Three-dimensional cosmic-ray simulations: Heliographic latitude and current-sheet tilt

We present the results from a study of the variations of the cosmic-ray intensity with time, heliographic latitude, and longitude, and for varying interplanetary conditions, using our three-dimensional, time-dependent computer code for cosmic-ray transport in the heliosphere. Our code also produces a solar-wind and interplanetary magnetic field (IMF) configuration which is compared with observations. Because of the fully threedimensional nature of the model calculations, we are able to model time variations which would be expected to be observed along Ulysses's trajectory as it moves to high latitudes. In particular we can model the approximately 13-and 26-day solar-rotation induced variations in cosmic rays, solar wind and IMF, as a function of increasing heliographic latitude, as one moves poleward of the interplanetary current sheet. Our preliminary model results seem to be in general form quite similar to published data, but depend on the physical parameters used such as cosmic-ray diffusion coefficients, boundary conditions, and the nature of the solar wind and IMF and current sheet.     

Refractive Errors in Angle-of-Elevation Measurements

It is shown that the errors associated with radio elevation measurements may be investigated systematically using a variational technique. The error occurring when spaced antennas are used is compared with that for a single directional antenna. Integral expressions are obtained for the refractive errors.     

Present-Day Sea Level Change: Observations and Causes

We investigate climate-related processes causing variations of the global mean sea level on interannual to decadal time scale. We focus on thermal expansion of the oceans and continental water mass balance. We show that during the 1990s where global mean sea level change has been measured by Topex/Poseidon satellite altimetry, thermal expansion is the dominant contribution to the observed 2.5 mm/yr sea level rise. For the past decades, exchange of water between continental reservoirs and oceans had a small, but not totally negligible contribution (about 0.2 mm/yr) to sea level rise. For the last four decades, thermal contribution is estimated to about 0.5 mm/yr, with a possible accelerated rate of thermosteric rise during the 1990s. Topex/Poseidon shows an increase in mean sea level of 2.5 mm/yr over the last decade, a value about two times larger than reported by historical tide gauges. This would suggest that there has been significant acceleration of sea level rise in the recent past, possibly related to ocean warming. This revised version was published online in August 2006 with corrections to the Cover Date.     

The Genesis Solar-Wind Collector Materials

Genesis (NASA Discovery Mission #5) is a sample return mission. Collectors comprised of ultra-high purity materials will be exposed to the solar wind and then returned to Earth for laboratory analysis. There is a suite of fifteen types of ultra-pure materials distributed among several locations. Most of the materials are mounted on deployable panels (‘collector arrays’), with some as targets in the focal spot of an electrostatic mirror (the ‘concentrator’). Other materials are strategically placed on the spacecraft as additional targets of opportunity to maximize the area for solar-wind collection. Most of the collection area consists of hexagonal collectors in the arrays; approximately half are silicon, the rest are for solar-wind components not retained and/or not easily measured in silicon. There are a variety of materials both in collector arrays and elsewhere targeted for the analyses of specific solar-wind components. Engineering and science factors drove the selection process. Engineering required testing of physical properties such as the ability to withstand shaking on launch and thermal cycling during deployment. Science constraints included bulk purity, surface and interface cleanliness, retentiveness with respect to individual solar-wind components, and availability. A detailed report of material parameters planned as a resource for choosing materials for study will be published on a Genesis website, and will be updated as additional information is obtained. Some material is already linked to the Genesis plasma data website (genesis.lanl.gov). Genesis should provide a reservoir of materials for allocation to the scientific community throughout the 21st Century. This revised version was published online in August 2006 with corrections to the Cover Date.     

Variations of the magnetic fields in large solar flares

We present preliminary results from high resolution observations obtained with the Michelson Doppler Imager (MDI) instrument on the SOHO of two large solar flares of 14 July 2000 and 24 November 2000. We show that rapid variations of the line-of-sight magnetic field occured on a time scale of a few minutes during the flare explosions. The reversibility/irreversibility of the magnetic field of both active regions is a very good tool for understanding how the magnetic energy is released in these flares. The observed sharp increase of the magnetic energy density at the time of maximum of the solar flare could involve an unknown component which deposited supplementary energy into the system. This revised version was published online in August 2006 with corrections to the Cover Date.     

Current Injected Equivalent Circuit Approach to Modeling Switching DC-DC Converters

A new current injected equivalent circuit approach (CIECA) to modeling switching dc-dc converter power stages is developed, which starts with the current injected approach and results in either a set of equations which completely describe input and out-put properties or an equivalent linear circuit model valid at small signal, low frequency levels. This approach to modeling switching dc-dc converter power stages has the merits but not the demerits of both the electronic equivalent circuit state space average approach and the current injected control type approach, namely, 1) the modeling is very clear and is simple whether the converter operates in continuous or discontinuous inductor conduction modes, 2) the modeling results in an equivalent circuit which is very close to the actual converter, and 3) the equivalent circuit can be used directly in the computer for theoretical predictions like SPICE, etc.     

Error Analysis of Space-Stable Inertial Navigation Systems

The error equations for a space-stable inertial navigation system are derived. This is done by directly perturbing the mechanization equations in the inertial frame and then transforming in open-loop fashion to the local-level frame. A rotating inertial platform and velocity and altitude damping are considered. The relations between errors in space-stable and local-level systems are noted. Numerical results are presented for certain random error sources.     

Geomagnetic micropulsations and diagnostics of the magnetosphere

Plasma oscillations in a wide range of spectrum exist in the magnetosphere. Part of them penetrate the ionosphere and are recorded on the earth's surface. In the range of frequencies from millihertz to several hertz, the so-called micropulsations (ULF) are observed. In the range from hundred of hertz to several kilohertz the low-frequency emissions (VLF) are registered. Both types of emissions contain interesting and important information on the physical parameters of the magnetosphere and on the processes developing in it. The following paper describes the main problems of the diagnostics of the magnetosphere, which are based on the surface observations of micropulsations.In the first part of the paper, a short summary of theoretical conceptions on micropulsations is given. The main part of the paper describes the methods of diagnostics of the location of the boundary of the magnetosphere, of cold-plasma concentration in the outer regions of the magnetosphere, as well as of the energies and fluxes of fast charged particles in the geomagnetic trap. Some experimental results of the diagnostics of the parameters of the magnetosphere are given. Advantages and deficiencies of the existing methods of surface diagnostics are discussed, and the directions of further investigations are traced.     

Weak Signal Detection in Non-Gaussian Noise of Unknown Level

An adaptive threshold detector to test for the presence of a weak signal in additive non-Gaussian noise of unknown level is discussed. The detector consists of a locally optimum detector, a noise level estimator, and a decision device. The detection threshold is made adaptive according to the information provided by the noise level estimator in order to keep a fixed false-alarm probability. Asymptotic performance characteristics are obtained indicating relationships among the basic system parameters such as the reference noise sample size and the underlying noise statistics. It is shown that, as the reference noise sample size is made sufficiently large, the adaptive threshold detector attains the performance of a corresponding locally optimum detector for detecting the weak signal were the noise level known.     

Investigations of Stability & Dynamic Performances of a Current-Injected Regulator

The stability and dynamic performances of a buck/boost regulator employing a current-injected control are examined. Small-signal models for the power state, the multiloop error processor, and the duty-cycle pulse modulator are developed. The error-processor model which incorporates the current-injected loop, the dc loop, and the compensation network permits evaluation of the effects of each individual control loop and their combined efforts toward shaping the performance characteristics of the closed-loop system. Comparisons are made between this modeling approach and earlier approaches. Some important yet subtle dissimilarities are discussed. This model predicts the constant-frequency 50-percent duty-cycle instability which is inherent to the current-injected control.