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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Effects of Stoichiometry on Transformation Temperatures and Actuator-Type Performance of NiTiPd and NiTiPdX High-Temperature Shape Memory Alloys

High-temperature shape memory NiTiPd and NiTiPdX (X=Au, Pt, Hf) alloys were produced with titanium equivalent (Ti+Hf) compositions of 50.5, 50.0, 49.5, and 49.0 at.%. Thermo-mechanical testing in compression was used to evaluate the transformation temperatures, transformation strain, work output, and permanent deformation behavior of each alloy to study the effects of quaternary alloying and stoichiometry on high-temperature shape memory alloy behavior. Microstructural evaluation showed the presence of second phases for all alloy compositions. No load transformation temperatures in the stoichiometric alloys were relatively unchanged by Au and Pt substitutions, while the substitution of Hf for Ti causes a drop in transformation temperatures. The NiTiPd, NiTiPdAu and NiTiPdHf alloys exhibited transformation temperatures that were highest in the Ti-rich compositions, slightly lower at stoichiometry, and significantly reduced when the Ti equivalent composition was less than 50 at.%. For the NiTiPdPt alloy, transformation temperatures were highest for the Ti-rich compositions, lowest at stoichiometry, and slightly higher in the Ni-rich composition. When thermally cycled under constant stresses of up to 300 MPa, all of the alloys had transformation strains, and therefore work outputs, which increased with increasing stress. In each series of alloys, the transformation strain and thus work output was highest for stoichiometric or Ti-rich compositions while permanent strain associated with the constant-load thermal cycling was lowest for alloys with Ni-equivalent-rich compositions. Based on these results, basic rules for optimizing the composition of NiTiPd alloys for actuator performance will be discussed.

Bigelow, Glen S.↗
DOE OSTI2019

Methods of resolving artifacts in Hadamard-transformed data

Apparatus and methods are disclosed for processing data transformed according to an invertible transform (e.g., using a Hadamard transform) multiplexing scheme. In one example of the disclosed technology, a computer-implemented method includes generating transformed data by applying a Hadamard transform to intensity data generated by modulating input of analytes into a mass spectrometer according to a pseudorandom sequence (PRS). The exemplary method further includes identifying at least one pair of symmetric intensity peaks in the transformed data based on the PRS and removing data associated with the pair of symmetric peaks from the transformed data to produce modified data, which can be used to identify, characterize, and/or quantify the composition of the sample. In some examples, the exemplary method further includes validating peaks in the transformed data based on comparing the location of peaks in the untransformed intensity data.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Transformation-induced plasticity in bulk metallic glass composites evidenced by in-situ neutron diffraction

Transformation-induced plasticity in a strain-softening amorphous matrix consisting of austenite B2 phase was studied by in-situ neutron diffraction, coupled with molecular dynamic simulation. It was found that the martensitic transformation from B2 to B19' upon loading commenced at the macroscopic yielding which increased with the decrease of the fraction of the parent austenite B2 phase, and the threshold lattice strain for the martensitic transformation is almost the same in different samples, suggesting that the martensitic transformation in the current glassy matrix is strain-controlled. Analysis of load partition and strain accommodation unveiled that B2 has elastic anisotropy, and the desirable elastic match between B2 and the amorphous matrix ensures a good cooperative deformation. Additionally, molecular dynamic simulation revealed that atoms at the interface between B2 and the amorphous matrix deviated from the standard B2 lattices and acted as nucleation site for the martensitic transformation, eventually giving rise to the strain-controlled martensitic transformation. Our findings provide new insights into the mechanism of phase transformation-mediated plasticity at the microscopic level, and have useful implications for developing novel, high-performance bulk metallic glass composites.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Investigation on phase transformation mechanism of zeolite NaY under alkaline hydrothermal conditions

The phase transformation mechanism of zeolite NaY under alkaline hydrothermal conditions was investigated by UV Raman spectroscopy, X-ray diffraction, X-ray fluorescence and scanning electron microscopy techniques. The results revealed that the products and transformation rate are dependent on the alkalinities. All of the starting and resulting zeolites are constructed with the 4-ring and 6-ring secondary building units. The products have lower Si/Al ratio, higher framework density and smaller pore size, which are more stable under alkaline hydrothermal condition. During the phase transformation the fragments of faujasite are formed, then the fragments combine to form different zeolites depending on basicity. Zeolite NaY crystals are consumed as the reservoir for the transformation products during the recrystallization process. For the first time, a 4-membered ring intermediate was found at the early stage of the recrystallization process. A cooperative interaction of liquid and solid phases is required for inducing the phase transformation. - Graphical Abstract: Phase transformation of NaY zeolite under alkaline hydrothermal condition is achieved by the cooperative interaction of the liquid and solid phases. A 4-membered ring species is an intermediate for recrystallization process. Highlights: • The products and transformation rate are dependent on the alkalinity. • A 4-membered ring species is an intermediate for recrystallization process. • A cooperative interaction of liquid and solid phases is required.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Continuous activation of Nrf2 and its target antioxidant enzymes leads to arsenite-induced malignant transformation of human bronchial epithelial cells

Long-term exposure to arsenite leads to human lung cancer, but the underlying mechanisms of carcinogenesis remain obscure. The transcription factor of nuclear factor-erythroid-2 p45-related factor (Nrf2)-mediated antioxidant response represents a critical cellular defense mechanism and protection against various diseases. Paradoxically, emerging data suggest that the constitutive activation of Nrf2 is associated with cancer development, progression and chemotherapy resistance. However, the role of Nrf2 in the occurrence of cancer induced by long-term arsenite exposure remains to be fully understood. By establishing transformed human bronchial epithelial (HBE) cells via chronic low-dose arsenite treatment, we showed that, in acquiring this malignant phenotype, continuous low level of ROS and sustained enhancement of Nrf2 and its target antioxidant enzyme levels were observed in the later-stage of arsenite-induced cell transformation. The downregulation of Keap1 level may be responsible for the over-activation of Nrf2 and its target enzymes. To validate these observations, Nrf2 was knocked down in arsenite-transformed HBE cells by SiRNA transfection, and the levels of Nrf2 and its target antioxidant enzymes, ROS, cell proliferation, migration, and colony formation were determined following these treatments. Results showed that blocked Nrf2 expression significantly reduced Nrf2 and its target antioxidant enzyme levels, restored ROS levels, and eventually suppressed cell proliferation, migration, and colony formation of the transformed cells. In summary, the results of the study strongly suggested that the continuous activation of Nrf2 and its target antioxidant enzymes led to the over-depletion of intracellular ROS levels, which contributed to arsenite-induced HBE cell transformation. - Highlights: • Low level, long term arsenite exposure induces malignant transformation in vitro. • Long term arsenite exposure reduces ROS and MDA levels. • Long term arsenite exposure enhances Nrf2-mediated antioxidant levels. • Knockdown of Nrf2 reduces malignant degree of arsenite-transformed cells.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

Uncovering the role of nanoscale precipitates on martensitic transformation and superelasticity

Here we characterize the role of coherent nanoscale B2 Ni 50 Al 50 precipitates on the temperature- and stress-induced martensitic phase transformation in nanocrystalline Ni 63 Al 37 shape memory alloys using multi-million-atoms molecular dynamics (MD) simulations. We studied two types of precipitates: one with single crystal precipitates (SXP) and a second where grain boundaries cut through precipitates (PXP). Simulations reveal that the presence of B2 precipitates stabilizes the cyclic flag-shaped stress-strain response, characteristic of superelasticity, and reduces remnant strain. In contrast, single-phase nanocrystalline Ni 63 Al 37 exhibits degradation of the reverse transformation during cyclic loading and, eventually, incomplete reversible transformation within a few cycles. This is consistent with previous experimental findings of ultra-low fatigue in Ni-Ti-Cu alloys with Ti 2 Cu precipitates. The simulations reveal that the presence of precipitates significantly improves the reversibility of the transformation by acting as elastic zones that partially shield the martensitic transformation and drive the reverse transformation. A detailed analysis of the MD trajectories reveals that the martensitic transformation of the matrix induces ultra-large elastic deformation in some of the B2 precipitates (approximately 12%) to the point of resulting in a martensite-like atomic structure.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Quantum decoration transformation for spin models

It is quite relevant the extension of decoration transformation for quantum spin models since most of the real materials could be well described by Heisenberg type models. Here we propose an exact quantum decoration transformation and also showing interesting properties such as the persistence of symmetry and the symmetry breaking during this transformation. Although the proposed transformation, in principle, cannot be used to map exactly a quantum spin lattice model into another quantum spin lattice model, since the operators are non-commutative. However, it is possible the mapping in the “classical” limit, establishing an equivalence between both quantum spin lattice models. To study the validity of this approach for quantum spin lattice model, we use the Zassenhaus formula, and we verify how the correction could influence the decoration transformation. But this correction could be useless to improve the quantum decoration transformation because it involves the second-nearest-neighbor and further nearest neighbor couplings, which leads into a cumbersome task to establish the equivalence between both lattice models. This correction also gives us valuable information about its contribution, for most of the Heisenberg type models, this correction could be irrelevant at least up to the third order term of Zassenhaus formula. This transformation is applied to a finite size Heisenberg chain, comparing with the exact numerical results, our result is consistent for weak xy-anisotropy coupling. We also apply to bond-alternating Ising–Heisenberg chain model, obtaining an accurate result in the limit of the quasi-Ising chain.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

A transformed path integral approach for solution of the Fokker–Planck equation

A novel path integral (PI) based method for solution of the Fokker–Planck equation is presented. The proposed method, termed the transformed path integral (TPI) method, utilizes a new formulation for the underlying short-time propagator to perform the evolution of the probability density function (PDF) in a transformed computational domain where a more accurate representation of the PDF can be ensured. The new formulation, based on a dynamic transformation of the original state space with the statistics of the PDF as parameters, preserves the non-negativity of the PDF and incorporates short-time properties of the underlying stochastic process. New update equations for the state PDF in a transformed space and the parameters of the transformation (including mean and covariance) that better accommodate nonlinearities in drift and non-Gaussian behavior in distributions are proposed (based on properties of the SDE). Owing to the choice of transformation considered, the proposed method maps a fixed grid in transformed space to a dynamically adaptive grid in the original state space. The TPI method, in contrast to conventional methods such as Monte Carlo simulations and fixed grid approaches, is able to better represent the distributions (especially the tail information) and better address challenges in processes with large diffusion, large drift and large concentration of PDF. Additionally, in the proposed TPI method, error bounds on the probability in the computational domain can be obtained using the Chebyshev's inequality. The benefits of the TPI method over conventional methods are illustrated through simulations of linear and nonlinear drift processes in one-dimensional and multidimensional state spaces. The effects of spatial and temporal grid resolutions as well as that of the diffusion coefficient on the error in the PDF are also characterized.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Coupled nonlinear elasticity, plastic slip, twinning, and phase transformation in single crystal titanium for plate impact loading

High purity single crystal titanium (Ti) under shockwave loading in plate impact experiment is modelled and simulated, with help of the finite element. A thermodynamically consistent system of equations is formulated in the frame of large deformation to consider material anisotropy, rate dependence, and multi-physics including nonlinear elasticity, dislocation based plastic slip, deformation twinning, and phase transformation. A novel kinematics is proposed to consider phase transformation in the α twin variants and also to consider the dislocation based slip in all of components of parent material, primary twins and the ω phase. The thermodynamically consistent driving forces for plastic slip, twinning, and phase transformation are developed based upon the second law of thermodynamics. For nonlinear elasticity, the stiffness matrix is dependent on the volume fractions of all components, and the volumetric part of Cauchy stress is obtained from the nonlinear equation of state. Dislocation based plastic slip in multi-variant and multiphase heterogeneous materials is developed and interactions of dislocations among all slip modes are taken into account. A mechanism for dislocation density evolution during twinning and phase transformation is proposed. The shock loading along the [0001] and [10$\bar{1}1$ directions of single crystal high purity Ti is investigated computationally. Very good correspondence between simulation and experiment is obtained, which includes pole figures, volume fractions of components, free surface velocity, peak pressure, and phase transformation pressure. Multiple experimental phenomena are interpreted based upon the progression of dislocation slip, deformation twinning, and phase transformation. In compression with the [10$\bar{1}1$ crystal, a higher volume fraction in the primary twins but a lower secondary twin volume fraction in the [0001] crystal in experiment was observed. Finally, the higher propensity for phase transformation occurs in the [0001] crystal is reproduced. In addition to material texture, distributions of temperature, stresses, and plastic strains dependent on the impact loading directions are revealed.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Structural phase transformation of as-prepared Mg–Mn nanoferrites by annealing temperature

As-prepared Mg{sub 0.2}Mn{sub 0.8}Fe{sub 2}O{sub 4} nanoferrite samples by coprecipitation method were annealed at different temperatures T. XRD, TEM, IR, VSM and Mössbauer techniques were used to characterize the samples. This study proved the transformation of the sample structure from cubic spinel to Z-type hexagonal phase at 700 °C. This transformation was assigned to Jahn–Teller effect of the Mn{sup 3+} and Fe{sup 2+} ions and/or atomic disorder in the crystal lattice. All the deduced structural parameters were affected by the transformation process. The infrared and structural parameters showed dependence on T, whereas tetrahedral band position did not. TEM images showed agglomeration of the nanoparticles, where the average particle size ranged 25–55 nm and was a little higher than R. Study on the elastic properties proved the weakening of inter-atomic bonds inside the crystal lattice as T increases. The magnetic properties were affected by the transformation process and showed T dependence, whereas M{sub s} and H{sub c} proved dependence on porosity. Hyperfine interaction parameters, area ratio (B/A) and spontaneous magnetization were discussed as functions of T. - Graphical abstract: The XRD patterns of as-prepared (AP) and annealed Mg{sub 0.2}Mn{sub 0.8}Fe{sub 2}O{sub 4} nanoparticles. - Highlights: • As-prepared Mg–Mn nanoferrites were annealed at different temperatures T. • Sample structure was transformed from cubic to Z-type hexagonal with T. • This transformation was attributed to Jahn–Teller effect and atomic disorder. • The deduced parameters were affected by annealing and transformation process. • The porosity was affected the saturation magnetization and coercivity.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Microstructures and phase transformations of Ti-30Zr-xNb (x = 5, 7, 9, 13 at.%) shape memory alloys

The microstructures, phase transformations and shape memory properties of Ti-30Zr-xNb (x = 5, 7, 9, 13 at.%) alloys were investigated. The X-ray diffraction and transmission electron microscopy observations showed that the Ti-30Zr-5Nb, Ti-30Zr-7/9Nb and Ti-30Zr-13Nb alloys were composed of the hcp α′-martensite, orthorhombic α″-martensite and β phases, respectively. The results indicated the enhanced β-stabilizing effect of Nb in Ti-30Zr-xNb alloys than that in Ti-Nb alloys due to the high content of Zr. The differential scanning calorimetry test indicated that the Ti-30Zr-5Nb alloy displayed a reversible transformation with a high martensitic transformation start temperature of 776 K and a reverse martensitic transformation start temperature (A{sub s}) of 790 K. For the Ti-30Zr-7Nb and Ti-30Zr-9Nb alloys, the martensitic transformation temperatures decreased with the increasing Nb content. Moreover, an ω phase transformation occurred in the both alloys upon heating at a temperature lower than the corresponding A{sub s}, which is prompted by more addition of Nb. Although the critical stress in tension of the three martensitic alloys decreased with increasing Nb content, the Ti-30Zr-9Nb alloy showed a critical stress of as high as 300 MPa. Among all the alloys, the Ti-30Zr-9Nb alloy exhibited the maximum shape memory effect of 1.61%, due to the lowest critical stress for the martensite reorientation. - Highlights: •Ti-30Zr-5Nb alloy is composed of hcp α′-martensite with the M{sub s} of 776 K. •Ti-30Zr-7Nb and Ti-30Zr-9Nb alloys are predominated by orthorhombic α″-martensite. •Ti-30Zr-13Nb alloy consists of a single β phase due to the β-stabilizing effect of Nb. •The martensitic transformation temperatures decrease with increasing Nb content. •Ti-30Zr-9Nb alloy shows the maximum shape memory effect of 1.61%.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Effect of laser scanning speed on the microstructure, phase transformation and mechanical property of NiTi alloys fabricated by $\mathrm{LPBF}$

This study investigated the effects of laser scanning speed on the microstructure, phase transformation and properties of NiTi alloys fabricated by laser powder bed fusion (LPBF). In this study, the contributions of metallurgical factors under different scanning speeds, such as Ni evaporation, Ni4Ti3 precipitation, dislocations and internal stress, to the transformation temperature and transformation latent heat were clarified through specially designed experiments. Ni evaporation is found to have the most profound effect, followed by precipitation. Increasing scanning speed is found to reduce Ni loss, thus cause less increase in the transformation temperature and transformation heat of the LPBF-NiTi alloys. Increasing scanning speed also increases the microstructure non-uniformity and thus widens the transformation temperature interval. The orientations of residual stress exhibit strong crystallographic stiffness dependence. The LPBF-NiTi alloys with different scanning speeds all exhibited high strains (>13.4%) and excellent shape memory effect. A LPBF-NiTi honeycomb structure exhibited 96% shape recovery rate after a 60% pre-compressive deformation. Besides, there is an optimum scanning speed for minimum porosity and smallest average pore size. However, the pore structure is found to have weak influence on the tensile behaviour of the LPBF-NiTi alloys, possibly due to the high defect tolerance of the martensitic transformation.

36 MATERIALS SCIENCE↗
DOE OSTI2014

OCT4 as a target of miR-34a stimulates p63 but inhibits p53 to promote human cell transformation

Human cell transformation is a key step for oncogenic development, which involves multiple pathways; however, the mechanism remains unclear. To test our hypothesis whether cell oncogenic transformation shares some mechanisms with the process of reprogramming non-stem cells to induced pluripotent stem cells (iPSC), we studied the relationship among the key factors for promoting or inhibiting iPSC in radiation-transformed human epithelial cell lines derived from different tissues (lung, breast and colon). We unexpectedly found that p63 and OCT4 were highly expressed (accompanied by low expressed p53 and miR-34a) in all transformed cell lines examined when compared with their non-transformed counterparts. We further elucidated the relationship of these factors: the 3p strand of miR-34a directly targeted OCT4 by binding to the 30 untranslated region (30 -UTR) of OCT4 and, OCT4, in turn, stimulated p63 but inhibited p53 expression by binding to a specific region of the p63 or p53 promoter. Moreover, we revealed that the effects of OCT4 on promoting cell oncogenic transformation were by affecting p63 and p53. These results support that a positive loop exists in human cells: OCT4 upregulation as a consequence of inhibition of miR-34a, promotes p63 but suppresses p53 expression, which further stimulates OCT4 upregulation by downregulating miR-34a. This functional loop contributes significantly to cell transformation and, most likely, also to the iPSC process.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2014

Effect of niobium addition on the martensitic transformation and magnetocaloric effect in low hysteresis NiCoMnSn magnetic shape memory alloys

The effect of Nb substitution for Ni in Ni{sub 45}Co{sub 5}Mn{sub 40}Sn{sub 10} magnetic shape memory alloys on their magnetic properties, martensitic transformation characteristics, transformation hysteresis, and magnetocaloric properties was studied using wavelength-dispersive X-ray spectroscopy, differential scanning calorimetry, and the temperature and field dependence of the magnetization. Ni{sub 45}Co{sub 5}Mn{sub 40}Sn{sub 10} alloy has a very low transformation hysteresis; however, the martensitic transformation temperatures are notably above room temperature, which is not desirable for magnetic refrigeration applications. In this study, small quantities of Nb substitution were shown to drastically shift the transformation temperatures to lower temperatures, at a rate of 68 K/at. % Nb, which is needed for household refrigeration. The austenite Curie temperature also decreased with increasing Nb content. However, a decrease in the latent heat of the martensitic transition was observed, which negatively affects the magnetic field-induced adiabatic temperature change capability. Still, the relatively large transformation entropy and the low transformation hysteresis make the Nb-doped Ni{sub 45}Co{sub 5}Mn{sub 40}Sn{sub 10} alloys potential candidates for solid state refrigeration near room temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Pressure, temperature, and electric field dependence of phase transformations in niobium modified 95/5 lead zirconate titanate

Ceramic niobium modified 95/5 lead zirconate-lead titanate (PZT) undergoes a pressure induced ferroelectric to antiferroelectric phase transformation accompanied by an elimination of polarization and a volume reduction. Electric field and temperature drive the reverse transformation from the antiferroelectric to ferroelectric phase. The phase transformation was monitored under pressure, temperature, and electric field loading. Pressures and temperatures were varied in discrete steps from 0 MPa to 500 MPa and 25 °C to 125 °C, respectively. Cyclic bipolar electric fields were applied with peak amplitudes of up to 6 MV m{sup −1} at each pressure and temperature combination. The resulting electric displacement–electric field hysteresis loops were open “D” shaped at low pressure, characteristic of soft ferroelectric PZT. Just below the phase transformation pressure, the hysteresis loops took on an “S” shape, which split into a double hysteresis loop just above the phase transformation pressure. Far above the phase transformation pressure, when the applied electric field is insufficient to drive an antiferroelectric to ferroelectric phase transformation, the hysteresis loops collapse to linear dielectric behavior. Phase stability maps were generated from the experimental data at each of the temperature steps and used to form a three dimensional pressure–temperature–electric field phase diagram.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

A High-Rate, Single-Crystal Model for Cyclotrimethylene Trinitramine including Phase Transformations and Plastic Slip

A continuum model for the high-rate, thermo-mechanical deformation of single-crystal cyclotrimethylene trinitramine (RDX) is developed. The model includes the effects of anisotropy, large deformations, nonlinear thermo-elasticity, phase transformations, and plastic slip. A multiplicative decomposition of the deformation gradient is used. The volumetric elastic component of the deformation is accounted for through a free-energy based equation of state for the low- (α) and high-pressure (γ) polymorphs of RDX. Crystal plasticity is addressed using a phenomenological thermal activation model. The deformation gradient for the phase transformation is based on an approach that has been applied to martensitic transformations. Simulations were conducted and compared to high-rate, impact loading of oriented RDX single crystals. The simulations considered multiple orientations of the crystal relative to the direction of shock loading and multiple sample thicknesses. Thirteen slip systems, which were inferred from indentation and x-ray topography, were used to model the α-polymorph. It is shown that by increasing the number of slip systems from the previously considered number of six (6) to thirteen (13) in the α-polymorph, better comparisons with data may be obtained. Simulations of impact conditions in the vicinity of the α- to γ-polymorph transformation (3.8 GPa) are considered. Eleven of the simulations, which were at pressures below the transformation value (3.0 GPa), were compared to experimental data. Comparison of the model was also made with available data for one experiment above the transformation pressure (4.4 GPa). Also, simulations are provided for a nominal pressure of 7.5 GPa to demonstrate the effect of the transformation kinetics on the deformation of a high-rate plate impact problem.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Restoring permutational invariance in the Jordan–Wigner transformation

The Jordan–Wigner transformation is a powerful tool for converting systems of spins into systems of fermions, or vice versa. While this mapping is exact, the transformation itself depends on the labelling of the spins. One consequence of this dependence is that approximate solutions of a Jordan–Wigner-transformed Hamiltonian may depend on the (physically inconsequential) labelling of the spins. In this work, we turn to an extended Jordan–Wigner transformation which remedies this problem and which may also introduce some correlation atop the Hartree–Fock solution of a transformed spin Hamiltonian. We demonstrate that this extended Jordan–Wigner transformation can be thought of as arising from a unitary version of the Lie algebraic similarity transformation (LAST) theory. Here, we show how these ideas, particularly in combination with the standard (non-unitary) version of LAST, can provide a potentially powerful tool for the treatment of the XXZ and J 1 –J 2 Heisenberg Hamiltonians.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

High-Frequency Transformer Design for Modular Power Conversion From Medium-Voltage AC to 400 VDC

This paper presents a high-frequency modular medium-voltage AC (4160 VAC or 13.8 kVAC) to low-voltage DC (400 VDC) system that is scalable in order to be used for different scale microgrids. A 15 kW, 500 kHz DC/DC converter is demonstrated as the most important stage of the system overall, which can be scalable to a 225 kW 4160 VAC to 400 VDC system. Motivation of a CLLC resonant converter and its design parameters determination is carefully illustrated. The high-frequency transformer is the key element for the DC/DC converter. Then, the paper focuses on high-frequency transformer design to realize high-voltage insulation, high efficiency, and high density at the same time. Based on a split winding UU core transformer structure, transformer insulation materials and dimension parameters are determined referring to the IEEE insulation standard. The transformer magnetic loss model is reviewed based on which loss design tradeoff is carefully analyzed. Different working frequency impact on transformer design over three different core materials is also presented. Finally, a 500 kHz transformer prototype has been developed and demonstrated with the IEEE standard required insulation tests. A whole CLLC resonant converter is also present with experiments results. Here, the converter holds outstanding 98% efficiency and 2.9 kW/L power density.

42 ENGINEERING↗