27,601 research outputs found
Measuring Strong and Weak Phases in Time-Independent B Decays
Flavor SU(3) symmetry implies certain relations among -decay amplitudes to
, and final states, when annihilation-like
diagrams are neglected. Using three triangle relations, we show how to measure
the weak CKM phases and using time-independent rate
measurements only. In addition, one obtains all the strong final-state phases
and the magnitudes of individual terms describing tree (spectator),
color-suppressed and penguin diagrams. Many independent measurements of these
quantities can be made with this method, which helps to eliminate possible
discrete ambiguities and to estimate the size of SU(3)-breaking effects.Comment: 2 figures available from the authors upon request, 12
pages,UdeM-LPN-TH-94-19
On the propagation speed of evanescent modes
The group-velocity of evanescent waves (in undersized waveguides, for
instance) was theoretically predicted, and has been experimentally verified, to
be Superluminal (v_g > c). By contrast, it is known that the precursor speed in
vacuum cannot be larger than c. In this paper, by computer simulations based on
Maxwell equations only, we show the existence of both phenomena. In other
words, we verify the actual possibility of Superluminal group velocities,
without violating the so-called (naive) Einstein causality. (Subject classes:
General physics, Classical physics, Optics, Special Relativity; PACS nos.:
73.40Gk, 03.80+z, 03.65Bz; Keywords: evanescent waves; tunnelling photons;
Hartman effect; group velocity; Superluminal waves; precursors; transient
waves; front velocity; Maxwell equations; electromagnetic waves; computer
simulations; Special Relativity; Extended Relativity).Comment: plain LaTeX file (14 pages), plus 15 figures in .jp
The ontology of temperature in nonequilibrium systems
The laws of thermodynamics provide a clear concept of the temperature for an
equilibrium system in the continuum limit. Meanwhile, the equipartition theorem
allows one to make a connection between the ensemble average of the kinetic
energy and the uniform temperature. When a system or its environment is far
from equilibrium, however, such an association does not necessarily apply. In
small systems, the regression hypothesis may not even apply. Herein, we show
that in small nonequilibrium systems, the regression hypothesis still holds
though with a generalized definition of the temperature. The latter must now be
defined for each such manifestation.Comment: J.Chem.Phys. (in press); 23 pages, 3 figures, 1 tabl
Evolved stars in the Local Group galaxies. I. AGB evolution and dust production in IC 1613
We used models of thermally-pulsing asymptotic giant branch (AGB) stars, that
also describe the dust-formation process in the wind, to interpret the
combination of near- and mid-infrared photometric data of the dwarf galaxy IC
1613. This is the first time that this approach is extended to an environment
different from the Milky Way and the Magellanic Clouds (MCs). Our analysis,
based on synthetic population techniques, shows a nice agreement between the
observations and the expected distribution of stars in the colour-magnitude
diagrams obtained with JHK and Spitzer bands. This allows a characterization of
the individual stars in the AGB sample in terms of mass, chemical composition,
and formation epoch of the progenitors. We identify the stars exhibiting the
largest degree of obscuration as carbon stars evolving through the final AGB
phases, descending from 1-1.25Msun objects of metallicity Z=0.001 and from
1.5-2.5Msun stars with Z=0.002. Oxygen-rich stars constitute the majority of
the sample (65%), mainly low mass stars (<2Msun) that produce a negligible
amount of dust (<10^{-7}Msun/yr). We predict the overall dust-production rate
from IC 1613, mostly determined by carbon stars, to be 6x10^{-7}Msun/yr with an
uncertainty of 30%. The capability of the current generation of models to
interpret the AGB population in an environment different from the MCs opens the
possibility to extend this kind of analysis to other Local Group galaxies.Comment: 14 pages, 6 figures, accepted for publication on MNRA
Symmetric and Asymmetric Coalescence of Drops on a Substrate
The coalescence of viscous drops on a substrate is studied experimentally and
theoretically. We consider cases where the drops can have different contact
angles, leading to a very asymmetric coalescence process. Side view experiments
reveal that the "bridge" connecting the drops evolves with self-similar
dynamics, providing a new perspective on the coalescence of sessile drops. We
show that the universal shape of the bridge is accurately described by
similarity solutions of the one-dimensional lubrication equation. Our theory
predicts a bridge that grows linearly in time and stresses the strong
dependence on the contact angles. Without any adjustable parameters, we find
quantitative agreement with all experimental observations.Comment: 5 pages, 4 figure
Generalized hydrodynamics of a dilute finite-sized particles suspension: Dynamic viscosity
We present a mesoscopic hydrodynamic description of the dynamics of colloidal
suspensions. We consider the system as a gas of Brownian particles suspended in
a Newtonian heat bath subjected to stationary non-equilibrium conditions
imposed by a velocity field. Using results already obtained in previous studies
in the field by means of a generalized Fokker-Planck equation, we obtain a set
of coupled differential equations for the local diffusion current and the
evolution of the total stress tensor. We find that the dynamic shear viscosity
of the system contains contributions arising from the finite size of the
particles.Comment: To appear in Physical Review
Preoperative digital three-dimensional planning for rhinoplasty
BACKGROUND: This report describes preoperative digital planning for rhinoplasty using a new three-dimensional (3D) radiologic viewer that allows both patients and surgeons to visualize on a common monitor the 3D real aspect of the nose in its inner and outer sides.
METHODS: In the period 2002 to 2008, 210 patients underwent rhinoplasty procedures in the authors' clinic. The patients were randomly divided into three groups according to the type of preoperative planning used: photos only, a simulated result by Adobe Photoshop, or the 3D radiologic viewer. The parameters evaluated included the number of patients that underwent surgery after the first consultation, the number of patients who asked for a reintervention, patient satisfaction (according to a test given to the patients 12 months postoperatively), the surgical time required for a functional intervention, and the improvement in nasal function by postoperative rhinomanometry and subjective evaluation.
RESULTS: Computer-aided technologies led to a higher number of patients deciding to undergo a rhinoplasty. Simulation of the postoperative results was not as useful in the postoperative period due to the higher number of reintervention requests.
CONCLUSION: The patients undergoing rhinoplasties preferred new technologies in the preoperative period. The advantages of using the 3D radiologic viewer included improved preoperative planning, reduction in intraoperative stress, a higher number of patients undergoing surgery, reduction in postoperative surgical corrections, reduction in surgical time for the functional intervention, a higher rate of improvement in nasal function, a higher percentage of postoperative satisfaction, and reduced costs
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