90 research outputs found
Elinvar effect in Ti simulated by on-the-fly trained moment tensor potential
A combination of quantum mechanics calculations with machine learning (ML)
techniques can lead to a paradigm shift in our ability to predict materials
properties from first principles. Here we show that on-the-fly training of an
interatomic potential described through moment tensors provides the same
accuracy as state-of-the-art {\it ab inito} molecular dynamics in predicting
high-temperature elastic properties of materials with two orders of magnitude
less computational effort. Using the technique, we investigate high-temperature
bcc phase of titanium and predict very weak, Elinvar, temperature dependence of
its elastic moduli, similar to the behavior of the so-called GUM Ti-based
alloys [T. Sato {\ it et al.}, Science {\bf 300}, 464 (2003)]. Given the fact
that GUM alloys have complex chemical compositions and operate at room
temperature, Elinvar properties of elemental bcc-Ti observed in the wide
temperature interval 1100--1700 K is unique.Comment: 15 pages, 4 figure
A Measurement of the Absorption of Liquid Argon Scintillation Light by Dissolved Nitrogen at the Part-Per-Million Level
We report on a measurement of the absorption length of scintillation light in
liquid argon due to dissolved nitrogen at the part-per-million (ppm) level. We
inject controlled quantities of nitrogen into a high purity volume of liquid
argon and monitor the light yield from an alpha source. The source is placed at
different distances from a cryogenic photomultiplier tube assembly. By
comparing the light yield from each position we extract the absorption cross
section of nitrogen. We find that nitrogen absorbs argon scintillation light
with strength of ,
corresponding to an absorption cross section of . We obtain the relationship
between absorption length and nitrogen concentration over the 0 to 50 ppm range
and discuss the implications for the design and data analysis of future large
liquid argon time projection chamber (LArTPC) detectors. Our results indicate
that for a current-generation LArTPC, where a concentration of 2 parts per
million of nitrogen is expected, the attenuation length due to nitrogen will be
meters.Comment: v2: Correct mistake in molecular absorption cross section
calculation, and a minor typo in fig
Discrete Fourier analysis with lattices on planar domains
A discrete Fourier analysis associated with translation lattices is developed
recently by the authors. It permits two lattices, one determining the integral
domain and the other determining the family of exponential functions. Possible
choices of lattices are discussed in the case of lattices that tile \RR^2 and
several new results on cubature and interpolation by trigonometric, as well as
algebraic, polynomials are obtained
Least Error Sample Distribution Function
Email: The empirical distribution function (ecdf) is unbiased in the usual sense, but shows certain order bias. Pyke suggested discrete ecdf using expectations of order statistics. Piecewise constant optimal ecdf saves 200%/N of sample size N. Results are compared with linear interpolation for U(0, 1), which require up to sixfold shorter samples at the same accuracy
Multi-Resolution Functional ANOVA for Large-Scale, Many-Input Computer Experiments
The Gaussian process is a standard tool for building emulators for both
deterministic and stochastic computer experiments. However, application of
Gaussian process models is greatly limited in practice, particularly for
large-scale and many-input computer experiments that have become typical. We
propose a multi-resolution functional ANOVA model as a computationally feasible
emulation alternative. More generally, this model can be used for large-scale
and many-input non-linear regression problems. An overlapping group lasso
approach is used for estimation, ensuring computational feasibility in a
large-scale and many-input setting. New results on consistency and inference
for the (potentially overlapping) group lasso in a high-dimensional setting are
developed and applied to the proposed multi-resolution functional ANOVA model.
Importantly, these results allow us to quantify the uncertainty in our
predictions. Numerical examples demonstrate that the proposed model enjoys
marked computational advantages. Data capabilities, both in terms of sample
size and dimension, meet or exceed best available emulation tools while meeting
or exceeding emulation accuracy
GPU acceleration of a fully 3D iterative reconstruction software for PET using CUDA
Proceeding of: 2009 IEEE Nuclear Science Symposium Conference Record (NSS/MIC), Orlando, Florida, 25-31 October 2009A CUDA implementation of the existing software FIRST (Fast Iterative Reconstruction Software for (PET) Tomography) is presented. This implementation uses consumer graphics processing units (GPUs) to accelerate the compute-intensive parts of the reconstruction: forward and backward projection. FIRST was originally developed in FORTRAN, and it has been migrated to C language to be used with NVIDIA C for CUDA, as well as for a straightforward implementation and performance comparison between the C versions of the code running on the CPU and on the GPU. We measured the execution time of the CUDA version compared to the fastest available CPU. The CUDA implementation includes a loop re-ordering and an optimized memory allocation, which improves even more the performance of the reconstruction on the GPUs.This work was supported in part by MEC (FPA2007-62216), CDTEAM (Programa CENIT, Ministerio de Industria), UCM (Grupos UCM, 910059), CPAN (Consolider-Ingenio 2010)
CSPD-2007-00042 and the RECAVA-RETIC networ
A three-dimensional current meter for estuarine applications
A curr ent meter that is capable of measuring the high-frequency fluctuations of the three-dimensional velocity vector has been developed. The meter works on a doppler-shift principle. At high velocities, the meter has been shown to have an accuracy of better than 3%
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