1,324 research outputs found
Intracytoplasmic Sperm Injection after Vitrification of Immature Oocytes in Follicular Fluid Increases Bovine Embryo Production
Background: Despite the low efficiency caused by its harmful effects, vitrification is the technique of choice for oocyte cryopeservation, especially at the germinal vesicle (GV) stage. This enables the banking of female gametes without linkage to the male genotype. Follicular fluid (FF), in vivo, is known to provide an adequate environment to the immature oocyte. The intra-cytoplasmic sperm injection (ICSI), by the other hand, can be used to bypass any sperm penetration disorder, including the ones caused by cryopreservation. This study aimed to evaluate oocyte vitrification in FF based solution, and to asses ICSI efficiency in the fertilization of vitrified/warmed bovine GV oocytes.Material, Methods & Results: Follicles of 2-8 mm in diameter were aspirated from bovine ovaries obtained from a slaughterhouse, selected and maintained into FF from aspiration, until their allocation in the experimental groups. The FF used to prepare the vitrification solution was centrifuged, heat inactivated, filtered through a 0.22 mm pore and stored at -20°C. Oocyte vitrification was done into one of these three solutions: The standard solution TCM-Hepes (TH-Vitri) was compared to a totally FF based solution (FF-Vitri), and to a 50:50 (v/v) mix of both solutions (TH:FF-Vitri). Oocytes were submitted to in vitro embryo production in order to assess embryo production efficiency. A second set of experiments using the FF-Vitri solution compared IVF versus ICSI. With basis on cleaved structures, the morula + blastocyst rate obtained in the Fresh Control (43.9%) was similar to FF-Vitri (31.1%). Conversely, the TH-Vitri (15.7%) and the TH:FF-Vitri (20.4%) rates were significantly lower than the Fresh Control. ICSI showed a positive effect in comparison with IVF. The embryo development rate of Vitri-IVF (18.8%) was the lowest, whereas Vitri-ICSI (37.3%) was similar to the Fresh-IVF (43.9%), but lower than the Fresh-ICSI (57.8%).Discussion: Oocytes cryopreserved in TH based solution are known to show certain rigidity in the zona pellucida, being this event a possible cause to spermatozoa penetration disruption. Our results agree with that, since the fertilization rate for TH-Vitri was significantly lower than for the FF-Vitri. In contrast, GV oocytes vitrified in total versus partial FF based solution showed similar maturation and fertilization rates as the Fresh Control, evidencing the beneficial effect of FF during the course of vitrification. It is possible that FF helped to adjust oocyte maturation, allowing a better nuclear-cytoplasmic synchrony. Also, it might have provided some protection due to its antioxidant properties. The releasing of cortical granules induced by freezing, lead to a zona pellucida hardening and failure in sperm penetration. Factors present in the FF might block this premature releasing of cortical granules, thus ensuring that the egg retains its ability to be fertilized after maturation. The blastocysts produced from the FF-Vitri oocytes were the only ones that had the average ICM similar to the Fresh Control, evidencing that besides the similarity in morula + blastocyst rates, the embryos derived from oocytes vitrified in FF solution have also yielded best quality. When vitrified warmed oocytes were submitted to ICSI, there was an increase in the blastocyst production. This increment of embryo production with ICSI evidences a pathway to overcome the zona pellucida biological barrier. In conclusion, the use of FF as base for vitrification solution improves further embryo development; ICSI increases the embryo production of vitrified/warmed bovine GV stage oocytes
Absolute Objects and Counterexamples: Jones-Geroch Dust, Torretti Constant Curvature, Tetrad-Spinor, and Scalar Density
James L. Anderson analyzed the novelty of Einstein's theory of gravity as its
lack of "absolute objects." Michael Friedman's related work has been criticized
by Roger Jones and Robert Geroch for implausibly admitting as absolute the
timelike 4-velocity field of dust in cosmological models in Einstein's theory.
Using the Rosen-Sorkin Lagrange multiplier trick, I complete Anna Maidens's
argument that the problem is not solved by prohibiting variation of absolute
objects in an action principle. Recalling Anderson's proscription of
"irrelevant" variables, I generalize that proscription to locally irrelevant
variables that do no work in some places in some models. This move vindicates
Friedman's intuitions and removes the Jones-Geroch counterexample: some regions
of some models of gravity with dust are dust-free and so naturally lack a
timelike 4-velocity, so diffeomorphic equivalence to (1,0,0,0) is spoiled.
Torretti's example involving constant curvature spaces is shown to have an
absolute object on Anderson's analysis, viz., the conformal spatial metric
density. The previously neglected threat of an absolute object from an
orthonormal tetrad used for coupling spinors to gravity appears resolvable by
eliminating irrelevant fields. However, given Anderson's definition, GTR itself
has an absolute object (as Robert Geroch has observed recently): a change of
variables to a conformal metric density and a scalar density shows that the
latter is absolute.Comment: Minor editing, small content additions, added references. Forthcoming
in_Studies in History and Philosophy of Modern Physics_, June 200
Proposing new variables for the identification of strategic groups in franchising
The identification of strategic groups in the Spanish franchising area is the
main aim of this study. The authors have added some new strategic variables (not
used before) to the study and have classified franchisors between sectors and
distribution strategy. The results reveal the existence of four perfectly differentiated
strategic groups (types of franchisors). One of the major implications of this study is
that the variables that build a strategic group vary depending on the respective sector the network operates in and its distribution strategy. This fact indicates that including sector and distribution strategy is absolutely necessary to achieve good classifications of franchisor type
Silica in Protoplanetary Disks
Mid-infrared spectra of a few T Tauri stars (TTS) taken with the Infrared
Spectrograph (IRS) on board the Spitzer Space Telescope show prominent narrow
emission features indicating silica (crystalline silicon dioxide). Silica is
not a major constituent of the interstellar medium; therefore, any silica
present in the circumstellar protoplanetary disks of TTS must be largely the
result of processing of primitive dust material in the disks surrouding these
stars. We model the silica emission features in our spectra using the opacities
of various polymorphs of silica and their amorphous versions computed from
earth-based laboratory measurements. This modeling indicates that the two
polymorphs of silica, tridymite and cristobalite, which form at successively
higher temperatures and low pressures, are the dominant forms of silica in the
TTS of our sample. These high temperature, low pressure polymorphs of silica
present in protoplanetary disks are consistent with a grain composed mostly of
tridymite named Ada found in the cometary dust samples collected from the
STARDUST mission to Comet 81P/Wild 2. The silica in these protoplanetary disks
may arise from incongruent melting of enstatite or from incongruent melting of
amorphous pyroxene, the latter being analogous to the former. The high
temperatures of 1200K-1300K and rapid cooling required to crystallize tridymite
or cristobalite set constraints on the mechanisms that could have formed the
silica in these protoplanetary disks, suggestive of processing of these grains
during the transient heating events hypothesized to create chondrules.Comment: 47 pages, 9 figures, to appear in the 1 January, 2009 issue of the
Astrophysical Journa
âWhat are you going to do, confiscate their passports?â Professional perspectives on cross-border reproductive travel
Objective: This article reports findings from a UK-based study which explored the phenomenon of overseas travel for fertility treatment. The first phase of this project aimed to explore how infertility clinicians and others professionally involved in fertility treatment understand the nature and consequences of cross-border reproductive travel. Background: There are indications that, for a variety of reasons, people from the UK are increasingly travelling across national borders to access assisted reproductive technologies. While research with patients is growing, little is known about how âfertility tourismâ is perceived by health professionals and others with a close association with infertility patients. Methods: Using an interpretivist approach, this exploratory research included focussed discussions with 20 people professionally knowledgeable about patients who had either been abroad or were considering having treatment outside the UK. Semi-structured interviews were recorded, transcribed verbatim and subjected to a thematic analysis. Results: Three conceptual categories are developed from the data: âthe autonomous patientâ; âcross-border travel as riskâ, and âprofessional responsibilities in harm minimisationâ. Professionals construct nuanced, complex and sometimes contradictory narratives of the âfertility travellerâ, as vulnerable and knowledgeable; as engaged in risky behaviour and in its active minimisation. Conclusions: There is little support for the suggestion that states should seek to prevent cross-border treatment. Rather, an argument is made for less direct strategies to safeguard patient interests. Further research is required to assess the impact of professional views and actions on patient choices and patient experiences of treatment, before, during and after travelling abroad
To copy or to innovate? The role of personality and social networks on children's learning strategies
In our technologically complex world, children frequently have problems to solve and skills to learn. They can develop solutions through learning strategies involving social learning or asocial endeavors. While evidence is emerging that children may differ individually in their propensity to adopt different learning strategies, little is known about what underlies these differences. In this article, we reflect on recent research with children, adults, and nonhuman animals regarding individual differences in learning strategies. We suggest that characteristics of children's personalities and children's positions in their social networks are pertinent to individual differences in their learning strategies. These are likely pivotal factors in the learning strategies children adopt, and thus can help us understand who copies and who innovates, an important question for cultural evolution. We also discuss how methodological issues constrain developmental researchers in this field and provide suggestions for ongoing work
The relativity of inertia and reality of nothing
We first see that the inertia of Newtonian mechanics is absolute and
troublesome. General relativity can be viewed as Einstein's attempt to remedy,
by making inertia relative, to matter---perhaps imperfectly though, as at least
a couple of freedom degrees separate inertia from matter in his theory. We
consider ways the relationist (for whom it is of course unwelcome) can try to
overcome such undetermination, dismissing it as physically meaningless,
especially by insisting on the right transformation properties.Comment: This is the best version available (the Studies version having
suffered the many initiatives of an imaginative and zealous typesetter
Habitat continuity and stepping-stone oceanographic distances explain population genetic connectivity of the brown alga Cystoseira amentacea
Effective predictive and management approaches for species occurring in a metapopulation structure require good understanding of interpopulation connectivity. In this study, we ask whether population genetic structure of marine species with fragmented distributions can be predicted by stepping-stone oceanographic transport and habitat continuity, using as model an ecosystem-structuring brown alga, Cystoseira amentacea var. stricta. To answer this question, we analysed the genetic structure and estimated the connectivity of populations along discontinuous rocky habitat patches in southern Italy, using microsatellite markers at multiple scales. In addition, we modelled the effect of rocky habitat continuity and ocean circulation on gene flow by simulating Lagrangian particle dispersal based on ocean surface currents allowing multigenerational stepping-stone dynamics. Populations were highly differentiated, at scales from few metres up to thousands of kilometres. The best possible model fit to explain the genetic results combined current direction, rocky habitat extension and distance along the coast among rocky sites. We conclude that a combination of variable suitable habitat and oceanographic transport is a useful predictor of genetic structure. This relationship provides insight into the mechanisms of dispersal and the role of life-history traits. Our results highlight the importance of spatially explicit modelling of stepping-stone dynamics and oceanographic directional transport coupled with habitat suitability, to better describe and predict marine population structure and differentiation. This study also suggests the appropriate spatial scales for the conservation, restoration and management of species that are increasingly affected by habitat modifications.MARES Grant (Doctoral Programme in Marine Ecosystem Health and Conservation) [EU-512002-1-2010-1-BE-EMJD]; Ghent University [FPA 2011-0016]; FCT (Portugal); project TETRIS; [SFRH/BPD/63703/2009]; [SFRH/BPD/107878/2015]; [SFRH/BPD/111003/2015]info:eu-repo/semantics/publishedVersio
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