41,460 research outputs found
Reflexion M\"ossbauer analysis of the in situ oxidation products hydroxycarbonate green rust
The purpose of this study is to determine the nature of the oxidation
products of FeII-III hydroxycarbonate FeII4FeIII2(OH)12CO3~3H2O (green rust
GR(CO32-)) by using the miniaturised M\"ossbauer spectrometer MIMOS II. Two
M\"ossbauer measurements methods are used: method (i) with green rust pastes
coated with glycerol and spread into Plexiglas sample holders, and method (ii)
with green rust pastes in the same sample holders but introduced into a
gas-tight cell with a beryllium window under a continuous nitrogen flow. Method
(ii) allows us to follow the continuous deprotonation of GR(CO32-) into the
fully ferric deprotonated form FeIII6O4(OH)8CO3~3H2O by adding the correct
amount of H2O2, without any further oxidation or degradation of the samples
Method for locating low-energy solutions within DFT+U
The widely employed DFT+U formalism is known to give rise to many self-consistent yet energetically distinct solutions in correlated systems, which can be highly problematic for reliably predicting the thermodynamic and physical properties of such materials. Here we study this phenomenon in the bulk materials UO_2, CoO, and NiO, and in a CeO_2 surface. We show that the following factors affect which self-consistent solution a DFT+U calculation reaches: (i) the magnitude of U; (ii) initial correlated orbital occupations; (iii) lattice geometry; (iv) whether lattice symmetry is enforced on the charge density; and (v) even electronic mixing parameters. These various solutions may differ in total energy by hundreds of meV per atom, so identifying or approximating the ground state is critical in the DFT+U scheme. We propose an efficient U-ramping method for locating low-energy solutions, which we validate in a range of test cases. We also suggest that this method may be applicable to hybrid functional calculations
Complete limiting stress solutions for the bearing capacity of strip footings on a Mohr-Coulomb soil
Buku Cerita Bergambar Kisah 12 Murid Yesus Dengan Pendekatan Interaktif Untuk Anak Usia 5-7 Tahun
Perancangan ini dibuat karena kurangnya keinginan anak-anak untuk mempelajari dan mengenal lebih dalam kisah-kisah yang ada di dalam Alkitab. Tujuan dari perancangan ini agar memudahkan anak-anak untuk mengerti kisah yang ada di dalam Alkitab dengan menggunakan media-media pendukung seperti alat peraga sebagai media interaktif dan sarana pembelajaran yang tidak membuat anak-anak merasa cepat bosan. Perancangan ini menggunakan media peraga berupa boneka tangan yang bertujuan agar anak-anak juga dapat berperan dalam kisah yang ada di dalam buku perancangan ini
Percolation-to-hopping crossover in conductor-insulator composites
Here, we show that the conductivity of conductor-insulator composites in
which electrons can tunnel from each conducting particle to all others may
display both percolation and tunneling (i.e. hopping) regimes depending on few
characteristics of the composite. Specifically, we find that the relevant
parameters that give rise to one regime or the other are (where is
the size of the conducting particles and is the tunneling length) and the
specific composite microstructure. For large values of , percolation
arises when the composite microstructure can be modeled as a regular lattice
that is fractionally occupied by conducting particle, while the tunneling
regime is always obtained for equilibrium distributions of conducting particles
in a continuum insulating matrix. As decreases the percolating behavior
of the conductivity of lattice-like composites gradually crosses over to the
tunneling-like regime characterizing particle dispersions in the continuum. For
values lower than the conductivity has tunneling-like
behavior independent of the specific microstructure of the composite.Comment: 8 pages, 5 figure
A real-space grid implementation of the Projector Augmented Wave method
A grid-based real-space implementation of the Projector Augmented Wave (PAW)
method of P. E. Blochl [Phys. Rev. B 50, 17953 (1994)] for Density Functional
Theory (DFT) calculations is presented. The use of uniform 3D real-space grids
for representing wave functions, densities and potentials allows for flexible
boundary conditions, efficient multigrid algorithms for solving Poisson and
Kohn-Sham equations, and efficient parallelization using simple real-space
domain-decomposition. We use the PAW method to perform all-electron
calculations in the frozen core approximation, with smooth valence wave
functions that can be represented on relatively coarse grids. We demonstrate
the accuracy of the method by calculating the atomization energies of twenty
small molecules, and the bulk modulus and lattice constants of bulk aluminum.
We show that the approach in terms of computational efficiency is comparable to
standard plane-wave methods, but the memory requirements are higher.Comment: 13 pages, 3 figures, accepted for publication in Physical Review
Intermittent permeation of cylindrical nanopores by water
Molecular Dynamics simulations of water molecules in nanometre sized
cylindrical channels connecting two reservoirs show that the permeation of
water is very sensitive to the channel radius and to electric polarization of
the embedding material. At threshold, the permeation is {\emph{intermittent}}
on a nanosecond timescale, and strongly enhanced by the presence of an ion
inside the channel, providing a possible mechanism for gating. Confined water
remains surprisingly fluid and bulk-like. Its behaviour differs strikingly from
that of a reference Lennard-Jones fluid, which tends to contract into a highly
layered structure inside the channel.Comment: 4 pages, 4 figure
On the frequency and remnants of Hypernovae
Under the hypothesis that some fraction of massive stellar core collapses
give rise to unusually energetic events, termed hypernovae, I examine the
required rates assuming some fraction of such events yield gamma ray bursts. I
then discuss evidence from studies of pulsars and r-process nucleosynthesis
that independently suggests the existence of a class of unusually energetic
events. Finally I describe a scenario which links these different lines of
evidence as supporting the hypernova hypothesis.Comment: TeX, To appear in ApJ Letter
Theoretical Support for the Hydrodynamic Mechanism of Pulsar Kicks
The collapse of a massive star's core, followed by a neutrino-driven,
asymmetric supernova explosion, can naturally lead to pulsar recoils and
neutron star kicks. Here, we present a two-dimensional, radiation-hydrodynamic
simulation in which core collapse leads to significant acceleration of a
fully-formed, nascent neutron star (NS) via an induced, neutrino-driven
explosion. During the explosion, a ~10% anisotropy in the low-mass,
high-velocity ejecta lead to recoil of the high-mass neutron star. At the end
of our simulation, the NS has achieved a velocity of ~150 km s and is
accelerating at ~350 km s, but has yet to reach the ballistic regime.
The recoil is due almost entirely to hydrodynamical processes, with anisotropic
neutrino emission contributing less than 2% to the overall kick magnitude.
Since the observed distribution of neutron star kick velocities peaks at
~300-400 km s, recoil due to anisotropic core-collapse supernovae
provides a natural, non-exotic mechanism with which to obtain neutron star
kicks.Comment: Replaced with Phys. Rev. D accepted versio
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