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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 199 records · Page 11
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DOE OSTI2015

On a hierarchy of nonlinearly dispersive generalized Korteweg - de Vries evolution equations

We propose a hierarchy of nonlinearly dispersive generalized Korteweg–de Vries (KdV) evolution equations based on a modification of the Lagrangian density whose induced action functional the KdV equation extremizes. Two recent nonlinear evolution equations describing wave propagation in certain generalized continua with an inherent material length scale are members of the proposed hierarchy. Like KdV, the equations from the proposed hierarchy possess Hamiltonian structure. Unlike KdV, the solutions to these equations can be compact (i.e., they vanish outside of some open interval) and, in addition, peaked. Implicit solutions for these peaked, compact traveling waves (“peakompactons”) are presented.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Strong Local-Nonlocal Coupling for Integrated Fracture Modeling

Peridynamics, a nonlocal extension of continuum mechanics, is unique in its ability to capture pervasive material failure. Its use in the majority of system-level analyses carried out at Sandia, however, is severely limited, due in large part to computational expense and the challenge posed by the imposition of nonlocal boundary conditions. Combined analyses in which peridynamics is employed only in regions susceptible to material failure are therefore highly desirable, yet available coupling strategies have remained severely limited. This report is a summary of the Laboratory Directed Research and Development (LDRD) project “Strong Local-Nonlocal Coupling for Integrated Fracture Modeling,” completed within the Computing and Information Sciences (CIS) Investment Area at Sandia National Laboratories. A number of challenges inherent to coupling local and nonlocal models are addressed. A primary result is the extension of peridynamics to facilitate a variable nonlocal length scale. This approach, termed the peridynamic partial stress, can greatly reduce the mathematical incompatibility between local and nonlocal equations through reduction of the peridynamic horizon in the vicinity of a model interface. A second result is the formulation of a blending-based coupling approach that may be applied either as the primary coupling strategy, or in combination with the peridynamic partial stress. This blending-based approach is distinct from general blending methods, such as the Arlequin approach, in that it is specific to the coupling of peridynamics and classical continuum mechanics. Facilitating the coupling of peridynamics and classical continuum mechanics has also required innovations aimed directly at peridynamic models. Specifically, the properties of peridynamic constitutive models near domain boundaries and shortcomings in available discretization strategies have been addressed. The results are a class of position-aware peridynamic constitutive laws for dramatically improved consistency at domain boundaries, and an enhancement to the meshfree discretization applied to peridynamic models that removes irregularities at the limit of the nonlocal length scale and dramatically improves convergence behavior. Finally, a novel approach for modeling ductile failure has been developed, motivated by the desire to apply coupled local-nonlocal models to a wide variety of materials, including ductile metals, which have received minimal attention in the peridynamic literature. Software implementation of the partial-stress coupling strategy, the position-aware peridynamic constitutive models, and the strategies for improving the convergence behavior of peridynamic models was completed within the Peridigm and Albany codes, developed at Sandia National Laboratories and made publicly available under the open-source 3-clause BSD license.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Cobalt-Catalyzed Hydrogenation Reactions Enabled by Ligand-Based Storage of Dihydrogen

The use of supporting ligands that can store either protons or electrons has emerged as a powerful strategy in catalysis. While these strategies are potent individually, natural systems mediate remarkable transformations by combining the storage of both protons and electrons in the secondary coordination sphere. As such, there has been recent interest in using this strategy to enable fundamentally different transformations. Furthermore, outsourcing H-atom or hydrogen storage to ancillary ligands can also enable alternative mechanistic pathways and thereby selectivity. Here, we describe the application of this strategy to facilitate radical reactivity in Co-based hydrogenation catalysis. Metalation of previously reported dihydrazonopyrrole ligands with Co results in paramagnetic complexes, which are best described as having Co(II) oxidation states. These complexes catalytically hydrogenate olefins with low catalyst loadings under mild conditions (1 atm H 2 , 23 °C). Mechanistic, spectroscopic, and computational investigations indicate that this system goes through a radical hydrogen-atom transfer (HAT) type pathway that is distinct from classic organometallic mechanisms and is supported by the ability of the ligand to store H 2 . These results show how ancillary ligands can facilitate efficient catalysis, and furthermore how classic organometallic mechanisms for catalysis can be altered by the secondary coordination sphere.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Heterolysis of H 2 Across a Classical Lewis Pair, 2,6-Lutidine∙BCl3: Synthesis, Characterization, and Mechanism

In this study, we report that 2,6-lutidine∙trichloroborane (Lut∙BCl 3 ) reacts with H 2 in toluene, bromobenzene, dichloromethane, and Lut solvents producing the neutral hydride, Lut∙BHCl 2 . The mechanism was modeled with density functional theory, and energies of stationary states were calculated at the G3(MP2)B3 level of theory. Lut∙BCl 3 was calculated to react with H 2 and form the ion pair, [LutH + ][HBCl 3 – ], with a barrier of ΔH ≠ =24.7 kcal mol –1 (ΔG ≠ =29.8 kcal mol –1 ). Metathesis with a second molecule of Lut∙BCl 3 produced Lut∙BHCl 2 and [LutH + ][BCl 4 – ]. The overall reaction is exothermic by 6.0 kcal mol –1 (Δ r G°=–1.1). Alternate pathways were explored involving the borenium cation (LutBCl 2 + ) and the four-membered boracycle [(CH 2 {NC 5 H 3 Me})BCl 2 ]. Barriers for addition of H 2 across the Lut/LutBCl 2 + pair and the boracycle B—C bond are substantially higher (ΔG ≠ =42.1 and 49.4 kcal mol –1 , respectively), such that these pathways are excluded. The barrier for addition of H 2 to the boracycle B—N bond is comparable (ΔH ≠ =28.5 and ΔG ≠ =32 kcal mol –1 ). Conversion of the intermediate 2-(BHCl 2 CH 2 )-6-Me(C 5 H 3 NH) to Lut∙BHCl 2 may occur by intermolecular steps involving proton/hydride transfers to Lut/BCl 3 . Intramolecular protodeboronation, which could form Lut∙BHCl 2 directly, is prohibited by a high barrier (ΔH ≠ =52, ΔG ≠ =51 kcal mol –1 ).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

A reductionist perspective on quantum statistical mechanics: Coarse-graining of path integrals

Computational modeling of the condensed phase based on classical statistical mechanics has been rapidly developing over the last few decades and has yielded important information on various systems containing up to millions of atoms. However, if a system of interest contains important quantum effects, well-developed classical techniques cannot be used. One way of treating finite temperature quantum systems at equilibrium has been based on Feynman’s imaginary time path integral approach and the ensuing quantum-classical isomorphism. This isomorphism is exact only in the limit of infinitely many classical quasiparticles representing each physical quantum particle. In this work, we present a reductionist perspective on this problem based on the emerging methodology of coarse-graining. This perspective allows for the representations of one quantum particle with only two classical-like quasiparticles and their conjugate momenta. One of these coupled quasiparticles is the centroid particle of the quantum path integral quasiparticle distribution. Only this quasiparticle feels the potential energy function. The other quasiparticle directly provides the observable averages of quantum mechanical operators. The theory offers a simplified perspective on quantum statistical mechanics, revealing its most reductionist connection to classical statistical physics. By doing so, it can facilitate a simpler representation of certain quantum effects in complex molecular environments.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

SPALLMAP

Boiler tubes in steam power plants experience exfoliation of oxide grown on the inner side of the tubes. In extreme cases, the exfoliation cause significant tube blockages that lead to forced power plant outages. It is thus desired to predict through modeling the propensity of exfoliation events in order to inform power plant operators of possible tube blockages. SpallMap solves for the stress-strain equations in an axisymmetric geometry, tracking the stress/strain evolution during boiler operation including outages at one-location along a boiler tube and compares it with scale damage criteria represented by Armitt diagram. The SPALLMAP code contains modules developed for oxide growth, stress analysis, and classical fracture mechanics correlations by taking into account the following phenomena and features, (a) Non-uniform thermal expansion coefficient of oxides and metal substrates, (b) Plant operation schedule with periodic alternate full-load and partial-load regimes, (c) axisymmetric formulation for cylindrical tubes, (d) Multiple oxide layers, (e) oxide-growth induced stresses, and (f) damage criteria from classical fracture mechanics. The computer program is written in FORTRAN90. Its modular structure was sought for allowing the best flexibility in updating the program by implementing new constitutive equations due to availability of new material property data and/or new physical phenomena.

Sabau, Adrian↗
DOE OSTI2016

Violation of the Leggett-Garg Inequality in Neutrino Oscillations

We present that the Leggett-Garg inequality, an analogue of Bell’s inequality involving correlations of measurements on a system at different times, stands as one of the hallmark tests of quantum mechanics against classical predictions. The phenomenon of neutrino oscillations should adhere to quantum-mechanical predictions and provide an observable violation of the Leggett-Garg inequality. We demonstrate how oscillation phenomena can be used to test for violations of the classical bound by performing measurements on an ensemble of neutrinos at distinct energies, as opposed to a single neutrino at distinct times. Lastly, a study of the MINOS experiment’s data shows a greater than 6σ violation over a distance of 735 km, representing the longest distance over which either the Leggett-Garg inequality or Bell’s inequality has been tested.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Tuning crystallization pathways through sequence engineering of biomimetic polymers

Two-step nucleation pathways in which disordered, amorphous, or dense liquid states precede the appearance of crystalline phases have been reported for a wide range of materials, but the dynamics of such pathways are poorly understood. Moreover, whether these pathways are general features of crystallizing systems or a consequence of system-specific structural details that select for direct versus two-step processes is unknown. Using atomic force microscopy to directly observe crystallization of sequence-defined polymers, we show that crystallization pathways are indeed sequence dependent. When a short hydrophobic region is added to a sequence that directly forms crystalline particles, crystallization instead follows a two-step pathway that begins with the creation of disordered clusters of 10–20 molecules and is characterized by highly non-linear crystallization kinetics in which clusters transform into ordered structures that then enter the growth phase. The results shed new light on non-classical crystallization mechanisms and have implications for the design of self-assembling polymer systems.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Classical eikonal from Magnus expansion

In a classical scattering problem, the classical eikonal is defined as the generator of the canonical transformation that maps in-states to out-states. It can be regarded as the classical limit of the log of the quantum S-matrix. In a classical analog of the Born approximation in quantum mechanics, the classical eikonal admits an expansion in oriented tree graphs, where oriented edges denote retarded/advanced worldline propagators. The Magnus expansion, which takes the log of a time-ordered exponential integral, offers an efficient method to compute the coefficients of the tree graphs to all orders. We exploit a Hopf algebra structure behind the Magnus expansion to develop a fast algorithm which can compute the tree coefficients up to the 12th order (over half a million trees) in less than an hour. In a relativistic setting, our methods can be applied to the post-Minkowskian (PM) expansion for gravitational binaries in the worldline formalism. We demonstrate the methods by computing the 3PM eikonal and find agreement with previous results based on amplitude methods. Importantly, the Magnus expansion yields a finite eikonal, while the naïve eikonal based on the time-symmetric propagator is infrared-divergent from 3PM on.

Black Holes↗
DOE OSTI2018

Solid Mechanics Code Verification: Contrasting Classical and Manufactured Reference Solutions

Verification results for Sierra/SM using inexact reference solutions have often exhibited unsatisfactory convergence behavior. With an understanding of the convergence behavior for these types of tests, one can avoid falsely attributing pathologies of the test with incorrectness of the code. Simple theoretical results highlight that for an inexact reference solution two conditions must be met to observe asymptotic convergence. These conditions, and the resulting types of convergence behaviors, are further illustrated with graphical examples depicting the exact, inexact reference, and sequence of numerical solutions as vectors (in a function space). A stress concentration problem is adopted to contrast convergence behaviors when using inexact (classical linear elastic) and exact (manufactured) reference solutions. Convergence is not initially attained with the classical solution. Convergence with the manufactured solution indicates the convergence failure with the classical reference did not result from code error and provides insight on how for this problem asymptotic convergence could be attained with the classical reference solution by modifying the computational models.

42 ENGINEERING↗
DOE OSTI2016

Classical molecular dynamics simulation of electronically non-adiabatic processes

Both classical and quantum mechanics (as well as hybrids thereof, i.e., semiclassical approaches) find widespread use in simulating dynamical processes in molecular systems. For large chemical systems, however, which involve potential energy surfaces (PES) of general/arbitrary form, it is usually the case that only classical molecular dynamics (MD) approaches are feasible, and their use is thus ubiquitous nowadays, at least for chemical processes involving dynamics on a single PES (i.e., within a single Born-Oppenheimer electronic state). Our paper reviews recent developments in an approach which extends standard classical MD methods to the treatment of electronically non-adiabatic processes, i.e., those that involve transitions between different electronic states. This approach treats nuclear and electronic degrees of freedom (DOF) equivalently (i.e., by classical mechanics, thereby retaining the simplicity of standard MD), and provides "quantization" of the electronic states through a symmetrical quasi-classical (SQC) windowing model. The approach is seen to be capable of treating extreme regimes of strong and weak coupling between the electronic states, as well as accurately describing coherence effects in the electronic DOF (including the de-coherence of such effects caused by coupling to the nuclear DOF). A survey of recent applications is presented to illustrate the performance of the approach. We also described is a newly developed variation on the original SQC model (found universally superior to the original) and a general extension of the SQC model to obtain the full electronic density matrix (at no additional cost/complexity).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

An atomic-scale evaluation of the fracture toughness of silica glass

Using an atomistic technique consistent with continuum balance laws and drawing on classical fracture mechanics theory, we estimate the resistance to fracture propagation of amorphous silica. Here, we discuss correspondence and deviations from classical linear elastic fracture mechanics theory including size dependence, rigid/floppy modes of deformation, and the effects of surface energy and stress.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Cold energy

Deviations in Q for resonant superconducting radio frequency niobium accelerator cavities are generally correlated with resistivity loss mechanisms. Field dependent Qs are not well modeled by these classical loss mechanisms, but rather can represent a form of precision cavity surface thermometry. When the field dependent Q variation shows improvement with increasing B field level the classical treatment of this problem is inadequate. To justify this behavior hydrogen as a ubiquitous impurity in niobium, which creates measurable property changes, even at very low concentrations is typically considered the cause of such anomalous behavior. This maybe the case in some instances, but more importantly any system operating with a highly coherent field with a significant time dependent magnetic component at near 2° K will have the ability to organize the remaining free spins within the London penetration depth to form a coupled energy reservoir in the form of low mass spin waves. The niobium resonant cavities are composed of a single isotope with a large nuclear spin. When the other loss mechanisms are stripped away this may be the gain medium activated by the low level residual magnetic fields. It was found that one resonant cavity heat treatment produced optimum surface properties and then functioned as a MASER extracting energy from the 2° K thermal bath while cooling the cavity walls. The cavity operating in this mode is a simulator of what can take place in the wider but not colder universe using the cosmic microwave background (CMB) as a thermal source. The low mass, long lifetimes, and the scale of the magnetic spin waves on the weakly magnetized interstellar medium allows energy to be stored that is many orders of magnitude colder than the cosmic microwave background. A linear accelerator cavity becomes a tool to explore the properties of the long wave length magnetic spin waves that populate this cold low energy regime.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

Modification of Lie's transform perturbation theory for charged particle motion in a magnetic field

It is pointed out that the conventional Lie transform perturbation theory for the guiding center motion of charged particles in a magnetic field needs to be modified for ordering inconsistency. There are two reasons. First, the ordering difference between the temporal variation of gyrophase and that of the other phase space coordinates needs to be taken into account. Second, it is also important to note that the parametric limit of the derivative of a function is not equivalent to the derivative of the limit function. When these facts are taken into account, the near identity transformation rule for one form related to the Lagrangian is modified. With the modified near identity transformation rule, the drift motion of charged particles can be described in the first order, instead of the second order and beyond through a tedious expansion process as in the conventional formulation. Here, this resolves the discrepancy between the direct and Lie transform treatments in the Lagrangian perturbation theory for charged particle motion in a magnetic field.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Perturbative Stability and Error-Correction Thresholds of Quantum Codes

Topologically ordered phases are stable to local perturbations, and topological quantum error-correcting codes enjoy thresholds to local errors. We connect the two notions of stability by constructing classical statistical mechanics models for decoding general Calderbank-Shor-Steane codes and classical linear codes. Our construction encodes correction success probabilities under uncorrelated bit-flip and phase-flip errors, and simultaneously describes a generalized ℤ 2 lattice-gauge theory with quenched disorder. We observe that the clean limit of the latter is precisely the discretized imaginary-time path integral of the corresponding quantum code Hamiltonian when the errors are turned into a perturbative 𝑋 or 𝑍 magnetic field. Motivated by error-correction considerations, we define general order parameters for all such generalized ℤ 2 lattice-gauge theories, and show that they are generally lower bounded by success probabilities of error correction. For CSS codes satisfying the low-density parity-check condition and with a sufficiently large code distance, we prove the existence of a low-temperature ordered phase of the corresponding lattice-gauge theories, particularly for those lacking Euclidean spatial locality and/or when there is a nonzero code rate. We further argue that these results provide evidence for stable phases in the corresponding perturbed quantum Hamiltonians, obtained in the limit of continuous imaginary time. To do so, we distinguish space- and timelike defects in the lattice-gauge theory. A high free-energy cost of spacelike defects corresponds to a successful “memory experiment” and suppresses the energy splitting among the ground states, while a high free-energy cost of timelike defects corresponds to a successful “stability experiment” and points to a nonzero gap to local excitations.

quantum error correction↗
DOE OSTI2014

Attractive Inverse Square Potential, U ( 1 ) Gauge, and Winding Transitions

The inverse square potential arises in a variety of different quantum phenomena, yet notoriously it must be handled with care: it suffers from pathologies rooted in the mathematical foundations of quantum mechanics. Here, we show that its recently studied conformality breaking corresponds to an infinitely smooth winding-unwinding topological transition for the classical statistical mechanics of a one-dimensional system: this describes the tangling or untangling of floppy polymers under a biasing torque. When the ratio between torque and temperature exceeds a critical value the polymer undergoes tangled oscillations, with an extensive winding number. At lower torque or higher temperature the winding number per unit length is zero. Approaching criticality, the correlation length of the order parameter—the extensive winding number—follows a Kosterlitz-Thouless-type law. Finally, the model is described by the Wilson line of a ( 0 + 1 ) U ( 1 ) gauge theory, and applies to the tangling or untangling of floppy polymers and to the winding or diffusing kinetics in diffusion-convection reactions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Heat control in opto-mechanical system using quantum non-classicality

Cooling of matter to the quantum ground state is a primary directive of quantum control. In other words, to extract entropy from a quantum system, efficient indirect quantum measurements may be implemented. The main objective is the cooling of the oscillator either to its motional ground state or to non-classical states, such as low-number Fock states, squeezed states or entangled states. It is shown that the use of quantum control procedure is better choice for even experimental realizations because it leads to a squeezed steady state with less than one phonon on average. The steady state of system corresponds to cooling of the system.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗