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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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Correlation functions from tensor network influence functionals: The case of the spin-boson model

We investigate the application of matrix product state (MPS) representations of the influence functionals (IFs) for the calculation of real-time equilibrium correlation functions in open quantum systems. Focusing specifically on the unbiased spin-boson model, we explore the use of IF-MPSs for complex time propagation, as well as IF-MPSs for constructing correlation functions in the steady state. We examine three different IF approaches: one based on the Kadanoff–Baym contour targeting correlation functions at all times, one based on a complex contour targeting the correlation function at a single time, and a steady state formulation, which avoids imaginary or complex times, while providing access to correlation functions at all times. We show that within the IF language, the steady state formulation provides a powerful approach to evaluate equilibrium correlation functions.

Chemistry↗
DOE OSTI2022

Sphere and disk partition functions in Liouville and in matrix integrals

We compute the sphere and disk partition functions in semiclassical Liouville and analogous quantities in double-scaled matrix integrals. The quantity sphere/disk2 is unambiguous and we find a precise numerical match between the Liouville answer and the matrix integral answer. An application is to show that the sphere partition function in JT gravity is infinite.

2D Gravity↗
DOE OSTI2022

A two-phase model that unifies and extends the classical models of membrane transport

Two models describe solvent transport through swollen, nonporous membranes. The pore-flow model, based on fluid mechanics, works for porous membranes, whereas the solution-diffusion model invokes molecular diffusion to treat nonporous membranes. Both approaches make valid arguments for swollen polymer membranes, but they disagree in their predictions of intramembrane pressure and concentration profiles. Using a fluid-solid model that treats the solvent and membrane matrix as separate phases, we show both classical models to be valid, to represent complementary approaches to the same phenomenon, and to make identical predictions. The fluid-solid model clarifies recent reverse osmosis measurements; provides a predictive and mechanistic basis for empirical high-pressure limiting flux phenomena, in quantitative agreement with classic measurements; and gives a framework to treat nonporous but mechanically heterogeneous membrane materials.

Science & Technology - Other Topics↗
DOE OSTI2018

Gogny-force-derived effective shell-model Hamiltonian

The density-dependent finite-range Gogny force has been used to derive the effective Hamiltonian for the shell-model calculations of nuclei. The density dependence simulates an equivalent three-body force, while the finite range gives a Gaussian distribution of the interaction in the momentum space and hence leads to an automatic smooth decoupling between low-momentum and high-momentum components of the interaction, which is important for finite-space shell-model calculations. Two-body interaction matrix elements, single-particle energies, and the core energy of the shell model can be determined by the unified Gogny force. The analytical form of the Gogny force is advantageous to treat cross-shell cases, while it is difficult to determine the cross-shell matrix elements and single-particle energies using an empirical Hamiltonian by fitting experimental data with a large number of matrix elements. In this paper, we have applied the Gogny-force effective shell-model Hamiltonian to the p- and sd-shell nuclei. The results show good agreements with experimental data and other calculations using empirical Hamiltonians. The experimentally known neutron drip line of oxygen isotopes and the ground states of typical nuclei 10B and 18N can be reproduced, in which the role of three-body force is non-negligible. Here, the Gogny-force-derived effective Hamiltonian has also been applied to the cross-shell calculations of the sd–pf shell.

20 ≤ A ≤ 38↗
DOE OSTI2015

50 years of CP violation — What have we learned?

Early after the discovery of CP violation, the explanation of how the Standard Model of particle physics could allow CP violation was quickly given, but it took many years for the original observation to be unequivocally explained on that basis. It was also proposed that this observation opened up the possibility that we could now explain the fact that the universe is made of matter. Remarkably, 50 years later we have no evidence in particle physics that there is any CP violation except that of the Kobayashi Maskawa mechanism of the standard model. Yet we fail completely to explain the baryon asymmetry of the Universe through that mechanism. After reviewing the main points in the history I describe the present experimental attempts to find CP violation beyond the standard model, and explain the theoretical attempts to explain the matter in the Universe.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Recent theoretical results for 0νββ-decay including R0νECEC and 0νββM

The most recent (2015) results for 0νββ nuclear matrix elements in the interacting boson model (IBM-2) with light and heavy neutrino exchange, including R0νECEC, are given for all nuclei of interest from {sup 48}Ca to {sup 238}U. Predictions for half-lives and limits for average neutrino mass are also made. Possible additional scenarios, such as Majoron emission, is also discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Reconciling disparate views of template-directed nucleation through measurement of calcite nucleation kinetics and binding energies

The physical basis for how macromolecules regulate the onset of mineral formation in calcifying tissues is not well established. A popular conceptual model assumes the organic matrix provides a stereochemical match during cooperative organization of solute ions. In contrast, another uses simple binding assays to identify good promoters of nucleation. Here, we reconcile these two views and provide a mechanistic explanation for template-directed nucleation by correlating heterogeneous nucleation barriers with crystal–substrate-binding free energies. We first measure the kinetics of calcite nucleation onto model substrates that present different functional group chemistries (carboxyl, thiol, phosphate, and hydroxyl) and conformations (C11 and C16 chain lengths). We find rates are substrate-specific and obey predictions of classical nucleation theory at supersaturations that extend above the solubility of amorphous calcium carbonate. Analysis of the kinetic data shows the thermodynamic barrier to nucleation is reduced by minimizing the interfacial free energy of the system, ?. We then use dynamic force spectroscopy to independently measure calcite–substrate-binding free energies, ?Gb. Moreover, we show that within the classical theory of nucleation, ? and ?Gb should be linearly related. The results bear out this prediction and demonstrate that low-energy barriers to nucleation correlate with strong crystal–substrate binding. This relationship is general to all functional group chemistries and conformations. These findings provide a physical model that reconciles the long-standing concept of templated nucleation through stereochemical matching with the conventional wisdom that good binders are good nucleators. The alternative perspectives become internally consistent when viewed through the lens of crystal–substrate binding.

Hamm, Laura M.↗
DOE OSTI2017

Eigendecomposition model of resistance temperature detector with applications to S-CO 2 cycle sensing

Super-critical carbon dioxide (S-CO2) is a promising thermodynamic cycle for advanced nuclear reactors and solar energy conversion applications. Dynamic control of the proposed recompression S-CO2 cycle is accomplished with input from resistance temperature detector (RTD) measurements of the process fluid. One of the challenges in practical implementation of S-CO2 cycle is high corrosion rate of component and sensor materials. In this paper, we develop a mathematical model of RTD sensing using eigendecomposition model of radial heat transfer in a layered long cylinder. We show that the value of RTD time constant primarily depends on the rate of heat transfer from the fluid to the outer wall of RTD. We also show that for typical material properties, RTD time constant can be calculated as the sum of reciprocal eigen-values of the heat transfer matrix. Using the computational model and a set of RTD and CO2 fluid thermophysical parameter values, we calculate the value of time constant of thermowell-mounted RTD sensor at the hot side of the precooler in the S-CO2 cycle. The eigendecomposition model of RTD will be used in future studies to model sensor degradation and its impact on control of S-CO2. (C) 2016 Elsevier B.V. All rights reserved.

finite element↗
DOE OSTI2014

Comparative analysis of quantum cascade laser modeling based on density matrices and non-equilibrium Green's functions

We study the operation of an 8.5 μm quantum cascade laser based on GaInAs/AlInAs lattice matched to InP using three different simulation models based on density matrix (DM) and non-equilibrium Green's function (NEGF) formulations. The latter advanced scheme serves as a validation for the simpler DM schemes and, at the same time, provides additional insight, such as the temperatures of the sub-band carrier distributions. We find that for the particular quantum cascade laser studied here, the behavior is well described by simple quantum mechanical estimates based on Fermi's golden rule. As a consequence, the DM model, which includes second order currents, agrees well with the NEGF results. Both these simulations are in accordance with previously reported data and a second regrown device.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

EMUlator: An Elementary Metabolite Unit (EMU) Based Isotope Simulator Enabled by Adjacency Matrix

Stable isotope based metabolic flux analysis is currently the unique methodology that allows the experimental study of the integrated responses of metabolic networks. This method primarily relies on isotope labeling and modeling, which could be a challenge in both experimental and computational biology. Specifically, the algorithm implementation for isotope simulation is a critical step, limiting extensive usage of this powerful approach. In this work, we introduce EMUlator a Python-based isotope simulator which is developed on Elementary Metabolite Unit (EMU) algorithm, an efficient and powerful algorithm for isotope modeling. We propose a novel adjacency matrix method to implement EMU modeling and exemplify it stepwise. This method is intuitively straightforward and can be conveniently mastered for various customized purposes. We apply this arithmetic pipeline to understand the phosphoketolase flux in the metabolic network of an industrial microbe Clostridium acetobutylicum . The resulting design enables a high-throughput and non-invasive approach for estimating phosphoketolase flux in vivo . Our computational insights allow the systematic design and prediction of isotope-based metabolic models and yield a comprehensive understanding of their limitations and potentials.

09 BIOMASS FUELS↗
DOE OSTI2021

Effect of surface disorder on the chiral surface states of a three-dimensional quantum Hall system

We investigate the effect of surface disorder on the chiral surface states of a three-dimensional quantum Hall system. Utilizing a transfer-matrix method, we find that the localization length of the surface state along the magnetic field decreases with the surface disorder strength in the weak disorder regime but increases anomalously in the strong disorder regime. In the strong disorder regime, the surface states mainly locate at the first inward layer to avoid the strong disorder in the outmost layer. The anomalous increase of the localization length can be explained by an effective model, which maps the strong disorder on the surface layer to the weak disorder on the first inward layer. Our work demonstrates that surface disorder can be an effective way to control the transport behavior of the surface states along the magnetic field. We also investigate the effect of surface disorder on the full distribution of conductances P(g) of the surface states in the quasi-one-dimensional (1D) regime for various surface disorder strengths. In particular, we find that P(g) is Gaussian in the quasi-1D metal regime and log-normal in the quasi-1D insulator regime. In the crossover regime, P(g) exhibits highly nontrivial forms, whose shapes coincide with the results obtained from the Dorokhov-Mello-Pereyra-Kumar equation of a weakly disordered quasi-1D wire in the absence of time-reversal symmetry. Our results suggest that P(g) is fully determined by the average conductance, independent of the details of the system, in agreement with the single-parameter scaling hypothesis.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Atomistically informed stochastic multiscale model to predict the behavior of carbon nanotube-enhanced nanocomposites

A comprehensive, point-information-to-continuum-level analysis framework is presented in this paper to accurately characterize the behavior of carbon nanotube (CNT)-enhanced composite materials. Molecular dynamics (MD) simulations are performed to study sub-nanoscale interactions of the CNT with the polymeric phase of the nanocomposite. The effect of cross-linking between the epoxy resin and the hardener on the mechanical properties of the polymer is investigated; furthermore, the effect of CNT weight fraction on the probability distribution of polymer cross-linking degree is also studied through stochastic models. The stochastic distributions obtained from MD simulations provide a basis to simulate local variations in the matrix properties in the continuum model at the microscale. The inclusion of an atomistically informed elastic-plastic model at the microscale reveals a significant deviation of the mechanical properties from those obtained based on classical homogenization approaches. Microstructural variability arising from heterogeneous cross-linking degree in the polymer phase and variations in fiber geometry and spacing is also found to cause deviations in the mechanical response when compared to the assumption of a perfectly ordered fiber-matrix microstructure.

Subramanian, Nithya↗
DOE OSTI2020

An extended moments model of quantum efficiency for metals and semiconductors

The complexity of photocathode designs and detector materials, and the need to model their performance for short pulse durations, response to high frequency photons, presence of coatings and/or thinness of the absorptive layer, necessitates modifications to three-step and moments models of photoemission that are used in simulation codes. Here, methods to include input from computationally intensive approaches, such as density functional theory to model optical properties and transfer matrix approaches to treat emission from the surface or transport past coatings, by means of parametric models are demonstrated. First, a technique to accurately represent optical behavior so as to model reflectivity and penetration depth is given. Second, modifications to bulk models arising from the usage of thin film architectures, and a means to rapidly calculate them, is provided. Third, a parameterization to model the impact of wells associated with coatings and surface layers on the transmission probably is given. In all cases, the methods are computationally efficient and designed to allow for including input from numerically intensive approaches that would otherwise be unavailable for simulations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Lattice Clifford fractons and their Chern-Simons-like theory

We use Dirac matrix representations of the Clifford algebra to build fracton models on the lattice and their effective Chern-Simons-like theory. As an example, we build lattice fractons in odd D spatial dimensions and their (D+1) spacetime dimensional effective theory. The model possesses an anti-symmetric K matrix resembling that of hierarchical quantum Hall states. The gauge charges are conserved in sub-dimensional manifolds which ensures the fractonic behavior. The construction extends to any lattice fracton model built from commuting projectors and with tensor products of spin-1/2 degrees of freedom at the sites.

Fontana, Weslei↗
DOE OSTI2019

The Influence of MS Imaging Parameters on UV-MALDI Desorption and Ion Yield

Ultraviolet matrix-assisted laser desorption/ionization mass spectrometry imaging (UV-MALDI MSI) is a widely used technique for imaging molecular distributions within biological systems. While much work exists concerning desorption in UV-MALDI MS, the effects of commonly varied parameters for imaging applications (repetition rate, use of continuous raster mode and raster speed), which determine spatial resolution and limits of detection for the technique, remain largely unknown. We use multiple surface characterization modalities to obtain quantitative measurements of material desorption and analyte ion yield in thin film model systems of two matrix compounds, arising from different UV-MALDI MSI sampling conditions. Observed changes in resulting ablation feature point to matrix-dependent spatial resolution and laser-induced matrix modification effects. Analyte ion yields of 10{sup −9} to 10{sup −6} are observed. Complex changes in ion yield, between spot and raster sampling and arising from varied laser repetition rate and raster speed, are observed. .

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Computational Assessment of Hydrodynamic Loads on Rockeries for River Bank Protection

Colorado experienced an extreme flooding event in September of 2013 that ravaged canyon roadways southeast of Estes Park, CO. Central Federal Lands was asked to rebuild SH 34 and CO 43 after the floods. To minimize river encroachments in narrow canyons, roadway fill embankments must be over steepened. Using a rockery to stabilize the roadway embankment rather than traditional vertical, concrete structures was the solution. However, no analytical techniques were available for evaluating the hydraulic stability of such structures. Argonne National Laboratory was employed to estimate the hydrodynamic forces by using advanced, computational fluid dynamics (CFD). An investigation was conducted on a section of a model rockery comprised of large boulders exposed to a variety of hydraulic flow conditions. A repeatable geometric section of a typical rockery structure was modeled and used to create boundaries for the CFD model. The test case matrix covers computer simulations of various rockery and channel geometries. The geometrical parameters taken into account are: rockery height, outside face batter angle of the rockery, rockery base width, river bed width, and the hydraulic parameters are: flow depth, flow velocity, and hydraulic angle of attack. Two failure mechanisms of rockery structures, sliding and overturning, are considered. The existing design equations for both modes are modified by addition of hydrodynamic force terms. The new terms were calculated for a parametric set of geometry and condition variation using the CFD model. Moreover, formulas for dimensionless hydraulic force coefficients are proposed that can be used in the design of new rockeries or in evaluation of existing dry-stack rockeries in river environments.

42 ENGINEERING↗
DOE OSTI2020

Entropy production in model colloidal suspensions under shear via the fluctuation theorem

Dissipative systems often exhibit novel and unexpected properties. This is, for instance, the case of simple liquids, which, when subjected to shear and after reaching a steady state, can exhibit a negative entropy production over finite length scales and timescales. This result, among others, is captured by nonequilibrium relations known as fluctuation theorems. Using nonequilibrium molecular dynamics simulations, we examine how, by fine-tuning the properties of the components of a complex fluid, we can steer the nonequilibrium response of the fluid. More specifically, we show how we control the nonequilibrium probability distribution for the shear stress and, in turn, how often states with a negative entropy production can occur. To achieve this, we start by characterizing how the size for the liquid matrix impacts the probability of observing negative entropy states, as well as the timescale over which these can be observed. We then measure how the addition of larger particles to this liquid matrix, i.e., simulating a model colloidal suspension, results in an increase in the occurrence of such states. As a result, this suggests how modifications in the composition of the mixture and in the properties of its components lead to an increase in the probability of observing states of negative entropy production and, thus, for the system to run in reverse.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Transfer matrix computation of critical polynomials for two-dimensional Potts models

We showed, In our previous work, that critical manifolds of the q-state Potts model can be studied by means of a graph polynomial P B (q, v), henceforth referred to as the critical polynomial. This polynomial may be defined on any periodic two-dimensional lattice. It depends on a finite subgraph B, called the basis, and the manner in which B is tiled to construct the lattice. The real roots v = e K — 1 of P B (q, v) either give the exact critical points for the lattice, or provide approximations that, in principle, can be made arbitrarily accurate by increasing the size of B in an appropriate way. In earlier work, P B (q, v) was defined by a contraction-deletion identity, similar to that satisfied by the Tutte polynomial. Here, we give a probabilistic definition of P B (q, v), which facilitates its computation, using the transfer matrix, on much larger B than was previously possible.We present results for the critical polynomial on the (4, 8 2 ), kagome, and (3, 12 2 ) lattices for bases of up to respectively 96, 162, and 243 edges, compared to the limit of 36 edges with contraction-deletion. We discuss in detail the role of the symmetries and the embedding of B. The critical temperatures v c obtained for ferromagnetic (v > 0) Potts models are at least as precise as the best available results from Monte Carlo simulations or series expansions. For instance, with q = 3 we obtain v c (4, 8 2 ) = 3.742 489 (4), v c (kagome) = 1.876 459 7 (2), and v c (3, 12 2 ) = 5.033 078 49 (4), the precision being comparable or superior to the best simulation results. More generally, we trace the critical manifolds in the real (q, v) plane and discuss the intricate structure of the phase diagram in the antiferromagnetic (v < 0) region.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗