Global Analysis of Solar Neutrino and KamLAND Data

A global analysis of the data from all the solar neutrino experiments combined with the recent KamLAND data is presented. A formula frequently used in the literature gives survival probability for three active solar neutrino flavors in terms of a suitably-modified two-flavor survival probability. Corrections to this formula, which depend on $\theta_{13}$ and $\delta m_{31}^2$, are calculated. For the mass scale suggested by the atmospheric neutrino experiments the contributions of $\delta m_{31}^2$ to these corrections is found to be negligible. The role of $\theta_{13}$ in solar neutrino physics is elaborated. For electron neutrino oscillations into another active flavor, we find best fit values of $\tan^2 \theta_{12} \sim 0.46$, $\tan^2 \theta_{13} \sim 0$, and $\delta m_{21}^2 \sim 7.1 \times 10^{-5}$ eV$^2$. It is found that the combined solar neutrino and KamLAND date provide the limit $\cos^4 \theta_{13} < 0.8$ at the 90 % confidence level.Comment: 17 pages of REVTEX, 6 figures; several typos are correcte

Excitons in van der Waals materials : From monolayer to bulk hexagonal boron nitride

We present a general picture of the exciton properties of layered materials in terms of the excitations of their single-layer building blocks. To this end, we derive a model excitonic Hamiltonian by drawing an analogy with molecular crystals, which are other prototypical van der Waals materials. We employ this simplified model to analyze in detail the excitation spectrum of hexagonal boron nitride (hBN) that we have obtained from the ab initio solution of the many-body Bethe-Salpeter equation as a function of momentum. In this way, we identify the character of the lowest-energy excitons in hBN, discuss the effects of the interlayer hopping and the electron-hole exchange interaction on the exciton dispersion, and illustrate the relation between exciton and plasmon excitations in layered materials.Peer reviewe

Preconditioning of the generalized Stokes problem arising from the approximation of the time-dependent Navier-Stokes equations

The paper considers standard iterative methods for solving the generalized Stokes problem arising from the time and space approximation of the time-dependent incompressible Navier-Stokes equations. Various preconditioning techniques are considered (Cahouet&Chabard and augmented Lagrangian), and one investigates whether these methods can compete with traditional pressure-correction and velocity-correction methods in terms of CPU time per degree of freedom and per time step. Numerical tests on fine unstructured meshes (68 millions degrees of freedoms) demonstrate convergence rates that are independent of the mesh size and improve with the Reynolds number. Three conclusions are drawn from the paper: (1) Although very good parallel scalability is observed for the augmented Lagrangian method, thorough tests on large problems reveal that the overall CPU time per degree of freedom and per time step is best for the standard Cahouet&Chabar preconditioner. (2) Whether solving the pressure Schur complement problem or solving the full couple system at once does not make any significant difference in term of CPU time per degree of freedom and per time step. (3) All the methods tested in the paper, whether matrix-free or not, are on average 30 times slower than traditional pressure-correction and velocity-correction methods. Hence, although all these methods are very efficient for solving steady state problems, they are not yet competitive for solving time-dependent problems

BLUE-based NO2 data assimilation at urban scale

International audienceWe aim at optimally combining air quality computations, from the Gaussian model ADMS Urban, and ground observations at urban scale. An ADMS simulation generated NO2 concentration fields across Clermont-Ferrand (France) down to street level, every 3 h for the full year 2008. A monitoring network composed of nine fixed stations provided hourly observations to be assimilated. Every 3 h, we compute the so-called BLUE (best linear unbiased estimator), which is a concentration field merging ADMS outputs and ground observations. Its error variance is supposed to be minimal under given assumptions regarding the errors on observations and model simulations. A key step lies in the modeling of error covariances between the computed NO2 concentrations across the city. We introduce a parameterized covariance which heavily relies on the road network. The covariance between two locations depends on the distance of each location to the road network and on the distance between the locations along the road network. Efficient parameters for the covariances are primarily chosen according to prior assumptions, χ2 diagnosis and leave-one-out cross-validations. According to the cross-validations, the improvements due to the assimilation seem moderately far from the observation network, but the root mean square error roughly decreases by 30-50% in the main city where the station density is high. The method is computationally tractable for the generation of improved concentration fields over a long period, or for day-to-day forecasts

All-MOS implementation of RC networks for time-controlled Gaussian spatial filtering

This paper addresses the design and VLSI implementation of MOS-based RC networks capable of performing time-controlled Gaussian filtering. In these networks, all the resistors are substituted one by one by a single MOS transistor biased in the ohmic region. The design of this elementary transistor is carefully realized according to the value of the ideal resistor to be emulated. For a prescribed signal range, the MOSFET in triode region delivers an interval of instantaneous resistance values. We demonstrate that, for the elementary 2-node network, establishing the design equation at a particular point within this interval guarantees minimum error. This equation is then corroborated for networks of arbitrary size by analyzing them from a stochastic point of view. Following the design methodology proposed, the error committed by an MOS-based grid when compared with its equivalent ideal RC network is, despite the intrinsic nonlinearities of the transistors, below 1% even under mismatch conditions of 10%. In terms of image processing, this error hardly affects the outcome, which is perceptually equivalent to that of the ideal network. These results, extracted from simulation, are verified in a prototype vision chip with QCIF resolution manufactured in the AMS 0.35µm CMOS-OPTO process. This prototype incorporates a focal-plane MOS-based RC network that performs fully programmable Gaussian filtering.Junta de Andalucía 2006-TIC-2352Ministerio de Ciencia e Innovación TEC 2009-1181

A fast weakly intrusive multiscale method in explicit dynamics

This paper presents new developments on a weakly intrusive approach for the simplified implementation of space and time multiscale methods within an explicit dynamics software. The 'substitution' method proposed in previous works allows to take advantage of a global coarse model, typically used in an industrial context, running separate, refined in space and in time, local analyses only where needed. The proposed technique is iterative, but the explicit character of the method allows to perform the global computation only once per global time step, while a repeated solution is required for the small local problems only. Nevertheless, a desirable goal is to reach convergence with a reduced number of iterations. To this purpose, we propose here a new iterative algorithm based on an improved interface inertia operator. The new operator exploits a combined property of velocity Hermite time interpolation on the interface and of the central difference integration scheme, allowing the consistent upscaling of interface inertia contributions from the lower scale. This property is exploited to construct an improved mass matrix operator for the interface coupling, allowing to significantly enhance the convergence rate. The efficiency and robustness of the procedure are demonstrated through several examples of growing complexity. Copyright {\copyright} 2014 John Wiley \& Sons, Ltd

Quantum concentration inequalities

We establish transportation cost inequalities (TCI) with respect to the quantum Wasserstein distance by introducing quantum extensions of well-known classical methods: first, using a non-commutative version of Ollivier's coarse Ricci curvature, we prove that high temperature Gibbs states of commuting Hamiltonians on arbitrary hypergraphs $H=(V,E)$ satisfy a TCI with constant scaling as $O(|V|)$. Second, we argue that the temperature range for which the TCI holds can be enlarged by relating it to recently established modified logarithmic Sobolev inequalities. Third, we prove that the inequality still holds for fixed points of arbitrary reversible local quantum Markov semigroups on regular lattices, albeit with slightly worsened constants, under a seemingly weaker condition of local indistinguishability of the fixed points. Finally, we use our framework to prove Gaussian concentration bounds for the distribution of eigenvalues of quasi-local observables and argue the usefulness of the TCI in proving the equivalence of the canonical and microcanonical ensembles and an exponential improvement over the weak Eigenstate Thermalization Hypothesis.Comment: 31 pages, one figur

Numerical Calculation of Convection with Reduced Speed of Sound Technique

Context. The anelastic approximation is often adopted in numerical calculation with low Mach number, such as stellar internal convection. This approximation requires frequent global communication, because of an elliptic partial differential equation. Frequent global communication is negative factor for the parallel computing with a large number of CPUs. Aims. The main purpose of this paper is to test the validity of a method that artificially reduces the speed of sound for the compressible fluid equations in the context of stellar internal convection. The reduction of speed of sound allows for larger time steps in spite of low Mach number, while the numerical scheme remains fully explicit and the mathematical system is hyperbolic and thus does not require frequent global communication. Methods. Two and three dimensional compressible hydrodynamic equations are solved numerically. Some statistical quantities of solutions computed with different effective Mach numbers (due to reduction of speed of sound) are compared to test the validity of our approach. Results. Numerical simulations with artificially reduced speed of sound are a valid approach as long as the effective Mach number (based on the reduced speed of sound) remains less than 0.7.Comment: 16 pages, 10 figures, accepted to A&

Hybrid-VPIC: an Open-Source Kinetic/Fluid Hybrid Particle-in-Cell Code

Hybrid-VPIC is an extension of the open-source high-performance particle-in-cell (PIC) code VPIC incorporating hybrid kinetic ion/fluid electron solvers. This paper describes the models that are available in the code and gives an overview of applications of the code to space and laboratory plasma physics problems. Particular choices in how the hybrid solvers were implemented are documented for reference by users. A few solutions for handling numerical complications particular to hybrid codes are also described. Special emphasis is given to the computationally taxing problem of modeling mix in collisional high-energy-density regimes, for which more accurate electron fluid transport coefficients have been implemented for the first time in a hybrid PIC code