University of California, Santa Barbara

About: University of California, Santa Barbara is a education organization based out in Santa Barbara, California, United States. It is known for research contribution in the topics: Population & Laser. The organization has 30281 authors who have published 80852 publications receiving 4626827 citations. The organization is also known as: UC Santa Barbara & UCSB.

Interdiffusion of PCBM and P3HT Reveals Miscibility in a Photovoltaically Active Blend

Abstract: Developing a better understanding of the evolution of morphology in plastic solar cells is the key to designing new materials and structures that achieve photoconversion efficiencies greater than 10% In the most extensively characterized system, the poly(3-hexyl thiophene) (P3HT):[6,6]-phenyl-C61-butyric-acid-methyl-ester (PCBM) bulk heterojunction, the origins and evolution of the blend morphology during processes such as thermal annealing are not well understood In this work, we use a model system, a bilayer of P3HT and PCBM, to develop a more complete understanding of the miscibility and diffusion of PCBM within P3HT during thermal annealing We find that PCBM aggregates and/or molecular species are miscible and mobile in disordered P3HT, without disrupting the ordered lamellar stacking of P3HT chains The fast diffusion of PCBM into the amorphous regions of P3HT suggests the favorability of mixing in this system, opposing the belief that phase-pure domains form in BHJs due to immiscibility of these two components

First M87 Event Horizon Telescope Results. III. Data Processing and Calibration

Abstract: We present the calibration and reduction of Event Horizon Telescope (EHT) 1.3 mm radio wavelength observations of the supermassive black hole candidate at the center of the radio galaxy M87 and the quasar 3C 279, taken during the 2017 April 5–11 observing campaign. These global very long baseline interferometric observations include for the first time the highly sensitive Atacama Large Millimeter/submillimeter Array (ALMA); reaching an angular resolution of 25 μas, with characteristic sensitivity limits of ~1 mJy on baselines to ALMA and ~10 mJy on other baselines. The observations present challenges for existing data processing tools, arising from the rapid atmospheric phase fluctuations, wide recording bandwidth, and highly heterogeneous array. In response, we developed three independent pipelines for phase calibration and fringe detection, each tailored to the specific needs of the EHT. The final data products include calibrated total intensity amplitude and phase information. They are validated through a series of quality assurance tests that show consistency across pipelines and set limits on baseline systematic errors of 2% in amplitude and 1° in phase. The M87 data reveal the presence of two nulls in correlated flux density at ~3.4 and ~8.3 Gλ and temporal evolution in closure quantities, indicating intrinsic variability of compact structure on a timescale of days, or several light-crossing times for a few billion solar-mass black hole. These measurements provide the first opportunity to image horizon-scale structure in M87.

NeTra: a toolbox for navigating large image databases

Abstract: We present here an implementation of NeTra, a prototype image retrieval system that uses color, texture, shape and spatial location information in segmented image regions to search and retrieve similar regions from the database. A distinguishing aspect of this system is its incorporation of a robust automated image segmentation algorithm that allows object- or region-based search. Image segmentation significantly improves the quality of image retrieval when images contain multiple complex objects. Images are segmented into homogeneous regions at the time, of ingest into the database, and image attributes that represent each of these regions are computed. In addition to image segmentation, other important components of the system include an efficient color representation, and indexing of color, texture, and shape features for fast search and retrieval. This representation allows the user to compose interesting queries such as "retrieve all images that contain regions that have the color of object A, texture of object B, shape of object C, and lie in the upper of the image", where the individual objects could be regions belonging to different images. A Java-based web implementation of NeTra is available at http://vivaldi.ece.ucsb.edu/Netra.

Linking litter calcium, earthworms and soil properties: a common garden test with 14 tree species

Abstract: Tree species can influence biogeochemistry through variation in the quantity and chemistry of their litter, and associated impacts on the soil heterotrophic community. However, the role that different plant traits play in these processes is not well understood, nor is it clear whether species effects on soils largely reflect a gymnosperm vs. angiosperm contrast. Using a replicated, long-term monoculture plot experiment, we examined variation in soils among 14 gymnosperm and angiosperm tree species 30 years after plot establishment, and assessed the role of litter chemistry vis-a`-vis such variation. Differences in litter calcium concentrations among tree species resulted in profound changes in soil acidity and fertility that were similar within and among tree groups. Tree species rich in calcium were associated with increased native earthworm abundance and diversity, as well as increased soil pH, exchangeable calcium, per cent base saturation and forest floor turnover rate.