发动机亚定故障方程组整体优化解分布函数模型

提出了求解发动机亚定故障方程组整体优化解的分布函数模型.该模型利用一种可以控制自变量数值在整体解中分布的分布函数与亚定故障方程组的残差平方和构成复合目标函数,同时以物理合理性准则作为约束条件,构成一个非线性规划问题.分布函数模型可以在小于、等于特别是大于故障方程个数的各种复杂情况下给出全面的故障诊断信息,从而为目前迫切需要解决的发动机性能监控与故障诊断中在测量参数不足的情况下,对发动机进行全面性能诊断的技术难题提供出一种切实可行而又十分有效的数学模型.首次提出了作为评价发动机全面性能诊断算法有效性指标的相似度的概念,并且以JT9D发动机全面性能诊断问题为例,利用Monte Carlo随机模拟方法确定了分布函数模型可以达到的相似度值.研究结果表明,分布函数模型的相似度可达0.9以上.还利用JT9D发动机的实际故障样本对分布函数模型进行了检验.     

Optimal control in the east/west station-keeping manoeuvres for geostationary satellites

This paper addresses the optimal computation in terms of fuel consumption of the sequentially required tangential correction manoeuvres to control geostationary satellites within the longitude band. In fact, by using optimal control techniques, the Sun pointing perigee strategy (which only determines the best time of the day for the tangential manoeuvres) is formulated as a nonlinear programming problem with inequality constraints so that the proposed approach provides an optimal way to determine the remaining parameters for the station keeping, i.e., the time interval between successive corrections and the value for the eccentricity control to totally optimize the computation. Furthermore, by minimizing a cost function derived for the total manoeuvres sizes required in a year, a numerical simulation is performed to illustrate this approach. The computation shows how geostationary mission lifetimes may be extended up to half a year or more.

Resumen

En este papel se trata el cálculo óptimo en términos de consumo de fuel de las maniobras tangenciales periódicas necesarias para controlar satélites geoestacionarios dentro de la banda en longitud. En concreto, utilizando técnicas de control optimal, la estrategia perigeo hacia el Sol (que solo determina la mejor hora del día para las maniobras tangenciales) se formula como un problema de programación no lineal con constreñimientos, de tal forma que el tratamiento propuesto proporciona una forma óptima de determinar los parámetros restantes para el mantenimiento en estación, esto es, el intervalo de tiempo entre dos correciones sucesivas y el valor para el control de excentricidad para optimizar totalmente el cálculo. Además, mediante la minimización de una función de coste obtenida para todas las maniobras necesarias en un año, se realiza una simulación numérica para ilustrar esta metodología. Los cálculos muestran cómo se puede extender el tiempo de vida de una misión geostacionaria hasta medio año o más.     

民机大机群可靠性监控实践

结合运七飞机可靠性监控，对多个地区和使用单位和实施大机群可靠性监控的内容和方法作了重点论述。所提出的新方法－分布控制法，用在鉴别可靠性监控参数的警戒状况。该方法和内容，已用于运七可靠性监控中心的具体实践，监控效果好。     

飞机备件需求量的确定方法

飞机备件需求量计算是航空备件计划管理的一项重要内容。对飞机备件的分类及其特性进行了分析，并建立了循环件、非循环件和消耗件的需求量计算实用关系式。对需求量计划在实际中的应用问题，提出些看法和建议。     

Production and evolution of millisecond X-ray and radio pulsars

Observations using the Rossi X-ray Timing Explorer (RXTE) have discovered dozens of accreting neutron stars with millisecond spin periods in low-mass binary star systems. Eighteen are millisecond X-ray pulsars powered by accretion or nuclear burning or both. These stars have magnetic fields strong enough for them to become millisecond rotation-powered (radio) pulsars when accretion ceases. Few, if any, accretion- or rotation-powered pulsars have spin rates higher than 750 Hz. There is strong evidence that the spin-up of some accreting neutron stars is limited by magnetic spin-equilibrium whereas the spin-up of others is halted when accretion ends. Further study will show whether the spin rates of some accretion- or rotation-powered pulsars are or were limited by emission of gravitational radiation.     

XMM-Newton observations of low luminosity Be/X-ray candidates

A small number of early Be stars exhibit X-ray luminosities intermediate between those typical of early type stars and those radiated by Be/X-ray binaries in the quiescent state. We report on XMM-Newton observations of two such Be stars, HD 161103 and SAO 49725 which were originally discovered in a systematic cross-correlation between the ROSAT all-sky survey and SIMBAD. The new observations confirm the X-ray luminosity detected by ROSAT (L_X  10³² erg s⁻¹) and the hardness of their X-ray spectra (thin thermal with kT  8–10 keV or power law with photon index of 1.7) which are both unusual for normal early type stars. We discuss the possible origin of this excess X-ray emission in the light of the models proposed for γ-Cas, magnetic disc-star interaction or accretion onto a compact companion object, neutron star or white dwarf, and compare the properties of these two sources with those of the new massive systems discovered in the XMM- Newton/SSC survey of the Galactic plane.     

Using LASCO-C1 spectroscopy for coronal diagnostics

The LASCO-C1 telescope was designed to perform spectral analysis of coronal structures by means of a tunable Fabry–Pérot interferometer acquiring images at different wavelengths. Results from spectral scans of the Fe xiv 5303 Å green coronal emission line are presented. Physical quantities like the ion temperature (line widths), and the flow velocity along the line of sight (Doppler shifts) are obtained over the entire corona.     

Signature of coronal holes and streamers in the interplanetary space

The properties of different solar wind streams depend on the large scale structure of the coronal magnetic field. We present average values and distributions of bulk parameters (density, velocity, temperature, mass flux, momentum, and kinetic and thermal energy, ratio of thermal and magnetic pressure, as well as the helium abundance) as observed on board the Prognoz 7 satellite in different types of the solar wind streams. Maximum mass flux is recorded in the streams emanating from the coronal streamers while maximum thermal and kinetic energy fluxes are observed in the streams from the coronal holes. The momentum fluxes are equal in both types of streams. The maximum ratio of thermal and magnetic pressure is observed in heliospheric current sheet. The helium abundance in streams from coronal holes is higher than in streams from streamers, and its dependences on density and mass flux are different in different types of the streams. Also, the dynamics of -particle velocity and temperature relative to protons in streams from coronal holes and streamers is discussed.     

The dynamic chromosphere: Pushing the boundaries of observations and models

The interface between the bright solar surface and the million-degree corona continues to hold the key to many unsolved problems in solar physics. Advances in instrumentation now allow us to observe the dynamic structures of the solar chromosphere down to less than $0_{.}^{″}1$ with cadences of just a few seconds and in multiple polarisation states. Such observational progress has been matched by the ever-increasing sophistication of numerical models, which have become necessary to interpret the complex observations. With an emphasis on the quiet Sun, I will review recent progress in the observation and modelling of the chromosphere. Models have come a long way from 1D static atmospheres, but their predictions still fail to reproduce several key observed features. Nevertheless, they have given us invaluable insight into the physical processes that energise the atmosphere. With more physics being added to models, the gap between predictions and observations is narrowing. With the next generation of solar observatories just around the corner, the big question is: will they close the gap?     

Study of the solar Slow Sonic,Alfvén and Fast Magnetosonic transition surfaces

In this paper we study the shape, extend and time variations of the solar wind transition surfaces using the Lima and Priest (1993) hydrodynamic model adequately adapted for the case of the solar wind flow. The transition surfaces, namely the Slow (Sonic), the Alfvén, and the Fast Magnetosonic surface, are important boundaries around the Sun and play a crucial role in the development of the solar wind and the structure of the inner heliosphere. We determine the shape and dimension of these surfaces as a function of heliographic latitude using measurements from Ulysses spacecraft, and we also study their temporal variation using data from spacecrafts at 1 AU (OMNI database). Furthermore, we establish their dependence with the solar activity, demonstrating their shape and location for the last two solar cycles. From this we noticed that the temporal variation of all transition surfaces follows the 11-year solar cycle. Finally, from the OMNI database, we have studied the temporal variation over the past 40 years of the plasma β parameter, the kinetic to magnetic and the kinetic to thermal energy ratios, at a distance of 1 AU from the Sun.