Low Variance Estimates Research Articles

Application of dual-beam and split-beam target tracking in fisheries acoustics

Dual-beam and split-beam acoustical techniques were originally developed to provide direct in situ measurements of the target strength of individual fish and plankton. The amount of information that can be extracted from these acoustic systems can be significantly increased when the techniques are used in conjunction with ping-to-ping target tracking. For example, target tracking can be used to isolate multiple target-strength measurements from an individual fish or plankton. These measurements can then be averaged to provide a lower variance estimate of the target strength. The measurement of the angular location of the target provided by split-beam systems further enhances the usefulness of tracking. The angular data measured on subsequent pings can be used to resolve returns from single and multiple targets and estimate the direction and speed of the fish as they pass through the beam. Information on fish speed and direction is particularly useful for fixed location acoustic studies. This paper uses a combination of actual data, simulation results, and analysis to describe the various applications and expected performance of acoustic systems that combine dual-beam and split-beam techniques with target tracking.

Optimal design of biaxial tests for structural material characterization of flat tissues.

A rational methodology is developed for optimal design of biaxial stretch tests intended for estimating material parameters of flat tissues. It is applied to a structural model with a variety of constitutive equations and test protocols, and for a wide range of parameter levels. The results show nearly identical optimal designs under all circumstances. Optimality is obtained with two uniaxial stretch tests at mutually normal directions inclined by 22.5 deg to the axes of material symmetry. Protocols which include additional equibiaxial tests provide superior estimation with lower variance of estimates. Tests performed at angles 0, 45, and 90 deg to the axes of material symmetry provide unreliable estimates. The optimal sampling is variable and depends on the protocols and model parameters. In conclusion, the results indicate that biaxial tests can be improved over presently common procedures and show that this conclusion applies for a variety of circumstances.

Modified sparse time domain technique for rotor stability testing

Because of nonlinear and complex interactions involved with the dynamic and aeroelastic stability of a rotor system, detailed and accurate knowledge of the stability characteristics are essential to prove design safety and to validate theoretical analysis. The task of determining these characteristics for a rotor from tests becomes complicated because of the presence of substantial amplitudes of the undamped harmonics, the possibility of close modes, and the complexity associated with the excitation of the modes in the rotating environment. Time domain modal parameter estimation methods are very useful for damping estimation when there are close modes, but they are very sensitive to noise. Subspace methods substantially improve the time domain estimates for noisy data, but they require higher computation time. A simple method is developed that retains the low variance estimation property of the subspace methods, but which is comparable in computation cost to methods that do not use the subspace approach. Its performance is evaluated for multi-output and single-output implementations and compared to the standard sparse time domain method. It is found that the modified method is more accurate in terms of the bias and standard deviation of the damping estimates, and it is faster when the number of modes is much less than the order of the data matrix.

An Analysis of the Dimensionality and Reliability of the Lennox and Wolfe Revised Self-Monitoring Scale

The Lennox and Wolfe (1984) Revised Self-Monitoring Scale (RSMS) was analyzed, using confirmatory factor analysis procedures, to investigate the scale's dimensionality and reliability. The results revealed that the predicted two-factor correlated structure was the best representation of the four models examined. Coefficient alpha estimates of internal consistency and construct reliability estimates also revealed a reasonable pattern of reliability. However, a number of the factor loadings were low, which may account for the low shared variance estimates for the two factors. Additional correlational tests revealed only minimal overlap between the RSMS and the 25-item original (Snyder, 1974) and 18-item revised version of Snyder and Gangestad's (1986) Self-Monitoring Scale (SMS).

Application of dual‐beam and split‐beam target tracking in fisheries acoustics

Ehrenberg, J. E. and Torkelson, T. C. 1996. Application of dual‐beam and split‐beam target tracking in fisheries acoustics. ‐ ICES Journal of Marine Science, 53: 329–334. Dual‐beam and split‐beam acoustical techniques were originally developed to provide direct in situ measurements of the target strength of individual fish and plankton. The amount of information that can be extracted from these acoustic systems can be significantly increased when the techniques are used in conjunction with ping‐to‐ping target tracking. For example, target tracking can be used to isolate multiple target‐strength measurements from an individual fish or plankton. These measurements can then be averaged to provide a lower variance estimate of the target strength. The measurement of the angular location of the target provided by split‐beam systems further enhances the usefulness of tracking. The angular data measured on subsequent pings can be used to resolve returns from single and multiple targets and estimate the direction ...

Linear transverse susceptibility of Ising systems.

The transverse susceptibility of Ising systems is measured using Monte Carlo methods and low-variance estimators. Data are given for a spin-(1/2) model on an fcc lattice and for a spin-1 (Blume-Capel) model, with different local anisotropies, on a cubic lattice. In each case a sharp peak is found just above the transition temperature. Real-time dynamics may also be studied. A low-variance Monte Carlo estimator is given for an Ising system having an arbitrary spin and lattice structure.

Quantification of microvasculature in the canine spinal cord.

Capillary density and capillary orientation in canine spinal cords were estimated by calculating actual lengths, surfaces, and volumes of capillary segments in tissue sections. Transverse, sagittal, and frontal section planes were samples from dorsal, ventral, and lateral funiculi and from dorsal and ventral gray horns of spinal segments C3, T6, and L3 from three dogs. Capillaries were defined as vessels less than 10 micrometer in diameter. Electron microscopy of 104 such vessels revealed no muscle coat but collagen fibrils between endothelium and astrocyte process in 68% of the white matter capillaries and 16% of those in gray matter. Capillary diameter was significantly different among regions in some cases, but consistent patterns of variation were not found. Capillary density was four to five times greater in gray matter than in white matter. Capillary density differed significantly among the same-size dogs, but within dogs, density was similar among segments and within gray matter and white matter regions. In 62% of the transverse sections, capillary orientation was always along the craniocaudal axis of the spinal cord. The craniocaudal orientation was significant in 96% of the white matter sections and 78% of the gray sections, and in 97% of the cervical and thoracic sections but only 73% of the lumbar sagittal and frontal sections. Because capillary orientation is neither isotropic nor regular, unbiased, low-variance estimates of capillary density cannot be expected without resorting to excessive sampling. An efficient method of quantifying spinal capillaries for comparative purposes by counting number of profiles per unit area is recommended.

Refined instrumental variable methods of recursive time-series analysis Part II. Multivariable systems

Abstract This paper describes the refined IVAML algorithm for estimating the parameters in the multivariable analogue of the single input,. single output model considered in Part I. It also shows that similar refined algorithms can be constructed for other multivariable model forms, including the ARMAX, dynamic adjustment (DA) with autoregressive errors and the multivariable transfer function (MTF). The performance of the algorithm is evaluated by Monte Carlo analysis applied to four simulation models with between 25 and 39 parameters and it is carried out for various sample sizes and signal/noise ratios. As in the SISO model version, the analysis indicates that the algorithm yields asymptotically efficient estimation results, whilst providing low variance estimates of the basic system parameters for medium sample sizes.