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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 1,261 records · Page 70
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Novel modification of Hall-type ion source (study and the first results)

We present the original approach to use plasma accelerators with closed electron drift (Hall-type ion sources), which, unlike traditional accelerators with metal and dielectric walls, have open walls and can be applied for creation cost effective low maintenance plasma devices based on plasma lens configuration for production of converging towards axis accelerated ion beams. The paper describes pilot sample of Hall-type plasma accelerator, the first experimental results, one-dimensional theoretical model, and exact analytical solutions following from it.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

The role of electro-explosion alloying with titanium diboride and treatment with pulsed electron beam in the surface modification of VT6 alloy

The paper presents the results of the investigation of VT6 titanium alloy subjected to electro-explosion alloying with TiB{sub 2} and irradiation with pulsed electron beam. It was established that electro-explosion alloying resulted in a high level of roughness of the surface layer with high adhesion of the modified layer and matrix. Further irradiation of the material with electron beam resulted in the smoothing of the surface of alloying and formation of a porous structure with various scale levels in the surface layer. It was also established that the energetic exposure causes the formation of a gradient structure with a changing elemental composition along the direction from the surface of alloying.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Wave induced density modification in RF sheaths and close to wave launchers

With the return to full metal walls - a necessary step towards viable fusion machines - and due to the high power densities of current-day ICRH (Ion Cyclotron Resonance Heating) or RF (radio frequency) antennas, there is ample renewed interest in exploring the reasons for wave-induced sputtering and formation of hot spots. Moreover, there is experimental evidence on various machines that RF waves influence the density profile close to the wave launchers so that waves indirectly influence their own coupling efficiency. The present study presents a return to first principles and describes the wave-particle interaction using a 2-time scale model involving the equation of motion, the continuity equation and the wave equation on each of the time scales. Through the changing density pattern, the fast time scale dynamics is affected by the slow time scale events. In turn, the slow time scale density and flows are modified by the presence of the RF waves through quasilinear terms. Although finite zero order flows are identified, the usual cold plasma dielectric tensor - ignoring such flows - is adopted as a first approximation to describe the wave response to the RF driver. The resulting set of equations is composed of linear and nonlinear equations and is tackled in 1D in the present paper. Whereas the former can be solved using standard numerical techniques, the latter require special handling. At the price of multiple iterations, a simple ’derivative switch-on’ procedure allows to reformulate the nonlinear problem as a sequence of linear problems. Analytical expressions allow a first crude assessment - revealing that the ponderomotive potential plays a role similar to that of the electrostatic potential arising from charge separation - but numerical implementation is required to get a feeling of the full dynamics. A few tentative examples are provided to illustrate the phenomena involved.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Surface modification of Ti alloy by electro-explosive alloying and electron-beam treatment

By methods of modern physical metallurgy the analysis of structure phase states of titanium alloy VT6 is carried out after electric explosion alloying with boron carbide and subsequent irradiation by pulsed electron beam. The formation of an electro-explosive alloying zone of a thickness up to 50 µm, having a gradient structure, characterized by decrease in the concentration of carbon and boron with increasing distance to the treatable surface has been revealed. Subsequent electron-beam treatment of alloying zone leads to smoothing of the alloying area surface and is accompanied by the multilayer structure formation at the depth of 30 µm with alternating layers with different alloying degrees having the structure of submicro - and nanoscale level.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Temperature induced modification of the mid-infrared response of single-walled carbon nanotubes

The temperature dependences of the absorbance spectra of thin free-standing single-walled carbon nanotube (SWCNT) films were studied in the infrared range (700–6200 cm{sup −1}) while heating the air from 300 to 575 K. The observed temperature variation in the infrared absorbance spectra has been explained by two different physical factors. The first one is the strong temperature dependence of the conductivity of p-type doped semiconducting SWCNTs. The second one is the temperature dependence of electron relaxation time of intraband electron transitions in metallic SWCNTs. The possibility of the separation of contributions from the interband and intraband transitions to the infrared spectra of SWCNT films has been demonstrated.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Electrical conductivity modification using silver nano particles of Jatropha Multifida L. and Pterocarpus Indicus w. extracts films

Natural polymers can be extracted from leaf or stem of plants. Pterocarpus Indicus W. (PIW) and Jatropha Multifida L. (JIL) plants are good candidate as natural polymer sources. PIW and JIW polymers contain chemical compound so-called flavonoids which has C{sub 6}-C{sub 3}-C{sub 6} carbons conjugated configuration. The renewable type of polymer as well as their abundancy of flavonoid provide us to explore their physical properties. A number of research have been reported related to broad synthesis method and mechanical properties. So far there is no specific report of electrical conductivity associated to PIW and JIL natural polymers. In order to obtain electrical conductivity and its crystallinity of the extracted polymer films, it was induced on them a various fraction of silver nano particles. The film has been prepared by means of spin coating method on nickel substrate. It was revealed that FTIR spectra confirm the existing of rutine flavonoid. The crystallinity of the samples increase from 0.66%, to 4.11% associated to the respective various of silver fractions of 0.1 M to 0.5 M. SEM images show that there are some grains of silver in the film. The nature of electric conductivity increases a long with the addition of silver. The electrical conductivity increase significantly from 3.22 S/cm, to 542.85 S/cm. On the other hand, PIW films also shows similar trends that increase of Ag induce the increase its crystallinity as well as its electrical conductivity at semiconducting level. This result opens a prospective research and application of the green renewable polymer as optoelectronic materials.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Correlation between surface modification and photoluminescence properties of β-Ga{sub 2}O{sub 3} nanostructures

In this work three different growth methods have been used to grow β-Ga{sub 2}O{sub 3} nanostructures. The nanostructures were characterized by Grazing Incident X-Ray Diffraction, Scanning Electron Microscopy, Transmission Electron Microscopy and Photoluminescence Spectroscopy. Photoluminescence spectra for all the samples of β-Ga{sub 2}O{sub 3} nanostructures exhibit an UV and blue emission band. The relative intensity of UV and blue luminescence is strongly affected by the surface defects present on the nanostructures. Our study shows that Photoluminescence intensity of UV and blue luminescence can be reliably used to determine the quality of β-Ga{sub 2}O{sub 3} nanostructures. Further the work opens up the possibility of using UV excitation and subsequent Photoluminescence analysis as a possible means for oxygen sensing. The Photoluminescence mechanism in β-Ga{sub 2}O{sub 3} nanostructures is also discussed.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Structural modification of strontium hexaferrite through destruction process and ionic substitution

Synthesis of single phased SrO.6Fe{sub 2-x}Mn{sub x/2}Ti{sub x/2}O{sub 3} (x = 0.0; 0.5; and 1.0) nanoparticles has been prepared through mechanical alloying, assisted with the ultrasonic destruction process. Monocrystalline particles were obtained when x = 0 treated with ultrasonic destruction at 55 μm of transducer amplitude. Average particle size and crystallite size were reduced significantly from 723 nm to ∼87 nm for x = 0. The particle size was not significantly reduced when x = 0.5 and x = 1 was changed. On the other hand, substitution of Ti elements on some of Fe elements expectedly had a major effect on reducing particle size. This was proven by larger size on both particle and crystallite size at x = 1 rather than x = 0.5, with comparison respectively 2:1 (in nm). In addition, a higher transducer power was required for modifying Strontium Hexaferrite (SHF) with more Ti elements and a bigger size of pre-ultrasonic destructed sample. It is concluded that the amplitude of the transducer in ultrasonic destruction process and the element of ionic substitution affects both average particle size and crystallite size of SHF.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Modification in band gap of zirconium complexes

The optical properties of zirconium complexes with amino acid based Schiff bases are reported here. The zirconium complexes show interesting stereo chemical features, which are applicable in organometallic and organic synthesis as well as in catalysis. The band gaps of both Schiff bases and zirconium complexes were obtained by UV-Visible spectroscopy. It was found that the band gap of zirconium complexes has been modified after adding zirconium compound to the Schiff bases.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Modifications of band gap in Si/Ge multilayers through vacuum annealing

In the present paper, important experimental findings and their impact on physical properties of Si/Ge systems are presented with the focus on structural and electronic properties investigations also covering band gap engineering. The use of synchrotron radiation based valence band photoemission spectroscopy technique has been demonstrated which provides the variation in bandgap values as a function of annealing on [Si/Ge]{sub x10} multilayers structure. For this purpose, the required VB offsets are obtained by considering the corresponding VB maximum of as prepared sample as a reference. The bandgap values thus obtained show a gradually decreasing pattern with increasing temperature, which is discussed in terms of the effect of various factors such as: (i) quantum confinement effect normally observed in confined systems (ii) change in the annealing induced intermixing leading to the formation of SiGe alloy and (iii) roughness at the surface/interface.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Study of structural modification of PVA by incorporating Ag nanoparticles

Nanocomposites of PVA with Ag nanoparticles dispersed in it were synthesized using solution casting method. The morphology and size distribution of Ag nanoparticles embedded in PVA matrix were obtained by transmission electron microscopy (TEM) and Field emission scanning electron microscopy (FE-SEM). Raman spectroscopy was used to examine structural changes taking place inside polyvinyl alcohol (PVA) matrix due to incorporation of Ag nanoparticle. Raman analysis indicates that Ag nanoparticles interact with PVA through H-bonding.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Enhanced flashover strength in polyethylene nanodielectrics by secondary electron emission modification

This work studies the correlation between secondary electron emission (SEE) characteristics and impulse surface flashover in polyethylene nanodielectrics both theoretically and experimentally, and illustrates the enhancement of flashover voltage in low-density polyethylene (LDPE) through incorporating Al{sub 2}O{sub 3} nanoparticles. SEE characteristics play key roles in surface charging and gas desorption during surface flashover. This work demonstrates that the presence of Al{sub 2}O{sub 3} nanoparticles decreases the SEE coefficient of LDPE and enhances the impact energy at the equilibrium state of surface charging. These changes can be explained by the increase of surface roughness and of surface ionization energy, and the strong interaction between nanoparticles and the polymer dielectric matrix. The surface charge and flashover voltage are calculated according to the secondary electron emission avalanche (SEEA) model, which reveals that the positive surface charges are reduced near the cathode triple point, while the presence of more nanoparticles in high loading samples enhances the gas desorption. Consequently, the surface flashover performance of LDPE/Al{sub 2}O{sub 3} nanodielectrics is improved.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Modification of the spectrum of high harmonics by a weak vacuum ultraviolet field

Within the framework of the time-dependent effective range theory, we have calculated the spectra of high harmonics in a field containing an intense low-frequency component and a weak (perturbative) high-frequency component with a photon energy exceeding the ionisation potential of the atomic target. We have presented a quantum-mechanical substantiation of the quasi-classical theory [A.V. Flegel et al. Quantum Electron., 47, 222 (2017)], which describes additional generation channels of high harmonics induced by a weak high-frequency field. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Laplace plane modifications arising from solar radiation pressure

The dynamical effects of solar radiation pressure (SRP) in the solar system have been rigorously studied since the early 1900s. This non-gravitational perturbation plays a significant role in the evolution of dust particles in circumplanetary orbits, as well as in the orbital motion about asteroids and comets. For gravitationally dominated orbits, SRP is negligible and the resulting motion is largely governed by the oblateness of the primary and the attraction of the Sun. The interplay between these gravitational perturbations gives rise to three mutually perpendicular planes of equilibrium for circular satellite orbits. The classical Laplace plane lies between the equatorial and orbital planes of the primary, and is the mean reference plane about whose axis the pole of a satellite's orbit precesses. From a previously derived solution for the secular motion of an orbiter about a small body in a SRP dominated environment, we find that SRP acting alone will cause an initially circular orbit to precess around the pole of the primary's heliocentric orbital plane. When the gravitational and non-gravitational perturbations act in concert, the resulting equilibrium planes turn out to be qualitatively different, in some cases, from those obtained without considering the radiation pressure. The warping of the surfaces swept out by the modified equilibria as the semi-major axis varies depends critically on the cross-sectional area of the body exposed. These results, together with an adiabatic invariance argument on Poynting-Robertson drag, provide a natural qualitative explanation for the initial albedo dichotomy of Saturn's moon, Iapetus.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

The modification of the nonlinear guiding center theory

We modify the NonLinear Guiding Center theory for perpendicular diffusion by replacing the spectral amplitude of the two-component model of magnetic turbulence with that of the two-dimensional model (following Shalchi), and replacing the constant a {sup 2}, which indicates the degree particles following the magnetic field line, with the variable a'{sup 2} as a function of the magnetic turbulence. We combine the modified model with the NonLinear PArallel diffusion theory to solve perpendicular and parallel diffusion coefficients simultaneously. It is shown that the new model agrees better with simulations. Furthermore, we fit the numerical results of the new model with polynomials, so that the parallel and perpendicular diffusion coefficients can be calculated directly without iteration of integrations, and many numerical calculations can be reduced.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Modification of the parallel scattering mean free path of cosmic rays in the presence of adiabatic focusing

The cosmic ray mean free path in a large-scale nonuniform guide magnetic field with superposed magnetostatic turbulence is calculated to clarify some conflicting results in the literature. A new, exact integro-differential equation for the cosmic-ray anisotropy is derived from the Fokker-Planck transport equation. A perturbation analysis of this integro-differential equation leads to an analytical expression for the cosmic ray anisotropy and the focused transport equation for the isotropic part of the cosmic ray distribution function. The derived parallel spatial diffusion coefficient and the associated cosmic ray mean free path include the effect of adiabatic focusing and reduce to the standard forms in the limit of a uniform guide magnetic field. For the illustrative case of isotropic pitch angle scattering, the derived mean free path agrees with the earlier expressions of Beeck and Wibberenz, Bieber and Burger, Kota, and Litvinenko, but disagrees with the result of Shalchi. The disagreement with the expression of Shalchi is particularly strong in the limit of strong adiabatic focusing.

79 ASTRONOMY AND ASTROPHYSICS↗