发动机维护服务的现状与未来

航空发动机大修业务开始企稳,而且预计未来还将有所增加. 据MRO Prospector统计,目前在役的窄体飞机机队数量约是宽体飞机的3倍,2011年窄体飞机的发动机返厂维修量将会有大幅增加.     

Cataractogenic potential of ionizing radiations in animal models that simulate man.

Aspects of experiments on radiation-induced lenticular opacification during the life spans of two animal models, the New Zealand white rabbit and the rhesus monkey, are compared and contrasted with published results from a life span study of another animal model, the beagle dog, and the most recent data from the ongoing study of the survivors from radiation exposure at Hiroshima and Nagasaki. An important connection among the three animal studies is that all the measurements of cataract indices were made by one of the authors (A.C.L.), so variation form personal subjectivity was reduced to a minimum. The primary objective of the rabbit experiments (radiations involved: 56Fe, 40Ar and 20Ne ions and 60Co gamma photons) is an evaluation of hazards to astronauts from galactic particulate radiations. An analogous evaluation of hazards from solar flares during space flight is being made with monkeys exposed to 32, 55, 138 and 400 MeV protons. Conclusions are drawn about the proper use of animal models to simulate radiation responses in man and the levels of radiation-induced lenticular opacification that pose risks to man in space.     

Design of a modern pitch pointing control system

The development of a pitch pointing control system for an advanced high performance fighter aircraft using eigenstructure assignment and command generator tracking schemes is presented. A desired eigenstructure is first chosen to achieve a desired decoupling (i.e., pitch attitude and flight path angle), and to obtain a desired damping and rise time. The command generator tracker is next used to ensure zero steady-state error-to-step commands. The stability robustness to the parameter variations of the closed-loop system is evaluated in the sense of the conditioning of the achieved eigenstructure by using singular value analysis technique. The analysis and synthesis techniques for the pitch pointing control system are illustrated by applying the techniques to F-15 aircraft as a part of the NASA/USAF program named ACTIVE (Advanced Controls for integrated Vehicles)     

Analysis of CGSDS file delivery protocol: immediate NAK mode

We analyze the immediate negative acknowledgment (NAK) mode of the consultative committee for space data systems (CCSDS) file delivery protocol for the single-hop file transfer operation. We propose a timer setting rule that minimizes the expected time taken to transfer a file under the constraint that the throughput efficiency is maximized. Then, we derive the expected file delivery time and compare it with that of the deferred NAK mode. The main contribution is the closed-form expression for evaluating the performance metrics.     

Laminar dust flames in a reduced-gravity environment

The propagation of laminar dust flames in suspensions of iron in gaseous oxidizers was studied in a low-gravity environment onboard a parabolic flight aircraft. The reduction of buoyancy-induced convective flows and particle settling permitted the measurement of fundamental combustion parameters, such as the burning velocity and the flame quenching distance over a wide range of particle sizes and in different gaseous mixtures. Experimentally measured flame speeds and quenching distances were found in good agreement with theoretical predictions of a simplified analytical model that assumes particles burning in a diffusive mode. However, the comparison of flame speeds in oxygen–argon and oxygen–helium iron suspensions indicates the possibility that fine micron-sized particles burn in the kinetic mode. Furthermore, when the particle spacing is large compared to the scale of the reaction zone, a theoretical analysis suggests the existence of a new so-called discrete flame propagation regime. Discrete flames are strongly dependent on particle density fluctuations and demonstrate directed percolation behavior near flame propagation limits. The experimental observation of discrete flames in particle suspensions will require low levels of gravity over extended periods available only on orbital platforms.     

Reactions to receipt of a message from extraterrestrial intelligence: a cross-cultural empirical study

If we ever receive a message from extraterrestrial intelligence (ETI), the societal impact may be significant. To date, several authors have speculated on factors that may predict people’s reactions, but there have been no systematic empirical studies on the range of responses. One obstacle to conducting such studies is that there has been no questionnaire to assess such reactions. In the current study we have designed a psychometrically sound set of scales to assess six beliefs: (1) that extraterrestrial life exists, (2) that ETI would be benevolent and that we should respond to a message, (3) that ETI would be malevolent, (4) that message receipt would be unsettling, (5) that message receipt would be religiously significant and (6) that experts should determine the content of a reply. We report on the construction and use of these new scales, drawing on data gathered from American and Chinese undergraduate students. Respondents also completed measures of alienation, optimism, anthropocentrism and religiosity. This allowed us to predict beliefs about ETI based on personal characteristics and beliefs of the respondents.     

On mapping a tracking algorithm onto parallel processors

The problem of mapping the tasks of a multitarget tracking algorithm onto parallel computing architectures to maximize speedup is considered. An asymptotically optimal mapping algorithm is developed and applied to study the effects of task granularity and processor architectures on the speedup. From the simulation results, it is concluded that task granularity and the parallelization of clustering and global hypotheses formation stages of the tracking algorithm are major determinants of speedup     

Analysis and Design of a Standardized Control Module for Switching Regulators

Three basic switching regulators: buck, boost, and buck/boost, employing a multiloop standardized control module (SCM) were characterized by a common small signal block diagram. Employing the unified model, regulator performances such as stability, audiosusceptibility, output impedance, and step load transient are analyzed and key performance indexes are expressed in simple analytical forms. More importantly, the performance characteristics of all three regulators are shown to enjoy common properties due to the unique SCM control scheme which nullifies the positive zero and provides adaptive compensation to the moving poles of the boost and buck/boost converters. This allows a simple unified design procedure to be devised for selecting the key SCM control parameters for an arbitrarily given power stage configuration and parameter values, such that all regulator performance specifications can be met and optimized concurrently in a single design attempt.     

High-frequency AC power distribution in Space Station

A utility-type, 20-kHz, AC power distribution system for the space station employing resonant power-conversion techniques is presented. The system converts raw DC voltage from photovoltaic cells or three-phase, low-frequency AC voltage from a solar dynamic generator into a regulated, 20-G kHz AC voltage for distribution among various loads. Operations of the components of the system such as driver inverter, DC receiver, bidirectional receiver, and three-phase AC receiver are discussed. EASY5 computer modeling and simulations were performed to study the local and global performance of the system. Simulation results show that the system has fast response and good transient behavior. The AC bus voltage is effectively regulated using the phase-control scheme, which is demonstrated with both line and load variations. The feasibility of paralleling the outputs of driver modules is illustrated with the driver modules synchronized and sharing a common feedback loop. A high-frequency, sinusoidal AC voltage is generated in the three-phase, AC input case, when the driver modules are phased 120° away from one another and their outputs are connected in series