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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 1,225 records · Page 68
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

First-principles derivation of magnetic interactions in the triangular quantum spin liquid candidates KYb C h 2 ( C h = S , Se , Te ) and A YbSe 2 ( A = Na , Rb )

The AYb Ch 2 (A=alkali metal, Ch=chalcogen) delafossites are a family of crystals which have a triangular lattice of effective S=1/2 moments on their Yb atoms. They hold great promise for the realization of the triangular quantum spin liquid state because of their defect-minimized growth and the ability to interchange chemical constituencies among the family. Here we use ab initio computations to evaluate the exchange couplings of four realized (and one theoretical) rhombohedral delafossite structures and examine the influence of chemical substitution on promoting the development of a quantum spin liquid state. We find good agreement with experiment regarding the antiferromagnetic nearest-neighbor exchange J 1 , but our calculations underestimate J 2 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

The role of aldo‐keto reductase 1 C 3 ( AKR 1 C 3)‐mediated prostaglandin D 2 ( PGD 2) metabolism in keloids

Abstract Keloids are progressively expanding scars, mostly prevalent in individuals of African descent. Previous data identified increased mast cell number and activation state in keloids suggesting a role in disease progression. The major eicosanoid secreted by mast cells is prostaglandin D2 ( PGD 2), a relatively unstable pro‐inflammatory mediator which can be spontaneously converted to 15‐deoxy‐(Delta12,14)‐prostaglandin J2(15d‐PGJ2) or enzymatically metabolized to 9α,11β‐ PGF 2 by aldo‐keto reductase 1C3 ( AKR 1C3). In this work, we investigated the possible role of PGD 2 and its metabolites in keloids using CRL 1762 keloid fibroblasts ( KF ) and immunohistochemical staining. Our data suggested approximately 3‐fold increase of tryptase‐positive mast cell count in keloids compared with normal skin. Furthermore, AKR 1C3 was overexpressed in the fibrotic area of keloids while relatively weak staining detected in normal skin. Metabolism of PGD 2 to 9 α ,11 β ‐ PGF 2 by both, KF and normal fibroblasts, was dependent on AKR 1C3 as this reaction was attenuated in the presence of the AKR 1C3 inhibitor, 2′‐hydroxyflavanone, or in cells with decreased AKR 1C3 expression. 15d‐ PGJ 2, but not the other tested PG s, inhibited KF proliferation, attenuated KF ‐mediated collagen gel contraction and increased caspase‐3 activation. In addition, treatment with 15d‐ PGJ 2 activated P38‐ MAPK , induced reactive oxygen species and upregulated superoxide dismutase‐1 ( SOD ‐1). Finally, inhibition of P38‐ MAPK further augmented 15d‐ PGJ 2‐induced caspase‐3 cleavage and attenuated its effect on SOD ‐1 transcription. This work suggests that localized dual inhibition of AKR 1C3 and P38‐ MAPK may inhibit keloid progression. Inhibiting AKR 1C3 activity may generate oxidative environment due to redirection of PGD 2 metabolism towards 15d‐ PGJ 2 while inhibition of P38‐ MAPK will sensitize keloid cells to ROS ‐induced apoptosis.

Mantel, Alon↗
DOE OSTI2013

SU‐C‐105‐05: Reference Dosimetry of High‐Energy Electron Beams with a Farmer‐Type Ionization Chamber

Purpose: To investigate gradient effects and provide Monte Carlo calculated beam quality conversion factors to characterize the Farmer‐type NE2571 ion chamber for high‐energy reference dosimetry of clinical electron beams. Methods: The EGSnrc code system is used to calculate the absorbed dose to water and to the gas in a fully modeled NE2571 chamber as a function of depth in a water phantom. Electron beams incident on the surface of the phantom are modeled using realistic BEAMnrc accelerator simulations and electron beam spectra. Beam quality conversion factors are determined using calculated doses to water and to air in the chamber in high‐energy electron beams and in a cobalt‐60 reference field. Calculated water‐to‐air stopping power ratios are employed for investigation of the overall ion chamber perturbation factor. Results: An upstream shift of 0.3–0.4 multiplied by the chamber radius, r-cav, both minimizes the variation of the overall ion chamber perturbation factor with depth and reduces the difference between the beam quality specifier (R{sub 5} {sub 0}) calculated using ion chamber simulations and that obtained with simulations of dose‐to‐water in the phantom. Beam quality conversion factors are obtained at the reference depth and gradient effects are optimized using a shift of 0.2r-cav. The photon‐electron conversion factor, k-ecal, amounts to 0.906 when gradient effects are minimized using the shift established here and 0.903 if no shift of the data is used. Systematic uncertainties in beam quality conversion factors are investigated and amount to between 0.4 to 1.1% depending on assumptions used. Conclusion: The calculations obtained in this work characterize the use of an NE2571 ion chamber for reference dosimetry of high‐energy electron beams. These results will be useful as the AAPM continues to review their reference dosimetry protocols.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

WE-C-TOUR-T-00: Exhibit Hall Guided Tours-Microdosimeters for Therapy (Wednesday) WE-C-TOUR-T-01

Tour Leader: Indra Das, NYU Langone Medical Center, New York, NY Tour Guides: Hsui Ai, Indiana University School of Medicine, Indianapolis, IN Paulina Galvis, NYU Langone Medical Center, New York, NY Olga Volotoskova, NYU Langone Medical Center, New York, NY Participating Vendors: IBA PTW – New York RTI Electronics, Inc. Standard Imaging, Inc. Sun Nuclear Corporation Small fields are increasing used in specialized radiation treatments such as Gammaknife, Cyberknife, Tomotherapy, IMRT, VMAT, SRS and SBRT. Due to small field size electron transport creates lateral electronic disequilibrium and thus dosimetry could be very difficult. Microdetectors are used for small field dosimetry which will be discussed in preface of this tour as below: Understanding small field e.g. meaning and definition of small field IAEA definition and approach Characteristics of microdetectors in terms of perturbation, recombination, correction Suitability of microdetectors in small field dosimetry.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

Phase Contrast Imaging Diagnostic on DIII-D (1994-2007); Phase Contrast Imaging Diagnostic on DIII-D and Alcator C-Mod (2007-2010); Experimental Study of Waves, Turbulence and Transport, and Model Validation with Phase Contrast Imaging on DIII-D and Alcator C-Mod (2010-2012); Phase Contrast Imaging Diagnostic Upgrade on DIII-D for Measuring High-k Turbulence and Alfven modes (2021-2016); Phase Contrast Imaging Diagnostic Upgrade on DIII-D for Full Multi-Scale Measurements (2016-2020) (Final Report)

This report describes the first twenty-five years of development and use of the Phase Contrast Imaging (PCI) diagnostic for measuring plasma fluctuations on the DIII–D tokamak. One of the key challenges in moving tokamak technology forward to the stage of a nuclear reactor remains understanding how energy and particles are transported across the magnetic field by the action of turbulence and waves, and PCI provides a highly flexible and capable measurement of these fluctuations. The PCI diagnostic uses a laser beam to probe the plasma and optical filtering to produce an amplitude variation on a linear detector array which provides an image of the density waves in the plasma. The PCI covers an exceptional range in frequency and wavelength of the measured fluctuations, allowing observation of plasma-sized magnetohydrodynamic (MHD) modes and ion- and electron-scale turbulence. Modulation of the beam amplitude allows measurement of radio frequency (RF) waves.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗