绿色制造中的干切削技术

冷却润滑液的存储、使用以及废弃处理需要专门的物流系统,因而费用很高;冷却润滑液处理不当会对人的健康以及环境造成危害;工件经过湿加工后必须进行清洁处理,这都费时费力,同时增加了对系统的要求.基于上述原因,近年来干切削技术受到广泛关注.     

Analysis of Multimodal Systems

The estimation of a multimodal linear system whose mode-to-mode transitions are described by a finite-state Markov chain is described. The problem has application in studying separation standards in an air traffic control environment. An optimal solution is formulated which is computationally infeasible. A suboptimal estimator is then derived which closely approximates the optimal estimator. An example is presented to illustrate the technique.     

Satellite fault diagnosis using a bank of interacting Kalman filters

The main objective of this work is development and testing of a detection, isolation, and diagnosis algorithm based on interacting multiple model (IMM) filters for both partial (soft) and total (hard) reaction wheels faults in a spacecraft. This is shown to be accomplished under a number of different faulty mode scenarios for these actuators associated with the attitude control system (ACS) of a satellite. Various operating and faulty conditions due to changes and anomalies in the temperature, the power supply line voltage, and the loss of effectiveness of the torque and the current are considered in each reaction wheel associated with the three axes of the satellite. Once a fault mode is detected and isolated the recovery procedure can subsequently be engaged by invoking appropriate switching control strategies for the ACS. The application of a bank of interacting multiple Kalman filters for detection and diagnosis of anticipated reaction wheel failures in the ACS is described and developed. Compared with other model-based fault detection, diagnosis and isolation(FDDI) strategies developed in the control systems literature, our FDDI strategy is shown, through extensive numerical simulations, to be more accurate and robust with potential for extension to a number of other application areas.     

Probing the era of galaxy formation via TeV gamma ray absorption by the near infrared extragalactic background

We present models of the extragalactic background light (EBL) based on several scenarios of galaxy formation and evolution. We have treated galaxy formation with the Press-Schecter approximation for both cold dark matter (CDM) and cold+hot dark matter (CHDM) models, representing a moderate (z _f 3) and a late (z _f 1) era of galaxy formation respectively. Galaxy evolution has been treated by considering a variety of stellar types, different initial mass functions and star formation histories, and with an accounting of dust absorption and emission. We find that the dominant factor influencing the EBL is the epoch of galaxy formation. A recently proposed method for observing the EBL utilizing the absorption of 0.1 to 10 TeV gamma-rays from active galactic nuclei (AGN) is shown to be capable of discriminating between different galaxy formation epochs. The one AGN viewed in TeV light, Mrk 421, does show some evidence for a cutoff above 3 TeV; based on the EBL models presented here, we suggest that this is due to extinction in the source. The large absorption predicted at energies > 200 GeV for sources at z > 0.5 indicates that observations of TeV gamma-ray bursts (GRB) would constrain or eliminate models in which the GRB sources lie at cosmological distances.Now at University of Chicago, Dept. of Astronomy & Astrophysics.     

Aerosols on the Giant Planets and Titan

On the giant planets and Titan, like on the terrestrial planets, aerosols play an important part in the physico-chemistry of the upper atmosphere (P ≤ 0.5 bar). Above all, aerosols significantly affect radiative transfer processes, mainly through light scattering, thus influencing the atmospheric energy budget and dynamics. Because there is usually significant coupling between atmospheric circulation and haze production, aerosols may constitute useful tracers of atmospheric dynamics.More generally, since their production is directly linked to some kind of energy deposition, their study may also provide clues to external sources of energy as well as their variability. Finally, aerosols indirectly influence other processes such as cloud formation and disequilibrium chemistry, by acting either as condensation nuclei or as reaction sites for surface chemistry. Here, I present a review of observational and modeling results based on remote sensing data, and also some insights derived from laboratory simulations. Despite our knowledge of the effects of aerosols in outer planetary atmospheres, however, relatively little is understood about the pathways which produce them, either endogenously (as end-products of gas-phase photochemical or shock reactions) or exogenously (as residues of meteroid ablation).     

PHD filters of higher order in target number

The multitarget recursive Bayes nonlinear filter is the theoretically optimal approach to multisensor-multitarget detection, tracking, and identification. For applications in which this filter is appropriate, it is likely to be tractable for only a small number of targets. In earlier papers we derived closed-form equations for an approximation of this filter based on propagation of a first-order multitarget moment called the probability hypothesis density (PHD). In a recent paper, Erdinc, Willett, and Bar-Shalom argued for the need for a PHD-type filter which remains first-order in the states of individual targets, but which is higher-order in target number. In this paper we show that this is indeed possible. We derive a closed-form cardinalized PHD (CPHD) filter, which propagates not only the PHD but also the entire probability distribution on target number.     

Matched Filter Criteria and Range Weighting for Weather Radar

The effective weighting function for weather radar is defined. This weighting function considers the effects of both the transmitted signal and the receiver filter. It is used to assign effective ranges to samples taken at prescribed times. For uniformly distributed targets it is shown that "signal"-to-noise ratio depends on the receiver filter, transmitted signal envelope, and receiver noise spectral density. Maximization of this signal-to-noise ratio when range resolution constraints are imposed is discussed, and a receiver design approach specifically adapted for Doppler weather radars is developed.     

Susceptibility of DS/FH,M, Binary DPSK to Partial and Full Band Barrage Jamming

Spread spectrum signaling schemes have been proposed to counter unfriendly, electrical jamming threats. In order to establish their effectiveness, such schemes must be analyzed. This work takes a step in this direction by developing the susceptibility equation, or equivalently, the probability of error, of a direct sequence/frequency hopped (DS/FH), binary differential phase-shift keying (DPSK) system when subjected to a barrage jamming signal. Specific system models are established for the receiving system as well as for the jamming signal and the spread spectrum techniques. Both partial and full band jamming strategies are considered. Graphical results are presented with the conclusions summarizing the spread spectrum effectiveness and the deficiencies of the FH processing gain definition.     

Detection of polyphase pulse compression waveforms using the radon-ambiguity transform

The recently developed Radon-ambiguity transform (RAT) detects unknown linear frequency modulated (LFM) signals by computing line integrals through the origin of the signal's ambiguity function (AF) magnitude. It is shown that this method also detects the step LFM and frequency-derived polyphase pulse compression waveforms with varying performance degradation. Simulations are provided to estimate the detection loss relative to the LFM.