1. The original rough formulation of the expectancy theory is difficult to distinguish from the alternative stimulus-response doctrines. Part of this difficulty results from the fact that implicit in this rough formulation, is a definition of the matrix "x expects a goal at location L," which makes it equivalent to the matrix "x runs down the practiced path," when certain conditions are fulfilled. Because of this difficulty, we have rejected this definition. 2. We have suggested instead a definition of the matrix "x expects a goal at location L" which makes it equivalent to the matrix "x runs down the path which points directly to the location L," when certain conditions are fulfilled. 3. To determine whether rats will run down such a path, whenever the original path is blocked, we have run 56 female rats in a situation which conformed to these conditions. 4. Thirty-six percent of the rats chose the path which pointed directly towards the location of the goal. The remaining rats were distributed over the other paths in a chance fashion. 5. We have concluded (1) that rats do learn to expect goals in specific locations, (2) that there are important similarities between this behavior and human symbolic behavior, and (3) that these similarities justify our using the word 'expectation' as a name for the disposition to short-cut when the original patch is blocked.

Single-mode lightwave has completely replaced multimode as the technology of choice for long-haul, metropolitan interoffice, and subscriber loop systems. This article discusses the design principles and performance of four kinds of single-mode fibers developed by AT&T Bell Laboratories. AT&T Technologies has shipped over a thousand megameters of a fiber (in cable form) optimized for 1310-nm systems. This fiber is known as a depressed-cladding single-mode fiber, because of its refractive-index profile. It was designed to provide low intrinsic loss, high bandwidth, low splice loss, and a high resistance to macrobending- and microbending-induced losses. Three other fibers that offer new possibilities to system designers are: dispersion-shifted fiber that is optimized for 1550-nm systems; dispersion-flattened fiber that has high bandwidth over a wide wavelength range; and polarization-maintaining fiber that can be used with phase-sensitive receivers.

A new depressed-clad triangular-index-profile single-mode fibre with dispersion minimum shifted to the 1.55 ¿m region is investigated. Fibres with high cutoff wavelength (¿1.1 ¿m) and low dispersion slope (¿0.052 ps/km nm2) at their minimum dispersion wavelength (¿1.55 ¿m) were fabricated. Results from 226.7 km of fibre show an average loss of 0.241 dB/km at 1.55 ¿m and 0.232 dB/km at the loss min...

Conventional dual-window single-mode fiber has minimum attenuation in its 1.55-μm window. Because of high chromatic dispersion at this wavelength, its full capacity can be utilized only in a system using unconventional single-frequency lasers. Alternatively, a high-bit-rate system with repeater spacing over 100 km is possible with conventional multimode lasers when dispersion-shifted single-mode fiber is used.

The influence of microstructure, strain rate, and test temperature on the tensile properties of 18Ni(350) maraging steel was examined. The strain-rate and temperature dependence of the yield strength is less than that observed in low-strength carbon steels. The results suggest that the thermally activated flow process involves both the by-passing of a linear barrier, i.e., the disruption associated with a dislocation core, and the by-passing of a localized obstacle, the latter being specific to the microstructure being examined. The tensile ductility of aged 18Ni(350) maraging steel also undergoes a ductile-brittle transition. The extent of this ductility loss depends upon the matrix solute content and the presence of either reverted austenite or a highly dislocated substructure.

Beta-III titanium (Ti-11.5Mo-5.5Zr-4.5Sn) was solutionized above the β-transus, water-quenched and deformed by rolling at room temperature. The deformation accelerated the aging kinetics at all temperatures up to the β transus. The thermomechanically treated (TMT) alloy always had higher strength than the conventionally heat treated (CHT) alloy; the effect being most marked when the aging product was normally α in a β matrix. In addition, the ductility and notched impact resistance of TMT β-III was greater than that of the CHT alloy in the over-aged condition. The TMT did not alter the morphology of the ellipsoidal α phase formed at low aging temperatures and short aging times, respectively. Here the strengthening increase is attributed to strain hardening of the initial β + ω microstructure. The deformation did substantially change the morphology of the Widmanst�tten α phase that formed at higher aging temperatures. In particular, the Widmanst�tten α plates were much finer and the β grain boundaries were no longer a preferred precipitation site following TMT. At the highest aging temperatures, the TMT material developed a cell structure of about 1 μ in diameter.