An extended chirp scaling algorithm for spaceborne sliding spotlight synthetic aperture radar imaging

A system impulse response with low sidelobes is critical in synthetic aperture radar（SAR） images because sidelobes contribute to noise and interfere with nearby scatterers. However,the conventional tricks of sidelobe suppression are unable to be exactly applied to the case of spaceborne sliding spotlight SAR due to great azimuth shifts in both time and frequency domains. In this paper, an extended chirp scaling algorithm is presented for spaceborne sliding spotlight SAR data imaging. The proposed algorithm firstly uses the spectral analysis（SPECAN） technique to avoid the azimuth spectrum folding effect and then employs the chirp scaling（CS） algorithm to achieve data focusing, i.e., the so-called two-step approach. To suppress the sidelobe level, an efficient strategy for the azimuth spectral weighting which only involves matrix multiplications and short fast Fourier transformations（FFTs） is proposed, which is a post-process executed on the focused SAR image and particularly simple to be implemented. The SAR image processed by the proposed extended CS algorithm is very precise and perfectly phase-preserving. In the end, computer simulation results verify the analysis and confirm the validity of the proposed algorithm.     

Oxygen and carbon abundances for the WO stars

We present relative carbon and oxygen abundances derived via an optically thin recombination line analysis for five WO stars, and compare the derived abundances to recent evolutionary models. New recombination coefficients for O⁴⁺, O⁵⁺ and O⁶⁺ ions have allowed total oxygen abundances to be derived. The final C/He values range between 0.4 and 0.8 by number, consistent with C/He ratios previously derived for WC stars. O/He values range between 0.1–0.4, with C/O ratios between 2.1–4.8.A comparison of the derived abundances with the evolutionary models of Maeder (1990) and Schaller et al. (1992) shows promising agreement. We find reasonably tight agreement between the abundances derived for the WO stars. The degree of enhancement for the oxygen abundances in regions of low metallicity predicted by Maeder (1990) is not corroborated by our results.Additionally we present a revised, quantified classification scheme for WO subtypes. We extend the class to lower excitation, WO5, and place MS 4 (=WR 30a) in this class. Equivalent widths of the strongest lines of MS 4 are also presented. Finally, we present new observations of DR 1, a WO3 star located in the dwarf irregular galaxy IC 1613.     

HD 190918: Arbiter between models for Wolf-Rayet stars

New orbital elements for the 112.4 day WN4.5+O9.5Ia spectroscopic binary HD 190918 are presented. Solutions consistent with the O star being a main sequence star or a supergiant are obtained wheni=25° or 20°, respectively. We predict the X-ray flux to be expected from this system and note how an observation of the X-ray flux from HD 190918 would help one to choose the most probable value of the inclination.     

A parallel square-root algorithm for modified extended Kalmanfilter

A parallel square-root algorithm and its systolic array implementation are proposed for performing modified extended Kalman filtering (MEKF). The proposed parallel square-root algorithm is designed based on the singular value decomposition (SVD) and the Faddeev algorithm, and a very large scale integration (VLSI) systolic array architecture is developed for its implementation. Compared to other square root Kalman filtering algorithms, the proposed method is more numerically stable. The VLSI architecture described has good parallel and pipelining characteristics in applying to the MEKF and achieves higher efficiency. For n-dimensional state vector estimations, the proposed architecture consists of O(2n²) processing elements and uses O ((s+17)n) time-steps for a complete iteration at each instant, in contrast to the complexity of O((s+6) n³) time-steps for a sequential implementation, where s≈log n     

Stage separation of recoverable liquid launch vehicle by using moving pulsating ball analogue for propellant sloshing

In the process of stage separation of recoverable liquid launch vehicles,because of the large amount of residual fuel in the storage tanks,the influence of liquid sloshing on separation safety must be considered.Considering calculation simplicity and operation practicability,the Moving Pulsating Ball Model(MPBM) of large amplitude liquid sloshing is introduced into the calculation of launch vehicle stage separation.Combining the dynamic equation of the model with the energy relationship during \"breathing movement\",the formula calculating the force of liquid on the rigid body is derived.Compared with the calculations of commercial CFD calculation software,the accuracy of MPBM model is verified.Then,all the external forces and moments are applied to the rigid body of the stages,so that the translational and rotational dynamic equations of the stages are obtained respectively.According to the relative position of the two stages,the geometric shape of the interstage section and the engine of the second stage,the minimum clearance in the separation process can be decided to guarantee that the separation process is safe.     

Parameter extraction for the extended cantilever model of magneticcomponent windings

The extended cantilever model (ECM) for transformer or inductor windings is convenient from the parameter extraction standpoint since, theoretically, each model parameter can be extracted from a single measurement of an open-circuit voltage or a short-circuit current. The impedance of the sensor used to measure a short-circuit current, however, makes the “short” less ideal, and it has been believed that each parameter in the ECM cannot be directly measured unless the impedance of the current sensor is negligible. It is shown that as long as the ECM parameters are reactive (inductive or capacitive) and the current sensor resistive, the current-sense resistance does not have to be restrictively small for the ECM parameters to be directly measurable. A linear, broadband formulation is also presented for extraction of the model admittances using current sensors with significant impedances     

大型整体金属结构增材制造技术适航验证

针对民用飞机主承力结构金属增材制造技术适航验证方面存在的问题,开展金属结构增材制造技术适航验证研究。通过增材制造技术适用适航条款分析,给出了民用飞机金属结构增材制造技术适航验证思路,包括材料规范的建立、增材制造工艺的认证、材料强度性能的确定、结构特殊系数的选取和结构性能的验证,对每项验证方法给出了具体实施途径。以某型号前起落架支柱外筒增材制造A-100超高强度钢为例,给出了大型整体金属结构增材制造技术适航验证具体实施方案。     

Evolution of low-mass stars. implications for the dark matter distribution in the halo

We present up-to-date evolutionary models of low-mass stars, from M0.6 M down to the hydrogen burning minimum mass, using recent equation of state and synthetic spectra calculations. Comparison is made with observed luminosity function for these objects. We also present implications for the dark-matter distribution in the galactic halo.     

Hydrodynamic atmosphere models for hot luminous stars II. Method and improvements over unified models

In a paper submitted to A&A we present the first line blanketed hydrodynamic models of spherically expanding atmospheres of hot stars. This paper is complementary to the submitted paper. Here, we emphasize the advantages and the weak points of our approach and we present additional technical aspects.The models are characterised by a simultaneous solution of the equation of motion, the non-LTE populations of H and He, and radiation transfer in a line blanketed atmosphere. The entire domain from the optically thick photosphere out to the terminal velocity of the wind is treated. The radiative forces are evaluated consistently with the depth-dependent radiation field, taking into account multiple scattering by metal lines and line overlap.     

A novel two-stage extended Kalman filter algorithm for reaction flywheels fault estimation

This paper investigates the problem of two-stage extended Kalman filter(TSEKF)-based fault estimation for reaction flywheels in satellite attitude control systems(ACSs). Firstly, based on the separate-bias principle, a satellite ACSs with actuator fault is transformed into an augmented nonlinear discrete stochastic model; then, a novel TSEKF is suggested such that it can simultaneously estimate satellite attitude information and actuator faults no matter they are additive or multiplicative; finally, the proposed approach is respectively applied to estimating bias faults and loss of effectiveness for reaction flywheels in satellite ACSs, and simulation results demonstrate the effectiveness of the proposed fault estimation approach.     

Comments on “A method for improving extended Kalman filterperformance for angle-only passive ranging”

Some history of this bearings-only problem at Sperry dating from 1965 is presented. The erratic estimation problems were soon recognised and labeled the “Collapse of the Covariance Matrix Problem”. A solution was soon found as a relation transformation on the covariance matrix. The angle of rotation was the difference between estimates of bearing before and after a measurement update. Based on a comparison of covariance analyses for simulated problems using the true bearings with Monte Carlo results it was concluded that no further significant improvement could be achieved. This conclusion is yet to be disproved     

Astrometric search for unseen stellar and sub-stellar companions to nearby stars and the possibility of their detection

Unseen companions to nearby stars are found astrometrically through perturbations in the proper motion from photographs taken with long-focus telescopes. The number of known unseen astrometric companions to nearby stars with photocentric orbits has grown by thirty percent in the last few years. Individual cases are discussed and optimum epochs given for resolution of the components. Orbital analysis of the photocentric positions on the photographic plates provides all information for accurate mass determination of the components except for m and angular separation, , of the two components which must come from another technique. There are potentially thirty low luminosity stars including some likely sub-stellar objects whose masses could be instantly found with the observations of these additional two parameters.A list of the stars known within five parsecs as of 1978 July is given and the status of unseen companions to these stars is discussed on the basis of long interval astrometric coverage.     

Experimental work on the aerodynamics of integrated slender wings for supersonic flight

This paper reviews an extensive programme of experimental work which was aimed at the production of integrated slender wings which had volume distributions and cross-section shapes compatible with the requirements of a supersonic transport aircraft. The wings were also to be cambered so that they were trimmed at the cruise condition about a centre of gravity position located at the aerodynamic centre position at the approach condition; furthermore the camber was to be chosen so that the drag was as low as possible. The main work was carried out about 20 years ago, but the involvement in specific design applications resulted in no overall account of the programme being published, although a number of reports on individual wings, or groups of wings, have appeared. This paper reviews the whole programme from the initial tests on very simple delta wings with diamond cross-sections to the final tests on realistic shapes which achieved almost all of the design requirements.     

Organization, selection, and training of crews for extended spaceflight: findings from analogs and implications

Ample research evidence from space analogs points to the crucial role that teamwork plays in the performance of small groups in isolation and confinement. This paper surveys findings about the impacts of group behavior and social interaction on crew morale, coordination, and productivity. Implications for the organization, selection, and training of crews for extended spaceflight are discussed.     

A progressive approach to predict shot peening process parameters for forming integral panel of AI7050-T7451

In this paper,a progressive approach to predict the multiple shot peening process parameters for complex integral panel is proposed.Firstly,the invariable param...     

Dynamic modeling of a hose-drogue aerial refueling system and integral sliding mode backstepping control for the hose whipping phenomenon

Dynamic modeling of a hose-drogue aerial refueling system（HDARS） and an integral sliding mode backstepping controller design for the hose whipping phenomenon（HWP） during probe-drogue coupling are studied. Firstly, a dynamic model of the variable-length hose-drogue assembly is built for the sake of exploiting suppression methods for the whipping phenomenon.Based on the lumped parameter method, the hose is modeled by a series of variable-length links connected with frictionless joints. A set of iterative equations of the hose＇s three-dimensional motion is derived subject to hose reeling in/out, tanker motion, gravity, and aerodynamic loads accounting for the effects of steady wind, atmospheric turbulence, and tanker wake. Secondly,relying on a permanent magnet synchronous motor and high-precision position sensors, a new active control strategy for the HWP on the basis of the relative position between the tanker and the receiver is proposed. Considering the strict-feedback configuration of the permanent magnet synchronous motor, a rotor position control law based on the backstepping method is designed to insure global stability. An integral of the rotor position error and an exponential sliding mode reaching law of the current errors are applied to enhance control accuracy and robustness. Finally,the simulation results show the effectiveness of the proposed model and control laws.