A single-loop second-order ΔΣ frequency discriminator

2002 ◽  
Author(s):  
W.T. Bax ◽  
M.A. Copeland ◽  
T.A.D. Riley
Keyword(s):  
Second Order ◽  
Single Loop ◽  
Frequency Discriminator

Matrix Analysis of Second-Order Kinematic Constraints of Single-Loop Linkages in Screw Coordinates

2018 ◽  
Author(s):  
Liheng Wu ◽  
Andreas Müller ◽  
Jian S. Dai
Keyword(s):  
Quadratic Forms ◽  
Hessian Matrix ◽  
Coefficient Matrix ◽  
Higher Order ◽  
Second Order ◽  
Matrix Analysis ◽  
Kinematic Constraints ◽  
Single Loop ◽  
Order Analysis ◽  
Order Constraints

Higher order loop constraints play a key role in the local mobility, singularity and dynamic analysis of closed loop linkages. Recently, closed forms of higher order kinematic constraints have been achieved with nested Lie product in screw coordinates, and are purely algebraic operations. However, the complexity of expressions makes the higher order analysis complicated and highly reliant on computer implementations. In this paper matrix expressions of first and second-order kinematic constraints, i.e. involving the Jacobian and Hessian matrix, are formulated explicitly for single-loop linkages in terms of screw coordinates. For overconstrained linkages, which possess self-stress, the first- and second-order constraints are reduced to a set of quadratic forms. The test for the order of mobility relies on solutions of higher order constraints. Second-order mobility analysis boils down to testing the property of coefficient matrix of the quadratic forms (i.e. the Hessian) rather than to solving them. Thus, the second-order analysis is simplified.

Reduced-Order Autoregressive Modeling for Center-Frequency Estimation

1985 ◽  
Vol 7 (3) ◽  
pp. 244-251 ◽  
Author(s):  
Roman Kuc ◽  
Hilda Li
Keyword(s):  
Random Process ◽  
Linear Prediction ◽  
Second Order ◽  
Ar Model ◽  
Center Frequency ◽  
Zero Crossing ◽  
Reduced Order ◽  
Frequency Discriminator ◽  
Parameter Values ◽  
The Ideal

The center frequency of a narrowband, discrete-time random process, such as a reflected ultrasound signal, is estimated from the parameter values of a reduced, second-order autoregressive (AR) model. This approach is proposed as a fast estimator that performs better than the zero-crossing count estimate for determining the center-frequency location. The parameter values are obtained through a linear prediction analysis on the correlated random process, which in this case is identical to the maximum entropy method for spectral estimation. The frequency of the maximum of the second-order model spectrum is determined from these parameters and is used as the center-frequency estimate. This estimate can be computed very efficiently, requiring only the estimates of the first three terms of the process autocorrelation function. The bias and variance properties of this estimator are determined for a random process having a Gaussian-shaped spectrum and compared to those of the ideal FM frequency discriminator, zero-crossing count estimator and a correlation estimator. It is found that the variance values for the reduced-order AR model center-frequency estimator lie between those for the ideal FM frequency discriminator and the zero-crossing count estimator.

Disappearance Voltage Determinations Using a Convergent Beam

1971 ◽  
Vol 29 ◽  
pp. 184-185
Author(s):  
W. L. Bell
Keyword(s):  
Second Order ◽  
Objective Method ◽  
Uniform Thickness ◽  
Rocking Curve ◽  
Crystal Perfection ◽  
Kikuchi Line ◽  
Central Maximum ◽  
Diffraction Patterns ◽  
Convergent Beam ◽  
Beam Technique

Disappearance voltages for second order reflections can be determined experimentally in a variety of ways. The more subjective methods, such as Kikuchi line disappearance and bend contour imaging, involve comparing a series of diffraction patterns or micrographs taken at intervals throughout the disappearance range and selecting that voltage which gives the strongest disappearance effect. The estimated accuracies of these methods are both to within 10 kV, or about 2-4%, of the true disappearance voltage, which is quite sufficient for using these voltages in further calculations. However, it is the necessity of determining this information by comparisons of exposed plates rather than while operating the microscope that detracts from the immediate usefulness of these methods if there is reason to perform experiments at an unknown disappearance voltage.The convergent beam technique for determining the disappearance voltage has been found to be a highly objective method when it is applicable, i.e. when reasonable crystal perfection exists and an area of uniform thickness can be found. The criterion for determining this voltage is that the central maximum disappear from the rocking curve for the second order spot.

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