1,766 research outputs found
Spinning test particles and clock effect in Kerr spacetime
We study the motion of spinning test particles in Kerr spacetime using the
Mathisson-Papapetrou equations; we impose different supplementary conditions
among the well known Corinaldesi-Papapetrou, Pirani and Tulczyjew's and analyze
their physical implications in order to decide which is the most natural to
use. We find that if the particle's center of mass world line, namely the one
chosen for the multipole reduction, is a spatially circular orbit (sustained by
the tidal forces due to the spin) then the generalized momentum of the test
particle is also tangent to a spatially circular orbit intersecting the center
of mass line at a point. There exists one such orbit for each point of the
center of mass line where they intersect; although fictitious, these orbits are
essential to define the properties of the spinning particle along its physical
motion. In the small spin limit, the particle's orbit is almost a geodesic and
the difference of its angular velocity with respect to the geodesic value can
be of arbitrary sign, corresponding to the spin-up and spin-down possible
alignment along the z-axis. We also find that the choice of the supplementary
conditions leads to clock effects of substantially different magnitude. In
fact, for co-rotating and counter-rotating particles having the same spin
magnitude and orientation, the gravitomagnetic clock effect induced by the
background metric can be magnified or inhibited and even suppressed by the
contribution of the individual particle's spin. Quite surprisingly this
contribution can be itself made vanishing leading to a clock effect
undistiguishable from that of non spinning particles. The results of our
analysis can be observationally tested.Comment: IOP macros, eps figures n. 12, to appear on Classical and Quantum
Gravity, 200
Spin precession in the Schwarzschild spacetime: circular orbits
We study the behavior of nonzero rest mass spinning test particles moving
along circular orbits in the Schwarzschild spacetime in the case in which the
components of the spin tensor are allowed to vary along the orbit, generalizing
some previous work.Comment: To appear on Classical and Quantum Gravity, 200
Circulating endothelial progenitor cells are actively involved in the reparative mechanisms of stable ischemic myocardium
Background: Myocardial fibrosis (MF) is an adverse correlate of severe aortic valve stenosis (SAVS). microRNA expression modulates different pathophysiological pathways in cardiovascular disease. In particular miRNAÂ21, has been associated to MF due to pressure overload. NonÂinvasive estimation of MF, using speckleÂtracking echocardiography (2DÂSTE), could be useful in determining early myocardial damage.
Purpose: To analyze the correlation between 2DÂSTE parameters, MF, plasmatic and tissue miRNAÂ21 in SAVS.
Methods: We evaluated 36 consecutive patients (75.2±8 y.o., 63% F) with SAVS and preserved ejection fraction (EF), undergoing to surgical aortic valve replacement (AVR; Euroscore II 2.28±1.13%; Logistic Euroscore: 6±4.1%). Clinical, ECG, biohumoral evaluation (including plasma miRNAÂ21) and a complete echocardiography, including 2DÂSTE, was performed before AVR. 28 patients eventually underwent AVR and, in 23 of them, a basal interventricular septum biopsy was performed. MF and tissue miRNAÂ21 expression (microÂdissection) were evaluated in each sample.
Results: All patients with SAVS (AVAi 0.33±0.1 cm2/m2; V max 4.4±0.4 m/sec; Mean Grad. 50±9 mmHg) showed concentric hypertrophy (LVMi 147±20.7 g/m2, RWT 0.51±0.07), diastolic dysfunction and increased ValvuloÂArterial Impedance (ZVA: 5.9±2.3 mmHg/ml/m2).
Despite a preserved EF (66±11%), an altered global and septal deformation (Global longitudinal strain, GLS â13±6.1; Global longitudinal strain rate, GLSr â0.8±0.2 1/sec; Global early diastolic Sr, GLSrE 1±0.35 1/sec; Septal longitudinal strain, SLS â8.6±2.8%; SLÂSr â0,6±0.1 1/sec; SLÂSrE 0.6±0.29 1/sec) were observed.
We found a significant association between MF and 2DÂSTE parameters, stroke volume and endÂdiastolic pressure (all p<0.05).
Tissue miRNAÂ21 was mainly expressed in fibrous tissue than in myocardium (p<0.0001). Myocardial miRNAÂ21 was associated with AVAi (r=0.46; p=0.043) and cardiac index (r=0.5; p=0.02) while fibrous tissue miRNAÂ21 was associated to GLS (r=0.8; p=0.0003), GLSrE (r=â0.72; p=0.005), SLS (r=0.6; p=0.01), SLÂSr (r=0.54; p=0.03), SLÂSrE (r=0.5; p=0.04) and PAPs (r=0.66; p=0.004). Plasma miRNAÂ21 was associated to MF (r=0.5; p=0.02) and septal longitudinal strain (r=0.38; p=0.037).
Conclusions: In SAVS with preserved EF, MF is associated to impaired myocardial deformation. miRNAÂ21 has a potential pathophysiological role in fibrogenesis. NonÂinvasive evaluation of plasmatic miRNAÂ21 and 2DÂSTE could be useful in risk stratification, to optimize the timing of surgery in SAVS patients
Kerr metric, static observers and Fermi coordinates
The coordinate transformation which maps the Kerr metric written in standard
Boyer-Lindquist coordinates to its corresponding form adapted to the natural
local coordinates of an observer at rest at a fixed position in the equatorial
plane, i.e., Fermi coordinates for the neighborhood of a static observer world
line, is derived and discussed in a way which extends to any uniformly
circularly orbiting observer there.Comment: 15 page latex iopart class documen
HST survey of the Orion Nebula Cluster in the HO 1.4 m absorption band: I. A census of substellar and planetary mass objects
In order to obtain a complete census of the stellar and sub-stellar
population, down to a few M in the Myr old Orion Nebula
Cluster, we used the infrared channel of the Wide Field Camera 3 of the Hubble
Space Telescope with the F139M and F130N filters. These bandpasses correspond
to the m HO absorption feature and an adjacent line-free continuum
region. Out of detected sources, (about ) appear fainter
than m (Vega mag) in the F130N filter, a brightness corresponding to
the hydrogen-burning limit mass (M) at Myr. Of
these, however, only sources have a negative F130M-139N color index,
indicative of the presence of HO vapor in absorption, and can therefore be
classified as bona-fide M and L dwarfs, with effective temperatures T K at an assumed Myr cluster age. On our color-magnitude diagram, this
population of sources with HO absorption appears clearly distinct from the
larger background population of highly reddened stars and galaxies with
positive F130M-F139N color index, and can be traced down to the sensitivity
limit of our survey, m, corresponding to a Myr old
M, planetary mass object under about 2 magnitudes of visual
extinction. Theoretical models of the BT-Settl family predicting substellar
isochrones of and Myr (down to M) fail to reproduce
the observed HO color index at MM. We perform a
Bayesian analysis to determine extinction, mass and effective temperature of
each sub-stellar member of our sample, together with its membership
probability.Comment: Accepted for publication in the Astrophysical Journal. The resolution
of several figures has been downgraded to comply with the size limit of arXiv
submission
Spinning test particles and clock effect in Schwarzschild spacetime
We study the behaviour of spinning test particles in the Schwarzschild
spacetime. Using Mathisson-Papapetrou equations of motion we confine our
attention to spatially circular orbits and search for observable effects which
could eventually discriminate among the standard supplementary conditions
namely the Corinaldesi-Papapetrou, Pirani and Tulczyjew. We find that if the
world line chosen for the multipole reduction and whose unit tangent we denote
as is a circular orbit then also the generalized momentum of the
spinning test particle is tangent to a circular orbit even though and
are not parallel four-vectors. These orbits are shown to exist because the spin
induced tidal forces provide the required acceleration no matter what
supplementary condition we select. Of course, in the limit of a small spin the
particle's orbit is close of being a circular geodesic and the (small)
deviation of the angular velocities from the geodesic values can be of an
arbitrary sign, corresponding to the possible spin-up and spin-down alignment
to the z-axis. When two spinning particles orbit around a gravitating source in
opposite directions, they make one loop with respect to a given static observer
with different arrival times. This difference is termed clock effect. We find
that a nonzero gravitomagnetic clock effect appears for oppositely orbiting
both spin-up or spin-down particles even in the Schwarzschild spacetime. This
allows us to establish a formal analogy with the case of (spin-less) geodesics
on the equatorial plane of the Kerr spacetime. This result can be verified
experimentally.Comment: IOP macros, eps figures n. 2, to appear on Classical and Quantum
gravity, 200
Habitat Suitability Modeling to Identify the Potential Nursery Grounds of the Atlantic Mackerel and Its Relation to Oceanographic Conditions in the Mediterranean Sea
Our knowledge for the distribution of Atlantic mackerel (Scomber scombrus) in the Mediterranean Sea is limited and fragmented. In the current work habitat suitability modeling was applied to summer acoustic surveys data of Atlantic mackerel juveniles derived from the north part of the Mediterranean (i.e., acoustic data from the Gulf of Lions, pelagic trawls held during acoustic surveys in Spanish Mediterranean waters, south Adriatic Sea, Strait of Sicily, and North Aegean Sea) using generalized additive models (GAMs) along with satellite environmental and bathymetry data. Bathymetry along with sea surface temperature and circulation patterns, expressed through sea level anomaly and the zonal component of the absolute geostrophic velocity, were the environmental variables best to describe nursery grounds. The selected model was used to produce maps presenting the potential nursery grounds of Atlantic mackerel throughout the Mediterranean Sea as a measure of habitat adequacy. However, the assessed potential nursery grounds were generally marked as âoccasional,â implying that although there are areas presenting high probability to encounter Atlantic mackerel, this picture can largely vary from year to year stressing the high susceptibility of the species to environmental conditions. In a further step and toward a spatial management perspective, we have estimated and visualized the overlap between Atlantic mackerel and anchovy/ sardine juvenile grounds throughout the basin. Results showed that although the degree of overlapping was generally low, not exceeding 15% in general, this varied at a regional level going up to 30%. The potential of the output of this work for management purposes like the implementation of spatially-explicit management tools is discussedVersiĂłn del edito
Density dependence in the spatial behaviour of anchovy and sardine across Mediterranean systems
A spatial indicatorâthe spreading area indexâis used to describe anchovy and sardine spatial distribution in relation to biomass variation and to look for ecosystem differences within the Mediterranean basin. Specifically, the variation in the spreading area index in relation to biomass was examined for different areas of the Mediterranean Sea (i.e. Aegean Sea, western Adriatic Sea, Strait of Sicily, Gulf of Lion, and Spanish Mediterranean waters). In order to
capture the spatial variability of the population at different levels of fish density, acoustic survey data for the years of highest, lowest, and intermediate abundance were used. In a subsequent step standardized values of spreading area and biomass were estimated to allow comparisons.
Results showed pronounced area differences. A significant relationship was revealed in the case of anchovy for areas with extended continental shelf (i.e. Aegean Sea, Adriatic Sea, and Gulf of Lion), indicating an increase in biomass with an increase in the spreading area. No relationship was found for areas dominated by narrow continental shelf and strong currents (i.e. Spanish Mediterranean waters and the Strait of Sicily). With regard to sardine, an increase in biomass was followed by an increase in the spreading area when estimates from the Aegean Sea, the Adriatic Sea, and the Strait of Sicily were considered together. The relationship was even more AbstractsâTheme Session B 9 pronounced when analysis was limited to the Aegean Sea and the Strait of Sicily. No relationship was found for the Spanish Mediterranean waters and the Gulf of Lion. This clearly implies that spatial indicators should be integrated into ecosystem management, taking into account that they can be areaâ or ecosystemâdependent
Methods and approaches for blind test predictions of out-of-plane behavior of masonry walls: a numerical comparative study
Earthquakes cause severe damage to masonry structures due to inertial forces acting in the normal direction to the plane of the walls. The out-of-plane behavior of masonry walls is complex and depends on several parameters, such as material and geometric properties of walls, connections between structural elements, the characteristics of the input motions, among others. Different analytical methods and advanced numerical modeling are usually used for evaluating the out-of-plane behavior of masonry structures. Furthermore, different types of structural analysis can be adopted for this complex behavior, such as limit analysis, pushover, or nonlinear dynamic analysis.Aiming to evaluate the capabilities of different approaches to similar problems, blind predictions were made using different approaches. For this purpose, two idealized structures were tested on a shaking table and several experts on masonry structures were invited to present blind predictions on the response of the structures, aiming at evaluating the available tools for the out-of-plane assessment of masonry structures. This article presents the results of the blind test predictions and the comparison with the experimental results, namely in terms of formed collapsed mechanisms and control outputs (PGA or maximum displacements), taking into account the selected tools to perform the analysis.info:eu-repo/semantics/publishedVersio
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