舰船运动航迹相关临界度的仿真模型

以雷达航迹与红外线角度航迹的相关为例 ,分析舰船运动航迹相关的临界度指标 ,建立状态方程 ,进行相应的运算和统计计算 ,并给出准确的仿真输出结果 .     

Quasi-steady flight to quasi-steady flight transition in a windshear: Trajectory optimization and guidance

This paper is concerned with the near-optimum guidance of an aircraft from quasi-steady flight to quasi-steady flight in a windshear. The take-off problem is considered with reference to flight in a vertical plane. In addition to the horizontal shear, the presence of a downdraft is considered. It is assumed that the power setting is held at the maximum value and that the aircraft is controlled through the angle of attack. Inequality constraints are imposed on both the angle of attack and its time derivative.First, trajectory optimization is considered. The optimal transition problem is formulated as a Chebyshev problem of optimal control: the performance index being minimized is the peak value of the modulus of the difference between the absolute path inclination and a reference value, assumed constant. Two types of optimal trajectories are studied: type 1 is concerned with gamma recovery (recovery of the initial value of the relative path inclination); and type 2 is concerned with quasisteady flight recovery (recovery of the initial values of the relative velocity, the relative path inclination, and the relative angle of attack). The numerical results show that the type 1 trajectory and the type 2 trajectory are nearly the same in the shear portion, while they diverge to a considerable degree in the aftershear portion of the optimal trajectory.Next, trajectory guidance is considered. A guidance scheme is developed so as to achieve near-optimum quasi-steady flight recovery in a windshear. The guidance scheme for quasi-steady flight recovery includes three parts in sequence. The first part refers to the shear portion of the trajectory and is based on the result that this portion of the trajectory depends only mildly on the boundary conditions; therefore, any of the guidance schemes already developed for type 1 trajectories can be employed (for instance, variable gamma guidance). The second part (constant gamma guidance) refers to the initial aftershear portion of the trajectory and is designed to achieve almost velocity recovery. The third part (constant rate of climb guidance) refers to the final aftershear portion of the trajectory and is designed to achieve almost complete restoration of the initial quasi-steady state.While the shear guidance and the initial aftershear guidance employ constant gain coefficients, the final aftershear guidance employs a variable gain coefficient. This is done in order to obtain accuracy and prompt response, while avoiding oscillations and overshoots. The numerical results show that the guidance scheme for quasi-steady flight recovery yields a transition from quasi-steady flight to quasi-steady flight which is close to that of the optimal trajectory, ensures the restoration of the initial quasi-steady state, and has good stability properties.This paper is based on Refs. 1 and 2.This research was supported by NASA-Langley Research Center, Grant No. NAG-1-516, and by Boeing Commercial Aircraft Company. The authors are indebted to Dr. R. L. Bowles, NASA-Langley Research Center, for helpful discussions.     

紫激光作用下四甲基硅的光谱和质谱研究

本文利用平行板电极装置及飞行时间质谱仪相结合的方法对四甲基硅进行了多光子电离（ＭＰＩ）光谱及飞行时间（ＴＯＦ）质谱的研究。得到了激光激发波长在４０２～３９２ｎｍ内的多光子电离光谱，获得了某些波长处的飞行时间质谱，并据此讨论了该分子在这个区域内可能的ＭＰＩ机理。     

大气气溶胶单粒子粒径和化学成分的LDI测量

介绍了当前应用较为广泛的大气气溶胶单粒子粒径与化学成分实时在线测量技术－激光解吸附电离（LDI）飞行时间质谱技术的原理和在气溶胶单粒子化学成分测量领域的应用。此外，还对气溶胶单粒子进样系统和气溶胶单粒子粒径的测量方法作了详细阐述。     

SCORPION: A system for coincidences between recoil and projectile ions at NSC, New Delhi

An on-line facility to measure coincidences between the recoil ions and the scattered projectiles (SCORPION) has been designed, fabricated and commissioned at Nuclear Science Centre (NSC), New Delhi. The facility consists of a four jaw slit assembly, a time of flight (TOF) spectrometer, a parallel plate electrostatic charge analyser and a one dimensional position sensitive parallel plate avalanche counter (PPAC). Details of the design and working principles of various components and the test results obtained for the Si ^q+-Ar collision system are presented to highlight the performance of the system. A multiple loss of up to four electrons has been observed for 60 MeV Si⁴⁺ ions colliding with argon atoms in a single collision condition. Spectra of recoil ions detected in coincidence with a particular charge state of the scattered projectile show a bell shaped distribution as a function of the recoil charge state (r) for the electron loss events. However, the yield of recoil ions drops asr increases for the direct ionization channel. Also for electron loss, the peak of the recoil ion distribution is seen to shift to a higher recoil charge state as the number of lost electrons from the projectile increases.     

Guidance strategies for near-optimum take-off performance in a windshear

This paper is concerned with guidance strategies for near-optimum performance in a windshear. This is a wind characterized by sharp change in intensity and direction over a relatively small region of space. The take-off problem is considered with reference to flight in a vertical plane.First, trajectories for optimum performance in a windshear are determined for different windshear models and different windshear intensities. Use is made of the methods of optimal control theory in conjunction with the dual sequential gradient-restoration algorithm (DSGRA) for optimal control problems. In this approach, global information on the wind flow field is needed.Then, guidance strategies for near-optimum performance in a wind-shear are developed, starting from the optimal trajectories. Specifically, three guidance schemes are presented: (A) gamma guidance, based on the relative path inclination; (B) theta guidance, based on the pitch attitude angle; and (C) acceleration guidance, based on the relative acceleration. In this approach, local information on the wind flow field is needed.Next, several alternative schemes are investigated for the sake of completeness, more specifically: (D) constant alpha guidance; (E) constant velocity guidance; (F) constant theta guidance; (G) constant relative path inclination guidance; (H) constant absolute path inclination guidance; and (I) linear altitude distribution guidance.Numerical experiments show that guidance schemes (A)–(C) produce trajectories which are quite close to the optimum trajectories. In addition, the near-optimum trajectories associated with guidance schemes (A)–(C) are considerably superior to the trajectories arising from the alternative guidance schemes (D)–(I).An important characteristic of guidance schemes (A)–(C) is their simplicity. Indeed, these guidance schemes are implementable using available instrumentation and/or modification of available instrumentation.Portions of this were presented at the AIAA 24th Aerospace Sciences Meeting, Reno, Nevada, January 6–9, 1986. The authors are indebted to Boeing Commercial Aircraft Company, Seattle, Washington and to Pratt and Whittney Aircraft, East Hartford, Connecticut for supplying some of the technical data pertaining to this study.The authors are indebted to Dr. R. L. Bowles, NASA-Langley Research Center, Hampton, Virginia for helpful discussions. They are also indebted to Mr. Z. G. Zhao, Aero-Astronautics Group, Rice University, Houston, Texas for analytical and computational assistance.This research was supported by NASA-Langley Research Center, Grant No. NAG-1-516. This paper, a continuation of Ref.1, is based in part on Refs. 2–3.     

Comparison of nanosecond laser ablation at 1064 and 308 nm wavelength

To study the solid Cu ablation in vacuum, two different laser sources operating at 1064 and 308 nm wavelength are employed at similar values of laser fluences. The infrared laser is a Q-switched Nd:Yag having 9 ns pulse width (INFN-LNS, Catania), while the ultraviolet one is a XeCl excimer having 20 ns pulse width (INFN-LEA, Lecce). Both experiments produced a narrow angular distribution of the ejected material along the normal to the target surface. The ablation showed a threshold laser power density, of about 7 and 3 J/cm² at 1064 and 308 nm, respectively, below which the ablation effect was negligible. The laser interaction produces a plasma at the target surface, which expands very fast in the vacuum chamber. Time-of-flight (TOF) measurements of the ion emission indicated an average ion velocity of the order of 4.7×10⁴ and 2.3×10⁴ m/s for the infrared and ultraviolet radiation, respectively. We also estimated approximately the corresponding temperature of the plasma from which ions originated, i.e. about 10⁶ and 10⁵ K for IR and UV wavelength, respectively. A discussion of the analysis of the ablation mechanism is presented. At the used laser power densities the produced Cu ions showed ionisation states between 1+ and 5+ in both cases.     

Summary of ISO/TC 201 standard: XXII. ISO 22048:2004—Surface chemical analysis—Information format for static secondary ion mass spectrometry

This International Standard provides a digital format to store and transfer between computers, in a compact way, important calibration and instrumental parameter data necessary to make effective use of spectral data files from static SIMS instruments. This format is designed to supplement the data transfer format specified in ISO 14976. Copyright © 2004 John Wiley & Sons, Ltd.     

Comparative study of organic dyes with time-of-flight static secondary ion mass spectrometry and related techniques

A series of cationic, zwitterionic and anionic fluorinated carbocyanine dyes, spin-coated on Si substrates, were measured with time-of-flight static secondary ion mass spectrometry (TOF-S-SIMS) under Ga(+) primary ion bombardment. Detailed fragmentation patterns were developed for all dyes measured. In the positive mode, the resulting spectra showed very intense signals for the precursor ions of the cationic dyes, whereas the protonated signals of the anionic dyes were hardly detected. Differences of three orders of magnitude were repeatedly observed for the secondary ion signal intensities of cationic and anionic dyes, respectively. All measured dyes yielded mass spectra containing several characteristic fragment ions. Although the secondary ion yields were still higher for the cationic than the anionic dye fragments, the difference was reduced to a factor of < or =10. This result and the fact that M(+), [M + H](+) or [M + 2H](+) are even-electron species make it very likely that the recorded fragments were not formed directly out of the (protonated) parent ions M(+), [M + H](+) or [M + 2H](+). In the negative mode, none of the recorded spectra contained molecular information. Only signals originating from some characteristic elements of the molecules (F, Cl), the anionic counter ion signal and some low-mass organic ions were detected. A comparative study was made between TOF-S-SIMS, using Ga(+) primary ions, and other mass spectrometric techniques, namely fast atom bombardment (FAB), electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI). The measurements showed that MALDI, ESI and FAB all give rise to spectra containing molecular ion signals. ESI and FAB produced M(+) and [M + H](+) signals, originating from the cationic and zwitterionic dyes, in the positive mode and M(-) and [M - H](-) signals of the anionic and zwitterionic dyes in the negative mode. With MALDI, molecular ion signals were measured in both modes for all the dyes. Structural fragment ions were detected for FAB, ESI and MALDI in both the positive and negative modes. Compared with the other techniques, TOF-S-SIMS induced a higher degree of fragmentation.