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At least 1,423 records · Page 79

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DOE OSTI2014

Comparative study of optical and structural properties of electrospun 1-dimensional CaYAl{sub 3}O{sub 7}:Eu{sup 3+} nanofibers and bulk phosphor

We report the optical and structural studies of Eu{sup 3+}-doped 1-dimensional CaYAl{sub 3}O{sub 7} nano-fiber phosphor. CaYAl{sub 3}O{sub 7}:Eu{sup 3+} phosphors were synthesized by electrospinning technique and the pristine nano-fibers were annealed at 900 °C to form well crystallized uniform fibers. Under ultraviolet excitation, the CaYAl{sub 3}O{sub 7}:Eu{sup 3+} exhibited red emission, due to transitions in the 4f states of Eu{sup 3+}. In order to explore the difference between the quantum efficiency of nano-fiber and bulk CaYAl{sub 3}O{sub 7}:Eu{sup 3+} phosphor, detailed structural and optical analyses were carried out. The structural analysis of the CaYAl{sub 3}O{sub 7}:Eu{sup 3+} nano-fibers indicates that the structural environment surrounding the dopant Eu{sup 3+} ion was more unstable in nano-fiber when compared to a bulk sample. Decay curves for both the samples when fitted with double exponential decay model indicate that the nano-fiber has shorter decay time, arising from the larger contribution from the non-radiative decay, due to defect levels introduced in the host lattice. - Highlights: • Synthesis of red nano-phosphor through electrospinning • Luminescence properties of bulk and nano-phosphors are compared. • Inferior emission intensity of the nano-phosphor is analyzed using MEM. • Charge cloud around nano-phosphor was found to be oblique.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Microstructure and nanoindentation of the rostrum of Curculio longinasus Chittenden, 1927 (Coleoptera: Curculionidae)

The rostrum is an extension of the cuticle of the head of weevils (Coleoptera: Curculionidae) and is often used to bore holes for oviposition (the process of laying eggs) into host plant tissue where larval development occurs. In members of the genus Curculio Linnaeus, 1758, the rostrum is long, slender, and strongly curved, but is nevertheless used to excavate straight bore-holes in the fruit of various host plants, through significant deformation of this structure. In this study, scanning electron microscopy (SEM) was used to examine the rostrum of Curculio longinasus Chittenden, 1927, leading to a microstructural model that describes its deformation behavior. Specifically, we used the continuous stiffness measurement (CSM) technique in nanoindentation to measure the Young's modulus and hardness of rostrum. The values of Young's modulus and hardness for the endocuticle were measured to be 8.91 ± 0.93 GPa and 558 ± 60 MPa, respectively. These results are critical for generating accurate finite element models of the head's mechanical behavior while it undergoes deformation. - Highlights: •SEM was used to examine the rostrum of Curculio longinasus Chittenden, 1927. •Nanoindentation to measure the Young's modulus and hardness of rostrum. •Results are critical for finite element models of the head's mechanical behavior.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Source complexity of the 2015 Mw 7.9 Bonin earthquake

The 30 May 2015 Mw 7.9 Bonin earthquake, one of the largest and deepest earthquakes ever recorded by modern seismology, provides a unique opportunity to study the source process and physical mechanisms of deep-focus earthquakes. We develop a novel back-projection technique that allows source imaging in full three-dimensional space with high depth resolution. Our results indicate an initial SW-NE bilateral source propagation followed by a northwest source extension. The multiple-source inversion reveals a two-step source process with propagating directions near-perpendicular to each other, consistent with the 3D back-projection result. The spatial distribution and focal mechanisms of the sub-events cannot be modeled by a single planar rupture, which may display a curved rupture plane or sub-events crossing multiple fault interfaces. Thus, the complex source process can be best explained by stress or structure heterogeneity within the deep slab.

58 GEOSCIENCES↗

DOE OSTI2015

Structure-charge relationship - the case of hematite (001)

We present a multidisciplinary study on the hematite (001)–aqueous solution interface, in particular the relationship between surface structure (studied via surface diffraction in a humid atmosphere) and the macroscopic charging (studied via surface- and zeta-potential measurements in electrolyte solutions as a function of pH). Upon aging in water changes in the surface structure are observed, that are accompanied by drastic changes in the zeta-potential. Surprisingly the surface potential is not accordingly affected. We interpret our results by increasing hydration of the surface with time and enhanced reactivity of singly-coordinated hydroxyl groups that cause the isoelectric point of the surface to shift to values that are reminiscent of those typically reported for hematite particles. In its initial stages after preparation the hematite surface is very flat and only weakly hydrated. Our model links the entailing weak water structure with the observed low isoelectric point reminiscent of hydrophobic surfaces. The absence of an aging effect on the surface potential vs. pH curves is interpreted as domination of the surface potential by the doubly coordinated hydroxyls, which are present on both surfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2026

Enhanced coercivity in Fe5C2/SiO2 core/shell nanocrystals

Rod-shaped Fe5C2 and core/shell Fe5C2/SiO2 nanocrystals were synthesized via a solution-based chemical method. Structural analysis confirmed the monoclinic phase of Fe5C2 with space group C2/c. Zero-field-cooling (ZFC) and field-cooling (FC) magnetization curves revealed distinct magnetic behaviors: uncoated Fe5C2 exhibited a low-temperature FC plateau indicative of strong dipolar interactions, while Fe5C2/SiO2 showed a monotonic increase in FC magnetization, suggesting reduced dipolar interactions due to SiO2 surface passivation. Isothermal remanent magnetization (IRM) and DC demagnetization (DCD) measurements supported this trend, with δM plots confirming weaker dipolar interactions in the coated sample. Bloch’s law fitting of temperature-dependent saturation magnetization showed a smaller Bloch’s constant for pure Fe5C2 and a larger value for Fe5C2/SiO2, reflecting enhanced surface disorder and reduced exchange coupling in the latter. Notably, Fe5C2/SiO2 demonstrated increased coercivity, attributed to decreased dipolar interaction and elevated surface anisotropy. Kneller’s law fitting yielded higher blocking temperatures for Fe5C2 (476 K) than Fe5C2/SiO2 (456 K), highlighting the impact of dipolar interactions on magnetic relaxation. These findings illustrate how SiO2 coatings effectively modulate dipolar interactions and enhance coercivity in Fe5C2 nanocrystals.

Joshi, Pramanand [Department of Physics, Universit↗

DOE OSTI2019

Analysis of the NorthStar Inconel 718 Window

NorthStar Medical Radioisotopes, LLC, is planning to produce the important medical radioisotope molybdenum-99 (Mo-99) through photonuclear reactions in molybdenum-100 (Mo-100). In this approach, a target comprising multiple thin disks of enriched molybdenum metal will be bombarded with a 40-MeV electron beam. Because enriched Mo-100 is expensive, there is a desire to utilize as much beam power as possible to achieve maximum production yield and minimize the size of the target. This requirement leads to very high beam power density (heat deposition in the target), which sets challenging requirements for cooling of the target. In the latest concept developed by NorthStar, a stack of target (sintered molybdenum) disks is irradiated from two sides by a 40-MeV electron beam, with a total power of 240 kW (120 kW from each side). As shown in Figure 1, the target disks are cooled by pressurized helium gas flowing through channels between the disks. A housing encloses the target disks and helium coolant. Thinned regions on opposite sides of the housing act as windows, forming the pressure boundary between the helium within the housing and the evacuated beam tube. A pulsed (50-Hz) 40-MeV electron beam is used, with 120 kW total power and a 10% duty cycle. The pulsing beam creates a corresponding cyclic thermal load within the window material. To examine the effects of the cyclic thermal load on the window, a combination of analyses was performed, including computational fluid dynamics (CFD) and finite element analysis (FEA). The analyses presented in this report were primarily performed using the finite element method. However, because of the curved surface of the window, CFD analysis was used to calculate the convective cooling boundary included in the FEA model. Transient thermal and structural models were used to explore the window geometry, including thickness, radius of curvature, and diameter, while staying within the temperature and stress limits of the material as well as maintaining mechanical stability (i.e., avoiding buckling). Additionally, variations in the size and location of the electron beam were evaluated. Multiple parameters for the window and the electron beam were examined throughout the analysis. Upper and lower bounds were established for the window geometry parameters, and limitations were established for the size and position of the electron beam.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

NASA NTRS1975

Applications of Computer Graphics in Engineering

Various applications of interactive computer graphics to the following areas of science and engineering were described: design and analysis of structures, configuration geometry, animation, flutter analysis, design and manufacturing, aircraft design and integration, wind tunnel data analysis, architecture and construction, flight simulation, hydrodynamics, curve and surface fitting, gas turbine engine design, analysis, and manufacturing, packaging of printed circuit boards, spacecraft design.

Source record↗

NASA NTRS1980

Electromagnetic scattering from two identical pseudospheres

In an attempt to gain some insight into the problem of how close particles have to be on the average before phase effects become important, the cross section and phase matrices for two identical particles as a function of the distance between their centers for both broadside and end-on illumination have been calculated. The point dipole approximation is employed to build two pseudospherical particles each consisting of 32 dipoles with an effective size parameter of 0.9283 and refractive index of 1.54-0.0i. In regard to cross sections, it is found that in certain cases several percent deviation from the converged value, which is twice the single particle cross section, could be found up to distances of separation of 25 single particle diameters. The maxima and minima in the cross section curves can be explained in terms of simple interference effects. Also the element P11 of the phase matrix showed a great deal of structure, and the position of maxima and minima could be explained by phase shift analysis.

Kattawar, G. W.↗

NASA NTRS1982

The path and surviving tail of a comet that fell into the sun

A satisfactory orbital solution for Comet Howard-Koomen-Michels 1979 XI is found on the assumption that the comet's line of apsides coincided with that of the Kreutz sungrazing comet group. The derived perihelion distance then shows that this is the first known case of a comet falling into the sun. A dust tail that survived the comet is studied as a particle flow phenomenon controlled by no force other than solar gravity and solar radiation pressure. The tail's outline is interpreted in terms of an onset of dust production, a peak repulsive force on the particles, and a circumsolar dustfree zone due to particle sublimation. It is shown that the surviving debris consisted mostly of absorbing, submicron size particles in hyperbolic trajectories convex to the sun and curving toward the earth. The tail width may be a product of the interaction of charged dust in the tail with a complicated structure of the coronal magnetic field.

Sekanina, Z.↗

NASA NTRS1982

Photovoltaic properties of ferroelectric BaTiO3 thin films RF sputter deposited on silicon

Ferroelectric thin films of BaTiO3 have been successfully deposited on n-type silicon substrates at temperatures above 500 C by RF sputtering in an O2/Ar atmosphere. Analysis by X-ray diffraction patterns show that films deposited at room temperature are amorphous. At temperatures above 500 C, crystalline BaTiO3 films with a tetragonal structure are obtained. The polarization-electric field (P-E) hysteresis loops and a broad peak in the dielectric constant versus temperature curve at Curie point indicate that the RF sputtered BaTiO3 films are ferroelectric. An anomalous photovoltaic effect is observed in these thin films which is related to the remanent polarization of the material. The results on open-circuit and short-circuit measurements provide an important basis for a better understanding of the role of photovoltaic field, photovoltaic current, and the pyroelectric properties in photoferroelectric domain switching.

Dharmadhikari, V. S.↗

NASA NTRS1984

Intersection of parametric surfaces using lookup tables

When primitive structures in the form of parametric surfaces are combined and modified interactively to form complex intersecting surfaces, it becomes important to find the curves of intersection. One must distinguish between finding the shape of the intersection curve, which may only be useful for display purposes, and finding an accurate mathematical representation of the curve, which is important for any meaningful geometric modeling, analysis, design, or manufacturing involving the intersection. The intersection curve between two or more parametric surfaces is important in a variety of computer-aided design and manufacture areas. A few examples are shape design, analysis of groins, design of fillets, and computation of numerically controlled tooling paths. The algorithm presented here provides a mathematical representation of the intersection curve to a specified accuracy. It also provides the database that can simplify operations such as hidden-surface removal, surface rendering, profile identification, and interference or clearance computations.

Hanna, S. L.↗

NASA NTRS1984

Design of a composite wing extension for a general aviation aircraft

A composite wing extension was designed for a typical general aviation aircraft to improve lift curve slope, dihedral effect, and lift to drag ratio. Advanced composite materials were used in the design to evaluate their use as primary structural components in general aviation aircraft. Extensive wind tunnel tests were used to evaluate six extension shapes. The extension shape chosen as the best choice was 28 inches long with a total area of 17 square feet. Subsequent flight tests showed the wing extension's predicted aerodynamic improvements to be correct. The structural design of the wing extension consisted of a hybrid laminate carbon core with outer layers of Kevlar - layed up over a foam interior which acted as an internal support. The laminate skin of the wing extension was designed from strength requirements, and the foam core was included to prevent buckling. A joint lap was recommended to attach the wing extension to the main wing structure.

Adney, P. S.↗

NASA NTRS1991

Experiments with conjugate gradient algorithms for homotopy curve tracking

There are algorithms for finding zeros or fixed points of nonlinear systems of equations that are globally convergent for almost all starting points, i.e., with probability one. The essence of all such algorithms is the construction of an appropriate homotopy map and then tracking some smooth curve in the zero set of this homotopy map. HOMPACK is a mathematical software package implementing globally convergent homotopy algorithms with three different techniques for tracking a homotopy zero curve, and has separate routines for dense and sparse Jacobian matrices. The HOMPACK algorithms for sparse Jacobian matrices use a preconditioned conjugate gradient algorithm for the computation of the kernel of the homotopy Jacobian matrix, a required linear algebra step for homotopy curve tracking. Here, variants of the conjugate gradient algorithm are implemented in the context of homotopy curve tracking and compared with Craig's preconditioned conjugate gradient method used in HOMPACK. The test problems used include actual large scale, sparse structural mechanics problems.

Irani, Kashmira M.↗

NASA NTRS1992

Algebraic surface grid generation in three-dimensional space

An interactive program for algebraic generation of structured surface grids in three dimensional space was developed on the IRIS4D series workstations. Interactive tools are available to ease construction of edge curves and surfaces in 3-D space. Addition, removal, or redistribution of points at arbitrary locations on a general 3-D surface or curve is possible. Also, redistribution of surface grid points may be accomplished through use of conventional surface splines or a method called 'surface constrained transfinite interpolation'. This method allows the user to redistribute the grid points on the edges of a surface patch; the effect of the redistribution is then propagated to the remainder of the surface through a transfinite interpolation procedure where the grid points will be constrained to lie on the surface. The program was written to be highly functional and easy to use. A host of utilities are available to ease the grid generation process. Generality of the program allows the creation of single and multizonal surface grids according to the user requirements. The program communicates with the user through popup menus, windows, and the mouse.

Warsi, Saif↗

NASA NTRS1992

Material characterization of composite laminates using low-frequency plate wave dispersion data

A recently developed ultrasonic techique which has been successful in monitoring the integrity of advanced structures is described. The technique is based on a two-transducer contact type arrangement that can be used to determine the dispersion curves of guided waves generated within the specimen. The phase velocity of antisymmetric plate waves is determined through spectral analysis of signals recorded from a lead break source on the surface of graphite epoxy laminates. The influence of all five stiffness constants on the dispersion curves of both symmetric and antisymmetric plate waves is theoretically investigated for propagation at 0, 45, and 90 deg to the fibers. All but c12 were found to have a strong influence on the dispersion curves in this frequency range. The fit with the theoretically predicted dispersion curves was excellent for propagation parallel and perpendicular to the fibers in the unidirectional specimen and good for the other cases considered.

Mal, Ajit K.↗

NASA NTRS2017

Unsteady Aerodynamic Force Sensing from Strain Data

A simple approach for computing unsteady aerodynamic forces from simulated measured strain data is proposed in this study. First, the deflection and slope of the structure are computed from the unsteady strain using the two-step approach. Velocities and accelerations of the structure are computed using the autoregressive moving average model, on-line parameter estimator, low-pass filter, and a least-squares curve fitting method together with analytical derivatives with respect to time. Finally, aerodynamic forces over the wing are computed using modal aerodynamic influence coefficient matrices, a rational function approximation, and a time-marching algorithm.

aerodynamic load sensing↗

DOE OSTI2015

Explosive bulk charge

An explosive bulk charge, including: a first contact surface configured to be selectively disposed substantially adjacent to a structure or material; a second end surface configured to selectively receive a detonator; and a curvilinear side surface joining the first contact surface and the second end surface. The first contact surface, the second end surface, and the curvilinear side surface form a bi-truncated hemispherical structure. The first contact surface, the second end surface, and the curvilinear side surface are formed from an explosive material. Optionally, the first contact surface and the second end surface each have a substantially circular shape. Optionally, the first contact surface and the second end surface consist of planar structures that are aligned substantially parallel or slightly tilted with respect to one another. The curvilinear side surface has one of a smooth curved geometry, an elliptical geometry, and a parabolic geometry.

02 PETROLEUM↗

NASA NTRS1977

The time structure of the gamma-ray emission from the Crab and Vela pulsars

High resolution data on the pulsed gamma-ray emission from the Crab and Vela pulsars are presented. The light curves of these two pulsars at gamma-ray energies show striking similarities. The measured pulsed intensity from Vela at energies greater than 50 MeV was found to be .000013 sq cm/sec. The energy spectrum is not consistent with a power law.

Source record↗