Liquid phase epitaxy and magneto-optical properties at 1.152 µm and 1.064 µm of garnet films on GdGaG

Several ferrimagnetic garnet compositions have been studied in view of their use in integrated optics. Films of (Sc,Ga):YIG, (Gd,Ga):YIG, (Pr,Ga):YbIG and (Pr,Bi,Ga):YbIG have been grown by liquid phase epitaxy on <111> GdGaG and fully characterized by classical and guided waves experiments at 1.152 and 1.064μm wavelengthes.     

68 kbit capacity 16 µm-period magnetic bubble memory chip design with 2 µm minimum features

A bubble propagating structure that operates well on a 14 μm to 18 μm propagate period with a nominal 2 μm minimum feature size has been designed. The structure consists of only 1 discrete permalloy feature per circuit period. Sixty-eight kbit-capacity memory chips based on such structures have been designed, built, characterized, packaged and the packages have been characterized. The chip is organized as a set of minor (storage) loops with separate write and read major lines. The bubble manipulating functions, of which the replicate and transfer gates are the most critical, have also been designed with 2 μm minimum features. The design is adequate to provide a 14 Oe bias field margin range with drive fields of about 35 Oe, using a bubble garnet material with approximately 170 Oe free bubble collapse field. Sixty-eight kbit single loop shift register type chips designed using similar propagating structures, however, provide over 20 Oe bias field margin ranges with drive fields of about 35 Oe.     

A fast access memory design using 3µm bubble 80K chip

A fast-access, non-volatile memory system using 3- μm bubble 80-kbit chips has been designed for an experimental model and evaluated from a systems viewpoint. The goal of this project is to investigate from both the side of technology and cost if the memories built with major-minor organized 3 μm bubble chips are acceptable in the commercial market. This paper describes the practical design of a bubble memory system, with a capacity of 8-Mbits and an average access time of approximately 1 ms at drive frequencies of up to 500 kHz, which involves memory system organization, redundancy design using chips with excess minor loops, packaging, electronic circuits scheme and other considerations. The results of the experiment and the system cost estimate based on this design are also described.     

Permalloy disk replicator for amorphous film 2 µm bubble devices

A permalloy disk replicator in an amorphous film 2 μm bubble device has been Studied for different geometrical dimensions, and from quasi-static to 200 kHz operating frequency. Distinct regions of the margin plot are observed, and their dependence on geometry is analyzed. It is found that for reliable replication over a wide margin range, the poles from the replicator disk, from the neighboring propagation channel, and from the previously replicated bubbles must be carefully balanced. A replicator with 20% margins on 2-micron GdCoMo films is shown and methods for further improvements are discussed.     

Operation of a 100-bit, 2.6 µm bubble shift register

Complete circuit operation for a small 100-bit serial shift register memory with a 10.6 μm period fabricated on a garnet wafer using electron beam lithography and single level all-permalloy technology is reported. Overall circuit operation including generation, propagation, and detection was achieved with a 6 Oe bias margin using a 1 kHz rotating field. Although the circuit design and fabrication techniques were not optimized, we believe that this is the first published report of complete circuit operation for a single level device with bubbles as small as 2.6 μm. The performance of two different types of chevron expander detectors and two different generators was evaluated and circuits combining disk generators with herringbone detectors were found to provide the best overall operating margin. At low speeds (∼5 Hz) high-bias failures were caused by failure of the domains to strip out fully in the detector while the low bias limit was determined by the introduction of spurious bubbles into the track near the generator.     

Operation of 3µm bubble serial loop devices designed on single level masking

An all-permalloy single mask level design for a serial loop circuit has been developed and successfully operated using 3 μm bubbles. The design of individual elements for a single level circuit such as generator, replicator and annihilator which were compatible with half-disk propagation patterns was successfully investigated and optimization of permalloy and SiO2spacer film thickness was achieved. The small capacity test chips fabricated provided 13-16 Oe "window margins" with circular drive field ranges of 40 to 50 Oe at 100 kHz. The critical stretching pulse phase margin for replication, which was the minimum phase margin for all functions was found to be 10 degrees. Details of design and characteristics are also discussed including operating margin dependence on frequency and temperature.     

New ion-implantation method for 4-µm period bubble device

It is well-known that bubble propagation margins for ion-implanted bubble devices depend strongly on ion-implantation conditions. A new ion-implantation method is reported that can significantly improve bubble propagation margins for minor loops with 4 × 4 μm bit cell size. The implantation was done through a Mo thin film layer so that the lattice strain and the anisotropy field change would be more uniform through the depth of the implanted layer. With this method, minor loops can be formed by hydrogen single implantation. Consequently simplification of the implantation process is achieved.     

Enhanced three-dimensional reconstruction from confocal scanning microscope images. II. Depth discrimination versus signal-to-noise ratio in partially confocal images

The enhanced depth discrimination of a confocal scanning optical microscope is produced by a pinhole aperture placed in front of the detector to reject out-of-focus light. Strictly confocal behavior is impractical because an infinitesimally small aperture would collect very little light and would result in images with a poor signal-to-noise ratio (SNR), while a finite-sized partially confocal aperture provides a better SNR but reduced depth discrimination. Reconstruction algorithms, such as the expectationmaximization algorithm for maximum likelihood, can be applied to partially confocal images in order to achieve better resolution, but because they are sensitive to noise in the data, there is a practical trade-off involved. With a small aperture, fewer iterations of the reconstruction algorithm are necessary to achieve the desired resolution, but the low a priori SNR will result in a noisy reconstruction, at least when no regularization is used. With a larger aperture the a priori SNR is larger but the resolution is lower, and more iterations of the algorithm are necessary to reach the desired resolution; at some point the a posteriori SNR is lower than the a priori value. We present a theoretical analysis of the SNR-toresolution trade-off partially confocal imaging, and we present two studies that use the expectationmaximization algorithm as a postprocessor; these studies show that a for a given task there is an optimum aperture size, departures from which result in a lower a posteriori SNR.     

A matrix-based two-dimensional regularization algorithm for signal-to-noise ratio enhancement of multidimensional spectral data

We present a new spectral image processing algorithm, the "matrix maximum entropy method" (MxMEM), which offers efficient signal-to-noise ratio (SNR) enhancement of multidimensional spectral data. MxMEM is based upon two previous regularization methods that employ the maximum entropy concept. The first is a one-dimensional (1D) algorithm, which smoothes individual vectors, called the two-point maximum entropy method (TPMEM). The second is a two-dimensional (2D) form called 2D TPMEM, that smoothes images but processes them one vector at a time. MxMEM is a truly two dimensional image processing algorithm in that its "smoothing engine" performs two-dimensional processing in every iteration. We demonstrate that this matrix-based construction makes more effective use of two-dimensionally embedded information and thus confers significant advantages over other regularization approaches. In addition, we utilize the concept that individual related Raman spectra can be combined in a matrix to form an artificial Raman "image". We show that, when processed as an image, superior SNR enhancement is achieved compared to processing the same data by TPMEM one spectrum at a time.     

Experimental measurements of estimator bias and the signal-to-noise ratio for deconvolution from wave-front sensing

Deconvolution from wave-front sensing (DWFS) has been proposed as a method for achieving high-resolution images of astronomical objects from ground-based telescopes. The technique consists of the simultaneous measurement of a short-exposure focal-plane speckled image, as well as the wave front, by use of a Shack-Hartmann sensor placed at the pupil plane. In early studies it was suspected that some problems would occur in poor seeing conditions; however, it was usually assumed that the technique would work well as long as the wave-front sensor subaperture spacing was less than r(0) (L/r(0) < 1). Atmosphere-induced phase errors in the pupil of a telescope imaging system produce both phase errors and magnitude errors in the effective short-exposure optical transfer function (OTF) of the system. Recently it has been shown that the commonly used estimator for this technique produces biased estimates of the magnitude errors. The significance of this bias problem is that one cannot properly estimate or correct for the frame-to-frame fluctuations in the magnitude of the OTF but can do so only for fluctuations in the phase. An auxiliary estimate must also be used to correct for the mean value of the magnitude error. The inability to compensate for the magnitude fluctuations results in a signal-to-noise ratio (SNR) that is less favorable for the technique than was previously thought. In some situations simpler techniques, such as the Knox-Thompson and bispectrum methods, which require only speckle gram data from the focal plane of the imaging system, can produce better results. We present experimental measurements based on observations of bright stars and the Jovian moon Ganymede that confirm previous theoretical predictions.     

如何评估回收率测量结果不确定度

加标回收率方法是测定复杂基体中待测物的重要而普遍适用的方法。然而,人们对回收率测量结果不确定度的评估和它对待测物测量结果不确定度评估中的贡献却关注较少。现就回收率测量结果不确定度评估及如何对待测物测量结果的修正进行讨论。     

The use of a generalized signal-to-noise ratio to identify adjustment and dispersion factors in taguchi experiments

A signal-to-noise ratio proposed by Taguchi for ‘nominal the best’ can be made more flexible and used additionally for the cases ‘smaller the better’ and ‘larger the better’. The main feature which distinguishes this generalized ratio from Taguchi's signal-to-noise ratios is that its precise form is determined by the experimental data. Taken together with a transformation of the mean response it effectively identifies adjustment (signal) factors and dispersion factors. Examples are given to illustrate the routine operational procedure and also to demonstrate that Taguchi's signal-to-noise ratios can lead to inefficient, and sometimes incorrect, identification of design factors. Two important considerations are to preserve the evident appeal of the Taguchi method to engineers and also to provide a theoretical justification which is acceptable to statisticians. The principal objective of the joint transformation is to achieve approximate functional independence between the mean and variance in the new metric. This, in turn, leads to efficient identification of adjustment and dispersion factors. A comparison is made with a similar approach using Box and Cox transformations.     

Design and test results of a pulsed quadrupole magnet with 2 µs rise time

Major polarization losses will be encountered during acceleration of polarized protons in the Brookhaven AGS due to eight intrinsic depolarizing resonances. Pulsing a set of 12 vertical tune shift quadrupole magnets with a 2μs rise time, 3 ms fall, and 60 ms repetition rate should reduce these losses. [1] This requires a gradient of 1.87 T/M over the 8.89 × 12.7 cm vacuum chamber.     

Direct frequency counting with enhanced beat signal-to-noise ratio for absolute frequency measurement of a He-Ne/I2 laser at 633 nm

We obtain a heterodyne beat signal between an iodine-stabilized He-Ne laser at 633 nm and a low power comb mode of an optical frequency synthesizer with an enhanced signal-to-noise ratio (SNR) up to approximately 35 dB. This is accomplished by the adoption of a fiber coupler and the reduction of the shot noise induced by adjacent comb modes. SNR is improved more than 15 dB compared with that of conventional methods. We measure the absolute frequency of the He-Ne laser mentioned above directly utilizing the enhanced SNR. A quantitative analysis of SNR and some information on experimental criteria for the correct frequency counting are given.     

Limitation of the achievable signal-to-noise ratio in optical coherence tomography due to mismatch of the balanced receiver

Owing to the limited spectral response of the fiber directional coupler used in a balanced optical coherence tomography configuration, the spectra are different in the two outputs. This affects unfavorably operation of the balanced photodetector unit. Excess photon noise makes a larger contribution than a directional coupler with a flat spectral response. A theoretical model is developed that shows that an optimum set of parameters may be defined to maximize the achievable signal-to-noise ratio. The model leads to a redefinition of the effective noise bandwidth, which takes into account the nonflat response of the directional coupler used. The model also predicts a limitation on the signal-to-noise ratio even when the stray reflectances in the interferometer are brought to zero.     

Effect of signal-to-noise ratio and number of data points upon precision in measurement of peak amplitude,position and width in fourier transform spectrometry

Chen, L., Cottrell, C.E. and Marshall, A.G., 1986. Effect of signal-to-noise ratio and number of data points upon precision in measurement of peak amplitude, position and width in Fourier transform spectrometry. Chemometrics and Intelligent Laboratory Systems, 1: 51–58.The theoretical precision in determining experimental spectral peak parameters (height, width, and position) should depend in a calculable way upon the peak shape, signal-to-noise ratio, and number of data points per line width. Expressions for precision in peak position and width for absorption-mode Lorentzian and Gaussian line shapes have been derived previously. We have extended the theory to include absorption-mode sinc as well as magnitude-mode Lorentzian and sinc line shapes, and have computed the predicted precision in peak amplitude as well as in position and width. Experimental (Fourier transform ion cyclotron resonance mass spectrometry and Fourier transform nuclear magnetic resonance spectrometry) precision for each of these parameters is found to be significantly poorer (e.g., factor of 5) than the theoretical predictions. The present results provide a direct test of the nature of noise (e.g., vertical vs. horizontal) in Fourier transform spectra, and suggest that experimental measurements of Fourier transform spectral line shape parameters may be much less precise than previously suspected.     

A device for the measurement of the horizontal to vertical stress ratio in powders

A new experimental device for the measurement of the hzorizontal to vertical stress ratio was developed. The tester is designed to conduct the required measurements using a single standard load cell without the need to apply strain gauges on custom built parts. Three different procedures were tested with free-flowing incompressible powders to determine the most precise procedure. This optimal procedure included the preliminary twisting of the cell lid to pre-shear the sample and was modified to conduct experiments with cohesive compressible powders. The results obtained from the best procedure were compared with those from commonly used estimating equations for the horizontal to vertical stress ratio as a function of the angle of internal friction. The obtained results were consistent with the Koenen equation (Koenen in Centralblatt der Bauverwaltung 16:446–449, 1896) for free-flowing materials and with the DIN 1055 equation (DIN 1055 Teil 6, Lastannahmen für Bauten, Lasten in Silozellen, 1987) for cohesive materials.     

Widening the effective field of view of adaptive-optics telescopes by deconvolution from wave-front sensing: average and signal-to-noise ratio performance

A fundamental problem of adaptive-optics systems is the very narrow corrected field of view that can be obtained because turbulence is extended in altitude throughout the atmosphere. The correctable field of view is of the order of 5-10 μrad at visible wavelengths and increases as the wavelength increases. Previous concepts to broaden the corrected field of view have been hardware oriented, requiring multiple wave-front sensor (WFS) measurements to control multiple deformable mirrors. We analyze the average and the signal-to-noise-ratio performance of an image measurement and postprocessing technique that uses simultaneous measurements of a short-exposure compensated image measured in an off-axis direction; an additional WFS measurement is taken in the off-axis direction. Results are presented for infinite-altitude WFS beacons driving both the WFS for the adaptive optics and the WFS looking in the off-axis direction, a variety of seeing and WFS light-level conditions, and off-axis angles from two to six times the isoplanatic angle. This technique improves the average effective transfer function out to a field angle of at least six times the isoplanatic angle while providing a higher signal-to-noise ratio in the spatial frequency domain.