Stimulated electromagnetic emissions by high-frequency electromagnetic pumping of the ionospheric plasma

A high frequency electromagnetic pump wave transmitted into the ionospheric plasma from the ground can stimulate electromagnetic radiation with frequencies around that of the ionospherically reflected pump wave. The numerous spectral features of these stimulated electromagnetic emissions (SEE) and their temporal evolution on a wide range of time scales are reviewed and related theoretical, numerical, and simulation results are discussed. On long (thermal) time scales the SEE constitutes a self-organization of the ionospheric plasma which depends on the interaction of nonlinear processes in a hierarchy of time scales in response to the electromagnetic pumping. Particularly, the appearance of the rich SEE spectrum is associated with the slow self-structuring of the plasma density into a spectrum of magnetic field-aligned density striations. The dependence of the SEE on electron gyroharmonic effects and the presence of density striations suggests that the existence of a magnetic field in the plasma is important for plasma turbulence to dissipate into non-thermal electromagnetic radiation during the long time quasi-stationary state of the turbulence evolution.     

A program to measure new energetic particle nuclear interaction cross sections.

The Transport Collaboration, consisting of researchers from institutions in France, Germany, Italy and the USA, has established a program to make new measurements of nuclear interaction cross sections for heavy projectiles (Z > or = 2) in targets of liquid H2, He and heavier materials. Such cross sections directly affect calculations of galactic and solar cosmic ray transport through matter and are needed for accurate radiation hazard assessment. To date, the collaboration has obtained data using the LBL Bevalac HISS facility with 20 projectiles from 4He to 58Ni in the energy range 393-910 MeV/nucleon. Preliminary results from the analysis of these data are presented here and compared to other measurements and to cross section prediction formulae.     

Performance analysis for DOA estimation algorithms: unification,simplification, and observations

Subspace based direction-of-arrival (DOA) estimation has motivated many performance studies, but limitations such as the assumption of an infinite amount of data and analysis of individual algorithms generally exist in these performance studies. The authors have previously proposed a unified performance analysis based on a finite amount of data and achieved a tractable expression for the mean-squared DOA estimation error for the multiple signal classification (MUSIC). Min-Norm, estimation of signal parameters using rotational invariance techniques (ESPRIT), and state-space realization algorithms. However, this expression uses the singular values and vectors of a data matrix, which are obtained by the highly nonlinear transformation of the singular value decomposition (SVD). Thus the effects of the original data parameters such as numbers of sensors and snapshots, source coherence and separations were not explicitly analyzed. The authors unify and simplify this previous result and derive a unified expression based on the original data parameters. They analytically observe the effects of these parameters on the estimation error     

Image texture synthesis-by-analysis using moving-average models

A synthesis-by-analysis model for texture replication or simulation is presented. This model can closely replicate a given textured image or produce another image that although distinct from the original, has the same general visual characteristics and the same first and second-order gray-level statistics as the original image. The texture synthesis algorithm, proposed contains three distinct components: a moving-average (MA) filter, a filter excitation function, and a gray-level histogram. The analysis portion of the texture synthesis algorithm derives the three from a given image. The synthesis portion convolves the MA filter kernel with the excitation function, adds noise, and modifies the histogram of the result. The advantages of this texture model over others include conceptually and computationally simple and robust parameter estimation, inherent stability, parsimony in the number of parameters, and synthesis through convolution. The authors describe a procedure for deriving the correct MA kernel using a signal enhancement algorithm, demonstrate the effectiveness of the model by using it to mimic several diverse textured images, discuss its applicability to the problem of infrared background simulation, and include detailed algorithms for the implementation of the model     

Security intrusion process: an empirical model

This paper describes a security model developed from empirical data collected from a realistic intrusion experiment in which a number of undergraduate students were invited to attack a distributed computer system. Relevant data, with respect to their intrusion activities, were recorded continuously. We have worked out a hypothesis on typical attacker behavior based on experiences from this and other similar experiments. The hypothesis suggests that the attacking process can be split into three phases: the learning phase, the standard attack phase and the innovative attack phase. The probability for successful attacks during the learning phase is expected to be small and, if a breach occurs, it is rather a result of pure luck than deliberate action. During the standard attack phase, this probability is considerably higher, whereas it decreases again in the innovative attack phase. The collected data indicates that the breaches during the standard attack phase are statistically equivalent. Furthermore, the times between breaches seem to be exponentially distributed, which means that traditional methods for reliability modelling of component failures may be applicable     

Market-based systems for instrument development and science planning

Market-based systems are those systems in which currency is used to express demand for a limited resource. In these systems, users `own' currency and exchange it for a desired commodity. Though used for thousands of years, market-based applications to space missions are still in their infancy. The first successful application was in 1992 with the Cassini Mission to Saturn. In this case, the sum total of mass and dollars for the science instruments had to fit within the allocated resource envelope. Results from the use of a market-based system show that the entire science payload grew from original estimates by only +1% for cost, and by –7% for mass. The next application was for Space Shuttle Secondary Payloads. In this application, available shuttle lift mass, number of lockers for secondary payloads, and available astronaut time had to be allocated between 5 NASA Users. Experiments showed that a market-based system can reduce the size of the required workforce needed to produce a manifest of the same quality as one produced `by committee.' Finally, a market-based system was experimentally applied to LightSAR science planning, a proposed joint NASA/Commercial RADAR mission. In this application, users were able to produce a conflict-free timeline of events remotely, of high science value, in about half the time required by more traditional methods.     

Energy conversion of the flare due to direct electric fields from the sheared reconnection

In this paper we present a new mechanism of the main energy conversion of the solar flare. Since a flare inducing prominence (flux tube) rises V_z ? 300 km s⁻¹, the plasmas below it cannot continuously eject with Alfvén speeds of V_A = 3000 km s⁻¹ but probably with V_z ≈ ±100 km s⁻¹. Plasma up and downflows with V_A will within a short duration be blocked between the chromosphere where reconnected flux tubes are piling up, and the slowly rising flux rope. Hence the Petschek slow shock mechanism is difficult to be realized as a major energy converting mechanism.     

A two-dimensional position-sensitive spectroscopic proportional counter for balloon-borne hard X-ray astronomy

A new design of position sensitive spectroscopic proportional counter is described, for use in a balloon borne hard x-ray telescope. Initial position and spectral resolution data from a one-dimensional laboratory prototype are reported. With this device, the final telescope will have an angular resolution of better than 10 minutes of arc.     

Preliminary results of Cytos 2 experiment.

Cytos 2 experiment, carried out during the French-Soviet manned flight (July 1982), has studied the antibiotics sensitivity of bacteria cultivated in vitro during the orbital flight. The results show an increase of the antibiotics resistance and a larger thickness of the cellular envelope for the inflight cells. The increase of antibiotics resistance can be related to a stimulating effect of space on the cell growth rate or to changes of the cellular envelope structure.     

Investigation of natural and artificial stimulation of the ionospheric Alfvén resonator at high latitude

A brief review is provided of recent progress in understanding the ionospheric Alfvén resonator (IAR) at high latitude. Firstly, naturally occurring resonances of the IAR as detected by pulsation magnetometers in the auroral zone at Sodankylä and in the polar cap at Barentsburg are considered. The characteristics of the IAR in the two regions are broadly similar, although the effects of solar illumination are less clear at the higher latitudes. Secondly we review recent attempts to stimulate the IAR through high-power radio frequency experiments both in the auroral zone at Tromsø with the European Incoherent SCATter (EISCAT) heater, and within the polar cap at Longyearbyen with the Space Plasma Exploration by Active Radar (SPEAR) facility. In the auroral zone at, Tromsø the stimulated IAR has been observed by ground-based magnetometers, and through electron acceleration observed on the FAST spacecraft. At SPEAR in the polar cap, the stimulated IAR has been investigated, with ground magnetometers, with the first results indicative of a positive detection.