Room temperature Dy:YLF laser operation at 4.34 μm

A Dy:YLF laser operating on the ⁶H_11/2 to ⁶H_13/2 transition at 4.34 μm and using a laser pumping scheme is reported. This pumping scheme is necessitated by the short upper-laser-level lifetime and the small effective stimulated-emission cross section. A suitable laser for this application is the Er:YLF laser operating at 1.73 μm. A simple model that approximates Dy:YLF laser performance well is presented. Results on laser performance, including a determination of the slope efficiency and threshold as a function of the output mirror reflectivity and a correlation of the pulse length with the laser output energy, are reported. Overall laser efficiency is found to be limited primarily by the ratio of the pump wavelength to laser output wavelength and the terminated four-level laser operation     

Acceptability of Whey-Soy Drink Mix Prepared with Cottage Cheese Whey

Flavor score of commercially produced whey-soy drink mix containing 41% sweet whey solids was correlated with the lactic acid content of the dehydrated material (?.75). Experimental samples prepared with a 1:1 mixture of acid whey to sweet whey and neutralized acid whey showed lower initial flavor scores than a control prepared with only sweet whey. Both samples contained over 1% total lactate reported as lactic acid compared to .4% for the control. A sample prepared with a 1:5 mixture of acid to sweet whey contained .77% lactic acid. Flavor scores of this sample after 158 days storage at 37 C, although not significantly different from the control stored under similar conditions, showed a downward trend over time. Therefore, use of small amounts of acid whey in the formulation could lead to impaired storage stability as measured by flavor acceptability during prolonged storage under adverse conditions.     

On the detection of simple points in higher dimensions using cubical homology.

Simple point detection is an important task for several problems in discrete geometry, such as topology preserving thinning in image processing to compute discrete skeletons. In this paper, the approach to simple point detection is based on techniques from cubical homology, a framework ideally suited for problems in image processing. A (d-dimensional) unitary cube (for a d-dimensional digital image) is associated with every discrete picture element, instead of a point in epsilon(d) (the d-dimensional Euclidean space) as has been done previously. A simple point in this setting then refers to the removal of a unitary cube without changing the topology of the cubical complex induced by the digital image. The main result is a characterization of a simple point p (i.e., simple unitary cube) in terms of the homology groups of the (3d - 1) neighborhood of p for arbitrary, finite dimensions     

A network of electronic neural oscillators reproduces the dynamics of the periodically forced pyloric pacemaker group

Low-dimensional oscillators are a valuable model for the neuronal activity of isolated neurons. When coupled, the self-sustained oscillations of individual free oscillators are replaced by a collective network dynamics. Here, dynamical features of such a network, consisting of three electronic implementations of the Hindmarsh-Rose mathematical model of bursting neurons, are compared to those of a biological neural motor system, specifically the pyloric CPG of the crustacean stomatogastric nervous system. We demonstrate that the network of electronic neurons exhibits realistic synchronized bursting behavior comparable to the biological system. Dynamical properties were analyzed by injecting sinusoidal currents into one of the oscillators. The temporal bursting structure of the electronic neurons in response to periodic stimulation is shown to bear a remarkable resemblance to that observed in the corresponding biological network. These findings provide strong evidence that coupled nonlinear oscillators realistically reproduce the network dynamics experimentally observed in assemblies of several neurons.     

Variable Frequency Microwave Curing of Amide-Epoxy Based Polymers

Irradiation of a dielectric material with microwave irradiation results in energy transfer due to rotational-vibrational transitions within the molecule. The energy transfer results in a local rise in temperature within the material. Microwave-induced reactions can occur at a lower average temperature than convective heating resulting in faster thermal curing of polymer dielectrics because the energy absorption is localized at particular sites. In this study, variable frequency microwave (VFM) curing of epoxy-based dielectric films was investigated. The microwave energy was swept through a range of frequencies to dissipate standing waves so that metallic conductors could be present with the dielectric films. The rate of reaction and film properties of polyamideimide (PAI) and bisphenol A epoxy resin (BPAEp) were studied. Benzanilide and BPAEp were used as model compounds for the reaction between the amide and epoxy. Compared to convective heating, the microwave reaction rates were higher at each isothermal cure temperature. The resulting mechanical properties of the films cured by microwave heated were superior to thermally cured materials. The elastic modulus of VFM cured PAI/BPAEp films was less than that of thermally cured films and the elongation to break was twice as high. Further, the adhesion to copper was improved with microwave processing. The chemical structure of the VFM cured polymer was different from the thermally cured polymer, based on Fourier transform infrared analysis, and is likely the origin of the improved properties.     

2.4 GHz continuously variable ferroelectric phase shifters using all-pass networks

Continuously variable ferroelectric (BST on sapphire) phase shifters based on all-pass networks are presented. An all-pass network phase shifter consists of only lumped LC elements, and thus the total size of the phase shifter is kept to less than 2.2 mm /spl times/ 2.6 mm at 2.4 GHz. The tunability (C/sub max//C/sub min/) of a BST interdigital capacitor is over 2.9 with a bias voltage of 140 V. The phase shifter provides more than 121/spl deg/ phase shift with the maximum insertion loss of 1.8 dB and the worst case return loss of 12.5 dB from 2.4 GHz to 2.5 GHz. By cascading two identical phase shifters, more than 255/spl deg/ phase shift is obtained with the maximum insertion loss of 3.75 dB. The loss figure-of-merit of both the single- and double-section phase shifters is over 65/spl deg//dB from 2.4 GHz to 2.5 GHz.     

Travelling-wave photodetectors with 172-GHz bandwidth and 76-GHzbandwidth-efficiency product

Results of the first fabrication and measurement of travelling-wave photodetectors are reported. The devices have bandwidths as high as 172 GHz, the highest reported for a p-i-n photodetector, and bandwidth-efficiency products as large as 76 GHz, the largest reported for any photodetector without gain. Comparisons with vertically illuminated and waveguide photodetectors fabricated on the same wafer establish the superior performance of travelling-wave photodetectors. Microwave loss on the travelling-wave photodetector structure is identified as a bandwidth limitation     

A multiple-layer finite-element model of the surface EMG signal

The effect of skin, muscle, fat, and bone tissue on simulated surface electromyographic (EMG) signals was examined using a finite-element model. The amplitude and frequency content of the surface potential were observed to increase when the outer layer of a homogeneous muscle model was replaced with highly resistive skin or fat tissue. The rate at which the surface potential decreased as the fiber was moved deeper within the muscle also increased. Similarly, the rate at which the surface potential decayed around the surface of the model, for a constant fiber depth, increased. When layers of subcutaneous fat of increasing thickness were then added to the model, EMG amplitude, frequency content, and the rate of decay of the surface EMG signal around the limb decreased, due to the increased distance between the electrodes and the active fiber. The influence of bone on the surface potential was observed to vary considerably, depending on its location. When located close to the surface of the volume conductor, the surface EMG signal between the bone and the source and directly over the bone increased, accompanied by a slight decrease on the side of the bone distal to the active fiber. The results emphasize the importance of distinguishing between the effects of material properties and the distance between source and electrode when considering the influence of subcutaneous tissue, and suggest possible distortions in the surface EMG signal in regions where a bone is located close to the skin surface.     

Materials study of silicon-on-lnsulator material by TEM

Silicon-on-insulator (SOI) technology addresses the need for many different device applications, such as radiation tolerant devices, high voltage, and three-dimensional circuitry applications. Isolated silicon epitaxy (ISE) is a commercialised process which results in excellent SOI material quality with proven results, having overcome most of the obstacles of other processes, although only having reduced, not eliminated, threading dislocations. The remaining isolated dislocations have been examined in detail by transmission electron microscopy (TEM). These have been diagnosed as normal lattice dislocations, with no faults or twins in the material. The nature, source, and behavior of the remaining dislocations is discussed.