529 research outputs found
Using Ginkgo’s memory accessor for improving the accuracy of memory-bound low precision BLAS
The roofline model not only provides a powerful tool to relate an application\u27s performance with the specific constraints imposed by the target hardware but also offers a graphic representation of the balance between memory access cost and compute throughput. In this work, we present a strategy to break up the tight coupling between the precision format used for arithmetic operations and the storage format employed for memory operations. (At a high level, this idea is equivalent to compressing/decompressing the data in registers before/after invoking store/load memory operations.) In practice, we demonstrate that a “memory accessor” that hides the data compression behind the memory access, can virtually push the bandwidth-induced roofline, yielding higher performance for memory-bound applications using high precision arithmetic that can handle the numerical effects associated with lossy compression. We also demonstrate that memory-bound applications operating on low precision data can increase the accuracy by relying on the memory accessor to perform all arithmetic operations in high precision. In particular, we demonstrate that memory-bound BLAS operations (including the sparse matrix-vector product) can be re-engineered with the memory accessor and that the resulting accessor-enabled BLAS routines achieve lower rounding errors while delivering the same performance as the fast low precision BLAS
Process for the modification of polymers, in particular polymer nanoparticles
The present invention relates to a highly efficient and ultra fast process for the photo-initiated preparation of polymers by polymerization using photoinitiators comprising a phosphorous oxide or -sulfide group and modification of said polymers. In particular the invention relates to an ultra fast process for the photo-initiated preparation of latices comprising polymer nanoparticles by heterophase polymerization using photoinitiators comprising a phosphorous oxide or -sulfide group and their modification. In another aspect, the invention relates to polymers and polymer nanoparticles obtainable by said process
Spin-orbit coupling and phase-coherence in InAs nanowires
We investigated the magnetotransport of InAs nanowires grown by selective
area metal-organic vapor phase epitaxy. In the temperature range between 0.5
and 30 K reproducible fluctuations in the conductance upon variation of the
magnetic field or the back-gate voltage are observed, which are attributed to
electron interference effects in small disordered conductors. From the
correlation field of the magnetoconductance fluctuations the phase-coherence
length l_phi is determined. At the lowest temperatures l_phi is found to be at
least 300 nm, while for temperatures exceeding 2 K a monotonous decrease of
l_phi with temperature is observed. A direct observation of the weak
antilocalization effect indicating the presence of spin-orbit coupling is
masked by the strong magnetoconductance fluctuations. However, by averaging the
magnetoconductance over a range of gate voltages a clear peak in the
magnetoconductance due to the weak antilocalization effect was resolved. By
comparison of the experimental data to simulations based on a recursive
two-dimensional Green's function approach a spin-orbit scattering length of
approximately 70 nm was extracted, indicating the presence of strong spin-orbit
coupling.Comment: 8 pages, 7 figure
Supercurrent in Nb/InAs-Nanowire/Nb Josephson junctions
We report on the fabrication and measurements of planar mesoscopic Josephson
junctions formed by InAs nanowires coupled to superconducting Nb terminals. The
use of Si-doped InAs-nanowires with different bulk carrier concentrations
allowed to tune the properties of the junctions. We have studied the junction
characteristics as a function of temperature, gate voltage, and magnetic field.
In junctions with high doping concentrations in the nanowire Josephson
supercurrent values up to 100\,nA are found. Owing to the use of Nb as
superconductor the Josephson coupling persists at temperatures up to 4K. In all
junctions the critical current monotonously decreased with the magnetic field,
which can be explained by a recently developed theoretical model for the
proximity effect in ultra-small Josephson junctions. For the low-doped
Josephson junctions a control of the critical current by varying the gate
voltage has been demonstrated. We have studied conductance fluctuations in
nanowires coupled to superconducting and normal metal terminals. The
conductance fluctuation amplitude is found to be about 6 times larger in
superconducting contacted nanowires. The enhancement of the conductance
fluctuations is attributed to phase-coherent Andreev reflection as well as to
the large number of phase-coherent channels due to the large superconducting
gap of the Nb electrodes.Comment: 5 Figure, submitted to Journal of Applied Physic
Automated Identification and Tracking of Deformation Twin Structures in Molecular Dynamics Simulations
Deformation twinning significantly influences the microstructure, texture,
and mechanical properties of metals, necessitating comprehensive studies of
twin formation and interactions. While experimental methods excel at analyzing
individual samples, they often lack the capability for temporal analysis of
twinned structures. Molecular dynamics simulations offer a temporal dimension,
yet the absence of suitable tools for automated crystal twin identification has
been a significant limitation. In this article, we introduce a novel
computational tool integrated into the visualization and analysis software
OVITO. Our tool automates the identification of coherent twin boundaries, links
related twin boundaries, validates twin structures through orientation
analysis, and tracks twins over time, providing quantifiable data and enabling
in-depth investigations. Validation on a copper single crystal under shear
loading demonstrates successful tracking of various twins, revealing their
genesis and growth over multiple timesteps. This innovative approach promises
to advance the computational materials science domain by facilitating the study
of deformation twinning, offering profound insights into the behavior and
mechanical performance of materials
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