183 research outputs found
Mitochondrial dysfunction and oxidative stress caused by cryopreservation in reproductive cells
Mitochondria, fundamental organelles in cell metabolism, and ATP synthesis are respon-sible for generating reactive oxygen species (ROS), calcium homeostasis, and cell death. Mitochon-dria produce most ROS, and when levels exceed the antioxidant defenses, oxidative stress (OS) is generated. These changes may eventually impair the electron transport chain, resulting in decreased ATP synthesis, increased ROS production, altered mitochondrial membrane permeability, and dis-ruption of calcium homeostasis. Mitochondria play a key role in the gamete competence to facilitate normal embryo development. However, iatrogenic factors in assisted reproductive technologies (ART) may affect their functional competence, leading to an abnormal reproductive outcome. Cry-opreservation, a fundamental technology in ART, may compromise mitochondrial function leading to elevated intracellular OS that decreases sperm and oocytes’ competence and the dynamics of fertilization and embryo development. This article aims to review the role played by mitochondria and ROS in sperm and oocyte function and the close, biunivocal relationships between mitochon-drial damage and ROS generation during cryopreservation of gametes and gonadal tissues in different species. Based on current literature, we propose tentative hypothesis of mechanisms involved in cryopreservation-associated mitochondrial dysfunction in gametes, and discuss the role played by antioxidants and other agents to retain the competence of cryopreserved reproductive cells and tissues
On the Thermodynamic Limit in Random Resistors Networks
We study a random resistors network model on a euclidean geometry \bt{Z}^d.
We formulate the model in terms of a variational principle and show that, under
appropriate boundary conditions, the thermodynamic limit of the dissipation per
unit volume is finite almost surely and in the mean. Moreover, we show that for
a particular thermodynamic limit the result is also independent of the boundary
conditions.Comment: 14 pages, LaTeX IOP journal preprint style file `ioplppt.sty',
revised version to appear in Journal of Physics
Variación ontogenética en la histología ósea de Caypullisaurus bonapartei Fernández, 1997 (Ichthyosauria: Ophthalmosauridae)
Fil: Talevi, Marianella. Universidad Nacional de Río Negro. Instituto de Investigación en Paleobiología y Geología. Río Negro, Argentina.Fil: Fernández, Marta S. Universidad Nacional de La Plata. Museo de La Plata. División Paleontología de Vertebrados. Buenos Aires, Argentina.Fil: Salgado, Leonardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Buenos Aires, Argentina.Fil: Talevi, Marianella. Consejo Nacional de Investigaciones Científicas y Técnicas. Buenos Aires, Argentina.Fil: Fernández, Marta S. Consejo Nacional de Investigaciones Científicas y Técnicas. Buenos Aires, Argentina.Fil: Salgado, Leonardo. Universidad Nacional del Comahue. Museo de Geología y Paleontología. Neuquén, Argentina.ONTOGENETIC VARIATION IN THE BONE HISTOLOGY OF CAYPULLISAURUS BONAPARTEI FERNÁNDEZ, 1997 (ICHTHYOSAURIA: OPHTHALMOSAURIDAE). In order to explore the osteohistological ontogenetic variation in ichthyosaurs, we studied the bone microstructure of the ophtalmosaurid Caypullisaurus bonapartei Fernandez. The analyzed thin sections were obtained from three ribs belonging to different individuals (MLP85-I-15-1, 83-XI-15-1 and 83-XI-16-1), from the Vaca Muerta Formation (Tithonian,
Late Jurassic), in the Neuquén Basin (Argentina). The ontogenetic stages of these specimens have previously been determined based on the morphology of the humerus and the sclerotic rings. The first specimen is composed entirely of finely spongy tissue distributed around the medullary cavity. Microscopically, the spongy bone is secondary, with abundant inner spaces delimited by bone trabeculae. There are numerous overlapping generations of lamellar bone. The second specimen (a juvenile) shows primary spongy bone surrounding the medullary cavity and Sharpey’s fibers. The third specimen lacks a medullary cavity; instead, the medullary region is occupied by secondary spongy bone, uniformly distributed through the entire section. These results suggest that the macroscopic changes classically attributable to ontogeny have a correlation in bone microstructure. The bones of immature individuals show some primary bone, while the bones of the mature specimens are characterized by the exclusive presence of secondary bone. These features are easily identifiable, and provide an auxiliary criterion for the determination of ontogenetic stages in incomplete and fragmentary specimens.Con el objetivo de explorar las posibles modificaciones osteohistológicas atribuibles a variaciones ontogenéticas en ictiosaurios, se estudió la microestructura ósea del oftalmosáurido Caypullisaurus bonapartei Fernandez. Se seleccionaron y analizaron secciones delgadas obtenidas a partir de costillas de tres ejemplares (MLP85-I-15-1, 83-XI-15-1 y 83-XI-16-1) exhumados de la Formación Vaca Muerta (Titoniano,
Jurásico Tardío) en la Cuenca Neuquina (Argentina). El estado madurativo de estos ejemplares había sido determinado previamente con base en la morfología del húmero y de los anillos escleróticos. Las secciones correspondientes al primer ejemplar se componen por un tejido esponjoso que se distribuye uniformemente alrededor de la cavidad medular. Microscópicamente, el hueso esponjoso es de origen secundario con abundantes espacios internos delimitados por trabéculas óseas donde se observan numerosas generaciones de tejido lamelar superpuestas entre sí. En el segundo ejemplar (juvenil) se observa un tejido esponjoso de origen primario rodeando la cavidad medular y se observan fibras de Sharpey. En el tercer ejemplar, la cavidad medular se encuentra ocupada por un tejido esponjoso secundario que se distribuye uniformemente en toda la sección. Estos resultados sugieren que las modificaciones macroscópicas clásicamente atribuibles a la ontogenia tienen un correlato en la microestructura ósea. Así, en los huesos de individuos inmaduros se observa la presencia de tejido primario, en tanto que los huesos de los individuos maduros están caracterizados por la presencia de tejido remodelado. Estas características son claramente identificables y brindan un criterio auxiliar para la determinación de estadios ontogenéticos cuando no se cuenta con material
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Light hadron spectroscopy with O(a) improved dynamical fermions
We present the first results for the static quark potential and the light
hadron spectrum using dynamical fermions at using an O(a) improved
Wilson fermion action together with the standard Wilson plaquette action for
the gauge part. Sea quark masses were chosen such that the pseudoscalar-vector
mass ratio, m_PS/m_V$, varies from 0.86 to 0.67. Finite-size effects are
studied by using three different volumes, 8^3\cdot 24, 12^3\cdot 24 and
16^3\cdot 24. Comparing our results to previous ones obtained using the
quenched approximation, we find evidence for sea quark effects in quantities
like the static quark potential and the vector-pseudoscalar hyperfine
splitting.Comment: 38 pages, 14 Postscript figure, LaTe
Non-perturbative improvement of operators with Wilson fermions
We outline two methods of constructing improved composite operators using Wilson fermions
Non-perturbative improvement of composite operators with Wilson fermions
We propose a method to improve lattice operators composed of Wilson fermions
which allows the removal of all corrections of , including those
proportional to the quark mass, leaving only errors of . The method
exploits the fact that chiral symmetry is restored at short distances. By
imposing this requirement on correlation functions of improved lattice
operators at short distances, the coefficients which appear in these operators
can be determined. The method is an extension of the improvement program of the
ALPHA collaboration, which, up to now, has only been applicable in the chiral
limit. The extension to quarks with non-zero masses is particularly important
for applications in heavy quark physics.Comment: 15 pages, Late
String Breaking in Non-Abelian Gauge Theories with Fundamental Matter Fields
We present clear numerical evidence for string breaking in three-dimensional
SU(2) gauge theory with fundamental bosonic matter through a mixing analysis
between Wilson loops and meson operators representing bound states of a static
source and a dynamical scalar. The breaking scale is calculated in the
continuum limit. In units of the lightest glueball we find . The implications of our results for QCD are discussed.Comment: 4 pages, 2 figures; equations (4)-(6) corrected, numerical results
and conclusions unchange
Speeding up finite step-size updating of full QCD on the lattice
We propose various improvements of finite step-size updating for full QCD on
the lattice that might turn finite step-size updating into a viable alternative
to the hybrid Monte Carlo algorithm. These improvements are noise reduction of
the noisy estimator of the fermion determinant, unbiased inclusion of the
hopping parameter expansion and a multi-level Metropolis scheme. First
numerical tests are performed for the 2 dimensional Schwinger model with two
flavours of Wilson fermions and for QCD two flavours of Wilson fermions and
Schr"odinger functional boundary conditions.Comment: 22 pages, 1 figur
String Breaking in Lattice Quantum Chromodynamics
The separation of a heavy quark and antiquark pair leads to the formation of
a tube of flux, or string, which should break in the presence of light
quark-antiquark pairs. This expected zero temperature phenomenon has proven
elusive in simulations of lattice QCD. We present simulation results that show
that the string does break in the confining phase at nonzero temperature.Comment: 11 pages RevTeX, including 4 encapsulated Postscript figures.
version2: minor corrections to reference
The Kaon B-parameter with the Wilson Quark Action using Chiral Ward Identities
A lattice QCD calculation of the kaon parameter is carried out with
the Wilson quark action in the quenched approximation at .
The mixing problem of the four-quark operators is solved
non-perturbatively with full use of chiral Ward identities employing four
external quarks with an equal off-shell momentum in the Landau gauge. This
method, without invoking any effective theory, enables us to construct the weak
four-quark operators exhibiting good chiral behavior. Our results for
with the non-perturbative mixing coefficients show small scaling violation
beyond the lattice cut-off GeV. Our estimate concludes
at GeV, which agrees with the value
obtained with the Kogut-Susskind quark action. For comparison we also calculate
with one-loop perturbative mixing coefficients. While this yields
incorrect values at finite lattice spacing, a linear extrapolation to the
continuum limit as a function of leads to a result consistent with those
obtained with the Ward identity method.Comment: 42 pages, 22 Postscript figures, added a new reference[26
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