High Frequency Ripple Research Articles

A Soft Switching Half-Bridge Doubler Boost Converter Operating with Unity Power Factor

This paper proposes a half-bridge doubler boost converter associated with an active commutation cell in order to minimize commutation losses. The converter operates with unity power factor and is able to provide high output voltages. The voltages across the semiconductor devices are low and approximately equal to the output voltage, as doubled output voltages and reduced high frequency ripple can be achieved. A detailed mathematical analysis concerning its operation is presented, since simulation and experimental results describe the converter performance.

High voltage generator for the power supply of photomultipliers in the time of flight system of Alpha Magnetic Spectrometer-2 experiment

In this report, the behaviour of the first prototype high voltage generator (HVG) that might be used in the time of flight (TOF) system for the AMS-2 experiment is described. The system receives a positive continuous voltage about 100–120 V as input, and it provides a programmable negative continuous voltage from −1600 to −2400 V as output, versus a total load of 50 MΩ. The most important aspect is the absence of a transformer which usually is used in the step-up DC–DC converters. In the TOF system of alpha magnetic spectrometer (AMS)-2 experiment there is a big magnetic field, higher than 2 kG, that does not allow to use a transformer, therefore this prompted us to use the Cockroft–Walton system. The power consumption is about 300 mW and the peak-to-peak high frequency ripple is lower than 0.3% of the output high voltage. We also estimated the reliability of the HVG and we obtained a failure probability lower than 0.5% after three years of continuous functioning. Besides, in this report, much importance was given to the calculation of a simple model of the system to estimate the stability margins.

First Results of a Monochromized 200KV TEM

FEI is currently finishing the construction of a monochromized 200kV (S)TEM which aims at 0.1 eV resolution in Electron Energy Loss Spectroscopy (EELS). This requires improvement of the 200kV supply, improvement of the EELS spectrometer, and the incorporation of an electron beam monochromator. This microscope will be delivered to the National Centre for High Resolution Electron Microscope at the University of Delft.The present 200kV supply contributes 0.2 eV to the energy resolution because of its instabilities, drift and high frequency ripple. in order to reduce this, mechanical as well as electrical damping elements are being added, and sources of cross-talk between the high frequency generator and the high tension are eliminated. in this paper, we present preliminary results obtained with a standard 200kV supply; we expect to present results of the improved 200kV supply at the conference.The resolution of a present-day standard 200kV spectrometer is now typically 0.4 eV. in order to improve on this, GATAN has developed a HR-EELS spectrometer for the monochromized TEM.

Correction for Traub et al., A Model of High-Frequency Ripples in the Hippocampus Based on Synaptic Coupling Plus Axon-Axon Gap Junctions between Pyramidal Neurons

Correction: In the article, “A Model of High-Frequency Ripples in the Hippocampus Based on Synaptic Coupling Plus Axon-Axon Gap Junctions between Pyramidal Neurons,” by R. D. Traub and A. Bibbig, which appeared on pages 2086–2093 of the March 15, 2000 issue, two numbers were reported

A Model of High-Frequency Ripples in the Hippocampus Based on Synaptic Coupling Plus Axon–Axon Gap Junctions between Pyramidal Neurons

So-called 200 Hz ripples occur as transient EEG oscillations superimposed on physiological sharp waves in a number of limbic regions of the rat, either awake or anesthetized. In CA1, ripples have maximum amplitude in stratum pyramidale. Many pyramidal cells fail to fire during a ripple, or fire infrequently, superimposed on the sharp wave-associated depolarization, whereas interneurons can fire at high frequencies, possibly as fast as the ripple itself. Recently, we have predicted that networks of pyramidal cells, interconnected by axon-axon gap junctions and without interconnecting chemical synapses, can generate coherent population oscillations at >100 Hz. Here, we show that such networks, to which interneurons have been added along with chemical synaptic interactions between respective cell types, can generate population ripples superimposed on afferent input-induced intracellular depolarizations. During simulated ripples, interneurons fire at high rates, whereas pyramidal cells fire at lower rates. The model oscillation is generated by the electrically coupled pyramidal cell axons, which then phasically excite interneurons at ripple frequency. The oscillation occurs transiently because rippling can express itself only when axons and cells are sufficiently depolarized. Our model predicts the occurrence of spikelets (fast prepotentials) in some pyramidal cells during sharp waves.

High-Frequency Oscillations in the Output Networks of the Hippocampal–Entorhinal Axis of the Freely Behaving Rat

Population bursts of the CA3 network, which occur during eating, drinking, awake immobility, and slow-wave sleep, produce a large field excitatory postsynaptic potential throughout stratum radiatum of the CA1 field (sharp wave). The CA3 burst sets into motion a short-lived, dynamic interaction between CA1 pyramidal cells and interneurons, the product of which is a 200 Hz oscillatory field potential (ripple) and phase-related discharge of the CA1 network. Although many CA1 pyramidal neurons discharge during the time (50-100 msec) of each sharp wave, each wave of a ripple (approximately 5 msec) reflects the synchronization of more discrete subsets of CA1 neurons. When we used multi-site recordings in freely behaving rats, we observed ripples throughout the longitudinal extent (approximately 4-5 mm) of the dorsal CA1 region that were coherent for multiple cycles of each ripple. High-frequency ripples were also observed throughout the hippocampal-entorhinal output pathway that were concurrent but less coherent on a cycle-by-cycle basis. Single and multiunit neuronal activity was phase-related to local ripples throughout the hippocampal-entorhinal output pathway. Entorhinal ripples occurred 5-30 msec after the CA1 ripples and were related to the occurrence of an entorhinal sharp wave. Thus, during each hippocampal sharp wave, there is powerful synchronization among the neuronal networks that connect the hippocampus to the neocortex. We suggest that this population interaction (1) biologically constrains theoretical models of hippocampal function and dysfunction and (2) has the capacity to support an "off-line" memory consolidation process.

Development of ultra high resolution analytical electron microscope ISI-EM-002A

Total design concept of EM-002A is to realize the following essential performance, that is, 1) attainment to ultimate high resolution as the conventional electron microscope, 2) complete compatibility of the high resolution mode and the analytical mode, 3) identification of the analyzed region and the observed image with atomic-level resolution, 4) observation of ultra fine structure of the biological specimen with maximum high contrast and so on.[Electron source] Accelerating voltage ranges from 20kV to 120kV in 6 steps Double Cockroft-Walton circuit is used as the high voltage generator and the high frequency ripple voltage is reduced to 0.1V. Electron gun assembly is composed of high voltage alumina insulator, whose shape is so well designed as to suppress micro-discharge to the negligible order.[Objective lens and specimen chamber] The objective lens is a strong symmetrical lens where the specimen chamber is located between the symmetrical upper and lower objective lens magnetic circuits. The objective lens has two powerful pole pieces, one being used for the ultra high resolution mode and the other for the standard mode.

Development of Accumulator for High Frequency Ripple Absorption

A new accumulator is developed which is possible to absorb ripples by pump and cavitation in valve, ranging from several hundred to several thousand c/sec in the hydraulic system. (Acc: abreviation of Accumulator) The attenuation of Acc in the case of constant flow source and constant pressure source when the pipe is terminated with a throttling load, was computed and compared with experimental values. Observation of the bladders of hat and belows type used in this experiment, was made and by life test, the endurance limit of them was investigated. By improving the bladder's profile and smoothing stress distribution, the author affirmed that this Acc had good endurance limit under ripple pressure of about ±15 kg/cm2.

Development of Accumulator for High Frequency Ripple Absorption

Development of Accumulator for High Frequency Ripple Absorption

Ripple Filter Systems of the Zero Gradient Synchrotron and Means for Long, Magnetically Controlled Beam Spills

Ripple frequencies in the ring magnet guide field of the Zero Gradient Synchrotron (ZGS) range from less than 1 Hz to several kHz. Filter systems which reduce the ripple components to negligible magnitudes are described, as is the use of these systems for long, magnetically controlled beam spills. High frequency ripple is attenuated by an improved LCR filter. Low frequency ripple is reduced by a feedback loop from B to the rectifier phase control of the ring magnet power supply (RMPS). The attenuation of the mid-frequency components is accomplished with a feedback loop from B to a ripple bucking coil in each octant of the ZGS. Two modes of operation for magnetically controlled beam spills without RF structure are discussed. In one mode the feedback to the low frequency loop. is a signal from a spilled beam monitor. In the second mode the spilled beam monitor drives both the low frequency and the mid frequency loops.

On the nature of atmospherics—IV

The modern study of the rapid changes of the earth’s electric field associated with lightning flashes was initiated by C. T. R. Wilson in 1916. Wilson made observations on the net changes of the earth’s field due to the destruction of near-by thundercloud moments by lightning flashes and, since interest was centred solely in the magnitude of the initial and final values of the field, a relatively sluggish electrical indicator (capillary electrometer) was found most convenient. In observations of essentially the same character, Appleton, Watt, and Herd, using a string electrometer as well as a capillary electrometer, made measurements at greater distances from the discharge channel. The work of Wilson, at distances usually within the region of audible thunder, had shown that the net changes of the earth’s field associated with lightning flashes were more frequently positive than negative in sign. On the other hand, Appleton, Watt, and Herd found the opposite preponderance, and this led them to conclude that a thundercloud is frequently, if not always, bipolar and, further, that in order to account for the signs of the field changes it must be assumed that a very frequently occurring type of bipolar thundercloud is one with the positive charge uppermost. These conclusions were later confirmed by Schonland and Craib in observations made in South African thunderstorms. The measurements made by Appleton, Watt, and Herd on disturbances of the earth’s electric field also included observations on the wave-form of those naturally occurring electric waves known to radio-engineers as atmospherics. In this series of observations the potential variations developed across a condenser or resistance included in a damped wireless antenna were examined visually by means of a sensitive cathode-ray oscillograph. The results of a statistical analysis of a large number of individual drawings of wave-forms showed the type of atmospheric observed to be a relatively long aperiodic or quasi-periodic electrical disturbance of duration 2 to 3 milliseconds (msec.) and intensity 0·1 volt per metre (v. /m.). High-frequency ripples on the main gross structure of quasi-frequencies up to 10 kilocycles per second (kc. /s.) were, however, noted and the interferent effects of atmospherics were attributed to such high-frequency components rather than to the effect of the relatively slow main disturbance.