1,194 research outputs found
Synthesis and Magnetic Characterization of Metal-filled Double-sided Porous Silicon Samples
A magnetic semiconductor/metal nanocomposite with a nanostructured silicon wafer as base material and incorporated metallic nanostructures (Ni, Co, NiCo) is fabricated in two electrochemical steps. First, the silicon template is anodized in an HF-electrolyte to obtain a porous structure with oriented pores grown perpendicular to the surface. This etching procedure is carried out either in forming a sample with a single porous layer on one side or in producing a double-sided specimen with a porous layer on each side. Second, this matrix is used for deposition of transition metals as Ni, Co or an alloy of these. The achieved hybrid material with incorporated Ni- and Co-nanostructures within one sample is investigated magnetically. The obtained results are compared with the ones gained from samples containing a single metal
sp magnetism in clusters of gold-thiolates
Using calculations from first principles, we herein consider the bond made
between thiolat e with a range of different Au clusters, with a particular
focus on the spin moments inv olved in each case. For odd number of gold atoms,
the clusters show a spin moment of 1.~ . The variation of spin moment
with particle size is particularly dramatic, with t he spin moment being zero
for even numbers of gold atoms. This variation may be linked w ith changes in
the odd-even oscillations that occur with the number of gold atoms, and is
associated with the formation of a S-Au bond. This bond leads to the presence
of an extra electron that is mainly sp in character in the gold part. Our
results sugg est that any thiolate-induced magnetism that occurs in gold
nanoparticles may be locali zed in a shell below the surface, and can be
controlled by modifying the coverage of the thiolates
Left atrial pump strain predicts long-term survival after transcatheter aortic valve implantation
BACKGROUND
This study aims at investigating left atrial (LA) deformation by left atrial reservoir (LARS) and pump strain (LAPS) and its implications for long-term survival in patients with severe aortic stenosis (AS) undergoing transcatheter aortic valve implantation (TAVI).
METHODS
Speckle tracking echocardiography was performed in 198 patients with severe AS undergoing TAVI. Association of strain parameters with cardiovascular mortality was determined.
RESULTS
Over a follow-up time of 5 years, 49 patients (24.7%) died. LAPS was more impaired in non-survivors than survivors (P = 0.010), whereas no difference was found for LARS (P = 0.114), LA ejection fraction (P = 0.241), and LA volume index (P = 0.292). Kaplan-Meier analyses yielded a reduced survival probability according to the optimal threshold for LAPS (P = 0.002). A more impaired LAPS was associated with increased mortality risk (HR 1.12 [95% CI 1.02-1.22]; P = 0.014) independent of LVEF, LAVI, age, and sex. Addition of LAPS improved multivariable echocardiographic (LVEF, LAVI) and clinical (age, sex) models with potential incremental value for mortality prediction (P = 0.013 and P = 0.031, respectively). In contrast, LARS and LAVI were not associated with mortality.
CONCLUSIONS
In patients undergoing aortic valve replacement for severe AS, LAPS was impaired in patients dying during long-term follow-up after TAVI, differentiated survivors from non-survivors, was independently associated with long-term mortality, and yielded potential incremental value for survival prediction after TAVI. LAPS seems useful for risk stratification in severe AS and timely valve replacement
Mathisson-Papapetrou equations in metric and gauge theories of gravity in a Lagrangian formulation
We present a simple method to derive the semiclassical equations of motion
for a spinning particle in a gravitational field. We investigate the cases of
classical, rotating particles (pole-dipole particles), as well as particles
with intrinsic spin. We show that, starting with a simple Lagrangian, one can
derive equations for the spin evolution and momentum propagation in the
framework of metric theories of gravity and in theories based on a
Riemann-Cartan geometry (Poincare gauge theory), without explicitly referring
to matter current densities (spin and energy-momentum). Our results agree with
those derived from the multipole expansion of the current densities by the
conventional Papapetrou method and from the WKB analysis for elementary
particles.Comment: 28 page
Stochastic Gravity
Gravity is treated as a stochastic phenomenon based on fluctuations of the
metric tensor of general relativity. By using a (3+1) slicing of spacetime, a
Langevin equation for the dynamical conjugate momentum and a Fokker-Planck
equation for its probability distribution are derived. The Raychaudhuri
equation for a congruence of timelike or null geodesics leads to a stochastic
differential equation for the expansion parameter in terms of the
proper time . For sufficiently strong metric fluctuations, it is shown that
caustic singularities in spacetime can be avoided for converging geodesics. The
formalism is applied to the gravitational collapse of a star and the
Friedmann-Robertson-Walker cosmological model. It is found that owing to the
stochastic behavior of the geometry, the singularity in gravitational collapse
and the big-bang have a zero probability of occurring. Moreover, as a star
collapses the probability of a distant observer seeing an infinite red shift at
the Schwarzschild radius of the star is zero. Therefore, there is a vanishing
probability of a Schwarzschild black hole event horizon forming during
gravitational collapse.Comment: Revised version. Eq. (108) has been modified. Additional comments
have been added to text. Revtex 39 page
Stochastic Quantization of Scalar Fields in Einstein and Rindler Spacetime
We consider the stochastic quantization method for scalar fields defined in a
curved manifold and also in a flat space-time with event horizon. The two-point
function associated to a massive self-interacting scalar field is evaluated, up
to the first order level in the coupling constant, for the case of an Einstein
and also a Rindler Euclidean metric, respectively. Its value for the asymptotic
limit of the Markov parameter is exhibited. The divergences therein are taken
care of by employing a covariant stochastic regularization
Axial Torsion-Dirac spin Effect in Rotating Frame with Relativistic Factor
In the framework of spacetime with torsion and without curvature, the Dirac
particle spin precession in the rotational system is studied. We write out the
equivalent tetrad of rotating frame, in the polar coordinate system, through
considering the relativistic factor, and the resultant equivalent metric is a
flat Minkowski one. The obtained rotation-spin coupling formula can be applied
to the high speed rotating case, which is consistent with the expectation.Comment: 6 page
Efeito de duas doses de benzoato de estradiol associado a progesterona sobre o desenvolvimento folicular em novilhas submetidas à aspiração folicular.
Edição dos resumos do XXI Annual Meeting of the Brazilian Embryo Technology Society (SBTE), Salvador, BA, ago. 2007
On a class of invariant coframe operators with application to gravity
Let a differential 4D-manifold with a smooth coframe field be given. Consider
the operators on it that are linear in the second order derivatives or
quadratic in the first order derivatives of the coframe, both with coefficients
that depend on the coframe variables. The paper exhibits the class of operators
that are invariant under a general change of coordinates, and, also, invariant
under the global SO(1,3)-transformation of the coframe. A general class of
field equations is constructed. We display two subclasses in it. The subclass
of field equations that are derivable from action principles by free variations
and the subclass of field equations for which spherical-symmetric solutions,
Minkowskian at infinity exist. Then, for the spherical-symmetric solutions, the
resulting metric is computed. Invoking the Geodesic Postulate, we find all the
equations that are experimentally (by the 3 classical tests) indistinguishable
from Einstein field equations. This family includes, of course, also Einstein
equations. Moreover, it is shown, explicitly, how to exhibit it. The basic tool
employed in the paper is an invariant formulation reminiscent of Cartan's
structural equations. The article sheds light on the possibilities and
limitations of the coframe gravity. It may also serve as a general procedure to
derive covariant field equations
Monopolin subunit Csm1 associates with MIND complex to establish monopolar attachment of sister kinetochores at meiosis I
Sexually reproducing organisms halve their cellular ploidy during gametogenesis by undergoing a specialized form of cell division known as meiosis. During meiosis, a single round of DNA replication is followed by two rounds of nuclear divisions (referred to as meiosis I and II). While sister kinetochores bind to microtubules emanating from opposite spindle poles during mitosis, they bind to microtubules originating from the same spindle pole during meiosis I. This phenomenon is referred to as mono-orientation and is essential for setting up the reductional mode of chromosome segregation during meiosis I. In budding yeast, mono-orientation depends on a four component protein complex referred to as monopolin which consists of two nucleolar proteins Csm1 and Lrs4, meiosis-specific protein Mam1 of unknown function and casein kinase Hrr25. Monopolin complex binds to kinetochores during meiosis I and prevents bipolar attachments. Although monopolin associates with kinetochores during meiosis I, its binding site(s) on the kinetochore is not known and its mechanism of action has not been established. By carrying out an imaging-based screen we have found that the MIND complex, a component of the central kinetochore, is required for monopolin association with kinetochores during meiosis. Furthermore, we demonstrate that interaction of monopolin subunit Csm1 with the N-terminal domain of MIND complex subunit Dsn1, is essential for both the association of monopolin with kinetochores and for monopolar attachment of sister kinetochores during meiosis I. As such this provides the first functional evidence for a monopolin-binding site at the kinetochore
- …