National and Regional Grids

The title of this paper provides a point of departure for the broadest possible discussion of electric power transmission and presents an opportunity to comment on some misconceptions regarding power systems. The subject of transmission is discussed in terms of 1) the grid concept, 2) its system function, and 3) its probable future development and some of the problems facing such development.     

Power management and distribution system for a more-electricaircraft (MADMEL)

A five-phase Power Management and Distribution System for a More-Electric Aircraft (MADMEL) program was awarded by the Air Force to Northrop/Grumman Military Aircraft Division in September 1991. The objective of the program is to design, develop, and demonstrate an advanced electrical power generation and distribution system for a More-Electric Aircraft (MEA). The MEA emphasizes the use of electrical power in place of hydraulics, pneumatic, and mechanical power to optimize the performance and life cycle cost of the aircraft. This paper presents an overview of the MADMEL program and a top-level summary of the program results, development and test of major components to date. In Phase I and Phase II studies, the electrical load requirements were established and the electrical power system architecture was defined for both near-term (NT-year 1996) and far-term (FT-year 2003) MEA application. The detailed design and specification for the Electrical Power System (EPS), its interface with the Vehicle Management System, and the test set-up were developed under Phase III. Phase IV, fabrication and testing of the subsystem level hardware, has been completed. Overall system level integration and testing, Phase V, is scheduled to be completed by September 1999     

Editorial: Cognitive Semantics and Spatio-Temporal Ontologies

How do people describe the location of a target object to another? This task requires a reference object or frame and terms of reference. Traditional linguistic analyses have loosely organized perspectives around people, objects, or environments as reference objects, using reference terms based on a viewpoint or the intrinsic sides of an object, such as left, right, front, and back or based on the environment, such as north, south, east, and west. In actual communication, social, spatial, and cognitive factors may also affect perspective choice. We examine those factors by varying the spatial information (landmarks and cardinal directions), the communication task (relative cognitive burden to speakers and addressees), and the culture of participants (American and Japanese). Speakers used addressees' perspectives more when addressees had the greater cognitive burden. They also used landmarks and cardinal directions when they were available, especially to avoid difficult discriminations like left/right. Some cases appearing to be perspective taking can be interpreted as using a person as a landmark. Finally, terms like near indicating close proximity were preferred to far and to terms requiring projection of directions. Globally, perspective choices of American and Japanese samples were strikingly similar; that is, Japanese did not select addressees' perspectives more than Americans. The traditional linguistic analyses need to be enhanced to account for effects of cognitive, situational, and social factors.     

On The 53Mn Heterogeneity In The Early Solar System

It is well established that the prolonged and thorough mixing of numerous nucleosynthetic components that constitutes the matter in the solar nebula resulted in an essential isotopic homogeneity of the solar system material. This may or may not be true for the short-lived radionuclides which were injected into or formed within the solar nebula just prior to or during solar system formation. Distinguishing between their heterogeneous or homogeneous distribution is important because the short- lived radionuclides are now widely used for the relative chronology of various objects and processes in the early solar system and as constraints for models of nucleosynthesis. The recent studies of the ⁵³Mn-⁵³Cr isotope system (half life of ⁵³Mn is 3.7 Ma) in various solar system objects have shown that the relative abundance of radiogenic ⁵³Cr is consistent with essentially homogeneous distribution of ⁵³Mn in the asteroid belt. Thus, the relative ⁵³Mn-⁵³Cr chronometer can be directly used for dating samples which originated in the asteroid belt. Importantly, however, all meteorite groups studied so far indicate a clear excess of ⁵³Cr as compared to Earth and to a lunar sample, which exhibits also a terrestrial ⁵³Cr/⁵²Cr ratio. The results from the Martian (SNC) meteorites show that their ⁵³Cr excesses are less than half of those found in the asteroid belt bodies. Thus, the characteristic ⁵³Cr/⁵²Cr ratio of Mars is intermediate between that of the Earth-Moon system and those of the other meteorites. If these ⁵³Cr variations are viewed as a function of the heliocentric distance, the radial dependence of the relative abundances of radiogenic ⁵³Cr is indicated. This observed gradient can be explained by either an early, volatility controlled, Mn/Cr fractionation within the nebula or by an initial radial heterogeneous distribution of ⁵³Mn. Although model calculations of the Mn/Cr ratios in the bulk terrestrial planets seem to be inconsistent with the volatility driven scenario, the precision of these calculations is inadequate for eliminating this possibility. In contrast, recent studies of the ⁵³Mn-⁵³Cr system in the enstatite chondrites indicate that, while their bulk Mn/Cr ratios are essentially the same as in ordinary chondrites, the ⁵³Cr excess in bulk enstatite chondrites is three times lower than that in the bulk ordinary chondrites. This difference cannot be explained by a Mn/Cr fractionation and, thus, strongly suggests that a radial heterogeneous distribution of ⁵³Mn must have existed in at least the early inner solar system. Using the observed gradient and the ⁵³Cr/⁵²Cr ratio of the bulk enstatite chondrites, their parent body(ies) formed at ∼1.4 AU or somewhat closer to the Sun. This revised version was published online in June 2006 with corrections to the Cover Date.     

Switching in sequential tree networks

Recursive analytical expressions for speedup and solution time for a multilevel tree sequentially processing a divisible load under cut through switching are developed. Such cut through switching is shown to be more efficient than store and forward switching. Aerospace applications include sensor networks, radar, and satellite imagery processing.     

Some regularities in the relationship of limb coronal mass ejections with eruptive prominences and post-eruptive arcades

A positive correlation is shown to exist between the angular sizes (in the sky plane) of eruptive prominences and/or post-eruptive arcades and coronal mass ejections (CMEs) associated with them. New regularities are found that characterize the relationship between the latitude of eruptive prominences (post-eruptive arcades) and the latitude position of CMEs associated with them in the field of view of a coronagraph. An interpretation of these regularities is given.     

Effects of Local Detachment of a Melt from Ampoule Walls,Crystal Vibration,and Magnetic Field at Crystal Growth under Zero Gravity

A numerical investigation of the melt flow and heat and mass transfer is carried out at the crystal growth under zero gravity, when the melt detachment from ampoule walls, crystal vibration, and various magnetic fields are active. Specific features of the melt flow are demonstrated depending on the size of a detachment zone adjacent to the crystallization boundary. The velocity of the averaged flow generated by crystal vibration is determined as a function of the vibration intensity. It is shown that the crystal vibration cannot compensate a thermal capillary flow (caused by detachment of the melt from the ampoule wall) and reduce the macrosegregation of impurities. It is shown that the application of steady and rotating magnetic fields are inefficient for all ampoule methods of crystal growth under microgravity conditions.     

Stochastic game approach to air operations

A command and control (C/sup 2/) problem for military air operations is addressed. Specifically, we consider C/sup 2/ problems for air vehicles against ground-based targets and defensive systems. The problem is viewed as a stochastic game. We restrict our attention to the C/sup 2/ level where the problem may consist of a few unmanned combat air vehicles (UCAVs) or aircraft (or possibly teams of vehicles), less than say, a half-dozen enemy surface-to-air missile air defense units (SAMs), a few enemy assets (viewed as targets from our standpoint), and some enemy decoys (assumed to mimic SAM radar signatures). At this low level, some targets are mapped out and possible SAM sites that are unavoidably part of the situation are known. One may then employ a discrete stochastic game problem formulation to determine which of these SAMs should optimally be engaged (if any), and by what series of air vehicle operations. We provide analysis, numerical implementation, and simulation for full state-feedback and measurement feedback control within this C/sup 2/ context. Sensitivity to parameter uncertainty is discussed. Some insight into the structure of optimal and near-optimal strategies for C/sup 2/ is obtained. The analysis is extended to the case of observations which may be affected by adversarial inputs. A heuristic based on risk-sensitive control is applied, and it is found that this produces improved results over more standard approaches.     

On electromagnetic phenomena in Mercury’s magnetosphere

Mercury has a small but intriguing magnetosphere. In this brief review, we discuss some similarities and differences between Mercury’s and Earth’s magnetospheres. In particular, we discuss how electric and magnetic field measurements can be used as a diagnostic tool to improve our understanding of the dynamics of Mercury’s magnetosphere. These points are of interest to the upcoming ESA-JAXA BepiColombo mission to Mercury.