12,298 research outputs found
Gravitational Wave Emission and Mass Extraction from a Perturbed Schwarzschild Black Hole (continue)
A relativistic model for the emission of gravitational waves from an
initially unperturbed Schwarzschild black hole, or spherical collapsing
configuration, is completely integrated. The model consists basically of
gravitational perturbations of the Robinson-Trautman type on the Schwarzschild
spacetime. In our scheme of perturbation, gravitational waves may extract mass
from the collapsing configuration. Robinson-Trautmann perturbations also
include another mode of emission of mass, which we denote shell emission mode:
in the equatorial plane of the configuration, a timelike shell of
matter may be present, whose stress-energy tensor is modelled by neutrinos and
strings emitted radially on the shell; no gravitational waves are present in
this mode. The invariant characterization of gravitational wave perturbations
and of the gravitational wave zone is made through the analysis of the
structure of the curvature tensor and the use of the Peeling Theorem.Comment: 26 pages, LaTex, no figure
Combining exclusive semi-leptonic and hadronic B decays to measure |V_ub|
The Cabibbo-Kobayashi-Maskawa matrix element |V_ub| can be extracted from the
rate for the semi-leptonic decay B -> pi + l + antineutrino_l, with little
theoretical uncertainty, provided the hadronic form factor for the B -> pi
transition can be measured from some other B decay. In here, we suggest using
the decay B -> pi J\psi. This is a color suppressed decay, and it cannot be
properly described within the usual factorization approximation; we use instead
a simple and very general phenomenological model for the b d J\psi vertex. In
order to relate the hadronic form factors in the B -> pi J\psi and B -> pi + l
+ antineutrino_l decays, we use form factor relations that hold for
heavy-to-light transitions at large recoil.Comment: Latex, 7 pages, no figure
Exercícios de álgebra linear
Estes textos contêm uma seleção de exercícios para apoio às aulas de Álgebra Linear para cursos de Engenharia e Ciências, bem como as resoluções de alguns exercícios. Apresentam-se também algumas provas de avaliação para esses cursos e as respetivas resoluções
Complementos de análise numérica: valores e vectores próprios
Texto de apoio à disciplina de Complementos de Análise Numérica
Surface roughness and interfacial slip boundary condition for quartz crystal microbalances
The response of a quartz crystal microbalance (QCM) is considered using a wave equation for the substrate and the Navier-Stokes equations for a finite liquid layer under a slip boundary condition. It is shown that when the slip length to shear wave penetration depth is small, the first order effect of slip is only present in the frequency response. Importantly, in this approximation the frequency response satisfies an additivity relation with a net response equal to a Kanazawa liquid term plus an additional Sauerbrey "rigid" liquid mass. For the slip length to result in an enhanced frequency decrease compared to a no-slip boundary condition, it is shown that the slip length must be negative so that the slip plane is located on the liquid side of the interface. It is argued that the physical application of such a negative slip length could be to the liquid phase response of a QCM with a completely wetted rough surface. Effectively, the model recovers the starting assumption of additivity used in the trapped mass model for the liquid phase response of a QCM having a rough surface. When applying the slip boundary condition to the rough surface problem, slip is not at a molecular level, but is a formal hydrodynamic boundary condition which relates the response of the QCM to that expected from a QCM with a smooth surface. Finally, possible interpretations of the results in terms of acoustic reflectivity are developed and the potential limitations of the additivity result should vapour trapping occur are discussed
The Mass-to-Light Ratio of Binary Galaxies
We report on the mass-to-light ratio determination based on a newly selected
binary galaxy sample, which includes a large number of pairs whose separations
exceed a few hundred kpc. The probability distributions of the projected
separation and the velocity difference have been calculated considering the
contamination of optical pairs, and the mass-to-light ratio has been determined
based on the maximum likelihood method. The best estimate of in the B
band for 57 pairs is found to be 28 36 depending on the orbital
parameters and the distribution of optical pairs (solar unit, km
s Mpc). The best estimate of for 30 pure spiral pairs is
found to be 12 16. These results are relatively smaller than those
obtained in previous studies, but consistent with each other within the errors.
Although the number of pairs with large separation is significantly increased
compared to previous samples, does not show any tendency of increase, but
found to be almost independent of the separation of pairs beyond 100 kpc. The
constancy of beyond 100 kpc may indicate that the typical halo size of
spiral galaxies is less than kpc.Comment: 18 pages + 8 figures, to appear in ApJ Vol. 516 (May 10
Fourier Eigenfunctions, Uncertainty Gabor Principle and Isoresolution Wavelets
Shape-invariant signals under Fourier transform are investigated leading to a
class of eigenfunctions for the Fourier operator. The classical uncertainty
Gabor-Heisenberg principle is revisited and the concept of isoresolution in
joint time-frequency analysis is introduced. It is shown that any Fourier
eigenfunction achieve isoresolution. It is shown that an isoresolution wavelet
can be derived from each known wavelet family by a suitable scaling.Comment: 6 pages, XX Simp\'osio Bras. de Telecomunica\c{c}\~oes, Rio de
Janeiro, Brazil, 2003. Fixed typo
Experimental realization of the Yang-Baxter Equation via NMR interferometry
The Yang-Baxter equation is an important tool in theoretical physics, with
many applications in different domains that span from condensed matter to
string theory. Recently, the interest on the equation has increased due to its
connection to quantum information processing. It has been shown that the
Yang-Baxter equation is closely related to quantum entanglement and quantum
computation. Therefore, owing to the broad relevance of this equation, besides
theoretical studies, it also became significant to pursue its experimental
implementation. Here, we show an experimental realization of the Yang-Baxter
equation and verify its validity through a Nuclear Magnetic Resonance (NMR)
interferometric setup. Our experiment was performed on a liquid state
Iodotrifluoroethylene sample which contains molecules with three qubits. We use
Controlled-transfer gates that allow us to build a pseudo-pure state from which
we are able to apply a quantum information protocol that implements the
Yang-Baxter equation.Comment: 10 pages and 6 figure
On The Determination of MDI High-Degree Mode Frequencies
The characteristic of the solar acoustic spectrum is such that mode lifetimes
get shorter and spatial leaks get closer in frequency as the degree of a mode
increases for a given order. A direct consequence of this property is that
individual p-modes are only resolved at low and intermediate degrees, and that
at high degrees, individual modes blend into ridges. Once modes have blended
into ridges, the power distribution of the ridge defines the ridge central
frequency and it will mask the true underlying mode frequency. An accurate
model of the amplitude of the peaks that contribute to the ridge power
distribution is needed to recover the underlying mode frequency from fitting
the ridge.
We present the results of fitting high degree power ridges (up to l = 900)
computed from several two to three-month-long time-series of full-disk
observations taken with the Michelson Doppler Imager (MDI) on-board the Solar
and Heliospheric Observatory between 1996 and 1999.
We also present a detailed discussion of the modeling of the ridge power
distribution, and the contribution of the various observational and
instrumental effects on the spatial leakage, in the context of the MDI
instrument. We have constructed a physically motivated model (rather than some
ad hoc correction scheme) resulting in a methodology that can produce an
unbiased determination of high-degree modes, once the instrumental
characteristics are well understood.
Finally, we present changes in high degree mode parameters with epoch and
thus solar activity level and discuss their significance.Comment: 59 pages, 38 figures -- High-resolution version at
http://www-sgk.harvard.edu:1080/~sylvain/preprints/ -- Manuscript submitted
to Ap
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