An Evening Spent with Bill van Zwet

Willem Rutger van Zwet was born in Leiden, the Netherlands, on March 31, 1934. He received his high school education at the Gymnasium Haganum in The Hague and obtained his Masters degree in Mathematics at the University of Leiden in 1959. After serving in the army for almost two years, he obtained his Ph.D. at the University of Amsterdam in 1964, with Jan Hemelrijk as advisor. In 1965, he was appointed Associate Professor of Statistics at the University of Leiden and promoted to Full Professor in 1968. He remained in Leiden until his retirement in 1999, while also serving as Associate Professor at the University of Oregon (1965), William Newman Professor at the University of North Carolina at Chapel Hill (1990--1996), frequent visitor and Miller Professor (1997) at the University of California at Berkeley, director of the Thomas Stieltjes Institute of Mathematics in the Netherlands (1992--1999), and founding director of the European research institute EURANDOM (1997--2000). At Leiden, he was Dean of the School of Mathematics and Natural Sciences (1982--1984). He served as chair of the scientific council and member of the board of the Mathematics Centre at Amsterdam (1983--1996) and the Leiden University Fund (1993--2005).Comment: Published in at http://dx.doi.org/10.1214/08-STS261 the Statistical Science (http://www.imstat.org/sts/) by the Institute of Mathematical Statistics (http://www.imstat.org

Demographic fluctuations in a population of anomalously diffusing individuals

The phenomenon of spatial clustering induced by death and reproduction in a population of anomalously diffusing individuals is studied analytically. The possibility of social behaviors affecting the migration strategies has been taken into exam, in the case anomalous diffusion is produced by means of a continuous time random walk (CTRW). In the case of independently diffusing individuals, the dynamics appears to coincide with that of (dying and reproducing) Brownian walkers. In the strongly social case, the dynamics coincides with that of non-migrating individuals. In both limits, the growth rate of the fluctuations becomes independent of the Hurst exponent of the CTRW. The social behaviors that arise when transport in a population is induced by a spatial distribution of random traps, have been analyzed.Comment: 10 pages, 6 figure

Inverted and mirror repeats in model nucleotide sequences

We analytically and numerically study the probabilistic properties of inverted and mirror repeats in model sequences of nucleic acids. We consider both perfect and non-perfect repeats, i.e. repeats with mismatches and gaps. The considered sequence models are independent identically distributed (i.i.d.) sequences, Markov processes and long range sequences. We show that the number of repeats in correlated sequences is significantly larger than in i.i.d. sequences and that this discrepancy increases exponentially with the repeat length for long range sequences.Comment: 12 pages, 6 figure

Do Chimpanzees ave Expectations About Reward Presentation Following Correct Performance on Computerized Cognitive Testing?

To investigate whether 2 chimpanzees had expectations regarding the outcome of their responses on a computerized task, food reward that typically was given for correct responses was withheld on some correctly completed trials. There were two types of these probe trials: those which the chimpanzees performed correctly on their own, and those during which the chimpanzees needed the experimenter\u27s assistance to complete the trial correctly. For both chimpanzees, reward procurement behaviors directed toward the experimenter occurred significantly more often on correctly completed probe trials than on incorrectly completed trials. This indicated increased expectation of food reward on correct trials as compared to incorrect trials. For 1 of the 2 chimpanzees, reward procurement behaviors were significantly more likely to occur on probe trials on which the chimpanzee received no assistance from the experimenter than on trials in which the experimenter assisted the chimpanzee. This behavioral difference was not predicated on reinforcement history, as all correctly completed nonprobe trials were rewarded whether or not assistance was provided by the experimenter. These data indicate that this chimpanzee may have a rudimentary sense of equity regarding what outcome should accompany the successful completion of trials that is dependent on the level of assistance provided by an experimenter during the trial

The Evolutionary and Developmental Foundations of Mathematics

Recent behavioral and neuroimaging studies with humans and monkeys provide compelling evidence of shared numerical capacities across species. Our understanding of the emergence of human mathematical competence is well-served by these kinds of comparative assessments

Animal Memory: Rats Bind Event Details into Episodic Memories

SummaryA recent study shows that rats remember multiple details of an event in a way that suggests those details are bound into episodic memories that the rats use when faced with a foraging task

High fidelity sorting of remarkably similar components via metal-mediated assembly.

Subtle differences in ligand coordination angle and rigidity lead to high fidelity sorting between individual components displaying identical coordination motifs upon metal-mediated self-assembly. Narcissistic self-sorting can be achieved between highly similar ligands that vary minimally in rigidity and internal coordination angle upon combination with Fe(ii) ions and 2-formylpyridine. Selective, sequential cage formation can be precisely controlled in a single flask from a mix of three different core ligands (and 33 total components) differing only in the hybridization of one group that is uninvolved in the metal coordination process

Fourth-grade teachers\u27 perceptions of Nebraska\u27s state standards process in elementary schools

The purpose of this study was to explore fourth-grade teachers\u27 perceptions of Nebraska\u27s state standards process. Specifically, research questions sought to determine fourth-grade teachers\u27 perceptions of the possible effects of state standards on schools, students, teachers, and administrators. The questions also explored any differences between subgroups based on teachers\u27 gender, teachers\u27 years of experience, schools\u27 socio-economic status, school enrollment, and percentage of students that have met the state standards