3,020 research outputs found
Spin configuration in a frustrated ferromagnetic/antiferromagnetic thin film system
We have studied the magnetic configuration in ultrathin antiferromagnetic Mn
films grown around monoatomic steps on an Fe(001) surface by spin-polarized
scanning tunneling microscopy/spectroscopy and ab-initio-parametrized
self-consistent real-space tight binding calculations in which the spin
quantization axis is independent for each site thus allowing noncollinear
magnetism. Mn grown on Fe(001) presents a layered antiferromagnetic structure.
In the regions where the Mn films overgrows Fe steps the magnetization of the
surface layer is reversed across the steps. Around these defects a frustration
of the antiferromagnetic order occurs. Due to the weakened magnetic coupling at
the central Mn layers, the amount of frustration is smaller than in Cr and the
width of the wall induced by the step does not change with the thickness, at
least for coverages up to seven monolayers.Comment: 10 pages, 5 figure
Structural Properties and Relative Stability of (Meta)Stable Ordered, Partially-ordered and Disordered Al-Li Alloy Phases
We resolve issues that have plagued reliable prediction of relative phase
stability for solid-solutions and compounds. Due to its commercially important
phase diagram, we showcase Al-Li system because historically density-functional
theory (DFT) results show large scatter and limited success in predicting the
structural properties and stability of solid-solutions relative to ordered
compounds. Using recent advances in an optimal basis-set representation of the
topology of electronic charge density (and, hence, atomic size), we present DFT
results that agree reasonably well with all known experimental data for the
structural properties and formation energies of ordered, off-stoichiometric
partially-ordered and disordered alloys, opening the way for reliable study in
complex alloys.Comment: 7 pages, 2 figures, 2 Table
On The Application of Flow Forming to the Fabrication of Type B Radioactive Material Package Containment Vessels, Rev. 1
How mRNA localization and protein synthesis sites influence dendritic protein distribution and dynamics
In this issue ofNeuron,Fonkeu et al. (2019)present a mathematical model of mRNA and protein synthesis,degradation, diffusion, and trafficking in neuronal dendrites. The model can predict the spatial distributionand temporal dynamics of proteins along dendrites. The authors use the model to account forin situimagingdata of CaMKII⍺mRNA and protein in hippocampal neurons
Sound modes broadening for Fibonacci one dimensional quasicrystals
We investigate vibrational excitation broadening in one dimensional Fibonacci
model of quasicrystals (QCs). The chain is constructed from particles with two
masses following the Fibonacci inflation rule. The eigenmode spectrum depends
crucially on the mass ratio. We calculate the eigenstates and eigenfunctions.
All calculations performed self-consistently within the regular expansion over
the three wave coupling constant. The approach can be extended to three
dimensional systems. We find that in the intermediate range of mode coupling
constants, three-wave broadening for the both types of systems (1D Fibonacci
and 3D QCs) depends universally on frequency. Our general qualitative
conclusion is that for a system with a non-simple elementary cell phonon
spectrum broadening is always larger than for a system with a primitive cell
(provided all other characteristics are the same).Comment: 2o pages, 15 figure
Continuum elastic sphere vibrations as a model for low-lying optical modes in icosahedral quasicrystals
The nearly dispersionless, so-called "optical" vibrational modes observed by
inelastic neutron scattering from icosahedral Al-Pd-Mn and Zn-Mg-Y
quasicrystals are found to correspond well to modes of a continuum elastic
sphere that has the same diameter as the corresponding icosahedral basic units
of the quasicrystal. When the sphere is considered as free, most of the
experimentally found modes can be accounted for, in both systems. Taking into
account the mechanical connection between the clusters and the remainder of the
quasicrystal allows a complete assignment of all optical modes in the case of
Al-Pd-Mn. This approach provides support to the relevance of clusters in the
vibrational properties of quasicrystals.Comment: 9 pages without figure
Spatially continuous snow depth mapping by aeroplane photogrammetry for annual peak of winter from 2017 to 2021 in open areas
Information on snow depth and its spatial distribution is important for
numerous applications, including natural hazard management, snow water
equivalent estimation for hydropower, the study of the distribution and
evolution of flora and fauna, and the validation of snow hydrological
models. Due to its heterogeneity and complexity, specific remote sensing
tools are required to accurately map the snow depth distribution in Alpine
terrain. To cover large areas (>100 km2),
airborne laser scanning (ALS) or aerial photogrammetry with large-format
cameras is needed. While both systems require piloted aircraft for data
acquisition, ALS is typically more expensive than photogrammetry but yields
better results in forested terrain. While photogrammetry is slightly
cheaper, it is limited due to its dependency on favourable acquisition
conditions (weather, light conditions). In this study, we present
photogrammetrically processed high-spatial-resolution (0.5 m) annual snow
depth maps, recorded during the peak of winter over a 5-year period under
different acquisition conditions over a study area around Davos,
Switzerland. Compared to previously carried out studies, using the Vexcel
UltraCam Eagle Mark 3 (M3) sensor improves the average ground sampling distance to
0.1 m at similar flight altitudes above ground. This allows for very
detailed snow depth maps in open areas, calculated by subtracting a snow-off
digital terrain model (DTM, acquired with ALS) from the snow-on digital
surface models (DSMs) processed from the airborne imagery. Despite
challenging acquisition conditions during the recording of the UltraCam
images (clouds, shaded areas and fresh snow), 99 % of unforested areas
were successfully photogrammetrically reconstructed. We applied masks (high
vegetation, settlements, water, glaciers) to increase the reliability of the
snow depth calculations. An extensive accuracy assessment was carried out
using check points, the comparison to DSMs derived from unpiloted aerial
systems and the comparison of snow-free DSM pixels to the ALS DTM. The
results show a root mean square error of approximately 0.25 m for the
UltraCam X and 0.15 m for the successor, the UltraCam Eagle M3. We developed
a consistent and reliable photogrammetric workflow for accurate snow depth
distribution mapping over large regions, capable of analysing snow
distribution in complex terrain. This enables more detailed investigations
on seasonal snow dynamics and can be used for numerous applications related
to snow depth distribution, as well as serving as a ground reference for new
modelling approaches and satellite-based snow depth mapping.</p
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Neutron Source Strength Estimates from (a, n) Reactions in Binary Mixtures of Actinide Particles and Light Element Particles
The cumulative distribution of package dose rates, based on the 18 batches of historical PuO{sub 2} particle size distributions, is shown in Fig. 6 for ''Hanford 10-13% Pu-240'' plutonium. The calculated dose rates for all batches range from about 50 mrem/h to about 2,200 mrem/h, with over 50% of the batches being less than the 200 mrem/h limit for public transportation. A more refined analysis would show that almost all of the batches would be less than 200 mrem/h, but some could exceed this limit as seen by the distribution shape. Without detailed characterization of the BeO particle size distribution, additional analysis would not remove the uncertainty in these calculations. Because the actual amount of beryllium contamination is likely to be much less than 500 g, the dose rates would be expected to be much lower than those shown here. Based on the particle size distribution analysis of the 18 batches analyzed, it is also likely that most of the 3013 cans to be loaded in the 9975 Package will have dose rates that are less than the 200 mrem/h limit for the package surface. However, extra care will be required in performing, and verifying, the dose rate measurements at the surface of the package, prior to shipment
Quantum Particles Constrained on Cylindrical Surfaces with Non-constant Diameter
We present a theoretical formulation of the one-electron problem constrained
on the surface of a cylindrical tubule with varying diameter. Because of the
cylindrical symmetry, we may reduce the problem to a one-dimensional equation
for each angular momentum quantum number along the cylindrical axis. The
geometrical properties of the surface determine the electronic structures
through the geometry dependent term in the equation. Magnetic fields parallel
to the axis can readily be incorporated. Our formulation is applied to simple
examples such as the catenoid and the sinusoidal tubules. The existence of
bound states as well as the band structures, which are induced geometrically,
for these surfaces are shown. To show that the electronic structures can be
altered significantly by applying a magnetic field, Aharonov-Bohm effects in
these examples are demonstrated.Comment: 7 pages, 7 figures, submitted to J. Phys. Soc. Jp
Interaction-free measurement and forward scattering
Interaction-free measurement is shown to arise from the forward-scattered
wave accompanying absorption: a "quantum silhouette" of the absorber.
Accordingly, the process is not free of interaction. For a perfect absorber the
forward-scattered wave is locked both in amplitude and in phase. For an
imperfect one it has a nontrivial phase of dynamical origin (``colored
silhouette"), measurable by interferometry. Other examples of quantum
silhouettes, all controlled by unitarity, are briefly discussed.Comment: 4 pages in RevTex + 1 figure in eps; submitted to Phys. Rev. A since
09Jan98; now update
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