Characterizing Quantum-Dot Blinking Using Noise Power Spectra

Fluctuations in the fluorescence from macroscopic ensembles of colloidal semiconductor quantum dots have the spectral form of 1/f noise. The measured power spectral density reflects the fluorescence intermittency of individual dots with power-law distributions of "on" and "off" times, and can thus serve as a simple method for characterizing such blinking behavior

Leaf Area of Mature Northwestern Coniferous Forests: Relation to Site Water Balance

Leaf area of nature coniferous forest communities of western Oregon appears to be related primarily to site H2O balance rather than characteristics of tree species composing the community. Leaf areas were determined for stands in communities ranked along measured gradients of precipitation and evaporative potential. Nine coniferous and 1 deciduous tree species were found in the various stands along these gradients. Leaf areas of these stands were linearly correlated with a simple site H2O balance index computed from measurements of growing season precipitation, open pan evaporation, and estimates of soil H2O storage. Species composition had no apparent influence on the relation between community leaf area and site H2O balance

Daisy

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Multidimensional optical fractionation with holographic verification

The trajectories of colloidal particles driven through a periodic potential energy landscape can become kinetically locked in to directions dictated by the landscape's symmetries. When the landscape is realized with forces exerted by a structured light field, the path a given particle follows has been predicted to depend exquisitely sensitively on such properties as the particle's size and refractive index These predictions, however, have not been tested experimentally. Here, we describe measurements of colloidal silica spheres' transport through arrays of holographic optical traps that use holographic video microscopy to track individual spheres' motions in three dimensions and simultaneously to measure each sphere's radius and refractive index with part-per-thousand resolution. These measurements confirm previously untested predictions for the threshold of kinetically locked-in transport, and demonstrate the ability of optical fractionation to sort colloidal spheres with part-per-thousand resolution on multiple characteristics simultaneously.Comment: 4 pages, 2 figures. Accepted for publication in Physical Review Letter

Brownian Dynamics of a Sphere Between Parallel Walls

We describe direct imaging measurements of a colloidal sphere's diffusion between two parallel surfaces. The dynamics of this deceptively simple hydrodynamically coupled system have proved difficult to analyze. Comparison with approximate formulations of a confined sphere's hydrodynamic mobility reveals good agreement with both a leading-order superposition approximation as well as a more general all-images stokeslet analysis.Comment: 4 pages, 3 figures, REVTeX with PostScript figure

Elementary School Education in Rainforest Conservation and Reforestation in Mindanao, Philippines

A series of four interactive interdisciplinary (but based on science books0 for grades two through five were created to provide educational materials on tropical rainforests for elementary schools in the Philippines. The books were produced in conjunction with Philippine and American teachers, administrators, and science education consultants. They were then used and assessed for a year in actual classrooms in a variety of six Philippine schools in Mindanao. Comparative tests before and after using the materials were given to both teachers and students in participating schools. We observed highly significant measurable learning and improvements in understanding about rainforests. There was much variability in outcomes among the different schools. A highly significant general trend among students however, was for greater improvement (gain) for students who had lower pretest scores. That trend for individual students extended to the schools, which reduced the discrepancies between public rural mountain schools and schools in urban or city settings including a private city school

Reverse Civic and Legal Exclusions for Persons With Criminal Charges and Convictions

This policy action statement was developed by members of the network engaged in the Grand Challenge to Promote Smart Decarceration. The Grand Challenges initiative’s policy action statements present proposals emerging from Social Innovation for America’s Renewal, a policy conference organized by the Center for Social Development at Washington University in collaboration with theAmerican Academy of Social Work & Social Welfare, which is leading the Grand Challenges for Social Work initiative to champion social progress through a national agenda powered by science