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701.
The European way of doing space differs from others in that, while carried out cooperatively, there is no fully integrated space policy. This is inevitable in a non-sovereign entity whose members do not have the same priorities in many vital sectors such as energy, industry and political economy, and has nevertheless produced some excellent programmes. But, against the background of the worldwide increase in space players and capabilities, Europe's current lack of ambition and foresight, and its limited ability to respond to external developments are worrying. It needs to be more open about its governance and financing plans, something missing from the latest European Commission communication. In these difficult economic times a complete rethinking of future space plans would enable Europe to prioritise on the strategic niches which must be preserved, while proper investigation of the management failures of the flagship programmes might help avoid such difficulties in the future. 相似文献
702.
Hart Walter G. McGowan Gerald F. DuPont T. E. 《IEEE transactions on aerospace and electronic systems》1968,(4):592-606
The design of an adaptive tracking filter control system and its application to large flexible booster vehicles is described. The problem of elastic vehicle stability is considered along with its solution by conventional and adaptive techniques. The improvement in vehicle stability, which may be achieved with the adaptive tracking filter technique as compared to conventional techniques, is shown. The control system evolved uses two adaptive tracking filters to phase stabilize the first and second bending modes, in addition to conventional compensation techniques. The application of this adaptive technique to a vehicle in which the modal frequencies are in close proximity (<2.5 percent separation) is discussed. The mechanization of the adaptive control system involves the selection of design techniques and components that are electrically and physically compatible with the intended airborne application. The development of a suitable frequency tracking technique and tracking filter is described, in addition to the electronic and mechanical design of the adaptive control system prototype. 相似文献
703.
F.J. Montojo T. López Moratalla C. Abad 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
In the project titled “Astrometric Positioning of Geostationary Satellite” (PASAGE), carried out by the Real Instituto y Observatorio de la Armada (ROA), optical observation techniques were developed to allow satellites to be located in the geostationary ring with angular accuracies of up to a few tenths of an arcsec. These techniques do not necessarily require the use of large telescopes or especially dark areas, and furthermore, because optical observation is a passive method, they could be directly applicable to the detection and monitoring of passive objects such as space debris in the geostationary ring. 相似文献
704.
A prominent neuroscientist A. Damasio has observed that “More may have been learned about the brain and the mind in the 1990s... than during the entire previous history of psychology and neuroscience” (1999). This progress, which should continue at an exponentially increasing pace as we move into the 21st century, sets the stage for another revolution-in the scientific formulation of intentional behavior. Just as applied sciences such as fluid mechanics and solid-state electronics benefited from breakthroughs in physics, so it may be expected that social psychology and economics, for example, will similarly benefit from our expanding knowledge of psychosomatic and psychological function. Economics, however, with its basic concepts dating from the nineteenth century, must endure an extensive renewal. Toward this end, a new mathematical theory of behavior was formulated in the early 1990s based on the contributions of prominent psychologists and economists over the past two centuries. Presentation of the new approach at international conferences continued in 2000 with attention moving beyond the fundamentals into macroeconomic concerns including business cycles, productivity, and unemployment 相似文献
705.
706.
Formation and Evolution of Corotating Interaction Regions and their Three Dimensional Structure 总被引:1,自引:0,他引:1
Corotating interaction regions are a consequence of spatial variability in the coronal expansion and solar rotation, which
cause solar wind flows of different speeds to become radially aligned. Compressive interaction regions are produced where
high-speed wind runs into slower plasma ahead. When the flow pattern emanating from the Sun is roughly time-stationary these
compression regions form spirals in the solar equatorial plane that corotate with the Sun, hence the name corotating interaction
regions, or CIRs. The leading edge of a CIR is a forward pressure wave that propagates into the slower plasma ahead, while
the trailing edge is a reverse pressure wave that propagates back into the trailing high-speed flow. At large heliocentric
distances the pressure waves bounding a CIR commonly steepen into forward and reverse shocks. Spatial variation in the solar
wind outflow from the Sun is a consequence of the solar magnetic field, which modulates the coronal expansion. Because the
magnetic equator of the Sun is commonly both warped and tilted with respect to the heliographic equator, CIRs commonly have
substantial north-south tilts that are opposed in the northern and southern hemispheres. Thus, with increasing heliocentric
distance the forward waves in both hemispheres propagate toward and eventually across the solar equatorial plane, while the
reverse shocks propagate poleward to higher latitudes. This paper provides an overview of observations and numerical models
that describe the physical origin and radial evolution of these complex three-dimensional (3-D) heliospheric structures.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
707.
708.
Electronic devices are a help for the blind. Some electronic devices push video signals directly to the brain but the device presented in this paper uses a sensitive and ready sensorial system: the auditory system. This article presents a low cost electronic device that enables the blind to distinguish the color and distance of objects. The project was first published in the UK and that system with the intensity of musical notes proportional to the brightness has proven to be annoying as the musical notes sound uninterrupted. In order to solve this problem, a new system for brightness perception was designed so a brief musical note is sounded when the sensor detects an increase of brightness and another brief musical note, one octave below, is sounded when the sensor detects a decrease in brightness 相似文献
709.
The DoD has many acquisition programs that are aggressively implementing open architecture principles in new avionics systems. Since “open” is an unclear attribute, projects eventually give in to a point solution that has no flexibility to cost effectively keep up with rapid changes in technology. The Open Systems Development Initiative (OSDI) project utilized COTS products to study the feasibility of building an open system that has plug-and-play capabilities. Lessons learned from the AV-8B Open Systems Core Avionics Requirements (OSCAR) and the F/A-18 Advanced Mission Computers and Displays (AMC&D) programs clearly indicated that understanding the underlying interfaces is crucial to keeping the system as open as possible to take advantage of the rapid changes in technology. A matrix of Key Open Standard Interfaces (KOSI), called the KOSI matrix, was developed and an applicable standard was identified for each interface. A list of non-conforming interfaces was also identified and the use of extensions or wrappers was investigated in an attempt to comply with standards. Standardization, rather than optimization of such interfaces, was considered more beneficial. It became evident that, with the exception of ruggedization, there is no difference in the use of COTS products for either commercial or military systems. Performing a KOSI analysis helped identify the key interfaces and standards, thus enabling the OSDI system to be scalable, portable and interoperable. A good KOSI matrix provides a vehicle for clear communication and helps systems integration and technology insertion to be less painful than what it is today. It helps reduce time-to-market and provides guidance to systems engineers and vendors to keep the system open 相似文献
710.
An improved method for frame synchronization of PCM telemetered data is described and performance analyses are presented. This method is based on the utilization of a threshold detector whose level is selfvarying according to the characteristics of the received data. It is simple to implement and simpler from an operational point of view than the frame synchronizers currently in use in that a threshold control is altogether eliminated. Analyses show, furthermore, that a synchronizer using a self-varying threshold always has a higher probability of detecting the synchronization code no matter what the frame length, sync code length, or error level. 相似文献