Regional interfuel substitution by electric companies: The short-term prospects

This paper uses a translog price possibility frontier to measure the extent of regional interfuel substitution effects in the electric utility industry in the United States. Monthly data based on Department of Energy regions serve as the vehicle around which the estimation is performed. Given the nonlinear character of the price possibility frontier specification, an iterative Zellner seemingly unrelated regression technique is used for estimating the parameters of the model. The results suggest that relative changes in fuel prices have significant effects on fossil fuel consumption. This, in turn, has important implications for public policy. In particular, the market system appears better able to deal with exogenous shifts in energy supplies than has frequently been assumed in the formulation of energy policy toward the energy crisis.The author is an economist with the Department of Energy, Office of Conservation and Solar Applications. The views expressed are those of the author and do not necessarily represent the policies of the Department of Energy or the views of other Department of Energy staff members.     

Models for estimating undiscovered oil resources

This paper is directed at estimating total producible oil in the United States. Two specific models are suggested and estimated in a fashion consistent with the theoretical considerations. The results suggest that approximately 159 billion barrels are ultimately recoverable and producible, of which 114 billion barrels had been produced by the end of 1977.     

Stability of vitamin C in fruits and fruit blends

The levels of the two biologically active forms of vitamin C, ascorbic acid (AA) and dehydroascorbic acid (DHAA), were determined in individual fruits, in fruit blends and in model systems over a 3-h incubation period at room temperature. There was essentially no reduction in the AA content in the orange juice sample and in the model solution of analytical ^l-ascorbic acid. A rapid decrease in the AA content was observed in the banana, apple and guava samples and in blends consisting of orange juice-banana-apple or L -ascorbic acid-banana-apple blends. However, the reduction in AA was concomitant with a quantitative increase in DHAA content.     

Lexical acquisition: Where is the semantics?

In this paper, which motivates lexical acquisition, we explain why existing lexicons are not complete and describe the impact of lexical gaps. We survey acquisition methods relative to their required resources and show that learning algorithms must be designed so that they rely on resources that are technologically available. We discuss in this light the availability and accessibility of machine-readable dictionaries and corpora. Finally we investigate the aspect of lexical semantics, addressing the question, What is the resource from which lexical semantics can be acquired? The answer is not clear because semantics is nowhere to be found explicitly. Thus, we resort to learning semantics by bootstrapping from secondary clues.     

Ion-exchanged waveguide lasers in Er3+/Yb3+ codoped silicate glass

We investigated an Er(3+)/Yb(3+) codoped silicate glass as a host material for waveguide lasers operating near 1.5 mum. Spectroscopic properties of the glass are reported. Waveguide lasers were fabricated by K(+)-ion exchange from a nitrate melt. The waveguides support a single transverse mode at 1.5 mum. An investigation of the laser performance as a function of the Yb:Er ratio was performed, indicating an optimal ratio of approximately 5:1. Slope efficiencies of as great as 6.5% and output powers as high as 19.6 mW at 1.54 mum were realized. The experimental results are compared with a waveguide laser model that is used to extract the Er(3+) upconversion coefficients and the Yb(3+)-Er(3+) cross-relaxation coefficients. The results indicate the possibility of obtaining high-performance waveguide lasers from a durable silicate host glass.     

Heavy‐Metal‐Free Colloidal Semiconductor Nanorods: Recent Advances and Future Perspectives

Quasi‐1D colloidal semiconductor nanorods (NRs) are at the forefront of nanoparticle (NP) research owing to their intriguing size‐dependent and shape‐dependent optical and electronic properties. The past decade has witnessed significant advances in both fundamental understanding of the growth mechanisms and applications of these stimulating materials. Herein, the state‐of‐the‐art of colloidal semiconductor NRs is reviewed, with special emphasis on heavy‐metal‐free materials. The main growth mechanisms of heavy‐metal‐free colloidal semiconductor NRs are first elaborated, including anisotropic‐controlled growth, oriented attachment, solution–liquid–solid method, and cation exchange. Then, structural engineering and properties of semiconductor NRs are discussed, with a comprehensive overview of core/shell structures, alloying, and doping, as well as semiconductor–metal hybrid nanostructures, followed by highlighted practical applications in terms of photocatalysis, photodetectors, solar cells, and biomedicine. Finally, challenges and future opportunities in this fascinating research area are proposed.