About: Oscillation is a research topic. Over the lifetime, 28706 publications have been published within this topic receiving 324621 citations.
Papers published on a yearly basis
TL;DR: In this article, an analysis of laser action in a periodic structure is presented, where the resonant frequencies and threshold criteria for the modes of oscillation have been determined for both index and gain periodicities.
Abstract: An analysis of laser action in a periodic structure is presented. A model of two counter‐running waves coupled by backward Bragg scattering is used. The resonant frequencies and threshold criteria for the modes of oscillation have been determined for both index and gain periodicities. Analytical approximations are given for both the high‐ and low‐gain cases, and computational results for the intermediate regimes.
TL;DR: In this article, the authors presented theoretical calculations of the large-signal admittance and efficiency achievable in a silicon p-n-v-ns Read IMPATT diode.
Abstract: This paper presents theoretical calculations of the large-signal admittance and efficiency achievable in a silicon p-n-v-ns Read IMPATT diode. A simplified theory is employed to obtain a starting design. This design is then modified to achieve higher efficiency operation as specific device limitations are reached in large-signal (computer) operation. Self-consistent numerical solutions are obtained for equations describing carrier transport, carrier generation, and space-charge balance. The solutions describe the evolution in time of the diode and its associated resonant circuit. Detailed solutions are presented of the hole and electron concentrations, electric field, and terminal current and voltage at various points in time during a cycle of oscillation. Large-signal values of the diode's negative conductance, susceptance, average voltage, and power-generating efficiency are presented as a function of oscillation amplitude for a fixed average current density. For the structure studied, the largest microwave power-generating efficiency (18 percent at 9.6 GHz) has been obtained at a current density of 200 A/cm2, but efficiencies near 10 percent were obtained over a range of current density from 100 to 1000 A/cm2.
TL;DR: The 40-50-day cyclone oscillation is the result of large-scale circulation cells oriented in the equatorial plane that move eastward from at least the Indian Ocean to the central Pacific as discussed by the authors.
Abstract: Observational aspects of the 40–50-day oscillation are reviewed. The oscillation is the result of large-scale circulation cells oriented in the equatorial plane that move eastward from at least the Indian Ocean to the central Pacific. Anomalies in zonal winds and the velocity potential in the upper troposphere often propagate the full circumference of the globe. Related, complex convective regions also show an eastward movement. There is a zonally symmetric component to the oscillation. It is manifest in changes in surface pressure and in the relative atmospheric angular momentum. The oscillation is an important factor in the timing of active and break phases of the Indian and Australian monsoons. It affects ocean waves, currents, and air-sea interaction. The oscillation was particularly active during the First GARP (Global Atmospheric Research Program) Global Experiment year, and some features that were evident during the Monsoon Experiment are described.
TL;DR: In this paper, the authors review the fundamentals, applications and future tendencies of dynamic atomic force microscopy (AFM) methods and present a detailed quantitative comparison between theoretical simulations and experiment.
Abstract: In this report we review the fundamentals, applications and future tendencies of dynamic atomic force microscopy (AFM) methods. Our focus is on understanding why the changes observed in the dynamic properties of a vibrating tip that interacts with a surface make possible to obtain molecular resolution images of membrane proteins in aqueous solutions or to resolve atomic-scale surface defects in ultra high vacuum (UHV). Our description of the two major dynamic AFM modes, amplitude modulation atomic force microscopy (AM-AFM) and frequency modulation atomic force microscopy (FM-AFM) emphasises their common points without ignoring the differences in experimental set-ups and operating conditions. Those differences are introduced by the different feedback parameters, oscillation amplitude in AM-AFM and frequency shift and excitation amplitude in FM-AFM, used to track the topography and composition of a surface. The theoretical analysis of AM-AFM (also known as tapping-mode) emphasises the coexistence, in many situations of interests, of two stable oscillation states, a low and high amplitude solution. The coexistence of those oscillation states is a consequence of the presence of attractive and repulsive components in the interaction force and their non-linear dependence on the tip–surface separation. We show that key relevant experimental properties such as the lateral resolution, image contrast and sample deformation are highly dependent on the oscillation state chosen to operate the instrument. AM-AFM allows to obtain simultaneous topographic and compositional contrast in heterogeneous samples by recording the phase angle difference between the external excitation and the tip motion (phase imaging). Significant applications of AM-AFM such as high-resolution imaging of biomolecules and polymers, large-scale patterning of silicon surfaces, manipulation of single nanoparticles or the fabrication of single electron devices are also reviewed. FM-AFM (also called non-contact AFM—NC-AFM) has achieved the long-standing goal of true atomic resolution with AFM in UHV. Our analysis starts with a discussion of the relation between frequency shifts and tip–surface interactions, emphasising the ability of perturbation theory to describe the measured frequency shift. We discuss the role of short-range chemical interactions in the atomic contrast, with particular attention to semiconductor and ionic (alkali halides and oxides) surfaces. Also included is a detailed quantitative comparison between theoretical simulations and experiment. Inversion procedures, the determination of the tip–sample interaction from the frequency shift versus distance curves above specific sites, are also reviewed. We finish with a discussion of the optimal range of experimental operation parameters, and the use of damping (excitation amplitude) as a source of atomic contrast, including the possible interpretation in terms of microscopic dissipation mechanisms.
TL;DR: In this article, a coupled atmosphere-ocean model is developed and used to study the ENSO (El Niñ/Southern Oscillation) phenomenon, which reproduces certain key features of the observed phenomenon including the recurrence of warm events at irregular intervals with a preference for three to four years.
Abstract: A coupled atmosphere-ocean model is developed and used to study the ENSO (El Niñ/Southern Oscillation) phenomenon. With no anomalous external forcing, the coupled model reproduces certain key features of the observed phenomenon. including the recurrence of warm events at irregular intervals with a preference for three to four years. It is shown that the mean sea surface temperature, wind and ocean current fields determine the characteristic spatial structure of ENSO anomalies. The tendency for phase-locking of anomalies is explained in terms of a variation in coupling strength associated with the annual cycle in the mean fields. Sensitivity studies reveal that both the amplitude and the time of scale of the oscillation are sensitive to several parameters that affect the strength of the atmosphere–ocean coupling. Stronger coupling implies larger oscillations with a longer time scale. A critical element of the model oscilliation is the variability in the equatorial heat content of the upper o...
Trending Questions (10)