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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 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Atomic Dynamics of Multi‐Interfacial Migration and Transformations

Redox-induced interconversions of metal oxidation states typically result in multiple phase boundaries that separate chemically and structurally distinct oxides and suboxides. Directly probing such multi-interfacial reactions is challenging because of the difficulty in simultaneously resolving the multiple reaction fronts at the atomic scale. Using the example of CuO reduction in H 2 gas, a reaction pathway of CuO → monoclinic m-Cu 4 O 3 → Cu 2 O is demonstrated and identifies interfacial reaction fronts at the atomic scale, where the Cu 2 O/m-Cu 4 O 3 interface shows a diffuse-type interfacial transformation; while the lateral flow of interfacial ledges appears to control the m-Cu 4 O 3 /CuO transformation. Together with atomistic modeling, it is shown that such a multi-interface transformation results from the surface-reaction-induced formation of oxygen vacancies that diffuse into deeper atomic layers, thereby resulting in the formation of the lower oxides of Cu 2 O and m-Cu 4 O 3 , and activate the interfacial transformations. In conclusion, these results demonstrate the lively dynamics at the reaction fronts of the multiple interfaces and have substantial implications for controlling the microstructure and interphase boundaries by coupling the interplay between the surface reaction dynamics and the resulting mass transport and phase evolution in the subsurface and bulk.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Development of a shuttle plasmid without host restriction sites for efficient transformation and heterologous gene expression in Clostridium cellulovorans

Clostridium cellulovorans capable of producing large amounts of acetate and butyrate from cellulose is a promising candidate for biofuels and biochemicals production from lignocellulosic biomass. However, the restriction modification (RM) systems of C. cellulovorans hindered the application of existing shuttle plasmids for metabolic engineering of this organism. To overcome the hurdle of plasmid digestion by host, a new shuttle plasmid (pYL001) was developed to remove all restriction sites of two major RM systems of C. cellulovorans , Cce 743 I and Cce 743 II. The pYL001 plasmid remained intact after challenge by C. cellulovorans cell extract. Post-electroporation treatments and culturing conditions were also modified to improve cell growth and colony formation on agar plates. With the improvements, the pYL001 plasmid, without in-vivo methylation, was readily transformed into C. cellulovorans with colonies of recombinant cells formed on agar plates within 24 h. Three pYL001-derived recombinant plasmids free of Cce 743 I/ Cce 743 II restriction sites, after synonymous mutation of the heterologous genes, were constructed and transformed into C. cellulovorans . Functional expression of these genes was confirmed with butanol and ethanol production from glucose in batch fermentations by the transformants. In conclusion, the pYL001 plasmid and improved transformation method can facilitate further metabolic engineering of C. cellulovorans for cellulosic butanol production.

09 BIOMASS FUELS↗
DOE OSTI2018

On Eigenfunctions of the Fourier Transform

A nontrivial example of an eigenfunction in the sense of the theory of distributions for the planar Fourier transform was described by the authors in their previous work. In this paper, a method for obtaining other eigenfunctions is proposed. Positive homogeneous distributions in ℝ{sup n} of order −n/2 are considered, and it is shown that F(ω)|x|{sup −n/2}, |ω| = 1, is an eigenfunction in the sense of the theory of distributions of the Fourier transform if and only if F(ω) is an eigenfunction of a certain singular integral operator on the unit sphere of ℝ{sup n}. Since Y{sub m,n}{sup (k)}(ω)|x|{sup −n/2}, where Y{sub m,n}{sup (k)} denote the spherical functions of order m in ℝ{sup n}, are eigenfunctions of the Fourier transform, it follows that Y{sub m,n}{sup (k)} are eigenfunctions of the above-mentioned singular integral operator. In the planar case, all eigenfunctions of the Fourier transform of the form F(ω)|x|{sup −1} are described by means of the Fourier coefficients of F(ω).

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2016

Phase transformation dependence on initial plastic deformation mode in Si via nanoindentation

Silicon in its diamond-cubic phase is known to phase transform to a technologically interesting mixture of the body-centred cubic and rhombohedral phases under nanoindentation pressure. In this study, we demonstrate that during plastic deformation the sample can traverse two distinct pathways, one that initially nucleates a phase transformation while the other initially nucleates crystalline defects. These two pathways remain distinct even after sufficient pressure is applied such that both deformation mechanisms are present within the sample. Here, it is further shown that the indents that initially nucleate a phase transformation generate larger, more uniform volumes of the phase transformed material than indents that initially nucleate crystalline defects.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Stability of Phase Transformation Temperatures During Cycling of Ti-15.8Nb-4.94Al-0.06Sc Shape Memory Alloy

The active ω phase formation decreases the martensitic transformation temperatures sharply and can even suppress the martensitic transformation during thermal cycling in Ti-Nb-based alloys. No ω phase is observed in the present Ti-15.8Nb-4.94Al-0.06Sc alloy when it is annealed at 650 °C for 4 h or subsequently aged at 200 and 250 °C for 2 h. The exclusion of ω phase remarkably improves the stability of phase transformation temperatures during thermal cycling. The martensitic transformation start temperature of the present alloy decreases by 30 °C but tends to be stable gradually during the 20 thermal cycles, owing to the saturation of lattice defects.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Numerical Simulation of Residual Stress for Laser Welding of Ti-6Al-4V Alloy Considering Solid-State Phase Transformation

In the present work, a thermal-metallurgical-mechanical model which considered the influence of phase transformation was used to predict the residual stress field of Ti-6Al-4V after laser welding. In this model, the Johnson–Mehl–Avrami equation was used to predict diffusional solid-state phase transformations: α phase to β phase during heating and β phase to α phase during cooling. The Koistinen–Marburger equation was used to predict diffusionless solid-state phase transformation of β phase to martensite during cooling. The properties of material were obtained using a mixing rule based on the phase fraction and the property of each pure phase. By applying this model, the effect of solid-state phase transformations of Ti-6Al-4V alloy on temperature field and stress field during laser welding was considered in the simulation. In addition, experiments were carried out for comparison, which significantly verified the accuracy of the applied model.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Numerical and Experimental Analysis of Dissimilar Repair Welding Residual Stress in P91 Steel Considering Solid-State Phase Transformation

Repair welding is a popular method to repair the cracked zones of pipes in power plants. However, residual stresses induced by repair welding are inevitably generated and have a significant effect on the performance of repair-welded components during service. The purpose of this research is to investigate the effects of solid-state phase transformation (SSPT) on the repair welding residual stress distribution of multi-layer and multi-pass welding in P91 steel. Based on thermal elastic-plastic theory, a three-dimensional thermal–metallurgical–mechanical finite element model considering the SSPT is established, and shielded metal arc welding (SMAW) heat input is modelled as one double elliptical heat source. The effect of phase transformation on residual stress is investigated by considering effects with and without phase transformation in the database of materials. The results show that transverse compressive stress and a low longitudinal stress area are generated in the final pass due to martensite transformation. Compared with different zones along the thickness direction, the effect of SSPT is greater around the outer surface than around the internal fusion zone. The rationality of the developed finite element model is verified by the experimental method, and good agreement is obtained between those results from the numerical analysis and experimental methods.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Natural transformation as a tool in Acinetobacter baylyi : Streamlined engineering and mutational analysis

Natural transformation and homologous recombination in a soil bacterium, Acinetobacter baylyi ADP1, occur with exceptionally high efficiency. These genetic features can be harnessed to address a wide variety of fundamental and applied scientific topics. Recent advances in synthetic biology and laboratory evolution have led to renewed appreciation for the use of A. baylyi as a model organism. To complement several review articles that highlight new tool sets, this chapter focuses on simple protocols and examples of transformation assays that facilitate genetic analysis and engineering. Whole genome sequencing often reveals extensive genetic variation among closely related isolates that can confound the association of genotypic and phenotypic changes. In A. baylyi, such associations can be deciphered in unique ways by directly transforming cells with linear DNA fragments. The resulting allelic replacement, which occurs at high frequency, rapidly generates desired mutants via targeted chromosomal editing. Diverse screening and selection methods can be used to test hypotheses and streamline experimental strategies to reveal the significance of specific DNA sequences. Moreover, large procedural variations are well tolerated, and techniques can be readily adapted for new purposes. Furthermore, one goal of highlighting natural transformation methodology in A. baylyi is to expand the community of researchers using this versatile bacterial host.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

The role of deviatoric stress and dislocations on the α to ω phase transformation in Ti

Under extreme conditions, α-Ti becomes unstable and transforms either into β-Ti at high temperature or into ω-Ti at high pressure. In what concerns the α to ω phase transformation (PT), there has been a wide range of experimentally reported transition pressures from approximately 2 to 15 GPa at room temperature. Deviatoric stresses and internal defects are often assumed to be the root cause of this variation. Here, in this study, these postulates are revisited using both continuum mechanics and molecular dynamics (MD) simulations. First, a simple continuum model, assuming linear elasticity and isotropic plasticity, is developed to describe the effects of applied stress and dislocations on the stability of an ω nucleus in an infinite α domain. Second, a new MD simulation method is developed to generate an ω nucleus in the α domain utilizing the displacement field identified from the topological analysis. Results from MD simulations show that despite the fact that phase diagrams typically delineate the limits between two phases in terms of only P and T, deviatoric stress promotes the α to ω phase transformation by reducing the critical radius above which an ω nucleus is stable. Furthermore, the required deviatoric stress to nucleate and stabilize a nanoscale ω nucleus is likely emanating from the internal stress of defects such as dislocations. The MD-informed micromechanics models are used to identify favorable configurations where dislocations help favor the α to ω transformation. These configurations show that the interaction with a basal or prismatic dislocation reduces the critical radius of a ω nucleus by about 10 or 16 %, respectively. In addition, prismatic edge dislocations are found to promote the growth of ω nucleus when interacting with the ($\bar{1}$$\bar{1}$20) α //(0001) ω interface. Importantly, a simple model of the arrival of dislocation at an ω nucleus suggests that PT does not necessarily require a pile-up to be present but could alternatively be mediated by a constant rapid flow of dislocations.

36 MATERIALS SCIENCE↗
DOE OSTI2013

The equation-transform model for Dirac–Morse problem including Coulomb tensor interaction

The approximate solutions of Dirac equation with Morse potential in the presence of Coulomb-like tensor potential are obtained by using Laplace transform (LT) approach. The energy eigenvalue equation of the Dirac particles is found and some numerical results are obtained. By using convolution integral, the corresponding radial wave functions are presented in terms of confluent hypergeometric functions. -- Highlights: •The Dirac equation with tensor interaction is solved by using Laplace transform. •For solving this equation, we introduce the equation-transform model. •Numerical results and plots for pseudospin and spin symmetric solutions are given. •The obtained numerical results by using transform method are compared with orthogonal polynomial method.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Lorentz transformations of the thermodynamic quantities

In modern physics there exist several formulations of relativistic thermodynamics of a moving body. The Planck and Ott formalisms are the main ones. However, it is not clear which one is correct. In the present paper, we have solved this problem. We have required the equivalence of the dynamical Hamiltonian of a system to the fundamental thermodynamic potential in addition to the principle of entropy invariance and derived the first law of thermodynamics from this fundamental potential. We have found that in the case of momentum being an independent variable in the Hamiltonian, the Lorentz transformations of the thermodynamic quantities belong to the Planck formalism. However, if we suppose that the velocity is an independent variable in the Hamiltonian (though it is not correct from the point of view of the relativistic dynamics), the Lorentz transformations of the thermodynamic quantities belong to the Ott formalism. It demonstrates that the Ott formalism cannot be appropriate. Moreover, we have proved that in the Planck description the first law of thermodynamics is covariant and the Legendre transform of the Lagrangian is preserved. However, in the Ott description the first law of thermodynamics is not covariant and the Legendre transform is violated. Thus we have demonstrated that only the Planck formulation of relativistic thermodynamics of a moving body is properly defined and the Ott formalism should be discarded.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

The PDZ-binding motif of Yes-associated protein is required for its co-activation of TEAD-mediated CTGF transcription and oncogenic cell transforming activity

Highlights: •Loss of the PDZ-binding motif inhibits constitutively active YAP (5SA)-induced oncogenic cell transformation. •The PDZ-binding motif of YAP promotes its nuclear localization in cultured cells and mouse liver. •Loss of the PDZ-binding motif inhibits YAP (5SA)-induced CTGF transcription in cultured cells and mouse liver. -- Abstract: YAP is a transcriptional co-activator that acts downstream of the Hippo signaling pathway and regulates multiple cellular processes, including proliferation. Hippo pathway-dependent phosphorylation of YAP negatively regulates its function. Conversely, attenuation of Hippo-mediated phosphorylation of YAP increases its ability to stimulate proliferation and eventually induces oncogenic transformation. The C-terminus of YAP contains a highly conserved PDZ-binding motif that regulates YAP’s functions in multiple ways. However, to date, the importance of the PDZ-binding motif to the oncogenic cell transforming activity of YAP has not been determined. In this study, we disrupted the PDZ-binding motif in the YAP (5SA) protein, in which the sites normally targeted by Hippo pathway-dependent phosphorylation are mutated. We found that loss of the PDZ-binding motif significantly inhibited the oncogenic transformation of cultured cells induced by YAP (5SA). In addition, the increased nuclear localization of YAP (5SA) and its enhanced activation of TEAD-dependent transcription of the cell proliferation gene CTGF were strongly reduced when the PDZ-binding motif was deleted. Similarly, in mouse liver, deletion of the PDZ-binding motif suppressed nuclear localization of YAP (5SA) and YAP (5SA)-induced CTGF expression. Taken together, our results indicate that the PDZ-binding motif of YAP is critical for YAP-mediated oncogenesis, and that this effect is mediated by YAP’s co-activation of TEAD-mediated CTGF transcription.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

Unravelling the sintering temperature-induced phase transformations in Ba(Fe 0.7 Ta 0.3 )O 3-δ ceramics

This work reports on the fundamental details of the crystal structure and phase transformations in Ba(Fe 0.7 Ta 0.3 )O 3-δ , the best known temperature-independent oxygen-sensing ceramic material for applications in extreme environments. Ba(Fe 0.7 Ta 0.3 )O 3-δ ceramics were synthesized using conventional solid-state ceramic reaction under variable sintering temperatures (T s = 1200–1350 °C). Combined X-ray diffraction (XRD) and high-resolution transmission electron microscopy (TEM) measurements revealed the T s -induced phase transformations and their origin in Ba(Fe 0.7 Ta 0.3 )O 3-δ . Associated with phase transformations, pseudo-cubic (PC) reflections, such as {200} PC , {211} PC , and {220} PC , exhibited distinct anomalies with increasing T s . At T s = 1200 °C, Ba(Fe 0.7 Ta 0.3 )O 3-δ stabilized in mixed orthorhombic + rhombohedral phases (Amm2 + R3m). With increasing T s (≥1250 °C), Ba(Fe 0.7 Ta 0.3 )O 3-δ ceramics stabilized in tetragonal/rhombohedral [P4mm + R3m] mixed phases, while variations in the quantity of the respective phases were observed. Because both structure and crystal chemistry play key roles in achieving enhanced performance in chemical sensing and catalytic converters, detailed understanding of the phase transformations and crystal structure of Ba(Fe 0.7 Ta 0.3 )O 3-δ ceramics, as derived in this work, will be useful to develop chemical sensors with optimum performance for high-temperature and corrosive environments.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Structural deformation and transformation of θ'-Al 2 Cu precipitate in Al matrix via interfacial diffusion

Metastable θ'-Al 2 Cu precipitates enhance mechanical properties of Al alloy, but gradually transform to θ phase due to diffusion related coarsening at higher temperatures (>200°C). To improve understanding of the phase instability and transformation of θ'-Al 2 Cu, we investigated the interfacial atomic mobility of θ'-Al2Cu precipitate in Al matrix via molecular dynamics (MD). To characterize the interfacial atomic mobility, diffusion properties (activation energy, diffusivity, and jump attempt frequency) with respect to atomic species, interfacial structure, and temperature are calculated using atomic trajectories from MD. For the enhanced accuracy of this analysis, especially at low temperatures, temporal scale of molecular dynamics is significantly extended by employing the parallel replica dynamics. This study, as the first MD investigation on atomic diffusion of θ'-Al 2 Cu in Al matrix, suggests and discusses (i) structural deformation activated at the semi-coherent θ'-Al 2 Cu/Al interfaces, (ii) transformation initiated at the edge of the coherent θ'-Al 2 Cu/Al interface, and (iii) directional dependence of diffusion properties. Overall, these findings are expected to be employed in a larger scale phase-field modeling of precipitate growth, and to contribute to the understanding of phase transformation process and the development of alloys with θ'-phase retained to higher temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2020

A deep insight on the coal ash-to-slag transformation behavior during the entrained flow gasification process

Recent research provided deep insight on the coal ash-to-slag transformation characterization during the entrained flow gasification process, with experimentation on a 40 kg/hr (dry basis) coal-fed opposed multi-burner (OMB) entrained flow gasifier and simulation via FactSage™ software. A general mechanism is presented to relate the gasifier design temperature, ash fluid temperature, and operating temperature with the degree of the slag polymerization. The change of the high temperature zone, the corresponding particle residence time in the high temperature zone, and syngas composition have obvious effects on the slag mineral transformation behavior. Mineral types formed on the wall of the gasifier chamber were mainly anorthite (CaAl 2 Si 2 O 8 ), aluminum oxide (Al 2 O 3 ), and calcium sulfide (CaS). These minerals transformed to anorthite and diopside (CaMgSi 2 O 6 ) at the slag hole zone, while the minerals at the lock hopper were anorthite, orthoclase (KAlSi 3 O 8 ), quartz (SiO 2 ), gypsum (CaSO 4 ), calcite (CaCO 3 ), and halite (NaCl). FactSage™ predicted minerals as anorthite, diopside, orthoclase, and albite (NaAlSi 3 O 8 ), etc., where the slag temperature was below the ash fluid temperature and when the ratios of CO/CO 2 and (CO + H 2 )/CO 2 were lower than 1.0 and 2.0, respectively. By simulation, residual carbon was found to be the dominant factor over syngas composition to cause mineral transformation, and this was verified experimentally. The Ca-based crystals, typically anorthite, was shifted to diopside, near the slag hole zone, and a linear relationship was found between the content ratios of diopside/(anorthite + diopside), CaO/SiO 2 , and (CaO + MgO)/SiO 2 . A dimensionless number, θ, was defined to characterize the changing chemical composition and the degree of slag polymerization, with temperature deviation from the design condition. Three zones of θ were identified and related to the deviation between the actual gasification condition from the design condition. Finally, a low slag polymerization degree corresponded with a higher temperature deviation between the actual condition and design condition, and this proved that increased residual carbon content and changing iron valence state increased the mineral types when the slag temperature was below the ash fluid temperature.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2017

Martensitic transformation in a B2-containing CuZr-based BMG composite revealed by in situ neutron diffraction

Here, CuZr-based bulk-metallic-glass (BMG) composites reinforced by a B2-type CuZr crystalline-phase (CP) have been widely studied, and exhibit that the plastic deformation of the CP induces martensitic transformation from the B2 to B19', which plays a dominant role in the deformation behavior and mechanical properties. In the present study, 2.0% Co containing CuZr-based BMG composites were investigated using in-situ neutron-diffraction technique. The in-situ neutron-diffraction results reveal the continuous load transfer from the glass matrix to B2 CP and martensitic transformation from the B2 CP to B19' during the deformation of the composite. Moreover, it was found that the martensitic transformation is initiated at the applied stress higher than 1500 MPa, and is significantly suppressed during the deformation, as compared to other 0.5% Co-containing CuZr-based BMG composites. Based on these in-situ neutron-diffraction results, the martensitic transformation is strongly affected by the amount of the addition of Co, which determines the mechanical properties of CP-reinforced BMG composites, such as ductility and hardening capability.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Lüders-like martensitic transformation in a Cu/carbon-steel nanocomposite: An in situ synchrotron study

In this paper, a Cu/carbon-steel nanocomposite is fabricated by pressing, rolling and wire drawing. The average layer thickness is about 69 nm for steel and 67 nm for Cu. Cu suppresses the growth of prior austenite at elevated temperature, and thus the steel layer thickness barely increases during austenization. Subsequent quenching results in a large amount of metastable retained austenite within the steel layers. The martensitic transformation behavior of the composite during plastic deformation is investigated by in situ tensile test using synchrotron X-ray diffraction at room temperature. It is found that the retained austenite, rather than Cu, dominates the plastic deformation of the nanocomposite. Finally, in situ results verify that the transformation of retained austenite initiates in a manner of Lüders-like band due to stress-induced martensitic transformation, followed by strain-induced martensitic transformation until fracture.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Transformation of rutile to TiO{sub 2}-II in a high pressure hydrothermal environment

The high pressure transformation of rutile to TiO{sub 2}-II with the α-PbO{sub 2} structure is known to be kinetically hindered. In this study we show that a hydrothermal environment at 6 GPa and 650 °C provides appreciable rates for producing single phase bulk samples of TiO{sub 2}-II. So obtained TiO{sub 2}-II was characterized by scanning electron microscopy, powder X-ray diffraction, Raman and Far-IR spectroscopy. The structural properties are identical to TiO{sub 2}-II from dry transitions. Transmission electron microscopy studies strongly indicate that Ostwald ripening processes play an important role in the hydrothermally assisted transformation and subsequent growth of TiO{sub 2}-II crystals. TiO{sub 2}-II is thermally stable to about 550 °C. At 600 °C the onset of the transformation to rutile is observed. The thermal expansion in the temperature range from room temperature to 500 °C is highly anisotropic, virtually affecting only the c unit cell parameter (α{sub c}=7.1(2)×10{sup −6} °C{sup −1}). The pressure–temperature conditions for the hydrothermally assisted transformation of rutile are viable for industrial production settings, and in light of the large technological significance of TiO{sub 2}, TiO{sub 2}-II may present an interesting target for large-scale synthesis. - Graphical abstract: Highly crystalline TiO{sub 2}-II, which is the high pressure form of titania with the α-PbO{sub 2} structure, can be prepared from rutile at 6 GPa and 650 °C when employing a hydrothermal environment. Display Omitted.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗