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We report the results of a study with proton-induced X-ray emissions (PIXE) of the distribution and concentration of 15 chemical elements (Na to Sr in periodic chart) in four microstructural and two mineralogical regions of shell of rapidly growing adult oysters [Crassostrea virginica (Gmelin)]. Hatchery-raised oysters were grown in Broadkill Estuary, Delaware, USA, for 16 wk in summer 1978. Their valve edges were filed as a marker, and the oysters were replaced in the estuary, where they grew rapidly. Shell deposited after marking had a normal microstructure and mineralogy after a narrow zone of disturbance. After 17 d oysters were sacrificed, and different mineralogical and microstructural regions of valves of three oysters, and parts of valves of two oysters, were analyzed for the elements Na to Sr. Quadrats (2.5 × 0.45 mm) included three calcitic groups (prismatic, foliated, chalky) and one aragonitic (myostracal) microstructural group; four quadrats were on the exterior and five on the interior of right and left valves. Inhalant and exhalant margins of valves and ground right and left valves of one oyster were also analyzed. Elemental chemistry of different regions of shell varied among the three microstructural groups within the single calcitic polymorph, between aragonitic and calcitic regions, and between exhalant and inhalant margins of the valves. Elements were most concentrated in the prismatic region of the right valve. Element concentrations were similar in ground right and left valves, except for higher levels of Si, Fe, and Zn in the right valve (corresponding to their high contents in prismatic shell) and of Cl in the left valve (reflecting high concentration in chalky shell, abundant in this valve). Na, Mg, Cl, Cr, Cu, Zn and Br were more concentrated in prismatic than in foliated shell. Chalky shell contained higher concentrations of Na than did prismatic shell, and high concentrations (but lower than in prismatic shell) of Mg, Cl, Ti, Mn, Fe, Zn and Br. Element concentration in myostracum was approximately the same as, or lower than, in foliated shell, except for Sr, which was higher than that in any other shell group. In the right valve most elements were concentrated in inhalant margins, and on the left valve, in exhalant margins. With increased weathering of the exterior surface of prismatic shell, Mg, Si, and Mn increased in concentration and Na, Al, Cl, Ti, Cr, Fe, Br, and Sr decreased.

New systolic architectures are proposed for the computation of the Fourier transform based on the generation of the coefficients of the transform during the computation. These architectures require less input/output pins on the chip. The new architectures are also extremely modular and cascadeable, thus, amenable for efficient VLSI implementation. VLSI complexity of the architectures are compared with the existing parallel architectures. © 1992 IEEE.

This study investigated the outcomes of a demonstration project that provided free medical coverage to former Aid to Families with Dependent Children (AFDC) recipients who were holding jobs with limited or no health benefits. Data were collected on the Medicaid expenditures of 54 eligible participants and their dependents for up to two years before they exited welfare; the expenditures averaged 56 percent less for adults and 45 percent less for children than the respective AFDC averages for the county. Because only 22 percent of the eligible participants took advantage of the program, telephone interviews also were conducted with 24 people who did not participate in or dropped out of the health plan. The main reasons cited for not enrolling were a misunderstanding of the program, a claim that no notification of the program was received, and a lack of interest. These results and their policy implications are presented in the context of the Family Support Act's mandate that states extend medical assistance coverage to AFDC recipients whose cases are closed because of employment. © 1991 by the National Association of Social Workers, Inc.

The ideal user of scientific and technical information: shall we design one? The positive personality traits one would wish for in a spouse would do nicely for a start: patient; thoughtful; caring; able to see our (the librarians') virtues through the fog of early-morning not yet-wakefulness or late evening exhaustion; able to communicate needs and wants clearly and without a lot of emotional overtones; willing to work hard to obtain desired results; and apprecia tive of what We (librarians) do. Add to this other talents which, while useful, are less often associated with marriage: the ability to understand and retain complex organizational details; patience with less-than-perfect systems; an intuitive understanding of how information is organized; and a sense of how best to cope with the inter-face between the deluge of possible information resources and the limited needs of one particular user (not to mention limited capacities for retaining and controlling that information flood once the gates are open). © 1991 by The Haworth Press, Inc. All rights reserved.

Max M. Mintz; Battles of the Revolutionary War, 1775–1781. By W. J. Wood. (Chapel Hill: Algonquin, 1990. xxxii + 315 pp. $24.95.), Journal of American History,

Nehama Aschkenasy Eves Journey: Feminine Images in Hebraic Literary Tradition Philadelphia: University of Pennsylvania Press, 1986. ISBN 0‐8122‐8033‐4. Hardcover, $36.95. Pp. xv+269. Copyright © 1991, Wiley Blackwell. All rights reserved

Twenty acquisition curves were obtained from each of 8 pigeons in a free-operant choice procedure. Every condition began with a phase in which two response keys had equal probabilities of reinforcement, and, as a result, subjects' responses were divided fairly evenly between the two keys. This was followed by a phase in which one key had a higher probability of reinforcement than the other, and the development of preference was observed. In all but a few cases, response proportions increased for the key with the higher probability of reinforcement. In most conditions, the two probabilities differed by .06, but the actual probabilities varied (from .16 and .10 in one condition to .07 and .01 in another). Development of preference for the key with the higher probability of reinforcement was slower when the ratio of the two reinforcement probabilities was small (.16/.10) than when it was large (.07/.01). This finding is inconsistent with the predictions of several different quantitative models of acquisition, including the kinetic model (Myerson & Miezin, 1980) and the ratio-invariance model (Horner & Staddon, 1987). However, the finding is consistent with a hypothesis based on Weber's law, which states that the two alternatives are more discriminable when the ratio of their reinforcement probabilities is larger, and, as a result, the acquisition of preference is faster.

Two experiments measured pigeons' choices between probabilistic reinforcers and certain but delayed reinforcers. In Experiment 1, a peck on a red key led to a 5-s delay and then a possible reinforcer (with a probability of .2). A peck on a green key led to a certain reinforcer after an adjusting delay. This delay was adjusted over trials so as to estimate an indifference point, or a duration at which the two alternatives were chosen about equally often. In all conditions, red houselights were present during the 5-s delay on reinforced trials with the probabilistic alternative, but the houselight colors on nonreinforced trials differed across conditions. Subjects showed a stronger preference for the probabilistic alternative when the houselights were a different color (white or blue) during the delay on nonreinforced trials than when they were red on both reinforced and nonreinforced trials. These results supported the hypothesis that the value or effectiveness of a probabilistic reinforcer is inversely related to the cumulative time per reinforcer spent in the presence of stimuli associated with the probabilistic alternative. Experiment 2 tested some quantitative versions of this hypothesis by varying the delay for the probabilistic alternative (either 0 s or 2 s) and the probability of reinforcement (from .1 to 1.0). The results were best described by an equation that took into account both the cumulative durations of stimuli associated with the probabilistic reinforcer and the variability in these durations from one reinforcer to the next.