Analysis of a Lubrication Fluid Flow in the Leak-Proof Pump Electric Motor

Steady-state flow of viscous lubrication fluid in the nonsymmetrical clearance between two out-of-line cylinders of the bearing unit in the aircraft electric motor is discussed. An analytical solution of the task based on application of the perturbation theory is presented.     

Aerodynamic Design Method of Integrated Aircraft with Submerged Intake Devices and Power Plant Included into Airframe Carrying System

This paper presents a theoretically and practically grounded architecture of design methods combination. A possibility and completeness of developing integral design solutions and intensifying the design process are provided by redistribution of emphases of numerical and natural experiments.     

Equalization of QPSK Data Transmission in Specular Multipath

This paper gives performance results for transversal-filter equalization of quadriphase phase-shift-keyed (QPSK) signals with two-component multipath and demodulator phase error. An analytical expression for optimum, minimum mean-square-error tap weights in terms of the multipath and signal parameters is given. Probability of error results for no equalization and equalization with adaptive decision-feedback tap-weight adjustment are compared. The results show that significant improvement can be obtained with relatively simple equalizer structures.     

Optimal Inputs for Nonlinear Process Parameter Estimation

The sensitivity of observed data to an unknown parameter is enhanced by utilizing optimal inputs. The derivation is given for the optimal input of an nth-order nonlinear differential equation. To obtain the optimal input, the solution of 4n two-point boundary value equations is required. Numerical resutis are given for a second order linear example. The optimal return is compared with the return obtained for a step input. The existence of a critical time length is demonstrated.     

Statistical Analysis of Velocity Measuring Systems Employing the Photon Correlation Technique

Velocities of fluid flows and solid objects can be measured by performing photon count correlations on laser light scattered from the measuring region, the most common optical configuration being the laser Doppler system. A statistical analysis for the counting process is presented for both the constant velocity case and for turbulent fluid flows with formulations for specific laser Doppler configurations. For turbulent flow, relationships are derived for the shape of the count correlation in terms of the mean velocity and rms turbulent intensity, taking into account the shape of the turbulence correlation curve. Experimental results recorded for both a constant velocity solid object and for an unseeded turbulent air flow in a wind tunnel are presented, and, in the latter case, comparisons are made with hot-wire measurements.     

Theoretical analysis of the sequential lobing technique

A theoretical analysis of the sequential lobing technique for target angle tracking is presented. The signal power received by each antenna beam is assumed to pass through a logarithmic amplifier. A rigorous statistical approach is adopted in the analysis for both non-fluctuating and fluctuating targets. Closed form expressions are derived for the normalized mean error and rms error of the angle estimate for Swerling 0, I, II, and III targets. Results are compared with those obtained using a simplified approach for the non-fluctuating target     

Structures for radar detection in compound Gaussian clutter

The problem of coherent radar target detection in a background of non-Gaussian clutter modeled by a compound Gaussian distribution is studied here. We show how the likelihood ratio may be recast into an estimator-correlator form that shows that an essential feature of the optimal detector is to compute an optimum estimate of the reciprocal of the unknown random local power level. We then proceed to show that the optimal detector may be recast into yet another form, namely a matched filter compared with a data-dependent threshold. With these reformulations of the optimal detector, the problem of obtaining suboptimal detectors may be systematically studied by either approximating the likelihood ratio directly, utilizing a suboptimal estimate in the estimator-correlator structure or utilizing a suboptimal function to model the data-dependent threshold in the matched filter interpretation. Each of these approaches is studied to obtain suboptimal detectors. The results indicate that for processing small numbers of pulses, a suboptimal detector that utilizes information about the nature of the non-Gaussian clutter can be implemented to obtain quasi-optimal performance. As the number of pulses to be processed increases, a suboptimal detector that does not require information about the specific nature of the non-Gaussian clutter may be implemented to obtain quasi-optimal performance     

Optical guidance for autonomous landing of spacecraft

An autonomous rendezvous guidance scheme for spacecraft to descend to small celestial bodies by using optical information is presented. First, a new guidance, navigation, and control (GNC) method based on fixation-point (FP) inheritance is proposed. A spacecraft can safely descend toward the target point on the celestial body by tracking and autonomously renewing the FPs on the surface. Next, we deal with the method of extracting the FPs. A spatial band-pass filter (BPF) is applied to pictures taken to enhance features having comparable size with the tracking window. Local variance of the filtered image is used as a criterion of the extraction. Then, the relative information between the spacecraft and the celestial body (position, velocity, attitude, etc.) is calculated from the image coordinates and the range measurements of the FPs from the spacecraft. To suppress observation noise and improve navigation accuracy, an application of the extended Kalman filter is also presented. Finally, simulations are conducted to verify the guidance precision and the fuel consumption of the proposed guidance scheme     

Fluctuations, Dissipation and Heating in the Corona

Mechanisms for the deposition of heat in the lower coronal plasma are discussed, emphasizing recent attempts to reconcile the fluid and kinetic perspectives. Structures at the MHD scales are believed to act as reservoirs for fluctuation energy, which in turn drive a nonlinear cascade process. Kinetic processes act at smaller spatial scales and more rapid time scales. Cascade-driven processes are contrasted with direct cyclotron absorption, and this distinction is echoed in the contrast between frequency and wavenumber spectra of the fluctuations. Observational constraints are also discussed, along with estimates of the relative efficiency of cascade and cyclotron processes. This revised version was published online in June 2006 with corrections to the Cover Date.