4,849 research outputs found
Reconstruction of primordial density fields
The Monge-Ampere-Kantorovich (MAK) reconstruction is tested against
cosmological N-body simulations. Using only the present mass distribution
sampled with particles, and the assumption of homogeneity of the primordial
distribution, MAK recovers for each particle the non-linear displacement field
between its present position and its Lagrangian position on a primordial
uniform grid. To test the method, we examine a standard LCDM N-body simulation
with Gaussian initial conditions and 6 models with non-Gaussian initial
conditions: a chi-squared model, a model with primordial voids and four weakly
non-Gaussian models. Our extensive analyses of the Gaussian simulation show
that the level of accuracy of the reconstruction of the nonlinear displacement
field achieved by MAK is unprecedented, at scales as small as about 3 Mpc. In
particular, it captures in a nontrivial way the nonlinear contribution from
gravitational instability, well beyond the Zel'dovich approximation. This is
also confirmed by our analyses of the non-Gaussian samples. Applying the
spherical collapse model to the probability distribution function of the
divergence of the displacement field, we also show that from a
well-reconstructed displacement field, such as that given by MAK, it is
possible to accurately disentangle dynamical contributions induced by
gravitational clustering from possible initial non-Gaussianities, allowing one
to efficiently test the non-Gaussian nature of the primordial fluctuations. In
addition, a simple application of MAK using the Zel'dovich approximation allows
one to also recover accurately the present-day peculiar velocity field on
scales of about 8 Mpc.Comment: Version to appear in MNRAS, 24 pages, 21 figures appearing (uses 35
figure files), 1 tabl
Sub-Inertial Gravity Modes in the B8V Star KIC 7760680 Reveal Moderate Core Overshooting and Low Vertical Diffusive Mixing
KIC 7760680 is so far the richest slowly pulsating B star, by exhibiting 36
consecutive dipole () gravity (g-) modes. The monotonically decreasing
period spacing of the series, in addition to the local dips in the pattern
confirm that KIC 7760680 is a moderate rotator, with clear mode trapping in
chemically inhomogeneous layers. We employ the traditional approximation of
rotation to incorporate rotational effects on g-mode frequencies. Our detailed
forward asteroseismic modelling of this g-mode series reveals that KIC 7760680
is a moderately rotating B star with mass M. By
simultaneously matching the slope of the period spacing, and the number of
modes in the observed frequency range, we deduce that the equatorial rotation
frequency of KIC 7760680 is 0.4805 day, which is 26\% of its Roche break
up frequency. The relative deviation of the model frequencies and those
observed is less than one percent. We succeed to tightly constrain the
exponentially-decaying convective core overshooting parameter to . This means that convective core overshooting can
coexist with moderate rotation. Moreover, models with exponentially-decaying
overshoot from the core outperform those with the classical step-function
overshoot. The best value for extra diffusive mixing in the radiatively stable
envelope is confined to (with in cm sec), which is notably smaller than theoretical
predictions.Comment: 12 Figures, 2 Tables, all data publicly available for download;
accepted for publication in Astrophysical Journa
World War 2 Ace Fighter Flight Log
World War 2 flight log of Lieutenant Colonel William H. Mathis. Events include training and flights in Pacific Theater.https://digitalcommons.northgeorgia.edu/alumni/1003/thumbnail.jp
Experimentally Accessible Witnesses of Many-Body Localization
The phenomenon of many-body localized (MBL) systems has attracted significant interest in recent years, for its intriguing implications from a perspective of both condensed-matter and statistical physics: they are insulators even at non-zero temperature and fail to thermalize, violating expectations from quantum statistical mechanics. What is more, recent seminal experimental developments with ultra-cold atoms in optical lattices constituting analog quantum simulators have pushed many-body localized systems into the realm of physical systems that can be measured with high accuracy. In this work, we introduce experimentally accessible witnesses that directly probe distinct features of MBL, distinguishing it from its Anderson counterpart. We insist on building our toolbox from techniques available in the laboratory, including on-site addressing, super-lattices, and time-of-flight measurements, identifying witnesses based on fluctuations, density–density correlators, densities, and entanglement. We build upon the theory of out of equilibrium quantum systems, in conjunction with tensor network and exact simulations, showing the effectiveness of the tools for realistic models
Phase-field simulations of viscous fingering in shear-thinning fluids
A phase-field model for the Hele-Shaw flow of non-Newtonian fluids is
developed. It extends a previous model for Newtonian fluids to a wide range of
shear-dependent fluids. The model is applied to perform simulations of viscous
fingering in shear- thinning fluids, and it is found to be capable of
describing the complete crossover from the Newtonian regime at low shear rate
to the strongly shear-thinning regime at high shear rate. The width selection
of a single steady-state finger is studied in detail for a 2-plateaux
shear-thinning law (Carreau law) in both its weakly and strongly shear-thinning
limits, and the results are related to previous analyses. In the strongly
shear-thinning regime a rescaling is found for power-law (Ostwald-de-Waehle)
fluids that allows for a direct comparison between simulations and experiments
without any adjustable parameters, and good agreement is obtained
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