The role of magnetic field shear in solar flares

We present observational results and their physical implications garnered from the deliberations of the FBS Magnetic Shear Study Group on magnetic field shear in relation to flares. The observed character of magnetic shear and its involvement in the buildup and release of flare energy are reviewed and illustrated with emphasis on recent results from the Marshall Space Flight Center vector magnetograph. It is pointed out that the magnetic field in active regions can become sheared by several processes, including shear flow in the photosphere, flux emergence, magnetic reconnection, and flux submergence. Modeling studies of the buildup of stored magnetic energy by shearing are reported which show ample energy storage for flares. Observational evidence is presented that flares are triggered when the field shear reaches a critical degree, in qualitative agreement with some theoretical analyses of sheared force-free fields. Finally, a scenario is outlined for the class of flares resulting from large-scale magnetic shear; the overall instability driving the energy release results from positive feedback between reconnection and eruption of the sheared field.     

Importance Sampling Applied to Simulation of False Alarm Statistics

The application of importance sampling to the efficient simulation of low-probability events is discussed. Several examples are given to illustrate how the technique works for processes involving single and multiple statistical inputs. A procedure is also given for handling the case of multiple inputs where each is from a different statistical process.     

The giant planets and their satellites: Report on the Cospar Symposium,Ottawa, Canada,May 18–21, 1982

A $\text{Symposium on the Giant Planets and Their Satellites}$ was presented in conjunction with the Twenty-fourth Plenary Meeting of the Committee on Space Research. This paper summarizes the talks presented and places the remaining papers of this volume in context.     

Uniform Sampling Analysis of a Hybrid Phase-Locked Loop with a Sample-and-Hold Phase Detector

Phase-locked-loop (PLL) bit synchronizers often employ integrate-and-dump type phase detectors that provide phase error information only at discrete points in time. Usually these phase detectors are followed by sample-and-hold circuits to produce a stairstep error voltage as the input to a standard analog circuit loop filter. When the loop is configured in this manner, it is referred to as a hybrid PLL. Sampled-data analysis methods (Z transforms) are used to determine the stability and transient response of this loop.     

Leading Edge Estimation Errors

The leading edge estimator (LEE) of a pulse signal is defined as the instant at which a filtered version of the received noisy signal passes a preset threshold. A rigorous analysis for a rectangular pulse model of the signal results in an exact probability density function for the LEE, valid within the time interval of the leading edge of the filtered pulse. Possible occurrence of the threshold crossing outside of this interval is considered to be an anomalous estimate, since it leads to a gross error in comparison with the regular cases. It is found that the density function of the LEE error is asymmetrical and therefore biased, that the probability PA of anomalous estimation increases with the filter bandwidth, thus setting a well definable limit to the latter and that, for prespecified PA, the minimum bias and variance are proportional, respectively, to R-1 and R-2, minima being obtained by allowing for the largest bandwidth compatible with PA. On the other hand, for given bandwidth the variance decreases only as R-1. Here R is the signal-to-noise energy ratio. Results are presented in form of parameterized graphs.     

Non-linear magnetospheric amplification of VLF transmissions

Non-linear amplification of a monochromatic VLF transmission in the magnetosphere produces an output fluctuating in amplitude and phase, and so is not monochromatic. This output can usually be resolved into two waves: one similar to the input, but stronger, and a higher frequency sideband or “embryo emission”. The established theory is outlined as far as it goes.     

The Magellan project

Magellan is one of the future space projects being studied by the European Space Agency. The aim is to provide high resolution (λ/Δλ ≥ 2.5 × 10⁴) spectra in the far and extreme UV (between 500 and 1550 Å) of faint galactic and extragalactic objects (V ≤ 16^m). The instrument consists of a mechanical collimator, a concave holographic grating and a bidimensional photon-counting detector. A low resolution mode (λ/Δλ ≥ 10³) will provide spectra of objects as faint as 18^m.5. Magellan is planned as an observatory, operated in real time, and allowing interaction with the observer.     

Electric generators: technology status

The use of generators by the military is examined. The factors determining generator size and weight for a given power rating and the generator scaling laws are discussed. Size and weight reduction is shown to be primarily a function of improvements in material properties and cooling techniques     

Scaling of advanced power systems

Parts of a study conducted to examine state-of-the-art power systems applicable to future military spacecraft are summarized. The study focused on burst-mode megawatt-class CW power, such as might be applied to SDIO directed energy systems, but lower-power, continuous-duty subsystems were included in less detail. A set of simple mass and volume algorithms has been developed to approximate several prime systems, and these were incorporated into a Lotus 1-2-3 spreadsheet. Among the power subsystems included in that study were primary batteries, alkaline primary fuel cells, and combustion turbogenerators. These systems, which are the most likely candidates for mobile battlefield power, are described     

Energy and charge localization in irradiated DNA.

The relation between the site of energy deposition and the site of its biological action is an important question in radiobiology. Even at 77 degrees K, evidence is clear that these two sites must be separated since energy deposition is random but specific products are formed. Several processes that may contribute to this separation are: 1) hole migration and stabilization through deprotonation to give neutral oxidation product radicals; 2) electron trapping and transfer to form specific radical anions, possibly followed by protonation to give neutral reduction product radicals; and 3) recombination of spatially separated charges or radicals. These microscopic processes will be reviewed critically in an analysis using electron paramagnetic resonance spectroscopy (EPR) evidence for and against long-range transfer of energy and/or charge in frozen, hydrated DNA.