Changes In Signal Strength Research Articles

Relationships between quasi-periodic VLF emission and geomagnetic pulsation

Relationships between quasi-periodic VLF emissions (QP) and geomagnetic pulsations are examined, based on observations at Syowa Station, Antarctica. It is confirmed that QP emissions can be classified into two types according to whether or not QP emissions are accompanied by geomagnetic pulsations with approximately the same period. One type, associated with concurrent pulsations, is a daytime phenomenon and often occurs in moderate magnetic activity. The QP period ranges mostly from 20 to 60 s. The spectral form depends significantly on the modulation period. When the period is longer than 30–40 s, the upper frequency limit of the emission band varies almost synchronously with the change in signal strength and the pulsation wave form. The rising characteristic of the QP component which comprises diffuse noises occasionally with discrete emissions, is observed when the period is shorter than 30–40 s. It is very likely that the QP emission of this type is caused by the interaction between whistler turbulence and compressional hydromagnetic waves in the outer magnetosphere. Another type, without any corresponding pulsation has a broad maximum of occurrence in the afternoon-evening and is observed in quiet geomagnetic conditions. The QP component, consists of either diffuse noises or discrete periodic emissions or a combination of both, and generally shows a midfrequency rise. These characteristics are very similar to those of QP emissions observed at Eights ( L ≅ 4). It is suggested that this type of QP emission is a phenomenon occurring near the plasmapause and that is closely related to the bulge or detached regions of the plasmasphere.

An NMR investigation of rigor in porcine muscle

Sections of porcine L. dorsi muscle were frozen to arrest rigor at various times post mortem . 'H nmr spectra were recorded from −80 to +10°C. Thaw rigor was then allowed to proceed to completion at 0°C, the samples refrozen and the spectra re-recorded. Observable, ‘liquid-like’ nmr lines exhibited Arrhenius linewidth temperature dependence indicative of a single water phase of activation energy 6 to 8 kcals/mole, apparently independent of the state of rigor. No abrupt change in signal characteristics occurred at 0°C except on samples where thaw rigor had been induced where signal strength changes indicated a greater fraction of free, bulk water.

An automatic level controller for a double beam spectrophotometer

A simple electronic accessory for a double beam spectrophotometer is described which causes the instrument to be made insensitive to changes in signal strength over a range limited mainly by noise. High performance may be achieved at low cost.

An ultrasonic technique to monitor fatigue damage in aircraft structures.

A procedure is proposed for the development of a practical and reliable nondestructive technique toward the in situ monitoring within aircraft structures of fatigue damage, prior to and during propagation of running fatigue cracks. The technique utilizes precalibrated ultrasonic surface wave signal strength changes and can monitor both areas of uniform stress and points of stress concentration. Multiple sensor installations can be effectively monitored by a single portable instrument obtaining both manual readout and permanent oscillograph records, easily interpretable. The procedure is applicable to either continuous in-flight readout or intermittent readout during periodic ground maintenance checkouts. The requirements for establishing calibration data for both laboratory and field testing are presented along with a discussion of limitations in the technique. A proposed basis for interpretation of the ultrasonic data using a simple analytical cumulative damage model also is presented.

Evidence for Wave Motions in the E-Region in the Ionosphere

THE measurement of ‘drift’ in the ionosphere using the changes of signal strength of a radio wave reflected nearly vertically from the ionosphere and received by three antennae a fixed distance apart1 has often been difficult to interpret, and different methods of analysis appear to give different results. In an attempt to resolve some of these discrepancies it was decided to test the hypothesis that the scattering irregularities of electron density2 were due to hydrodynamic waves travelling horizontally in the ionosphere, rather than the movement being a drift of the medium as a whole.

Optical, electromagnetic, and satellite observations of high-altitude nuclear detonations: Part II

The radio effects of the Argus detonations were measured using (1) 30-Mc radars designed to obtain echoes from the aurora or from the earth's surface mirrored in an enhanced ionospheric layer, (2) VLF receivers for monitoring distant transmitters or atmospheric noise sources in search of changes in signal strength, (3) riometers for recording cosmic noise absorption or VHF shot-created noise at 30, 60, and 120 Mc. Results included (1) auroral echoes in the vicinity of the launch point after all three shots and near the conjugate points after the first and third shot, (2) sudden depressions of 6 to 12 db of the signal from England (19.6 kc) at Madrid and the Azores, (3) no ionospheric absorption at the conjugate location.

A New Approach to the Linear Design and Analysis of Phase-Locked Loops

Using the techniques and philosophy of control systems theory, the phase-locked loop is analyzed as a conventional feedback loop. The root-locus method yields graphs which specify how the transient response changes with signal strength. This method also reveals two thresholds which explain why a small change in signal strength or modulation may cause complete loss of detection. Charts show how the transients vary with various pole-zero patterns for both step and ramp inputs. The feedback equation shows why the phase-locked loop is an FM detector, and simplifies its design analysis to that of a simple audio network. The application of Wiener's criterion is simplified, and a new method of solution for the filter is presented which is applicable to almost any kind of signal. Because the phase-locked loop is nonlinear, there is no known solution for the filter except when the noise is white. The optimum transfer function may easily be reduced to the loop components. When used in an AM detector the phase-locked loop should be designed for minimum phase shift independent of the modulation.

Thermistor detectors in gas chromatography

AbstractDetails are given of a simple and easily constructed instrument, employing a thermistor detector, for work on gas chromatography. Some necessary precautions and conditions for use of a thermistor detector are outlined, changes in signal strength and direction with variation of detector position are discussed and the over‐all sensitivity and response to differing materials is described.

Further Results of a Study of Ultra-Short-Wave Transmission Phenomena*

Earlier published work has shown that, while the chief features of ultra-short-wave transmission over “air line” ranges are calculable from optical theory, there are deviations from this theory at the greater distances where a bending around the earth occurs. In this paper the results of a further study of these phenomena are given. It is shown that transmission to regions beyond the optical range is determined by conditions which are not constant and which, in fact, can produce great signal strength changes. The variable percentage of water vapor normally present in the atmosphere is suggested as a possible cause. The explanation seems, therefore, to involve a combination of diffraction and refraction, this latter variable with time, and at times predominant.