Higher mode sound transmission from a point source through a rectangular aperture.

This paper considers the higher-order scattered and transmitted wave fields that result when an acoustic wave from a point source impinges at an arbitrary angle on a rectangular aperture in a rigid, thick wall. In this analysis, it is assumed that free field conditions exist on both sides of the aperture. Although the full scattered and transmitted pressure fields contain both modal sum and modal coupling effects, the modal coupling effects of the higher-order modes are ignored such that an approximate analytical solution to the uncoupled analysis can be utilized. Experiments have been undertaken to measure the sound pressure levels in the transmitted field that result when sound from a point source impinges on the opposite side of a rectangular aperture. Measurements were made with the source located at the required position to drive a particular in-aperture higher-order mode. The source was also located at positions that did not directly excite any in-aperture higher-order mode at a cut-on frequency. These results indicate that the approximate analysis developed here gives accurate solutions whether or not any mode of the aperture is driven at cut-on. Thus, the method can be used for any relative location of a source from a rectangular aperture of any dimensions.

Analysis of spatial light modulator contrast ratios and optical correlation.

We have performed a general analysis of optical correlators with spatal light modulators (SLM's) whose primary defect is a finite contrast ratio (CR). Our mathematical analysis identifies three noise terms that appear in addition to the correlation term. The filter SLM contains either a phase-only filter (POF) or a binary-phase-only filter (BPOF). Insertion of a dc block at the center of the filter SLM decreases the noise background in the correlator plane; this dc block is larger than that required for the same level of performance in a correlator whose SLM's have transmissive (or reflective) dead zones. With a noise-free input and the dc block, our computer simulations that show the peak intensity falling off as the CR decreases are in quantitative agreement with the correlation term of the mathematical model. For a cluttered, disjoint noise input this agreement is only qualitative, and at low CR's the dc block is definitely required for the BPOF correlator if the secondary peaks in the output are to be brought below the correlation peak.

Effects of systematic phase errors on phase-only correlation.

The performance of phase-only optical correlators is usually reduced if the filter-plane phase differs from that prescribed for the classical matched filter. Current spatial light modulators, which frequently produce less than 2π phase modulation, and interface circuits, which quantize or incorrectly amplify signals placed on the spatial light modulator, both can produce systematic phase errors. We examine these effects using a model of correlation-peak amplitude as a function of phase error. The correlation peak is reasonably approximated as the product of an average of unity-amplitude error phasors multiplied by the average amplitude across the filter plane. The trends predicted by this new model compare favorably with computer simulations that use gray-scale images.

Effects of whole cottonseed or niacin or both on casein synthesis by lactating Holstein cows.

Forty Holstein cows in late lactation were offered diets containing niacin and whole cottonseed: 1) 0 g/d, 0%; 2) 0 g/d, 15%; 3) 6 g/d, 0%; and 4) 6 g/d, 15%, to evaluate effects on milk casein synthesis. Cows fed diet 1 had the highest DMI. The FCM (21.4 vs. 18.7 kg/d) and milk fat percentage (4.08 vs. 3.81) were higher for cows fed diet 1 than for those fed diet 4. Milk protein percentage (3.61 vs. 3.50) was higher for cows fed diet 1 than for those fed diet 2. Casein N, as a percentage of total N, was higher (71.9 vs. 68.0%) in milk from cows fed diet 1 than those fed diet 3. Insulin tended to be elevated in cows on the diets containing niacin, but glucose was not affected. Plasma niacin was elevated in cows on the diets supplemented with niacin compared with diet 1. Plasma AA were changed only slightly by treatments. The beneficial effect of niacin on milk casein synthesis, noted in our earlier work when cows were fed whole cottonseed, was not evident in this study with cows in late lactation and during hot weather.

Metrics for assessing pattern-recognition performance.

Various metrics used to measure correlation filter performance are discussed. Their similarities and deficiencies are noted, and modifications are suggested. A computer simulation is included to highlight these differences.

Effects of quadratic phase distortion on correlator performance.

The deformable mirror spatial light modulator (SLM) has an inherent distortion characteristic that can be approximated as a square-law transfer function. We examine the result of this distortion when this SLM is used in an optical correlator.

Spatial light modulators and their applications: introduction by the guest editors.

The feature in this issue of Applied Optics includes a collection of papers originally presented at the 1990 Lake Tahoe topical meeting on Spatial Light modulators. These papers emphasize materials and devices for spatial light modulation, smart pixels, and applications.

Modified two-focal-length optical correlator.

We present a modification to our previously reported 2f optical correlator. This modification removes a lens from the system and maintains a variable Fourier transform scale property while providing an equal correlation performance.

Single spatial light modulator joint transform correlator.

We describe a joint Fourier transform image correlator that employs thresholding at both the input plane and the Fourier plane. This suggests using a single binary spatial light modulator (SLM) to read in sequentially the binarized input signal and the binarized Fourier transform interference intensity. The performance of the single SLM joint Fourier transform correlator (JTC) is compared with that of the classical JTC in the areas of correlation peak intensity, peak-to-sidelobe ratio, signal-to-noise ratio (SNR), and correlation width. We show that the single SLM JTC outperforms the classical JTC in all such areas. Using a single binary SLM results in significant reduction in cost, size and complexity of the system.

Collimation invariant technique for measuring the focal length of a lens.

We report a method for measuring the effective focal length of a lens without knowing the degree of collimation or the location of the principal planes of the lens.

Amplitude encoded phase-only filters.

The phase-only filter (POF) and binary phase-only filter (BPOF) have been shown to have high optical efficiency, good target discrimination, and virtually no sidelobes. We present a simple method of amplitude encoding the signal phase information. These new filters have most of the same advantages of a POF or BPOF so that amplitude modulating spatial light modulators or photographic film can be used.

Image deconvolution by nonlinear signal processing.

We describe a nonlinear optical processor that can perform image deconvolution to restore a smeared or out-of-focus image. In this technique both the smeared image and the blur function are displayed side by side at the input plane of the processor. The joint power spectrum of the input signals is modified and hard clipped/ thresholded to remove the amplitude distortion effects and to restore the correct phase of the original image. The phase information is restored by multiplying the Fourier transform of the blurred image by the conjugate of the phase of the blur function transform. An amplitude mask averaged over an ensemble of images is assigned to the thresholded power spectrum to provide the amplitude magnitude of the restored image. An analysis of the nonlinear processor for image deconvolution is presented. Computer simulation of the proposed technique for a linearly smeared image is provided.

Two-focal-length optical correlator.

A two-focal-length coherent optical correlator design is presented that uses simple, single element lenses. Experimental autocorrelation results using a binary phase-only filter verify the performance of this compact design.

Effects of whole cottonseed, niacin, and niacinamide on in vitro rumen fermentation and on lactating Holstein cows.

In Experiment 1, effects of whole cottonseed (0, 5, 15, or 30% of the total ration DM) on in vitro ruminal fermentation showed increased ruminal pH and ammonia concentration but lowered microbial protein. Acetic acid concentration was greatest with diets of 15 and 30% whole cottonseed, but propionate and total VFA concentrations were reduced by increasing whole cottonseed from 0 to 30%. In Experiment 2, neither niacin nor niacinamide (0, 100, 200, or 400 ppm) altered substantially fermenter pH or ammonia concentration. Both niacin and niacinamide increased synthesis of microbial protein. Acetate and propionate concentrations were not altered by treatment. Total VFA concentration tended to be lower as concentration of niacin and niacinamide increased. In Experiment 3, 28 Holstein cows were used to determine the effects of supplemental niacin on feed intake, milk yield, and composition. Cows were fed individually complete mixed diets ad libitum containing either: 1) 0; 2) .015; 3) .03; or 4) .06% niacin. There was a trend for lower milk fat test with niacin supplementation. Milk protein percentage was higher without niacin than with niacin at .015 or .03% in the diet, but daily milk and protein yields were higher with .06% versus .015% of niacin. Supplemental niacin did not affect casein nitrogen, lactose or minerals percentage, or concentrations of plasma glucose and insulin.

Effects of niacin and whole cottonseed on ruminal fermentation, protein degradability, and nutrient digestibility.

Four mature nonlactating Holstein heifers fitted with ruminal and duodenal cannulae were used to investigate in vivo effects of niacin and whole cottonseed. Each heifer was assigned randomly to a treatment in a 2 X 2 factorial arrangement of treatment sequences within a 4 X 4 Latin square design. Heifers were fed isonitrogenous complete mixed rations individually twice daily. Diets contained corn-soybean meal concentrate, corn silage, chopped coastal bermudagrass hay, plus 1) 0% niacin and 0% whole cottonseed, 2) 0% niacin and 15% whole cottonseed, 3) .07% niacin and 0% whole cottonseed, or 4) .07% niacin and 15% whole cottonseed. Dry matter consumption, ruminal pH, ruminal ammonia and VFA concentrations, microbial N production, and DM and ADF digestion were not affected by treatment. Numbers of ruminal protozoa and RNA concentrations were reduced with whole cottonseed feeding and increased by addition of niacin. Whole cottonseed increased molar percentages of acetate while depressing propionate. Niacin supplementation resulted in greater digestion of both CP and NDF. Ether extract digestibility was highest in heifers fed whole cottonseed. Fiber digestion was not affected by whole cottonseed feeding.

Signal-dependent phase distortion in optical correlators.

We examine the effect of phase distortion inherent in a spatial light modulator on the performance of an optical correlator. We examine such areas as input plane distortion, input and Fourier plane distortion, effect of phase mismatch between these planes, and the effect of additive white noise. When large distortions are present and the proper compensation is incorporated into the filter, we find a significant enhancement in performance in that the correlation response converges to a function and the SNR increases significantly. A theory is presented to explain this behavior.

Influence of niacin and whole cottonseed on intake, milk yield and composition, and systemic responses of dairy cows.

Twenty-four Holstein cows (early postpartum) were used in a randomized complete block design with a 2 X 2 factorial arrangement of treatments to compare effects of nicotinic acid (niacin) and whole cottonseed. Cows were fed individually isonitrogenous complete mixed rations ad libitum, containing corn-soy concentrate, corn silage, chopped coastal bermudagrass hay, and either 1) 0% niacin and 0% whole cottonseed, 2) 0% niacin and 15% whole cottonseed, 3) .03% niacin and 0% whole cottonseed, or 4) .03% niacin and 15% whole cottonseed. Dry matter and energy consumption, actual milk yield, total milk solids, and milk fat yield were not affected by treatment. Either niacin or whole cottonseed increased milk fat percentage and 4% fat-corrected milk. Milk protein percentage and yield were higher with niacin supplementation but tended to be lower with cottonseed feeding. The milk protein depression with whole cottonseed was alleviated by niacin due to stimulation of mammary casein synthesis. Supplemental niacin tended to elevate glucose and insulin in blood plasma, but whole cottonseed tended to reduce these plasma components. Plasma urea nitrogen was higher in cows fed whole cottonseed. Plasma-free tryptophan tended to be slightly higher in cows receiving supplemental niacin.