Observation Of Low-frequency Oscillations Research Articles

Observations of low-frequency oscillations of the ionospheric electric field over fractures in the Earth’s crust

Observations of low-frequency oscillations of the ionospheric electric field over fractures in the Earth’s crust

Observations of low frequency oscillations due to transverse sheared flows

This Letter details observations of low frequency (i.e., ω⩽Ωi, where Ωi is the ion cyclotron frequency), coherent instabilities in the Auburn Linear Experiment for Instability Studies (ALEXIS). In the ALEXIS device, which is a 1.8-m long magnetized plasma column, the observed instabilities are excited by the presence of sheared flows in the plasma that are transverse to the axial magnetic field. The instabilities have long azimuthal wavelengths (m⩽2) and are localized in the plasma to regions where the sheared flow is maximized and are anticorrelated to both density gradients and field aligned currents.

Observation of low frequency oscillations in GaAs samples grown by molecular beam epitaxy at low temperatures

We have observed Low Frequency Oscillations (LFO) in a GaAs sample grown by molecular beam epitaxy (MBE) at 300 °C as a function of applied electric field, temperature and illumination intensity. Time series of the oscillations for different values of the applied electric field at room temperature were obtained. We have also obtained the jxE characteristics as a function of temperature and light intensity. We were able to control the LFO using three experimental parameters, the electrical field, which controls the oscillation frequency, and the temperature and illumination intensity, which control the carrier density and field-enhanced trapping. We were able to identify the LFO dependence on the carrier density and on the field-enhanced trapping.

Regular low frequency cardiac output oscillations observed in critically ill surgical patients

A serendipitous finding during development of an automated “electronic flow chart” system to gather data on ICU patients [1] was the observation of low frequency oscillations in blood pressure that were not explained by systematic variability in the environment. [2] This finding has since been confirmed by others. [3,4] In the present report, hemodynamic data for critically ill surgical patients was continuously collected and visualized on a computer workstation to search for patterns not noted by standard monitoring. With this system, we observed low-frequency periodic oscillations in the cardiac output of ten patients, with regular periodicities of 4 to 280 minutes (average = 34 minutes). The mortality rate in these patients was 40%, while the mortality was only 10.8% in 83 similarly monitored intensive care unit (ICU) patients who did not develop regular oscillations in cardiac output. Interestingly, these oscillatory patterns appear to be associated with inadequate resuscitation of increased metabolic rates. The mathematical definition of “chaos” refers to irregular behavior that appears to be random but is actually deterministic. [5] A surprising finding concerning transitions between states of apparent randomness and order in nonlinear systems is that many systems become more organized after being disturbed. Chaotic behavior in biological systems may represent a normal physiologic state, while the loss of chaotic behavior may herald a pathophysiologic state. [6] The mechanism of the regular low frequency oscillations in cardiac output remains to be determined, but the high mortality rate suggests that it is a pathophysiologic marker, perhaps due to inadequate oxygen delivery in under-resuscitated shock. © 1997 John Wiley & Sons, Inc.

Low frequency oscillations in turbulent Rayleigh-Benard convection: laboratory experiments

This is a report on observations of low frequency oscillations in turbulent Rayleigh-Benard convection, in the Rayleigh number ( R) range 10 7–10 8, with Prandtl number (Pr) equal to 7. It has been known that for convecting layers with large aspect ratio A, a steady large scale flow sets in at R = 2 × 10 6. Tilted transient plumes embedded in this flow, and maintaining it through Reynolds stresses, drift in one direction along the bottom of the layer, and in the opposite direction along the top. At a fixed point near the bottom or top boundary, there is a variability associated with the passage of these plumes. We call this the high frequency variability. A new kind of organization is observed for 10 7 < R < 10 8; clusters of transient tilted plumes travel in a horizontal direction as coherent units. These clusters are separated from each other by quiescent zones with almost no plumes. Now at a fixed point near the bottom boundary, there is a low frequency variability associated with the passage of clusters, as well as the high frequency variability from the passage of plumes within the cluster. Quantitative information on this low frequency oscillation derived from space-time portraits and from temperature time series is presented. Heat flux measurements show a Nusselt number ( N)-Rayleigh number relationship for 10 6 < R < 10 8 which is hysteretic for A = 12, but when the convecting layer is partitioned into 144 cells each with A = 1, hysteresis is not present and the N- R relationship then agrees with earlier results for single cells with A = 1.

Observations of low-frequency oscillations during relativistic-electron-beam-plasma interactions

During propagation of a relativistic electron beam in hydrogen gas at sub-torr pressures using a foil-less diode, low-frequency oscillations in the megahertz range are observed in the net current wave forms, and continue even after passage of the beam. The novel feature of the experiment is that both beam generation and propagation take place in the same low-pressure regime, and hence the beam parameters are functions of gas pressures. Analysis of the experimental results shows that the low-frequency oscillations result from the resistive-hose instability.

Tonks-Dattner共振においてパラメトリックに励起された低周波振動の観測

Tonks-Dattner共振においてパラメトリックに励起された低周波振動の観測

Observation of low‐frequency oscillations parametrically excited in tonks‐dattner resonances

Observation of low‐frequency oscillations parametrically excited in tonks‐dattner resonances

Observation of low-frequency oscillations in gallium-arsenide avalanche diodes

The operation of gallium-arsenide avalanche-diode oscillators in a low-frequency mode is reported. The onset of oscillation is accompanied by a significant decrease in the direct voltage across the diode which is characteristic of TRAPATT operation. Pulsed output powers of 880 mW with 3.5% efficiency at 1.5 GHz have been obtained.