A Sidon-type condition on set systems

Consider families of $k$-subsets (or blocks) on a ground set of size $v$. Recall that if all $t$-subsets occur with the same frequency $\lambda$, one obtains a $t$-design with index $\lambda$. On the other hand, if all $t$-subsets occur with different frequencies, such a family has been called (by Sarvate and others) a $t$-adesign. An elementary observation shows that such families always exist for $v > k \ge t$. Here, we study the smallest possible maximum frequency $\mu=\mu(t,k,v)$. The exact value of $\mu$ is noted for $t=1$ and an upper bound (best possible up to a constant multiple) is obtained for $t=2$ using PBD closure. Weaker, yet still reasonable asymptotic bounds on $\mu$ for higher $t$ follow from a probabilistic argument. Some connections are made with the famous Sidon problem of additive number theory.Comment: 6 page

Competing risks, left truncation and late entry effect in A-bomb survivors cohort

The cohort under study comprises A-bomb survivors residing in Hiroshima Prefecture since 1968. After this year, thousands of survivors were newly recognized every year. The aim of this study is to determine whether the survival experience of the late entrants to the cohort is significantly different from the registered population in 1968. Parametric models that account for left truncation and competing risks were developed by using sub-hazard functions. A Weibull distribution was used to determine the possible existence of a late entry effect in Hiroshima A-bomb survivors. The competing risks framework shows that there might be a late entry effect in the male and female groups. Our findings are congruent with previous studies analysing similar populations

The effects of team-skills training on transactive memory and performance

The existence of effective Transactive Memory Systems (TMS) in teams has been found to enhance task performance. Methods of developing Transactive Memory (TM) are therefore an important focus of research. This study aimed to explore one such method, the use of a generic team-skills training programme to develop TM and subsequent task performance. Sixteen three-member teams were all trained to complete a complex collaborative task, prior to which half the teams (n=8), completed a team-skills training programme. Results confirmed that those teams who had been trained to develop a range of team skills such as problem-solving, interpersonal relationships, goal setting and role allocation, evidenced significantly higher team skill, TM and performance than those who were not trained in such skills. Results are discussed with reference to the wider TM literature and the mechanisms through which team-skills training could facilitate the more rapid development of TM

Policy Barriers to School Improvement: What's Real and What's Imagined?

Some of the most promising reforms are happening where school leaders are thinking differently about how to get the strongest student outcomes from the limited resources available. But even principals who use their autonomy to aggressively reallocate resources say that persistent district, state, and federal barriers prohibit them from doing more.What are these barriers? What do they block principals from doing? Is there a way around them?CRPE researchers probed these questions with principals in three states (NH, CT, MD). These principals cited numerous district, state, and federal barriers standing in the way of school improvement. The barriers, 128 in all, fell into three categories: 1) barriers to instructional innovations, 2) barriers to allocating resources differently, and 3) barriers to improving teacher quality.Upon investigation, researchers found that principals have far more authority than they think. Only 31% of the barriers cited were "real" -- immovable statutes, policies, or managerial directives that bring the threat of real consequences if broken.The report recommends educating principals on the authority they already possess, to help them find workarounds to onerous rules. The report also outlines a number of specific state and district policy changes to grant schools the autonomy they need to improve student outcomes

Curculionidae and Chrysomelidae Found in Aquatic Habitats in Wisconsin

(excerpt) We became interested in aquatic weevils (Curculionidae) and leaf beetles (Chryso- melidae) during the Aquatic Entomology Course at the University of Wisconsin, in the spring of 1971. Many collections, taken from a variety of aquatic habitats in Wisconsin, contained weevils and leaf beetles. Most of the species were not fully treated in the keys found in aquatic entomology texts. We thought it would be useful to compile keys from the literature and present what is known of the distribution of these insects in Wisconsin. Nine species of weevils have been found in aquatic habitats in Wisconsin, representing seven genera, all belonging to the subtribe Hydronomi, and twenty-five species of leaf beetles, representing five genera in three subfamilies

The Effect of Base-Broadening Measures on Labor Supply and Investment: Considerations for Tax Reform

[Excerpt] This report attempts to show how options to broaden the tax base by placing limitations on itemized deductions can potentially work against the expansionary effects of reducing marginal tax rates. After base-broadening tax reform taxpayers may face lower statutory marginal rates but some taxpayers—those who itemize—may have more of their income is subject to tax, effectively increasing their marginal tax rates. The report also addresses other common base-broadening provisions that increase the effective marginal tax rate on the return to capital

A study to determine similarities and variances among medical-surgical nursing instructors in rating selected science principles underlying the nursing care of a patient with an ileostomy

Thesis (M.S.)--Boston Universit