5,464 research outputs found
Extraction of the CP-violating phase using and decays
Using the B{\sc a}B{\sc ar}\ measurements of the Dalitz plots for , , , , and decays, we demonstrate that it is
possible to cleanly extract the weak phase . We find four possible
solutions. Three of these -- , , and -- are in
disagreement with the SM, while one -- -- is consistent with the SM.
An advantage of this Dalitz-plot method is that one can obtain many independent
measurements of , thereby reducing its statistical error. An accurate
determination of the errors, however, requires detailed knowledge of the data.Comment: 9 pages, 2 figures, version accepted for publication in Physics
Letters
Thermal transport in 2D and 3D nanowire networks
We report on thermal transport properties in 2 and 3 dimensions
interconnected nanowire networks (strings and nodes). The thermal conductivity
of these nanostructures decreases in increasing the distance of the nodes,
reaching ultra-low values. This effect is much more pronounced in 3D networks
due to increased porosity, surface to volume ratio and the enhanced
backscattering at 3D nodes compared to 2D nodes. We propose a model to estimate
the thermal resistance related to the 2D and 3D interconnections in order to
provide an analytic description of thermal conductivity of such nanowire
networks; the latter is in good agreement with Molecular Dynamic results
Binding Energies in Benzene Dimers: Nonlocal Density Functional Calculations
The interaction energy and minimum energy structure for different geometries
of the benzene dimer has been calculated using the recently developed nonlocal
correlation energy functional for calculating dispersion interactions. The
comparison of this straightforward and relatively quick density functional
based method with recent calculations can elucidate how the former, quicker
method might be exploited in larger more complicated biological, organic,
aromatic, and even infinite systems such as molecules physisorbed on surfaces,
and van der Waals crystals.Comment: 17 pages, 6 figure
Chaos and Turbulent Nucleosynthesis Prior to a Supernova Explosion
Three-dimensional (3D), time dependent numerical simulations, of flow of
matter in stars, now have sufficient resolution to be fully turbulent. The late
stages of the evolution of massive stars, leading up to core collapse to a
neutron star (or black hole), and often to supernova explosion and
nucleosynthesis, are strongly convective because of vigorous neutrino cooling
and nuclear heating. Unlike models based on current stellar evolutionary
practice, these simulations show a chaotic dynamics characteristic of highly
turbulent flow. Theoretical analysis of this flow, both in the
Reynolds-averaged Navier-Stokes (RANS) framework and by simple dynamic models,
show an encouraging consistency with the numerical results. It may now be
possible to develop physically realistic and robust procedures for convection
and mixing which (unlike 3D numerical simulation) may be applied throughout the
long life times of stars. In addition, a new picture of the presupernova stages
is emerging which is more dynamic and interesting (i.e., predictive of new and
newly observed phenomena) than our previous one.Comment: 11 pages, 2 figures, Submitted to AIP Advances: Stardust, added
figures and modest rewritin
Degrees of Freedom of Certain Interference Alignment Schemes with Distributed CSIT
In this work, we consider the use of interference alignment (IA) in a MIMO
interference channel (IC) under the assumption that each transmitter (TX) has
access to channel state information (CSI) that generally differs from that
available to other TXs. This setting is referred to as distributed CSIT. In a
setting where CSI accuracy is controlled by a set of power exponents, we show
that in the static 3-user MIMO square IC, the number of degrees-of-freedom
(DoF) that can be achieved with distributed CSIT is at least equal to the DoF
achieved with the worst accuracy taken across the TXs and across the
interfering links. We conjecture further that this represents exactly the DoF
achieved. This result is in strong contrast with the centralized CSIT
configuration usually studied (where all the TXs share the same, possibly
imperfect, channel estimate) for which it was shown that the DoF achieved at
receiver (RX) i is solely limited by the quality of its own feedback. This
shows the critical impact of CSI discrepancies between the TXs, and highlights
the price paid by distributed precoding.Comment: This is an extended version of a conference submission which will be
presented at the IEEE conference SPAWC, Darmstadt, June 201
Toward a consistent use of overshooting parametrizations in 1D stellar evolution codes
Several parametrizations for overshooting in 1D stellar evolution
calculations coexist in the literature. These parametrizations are used
somewhat arbitrarily in stellar evolution codes, based on what works best for a
given problem, or even for historical reasons related to the development of
each code. We bring attention to the fact that these different parametrizations
correspond to different physical regimes of overshooting, depending whether the
effects of radiation are dominant, marginal, or negligible. Our analysis is
based on previously published theoretical results, as well as multidimensional
hydrodynamical simulations of stellar convection where the interaction between
the convective region and a stably-stratified region is observed. Although the
underlying hydrodynamical processes are the same, the outcome of the
overshooting process is profoundly affected by radiative effects. Using a
simple picture of the scales involved in the overshooting process, we show how
three regimes are obtained, depending on the importance of radiative effects.
These three regimes correspond to the different behaviors observed in
hydrodynamical simulations so far, and to the three types of parametrizations
used in 1D codes. We suggest that the existing parametrizations for
overshooting should coexist in 1D stellar evolution codes, and should be
applied consistently at convective boundaries depending on the local physical
conditions.Comment: 5 pages, 2 figures, to appear in A&A as a regular paper. Last
version: language editing + typos in Eq. (6) & (9) correcte
Turbulent convection in stellar interiors. III. Mean-field analysis and stratification effects
We present 3D implicit large eddy simulations (ILES) of the turbulent
convection in the envelope of a 5 Msun red giant star and in the oxygen-burning
shell of a 23 Msun supernova progenitor. The numerical models are analyzed in
the framework of 1D Reynolds-Averaged Navier-Stokes (RANS) equations. The
effects of pressure fluctuations are more important in the red giant model,
owing to larger stratification of the convective zone. We show how this impacts
different terms in the mean-field equations. We clarify the driving sources of
kinetic energy, and show that the rate of turbulent dissipation is comparable
to the convective luminosity. Although our flows have low Mach number and are
nearly adiabatic, our analysis is general and can be applied to photospheric
convection as well. The robustness of our analysis of turbulent convection is
supported by the insensitivity of the mean-field balances to linear mesh
resolution. We find robust results for the turbulent convection zone and the
stable layers in the oxygen-burning shell model, and robust results everywhere
in the red giant model, but the mean fields are not well converged in the
narrow boundary regions (which contain steep gradients) in the oxygen-burning
shell model. This last result illustrates the importance of unresolved physics
at the convective boundary, which governs the mixing there.Comment: 26 pages, 20 figures, Accepted for publication in Ap
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