thermocline. Test runs to the LCS model show that Yanai waves from several modes superpose to form a beam (wave packet) that carries energy downward as well as eastward. Reflections of such beams from the near-surface pycnocline and bottom act to maintain near-surface energy levels, accounting for the eastward intensification of the near-surface, equatorial υ field in the control runs.
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Philidet, J., K. Belkacem i M. J. Goupil. "Coupling between turbulence and solar-like oscillations: A combined Lagrangian PDF/SPH approach". Astronomy & Astrophysics 664 (sierpień 2022): A164. http://dx.doi.org/10.1051/0004-6361/202142947.
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Context. The ever-increasing quality of asteroseismic measurements offers a unique opportunity to use the observed global acoustic modes to infer the physical properties of stellar interiors. In solar-like oscillators, the finite lifetime of the modes allows their amplitudes and linewidths to be estimated, which provide invaluable information on the highly turbulent motions at the top of the convective envelope. But exploiting these observables requires a realistic theoretical framework for the description of the turbulence–oscillation coupling. Aims. The first paper of this series established a linear stochastic wave equation for solar-like p-modes, correctly taking the effect of turbulence thereon into account. In this second paper, we aim at deriving simultaneous expressions for the excitation rate, damping rate, and modal surface effect associated with any given p-mode, as an explicit function of the statistical properties of the turbulent velocity field. Methods. We reduce the stochastic wave equation to complex amplitude equations for the normal oscillating modes of the system. We then derive the equivalent Fokker-Planck equation that governs the evolution of the probability density function jointly associated with the real amplitudes and phases of all the oscillating modes of the system simultaneously. The effect of the finite-memory time of the turbulent fluctuations (comparable to the period of the modes) on the modes themselves is consistently and rigorously accounted for, by means of the simplified amplitude equation formalism. This formalism accounts for mutual linear mode coupling in full, and we then turn to the special single-mode case. This allows us to derive evolution equations for the mean energy and mean phase of each mode, from which the excitation rate, the damping rate, and the modal surface effect naturally arise. Results. The expressions obtained here (1) are written as explicit functions of the statistical properties of turbulence, thus allowing for any prescription thereof to be tested against observations, (2) include the contribution of the turbulent dissipation more realistically, and (3) concern the excitation rate, the damping rate, and the modal surface effect of the modes simultaneously. We show that the expression for the excitation rate of the modes is identical to previous results obtained through a different modelling approach, thus supporting the validity of the formalism presented here. We also recover the fact that the damping rate and modal surface effect correspond to the real and imaginary part of the same single complex quantity. We explicitly separate the different physical contributions to these observables, in particular the turbulent pressure contribution and the joint effect of the pressure-rate-of-strain correlation and the turbulent dissipation. We show that the former dominates for high-frequency modes and the latter for low-frequency modes. To illustrate the usefulness of this formalism, we apply it to a simplified case where we can quantify the relative importance of these two contributions, and in particular the threshold between the two frequency regimes, as a function of the turbulent frequency and the degree of anisotropy of both the Reynolds-stress tensor and the dissipation of turbulent energy. Conclusions. The formalism developed in these first two papers, applied to the case of a simplified Lagrangian stochastic model for proof-of-concept purposes, indeed proves to be viable, relevant, and useful for addressing the issue of turbulence–oscillation coupling in the context of solar-like oscillators. It opens the door to subsequent studies physically more appropriate to the stellar case. It will also allow, once mode coupling is included (i.e. by going beyond the single-mode case), for a realistic description of mode-mode scattering and its influence on mode damping, mode frequency, and the energy distribution across the solar p-mode eigenspectrum.
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BRACK, M., P. WINKLER i M. V. N. MURTHY. "COUPLING OF SURFACE AND VOLUME DIPOLE OSCILLATIONS IN C60 MOLECULES". International Journal of Modern Physics E 17, nr 01 (styczeń 2008): 138–50. http://dx.doi.org/10.1142/s021830130800963x.
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We first give a short review of the "local-current approximation" (LCA), derived from a general variation principle, which serves as a semiclassical description of strongly collective excitations in finite fermion systems starting from their quantum-mechanical mean-field ground state. We illustrate it for the example of coupled translational and compressional dipole excitations in metal clusters. We then discuss collective electronic dipole excitations in C 60 molecules (Buckminster fullerenes). We show that the coupling of the pure translational mode ("surface plasmon") with compressional volume modes in the semiclasscial LCA yields semi-quantitative agreement with microscopic time-dependent density functional (TDLDA) calculations, while both theories yield qualitative agreement with the recent experimental observation of a "volume plasmon".
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Acosta, Pedro R. "Stability Analysis of a Class of Second Order Sliding Mode Control Including Delay in Input". Mathematical Problems in Engineering 2013 (2013): 1–9. http://dx.doi.org/10.1155/2013/523527.
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This paper deals with a class of second order sliding mode systems. Based on the derivative of the sliding surface, sufficient conditions are given for stability. However, the discontinuous control signal depend neither on the derivative of sliding surface nor on its estimate. Time delay in control input is also an important issue in sliding mode control for engineering applications. Therefore, also sufficient conditions are given for the time delay size on the discontinuous input signal, so that this class of second order sliding mode systems might have amplitude bounded oscillations. Moreover, amplitude of such oscillations may be estimated. Some numerical examples are given to validate the results. At the end, some conclusions are given on the possibilities of the results as well as their limitations.
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Pedersen, May G. "Internal Rotation and Inclinations of Slowly Pulsating B Stars: Evidence of Interior Angular Momentum Transport". Astrophysical Journal 940, nr 1 (1.11.2022): 49. http://dx.doi.org/10.3847/1538-4357/ac947f.
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Abstract One of the largest uncertainties in stellar structure and evolution theory is the transport of angular momentum in the stellar interiors. Asteroseismology offers a powerful tool for measuring the internal rotation frequencies of pulsating stars, but the number of such measurements has remained few for ≳3 M ⊙ main-sequence stars. In this work, we compile a list of 52 slowly pulsating B stars for which the interior rotation has been measured asteroseismically. The measurements of the spin parameters, which describe the relative importance of rotation, for the gravito-inertial mode oscillations show that for 40 of the stars the oscillations fall within the subinertial regime. We find that the core rotation frequencies of the stars decrease as a function of age and show evidence of angular momentum transport occurring on the main sequence. Finally, we derive the inclination angles of the stars, showing that they are generally consistent with the expectations from surface cancellation effects for the given oscillation modes.
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DIJKSTRA, HENK A., i M. JEROEN MOLEMAKER. "Symmetry breaking and overturning oscillations in thermohaline-driven flows". Journal of Fluid Mechanics 331 (25.01.1997): 169–98. http://dx.doi.org/10.1017/s0022112096003874.
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The bifurcation structure of thermohaline-driven flows is studied within one of the simplest zonally averaged models which captures thermohaline transport: a Boussinesq model of surface-forced thermohaline flow in a two-dimensional rectangular basin. Under mixed boundary conditions, i.e. prescribed surface temperature and fresh-water flux, it is shown that symmetry breaking originates from a codimension-two singularity which arises through the intersection of the paths of two symmetry-breaking pitchfork bifurcations. The physical mechanism of symmetry breaking of both the thermally and salinity dominated symmetric solution is described in detail from the perturbation structures near bifurcation. Limit cycles with an oscillation period in the order of the overturning time scale arise through Hopf bifurcations on the branches of asymmetric steady solutions. The physical mechanism of oscillation is described in terms of the most unstable mode just at the Hopf bifurcation. The occurrence of these oscillations is quite sensitive to the shape of the prescribed fresh-water flux. Symmetry breaking still occurs when, instead of a fixed temperature, a Newtonian cooling condition is prescribed at the surface. There is only quantitative sensitivity, i.e. the positions of the bifurcation points shift with the surface heat transfer coefficient. There are no qualitative changes in the bifurcation diagram except in the limit where both the surface heat flux and fresh-water flux are prescribed. The bifurcation structure at large aspect ratio is shown to converge to that obtained by asymptotic theory. The complete structure of symmetric and asymmetric multiple equilibria is shown to originate from a codimension-three bifurcation, which arises through the intersection of a cusp and the codimension-two singularity responsible for symmetry breaking.