Institute of Radiophysics and Electronics

Stimulated transitions are relatively enormously more probable at radio than at optical frequencies and it is this which makes it possible for negative absorption to arise at radio wavelengths when the medium will behave like an amplifier to the incident radiation. A necessary condition for the existence of this phenomenon is that the kinetic energy distribution F(?) of the radiating electrons be markedly non-thermal with an appreciable excess of high energy electrons such that ¶F/¶? is positive over a finite range of the kinetic energy ?. However, this condition is not sufficient, since it is shown that an electron gas in which free·free transitions provide the dominant radiation process can never exhibit negative absorption whatever the form of F(?), and it is further necessary that the stimulated transition probability should have a maximum at some finite value of the kinetic energy, the most favourable case occurring when this maximum is a sharp one at the value of ? at which ¶F/¶? has a positive maximum. These conditions can both be met in principle for the cases in which the dominant radiation process is due (a) to Cerenkov effect, (b) to gyro radiation by non-relativistic electrons, (c) to synchrotron-type radiation by highly relativistic electrons, and it is shown that negative absorption can arise in all these cases; the relevance of these results to radio astronomy is discussed briefly.

The paper describes an investigation aimed at finding out whether solar radio bursts of spectral type III are due to disturbances which travel out through the corona with velocities exceeding O·lc, as predicted by the well-known hypothesis that the emissions are due to plasma oscillations. If the proposition is correct, emissions at different frequencies would be generated at different levels in the corona-the lower the frequency the higher the source. This property is tested by simultaneous directional observations at a number of frequencies between 40 and 70 Mc/s, using a swept-frequency interferometer.

The characteristics of bursts of spectral type II are studied in a sample of 65 bursts. Approximately half the bursts show harmonic structure and about half are compound type III-type II events. Band splitting, the doubling of both the fundamental and second harmonic bands, is also relatively common. A rather less common feature is the appearance of herring-bone structure in which the slowly drifting band of the type II burst appears to be a source from which rapidly drifting elements diverge towards lower and higher frequencies.

A new catalogue of 125 galactic SNRs is presented. A surface brightness-diameter relationship, corrected for variation in height I z I above the galactic plane, is derived and applied to the catalogue to yield I z I-corrected distances and diameters. A birth rate of about one every 30 or 40 years is indicated from the number-diameter diagram.

Radiotherapy is widely used to treat human cancer. Patients locally recurring after radiotherapy, however, have increased risk of metastatic progression and poor prognosis. The clinical management of postradiation recurrences remains an unresolved issue. Tumors growing in preirradiated tissues have an increased fraction of hypoxic cells and are more metastatic, a condition known as tumor bed effect. The transcription factor hypoxia inducible factor (HIF)-1 promotes invasion and metastasis of hypoxic tumors, but its role in the tumor bed effect has not been reported. Here, we show that tumor cells derived from SCCVII and HCT116 tumors growing in a preirradiated bed, or selected in vitro through repeated cycles of severe hypoxia, retain invasive and metastatic capacities when returned to normoxia. HIF activity, although facilitating metastatic spreading of tumors growing in a preirradiated bed, is not essential. Through gene expression profiling and gain- and loss-of-function experiments, we identified the matricellular protein CYR61 and alphaVbeta5 integrin as proteins cooperating to mediate these effects. The anti-alphaV integrin monoclonal antibody 17E6 and the small molecular alphaVbeta3/alphaVbeta5 integrin inhibitor EMD121974 suppressed invasion and metastasis induced by CYR61 and attenuated metastasis of tumors growing within a preirradiated field. These results represent a conceptual advance to the understanding of the tumor bed effect and identify CYR61 and alphaVbeta5 integrin as proteins that cooperate to mediate metastasis. They also identify alphaV integrin inhibition as a potential therapeutic approach for preventing metastasis in patients at risk for postradiation recurrences.

(1968). Electromagnetic waves in metals in a magnetic field. Advances in Physics: Vol. 17, No. 69, pp. 605-747.

A low resolution (202) survey of the neutral hydrogen in the Magellanic Clouds has produced two important additions to our knowledge of the system. (1) A bridge of gas between the Small and Large Cloud has been mapped. (2) The Small Cloud profiles show double peaks over a wide area, suggesting the possibility of two substantially separate masses of gas.

The 211 +-212 transition of thioformaldehyde (HCHS) has been observed in absorption in the direction of SagittariusB2. For a rest frequency of 3139· 38 MHz the peak absorption occurs at a radial velocity of 60 ± 4 km s -1. The half-width of the absorption profile is equivalent to 20 kms-1 and the column density of HCHS is greater than 1016 molecules cm - 2. Comparison with the 211 +-212 absorption of formaldehyde (HCHO) at 15 GHz allows the relative abundance of the two molecular species to be computed as a function of the rotational excitation temperature. For thermal equilibrium the strength of the 110-111 absorption in SgrB2 by thioformaldehyde predicted from the 211+-212 HCHS observations is considerably greater than the limits set by a number of observers for the 110-111 transition at 1046 MHz.

The first meaningful observation with the 80 MHz Cul-goora radioheliograph was made on 2 September 1967, a few weeks before the instrument was officially commissioned. Systematic observations, normally for 4 to 6 hours per day, began late in February 1968 and the Sun has since been observed on 438 days. The remaining days and many nights have been used for investigations of radio sources and the interplanetary medium and for maintenance and instrumental extension. The standard of reliability thus achieved has been due to the sustained efforts of K. V. Sheridan, W. J. Payten, K. R. McAlister, M. Beard and their colleagues. These first two years have been a period mainly of exploration—a phase of great interest to those engaged in observing, though possibly bewildering to those not. The present review is a first attempt to collate and summarize what has so far been found and where possible to draw preliminary conclusions. The observations to be described and their discussion have been due to a joint effort on the part of a number of workers, particularly G. A. Dulk (on leave from the University of Colorado), K. Kai (on leave from the University of Tokyo), N. R. Labrum, D. J. McLean, A. C. Riddle, K. V. Sheridan, S. F. Smerd, R. T. Stewart, and the present writer. The period has also seen considerable development in the evolution of intricate computer programmes for analysing the data, particularly on the part of L. H. Heisler and D. J. McLean.

Abstract We discuss the advantages of the conversion of electromagnetic field problems to the Fredholm second‐kind integral equations (analytical regularization) and Fredholm second‐kind infinite‐matrix equations (analytical preconditioning). Special attention is paid to specific features of the characterization of metals and dielectrics in the optical range and their effect on the problem formulation and on the methods applicable to the mentioned conversion.

In this paper 80 MHz heliograph observations are described of a remarkable solar outburst on 1969 March 30 initiated by a flare on the invisible hemisphere of the Sun. The event raises several questions of theoretical interest, in particular the implication that the magnetohydrodynamic waves responsible for certain type II bursts must travel along curved paths.

Observational results are given concerning the relative positions on the Sun's disk of the fundamental and second-harmonic emissions of solar radio bursts of spectral types II and III. Contrary to simple theory, the results indicate that it is common for the harmonic emission in type II bursts to arrive from directions corresponding to much lower heights in the solar atmosphere than the fundamental. The results for type III bursts are inconclusive but suggest the same trend.

Patients with cardiac pacemakers are currently restricted from nuclear magnetic resonance imaging (MRI). The aim of the study was to analyze the influence of MRI on new generation pacemakers. Tests were performed using a phantom model with seven dual chamber and two single chamber systems in a 0.5 Tesla MRI scanner. Monitoring by telemetry and oscillography were used during the standard clinical scan sequences as well as a pacemaker inquiry after each sequence. Spin echo, gradient echo, and fast field echo sequences were performed with the following stimulation modes: VVI, VVIR, VOO, DDD, DDDR, and DOO. On entering the static magnetic field, the reed switch was activated followed by asynchronous stimulation. The subsequent scan showed no influence on the stimulation function nor on the pacemaker program. Event counter function remained intact. Pacemakers with automatic mode switching to demand pacing or programmed inactivation of the reed switch were triggered in the dual chamber mode and were inhibited in the one chamber mode during the scan. Alterations of pacemaker program or rapid pacing were not observed. MRI scan could induce voltage as high as intracardiac signals, but the stimulation threshold of the heart was not reached. Thus, pacemakers should be programmed in the asynchronous mode during scan to avoid inhibition and trigger mechanism.

A catalogue has been prepared of the radio sources observed between declinations +10° and ?20°, using the Sydney cross-type radio telescope at a wavelength of 3·5 m: a total of 1159 sources is listed in the area of 3·24 steradians. This supersedes an earlier catalogue of Mills and Slee in portion of the area, but the differences between the two are small. A number of new identifications with galaxies are suggested, and an analysis made of the statistics of the source distribution. It is concluded that cosmological effects displayed by the distribution, if present, are small. Possibilities are discussed of separating from this distribution the effects of the instrument, the finite angular sizes, and/or the physical clustering of the sources.

A catalogue of 297 radio sources between declinations -20° and -60°, has been compiled from observations with the Australian 210-ft telescope. The sources were selected from a survey at 75 cm wavelength as having flux densities in excess of 4 X 10-26 W m-2(cJs)-1. The survey did not cover a small area near the galactic plane. Additional measurements were made at wavelengths of 21 and 11 cm. Results on source identification, spectra, and polarization are discussed.

ABSTRACT A high pressure, water jet drilling system has been developed using a new force system to concurrently drill a bore hole and place a metal tube in the bore hole. The first commercial application has been horizontal radials for shallow heavy oil reservoirs. Many radials may be placed at the same elevation. Logging, and completion techniques have been developed.

A catalogue has been prepared of the radio sources observed between declinations _200 and _500 , using the Sydney cross-type radio telescope at a wavelength of 3·5 m ; a total of 892 sources is listed. This supplements an earlier catalogue in the declination zone + 10° to _20°. In addition to the positions and intensities of the sources, angular sizes of 50 of the strongest are given: several are found to have a size less than 15" arc. As before, identifications with bright optical objects have been sought, and a number of galaxies of apparently abnormal radio emission listed. Statistical analyses of the distribution of the radio sources give results very similar to those obtained using the earlier catalogue. \Vithin the uncertainty in the data, the distribution appears uniform in depth and there is a siguificantly greater number of sources of large apparent size than expected from chance blending effects.

Measurements of the concentration of cloud droplets and of the supersaturation spectrum of the cloud nucleus population in the air below cloud base showed a strong correlation between these properties. It is concluded that variations in the cloud nucleus content of the air are primarily responsible for variations of cloud droplet concentrations and colloidal stability.

We present an overview of Jupiter's low‐frequency radio emission morphology as observed by the planetary radio astronomy (PRA) instrument onboard the Voyager spacecraft. The PRA measurement capabilities and limitations are summarized following over two years of experience with the instrument. As a direct consequence of the PRA spacecraft observations, unprecedented in terms of their sensitivity and frequency coverage, at least three previously‐unrecognized emission components have been discovered: broadband and narrow‐band kilometric emission and the lesser‐arc decametric emission. Their properties are reviewed here. In addition, the fundamental structure of the decameter wavelength and hectometer wavelength emission, which is now believed to be almost exclusively in the form of complex but repeating arc structures in the frequencytime domain, is described here for the first time. Dramatic changes in the emission morphology of some components as a function of the sun‐Jupiter‐spacecraft angle (local time) are described. Finally, the PRA in situ measurements of the Io plasma torus hot‐to‐cold electron density and temperature ratios are summarized.

Parkes 2·7 and 5·0 GHz polarization maps have been combined to obtain distributions of magnetic field, Faraday rotation and depolarization for 20 supernova remnants.