Microflares and the Statistics of X-ray Flares

This review surveys the statistics of solar X-ray flares, emphasising the new views that RHESSI has given us of the weaker events (the microflares). The new data reveal that these microflares strongly resemble more energetic events in most respects; they occur solely within active regions and exhibit high-temperature/nonthermal emissions in approximately the same proportion as major events. We discuss the distributions of flare parameters (e.g., peak flux) and how these parameters correlate, for instance via the Neupert effect. We also highlight the systematic biases involved in intercomparing data representing many decades of event magnitude. The intermittency of the flare/microflare occurrence, both in space and in time, argues that these discrete events do not explain general coronal heating, either in active regions or in the quiet Sun.     

Procedure and methodologies for managing the risk of space object reentry

This paper proposes a procedure for managing the risk of reentering space objects and risk assessment methodologies used for the process. The proposed procedure comprises three phases encompassing the whole reentry stages of space objects. Mathematical models for assessing the impact risk of the reentering space objects by utilizing the information available during different risk management phases and the recommended risk analysis results for public communication are presented. The concept of the conditional casualty expectation is proposed as the metric representing the reentry risk and the method to compute its profile is introduced. A case study on the risk management procedure with the dataset on an actual reentry event is conducted to demonstrate the efficacy of the proposed procedure.     

Damping Mechanisms for Oscillations in Solar Prominences

Small amplitude oscillations are a commonly observed feature in prominences/filaments. These oscillations appear to be of local nature, are associated to the fine structure of prominence plasmas, and simultaneous flows and counterflows are also present. The existing observational evidence reveals that small amplitude oscillations, after excited, are damped in short spatial and temporal scales by some as yet not well determined physical mechanism(s). Commonly, these oscillations have been interpreted in terms of linear magnetohydrodynamic (MHD) waves, and this paper reviews the theoretical damping mechanisms that have been recently put forward in order to explain the observed attenuation scales. These mechanisms include thermal effects, through non-adiabatic processes, mass flows, resonant damping in non-uniform media, and partial ionization effects. The relevance of each mechanism is assessed by comparing the spatial and time scales produced by each of them with those obtained from observations. Also, the application of the latest theoretical results to perform prominence seismology is discussed, aiming to determine physical parameters in prominence plasmas that are difficult to measure by direct means.     

Sprite-Producing Lightning-Ionosphere Coupling and Associated Low-Frequency Phenomena

Theoretical and experimental evidence is collected for additional ionization regions in the mesosphere above lightning discharges and their connection with transient luminous events (TLE). New insights are reported into the different appearances in the Very Low Frequency (VLF) link traces as affected by the mesospheric ionization regions. Based on these findings, physical processes going on in the ionization regions and their coupling to the primary lightning discharge process are conceptualized. Thereafter, some diagnostic potential is outlined. Finally, the ionization regions are considered as a transmitter of secondary low-frequency waves. The distinction is made between the primary electromagnetic waves emitted by the lightning and the secondary waves. As a consequence the Extremely Low Frequency (ELF) and Ultra Low Frequency (ULF) transient signatures observed on the ground are understood as a composite of both wave types. In addition a novel method is introduced to extract the charge moment change of a sprite producing lightning discharge.     

Recent Results from Titan��s Ionosphere

Titan has the most significant atmosphere of any moon in the solar system, with a pressure at the surface larger than the Earth??s. It also has a significant ionosphere, which is usually immersed in Saturn??s magnetosphere. Occasionally it exits into Saturn??s magnetosheath. In this paper we review several recent advances in our understanding of Titan??s ionosphere, and present some comparisons with the other unmagnetized objects Mars and Venus. We present aspects of the ionospheric structure, chemistry, electrodynamic coupling and transport processes. We also review observations of ionospheric photoelectrons at Titan, Mars and Venus. Where appropriate, we mention the effects on ionospheric escape.     

Soldier Identification System utilizing low probability ofintercept (LPI) techniques

This paper documents the design of a laser/radio frequency (RF) Soldier Identification (ID) System developed by Dynetics, Inc., Harris, Corp., and the US Army Communications and Electronics Command (CECOM). The Soldier ID system includes an Interrogation Unit with a programmable activation code. The Interrogation Unit consists of a directive, eye-safe laser and a spread-spectrum RF transceiver. This allows for a low probability of intercept (LPI) interrogation, which is of interest during covert operations. A Responder Unit is worn, for example, by a soldier and transmits an LPI spread-spectrum RF response, only after receiving the proper interrogation codes. The basic subsystems for the identification system are a Laser Interrogation Unit, an RF Responder Unit, and an electronic Programming Unit. The operating principles for the subsystem are reviewed, and the design issues are discussed. In addition to the preliminary design performed under Phase I of the program, a breadboard system was developed to validate the proof-of-principle concept. Hardware implementation is reviewed and test results are presented. The brassboard development and engineering plans are also presented     

Efficacy of an ototoxic aminoglycoside (gentamicin) on the differentiation of the inner ear of cichlid fish.

Previous investigations revealed that the growth of fish inner ear otoliths depends on the amplitude and the direction of gravity, thus suggesting the existence of a (negative) feedback mechanism. In the course of these experiments, it was shown that altered gravity both affected otolith size (and thus the provision of the proteinacious matrix) as well as the incorporation of calcium. It is hitherto unknown, as of whether sensory hair cells are involved either in the regulation of otolith growth or in the provision of otolithic material (such as protein or inorganic components) or even both. The ototoxic aminoglycoside gentamicin (GM) damages hair cells in many vertebrates (and is therefore used for the treatment of Meniere's disease in humans). The present study was thus designed to determine as of whether vestibular sensory cells are needed for otolith growth by applying GM in order to induce a (functionally relevant) loss of these cells. Developing cichlid fish Oreochromis mossambicus were therefore immersed in 120 mg/l GM for 10 or 21 days. At the beginning and at the end of the experimental periods, the fish were incubated in the calcium-tracer alizarin complexone (AC). After the experiment, otoliths were dissected and the area grown during GM-exposure (i.e., the area enclosed by the two AC labellings) was determined planimetrically. The results showed that incubating the animals in a GM-solution had no effect on otolith growth, but the development of otolith asymmetry was affected. Ultrastructural examinations of the sensory hair cells revealed that they had obviously not been affected by GM-treatment (no degenerative morphological features observed). Overall, the present results suggest that hair cells are not affected by GM concerning their possible role in (general) otolith growth, but that these cells indeed might have transitionally been impaired by GM resulting in a decreased capacity of regulating otolith symmetry.     

Development status and application of the electric propulsion system RIT-10 used for station-keeping

The German 10 mN high frequency ion thruster system RIT-10 designed at Giessen University, constructed at MBB, and tested essentially at DFVLR, has attained an engineering model status and stands shortly before qualification for space flight. First application is planned for RIT-10 as a north-south stationkeeping system in TV-Sat preoperational version where it is flown as an experiment in order to acquire experience for subsequent operational communication satellite missions. The paper first describes the existing hardware, then shortly discusses application aspects, the respective test program, and preflight and flight procedures considered to guarantee safe and efficient operation in space.     

Studies on precellular evolution: the encapsulation of polyribonucleotides by liposomes.

Liposomes are 5 to 50 micron vesicles with an internal aqueous environment, whose amphiphilic lipidic components self-assemble into systems with at least one double-layered membrane. Liposomes have been suggested as possible models of precellular systems formed in the early Archean Earth from lipids of non-enzymatic origin. Since it is generally accepted that RNA molecules preceded double-stranded DNA molecules as genetic material, we have studied the encapsulation of polyribonucleotides within liposomes made from dipalmitoyl phosphatidylcholine, and from egg yolk phosphatidylcholine to which cholesterol was added in some cases. The liposomes were prepared under anoxic conditions following the reverse phase evaporation method described by Szoka and Papahadjopoulos. Quantitative determinations show that approximately 50% of the available lipids form liposomes, and that up to 5% of the polyribonucleotides can be entrapped by them. We have also studied the encapsulation of polyribonucleotides in the presence of 1) urea and cyanamide, two non-electrolytes that have been used as prebiotic condensing agents, and 2) of Zn++ and Pb++, two cations employed in the non-enzymatic template-directed synthesis of polyribonucleotides from activated nucleotides.     

Perception of gravity by plants.

Physical principles can be used to predict some features about the gravity perception system in plants. The nature of the system has made it rather elusive, so this approach represents an additional source of information to help find it. For a gravitational stimulus to be detected, two masses must move relative to each other in a manner which causes a significant amount of work to be done on a receptor. Relative to cellular dimensions, the masses must be large, be dense and move noticeable distances. The main sources of noise are thermal motion and flexing of the plant tissue. Some new models for the function of amyloplasts as statoliths are presented.