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At least 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

A Telomerase-Activated Magnetic Resonance Imaging Probe for Consecutively Monitoring Tumor Growth Kinetics and In Situ Screening Inhibitors

Telomerase has long been considered as a biomarker for cancer diagnosis and a therapeutic target for drug discovery. Detecting telomerase activity in vivo could provide more direct information of tumor progression and response to drug treatment, which, however, is hampered by the lack of an effective probe that can generate an output signal without a tissue penetration depth limit. Here in this study, using the principle of distance-dependent magnetic resonance tuning, we constructed a telomerase-activated magnetic resonance imaging probe (TAMP) by connecting superparamagnetic ferroferric oxide nanoparticles (SPFONs) and paramagnetic Gd-DOTA (Gd(III) 1,4,7,10- tetraazacyclododecane-1,4,7,10-tetraazacyclododecane-1,4,7,10-tet-raacetic acid) complexes via telomerase-responsive DNA motifs. Upon telomerase-catalyzed extension of the primer in TAMP, Gd-DOTA-conjugated oligonucleotides can be liberated from the surface of SPFONs through a DNA strand displacement reaction, restoring the T 1 signal of the Gd-DOTA for a direct readout of the telomerase activity. Here we show that, by tracking telomerase activity, this probe provides consistent monitoring of tumor growth kinetics during progression and in response to drug treatment and enables in situ screening of telomerase inhibitors in whole-animal models. This study provides an alternative toolkit for cancer diagnosis, treatment response assessment, and anticancer drug screening.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Thermodynamic approach for enhancing superconducting critical current performance

Abstract The addition of artificial pinning centers has led to an impressive increase in the critical current density ( J c ) of superconductors, enabling record-breaking all-superconducting magnets and other applications. The J c of superconductors has reached ~0.2–0.3 J d , where J d is the depairing current density, and the numerical factor depends on the pinning optimization. By modifying λ and/or ξ, the penetration depth and coherence length, respectively, we can increase J d . For (Y 0.77 Gd 0.23 )Ba 2 Cu 3 O y ((Y,Gd)123), we can achieve this by controlling the carrier density, which is related to λ and ξ. We can also tune λ and ξ by controlling the chemical pressure in Fe-based superconductors, i.e., BaFe 2 (As 1− x P x ) 2 films. The variation in λ and ξ leads to an intrinsic improvement in J c via J d , allowing extremely high values of J c of 130 MA/cm 2 and 8.0 MA/cm 2 at 4.2 K, consistent with an enhancement in J d of a factor of 2 for both incoherent nanoparticle-doped (Y,Gd)123 coated conductors (CCs) and BaFe 2 (As 1− x P x ) 2 films, showing that this new material design is useful for achieving high critical current densities in a wide array of superconductors. The remarkably high vortex-pinning force in combination with this thermodynamic and pinning optimization route for the (Y,Gd)123 CCs reached ~3.17 TN/m 3 at 4.2 K and 18 T ( H || c ), the highest values ever reported for any superconductor.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Additive roles of antiferromagnetically coupled elements in the magnetic proximity effect in the GdFeCo/Pt system

Abstract Interfacial magnetic interactions between different elements are the origin of various spin-transport phenomena in multi-elemental magnetic systems. We investigate the coupling between the magnetic moments of the rare-earth, transition-metal, and heavy-metal elements across the interface in a GdFeCo/Pt thin film, an archetype system to investigate ferrimagnetic spintronics. The Pt magnetic moments induced by the antiferromagnetically aligned FeCo and Gd moments are measured using element-resolved x-ray measurements. It is revealed that the proximity-induced Pt magnetic moments are always aligned parallel to the FeCo magnetic moments, even below the ferrimagnetic compensation temperature where FeCo has a smaller moment than Gd. This is understood by a theoretical model showing distinct effects of the rare-earth Gd 4 f and transition-metal FeCo 3 d magnetic moments on the Pt electronic states. In particular, the Gd and FeCo work in-phase to align the Pt moment in the same direction, despite their antiferromagnetic configuration. The unexpected additive roles of the two antiferromagnetically coupled elements exemplify the importance of detailed interactions among the constituent elements in understanding magnetic and spintronic properties of thin film systems.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Influence of gadolinium doping on structural, optical, and electronic properties of polymeric graphitic carbon nitride

Polymeric graphitic carbon nitride (gCN) materials have received great attention in the fields of photo and electrocatalysis due to their distinct properties in metal-free systems with high physicochemical stability. Nevertheless, the activity of undoped gCN is limited due to its relatively low specific surface area, low conductivity, and poor dispersibility. Doping Gd atoms in a gCN matrix is an efficient strategy to fine-tune its catalytic activity and its electronic structure. Herein, the influence of various wt% of gadolinium (Gd) doped in melon-type carbon nitride was systematically investigated. Gadolinium-doped graphitic carbon nitride (GdgCN) was synthesized by adding gadolinium nitrate to dicyandiamide during polymerization. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) results revealed that the crystallinity and the morphological properties are influenced by the % of Gd doping. Furthermore, X-ray photoelectron spectroscopy (XPS) studies revealed that the gadolinium ions bonded with nitrogen atoms. Complementary density functional theory (DFT) calculations illustrate possible bonding configurations of Gd ions both in bulk material and on ultrathin melon layers and provide evidence for the corresponding bandgap modifications induced by gadolinium doping.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Direct measurement of reduced exchange stiffness and its impact on magnetic vortex behavior in PyGd alloys

Thin films composed of sputtered transition metal/rare earth (TM/RE) ferrimagnets have emerged as promising building blocks for future spintronic devices, offering tunable magnetic properties critical for data storage, memory, and logic applications. However, understanding how the combination of TM and RE elements influences effective magnetic properties, such as exchange stiffness (Aex), remains challenging. Magnetic vortices provide a versatile tool for probing these properties in thin film systems. By combining magnetic imaging via soft x-ray microscopy and micromagnetic modeling, we quantify the effective exchange stiffness in PyGd ferrimagnetic disks with varying Gd concentrations. Our results indicate a reduction in Aex to below 3 pJ/m for a 20% Gd concentration when compared to reference Py, and values below 2 pJ/m for 30% Gd, reflecting weak Ni–Gd exchange coupling. These findings highlight the critical role of rare earth content in tuning the exchange stiffness. The reduced exchange stiffness facilitates a linear field response of the magnetization up to the edge of the disk, as well as significant deformations in the vortex core itself when compared to films with larger Aex. Our results are in line with, albeit lower than, recent measurements of the exchange stiffness in intermixed PyGd. This reduced exchange stiffness has implications for the development of spintronic devices based on ferrimagnetic skyrmions.

Jacob, Liyan↗
DOE OSTI2022

Probing antiferromagnetic coupling in magnetic insulator/metal heterostructures

Using depth- and element-resolved characterization, we report insights into antiferromagnetic coupling in Y 3 ⁢Fe 5 ⁢O 12 /permalloy (YIG/Py) and Y 3 ⁢Fe 5 ⁢O 12 /Co (YIG/Co) thin-film heterostructures grown on Si/SiO 2 and Gd 3⁢ Ga 5⁢ O 12 substrates. We build on recent work demonstrating antiferromagnetic coupling in polycrystalline YIG/metallic-ferromagnetic systems by characterizing differences in the structural and magnetic properties which depend on the choice of ferromagnet (Py vs Co), seed layer (with and without Pt), and substrate (Si/SiO 2 vs Gd 3 ⁢Ga 5 ⁢O 12 ). These differences in the sample structure manifest as notable changes in interface coupling sign, magnetic reversal mechanisms, magnetic depth profiles, and domain structure. Through a combination of magnetometry, polarized neutron reflectometry, and x-ray photoemission electron microscopy, a comprehensive picture of the magnetic interactions is realized, with lateral- and depth resolution at submicrometer and nanometer scales, respectively. These results confirm that both Co and Py share a preference to align antiparallel to polycrystalline YIG grown on some substrates (Si/SiO 2 and Si/SiO 2 /Pt), while coupling ferromagnetically with highly oriented YIG on (111) Gd 3⁢ Ga 5 ⁢O 12 and (110) Gd 3 ⁢Ga 5⁢ O 12 /Pt substrates. The complex interplay among magnetic interactions at the YIG/ferromagnetic interface has important implications for spintronic and magnonic devices based on this platform.

Exchange interaction↗
DOE OSTI2022

High Performance SOFCs with a Superior Stability for Reliable and Durable Power Systems

Next generation of fuel cells, electrolyzers, and batteries requires higher power, faster kinetics, and larger energy density, which necessitate the use of compositionally complex oxides to achieve multifunctionalities and activity. These compositionally complex oxides may change their phases and structures during an electrochemical process – a so-called “electrochemically driven phase transformation”. The origin for such a phase change has remained obscure. More importantly, there is a need to develop high performance solid oxide fuel cells with an enhanced stability. In this work, the La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 (LSCF) cathode surface is modified by infiltration of Pr 6 O 11 and the power density at 0.8V and 750 °C is improved by 21%. In addition, by replacing the traditional barrier layer Gd 0.2 Ce 0.8 O 1.9 with mixed conducting Pr 0.1 Gd 0.1 Ce 0.8 O 1.9 , the power density increases by 38%. The different mechanism of promotions was investigated by electrochemical impedance spectroscopy. The ohmic resistance is dramatically reduced by applying the PGCO interlayer, and the distribution of relaxation time was used to analyze the mechanism for which the polarization resistance was decreased attributing to the mixed conduction nature in PrO x . An increase of power density at 0.8 V of 0.358 W/cm 2 (71%) is achieved with the implementation of both surface modification and buffer layer engineering. An experimental study and a theoretical analysis were then carried out on phase evolution in praseodymium nickelates. Nickelate-based electrodes show up to 60× greater phase transformation during operation when compared to thermally annealed ones. Theoretical analysis suggests that the presence of a reduced oxygen partial pressure at the interface between the oxygen electrode and the electrolyte is the origin for the phase change in an oxygen electrode. Guided by the theory, an addition of the electronic conduction in the interface layer leads to the significant suppression of phase change, while improving cell performance and performance stability. When an oxygen electrode is under polarization, the oxygen partial pressure at the interface between the oxygen electrode and the electrolyte is lower than that of incoming oxidant. Under a high polarization, the environment at the aforementioned interface may lead to phase transformation of the oxygen electrode. The local oxygen partial pressure is determined by the transport properties at the interfaces. An addition of the electronic conduction in the interface layer, for instance using (Pr,Gd)-doped ceria to replace Gd-doped ceria, results in improved cell performance and performance stability, while the phase transformation is significantly suppressed. This work provides a fundamental understanding of the origin for phase transformation in oxygen electrodes during operation and use this knowledge to develop a high-performance electrode that exhibits improved performance stability.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2023

Search for Astrophysical Electron Antineutrinos in Super-Kamiokande with 0.01% Gadolinium-loaded Water

We report the first search result for the flux of astrophysical electron antineutrinos for energies $\mathcal{O}$(10)$MeV$ in the gadolinium-loaded Super-Kamiokande (SK) detector. In 2020 June, gadolinium was introduced to the ultrapure water of the SK detector in order to detect neutrons more efficiently. In this new experimental phase, SK-Gd, we can search for electron antineutrinos via inverse beta decay with efficient background rejection thanks to the high efficiency of the neutron tagging technique. In this paper, we report the result for the initial stage of SK-Gd, during 2020 August 26, and 2022 June 1 with a 22.5 × 552 kton · day exposure at 0.01% Gd mass concentration. No significant excess over the expected background in the observed events is found for the neutrino energies below 31.3 MeV. Thus, the flux upper limits are placed at the 90% confidence level. The limits and sensitivities are already comparable with the previous SK result with pure water (22.5 × 2970 kton · day) owing to the enhanced neutron tagging. Operation with Gd increased to 0.03% started in 2022 June.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1984

On the proper Mach number and ratio of specific heats for modeling the Venus bow shock

Observational data from the Pioneer Venus Orbiter are used to investigate the physical characteristics of the Venus bow shock, and to explore some general issues in the numerical simulation of collisionless shocks. It is found that since equations from gas-dynamic (GD) models of the Venus shock cannot in general replace MHD equations, it is not immediately obvious what the optimum way is to describe the desired MHD situation with a GD code. Test case analysis shows that for quasi-perpendicular shocks it is safest to use the magnetospheric Mach number as an input to the GD code. It is also shown that when comparing GD predicted temperatures with MHD predicted temperatures total energy should be compared since the magnetic energy density provides a significant fraction of the internal energy of the MHD fluid for typical solar wind parameters. Some conclusions are also offered on the properties of the terrestrial shock.

Tatrallyay, M.↗
NASA NTRS1987

Rare-earth substitution in (BiYCa)3(FeSiGe)5O12 bubble films

The substitution of Y by Sm, Tb, Gd, and Ho in (BiYCa)3 FeSiGe)5O12 bubble garnet is shown to have large effects on the growth-induced anisotropy (GIA). The presently accepted film composition intended for 6-or 8-micron-period bubble memory devices demands partial substitution of Y by Gd and Ho. However, comparing films grown under the same growth conditions, it is observed that YGdHoBilG films posess less (GIA) than their Gd, Ho-free counterparts. Thus, to satisfy (GIA) requirements, the supercooling during growth must be increased by 20 K to 80 K with undesirable effects on defect densities. A new film composition containing Sm, Tb, and Gd has been formulated to satisfy all known material property specifications for 6- or 8-micron-period memory devices. It can be grown with only 45-50 K supercooling.

Luther, L. C.↗
NASA NTRS1994

High-Speed Hubble Space Telescope Ultraviolet photometry of two DB white dwarfs: Nonradial and radial pulsations

We observed two DB white dwarf stars with the High Speed Photometer aboard the Hubble Space Telescope. The two targets, the nonradial pulsator GD 358, and PG 0112+104, a non-pulsating white dwarf with similar temperature, were each observed for 1800 s with a time resolution of 10 ms. We used the F140LP configuration, which gives a broadband response in the UV between 1400 and 3000 A. The data clearly show the long period (about 700 s) pulsations in GD 358. Comparison with optical observations obtained two weeks earlier shows that the amplitude of the pulsations in the UV is approximately 1.4 times higher, consistent with nonradial pulsations due solely to temperature changes at constant radius. The high time resolution of these observations allows us to search for high-frequency pulsations (such as p modes or high overtone radial modes). No firm evidencefor high-frequency pulsations was seen in either object between 1 and 12 Hz. Correlation analysis of GD 358 shows no clear signal of multifrequency high overtone radial pulsations at the 0.00075 mag level, with no individual modes above the 0.0016 mag level. Upper limits for PG 0112+104 are approximately 2 times higher than for GD 358. Implications of this study for the theory of white dwarf pulsations are discussed.

Kawaler, Steven D.↗
NASA NTRS1995

The location of planetary bow shocks: A critical overview of theory and observations

A bow shock (BS has been observed in the collisionless solar wind upstream of every planet except Pluto, which has yet to be visited by a spacecraft. They are all of similar character, but their size relative to the planet varies widely, e.g., the planeto-centric distance to the BS nose ranges from about 1.4 R(sub V) for Venus to 88 R(sub J) or more for Jupiter. Comparisons are reviewed that show its location may be represented satisfactorily by a gasdynamic (GD) model, provided the properties of the solar wind and planetary magnetic field and ionosphere are known and used as input in the application. Factors that determine the location are discussed, and examples are presented to illustrate effects of their variation, including which part of a BS is influenced by a local variation of the magneto/ionopause (MIP) shape. The interplanetary magnetic field (IMF) has no influence on the BS location in the GD model, but is shown to have a small effect in corresponding solutions of the basic MHD model from which the GD model is derived as the limit for weak IMF. Nearly all GD and MHD solutions are for steady flow, but a solution for unsteady flow associated with the passage of an interplanetary shock is also presented. It shows that the BS moves rapidly from its initial to final location, e.g., in about minute for the earth. Since many changes in the solar wind occur over longer intervals, these results help explain the success of quasi-stationary solutions in modeling the BS in time-varying solar wind flows.

Spreiter, J. R.↗
NASA NTRS2002

Ree in Shergottite Augites and Whole Rocks

Redox variations have been reported among the shergottites. Eu and Gd partitioning experiments designed for the LEW86010 angrite, to infer a range of fo2 for the shergottites have been used. Fo2 using equilibria between Fe-Ti oxides have been inferred. There is fairly good agreement between the Fe-Ti oxide determinations and the estimates from Eu anomalies in terms of which meteorites are more or less oxidized. The Eu anomaly technique and the Fe-Ti oxide technique both essentially show the same trend, with Shergotty and Zagami being the most oxidized and QUE94201 and DaG 476 being the most reduced. Thus, the variation in fo2 appears to be both real and substantive. However, although the redox trends indicated by the two techniques are similar, there is as much as a two log unit offset between the results. One explanation for this offset is that the Eu calibration used for the shergottites was actually designed for the LEW86010 angrite, a silica-undersaturated basalt whose pyroxene (diopside) compositions are rather extreme. To correct this, a set of experiments on the redox relationship of Eu partitioning relative to Sm and Gd for pyroxene and melt compositions more relevant to Martian meteorites were conducted. We have taken the experimentally determined relationship between D (sup Augite/melt) (Sm,Eu,Gd) and fO2 and applied it to augite Eu and Gd data for the basaltic Shergottites of as well as previously unreported augite Sm data.

Musselwhite, D. S.↗
NASA NTRS2002

REE in Shergottite Augites and Whole Rocks

Redox variations have been reported among the shergottites. Eu and Gd were used in partitioning experiments designed for the LEW86010 angrite, to infer a range of fO2 for the shergottites. Inferred fO2 using equilibria between Fe-Ti oxides was used. There is fairly good agreement between the Fe- Ti oxide determinations and the estimates from Eu anomalies in terms of which meteorites are more or less oxidized. The Eu anomaly technique and the Fe-Ti oxide technique both essentially show the same trend, with Shergotty and Zagami being the most oxidized and QUE94201 and DaG 476 being the most reduced. Thus, the variation in fO2 appears to be both real and substantive. However, although the redox trends indicated by the two techniques are similar, there is as much as a two log unit offset between the results of presented. One explanation for this offset is that the Eu calibration used for the shergottites was actually designed for the LEW86010 angrite, a silica-undersaturated basalt whose pyroxene (diopside) compositions are rather extreme. To correct this, a set of experiments were conducted on the redox relationship of Eu partitioning relative to Sm and Gd for pyroxene and melt compositions more relevant to Martian meteorites. We have taken the experimentally determined relationship between (Sm,Eu,Gd) and fO2 and applied it to augite Eu and Gd data for the basaltic Shergottites as well as previously unreported augite Sm data.

Musselwhite, D. S.↗
NASA NTRS2006

Effects of Doping on Thermal Conductivity of Pyrochlore Oxides for Advanced Thermal Barrier Coatings

Pyrochlore oxides of general composition, A2B2O7, where A is a 3(+) cation (La to Lu) and B is a 4(+) cation (Zr, Hf, Ti, etc.) have high melting point, relatively high coefficient of thermal expansion, and low thermal conductivity which make them suitable for applications as high-temperature thermal barrier coatings. The effect of doping at the A site on the thermal conductivity of a pyrochlore oxide La2Zr2O7, has been investigated. Oxide powders of various compositions La2Zr2O7, La(1.7)Gd(0.3)Zr2O7, La(1.7)Yb(0.3)Zr2O7 and La(1.7)Gd(0.15)Yb(0.15)Zr2O7 were synthesized by the citric acid sol-gel method. These powders were hot pressed into discs and used for thermal conductivity measurements using a steady-state laser heat flux test technique. The rare earth oxide doped pyrochlores La(1.7)Gd(0.3)Zr2O7, La(1.7)Yb(0.3)Zr2O7 and La(1.7)Gd(0.15)Yb(0.15)Zr2O7 had lower thermal conductivity than the un-doped La2Zr2O7. The Gd2O3 and Yb2O3 co-doped composition showed the lowest thermal conductivity.

Bansal, Narottam P.↗
DOE OSTI2020

Materials Data on GdGe by Materials Project

GdGe crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. Gd is bonded in a 5-coordinate geometry to seven equivalent Ge atoms. There are five shorter (3.02 Å) and two longer (3.25 Å) Gd–Ge bond lengths. Ge is bonded in a 9-coordinate geometry to seven equivalent Gd and two equivalent Ge atoms. Both Ge–Ge bond lengths are 2.70 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on GdHg by Materials Project

GdHg is Tetraauricupride structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Gd is bonded in a body-centered cubic geometry to eight equivalent Hg atoms. All Gd–Hg bond lengths are 3.26 Å. Hg is bonded in a body-centered cubic geometry to eight equivalent Gd atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on GdPd by Materials Project

GdPd crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. Gd is bonded in a 7-coordinate geometry to seven equivalent Pd atoms. There are a spread of Gd–Pd bond distances ranging from 2.97–3.06 Å. Pd is bonded in a 7-coordinate geometry to seven equivalent Gd atoms.

36 MATERIALS SCIENCE↗