Theoretical model of electron temperature and electron density: Comparisons with IRI and MSIS

An earlier theoretical model (UW-87) accurately predicted the electron temperature in the daytime F-region but suggested N₂ concentrations significantly greater than the predictions of MSIS-86. This discrepancy is resolved when the model is developed to include the effects of vibrationally excited nitrogen molecules and electronically excited oxygen ions on the F-region recombination rate. The revised model (UW-92) continues to predict electron temperatures close to the layer peak with great accuracy but it is now more closely consistent with MSIS. However, the electron temperatures predicted by this model, which are in close agreement with EISCAT observations, are significantly higher than the values predicted by the international Reference Ionosphere.     

Sooting and disruption in spherically symmetrical combustion of decane droplets in air

Results of experiments are reported on the burning of individual decane droplets, initially between 1.0 and 1.2 mm in dia, in air at room temperature and atmospheric pressure. Use was made of the 2.2 s drop tower at the NASA Lewis Research Center and a newly designed droplet-combustion apparatus that promotes nearly spherically symmetrical combustion. Unanticipated disruptions were encountered and related to sooting behavior.     

Chemi-acoustic instability structure in irreversibly reacting systems

A basic understanding of the structure of the interactions between chemical and acoustic instabilities and the effects derived therefrom is sought for a medium undergoing one-step irreversible chemical reaction. Detailed examination of the acoustic-chemical system after the completion of the reaction shows the distinct presence of the chemical, acoustic, and mixed modes of instability. The chemical mode appears as a stationary yet spatially inhomogeneous entropy distribution, even though the medium initially (before reaction) is homogeneous throughout. The acoustic mode appears as a composite of both right- and left-travelling pressure or velocity waves, even though the initial acoustic wave is only right-travelling. The left-travelling wave is generated due to partial reflection or scattering as the right-travelling wave propagates in a spatially inhomogenous medium during the chemical reaction and is sustained even after the reaction is completed. The mixed modes of density and temperature fluctuations apparently retain to some degree the characteristics of both the acoustic and the chemical modes and may, under certain conditions, be dominated by either one of the modes of behavior. This is determined largely by the parameter Ω, the ratio of chemical to acoustic time scales.During reaction, it is found that the observed complicated behavior can be interpreted fruitfully in terms of the mode concept developed for the post-reaction behavior. It is observed that the temporal development of the physical fluctuating variables is dependent upon spatial position (the effect being stronger as Ω is reduced). Further, it is found that at specific values of Ω, the following effects are maximized: (a) acoustic amplification; (b) wave reflection; (c) reaction evolution enhancement.The energy contained in the fluctuations is found to be composed of an acoustic and a chemical part. The latter dominates during reaction. However, after reaction, the chemical part exactly balances any change in the acoustic part which occurs during reaction, thus resulting in no net change in the fluctuation energy. The chemical part seems to represent the loss (or gain) of mean thermal energy which was diverted by chemi-acoustic interactions into the increased (or decreased) acoustic energy of the system.     

Book reviews

The general significance of streamers of the solar corona is discussed in the frame of our knowledge of the solar wind phenomenon and the large-scale solar magnetic structure. Thermodynamical and geometric parameters of streamers observed and measured at total solar eclipses are reviewed. Both the low part (in the form of a helmet with a cusp) and the external part (in the form of a stalk extended at many solar radii) are considered. The modelling of streamers starts with the analysis of effects produced by the solar wind flow on a magnetic structure. Facts and arguments are presented in favor of a model with a current sheet and reconnection processes going on along the axis of the streamer, especially in the non-collisional part of the radially extended streamer. Further development of the Pneuman and Kopp (1971) model is discussed, including difficulties occurring in the interpretation of a stationary solution. An empirical model satisfying observations is presented. Future researchs on streamers were discussed with emphasis on observations to be done with the space-borne coronagraphs on the SOHO spacecraft.     

The Earth's ring current: Causes,generation, and decay

The development of currents due to arbitrary distributions of trapped particles in the geomagnetic field is described. These currents form the Earth's ring current and are responsible for world wide decreases of the surface magnetic field observed during magnetic storms. It is shown that we do not yet know the relative abundances of the ions forming the ring current. Because of this we do not understand how various sources mix to produce the ring current. Several possible generation mechanisms are discussed. Finally, the decay of the ring current is discussed and is shown to be due primarily to charge exchange with important secondary effects attributable to wave-particle interactions.     

Late cataractogenesis in primates and lagomorphs after exposure to particulate radiations.

Rhesus monkeys that were exposed in 1969, at the age of approximately 2 years, to low doses of "mixed-energy" protons (10- and 110-MeV) are exhibiting progressive (degenerative) lenticular changes. We have conducted regular examinations of this group of monkeys for cataractogenic development since 1987, i.e., 18 years after irradiation, and the animals began to show enhanced degrees of lenticular opacification two years later. The lenses of age-matched controls (median lifespan in captivity approximately 24 years) continue to exhibit much lower levels of opacification (senile cataracts). Trends in the new data are consistent with the cataractogenic patterns observed for other groups of monkeys that were exposed at similar ages in 1964 and 1965 to protons of different energies, and which we began to monitor only 20-21 years later. Therefore, the new information from the mixed-energy group of monkeys provides insight into the development of late cataractogenic sequelae in the other groups of animals during the 2-3 years before we began to measure them. Comparisons are also made here among recent results from the different groups of primates and from New Zealand white (NZW) rabbits that were exposed when young to 56Fe ions and monitored continuously thereafter. This is done because analogous expression of radiation-induced degenerative cataractogenesis also occurs late in the lifespan of the lagomorphs (control median lifespan in captivity approximately 5-7 years), but in this case the cataractogenic profile has been documented through most of the post-irradiation lifespan.     

Improving magnetosphere in situ observations using solar sails

Past and current magnetosphere missions employ conventional spacecraft formations for in situ observations of the geomagnetic tail. Conventional spacecraft flying in inertially fixed Keplerian orbits are only aligned with the geomagnetic tail once per year, since the geomagnetic tail is always aligned with the Earth-Sun line, and therefore, rotates annually. Solar sails are able to artificially create sun-synchronous orbits such that the orbit apse line remains aligned with the geomagnetic tail line throughout the entire year. This continuous presence in the geomagnetic tail can significantly increase the science phase for magnetosphere missions. In this paper, the problem of solar sail formation design is explored using nonlinear programming to design optimal two-craft, triangle, and tetrahedron solar sail formations, in terms of formation quality and formation stability. The designed formations are directly compared to the formations used in NASA’s Magnetospheric Multi-Scale mission.     

Group force mobility model and its obstacle avoidance capability

Many mobility models attempt to provide realistic simulation to many real world scenarios. However, existing mobility models, such as RPGM [X. Hong, M. Gerla, G. Pei, C. Chiang, A group mobility model for ad hoc wireless networks, in: Proceedings of ACM/IEEE MSWiM’99, Seattle, WA, August 1999, pp. 53–60] and others, fail to address many aspects. These limitations range from mobile node (MN) collision avoidance, obstacle avoidance, and the interaction of MNs within a group. Our research, the group force mobility model (GFMM) [S.A. Williams, D. Huang, A group force mobility model, Appeared at 9th Communications and Networking Simulation Symposium, April 2006], proposes a novel idea which introduces the concept of attraction and repulsion forces to address many of these limitations. Williams and Huang [A group force mobility model, Appeared at 9th Communications and Networking Simulation Symposium, April 2006] described some of the limitations and drawbacks that many models neglect. This model effectively simulates the interaction of MNs within a group, the interaction of groups to one another, the coherency of a group, and the avoidance of collision with groups, nodes, and obstacles. This paper provides an overview of GFMM and particularly illustrates the GFMM's ability to avoid collision with obstacles, which is a vital property to posses in order to provide a realistic simulaition. We compare our model with the commonly used RPGM model and provide statistical assessments based on connectivity metrics such as link changed, link duration, and relative speed. All will be detailed and explained in this paper.