Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “CoH”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

66 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2022

Global Total Ozone Recovery Trends Attributed to Ozone-Depleting Substance (ODS) Changes Derived From Five Merged Ozone Datasets

We report on updated trends using different merged zonal mean total ozone datasets from satellite and ground-based observations for the period from 1979 to 2020. This work is an update of the trends reported in Weber et al. (2018) using the same datasets up to 2016. Merged datasets used in this study include NASA MOD v8.7 and NOAA Cohesive Data (COH) v8.6, both based on data from the series of Solar Backscatter Ultraviolet (SBUV), SBUV-2, and Ozone Mapping and Profiler Suite (OMPS) satellite instruments (1978–present), as well as the Global Ozone Monitoring Experiment (GOME)-type Total Ozone – Essential Climate Variable (GTO-ECV) and GOME-SCIAMACHY-GOME-2 (GSG) merged datasets (both 1995–present), mainly comprising satellite data from GOME, SCIAMACHY, OMI, GOME-2A, GOME-2B, and TROPOMI. The fifth dataset consists of the annual mean zonal mean data from ground-based measurements collected at the World Ozone and Ultraviolet Radiation Data Centre (WOUDC). Trends were determined by applying a multiple linear regression (MLR) to annual mean zonal mean data. The addition of 4 more years consolidated the fact that total ozone is indeed slowly recovering in both hemispheres as a result of phasing out ozone-depleting substances (ODSs) as mandated by the Montreal Protocol. The near-global (60° S–60° N) ODS-related ozone trend of the median of all datasets after 1995 was 0.4 ± 0.2 (2σ) %/decade, which is roughly a third of the decreasing rate of 1.5 ± 0.6 %/decade from 1978 until 1995. The ratio of decline and increase is nearly identical to that of the EESC (equivalent effective stratospheric chlorine or stratospheric halogen) change rates before and after 1995, confirming the success of the Montreal Protocol. The observed total ozone time series are also in very good agreement with the median of 17 chemistry climate models from CCMI-1 (Chemistry-Climate Model Initiative Phase 1) with current ODS and GHG (greenhouse gas) scenarios (REF-C2 scenario). The positive ODS-related trends in the Northern Hemisphere (NH) after 1995 are only obtained with a sufficient number of terms in the MLR accounting properly for dynamical ozone changes (Brewer–Dobson circulation, Arctic Oscillation (AO), and Antarctic Oscillation (AAO)). A standard MLR (limited to solar, Quasi-Biennial Oscillation (QBO), volcanic, and El Niño–Southern Oscillation (ENSO)) leads to zero trends, showing that the small positive ODS-related trends have been balanced by negative trend contributions from atmospheric dynamics, resulting in nearly constant total ozone levels since 2000.

Total Column Ozone Trends↗
NASA NTRSDate not supplied

The Impact of Atmospheric Dynamics and Anthropogenic Very Short-Lived Chlorine Species on the Recovery of Extra-Polar Ozone

The successful implementation of the Montreal Protocol has led to a decrease in the atmospheric abundance of ozone-depleting substances and a slowing in the destruction of the ozone layer. Previous studies have suggested that atmospheric dynamics, or a rise in compounds not regulated by the Montreal Protocol, such as very short-lived chlorine species (VSL Cl), may lead to a slower than expected recovery of the ozone layer. In this presentation, we examine the expected recovery of total column ozone (TCO) and stratospheric column ozone (SCO) to values observed in 1980 using a novel multiple linear regression (MLR) model that involves a month-by-month regression. The MLR model is trained to TCO anomalies from six data records (SBUV v8.7 MOD, SBUV v8.6 COH, WOUDC, GSG, GTO-ECV, MSR-2) over 1979 to 2021 for the Northern Hemisphere (35N – 60N), the Southern Hemisphere (60S – 35S) and the Tropics (20S – 20N), and SCO anomalies from ML-TOMCAT for these same zonal bands. The MLR includes the effect of halogens (equivalent effective stratospheric chlorine (EESC)), total solar irradiance, stratospheric aerosol optical depth, quasi-biennial oscillation, and the El Niño Southern Oscillation as regressors. We also include the effect of atmospheric dynamics such as the Brewer-Dobson Circulation, Arctic Oscillation, and the Antarctic Oscillation, and VSL Cl species in the formulation of EESC. We use a novel approach to the MLR framework, by separating the observed and regressor time series into the respective months (separating all of the Januarys, Februarys, etc.). Then we conduct a regression for each month from 1979 to 2021 for the three zonal bands denoted above. The model results for each month are combined together to achieve a full monthly time series from 1979 to 2021. We use this novel approach to ascertain the effect of atmospheric dynamics on TCO and SCO, since the dynamical proxies affect ozone in a distinctly different manner for various months. In this presentation, we will quantify the role of both the inclusion of VSL Cl species in the formulation of EESC as well as atmospheric dynamics in explaining the slower than expected recovery of extra-polar TCO and SCO over the past decade.

Laura A. McBride↗
DOE OSTI2024

Layer-dependence study of two-dimensional ferromagnets: Fe3GeTe2 and Fe5Ge2Te2

We have investigated the electrical transport properties of nanodevices fabricated from exfoliated flakes of two-dimensional metallic ferromagnets Fe3GeTe2 (FGT) and Fe5Ge2Te2 (FG2T) down to below three layers in thickness. The per-layer anomalous Hall conductivity even in thick FGT and FG2T devices is found to be much smaller than ∼e2h, the approximate value calculated for thick undoped crystals. Moreover, we obtain a power-law scaling relation between the per-layer anomalous Hall and per-layer longitudinal conductivities with an exponent close to 1.6, which agrees with the universal value for poor ferromagnetic conductors. Both FGT and FG2T devices show clear layer-dependent Curie temperatures and layer-dependent perpendicular magnetic anisotropy, with FG2T dominating the former and FGT dominating the latter for all thicknesses. Despite their declining trend as the device thickness decreases, both Curie temperature and magnetic anisotropy retain a significant fraction of their bulk values (>60% and >80% of the bulk values, respectively, even in the thinnest FG2T device), indicating attractive potential for practical applications.

Physics↗
DOE OSTI2020

Comparison of GW band structure to semiempirical approach for an FeSe monolayer

We present the G 0 W 0 band structure, core levels, and deformation potential of monolayer FeSe in the paramagnetic phase based on a starting mean field of the Kohn-Sham density functional theory (DFT) with the Perdew, Burke, and Ernzerhof functional. We find the GW correction increases the bandwidth of the states forming the M pocket near the Fermi energy, while leaving the Γ pocket roughly unchanged. We then compare the G 0 W 0 quasiparticle band energies with the band structure from a simple empirical + A approach, which was recently proposed to capture the renormalization of the electron-phonon interaction going beyond DFT in FeSe, when used as a starting point in density functional perturbation theory. We show that this empirical correction succeeds in approximating the GW nonlocal and dynamical self-energy in monolayer FeSe and reproduces the GW band structure near the Fermi surface, the core energy levels, and the deformation potential (electron-phonon coupling).

36 MATERIALS SCIENCE↗
DOE OSTI2022

Strain-tuning of domain walls in multilayer graphene probed in the quantum Hall regime

Domain walls, topological defects that define the frontier between regions of different stacking order in multilayer graphene, have proved to host exciting physics. The ability to tune these topological defects in situ in an electronic transport experiment brings a wealth of possibilities in terms of fundamental understanding of domain walls as well as for electronic applications. Here, we demonstrate, through a MEMS (microelectromechanical system) actuator and magnetoresistance measurements, the effect of domain walls in multilayer graphene quantum Hall effect. Reversible and controlled uniaxial strain triggers the topological defects, manifested as addtional quantum Hall effect plateaus as well as a discrete and reversible modulation of the current across the device. Furthermore, our findings are supported by theoretical calculations and constitute indication of the in situ tuning of topological defects in multilayer graphene probed through electronic transport, opening the way for the use of reversible topological defects in electronic applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1988

Comparison of bioseparation methods for microgravity experiments

The efficiency of the 1-g version of the continuous-flow electrophoresis (CFE) system flown on Space Shuttle missions is compared with the efficiency of a commercial CFE for separating living cells (human kidney, liver, and pituitary-gland cells and T-lymphocytes). In addition, the CFE system and a reciprocal isoelectric focusing (RIEF) system are compared with respect to protein pyrification efficiency. Correlations were made among electrophoretic mobilities (EPMs), secretory functions of cells, and input sample concentrations. A significant reduction in mean and range EPM was observed when input sample concentrations exceeded a low threshohold. This effect was not observed in microgravity experiments conducted at sample concentrations three times greater than the threshold for the controls. Comparison of CFE and RIEF methods showed that there are apparent advantages for each method depending on the product. For example, RIEF purification of urokinase removed more protein impurities, but focused the enzyme at a pH different than the enzyme's known isoelectric point.

Morrison, Dennis R.↗
NASA NTRS1988

Antibody enhancement of free-flow electrophoresis

Specific T cell clones and antibodies (ABs) were developed to study the efficiency of purifying closely associated T cells using Continuous Flow Electrophoresis System. Enhanced separation is accomplished by tagging cells first with ABs directed against the antigenic determinants on the cell surface and then with ABs against the Fc portion of the first AB. This second AB protrudes sufficiently beyond the cell membrane and glycocalyx to become the major overall cell surface potential determinant and thus causes a reduction of electrophoretic mobility. This project was divided into three phases. Phase one included development of specific T cell clones and separation of these specific clones. Phase two extends these principles to the separation of T cells from spleen cells and immunized lymph node cells. Phase three applies this double antibody technique to the separation of T cytotoxic cells from bone marrow.

Cohly, H. H. P.↗
NASA NTRS1989

Antigen presentation by non-immune B-cell hybridoma clones: presentation of synthetic antigenic sites reveals clones that exhibit no specificity and clones that present only one epitope

Recently, we reported the preparation and antigen-presenting properties of hybridoma B-cell clones obtained after fusing non-secreting, non-antigen presenting Balb/c 653-myeloma cells with non-immune SJL spleen cells. It was found that antigen presentation at the clonal level can be specific or non-specific, depending on the particular B-cell clone. In the present work, one specific and one general presenter B-cell clones were tested for their epitope presentation ability to SJL T-cells that were specific to lysozyme or myoglobin. B-cell clone A1G12, a general presenter which presented both lysozyme and myoglobin to their respective T-cell lines, was found to present all five myoglobin epitopes while clone A1L16, a lysozyme specific presenter presented only one of the three epitopes of lysozyme. The latter reveals a hitherto unknown submolecular specificity (to a given epitope within a protein) for antigen presenting cells at the clonal level. Therefore, the specificity of T-cell recognition does not only derive from the T-cell but may also be dependent on the epitope specificity of the antigen-presenting B-cell.

Hybridomas/immunology↗
NASA NTRS1989

Presentation of antigen to T lymphocytes by non-immune B-cell hybridoma clones: evidence for specific and non-specific presentation

Non-immune SJL (H-2s) spleen cells were fused with non-secreting, non-antigen presenting (H-2d) Balb/c 653-myeloma cells and the hybridomas were cloned by two limiting dilutions. The resulting hybrid B-cell clones were tested for their antigen presentation capability to SJL T-cell lines that were specific for either lysozyme or myoglobin. In proliferative assays, 53% of the antigen presenting B-cell clones presented both myoglobin and lysozyme (general presenters) while the other 47% presented specifically either myoglobin or lysozyme (specific presenters). The ability to selectively present either myoglobin or lysozyme indicates that antigen presentation at the clonal level can be specific or non-specific depending on the particular B-cell clone.

B-Lymphocytes/immunology↗
NASA NTRS1988

Presentation of antigen to T lymphocytes by non-immune B-cell hybridoma clones: evidence for specific and non-specific presentation

Non-immune SJL (H-2s) spleen cells were fused with (H-2d) Balb/c 653-myeloma cells and the hybridomas were cloned by two limiting dilutions. The resulting hybrid B- cell clones were tested for their antigen presentation capability to SJL T-cell lines that were specific for either lysozyme or myoglobin. In proliferative assays, 53% of the antigen presenting B-cell clones were able to present both myoglobin and lysozyme (general presenters) while the other 47% presented specifically either myoglobin or lysozyme (specific presenters). The ability to selectively present either myoglobin or lysozyme indicates that antigen presentation at the clonal level can be specific or non-specific depending on the particular B-cell clone.

T-Lymphocytes/immunology↗
NASA NTRS1988

Conformation-dependent recognition of a protein by T-lymphocytes: apomyoglobin-specific T-cell clone recognizes conformational changes between apomyoglobin and myoglobin

A T-cell clone specific to apomyoglobin was generated. It was prepared from a T-cell culture obtained by in vitro driving of lymph node cells with apomyoglobin from SJL mice that have been primed in vivo with apomyoglobin. In proliferative assays, the T-cell clone responded to apomyoglobin but did not recognize native myoglobin or any of the synthetic peptides corresponding to the six T sites of myoglobin. The demonstration that a T-cell clone can be isolated, whose specificity is directed entirely to apomyoglobin and not to its counterpart myoglobin, with an identical amino acid composition, indicates the importance of the three-dimensional structure in the presentation of the protein to T cells.

Apoproteins/immunology↗