6,447 research outputs found
Experimental hydrodynamics of the accelerated turbulent boundary layer with and without mass injection
Hydrodynamics of accelerated turbulent boundary layer with and without mass injectio
Simulating quantum correlations as a distributed sampling problem
It is known that quantum correlations exhibited by a maximally entangled
qubit pair can be simulated with the help of shared randomness, supplemented
with additional resources, such as communication, post-selection or non-local
boxes. For instance, in the case of projective measurements, it is possible to
solve this problem with protocols using one bit of communication or making one
use of a non-local box. We show that this problem reduces to a distributed
sampling problem. We give a new method to obtain samples from a biased
distribution, starting with shared random variables following a uniform
distribution, and use it to build distributed sampling protocols. This approach
allows us to derive, in a simpler and unified way, many existing protocols for
projective measurements, and extend them to positive operator value
measurements. Moreover, this approach naturally leads to a local hidden
variable model for Werner states.Comment: 13 pages, 2 figure
Spin dynamics in the ordered spin ice TbSnO
Geometrical frustration is a central challenge in contemporary condensed
matter physics, a crucible favourable to the emergence of novel physics. The
pyrochlore magnets, with rare earth magnetic moments localized at the vertices
of corner-sharing tetrahedra, play a prominent role in this field, with a rich
variety of exotic ground states ranging from the "spin ices" \hoti\ and \dyti\
to the "spin liquid" and "ordered spin ice" ground states in \tbti\ and \tbsn.
Inelastic neutron scattering provides valuable information for understanding
the nature of these ground states, shedding light on the crystal electric field
(CEF) level scheme and on the interactions between magnetic moments. We have
performed such measurements with unprecedented neutron flux and energy
resolution, in the "ordered spin ice" \tbsn. We argue that a new interaction,
which involves the spin lattice coupling through a low temperature distortion
of the trigonal crystal field, is necessary to account for the data
Simulation of bipartite qudit correlations
We present a protocol to simulate the quantum correlations of an arbitrary
bipartite state, when the parties perform a measurement according to two
traceless binary observables. We show that bits of classical
communication is enough on average, where is the dimension of both systems.
To obtain this result, we use the sampling approach for simulating the quantum
correlations. We discuss how to use this method in the case of qudits.Comment: 7 page
Dark energy with non-adiabatic sound speed: initial conditions and detectability
Assuming that the universe contains a dark energy fluid with a constant
linear equation of state and a constant sound speed, we study the prospects of
detecting dark energy perturbations using CMB data from Planck,
cross-correlated with galaxy distribution maps from a survey like LSST. We
update previous estimates by carrying a full exploration of the mock data
likelihood for key fiducial models. We find that it will only be possible to
exclude values of the sound speed very close to zero, while Planck data alone
is not powerful enough for achieving any detection, even with lensing
extraction. We also discuss the issue of initial conditions for dark energy
perturbations in the radiation and matter epochs, generalizing the usual
adiabatic conditions to include the sound speed effect. However, for most
purposes, the existence of attractor solutions renders the perturbation
evolution nearly independent of these initial conditions.Comment: 16 pages, 2 figures, version accepted in JCA
Density-based mixing parameter for hybrid functionals
A very popular ab-initio scheme to calculate electronic properties in solids
is the use of hybrid functionals in density functional theory (DFT) that mixes
a portion of Fock exchange with DFT functionals. In spite of their success, a
major problem still remains, related to the use of one single mixing parameter
for all materials. Guided by physical arguments that connect the mixing
parameter to the dielectric properties of the solid, and ultimately to its band
gap, we propose a method to calculate this parameter from the electronic
density alone. This method is able to cut significantly the error of
traditional hybrid functionals for large and small gap materials, while
retaining a good description of structural properties. Moreover, its
implementation is simple and leads to a negligible increase of the
computational time.Comment: submitte
Comparing Simulations of AGN Feedback
We perform adaptive mesh refinement (AMR) and smoothed particle hydrodynamics
(SPH) cosmological zoom simulations of a region around a forming galaxy
cluster, comparing the ability of the methods to handle successively more
complex baryonic physics. In the simplest, non-radiative case, the two methods
are in good agreement with each other, but the SPH simulations generate central
cores with slightly lower entropies and virial shocks at slightly larger radii,
consistent with what has been seen in previous studies. The inclusion of
radiative cooling, star formation, and stellar feedback leads to much larger
differences between the two methods. Most dramatically, at z=5, rapid cooling
in the AMR case moves the accretion shock well within the virial radius, while
this shock remains near the virial radius in the SPH case, due to excess
heating, coupled with poorer capturing of the shock width. On the other hand,
the addition of feedback from active galactic nuclei (AGN) to the simulations
results in much better agreement between the methods. In this case both
simulations display halo gas entropies of 100 keV cm^2, similar decrements in
the star-formation rate, and a drop in the halo baryon content of roughly 30%.
This is consistent with AGN growth being self-regulated, regardless of the
numerical method. However, the simulations with AGN feedback continue to differ
in aspects that are not self-regulated, such that in SPH a larger volume of gas
is impacted by feedback, and the cluster still has a lower entropy central
core.Comment: 22 pages, 20 figures, 3 tables, Accepted to ApJ, comments welcom
Phase behavior of a confined nano-droplet in the grand-canonical ensemble: the reverse liquid-vapor transition
The equilibrium density distribution and thermodynamic properties of a
Lennard-Jones fluid confined to nano-sized spherical cavities at constant
chemical potential was determined using Monte Carlo simulations. The results
describe both a single cavity with semipermeable walls as well as a collection
of closed cavities formed at constant chemical potential. The results are
compared to calculations using classical Density Functional Theory (DFT). It is
found that the DFT calculations give a quantitatively accurate description of
the pressure and structure of the fluid. Both theory and simulation show the
presence of a ``reverse'' liquid-vapor transition whereby the equilibrium state
is a liquid at large volumes but becomes a vapor at small volumes.Comment: 13 pages, 8 figures, to appear in J. Phys. : Cond. Mat
On the number of simple arrangements of five double pseudolines
We describe an incremental algorithm to enumerate the isomorphism classes of
double pseudoline arrangements. The correction of our algorithm is based on the
connectedness under mutations of the spaces of one-extensions of double
pseudoline arrangements, proved in this paper. Counting results derived from an
implementation of our algorithm are also reported.Comment: 24 pages, 16 figures, 6 table
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