The rate of colonization by macro-invertebrates on artificial substrate samplers

The influence of exposure time upon macro-invertebrate colonization on modified Hester-Dendy substrate samplers was investigated over a 60-day period. The duration of exposure affected the number of individuals, taxa and community diversity. The numbers of individuals colonizing the samplers reached a maximum after 39 days and then began to decrease, due to the emergence of adult insects. Coefficients of variation for the four replicate samples retrieved each sampling day fluctuated extensively throughout the study. No tendencies toward increasing or decreasing coefficients of variation were noted with increasing time of sampler exposure. The number of taxa colonizing the samplers increased throughout the study period. The community diversity index was calculated for each sampling day and this function tended to increase throughout the same period. This supports the hypothesis that an exposure period of 6 weeks, as recommended by the United States Environmental Protection Agency, may not always provide adequate opportunity for a truly representative community of macro-invertebrates to colonize multiplate samplers. Many of the taxa were collected in quite substantial proportions after periods of absence or extreme sparseness. This is attributed to the growth of periphyton and the collection of other materials that created food and new habitats suitable for the colonization of new taxa. Investigation of the relationship between ‘equitability’ and length of exposure revealed that equitability did not vary like diversity with increased time of exposure.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72073/1/j.1365-2427.1979.tb01522.x.pd

Letter from W. T. Sinclair to I. M. Terrell

Copy of a letter to I. M. Terrell from W. T. Sinclair concerning a $100.00 donation from Mr. Joseph S. Cullinan to the Houston College

Robust antiferromagnetism and structural disorder in Bi_xCa_1-xFeO₃ perovskites

An investigation of Ca substitution in the multiferroic material BiFeO3 shows that a wide range of perovskites BixCa1-xFeO3 (0.4 &lt;= x &lt;= 1.0) can be prepared by sintering in air at 810-960 degrees C. 0.4 &lt;= x &lt; 0.8 samples are cubic Pm&lt;(3)over bar&gt;m, whereas x = 0.8 and 0.9 show a coexistence of the cubic and the rhombohedral R3c BiFeO3-type structure. Considerable disorder arising from Bi3+ lone-pair distortions is evidenced by synchrotron X-ray and neutron studies of the average structures of the cubic phases, and electron microscopy reveals commensurate and incommensurate local superstructures. The BixCa1-xFeO3 (0.4 &lt;= x &lt;= 1.0) materials show a remarkably robust antiferromagnetic order with T-N = 623-643 K and ordered moments of 3.6-4.1 mu(B). They are "leaky" dielectrics with relative permittivities of similar to 30-100 and bulk resistivities similar to 50-500 k Omega cm at room temperature. The activation energy for bulk conduction increases from 0.27 eV for x = 0.4 to 0.5 eV for x = 1, but with a discontinuity at the cubic-rhombohedral boundary. Further processing of the x = 0.8 and 0.9 compositions to reduce conductivity through control of oxygen content could lead to improved BiFeO3-based multiferroics.</p

Simple permutations mix well

We study the random composition of a small family of O(n 3) simple permutations on {0, 1} n. Specifically we ask what is the number of compositions needed to achieve a permutation that is close to k-wise independent. We improve on a result of Gowers [7] and show that up to a polylogarithmic factor, n 3 k 3 compositions of random permutations from this family suffice. Additionally, we introduce a new notion analogous to closeness to k-wise independence against adaptive adversaries and show the constructed permutation has the stronger property. This question is essentially about the rapid mixing of the random walk on a certain graph which we establish using a new approach to construct the so called canonical paths, which may be of independent interest. We also show that if we are willing to use a much larger family of simple permutations then we can guaranty closeness to k-wise independence with fewer compositions and fewer random bits.