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Vitrification of mammalian spermatozoa in the absence of cryoprotectants: from past practical difficulties to present success
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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
Developmental rate and ultrastructure of vitrified human pronuclear oocytes after step-wise versus direct rehydration
No full textAbstract
BACKGROUND:
This study compared the viability of human pronuclear oocytes subjected to vitrification followed by post-thaw step-wise removal of cryoprotectants versus direct rehydration, in terms of their subsequent in vitro survival and ultrastructural features.
METHODS:
A total of 115 three-pronuclei stage oocytes were cryopreserved in super-open-pulled straws by vitrification in 40% ethylene glycol + 0.75 mol/l sucrose for either 1 min or 10 s at 38 degrees C, followed by direct plunging into liquid nitrogen. After thawing, oocytes vitrified for 1 min (group 1) or 10 s (group 2) were expelled into a graded series of sucrose solutions (1.0, 0.75, 0.5, 0.25 and 0.12 mol/l) for removal of the cryoprotectant in five 2.5 min steps. A second batch of oocytes vitrified for either 1 min (group 3) or 10 s (group 4) were directly expelled into culture medium at 38 degrees C after thawing. Finally, the ultrastructural changes occurring in oocytes in each of the treatment groups were evaluated.
RESULTS:
Oocyte development (division to two-blastomere stage) rates after in vitro culture were 82, 83, 0 and 0% for groups 1, 2, 3 and 4, respectively. The harsh osmotic process involved in direct rehydration provoked ultrastructural changes, including the disruption of cytoplasmic and pronuclear membranes as well as intracellular organelles.
CONCLUSION:
The direct post-thaw rehydration of human pronuclear oocytes has lethal osmotic effects, such that protocols for vitrifying human pronuclear oocytes should include the step-wise removal of the cryoprotectant
DNA integrity and motility of human spermatozoa after standard slow freezing versus cryoprotectant-free vitrification
No full textAbstract
BACKGROUND:
In contrast to the technique of conventional freezing, the vitrification of spermatozoa requires high cooling rates (720 000 degrees K/min), which could be damaging for spermatozoa. The aim of our study was to compare slowly frozen and vitrified spermatozoa in terms of their post-thaw DNA integrity and motility.
METHODS:
Semen samples were prepared according to the routine swim-up technique and divided into aliquots for comparison of fresh, conventionally frozen and vitrified spermatozoa from the same ejaculate in the presence or absence of cryoprotectants. Spermatozoa motility and DNA integrity were determined.
RESULTS:
The motility of spermatozoa conventionally (slowly) frozen with a cryoprotectant was similar to that recorded for spermatozoa vitrified in the absence of cryoprotectant (47 versus 52%). The DNA integrity was unaffected by the cryopreservation method or presence of cryoprotectants.
CONCLUSION:
The vitrification of human spermatozoa in the absence of conventional cryoprotectants is indeed feasible. The DNA integrity of vitrified sperm is comparable with that shown by standard slow-frozen/thawed spermatozoa, yet the method is quick and simple and does not require special cryobiological equipment
Cryoprotectant-free cryopreservation of human spermatozoa by vitrification and freezing in vapor: effect on motility, DNA integrity, and fertilization ability
No full textAbstract
Human spermatozoa can be successfully cryopreserved avoiding the use of cryoprotectants through vitrification at very high cooling rates (up to 7.2 x 10(5) degrees C/min). This is achieved by directly plunging a copper cryoloop loaded with a sperm suspension into liquid nitrogen. After storage, vitrified spermatozoa are instantly thawed by melting in an agitated, warm medium. The goal of the present study was to compare the quality of spermatozoa cryopreserved using this rapid vitrification method with that of spermatozoa cooled relatively slowly by preexposure of the loaded cryoloop to liquid nitrogen vapor (-160 degrees C) with speed in the range 150-250 degrees C/min) before immersion into liquid nitrogen. Both cooling modes led to comparable results in terms of the motility, fertilization ability, and DNA integrity of the warmed spermatozoa. In both cases, instant thawing by melting in a warm medium was essential for successful cryopreservation. Our findings suggest that optimal regimes for the cryoprotectant-free cryopreservation of spermatozoa need not be restricted to very fast cooling before storage in liquid nitrogen, a wide range of cooling rates being acceptable. Herein, we discuss the implications of this finding in the light of the physics of extra- and intracellular vitrification
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
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