5,361 research outputs found
From white elephant to Nobel Prize: Dennis Gaborâs wavefront reconstruction
Dennis Gabor devised a new concept for optical imaging in 1947 that went by a variety of names over the following decade: holoscopy, wavefront reconstruction, interference microscopy, diffraction microscopy and Gaboroscopy. A well-connected and creative research engineer, Gabor worked actively to publicize and exploit his concept, but the scheme failed to capture the interest of many researchers. Gaborâs theory was repeatedly deemed unintuitive and baffling; the technique was appraised by his contemporaries to be of dubious practicality and, at best, constrained to a narrow branch of science. By the late 1950s, Gaborâs subject had been assessed by its handful of practitioners to be a white elephant. Nevertheless, the concept was later rehabilitated by the research of Emmett Leith and Juris Upatnieks at the University of Michigan, and Yury Denisyuk at the Vavilov Institute in Leningrad. What had been judged a failure was recast as a success: evaluations of Gaborâs work were transformed during the 1960s, when it was represented as the foundation on which to construct the new and distinctly different subject of holography, a re-evaluation that gained the Nobel Prize for Physics for Gabor alone in 1971. This paper focuses on the difficulties experienced in constructing a meaningful subject, a practical application and a viable technical community from Gaborâs ideas during the decade 1947-1957
On interpretations and constructions of classical dynamical r-matrices
In this note we complement recent results on the exchange -matrices
appearing in the chiral WZNW model by providing a direct, purely
finite-dimensional description of the relationship between the monodromy
dependent 2-form that enters the chiral WZNW symplectic form and the exchange
-matrix that governs the corresponding Poisson brackets. We also develop the
special case in which the exchange -matrix becomes the `canonical' solution
of the classical dynamical Yang-Baxter equation on an arbitrary self-dual Lie
algebra.Comment: 8 pages, LaTeX, based on a talk given by L.F. at the QTS2 symposium,
18-21 July 2001, Krakow, Poland. References are updated, and a typo is
removed in v2; a misprint in equation (A.13) is corrected in v
Predators do not spill over from forest fragments to maize fields in a landscape mosaic in central Argentina
South America is undergoing a rapid and large scale conversion of natural habitats to cultivated land. Ecosystem services (ESs) still remain important but their level and sustainability are not known. We quantified predation intensity in an Argentinian agricultural landscape containing remnants of the original chaco serrano forest by using artificial sentinel prey. We sought to identify the main predators, and the effect of landscape configuration and maize phenology on predation pressure by invertebrate and vertebrate predators in this landscape. The most common predators were chewing insects (50.4% predation events), birds (22.7%), and ants (17.5%). Overall predation rates in forest fragments (41.6% d-1) were significantly higher than in the surrounding maize fields (21.5% d-1). Invertebrate predation was higher inside and at the edge of forest fragments than within fields, and did not change with increasing distance from a fragment edge, indicating a lack of spillover from the native habitat remnants to the cultivated matrix at the local scale. Distance from a continuous forest had a positive impact on predation by invertebrates and a negative impact on vertebrate predation.Fil: Ferrante, Marco. Aarhus University. Flakkebjerg Research Centre. Department of Agroecology; DinamarcaFil: GonzĂĄlez, Ezequiel. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - CĂłrdoba. Instituto Multidisciplinario de BiologĂa Vegetal. Universidad Nacional de CĂłrdoba. Facultad de Ciencias Exactas FĂsicas y Naturales. Instituto Multidisciplinario de BiologĂa Vegetal; ArgentinaFil: Gabor L., Lovei. Aarhus University. Flakkebjerg Research Centre. Department of Agroecology; Dinamarc
Ultrafast photocurrent measurement of the escape time of electrons and holes from carbon nanotube PN junction photodiodes
Ultrafast photocurrent measurements are performed on individual carbon
nanotube PN junction photodiodes. The photocurrent response to sub-picosecond
pulses separated by a variable time delay {\Delta}t shows strong photocurrent
suppression when two pulses overlap ({\Delta}t = 0). The picosecond-scale decay
time of photocurrent suppression scales inversely with the applied bias VSD,
and is twice as long for photon energy above the second subband E22 as compared
to lower energy. The observed photocurrent behavior is well described by an
escape time model that accounts for carrier effective mass.Comment: 8 pages Main text, 4 Figure
Resolving environmental drivers of microbial community structure in Antarctic soils
Antarctic soils are extremely cold, dry, and oligotrophic, yet harbour surprisingly high bacterial diversity. The severity of environmental conditions has constrained the development of multi-trophic communities, and species richness and distribution is thought to be driven primarily by abiotic factors. Sites in northern and southern Victoria Land were sampled for bacterial community structure and soil physicochemical properties in conjunction with the US and New Zealand Latitudinal Gradient Project. Bacterial community structure was determined using a high-resolution molecular fingerprinting method for 80 soil samples from Taylor Valley and Cape Hallett sites which are separated by five degrees of latitude and have distinct soil chemistry. Taylor Valley is part of the McMurdo Dry Valleys, while Cape Hallett is the site of a penguin rookery and contains ornithogenic soils. The influence of soil moisture, pH, conductivity, ammonia, nitrate, total nitrogen and organic carbon on community structure was revealed using Spearman rank correlation, Mantel test, and principal components analysis. High spatial variability was detected in bacterial communities and community structure was correlated with soil moisture and pH. Both unique and shared bacterial community members were detected at Taylor Valley and Cape Hallett despite the considerable distance between the sites
- âŠ