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At least 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Quantum optimization of maximum independent set using Rydberg atom arrays

Realizing quantum speedup for practically relevant, computationally hard problems is a central challenge in quantum information science. Using Rydberg atom arrays with up to 289 qubits in two spatial dimensions, we experimentally investigate quantum algorithms for solving the maximum independent set problem. We use a hardware-efficient encoding associated with Rydberg blockade, realize closed-loop optimization to test several variational algorithms, and subsequently apply them to systematically explore a class of graphs with programmable connectivity. We find that the problem hardness is controlled by the solution degeneracy and number of local minima, and we experimentally benchmark the quantum algorithm’s performance against classical simulated annealing. On the hardest graphs, we observe a superlinear quantum speedup in finding exact solutions in the deep circuit regime and analyze its origins.

Science & Technology - Other Topics↗
DOE OSTI2023

Topological kinetic crossover in a nanomagnet array

Ergodic kinetics, which are critical to equilibrium thermodynamics, can be constrained by a system’s topology. Here, we studied a model nanomagnetic array in which such constraints visibly affect the behavior of the magnetic moments. In this system, magnetic excitations connect into thermally active one-dimensional strings whose motion can be imaged in real time. At high temperatures, our data showed the merging, breaking, and reconnecting of strings, resulting in the system transitioning between topologically distinct configurations. Below a crossover temperature, the string motion is dominated by simple changes in length and shape. In this low-temperature regime, the system is energetically stable because of its inability to explore all possible topological configurations. This kinetic crossover suggests a generalizable conception of topologically broken ergodicity and limited equilibration.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Multi-omic Analyses of Extensively Decayed Pinus contorta Reveal Expression of a Diverse Array of Lignocellulose-Degrading Enzymes

Fungi play a key role cycling nutrients in forest ecosystems, but the mechanisms remain uncertain. To clarify the enzymatic processes involved in wood decomposition, the metatranscriptomics and metaproteomics of extensively decayed lodgepole pine were examined by RNA sequencing (RNA-seq) and liquid chromatography-tandem mass spectrometry (LC-MS/MS), respectively. Following de novo metatranscriptome assembly, 52,011 contigs were searched for functional domains and homology to database entries. Contigs similar to basidiomycete transcripts dominated, and many of these were most closely related to ligninolytic white rot fungi or cellulolytic brown rot fungi. A diverse array of carbohydrate-active enzymes (CAZymes) representing a total of 132 families or subfamilies were identified. Among these were 672 glycoside hydrolases, including highly expressed cellulases or hemicellulases. The CAZymes also included 162 predicted redox enzymes classified within auxiliary activity (AA) families. Eighteen of these were manganese peroxidases, which are key components of ligninolytic white rot fungi. The expression of other redox enzymes supported the working of hydroquinone reduction cycles capable of generating reactive hydroxyl radicals. These have been implicated as diffusible oxidants responsible for cellulose depolymerization by brown rot fungi. Finally, enzyme diversity and the coexistence of brown and white rot fungi suggest complex interactions of fungal species and degradative strategies during the decay of lodgepole pine.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Testing the Technique for the Cluster Analysis of Acoustic Emission Pulse Arrays under the Formation of a Conical Glass Granulate Pile

The technique for the cluster analysis and the classification of registered acoustic emission (AE) data arrays was used for the determination of the isolated phases upon the transition from the regular to the avalanche process of damage accumulation in a physical simulation model. The damage accumulation phases were modeled in the process of formation of a conical glass granulate pile. Their registration was performed by an AE control system synchronized with a high-speed video camera.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Temperature, Time, Concentration, Annealing, and Substrates on ZnO Nanorod Arrays Growth by Hydrothermal Process on Hot Plate

Well aligned 1D ZnO nanostructures are important for optoelectronic and nanoscale electronic devices. In this report, 1D ZnO nanorods were synthesized by very simple, low cost, low temperature hydrothermal process. An effect of concentration, growth time, growth temperature, seed layer annealing, and seed layer thickness was investigated. The synthesized ZnO nanorods were characterized by scanning and transmission electron microscopies, X-ray diffraction, Raman and ultraviolet–visible spectroscopies. Growth parameters were found to influence strongly on the morphology, orientation, diameter, length, and density of the ZnO nanorod arrays. The growth temperature 80–90°C, seed layer annealing at 300–400°C, growth time 3 h, 0.025 M precursor concentration, and 0.2–0.3 M seed layer solution concentrations are more favorable conditions for better orientation and excellent crystallinity of the ZnO nanorods.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Extraordinary light transmission through a metal film perforated by a subwavelength hole array

It is shown that, depending on the incident wave frequency and the system geometry, the extraordinary transmission of light through a metal film perforated by an array of subwavelength holes can be described by one of the three mechanisms: the “transparency window” in the metal, excitation of the Fabry–Perot resonance of a collective mode produced by the hybridization of evanescence modes of the holes and surface plasmons, and excitation of a plasmon on the rear boundary of the film. The excitation of a plasmon resonance on the front boundary of the metal film does not make any substantial contribution to the transmission coefficient, although introduces a contribution to the reflection coefficient.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Energy Spectrum of Ultrahigh-Energy Cosmic Rays according to Data from the Ground-Based Scintillation Detectors of the Yakutsk EAS Array

The energy spectrum of cosmic rays with energies E{sub 0} ≥ 10{sup 17} eV over the period of continuous observations in 1974–2017 is analyzed. A refined formula for estimating the primary particle energy is used for individual events. It is derived from our calculations of the responses of the ground-based and underground scintillation detectors of the Yakutsk extensive air shower array within the QGSjet-01-d, QGSjet-II-04, SIBYLL-2.1, and EPOS-LHC models by applying the CORSIKA package. The new estimate of E{sub 0} is appreciably lower than its previously used value.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Energy Spectrum of Ultrahigh-Energy Cosmic Rays according to Data from Ground-Based Scintillation Detectors of the Yakutsk EAS Array

Results obtained from an analysis of the energy spectrum of cosmic rays with energies in the region of E{sub 0} ≥ 10{sup 17} eV over the period of continuous observations from 1974 to 2017 are presented. A refined expression for estimating the primary-particle energy is used for individual events. This expression is derived from calculations aimed at determining the responses of the ground-based and underground scintillation detectors of the Yakutsk array for studying extensive air showers (EAS) and performed within theQGSJET-01-d, QGSJET-II-04, SIBYLL-2.1, and EPOS-LHCmodels by employing the CORSIKA code package. The new estimate of E{sub 0} is substantially lower than its counterpart used earlier.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Prototype Scintillation Detector with Photosensors Based on Silicon Photomultiplier Arrays

A prototype scintillation detector with photosensors based on silicon photomultiplier (SiPM) arrays is described. Such a method of data-taking will make it possible to obtain an image (snapshot) of the event and, thereby, to separate different types of events (particle interactions) in the detector. For this purpose, the characteristics of SiPMs have been studied and a calibration measurement technique developed.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Förster Energy Transfer in Arrays of Epitaxial CdSe/ZnSe Quantum Dots Involving Bright and Dark Excitons

Using time-resolved photoluminescence (PL) spectroscopy, we establish the presence of the Förster energy transfer mechanism between two arrays of epitaxial CdSe/ZnSe quantum dots (QDs) of different sizes. The mechanism operates through dipole–dipole interaction between ground excitonic states of the smaller QDs and excited states of the larger QDs. The dependence of energy transfer efficiency on the width of barrier separating the QD insets is shown to be in line with the Förster mechanism. The temperature dependence of the PL decay times and PL intensity suggests the involvement of dark excitons in the energy transfer process.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Tunnel Emission from Nanostructured Field-Emission Array Cathodes with a Fluorine–Carbon Coating

Variations of the morphology and field-emission properties of surface-structured n- and p-type silicon wafers have been studied. The silicon surface has been structured by etching in a fluorine–carbon plasma and depositing subnanodimensional island carbon masks. It has been shown that surface structuring in a fluorine–carbon plasma makes it possible to reach desired field-emission currents in electric fields of different strengths. Physicochemical models of field emission mechanisms and models of destruction of surface-modified multipoint silicon array cathodes have been considered.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Interference of Spin Waves in Arrays of Microwaveguides Based on Yttrium-Iron Garnet Films

Effects of propagation and interference of spin waves in an eight-port magnonic structure in the form of a 2 × 2 array of microwaveguides based on yttrium-iron garnet films with microantennas placed at the waveguide ends are studied experimentally and numerically. It is shown that conditions for a constructive and destructive interference of spin waves, which is necessary for creating spin-wave logic devices, can be implemented at output transducers by changing the phase of input signals.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

The Influence of EL2 Centers on the Photoelectric Response of an Array of Radial GaAs/AlGaAs Nanowires

We have studied the role of EL2 centers in formation of the photoelectric response of an array of radial n-type GaAs/Al{sub x}Ga{sub 1 –x}As (x = 0.3) nanowires (NWs) grown by molecular beam epitaxy on a p-type silicon substrate. Results revealed a significant decrease in the time of NW photoresponse recovery as compared to that in a bulk crystal upon the transition of EL2 centers from a metastable nonactive state to the normal ground state.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Modifiable Array Data Structures for Mesh Topology

Topological data structures are useful in many areas, including the various mesh data structures used in finite element and finite volume applications. Here, we present a mesh data structure which is both flexible enough to support general mesh adaptivity and is compactly stored in a few large arrays. This structure can efficiently store full topological information for meshes with mixed element types. It allows both constant-time adjacency queries and constant-time addition and removal of mesh entities. We compare this structure to similar structures for finite elements and graphics and present its performance for adjacency queries. We also present its use in adaptive simulation applications.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2026

Unraveling TeV halos with the Cherenkov Telescope Array

Pulsars are observed to emit bright and spatially extended gamma-ray emission at multi-TeV energies. These so-called "TeV halos" are now understood to be a nearly universal feature of middle-aged pulsars. However, many of the key physical processes that govern these systems, particularly those affecting particle diffusion, remain poorly constrained. We aim to evaluate the ability of the Cherenkov Telescope Array (CTA) to probe the physical properties of TeV halos, with a focus on the nearby and well-studied case of the Geminga pulsar. We simulate gamma-ray emission from various TeV halo models, incorporating different assumptions for the injected electron spectrum, spin-down evolution, and energy-dependent diffusion. These models are then used to forecast CTA's sensitivity to spectral and spatial differences, based on realistic mock observations and instrument response simulations. We find that CTA will be able to distinguish between a wide range of TeV halo models that are currently consistent with existing data. In particular, CTA observations can constrain the normalization, energy dependence, and spatial extent of the diffusion coefficient surrounding Geminga, as well as the spectral shape of the injected electron population.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Pt-Ni/WC Alloy Nanorods Arrays as ORR Catalyst for PEM Fuel Cells

Polymer electrolyte membrane fuel cells (PEMFCs) among the other types of fuel cell technology are attractive power sources, especially for electric vehicle applications. While significant progress and plausible prospects of PEMFCs have been achieved, there are still some challenges related to the performance, durability, and cost that need to be overcome to make them economically viable for widespread commercialization. Our strategy is to develop thin films of high-active and stable catalyst coated on vertically aligned nanorod arrays of conductive and stable support. In this work, we fabricated tungsten carbide (WC) nanorods as support and coated them with a platinum-nickel (Pt-Ni) alloy shell denoted as Pt-Ni/WC catalysts. The Pt- Ni/WC nanorods were deposited on glassy carbon disks as well as on silicon substrates for evaluation of their electrocatalytic oxygen reduction reaction (ORR) activity and physical properties. Cyclic voltammetry experiments using rotating disk electrode were performed in perchloric acid (0.1 M HClO4) electrolyte at room temperature to characterize the ORR activity and stability of Pt-Ni/WC nanorods catalysts. Scanning electron microscopy and X-ray diffraction techniques were utilized to study the morphology and crystallographic properties, respectively.

Begum, Mahbuba↗
DOE OSTI2018

OpenMSI Arrayed Analysis Tools (OMAAT) v2.0

Mass spectrometry (MS) is an analytical technique that enables all chemical species within a complex mixture to be resolved and identified based on their mass:charge ratio. MS is an increasingly important tool in life science research and development because it can resolve or separate small molecules, peptides, lipids, proteins, biopolymers and fragments of all of these structures. Unfortunately, the use of MS has been limited for lack of software tools to visualize, manipulate, store and transfer MS data. Ben Bowen, Oliver Ruebel and colleagues made a huge advance on the resolution of these limitations with the invention of "OpenMSI" (#2013-004), a computational method that makes the handling of these very large files (up to 50 Tb) much easier, especially for scientists with limited background in bioinformatics or sophisticated software applications of the type needed to handle such data files. With the OpenMSI Arrayed Analysis Tool (OMAAT, #2016-188) invention, the authors take MS data analysis one step further by providing tolls for automatic sample position optimization and ion selection. Even though sample deposition technologies have improved greatly, there is always the chance of encountering outliers in a predefined roster, especially in very large sample sets. Manual curation of the data would be extremely time consuming, so the inventors have included an algorithm that automatically finds the outliers. OMAAT is written in Python with accompanying Jupyter (formerly iPython) notebook and is fully integrated with OpenMSI.

Bowen, Benjamin↗
DOE OSTI2022

A Primer on Phased Array Radar Technology for the Atmospheric Sciences

The scientific community has expressed interest in the potential of phased array radars (PARs) to observe the atmosphere with finer spatial and temporal scales. Although convergence has occurred between the meteorological and engineering communities, the need exists to increase access of PAR to meteorologists. Here, we facilitate these interdisciplinary efforts in the field of ground-based PARs for atmospheric studies. We cover high-level technical concepts and terminology for PARs as applied to studies of the atmosphere. A historical perspective is provided as context along with an overview of PAR system architectures, technical challenges, and opportunities. Envisioned scan strategies are summarized because they are distinct from traditional mechanically scanned radars and are the most advantageous for high-resolution studies of the atmosphere. Further, open access to PAR data is emphasized as a mechanism to educate the future generation of atmospheric scientists. Finally, a vision for the future of operational networks, research facilities, and expansion into complementary radar wavelengths is provided.

47 OTHER INSTRUMENTATION↗