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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Absence of Nanostructuring in NaPb m SbTe m+2 : Solid Solutions with High Thermoelectric Performance in the Intermediate Temperature Regime

Thermoelectric devices directly convert heat into electrical energy and are highly desired for emerging applications in waste heat recovery. Currently, PbTe based compounds are the leading thermoelectric materials in the intermediate temperature regime (~800 K); however, integration into commercial devices has been limited. This is largely because the performance of PbTe, which is maximized ~900 K, is too low over the temperatures of interest for most potential commercial applications (generally under 600 K). Improving the low temperature performance of PbTe based materials is therefore critical to achieve usage outside of existing niche applications. Here, we provide an in-depth study of the cubic NaPb m SbTe m+2 system of compounds (m = 1-20) and report that it is an excellent class of low- to medium-temperature thermoelectrics when m = 10-20. Here, we show that the as-cast polycrystalline ingots exhibit degenerate p-type conduction and high maximum ZTs of 1.2-1.4 at 650 K when m = 6-20. Because the ingots are found to be extremely brittle, we utilize spark plasma sintering (SPS) to prepare more mechanically robust samples, and surprisingly, find that SPS results in an undesired change in charge transport toward n-type behavior. We show this unanticipated transition from p-type behavior as ingots to n-type after SPS is due to dissolution of secondary phases that are present in the ingots into the primary matrix during the SPS process, resulting in a transformation from an inhomogeneous state to a solid solution without any observable evidence of nanoscale precipitation. This is in sharp contrast to the seemingly similar AgPb m SbTe m+2 (LAST) system, which is heavily nanostructured. The SPSed NaPb m SbTe m+2 is doped p-type by tuning the cation stoichiometry, i.e., Na 1+x Pb m-x Sb 1-y Te m+2 . The optimized compounds have very low lattice thermal conductivities of 1.1-0.55 W·m -1 ·K -1 over 300-650 K, which enhances the low intermediate temperature performance and gives rise to maximum ZT values up to 1.6 at 673 K as well as an excellent ZT avg of 1.1 over 323-673 K for m = 10, 20, making Na 1+x Pb m-x Sb 1-y Te m+2 among the highest performing PbTe-based thermoelectrics under 650 K.

Electrical conductivity↗
DOE OSTI2014

A note on the application of the Prigogine theorem to rotation of tokamak-plasmas in absence of external torques

Rotation of tokamak-plasmas, not at the mechanical equilibrium, is investigated using the Prigogine thermodynamic theorem. This theorem establishes that, for systems confined in rectangular boxes, the global motion of the system with barycentric velocity does not contribute to dissipation. This result, suitably applied to toroidally confined plasmas, suggests that the global barycentric rotations of the plasma, in the toroidal and poloidal directions, are pure reversible processes. In case of negligible viscosity and by supposing the validity of the balance equation for the internal forces, we show that the plasma, even not in the mechanical equilibrium, may freely rotate in the toroidal direction with an angular frequency, which may be higher than the neoclassical estimation. In addition, its toroidal rotation may cause the plasma to rotate globally in the poloidal direction at a speed faster than the expression found by the neoclassical theory. The eventual configuration is attained when the toroidal and poloidal angular frequencies reaches the values that minimize dissipation. The physical interpretation able to explain the reason why some layers of plasma may freely rotate in one direction while, at the same time, others may freely rotate in the opposite direction, is also provided. Invariance properties, herein studied, suggest that the dynamic phase equation might be of the second order in time. We then conclude that a deep and exhaustive study of the invariance properties of the dynamical and thermodynamic equations is the most correct and appropriate way for understanding the triggering mechanism leading to intrinsic plasma-rotation in toroidal magnetic configurations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Absence of anomalous Nernst effect in spin Seebeck effect of Pt/YIG

The Pt/YIG structure has been widely used to study spin Seebeck effect (SSE), inverse spin Hall effect, and other pure spin current phenomena. However, the magnetic proximity effect in Pt when in contact with YIG, and the potential anomalous Nernst effect (ANE) may compromise the spin current phenomena in Pt/YIG. By inserting a Cu layer of various thicknesses between Pt and YIG, we have separated the signals from the SSE and that of the ANE. It is demonstrated that the thermal voltage in Pt/YIG mainly comes from spin current due to the longitudinal SSE with negligible contribution from the ANE.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Absence of evidence for chiral Majorana modes in quantum anomalous Hall-superconductor devices

A quantum anomalous Hall (QAH) insulator coupled to an s-wave superconductor is predicted to harbor chiral Majorana modes. A recent experiment interprets the half-quantized two-terminal conductance plateau as evidence for these modes in a millimeter-size QAH-niobium hybrid device. However, non-Majorana mechanisms can also generate similar signatures, especially in disordered samples. Here, we studied similar hybrid devices with a well-controlled and transparent interface between the superconductor and the QAH insulator. When the devices are in the QAH state with well-aligned magnetization, the two-terminal conductance is always half-quantized. Our experiment provides a comprehensive understanding of the superconducting proximity effect observed in QAH-superconductor hybrid devices and shows that the half-quantized conductance plateau is unlikely to be induced by chiral Majorana fermions in samples with a highly transparent interface.

Science & Technology - Other Topics↗
DOE OSTI2018

Wound healing-related properties detected in an experimental model with a collagen gel contraction assay are affected in the absence of tenascin-X

Highlights: • Contraction of collagen gels containing MEFs is promoted in the absence of TNX. • Activities of MMPs in collagen gels with MEFs are increased in the absence of TNX. • TGF-β1 level in collagen gels including MEFs is increased in the absence of TNX. • Actin polymerization of MEFs in collagen gels is activated in the absence of TNX. • Cell migration of MEFs in collagen gels is promoted in the absence of TNX. Patients with tenascin-X (TNX)-deficient type Ehlers-Danlos syndrome (EDS) do not exhibit delayed wound healing, unlike classic type EDS patients, who exhibit mutations in collagen genes. Similarly, in TNX-knockout (KO) mice, wound closure of the skin is normal even though these mice exhibit a reduced breaking strength. Therefore, we speculated that the wound healing process may be affected in the absence of TNX. In this study, to investigate the effects of TNX absence on wound healing-related properties, we performed collagen gel contraction assays with wild-type (WT) and TNX-KO mouse embryonic fibroblasts (MEFs). Collagen gels with embedded TNX-KO MEFs showed significantly greater contraction than those containing WT MEFs. Subsequently, we assessed collagen gel contraction-related properties, such as the activities of matrix metalloproteinase (MMP)-2 and MMP-9 and the protein and mRNA expression levels of transforming growth factor β1 (TGF-β1) in the collagen gels. The activities of MMP-2 and MMP-9 and the expression level of TGF-β1 were elevated in the absence of TNX. Furthermore, filopodia-like protrusion formation, cell proliferation, migration, and collagen expression in MEFs were promoted in the absence of TNX. These results indicate that these wound healing-related properties are affected in a TNX-deficient extracellular environment.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Distorted antibody repertoire developed in the absence of pre-B cell receptor formation

Highlights: • Leaky B cells in SLC-deficient mice circumvent the pre-BCR checkpoint. • Antibody repertoires differing in VDJ-usage exist in leaky B cells in λ5{sup −}/{sup −} mice. • Leaky B cells do not originate from B1 or particular B2 cells. • The CDR-H3 middle loop in λ5{sup −}/{sup −} bone marrow B cells is enriched in arginines. The pre-B cell receptor (pre-BCR), consisting of the μ heavy chain (μHC) and the surrogate light chain (SLC, Vpre-B and λ5), plays important roles during B cell development. The formation of the pre-BCR, which enables the nascent immunoglobulin HC to associate with the SLC, is considered a prerequisite for B cell development. However, a significant number of peripheral mature (leaky) B cells exist in SLC-deficient mice. These leaky B cells develop in the absence of pre-BCR and do not undergo the pre-BCR checkpoint. The antibody repertoires of leaky B cells thus reflect the absence of pre-BCR function. To investigate how the absence of the pre-BCR is circumvented by these leaky-B cells and examine the effect of the pre-BCR checkpoint on the antibody system, we analyzed the antibody repertoires of λ5-deficient (λ5{sup −/−}) mice using next-generation sequencing. In λ5{sup −/−} mice, spleen B cells displayed different patterns of VDJ-usage, relative to those in wild-type (WT) mice. Moreover, leaky B cells were neither derived from unusual B2 cells, characterized by particular LC gene rearrangements in the absence of pre-BCR signaling, nor from B1 cells, originating from different B cell progenitors. Analysis of the CDR-H3 amino acid sequences of μ-chain repertoires revealed that certain bone marrow B cells with particular CDR-H3 profiles undergo clonal expansion in λ5{sup −/−} mice. Part of these CDR-H3s contain arginine(s) in the middle of the CDR-H3 loop in λ5{sup −/−} mice, whereas few arginine(s) exist in this middle loop in WT CDR-H3s in the absence of clonal expansion. This CDR-H3 feature in λ5{sup −/−} mice presumably reflects the role of the pre-BCR in autoantibody regulation, since arginine(s) are often found in the antigen-binding site of autoantibodies. Here, we present a unique viewpoint on the role of pre-BCR, by assessing the whole antibody repertoire formed in SLC-deficient mice.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

A Prospective Study of Ventilation Rates and Illness Absence in California Office Buildings

Background – This study investigated the associations of ventilation rates (VRs), estimated from indoor CO2 concentrations, in offices with the amount of respiratory infections, illness absences, and building-related health symptoms in occupants. Methods – Office buildings were recruited from three California climate zones. In one or more study spaces within each building, real-time logging sensors measured carbon dioxide, temperature, and relative humidity for one year. Ventilation rates were estimated using daily peak CO2 levels, and also using an alternative metric. Data on occupants and health outcomes were collected through web-based surveys every three months. Multivariate models were used to assess relationships between metrics of ventilation rate or CO2 and occupant outcomes. For all outcomes, negative associations were hypothesized with VR metrics, and positive associations with CO2 metrics. Results – Difficulty recruiting buildings and low survey response limited sample size and study power. In 16 studied spaces within 9 office buildings, VRs were uniformly high over the year, from twice to over nine times the California office VR standard (7 L/s or 15 cfm per person). VR and CO2 metrics had no statistically significant relationships with occupant outcomes, except for a small significantly positive association of the alternative VR metric with respiratory illness-related absence, contrary to hypotheses. Conclusions– The very high time-averaged VRs in the California office buildings studied presumably resulted from “economizer cycles” bringing in large volumes of outdoor air; however, in almost all buildings even the estimated minimum VRs supplied (without the economizer) substantially exceeded the minimum required VR. These high VRs may explain the absence of hypothesized relationships with occupant outcomes. Among uniformly high VRs, little variation in contaminant concentration and occupant effects would be expected. These findings may provide initial evidence for an upper bound of the range of VRs within which increased VRs provide benefits in reducing illness absence.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Association of Cortical ß-Amyloid Protein in the Absence of Insoluble Deposits With Alzheimer Disease.

IMPORTANCE: ß-Amyloid deposits are a pathologic hallmark of Alzheimer disease (AD). However, the extent to which cortical ß-amyloid protein in the absence of insoluble deposits is associated with classic features of AD appear to be unknown. OBJECTIVE: To examine the associations of cortical ß-amyloid protein in the absence of insoluble deposits with cognitive decline, neurofibrillary tangles, other age-associated neuropathologic conditions, and APOE. DESIGN, SETTING, AND PARTICIPANTS: This analysis combines data from 2 community-based clinicopathologic cohort studies of aging. The Religious Orders Study started in 1994, and the Rush Memory and Aging Project started in 1997. Both studies are ongoing. Participants without known dementia were enrolled and agreed to annual clinical evaluations and brain donation after death. Primary analyses focused on individuals without ß-amyloid deposits. Data analyses occurred in mid-September 2018. MAIN OUTCOMES AND MEASURES: ß-Amyloid protein abundance was measured by targeted proteomics using selected reaction monitoring. ß-Amyloid deposits were detected using immunohistochemistry. Other neuropathologic indices were quantified via uniform structured evaluation. Linear mixed models were used to examine the association of ß-amyloid protein with cognitive decline. Regression models examined the protein associations with neuropathologic outcomes and the APOE genotype. RESULTS: By mid-September 2018, 3575 older persons were enrolled, and 1559 had died and undergone brain autopsy. Proteomic data were collected in 1208 individuals, and 5 with missing cognitive scores were excluded. Of the remaining 1203, primary analyses focused on 148 individuals (12.3%) without ß-amyloid deposits. In this group, the mean (SD) age at death was 87.0 (7.0) years, and 84 individuals (56.8%) were women. In the absence of ß-amyloid deposits, we did not observe an association of ß-amyloid protein with decline in episodic memory, but the protein was associated with faster rates of decline in processing speed (mean [SE] change, -0.014 [0.005]; P?=?.008) and visuospatial abilities (mean [SE] change, -0.013 [0.005]; P?=?.006). We did not observe protein association with paired helical filament tau tangle density. The protein was associated with amyloid angiopathy (odds ratio, 1.38 [95% CI, 1.15-1.67]; P?<?.001) but no other brain pathology. The associations with cognitive decline were unchanged after controlling for amyloid angiopathy. Neither APOE e4 nor a polygenic Alzheimer risk score was associated with ß-amyloid protein. CONCLUSIONS AND RELEVANCE: Cortical ß-amyloid protein was associated with faster cognitive decline in the absence of ß-amyloid deposits, which supports the role of cortical soluble ß-amyloid as a neurotoxic agent in aging. The lack of protein association with paired helical filament tau tangles, episodic memory decline, or strong genetic drivers of deposited ß-amyloid suggests an underlying neuropathologic change that may differ from that of AD.

Alzheimer’s disease, Insoluble deposits↗