Добірка наукової літератури з теми "Surface mode oscillations"
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Статті в журналах з теми "Surface mode oscillations"
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Klimov, Alexandr V., and 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, no. 1 (June 24, 2023): 87–96. http://dx.doi.org/10.17816/2074-0530-115233.
Повний текст джерелаАнотація:
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.
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Zhileykin, Mikhail M., Pavel V. Sirotin, Sergey S. Nosikov, and 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, no. 1 (May 23, 2023): 39–48. http://dx.doi.org/10.17816/0321-4443-321266.
Повний текст джерелаАнотація:
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.
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H Thomas, John. "Oscillations in Sunspots." Australian Journal of Physics 38, no. 6 (1985): 811. http://dx.doi.org/10.1071/ph850811.
Повний текст джерелаАнотація:
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, and M. J. Whelan. "Theoretical Investigations of RHEED Oscillations." Microscopy and Microanalysis 5, S2 (August 1999): 710–11. http://dx.doi.org/10.1017/s1431927600016871.
Повний текст джерелаАнотація:
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, and Benlong Wang. "Dynamics and surface stability of a cylindrical cavitation bubble in a rectilinear vortex." Journal of Fluid Mechanics 865 (March 1, 2019): 963–92. http://dx.doi.org/10.1017/jfm.2019.103.
Повний текст джерелаАнотація:
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.
Повний текст джерелаАнотація:
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, and 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, no. 2 (April 28, 2023): 17–22. http://dx.doi.org/10.24143/2072-9502-2023-2-17-22.
Повний текст джерелаАнотація:
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, and 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, no. 10 (October 1, 2020): 3009–24. http://dx.doi.org/10.1175/jpo-d-20-0063.1.
Повний текст джерелаАнотація:
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, no. 5 (August 15, 1987): 2607–13. http://dx.doi.org/10.1103/physrevb.36.2607.
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MacLeod, Morgan, Michelle Vick, and Abraham Loeb. "Tidal Wave Breaking in the Eccentric Lead-in to Mass Transfer and Common Envelope Phases." Astrophysical Journal 937, no. 1 (September 1, 2022): 37. http://dx.doi.org/10.3847/1538-4357/ac8aff.
Повний текст джерелаАнотація:
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).
Дисертації з теми "Surface mode oscillations"
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Cleve, Sarah. "Microstreaming induced in the vicinity of an acoustically excited, nonspherically oscillating microbubble." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEC028/document.
Повний текст джерелаАнотація:
Des bulles micrométriques sont utilisées dans divers domaines, notamment dans des applications médicales basées sur les ultrasons. Il est possible d’exploiter différents effets des bulles, comme par exemple leur résonance acoustique ou leur effet destructeur en cavitation inertielle. Un autre mécanisme exploitable est la génération de micro-écoulements, appelé microstreaming, induits autour d’une bulle. Ces écoulements sont relativement lents par rapport aux oscillations rapides de la bulle. Le microstreaming et les contraintes de cisaillement associées jouent un rôle important dans la perméabilisation d’une membrane cellulaire, mais il manque encore une compréhension détaillée de l’écoulement induit. Afin d’améliorer la compréhension des phénomènes physiques, ce travail se concentre sur les écoulements induits autour d’une bulle d’air dans piégée et excitée acoustiquement dans de l’eau et oscillante en modes de surface. La partie expérimentale se décompose de deux étapes. Dans un premier temps, il est nécessaire de contrôler la dynamique de la bulle, en particulier ses modes de surface et son orientation. Ceci est réalisé par coalescence entre deux bulles. Dans un second temps, le microstreaming est généré et enregistré simultanément à la dynamique de bulle. De cette manière il est possible de corréler les motifs d'écoulement aux oscillations de la bulle. Le grand nombre de motifs obtenus peut être classé selon le mode dominant et la taille de la bulle. Une étude plus détaillée de la dynamique de bulle permet de déduire les paramètres importants qui mènent à une telle variété de motifs de microstreaming. Afin de confirmer les résultats expérimentaux, un modèle analytique a été développé. Il est basé sur les équations de la mécanique des fluides de deuxième ordre et moyennées en temps, la dynamique d'interface de la bulle obtenue expérimentalement sert de donnée d’entrée au modèle. Ce manuscrit contient en supplément une section sur la génération de microjets par l'implosion d'agents de contraste. Ces jets peuvent apparaître en cas d’excitation acoustique suffisamment élevée. L’impact de ces jets sur parois présente un autre mécanisme responsable de la perméabilisation de membranes cellulairesMicrobubbles find use in several domains, one of them being medical ultrasound applications. Different characteristics of those bubbles such as their acoustic resonance or their destructive effect during inertial cavitation can be exploited. Another phenomenon induced around acoustically excited bubbles is microstreaming, that means a relatively slow mean flow with respect to the fast bubble oscillations. Microstreaming and its associated shear stresses are commonly agreed to play a role in the permeabilization of cell membranes, a detailed understanding of the induced flows is however missing. To acquire basic physical knowledge, this work focuses on the characterization of streaming induced around an air bubble in water, more precisely around a single acoustically trapped and excited, nonspherically oscillating bubble. The experimental part consists of two steps. First, the bubble dynamics, in particular the triggered shape mode and the orientation of the bubble have to be controlled. For this, the use of bubble coalescence proves to be an adequate method. In a second step, the microstreaming is recorded in parallel to bubble dynamics. This allows to correlate the obtained streaming patterns to the respective shape oscillations. The large number of obtained pattern types can be classified, in particular with respect to the mode number and bubble size. A close investigation of the bubble dynamics allows furthermore deducing the important physical mechanisms which lead to such a variety of streaming patterns. In order to confirm the experimental findings, an analytical model has been developed. It is based upon time-averaged second-order fluid mechanics equations and the experimentally obtained bubble dynamics serves as input parameters. Supplementary to the microstreaming work, this manuscript contains a short section on directed jetting of contrast agent microbubbles, which might appear at high acoustic driving. The impact of those microjets on cell membranes presents another mechanism made responsible for the permeabilization of cell membranes
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Chen, Chia-Jeng. "Hydro-climatic forecasting using sea surface temperatures." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/48974.
Повний текст джерелаАнотація:
A key determinant of atmospheric circulation patterns and regional climatic conditions is sea surface temperature (SST). This has been the motivation for the development of various teleconnection methods aiming to forecast hydro-climatic variables. Among such methods are linear projections based on teleconnection gross indices (such as the ENSO, IOD, and NAO) or leading empirical orthogonal functions (EOFs). However, these methods deteriorate drastically if the predefined indices or EOFs cannot account for climatic variability in the region of interest. This study introduces a new hydro-climatic forecasting method that identifies SST predictors in the form of dipole structures. An SST dipole that mimics major teleconnection patterns is defined as a function of average SST anomalies over two oceanic areas of appropriate sizes and geographic locations. The screening process of SST-dipole predictors is based on an optimization algorithm that sifts through all possible dipole configurations (with progressively refined data resolutions) and identifies dipoles with the strongest teleconnection to the external hydro-climatic series. The strength of the teleconnection is measured by the Gerrity Skill Score. The significant dipoles are cross-validated and used to generate ensemble hydro-climatic forecasts. The dipole teleconnection method is applied to the forecasting of seasonal precipitation over the southeastern US and East Africa, and the forecasting of streamflow-related variables in the Yangtze and Congo Rivers. These studies show that the new method is indeed able to identify dipoles related to well-known patterns (e.g., ENSO and IOD) as well as to quantify more prominent predictor-predictand relationships at different lead times. Furthermore, the dipole method compares favorably with existing statistical forecasting schemes. An operational forecasting framework to support better water resources management through coupling with detailed hydrologic and water resources models is also demonstrated.
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Achlan, Moustafa. "Surface Plasmon Polariton and Wave Guide Modes in a Six Layer Thin Film Stack." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS109.
Повний текст джерелаАнотація:
Dans cette thèse, nous étudions les propriétés optiques d'un système multicouche (air-Au-SiO₂-Au-Ti-verre). Les interfaces sont planes et la modélisation est réalisée en utilisant les coefficients de Fresnel à l'interface et la propagation d'ondes planes dans les couches. Deux modèles sont utilisés où l'échantillon est : i) excité par une source à l'infini ; ii) excité par une source locale. Dans l'expérience que nous avons modélisée l'empilement est excité par les électrons tunnel inélastiques dans un microscope à effet tunnel (STM). Dans le modèle, le courant tunnel inélastique est remplacé par un dipôle oscillant vertical. En utilisant ces modèles, nous avons calculé les flux réfléchis (reflectance) et transmis (transmittance) d'une source de lumière à l'infini et le flux transmis de l'excitation locale. La reflectance, transmittance et le flux transmis montrent des modes plasmoniques (surface plasmon polaritons (SPP)) et photoniques (guide d'onde (WG)). A des longueurs d'onde particulières, les courbes de dispersion des SPP et WG présentent un croisement évité. Le choix des épaisseurs d'or et de silice a deux contraintes: une amplitude importante des observables et une large dépendance en longueurs d'onde du vecteur d'onde dans le plan. Nous étudions aussi l'influence des épaisseurs sur les observables. Nous avons trouvé que les observables ont des amplitudes importantes à pour une épaisseur d'or de [10, 90 nm] pour l'empilement de trois couches et de [10, 50 nm] pour celui de six couches. Les modes de guide d'onde apparaissent pour une épaisseur de la couche de silice de >190 nm. Afin de caractériser la localisation du champ dans l'empilement et déterminer la nature du mode, nous avons calculé le champ électrique en fonction de la coordonnée de pénétration z. Nous avons trouvé que pour le mode SPP le champ est localisé à l'interface Au-air, tandis que le champ électrique du guide d'onde est confiné dans la couche de silice. Les résultats théoriques présentés sont en bon accord avec les résultats des études expérimentales menées dans notre groupeIn this thesis, we investigate the optical properties of a six-layer stack (air-Au-SiO₂-Au-Ti-glass). The interfaces are flat and the modeling is performed using elementary Fresnel expressions at the interface and plane wave propagation in the layers. Two models are used where the sample is: i) excited by a source at infinity (excitation by source at infinity (ESI)); ii) excited by a local source. In the experiments we are modeling this source consists of the inelastic tunneling electrons from a scanning tunneling microscope (STM). In our modeling this source is replaced by a vertical oscillating dipole. Using these two models one calculates the reflected (reflectance) and the transmitted (transmittance) flux from a source at infinity and the transmitted flux of a local source. Surface plasmon polariton (SPP) and wave guide (WG) modes may be identified in the reflectance, transmittance and transmitted flux. In a particular wavelength domain the SPP and WG repel each other giving rise to an avoided crossing. The choice of the gold (Au) and silica (SiO₂) thicknesses of the six-layer stack is guided by two requirements: high amplitude of the observable and wide wavelength dependence of the in-plane wave vector. We also study the influence of the gold and silica thicknesses on the observables. We find that the observables are significant for dAu[10, 90 nm] for the three and dAu[10, 50 nm] for six layer stacks and this predictive study guided the choice of the experimental sample thicknesses. The wave guide mode appears for dSiO₂ >190 nm. The electric field as a function of the penetration coordinate z is calculated in order to characterize the location of the field in the stack and to assign the nature of the modes. We observe that for the SPP the electric field is confined at the Au-air interface whereas, the electric fields corresponding to the WG mode are confined inside SiO₂ layer. Our calculations presented in this work are in good agreement with the experimental measurements performed in our group
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Chen, Lihui. "Synthesis and Plasmonic Properties of Copper-based Nanocrystals." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/217134.
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Maliniemi, V. (Ville). "Observations of solar wind related climate effects in the Northern Hemisphere winter." Doctoral thesis, University of Oulu, 2016. http://urn.fi/urn:isbn:9789526213545.
Повний текст джерелаАнотація:
Abstract
This thesis studies the long-term relation between the solar wind driven energetic particle forcing into the atmosphere and the tropospheric circulation in the Northern Hemisphere winter. The work covers the period of more than one hundred years since the turn of the 20th century to present. The thesis makes a statistical analysis of satellite measurements of precipitating energetic electrons, sunspot number data and geomagnetic activity, and compares them with temperature and pressure measurements made at the Earth's surface.
Recent results, both observational and from chemistry climate models, have indicated significant effects in the Earth's middle atmosphere due to the energetic electrons precipitating from the magnetosphere. These effects include the formation of reactive hydrogen and nitrogen oxides in the high latitude mesosphere and the depletion of ozone caused by them. Ozone is a radiatively active and important gas, which affects the thermal structure and dynamics of the middle atmosphere. Accordingly, the depletion of ozone can intensify the large scale stratospheric circulation pattern called the polar vortex. Winter weather conditions on the surface have been shown to be dependent on the polar vortex strength.
This thesis shows that there is a significant relation between the average fluxes of medium energy (ten to hundred keVs) precipitating electrons and surface temperatures in parts of the Northern Hemisphere in winter time. Temperatures are positively correlated with electron fluxes in North Eurasia and negatively correlated in Greenland during the period 1980-2010 which is covered by direct satellite observations of precipitating particles. This difference is especially notable when major sudden stratospheric warmings and the quasi-biennial oscillation (QBO), which both are known to affect the polar vortex strength, are taken into account. When extended to the late 19th century, the analysis shows that a similar temperature pattern is predominated during the declining phase of the sunspot cycle. The high speed solar wind streams and energetic particle precipitation typically maximize also at the declining phase of the solar cycle. This specific temperature pattern is related to the variability of the northern annular mode (NAM), which is the most significant circulation pattern in the Northern Hemisphere winter. Before the space era, geomagnetic activity measured by ground observations can be used as a proxy for energetic particle precipitation. Earlier studies have found a significant positive correlation between geomagnetic activity and NAM since the 1960s. We find that, when the QBO measured at 30 hPa height is in the easterly phase, a positive correlation is extended to the beginning of 1900s. We also show that high geomagnetic activity causes a stronger effect in the Northern Hemisphere winter than high sunspot activity, especially in the Atlantic and Eurasia.
A comprehensive knowledge of the Earth's climate system and all its drivers is crucial for the future projection of climate. Solar variability effects have been estimated to produce only a small factor to the global climate change. However, there is increasing evidence, including the results presented in this thesis, that the different forms of solar variability can have a substantial effect to regional and seasonal climate variability. With this new evidence, the solar wind related particle effects in the atmosphere are now gaining increasing attention. These effects will soon be included in the next coupled model inter comparison project (CMIP6) as an additional solar related climate effect. This emphasizes the relevance of this thesis.
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Awo, Founi Mesmin. "Modes interannnuels de la variabilité climatique de l'Atlantique tropical, dynamiques oscillatoires et signatures en salinité de surface de la mer." Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30171/document.
Повний текст джерелаАнотація:
Dans cette thèse, nous avons abordé plusieurs thématiques liées aux modes de variabilité climatique dans l'Atlantique tropical à l'échelle interannuelle. Les analyses statistiques nous ont permis dans un premier temps de mettre en évidence les deux principaux modes dominants de cette variabilité interannuelle: un mode équatorial et un mode méridien. Le mode équatorial est responsable d'anomalies de température de surface de la mer (SST) principalement dans le Golfe de Guinée et est identifié par des variations de la pente du niveau de la mer dans la bande équatoriale. Il est dû à des rétroactions dynamiques entre le vent, le niveau de la mer et la SST. Quant au mode méridien, il se manifeste par des fluctuations inter-hémisphériques de SST et est contrôlé par des rétroactions dynamiques et thermodynamiques entre le vent, l'évaporation et la SST. L'évaluation du couplage de ces variables clés du mode méridien nous a permis de proposer un modèle conceptuel pour expliquer les principaux mécanismes responsables des oscillations du mode méridien. Le modèle a montré que le mode méridien résulte de la superposition d'un mécanisme auto-entretenu basé sur les rétroactions positives et négatives générant des oscillations régulières de haute fréquence (2-3 ans) et d'un autre mécanisme d'oscillation basse fréquence (4-9 ans) lié à l'influence d'ENSO du Pacifique Est. Comme l'évolution de ces deux modes est fortement liée au déplacement méridien de la zone de convergence intertropicale (ITCZ) qui transporte les pluies, nous avons ensuite identifié la signature de ces modes sur la salinité de la surface de la mer à l'aide observations in situ et d'une simulation numérique régionale. Les processus océaniques et/ou atmosphériques responsables de la signature de chaque mode ont été également identifiés grâce à un bilan de sel dans la couche de mélange du modèle validé. Le bilan de sel a révélé que le forçage atmosphérique, lié à la migration de l'ITCZ, contrôle la région équatoriale tandis que l'advection, due à la modulation des courants, du gradient vertical et le mélange à la base de la couche de mélange, explique les variations de SSS dans les régions sous l'influence des panaches. [...]In this thesis, we investigate several topics related to the interannual climatic modes in the tropical Atlantic. Statistical analyses allows us to extract the two main dominant modes of interannual variability: an equatorial mode and a meridional mode. The equatorial mode is responsible for Sea Surface Temperature (SST) anomalies mainly found in the Gulf of Guinea and is linked to variations of the sea-level slope in the equatorial band. It is due to dynamic feedbacks between zonal wind, sea level and SST. The meridional mode is characterised by inter-hemispheric SST fluctuations and is controlled by dynamic and thermodynamic feedbacks between the wind, evaporation and SST. After quantifying the coupling between key variables involved in the meridional mode, we develop a conceptual model to explain the main mechanisms responsible for meridional mode oscillations. The model shows that the meridional mode results from the superposition of a self-sustaining mechanism based on positive and negative feedbacks generating regular oscillations of high frequency (2-3 years) and another low frequency oscillation mechanism (4-9 years) related to the influence of ENSO. As the evolution of these two modes is strongly linked to the meridional shift of the Intertropical Convergence Zone (ITCZ) and associated rainfall maximum, we identify the signature of these modes on Sea Surface Salinity (SSS) using in situ observations and a regional numerical simulation. Oceanic and/or atmospheric processes responsible for the signature of each mode are also identified through a mixed-layer salt budget in the validated model. The salt balance reveals that the atmospheric forcing, related to the ITCZ migration, controls the equatorial region while the advection, due to the modulation of current dynamics, the vertical gradient and mixing at the base of the mixed layer, explains SSS variations in regions under the influence of plumes. Finally, we study the Equatorial Kelvin wave characteristics and influences on the density that are involved in the meridional and equatorial mode connection processes, using a very simplified model of gravity wave propagation along the equator. After a brief description of this model, which was initially constructed to study dynamics in the equatorial Pacific, we apply it to the specific case of the equatorial Atlantic by validating its analytical and numerical solutions under adiabatic conditions. [...]
7
Ayina, Ludos-Hervé. "Etude des modes de variabilité de l'océan Atlantique tropical et de leur sensibilité à l'impact des décharges fluviatiles et des précipitations." Paris 6, 2002. http://www.theses.fr/2002PA066019.
Повний текст джерела
8
Thakore, Vaibhav. "Nonlinear dynamic modeling, simulation and characterization of the mesoscale neuron-electrode interface." Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5529.
Повний текст джерелаАнотація:
Extracellular neuroelectronic interfacing has important applications in the fields of neural prosthetics, biological computation and whole-cell biosensing for drug screening and toxin detection. While the field of neuroelectronic interfacing holds great promise, the recording of high-fidelity signals from extracellular devices has long suffered from the problem of low signal-to-noise ratios and changes in signal shapes due to the presence of highly dispersive dielectric medium in the neuron-microelectrode cleft. This has made it difficult to correlate the extracellularly recorded signals with the intracellular signals recorded using conventional patch-clamp electrophysiology. For bringing about an improvement in the signal-to-noise ratio of the signals recorded on the extracellular microelectrodes and to explore strategies for engineering the neuron-electrode interface there exists a need to model, simulate and characterize the cell-sensor interface to better understand the mechanism of signal transduction across the interface. Efforts to date for modeling the neuron-electrode interface have primarily focused on the use of point or area contact linear equivalent circuit models for a description of the interface with an assumption of passive linearity for the dynamics of the interfacial medium in the cell-electrode cleft. In this dissertation, results are presented from a nonlinear dynamic characterization of the neuroelectronic junction based on Volterra-Wiener modeling which showed that the process of signal transduction at the interface may have nonlinear contributions from the interfacial medium. An optimization based study of linear equivalent circuit models for representing signals recorded at the neuron-electrode interface subsequently proved conclusively that the process of signal transduction across the interface is indeed nonlinear. Following this a theoretical framework for the extraction of the complex nonlinear material parameters of the interfacial medium like the dielectric permittivity, conductivity and diffusivity tensors based on dynamic nonlinear Volterra-Wiener modeling was developed. Within this framework, the use of Gaussian bandlimited white noise for nonlinear impedance spectroscopy was shown to offer considerable advantages over the use of sinusoidal inputs for nonlinear harmonic analysis currently employed in impedance characterization of nonlinear electrochemical systems. Signal transduction at the neuron-microelectrode interface is mediated by the interfacial medium confined to a thin cleft with thickness on the scale of 20-110 nm giving rise to Knudsen numbers (ratio of mean free path to characteristic system length) in the range of 0.015 and 0.003 for ionic electrodiffusion. At these Knudsen numbers, the continuum assumptions made in the use of Poisson-Nernst-Planck system of equations for modeling ionic electrodiffusion are not valid. Therefore, a lattice Boltzmann method (LBM) based multiphysics solver suitable for modeling ionic electrodiffusion at the mesoscale neuron-microelectrode interface was developed. Additionally, a molecular speed dependent relaxation time was proposed for use in the lattice Boltzmann equation. Such a relaxation time holds promise for enhancing the numerical stability of lattice Boltzmann algorithms as it helped recover a physically correct description of microscopic phenomena related to particle collisions governed by their local density on the lattice. Next, using this multiphysics solver simulations were carried out for the charge relaxation dynamics of an electrolytic nanocapacitor with the intention of ultimately employing it for a simulation of the capacitive coupling between the neuron and the planar microelectrode on a microelectrode array (MEA). Simulations of the charge relaxation dynamics for a step potential applied at t = 0 to the capacitor electrodes were carried out for varying conditions of electric double layer (EDL) overlap, solvent viscosity, electrode spacing and ratio of cation to anion diffusivity. For a large EDL overlap, an anomalous plasma-like collective behavior of oscillating ions at a frequency much lower than the plasma frequency of the electrolyte was observed and as such it appears to be purely an effect of nanoscale confinement. Results from these simulations are then discussed in the context of the dynamics of the interfacial medium in the neuron-microelectrode cleft. In conclusion, a synergistic approach to engineering the neuron-microelectrode interface is outlined through a use of the nonlinear dynamic modeling, simulation and characterization tools developed as part of this dissertation research.Ph.D.
Doctorate
Physics
Sciences
Physics
9
Rath, Pranaya Kishore. "Experimental Investigation of Electrons In and Above Liquid Helium." Thesis, 2022. https://etd.iisc.ac.in/handle/2005/5838.
Повний текст джерелаАнотація:
Electrons on the surface of liquid helium form a nearly ideal 2-dimensional electron system (2DES). An electron density up to 2 × 10^9 cm-2, known as the critical electron density, can be achieved on the liquid helium surface, above which an electro-hydrodynamic (EHD) instability sets in, which results in the formation of MEBs. Due to this limitation in maximum possible density, only the classical liquid and solid phases of the 2DES can be accessed in this system.
But at the same time, on the surface of thin liquid helium film and with the multi-electron bubbles (MEBs), it may be possible to achieve high electron density than that of the critical electron density. This can allow the observation of quantum melting, i.e., the phase transition between the quantum solid to the liquid phase of the 2DES. Although extensive theoretical and experimental studies have already been done, the quantum melting transition has not been
achieved experimentally on these systems yet. In this thesis, we have used multiple new experimental approaches to obtain electron densities higher than what has been achieved before and to study the MEBs effectively.
First, we studied the temporal dynamics of the EHD instability and the effect of the applied electric field and charge density on the instability. The unstable wave vectors were determined experimentally, and their temporal growth was studied carefully. The determined unstable wave vectors were found to be a good match with the theoretically expected values obtained from the dispersion relation. At the same time, the analysis of the growth rate of unstable
vectors were found to be limited by the kinematic viscosity of the liquid helium.
Next, we investigated the lifetime of MEBs trapped on a dielectric surface and compared the result with previous results on free bubbles in bulk liquid helium. The reduced lifetime of trapped bubbles suggested an impact of convective heat flow around the bubbles on their lifetimes. Then we performed an experimental investigation that confirmed the effect of
convective heat flow direction inside the experimental cell on the lifetime of such trapped MEBs. Determination of the electronic phase inside an MEB is one of the biggest challenges of the time. Unfortunately, there is no direct way or technique for such investigation. We discussed how the MEB surface fluctuation with an external oscillating electric field could be observed, which may allow a possible way of studying the phase of the 2DES. We studied the surface fluctuations of electrically excited MEBs and observed different normal mechanical modes of the bubble wall. Then we extended our discussion on why liquid helium-4 is not a suitable medium to study the MEBs at low temperatures (below λ), where interesting phenomena occur, and how liquid helium-3, based on its physical property, can be a suitable replacement for this purpose. We generated MEBs inside liquid helium for the first time. The generated MEBs at 1.1 K were found to be stable with long lifetimes. This result opens the possibility of studying the MEBs at much lower temperatures where quantum properties dominate over classical for the 2DES.
Finally, we discussed the problem associated with achieving high electron density on the thin helium film and how integrating an NEA material as a substrate can help us overcome the problem. We fabricated NEA materials, i.e., cBN pellet, and optimized the rf sputtering deposition of cBN film. We performed a preliminary pick-up measurement on the charged thin helium with these materials as substrates, which showed some positive indications that need to
be confirmed with further advanced experimental investigations.INSPIRE, DST India
10
Das, Surajit. "Role Of Sea Surface Temperature Gradient In Intraseasonal Oscillation Of Convection In An Aquaplanet Model." Thesis, 2012. https://etd.iisc.ac.in/handle/2005/2583.
Повний текст джерелаАнотація:
In this thesis we examine intra-seasonal oscillations (ISO) in the aqua-planet setup of the Community Atmospheric Model (CAM) version 5.1, mainly based on July and January climatological sea surface temperature (SST). We investigate mainly two questions -what should be the SST distribution for the existence of (a) northward moving ISO in summer, and (b) eastward moving MJO-like modes in winter. In the first part of the thesis we discuss the northward propagation. A series of experiments were performed with zonally symmetric and asymmetric SST distributions. The basic lower boundary condition is specified from zonally averaged observed July and January SST.
The zonally symmetric July SST experiment produced an inter tropical convergence zone (ITCZ) on both sides of the equator. Poleward movement is not clear, and it is confined to the region between the double ITCZ. In July, the Bay of Bengal (BOB) and West Pacific SST is high compared to the rest of the northern tropics. When we impose a zonally asymmetric SST structure with warm SST spanning about 80 of longitude, the model shows a monsoon-like circulation, and some northward propagating convective events. Analysis of these events shows that two adjacent cells with cyclonic and anticyclonic vorticity are created over the warm SST anomaly and to the west. The propagation occurs due to the convective region drawn north in the convergence zone between these vortices.
Zonally propagating Madden-Julian oscillations (MJO) are discussed in the second part of the thesis. All the experiments in this part are based on the zonally symmetric SST. The zonally symmetric January SST configuration gives an MJO-like mode, with zonal wave number 1 and a period of 40-90 days. The SST structure has a nearly meridionally symmetric structure, with local SST maxima on either side of the equator, and a small dip in the equatorial region. If we replace this dip with an SST maximum, the time-scale of MJO becomes significantly smaller (20-40 days). The implication is that an SST maximum in the equatorial region reduces the strength of MJO, and a flat SST profile in the equatorial region is required for more energetic of MJO. This result was tested and found to be valid in a series of further experiments.
Книги з теми "Surface mode oscillations"
1
Mann, Peter. Near-Equilibrium Oscillations. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198822370.003.0012.
Повний текст джерелаАнотація:
In this chapter, the theory of near-equilibrium oscillations is developed and normal mode analysis is performed. This topic requires a little bit of linear algebra when dealing with matrices, as well as an understanding of differential equations. The chapter explores small perturbations (small nudges or tiny shifts) to a stable equilibrium point in configuration space and introduces the characteristic equation. Interdisciplinary examples are then investigated, including a surface science example in which the bond frequencies of surface adsorbates are calculated, an example in which the motion of atoms in a triatomic molecule is examined and an example in which the molecular physics of atomic force microscopy is analysed. The properties of the eigenvalue problem for small oscillations are also investigated.
2
Yang, Kun. Observed Regional Climate Change in Tibet over the Last Decades. Oxford University Press, 2017. http://dx.doi.org/10.1093/acrefore/9780190228620.013.587.
Повний текст джерелаАнотація:
The Tibetan Plateau (TP) is subjected to strong interactions among the atmosphere, hydrosphere, cryosphere, and biosphere. The Plateau exerts huge thermal forcing on the mid-troposphere over the mid-latitude of the Northern Hemisphere during spring and summer. This region also contains the headwaters of major rivers in Asia and provides a large portion of the water resources used for economic activities in adjacent regions. Since the beginning of the 1980s, the TP has undergone evident climate changes, with overall surface air warming and moistening, solar dimming, and decrease in wind speed. Surface warming, which depends on elevation and its horizontal pattern (warming in most of the TP but cooling in the westernmost TP), was consistent with glacial changes. Accompanying the warming was air moistening, with a sudden increase in precipitable water in 1998. Both triggered more deep clouds, which resulted in solar dimming. Surface wind speed declined from the 1970s and started to recover in 2002, as a result of atmospheric circulation adjustment caused by the differential surface warming between Asian high latitudes and low latitudes.The climate changes over the TP have changed energy and water cycles and has thus reshaped the local environment. Thermal forcing over the TP has weakened. The warming and decrease in wind speed lowered the Bowen ratio and has led to less surface sensible heating. Atmospheric radiative cooling has been enhanced, mainly through outgoing longwave emission from the warming planetary system and slightly enhanced solar radiation reflection. The trend in both energy terms has contributed to the weakening of thermal forcing over the Plateau. The water cycle has been significantly altered by the climate changes. The monsoon-impacted region (i.e., the southern and eastern regions of the TP) has received less precipitation, more evaporation, less soil moisture and less runoff, which has resulted in the general shrinkage of lakes and pools in this region, although glacier melt has increased. The region dominated by westerlies (i.e., central, northern and western regions of the TP) received more precipitation, more evaporation, more soil moisture and more runoff, which together with more glacier melt resulted in the general expansion of lakes in this region. The overall wetting in the TP is due to both the warmer and moister conditions at the surface, which increased convective available potential energy and may eventually depend on decadal variability of atmospheric circulations such as Atlantic Multi-decadal Oscillation and an intensified Siberian High. The drying process in the southern region is perhaps related to the expansion of Hadley circulation. All these processes have not been well understood.
3
Horing, Norman J. Morgenstern. Random Phase Approximation Plasma Phenomenology, Semiclassical and Hydrodynamic Models; Electrodynamics. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198791942.003.0010.
Повний текст джерелаАнотація:
Chapter 10 reviews both homogeneous and inhomogeneous quantum plasma dielectric response phenomenology starting with the RPA polarizability ring diagram in terms of thermal Green’s functions, also energy eigenfunctions. The homogeneous dynamic, non-local inverse dielectric screening functions (K) are exhibited for 3D, 2D, and 1D, encompassing the non-local plasmon spectra and static shielding (e.g. Friedel oscillations and Debye-Thomas-Fermi shielding). The role of a quantizing magnetic field in K is reviewed. Analytically simpler models are described: the semiclassical and classical limits and the hydrodynamic model, including surface plasmons. Exchange and correlation energies are discussed. The van der Waals interaction of two neutral polarizable systems (e.g. physisorption) is described by their individual two-particle Green’s functions: It devolves upon the role of the dynamic, non-local plasma image potential due to screening. The inverse dielectric screening function K also plays a central role in energy loss spectroscopy. Chapter 10 introduces electromagnetic dyadic Green’s functions and the inverse dielectric tensor; also the RPA dynamic, non-local conductivity tensor with application to a planar quantum well. Kramers–Krönig relations are discussed. Determination of electromagnetic response of a compound nanostructure system having several nanostructured parts is discussed, with applications to a quantum well in bulk plasma and also to a superlattice, resulting in coupled plasmon spectra and polaritons.
4
Goswami, B. N., and Soumi Chakravorty. Dynamics of the Indian Summer Monsoon Climate. Oxford University Press, 2017. http://dx.doi.org/10.1093/acrefore/9780190228620.013.613.
Повний текст джерелаАнотація:
Lifeline for about one-sixth of the world’s population in the subcontinent, the Indian summer monsoon (ISM) is an integral part of the annual cycle of the winds (reversal of winds with seasons), coupled with a strong annual cycle of precipitation (wet summer and dry winter). For over a century, high socioeconomic impacts of ISM rainfall (ISMR) in the region have driven scientists to attempt to predict the year-to-year variations of ISM rainfall. A remarkably stable phenomenon, making its appearance every year without fail, the ISM climate exhibits a rather small year-to-year variation (the standard deviation of the seasonal mean being 10% of the long-term mean), but it has proven to be an extremely challenging system to predict. Even the most skillful, sophisticated models are barely useful with skill significantly below the potential limit on predictability. Understanding what drives the mean ISM climate and its variability on different timescales is, therefore, critical to advancing skills in predicting the monsoon. A conceptual ISM model helps explain what maintains not only the mean ISM but also its variability on interannual and longer timescales.The annual ISM precipitation cycle can be described as a manifestation of the seasonal migration of the intertropical convergence zone (ITCZ) or the zonally oriented cloud (rain) band characterized by a sudden “onset.” The other important feature of ISM is the deep overturning meridional (regional Hadley circulation) that is associated with it, driven primarily by the latent heat release associated with the ISM (ITCZ) precipitation. The dynamics of the monsoon climate, therefore, is an extension of the dynamics of the ITCZ. The classical land–sea surface temperature gradient model of ISM may explain the seasonal reversal of the surface winds, but it fails to explain the onset and the deep vertical structure of the ISM circulation. While the surface temperature over land cools after the onset, reversing the north–south surface temperature gradient and making it inadequate to sustain the monsoon after onset, it is the tropospheric temperature gradient that becomes positive at the time of onset and remains strongly positive thereafter, maintaining the monsoon. The change in sign of the tropospheric temperature (TT) gradient is dynamically responsible for a symmetric instability, leading to the onset and subsequent northward progression of the ITCZ. The unified ISM model in terms of the TT gradient provides a platform to understand the drivers of ISM variability by identifying processes that affect TT in the north and the south and influence the gradient.The predictability of the seasonal mean ISM is limited by interactions of the annual cycle and higher frequency monsoon variability within the season. The monsoon intraseasonal oscillation (MISO) has a seminal role in influencing the seasonal mean and its interannual variability. While ISM climate on long timescales (e.g., multimillennium) largely follows the solar forcing, on shorter timescales the ISM variability is governed by the internal dynamics arising from ocean–atmosphere–land interactions, regional as well as remote, together with teleconnections with other climate modes. Also important is the role of anthropogenic forcing, such as the greenhouse gases and aerosols versus the natural multidecadal variability in the context of the recent six-decade long decreasing trend of ISM rainfall.
5
Hameed, Saji N. The Indian Ocean Dipole. Oxford University Press, 2018. http://dx.doi.org/10.1093/acrefore/9780190228620.013.619.
Повний текст джерелаАнотація:
Discovered at the very end of the 20th century, the Indian Ocean Dipole (IOD) is a mode of natural climate variability that arises out of coupled ocean–atmosphere interaction in the Indian Ocean. It is associated with some of the largest changes of ocean–atmosphere state over the equatorial Indian Ocean on interannual time scales. IOD variability is prominent during the boreal summer and fall seasons, with its maximum intensity developing at the end of the boreal-fall season. Between the peaks of its negative and positive phases, IOD manifests a markedly zonal see-saw in anomalous sea surface temperature (SST) and rainfall—leading, in its positive phase, to a pronounced cooling of the eastern equatorial Indian Ocean, and a moderate warming of the western and central equatorial Indian Ocean; this is accompanied by deficit rainfall over the eastern Indian Ocean and surplus rainfall over the western Indian Ocean. Changes in midtropospheric heating accompanying the rainfall anomalies drive wind anomalies that anomalously lift the thermocline in the equatorial eastern Indian Ocean and anomalously deepen them in the central Indian Ocean. The thermocline anomalies further modulate coastal and open-ocean upwelling, thereby influencing biological productivity and fish catches across the Indian Ocean. The hydrometeorological anomalies that accompany IOD exacerbate forest fires in Indonesia and Australia and bring floods and infectious diseases to equatorial East Africa. The coupled ocean–atmosphere instability that is responsible for generating and sustaining IOD develops on a mean state that is strongly modulated by the seasonal cycle of the Austral-Asian monsoon; this setting gives the IOD its unique character and dynamics, including a strong phase-lock to the seasonal cycle. While IOD operates independently of the El Niño and Southern Oscillation (ENSO), the proximity between the Indian and Pacific Oceans, and the existence of oceanic and atmospheric pathways, facilitate mutual interactions between these tropical climate modes.
6
Kucharski, Fred, and Muhammad Adnan Abid. Interannual Variability of the Indian Monsoon and Its Link to ENSO. Oxford University Press, 2017. http://dx.doi.org/10.1093/acrefore/9780190228620.013.615.
Повний текст джерелаАнотація:
The interannual variability of Indian summer monsoon is probably one of the most intensively studied phenomena in the research area of climate variability. This is because even relatively small variations of about 10% to 20% from the mean rainfall may have dramatic consequences for regional agricultural production. Forecasting such variations months in advance could help agricultural planning substantially. Unfortunately, a perfect forecast of Indian monsoon variations, like any other regional climate variations, is impossible in a long-term prediction (that is, more than 2 weeks or so in advance). The reason is that part of the atmospheric variations influencing the monsoon have an inherent predictability limit of about 2 weeks. Therefore, such predictions will always be probabilistic, and only likelihoods of droughts, excessive rains, or normal conditions may be provided. However, even such probabilistic information may still be useful for agricultural planning. In research regarding interannual Indian monsoon rainfall variations, the main focus is therefore to identify the remaining predictable component and to estimate what fraction of the total variation this component accounts for. It turns out that slowly varying (with respect to atmospheric intrinsic variability) sea-surface temperatures (SSTs) provide the dominant part of the predictable component of Indian monsoon variability. Of the predictable part arising from SSTs, it is the El Niño Southern Oscillation (ENSO) that provides the main part. This is not to say that other forcings may be neglected. Other forcings that have been identified are, for example, SST patterns in the Indian Ocean, Atlantic Ocean, and parts of the Pacific Ocean different from the traditional ENSO region, and springtime snow depth in the Himalayas, as well as aerosols. These other forcings may interact constructively or destructively with the ENSO impact and thus enhance or reduce the ENSO-induced predictable signal. This may result in decade-long changes in the connection between ENSO and the Indian monsoon. The physical mechanism for the connection between ENSO and the Indian monsoon may be understood as large-scale adjustment of atmospheric heatings and circulations to the ENSO-induced SST variations. These adjustments modify the Walker circulation and connect the rising/sinking motion in the central-eastern Pacific during a warm/cold ENSO event with sinking/rising motion in the Indian region, leading to reduced/increased rainfall.
7
Nash, David. Changes in Precipitation Over Southern Africa During Recent Centuries. Oxford University Press, 2017. http://dx.doi.org/10.1093/acrefore/9780190228620.013.539.
Повний текст джерелаАнотація:
Precipitation levels in southern Africa exhibit a marked east–west gradient and are characterized by strong seasonality and high interannual variability. Much of the mainland south of 15°S exhibits a semiarid to dry subhumid climate. More than 66 percent of rainfall in the extreme southwest of the subcontinent occurs between April and September. Rainfall in this region—termed the winter rainfall zone (WRZ)—is most commonly associated with the passage of midlatitude frontal systems embedded in the austral westerlies. In contrast, more than 66 percent of mean annual precipitation over much of the remainder of the subcontinent falls between October and March. Climates in this summer rainfall zone (SRZ) are dictated by the seasonal interplay between subtropical high-pressure systems and the migration of easterly flows associated with the Intertropical Convergence Zone. Fluctuations in both SRZ and WRZ rainfall are linked to the variability of sea-surface temperatures in the oceans surrounding southern Africa and are modulated by the interplay of large-scale modes of climate variability, including the El Niño-Southern Oscillation (ENSO), Southern Indian Ocean Dipole, and Southern Annular Mode.Ideas about long-term rainfall variability in southern Africa have shifted over time. During the early to mid-19th century, the prevailing narrative was that the climate was progressively desiccating. By the late 19th to early 20th century, when gauged precipitation data became more readily available, debate shifted toward the identification of cyclical rainfall variation. The integration of gauge data, evidence from historical documents, and information from natural proxies such as tree rings during the late 20th and early 21st centuries, has allowed the nature of precipitation variability since ~1800 to be more fully explored.Drought episodes affecting large areas of the SRZ occurred during the first decade of the 19th century, in the early and late 1820s, late 1850s–mid-1860s, mid-late 1870s, earlymid-1880s, and mid-late 1890s. Of these episodes, the drought during the early 1860s was the most severe of the 19th century, with those of the 1820s and 1890s the most protracted. Many of these droughts correspond with more extreme ENSO warm phases.Widespread wetter conditions are less easily identified. The year 1816 appears to have been relatively wet across the Kalahari and other areas of south central Africa. Other wetter episodes were centered on the late 1830s–early 1840s, 1855, 1870, and 1890. In the WRZ, drier conditions occurred during the first decade of the 19th century, for much of the mid-late 1830s through to the mid-1840s, during the late 1850s and early 1860s, and in the early-mid-1880s and mid-late 1890s. As for the SRZ, markedly wetter years are less easily identified, although the periods around 1815, the early 1830s, mid-1840s, mid-late 1870s, and early 1890s saw enhanced rainfall. Reconstructed rainfall anomalies for the SRZ suggest that, on average, the region was significantly wetter during the 19th century than the 20th and that there appears to have been a drying trend during the 20th century that has continued into the early 21st. In the WRZ, average annual rainfall levels appear to have been relatively consistent between the 19th and 20th centuries, although rainfall variability increased during the 20th century compared to the 19th.
8
Stańczykiewicz, Arkadiusz. Prawdopodobieństwo wystąpienia szkód w odnowieniach podokapowych wskutek pozyskiwania drewna oraz model ich szacowania. Publishing House of the University of Agriculture in Krakow, 2018. http://dx.doi.org/10.15576/978-83-66602-34-2.
Повний текст джерелаАнотація:
An analysis of the existing literature on the issue of damage to regeneration caused by timber harvesting, revealed that a great majority of results reported in those publications was obtained through laborious and time-consuming field research conducted in two stages. Field research methods for gathering data, employed by various authors, differed in terms of the manner of establishing trial plots, the accuracy of counting and evaluating the number of saplings growing on the investigated sites, classification systems used for distinguishing particular groups of regeneration based on quantitative (diameter at breast height, tree height) and qualitative features (biosocial position within the certain layer and the entire stand), classification systems used for identifying types of damage caused by cutting and felling, as well as transporting operations, and finally the duration of observation intervals and time spent on gathering data on the response of damaged saplings from both, the individual and collective perspectives. Obviously, the most reliable manner of gathering such data would be to count all damaged elements of the environment being a subject of interest of particular investigators at the certain point of time. However, due to time and work consumption of this approach, which is besides very costly, any research should be designed in such a manner as to reduce the above-mentioned factors. This paper aimed to (1) analyse the probability of occurrence of damage to regeneration depending on the form of timber assortments dragged from the felling site to the skidding routes, and timber harvesting technology employed in logging works, and (2) identify a method ensuring that gathered data is sufficient for performing reliable evaluation of share of damage to regeneration at acceptable accuracy level, without necessity to establish trial plots before commencing harvesting works. The scope of these studies enclosed a comparison between two motor-manual methods of timber harvesting in thinned stands, with dragging of timber in the first stage of skidding from the stand to landings. According to one of these methods, a classical one, operations of felling and delimbing of trees were carried out by sawmen at the felling site. Timber obtained using different methods was skidded by carters and horses, and operators of a light-duty cable winch, driven by the chainsaw’s engine, as well as operators of cable winches combined with farm tractors. In the latter, alternative method, sawmen performed only cutting and felling of trees. Delimbing and cross-cutting of trunks, dragged from the felling sites, was carried out by operators of processors combined with farm tractors, worked on skidding routes. The research was conducted in the years 2002–2010 in stands within the age classes II–IV mostly, located in the territories of Regional Directorates of State Forests in Krakow and Katowice, and in the Forest Experimental Unit in Krynica-Zdrój. In the course of a preliminary stage of investigations 102 trial plots were established in stands within early and late tinning treatments. As a result of the field research carried out in two stages, more than 3.25 thsd. circular sites were established and marked, on the surface of which over 25 thsd. saplings constituting the regeneration layer were inventoried. Based on the results of investigations and analyses it was revealed that regardless of the category of thinning treatment, the highest probability of occurrence of destroying P(ZN) to regeneration (0.24–0.44) should be expected when the first stage of timber skidding is performed using cable winches. Slightly lower values of probability (0.17–0.33) should be expected in stands where timber is skidded by horses, while in respect to processor-based skidding technology the probability of destroying occurrence oscillates between 0.12 and 0.27, depending on the particular layer of regeneration. P(ZN) values, very close to those of skidding technology engaging processors, were recorded for skidding performed using the light-duty cable winch driven by the chainsaw’s engine (0.16–0.27). The highest probability of damage P(USZK) to regeneration (0.16–0.31) can be expected when processors are used in the first stage of timber skidding. Slightly lower values of probability (0.14–0.23) were obtained when skidding was performed with the use of cable winches, whereas engaging horses for hauling of trunks results in probability of damage occnrrence oscillating between 0.05–0.20, depending on the particular layer of regeneration. With regard to the probability of occurrence of both, destroying and damage P(ZNUSZK) to regeneration (0.33–0.54), the highest values can be expected when cable winches are engaged in the first stage of skidding. Little lower (0.30–0.43) was the probability of their occurrence if processor-based technology of skidding was employed, while in respect to horse skidding these values oscillated between 0.27–0.41, depending on the layer of regeneration. The lowest values of probability of occurrence of damage P(USZK), and destroying and damage treated collectively P(ZNUSZK), within all layers of regeneration, were recorded in stands where thinning treatments were performed using the light-duty cable winch driven by the chainsaw’s engine. The models evaluated and respective equations, developed based on those models, for evaluating the number of destroyed saplings ZNha (tab. 40, 42, 44, 46, 48) could be used for determining the share of damage expressed as a percentage, upon conducting only one field research at the investigated felling sites, once the timber harvesting and skidding would have been completed. As revealed by the results of analyses, evaluation of statistically significant regression models was possible for all layers of regeneration (tab. 39, 41, 43, 45, 47). Nevertheless, the smallest part of these models that could be considered positively verified, were those for the natural young regeneration, although almost a half of them revealed to be significant. Within the medium-sized regeneration over three-fourths of all models could be considered positively verified, four of which explained more than 50% of variability. Within the high-sized regeneration almost two-thirds of evaluated regression models were statistically significant, five of which were verified positively, moreover, one of them explained more than 50% of variability. The most promising results were those obtained for the advance growth. Nearly 90% of the evaluated models revealed to be statistically significant, ten of which could be considered positively verified. Furthermore, four statistically significant models explained over 50% of general variability. With regard to the entire regeneration more than 80% of evaluated models were statistically significant. However, due to insignificant coefficients of regression, eight of them could be considered positively verified. At this point it should be stressed that in respect to logging technology employing the light-duty cable winch FKS it was impossible to evaluate statistically significant models of regression. Whereas, in the case of processor-based logging technology, firstly regarding the advance growth, and then the entire regeneration, all of the evaluated statistically significant models could be considered positively verified, in terms of both, all of the stands, and particular categories of thinning treatments individually. This latter case also revealed the highest degree of matching of evaluated models (R2 popr 0.73–0.76 for advance growth and 0.78–0.94 for the entire regeneration). A significant impact of the kind of form of hauled timber on the probability of damage occurrence P(USZK), mainly in early thinning treatments, could have been reflected in the results obtained for all stands (early and late thinning treated collectively). Moreover, due to an insignificant impact of the form of hauled timber and logging technology employed, on the probability of occurrence of damage in late thinned stands, and a significant impact of the above-mentioned variables on early thinned stands, it should be assumed that for performing an evaluation of destroying and damage caused by timber harvesting the both thinning treatment categories should be analysed separately. Furthermore, when evaluating the probability of occurrence of destroying and damage caused by timber harvesting, the layers of natural young regeneration and advance growth should be analysed separately. As proved by the results presented in this paper, varying values of probability computed for each of the layers of regeneration seem to indicate that when investigating damage to regeneration caused by timber harvesting, it would be reasonable and recommended to perform a separate analysis of damage to the highest saplings as well, namely individuals with diameter at breast height close to 7 cm. In respect to studies on damage to regeneration caused by logging technologies mentioned above, the evaluation of number of destroyed saplings within the advance growth can be carried out using the proportions of damaged and undamaged saplings per 1 ha of the stand. The numbers evaluated in this manner can be used to calculate the damage share expressed in relative values (percentage of damaged saplings compared with the entire number of saplings before commencing the logging works). However, one should keep in mind that this is true only if the field research have been carried out based on the methodology described in this paper.
Частини книг з теми "Surface mode oscillations"
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Shaw, Stephen J. "Surface mode deformations on an oscillating bubble." In Fluid Mechanics and Its Applications, 355–63. Dordrecht: Springer Netherlands, 1994. http://dx.doi.org/10.1007/978-94-011-0938-3_33.
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Glampedakis, Kostas, Lars Samuelsson, and Nils Andersson. "A toy model for global magnetar oscillation." In Isolated Neutron Stars: From the Surface to the Interior, 607–11. Dordrecht: Springer Netherlands, 2007. http://dx.doi.org/10.1007/978-1-4020-5998-8_84.
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Jian, Lijun, Xiao Zeng, and Jie Pei. "The Potential Force Interface Tension Model in MPS Method for Stratification Simulation." In Springer Proceedings in Physics, 288–96. Singapore: Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-99-1023-6_27.
Повний текст джерелаАнотація:
AbstractIn the analysis of phenomenology of serious accident, stratification behavior is important in the late in-vessel stage of core melt. Traditional numerical methods have difficulties in analyzing stratification process accompanying with free surface, which need extra processes such as empirical correlations. The Moving Particle Semi-implicit (MPS) method has a natural advantage in calculating multiphase flows with free surface. In this paper, we apply the potential force surface tension model to the MPS program and extend the original surface tension model to the interface tension calculation of multiple flows. The improved MPS method is verified by a classical dam break problem. The surface tension model is verified by the cases of droplet oscillation, droplet on solid wall and floating droplet. Finally, the two-dimensional dam-break stratification experiment of silicone oil and salt water is simulated, and the simulation results agree with the experiment.
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Holm, Darryl D., Ruiao Hu, and Oliver D. Street. "Coupling of Waves to Sea Surface Currents Via Horizontal Density Gradients." In Mathematics of Planet Earth, 109–33. Cham: Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-031-18988-3_8.
Повний текст джерелаАнотація:
AbstractThe mathematical models and numerical simulations reported here are motivated by satellite observations of horizontal gradients of sea surface temperature and salinity that are closely coordinated with the slowly varying envelope of the rapidly oscillating waves. This coordination of gradients of fluid material properties with wave envelopes tends to occur when strong horizontal buoyancy gradients are present. The nonlinear models of this coordinated movement presented here may provide future opportunities for the optimal design of satellite imagery that could simultaneously capture the dynamics of both waves and currents directly.The model derived here appears in two levels of approximation: first for rapidly oscillating waves, and then for their slowly varying envelope (SVE) approximation obtained by using the WKB approach. The WKB wave-current-buoyancy interaction model derived here for a free surface with significant horizontal buoyancy gradients indicates that the mechanism for the emergence of these correlations is the ponderomotive force of the slowly varying envelope of rapidly oscillating waves acting on the surface currents via the horizontal buoyancy gradient. In this model, the buoyancy gradient appears explicitly in the WKB wave momentum, which in turn generates density-weighted potential vorticity whenever the buoyancy gradient is not aligned with the wave-envelope gradient.
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Alper, Said Emre, and Tayfun Akin. "A Symmetric Surface Micromachined Gyroscope with Decoupled Oscillation Modes." In Transducers ’01 Eurosensors XV, 456–59. Berlin, Heidelberg: Springer Berlin Heidelberg, 2001. http://dx.doi.org/10.1007/978-3-642-59497-7_108.
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Gjonaj, Erion, Yun Ouedraogo, and Sebastian Schöps. "Modelling of Droplet Dynamics in Strong Electric Fields." In Fluid Mechanics and Its Applications, 107–25. Cham: Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-031-09008-0_6.
Повний текст джерелаАнотація:
AbstractWe describe a modelling approach for the simulation of droplet dynamics in strong electric fields. The model accounts for electroquasistatic fields, convective and conductive currents, contact angle dynamics and charging effects associated with droplet breakup processes. Two classes of applications are considered. The first refers to the problem of water droplet oscillations on the surface of outdoor high-voltage insulators. The contact angle characteristics resulting from this analysis provides a measure for the estimation of the electric field inception thresholds for electrical discharges on the surface. The second class of applications consists in the numerical characterization of electrosprays. Detailed simulations confirm the scaling law for the first electrospray ejection and, furthermore, provide insight on the charge-radius characteristics for transient as well as steady state electrosprays.
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Lebreton, Y., G. Berthomieu, and J. Provost. "A Solar Model With Turbulent Diffusion Mixing: Surface Abundances And Oscillations." In Advances in Helio- and Asteroseismology, 95–98. Dordrecht: Springer Netherlands, 1988. http://dx.doi.org/10.1007/978-94-009-4009-3_20.
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Stępień, Jan, and Janusz Stafiej. "Potential Oscillations in Cellular Automaton Based Model for Passivation of Metal Surface." In Developments in Language Theory, 92–101. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-99813-8_8.
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Garrett, Steven L. "Attenuation of Sound." In Understanding Acoustics, 673–98. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-44787-8_14.
Повний текст джерелаАнотація:
Abstract We will capitalize on our understanding of thermoviscous loss to develop an understanding of the attenuation of sound waves in fluids that are not influenced by proximity to solid surfaces. Such dissipation mechanisms are particularly important at very high frequencies and short distances (for ultrasound) or very low frequencies over geological distances (for infrasound). The Standard Linear Model of viscoelasticity introduced the nondimensional frequency, ωτR, that controlled the medium’s elastic (in-phase) and dissipative (quadrature) responses. Those response curves were “universal” in the sense that causality linked the elastic and dissipative responses through the Kramers-Kronig relations. That relaxation-time perspective is essential for attenuation of sound in media that can be characterized by one or more relaxation times related to those internal degrees of freedom that make their equation of state a function of frequency. Examples of these relaxation-time effects include the rate of collisions between different molecular species in a gas (e.g., nitrogen and water vapor in air), the pressure dependence of ionic association-dissociation of dissolved salts in sea water (e.g., MgSO4 and H3BO3), and evaporation-condensation effects when a fluid is oscillating about equilibrium with its vapor (e.g., fog droplets in air or gas bubbles in liquids).
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Bissembayev, Kuatbay, and Tolegen Dikambay. "Periodic Modes of Spatial Oscillations of a Vibration-Proof Body on Three Rolling-Contact Bearings with Expanded Surfaces in Non-resonance Conditions." In Proceedings of 14th International Conference on Electromechanics and Robotics “Zavalishin's Readings”, 763–76. Singapore: Springer Singapore, 2019. http://dx.doi.org/10.1007/978-981-13-9267-2_64.
Повний текст джерелаТези доповідей конференцій з теми "Surface mode oscillations"
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Smith, Elizabeth T., William W. Schultz, and Elijah Kannatey-Asibu. "Modeling Oscillations During Conduction Mode Laser Welding." In ASME 1999 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/imece1999-0725.
Повний текст джерелаАнотація:
Abstract Thermal, optical, and acoustic signals are generated during laser welding by the many physical phenomena which govern the laser beam-material interactions involved in welding. The objective of this study is to analyze one potential source of these signals — oscillations of the molten weld pool. Weld pool oscillations are modeled as gravity-capillary waves in a partially penetrating, conduction mode weld pool. The weld pool is assumed to be stationary and cylindrical, containing inviscid, incompressible, irrotational liquid metal. Dynamic and kinematic boundary conditions are imposed at the free surface of the pool, with impenetrability providing a boundary condition at solid boundaries. Two different edge conditions are examined. First, the free surface is assumed to meet the boundary orthogonally. Second, the contact line is assumed to remain fixed during pool motion. Solution of the governing equations subject to the boundary conditions provides the natural frequencies of oscillation and mode shapes governing pool motion. Results from the analytic model agree well with preliminary experimental data. The dominant mode of oscillation can be characterized as a sloshing of material from the front to the back of the pool, occurring at approximately 700Hz for the conditions examined.
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Mahjoub, Mohamed, Ngoc-Ha Dao, Khac-Long Nguyen, and Stéphane Menand. "Combining Downhole Axial and Surface Oscillation Tools, What Are the Consequences on Tool Face Control Performance?" In IADC/SPE International Drilling Conference and Exhibition. SPE, 2022. http://dx.doi.org/10.2118/208708-ms.
Повний текст джерелаАнотація:
Abstract When drilling in sliding mode, axial oscillation tools (AOT) and surface oscillation tools (SOT) are two possible solutions that are used in the industry to overcome the friction forces, especially in unconventional well trajectories with a long lateral section. The AOT is assembled in the drillstring and run in hole such that it is generally placed in the middle of the lateral section. It is actuated by the mud flow to produce high-frequency axial vibrations. As for the SOT, it is placed at surface and produces low-frequency torsional oscillations in the drillstring by alternating the rotation direction. For some challenging trajectories, the idea of combining both tools, where the SOT reduces the friction on the top part of the trajectory and the AOT deals with the bottom part, seems appealing. However, when coupling the two types of oscillations, one should be careful to the possible implications on tool face control performance. In this paper, time-domain dynamics modeling is used to investigate the AOT and SOT behavior, whether they are employed separately or together. When simulated separately, the tools' influence zones can be identified, and their operating parameters can be tuned accordingly. When combining both tools, if their influence zones are overlapping, coupled axial and torsional oscillations occur and could have consequences on the tool face orientation (TFO). The observations obtained from simulations are confronted to data coming from a well drilled with both tools. Numerical simulations show that the AOT helps the propagation of the torsional motion downhole, because it takes a part of the friction that opposes the torsional oscillations. If the SOT and AOT parameters are jointly well calibrated, then the steering from surface becomes faster, and the tool face control becomes more accurate. However, if the SOT's parameters are calibrated without regard to the AOT influence, then TFO variations could be obtained, indicating unstable tool face control leading to a tortuous well bore. The use of time-domain modeling to jointly characterize the behavior of downhole axial and surface oscillation tools introduced in this work allows a better understanding of the coupling between the two tools. This work provides an opportunity to increase the extent of the lateral sections without impairing the wellbore quality.
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Schro¨der, J. J., and S. Alraun. "An Extra Mode of Enhanced Heat Transfer by Oscillating Bubbles in Minichannels and Microchannels." In ASME 2003 1st International Conference on Microchannels and Minichannels. ASMEDC, 2003. http://dx.doi.org/10.1115/icmm2003-1083.
Повний текст джерелаАнотація:
Experimental investigations on heat transfer in tubular micro- or minichannel arrangements more often report on two-phase flow instabilities, pulsations or oscillations, which result in a remarkable influence on heat transfer efficiency. In order to explain the piston-like oscillations of the steam-plugs and water-slugs (-columns), the authors studied the somehow similar process which occurs in the worldwide known toy steam boat. Experiments have been performed which used a demonstration plant made of glass. By controlled electrical heating, high-speed video, pressure and local temperature measurements, the paths of energy have been disclosed. The results are as surprising as the effect of making gold from sand with respect to an equivalent axial heat-conductivity of the water-filled glass tube. Initiated by these results, an abstracting model is presented that analytically quantifies this new regenerating (oscillating and conducting) heat transfer mode e.g. concerning the combination of a heat recharging tube wall and an oscillating water column in a field of diminishing temperatures between the temperature of the boiler surface and the subcooled bulk water. By introducing these heat transfer details, the steam boat can give an answer, not only on frequency and amplitude of the oscillations, but on the steady state conditions for — or time-dependency of — the location of zero-crossing as well. Experimental results and model calculations are in good agreement and need no fitting factors. This is the base to discuss that process along with its physical parameters and compare it to the above mentioned observations in flow-boilers or pulsating heat pipes etc. which use microchannels or minichannels.
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Mortazavi, Mehdi, and Taylor Pedley. "Dynamics of Droplets in Core Gas Flow Superimposed With Acoustic Pressure Waves." In ASME 2021 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/imece2021-72011.
Повний текст джерелаАнотація:
Abstract During the operation of a proton exchange membrane fuel cell, water is produced in the cathode electrode. Accumulation of produced water in the flow channel can block the transport of reactants, which ultimately lowers the performance of the cell. The water content in the flow channel can be efficiently removed from the channel with an external excitation. Previously, the author reported utilization of acoustic pressure waves in order to remove the water content from the flow channel [1]. However, the dynamics of liquid water droplets during this removal process were not investigated. The current study investigates dynamics of water droplets on the surface of the gas diffusion layer (GDL) when acoustic pressure waves are superimposed on the core gas flow. Two different modes of superimposition were implemented; (i) continuous, and (ii) on demand. Study of droplet dynamics was achieved by visualizing the droplet from the side-view with a high-speed camera. When the superimposition was done in the continuous mode at 20 Hz, the droplet went through the rocking motion on the surface of the GDL. For 60 and 80 Hz of superimposition, in addition to the rocking motion, droplets underwent the prolate mode of oscillation, which was characterized by vertical oscillations. For higher frequencies of acoustic pressure waves, in addition to rocking and prolate modes of oscillation, droplets underwent the oblate mode of oscillation, which featured horizontal oscillations. The on on demand experiments demonstrated that the liquid water droplet detached from the surface of the GDL only when the droplet size was large enough.
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Lakis, A. A., and S. Neagu. "Free Surface Effects on the Dynamics of Cylindrical Shells Partially Filled With Liquid." In ASME 1997 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/imece1997-0102.
Повний текст джерелаАнотація:
Abstract This paper presents an analytical model for the dynamic analysis of thin cylindrical shells partially filled with liquid. The method used is a combination of finite element analysis and classical shell theory, and the objective is to determine the specific displacement functions which best represent the real deformations. The effect of oscillations of the free surface of the liquid on fluid-shell vibration is studied, and consideration is given to the influence of such parameters as: the circumferential mode, the axial mode, the structural damping, the length of the shell and the forces induced by the liquid. The shell is divided into cylindrical finite elements and the displacement functions are derived using Sanders’ thin shell theory. The stiffness and mass matrices of the shell are derived analytically. For the liquid contained in the shell, boundary conditions are prescribed and the behaviour of the liquid is expressed by a potential function. The kinetic and potential energies of the liquid are evaluated in order to establish the influence of surface oscillation on fluid-shell vibration.
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Zagitov, R. A., N. V. Shuvaev, A. N. Dushko, and Yu N. Shmotin. "Numerical Simulation of Unsteady Flow Around Oscillating Blade." In ASME Turbo Expo 2012: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/gt2012-69458.
Повний текст джерелаАнотація:
The paper is pointed to the problem of numerical simulation of unsteady flow around an oscillating blade in jet engine compressor. Single compressor rotor blade row is considered. It is assumed that mode shape and frequency of blade oscillation is not influenced by airflow. The system of governing equations is transformed to a moving coordinate system to describe blade oscillations. Multi-block structured “H-O” grid is used for spatial discretization. Inner boundary of “O”-grid (representing blade airfoil surface) is moved to describe blade airfoil oscillation. To minimize discretization error, special morphing procedure was developed for “O”-grid to accommodate blade airfoil surface motion. Other grid blocks remain steady. Nonlinear harmonic method is applied to integrate Euler equations on time variable. For spatial derivation Dispersion-Relation-Preserving methodology is applied. To maintain solution accuracy nonreflecting boundary conditions are implemented on artificial boundaries (inlet and outlet). Resulting system of nonlinear algebraic equations is resolved numerically. As an alternative, time-marching method is realized in ANSYS CFX by means of user routines. Numerical and experimental cascade results are compared.
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Buffum, Daniel H., and Sanford Fleeter. "The Aerodynamics of an Oscillating Cascade in a Compressible Flow Field." In ASME 1989 International Gas Turbine and Aeroengine Congress and Exposition. American Society of Mechanical Engineers, 1989. http://dx.doi.org/10.1115/89-gt-271.
Повний текст джерелаАнотація:
Fundamental experiments are performed in the NASA Lewis Research Center Transonic Oscillating Cascade Facility to investigate and quantify the aerodynamics of a cascade of biconvex 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 degrees, with the harmonic torsional airfoil cascade oscillations at realistic high reduced frequency and unsteady data obtained at several interblade phase 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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Zhao, Xiaopeng, and Harry Dankowicz. "Characterization of Intermittent Contact in Tapping Mode Atomic Force Microscopy." In ASME 2005 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2005. http://dx.doi.org/10.1115/detc2005-84741.
Повний текст джерелаАнотація:
Tapping-mode atomic force microscopy has wide applications for probing the nanoscale surface and subsurface properties of numerous materials in a variety of environments. Strongly nonlinear effects due to large variations in the force field on the probe tip over very small length scales and the intermittency of contact with the sample, however, result in strong dynamical instabilities. These can result in a sudden loss of stability of low-contact-velocity oscillations of the atomic-force-microscope tip in favor of oscillations with high contact velocity, coexistence of stable oscillatory motions, and destructive, nonrepeatable, and unreliable characterization of the nanostructure. In this paper, dynamical systems tools for piecewise smooth systems are employed to characterize the loss of stability and associated parameter hysteresis phenomena.
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Rhee, J. K., T. B. Norris, Y. Arakawa, M. Nishioka, and C. Weisbuch. "Dynamics of Coherently Excited Semiconductor Microcavities." In International Conference on Ultrafast Phenomena. Washington, D.C.: Optica Publishing Group, 1994. http://dx.doi.org/10.1364/up.1994.tue.5.
Повний текст джерелаАнотація:
Recently, cavity quantum electrodynamic (QED) effects in semiconductor microcavities have been of considerable interest since, in the weak-coupling regime they play an important role in selectively increasing spontaneous emission into the lasing mode of vertical-cavity surface-emitting lasers (VCSEL’s) [1,2], enabling low-threshold, high speed, and high efficiency. In a strong-coupling regime, the normal modes of the coupled system are superpositions of the exciton and cavity modes. Hence the impulsively excited system will evolve in time with the energy oscillating between the exciton and cavity modes. This is known as a vacuum-Rabi oscillation (VRO), with a frequency of Ω=d¯⋅E¯/@@h, where d¯ is the transition dipole moment of atoms and E¯ the vacuum-field strength. Of course, VRO are observable only when the cavity lifetime and exciton dephasing time are long enough compared to VRO period. Recently, Weisbuch et al. [3] have reported an observation of the normal-mode vacuum Rabi splitting in 2-D-exciton/planar-DBR microcavities. The observed splittings were as large as 6 meV in reflection and transmission spectra, implying 690-fs vacuum Rabi oscillations.
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Koch, M., J. Shah, H. Wang, T. C. Damen, J. E. Cunningham, and W. Y. Jan. "Ultrafast oscillations in the optical emission from a semiconductor microcavity." In International Conference on Ultrafast Phenomena. Washington, D.C.: Optica Publishing Group, 1996. http://dx.doi.org/10.1364/up.1996.thb.2.
Повний текст джерелаАнотація:
We report here the first investigation of femtosecond time-resolved emission from a semiconductor microcavity resonantly excited with intense femtosecond pulses. The emission intensity, which exhibits a strong threshold behavior, shows novel, well-pronounced oscillations that have a period of 600 fs and that last for several picoseconds. These THz oscillations can be associated with the appearance of a new mode in the spectrum and become more pronounced with pump intensify. The frequency of these oscillations is 20 times higher than those reported previously [1]. Our investigation probes novel aspects of semiconductor microcavities and vertical-cavity surface-emitting lasers that have attracted considerable interest recently [1-6]. Observations reported earlier include: coherent vacuum Rabi oscillations after weak resonant optical excitation [2-4], the emission of single pulses after nonresonant optical pumping [5], and relaxation oscillations after electrical pumping [1].
Звіти організацій з теми "Surface mode oscillations"
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Yeates, Elissa, Kayla Cotterman, and Angela Rhodes. Hydrologic impacts on human health : El Niño Southern Oscillation and cholera. Engineer Research and Development Center (U.S.), January 2020. http://dx.doi.org/10.21079/11681/39483.
Повний текст джерелаАнотація:
A non-stationary climate imposes considerable challenges regarding potential public health concerns. The El Niño Southern Oscillation (ENSO) cycle, which occurs every 2 to 7 years, correlates positively with occurrences of the waterborne disease cholera. The warm sea surface temperatures and extreme weather associated with ENSO create optimal conditions for breeding the Vibrio cholerae pathogen and for human exposure to the pathogenic waters. This work explored the impacts of ENSO on cholera occurrence rates over the past 50 years by examining annual rates of suspected cholera cases per country in relation to ENSO Index values. This study provides a relationship indicating when hydrologic conditions are optimal for cholera growth, and presents a statistical approach to answer three questions: Are cholera outbreaks more likely to occur in an El Niño year? What other factors impact cholera outbreaks? How will the future climate impact cholera incidence rates as it relates to conditions found in ENSO? Cholera outbreaks from the 1960s to the present are examined focusing on regions of Central and South America, and southern Asia. By examining the predictive relationship between climate variability and cholera, we can draw conclusions about future vulnerability to cholera and other waterborne pathogenic diseases.