776 research outputs found
Variational approach to gravitational theories with two independent connections
A new variational approach for general relativity and modified theories of
gravity is presented. In addition to the metric tensor, two independent affine
connections enter the action as dynamical variables. In the matter action the
dependence upon one of the connections is left completely unspecified. When the
variation is applied to the Einstein-Hilbert action the Einstein field
equations are recovered. However when applied to and Scalar-Tensor
theories, it yields gravitational field equations which differ from their
equivalents obtained with a metric or Palatini variation and reduce to the
former ones only when no connections appear in the matter action.Comment: 11 pages, no figure
Different approaches for assessing sperm function
Different approaches can be used to assess sperm function in different conditions, i.e. sperm storage, freezing-thawing or activation by induction of capacitation and acrosome reaction. In this review we will focus on the assays routinely performed in our laboratories, giving a literature support to critically analyse different approaches. In fact, researchers usually tend to look for the \u201cone shot\u201c parameter that could explain itself a specific process; it is our conviction that a multiparametric approach is still more valid, as some changes in sperm function are very complex and could be explained only by operating in different ways. Sperm motility, the most evident sperm characteristic, should be assessed by computer-aided sperm analysers that permit an objective evaluation of the motility and its kinematic parameters. Commercial and open source instruments are available and could be profitably used together with specific statistical approaches. The use of microscopy, and particularly fluorescent microscopy, could be a very useful tool to assess different parameters in sperm cells both by fluorophores that give indication of a determined function, and by immunolocalization of proteins, that permits the discover of new features or to explain particular sperm functions. The same substrates could be used also in flow cytometry: the difference is that it permits to study wider sperm populations (and their sub-population distribution). Flow cytometry is undergoing a very wide use in spermatology and technical and experimental rigor is needed to obtain reliable results. Metabolic assessment of sperm features, particularly energetic supply, ATP formation and other enzyme activities, could represent a very important challenge to acquire new information and complete/integrate those derived from other techniques. Finally, functional assays such as oocyte binding and in vitro fertilization, represent a very strong tool to assess sperm function in vitro, as they could evidence the functional intactness of some pathways
Hamilton--Jacobi equations for Wasserstein controlled gradient flows: existence of viscosity solutions
This work is the third part of a program initiated in arXiv:2111.13258,
arXiv:2302.06571 aiming at the development of an intrinsic geometric
well-posedness theory for Hamilton-Jacobi equations related to controlled
gradient flow problems in metric spaces. In this paper, we finish our analysis
in the context of Wasserstein gradient flows with underlying energy functional
satisfying McCann's condition. More prescisely, we establish that the value
function for a linearly controlled gradient flow problem whose running cost is
quadratic in the control variable and just continuous in the state variable
yields a viscosity solution to the Hamilton-Jacobi equation in terms of two
operators introduced in our former works, acting as rigorous upper and lower
bounds for the formal Hamiltonian at hand. The definition of these operators is
directly inspired by the Evolutional Variational Inequality formulation of
gradient flows (EVI): one of the main innovations of this work is to introduce
a controlled version of EVI, which turns out to be crucial in establishing
regularity properties, energy and metric bounds along optimzing sequences in
the controlled gradient flow problem that defines the candidate solution
Good and bad tetrads in f(T) gravity
We investigate the importance of choosing good tetrads for the study of the
field equations of gravity. It is well known that this theory is not
invariant under local Lorentz transformations, and therefore the choice of
tetrad plays a crucial role in such models. Different tetrads will lead to
different field equations which in turn have different solutions. We suggest to
speak of a good tetrad if it imposes no restrictions on the form of .
Employing local rotations, we construct good tetrads in the context of
homogeneity and isotropy, and spherical symmetry, where we show how to find
Schwarzschild-de Sitter solutions in vacuum. Our principal approach should be
applicable to other symmetries as well.Comment: 25 page
Inflationary Perturbations in Palatini Generalised Gravity
We examine the generation of primordial perturbations during an inflationary
epoch in generalised theories of gravity when the equations of motion are
derived using the Palatini variational principle. Both f(R) and Scalar-Tensor
theories are considered and we compare our results with those obtained under
the conventional metric formalism. Non-linear generalisations of the action
lead to different theories under the two variational choices and we obtain
distinct results for scalar and tensor spectral indices and their ratio. We
find the following general result; inflation driven solely by f(R)
modifications alone do not result in suitable curvature perturbations whilst
Scalar-Tensor theories generate nearly scalar invariant curvature perturbations
but no tensor modes.Comment: 9 page
EFFECTS OF RESVERATROL ON VITRIFIED PORCINE OOCYTES
Vitrified MII porcine oocytes are characterized by reduced developmental competence, associated with the activation of the apoptotic pathway. Resveratrol (R), a polyphenolic compound present in several vegetal sources, has been reported to exert, among all its other biological effects, an antiapoptotic one. The aim of this study was to determine the effects of R (2\u2009\ub5M) on the apoptotic status of porcine oocytes vitrified by Cryotop method, evaluating phosphatidylserine (PS) exteriorization and caspases activation. R was added during IVM (A); 2\u2009h postwarming incubation (B); vitrification/warming and 2\u2009h postwarming incubation (C); all previous phases (D). Data on PS exteriorization showed, in each treated group, a significantly higher (P<0.05) percentage of live nonapoptotic oocytes as compared with CTR; moreover, the percentage of live apoptotic oocytes was significantly (P<0.05) lower in all R-treated groups relative to CTR. The results on caspase activation showed a tendency to an increase of viable oocytes with inactive caspases in B, C, and D, while a significant (P<0.05) increase in A compared to CTR was recorded. These data demonstrate that R supplementation in various phases of IVM and vitrification/warming procedure can modulate the apoptotic process, improving the resistance of porcine oocytes to cryopreservation-induced damage
Extensive carrier testing and CF birth prevalence: evidence for a negative correlation
Aim of the study was to evaluate if extensive CF carrier testing may be connected
with the progressive decrease of CF birth incidence recorded in North Eastern Italy.
From 1993 to 2007 an average 52,000 newborns per year underwent Neonatal
Screening (NS), and 198 newborns with CF were detected (1/3937). A time related
contraction in birth prevalence was confirmed, with an average annual percent
decrease of 0.15 per 10,000 neonates (Poisson regression analysis p 0.003). In
the NS area two sections were identified: the Western Region (WR), where CF
carrier testing is not offered to couples from the general population, and the
Eastern Region (ER), where CF carrier testing is widely offered to couples from
the general population. In ER from 1995 to 2007 such testing practice has been
steadily expanding, with a total of 87,721 CF carrier tests performed, 3460 carriers
identified, and 238 carrier couples detected (data collection in progress). The
prevalence of CF decreased by time (p<0.001) but the rate of decrease was more
enhanced in ER as suggested by the existence of a statistically significant (p = 0.014)
interaction term between time and region in the Poisson regression model. The
overall negative trend in North Eastern Italy is due to a contraction of CF births
in its Eastern part. In ER a negative correlation was found between CF incidence
and the number of carrier tests (p 0.012). Prenatal diagnosis data collection is in
progress. These data support the hypothesis that carrier screening may modify the
incidence of CF
Massive black hole binaries in LISA: multimessenger prospects and electromagnetic counterparts
In the next decade, the Laser Interferometer Space Antenna (LISA) will detect
the coalescence of massive black hole binaries (MBHBs) in the range , up to . Their gravitational wave (GW) signal
is expected to be accompanied by an electromagnetic counterpart (EMcp),
generated by the gas accreting on the binary or on the remnant BH. In this
work, we present the number and characteristics (such as redshift and mass
distribution, apparent magnitudes or fluxes) of EMcps detectable jointly by
LISA and some representative EM telescopes. We combine state-of-the-art
astrophysical models for the galaxies formation and evolution to build the
MBHBs catalogues, with Bayesian tools to estimate the binary sky position
uncertainty from the GW signal. Exploiting additional information from the
astrophysical models, such as the amount of accreted gas and the BH spins, we
evaluate the expected EM emission in the soft X-ray, optical and radio bands.
Overall, we predict between 7 and 21 EMcps in 4 yrs of joint observations by
LISA and the considered EM facilities, depending on the astrophysical model. We
also explore the impact of the hydrogen and dust obscuration of the optical and
X-ray emissions, as well as of the collimation of the radio emission: these
effects reduce the number to EMcps to 2 or 3, depending on the astrophysical
model, again in 4 yrs of observations. Most of the EMcps are characterised by
faint EM emission, challenging the observational capabilities of future
telescopes. Finally, we also find that systems with multi-modal sky position
posterior distributions represent only a minority of cases and do not affect
significantly the number of EMcps.Comment: 28 pages, 18 figures. Submitted to PR
Interacting spin-2 fields in three dimensions
Using the frame formulation of multi-gravity in three dimensions, we show
that demanding the presence of secondary constraints which remove the
Boulware-Deser ghosts restricts the possible interaction terms of the theory
and identifies invertible frame field combinations whose effective metric may
consistently couple to matter. The resulting ghost-free theories can be
represented by theory graphs which are trees. In the case of three frame
fields, we explicitly show that the requirement of positive masses and energies
for the bulk spin-2 modes in AdS is consistent with a positive central
charge for the putative dual CFT.Comment: 26 pages, 3 figures, v2: minor changes, matches published versio
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