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At least 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Restricting loop expansions in gauge theories coupled to matter

Highlights: • Lagrange multiplier fields are used to restrict radiative effects to one-loop order. • This approach is exemplified in the Yang-Mills theory coupled to a scalar matter field. • We showed that it can be used with the Einstein–Hilbert action coupled to matter. • The resulting quantum gravity theory is both renormalizable and unitary. Quantizing any model in which a Lagrange multiplier (LM) field is used to restrict field configurations to those that satisfy the classical equations of motion, leads to at most one-loop radiative corrections. This approach can be used with both the Yang–Mills (YM) and Einstein–Hilbert (EH) action; the resulting theory is both renormalizable and unitary, has a positive energy spectrum and has no negative norm states contributing to physical processes. Although this approach cannot be consistently used with scalar fields alone, scalar fields can be coupled to gauge fields so that loop effects in the gauge sector are restricted to one-loop order in a way that satisfies the usual criterion for a consistent quantum field theory. The tree-level diagrams are those of the classical theory in which the metric couples to the energy–momentum tensor.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Entanglement between valence and sea quarks in hadrons of 1+1 dimensional QCD

The conceptual interpretation of valence- and sea-quark separation, which is a key aspect of the parton model and of an intuitive picture of hadron structure, becomes obscured by quantum effects in QCD. This suggests that there may be measures of entanglement between quark degrees of freedom that are present in QCD, but absent in the intuitive picture with a clear valence-sea (VS) separation. In this paper, we define the first rigorous measure of VS entanglement in QCD in an attempt to bring conceptual clarity to this issue, and, potentially, to find a measure of the applicability of the parton model to QCD bound states. This VS entanglement vanishes in the large-N c limit, and it remains low when finite-N c states resemble their large-N c counterparts. We perform a numerical study of VS entanglement in 1 + 1 dimensional discrete light-cone quantized QCD, and in the process develop a method for building the color-singlet basis of 1 + 1d QCD that is manifestly complete and orthogonal by construction. We calculate this VS entanglement entropy for the first time and find that it is relatively low for the first few excited states of both mesons and baryons compared to all other states in the spectrum, with the VS entropy of ground state hadrons providing a minimum. We also see that for ground state mesons the entropy is well described in the 1/N c approximation. These results suggest that low energy hadrons may be the only QCD bound states for which the large-N c expansion, and perhaps the parton model, provide an accurate description. This work also provides the first evidence that the VS entanglement entropy of QCD in 3 + 1d, which would likely serve as an order parameter for the transition between quark and hadron degrees of freedom, may be perturbatively accessible through a large-N c expansion.

1+1 dimensional QCD↗
DOE OSTI2023

NeRVI: Compressive neural representation of visualization images for communicating volume visualization results

We present NeRVI, a new deep-learning approach that compresses a large collection of visualization images generated from time-varying data for communicating volume visualization results. Based on an image-based implicit neural representation, our approach represents tens of thousands of high-resolution rendering images parametrized by different parameters via a hybrid model of multilayer perceptrons and convolutional neural networks. Here, our model predicts images and corresponding masks, and the masks are utilized for loss computation and network training to capture fine structural details and small components. In conjunction with model quantization and weight encoding, NeRVI yields highly compact compressive neural representations while preserving the image fidelity well. We demonstrate the effectiveness of NeRVI with isosurface rendering and direct volume rendering images generated from multiple data sets and compare NeRVI with other state-of-the-art deep learning-based (InSituNet, SIREN, NeRF, and NeRV) methods. Quantitative and qualitative results show that NeRVI provides an alternative solution that augments domain scientists' ability to manage, represent, and communicate scientific visualization output.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

A multilayer multiconfiguration time-dependent Hartree study of the nonequilibrium Anderson impurity model at zero temperature

Quantum transport is studied for the nonequilibrium Anderson impurity model at zero temperature employing the multilayer multiconfiguration time-dependent Hartree theory within the second quantization representation (ML-MCTDH-SQR) of Fock space. To address both linear and nonlinear conductance in the Kondo regime, two new techniques of the ML-MCTDH-SQR simulation methodology are introduced: (i) the use of correlated initial states, which is achieved by imaginary time propagation of the overall Hamiltonian at zero voltage and (ii) the adoption of the logarithmic discretization of the electronic continuum. Employing the improved methodology, the signature of the Kondo effect is analyzed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Quantum microgrid state estimation

This paper investigates the feasibility and efficiency of quantum-circuit-based algorithms for microgrid state estimation. Here, our new contributions include: (1) a general quantum state estimation (GQSE) formulation is devised for swing-bus-contained microgrids through the quantized Gaussian–Newton iteration, (2) a preconditioned quantum linear solver (PQLS) is developed for tackling the ill-conditioned GQSE with limited quantum resources, and (3) an enhanced quantum state estimation (EQSE) algorithm is further established for hierarchical-control-based microgrids with exogenous disturbances. Extensive case studies demonstrate the correctness of GQSE, PQLS and EQSE in two typical microgrids. The robustness and convergence performance of EQSE are also verified.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2017

One possible source of mass-independent fractionation of sulfur isotopes in the Archean atmosphere of Earth

Energy transfer mechanism for recombination of two sulfur atoms into a diatomic molecule, S 2 , is studied theoretically and computationally to determine whether the rate coefficient of this process can be significantly affected by isotopic substitutions, and whether the resultant isotope effect is expected to be mass-dependent or mass-independent. This is one of sulfur polymerization processes thought to be important in the anoxic atmosphere of the Archean Earth and, potentially, relevant to mass-independent fractionation of sulfur isotopes. A simplified theoretical approach is employed, in which all properties of S 2 molecule are characterized rather accurately, whereas the process of stabilization of metastable S 2 * by bath gas collisions is described approximately. Properties of individual scattering resonances in S 2 are studied in detail, and it is found that most important contributions to the recombination process come from ro-vibrational states formed near the top of centrifugal barrier, and that the number of such states is about 50 (in 32 S 32 S). Absolute value of recombination rate coefficient is computed to be 1.22 x 10 -33 cm 6 /s (for 32 S 32 S at room temperature and atmospheric pressure), close to experimental result. Two distinct isotope effects are identified. One is a classical mass-dependent effect due to translational partition function, which leads to a weak, smooth, and negative mass-dependence of rate coefficient (4% decrease when the mass is raised from 32 S 32 S to 34 S 34 S). Second effect, due to quantized resonances, is two orders of magnitude stronger, but is local. In practice, due to presence of multiple individual resonances, this phenomenon leads to irregular mass-independent variations of rate coefficients in the ranges ±5%. It is also demonstrated that in real molecules this irregular behavior is expected to be somewhat smoother, and the isotope effect is somewhat smaller, due to dependence of stabilization cross section on properties of individual resonances (not described by present model). So additional calculations of stabilization cross sections are needed in order to give quantitative prediction of this mass-independent isotope effect, and to determine its relevance to mass-independent fractionation of sulfur isotopes in the Archean rock record.

58 GEOSCIENCES↗
DOE OSTI2018

Anisotropic magnetocaloric response in AlFe 2 B 2

Experimental investigations of the magnetocaloric response of the intermetallic layered AlFe 2 B 2 compound along the principle axes of the orthorhombic cell were carried out using aligned plate-like crystallites with an anisotropic [101] growth habit. Results were confirmed to be consistent with density functional theory calculations. Field-dependent magnetization data confirm that the a-axis is the easy direction of magnetization within the (ac) plane. The magnetocrystalline anisotropy energy required to rotate the spin quantization vector from the c-to the a-axis direction is determined as K~0.9 MJ/m 3 at 50 K. Magnetic entropy change curves measured near the Curie transition temperature of 285 K reveal a large rotating magnetic entropy change of 1.3 J kg -1 K -1 at μ 0 H app = 2 T, consistent with large differences in magnetic entropy change ΔS mag measured along the a- and c-axes. Overall, this study provides insight of both fundamental and applied relevance concerning pathways for maximizing the magnetocaloric potential of AlFe 2 B 2 for thermal management applications.

36 MATERIALS SCIENCE↗
DOE OSTI2024

An efficient quantum circuit for block encoding a pairing Hamiltonian

We present an efficient quantum circuit for block encoding a pairing Hamiltonian often studied in nuclear physics. Our block encoding scheme does not require mapping the creation and annihilation operators to the Pauli operators and representing the Hamiltonian as a linear combination of unitaries. Instead, we show how to encode the Hamiltonian directly using controlled swap operations. We analyze the gate complexity of the block encoding circuit and show that it scales polynomially with respect to the number of qubits required to represent a quantum state associated with the pairing Hamiltonian. We also show how the block encoding circuit can be combined with the quantum singular value transformation to construct an efficient quantum circuit for approximating the density of states of a pairing Hamiltonian. The techniques presented can be extended to encode more general second-quantized Hamiltonians.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2020

Online multimedia retrieval on CPU–GPU platforms with adaptive work partition

Nearest neighbors search is a core operation found in several online multimedia services. These services have to handle very large databases, while, at the same time, they must minimize the query response times observed by users. This is specially complex because those services deal with fluctuating query workloads (rates). Consequently, they must adapt at run-time to minimize the response times as the load varies. In this paper, we address the aforementioned challenges with a distributed memory parallelization of the product quantization nearest neighbor search, also known as IVFADC, for hybrid CPU–GPU machines. Overall, our parallel IVFADC implements an out-of-GPU memory execution scheme to use the GPU for databases in which the index does not fit in its memory, which is crucial for searching in very large databases. The careful use of CPU and GPU with work stealing led to an average response time reduction of 2.4 as compared to using the GPU only. Also, our approach to adapt the system to fluctuating loads, called Dynamic Query Processing Policy (DQPP), attained a response time reduction of up to 5 vs. the best static (BS) policy for moderate loads. The system has attained high query processing rates and near-linear scalability in all experiments. We have evaluated our system on a machine with up to 256 NVIDIA V100 GPUs processing a database of 256 billion SIFT features vectors.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2014

Synthesis, structural and optical properties of Sm{sup 3+} and Nd{sup 3+} doped cadmium sulfide nanocrystals

Graphical abstract: Samarium (Sm{sup 3+}) and neodymium (Nd{sup 3+}) doped cadmium sulfide nanocrystals have been prepared via precipitation method. The structural and the luminescent properties of the as-synthesised nanocrystals have been discussed. - Highlights: • Cubic phase lanthanide ion doped cadmium sulfide nanocrystals were prepared by co-precipitation method. • HRTEM displays randomly aggregated nanoparticles with well-defined lattice fringes. • Energy gap and optical properties were affected by the different doping ions. • Effect of Sm and Nd ion doping on photo-emission of CdS nanocrystals was clarified. - Abstract: Cubic phase samarium (Sm{sup 3+}) and neodymium (Nd{sup 3+}) doped cadmium sulfide nanocrystals were synthesized through the chemical co-precipitation method. The crystallite size computed with high intense (1 1 1) peak using Scherrer formula was ∼3 nm. Morphology was examined with scanning electron microscopy (SEM). The transmission electron microscopy (TEM) images further established the formation of nanoclusters and EDAX spectra confirms the presence of cadmium, sulphide and rare earth elements in the sample. SAED pattern shows the crystallinity of the synthesized sample. Blue shift in the bandgap energy in the reflectance UV spectra, illustrates size quantization effect and dopant ion incorporation into the host lattice. The effect of doping concentrations of Sm{sup 3+} and Nd{sup 3+} on the luminescence spectra of CdS was studied. The emission spectra revealed that the intensity increased considerably in the presence of dopant ions. The variation in the optical properties and the enhancement in the luminescence were discussed for different doping levels.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Digital atomic scale fabrication an inverse Moore's Law – A path to atomically precise manufacturing

There is an exciting opportunity to start a second digital revolution that will supersede the first digital revolution in information technology (IT) as the primary driver of scientific, technological, and economic growth. This new revolution will be digital fabrication technology. Here, the digital IT revolution has been largely driven by digital algorithms such as error detection and correction and Moore's Law which has given us an exponential trend in product capabilities. However, the longstanding trend in improving manufacturing precision which has enabled Moore's Law simply cannot be continued much longer because we are running into the limits imposed by the quantized nature of matter. At this scale, matter can no longer be treated in an analogue fashion i.e. as an infinitely divisible medium, but must be treated as an integer number of discrete atomic distances, i.e. in a digital fashion. By embracing this digital nature of matter, we can conceive of a digital fabrication technology, where the digital processes are the making and breaking of chemical bonds, there is a digital address grid that is spatial in nature, and error detection and correction processes can be developed. This digital fabrication technology will have the similarly huge advantages over analog fabrication that digital IT has over analog IT. We remind the reader that effective digital technologies are not exclusively digital in their operation. Digital electronics is carried out by analog transistors that are embedded in circuitry designed to accept their output in a digital fashion. Digital fabrication technology is not synonymous with Atomically Precise Manufacturing (APM) but should lead to that important capability. Furthermore this digital fabrication technology will start a new exponential manufacturing trend that will replace Moore's law and will not be just for information processing and therefore will have an even larger impact than Moore's Law. Like any exponential trend Digital Fabrication will start slowly in a few niche markets, but the time for investing in the development of this new technology is now.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2026

Unveiling field-transverse spin anisotropy in the spin liquid candidate α-RuCl3 via spin Hall magnetoresistance

α-RuCl3 has emerged as a possible candidate for a quantum spin liquid (QSL) that promises exotic quasiparticles relevant for fault-tolerant quantum computation. Here, we report spin-sensitive transport measurements using a proximal spin Hall metal, platinum (Pt), to probe magnetic moments in the insulator α-RuCl3. We observe spin Hall magnetoresistance (SMR), where both the transverse and longitudinal resistivities exhibit angular oscillations between the in-plane magnetic field and the current, driven by the interplay between the spin Hall effect in Pt and local magnetic moments in α-RuCl3. These oscillations occur from 1.5 to 18 T, covering the zigzag antiferromagnetic, putative QSL, and supposedly partially field-polarized phases. The phase of the SMR oscillations suggests that the local moments, whether static or fluctuating, develop spin anisotropy with a quantization axis in-plane and largely transverse to the magnetic field across all fields from 1.5 to 18 T. Temperature dependence indicates that the spin anisotropy operates at an energy scale similar to that of the reported QSL signatures in α-RuCl3.

Idzuchi, Hiroshi [Tohoku University, Japan]↗
DOE OSTI2015

FPGA-based Klystron linearization implementations in scope of ILC

We report the development and implementation of four FPGA-based predistortion-type klystron linearization algorithms. Klystron linearization is essential for the realization of ILC, since it is required to operate the klystrons 7% in power below their saturation. The work presented was performed in international collaborations at the Fermi National Accelerator Laboratory (FNAL), USA and the Deutsches Elektronen Synchrotron (DESY), Germany. With the newly developed algorithms, the generation of correction factors on the FPGA was improved compared to past algorithms, avoiding quantization and decreasing memory requirements. At FNAL, three algorithms were tested at the Advanced Superconducting Test Accelerator (ASTA), demonstrating a successful implementation for one algorithm and a proof of principle for two algorithms. Furthermore, the functionality of the algorithm implemented at DESY was demonstrated successfully in a simulation.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

A simulation model of front-end electronics for high-precision timing measurements with low-gain avalanche detectors

Here, we report simulation results of a study aiming to optimize parameters of a detector that uses low-gain avalanche detectors (LGAD) for high-precision timing measurements. The detector is assumed to be composed of a 50μm LGAD sensor coupled to front-end readout electronics which is used to measure the time of arrival of minimum ionizing particles. The simulation includes modeling of signal fluctuations in the LGAD sensor, variations of the analog bandwidth and signal-to-noise ratio (SNR) of the front-end electronics, time bin quantization, and radiation damage of the LGAD sensors. Two approaches to measure the timestamp are considered: leading edge and constant fraction. Simulated LGAD pulses before irradiation, and after irradiation with neutron fluences of 5×10 14 n/cm 2 and 1×10 15 n/cm 2 , are studied. The time resolution for a 50μm LGADs was found to be 35 ps for front-end electronics bandwidths larger than 350 MHz and SNRs larger than 30. The time resolution at SNR of 30 for fluences of 5×10 14 n/cm 2 and 1×10 15 n/cm 2 were found to be 31 ps and 37 ps, respectively.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

New quantum effects in relativistic magnetohydrodynamics

Chiral anomaly induces a new kind of macroscopic quantum behavior in relativistic magnetohydrodynamics, including the chiral magnetic effect. In this talk we present two new quantum effects present in fluids that contain charged chiralfermions: 1) the turbulent inverse cascade driven by the chiral anomaly; 2) quantized chiral magnetic current induced by the reconnections of magnetic flux. Furthermore,we discuss the implications for the evolution of the quark-gluon plasma produced in heavy ion collisions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Monte Carlo simulations for understanding the transport properties of metallic nanowires

We report the conductance calculation of metallic nanowires of different metals under the application of a tensile force. The elongation induced by the tensile force was simulated by means of the canonical Monte Carlo method combined with the embedded atom method to compute the energy of the system. We studied nanowires composed of Ag, Au, Pt and Cu. The conductance was calculated by means of the Landauer formula and the non-equilibrium Green function formalism. As previously verified experimentally and using other simulation techniques, the conductance is quantized. In addition to this, we have found that there is a strong correlation between the magnitude of the conductance and the width of the nanowire at its thinnest point. Conductance histograms were analyzed for all the different metals.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Hamiltonian nature of monopole dynamics

Classical electromagnetism with magnetic monopoles is not a Hamiltonian field theory because the Jacobi identity for the Poisson bracket fails. The Jacobi identity is recovered only if all of the species have the same ratio of electric to magnetic charge or if an electron and a monopole can never collide. Without the Jacobi identity, there are no local canonical coordinates or Lagrangian action principle. In order to build a quantum field of magnetic monopoles, we either must explain why the positions of electrons and monopoles can never coincide or we must resort to new quantization techniques.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗