Search NASA⌕ Search

SEARCH · Search NASA

Results for “Structural Effects”

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.

At least 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Interplay of energy dissipation, ion-induced mixing, and crystal structure recovery, and surface effects in ion-irradiated magnetic Fe/Cr/Fe trilayers

The influence of the ion irradiation by 30 keV Ga{sup +} ions on the crystal structure, chemical ordering, magnetic properties, and topography of epitaxial Fe/Cr/Fe trilayers was investigated by different analytical techniques. We present direct experimental evidence, supported by theoretical estimates, that two processes take place concurrently due to the Ga-ion implantation. (i) A complete atom mixing of the Cr atoms within the Fe multilayers is occurring due to the collision cascades during the ballistic regime, and (ii) an essentially complete recovery of the initial single-crystal quality of the Fe multilayers by healing the melted and damaged area through the thermal spike phase occurs. Based on the experimental range distributions and theoretical modeling, channeling of Ga{sup +} ions in the experiments is found to contribute weakly to ion penetration and stopping, and the relative fraction of the well-channeled ions is marginally small. On the other hand, this weak channeling is sufficient to reduce the sputter yield by a factor of more than 5 in comparison with the sputtering of polycrystalline samples, evidence for the fact that the magnitude of channeling is not of primary importance for the sputtering. We offer an explanation for the observation of dramatic and abrupt changes in the surface roughness with increasing fluences in terms of a transformation from a single-phase single-crystal implanted region (bcc-Fe) to a mixture of the polycrystalline {alpha}-Fe-like bcc and {alpha}-Fe{sub 3}Ga structures within the outer half of the original Fe/Cr/Fe trilayer at fluences above 6.25 x 10{sup 16} ion/cm{sup 2}. The wall-like elevations appearing at the boundary of the irradiated areas were analyzed experimentally by varying the irradiation conditions. We showed that the wall size is governed by the ion-current density applied. A physical explanation for the appearance of such topographic features is presented, which would be valid for any material irradiated by a focused ion beam.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Skeletal Dysplasia Mutations Effect on Human Filamins’ Structure and Mechanosensing

Cells’ ability to sense mechanical cues in their environment is crucial for fundamental cellular processes, leading defects in mechanosensing to be linked to many diseases. The actin cross-linking protein Filamin has an important role in the conversion of mechanical forces into biochemical signals. Here, we reveal how mutations in Filamin genes known to cause Larsen syndrome and Frontometaphyseal dysplasia can affect the structure and therefore function of Filamin domains 16 and 17. Employing X-ray crystallography, the structure of these domains was first solved for the human Filamin B. The interaction seen between domains 16 and 17 is broken by shear force as revealed by steered molecular dynamics simulations. The effects of skeletal dysplasia associated mutations of the structure and mechanosensing properties of Filamin were studied by combining various experimental and theoretical techniques. The results showed that Larsen syndrome associated mutations destabilize or even unfold domain 17. Interestingly, those Filamin functions that are mediated via domain 17 interactions with other proteins are not necessarily affected as strongly interacting peptide binding to mutated domain 17 induces at least partial domain folding. Mutation associated to Frontometaphyseal dysplasia, in turn, transforms 16–17 fragment from compact to an elongated form destroying the force-regulated domain pair.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2015

Effects of rapid thermal annealing on the structural and local atomic properties of ZnO: Ge nanocomposite thin films

We have investigated the structural and local atomic properties of Ge nanocrystals (Ge-ncs) embedded ZnO (ZnO: Ge) thin films. The films were deposited by sequential sputtering of ZnO and Ge thin film layers on z-cut quartz substrates followed by an ex-situ rapid thermal annealing (RTA) at 600 °C for 30, 60, and 90 s under forming gas atmosphere. Effects of RTA time on the evolution of Ge-ncs were investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), hard x-ray photoelectron spectroscopy (HAXPES), and extended x-ray absorption fine structure (EXAFS). XRD patterns have clearly shown that fcc diamond phase Ge-ncs of sizes ranging between 18 and 27 nm are formed upon RTA and no Ge-oxide peak has been detected. However, cross-section SEM images have clearly revealed that after RTA process, Ge layers form varying size nanoclusters composed of Ge-ncs regions. EXAFS performed at the Ge K-edge to probe the local atomic structure of the Ge-ncs has revealed that as prepared ZnO:Ge possesses Ge-oxide but subsequent RTA leads to crystalline Ge structure without the oxide layer. In order to study the occupied electronic structure, HAXPES has been utilized. The peak separation between the Zn 2p and Ge 3d shows no significant change due to RTA. This implies little change in the valence band offset due to RTA.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Effect of aluminum substitution on structural and electromagnetic properties of nanocrystalline MgCuMn ferrites

The effect of substitution of nonmagnetic Al{sup 3+} ions on the structural and electromagnetic properties were studied in nanocrystalline ferrite series of Mg{sub 0.8}Cu{sub 0.2}Al{sub x}Fe{sub 1.95-x}Mn{sub 0.05}O{sub 4} where x varies 0-0.4 in steps of 0.1. This series was synthesized by using microwave hydrothermal method. The nanocrystalline ferrite phase was observed at temperature 150°C/40 min. Synthesized powders were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The synthesized powders were densified using microwave sintering method at 950°C/40 min. The sintered samples were characterized using XRD. Surface morphology was observed by using field effective scanning electron microscopy (FESEM). The electrical and magnetic properties were measured at room temperature. These results led us to interfere that the values of d.c resistivity increases and dielectric constant, initial permeability, saturation magnetization and Curie temperature were observed to be decreased with the substitution of Al{sup 3+} ions with those of Fe{sup 3+}. The low dielectric and magnetic losses and low magnetization exhibited by aluminum substituted MgCuMn ferrites makes them find applications in microwave devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Finite size effects in the static structure factor of dusty plasmas

Based on the previously developed pseudopotential model of the dust particles interaction, which takes into account both the finite size and screening effects, the equilibrium distribution functions are investigated in a broad range of plasma parameters. The treatment stems entirely from the renormalization theory of plasma particles interactions which leads to the so-called generalized Poisson-Boltzmann equation. In particular, an analytical expression for the static structure factor of the dust particles is proposed and its non-monotonic behavior in the hyper-netted chain approximation is found in a specified domain of plasma parameters to indicate the formation of short- or even long-range order in the system.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

The effects of post-growth annealing on the structural and magnetic properties of BaFe 2 As 2

Here, we investigate the effects of post-growth annealing on the structural and magnetic properties of BaFe 2 As 2 . Magnetic susceptibility measurements, which exhibit a signal corresponding to the magnetic phase transition, and high-resolution x-ray diffraction measurements, which directly probe the structural order parameter, show that annealing causes the ordering temperatures of both the phase transitions to increase, sharpen and converge. In the as grown sample, our measurements show two distinct transitions corresponding to structural and magnetic ordering, which are separated in temperature by approximately 1 K. After 46 days (d) of annealing at 700 °C, the two become concurrent in temperature. These measurements demonstrate that the structural phase transition is second-order like when the magnetic and structural phase transitions are separated in temperature, and first-order like when the two phase transition temperatures coincide. This observation indicates that annealing causes the system to cross a hitherto undiscovered tricritical point. In addition, x-ray diffraction measurements show that the c-axis lattice parameter increases with annealing up to 30 d, but remains constant for longer annealing times. Comparisons of BaFe 2 As 2 to SrFe 2 As 2 are made when possible.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Effect of the composition and structure of carbofunctional oligodimethylsiloxanes on their colloidal-chemical properties

The effect of the composition and structure of oligodimethylsiloxanes containing carboxy- and amino-functional substituents at the silicon atom on their colloidal-chemical properties was studied. It was established that their colloidal-chemical properties are affected not only by the nature and concentration of functional groups, but also by the molecular weight of the organosilicon compound.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Study on effect of annealing conditions on structural, magnetic and superconducting properties of MgB{sub 2} bulk samples

Effect of annealing conditions on structural, magnetic and superconducting properties of Magnesium Diboride (MgB{sub 2}) bulk superconductor samples prepared by solid state route method are compared. The samples are made by taking Magnesium and Boron powders in stoichiometric ratio, grounded well and pelletized at pressure of about 10Tonnes. These pellets are annealed in both Argon and vacuum environment separately up to 800°c for two hours. Both the samples show clear superconducting transition at Tc ∼ 38 k. This is further conformed by AC/DC magnetization (M-T), Resistivity [ρ (T, H)] measurements under magnetic field up to 14 Tesla as well. Rietveld refinement of X-ray diffraction of both samples conformed the MgB{sub 2} phase formation with P6/mmm space group symmetry. Scanning Electron Microscopy images of the surface revile more agglomeration of grains in case of Argon annealed samples. This result in more critical current density (J{sub c}) of Argon annealed samples than vacuum annealed one calculated from Bean's critical state model. This high Jc is explained in terms of more inter grain connectivity for Argon annealed sample than vacuum annealed sample.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Study of radiation effects on the cell structure and evaluation of the dose delivered by x-ray and {alpha}-particles microscopy

Hard X-ray fluorescence microscopy and magnified phase contrast imaging are combined to study radiation effects on cells. Experiments were performed on freeze-dried cells at the nano-imaging station ID22NI of the European synchrotron radiation facility. Quantitative phase contrast imaging provides maps of the projected mass and is used to evaluate the structural changes due to irradiation during X-ray fluorescence experiments. Complementary to phase contrast imaging, scanning transmission ion microscopy is performed and doses of all the experiments are compared. We demonstrate the sensitivity of the proposed approach to study radiation-induced damage at the sub-cellular level.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Simulation of the β-voltaic effect in silicon pin structures irradiated with electrons from a nickel-63 β source

The prospects of β voltaics as electric-power sources for semiconductor circuits are considered. Experimental studies show that charging of the surface and a decrease in the electrovoltaic power are important. Simulation of the β-voltaic effect induced by electrons from a nickel-63 source on silicon pin structures is performed; it is shown that the coefficient of the collection of generated charge carriers can be as high as 13%. The dose dependences of the performance efficiency of silicon β-voltaic structures are determined for the case of irradiation with α particles and γ-ray photons; it is shown that 1.3 × 10{sup 14} and 10{sup 20} cm{sup –2}, respectively, are the threshold doses, above which a rapid decrease in efficiency occurs. The optimal parameters of microchannel structures in β-voltaic electronics, in which the width of the channels and the distance between them correspond to 3 and 10 μm, are determined.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Correlation effects on coupled electronic and structural properties of doped rare-earth trihydrides

Rare-earth trihydride (𝑅⁢H 3 ) compounds exhibit intriguing coupled electronic and structural properties as a function of doping, hydrogen vacancies, and thermodynamic conditions. Theoretical studies of these materials typically rely on density functional theory (DFT), including the use of small supercells that may underestimate strong correlation effects and structural distortions which in turn may influence their metallicity. Here, we elucidate the roles of lattice distortions and correlation effects on the electronic properties of pristine and doped 𝑅⁢H 3 compounds by adopting DFT +U and quantum Monte Carlo (QMC) methods. Linear-response constrained DFT (LR-cDFT) methods find Hubbard U ≈ 2 eV for 𝑅 𝑑 orbitals and U ≈ 6 eV for H 𝑠 ⁡/N 𝑝 /O 𝑝 orbitals. The small U on Lu 𝑑 orbitals is consistent with QMC calculations on LuH 3 and LuH 2.875 ⁢N 0.125 . In pure face-centered-cubic (FCC) 𝑅⁢H 3 (𝑅 = Lu,Y) compounds, neither DFT nor DFT +U with the self-consistently determined U is enough to create a band gap, however a supercell with hydrogen distortions creates a small gap whose magnitude increases when performing DFT +U with self-consistently determined U values. Furthermore, correlation effects, in turn, have a moderate influence on the coupled structural and electronic properties of doped 𝑅⁢H 3 compounds and may be important when considering the competition between structural distortions and superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Study of the effects of corrugated wall structures due to blanket modules around ICRH antennas

In future fusion reactors, and in ITER, the first wall will be covered by blanket modules. These blanket modules, whose dimensions are of the order of the ICRF wavelengths, together with the clearance gaps between them will constitute a corrugated structure which will interact with the electromagnetic waves launched by ICRF antennas. The conditions in which the grooves constituted by the clearance gaps between the blanket modules can become resonant are studied. Simple analytical models and numerical simulations show that mushroom type structures (with larger gaps at the back than at the front) can bring down the resonance frequencies, which could lead to large voltages in the gaps between the blanket modules and perturb the RF properties of the antenna if they are in the ICRF operating range. The effect on the wave propagation along the wall structure, which is acting as a spatially periodic (toroidally and poloidally) corrugated structure, and hence constitutes a slow wave structure modifying the wall boundary condition, is examined.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Effective collision strengths for fine-structure transitions in Si VII

The effective collision strengths for electron-impact excitation of fine-structure transitions in Si VII are calculated as a function of electron temperature in the range 5000-2,000,000 K. The B-spline Breit-Pauli R-matrix method has been used to calculate collision strengths by electron impact. The target wave functions have been obtained using the multi-configuration Hartree-Fock method with term-dependent non-orthogonal orbitals. The 92 fine-structure levels belonging to the 46 LS states of 2s {sup 2}2p {sup 4}, 2s2p {sup 5}, 2p {sup 6}, 2s {sup 2}2p {sup 3}3s, 2s {sup 2}2p {sup 3}3p, 2s {sup 2}2p {sup 3}3d, and 2s2p {sup 4}3s configurations are included in our calculations of oscillator strengths and collision strengths. There are 4186 possible fine-structure allowed and forbidden transitions among the 92 levels. The present excitation energies, oscillator strengths, and collision strengths have been compared with previous theoretical results and available experimental data. Generally, a good agreement is found with the 6 LS-state close-coupling approximation results of Butler and Zeippen and the 44 LS-state distorted wave calculation of Bhatia and Landi.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2012

Effect of cerium on structure modifications of a hybrid sol–gel coating, its mechanical properties and anti-corrosion behavior

Highlights: ► New sol–gel routes to replace chromates for corrosion protection of aluminum. ► Effect of cerium concentration on the microstructure of xerogel. ► Electrochemical and mechanical performances of hybrid coating with different cerium contents. ► Good correlation between the different results with an optimal cerium content of 0.01 M. -- Abstract: An organic–inorganic hybrid coating was developed to improve the corrosion resistance of the aluminum alloy AA 2024-T3. Organic and inorganic coatings derived from glycidoxypropyl-trimethoxysilane (GPTMS) and aluminum tri-sec-butoxide Al(O{sup s}Bu){sub 3}, with different cerium contents, were deposited onto aluminum by dip-coating process. Corrosion resistance and mechanical properties were investigated by electrochemical impedance measurements and nano-indentation respectively. An optimal cerium concentration of 0.01 M was evidenced. To correlate and explain the hybrid coating performances in relation to the cerium content, NMR experiments were performed. It has been shown that when the cerium concentration in the hybrid is higher than 0.01 M there are important modifications in the hybrid structure that account for the mechanical properties and anti-corrosion behavior of the sol–gel coating.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Inclusion of electronic polarizability effect in high pressure structural properties of alloy of rare-earth antimonides

In the present paper, we have investigated the high-pressure structural phase transition of rare-earth antimonides (NdSb and DySb). We studied theoretically the structural properties of alloy of these compounds (NdSb and DySb) by using the three-body potential model with the effect of electronic polarizability (TBIPE{sub P}). These compounds exhibit first order crystallographic phase transition from NaCl (B{sub 1}) to CsCl (B{sub 2}) phase at 17.8 GPa and 22.6 GPa respectively. The study has been extended to mixed crystals and the effect of composition on transition pressure and volume change is investigated. The phase transition pressures and associated volume collapse obtained from present potential model (TBIPE{sub P}) show a good agreement with available experimental data.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Evaluation of flow-induced plate deflection for University of Missouri research reactor low-enriched uranium fuel element

The University of Missouri Research Reactor (MURR), located on the campus of the University of Missouri in Columbia, Missouri, is one of the six United States (U.S.) High Performance Research Reactors (USHPRR), including one critical facility, that are actively collaborating with the U.S. Department of Energy (DOE) National Nuclear Security Administration (NNSA) Office of Material Management and Minimization (M3) Reactor Conversion Program to convert from highly enriched uranium (HEU, ≥20 wt% U-235) fuel to low-enriched uranium (LEU, <20 wt% U-235) fuel. A new type of very high-density LEU fuel based on a monolithic alloy of uranium and 10 wt% molybdenum (U-10Mo) is expected to allow conversion of some USHPRR, including MURR. In the design of its fuel elements, MURR is using thin parallel curved fuel plates separated by coolant channels. In this work, fluid-structure interaction (FSI) analysis of the MURR LEU fuel element is performed at the element level (as compared to the plate level analysis), which models all components of the LEU fuel element, including fuel plates and the supporting structures. Therefore, the effect of supporting structures on the flow distribution within the element and the fuel plate deflection are evaluated. In addition to the element nominal flow rate and dimensions, the tolerances in the geometry of the coolant channel and plate thickness, the effect of a comb on plate deflection, and the uncertainty of the flow rate per element are evaluated. For the LEU fuel plates, which are thinner than the current HEU plates, the predicted plate deflection is found to be small compared to the fabrication and assembly tolerances. Thus, the FSI-induced deflections are not expected to noticeably reduce the coolant flow rate or predicted safety margins in the limiting channels for the MURR LEU fuel element. In addition to the simulation work, a hydraulic performance test of the MURR LEU fuel element is currently being planned to support conversion to the use of LEU fuel.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

Effect of Cu2+ Activation on Interfacial Water Structure at the Sphalerite Surface as Studied by Molecular Dynamics Simulation

In the first part of this paper, an experimental contact angle study of the fresh and Cu2+ activated sphalerite-ZnS surface as well as the covellite-CuS (001) surface is reported describing the increased hydrophobic character of the surface during Cu2+ activation. In addition to these experimental results, the fresh sphalerite-ZnS (110), copper-zinc sulfide-CuZnS2 (110), villamaninite- CuS2 (100), and covellite-CuS (001) surfaces were examined using Molecular Dynamics Simulation (MDS). Our MDS results on the behavior of interfacial water at the fresh sphalerite-ZnS (110), copper-zinc sulfide-CuZnS2 (110), villamaninite-CuS2 (100), and covellite-CuS (001) surfaces include simulated contact angles, water number density distribution, water dipole orientation, water residence time, and hydrogen-bonding considerations. The copper content at the Cu2+ activated sphalerite surface seems to account for the increased hydrophobicity as revealed by both experimental and MD simulated contact angle measurements. The relatively greater hydrophobic character developed at the Cu2+ activated sphalerite surface and at the copper-zinc sulfide surface has been described by MDS, based on the structure of interfacial water and its dynamic properties. L.X.D. acknowledges funding from the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences.

Jin, Jiaqi↗