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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Fission Chain Restart Theory

We present that fast nanosecond timescale neutron and gamma-ray counting can be performed with a (liquid) scintillator array. Fission chains in metal evolve over a timescale of tens of nanoseconds. If the metal is surrounded by moderator, neutrons leaking from the metal can thermalize and diffuse in the moderator. With finite probability, the diffusing neutrons can return to the metal and restart the fast fission chain. The timescale for this restart process is microseconds. A theory describing time evolving fission chains for metal surrounded by moderator, including this restart process, is presented. Finally, this theory is sufficiently simple for it to be implemented for real-time analysis.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

An updated LLVM-based quantum research compiler with further OpenQASM support

Abstract Quantum computing is a rapidly growing field with the potential to change how we solve previously intractable problems. Emerging hardware is approaching a complexity that requires increasingly sophisticated programming and control. Scaffold is an older quantum programming language that was originally designed for resource estimation for far-future, large quantum machines, and ScaffCC is the corresponding LLVM-based compiler. For the first time, we provide a full and complete overview of the language itself, the compiler as well as its pass structure. While previous works Abhari et al (2015 Parallel Comput. 45 2–17), Abhari et al (2012 Scaffold: quantum programming language https://cs.princeton.edu/research/techreps/TR-934-12 ), have piecemeal descriptions of different portions of this toolchain, we provide a more full and complete description in this paper. We also introduce updates to ScaffCC including conditional measurement and multidimensional qubit arrays designed to keep in step with modern quantum assembly languages, as well as an alternate toolchain targeted at maintaining correctness and low resource count for noisy-intermediate scale quantum (NISQ) machines, and compatibility with current versions of LLVM and Clang. Our goal is to provide the research community with a functional LLVM framework for quantum program analysis, optimization, and generation of executable code.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Microwave-optical quantum frequency conversion

Photons at microwave and optical frequencies are principal carriers for quantum information. While microwave photons can be effectively controlled at the local circuit level, optical photons can propagate over long distances. High-fidelity conversion between microwave and optical photons will allow the distribution of quantum states across different quantum technology nodes and enhance the scalability of hybrid quantum systems toward a future “Quantum Internet.” Despite a frequency difference of five orders of magnitude, there has been significant progress recently toward the transfer between microwave and optical photons with steadily improved efficiency in a coherent and bidirectional manner. In this review, we summarize this progress, emphasizing integrated device approaches, and provide a perspective for device implementation that enables quantum state transfer and entanglement distribution across microwave and optical domains.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2012

IER-163 Post-Experiment MCNP Calculations (U)

IER-163 has been modeled with high fidelity in MCNP6. The model k eff was high, as in other similar calculations. The fission ratio 238 U(n,f)/ 235 U(n,f) was 12.6% too small compared with measurements; the ratio 239 Pu(n,f)/ 235 U(n,f) was 11.5% too small compared with measurements; the iridium ratio 193 Ir(n,n´)/ 191 Ir(n,γ) was 16.4% too large; and the gold ratios 197 Au(n,2n)/ 197 Au(n,γ), 197 Au(n,2n)/ 235 U(n,f), and 197 Au(n,γ)/ 235 U(n,f) were within one standard deviation of the measured values. It is suggested that the calculated 235 U fission rate is too large and the calculated 238 U fission rate is too small.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2012

Integral Criticality Estimators in MCATK(U)

The Monte Carlo Application Toolkit (MCATK) is a component-based software toolset for delivering customized particle transport solutions using the Monte Carlo method. Currently under development in the XCP-MCC group at Los Alamos National Laboratory, the toolkit has the ability to estimate the k eff and α eigenvalues for static geometries. This paper presents a description of the estimators and variance reduction techniques available in the toolkit and includes a preview of those slated for future releases. Along with the description of the underlying algorithms is a description of the available user inputs for controlling the iterations. The paper concludes with a comparison of the MCATK results with those provided by analytic solutions. The results match within expected statistical uncertainties and demonstrate MCATK's usefulness in estimating these important quantities.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2013

THE FREE GAS THERMAL TREATMENT IN MCATK: Sampling the Thermal Motion of the Target Nucleus (U)

The free gas thermal treatment for neutron scattering, as formulated for Monte Carlo by Coveyou et al., is implemented and tested in the MCATK software library. This treatment is necessary for two reasons: 1) to handle the kinematics of a neutron colliding with a target nucleus in thermal motion and 2) to accurately use ACE scattering data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS2009

Physical Principle for Generation of Randomness

A physical principle (more precisely, a principle that incorporates mathematical models used in physics) has been conceived as the basis of a method of generating randomness in Monte Carlo simulations. The principle eliminates the need for conventional random-number generators. The Monte Carlo simulation method is among the most powerful computational methods for solving high-dimensional problems in physics, chemistry, economics, and information processing. The Monte Carlo simulation method is especially effective for solving problems in which computational complexity increases exponentially with dimensionality. The main advantage of the Monte Carlo simulation method over other methods is that the demand on computational resources becomes independent of dimensionality. As augmented by the present principle, the Monte Carlo simulation method becomes an even more powerful computational method that is especially useful for solving problems associated with dynamics of fluids, planning, scheduling, and combinatorial optimization. The present principle is based on coupling of dynamical equations with the corresponding Liouville equation. The randomness is generated by non-Lipschitz instability of dynamics triggered and controlled by feedback from the Liouville equation. (In non-Lipschitz dynamics, the derivatives of solutions of the dynamical equations are not required to be bounded.)

Zak, Michail↗
DOE OSTI2012

Data Assimilation for Inner-Magnetospheric Plasma Systems

Data assimilation are methods that combine information from a model, observational data, and corresponding error statistics, to provide an estimate of the true state of a system as accurately as possible. These methodologies are used in a wide range of problems, such as: Weather prediction, Radiation belt simulation, Solar Physics, and Orbital Dynamics simulation. Data Assimilation for Radiation Belt Models: (1) Wide range of assimilation methodologies, most are easy to implement and effective; (2) Data assimilation is an active area of research (both in theory and applications); (3) Huge benefit to space physics, community starting to accept and utilize; (4) Assimilation in space physics used for gap filling, forecast, nowcast and/or reanalysis, reduction and specification of uncertainties; and (5) Data assimilation offers paradigm shift from previous working relation between modelers and experimentalist, work more closely together.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

MCNP6 Cosmic-Source Option

MCNP is a Monte Carlo radiation transport code that has been under development for over half a century. Over the last decade, the development team of a high-energy offshoot of MCNP, called MCNPX, has implemented several physics and algorithm improvements important for modeling galactic cosmic-ray (GCR) interactions with matter. In this presentation, we discuss the latest of these improvements, a new Cosmic-Source option, that has been implemented in MCNP6.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2026

The DESI DR1 peculiar velocity survey: Growth rate measurements from the galaxy power spectrum

The large-scale structure of the Universe and its evolution encapsulate a wealth of cosmological information. A powerful means of unlocking this knowledge lies in measuring the auto-power spectrum and/or the cross-power spectrum of the galaxy density and momentum fields, followed by the estimation of cosmological parameters based on these spectrum measurements. In this study, we generalize the cross-power spectrum model to accommodate scenarios in which the density and momentum fields are derived from distinct galaxy surveys. The growth rate of the large-scale structures of the Universe, commonly represented as fσ 8 , was extracted by jointly fitting the monopole and quadrupole moments of the auto-density power spectrum, the monopole of the auto-momentum power spectrum, and the dipole of the cross-power spectrum. Our estimators, theoretical models, and parameter-fitting framework were tested using mocks, confirming their robustness and accuracy in retrieving the fiducial growth rate from simulation. These techniques were then applied to analyse the power spectrum of the DESI Bright Galaxy Survey and Peculiar Velocity Survey. The fit result of the growth rate is fσ8 = 0.440$^{+0.080}_{−0.096}$ at effective redshift zeff = 0.07. By synthesizing the fitting outcomes from correlation functions, maximum likelihood estimation, and the power spectrum, a consensus value is yielded of fσ 8 (z eff = 0.07) = 0.450$^{+0.055}_{−0.055}$, and correspondingly we obtain γ = 0.580$^{+0.110}_{−0.110}$, Ω m = 0.301$^{+0.011}_{−0.011}$, and σ 8 = 0.834$^{+0.032}_{−0.032}$. The measured fσ8 and γ are consistent with the prediction of the Λ cold dark matter model and general relativity.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Diffuse boosted cosmic neutrino background

Energetic cosmic rays scatter off the cosmic neutrino background throughout the history of the Universe, yielding a diffuse flux of cosmic relic neutrinos boosted to high energies. We calculate this flux under different assumptions of the cosmic-ray flux spectral slope and redshift evolution. The nonobservation of the diffuse flux of boosted relic neutrinos with current high-energy neutrino experiments already excludes an average cosmic neutrino background overdensity larger than ∼10 4 over cosmological distances. We discuss the future detectability of the diffuse flux of boosted relic neutrinos in light of neutrino overdensity estimates and cosmogenic neutrino backgrounds.

Astronomy & Astrophysics↗
DOE OSTI2024

Green's function methods for multiphysics simulations (Final Report)

Green's functions are important tools for analyzing mathematical properties of partial differential equations (PDEs), and for numerically solving PDEs, especially when equations for the same operator but with multiple right hand sides need to be solved simultaneously. This proposal aims at developing efficient and accurate numerical methods for computing Green's functions, which can be used to tackle a challenging question in multiphysics simulation of DOE-mission science problems: how to couple quantum physics with classical physics. The key mathematical difficulty is properly formulate a "boundary condition" for the region described by quantum physics, and conventional approaches often model such boundary conditions in an empirical way. The proposed Green's function methods use the Dirichlet-to-Neumann map to formulate a boundary condition that is non-empirical and can couple the quantum and classical regions in an in principle exact way. The key ingredient of the new methods is to construct the Dirichlet-to-Neumann map in an efficient, accurate and versatile manner. The new methods have provably low complexity and are ideally suited for massively parallel and emerging many-core computational systems.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS2002

Enhancing Science Teacher Training Using Water Resources and GLOBE

Heritage College, located on the Yakama Indian Reservation in south central Washington state, serves a multicultural, underserved, rural population and trains teachers to staff the disadvantaged school districts on and surrounding the reservation. In-service teachers and pre-service teachers in the area show strength in biology but have weak backgrounds in chemistry and mathematics. We are addressing this problem by providing a 2-year core of courses for 3 groups of 25 students (15 pre-service and 10 in-service teachers) using GLOBE to teach integrated physical science and mathematics. At the conclusion of the program, the students will qualify for science certification by Washington State. Water resources are the focal point of the curriculum because it is central to life in our desert area. The lack or excess of water, its uses, quality and distribution is being studied by using GIS, remote sensing and historical records. Students are learning the methodology to incorporate scientific protocols and data into all aspects of their future teaching curriculum. In addition, in each of the three years of the project, pre-service teachers attended a seminar series during the fall semester with presentations by collaborators from industry, agriculture, education and government agencies. Students used NASA educational materials in the presentations that they gave at the conclusion of the seminar series. All pre- and in-service teachers continue to have support via a local web site for Heritage College GLOBE participants.

Falco, James W.↗
DOE OSTI2016

Introduction to Numerical Methods [Slides]

These are slides for a lecture for the Parallel Computing Summer Research Internship at the National Security Education Center. This gives an introduction to numerical methods. Repetitive algorithms are used to obtain approximate solutions to mathematical problems, using sorting, searching, root finding, optimization, interpolation, extrapolation, least squares regression, Eigenvalue problems, ordinary differential equations, and partial differential equations. Many equations are shown. Discretizations allow us to approximate solutions to mathematical models of physical systems using a repetitive algorithm and introduce errors that can lead to numerical instabilities if we are not careful.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2024

Non-invertible Symmetries and their Applications (Final Report)

Symmetries have long been a staple of theoretical physics. Recent developments have led to extensions of the notion of symmetry to so-called generalized symmetries, a particularly interesting class of which are non-invertible symmetries. Whereas traditional symmetries form a group—a mathematical structure capturing the intuition that the composition of two symmetry transformations is another symmetry transformation, and that every symmetry transformation can be undone by an inverse transformation—non-invertible symmetries have the interesting property that they do not form a group. The current award was used to pursue the study of non-invertible symmetries, focusing on both their mathematical framework and physical applications.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗