N204: A Historical Survey

The history of dinitrogen tetroxide is sketched to show the stages in the establishment of its molecular formula, N2O4, by way of its preparation, identification, analysis and characterisation. From its first recorded appearance to the determination of its molecular formula towards the end of the 19th. century, more than a milennium has passed, from the dark ages of alchemy to the present “information explosion”.     

Book Reviews

‘Mega‐events’, such as the Olympic Games, have emerged as an important tool of urban and regional renewal through their ability to justify redevelopment and enhancement, attract inward investment, promote tourism and create new images for host cities. This paper complements previous research into the urban effects of the Summer Games by focusing on the infrastructural legacy of hosting the Winter Games, 1924–2002. The discussion concentrates upon the growing intensity of the intra‐urban competition to host the event and identifies four phases in the changing infrastructural implications of staging the Games. As a component of urban and regional policy, the Winter Olympics present both major risks and clear opportunities for the effective transformation of host centres.     

Inner functions and a pseudo-singular-value decomposition in super-optimal H∞ control

The inner functions and pseudo-singular-value decomposition (PSVD) which arise in super optimal H^∞ control are studied. New properties of non-square inner matrices are derived and a structural inner matrix is defined as an inner matrix with no transmission zeros. The uniqueness properties of the PSVD are derived and structural inner functions are used to characterize particular PSVDs     

Spectral characterization of the LANDSAT Thematic Mapper sensors

A summary of the spectral characteristics of the LANDSAT-4 and LANDSAT-5 Thematic Mapper instruments, the protoflight (TM/PF) and flight (TM/F) models, respectively, is presented. Data collected by the Hughes/Santa Barbara Research Center on the instruments and their components to determine compliance with the spectral coverage and spectral matching specifications served as the basis for the characterization. Compliance with the spectral coverage specifications (e.g. band locations) was determined by deriving band-by-band relative spectral response (RSR) curves from spectral measurements on the individual components contributing to the overall spectral response: filters, detectors and optical surfaces. The integrated system RSRs were not measured. The derived RSRs for the reflective bands were similar between TM/PF and the TM/F. The bandpasses between 50 per cent RSR points varied by only 2nm at most between the sensors and were: band 1, 452-518 nm; band 2, 528-609 nm; band 3, 625-693 nm; band 4, 776-904 nm; band 5, 1568-1784 nm and band 7, 2097-2348 nm. The upper-band edge of band 5 was outside the desired and specified range of 1750 ±20 nm; this implies that there will be more contribution from variable atmospheric water vapour absorption. In the emissive thermal band 6, the TM/PF and TM/F showed fundamentally different spectral responses. Though the lower band edges were both at approximately 104/mi, the TM/PF upper-band edge was detector limited at a temperature-dependent value of about 11·7μm, whereas the TM/F upper-band edge was filter limited at 12·4μm. Despite the TM/PF's band 6 narrow bandwidth, its radiometric performance exceeded requirements, so the band's narrowness was not a serious concern. Spectral matching measures the spectral differences between channels within a band by calibrating them all with one source and comparing their outputs to a spectrally different source. Satisfactory TM/PF spectral matching data were never obtained. TM/F channels were shown to have comparable or better spectral matching than past and existing MSS sensors.     

Singular perturbation approximation of balanced systems

This paper relates the singular perturbation approximation technique for model reduction to the direct truncation technique if the system model to be reduced is stable, minimal and internally balanced. It shows that these two methods constitute two fully compatible model-reduction techniques for a continuous-time system, and both methods yield a stable, minimal and internally balanced reduced-order system with the same L_∞-norm error bound on the reduction. Although the upper bound for both reductions is the same, the direct truncation method tends to have smaller errors at high frequencies and larger errors at low frequencies, while the singular perturbation approximation method will display the opposite character. It also shows that a certain bilinear mapping not only preserves the balanced structure between a continuous-time system and an associated discrete-time system, but also preserves the slow singular perturbation approximation structure. Hence the continuous-time results on the singular perturbation approximation of balanced systems are easily extended to the discrete-time case. Examples are used to show the compatibility and the differences in the two reduction techniques for a balanced system     

Adaptive-predictive game-playing programs

Abstract

predictive search (APS) is a new method by which systems can improve their search performance through experience. It is believed that the development of such methods is critical, as currently a tremendous number of computational results are potentially wasted by not integrating search and partial search results into the knowledge of a problem-solving system. In the APS model, pattern formation and associative recall are used to improve or replace search. In this paper, the theory, background, and motivations behind the model are presented and its application to two-player game-playing programs is discussed. In these programs, the system develops a knowledge base of patterns (boolean features) coupled with weights and, using pattern-oriented evaluation, performs only 1-ply search, yet competes respectably with programs that search more. The learning mechanism is a hybrid of machine learning and artificial intelligence techniques that have been successful in other settings. Specific examples and performance results are taken from the domains of Hexapawn, Tic-Tac-Toe, Pente, Othello, and chess.     

A Proton–magnetic–resonance Spectroscopic Investigation of Intramolecular Hydrogen Bonding in 4–Substituted–2–nitrodiphenylamine Disperse Dyes

Detection of long–range coupling constants, JNH, H5, in 100–MHz proton–magnetic–resonance spectra confirms the presence of intramolecular NH ON hydrogen bonding in some 2–nitrodiphenylamine disperse dyes. Measurements in polar and non–polar solvents on 2–nitrodiphenylamine and on twelve 4–substituted derivatives indicate weakening of the bonding, which is related to light fastness, when the 4–substituent is a strong electron acceptor.     

Optical, Structural, and Chemical Characteristics of Lead-Indium Phosphate and Lead-Scandium Phosphate Glasses

Two new glass systems based on a range of lead-indium phosphate and lead-scandium phosphate compositions have been developed and characterized. These glasses have a relatively high index of refraction ( n = 1.75 to 1.83) in the visible region and exhibit moderate dispersion (Abbe number ∼30). The ultraviolet absorption edge occurs near 300 nm and the glasses strongly absorb in the infrared at wavelengths greater than 2800 nm. Both glass types can be prepared at relatively low temperatures (900° to 1000°C) and are easily poured down to ∼800°C because of their low melt viscosities. The glasses exhibit good chemical durability and resistance to both weathering and intense γ-radiation. These materials have a glass transition temperature of about 430°C, a softening point of about 460°C, and thermal expansion coefficients in the range of 10.8 × 10⁻⁶ to 12.0 × 10⁻⁶/°C. The structure of these phosphate glasses is shown to consist of a distribution of chains of PO₄ tetrahedra held together by bonding between the non-bridging oxygens of the tetrahedra and the metal cations. The polyphosphate chain length distribution was determined by a liquid chromatographic technique. Potential aqueous corrosion mechanisms are discussed and some general guidelines for forming a chemically durable phosphate glass are given.     

DIFFUSION OF BEET DYE DURING ELECTRICAL AND CONVENTIONAL HEATING AT STEADY‐STATE TEMPERATURE1

Ohmic heating has been shown to alter mass transfer properties of fruit and vegetable tissue. Diffusion of beet dye from beetroot tissue into a fluid was studied during conventional and ohmic heating as a function of steady‐state temperature. The volume of beet dye diffusing into solution during ohmic heating was enhanced with respect to conventional heating at 42C and 58C, but not at 72C. This can be explained by examining the differences in electrical conductivity of beet tissue at these temperatures during conventional and ohmic heating. At 42 and 58C, the electrical conductivity of beet tissue heated ohmically is higher than the electrical conductivity of beet tissue heated conventionally. At 72C, the electrical conductivities of beet tissue during conventional and ohmic heating are equal. The extent of diffusion in the ohmic case is also positively correlated with applied voltage. These results suggest that food processes involving mass transfer can be enhanced by choosing conditions in which the electrical conductivity of a sample under ohmic conditions is maximized.