Design and characterization of dielectric filled TM110 microwave cavities for ultrafast electron microscopy.

Microwave cavities oscillating in the TM110 mode can be used as dynamic electron-optical elements inside an electron microscope. By filling the cavity with a dielectric material, it becomes more compact and power efficient, facilitating the implementation in an electron microscope. However, the incorporation of the dielectric material makes the manufacturing process more difficult. Presented here are the steps taken to characterize the dielectric material and to reproducibly fabricate dielectric filled cavities. Also presented are two versions with improved capabilities. The first, called a dual-mode cavity, is designed to support two modes simultaneously. The second has been optimized for low power consumption. With this optimized cavity, a magnetic field strength of 2.84 ± 0.07 mT was generated at an input power of 14.2 ± 0.2 W. Due to the low input powers and small dimensions, these dielectric cavities are ideal as electron-optical elements for electron microscopy setups.

A nonlinear system model for electrospinning sub-100 nm polyacrylonitrile fibres.

Solutions of polyacrylonitrile (PAN) were electrospun using a range of process parameters, resulting in fibre diameters from 10 to 320 nm. A nonlinear neural network system model was used to analyse the dependence of the fibre diameter on the process parameters, and used to simulate conditions for electrospinning 40-60 nm diameter fibres. These results indicated that flow rate is most important for determining fibre diameter. It was not possible to find the appropriate conditions for electrospinning sub-25 nm fibres. Precise control of the ambient temperature and relative humidity will be critical to producing electrospun fibres that are sub-25 nm. Further, it is unlikely that sub-25 nm fibres will be produced without significant changes in the electrospinning apparatus, for example, by use of focusing and jet-steering fields, alternate carrier gases to modify the discharge characteristics, or patterned electrospinning.

Rat platelets are deficient in internal Ca2+ release and require influx of extracellular Ca2+ for activation.

Calcium fluxes were studied in fura-2-labeled rat platelets. Thrombin, ADP and ionomycin induced rapid mobilization of internally stored Ca2+, which resulted in only a moderate increase of cytosolic [Ca2+]i. Thrombin and ADP stimulated influx of extracellular Ca2+, which was monitored as uptake of 45Ca2+ and of Mn2+. With either agonist, the influx of Ca2+ magnified the initial increase of [Ca2+]i. Since responses of rat platelets were dependent on external [Ca2+], we conclude that Ca2+ influx complements the mobilization of internal stores to reach sufficiently high [Ca2+]i for full activation. A regulatory effect of protein kinase C modulators was observed on both agonist-induced elevation of [Ca2+]i and receptor-mediated Ca2+ entry.

Back-propagation learning and nonidealities in analog neural network hardware.

Experimental results from adaptive learning using an optically controlled neural network are presented. The authors have used example problems in nonlinear system identification and signal prediction, two areas of potential neural network application, to study the capabilities of analog neural hardware. These experiments investigated the effects of a variety of nonidealities typical of analog hardware systems. They show that network using large arrays of nonuniform components can perform analog communications with a much higher degree of accuracy than might be expected given the degree of variation in the network's elements. The effects of other common nonidealities, such as noise, weight quantization, and dynamic range limitations, were also investigated.

Signal prediction by an optically controlled neural network.

Networks of interconnected nonlinear analog processors, or neurons, are finding increasing use in adaptive problems. Adaptive signal prediction has been widely used for many years but has been primarily restricted to linear systems and signals, for which the mathematical treatment of the problems is tractable. We present results using an optically controlled adaptive neural network for nonlinear signal prediction.

Amorphous silicon photoconductive arrays for artificial neural networks.

We have demonstrated an electronic implementation of an artificial neural network with 14,400 synaptic connections of variable strength using an array of a:Si:H photoconductors. This neural network has been configured as a Hopfield associative memory, and used to successfully perform simple pattern recognition. Our initial results suggested that, using these a-Si:H photoconductive arrays as the optically programmable synaptic matrix, neural networks of large sizes may be achieved. This paper describes the fabrication and device characteristics of a-Si:H photoconductive arrays as well as a model application of a neural network.