Discrete Frequency Bands Research Articles

Simultaneous multifrequency observations of Jovian S bursts

The millisecond component of the Jovian decameter emission has been studied at high resolution, in order to examine the short‐term behavior of the S‐burst drift rates and to define the drift rate spectrum at high frequencies. By using dynamic spectra having 300‐µs and 3.3‐kHz resolution and covering discrete frequency bands in the range 26–33 MHz, large systematic changes in the magnitude of the S‐burst drift rates are observed to take place on a time scale of seconds to minutes. It is noted that the drift rate variability is of sufficient magnitude to prevent reliable evaluation of the drift rate dependence on frequency, unless simultaneous or near‐simultaneous multifrequency measurements are made. In presenting such observations we fail to observe the predicted drift rate turnover in the spectrum, in spite of measurements made at frequencies within 0.6 to 4.4 MHz of the electron gyrofrequency at the Jovian foot of the Io flux tube. This result is interpreted in terms of an ionospheric electron source, rather than within the conventional theoretical framework of trapped particles initially accelerated at Io. Low‐resolution intensity‐time tracings reveal a characteristic organization of S bursts into groups, each of several seconds duration and consisting of tens to hundreds of bursts. Abrupt changes in mean drift rates from group to group suggest that some of the group structuring may be a source‐related rather than a scintillation‐related phenomenon. Finally, some evidence exists for systematic variations in the group‐to‐group mean drift rates, which may be due to predictiable temporal changes in the magnetic field gradient on the Io flux tube. These temporal changes are due to motion of the Io‐associated magnetic flux tube in the Jovian magnetosphere.

An investigation into the effects of sinusoidal and random vibrations on the strength and flow properties of bulk solids

This paper is concerned with the determination of the effects of vibration frequency, amplitude and energy input on the shear strength, yield loci and flow function of bulk solids. A modified Jenike shear cell fitted with a vibration exciter is used, the equipment being designed to permit the shear strength to be measured during the application of both discrete frequency and broad band random vibrations. Studies using pyrophyllite and iron ore show that the shear strength and flow function can be reduced significantly by transverse vibrations, there being particular frequency bands over which the shear strength is minimised. Measurements of compressibility during lateral vibrations are obtained and the results are compared with the frequency versus shear data. Dynamic system identification analysis is performed to provide information on the dynamic properties of bulk materials, particularly with regard to the distribution of vibration energy as a function of frequency.

Studies of central functional equivalence—I Time-varying distribution of power in discrete frequency bands of the egg as a function of drug exposure

Long-term recordings of the spontaneous EEG were made in Macaco mulattu monkeys with chronically implanted epidural electrodes. Power spectra were computed for 34-min segments of 4-sec continuous epochs over a bandwidth of 0.25–64.0 Hz with 0.25 Hz resolution. While analysis of ensemble spectral averages showed differences between a wide range of psychotropic agents, the examination of the time course of spectral changes, especially within certain discrete spectral bands, permitted distinctions between agents with mainly sedative or anxiolytic properties. Sedatives (e.g. glutethimide, amobarbital and meprobamate) produced their greatest energy increase in high-frequency bands (16–64 Hz) and the state was stable. In contrast, anxiolytic agents (e.g. chlordiazepoxide and clonazepam) showed energy increases of lesser magnitude only in lower frequency bands (8–32 Hz) and less state stability in those bands. Agents with mixed pharmacological effects (e.g. clorazepate and nitrazepam) produced mixed effects on the EEG spectra with this type of analysis.

Hand-arm vibration, Part III: Subjective response characteristics of individuals to hand-induced vibration

Tests were developed and conducted to determine an individual's subjective response to hand-induced vibration. These tests included equal sensations, threshold and annoyance tests. From the results of these tests, it was possible to make statements with regard to the physiological mechanisms that were responsible for an individual's perception of both discrete frequency and broad band vibration that was directed into the hand. By using the results of this and past investigations, it was possible to discuss an individual's perception of hand-induced vibration relative to the nature of the energy transfer that occurred between a vibrating handle and the hand. This discussion raised some questions with regard to the reliability of previous techniques that have been used to establish hazardous hand vibration criteria.

A small signal analysis of an impatt device having two avalanche layers interspaced by a drift layer

A small signal analysis of an IMPATT device ( p− n− i− p− n structure) having two avalanche layers interspaced by a drift layer is carried out. When the widths of the two avalanche layers are different the device exhibits discrete negative conductance frequency bands separated by positive conductance frequency bands. Oscillations are expected to occur more favourably in the lowest frequency band where the maximum and minimum values of magnitudes of negative conductance and negative Q occur, respectively. When the two avalanche layer widths are equal, the device impedance is a high Q-reactance whose magnitude depends on the d.c. current.

Dual-band reflector-feed element for frequency-reuse applications

Proposed frequency-reuse systems have created a need for reflector-feed elements that generate symmetrical primary patterns with low crosspolar content. The letter describes a horn radiator of only 1λ diameter that meets these requirements over two discrete frequency bands.

Verbal deficit in children with hearing loss.

This study was designed to explore the relation between language and/or verbal ability and reduced auditory acuity at discrete frequencies and various frequency bands in children with high frequency impairment. Correlations reveal significant relationships between reduced hearing levels at 1,000, 1,500, 2,000, and 3,000 cps and lowered verbal ability as measured by the Wechsler Intelligence Scale for Children.

Ultrashort electromagnetic waves from arc discharges at the plasma frequency and its second harmonic

The radiation detected at four discrete frequency bands from the positive column in argon at low pressure is compatible with that from a source comprising two modes of plasma waves—oscillations of a plasma plate and cylinder.

Triplet Audiometry: An Analysis of Band Discrimination in Speech Reception

The great redundancy of normal speech under favourable conditions, e.g. in the way it is proffered to a patient in routine speech audiometry, opens the possibility of determining a person's discrimination skill in a discrete band of frequencies. By the use of fdtered speech consisting of components that cover only that discrete frequency band we can measure in the normal way the articulation score in that particular part of the pitch range.