Optically timed submillimeter time-of-flight mass spectrometry

We demonstrate that using intense femtosecond laser pulses to optically time ion flight can lead to a miniature time-of-flight mass spectrometer. After laser ionization, the molecular ion is accelerated by a static electric field and detected using a second, delayed laser pulse. The relative positions of the two laser foci determine the ion flight distance while the time separation of the laser pulses fixes the ion flight time. We mass-resolve CS(2) or C(6)H(6) isotopes after a flight distance of 360 microm using either double ionization or Coulomb explosion detection.     

基于表面超声波无损评价激光熔覆层厚度的实验研究

针对目前激光熔覆层厚度无损评价的重要性,本工作结合表面超声波在介质中的传播特性对其进行测量,并在互相关函数基础上对熔覆层厚度进行了表征和评价。结果表明:随着激光熔覆层厚度的增加,表面超声波在其中的传播速率逐渐变小,在互相关函数计算微小时间差的基础上,建立了可用于评价激光熔覆层厚度的厚度-时间差关系曲线,并采用三次多项式对其进行拟合,进而得到可用于评价激光熔覆层厚度的拟合公式。最后采用不同厚度的激光熔覆层试样对拟合结果进行了验证,并同时对影响计算结果的因素进行了分析。结果表明:采用该方法对激光熔覆层厚度进行评价是可行的。     

飞行试验中UDP数据包丢失和失序处理研究

UDP协议是飞行试验中机载网络化测试系统进行数据传输时采用的主要传输协议。与TCP协议相比,UDP协议的主要特点是它是面向非连接的协议、网络开销低、传输速度快但传输不可靠、数据包会发生丢失和失序现象。由于处理飞行试验数据时必须考虑数据的时间相关性,试飞数据处理软件需要开辟适当的缓存区来对数据按照时间进行重新排序。根据飞行试验中网络数据包时间标签具有周期性的特点,给出了确定缓存区大小的公式,并讨论了数据包丢失和失序情况下缓存区的重排算法。最后以真实飞行试验数据的处理结果说明了算法的成功应用。     

A unified analytical model for the flight distance of flying microdroplet before solidification

Heat dissipation and solidification of a flying microdroplet are omnipresent in nature and industrial applications. The current study lacks a model to determine the critical flight distance before the microdroplet solidification, which is crucial for powder production and microdroplet jet printing in additive manufacturing. This study investigated the transient velocity and temperature attenuation of a flying microdroplet. Both the velocity and temperature of the microdroplet were found to be decayed exponentially with the flying time. Based on energy conversion and flying velocity integration, an analytical model was proposed to determine the critical flight distances that the microdroplet begins and ends to solidify. Moreover, the parameters affecting the critical flight distance were unified into a nondimensional formula. Finally, we validated the proposed models experimentally through the deposited morphologies of copper microdroplets induced by laser pulses.     

Varied threshold with laser flight time in scannerless range-gated ladar

We present a method based on maximum-likelihood estimation to calculate the threshold of the number of converted photoelectrons according to Poisson and Gaussian statistics. The calculations for detection and false-alarm probabilities are given including a proposal of error probability. An efficient approach of setting threshold according to laser flight time is discussed as the laser power decreases in propagation. Comparison of the fixed threshold and the varied threshold in Poisson and Gaussian statistics is provided. The varied threshold approach tends to keep the error probability at the lowest level. This varied threshold approach is found to have a similar effect on ranging accuracy as a threshold-fixed approach.     

New approach for air traffic management based on control theory

Air traffic management aims to provide solutions to congestion problems in air traffic networks (ATNs) which in turn are mainly generated by the variation in the capacity of air sectors or airports due to adverse weather conditions. Most of the existing approaches to dealing with these problems are based on mathematical programming techniques and inherit its computational difficulty. In this paper, we introduce a control scientist point of view to this topic by proposing an approach to solve the ground-holding problem based on discrete event systems control theory. An ATN can effectively be considered as a timed discrete event system and can be efficiently modelled based on a Time Petri net tool. The main advantage is an explicit representation of the position of each aircraft in the ATN at each time instant. The state space is modelled by a Discrete Time Reachability Graph and the capacity constraints on the air sectors are modelled by time floating general mutual exclusion constraints. Feasible flight plans can be constructed based on control synthesis techniques, while an algorithm to compute the optimal flight plan is proposed assuming a realistic cost function.     

Study on the Flight Safety of Russian Aviation Troops

Flight safety is foundation of supporting flight training and combat of aviation troops. PLAAF is equipped with a large amount of Russian-made aircraft,so a comprehensive analysis and study of the flight safety of Russian aviation troops is of great significance to our flight safety. This paper analyzes the flight safety of Russian aviation troops and the main reasons and problems in recent years,the main measures and experiences of the flight safety of Russian military are summarized,and the work plan of Russian aviation troops in the future are introduced.     

Mars orbiter laser altimeter: receiver model and performance analysis

The design, calibration, and performance of the Mars Orbiter Laser Altimeter (MOLA) receiver are described. The MOLA measurements include the range to the surface, which is determined by the laser-pulse time of flight; the height variability within the footprint determined by the laser echo pulse width; and the apparent surface reflectivity determined by the ratio of the echo to transmitted pulse energies.     

Laser rockets

The results of experimental and theoretical investigations of the dynamic characteristics of a laser rocket in the initial flight path segment are presented. The energy to a laser jet propulsor was delivered with the beam of a CO-or CO₂-pulsed laser with a pulse energy ranging from 0.1 to 3.0 kJ at a repetition frequency of 100 Hz.     

A compressive sensing algorithm using truncated SVD for three-dimensional laser imaging of space-continuous targets

For traditional array 3-D laser radars, the resolution of the intensity image and range profile is limited by the number and accuracy of sensors. Moreover, for a space-continuous target, peak detection in the pulsed time of flight is no longer suitable for super-resolution reconstruction algorithms. Hence, a compressive sensing algorithm for 3-D laser imaging is proposed. A range observation matrix composed of time interval basis vectors is constructed to acquire the range information regarding a target. However, the range observation matrix is generally ill-posed owing to the spatial continuity of the target. To address this shortage, truncated singular value decomposition is utilized to extract the peak values of echo pulses for image reconstruction. Simulation results demonstrate the effectiveness and performance of the proposed algorithm.     

Reduction of a time of flight experiment to tomography

We propose a novel generalization of time of flight analysis which yields unambiguous information about the velocity spectrum as a function of time of a point pulsed particle source. The records of several particle counters placed at various prescribed distances from the source are combined in a way derived from tomography theory to give a well defined set of moments of the source emission function. A variety of reconstructions can then be made, which we illustrate by computer examples. The resolution of the method is investigated. There are possible applications to plasma focus and laser fusion experiments.     

Sets of Piezoelectric Probeheads for Stress Evaluation with Subsurface Waves

This paper discusses the development of piezoelectric ultrasonic probeheads for measurements of time of flight of subsurface or surface wave ultrasonic pulses. Sets of such probes found application in ultrasonic stress evaluation. In precise measurements of time of flight using piezoelectric transducers, the main source of time scatter proved to be variation in the condition of liquid couplant layers. The thickness of this couplant layer depends on surface roughness of the sample being evaluated. Paper describes a new configuration of probes, composed of two transmitting and four receiving probes arranged along one line, designed to reduce coupling influence on readings. Presented is comparison of readings obtained with known sets of probes and with a new one. Also presented are results of residual stress evaluation performed with various 6-transducer sets of probes on railroad rails, monoblock railroad wheels and pillars of hydraulic press. All measurements were performed in industrial conditions, without any special surface preparation.     

加权SERVQUAL模型的航班延误服务补救质量评价研究

介绍航班延误和服务质量评价,体现航班延误服务补救质量评价的重要性。通过对旅客的问卷调查,将加权SERVQUAL评价模型应用于航班延误服务补救问题,对航班延误进行服务补救质量评价,最后为航空公司更好地提高航班延误后的服务质量提出了较详细的建议。     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

A new intelligent approach for air traffic control using gravitational search algorithm

Aircraft landing planning (ALP) is one of the most important challenging problems in the domain of air traffic control (ATC). Solving this NP-hard problem is a valuable aid in organizing air traffic in terminal control area (TCA), which itself leads to a decrease in aircraft fuel consumption, costs of airlines, and workload undertaken by air traffic controllers. In the present paper, the ALP problem is dealt with by applying effective rich knowledge to the optimization process (to remove obvious non-optimal solutions), and the first use of Gravitational Search Algorithm (GSA) in resolving such a case. In this regard, while the specific regulations for safe separation have been observed, the optimal landing time, the optimal runway, and the order of consecutive landings have been determined so that the main goal (minimizing total flight delays) would be best met. Results of simulations show that this approach, compared to previous ones, which are based on Genetic and Bionomic algorithms, GLS, and Scatter search method, considerably decreases total flight delays. Attaining zero in the total flight delays in three scenarios with real data shows that the suggested intelligent approach is more decisive than others in finding an optimal solution.     

缺陷/应力交互对碳钢L_(cr)波声弹性系数的影响

基于L_(cr)波声弹性理论,探讨缺陷及其尺寸对L_(cr)波评价应力的影响机理。结合"当量法"预制不同直径盲孔,采用互相关系数函数计算L_(cr)波时间差,通过线性拟合得到L_(cr)波声弹性系数,基于弹塑性变形和圆孔应力集中理论澄清盲孔直径对L_(cr)波声弹性系数的影响机理。结果表明:各直径盲孔L_(cr)波时间差随应力增大基本呈线性增加,但其非线性特征亦逐渐明显,线性阶段的最大应力值小于试样屈服强度;L_(cr)波声弹性系数随盲孔直径增大逐渐减小,并趋于平稳。分析认为,盲孔应力集中是导致上述结果的主要原因,试样各向异性组织及盲孔深度也是其重要因素。     

Laser Heating of a Material with Time-Dependent Laser Source

Hardening depths must be determined accurately when a material is subjected to laser heat treatment. In this paper, a semi-analytical method taking into account a time-dependent pulse shape is performed. A comparison between temporal temperatures is shown for five laser shapes. The distribution temperature and surface temperature during time processing are predicted based on a significant variety of material properties. The main result obtained is that an important time shift is observed from one temperature profile to another. It can be inferred that a hardened layer may be produced by using a time-dependent pulse shape instead of a time-independent pulse.     

Synthesis of Lanthanofullerenes by Laser Ablation Using Pulsed and CW-Nd:YAG Lasers

Endohedral lanthanum fullerenes, La@C₆₀, La@C₈₂ and La₂C₈₀, were synthesized by ablation of graphite and La₂O₃ in flowing Ar buffer gas with a 1064 nm beam from a pulsed-Nd: YAG laser in which the graphite was heated by the CW-Nd:YAG laser up to 2500 °C. The La-fullerenes were also prepared by laser ablation of a lanthanum-graphite composite rod. The extractant fullerenes from the carbon soot were analyzed by laser-desorption time of flight mass spectrometry (LD-TOF MS). The relative yield of La@C₈₂, increased with increasing temperature of the rod in the range of 700-2300 °C.     

快速和灵敏地分析常见氨基酸

利用基质辅助激光解吸电离飞行时间质谱(MALDI-TOF-MS)和电子轰击(EI)质谱法快速、灵敏地分析了常见的八种氨基酸。并讨论了在不同电离方式下这八种氨基酸的质谱行为,分析结果表明两种方法对测定氨基酸均具有独特之处。