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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 1,351 records · Page 75
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Estimation of Participation Factors Using the Synchrosqueezed Wavelet Transform

This paper proposes a data-driven approach for estimating participation factors for a power system using only simulation results on selected disturbances. The approach is purely response-based and does not need a linearized system model for eigen-analysis, which makes it applicable to systems whose detailed, complete mathematical models are not available. Considering the unavoidable nonlinearity as exhibited in the transient period of a system response, the Synchrosqueezed Wavelet Transform is applied to simulated responses for modal analysis to obtain participation factors. Based on simulations of Kundur's two-area system using both the electromagnetic transient model and phasor model, the participation factors estimated by the proposed approach are compared with two other signal processing tools, the Prony analysis and continuous wavelet transform, and are also benchmarked with conventional model-based participation factors.

participation factor↗
DOE OSTI2022

Predictive Direct DC-Link Control for 7.2 kV Three-Port Low-Inertia Solid-State Transformer With Active Power Decoupling

Promising for applications including renewable energy and electric vehicle fast charging, a medium-voltage (MV) solid-state transformer (SST) typically has multiple modules series stacked, which requires the modules to be single phase. One critical issue of the single-phase SST is the double-line-frequency power ripple. Traditionally, large passives are used to buffer the ripple, resulting in significantly increased volume and cost. This article for the first time proposes active power decoupling (APD) for the SST and a predictive direct DC-link control method, using a current-source single-stage SST as an example. An electrolytic capacitor-less buffer port is used to absorb the ripple, which tolerates up to a 30% voltage ripple for small capacitance. The APD SST control is challenging. First, the current-source SST realizes isolation, DC link, and multiport in a single stage. Second, different from conventional SSTs or APD converters, the low-inertia DC link in this SST has a 40% switching ripple, which is difficult to stabilize. To address the control challenge, a direct DC-link control architecture and a predictive control method are proposed. Simulation and experimental results verify the proposed control method on an MV SiC modular soft-switching solid-state transformer (M-S4T) prototype. Here, the proposed APD reduces the SST volume by 53.8%. Importantly, the proposed concept is not limited to the M-S4T but is generic to other SSTs or APD converters.

14 SOLAR ENERGY↗
NASA NTRS1994

Oncogenic transformation through the cell cycle and the LET dependent inverse dose rate effect

Synchronised populations of mouse C3H/10T-1/2 cells were obtained by a stringent mitotic dislodgment procedure. Mitotic cells rapidly attach and progress sequentially through the cell cycle. Irradiation (3 Gy of X rays) was carried out at intervals from 0 to 18 h after initiating cell cycle progression of the mitotic cells. Oncogenic transformation was enhanced 10-fold over cells irradiated soon after replating (G1 and S phases) for cells in a near 2 h period corresponding to cells in G2 phase but not in mitosis. The cell surviving fraction had a 2-1/2-fold variation with resistant peaks corresponding to the late G1 and late S phases. These findings provide experimental support for the hypothesis initiated by Rossi and Kellerer and developed by Brenner and Hall to explain the LET dependent inverse dose rate effect for oncogenic transformation.

NASA Discipline Radiation Health↗
DOE OSTI2025

Atomically Revealing Bulk Point Defect Dynamics in Hydrogen‐Driven γ‐Fe 2 O 3 → Fe 3 O 4 → FeO Transformation

Understanding how point defects in the bulk govern redox transformations is essential for advancing hydrogen-based metal production and designing high-performance oxide materials. This study reveals the atomic-scale mechanisms driving hydrogen-induced reduction of γ-Fe 2 O 3 to Fe 3 O 4 , focusing on how bulk vacancy dynamics dictate structural evolution and reaction kinetics. A key finding is the pronounced contrast in defect behavior between the two oxides: in γ-Fe 2 O 3 , intrinsic Fe vacancies promote oxygen vacancy clustering, destabilizing the local lattice and driving nanopore formation. In contrast, Fe 3 O 4 exhibits a higher oxygen vacancy formation energy and lacks intrinsic Fe vacancies, suppressing vacancy aggregation and maintaining a dense, pore-free structure. This divergence governs distinct reduction pathways—γ-Fe 2 O 3 undergoes an interface-reaction-limited transformation confined to the γ-Fe 2 O 3 /Fe 3 O 4 boundary, while Fe 3 O 4 supports a uniform increase in oxygen vacancy concentration, enabling bulk-phase reduction to lower-oxide FeO. Integrated in situ electron microscopy and density functional theory modeling uncover a vacancy-mediated mechanism, where synergistic cation-anion vacancy dynamics steer microstructure evolution and phase progression. These insights highlight the critical role of vacancy dynamics in controlling oxide reactivity and offer a pathway toward vacancy engineering to enhance reduction kinetics in hydrogen metallurgy and to tailor porosity, reactivity, and structural resilience in oxide-based catalysts and energy materials.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Salt-Assisted 2H-to-1T' Phase Transformation of Transition Metal Dichalcogenides [plus supplemental information]

Phase engineering of nanomaterials (PEN) has demonstrated great potential in the fields of catalysis, electronics, energy storage and conversion, and condensed matter physics. Recently, transition metal dichalcogenides (TMDs) with unconventional metastable phases (e.g., 1T and 1T') have attracted increasing research interest due to their unique and appealing physicochemical properties. However, there is still a lack of a simple, universal, and controlled method for the preparation of large-scale and high-purity unconventional-phase TMD crystals, restricting their further fundamental study and practical applications. Here, a facile, one-step salt-assisted general strategy is reported for the controlled phase transformation of commercially available TMDs with conventional 2H phase, yielding a large amount of metastable 1T'-phase TMDs, including WS 2 , WSe 2 , MoS 2 , and MoSe 2 . It is found that the easily accessible metal salts, such as K 2 C 2 O 4 ·H 2 O, K 2 CO 3 , Na 2 CO 3 , Rb 2 CO 3 , Cs 2 CO 3 , KHCO 3 , NaHCO 3 , and NaC 2 O 4 , can be used to assist the 2H-to-1T' phase transformation, greatly simplifying the synthetic process for producing metastable 1T'-TMDs. Importantly, this method can also be used to prepare 1T'-TMD alloys, such as 1T'-WS 2x Se 2(1–x) . We report this newly developed strategy is robust and highly effective, which can also be used for the phase engineering of other materials with various polymorphs.

1T′ phase↗
DOE OSTI2017

Test of 6-kVA Three-Phase Flux Transfer-Type Current-Limiting Transformer

A 6-kVA three-phase model of the flux transfer-type current-limiting transformer was developed and tested. In this device, the winding loops of YBCO superconducting tapes couple magnetically two independent iron cores: the primary-side iron core and the secondary-side iron core. The former and the latter are equipped with copper primary and secondary windings, respectively. Because the magnetic fluxes linked to the superconducting winding loops must be kept constant, the magnetic flux is transferred by the superconducting YBCO loops between the two iron cores in order to couple magnetically the primary and secondary coils. While the YBCO loops are superconducting, 100 % of the magnetic flux is transferred and the device shows the similar function as usual transformers. Once the YBCO loops become normal by a fault current in any of the windings, the power transfer between two iron cores is limited and the current in the secondary winding is limited naturally on a result of decoupling the iron cores.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

An Agrobacterium strain auxotrophic for methionine is useful for switchgrass transformation

Abstract Auxotrophic strains of Agrobacterium tumefaciens can contribute to the development of more efficient transformation systems, especially for crops historically considered recalcitrant. Homologous recombination was used to derive methionine auxotrophs of two common A. tumefaciens strains, LBA4404 and EHA105. The EHA105 strains were more efficient for switchgrass transformation, while both the EHA105 and LBA4404 strains worked equally well for the rice control. Event quality, as measured by transgene copy number, was not affected by auxotrophy, but was higher for the LBA4404 strains than the EHA105 strains. Ultimately, the use of auxotrophs reduced bacterial overgrowth during co-cultivation and decreased the need for antibiotics.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Control of Carbon Content in Steel by Introducing Proeutectoid Ferrite Transformation into Hot-Rolled Q&P Process

A processing strategy involving primary and secondary carbon partitioning is proposed for the hot-rolled quenching and partitioning process through the introduction of proeutectoid ferrite transformation after rolling. The microstructures of the steels were characterized using scanning electron microscopy, transmission electron microscopy, electron probe microanalysis, and x-ray diffraction, and the mechanical properties were evaluated using a universal tensile machine. The blocky retained austenite that distributed along the ferrite grain boundaries was promoted based on the coupling action of the primary and secondary carbon partitioning, which enhanced the transformation-induced plasticity effect during deformation despite the high carbon concentration. A ferrite formation temperature range of ~ 760 to 800 °C was proposed. In addition, from the perspective of industrialization, the observed ‘plateau trends’ for the retained austenite fraction and product of strength and elongation suggest the availability of a wide processing window of 215-362 °C for controlling the coiling temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Influence of Boron on Austenite to Ferrite Transformation Behavior of Low Carbon Steel Under Continuous Cooling

In the current work, the influence of boron on austenite to ferrite transformation behavior under continuous cooling condition and its associated features, e.g., final microstructure, mechanical properties, etc., in low carbon steel has been studied. The steels (C 0.04 wt.%, B 10-100 ppm) prepared in an open air laboratory furnace showed identical microstructures having ferrite grains of 20-25 µm. However, tensile test data indicate variation of yield strength and ultimate tensile strength with boron content. The yield point elongation and strain aging index both were found to decrease with increase in boron content or boron-to-nitrogen ratio. As the boron nitride precipitates stimulate the nucleation of ferrite phase, the dilation curves show an increase in austenite to ferrite transformation start temperature with boron content. The resulting microstructure and hardness value also corroborate the finding. Transmission electron microscopy findings revealed the presence of ultra-fine boron nitride (BN) precipitates in both grain boundary and grain body of the steel having boron concentration of 30 ppm and beyond. The presence of these precipitates also increased with boron content. Based on austenite decomposition behavior, related microstructure and hardness values it is conjectured that these BN precipitates may act as nucleating agent for polygonal ferrite during austenite decomposition, thereby softening the steel during fast cooling.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The Effects of Alloying Elements on the Continuous Cooling Transformation Behavior of 2¼Cr-1Mo Steels

The continuous cooling transformation (CCT) behavior of eight 2¼Cr-1Mo steels from a statistically designed matrix was determined. These steels contained two levels of carbon (0.07 and 0.16 wt.%), manganese (0.35 and 0.85%), chromium (1.5 and 2.8%), and molybdenum (0.3 and 1.25%). Each steel was tested in a quenching dilatometer at five to six cooling rates between 725 and 1.2 °C/min. For each CCT sample, the change in length, microstructure, and macrohardness were determined. The ferrite content was also measured for samples cooled near the ferrite nose. Pearson correlation and multiple regression analyses were performed for various CCT diagram parameters. The correlation analysis showed that carbon and chromium contents significantly affected the critical temperatures and the bainite and martensite transformation temperatures. Increasing carbon content significantly increased the hardness for the bainite and martensite range of cooling rates, but hardness at slower cooling rates was unaffected by alloying elements. Regression equations were obtained for the critical temperatures and the ferrite nose cooling rate.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effects of Solution Treatment on Microstructure Transformation, Tensile and Exfoliation Corrosion Properties of 7136 Aluminum Alloy

The effects of solution treatment on microstructure transformation and tensile properties of 7136 aluminum alloys were investigated by means of scanning electron microscopy, electron backscatter diffraction, differential scanning calorimeter, x-ray diffraction and tensile test, electrochemical evaluations, exfoliation corrosion tests, respectively. The results indicate that solution treatment had a significant effect on the microstructure transformation and tensile properties. Soluble constituents of 7136 aluminum alloys were more likely to form the η(MgZn{sub 2}) phase rather than the S(Al{sub 2}CuMg) phase. With increasing the solution temperature, the η phase was re-dissolved into the α(Al) matrix gradually. After solution treatment of 475 °C/1 h, the η phase was completely dissolved into the matrix, with insoluble Fe-rich phases remained. The dissolution of η phase would increase the strength and the corrosion resistance of the alloys. When continuing to increase the solution temperature, the recrystallized fraction increased obviously, resulting in the decrease in the strength and the corrosion resistance. Consequently, the strength and the corrosion resistance of the alloys increased firstly and then decreased with the increase in solution temperature. After solution treatment of 475 °C/1 h, the tensile strength and yield strength of the aged alloy reached their peaks, 738 and 715 MPa, respectively. The elongation of the alloy solution treated at 475 °C/1 h reached 11.2%, and its exfoliation corrosion rating got EB level. Furthermore, after the double-stage solution treatment of 450 °C/1 h + 475 °C/1 h, the recrystallized fraction decreased, resulting in a slight increase to 12.6% of the elongation, a slight increase in the corrosion resistance and a slight decrease in the strength.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Characterizing Transformation Phenomena and Elastic Moduli of Austenite and Oriented Martensite of Superelastic Thin NiTi Wire through Isothermal Dynamic Mechanical Analysis

In this paper, superelastic behavior of nickel-titanium thin wires is characterized using the method of dynamic mechanical analysis. Nominal dynamic storage modulus E{sup ′} is measured as function of nominal strain and stress during isothermal superelastic tensile tests at three testing temperatures above the reverse martensitic transformation finish temperature. The method brings new information on deformation mechanisms compared to the consideration of only tensile stress–strain curves. It is shown that determination of the elastic moduli E, especially at high strain, requires to calculate the true storage modulus E{sub t}{sup ′}. Using E{sub t}{sup ′} and not E{sup ′}, elastic modulus of oriented martensite E{sub M} is determined equal to 73 GPa of the same order than the elastic modulus of austenite E{sub A} equal to 70 GPa. Two models are then proposed to simulate experimental storage moduli evolution during the tests. A first model explains the E{sup ′} evolution during stress plateau by the localization phenomenon; it leads to express E{sup ′} as function of the nominal strain. A second model describes the evolution of E{sub t}{sup ′} after the stress plateau as function of true stress and test temperature. This model permits to determine the Clausius–Clapeyron coefficient of the forward transformation.

36 MATERIALS SCIENCE↗
DOE OSTI2019

The Evolution of Deformation-Induced Carbides during Divorced Eutectoid Transformation in GCr15 Steels

A series of rolling experiments were carried out using GCr15 steel to investigate the effect of initial microstructure on the spheroidizing process, and especially the effect of deformation-induced carbides (DIC) on the divorced eutectoid transformation (DET). The results indicated that the existence of DIC was beneficial to the spheroidizing process, the optimal initial microstructure for DET was lamellar pearlite, and DIC precipitated at grain boundaries. The average thickness of the cementite lamella and the size of DIC decreased with a decrease in rolling temperature in the critical temperature region. When the specimen was rolled at 1053 K, a small amount of DIC of size ~ 1 μm precipitated at grain boundaries. In contrast, the amount of DIC was increased when the rolling temperature was decreased to 1023 K, whereas the size of DIC was reduced to ~ 0.5 μm. Interrupted quenching experiments indicated that DIC (M{sub 7}C{sub 3}) were transformed to M{sub 3}C during the process of partial austenitization, and the evolution of spheroidization was influenced by the variation in the initial microstructure. For the specimens rolled at 1023 K, only ~ 60 min was needed to achieve the dissolution of DIC, which was the minimum, and the total time needed to achieve spheroidization was reduced to ~ 90 min.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microstructural and Textural Evolutions during β → α/ω Transformation in Biomedical Ti-15Mo Alloy and Its Effects on Mechanical Performance

This study investigated the precipitation behaviors and mechanical performance of Ti-15Mo alloy subjected to different treatment conditions. The microstructures were analyzed via scanning electron microscopy and transmission electron microscopy. The tensile properties and resultant fracture surfaces were investigated to determine the relationship between the phase transformation and mechanical performance. The Ti-15Mo alloy had a notable elongation due to no observable precipitation during solution treatment plus quenching (STQ). A high ultimate tensile strength (UTS) was obtained with a considerable amount of ω precipitates transformed during air cooling after solution treatment (ST). The coarse precipitates and additional precipitation free zones in the Ti-15Mo alloy treated with furnace cooling (FC) after ST induced a decrease in UTS. Furthermore, the absence of a continuous grain boundary α phase resulted in a lower strength in the specimen annealed at 600 °C after hot rolling. The alloy iso-aged after STQ exhibited good tensile properties with a UTS of 920 MPa and an elongation of 15%. The texture and variant relationship of the precipitates was analyzed with x-ray diffraction and electron backscatter diffraction. The common variants of the β matrix influenced the nucleation of precipitates in the Ti-15Mo alloy annealed after hot rolling, and the precipitates showed an obvious {01-10}α main texture. The variant selection of α precipitates at the grain boundary was caused by the two adjacent β grains in the alloy treated by FC after ST.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Modeling of Martensite Transformation in White Layer under Thermo-mechanical Coupling in Hard-Cutting Process

Martensite volume fraction determines the hardness and wear resistance of workpiece, predicting the martensite volume fraction of the white layer is of great significance for improving the surface quality of the workpiece. Accordingly, a theoretical model on the martensite volume fraction was developed in combination with the martensite transformation temperature model and the hard-cutting FE model. A finite element (FE) model of the hard-cutting was established to obtain the stress distribution of the workpieces. A calculation model of martensite phase transformation temperature M{sub S} under the influence of the cooling rate and stress was deduced based on the change of Gibbs free energy. A theoretical model of martensite volume fraction f{sub M} of the white layer was developed based on the M{sub S} and the FE simulations. The f{sub M} calculated by the theoretical model is in accordance with the experimental result. The effects of cutting speed, feed rate, flank wear and tool rake angle on the f{sub M} in the white layers were predicted and analyzed; the results show that the f{sub M} decreases first and then increases with the cutting speed, decreases with the feed rate and the flank wear, and increases with the tool rake angle.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Phase transformations in steels: Processing, microstructure, and performance

In this study, contemporary steel research is revealing new processing avenues to tailor microstructure and properties that, until recently, were only imaginable. Much of the technological versatility facilitating this development is provided by the understanding and utilization of the complex phase transformation sequences available in ferrous alloys. Today we have the opportunity to explore the diverse phenomena displayed by steels with specialized analytical and experimental tools. Advances in multi-scale characterization techniques provide a fresh perspective into microstructural relationships at the macro- and micro-scale, enabling a fundamental understanding of the role of phase transformations during processing and subsequent deformation.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Fast Fourier Transform for multivariate aggregate claims

The Fast Fourier Transform provides an alternative approximate method to evaluate the distribution of aggregate losses in insurance and finance. The efficiency of this method has already been proved for univariate and bivariate insurance models; therefore, in this paper, we extend it to a multivariate setting by considering its application to a particular model that includes losses of different types and dependency between them. Since the Fourier transform method works with truncated claims distributions, it can generate aliasing errors by wrapping around the probability mass that lies at the truncation point below this point. To eliminate this problem, we also discuss a suitable change of measure called exponential tilting that forces the tail of the distribution to decrease at exponential rate. Other possible errors are also discussed. We also illustrate the method on several numerical examples.

97 MATHEMATICS AND COMPUTING↗