41 research outputs found
Understanding person acquisition using an interactive activation and competition network
Face perception is one of the most developed visual skills that humans display, and recent work has attempted to examine the mechanisms involved in face perception through noting how neural networks achieve the same performance. The purpose of the present paper is to extend this approach to look not just at human face recognition, but also at human face acquisition. Experiment 1 presents empirical data to describe the acquisition over time of appropriate representations for newly encountered faces. These results are compared with those of Simulation 1, in which a modified IAC network capable of modelling the acquisition process is generated. Experiment 2 and Simulation 2 explore the mechanisms of learning further, and it is demonstrated that the acquisition of a set of associated new facts is easier than the acquisition of individual facts in isolation of one another. This is explained in terms of the advantage gained from additional inputs and mutual reinforcement of developing links within an interactive neural network system. <br/
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Irradiated-Microsphere Gamma Analyzer (IMGA): an integrated system for HTGR coated particle fuel performance assessment
The Irradiated-Microsphere Gamma Analyzer (IMGA) System, designed and built at ORNL, provides the capability of making statistically accurate failure fraction measurements on irradiated HTGR coated particle fuel. The IMGA records the gamma-ray energy spectra from fuel particles and performs quantitative analyses on these spectra; then, using chemical and physical properties of the gamma emitters it makes a failed-nonfailed decision concerning the ability of the coatings to retain fission products. Actual retention characteristics for the coatings are determined by measuring activity ratios for certain gamma emitters such as /sup 137/Cs//sup 95/Zr and /sup 144/Ce//sup 95/Zr for metallic fission product retention and /sup 134/Cs//sup 137/Cs for an indirect measure of gaseous fission product retention. Data from IMGA (which can be put in the form of n failures observed in N examinations) can be accurately described by the binomial probability distribution model. Using this model, a mathematical relationship between IMGA data (n,N), failure fraction, and confidence level was developed. To determine failure fractions of less than or equal to 1% at confidence levels near 95%, this model dictates that from several hundred to several thousand particles must be examined. The automated particle handler of the IMGA system provides this capability. As a demonstration of failure fraction determination, fuel rod C-3-1 from the OF-2 irradiation capsule was analyzed and failure fraction statistics were applied. Results showed that at the 1% failure fraction level, with a 95% confidence level, the fissile particle batch could not meet requirements; however, the fertile particle exceeded these requirements for the given irradiation temperature and burnup
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Neutron-detection apparatus
An atomic fission counting apparatus used for neutron detection is provided with spirally curved electrode plates uniformly spaced apart in a circular array and coated with fissile material
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New Method of Gamma Dose-Rate Measurement Using Energy-Sensitive Counters
A new concept of charge quantization and pulse-rate measurement was developed to monitor low-level gamma dose rates using energy-sensitive, air-equivalent counters. Applying this concept, the charge from each detected photon is quantized by level-sensitive comparators so that the resulting total output pulse rate is proportional to dose rate. The concept was tested with a proportional counter and a solid-state detector for wide-range dose-rate monitoring applications. The prototypic monitors cover a dose-rate range from background radiation levels 10 ..mu..R/h) to 10 R/h
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Recent developments in position-sensitive neutron counting
Continuing research on advanced methods of thermal neutron detection and position sensing with gas-filled counters was aimed at improving their performance and extending the limits of their applicability. High electron drift velocities obtained from measurements on gas mixtures containing CF/sub 4/ motivated us to evaluate the properties of /sup 3/He-CF/sub 4/ and Ar-CF/sub 4/ mixtures to show that these gases have the potential of improving the count rate capability, spatial resolution, and photon discrimination of neutron PSPCs (position-sensitive proportional counters) and fission counters. In support of the U.S. National Small-Angle Neutron Scattering (SANS) Facility we developed a large-area (65-cm x 65-cm) PSPC camera. RC position encoding was chosen for simplicity of construction, but since previous experience with this encoding method had been limited to smaller PSPCs (area < 25 cm x 25 cm), the main objective of this development was to show that RC encoding parameters and construction methods could be scaled up for larger area PSPCs. The use of the new counter gas mixtures enabled the development of position-sensitive transmission line fission counters (TLFCs) for neutron flux monitoring and a one-dimensional, curved PSPC for large-angle (130/sup 0/) neutron diffraction experiments. The main objective of these developments was to extend the capabilities of the LC-encoding method by mitigating the effects of interelectrode capacitance, and thereby increase the count rate capability
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New method of proportional counter feedback biasing for wide-range radiation dose-rate monitors
A prototypic wide-range radiation dose-rate monitor for civil defense applications has been developed and tested. The specified dose-rate range (0 to 500 R/h) was displayed on a single readout scale by using feedback-controlled biasing of a proportional counter. This new method is based on controlling the avalanche multiplication factor (gas gain) of the counter by varying its bias voltage in response to its measured output current (i.e., detected dose rate). The counter output current varies between 0 and 1.5 nA in a quasi-logarithmic response to dose rates between 0 and 500 R/h. The corresponding values of gas gain and bias voltage range from 1 to 300 and 200 to 1900 V respectively
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Concepts of remote signal transmission for liquid-metal fast breeder reactors
Sensors and remote signal transmission techniques suitable for LMFBR conditions are discussed. Some of the major problems which must be addressed during further development of sensors and techniques are listed
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Development of a high temperature, high sensitivity fission counter for liquid metal reactor in-vessel flux monitoring
Advanced liquid metal reactor concepts such as the Sodium Advanced Fast Reactor (SAFR) and the Power Reactor Inherently Safe Module (PRISM) have relatively large pressure vessels that necessitate in-vessel placement of the neutron detectors to achieve adequate count rates during source range operations. It is estimated that detector sensitivities of 5 to 10 counts/center dot/s/center dot//sup /minus/1//center dot/(neutron/(cm/sup 2//center dot/s))/sup /minus/1/ will be required for the initial core loading. The Instrumentation and Controls Division of Oak Ridge National Laboratory has designed and fabricated a fission counter to meet this requirement which is also capable of operating in uncooled instrument thimbles at primary coolant temperatures of 500 to 600/degree/C. Components are fabricated from Inconel-600, and high temperature alumina insulators are employed. The transmission line electrode configuration is utilized to minimize capacitive loading effects
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Digital neutron radiography using plane converters with multiwire proportional chambers
The work described here was completed more than three years ago, and represents, in large part the PhD and MS thesis research of two of the present authors. Much of it has been reported previously elsewhere. It constitutes an effort to develop and study a moderately low cost, moderate resolution, high sensitivity, on-line method for digital neutron radiography, intended for use where neutron fluence was limited by source strength, or received dose. The basic imaging system consisted of a position-sensitive gas proportional chamber together with its associated imaging electronics, and a plane neutron converter. Enriched-boron, gadolinium, and polyethylene (for fast neutrons) converters were analyzed and tested. Some work was done on digital data enhancement, and efforts to improve spatial resolution included pressurizing the proportional-chamber gas to reduce the track lengths of the neutron-interaction products