1,720,983 research outputs found
PARSIVEL snow observations: A critical assessment
Full text linkThe performance of the laser-optical Particle Size Velocity (PARSIVEL) disdrometer is evaluated to determine the characteristics of falling snow. PARSIVEL's measuring principle is reexamined to detect its limitations and pitfalls when applied to solid precipitation. This study uses snow observations taken during the Canadian Cloudsat/Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) Validation Project (C3VP) campaign, when two PARSIVEL instruments were collocated with a single two-dimensional disdrometer (2-DVD), which allows more detailed observation of snowflakes. When characterizing the snowflake size, PARSIVEL instruments inherently retrieve only one size parameter, which is approximately equal to the widest horizontal dimension (more accurately with large snowflakes) and that has no microphysical meaning. Unlike for raindrops, the equivolume PARSIVEL diameter-the PARSIVEL output variable-has no physical counterpart for snowflakes. PARSIVEL's fall velocity measurement may not be accurate for a single snowflake particle. This is due to the internally assumed relationship between horizontal and vertical snow particle dimensions. The uncertainty originates from the shape-related factor, which tends to depart more and more from unity with increasing snowflake sizes and can produce large errors. When averaging over a large number of snowflakes, the correction factor is size dependent with a systematic tendency to an underestimation of the fall speed (but never exceeding 20%). Compared to a collocated 2-DVD for long-lasting events, PARSIVEL seems to overestimate the number of small snowflakes and large particles. The disagreement between PARSIVEL and 2-DVD snow measurements can only be partly ascribed to PARSIVEL intrinsic limitations (border effects and sizing problems), but it has to deal with the difficulties and drawbacks of both instruments in fully characterizing snow properties. © 2010 American Meteorological Society
Evolution of drop size distribution in natural rain
Full text linkBoth numerical modeling and laboratory experiments document the possibility of a raindrop size distribution
(DSD) to evolve to an equilibrium stage (EDSD), where all the principal processes occur at steady rates.
The aim of this work is to observe the temporal behavior of the DSD and to directly investigate the conditions
favorable to the onset of the EDSD in natural rain. We exploited a large disdrometer dataset collected in the
framework of the Ground Validation activities related to the NASA Global Precipitation Measurement mission.
More than 200,000 one-minute data of two-dimensional video disdrometer (2DVD) are collected over USA to
represent a wide range of precipitation types. The original data are averaged over 2 min and an automatic
algorithm is used on a selected subset to identify samples with EDSD. Results show that the EDSD occurs mainly
in convective events and lasts for very short time intervals (2 to 4 min). It is more frequent for rain rate between
20 and 40 mm h−1 and it mostly occurs during sharp increase of precipitation rates
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Spatial Variability of Raindrop Size Distribution during MC3E
No full textThe retrieval of raindrop size distribution (DSD) from dual frequency precipitation radar (DPR) on board the
NASA’s Global Precipitation Measurement (GPM) core satellite is one of the key objectives of GPM mission.
The DPR algorithm developers adopted three-parameter gamma distribution and suggested methodologies for the
DSD retrieval process. The footprint of the DPR is nearly circular with approximately 5 km diameter and the DSD
variability within the footprint is one of the uncertainties of the retrieved size distribution. The highly variable
nature of DSD is also evident in retrieved precipitation estimates from ground-based radars.
This study investigates the spatial variability of DSD at two different spatial scales. The small-scale variability
of DSD was studied through disdrometer measurements at NASA-MC3E (Mid-latitude Continental Convective
Clouds Experiment) and compared with results from NASA Wallops Flight Facility (WFF) disdrometer measurements.
Seven two-dimensional video disdrometers (2DVD) were installed, and the distances between each
couple of instruments ranges from 0.4 to 9.2 km. A three-parameter exponential function was used to investigate
the spatial variability of fifteen DSD parameters. The correlation distance and the shape parameter of the function
was estimated for each parameter. The RMSE gives an indication about the goodness of the fit. The results were
compared with which obtained at WFF, where the twelve disdrometers installed (six 2DVD and six Parsivel2) had
a maximum distance of 2.3 km.
The results obtained are the first present in literature from high quality disdrometer network at two different
small scales. The results show that the most of DSD parameters are correlated within a satellite footprint or radar
pixel. The DSD integral parameters (i.e. RR, LWC, Z, etc.) have, generally, lower correlation distance than DSD
parameters (i.e. Dmass, Dmax, Nw, etc.)
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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