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At least 1,711 records · Page 95

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Improving Kinetic Consistency Across Elastic Model Transitions With Quadratic Inequality Constrained Weighted Least Squares (WLSQI)

Flexible body modeling presents a large challenge in the development of simulations to aid in design of flight control systems for launch and landing vehicles. Typically, the flexible body model is not a single continuous model but are rather discrete sets of Linear Time Invariant (LTI) Finite Element Models (FEM) incremented by propellant levels. This introduces the problem of smoothly transitioning modal and physical states of the vehicle when switching from one FEM to the next. This paper introduces a new approach to optimally transition flexible body states with weighted least squares, building off previous methods.

Convex Optimization↗

NASA NTRSDate not supplied

Improving Kinetic Consistency Across Elastic Model Transitions With Quadratic Inequality Constrained Weighted Least Squares (WLSQI)

GN&C↗

DOE OSTI2011

Photo-Curable Polymer Blend Dielectrics for Advancing Organic Field-Effect Transistor Applications

A solution method of photo-curable and -patternable polymer gate dielectrics was introduced by using blend solutions of poly(4-dimethylsilyl styrene) (PDMSS) and poly(melamine-co-formaldehyde) acrylate (PMFA). The fabrication was optimized to produce a smooth hydrophobic gate dielectric with good insulating and solvent-resistant properties. On the optimized PDMSS/PMFA blend gate dielectric, pentacene could grow into highly ordered structure, showing high electric performances for the resulting OFETs, as well as PTCDI-C13 and TES-ADT.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Corrosion testing needs and considerations for additively manufactured materials in nuclear reactors

Metal additive manufacturing holds significant promise as an enabling technology for the 21st century nuclear energy industry. Metal additive manufacturing (MAM) can allow the fabrication of novel materials and innovative component designs that are not achievable through conventional manufacturing. Due to its very different fabrication methods, as-fabricated MAM components are characteristically different from conventionally manufactured components. MAM materials exhibit very different microstructures from conventional cast or wrought materials. For example, austenitic stainless steels fabricated by laser powder bed fusion exhibit columnar grain structures, dislocation cell structures, and melt pool fingerprints. In addition, MAM fabrication may result in defects such as porosity, incomplete processing of the feedstock (e.g., lack of fusion in melt-based methods), and oxide inclusions. Heat treatments may further evolve the microstructure, microsegregation, and stresses within the component. Furthermore, MAM components have a rough surface with feature sizes on the order of the feedstock material, as opposed to smooth surfaces resulting from conventional machining and forming operations. As a result, the corrosion behavior of MAM components will likely be significantly different from that of conventionally formed components. Corrosive environments for structural materials within advanced reactor environments include molten fluoride and chloride salts, liquid sodium and lead-bismuth, and high-temperature helium. The Advanced Materials and Manufacturing Technologies program within the Department of Nuclear Energy in the United States Department of Energy is assessing the unique concerns of MAM component corrosion and testing methodologies in advanced nuclear reactor environments. We discuss these concerns and testing strategies in this paper.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2013

Fission matrix capability for MCNP, Part I - Theory

The theory underlying the fission matrix method is derived using a rigorous Green's function approach. The method is then used to investigate fundamental properties of the transport equation for a continuous-energy physics treatment. We provide evidence that an infinite set of discrete, real eigenvalues and eigenfunctions exist for the continuous-energy problem, and that the eigenvalue spectrum converges smoothly as the spatial mesh for the fission matrix is refined. We also derive equations for the adjoint solution. We show that if the mesh is sufficiently refined so that both forward and adjoint solutions are valid, then the adjoint fission matrix is identical to the transpose of the forward matrix. While the energy-dependent transport equation is strictly bi-orthogonal, we provide surprising results that the forward modes are very nearly self-adjoint for a variety of continuous-energy problems. A companion paper (Part II - Applications) describes the initial experience and results from implementing this fission matrix capability into the MCNP Monte Carlo code. (authors)

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2013

Three-dimensional, off-lattice Monte-Carlo kinetics simulations of interstellar grain chemistry and ice structure

The first off-lattice Monte Carlo kinetics model of interstellar dust grain surface chemistry is presented. The positions of all surface particles are determined explicitly, according to the local potential minima resulting from the pair-wise interactions of contiguous atoms and molecules, rather than by a pre-defined lattice structure. The model is capable of simulating chemical kinetics on any arbitrary dust grain morphology, as determined by the user-defined positions of each individual dust grain atom. A simple method is devised for the determination of the most likely diffusion pathways and their associated energy barriers for surface species. The model is applied to a small, idealized dust grain, adopting various gas densities and using a small chemical network. Hydrogen and oxygen atoms accrete onto the grain to produce H{sub 2}O, H{sub 2}, O{sub 2}, and H{sub 2}O{sub 2}. The off-lattice method allows the ice structure to evolve freely; the ice mantle porosity is found to be dependent on the gas density, which controls the accretion rate. A gas density of 2 × 10{sup 4} cm{sup –3}, appropriate for dark interstellar clouds, is found to produce a fairly smooth and non-porous ice mantle. At all densities, H{sub 2} molecules formed on the grains collect within the crevices that divide nodules of ice and within micropores (whose extreme inward curvature produces strong local potential minima). The larger pores produced in the high-density models are not typically filled with H{sub 2}. Direct deposition of water molecules onto the grain indicates that amorphous ices formed in this way may be significantly more porous than interstellar ices that are formed by surface chemistry.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

Communication: Smoothing out excited-state dynamics: Analytical gradients for dynamically weighted complete active space self-consistent field

State averaged complete active space self-consistent field (SA-CASSCF) is a workhorse for determining the excited-state electronic structure of molecules, particularly for states with multireference character; however, the method suffers from known issues that have prevented its wider adoption. One issue is the presence of discontinuities in potential energy surfaces when a state that is not included in the state averaging crosses with one that is. In this communication I introduce a new dynamical weight with spline (DWS) scheme that mimics SA-CASSCF while removing energy discontinuities due to unweighted state crossings. In addition, analytical gradients for DWS-CASSCF (and other dynamically weighted schemes) are derived for the first time, enabling energy-conserving excited-state ab initio molecular dynamics in instances where SA-CASSCF fails.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1973

Functional preservation of vascular smooth muscle tissue

The ionic and cellular feedback relationships operating to effect the vascular decompensatory modifications were examined to reveal procedures for implementing protective measures guarding against vascular collapse when returning from a weightless environment to that of the earth's gravity. The surgical procedures for preparing the rat cremaster, and the fixation methods are described. Abstracts of publications resulting from this research are included.

Alexander, W. C.↗

DOE OSTI2011

Evaluation of Common Angling-Induced Sources of Epithelial Damage for Popular Freshwater Sport Fish using Fluorescein

Angling is a popular recreational activity across the globe and a large proportion of fish captured by anglers are released due to voluntary or mandatory catch-and-release practices. The handling associated with hook removal and return of the fish to their environment can cause physical damage to the epidermal layer of the fish which may affect the condition and survival of released fish. This study investigated possible sources of epithelial damage associated with several different handling methods (i.e. landing net types, interactions with different boat floor surfaces, tournament procedures) commonly used in recreational angling for two popular freshwater sport fish species, largemouth bass (Micropterus salmoides) and northern pike (Esox lucius). Epithelial damage was examined using fluorescein, a non-toxic dye, which has been shown to detect latent epithelial damage. Northern pike exhibited extensive epithelial damage after exposure to several of the induced treatments (i.e., interaction with a carpeted surface, knotted nylon net, and line rolling) but relatively little epithelial damage when exposed to others (i.e., knotless rubber nets, smooth boat surfaces, or lip gripping devices). Largemouth bass did not show significant epithelial damage for any of the treatments, with the exception of fish caught in a semi-professional live release tournament. The detection of latent injuries using fluorescein can be an important management tool as it provides visual examples of potential damage that can be caused by different handling methods. Such visualizations can be used to encourage fish friendly angler behaviour and enhance the survival and welfare of released fish. It can also be used to test new products that are intended to or claim to reduce injury to fish that are to be released. Future research should evaluate the relationship between different levels of epithelial damage and mortality across a range of environmental conditions.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2015

Steady state in a gas of inelastic rough spheres heated by a uniform stochastic force

We study here the steady state attained in a granular gas of inelastic rough spheres that is subject to a spatially uniform random volume force. The stochastic force has the form of the so-called white noise and acts by adding impulse to the particle translational velocities. We work out an analytical solution of the corresponding velocity distribution function from a Sonine polynomial expansion that displays energy non-equipartition between the translational and rotational modes, translational and rotational kurtoses, and translational-rotational velocity correlations. By comparison with a numerical solution of the Boltzmann kinetic equation (by means of the direct simulation Monte Carlo method), we show that our analytical solution provides a good description that is quantitatively very accurate in certain ranges of inelasticity and roughness. We also find three important features that make the forced granular gas steady state very different from the homogeneous cooling state (attained by an unforced granular gas). First, the marginal velocity distributions are always close to a Maxwellian. Second, there is a continuous transition to the purely smooth limit (where the effects of particle rotations are ignored). And third, the angular translational-rotational velocity correlations show a preference for a quasiperpendicular mutual orientation (which is called “lifted-tennis-ball” behavior)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2023

Unified analysis of finite-size error for periodic Hartree-Fock and second order Møller-Plesset perturbation theory

Despite decades of practice, finite-size errors in many widely used electronic structure theories for periodic systems remain poorly understood. For periodic systems using a general Monkhorst-Pack grid, there has been no comprehensive and rigorous analysis of the finite-size error in the Hartree-Fock theory (HF) and the second order Møller-Plesset perturbation theory (MP2), which are the simplest wavefunction based method, and the simplest post-Hartree-Fock method, respectively. Such calculations can be viewed as a multi-dimensional integral discretized with certain trapezoidal rules. Due to the Coulomb singularity, the integrand has many points of discontinuity in general, and standard error analysis based on the Euler-Maclaurin formula gives overly pessimistic results. The lack of analytic understanding of finite-size errors also impedes the development of effective finite-size correction schemes. We propose a unified analysis to obtain sharp convergence rates of finite-size errors for the periodic HF and MP2 theories. Our main technical advancement is a generalization of the result of Lyness [Math. Comp. 30 (1976), pp. 1–23] for obtaining sharp convergence rates of the trapezoidal rule for a class of non-smooth integrands. Our result is applicable to three-dimensional bulk systems as well as low dimensional systems (such as nanowires and 2D materials). Our unified analysis also allows us to prove the effectiveness of the Madelung-constant correction to the Fock exchange energy, and the effectiveness of a recently proposed staggered mesh method for periodic MP2 calculations (see X. Xing, X. Li, and L. Lin [J. Chem. Theory Comput. 17 (2021), pp. 4733–4745]). In conclusion, our analysis connects the effectiveness of the staggered mesh method with integrands with removable singularities, and suggests a new staggered mesh method for reducing finite-size errors of periodic HF calculations.

97 MATHEMATICS AND COMPUTING↗

NASA NTRS1972

The Backup-Gilbert method and its application to the electrical conductivity problem

The theory of Backus and Gilbert gives a technique for solving the general linear inverse problem. Observational error and lack of data are shown to reduce the reliability of the solution in different ways: the former introduces statistical uncertainties in the model, while the latter smooths out the detail. Precision can be improved by sacrificing resolving power, and vice versa, so that some compromise may be made between the two in choosing the best model. Nonlinear inverse problems can be brought into the domain of the theory by linearizing about a typical solution. The inverse problem of electrical conductivity in the mantle is used to illustrate the Backus-Gilbert technique; an example of the tradeoff diagram is given.

Parker, R. L.↗

NASA NTRS2018

Contributions to HiLiftPW-3 Using Structured, Overset Grid Methods

The High-Lift Common Research Model (HL-CRM) and the JAXA Standard Model (JSM) were analyzed computationally using both the OVERFLOW and LAVA codes for the third AIAA High-Lift Prediction Workshop. Geometry descriptions and the test cases simulated are described. With the HL-CRM, the effects of surface smoothness during grid projection and the effect of partially sealing a flap gap were studied. Grid refinement studies were performed at two angles of attack using both codes. For the JSM, simulations were performed with and without the nacelle/pylon. Without the nacelle/pylon, evidence of multiple solutions was observed when a quadratic constitutive relation is used in the turbulence modeling; however, using time-accurate simulation seemed to alleviate this issue. With the nacelle/pylon, no evidence of multiple solutions was observed. Laminar-turbulent transition modeling was applied to both JSM configuration, and had an overall favorable impact on the lift predictions.

HiLiftPW-3↗

DOE OSTI2015

SU-F-BRA-02: Electromagnetic Tracking in Brachytherapy as An Advanced Modality for Treatment Quality Assurance

Purpose: To present the use of Electromagnetic Tracking (EMT) for quality assurance in brachytherapy by means of phantom studies and to assess the clinical applicability of EMT during HDR breast brachytherapy. Methods: An EMT system was investigated to examine its suitability for clinical applications in brachytherapy. A field generator served as electromagnetic field emitter. Sensors (magnetic sensitive only), connected to a control unit, were used and their respective position and orientation inside a pre-defined measurement volume (500 mm cube length) determined. Up to three 6DoF sensors were placed on the phantom’s surface to obtain additional reference coordinates used to derive relative measured positions of a smaller 5DoF sensor inserted in the 6F catheters of the implant. The catheters were successively measured by manual displacement of the sensor at ∼40 mm/s. The measured catheter tracks, acquired multiple times at various locations (CT and treatment room), were smoothed, divided into intervals (2.5 mm dwell step size), registered (rigid Iterative Closest Point transformation) and compared against the known phantom geometry. Results: The reference coordinates were used to exclude the influence of external (e.g., respiratory-induced) motion. Precision tests in a clinical setting showed variances below 1 mm (translational) and 1° (rotational), respectively. Our method for catheter reconstruction preserved the length of the tracked catheter (within 1 mm). The measured tracking accuracy was 1±0.3 mm (maximum: 2 mm). The results are less accurate in environments potentially interfering with the magnetic field, e.g., in the vicinity of ferromagnetic table components. Conclusion: Our EMT system is able to perform reproducible and accurate catheter tracking and reconstruction. Currently, measurements of the implant geometry in HDR breast treatments are initiated. Online implant monitoring by means of EM tracking may be a first step towards advanced brachytherapy treatment QA. The study was financially supported by ELEKTA | Nucletron. There are no further disclosures and conflicts.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2025

Fast methods for multisite charge transfer. Processes II. Analytic nuclear gradients and nonadiabatic dynamics for cCASSCF(1,n) and cCASSCF(2n-1,n) wavefunctions

In this work we derive and implement analytic nuclear gradients and derivative couplings for a constrained complete active space self-consistent field with a small active space designed to model electron or hole transfer. Using a Lagrangian formalism, we are able to differentiate both the CASSCF energy and the constraint (which is required for smooth surfaces over a wide range of parameter space), and the resulting efficient algorithm can be immediately applied to nonadiabatic dynamics simulations of charge transfer processes. Here, we run initial surface-hopping simulations of a proton coupled electron transfer event for a phenoxyl–phenol system.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Chemical and structural characterization of EUV photoresists as a function of depth by standing-wave x-ray photoelectron spectroscopy

The success in the miniaturization of the electronic device constituents depends mostly on the photolithographic techniques. Recently, to achieve patterning at the sub-10-nm node, extreme ultraviolet (EUV) lithography has been introduced into high volume production. Continued scaling of EUV via increased numerical aperture to achieve nodes at 3-nm and below requires the development of fundamentally new patterning materials and new characterization methods. Current EUV-resist film thicknesses are in the 20- to 40-nm range, and further thickness reduction is required for the next generation. Therefore, interfaces become exceedingly important, and the properties of the resist film would be dominated by top and bottom interfacial effects. X-ray photoelectron spectroscopy (XPS) combined with standing-wave excitation (SW-XPS), a fairly new method in the EUV lithography field, previously had been largely applied in multilayers and superlattices for characterizing the composition and electronic structure of buried layers and interfaces as a function of depth. We applied the SW-XPS method to organic/inorganic photoresists to provide depth-selective information on their structural and chemical conditions of as a function of temperature, EUV exposure, different underlayers, and other fundamental parameters. As a first attempt, we perform an SW-XPS feasibility study on self-assembled monolayer (SAM) films after exposure to an electron beam. By SW-XPS, we determined that the interface between the Al 2 O 3 underlayer and the SAMs is smooth, with a mean roughness of about 0.2 nm. Moreover, we determined that the SAM chains are, on average, tilted by 1/430 deg off the sample normal. The SW-XPS results also suggest that the SAM is not a perfectly aligned and uniform monolayer, with some areas having thickness higher than a single monolayer. We demonstrated that SW-XPS can provide useful information on ultrathin materials with high potential for being used as a characterization method of organic/inorganic photoresists.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Preparation of Fine Single Crystals of Rutheno-Cuprates by the Self-Flux Method with Alumina Boats

We investigate the single crystal growth of rutheno-cuprates, which are known to be magnetic superconductors. We attempted the single crystal growth of two systems, RuSr{sub 2}GdCu{sub 2}O{sub 8−δ} (RuGd-1212) and RuSr{sub 2}(Gd,Ce){sub 2}Cu{sub 2}O{sub 10−δ} (RuGd-1222), by the self-flux method with alumina boats. Fine cubic crystals of RuGd-1212 with a side length of approximately 5 μ m were obtained by slow cooling from 1350 to 940 {sup ∘}C. Plate-like RuGd-1222 crystals with a smooth plane were obtained at the surface of the precursor pellet. RuGd-1222 was more stable at high temperatures than RuGd-1212 and was also superconductive, but its superconductivity weakened as the cooling rate decreased. This weakening was induced by decomposition. Therefore, high-quality RuGd-1222 single crystals were difficult to obtain, and we failed to extract only the smooth planar crystal part. As a modified synthesis technique, we mixed a precursor containing Ru–Sr–Gd–Ce flux with RuGd-1222 powders and gradually cooled the mixture from 1350 to 1090 {sup ∘}C. A plate-like RuGd-1222 sample with a smooth surface and a size of 70 × 30μm{sup 2} was obtained from the side surface of the precursor pellet. By this technique, we could separate the planar crystal part. Semiquantitative composition analysis confirmed this planar crystal as a RuGd-1222 phase. The X-ray diffraction peak suggested the (0014) plane, implying that the plate-like precipitates are c-axis-oriented RuGd-1222 single crystals.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2020

Impact of the adhesion-force lever-arm “a” on the Rock ‘n’ Roll resuspension model and how to compute it from contact mechanics

The paper proposes a methodology to fill a gap in the context of mechanistic particle resuspension models related to the adhesion and lift force lever arms ( a ): to date, only one experimental observation exists from a centrifuge experiment with a specific particle/surface pair which found r P / a = 100 and assumed that the contact points were symmetric with respect to the particle center. However, the Reeks and Hall’s (2001) model is highly sensitive to this parameter, which therefore cannot be used as-is for different particle diameters or materials. This paper proposes a methodology to compute the adhesion and lift force lever arms ( a A and a L , respectively) based on Atomic Force Microcopy (AFM) surface roughness measurements and contact mechanics arguments. In practice, a spherical, perfectly smooth particle is brought in contact (computationally) with the measured surface roughness and is then rotated by the point of contact to determine the two or more asperities over which the particle would sit on the surface. A method to compute the asperity radius of curvature is devised to compute the asperity deformation and the correct partitioning of the total deformation between the particle and the asperity is presented. For the glass surface under consideration, the asperity deformation was negligible, i.e., it was below the van der Waals radius, which is the limit of applicability of contact mechanics. The Reeks and Hall’s (2001) model is then extended to account for the joint probability of a A and a L . Significant differences in particle resuspended after a day in common atmospheric conditions are found between the approach that uses the lever-arm distributions or their mean values. Also, important differences are found when comparing the lever-arm distribution and r P / a = 100. Hence, one should be cautious of using r P / a = 100 for surface/particle pairs differing from those in the original study. Finally, limits of applicability of the theories used are presented together with considerations regarding how to extend the method to non-spherical particles and different materials.

42 ENGINEERING↗