ATS-6 Energetic Particle Radiation Measurement at Synchronous Altitude

The Aerospace Corporation energetic electron-proton spectrometer operating on Applications Technology Satellite-6 (ATS-6) detects energetic electrons in four channels between 140 keV and greater than 32 MeV, and measures energetic protons in five energy channels between 2.3 and 80 MeV and energetic alpha particles in three channels between 9.4 and 94 MeV. After more than a year of operation in orbit, the experiment continues to return excellent data on the behavior of energetic magnetospheric electrons as well as information regarding the fluxes of solar protons and alpha particles.     

A methodology for addressing support equipment obsolescence

The rapid growth of technology over the last twenty years is providing vastly improved capabilities for both avionics and avionics test systems. Unfortunately, an environment of rapid technological growth breeds a corresponding environment of rapid technological obsolescence. Test systems developed fifteen years ago are becoming increasingly more difficult to support due to obsolescence issues and, additionally, such a test system does not reflect the current state-of-the-art for automatic test equipment. The ability of a test system to evolve is essential to providing cost-effective support systems for electronic systems. The F-15 Tactical Electronic Warfare System (TEWS) Intermediate Support System (TISS) was developed under the Modular Automatic Test Equipment (MATE) guidelines to support the suite of F-15 electronic warfare LRUs. MATE imposed hardware architecture constraints, which were factors that contributed to its abandonment. However, the modular aspect of MATE has provided a system that can easily evolve with technological advancements. Modularity is the cornerstone of modern software systems and this is the aspect that has been exploited in the evolution of the TISS     

Calculation of Probability of Detection with Target Scintillation

This paper presents a computational method for the calculation of probability of detection using measured radar target cross-section data. The described method can also be used for probability of detection calculations when the radar target cross section follows a specified probability density function. Using the computational procedure of the paper, a number of curves are generated which can be used for probability of detection calculations with exponential and Gaussian radar target cross-section distributions. The results obtained using theoretical distributions are compared with the corresponding results using actual target cross-section measurements. The results of computer runs are compared to the corresponding values in the literature where available.     

Adaptive cancellation method for geometry-induced nonstationary bistatic clutter environments

This paper describes and characterizes a new bistatic space-time adaptive processing (STAP) clutter mitigation method. The approach involves estimating and compensating aspects of the spatially varying bistatic clutter response in both angle and Doppler prior to adaptive clutter suppression. An important feature of the proposed method is its ability to extract requisite implementation information from the data itself, rather than rely on ancillary - and possibly erroneous or missing - system measurements. We justify the essence of the proposed method by showing its ability to align the dominant clutter subspaces of each range realization relative to a suitably chosen reference point as a means of homogenizing the space-time data set. Moreover, we numerically characterize performance using synthetic bistatic clutter data. For the examples considered herein, the proposed bistatic STAP method leads to maximum performance improvements between 17.25 dB and 20.75 dB relative to traditional STAP application, with average improvements of 6 dB to 10 dB.     

The Solar Chemical Composition

We present our current knowledge of the solar chemical composition based on the recent significant downward revision of the solar photospheric abundances of the most abundant metals. These new solar abundances result from the use of a 3D hydrodynamic model of the solar atmosphere instead of the classical 1D hydrostatic models, accounting for departures from LTE, and improved atomic and molecular data. With these abundances, the new solar metallicity, Z, decreases to Z=0.012, almost a factor of two lower than earlier widely used values. We compare our values with data from other sources and analyse a number of impacts of these new photospheric abundances. While resolving a number of longstanding problems, the new 3D-based solar photospheric composition also poses serious challenges for the standard solar model as judged by helioseismology.     

Coronal heating by dissipation of magnetic structure

Coronal loops are heated by the release of stored magnetic energy and by the dissipation of MHD waves. Both of these processes rely on the presence of internal structure in the loop. Tangled or sheared fields dissipate wave energy more efficiently than smooth fields. Also, a highly structured field contains a large reservoir of free magnetic energy which can be released in small reconnection events (microflares and nanoflares). The typical amount of internal structure in a loop depends on the balance between input at the photosphere and dissipation. This paper describes measures of magnetic structure, how these measures relate to the magnetic energy, and how photospheric motions affect the structure of a loop.The magnetic energy released during a reconnection event. can be estimated if one knows the equilibrium energy before and after the event. For a loop with highly tangled field lines, a direct solution of the equilibrium equations may be difficult. However, lower bounds can be placed on the energy of the equilibrium field, given a measure of the tangling known as the crossing number. These bounds lead to an estimate of the buildup of energy in a coronal loop caused by random photospheric motions. Parker's topological dissipation model can plausibly supply the 10⁷ erg cm^–2 s^–1 needed to heat the active region corona. The heating rate can be greatly enhanced by fragmentation of flux tubes, for example by the breakup of photospheric footpoints and the formation of new footpoints.     

Steady-state analysis of the constant-frequency clamped seriesresonant converter

A constant-frequency diode-clamped series resonant converter (CFCSRC) is proposed as a solution to problems associated with frequency-controlled resonant converters. This converter has two resonant frequencies, and control is achieved by varying the relative time spent at each switching frequency. Two zero-current-switching (ZCS) modes are examined and plotted in the output plane. An equation is given for the boundary between the two ZCS modes, as well as an expression for the boundary between ZCS and non-ZCS operation; both are plotted in the output plane. The output equation for the main mode is shown to be hyperbolic. Converter peak voltages limited to the input voltages, and peak currents are less than those of the frequency-controlled clamped series resonant converter over a large operating range. Data from a prototype converter are compared with theoretical data and are shown to be in good agreement with the theoretical model     

On the relation between the mass loss rate and the stellar parameters of OB-type stars

We discuss mass loss relations for OB-type stars as a function of luminosity, effective temperature, and mass. We conclude that a simple first order linear regression relation is as good as any other more sophisticated relation, with the advantage that the simple form consumes much less computer time when used in evolutionary codes.     

Multiple target tracking using products of position measurements

The continued development of the symmetric measurement equation (SME) filter for track maintenance in multiple target tracking (MTT) is considered, focusing on the case in which the SMEs are generated by forming sums of products of the original position measurements. The SME filter is developed for the case of N targets whose motions consist of random perturbations about constant-velocity trajectories. It is assumed that measurements of x-coordinate positions are available, and that the number of measurements is equal to the number of targets. Various analytical properties of the SME filter are studied. It is shown that under a very weak condition, the estimation error equation is locally exponentially stable. The performance of the SME filter is investigated by comparing it with an optimal (minimum-variance) estimator and by generating a computer simulation in the six-target case