1,720,970 research outputs found
Polychromatic polarization: Boosting the capabilities of the good old petrographic microscope
Get PDFPolychromatic polarizing microscopy (PPM) is a new optical technique that allows for the inspection of materials with low birefringence, which produces retardance between 1 nm and 300 nm. In this region, where minerals display interference colors in the near-black to gray scale and where observations by conventional microscopy are limited or hampered, PPM produces a full spectrum color palette in which the hue depends on orientation of the slow axis. We applied PPM to ordinary 30 μ.m rock thin sections, with particular interest in the subtle birefringence of garnet due both to non-isotropic growth or to strain induced by external stresses or inclusions. The PPM produces striking, colorful images that highlight various types of microstructures that are virtually undetectable by conventional polarizing microscopy. PPM opens new avenues for microstructural analysis of geological materials. The direct detection and imaging of microstructures will provide a fast, non-destructive, and inexpe..
The common morphospecies Cypridopsis vidua (O.F. MÜLLER, 1776) (Crustacea, Ostracoda) is not an obligate parthenogen
No full textThe common non-marine ostracod Cypridopsis vidua (O.F. Müller, 1776) is used as a proxy in various biological disciplines, such as (palaeo-)ecology, evolutionary biology, ecotoxicology and parasitology. This morphospecies was considered to be an obligate parthenogen. We report on the discovery of the first population of C. vidua with males from Woods Hole (MA, USA) and determine that it is a population with mixed reproduction. We describe the morphology of the males and of the sexual and asexual females. We illustrate a copula of a male and a sexual female as well insemination in a sexual female, showing that males are functional. Therefore, Cypridopsis vidua is a morphospecies with mixed reproduction, not a full apomictic parthenogen. We use, for the first time, polychromatic polarization microscope technology to illustrate soft parts of ostracods. In addition, we compare the sexual species C. bisexualis, C. okeechobei, C. howei and C. schwartzi and conclude that these species, especially the latter three, are morphologically very close to C. vidua
Polychromatic polarization microscope : bringing colors to a colorless world
Get PDF© The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 5 (2015): 17340, doi:10.1038/srep17340.Interference of two combined white light beams produces Newton colors if one of the beams is retarded relative to the other by from 400 nm to 2000 nm. In this case the corresponding interfering spectral components are added as two scalars at the beam combination. If the retardance is below 400 nm the two-beam interference produces grey shades only. The interference colors are widely used for analyzing birefringent samples in mineralogy. However, many of biological structures have retardance <100 nm. Therefore, cells and tissues under a regular polarization microscope are seen as grey image, which contrast disappears at certain orientations. Here we are proposing for the first time using vector interference of polarized light in which the full spectrum colors are created at retardance of several nanometers, with the hue determined by orientation of the birefringent structure. The previously colorless birefringent images of organelles, cells, and tissues become vividly colored. This approach can open up new possibilities for the study of biological specimens with weak birefringent structures, diagnosing various diseases, imaging low birefringent crystals, and creating new methods for controlling colors of the light beam.This publication was made possible by Grant Number R01-GM101701 from the National Institute of General Medical Sciences, National Institutes of Health
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
A Survey of Transposon Landscapes in the Putative Ancient Asexual Ostracod Darwinula stevensoni
No full textHow asexual reproduction shapes transposable element (TE) content and diversity in eukaryotic genomes remains debated. We performed an initial survey of TE load and diversity in the putative ancient asexual ostracod Darwinula stevensoni. We examined long contiguous stretches of DNA in clones from a genomic fosmid library, totaling about 2.5 Mb, and supplemented these data with results on TE abundance and diversity from an Illumina draft genome. In contrast to other TE studies in putatively ancient asexuals, which revealed relatively low TE content, we found that at least 19% of the fosmid dataset and 26% of the genome assembly corresponded to known transposons. We observed a high diversity of transposon families, including LINE, gypsy, PLE, mariner/Tc, hAT, CMC, Sola2, Ginger, Merlin, Harbinger, MITEs and helitrons, with the prevalence of DNA transposons. The predominantly low levels of sequence diversity indicate that many TEs are or have recently been active. In the fosmid data, no correlation was found between telomeric repeats and non-LTR retrotransposons, which are present near telomeres in other taxa. Most TEs in the fosmid data were located outside of introns and almost none were found in exons. We also report an N-terminal Myb/SANT-like DNA-binding domain in site-specific R4/Dong non-LTR retrotransposons. Although initial results on transposable loads need to be verified with high quality draft genomes, this study provides important first insights into TE dynamics in putative ancient asexual ostracods
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Quantitative orientation-independent differential interference contrast microscope with fast switching shear direction and bias modulation
Get PDFAuthor Posting. © Optical Society of America, 2013. This article is posted here by permission of Optical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Optical Society of America A: Optics, Image Science, and Vision 30 (2013): 769-782, doi:10.1364/JOSAA.30.000769.We describe a quantitative orientation-independent differential interference contrast (DIC) microscope, which allows bias retardation to be modulated and shear directions to be switched rapidly without any mechanical movement. The shear direction is switched by a regular liquid-crystal cell sandwiched between two standard DIC prisms. Another liquid-crystal cell modulates the bias. Techniques for measuring parameters of DIC prisms and calibrating the bias are shown. Two sets of raw DIC images with the orthogonal shear directions are captured within 1 s. Then the quantitative image of optical path gradient distribution within a thin optical section is computed. The gradient data are used to obtain a quantitative distribution of the optical path, which represents the refractive index gradient or height distribution. Computing enhanced regular DIC images with any desired shear direction is also possible.This publication was made possible
by Grant No. R01-GM101701 from the National Institute
of General Medical Sciences, National Institutes of Health
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