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At least 1,225 records · Page 68
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Accurate Density Calculation for Molten Slags in SiO{sub 2}-Al{sub 2}O{sub 3}-CaO-MgO-‘FeO’-‘Fe{sub 2}O{sub 3}’ Systems

A simple and accurate density calculation model for molten slags containing iron oxides in SiO{sub 2}-Al{sub 2}O{sub 3}-CaO-MgO-‘FeO’-‘Fe{sub 2}O{sub 3}’ systems is established in the present study, by extending a previous model developed for SiO{sub 2}-Al{sub 2}O{sub 3}-CaO-MgO systems. To quantitate the iron oxides in slags, a new method is proposed to recalculate all the iron oxides as ‘FeO’ and ‘Fe{sub 2}O{sub 3},’ which represent the iron oxides in equilibrium with metallic iron and the air atmosphere, respectively. This method is essentially different from most of the other models that dealt with ferrous (FeO) and ferric (Fe{sub 2}O{sub 3}) iron oxides. A total of 860 experimental data points for iron oxide-containing melts are critically collected for the optimization of the model parameters. The model achieves an excellent agreement with literature values with an average error of 1.96 pct and an overall absolute error of 0.092 g/cm{sup 3}. The compositional dependences from unary to multicomponent systems are discussed using the present model. The results show that the densities always increase with the increasing ‘FeO’ or ‘Fe{sub 2}O{sub 3},’ and the substitution of ‘FeO’ by ‘Fe{sub 2}O{sub 3}’ will cause a decrease in density. In the multicomponent systems, SiO{sub 2} tends to have a larger impact on the density of ‘Fe{sub 2}O{sub 3}’-containing systems compared with ‘FeO’-containing systems.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Compressive Properties and Energy Absorption of Aluminum Foams with a Wide Range of Relative Densities

Quasi-static uniaxial compressive experiments were conducted on aluminum foams with a wide range of relative densities (0.134-0.472). The compressive properties and energy absorption capacity were systematically characterized and compared in a more suitable way. The compressive stress instead of compressive strain achieved during energy absorption process was taken into consideration. The results show that aluminum foam is not a kind of energy absorption materials with a stationary plateau region at the plastic deformation stage. There exists a strain hardening phenomenon which makes the stress–strain curve incline at this stage. For every aluminum foam with certain relative density, there exists an optimal stress. Under its optimal stress condition, the foam can absorb the maximum energy compared to foams with whatever different relative densities. The optimal stress and corresponding maximum energy absorption capacity increase with the increase in the foam’s relative density.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of AC Current Density on the Stress Corrosion Cracking Behavior and Mechanism of E690 High-Strength Steel in Simulated Seawater

In this work, we studied the impact of alternating current (AC) density on the stress corrosion cracking (SCC) behavior and mechanism of E690 high-strength steel in simulated seawater with electrochemical measurements, U-bend immersion tests and slow strain rate tensile tests. Results demonstrate that AC enhances both anodic and cathodic processes, especially localized anodic dissolution and hydrogen evolution, which manifests as the increase in i{sub corr} with AC current density rising. Therefore, AC leads to higher SCC susceptibility. Accordingly, SCC is dominated by anodic dissolution (AD) at low AC current density while in a mixed control of AD and hydrogen embrittlement (HE) at high AC current density as a result of increasing hydrogen concentration. Besides, 50 A/m{sup 2} corresponds to the threshold hydrogen concentration of the “hydrogen-induced plasticity to HE” transformation, which is due to the different interactions of dislocation and hydrogen.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Density–stiffness scaling in minerals upon disordering: Irradiation vs. vitrification

When subjected to irradiation or vitrification, minerals become disordered at the atomic scale, which, in turn, affect their density and stiffness. However, the nature of the relationship between structural disorder, density, and stiffness remains poorly understood. In this work, based on molecular dynamics simulations, we investigate the effect of irradiation- and vitrification-induced disordering in a series of silicate minerals. We show that irradiation- and vitrification-induced disordering yield comparable, yet not fully equivalent variations in density and stiffness. Interestingly, we report the existence of a power law density–stiffness scaling exhibiting a scaling exponent that is similar to that observed in porous assembled cellular materials.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Rules for the crystallite size and dislocation density evolution in phases during α-ω transformation in Zr under high-pressure and severe plastic flow

The first in-situ X-ray diffraction (XRD) study of the evolution of the crystallite size and dislocation density in phases during plastic strain-induced phase transformation (PT) is performed utilizing α-ω PT in strongly pre-deformed commercially pure Zr as an important example. Rough diamond anvils (rough-DA) are introduced to intensify all occurring processes during heterogeneous compression of Zr in a diamond anvil cell (DAC). The main rule is found that during α-ω PT the crystallite size and dislocation density in ω-Zr depend solely on the volume fraction of ω-Zr and are independent of pressure, plastic strain tensor, its path, and initial nanostructure. Crystallite size in ω-Zr increases from 10 to 60 nm during the PT, while dislocation density reduces from 1.83×10 15 /m 2 to 0.6×10 15 /m 2 . Rough-DA produce a steady nanostructure in α-Zr before PT with smaller crystallite size and larger dislocation density than smooth-DA, leading to a reduction of the minimum pressure for α-ω PT to a record value 0.67 GPa, 9 times smaller than under hydrostatic loading and 5.1 times lower than the phase equilibrium pressure. In addition to strain, the kinetics of strain-induced PT unexpectedly depends on time. Also, strain-controlled part of kinetics is zero order, in contrast to the first-order kinetics with smooth-DA. The obtained results open a new window for understanding the mutual effects of nanostructure evolution and PT during severe plastic flow in various technological and natural processes. In conclusion, they may bring up economic strategies of producing nanocomposites and single-phase nanostructured materials with optimal properties.

Crystalline size↗
DOE OSTI2018

Level density of the sd-nuclei—Statistical shell-model predictions

Accurate knowledge of the nuclear level density is important both from a theoretical viewpoint as a powerful instrument for studying nuclear structure and for numerous applications. For example, astrophysical reactions responsible for the nucleosynthesis in the universe can be understood only if we know the nuclear level density. We use the configuration-interaction nuclear shell model to predict nuclear level density for all nuclei in the sd-shell, both total and for individual spins (only with positive parity). To avoid the diagonalization in large model spaces we use the moments method based on statistical properties of nuclear many-body systems. In the cases where the diagonalization is possible, the results of the moments method practically coincide with those from the shell-model calculations. Using the computed level densities, we fit the parameters of the Constant Temperature phenomenological model, which can be used by practitioners in their studies of nuclear reactions at excitation energies appropriate for the sd-shell nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Differentiating densities on smooth manifolds

Lebesgue integration of derivatives of strongly-oscillatory functions is a recurring challenge in computational science and engineering. Integration by parts is an effective remedy for huge computational costs associated with Monte Carlo integration schemes. In case of Lebesgue integrals over a smooth manifold, however, integration by parts gives rise to a derivative of the density implied by charts describing the domain manifold. This paper focuses on the computation of that derivative, which we call the density gradient function, on general smooth manifolds. We analytically derive formulas for the density gradient and present examples of manifolds determined by popular differential equation-driven systems. Furthermore, we highlight the significance of the density gradient by demonstrating a numerical example of Monte Carlo integration involving oscillatory integrands.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

Loss of PiT-2 results in abnormal bone development and decreased bone mineral density and length in mice

Highlights: • PiT-2 deficiency decreased mineral density in craniofacial and long bones in mice. • Bone length was reduced in long bones in PiT-2 deficient mice. • Trabecular and cortical bone mineral density were decreased in PiT-2 deficient mice. • Static bone morphometric parameters were altered in PiT-2 deficient mice. • PiT-2 deficiency altered craniofacial bone morphology. Normal bone mineralization requires phosphate oversaturation in bone matrix vesicles, as well as normal regulation of phosphate metabolism via the interplay among bone, intestine, and kidney. In turn, derangement of phosphate metabolism greatly affects bone function and structure. The type III sodium-dependent phosphate transporters, PiT-1 and PiT-2, are believed to be important in tissue phosphate metabolism and physiological bone formation, but their requirement and molecular roles in bone remain poorly investigated. In order to decipher the role of PiT-2 in bone, we examined normal bone development, growth, and mineralization in global PiT-2 homozygous knockout mice. PiT-2 deficiency resulted in reduced vertebral column, femur, and tibia length as well as mandibular dimensions. Micro-computed tomography analysis revealed that bone mineral density in the mandible, femur, and tibia were decreased, indicating that maintenance of bone function and structure is impaired in both craniofacial and long bones of PiT-2 deficient mice. Both cortical and trabecular thickness and mineral density were reduced in PiT-2 homozygous knockout mice compared with wild-type mice. These results suggest that PiT-2 is involved in normal bone development and growth and plays roles in cortical and trabecular bone metabolism feasibly by regulating local phosphate transport and mineralization processes in the bone. Further studies that evaluate bone cell-specific loss of PiT-2 are now warranted and may yield insight into complex mechanisms of bone development and growth, leading to identification of new therapeutic options for patients with bone diseases.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2025

High-current-density electrosynthesis of formate from captured CO 2 solution by MOF-derived bismuth nanosheets

Greenhouse gas emissions present a significant challenge to humanity, and utilizing renewable electricity to convert emitted CO 2 into value-added products offers a promising solution; however, traditional CO 2 capture and regeneration processes remain energy-intensive, restricting the overall system efficiency and decarbonization efficacy. In this study, an advanced direct reduction of captured CO 2 with large current densities for formate electrosynthesis was demonstrated without the need for CO 2 regeneration or compression. The bismuth nanosheet (DRM-BiNS) was synthesized by direct reduction of a Bi-based MOF, representing a new class of catalytic materials with a large surface area and interconnected pores, suitable for the direct reduction of captured CO 2 . By seamlessly combining experimentation and simulation, insights into the structure-parameter-performance relation were acquired in a flow cell setting, including critical membrane-electrode distance, cell orientation, and pumping flow rate. Important flow-cell components, such as catholyte volume, electrode substrate, membrane choice, and ionomer type, were also carefully examined to enhance the cell performance. In sharp contrast to prior studies limited to current densities below 20 mA/cm 2 in bicarbonate-based captured CO 2 solutions, this work demonstrates a remarkable current density of 300 mA/cm 2 with an FE to formate comparable to the case with gas-fed CO 2 reduction. Moreover, the process sustained an FE above 50% at a high current density of 500 mA/cm 2 . The DRM-BiNS catalyst exhibited outstanding selectivity, activity, and stability, significantly outperforming oxide-derived bismuth nanosheets (OD-BiNS) in captured CO 2 reduction. Furthermore, these findings offer critical insights into the development of sustainable and scalable CO 2 utilization technologies.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2021

Empirical estimation of densities in NaCl-KCl-UCl 3 and NaCl-KCl-YCl 3 molten salts using Redlich-Kister expansion

Densities of molten KCl-NaCl-UCl 3 and KCl-NaCl-YCl 3 ternary systems have been estimated using a multidimensional Redlich-Kister model. Temperature and composition dependent Redlich-Kister functions have been used to generate binary interaction parameters in the outlined ternary salt systems. These binary interactions have been used in the extrapolation to ternary system densities. The results of the density extrapolations by Muggianu interpolation scheme provide agreement within 2–3% for the NaCl-KCl-YCl 3 liquids and 11% in NaCl-KCl-UCl 3 liquids compared to the available experimental data. Modeling NaCl-KCl-UCl 3 molten phase density with a ternary interaction parameter improved the agreement within 4%. Thermophysical modeling used in this study has shown promising results for use in other material properties, such as viscosity, thermal conductivity, and heat capacity of the molten salts. Lastly, the outlined modeling method applied in these specific molten salt ternaries can be used for quaternary or higher multicomponent molten salt systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Effect of loading path on grain misorientation and geometrically necessary dislocation density in polycrystalline aluminum under reciprocating shear

Solid phase processing (SPP) is a promising alloy fabrication technique to produce fine and homogeneous grain structures for high-performance alloys. However, there is very limited modeling capability to understand and predict the grain refinement during SPP. In this work, the crystal plasticity theory was used to study elastic-plastic deformation in polycrystalline aluminums under large shear deformation. Two approaches, kernel averaged misorientation (KAM) and grain reference orientation deviation (GROD), were used to assess the grain misorientations. The geometrically necessary dislocation (GND) density was computed with the plastic strain rate. The deformation simulations were carried out under two loading conditions to investigate the effect of loading paths on the evolutions of grain misorientation and GND density. The results show that the regions with high misorientation and GND density first appear near grain boundaries. These regions then extend toward interior grains. The loading path affects dislocation system activation and dislocation recovery, hence dislocation evolution and misorientation. In conclusion, both two- and three-dimensional simulations showed that the spatial and temporal evolutions of GROD, KAM, and GND density in are closely correlated, which indicates they all can be used as criteria of grain refinement or recrystallization.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Investigations on the effect of current density on SiO/Si composite electrodes

An oxide layer on the surface of silicon particles is inevitable and is necessary for their application as anode materials for lithium ion batteries with high capacity and durability. However, a thick surficial oxide layer could significantly reduce the capacity of a Si anode. Here, Si nanoparticles with a thick surficial oxide layer of ~20 nm (Si@SiO x ) were fabricated through thermal oxidation and investigated electrochemically. The results revealed that very low current density is needed to activate Si@SiO x anodes during the first formation cycle. Once activated, the Si@SiO x anode can deliver reversible capacity as high as ~1000 mAh/g with low current density. Then, the Si@SiO x can be cycled at higher current densities of >700 mAh/g. Electrochemical impedance spectroscopy (EIS) shows that the lower current density results in lower charge-transfer resistance of the Si@SiO x anode, suggesting a higher degree of lithiation of the surficial oxide layer during low-current activation. EIS analysis also reveals that the lithiation of the surficial oxide is irreversible. We believe that the surface silicon oxide layer is lithiated and forms lithium silicate during the initial activation process. Lithium silicate has high conductivity and allows the lithiation/delithiation of Si core under the oxide layer during following charge and discharge.

25 ENERGY STORAGE↗
DOE OSTI2024

Development of real-time density feedback control on MAST-U in L-mode

In this paper we report on the development and demonstration of density feedback control for MAST-U. Sinusoidal perturbations are used to measure the frequency response from a deuterium gas valve (actuator) to line-integrated core electron density measured by the interferometer (sensor). In the frequency range relevant for control design, only two system-identification experiments were needed to regress a first-order dynamic model. This control-oriented model informs the offline design of a proportional integral controller with the established loop-shaping controller design method. After offline verification of the controller implementation, control is demonstrated by experimentally tracking a staircase reference for the line-integrated electron density. This paper demonstrates the efficiency of controller design using system-identification and loop-shaping, providing reliable density control for MAST-U.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

The use of geometric effects in diagnosing ion density in ICF-related dot spectroscopy experiments

Here, we describe a method to calculate the ion density of High Energy Density (HED) cylindrical plasmas used in dot spectroscopy experiments. This method requires only spectroscopic measurements of the Heα region obtained from two views (Face-on and Side-on). We make use of the fact that the geometry of the plasma affects the observed flux of optically thick lines. The ion density can be derived from the aspect ratio (height-to-radius) of the cylinder and the optical depth of the Heα-y line (1s2p 3 P 1 → 1s 2 1 S 0 ). The aspect ratio and the optical depth of the y line are obtained from the spectra using ratios measured from the two directions of emission of the optically thick Heα-w line (1s2p 1 P 1 → 1s 2 1 S 0 ) and the ratio of the optically thick to thin lines. The method can be applied to mid-Z elements at ion densities of 10 19 – 10 20 cm -3 and temperatures of a the order of keV, which is a relevant regime for Inertial Confinement Fusion (ICF)

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Grid-responsive hydrogen production: Capital utilization and current density vs. efficiency in variable electricity markets

To achieve low-cost hydrogen production from water electrolyzers, grid tied electrolysis may need to operate dynamically to minimize the cost of supplying energy to the electrolyzer stack and produce hydrogen during low-cost hours and turn off/down during high-cost hours. Operating systems in this way can decrease capital utilization (capacity factor) and electricity costs. This strategy would shift the dominant cost drivers away from electricity (and thus efficiency) to the capital costs of the system, due to the underutilized capital when operating at low-capacity factors. Increasing the operational current density of the system could, in effect, reduce the capital cost of the system while producing hydrogen at a lower efficiency on a per unit energy basis. In the variable electricity cost profiles analyzed in this paper, increasing the current density for liquid alkaline from 0.5 A/cm2 to 1.5 Ac/m2 and proton exchange membrane electrolyzers from 2 A/cm2 to 4 A/cm2 resulted in substantial reductions in the levelized cost of hydrogen. Additionally, as capacity factors and electricity costs decrease, the optimal operating current density of the electrolyzer systems analyzed increases. These findings suggest R&D efforts should focus on increasing the operational current densities, reducing the turn down ratios, and understanding the durability implications of those strategies on low-temperature liquid alkaline and proton exchange membrane electrolyzers.

08 HYDROGEN↗
DOE OSTI2024

A second-order-in-time, explicit approach addressing the redundancy in the low-Mach, variable-density Navier-Stokes equations

A novel algorithm for explicit temporal discretization of the variable-density, low-Mach Navier-Stokes equations is presented here in this study. Recognizing there is a redundancy between the mass conservation equation, the equation of state, and the transport equation(s) for the scalar(s) which characterize the thermochemical state, and that it destabilizes explicit methods, we demonstrate how to analytically eliminate the redundancy and propose an iterative scheme to solve the resulting transformed scalar equations. The method obtains second-order accuracy in time regardless of the number of iterations, so one can terminate this subproblem once stability is achieved. Hence, flows with larger density ratios can be simulated while still retaining the efficiency, low cost, and parallelizability of an explicit scheme. The temporal discretization algorithm is used within a pseudospectral direct numerical simulation which extends the method of Kim, Moin, and Moser for incompressible flow to the variable-density, low-Mach setting, where we demonstrate stability for density ratios up to ~25.7.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2019

Doppler-free, Stark broadened profiles at low plasma densities in helium

This paper utilizes Doppler-free saturation spectroscopy to measure Doppler-free, Stark broadened spectral profi les for the π-polarization of the HeI 2¹P → 6¹D transition in a low density (10¹⁰ ₋ 10¹² cm⁻³) helium plasma. The measurements were performed in an electron-cyclotron resonance discharge at 23 mTorr with electron density being diagnosed using a combination of Langmuir probe and microwave interferometry techniques. The Doppler-free pro files were observed to be nearly symmetric at n e < 10¹⁰ cm⁻³ but markedly asymmetric above this transition point. Electron density is extracted from the spectral data via fi tting to a spectral model based on quasi-static Stark broadening and compared to the measured n e . The quasi-static model is shown to be valid in the low-density regime for 2¹P → 6¹D helium transition.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Gaussian kernel density functions for compositional quantification in atom probe tomography

Highlights: • A methodology for compositional quantification from atom probe tomography is proposed. • A probability density function p(x) given discrete data points is constructed. • Each atom approximated by a Gaussian function with a particular smoothing parameter. • Density Kernel functions are used to find the optimum smoothing parameter. • The method is validated by using simulated data of semiconductor materials. - Abstract: Atom probe tomography (APT) has the ability to identify the nature and position of single atoms in a material with an almost 3D atomic resolution. However, the quantification of the material composition requires an appropriate treatment of the discrete APT data. When the amount of atoms selected to quantify the composition is relatively small, the spatial resolution is enhanced but the statistical error worsens. Conversely, the increase in the number of atoms considered reduces the spatial resolution, but improving the statistics. We have developed a methodology to reach an optimum equilibrium between the positional and the statistical error in an unsupervised form using Gaussian Kernel density functions. The validity of the method has been tested using APT simulated data of semiconductor materials. It has been proved that the chemical quantification in these materials requires the appropriate selection of the smoothing parameter, obtained without user intervention. In addition, the results have been compared to the usual techniques for composition measurement from APT data (voxelization and proximity histograms), showing better precision for high spatial resolution. This work supplies a data driven methodology based in Gaussian Kernel density functions for the accurate quantification of the composition from APT data.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗