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At least 1,729 records · Page 96

Advances in machine-learning-based sampling motivated by lattice quantum chromodynamics

Sampling from known probability distributions is a ubiquitous task in computational science, underlying calculations in domains from linguistics to biology and physics. Generative machine-learning (ML) models have emerged as a promising tool in this space, building on the success of this approach in applications such as image, text, and audio generation. Often, however, generative tasks in scientific domains have unique structures and features—such as complex symmetries and the requirement of exactness guarantees—that present both challenges and opportunities for ML. This Perspective outlines the advances in ML-based sampling motivated by lattice quantum field theory, in particular for the theory of quantum chromodynamics. Enabling calculations of the structure and interactions of matter from our most fundamental understanding of particle physics, lattice quantum chromodynamics is one of the main consumers of open-science supercomputing worldwide. Here, the design of ML algorithms for this application faces profound challenges, including the necessity of scaling custom ML architectures to the largest supercomputers, but also promises immense benefits, and is spurring a wave of development in ML-based sampling more broadly. In lattice field theory, if this approach can realize its early promise it will be a transformative step towards first-principles physics calculations in particle, nuclear and condensed matter physics that are intractable with traditional approaches.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

BEYONDPLANCK XIII. Intensity foreground sampling, degeneracies, and priors

We present the intensity foreground algorithms and model employed within the BEYONDPLANCK analysis framework. The BEYONDPLANCK analysis is aimed at integrating component separation and instrumental parameter sampling within a global framework, leading to complete end-to-end error propagation in the Planck Low Frequency Instrument (LFI) data analysis. Given the scope of the BEYONDPLANCK analysis, a limited set of data is included in the component separation process, leading to foreground parameter degeneracies. In order to properly constrain the Galactic foreground parameters, we improve upon the previous Commander component separation implementation by adding a suite of algorithmic techniques. These algorithms are designed to improve the stability and computational efficiency for weakly constrained posterior distributions. These are: (1) joint foreground spectral parameter and amplitude sampling, building on ideas from MIRAMARE; (2) component-based monopole determination; (3) joint spectral parameter and monopole sampling; and (4) application of informative spatial priors for component amplitude maps. We find that the only spectral parameter with a significant signal-to-noise ratio using the current BEYONDPLANCK data set is the peak frequency of the anomalous microwave emission component, for which we find $ν$ p = 25.3 ± 0.5 GHz; all others must be constrained through external priors. Future works will be aimed at integrating many more data sets into this analysis, both map and time-ordered based, thereby gradually eliminating the currently observed degeneracies in a controlled manner with respect to both instrumental systematic effects and astrophysical degeneracies. When this happens, the simple LFI-oriented data model employed in the current work will need to be generalized to account for both a richer astrophysical model and additional instrumental effects. This work will be organized within the Open Science-based COSMOGLOBE community effort.

79 ASTRONOMY AND ASTROPHYSICS↗

Rucio beyond ATLAS: experiences from Belle II, CMS, DUNE, EISCAT3D, LIGO/VIRGO, SKA, XENON

For many scientific projects, data management is an increasingly complicated challenge. The number of data-intensive instruments generating unprecedented volumes of data is growing and their accompanying workflows are becoming more complex. Their storage and computing resources are heterogeneous and are distributed at numerous geographical locations belonging to different administrative domains and organisations. These locations do not necessarily coincide with the places where data is produced nor where data is stored, analysed by researchers, or archived for safe long-term storage. To fulfil these needs, the data management system Rucio has been developed to allow the high-energy physics experiment ATLAS at LHC to manage its large volumes of data in an efficient and scalable way. But ATLAS is not alone, and several diverse scientific projects have started evaluating, adopting, and adapting the Rucio system for their own needs. As the Rucio community has grown, many improvements have been introduced, customisations have been added, and many bugs have been fixed. Additionally, new dataflows have been investigated and operational experiences have been documented. In this article we collect and compare the common successes, pitfalls, and oddities that arose in the evaluation efforts of multiple diverse experiments, and compare them with the ATLAS experience. This includes the high-energy physics experiments Belle II and CMS, the neutrino experiment DUNE, the scattering radar experiment EISCAT3D, the gravitational wave observatories LIGO and VIRGO, the SKA radio telescope, and the dark matter search experiment XENON.

Lassnig, Mario↗

HOSS!

The Hall-D Online Skim System (HOSS) was developed to simultaneously solve two issues for the high intensity GlueX experiment. One was to parallelize the writing of raw data files to disk in order to improve bandwidth. The other was to distribute the raw data across multiple compute nodes in order to produce calibration skims of the data online. The highly configurable system employs RDMA, RAM disks, and zeroMQ driven by Python to simultaneously store and process the full high intensity GlueX data stream.

Lawrence, David↗

Thoroughly testing and integrating hundreds of Pull Requests per month: ROOT’s new Cost-efficient and Feature Rich GitHub-based CI

ROOT is an open source framework, freely available on GitHub, at the heart of data acquisition, processing and analysis of HE(N)P experiments, and beyond. It is developed collaboratively: contributions are not authored only by ROOT team members, but also by the user community at large: developers and scientists from universities, labs as well as the private sector. More than 1500 GitHub Pull Requests are merged on average per year. It is in this context that code integration acquires a primary role. The review of code contributions isn’t enough: not only they need to be thoroughly reviewed, they also need to be thoroughly tested through a powerful CI infrastructure on several different platforms to comply with the high code quality standards of the project. Since the end of 2023, ROOT moved its continuous integration system from Jenkins to GitHub Actions. In this contribution, we characterise the transition to the GitHub CI, focussing on our strategy, its implementation and the lessons learned, as well as the advantages the new system offers with respect to the previous one. Particular emphasis will be given to the evaluation of the cost-benefit ratio for Jenkins and GitHub Actions for the ROOT project. We also describe how we manage to run in less than one hour thousands of unit, integration, functional and end-to-end tests on different flavours of Windows, four versions of macOS, as well as about ten of the most used Linux distributions, taking advantage of the CERN computing infrastructure.

Piparo, Danilo [CERN]↗

A new radiation stripline ICRF antenna design for EAST Tokamak

A new type of toroidal long Radiation Stripline Antenna (RSA) is presented, which can effectively improve antenna radiation, leading in reduction of max voltage on transmission line and decrease of the sensitivity to ELM's of the ICRF system at some frequencies. Based on the new concept, a 4-straps RSA is proposed for EAST device. Using 3-D computing simulator code (HFSS), RF current distribution, S-parameters and electromagnetic field distribution on and near the RSA ICRF antenna are analyzed and compared with present ICRF antenna on EAST.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Band to band tunneling in III-V semiconductors: Implications of complex band structure, strain, orientation, and off-zone center contribution

In this paper, we use a tight binding Hamiltonian with spin orbit coupling to study the real and complex band structures of relaxed and strained GaAs. A simple d orbital on-site energy shift coupled with appropriate scaling of the off-diagonal terms is found to correctly reproduce the band-edge shifts with strain. Four different 〈100〉 strain combinations, namely, uniaxial compressive, uniaxial tensile, biaxial compressive, and biaxial tensile strain are studied, revealing rich valence band structure and strong relative orientation dependent tunneling. It is found that complex bands are unable to provide unambiguous tunneling paths away from the Brillouin zone center. Tunneling current density distribution over the Brillouin zone is computed using non-equilibrium Green's function approach elucidating a physical picture of band to band tunneling.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Theoretical analysis of uranium-doped thorium dioxide: Introduction of a thoria force field with explicit polarization

Thorium dioxide is used industrially in high temperature applications, but more insight is needed into the behavior of the material as part of a mixed-oxide (MOX) nuclear fuel, incorporating uranium. We have developed a new interatomic potential model including polarizability via a shell model, and commensurate with a prominent existing UO{sub 2} potential, to conduct configurational analyses and to investigate the thermophysical properties of uranium-doped ThO{sub 2}. Using the GULP and Site Occupancy Disorder (SOD) computational codes, we have analyzed the distribution of low concentrations of uranium in the bulk material, where we have not observed the formation of uranium clusters or the dominance of a single preferred configuration. We have calculated thermophysical properties of pure thorium dioxide and Th{sub (1−x)}U{sub x}O{sub 2} which generated values in very good agreement with experimental data.

36 MATERIALS SCIENCE↗

Ultra-wide acoustic band gaps in pillar-based phononic crystal strips

An original approach for designing a one dimensional phononic crystal strip with an ultra-wide band gap is presented. The strip consists of periodic pillars erected on a tailored beam, enabling the generation of a band gap that is due to both Bragg scattering and local resonances. The optimized combination of both effects results in the lowering and the widening of the main band gap, ultimately leading to a gap-to-midgap ratio of 138%. The design method used to improve the band gap width is based on the flattening of phononic bands and relies on the study of the modal energy distribution within the unit cell. The computed transmission through a finite number of periods corroborates the dispersion diagram. The strong attenuation, in excess of 150 dB for only five periods, highlights the interest of such ultra-wide band gap phononic crystal strips.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Hysteresis of liquid adsorption in porous media by coarse-grained Monte Carlo with direct experimental validation

The effects of path-dependent wetting and drying manifest themselves in many types of physical systems, including nanomaterials, biological systems, and porous media such as soil. It is desirable to better understand how these hysteretic macroscopic properties result from a complex interplay between gasses, liquids, and solids at the pore scale. Coarse-Grained Monte Carlo (CGMC) is an appealing approach to model these phenomena in complex pore spaces, including ones determined experimentally. We present two-dimensional CGMC simulations of wetting and drying in two systems with pore spaces determined by sections from micro X-ray computed tomography: a system of randomly distributed spheres and a system of Ottawa sand. Results for the phase distribution, water uptake, and matric suction when corrected for extending to three dimensions show excellent agreement with experimental measurements on the same systems. This supports the hypothesis that CGMC can generate metastable configurations representative of experimental hysteresis and can also be used to predict hysteretic constitutive properties of particular experimental systems, given pore space images.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

An Eulerian crystal plasticity framework for modeling large anisotropic deformations in energetic materials under shocks

Here, this paper demonstrates a novel Eulerian computational framework for modeling anisotropic elastoplastic deformations of organic crystalline energetic materials (EM) under shocks. While Eulerian formulations are advantageous for handling large deformations, constitutive laws in such formulations have been limited to isotropic elastoplastic models, which may not fully capture the shock response of crystalline EM. The present Eulerian framework for high-strain rates, large deformation material dynamics of EM incorporates anisotropic isochoric elasticity via a hypo-elastic constitutive law and visco-plastic single-crystal models. The calculations are validated against atomistic calculations and experimental data and benchmarked against Lagrangian (finite element) crystal plasticity computations for shock-propagation in a monoclinic organic crystal, octahydro-1,3,5,7-tetranitro-1,3,5,7 tetrazocine (β-HMX). The Cauchy stress components and the resolved shear stresses calculated using the present Eulerian approach are shown to be in good agreement with the Lagrangian computations for different crystal orientations. The Eulerian framework is then used for computations of shock-induced inert void collapse in β-HMX to study the effects of crystal orientations on hotspot formation under different loading intensities. The computations show that the hotspot temperature distributions and the collapse profiles are sensitive to the crystal orientations at lower impact velocities (viz., 500 m/s); when the impact velocity is increased to 1000 m/s, the collapse is predominantly hydrodynamic and the role of anisotropy is modest. The present methodology will be useful to simulate energy localization in shocked porous energetic material microstructures and other situations where large deformations of single and polycrystals govern the thermomechanical response.

42 ENGINEERING↗

Azimuthal structures and turbulent transport in Penning discharge

Azimuthal structures in cylindrical Penning discharge are studied with a 2D3V radial–azimuthal PIC/MCC model with the axial magnetic field. The discharge is self-consistently supported by ionization due to the axial injection of electrons. It is shown that the steady-state discharge can be supported in two different regimes with different types of observed azimuthal structures. The transition between the regimes is controlled by the mechanism of the energy input to the discharge. In the first regime (low energy of the injected electrons), with the pronounced m = 1 spoke activity, the power input is dominated by the energy absorption due to the radial current and self-consistent electric field. In the other regime (higher energy of the injected electrons), with prevalent small-scale m > 1 spiral structures, and the lower values of the anomalous transport, the total energy deposited to the discharge is lower and is mostly due to the direct input of the kinetic energy from the axial electron beam. Here we show that the large (m = 1) spoke and small-scale structures occur as a result of Simon–Hoh and lower hybrid instabilities driven by the electric field, density gradient, and collisions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

Uncovering the three-dimensional structure of upconverting core–shell nanoparticles with multislice electron ptychography

In photon upconverting core–shell nanoparticles, structure strongly dictates performance. Typical imaging in scanning transmission electron microscopy has sufficient resolution to probe the atomic structure of these nanoparticles, but contrast, dose, and projection limitations make conventional methods insufficient for fully characterizing these structures. Phase retrieval techniques provide a promising alternative imaging mode, and, in particular, multislice electron ptychography can recover depth-dependent information. Here, we study beam-sensitive photon upconverting core–shell nanoparticles with a multislice ptychography approach using a low electron dose to avoid damage. Large strain fields arise in these heterostructures due to the mismatch in lattice parameter between the core and the shell. We reconstruct both a nanoparticle that appears defect-free and one that has a large break in the side and map the distribution of strain in 3D by computing distortion fields from high-resolution potential images of each slice. In the defect-free nanoparticle, we observe twisting of the shell, while in the broken nanoparticle, we measure the 3D position of the crack, the core, and dislocations. These results highlight the advantage of multislice electron ptychography to recover 3D information from a single scan, even under strict electron dose requirements from beam-sensitive samples.

74 ATOMIC AND MOLECULAR PHYSICS↗

A TWO-DIMENSIONAL MAP OF THE COLOR EXCESS IN NGC 3603

Using archival Hubble Space Telescope/Wide Field Camera 3 images centered on the young HD 97950 star cluster in the giant H II region NGC 3603, we computed the pixel-to-pixel distribution of the color excess, E(B - V){sub g}, of the gas associated with this cluster from its H{alpha}/Pa{beta} flux ratio. At the assumed distance of 6.9 kpc, the resulting median color excess within 1 pc from the cluster center is E(B - V){sub g} = 1.51 {+-} 0.04 mag. Outside the cluster (at r > 1 pc), the color excess is seen to increase with cluster-centric distance toward both north and south, reaching a value of about 2.2 mag at r = 2 pc from the cluster center. The radial dependence of E(B - V){sub g} westward of the cluster appears rather flat at about 1.55 mag over the distance range 1.2 pc <r < 3 pc. In the eastern direction, E(B - V){sub g} steadily increases from 1.5 mag at r = 1 pc to 1.7 mag at r = 2 pc and stays nearly constant at 1.7 mag for 2 pc <r < 3 pc. The different radial profiles and the pixel-to-pixel variations of E(B - V){sub g} clearly indicate the presence of significant differential reddening across the 4.9 pc x 4.3 pc area centered on the HD 97950 star cluster. We interpret the variations of E(B - V){sub g} as the result of stellar radiation and stellar winds interacting with an inhomogeneous dusty local interstellar medium whose density varies spatially. From the E(B - V){sub g} values measured along the rims of the prominent pillars MM1 and MM2 in the southwest and southeast of the HD 97950 cluster, we estimate an H{sub 2} column density of log{sub 10}(N{sub H{sub 2}})=21.7 and extrapolate it to log{sub 10}(N{sub H{sub 2}})=23 in the pillars' interior. We find the pillars to be closer to us than the central ionizing cluster and suggest that star formation may be occurring in the pillar heads.

79 ASTRONOMY AND ASTROPHYSICS↗

A statistical analysis of seeds and other high-contrast exoplanet surveys: massive planets or low-mass brown dwarfs?

We conduct a statistical analysis of a combined sample of direct imaging data, totalling nearly 250 stars. The stars cover a wide range of ages and spectral types, and include five detections (κ And b, two ∼60 M {sub J} brown dwarf companions in the Pleiades, PZ Tel B, and CD–35 2722B). For some analyses we add a currently unpublished set of SEEDS observations, including the detections GJ 504b and GJ 758B. We conduct a uniform, Bayesian analysis of all stellar ages using both membership in a kinematic moving group and activity/rotation age indicators. We then present a new statistical method for computing the likelihood of a substellar distribution function. By performing most of the integrals analytically, we achieve an enormous speedup over brute-force Monte Carlo. We use this method to place upper limits on the maximum semimajor axis of the distribution function derived from radial-velocity planets, finding model-dependent values of ∼30-100 AU. Finally, we model the entire substellar sample, from massive brown dwarfs to a theoretically motivated cutoff at ∼5 M {sub J}, with a single power-law distribution. We find that p(M, a)∝M {sup –0.65} {sup ±} {sup 0.60} a {sup –0.85} {sup ±} {sup 0.39} (1σ errors) provides an adequate fit to our data, with 1.0%-3.1% (68% confidence) of stars hosting 5-70 M {sub J} companions between 10 and 100 AU. This suggests that many of the directly imaged exoplanets known, including most (if not all) of the low-mass companions in our sample, formed by fragmentation in a cloud or disk, and represent the low-mass tail of the brown dwarfs.

79 ASTRONOMY AND ASTROPHYSICS↗

Global energetics of solar flares. II. Thermal energies

We present the second part of a project on the global energetics of solar flares and coronal mass ejections that includes about 400 M- and X-class flares observed with the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) during the first 3.5 yr of its mission. In this Paper II we compute the differential emission measure (DEM) distribution functions and associated multithermal energies, using a spatially-synthesized Gaussian DEM forward-fitting method. The multithermal DEM function yields a significantly higher (by an average factor of ≈14), but more comprehensive (multi-)thermal energy than an isothermal energy estimate from the same AIA data. We find a statistical energy ratio of E{sub th}/E{sub diss} ≈ 2–40% between the multithermal energy E{sub th} and the magnetically dissipated energy E{sub diss}, which is an order of magnitude higher than the estimates of Emslie et al. 2012. For the analyzed set of M- and X-class flares we find the following physical parameter ranges: L=10{sup 8.2}−10{sup 9.7} cm for the length scale of the flare areas, T{sub p}=10{sup 5.7}−10{sup 7.4} K for the DEM peak temperature, T{sub w}=10{sup 6.8}−10{sup 7.6} K for the emission measure-weighted temperature, n{sub p}=10{sup 10.3}−10{sup 11.8} cm{sup −3} for the average electron density, EM{sub p}=10{sup 47.3}−10{sup 50.3} cm{sup −3} for the DEM peak emission measure, and E{sub th}=10{sup 26.8}−10{sup 32.0} erg for the multithermal energies. The deduced multithermal energies are consistent with the RTV scaling law E{sub th,RTV}=7.3×10{sup −10} T{sub p}{sup 3}L{sub p}{sup 2}, which predicts extremal values of E{sub th,max}≈1.5×10{sup 33} erg for the largest flare and E{sub th,min}≈1×10{sup 24} erg for the smallest coronal nanoflare. The size distributions of the spatial parameters exhibit powerlaw tails that are consistent with the predictions of the fractal-diffusive self-organized criticality model combined with the RTV scaling law.

79 ASTRONOMY AND ASTROPHYSICS↗

SELECTING SAGITTARIUS: IDENTIFICATION AND CHEMICAL CHARACTERIZATION OF THE SAGITTARIUS STREAM

Wrapping around the Milky Way, the Sagittarius stream is the dominant substructure in the halo. Our statistical selection method has allowed us to identify 106 highly likely members of the Sagittarius stream. Spectroscopic analysis of metallicity and kinematics of all members provides us with a new mapping of the Sagittarius stream. We find correspondence between the velocity distribution of stream stars and those computed for a triaxial model of the Milky Way dark matter halo. The Sagittarius trailing arm exhibits a metallicity gradient, ranging from −0.59 to −0.97 dex over 142°. This is consistent with the scenario of tidal disruption from a progenitor dwarf galaxy that possessed an internal metallicity gradient. We note high metallicity dispersion in the leading arm, causing a lack of detectable gradient and possibly indicating orbital phase mixing. We additionally report on a potential detection of the Sextans dwarf spheroidal in our data.

79 ASTRONOMY AND ASTROPHYSICS↗

Image reconstruction in higher dimensions: myocardial perfusion imaging of tracer dynamics with cardiac motion due to deformation and respiration

Myocardial perfusion imaging (MPI) using slow rotating large field of view cameras requires spatiotemporal reconstruction of dynamically acquired data to capture the time variation of the radiotracer concentration. In vivo, MPI contains additional degrees of freedom involving unavoidable motion of the heart due to quasiperiodic beating and the effects of respiration, which can severely degrade the quality of the images. This work develops a technique for a single photon emission computed tomography (SPECT) that reconstructs the distribution of the radiotracer concentration in the myocardium using a tensor product of different sets of basis functions that approximately describe the spatiotemporal variation of the radiotracer concentration and the motion of the heart. In this study the temporal B-spline basis functions are chosen to reflect the dynamics of the radiotracer, while the intrinsic deformation and the extrinsic motion of the heart are described by a product of a discrete set of Gaussian basis functions. Reconstruction results are presented showing the dynamics of the tracer in the myocardium as it deforms due to cardiac beating, and is displaced due to respiratory motion. We find these results are compared with the conventional 4D-spatiotemporal reconstruction method that models only the temporal changes of the tracer activity. The higher dimensional reconstruction method proposed here improves bias, yet the signal-to-noise ratio (SNR) decreases slightly due to redistribution of the counts over the cardiac-respiratory gates. Finally, there is a trade-off between the number of gates and the number of projections per gate to achieve high contrast images.

60 APPLIED LIFE SCIENCES↗