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1
Xu, Jun, Zongjun Ning, Dong Li, Fanpeng Shi, Yuxiang Song e Yuzhi Yang. "An Investigation of the Loop Oscillations after a Solar Flare". Universe 10, n. 5 (29 aprile 2024): 201. http://dx.doi.org/10.3390/universe10050201.
Testo completoAbstract (sommario):
We study the loop oscillations after a solar flare on 19 January 2023, in the active region N11E40 3196, which is well observed by the SDO/AIA. After tracing the loop position and fitting, we find that the loop oscillations have a period between 3 and 9 min at various locations, such as from the leg to the top or from the inner to the outer loop. Their oscillating amplitudes decrease with time. Two loops display the position oscillation simultaneously with their brightness oscillation. After the analysis of the differential emission measure (DEM), we find that two of their loop position oscillations resulted from the plasma density fluctuation. Meanwhile, it is interesting that the brightness of these two position oscillations displays a typical period of about 4 min, similar to that of the position oscillation. This is possible due to both the plasma density and temperature fluctuation there. Our findings provide the physical clues for studying and understanding the mechanism of the loop position and brightness oscillations.
2
Klimov, Alexandr V., e 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, n. 1 (24 giugno 2023): 87–96. http://dx.doi.org/10.17816/2074-0530-115233.
Testo completoAbstract (sommario):
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.
3
SHUKLA, P. K. "Amplification of neutrino oscillations by a density ripple in dense plasmas". Journal of Plasma Physics 77, n. 3 (21 gennaio 2011): 289–91. http://dx.doi.org/10.1017/s002237781000070x.
Testo completoAbstract (sommario):
AbstractIt is shown that a pre-existing electron density ripple in a dense plasma can excite electron neutrino oscillations. For our purposes, we use the dispersion relation for neutrino oscillations and derive the Mathieu equation for the propagation of neutrino oscillations in the presence of a spatially oscillating electron density ripple. The Mathieu equation predicts instability of neutrino oscillations. The criterion under which instability occurs is presented. Analytical expressions for the neutrino oscillation frequency and the growth rate are obtained. The possible relevance of our investigation to non-thermal neutrino oscillations in dense plasma environments (e.g. the supernovae, the core of white dwarf stars etc.) is briefly mentioned.
4
Dolgopolov, S. I. "Mathematical simulation of hard excitation of cavitation self-oscillations in a liquid-propellant rocket engine feed system". Technical mechanics 2021, n. 1 (30 aprile 2021): 29–36. http://dx.doi.org/10.15407/itm2021.01.029.
Testo completoAbstract (sommario):
Hard self-oscillation excitation differs from soft excitation in that self-oscillations are set up only if the initial departure of an oscillating system from equilibrium is strong enough. Experimental studies of cavitation oscillations in hydraulic systems with cavitating pumps of liquid-propellant rocket engines ((LPREs) include works that describe hard excitation of cavitation oscillations. By mow, hard excitation regimes have not been explained theoretically, to let alone their mathematical simulation. This paper presents a mathematical model of hard excitation of cavitation oscillations in a LPRE feed system, which comprises a mathematical model of cavitation self-oscillations in a LPRE feed system that accounts for pump choking and an external disturbance model. A mechanism of hard excitation of cavitation oscillations in a LPRE feed system is proposed. It is well known that hard excitation of cavitation self-oscillations may take place in cases where the pump feed system is near the boundary of the cavitation self-oscillation region. In this case, the self-oscillation amplitudes are small, and they are limited only by one nonlinearity (cavity volume vs. pump inlet pressure and flow relationship). Under excitation of sufficient intensity, the pump inlet pressure and flow find themselves in the choking characteristic; this may be responsible for choking and developed cavitation self-oscillations, which remain of interrupted type and do not go into the initial small-amplitude oscillations even after excitation removal. A mathematical simulation of hard excitation of cavitation self-oscillations was conducted to determine the parameters of cavitation self-oscillations in a bench feed system of a test pump. The simulation results show that without an external disturbance the pump system exhibits small-amplitude self-oscillations. On an external disturbance, developed (interrupted) cavitation oscillations are set up in the system, which is in agreement with experimental data. The proposed mathematical model of hard excitation of cavitation self-oscillations in a LPRE feed system allows one to simulate a case observed in an experiment in which it was possible to eliminate cavitation self-oscillations by an external disturbance.
5
Li, Xiuchen, Jie Li, Zhaohui Zheng, Jinni Deng, Yi Pan e Xiaobin Ding. "A self-oscillating gel system with complex dynamic behavior based on a time delay between the oscillations". Soft Matter 18, n. 3 (2022): 482–86. http://dx.doi.org/10.1039/d1sm01635k.
Testo completoAbstract (sommario):
A series of self-oscillating gels with different cross-linking densities are designed and fabricated. Due to the time delay between chemical and mechanical oscillation, they exhibit different oscillating behaviors. The disrupted mechanical oscillations tend to be regular and periodic under inhibited conditions.
6
Li, Shubo, Chengxun Yuan, Iya P. Kurlyandskaya, V. I. Demidov, M. E. Koepke, Jingfeng Yao e Zhongxiang Zhou. "Measurements of fluctuating electron temperature and space potential in a magnetized plasma with a single magnetically insulated baffled probe (MIBP)". Plasma Sources Science and Technology 31, n. 3 (1 marzo 2022): 037001. http://dx.doi.org/10.1088/1361-6595/ac5228.
Testo completoAbstract (sommario):
Abstract A single magnetically insulated baffled probe (MIBP) was used to study the potential and electron temperature oscillations in a magnetized plasma. It was shown, that, although the MIBP cluster allows a more detailed study of such oscillations, the single MIBP may provide useful information about the oscillation amplitudes and, in some cases, cross-coherency and cross-phase. These quantities can characterize oscillations and distinguish co-oscillating plasma parameters in cases where the placing of a MIBP cluster in a plasma is difficult or impossible. For the reported plasma case, in which there are two types of oscillations, it is shown how to determine the maximum and minimum possible values of the electron temperature fluctuations. Detailed analysis showed that, in the studied plasma, there are two types of oscillations, both incoherent with each other.
7
Hehner, Marc T., Davide Gatti, Marios Kotsonis e Jochen Kriegseis. "Effects of actuation mode on plasma-induced spanwise flow oscillations". Journal of Physics D: Applied Physics 55, n. 20 (22 febbraio 2022): 205203. http://dx.doi.org/10.1088/1361-6463/ac526b.
Testo completoAbstract (sommario):
Abstract Two different plasma actuation strategies for producing near-wall flow oscillations, namely the burst-modulation and beat-frequency mode, are characterized with planar particle image velocimetry in quiescent air. Both concepts are anticipated to work as non-mechanical surrogates of oscillating walls aimed at turbulent flow drag reduction, with the added benefit of no moving parts, as the fluid is purely manipulated by plasma-generated body forces. The current work builds upon established flow-control and proof-of-concept demonstrators, as such, delivering an in-depth characterization of cause and impact of the plasma-induced flow oscillations. Various operational parameter combinations (oscillation frequency, duty cycle and input body force) are investigated. A universal performance diagram that is valid for plasma-based oscillations, independent of the actuation concept is derived. Results show that selected combinations of body force application methods suffice to reproduce oscillating wall dynamics from experimental data. Accordingly, the outcomes of this work can be exploited to create enhanced actuation models for numerical simulations of plasma-induced flow oscillations, by considering the body force as a function of the oscillation phase. Furthermore, as an advantage over physically displaced walls, the exerted body force appears not to be hampered by resonances and therefore remains constant independent of the oscillation frequency. Hence, the effects of individual parameter changes on the plasma actuator performance and fluid response as well as strategies to avoid undesired effects can be determined.
8
Shulaev, N. S., G. F. Efimova e A. Z. Abdullaev. "STUDY OF AN OSCILLATING CHARGE IN A DIPOLE-QUADRUPOLE SYSTEM". Petroleum Engineering 21, n. 1 (15 maggio 2023): 178–82. http://dx.doi.org/10.17122/ngdelo-2023-1-178-182.
Testo completoAbstract (sommario):
The solution of the problem of determining the magnitude of the component of the electric field intensity vector generated by an oscillating charge in a dipole-quadrupole system in a homogeneous medium is obtained. Two mutually perpendicular directions of charge oscillations in a cylindrical coordinate system are considered. From the analysis of the obtained dependences for the oscillation frequencies, it can be seen that in the first case, the frequency of «vertical» oscillations exceeds the frequency of «horizontal» oscillations. Knowing the maximum and minimum frequencies of the oscillating charge radiation spectrum, it is possible to calculate the molecular parameters. The analysis of the parameters of the radiation spectrum of a harmonically oscillating charge performing a non-relativistic motion can be used in the analysis of the electromagnetic radiation spectra of atoms and molecules in an excited state, as well as the parameters of the crystal lattice.
9
Kohutova, P., e A. Popovas. "Excitation and evolution of coronal oscillations in self-consistent 3D radiative MHD simulations of the solar atmosphere". Astronomy & Astrophysics 647 (marzo 2021): A81. http://dx.doi.org/10.1051/0004-6361/202039491.
Testo completoAbstract (sommario):
Context. Solar coronal loops are commonly subject to oscillations. Observations of coronal oscillations are used to infer physical properties of the coronal plasma using coronal seismology. Aims. Excitation and evolution of oscillations in coronal loops is typically studied using highly idealised models of magnetic flux tubes. In order to improve our understanding of coronal oscillations, it is necessary to consider the effect of realistic magnetic field topology and evolution. Methods. We study excitation and evolution of coronal oscillations in three-dimensional (3D) self-consistent simulations of solar atmosphere spanning from the convection zone to the solar corona using the radiation-magnetohydrodynamic (MHD) code Bifrost. We use forward-modelled extreme-ultraviolet emission and 3D tracing of magnetic field to analyse the oscillatory behaviour of individual magnetic loops. We further analyse the evolution of individual plasma velocity components along the loops using wavelet power spectra to capture changes in the oscillation periods. Results. Various types of oscillations commonly observed in the corona are present in the simulation. We detect standing oscillations in both transverse and longitudinal velocity components, including higher-order oscillation harmonics. We also show that self-consistent simulations reproduce the existence of two distinct regimes of transverse coronal oscillations: rapidly decaying oscillations triggered by impulsive events and sustained small-scale oscillations showing no observable damping. No harmonic drivers are detected at the footpoints of oscillating loops. Conclusions. Coronal loop oscillations are abundant in self-consistent 3D MHD simulations of the solar atmosphere. The dynamic evolution and variability of individual magnetic loops suggest that we need to re-evaluate our models of monolithic and static coronal loops with constant lengths in favour of more realistic models.
10
W. Hussein, Mohammed, e Kadhim A. Al-Asadi. "Synchronous Impact of the North Atlantic Oscillation (NAO) and Southern Oscillation Index (SOI( Poles on Temperature and Rain Over Iraq". Israa University Journal for Applied Science 7, n. 1 (1 ottobre 2023): 290–302. http://dx.doi.org/10.52865/exzs7896.
Testo completoAbstract (sommario):
Background: This study is an attempt to analyze the correlation of the impact of the North Atlantic Oscillation( NAO )and Southern Oscillation Index( SOI ) on the climate of Iraq. Method: This has been conducted based on the highest and lowest recorded values of the mentioned oscillations. The values of temperature and rain for the stations of Mosul, Baghdad, Rutba, Basrah and for a major climatic cycle from 1950-2018 were also relied upon. On the statistical analytical approach to find the correlation relationship between the studied oscillations and depending on the Pearson Correlation Coefficient. Results: The results brought to light that there is a strong and statistically significant correlation between the oscillations. The time series of oscillations were also analyzed during the fall season, due to the absence of a single effect of oscillations on the studied elements. Therefore, the analysis of the simultaneous behavior of oscillations on the climatic elements during the autumn was relied upon. In the meantime, four cases of simultaneous behavior for selected years of the study were found, recording the highest oscillations’ values. Such four cases were compared with the values of the elements for those years. Conclusion: It became clear from the four cases that there are two cases that show a regular behavior of the influence, as it became clear when the poles are NAO +, SOI - and vice versa that the climatic elements are affected more clearly with the oscillation's indicators and that the climate of Iraq has become more affected by the oscillations.
11
Mitura, Z., S. L. Dudarev e M. J. Whelan. "Theoretical Investigations of RHEED Oscillations". Microscopy and Microanalysis 5, S2 (agosto 1999): 710–11. http://dx.doi.org/10.1017/s1431927600016871.
Testo completoAbstract (sommario):
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.
12
Chon, Ki H., Ramakrishna Raghavan, Yu-Ming Chen, Donald J. Marsh e Kay-Pong Yip. "Interactions of TGF-dependent and myogenic oscillations in tubular pressure". American Journal of Physiology-Renal Physiology 288, n. 2 (febbraio 2005): F298—F307. http://dx.doi.org/10.1152/ajprenal.00164.2004.
Testo completoAbstract (sommario):
We have previously shown that there are two oscillating components in spontaneously fluctuating single-nephron blood flow obtained from Sprague-Dawley rats (Yip K-P, Holstein-Rathlou NH, and Marsh DJ. Am J Physiol Renal Physiol 264: F427–F434, 1993). The slow oscillation (20–30 mHz) is mediated by tubuloglomerular feedback (TGF), whereas the fast oscillation (100 mHz) is probably related to spontaneous myogenic activity. The fast oscillation is rarely detected in spontaneous tubular pressure because of its small magnitude and the fact that tubular compliance filters pressure waves. We detected myogenic oscillation superimposed on TGF-mediated oscillation when ambient tubular flow was interrupted. Two well-defined peaks are present in the mean power spectrum of stop-flow pressure (SFP) centering at 25 and 100 mHz ( n = 13), in addition to a small peak at 125–130 mHz. Bispectral analysis indicates that two of these oscillations (30 and 100 mHz) interact nonlinearly to produce the third oscillation at 125–130 mHz. The presence of nonlinear interactions between TGF and myogenic oscillations indicates that estimates of the relative contribution of each of these mechanisms in renal autoregulation need to account for this interaction. The magnitude of myogenic oscillations was considerably smaller in the SFP measured from spontaneously hypertensive rats (SHR, n = 13); consequently, nonlinear interactions were not observed with bispectral analysis. Reduced augmentation of myogenic oscillations in SFP of SHR might account for the failure in detecting nonlinear interactions in SHR.
13
Lizunov, Petro, e Valentyn Nedin. "Transmission shafts vibrations in transient rotating modes". Strength of Materials and Theory of Structures, n. 110 (26 giugno 2023): 229–37. http://dx.doi.org/10.32347/2410-2547.2023.110.229-237.
Testo completoAbstract (sommario):
The paper presents the investigation results of the transmission shaft dynamic behavior in transient modes of motion with change of the rotational speeds. Such modes occur during the transmission shaft transmits torque from engine to executive device. This process can be accompanied by vibration with change of frequency and amplitude of shaft oscillation. Therefore, the question of studying the dynamic behavior of such systems with identifying the impact of rotational speeds changing on them is relevant. In this regard, the study was done by developed software, in which a technique of computer simulation of the oscillating motion of considerable rotating rods under the action of inertia forces is implemented. Such software gives the possibility to model the oscillatory motion of rotating rods and determine the parameters by which the dynamic stability loss of the studying system can occur. Using this software, the diagrams of rod oscillating motion of the rotating shaft were drawn for definite parameters of the considered system. The process of oscillation is considered in space. The mathematical model of transverse oscillations is described by system of differential equations in rotating coordinate system that is tied to the shaft, but diagrams of oscillations is shown in inertial coordinate system. It is shown that when the speed of rotation changes, namely at the time interval of its increase, this process continues with growth of oscillation frequency during the acceleration time. Also shown that the amplitude of oscillations increases, too. After pass to next constant speed of rotation, the frequency of oscillations, as shown in diagrams, decreases back. Such increase of oscillation frequency during the acceleration can lead to undesirable consequences of destructive nature.
14
Ханин, Ю. Н., e Е. Е. Вдовин. "Квантовые осцилляции релаксации фотопроводимости в p-i-n-гетеродиодах GaAs/InAs/AlAs". Физика и техника полупроводников 52, n. 6 (2018): 591. http://dx.doi.org/10.21883/ftp.2018.06.45921.8679.
Testo completoAbstract (sommario):
AbstractThe photoconductivity and its relaxation characteristics in tunneling p – i – n GaAs/AlAs heterostructures under pulsed illumination is studied. Quantum oscillations in the photoconductivity are detected depending on the bias voltage with the period independent of the light wavelength, as well as an oscillating component of the relaxation curves caused by modulation of the recombination rate at the edge of a triangular quantum well in the undoped i layer, as in the case of photoconductivity oscillations. The common nature of oscillations of the steady-state photoconductivity and relaxation curves under pulsed illumination is directly confirmed by the lack of an oscillating component in both types of dependences of some studied p–i–n heterostructures. Simultaneous suppression of the observed oscillations of dependences of both types as the temperature increases to 80 K also confirms the proposed mechanism of their formation. The dependences of these oscillations on the magnetic field and light flux power are studied. Oscillation-amplitude suppression in a magnetic field of ~2 T perpendicular to the current is caused by the effect of the Lorentz force on the ballistic motion of carriers in the triangular-quantum-well region.
15
Singh, Vasundhara, Prakash Srirangam e Gour Gopal Roy. "Effect of Beam Oscillation on Microstructure and Mechanical Properties of Electron Beam Welded EN25 Steel". Materials 16, n. 7 (29 marzo 2023): 2717. http://dx.doi.org/10.3390/ma16072717.
Testo completoAbstract (sommario):
EN25 steels have been found to be applicable in shafts, gears, etc., but welding of EN25 steel was performed using electron beam welding with different oscillation beam diameters varying from 2 mm to 0.5 mm. The present study reports the effect of beam oscillation on the evolution of nonmetallic inclusions, microstructures, and mechanical properties of EN25 steel. Heat input calculations showed that the application of beam oscillations resulted in significantly lower heat inputs compared to their non-oscillating counterparts. The highest fraction of the retained austenite (9.35%) was observed in a weld prepared with beam oscillation at a 2-mm oscillation diameter, and it decreased to 3.27% at an oscillating diameter of 0.5 mm, and it further reduced to 0.36% for non-oscillating beam cases. Residual stresses were compressive in the fusion zone, irrespective of beam oscillation. Beam oscillation resulted in equiaxed grain in the recenter region of the fusion zone, attributed to heat mixing and the evolution of random texture. The application of beam oscillations resulted in a significant decrease in the size of the nonmetallic inclusions to 0.1–0.5 compared to 5–20 mm in base metal. All tensile samples failed in the base metal, indicating good strength of the weld. Fusion zone hardness (250–670 HNV) and wear properties (COF 0.7 to COF 0.45) improved irrespective of with and without beam oscillation.
16
Bathellier, Brice, Alan Carleton e Wulfram Gerstner. "Gamma Oscillations in a Nonlinear Regime: A Minimal Model Approach Using Heterogeneous Integrate-and-Fire Networks". Neural Computation 20, n. 12 (dicembre 2008): 2973–3002. http://dx.doi.org/10.1162/neco.2008.11-07-636.
Testo completoAbstract (sommario):
Fast oscillations and in particular gamma-band oscillation (20–80 Hz) are commonly observed during brain function and are at the center of several neural processing theories. In many cases, mathematical analysis of fast oscillations in neural networks has been focused on the transition between irregular and oscillatory firing viewed as an instability of the asynchronous activity. But in fact, brain slice experiments as well as detailed simulations of biological neural networks have produced a large corpus of results concerning the properties of fully developed oscillations that are far from this transition point. We propose here a mathematical approach to deal with nonlinear oscillations in a network of heterogeneous or noisy integrate-and-fire neurons connected by strong inhibition. This approach involves limited mathematical complexity and gives a good sense of the oscillation mechanism, making it an interesting tool to understand fast rhythmic activity in simulated or biological neural networks. A surprising result of our approach is that under some conditions, a change of the strength of inhibition only weakly influences the period of the oscillation. This is in contrast to standard theoretical and experimental models of interneuron network gamma oscillations (ING), where frequency tightly depends on inhibition strength, but it is similar to observations made in some in vitro preparations in the hippocampus and the olfactory bulb and in some detailed network models. This result is explained by the phenomenon of suppression that is known to occur in strongly coupled oscillating inhibitory networks but had not yet been related to the behavior of oscillation frequency.
17
Kozlov, Victor, Stanislav Subbotin e Ivan Karpunin. "Supercritical Dynamics of an Oscillating Interface of Immiscible Liquids in Axisymmetric Hele-Shaw Cells". Fluids 8, n. 7 (12 luglio 2023): 204. http://dx.doi.org/10.3390/fluids8070204.
Testo completoAbstract (sommario):
The oscillation of the liquid interface in axisymmetric Hele-Shaw cells (conical and flat) is experimentally studied. The cuvettes, which are thin conical layers of constant thickness and flat radial Hele-Shaw cells, are filled with two immiscible liquids of similar densities and a large contrast in viscosity. The axis of symmetry of the cell is oriented vertically; the interface without oscillations is axially symmetric. An oscillating pressure drop is set at the cell boundaries, due to which the interface performs radial oscillations in the form of an oscillating “tongue” of a low-viscosity liquid, periodically penetrating into a more viscous liquid. An increase in the oscillation amplitude leads to the development of a system of azimuthally periodic structures (fingers) at the interface. The fingers grow when the viscous liquid is forced out of the layer and reach their maximum in the phase of maximum displacement of the interface. In the reverse course, the structures decrease in size and, at a certain phase of oscillations, take the form of small pits directed toward the low-viscosity fluid. In a conical cell, a bifurcation of period doubling with an increase in amplitude is found; in a flat cell, it is absent. A slow azimuthal drift of finger structures is found. It is shown that the drift is associated with the inhomogeneity of the amplitude of fluid oscillations in different radial directions. The fingers move from the region of a larger to the region of a lower amplitude of the interface oscillations.
18
Zhileykin, Mikhail M., Pavel V. Sirotin, Sergey S. Nosikov e 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, n. 1 (23 maggio 2023): 39–48. http://dx.doi.org/10.17816/0321-4443-321266.
Testo completoAbstract (sommario):
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.
19
Nakariakov, Valery M., e Naga V. Yelagandula. "Damping Scenarios of Kink Oscillations of Solar Coronal Loops". Universe 9, n. 2 (11 febbraio 2023): 95. http://dx.doi.org/10.3390/universe9020095.
Testo completoAbstract (sommario):
The transition from the large-amplitude rapidly-decaying regime of kink oscillations of plasma loops observed in the corona of the Sun to the low-amplitude decayless oscillations is modelled. In this study, the decayless regime is associated with the energy supply from coronal plasma flows, i.e., self-oscillations, or random movements of footpoints of the oscillating loop. The damping is attributed to the linear effect of resonant absorption. We demonstrate that the decay of an impulsively excited kink oscillation to the self-oscillatory stationary amplitude differs from the exponential decay. The damping time is found to depend on the oscillation amplitude to the power of a negative constant whose magnitude is less than unity. In this scenario, a better model for the damping seems to be super-exponential. In the separately considered case of the decayless oscillatory regime supported by a random driver, the oscillation amplitude experiences an exponential decay to the decayless level. Implications of this finding for magnetohydrodynamic seismology of the solar corona based on the effect of resonant absorption are discussed.
20
Vrublevskyi, Ihor. "INCREASING OF VIBRATORY CONVEYING VELOCITY BY OPTIMIZING THE NORMAL VIBRATION". Ukrainian Journal of Mechanical Engineering and Materials Science 9, n. 2 (2023): 26–35. http://dx.doi.org/10.23939/ujmems2023.02.026.
Testo completoAbstract (sommario):
The paper is dedicated to researching the influence of normal vibration on the vibratory conveying velocity of particles on an inclined track that performs independent longitudinal and normal oscillations (two-component vibration). The study considers the optimizing conditions of the conveying velocity for different laws of oscillating components (harmonic, polyharmonic, oscillations with piecewise constant acceleration) with a limited value of the longitudinal acceleration of conveying track and with maximal normal acceleration that does not exceed the gravitational acceleration (non-hopping modes of moving, when particles slide without detachment from the surface). The optimization criterion is the maximal distance, traveled by the particle during the oscillation period, or the maximal value of dimensionless conveying velocity, depending on several dimensionless parameters. The maximal conveying velocity with polyharmonic normal oscillations is achieved at a certain ratio of the amplitudes of harmonic oscillation, which essentially depends on the track’s inclination angle to the horizon. The ratios of the amplitudes of harmonic oscillation, which practically do not reduce conveying velocity at any inclination angles, are proposed. Two-component vibratory conveying under normal oscillations with piecewise constant acceleration is considered in optimal non-hopping modes of a particle moving with one forward (or upward on an inclined track) sliding stage and one backward (or downward) sliding stage during the oscillation period. The equations for determining the dimensionless conveying velocity are derived for different values of dimensionless parameters, such as the inclination angle parameter (a ratio of an inclination angle tangent to a frictional coefficient) and the intensive vibration parameter (a ratio of the amplitudes of longitudinal and normal oscillations, divided by the frictional coefficient). The effectivity of polyharmonic normal oscillations in two-component vibratory conveying is compared with the effectivity of normal oscillations with piecewise constant acceleration. Maximal conveying velocity is achieved at certain values of phase difference angles between longitudinal and normal oscillations, which are called optimal. The value of dimensionless conveying velocity V increases with the increase of asymmetry of normal oscillations, which is described by the ratio n of the maximal acceleration of the track when moving down to the acceleration of gravity. This ratio n corresponds to the number of harmonics for polyharmonic oscillations. A comparison of values of V for normal oscillations with piecewise constant acceleration shows an advantage in velocity compared to polyharmonic normal oscillations at the same number n of harmonics, especially with increasing inclination angles. The research was carried out by the numerical step-by-step integration method, which allows for performing calculations with any given accuracy. The obtained results are demonstrated in figures and comparative tables.
21
Zaitsev, Valery V., Alexander V. Karlov e Husamuldin K. M. Alalvan. "Discrete time model of self-oscillations with spectral line widening". Physics of Wave Processes and Radio Systems 25, n. 4 (31 dicembre 2022): 27–32. http://dx.doi.org/10.18469/1810-3189.2022.25.4.27-32.
Testo completoAbstract (sommario):
An algorithm for generating quasi-harmonic self-oscillations with a uniformly widened spectral line is presented. The algorithm is based on the equation of motion of the Thomson-type DT-oscillator, which introduced a random effect in the form of band-pass white noise. Two types of effects are implemented: additive and parametric. Spectral characteristics of generated self-oscillations were analyzed by numerical experiment. The additive algorithm is shown to generate self-oscillations with amplitude-frequency fluctuations. Frequency fluctuations set the Lorentz (resonant) shape of the central part of the self-oscillation power spectrum, amplitude fluctuations form a noise pedestal of the spectral line. Based on the analysis of statistical characteristics of fluctuations in the frequency of the DT-oscillator with additive noise impact, a parametric algorithm for generating quasi-harmonic self-oscillations is proposed. In it, the resonance frequency of the oscillating system of the Thomson DT-oscillator is subject to random perturbations. The results of numerical experiments with generators of quasi-harmonic oscillations are given.
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Kontomaris, S. V., e A. Malamou. "Nonlinear oscillations in a constant gravitational field". Physica Scripta 97, n. 1 (1 gennaio 2022): 015202. http://dx.doi.org/10.1088/1402-4896/ac4552.
Testo completoAbstract (sommario):
Abstract Exploring non-linear oscillations is a challenging task since the related differential equations cannot be directly solved in terms of elementary functions. Thus, complicated mathematical or numerical methods are usually employed to find accurate or approximate expressions that describe the behavior of the system with respect to time. In this paper, the vertical oscillations of an object under the influence of its weight and an opposite force with magnitude F = cyn, where n > 0 are being explored. Accurate and approximate simple solutions regarding the object’s position with respect to time are presented and the dependence of the oscillation’s period from the oscillation’s range of displacements and the exponent n is revealed. In addition, the special case in which n = 3/2 (which describes the oscillation of a rigid sphere on an elastic half space) is also highlighted. Lastly, it is shown that similar cases (such as the case of a force with magnitude F = kx + λ×2) can be also treated using the same approach.
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Shen, Yuandeng. "Multi-wavelength observations of filament oscillations induced by shock waves". Proceedings of the International Astronomical Union 11, S320 (agosto 2015): 106–8. http://dx.doi.org/10.1017/s1743921316000193.
Testo completoAbstract (sommario):
AbstractTwo cases of filament oscillations induced by large-scale coronal shock waves are presented. For the first case, a chain of transverse oscillating filaments are observed in a proper order after the passing of a shock wave, and it is found that the they were triggered by the surface component of the dome-shaped shock wave. For the second case, simultaneous transverse oscillation of a limb prominence and longitudinal oscillation in an on-disk filament are launched by a single shock wave. It is found that the interaction angle between the shock wave and the prominence axis is the key to launch transverse or longitudinal filament oscillations. In addition, filament magnetic fields are estimated, using the measured parameters.
24
Fabrikant, A. L. "Harbour oscillations generated by shear flow". Journal of Fluid Mechanics 282 (10 gennaio 1995): 203–17. http://dx.doi.org/10.1017/s0022112095000103.
Testo completoAbstract (sommario):
A new mechanism that could be responsible for excitation of long-period oscillations in partially enclosed harbours is discussed. This mechanism is based on the interaction between a shear flow and the harbour-basin natural mode and does not suppose any external exciting forces caused by wind waves, tsunami, etc. The growth rate of harbour oscillations is found in terms of a plane-wave reflection coefficient integrated on the wavenumber spectrum of the oscillating outflow field near the harbour entrance. Analytical considerations for simple shear flows (vortex sheet and jet) show that the growth rate changes its sign depending on the ratio of oscillation frequency to flow speed.
25
Bakala, Pavel, Kateřina Goluchová, Eva Šrámková, Andrea Kotrlová, Gabriel Török, Frederic H. Vincent e Marek A. Abramowicz. "Simulations of flux variability of oscillating accretion fluid tori around Kerr black holes". Proceedings of the International Astronomical Union 10, S313 (settembre 2014): 380–81. http://dx.doi.org/10.1017/s1743921315002525.
Testo completoAbstract (sommario):
AbstractHigh frequency quasi-periodic oscillations (HF QPOs) are observed in the X-ray power-density spectra (PDS) of several microquasars and low mass X-ray binaries. Many proposed QPO models are based on oscillations of accretion toroidal fluid structures orbiting in the vicinity of a compact object. We study oscillating accretion tori orbiting in the vicinity of a Kerr black hole. We demonstrate that significant variation of the observed flux can be caused by the combination of radial and vertical oscillation modes of a slender, polytropic, perfect fluid, non-self-graviting torus with constant specific angular momentum. We investigate two combinations of the oscillating modes corresponding to the direct resonance QPO model and the modified relativistic precession QPO model.
26
Richards, G. A., e M. C. Janus. "Characterization of Oscillations During Premix Gas Turbine Combustion". Journal of Engineering for Gas Turbines and Power 120, n. 2 (1 aprile 1998): 294–302. http://dx.doi.org/10.1115/1.2818120.
Testo completoAbstract (sommario):
The use of premix combustion in stationary gas turbines can produce very low levels of Nox emissions. This benefit is widely recognized, but turbine developers routinely encounter problems with combustion oscillations during the testing of new premix combustors. Because of the associated pressure fluctuations, combustion oscillations must be eliminated in a final combustor design. Eliminating these oscillations is often time-consuming and costly because there is no single approach to solve an oscillation problem. Previous investigations of combustion stability have focused on rocket applications, industrial furnaces, and some aeroengine gas turbines. Comparatively little published data is available for premixed combustion at conditions typical of an industrial gas turbine. In this paper, we report experimental observations of oscillations produced by a fuel nozzle typical of industrial gas turbines. Tests are conducted in a specially designed combustor capable of providing the acoustic feedback needed to study oscillations. Tests results are presented for pressure up to 10 atmospheres, with inlet air temperatures up to 588 K (600 F) burning natural gas fuel. Based on theoretical considerations, it is expected that oscillations can be characterized by a nozzle reference velocity, with operating pressure playing a smaller role. This expectation is compared to observed data that shows both the benefits and limitations of characterizing the combustor oscillating behavior in terms of a reference velocity rather than other engine operating parameters. This approach to characterizing oscillations is then used to evaluate how geometric changes to the fuel nozzle will affect the boundary between stable and oscillating combustion.
27
Dolmetsch, R. E., e R. S. Lewis. "Signaling between intracellular Ca2+ stores and depletion-activated Ca2+ channels generates [Ca2+]i oscillations in T lymphocytes." Journal of General Physiology 103, n. 3 (1 marzo 1994): 365–88. http://dx.doi.org/10.1085/jgp.103.3.365.
Testo completoAbstract (sommario):
Stimulation through the antigen receptor (TCR) of T lymphocytes triggers cytosolic calcium ([Ca2+]i) oscillations that are critically dependent on Ca2+ entry across the plasma membrane. We have investigated the roles of Ca2+ influx and depletion of intracellular Ca2+ stores in the oscillation mechanism, using single-cell Ca2+ imaging techniques and agents that deplete the stores. Thapsigargin (TG; 5-25 nM), cyclopiazonic acid (CPA; 5-20 microM), and tert-butylhydroquinone (tBHQ; 80-200 microM), inhibitors of endoplasmic reticulum Ca(2+)-ATPases, as well as the Ca2+ ionophore ionomycin (5-40 nM), elicit [Ca2+]i oscillations in human T cells. The oscillation frequency is approximately 5 mHz (for ATPase inhibitors) to approximately 10 mHz (for ionomycin) at 22-24 degrees C. The [Ca2+]i oscillations resemble those evoked by TCR ligation in terms of their shape, amplitude, and an absolute dependence on Ca2+ influx. Ca(2+)-ATPase inhibitors and ionomycin induce oscillations only within a narrow range of drug concentrations that are expected to cause partial depletion of intracellular stores. Ca(2+)-induced Ca2+ release does not appear to be significantly involved, as rapid removal of extracellular Ca2+ elicits the same rate of [Ca2+]i decline during the rising and falling phases of the oscillation cycle. Both transmembrane Ca2+ influx and the content of ionomycin-releasable Ca2+ pools fluctuate in oscillating cells. From these data, we propose a model in which [Ca2+]i oscillations in T cells result from the interaction between intracellular Ca2+ stores and depletion-activated Ca2+ channels in the plasma membrane.
28
Liu, Cheng, Guowei Cai, Deyou Yang, Zhenglong Sun e Mingna Zhang. "The Online Identification of Dominated Inter-area Oscillations Interface Based on the Incremental Energy Function in Power System". Open Electrical & Electronic Engineering Journal 10, n. 1 (30 settembre 2016): 88–100. http://dx.doi.org/10.2174/1874129001610010088.
Testo completoAbstract (sommario):
The online identification of power system dominated inter-area oscillations interface based on the incremental energy function method is proposed in this paper. The dominant inter-area oscillations interface can be obtained by calculating branch oscillation potential energy, which is tie-line concentrated by oscillations energy. To get the oscillation energy caused by the different mechanism (free oscillation and forced oscillation), different fault position, different oscillation source. Power system dominated inter-area oscillations interface can be effectively obtained by proposed method, at the same time, dominated inter-area oscillations clusters also can be obtained. Finally, damping property of power system is effectively improved by configurating series damping controller in the dominant oscillation profile. The accuracy of the dominant oscillation interface identification is verified in this paper. At the same time, the proposed approach can also provides the basis for the configuration of damping control based on line.
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Csernovszky, Z., M. Hömöstrei e K. Kurucz. "Study of damped oscillations using Phyphox and Arduino controlled Hall-sensor". Journal of Physics: Conference Series 2693, n. 1 (1 gennaio 2024): 012004. http://dx.doi.org/10.1088/1742-6596/2693/1/012004.
Testo completoAbstract (sommario):
Abstract The paper presents physics education activities organized around the topic of damped oscillations. We used the Phyphox smartphone application for secondary school physics classes. These activities served as a basis for a physics education workshop, where an Arduino-controlled Hall-sensor and the Phyphox Magnetometer were presented. The problem of a damped pendulum, a vertical oscillation in water, and an LCr oscillating circuit was examined as part of a Phyphox project. Mechanical and electromagnetic damped oscillations can be demonstrated with our devices. Using our data, we could compare Hall-sensors of different devices, estimate some characteristics of the waves and help plan an LCr oscillating circuit. Activities for secondary school physics classes are suggested, based on the pedagogical goals.
30
Hayatdavoodi, Masoud, Yongbo Chen, Binbin Zhao e R. Cengiz Ertekin. "Experiments and computations of wave-induced oscillations of submerged horizontal plates". Physics of Fluids 35, n. 1 (gennaio 2023): 017121. http://dx.doi.org/10.1063/5.0132569.
Testo completoAbstract (sommario):
Wave-induced oscillations of submerged horizontal plates are studied by conducting laboratory experiments and by developing theoretical and computational models. These models include a linear solver based on the Green-function method, a nonlinear model based on Green–Naghdi wave equations, and a model based on computational fluid dynamics. The submerged horizontal plate oscillates in the vertical direction due to oscillatory wave loads. Oscillations of the plate are controlled by the use of a spring-damper system. Laboratory measurements and the models provide quantitative information on (i) how oscillations of submerged plates vary with wave conditions, plate characteristics, and the control system and (ii) how different models using different levels of assumptions predict the wave-induced oscillations. Particular attention is given to energy-production applications of the submerged oscillating plate, and discussion is provided on how the oscillation height and velocity vary with its initial submergence depth, stiffness of the attached spring, and the strength of the viscous damper. It is found that the oscillation varies almost linearly with the wave height, but nonlinearly with the wave period, initial submergence depth of the plate, damping, and the spring stiffness. Overall, it is found that nonlinearity plays an important role in this problem, while the effect of viscosity is negligible.
31
Mureşan, Raul C., Ovidiu F. Jurjuţ, Vasile V. Moca, Wolf Singer e Danko Nikolić. "The Oscillation Score: An Efficient Method for Estimating Oscillation Strength in Neuronal Activity". Journal of Neurophysiology 99, n. 3 (marzo 2008): 1333–53. http://dx.doi.org/10.1152/jn.00772.2007.
Testo completoAbstract (sommario):
We present a method that estimates the strength of neuronal oscillations at the cellular level, relying on autocorrelation histograms computed on spike trains. The method delivers a number, termed oscillation score, that estimates the degree to which a neuron is oscillating in a given frequency band. Moreover, it can also reliably identify the oscillation frequency and strength in the given band, independently of the oscillation in other frequency bands, and thus it can handle superimposed oscillations on multiple scales ( theta, alpha, beta, gamma, etc.). The method is relatively simple and fast. It can cope with a low number of spikes, converging exponentially fast with the number of spikes, to a stable estimation of the oscillation strength. It thus lends itself to the analysis of spike-sorted single-unit activity from electrophysiological recordings. We show that the method performs well on experimental data recorded from cat visual cortex and also compares favorably to other methods. In addition, we provide a measure, termed confidence score, that determines the stability of the oscillation score estimate over trials.
32
LI, QIAN SHU, e RUI ZHU. "MESOSCOPIC DESCRIPTION OF CHEMICAL SUPERCRITICAL HOPF BIFURCATION". International Journal of Bifurcation and Chaos 14, n. 07 (luglio 2004): 2393–97. http://dx.doi.org/10.1142/s0218127404010643.
Testo completoAbstract (sommario):
The mesoscopic dynamic behavior of the Oregonator model of the Belousov–Zhabotinsky chemical reaction is investigated as the model system experiences a supercritical Hopf bifurcation from focus to limit cycle oscillation. The study is performed by stochastically simulating the corresponding chemical master equation. Comparing the mesoscopic dynamic results with those obtained by the macroscopic dynamics, we find in the mesoscopic description a new type of oscillating state, in which large-amplitude oscillations and small-amplitude oscillations appear randomly alternately. This new state comes out spontaneously within a certain region called Hopf bifurcation range by us. In the mesoscopic description, the Hopf bifurcation point cannot be shown, being replaced by a Hopf bifurcation range. Furthermore, the applications of this new oscillating state to internal signal stochastic resonance are pointed out.
33
Fisher, C. E., e K. S. Ball. "Plume Dynamics in Natural Convection in a Horizontal Cylindrical Annulus". Journal of Heat Transfer 121, n. 3 (1 agosto 1999): 598–602. http://dx.doi.org/10.1115/1.2826021.
Testo completoAbstract (sommario):
Measurements of the unsteady temperature fluctuations in the plume region between differentially heated horizontal concentric cylinders are reported. In particular, power spectral density estimates of the temperature fluctuations within the plume show the development and breakdown of the oscillatory plume structure at high Rayleigh number, Rad, by two relatively independent processes: (1) the development of harmonic oscillations related to the dominant plume oscillation frequency, and (2) interactions between the oscillating plume and the adjacent relatively stagnant core flow (shear and entrainment). The harmonic oscillations are shown to be the dominant energy transfer mode at moderate Rad (up to Rad = 108), acting to disperse the plume energy without generating a broadband spectrum. The spectral density estimates show that while a distinct plume oscillation is still present near the inner cylinder at Rad = 109, the plume becomes increasingly turbulent as the outer cylinder is approached. A new correlation for the plume oscillation frequency, which is found to be proportional to Rad0.5, is also presented.
34
Manor, Yair, John Rinzel, Idan Segev e Yosef Yarom. "Low-Amplitude Oscillations in the Inferior Olive: A Model Based on Electrical Coupling of Neurons With Heterogeneous Channel Densities". Journal of Neurophysiology 77, n. 5 (1 maggio 1997): 2736–52. http://dx.doi.org/10.1152/jn.1997.77.5.2736.
Testo completoAbstract (sommario):
Manor, Yair, John Rinzel, Idan Segev, and Yosef Yarom. Low-amplitude oscillations in the inferior olive: a model based on electrical coupling of neurons with heterogeneous channel densities. J. Neurophysiol. 77: 2736–2752, 1997. The mechanism underlying subthreshold oscillations in inferior olivary cells is not known. To study this question, we developed a single-compartment, two-variable, Hodgkin-Huxley-like model for inferior olive neurons. The model consists of a leakage current and a low-threshold calcium current, whose kinetics were experimentally measured in slices. Depending on the maximal calcium and leak conductances, we found that a neuron model's response to current injection could be of four qualitatively different types: always stable, spontaneously oscillating, oscillating with injection of current, and bistable with injection of current. By the use of phase plane techniques, numerical integration, and bifurcation analysis, we subdivided the two-parameter space of channel densities into four regions corresponding to these behavioral types. We further developed, with the use of such techniques, an empirical rule of thumb that characterizes whether two cells when coupled electrically can generate sustained, synchronized oscillations like those observed in inferior olivary cells in slices, of low amplitude (0.1–10 mV) in the frequency range 4–10 Hz. We found that it is not necessary for either cell to be a spontaneous oscillator to obtain a sustained oscillation. On the other hand, two spontaneous oscillators always form an oscillating network when electrically coupled with any arbitrary coupling conductance. In the case of an oscillating pair of electrically coupled nonidentical cells, the coupling current varies periodically and is nonzero even for very large coupling values. The coupling current acts as an equalizing current to reconcile the differences between the two cells' ionic currents. It transiently depolarizes one cell and/or hyperpolarizes the other cell to obtain the regenerative response(s) required for the synchronized oscillation. We suggest that the subthreshold oscillations observed in the inferior olive can emerge from the electrical coupling between neurons with different channel densities, even if the inferior olive nucleus contains no or just a small proportion of spontaneously oscillating neurons.
35
Shi, Laishun, Jian Gao e Jingjing Chen. "Modeling study for oscillatory reaction of chlorite – iodide – ethyl acetoacetate". Canadian Journal of Chemistry 92, n. 5 (maggio 2014): 417–25. http://dx.doi.org/10.1139/cjc-2014-0072.
Testo completoAbstract (sommario):
Chlorine dioxide based chemical oscillating behavior was modeled by a simple scheme consisting of three component reactions. Furthermore, little is known about the influence of the pH value. In this study, four component reactions were used to model the chlorite – iodide – ethyl acetoacetate oscillating reaction by dynamic analysis software. The oscillatory phenomenon is observed for concentration changes of triiodide ion, chlorite ion, and hydrogen ion. The initial concentration of ethyl acetoacetate, chlorite ion, iodide ion, and hydrogen ion has great influence on oscillations. The amplitude and number of oscillations are associated with the initial reactant concentrations. The equation of the reaction rate of triiodide ion, chlorite ion, or hydrogen ion changing with reaction time and initial concentrations in the oscillation stage was obtained. The bifurcation surface between oscillatory and nonoscillatory behavior with different pH values was obtained. The spatial zone for the occurrence of oscillation is reduced with an increase in the pH value. The range of oscillation as concentrations of chlorine dioxide, iodine, and ethyl acetoacetate is well described by an equation. There is a lower limit on ethyl acetoacetate initial concentration for oscillation. However, there is a higher limit on chlorine dioxide and iodine concentration for oscillation. The concentrations of chlorine dioxide and iodine for oscillation decrease with an increase in the pH value. The results provide new theoretical evidence of the importance of pH value, which can affect the bifurcation surface between oscillatory and nonoscillatory behavior.
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Tagliazucchi, M., e I. Szleifer. "Dynamics of dissipative self-assembly of particles interacting through oscillatory forces". Faraday Discussions 186 (2016): 399–418. http://dx.doi.org/10.1039/c5fd00115c.
Testo completoAbstract (sommario):
Dissipative self-assembly is the formation of ordered structures far from equilibrium, which continuously uptake energy and dissipate it into the environment. Due to its dynamical nature, dissipative self-assembly can lead to new phenomena and possibilities of self-organization that are unavailable to equilibrium systems. Understanding the dynamics of dissipative self-assembly is required in order to direct the assembly to structures of interest. In the present work, Brownian dynamics simulations and analytical theory were used to study the dynamics of self-assembly of a mixture of particles coated with weak acids and bases under continuous oscillations of the pH. The pH of the system modulates the charge of the particles and, therefore, the interparticle forces oscillate in time. This system produces a variety of self-assembled structures, including colloidal molecules, fibers and different types of crystalline lattices. The most important conclusions of our study are: (i) in the limit of fast oscillations, the whole dynamics (and not only those at the non-equilibrium steady state) of a system of particles interacting through time-oscillating interparticle forces can be described by an effective potential that is the time average of the time-dependent potential over one oscillation period; (ii) the oscillation period is critical to determine the order of the system. In some cases the order is favored by very fast oscillations while in others small oscillation frequencies increase the order. In the latter case, it is shown that slow oscillations remove kinetic traps and, thus, allow the system to evolve towards the most stable non-equilibrium steady state.
37
Aboutalebi, Payam, Fares M’zoughi, Itziar Martija, Izaskun Garrido e Aitor J. Garrido. "Switching Control Strategy for Oscillating Water Columns Based on Response Amplitude Operators for Floating Offshore Wind Turbines Stabilization". Applied Sciences 11, n. 11 (5 giugno 2021): 5249. http://dx.doi.org/10.3390/app11115249.
Testo completoAbstract (sommario):
In this article, a new strategy for switching control has been proposed with the aim of reducing oscillations in floating offshore wind turbines. Such oscillations lead to a shortage in the system’s efficiency, lifespan and harvesting capability of wind and wave energies. In order to study the decreasing of undesired oscillations in the system, particularly in pitch and top tower fore-aft movements, a square-shaped platform barge equipped with four symmetric oscillating water columns has been considered. The oscillating water columns’ air flux valves allow to operate the air columns so that to control the barge movements caused by oscillatory motion of the waves. In order to design the control scheme, response amplitude operators have been used to evaluate the performance of the system for a range of wave frequency profiles. These response amplitude operators analysis makes it possible to implement a switching control strategy to adequately regulate the valves opening/closing transition. The obtained results show that the proposed controlled oscillating water column-based barge present a better performance compared to the traditional barge one. In the case study with the period of 10 s, the results indicate the significant oscillation reduction for the controlled oscillating water column-based system compared to the standard barge system by 30.8% in pitch angle and 25% in fore-aft displacement.
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Knizhnik, Kalman, Manuel Luna, Karin Muglach, Holly Gilbert, Therese Kucera e Judith Karpen. "Observational Study of Large Amplitude Longitudinal Oscillations in a Solar Filament". Proceedings of the International Astronomical Union 8, S300 (giugno 2013): 428–29. http://dx.doi.org/10.1017/s174392131301140x.
Testo completoAbstract (sommario):
AbstractOn 20 August 2010 an energetic disturbance triggered damped large-amplitude longitudinal (LAL) oscillations in almost an entire filament. In the present work we analyze this periodic motion in the filament to characterize the damping and restoring mechanism of the oscillation. Our method involves placing slits along the axis of the filament at different angles with respect to the spine of the filament, finding the angle at which the oscillation is clearest, and fitting the resulting oscillation pattern to decaying sinusoidal and Bessel functions. These functions represent the equations of motion of a pendulum damped by mass accretion. With this method we determine the period and the decaying time of the oscillation. Our preliminary results support the theory presented by Luna and Karpen (2012) that the restoring force of LAL oscillations is solar gravity in the tubes where the threads oscillate, and the damping mechanism is the ongoing accumulation of mass onto the oscillating threads. Following an earlier paper, we have determined the magnitude and radius of curvature of the dipped magnetic flux tubes hosting a thread along the filament, as well as the mass accretion rate of the filament threads, via the fitted parameters.
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Choi, Jeong Ryeol. "Quadrature Squeezing and Geometric-Phase Oscillations in Nano-Optics". Nanomaterials 10, n. 7 (17 luglio 2020): 1391. http://dx.doi.org/10.3390/nano10071391.
Testo completoAbstract (sommario):
The geometric phase, as well as the familiar dynamical phase, occurs in the evolution of a squeezed state in nano-optics as an extra phase. The outcome of the geometric phase in that state is somewhat intricate: its time behavior exhibits a combination of a linear increase and periodic oscillations. We focus in this work on the periodic oscillations of the geometric phase, which are novel and interesting. We confirm that such oscillations are due purely to the effects of squeezing in the quantum states, whereas the oscillation disappears when we remove the squeezing. As the degree of squeezing increases in q-quadrature, the amplitude of the geometric-phase oscillation becomes large. This implies that we can adjust the strength of such an oscillation by tuning the squeezing parameters. We also investigate geometric-phase oscillations for the case of a more general optical phenomenon where the squeezed state undergoes one-photon processes. It is shown that the geometric phase in this case exhibits additional intricate oscillations with small amplitudes, besides the principal oscillation. Such a sub-oscillation exhibits a beating-like behavior in time. The effects of geometric-phase oscillations are crucial in a wide range of wave interferences which are accompanied by rich physical phenomena such as Aharonov–Bohm oscillations, conductance fluctuations, antilocalizations, and nondissipative current flows.
40
Lanets, O. S., V. T. Dmytriv, V. M. Borovets, I. A. Derevenko e I. M. Horodetskyy. "Analytical Model of the Two-Mass Above Resonance System of the Eccentric-Pendulum Type Vibration Table". International Journal of Applied Mechanics and Engineering 25, n. 4 (1 dicembre 2020): 116–29. http://dx.doi.org/10.2478/ijame-2020-0053.
Testo completoAbstract (sommario):
AbstractThe article deals with atwo-mass above resonant oscillatory system of an eccentric-pendulum type vibrating table. Based on the model of a vibrating oscillatory system with three masses, the system of differential equations of motion of oscillating masses with five degrees of freedom is compiled using generalized Lagrange equations of the second kind. For given values of mechanical parameters of the oscillatory system and initial conditions, the autonomous system of differential equations of motion of oscillating masses is solved by the numerical Rosenbrock method. The results of analytical modelling are verified by experimental studies. The two-mass vibration system with eccentric-pendulum drive in resonant oscillation mode is characterized by an instantaneous start and stop of the drive without prolonged transient modes. Parasitic oscillations of the working body, as a body with distributed mass, are minimal at the frequency of forced oscillations.
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Potkonjak, N., Lj Kolar-Anić, T. Potkonjak, S. Nikola Blagojević e S. Anić. "Oscillatory Phenomena during Anodic Copper Electrodissolution in Trifluoroacetic Acid Solution". Materials Science Forum 518 (luglio 2006): 301–6. http://dx.doi.org/10.4028/www.scientific.net/msf.518.301.
Testo completoAbstract (sommario):
This work presents the current oscillation phenomena observed in an electrochemical Cu/0.5 M CF3COOH system. The dynamical response of this new oscillator was followed by both current density-potential (j-E) and current density-time (j-t) curves. The current oscillation phenomena of the investigated system were monitored over various potential scan rates and constant applied potentials as control parameters. The increase of potential scan rate significantly decreases both the potential range of current oscillations and the frequency of oscillations. At the j-t curves both the simple and the complex (period adding) oscillations were found. Moreover, with the increase of applied potential, the increase of period of oscillations and current oscillation amplitudes were observed. It appears that the period of current oscillations exponentially grows with applied potential.
42
Popov, Tzvetan, e Paul Szyszka. "Alpha oscillations govern interhemispheric spike timing coordination in the honey bee brain". Proceedings of the Royal Society B: Biological Sciences 287, n. 1921 (26 febbraio 2020): 20200115. http://dx.doi.org/10.1098/rspb.2020.0115.
Testo completoAbstract (sommario):
In 1929 Hans Berger discovered the alpha oscillations: prominent, ongoing oscillations around 10 Hz in the electroencephalogram of the human brain. These alpha oscillations are among the most widely studied brain signals, related to cognitive phenomena such as attention, memory and consciousness. However, the mechanisms by which alpha oscillations affect human cognition await demonstration. Here, we suggest the honey bee brain as an experimentally more accessible model system for investigating the functional role of alpha oscillations. We found a prominent spontaneous oscillation around 18 Hz that is reduced in amplitude upon olfactory stimulation. Similar to alpha oscillations in primates, the phase of this oscillation biased both timing of neuronal spikes and amplitude of high-frequency gamma activity (40–450 Hz). These results suggest a common role of alpha oscillations across phyla and provide an unprecedented new venue for causal studies on the relationship between neuronal spikes, brain oscillations and cognition.
43
Kornyushin, Yuri. "Uniform plasma oscillations in ellipsoid of conductive material". Facta universitatis - series: Physics, Chemistry and Technology 3, n. 1 (2004): 35–39. http://dx.doi.org/10.2298/fupct0401035k.
Testo completoAbstract (sommario):
The influence of the shape of a sample on the type of uniform dipole collective electrons oscillations is discussed. In samples of a bulk shape uniform bulk dipole oscillation (Langmuir oscillation) cannot exist. It exists in samples of a thin slab shape only. As uniform bulk dipole oscillations cannot penetrate ellipsoidal samples of conductive material they exist in the surface layer of a sample only (Mie oscillations). Frequencies of Mie oscillations are calculated for a sample of the shape of an arbitrary ellipsoid.
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Kontomaris, Stylianos Vasileios, Georgios Chliveros e Anna Malamou. "Approximate Solutions for Undamped Nonlinear Oscillations Using He’s Formulation". J 6, n. 1 (28 febbraio 2023): 140–51. http://dx.doi.org/10.3390/j6010010.
Testo completoAbstract (sommario):
Solving nonlinear oscillations is a challenging task due to the mathematical complexity of the related differential equations. In many cases, determining the oscillation’s period requires the solution of complicated integrals using numerical methods. To avoid the complexity, there are many empirical equations in the literature that can be used instead of rigorous mathematical analysis to provide an acceptable approximation. In this paper, a recently developed method, He’s formulation, is applied to find the period in many different cases of nonlinear oscillators. The cases are those of the Duffing equation, the Helmholtz nonlinear oscillator, the simple pendulum and the case of a vertical oscillation under the influence of a nonlinear elastic force. The results of the method are accurate; thus, He’s formulation is a strong tool for solving nonlinear oscillations.
45
Zhang, Sheng, Ming Bao, Mieko Arisawa e Masahiko Yamaguchi. "Stable and Unstable Concentration Oscillations Induced by Temperature Oscillations on Reversible Nonequilibrium Chemical Reactions of Helicene Oligomers". International Journal of Molecular Sciences 24, n. 1 (30 dicembre 2022): 693. http://dx.doi.org/10.3390/ijms24010693.
Testo completoAbstract (sommario):
Temperature oscillations can affect behaviors of living things. In this article, we describe the effect of triangle temperature oscillations on reversible nonequilibrium chemical reactions detected as concentration oscillations. When amplification through self-catalytic reactions is involved in the chemical reactions, concentration oscillations exhibit diverse nonequilibrium phenomena, which include equilibrium intersecting, equilibrium noncontact, and equilibrium sliding. Both stable and unstable concentration oscillations occur, during which repeated cycles provide the same and different concentration oscillations, respectively. Concentration oscillations are classified according to their waveforms in concentration/time profiles, the shapes of hysteresis curves in concentration/temperature profiles, the nature of self-catalytic reactions, and their relationships with equilibrium. An unstable concentration oscillation may be transformed into a stable concentration oscillation, which is described on the basis of the classifications. Experimental examples are shown using reversible association and dissociation reactions of helicene oligomers.
46
Zheng, L., J. L. Plawsky, P. C. Wayner, e S. DasGupta. "Stability and Oscillations in an Evaporating Corner Meniscus". Journal of Heat Transfer 126, n. 2 (1 aprile 2004): 169–78. http://dx.doi.org/10.1115/1.1652046.
Testo completoAbstract (sommario):
A Constrained Vapor Bubble Loop Thermosyphon, CVBLT, made of quartz was used to study the stability and oscillations of an evaporating curved wetting film of pentane in a corner. The film thickness profile was measured as a function of heat input, time, and axial position using image analyzing interferometry. The curvatures and apparent contact angles for the evaporating film under various operating conditions were obtained from the measured film thickness profiles. Instability (oscillation) of the liquid film was observed at relatively higher values of the heat input. The behavior of the curvature and the apparent contact angle of an oscillating film with changes in heat input was evaluated. Moving velocities of the oscillating film were calculated from the measured values of the liquid-wall wetted lengths and were found to be directly proportional to the difference between the instantaneous force acting on the curved film and the reference force. Using an augmented Young-Laplace pressure jump model, the effect of the excess free energy at the contact line on the oscillations was demonstrated.
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Salin, J. G. "A Theoretical Analysis of Timber Drying in Oscillating Climates". Holzforschung 57, n. 4 (26 giugno 2003): 427–32. http://dx.doi.org/10.1515/hf.2003.063.
Testo completoAbstract (sommario):
Summary In this study the influence of oscillating climates on the drying of timber is investigated theoretically. First, the effect of oscillations superimposed on an ordinary drying schedule is examined by solving the corresponding partial differential equations. It is shown that the average drying rate is not affected by the oscillations. Second, properly selected oscillation amplitudes and frequencies can result in enhanced mechano-sorptive creep in the board surface layer, which enables increased external driving forces with an unchanged risk of checking. This method is analysed by using a drying simulation model. It is shown that substantial reductions in the drying time can be obtained in theory. From a practical point of view the benefit is probably rather marginal.
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Chen, Yvonne Y., e Jeremy B. Caplan. "Rhythmic Activity and Individual Variability in Recognition Memory: Theta Oscillations Correlate with Performance whereas Alpha Oscillations Correlate with ERPs". Journal of Cognitive Neuroscience 29, n. 1 (gennaio 2017): 183–202. http://dx.doi.org/10.1162/jocn_a_01033.
Testo completoAbstract (sommario):
During study trials of a recognition memory task, alpha (∼10 Hz) oscillations decrease, and concurrently, theta (4–8 Hz) oscillations increase when later memory is successful versus unsuccessful (subsequent memory effect). Likewise, at test, reduced alpha and increased theta activity are associated with successful memory (retrieval success effect). Here we take an individual-differences approach to test three hypotheses about theta and alpha oscillations in verbal, old/new recognition, measuring the difference in oscillations between hit trials and miss trials. First, we test the hypothesis that theta and alpha oscillations have a moderately mutually exclusive relationship; but no support for this hypothesis was found. Second, we test the hypothesis that theta oscillations explain not only memory effects within participants, but also individual differences. Supporting this prediction, durations of theta (but not alpha) oscillations at study and at test correlated significantly with d′ across participants. Third, we test the hypothesis that theta and alpha oscillations reflect familiarity and recollection processes by comparing oscillation measures to ERPs that are implicated in familiarity and recollection. The alpha-oscillation effects correlated with some ERP measures, but inversely, suggesting that the actions of alpha oscillations on memory processes are distinct from the roles of familiarity- and recollection-linked ERP signals. The theta-oscillation measures, despite differentiating hits from misses, did not correlate with any ERP measure; thus, theta oscillations may reflect elaborative processes not tapped by recollection-related ERPs. Our findings are consistent with alpha oscillations reflecting visual inattention, which can modulate memory, and with theta oscillations supporting recognition memory in ways that complement the most commonly studied ERPs.
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Kucera, T. A., M. Luna, T. Török, K. Muglach, J. T. Karpen, C. Downs, X. Sun, B. J. Thompson e H. R. Gilbert. "Comparison of Two Methods for Deriving the Magnetic Field in a Filament Channel". Astrophysical Journal 940, n. 1 (1 novembre 2022): 34. http://dx.doi.org/10.3847/1538-4357/ac9377.
Testo completoAbstract (sommario):
Abstract Understanding the magnetic structure of filament channels is difficult but essential for identifying the mechanism (s) responsible for solar eruptions. In this paper we characterize the magnetic field in a well-observed filament channel with two independent methods, prominence seismology and magnetohydrodynamics flux-rope modeling, and compare the results. In 2014 May and June, active region 12076 exhibited a complex of filaments undergoing repeated oscillations over the course of 12 days. We measure the oscillation periods in the region with both Global Oscillation Network Group Hα and Solar Dynamics Observatory (SDO) Advanced Imaging Assembly EUV images, and then utilize the pendulum model of large-amplitude longitudinal oscillations to calculate the radius of curvature of the fields supporting the oscillating plasma from the derived periods. We also employ the regularized Biot–Savart laws formalism to construct a flux-rope model of the field of the central filament in the region based on an SDO Helioseismic and Magnetic Imager magnetogram. We compare the estimated radius of curvature, location, and angle of the magnetic field in the plane of the sky derived from the observed oscillations with the corresponding magnetic-field properties extracted from the flux-rope model. We find that the two models are broadly consistent, but detailed comparisons of the model and specific oscillations often differ. Model observation comparisons such as these are important for advancing our understanding of the structure of filament channels.
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Botros, K. K., G. H. Dunn e J. A. Hrycyk. "Riser-Relief Valve Dynamic Interactions (Extension to a Previous Model)". Journal of Pressure Vessel Technology 120, n. 2 (1 maggio 1998): 207–12. http://dx.doi.org/10.1115/1.2842242.
Testo completoAbstract (sommario):
Further investigation of the dynamic stability behavior of a typical pilot-operated relief valve is reported. The present study is an extension to Botros et al. (1997) model, which includes mapping of the oscillating frequencies and amplitudes with riser dimensionless length L/D; inclusion of the effects of a wedge-O-ring seal in the model; detailed analyses of the field tests revealing unknown values for model parameters. These model refinements resulted in a better agreement between simulation results and field measurements. Analysis of piston oscillation frequencies and amplitudes indicates that the piston oscillation frequency mirrors the riser’s one-quarter-wave resonance frequency for lower values of L/D. At L/D = 20 and higher, two modes of oscillations started to emerge with two distinct frequencies. Maximum oscillation amplitudes occurred at L/D corresponding to one-quarter wave. Wedge-O-ring seal mechanism helps in suppressing piston oscillations; but it must be used in conjunction with a proper lubricant, otherwise the piston may jam partway during the upward stroke.