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Goal a c q u i s i t i o n speed and accuracy were compared f o r subjects using f o u r d i f f e r e n t menu configurations o f a semantic hierarchy on an i n t e r a c t i v e computer terminal. Depth ( t h e number o f menu l e v e l s ) varied from one t o s i x , while breadth (the number o f choices per menu) varied from two t o 64. Goal a c q u i s i t i o n t i m e f o r t h e four experimental groups produced a U-shaped f u n c t i o n w i t h a minimum a t t h e configuration o f two l e v e l s w i t h e i g h t choices per l e v e l . E r r o r data corroborated t h e a c q u i s i t i o n times demonstrating t h a t t h e f a s t e s t conditions a1 so produced t h e l e a s t errors. Optimization o f t h e depth/breadth t r a d e o f f can be an important design consideration i n goal a c q u i s i t i o n tasks r e q u i r i n g speed and accuracy.

Solid state gas sensors are a core enabling technology to a range of measurement applications including industrial, safety, and environmental monitoring. The technology associated with solid-state gas sensors has evolved in recent years with advances in materials, and improvements in processing and miniaturization. In this review, we examine the state-of-the-art of solid state gas sensors with the goal of understanding the core technology and approaches, various sensor design methods to provide targeted functionality, and future prospects in the field. The structure, detection mechanism, and sensing properties of several types of solid state gas sensors will be discussed. In particular, electrochemical cells (solid and liquid), impedance/resistance based sensors (metal oxide, polymer, and carbon based structures), and mechanical sensing structures (resonators, cantilevers, and acoustic wave devices) as well as sensor arrays and supporting technologies, are described. Development areas for this field includes increased control of material properties for improved sensor response and durability, increased integration and miniaturization, and new material systems, including nano-materials and nano-structures, to address shortcomings of existing solid state gas sensors.

product is not thiocyanate but either the product of its further reaction with BrCN according to eq 1 or a further decomposition product of S(CN)2.BrCN + -SCN -Br + S(CN)2(1)The reactions of ADPaS and ATP0S are not useful for synthesizing adenosine 5'-[180]diphosphates or -triphosphates with chiral Pa or Pd because of the oxygen rearrangements in the polyphosphate systems described herein. These can be prevented by protecting the terminal phosphoryl groups with removable alkyl substituents, as demonstrated by the reactions of the RF and SP epimers of /3-(cyanoethyl)-ADPaS with BrCN in H2180 to produce high yields of the SP and RF epimers of 6-(cyanoethyl)-[a-180]ADP.22 The displacement of thiocyanate by H2180 proceeded with inversion of configuration at Pa, and the /3-cyanoethyl groups were easily removed by treatment with base to produce the SP and Rf epimers of [a-180]ADP.22Eckstein and Lowe and their collaborators have been able to desulfurize nucleoside phosphorothioates with electrophilic brominating agents in acidic solutions with inversion of configuration and without rearrangements in polyphosphates.19c•23 At neutral pHs these reactions also involved rearrangements, suggesting that our observations do not represent an isolated phenomenon observable only in the special case of reactions of BrCN with ADPaS or ATP/3S. This paper and our earlier communication4 provide the first evidence for involvement of cyc/o-diphosphates in chemical reactions. Dimeric phenylphosphonic anhydride is the only fourmembered ring organophosphorus compound reported in the literature that has two P-O-P bonds.24•25 Recently a cyclic phosphoric acid anhydride was postulated as a possible inter- (22)

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The “current icing potential” (CIP) algorithm combines satellite, radar, surface, lightning, and pilot-report observations with model output to create a detailed three-dimensional hourly diagnosis of the potential for the existence of icing and supercooled large droplets. It uses a physically based situational approach that is derived from basic and applied cloud physics, combined with forecaster and onboard flight experience from field programs. Both fuzzy logic and decision-tree logic are applied in this context. CIP determines the locations of clouds and precipitation and then estimates the potential for the presence of supercooled liquid water and supercooled large droplets within a given airspace. First developed in the winter of 1997/98, CIP became an operational National Weather Service and Federal Aviation Administration product in 2002, providing real-time diagnoses that allow users to make route-specific decisions to avoid potentially hazardous icing. The CIP algorithm, its individual components, and the logic behind them are described.

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