SPHERES, J\"ulich's High-Flux Neutron Backscattering Spectrometer at FRM II

SPHERES (SPectrometer with High Energy RESolution) is a third-generation neutron backscattering spectrometer, located at the 20 MW German neutron source FRM II and operated by the Juelich Centre for Neutron Science. It offers an energy resolution (fwhm) better than 0.65 micro-eV, a dynamic range of +-31 micro-eV, and a signal-to-noise ratio of up to 1750:1.Comment: 12 pages, 7 figures, 2 tables. Supplemental material consists of 3 pages, 2 figures, 2 table

Tensor hypercontraction: A universal technique for the resolution of matrix elements of local, finite-range NN-body potentials in many-body quantum problems

Configuration-space matrix elements of N-body potentials arise naturally and ubiquitously in the Ritz-Galerkin solution of many-body quantum problems. For the common specialization of local, finite-range potentials, we develop the eXact Tensor HyperContraction (X-THC) method, which provides a quantized renormalization of the coordinate-space form of the N-body potential, allowing for a highly separable tensor factorization of the configuration-space matrix elements. This representation allows for substantial computational savings in chemical, atomic, and nuclear physics simulations, particularly with respect to difficult "exchange-like" contractions.Comment: Third version of the manuscript after referee's comments. In press in PRL. Main text: 4 pages, 2 figures, 1 table; Supplemental material (also included): 14 pages, 2 figures, 2 table

Critical role of electronic correlations in determining crystal structure of transition metal compounds

The choice that a solid system "makes" when adopting a crystal structure (stable or metastable) is ultimately governed by the interactions between electrons forming chemical bonds. By analyzing 6 prototypical binary transition-metal compounds we demonstrate here that the orbitally-selective strong $d$-electron correlations influence dramatically the behavior of the energy as a function of the spatial arrangements of the atoms. Remarkably, we find that the main qualitative features of this complex behavior can be traced back to simple electrostatics, i.e., to the fact that the strong $d$-electron correlations influence substantially the charge transfer mechanism, which, in turn, controls the electrostatic interactions. This result advances our understanding of the influence of strong correlations on the crystal structure, opens a new avenue for extending structure prediction methodologies to strongly correlated materials, and paves the way for predicting and studying metastability and polymorphism in these systems.Comment: Main text: 8 pages, 4 figures, 1 table; Supplemental material: 2 pages, 1 figure, 2 table

Pediatric Critical Care and COVID-19

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2, disproportionally affects adults (children 60 centers in nearly 20 countries from the Americas and Europe. In this report, we provide preliminary insights into our first 17 patients. Methods The Critical Coronavirus and Kids Epidemiology is a cohort study of children <19 years old with severe or critical COVID-19. The study period runs from April through December 2020. For this report, we included patients enrolled through April 23. We defined critical COVID-19 as a positive severe acute respiratory syndrome coronavirus 2 test result and requiring ICU therapies (high-flow nasal cannula [HFNC], noninvasive ventilation [NIV], invasive mechanical ventilation [IMV], vasoactive support, continuous renal replacement therapy). Severe COVID-19 included those receiving mask or nasal oxygen exceeding the pediatric acute respiratory distress syndrome (ARDS) “at risk” threshold.8 Deidentified data were collected by using a modification of the International Severe Acute Respiratory and Emerging Infection Consortium form (https://isaric.tghn.org/COVID-19-CRF/). Local ethics approval was obtained with a waiver of need for consent. Results We enrolled 17 children from 10 PICUs in Chile, Colombia, Italy, Spain, and the United States. Detailed data are in the Supplemental Information. Most patients were male (65%), young (median 4 years; range 0.08–18 years), and without known COVID-19 exposure (14 of 17). Comorbidities (Table 1, Supplemental Table 3) were common (71%) but variable. Symptoms were heterogenous, with fever and cough being most frequent (Table 1, Supplemental Table 3). Most with gastrointestinal (GI) symptoms (4 of 6) were also diagnosed with myocarditis (Supplemental Table 4). All these were from Europe and without previous cardiovascular disease