2,384 research outputs found
Inclusive Measurement of the Charmless Semileptonic Branching Ratio of B-hadrons
From the study of the kinematics properties of the final state produced in the semileptonic decays , the inclusive charmless semileptonic branching ratio of -hadrons has been measured. Using the data collected between 1992 and 1995, one gets: , where represents any charmless hadronic states
Inclusive Measurement of the Charmless Semileptonic Branching Ratio of B-hadrons
From the study of the kinematics properties of the final state produced in the semileptonic decays , the inclusive charmless semileptonic branching ratio of -hadrons has been measured. Using the data collected between 1992 and 1995, one gets: , where represents any charmless hadronic states
Study of Charm Production in W Decays
The production rate of charm quark in W decays has been measured at LEP-2 energies with the ALEPH detector. The charm quarks are tagged by using an algorithm based on the kinematic properties of the jets, the number of identified leptons, the energy of fully reconstructed D mesons and on lifetime information
Imaging the symmetry breaking of molecular orbitals in carbon nanotubes
Carbon nanotubes have attracted considerable interest for their unique
electronic properties. They are fascinating candidates for fundamental studies
of one dimensional materials as well as for future molecular electronics
applications. The molecular orbitals of nanotubes are of particular importance
as they govern the transport properties and the chemical reactivity of the
system. Here we show for the first time a complete experimental investigation
of molecular orbitals of single wall carbon nanotubes using atomically resolved
scanning tunneling spectroscopy. Local conductance measurements show
spectacular carbon-carbon bond asymmetry at the Van Hove singularities for both
semiconducting and metallic tubes, demonstrating the symmetry breaking of
molecular orbitals in nanotubes. Whatever the tube, only two types of
complementary orbitals are alternatively observed. An analytical tight-binding
model describing the interference patterns of ? orbitals confirmed by ab initio
calculations, perfectly reproduces the experimental results
Dynamics of Enceladus and Dione inside the 2:1 Mean-Motion Resonance under Tidal Dissipation
In a previous work (Callegari and Yokoyama 2007, Celest. Mech. Dyn. Astr.
vol. 98), the main features of the motion of the pair Enceladus-Dione were
analyzed in the frozen regime, i.e., without considering the tidal evolution.
Here, the results of a great deal of numerical simulations of a pair of
satellites similar to Enceladus and Dione crossing the 2:1 mean-motion
resonance are shown. The resonance crossing is modeled with a linear tidal
theory, considering a two-degrees-of-freedom model written in the framework of
the general three-body planar problem. The main regimes of motion of the system
during the passage through resonance are studied in detail. We discuss our
results comparing them with classical scenarios of tidal evolution of the
system. We show new scenarios of evolution of the Enceladus-Dione system
through resonance not shown in previous approaches of the problem.Comment: 36 pages, 12 figures. Accepted in Celestial Mechanics and Dynamical
Astronom
Forming limit predictions for single-point incremental sheet metal forming
peer reviewedA characteristic of incremental sheet metal forming is that much higher deformations
can be achieved than conventional forming limits. In this paper it is investigated to which extent
the highly non-monotonic strain paths during such a process may be responsible for this high
formability. A Marciniak-Kuczynski (MK) model is used to predict the onset of necking of a
sheet subjected to the strain paths obtained by finite-element simulations. The predicted forming
limits are considerably higher than for monotonic loading, but still lower than the experimental
ones. This discrepancy is attributed to the strain gradient over the sheet thickness, which is not
taken into account in the currently used MK model
Carbon Nanotubes Synthesized in Channels of Alpo4-5 Single Crystals : First X-Ray Scattering Investigations
Following the synthesis of aligned single-wall carbon nanotubes in the
channels of AlPO4-5 zeolite single crystals, we present the first X-ray
diffraction and diffuse scattering results. They can be analysed in terms of a
partial filling of the zeolite channels by nanotubes with diameter around 4A.
The possible selection of only one type of nanotube during the synthesis, due
to the constraints imposed by the zeolite host, is discussed.Comment: to appear in Solid State Com
On the diffraction pattern of C60 peapods
We present detailed calculations of the diffraction pattern of a powder of
bundles of C peapods. The influence of all pertinent structural
parameters of the bundles on the diffraction diagram is discussed, which should
lead to a better interpretation of X-ray and neutron diffraction diagrams. We
illustrate our formalism for X-ray scattering experiments performed on peapod
samples synthesized from 2 different technics, which present different
structural parameters. We propose and test different criteria to solve the
difficult problem of the filling rate determination.Comment: Sumitted 19 May 200
Planets in Mean-Motion Resonances and the System Around HD45364
In some planetary systems, the orbital periods of two of its members present
a commensurability, usually known by mean-motion resonance. These resonances
greatly enhance the mutual gravitational influence of the planets. As a
consequence, these systems present uncommon behaviors, and their motions need
to be studied with specific methods. Some features are unique and allow us a
better understanding and characterization of these systems. Moreover,
mean-motion resonances are a result of an early migration of the orbits in an
accretion disk, so it is possible to derive constraints on their formation.
Here we review the dynamics of a pair of resonant planets and explain how their
orbits evolve in time. We apply our results to the HD 45365 planetary system.Comment: invited review, 17 pages, 6 figure
Low frequency Raman studies of multi-wall carbon nanotubes: experiments and theory
In this paper, we investigate the low frequency Raman spectra of multi-wall
carbon nanotubes (MWNT) prepared by the electric arc method. Low frequency
Raman modes are unambiguously identified on purified samples thanks to the
small internal diameter of the MWNT. We propose a model to describe these
modes. They originate from the radial breathing vibrations of the individual
walls coupled through the Van der Waals interaction between adjacent concentric
walls. The intensity of the modes is described in the framework of bond
polarization theory. Using this model and the structural characteristics of the
nanotubes obtained from transmission electron microscopy allows to simulate the
experimental low frequency Raman spectra with an excellent agreement. It
suggests that Raman spectroscopy can be as useful regarding the
characterization of MWNT as it is in the case of single-wall nanotubes.Comment: 4 pages, 2 eps fig., 2 jpeg fig., RevTex, submitted to Phys. Rev.
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