A generic length-scale equation for geophysical turbulence models

A generalization of a class of differential length-scale equations typically used in second-order turbulence models for oceanic flows is suggested. Commonly used models, like the k-ε model and the Mellor-Yamada model, can be recovered as special cases of this generic model, and thus can be rationally compared. In addition, a method is proposed that yields a generalized framework for the calibration of the most frequently used class of differential length-scale equations. The generic model, calibrated with this method, exhibits a greater range of applicability than any of the traditional models. Stratified flows, plane mixing layers, and turbulence introduced by breaking surface waves are considered besides some classical test cases

Interactions Between Teachers’ Attribution for Student Learning and Implementation of Evidence-Based Practices

This study investigated interactions between evidence-based practices implemented and attributions of factors contributing to achievement of student learning objectives. Conducted in three school districts in a mid-Atlantic state, 78 teachers completed an end-of-year survey. Internal attributions were significantly correlated with implementation of evidence-based teaching practices in general and in teaching students with disabilities. External attributions were statistically correlated to implementation of evidence- based practices in both reading and teaching students with disabilities. Perceptions of school support were significantly correlated with implementation of evidence-based teaching practices for teaching both reading and writing

Validation and intercomparison of two vertical-mixing schemes in the Mediterranean Sea

International audienceIn this study, two types of vertical turbulence closure models are tested in the Mediterranean Sea in a one-dimensional configuration. The numerical experiments are performed at different locations in the Mediterranean for which the year 2004 is simulated. The model results are then compared and validated with in-situ temperature observations. For the model simulations, initial profiles of temperature and salinity come from the ARGO (Array for Real-time Geostrophic Oceanography) profiles. The surface forcing (momentum, heat) is calculated from bulk formulae using 6-hourly atmospheric data from the European Center for Medium Range Weather Forecast (ECMWF). The vertical mixing schemes tested in this study are a second-order statistical model (k-?) and the non-local K-profile parameterization (KPP). Both schemes yield similar results in terms of reproducing the water column dynamics. A major source of discrepancy between model and observations comes from the uncertainties in the atmospheric forcing parameterization. At this point, net shortwave radiation data from NCEP atmospheric reanalysis has been used obtaining a more realistic Sea Surface Temperature (SST) compared with satellite observations for the summer months

Strong solutions of the thin film equation in spherical geometry

We study existence and long-time behaviour of strong solutions for the thin film equation using a priori estimates in a weighted Sobolev space. This equation can be classified as a doubly degenerate fourth-order parabolic and it models coating flow on the outer surface of a sphere. It is shown that the strong solution asymptotically decays to the flat profile

Thermochemistry of monazite-(La) and dissakisite-(La): implications for monazite and allanite stability in metapelites

Thermochemical properties have been either measured or estimated for synthetic monazite, LaPO4, and dissakisite, CaLaMgAl2(SiO4)3OH, the Mg-equivalent of allanite. A dissakisite formation enthalpy of −6,976.5±10.0kJmol−1 was derived from high-temperature drop-solution measurements in lead borate at 975K. A third-law entropy value of 104.9±1.6Jmol−1K−1 was retrieved from low-temperature heat capacity (C p) measured on synthetic LaPO4 with an adiabatic calorimeter in the 30-300K range. The C p values of lanthanum phases were measured in the 143-723K range by differential scanning calorimetry. In this study, La(OH)3 appeared as suitable for drop solution in lead borate and represents an attractive alternative to La2O3. Pseudo-sections were calculated with the THERIAK-DOMINO software using the thermochemical data retrieved here for a simplified metapelitic composition (La=∑REE+Y) and considering monazite and Fe-free epidotes along the dissakisite-clinozoïsite join, as the only REE-bearing minerals. Calculation shows a stability window for dissakisite-clinozoïsite epidotes (T between 250 and 550°C and P between 1 and 16kbar), included in a wide monazite field. The P-T extension of this stability window depends on the bulk-rock Ca-content. Assuming that synthetic LaPO4 and dissakisite-(La) are good analogues of natural monazite and allanite, these results are consistent with the REE-mineralogy sequence observed in metapelites, where (1) monazite is found to be stable below 250°C, (2) around 250-450°C, depending on the pressure, allanite forms at the expense of monazite and (3) towards amphibolite conditions, monazite reappears at the expense of allanit

Bit-Vector Model Counting using Statistical Estimation

Approximate model counting for bit-vector SMT formulas (generalizing \#SAT) has many applications such as probabilistic inference and quantitative information-flow security, but it is computationally difficult. Adding random parity constraints (XOR streamlining) and then checking satisfiability is an effective approximation technique, but it requires a prior hypothesis about the model count to produce useful results. We propose an approach inspired by statistical estimation to continually refine a probabilistic estimate of the model count for a formula, so that each XOR-streamlined query yields as much information as possible. We implement this approach, with an approximate probability model, as a wrapper around an off-the-shelf SMT solver or SAT solver. Experimental results show that the implementation is faster than the most similar previous approaches which used simpler refinement strategies. The technique also lets us model count formulas over floating-point constraints, which we demonstrate with an application to a vulnerability in differential privacy mechanisms

Baroclinic Interleaving Instability: A Second-Moment Closure Approach

Interleaving motions on a wide, baroclinic front are modeled using a second-moment closure to represent unresolved fluxes by turbulence and salt fingering. A linear perturbation analysis reveals two broad classes of unstable modes. First are scale-selective modes comparable with interleaving as observed in oceanic fronts. These correspond well with observations in some respects but grow by a very different mechanism, which ought to be easily distinguished in hydrographic profiles. The second mode type is the so-called ultraviolet catastrophe, which is expected to lead to steppy profiles even in the absence of interleaving. Both modes are driven by positive feedbacks between interleaving and the underlying small-scale mixing processes. Contrary to expectations, use of the second-moment closure in place of earlier empirical mixing models does not lead to improved agreement with observations.Keywords: Mixing, Diapycnal mixing, Instabilit

The Halo Mass of Optically Luminous Quasars at z ,F≈ ,F1-2 Measured via Gravitational Deflection of the Cosmic Microwave Background

© 2019. The American Astronomical Society. All rights reserved.We measure the average deflection of cosmic microwave background photons by quasars at 〈Z〉= 1.7. Our sample is selected from the Sloan Digital Sky Survey to cover the redshift range 0.9 ≤z≤2.2 with absolute i-band magnitudes of M i ≤-24 (K-corrected to z = 2). A stack of nearly 200,000 targets reveals an 8δ detection of Planck's estimate of the lensing convergence toward the quasars. We fit the signal with a model comprising a Navarro-Frenk-White density profile and a two-halo term accounting for correlated large-scale structure, which dominates the observed signal. The best-fitting model is described by an average halo mass log 10 (M h h -1 M)12.6 ±0.2 = and linear bias b=2.7±0.3 at 〈Z 〉= 1.7, in excellent agreement with clustering studies. We also report a hint, at a 90% confidence level, of a correlation between the convergence amplitude and luminosity, indicating that quasars brighter than Mi≲ -26 reside in halos of typical mass M h ≈ 10 13 h -1 M, scaling roughly as M h ∞ L opt 3/4 at M i ≲-24 mag, in good agreement with physically motivated quasar demography models. Although we acknowledge that this luminosity dependence is a marginal result, the observed Mh-L opt relationship could be interpreted as a reflection of the cutoff in the distribution of black hole accretion rates toward high Eddington ratios: the weak trend of Mh with Lopt observed at low luminosity becomes stronger for the most powerful quasars, which tend to be accreting close to the Eddington limit.Peer reviewedFinal Accepted Versio

A non-variational approach to nonlinear stability in stellar dynamics applied to the King model

In previous work by Y. Guo and G. Rein, nonlinear stability of equilibria in stellar dynamics, i.e., of steady states of the Vlasov-Poisson system, was accessed by variational techniques. Here we propose a different, non-variational technique and use it to prove nonlinear stability of the King model against a class of spherically symmetric, dynamically accessible perturbations. This model is very important in astrophysics and was out of reach of the previous techniques