126 research outputs found
EdgeAI: Machine learning via direct attached accelerator for streaming data processing at high shot rate x-ray free-electron lasers
We present a case for low batch-size inference with the potential for adaptive training of a lean encoder model. We do so in the context of a paradigmatic example of machine learning as applied in data acquisition at high data velocity scientific user facilities such as the Linac Coherent Light Source-II x-ray Free-Electron Laser. We discuss how a low-latency inference model operating at the data acquisition edge can capitalize on the naturally stochastic nature of such sources. We simulate the method of attosecond angular streaking to produce representative results whereby simulated input data reproduce high-resolution ground truth probability distributions. By minimizing the mean-squared error between the decoded output of the latent representation and the ground truth distributions, we ensure that the encoding layers and resulting latent representation maintains full fidelity for any downstream task, be it classification or regression. We present throughput results for data-parallel inference of various batch sizes, some with throughput exceeding 100 k images per second. We also show in situ training below 10 s per epoch for the full encoder–decoder model as would be relevant for streaming and adaptive real-time data production at our nation’s scientific light sources
Automating Dislocation Characterization in 3D Dark Field X-ray Microscopy
Mechanical properties in crystals are strongly correlated to the arrangement
of 1D line defects, termed dislocations. Recently, Dark field X-ray Microscopy
(DFXM) has emerged as a new tool to image and interpret dislocations within
crystals using multidimensional scans. However, the methods required to
reconstruct meaningful dislocation information from high-dimensional DFXM scans
are still nascent and require significant manual oversight (i.e.
\textit{supervision}). In this work, we present a new relatively unsupervised
method that extracts dislocation-specific information (features) from a 3D
dataset (, , ) using Gram-Schmidt orthogonalization to represent
the large dataset as an array of 3-component feature vectors for each position,
corresponding to the weak-beam conditions and the strong-beam condition. This
method offers key opportunities to significantly reduce dataset size while
preserving only the crystallographic information that is important for data
reconstruction
Models for Change Legacy Phase Evaluation Report
Note: This evaluation is accompanied by an evaluation of the National Campaign for this initiative as well as introduction to the evaluation effort by MacArthur's President, Julia Stasch, and a response to the evaluation from the program team. Access these related materials here: https://www.macfound.org/press/grantee-publications/evaluation-models-change-initiative.This report summarizes the findings of the Evaluation of the Models for Change Legacy Phase andreviews what has been achieved thus far to create fairer, more effective, and developmentallyappropriate justice systems throughout the United States; documents the progress that has been madein specific goal areas; and assesses current capacity to sustain and grow these efforts in the years ahead
Ultrafast absorption of intense x rays by nitrogen molecules
We devise a theoretical description for the response of nitrogen molecules
(N2) to ultrashort and intense x rays from the free electron laser (FEL) Linac
Coherent Light Source (LCLS). We set out from a rate-equation description for
the x-ray absorption by a nitrogen atom. The equations are formulated using all
one-x-ray-photon absorption cross sections and the Auger and radiative decay
widths of multiply-ionized nitrogen atoms. Cross sections are obtained with a
one-electron theory and decay widths are determined from ab initio computations
using the Dirac-Hartree-Slater (DHS) method. We also calculate all binding and
transition energies of nitrogen atoms in all charge states with the DHS method
as the difference of two self-consistent field calculations (Delta SCF method).
To describe the interaction with N2, a detailed investigation of intense
x-ray-induced ionization and molecular fragmentation are carried out. As a
figure of merit, we calculate ion yields and the average charge state measured
in recent experiments at the LCLS. We use a series of phenomenological models
of increasing sophistication to unravel the mechanisms of the interaction of x
rays with N2: a single atom, a symmetric-sharing model, and a
fragmentation-matrix model are developed. The role of the formation and decay
of single and double core holes, the metastable states of N_2^2+, and molecular
fragmentation are explained.Comment: 16 pages, 6 figures, 2 tables, RevTeX4.1, supporting materials in the
Data Conservancy, revise
Attoclock Ptychography
Dedicated simulations show that the application of time-domain ptychography to angular photo-electron streaking data allows shot-to-shot reconstruction of individual X-ray free electron laser pulses. Specifically, in this study, we use an extended ptychographic iterative engine to retrieve both the unknown X-ray pulse and the unknown streak field. We evaluate the quality of reconstruction versus spectral resolution, signal-to-noise and sampling size of the spectrogram
Light-induced picosecond rotational disordering of the inorganic sublattice in hybrid perovskites.
Femtosecond resolution electron scattering techniques are applied to resolve the first atomic-scale steps following absorption of a photon in the prototypical hybrid perovskite methylammonium lead iodide. Following above-gap photoexcitation, we directly resolve the transfer of energy from hot carriers to the lattice by recording changes in the mean square atomic displacements on 10-ps time scales. Measurements of the time-dependent pair distribution function show an unexpected broadening of the iodine-iodine correlation function while preserving the Pb-I distance. This indicates the formation of a rotationally disordered halide octahedral structure developing on picosecond time scales. This work shows the important role of light-induced structural deformations within the inorganic sublattice in elucidating the unique optoelectronic functionality exhibited by hybrid perovskites and provides new understanding of hot carrier-lattice interactions, which fundamentally determine solar cell efficiencies
A self-referenced in-situ arrival time monitor for X-ray free-electron lasers
We present a novel, highly versatile, and self-referenced arrival time
monitor for measuring the femtosecond time delay between a hard X-ray pulse
from a free-electron laser and an optical laser pulse, measured directly on the
same sample used for pump-probe experiments. Two chirped and picosecond long
optical supercontinuum pulses traverse the sample with a mutually fixed time
delay of 970 fs, while a femtosecond X-ray pulse arrives at an instant in
between both pulses. Behind the sample the supercontinuum pulses are temporally
overlapped to yield near-perfect destructive interference in the absence of the
X-ray pulse. Stimulation of the sample with an X-ray pulse delivers non-zero
contributions at certain optical wavelengths, which serve as a measure of the
relative arrival time of the X-ray pulse with an accuracy of better than 25 fs.
We find an excellent agreement of our monitor with the existing timing
diagnostics at the SACLA XFEL with a Pearson correlation value of 0.98. We
demonstrate a high sensitivity to measure X-ray pulses with pulse energies as
low as 30 J. Using a free-flowing liquid jet as interaction sample ensures
the full replacement of the sample volume for each X-ray/optical event, thus
enabling its utility even at MHz repetition rate XFEL sources
Bayesian inferencing and deterministic anisotropy for the retrieval of the molecular geometry in gas-phase diffraction experiments
Currently, our general approach to retrieve the molecular geometry from
ultrafast gas-phase diffraction heavily relies on complex geometric simulations
to make conclusive interpretations. In this manuscript, we develop a broadly
applicable ultrafast gas-phase diffraction method that approximates the
molecular frame geometry distribution using Bayesian
Inferencing. This method does not require complex molecular dynamics simulation
and can identify the unique molecular structure. We demonstrate this method's
viability by retrieving the ground state geometry distribution
for both simulated stretched NO and measured ground
state NO. Due to our statistical interpretation, we retrieve a
coordinate-space resolution on the order of 100~fm, depending on signal
quality, an improvement of order 100 compared to commonly used Fourier
transform based methods. By directly measuring the width of
, this is generally only accessible through simulation,
we open ultrafast gas-phase diffraction capabilities to measurements beyond
current analysis approaches. Our method also leverages deterministic ensemble
anisotropy; this provides an explicit dependence on the molecular frame angles.
This method's ability to retrieve the unique molecular structure with high
resolution, and without complex simulations, provides the potential to
effectively turn gas-phase ultrafast diffraction into a discovery oriented
technique, one that probes systems that are prohibitively difficult to
simulate.Comment: 16 pages, 8 figures, 2 tables. Please find the analysis code and
templates for new molecules at https://github.com/khegazy/BIG
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