Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “stabilization method”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,171 records · Page 65
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Controllable preparation of flower-like brookite TiO{sub 2} nanostructures via one-step hydrothermal method

Highlights: • Flower-like brookite TiO{sub 2} structures were prepared by hydrothermal method. • PVP not only acted as a dispersant but also stabilized the layered structure. • The resulted brookite TiO{sub 2} showed high photocatalytic activity under UV irradiation. - Abstract: Flower-like brookite TiO{sub 2} nanostructures were controllable prepared by a one-step hydrothermal method by changing experimental conditions, such as hydrothermal temperature, reaction time and the amount of polyvinylpyrrolidone. The photocatalytic activities of the samples were investigated by degradation of methylene blue (MB) in aqueous solution under UV light irradiation. It was found that the formation of brookite TiO{sub 2} nanostructures with various morphologies could be well controlled by the adjustment of hydrothermal temperature, reaction time and the amount of surfactant, and the morphology of the products changed from spindle-like structures to flower-like structures with the increase of hydrothermal temperature, reaction time and the amount of surfactant. The photocatalytic tests indicate that the flower-like brookite TiO{sub 2} nanostructures shows high photocatalytic activity in degradation of methylene blue (MB) under UV light irradiation. The formation mechanism of flower-like brookite TiO{sub 2} nanostructures was also discussed in detail based on the above investigations.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Stability of ternesite and the production at scale of ternesite-based clinkers

A method to synthesize high-purity ternesite is presented and the importance of reaction volume is highlighted; a brief description of the product morphology is also presented. Thermodynamic data for ternesite are derived and the limits of ternesite stability are then explored. An upper temperature stability limit of ≈ 1290 °C at 1 atm is determined; however, this temperature is dependent on the fugacity of the volatile components in the atmosphere. Thermodynamic predictions confirm that belite and ternesite rich calcium sulfoaluminate clinkers can be readily produced in a single stage process at temperatures above 1200 °C provided the atmosphere and temperature are controlled. To demonstrate this control at larger scales, a conventional 7.4-meter rotary kiln has been used to produce ≈ 20 kg of ternesite-containing clinkers. This demonstrates the usefulness of thermodynamic modelling as it has enabled ternesite-based clinkers to be readily produced at scale in a single-stage process using existing equipment without major modifications.

36 MATERIALS SCIENCE↗
DOE OSTI2021

A stable corridor for toroidal plasma compression

In this study, a toroidal plasma compressed by a collapsing flux conserver is analyzed to reveal stable scenarios of operation to high compression ratios. The resistive and ideal MHD stability is calculated in full toroidal geometry, using the asymptotic matching method in realistic conditions, and comparing with nonlinear simulations. The near edge current profile, controlled by toroidal field ramping during compression, is shown to be critical to stability due to coupling between poloidal components of the least stable mode. The extension of a length of shaft on axis is also found to be critical at high compression, as the resulting good curvature region in magnetic field stabilizes pressure driven modes that would otherwise be unstable. This work extends from previous studies, which initially showed the existence of a stable scenario, to include findings of more extensive stable zones, detailed effects of geometry, and nonlinear simulations of the instabilities. The nonlinear simulations of the compression are consistent with the linear analyses, confirming both the conservation and stability properties.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Ab initio density functional theory study of non-polar (101{sup ¯}0), (112{sup ¯}0) and semipolar (202{sup ¯}1) GaN surfaces

The atomic structures of non-polar GaN(101{sup ¯}0), (112{sup ¯}0) and semipolar GaN(202{sup ¯}1), (202{sup ¯}1{sup ¯}) surfaces were studied using ab initio calculations within density functional theory. The bulk-like truncated (1 × 1) structure with buckled Ga-N or Ga-Ga dimers was found stable on the non-polar GaN(101{sup ¯}0) surface in agreement with previous works. Ga-N heterodimers were found energetically stable on the GaN(112{sup ¯}0)-(1 × 1) surface. The formation of vacancies and substitution site defects was found unfavorable for non-polar GaN surfaces. Semipolar GaN(202{sup ¯}1)-(1 × 1) surface unit cells consist of non-polar (101{sup ¯}0) and semipolar (101{sup ¯}1) nano-facets. The (101{sup ¯}1) nano-facets consist of two-fold coordinated atoms, which form N-N dimers within a (2 × 1) surface unit cell on a GaN(202{sup ¯}1) surface. Dimers are not formed on the GaN(202{sup ¯}1{sup ¯}) surface. The stability of the surfaces with single (101{sup ¯}0) or (101{sup ¯}1) nano-facets was analyzed. A single non-polar (101{sup ¯}0)-(1 × 1) nano-facet was found stable on the GaN(202{sup ¯}1) surface, but unstable on the GaN(202{sup ¯}1{sup ¯}) surface. A single (101{sup ¯}1) nano-facet was found unstable. Semipolar GaN surfaces with (202{sup ¯}1) and (202{sup ¯}1{sup ¯}) polarity can be stabilized with a Ga overlayer at Ga-rich experimental conditions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Multifunctional reactive inks, methods of use and manufacture thereof

In one embodiment, a material includes a plurality of particles, a solvent system and one or more stabilizing agents; the particles are configured to complete a self-propagating and/or self-sustaining reaction upon initiation thereof. In another embodiment, a method includes dispersing a plurality of particles in solution to form a dispersion and adding a stabilizing agent to the dispersion in an amount sufficient to cause the dispersion to exhibit one or more predetermined rheological properties; again, the particles in the dispersion are configured to complete a self-propagating and/or self-sustaining reaction upon initiation thereof. In still another embodiment, a method includes depositing a material on a substrate; the material includes a plurality of particles configured to complete a self-propagating and/or self-sustaining reaction upon initiation thereof, a solvent system and one or more stabilizing agents.

Sullivan, Kyle↗
DOE OSTI2014

SU-E-J-253: Evaluation of 4DCT Images with Correlation of RPM Signals to Tumor Motion for Respiratory-Gated Radiotherapy

Purpose: The amplitudes of lung tumor target motion and RPM signals are different from each other. Also, RPM system does not have in-depth RPM signal analysis tool. We have developed an algorithm that analyzes RPM signals for its stability as well as correlativity to the tumor motion. Methods: We used a Philips Big Bore CT scanner with a Varian Real-Time Position Management™ (RPM) system attached. 4DCT images were reviewed and tumor motion amplitudes of full breathing in superior-inferior, anterior-posterior, and left-right directions were measured. RPM signals were analyzed with the algorithm developed with Matlab. Average signal period, amplitude and statistical stability of the full breathing pattern as well as the pattern around full expiration were calculated. RPM signal amplitudes were normalized to measured tumor motion amplitudes so that selected gating phases (30%–70% or 40%–60%) allow tumor motion under 5.0mm. Results: Twelve patient cases were analyzed in this study with GTV sizes ranged from 1.0cm to 3.0cm diameter. The periods and amplitudes of RPM signal ranged from 3.1seconds to 6.5seconds and from 0.2cm to 1.7cm, respectively. RPM signals were most stable at full expiration. The standard deviation of the RPM signal peaks at full expiration was <0.11cm, and that of gated amplitudes was <0.25cm. Tumor motion amplitudes were primary in superior-inferior direction and minor (<=0.2cm) in other directions on all analyzed cases, ranged from 0.2cm to 2.5cm. The amplitudes increases with the tumor located toward the diaphragm. The gated phases were selected so that the average gated tumor motion amplitude as well as that plus deviation became under 0.5cm in superior-inferior direction. Conclusion: We were able to determine the respiratory-gated phases in RPM signals employing measured tumor motion amplitudes as well as developed RPM signal analyzer through correlation process. The RPM signal amplitudes do not represent tumor motion because of its location.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Beyond Atomic Sizes and Hume-Rothery Rules: Understanding and Predicting High-Entropy Alloys

High-entropy alloys constitute a new class of materials that provide an excellent combination of strength, ductility, thermal stability, and oxidation resistance. Although they have attracted extensive attention due to their potential applications, little is known about why these compounds are stable or how to predict which combination of elements will form a single phase. Here, we present a review of the latest research done on these alloys focusing on the theoretical models devised during the last decade. We discuss semiempirical methods based on the Hume-Rothery rules and stability criteria based on enthalpies of mixing and size mismatch. To provide insights into the electronic and magnetic properties of high-entropy alloys, we show the results of first-principles calculations of the electronic structure of the disordered solid-solution phase based on both Korringa Kohn Rostoker coherent potential approximation and large supercell models of example face-centered cubic and body-centered cubic systems. Furthermore, we discuss in detail a model based on enthalpy considerations that can predict which elemental combinations are most likely to form a single-phase high-entropy alloy. The enthalpies are evaluated via first-principles high-throughput density functional theory calculations of the energies of formation of binary compounds, and therefore it requires no experimental or empirically derived input. Finally, the model correctly accounts for the specific combinations of metallic elements that are known to form single-phase alloys while rejecting similar combinations that have been tried and shown not to be single phase.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Hermite Methods for the Scalar Wave Equation

Arbitrary order dissipative and conservative Hermite methods for the scalar wave equation are presented here. Both methods use $(m+1)^d$ degrees of freedom per node for the displacement in $d$ dimensions; the dissipative and conservative methods achieve orders of accuracy $(2m-1)$ and $2m$, respectively. Stability and error analyses as well as implementation strategies for accelerators are also given.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2021

Structural stability and artificial buckling modes in topology optimization

Abstract This paper demonstrates how a strain energy transition approach can be used to remove artificial buckling modes that often occur in stability constrained topology optimization problems. To simulate the structural response, a nonlinear large deformation hyperelastic simulation is performed, wherein the fundamental load path is traversed using Newton’s method and the critical buckling load levels are estimated by an eigenvalue analysis. The goal of the optimization is to minimize displacement, subject to constraints on the lowest critical buckling loads and maximum volume. The topology optimization problem is regularized via the Helmholtz PDE-filter and the method of moving asymptotes is used to update the design. The stability and sensitivity analyses are outlined in detail. The effectiveness of the energy transition scheme is demonstrated in numerical examples.

Dalklint, Anna (ORCID:0000000346195205)↗
DOE OSTI2014

Theoretical investigation of the relative stability of Na{sup +}He{sub n} (n = 2–24) clusters: Many-body versus delocalization effects

The solvation of the Na{sup +} ion in helium clusters has been studied theoretically using optimization methods. A many-body empirical potential was developed to account for Na{sup +}–He and polarization interactions, and the most stable structures of Na{sup +}He{sub n} clusters were determined using the basin-hopping method. Vibrational delocalization was accounted for using zero-point energy corrections at the harmonic or anharmonic levels, the latter being evaluated from quantum Monte Carlo simulations for spinless particles. From the static perspective, many-body effects are found to play a minor role, and the structures obtained reflect homogeneous covering up to n = 10, followed by polyicosahedral packing above this size, the cluster obtained at n = 12 appearing particularly stable. The cationic impurity binds the closest helium atoms sufficiently to negate vibrational delocalization at small sizes. However, this snowball effect is obliterated earlier than shell completion, the nuclear wavefunctions of {sup 4}He{sub n}Na{sup +} with n = 5–7, and n > 10 already exhibiting multiple inherent structures. The decrease in the snowball size due to many-body effects is consistent with recent mass spectrometry measurements.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Enhanced Photo-Cross-Linking of Thymines in DNA Holliday Junction-Templated Squaraine Dimers

Programmable self-assembly of dyes using DNA templates to promote exciton delocalization in dye aggregates is gaining considerable interest. New methods to improve the rigidity of the DNA scaffold and thus the stability of the molecular dye aggregates to encourage exciton delocalization are desired. In these dye–DNA constructs, one potential way to increase the stability of the aggregates is to create an additional covalent bond via photo-cross-linking reactions between thymines in the DNA scaffold. Specifically, we report an approach to increase the yield of photo-cross-linking reaction between thymines in the core of a DNA Holliday junction while limiting the damage from UV irradiation to DNA. We investigated the effect of the distance between thymines on the photo-cross-linking reaction yields by using linkers with different lengths to tether the dyes to the DNA templates. By comprehensively evaluating the photo-cross-linking reaction yields of dye–DNA aggregates using linkers with different lengths, we conclude that interstrand thymines tend to photo-cross-link more efficiently with short linkers. A higher cross-linking yield was achieved due to the shorter intermolecular distance between thymines influenced by strong dye–dye interactions. Furthermore, our method establishes the possibility of improving the stability of DNA-scaffolded dye aggregates, thereby expanding their use in exciton-based applications such as light harvesting, nanoscale computing, quantum computing, and optoelectronics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Comparison of methods for numerical calculation of continuum damping

Continuum resonance damping is an important factor in determining the stability of certain global modes in fusion plasmas. A number of analytic and numerical approaches have been developed to compute this damping, particularly, in the case of the toroidicity-induced shear Alfvén eigenmode. This paper compares results obtained using an analytical perturbative approach with those found using resistive and complex contour numerical approaches. It is found that the perturbative method does not provide accurate agreement with reliable numerical methods for the range of parameters examined. This discrepancy exists even in the limit where damping approaches zero. When the perturbative technique is implemented using a standard finite element method, the damping estimate fails to converge with radial grid resolution. The finite elements used cannot accurately represent the eigenmode in the region of the continuum resonance, regardless of the number of radial grid points used.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Stabilized bases for high-order, interpolation semi-Lagrangian, element-based tracer transport

In a computational fluid model of the atmosphere, the advective transport of trace species, or tracers, can be computationally expensive. For efficiency, models often use semi-Lagrangian advection methods. High-order interpolation semi-Lagrangian (ISL) methods, in particular, can be extremely efficient, if the problem of property preservation specific to them can be addressed. Atmosphere models often use geometrically and logically nonuniform grids for efficiency and, as a result, element-based discretizations. Such grids and discretizations make stability a particular problem for ISL methods. Generally, high-order, element-based ISL methods that use the natural polynomial interpolant associated with a nodal finite-element discretization are unstable. Here, we derive new bases having order of accuracy up to nine, with positive nodal weights, that stabilize the element-based ISL method. We use these bases to construct the linear advection operator in the property-preserving Interpolation Semi-Lagrangian Element-based Transport (Islet) method. Then we discuss key software implementation details. Finally, we show performance results for the Energy Exascale Earth System Model's atmosphere dynamical core, comparing the original and new transport methods. These simulations used up to 27,600 Graphical Processing Units (GPU) on the Oak Ridge Leadership Computing Facility's Summit supercomputer.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2016

PID self tuning control based on Mamdani fuzzy logic control for quadrotor stabilization

Quadrotor as one type of UAV have the ability to perform Vertical Take Off and Landing (VTOL). It allows the Quadrotor to be stationary hovering in the air. PID (Proportional Integral Derivative) control system is one of the control methods that are commonly used. It is usually used to optimize the Quadrotor stabilization at least based on the three Eulerian angles (roll, pitch, and yaw) as input parameters for the control system. The three constants of PID can be obtained in various methods. The simplest method is tuning manually. This method has several weaknesses. For example if the three constants are not exact, the resulting response will deviate from the desired result. By combining the methods of PID with fuzzy logic systems where human expertise is implemented into the machine language is expected to further optimize the control system.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

Solid Solvation Assisted Electrical Doping Conserves High‐Performance in 500 nm Active Layer Organic Solar Cells

Abstract Organic solar cells (OSCs) process fascinating solution‐printing capability to achieve low‐cost and large‐scale manufacture. However, the rapid power conversion efficiency (PCE) decay with active layer thickness enlargement inhibits the implement of OSCs’ potential advantages. To overcome the bottlenecks of PCE decay in thick active layer OSCs, the electrical doping with componential selectivity in bulk heterojunction (BHJ) film is achieved by introducing a solid solvation additive. Benefiting from the higher exciton splitting efficiency together with the longer drift (L dr ) and diffusion (L diff ) lengths, an OSC with 100 nm BHJ film demonstrates a PCE increment from 16.44% to 18.24% with prolonged dark and illuminated storage stabilities. Applying the solid solvation assisted (SSA) doping method in the OSCs with 500 nm active layer, the PCE significantly increases by 31.9%, from the original value of 11.79% to 15.55%. It further improves to 15.84% in a ternary blend thick‐film device, which is the record value to the best of our knowledge. Besides, the SSA doping narrows the PCE gap between the 0.04 and 1 cm 2 devices. All improvements demonstrate the great potential of SSA doping for OSC commercial manufacture, since it optimizes the photovoltaic performance under all practical conditions of long‐term, thick‐film, and large‐area.

Chemistry↗
DOE OSTI2020

Understanding the Instability of the Halide Perovskite CsPbI 3 through Temperature-Dependent Structural Analysis

Despite the tremendous interest in halide perovskite solar cells, the structural reasons that cause the all-inorganic perovskite CsPbI 3 to be unstable at room temperature remain mysterious, especially since many tolerance-factor-based approaches predict CsPbI 3 should be stable as a perovskite. Here single-crystal X-ray diffraction and X-ray pair distribution function (PDF) measurements characterize bulk perovskite CsPbI3 from 100 to 295 K to elucidate its thermodynamic instability. While Cs occupies a single site from 100 to 150 K, it splits between two sites from 175 to 295 K with the second site having a lower effective coordination number, which, along with other structural parameters, suggests that Cs rattles in its coordination polyhedron. PDF measurements reveal that on the length scale of the unit cell, the Pb-I octahedra concurrently become greatly distorted, with one of the I-Pb-I angles approaching 82° compared to the ideal 90°. The rattling of Cs, low number of Cs-I contacts, and high degree of octahedral distortion cause the instability of perovskite-phase CsPbI 3 . These results reveal the limitations of tolerance factors in predicting perovskite stability and provide detailed structural information that suggests methods to engineer stable CsPbI 3 -based solar cells.

36 MATERIALS SCIENCE↗
DOE OSTI2024

A synthetic strategy for the preparation of alkoxy‐functionalized bis‐1,2,4‐triazinyl‐2,6‐pyridines

Heteroaryl-1,2,4-triazine complexants are commonly utilized in separation science for the selective chelation of minor An from Ln in simulated high-level waste. Furthermore, to facilitate access to relevant chemical entities for hypothesis-driven inquiry toward improved separations performance, a synthetic method to construct various alkoxy-complexant derivatives was required. In this work, a convergent synthetic strategy for the production of 3,3′- and 4,4′-tetraalkoxy-bis-1,2,4-triazinyl-2,6-pyridines from readily available starting materials via a dealkylation/alkylation/condensation approach is described. Synthetic method development, substrate scope, preliminary solubility, and hydrolytic stability data in various process-relevant diluents are reported herein.

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

Preparation and Property Research of Perfluoropolyether Oil-Based Ferrofluid

In this study, perfluoropolyether oil-based ferrofluid was prepared to satisfy special demands in applications which are too harsh to conventional ferrofluids. Fe{sub 3}O{sub 4} magnetic nanoparticles were synthesized by co-precipitation and modified by perfluoropolyether carboxylic acid surfactant in the atmosphere without protective gas. Perfluoropolyether oil-based ferrofluid was prepared with modified nanoparticles and perfluoropolyether by high-energy ball milling. Properties of ferrofluid fabricated were verified through a series of experiments. Ferrofluid stability was tested by interval point-density method; the average density change is merely 0.0077 g/ml, and change rate is 0.37% after 500 days. Saturation magnetization is 582.46 Gs, much larger than the other four ferrofluids. The average volatility rate is 7.4985*10{sup − 5} g/h/cm{sup 2} at 80 °C after 260 h. Viscosity increases to 1825.7 mPa⋅ s under − 20 °C and still have mobility at − 40 °C. The ferrofluid can resist air blast for 8 h under 200 °C without oxidation or decomposition. Perfluoropolyether oil-based ferrofluid cannot be damaged by water or organic solvents. In addition, the ferrofluid can survive in pH = 1 acid or pH = 14 alkali at least 279 days without corrosion.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗