Grassland fragmentation and habitat loss are hypothesized to be contributing to widespread grassland bird declines in North America due to the adverse effects of fragmentation on breeding bird abundance and reproductive success. To assess the effects of fragmentation on the reproductive success of grassland birds, we measured rates of nest predation and brood parasitism for four species of birds ( Grasshopper Sparrow [Ammodramus savannaru], Henslow's Sparrow[Ammodramus henslowii], Eastern Meadowlark [ Sturnella magna], and Dickcissel [ Spiza Americana] ) in 39 prairie fragments ranging from 24 to>40,000 ha in size in five states in the mid‐continental United States. Throughout the region, nest‐predation rates were significantly influenced by habitat fragmentation. Nest predation was highest in small (<100 ha ) and lowest in large ( >1000 ha ) prairie fragments. Rates of brood parasitism by Brown‐headed Cowbirds (   Molothrus ater ), however, were not consistently related to fragment size and instead were more strongly related to regional cowbird abundance, being significantly higher in regions with high cowbird abundance. Differences in nest‐predation rates between large fragments ( 54–68% of all nests lost to predators ) and small fragments ( 78–84% lost to predators ) suggest that fragmentation of prairie habitats may be contributing to regional declines of grassland birds. Maintaining grassland bird populations, therefore, may require protection and restoration of large prairie areas.

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Across many real-world domains, men engage in more risky behaviors than do women. To examine some of the beliefs and preferences that underlie this difference, 657 participants assessed their likelihood of engaging in various risky activities relating to four different domains (gambling, health, recreation, and social), and reported their perceptions of (1) probability of negative outcomes, (2) severity of potential negative outcomes, and (3) enjoyment expected from the risky activities. Women’s greater perceived likelihood of negative outcomes and lesser expectation of enjoyment partially mediated their lower propensity toward risky choices in gambling, recreation, and health domains. Perceptions of severity of potential outcomes was a partial mediator in the gambling and health domains. The genders did not differ in their propensity towards taking social risks. A fifth domain of activities associated with high potential payoffs and fixed minor costs was also assessed. In contrast to other domains, women reported being more likely to engage in behaviors in this domain. This gender difference was partially mediated by women’s more optimistic judgments of the probability of good outcomes and of outcomes being more intensely positive.

We introduce a new three-stage process for calculating the zeros of a polynomial with real coefficients. The algorithm finds either a linear or quadratic factor, working completely in real arithmetic. In the third stage the algorithm uses one of two variable-shift iterations corresponding to the linear or quadratic case. The iteration for a linear factor is a real arithmetic version of the third stage of the algorithm for complex polynomials which we studied in an earlier paper. A new variable-shift iteration is introduced in this paper which is suitable for quadratic factors. If the complex algorithm and the new real algorithm are applied to the same real polynomial, then the real algorithm is about four times as fast. We prove that the mathematical algorithm always converges and show that the rate of convergence of the third stage is faster than second order. The problem and algorithm may be recast into matrix form. The third stage is a quadratic form of shifted inverse powering and a quadratic form of generalized Rayleigh iteration. The results of extensive testing are summarized. For an ALGOL W program run on an.IBM 360/67 we found that for polynomials ranging in degree from 20 to 50, the time required to calculate all zeros averaged 2n milliseconds. An ALGOL 60 implementation of the algorithm and a program which calculates a posteriori bounds on the zeros may be found in Jenkins' 1969 Stanford dissertation [2]. TABLE OF CONTENTS 1. Introduction 545 2. Fixed-shift K polynomials 546 3. A variable-shift iteration for a quadratic factor 550 4. Convergence of the variable-shift iteration for a quadratic factor 550 5. Rate of convergence 554 6. The three-stage algorithm 555 7. Proof of global convergence of the three-stage algorithm 557 8. Variable-shift iteration for a quadratic factor is quadratic generalized Rayleigh iteration 559 9. Computer implementation of the algorithm 561 10. Numerical results 564 Acknowledgment 566 References 566 1, Introduction. We introduce a new three-stage algorithm for calculating the zeros of a real polynomial P, P(z)= ai Zn-i, ao=l, a. 4:0, i=o P(z)-I (zpi) mi i=1 *

The state-of-the-art in polynomial zero finding algorithms and programs is briefly summarized.Our focus in this paper is on principles for testing such programs. We view testing as requiring The results of part of this testing are described in this paper.

The subroutine CPOLY is a Fortran program to find all the zeros of a complex polynomial by the three-stage complex algorithm described in Jenkins and Traub [4]. (An algorithm for real polynomials is given in [5].) The algorithm is similar in spirit to the two-stage algorithms studied by Traub [1, 2]. The program finds the zeros one at a time in roughly increasing order of modulus and deflates the polynomial to one of lower degree. The program is extremely fast and the timing is quite insensitive to the distribution of zeros. Extensive testing of an Algol version of the program, reported in Jenkins [3], has shown the program to be very reliable.

An important problem in the field of force-reflecting systems and telerobotics is poor rendering of contact, particularly of contact with stiff surfaces. There are numerous possible sources of poor performance, including poor contact models, sampling errors, and delays due to computation or data transmission. In this paper we examine effects due to sample-and-hold, which is a fundamental property of both the discrete domain and also of the sensors and power amplifiers used in a force-reflecting system. We propose sample-and-hold be generalized to sample-estimate-hold. We show why ordinary sample-and-hold generates an active contact interface, and provide ways of improving the feeling of the interface. We have developed a suite of numerical methods for improving the performance of rendering of surfaces by force reflection. We have conducted both simulations and experiments to demonstrate the efficacy of the proposed .scheme. Our contributions are a new method of digitally processing force data, and a systematic method for coupling force-processing systems that run at different rates.

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