DNA damage and repair in oncogenic transformation by heavy ion radiation.

Energetic heavy ions are present in galactic cosmic rays and solar particle events. One of the most important late effects in risk assessment is carcinogenesis. We have studied the carcinogenic effects of heavy ions at the cellular and molecular levels and have obtained quantitative data on dose-response curves and on the repair of oncogenic lesions for heavy particles with various charges and energies. Studies with repair inhibitors and restriction endonucleases indicated that for oncogenic transformation DNA is the primary target. Results from heavy ion experiments showed that the cross section increased with LET and reached a maximum value of about 0.02 micrometer2 at about 500 keV/micrometer. This limited size of cross section suggests that only a fraction of cellular genomic DNA is important in radiogenic transformation. Free radical scavengers, such as DMSO, do not give any effect on induction of oncogenic transformation by 600 MeV/u iron particles, suggesting most oncogenic damage induced by high-LET heavy ions is through direct action. Repair studies with stationary phase cells showed that the amount of reparable oncogenic lesions decreased with an increase of LET and that heavy ions with LET greater than 200 keV/micrometer produced only irreparable oncogenic damage. An enhancement effect for oncogenic transformation was observed in cells irradiated by low-dose-rate argon ions (400 MeV/u; 120 keV/micrometer). Chromosomal aberrations, such as translocation and deletion, but not sister chromatid exchange, are essential for heavy-ion-induced oncogenic transformation. The basic mechanism(s) of misrepair of DNA damage, which form oncogenic lesions, is unknown.     

Heliospheric and Interstellar Phenomena Deduced From Pickup ion Observations

Pickup ions, created by ionization of slow moving atoms and molecules well inside the heliosphere, provide us with a new tool to probe remote regions in and beyond the heliosphere and to study injection and acceleration processes in the solar wind. Comprehensive and continuous measurements of H, He, C, N, O, Ne and other pickup ions, especially with the Solar Wind Ion Composition Spectrometer (SWICS) on both Ulysses and ACE, have given us a wealth of data that have been used to infer chemical and physical properties of the local interstellar cloud. With SWICS on Ulysses we discovered a new population of pickup ions, produced from atomic and molecular sources deep inside the heliosphere. The velocity distributions and composition of these “inner source” pickup ions are distinctly different from those of interstellar pickup ions, showing effects of strong adiabatic cooling, and a composition resembling that of the solar wind. Strong cooling indicates that the source of these pickup ions lies close to the Sun. The similarity of composition of inner source heavy ions to that of the solar wind implies that the dominant production mechanism for these pickup ions involves the absorption and re-emission of solar wind from interplanetary dust grains. While interstellar pickup ions are the seed population of the main Anomalous Cosmic Rays (ACRs), inner source pickup ions may be an important source of the rarer ACRs such as C, Mg, Si, S, and Fe. We present new results and review previous work with an emphasis on characteristics of the local interstellar cloud and properties of the inner source. This revised version was published online in August 2006 with corrections to the Cover Date.     

Developing countries and remote sensing: how intergovernmental factors impede progress

Developing countries lag significantly behind more advanced nations in the local adoption and application of satellite remote sensing technology. Narrowing this gap through appropriate international cooperation is, however, often constrained by national interests and priorities. The paper presents an overview of several of these inter-governmental constraints using as its main basis the outcomes of recent regional and international conferences hosted by the United Nations. Future enhancement of international cooperation in remote sensing will occur best within settings where both developing and technologically advanced countries are sensitive and responsive to each other's concerns.     

The applications of lower power satellites for direct television broadcasting

The use of 12 GHz satellites for TV broadcasting directly to individual homes and small communities has been the subject of analysis and design study by groups in many countries. Implementation of the concept has been slow to follow because of the high satellite transmitter powers of from 100 to 450 W that have usually been determined to be necessary. Accumulated experience in Canada with 12 GHz operation and the evolution of technology are leading to changes in the concept of direct broadcasting such that lower power satellites may be capable of meeting the requirements.

Hermes, the Canadian/U.S. 12/14 GHz Communications Technology Satellite, has been in use for over 3 years in a program of experiments and measurements. This program has included an extensive six month experiment in direct broadcasting to 7 small communities. Experience with Hermes has shown that the signal strength is stable over long periods of time and that in Canada, significant precipitation attenuation at 12 GHz is of relatively short duration and typically occurs only during certain seasons. Operation with low propagation margins is feasible if some picture degradation and some outages at these times are acceptable. The frequency and duration of occurrence of outages can be controlled by the Earth station G/T which is cost sensitive. An individual may choose to use a low cost system with a small antenna and accept a degraded picture and outages at some times. A small community may choose to pay more for a larger antenna and lower noise receiver to achieve better performance.

Developments in technology are reducing the noise figure of mass-producible receivers from more than 6 dB to as low as 4 dB. Another technology contribution is the use of reduced bandwidth and other signal processing techniques in low-cost receivers. While use of such techniques may introduce distortions that would be unacceptable in rebroadcasting systems, there is little impact for individual and community reception. Use of both technologies reduce the required satellite EIRP or ground terminal G/T.

A field trial was begun in April 1979 to test these concepts for use in television program delivery. One hundred Earth stations capable of being tuned across a 500 MHz band and having antennas with diameters of either 1.2 m or 1.8 m are being installed for a test in Canada to receive TV signals from the 20 W transponders of ANIK-B (peak EIRP of 51 dBw) on an experimental basis. The acceptability of the video signals and the technical performance of the low-cost terminals in the bands of non-technical users are being evaluated.

The paper will summarize the concept of TV broadcasting with lower power satellites and describe the results to date of the ANIK-B field trials.     

Atomic and molecular hydrogen in interstellar space

This paper reviews the present state of knowledge of the abundances and physical state of interstellar atomic and molecular hydrogen. Much new data in this area have been obtained in recent rocket observations. There have also been new developments as a result of ground-based infrared and 21-cm observations, and theoretical research.Rocket observations of the Lyman- interstellar absorption line of atomic hydrogen indicate that, in many directions in the sky, atomic hydrogen is up to a factor of 10 less abundant than previously indicated by 21-cm emission measurements. In the direction of the Orion Nebula, most of the absorbing gas appears to be concentrated in the near vicinity of the nebula and to have a temperature considerably lower than the average of 100 K obtained from 21-cm emission measurements. Molecular hydrogen appears essentially absent from the general interstellar medium, as confirmed by theoretical studies of photodissociation processes. However, ground-based infrared and 21-cm studies indicate that the hydrogen in dark dust clouds is mostly molecular.     

The Relativistic Proton Spectrometer (RPS) for the Radiation Belt Storm Probes Mission

The Relativistic Proton Spectrometer (RPS) on the Radiation Belt Storm Probes spacecraft is a particle spectrometer designed to measure the flux, angular distribution, and energy spectrum of protons from ～60 MeV to ～2000 MeV. RPS will investigate decades-old questions about the inner Van Allen belt proton environment: a nearby region of space that is relatively unexplored because of the hazards of spacecraft operation there and the difficulties in obtaining accurate proton measurements in an intense penetrating background. RPS is designed to provide the accuracy needed to answer questions about the sources and losses of the inner belt protons and to obtain the measurements required for the next-generation models of trapped protons in the magnetosphere. In addition to detailed information for individual protons, RPS features count rates at a 1-second timescale, internal radiation dosimetry, and information about electrostatic discharge events on the RBSP spacecraft that together will provide new information about space environmental hazards in the Earth’s magnetosphere.     

The Magnetic Field of Mercury

The magnetic field strength of Mercury at the planet’s surface is approximately 1% that of Earth’s surface field. This comparatively low field strength presents a number of challenges, both theoretically to understand how it is generated and observationally to distinguish the internal field from that due to the solar wind interaction. Conversely, the small field also means that Mercury offers an important opportunity to advance our understanding both of planetary magnetic field generation and magnetosphere-solar wind interactions. The observations from the Mariner 10 magnetometer in 1974 and 1975, and the MESSENGER Magnetometer and plasma instruments during the probe’s first two flybys of Mercury on 14 January and 6 October 2008, provide the basis for our current knowledge of the internal field. The external field arising from the interaction of the magnetosphere with the solar wind is more prominent near Mercury than for any other magnetized planet in the Solar System, and particular attention is therefore paid to indications in the observations of deficiencies in our understanding of the external field. The second MESSENGER flyby occurred over the opposite hemisphere from the other flybys, and these newest data constrain the tilt of the planetary moment from the planet’s spin axis to be less than 5°. Considered as a dipole field, the moment is in the range 240 to 270 nT-R _M ³ , where R _M is Mercury’s radius. Multipole solutions for the planetary field yield a smaller dipole term, 180 to 220 nT-R _M ³ , and higher-order terms that together yield an equatorial surface field from 250 to 290 nT. From the spatial distribution of the fit residuals, the equatorial data are seen to reflect a weaker northward field and a strongly radial field, neither of which can be explained by a centered-dipole matched to the field measured near the pole by Mariner 10. This disparity is a major factor controlling the higher-order terms in the multipole solutions. The residuals are not largest close to the planet, and when considered in magnetospheric coordinates the residuals indicate the presence of a cross-tail current extending to within 0.5R _M altitude on the nightside. A near-tail current with a density of 0.1 μA/m² could account for the low field intensities recorded near the equator. In addition, the MESSENGER flybys include the first plasma observations from Mercury and demonstrate that solar wind plasma is present at low altitudes, below 500 km. Although we can be confident in the dipole-only moment estimates, the data in hand remain subject to ambiguities for distinguishing internal from external contributions. The anticipated observations from orbit at Mercury, first from MESSENGER beginning in March 2011 and later from the dual-spacecraft BepiColombo mission, will be essential to elucidate the higher-order structure in the magnetic field of Mercury that will reveal the telltale signatures of the physics responsible for its generation.     

Measurement of the Abundance of Helium-3 in the Sun and in the Local Interstellar Cloud with SWICS on Ulysses

The abundance of 3He in the present day local interstellar cloud (LIC) and in the sun has important implications for the study of galactic evolution and for estimating the production of light nuclei in the early universe. Data from the Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses is used to measure the isotopic ratio of helium (3He/4He = ) both in the solar wind and the local interstellar cloud. For the solar wind, the unique high-latitude orbit of Ulysses allows us to study this ratio in the slow and highly dynamic wind in the ecliptic plane as well as the steady high-latitude wind of the polar coronal holes. The 3He+/4He+ ratio in the local cloud is derived from the isotopic ratio of pickup helium measured in the high-speed solar wind. In the LIC the ratio is found to be (2.48 _-0.62 ^+0.68 ) × 10^-4 with the 1- uncertainty resulting almost entirely from statistical error. In the solar wind, is determined with great statistical accuracy but shows systematic differences between fast and slow solar wind streams. The slow wind ratio is variable. Its weighted average value (4.08 ± 0.25) × 10-4 is, within uncertainties, in agreement with the Apollo SWC results. The high wind ratio is less variable but smaller. The average in the fast wind is (3.3 ± 0.3) × 10-4.     

Output of a Balanced Frequency Discriminator Driven by a Sine Wave and Gaussian Noise

The output of a realizable balanced frequency discriminator is calculated for an input consisting of a sine wave plus Gaussian noise. Explicit autocorrelation and power spectra are found for one practical embodiment of the discriminator for various input carrier-to-noise ratios, with the carrier tuned to center frequency and also off-center. The formulas also permit the calculation of the output for the case of a spectrum of noise slowly swept through the discriminator. Although qualitatively similar to results previously obtained with an ideal discriminator, substantial differences are also found. Measurements are made that closely verified the theoretical results. No limiting is assumed.