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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 1,657 records · Page 92
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Electron-vibration energy exchange models in nitrogen-containing plasma flows

The physics of vibrational kinetics in nitrogen-containing plasma produced by collisions with electrons is studied on the basis of recently derived cross sections and rate coefficients for the resonant vibrational-excitation by electron-impact. The temporal relaxation of the vibrational energy and of the vibrational distribution function is analyzed in a state-to-state approach. The electron and vibrational temperatures are varied in the range [0-50 000] K. Conclusions are drawn with respect to the derivation of reduced models and to the accuracy of a relaxation time formalism. An analytical fit of the vibrational relaxation time is given.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Behaviour and stability of Trivelpiece-Gould modes in non-neutral plasma containing small density fraction of background gas ions

It is shown that the frequencies of Trivelpiece-Gould (TG) modes in non-neutral plasma can get into the low-frequency range due to the Doppler shift caused by plasma rotation in crossed fields. TG modes interact with the ion modes that leads to plasma instability. In paper the frequency spectrum of 'cold' electron plasma completely filling a waveguide and containing small density fraction of ions of background gas is determined numerically. For ions the kinetic description is used. Oscillations having azimuthal number m= 2 are considered. In this case both low- and upper-hybrid TG modes get into the low-frequency range. The spectrum consists of families of 'modified' ion cyclotron (MIC) modes and electron TG modes with the frequencies equal to hybrid frequencies with the Doppler shift. The growth rates of upper-hybrid modes are much faster than the growth rates of low-hybrid and MIC modes.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Investigation of anisotropic photonic band gaps in three-dimensional magnetized plasma photonic crystals containing the uniaxial material

In this paper, the dispersive properties of three-dimensional (3D) magnetized plasma photonic crystals (MPPCs) composed of anisotropic dielectric (the uniaxial material) spheres immersed in homogeneous magnetized plasma background with face-centered-cubic (fcc) lattices are theoretically investigated by the plane wave expansion method, as the Voigt effects of magnetized plasma are considered. The equations for calculating the anisotropic photonic band gaps (PBGs) in the first irreducible Brillouin zone are theoretically deduced. The anisotropic PBGs and two flatbands regions can be obtained. The effects of the ordinary-refractive index, extraordinary-refractive index, filling factor, plasma frequency, and external magnetic field on the dispersive properties of the 3D MPPCs are investigated in detail, respectively, and some corresponding physical explanations are also given. The numerical results show that the anisotropy can open partial band gaps in 3D MPPCs with fcc lattices and the complete PBGs can be found compared to the conventional 3D MPPCs doped by the isotropic material. The bandwidths of PBGs can be tuned by introducing the magnetized plasma into 3D PCs containing the uniaxial material. It is also shown that the anisotropic PBGs can be manipulated by the ordinary-refractive index, extraordinary-refractive index, filling factor, plasma frequency, and external magnetic field, respectively. The locations of flatbands regions cannot be manipulated by any parameters except for the plasma frequency and external magnetic field. Introducing the uniaxial material can obtain the complete PBGs as the 3D MPPCs with high symmetry and also provides a way to design the tunable devices.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Wetting kinetics of water nano-droplet containing non-surfactant nanoparticles: A molecular dynamics study

In this Letter, dynamic wetting of water nano-droplets containing non-surfactant gold nanoparticles on a gold substrate is examined via molecular dynamics simulations. The results show that the addition of non-surfactant nanoparticles hinders the nano-second droplet wetting process, attributed to the increases in both surface tension of the nanofluid and friction between nanofluid and substrate. The droplet wetting kinetics decreases with increasing nanoparticle loading and water-particle interaction energy. The observed wetting suppression and the absence of nanoparticle ordering near the contact line of nano-sized droplets differ from the wetting behaviors reported from nanofluid droplets of micron size or larger.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2013

Q-factor of (In,Ga)N containing III-nitride microcavity grown by multiple deposition techniques

A 3λ/2 (In,Ga)N/GaN resonant cavity, designed for ∼415 nm operation, is grown by molecular beam epitaxy and is sandwiched between a 39.5-period (In,Al)N/GaN distributed Bragg reflector (DBR), grown on c-plane GaN-on-sapphire pseudo-substrate by metal-organic vapor phase epitaxy and an 8-period SiO{sub 2}/ZrO{sub 2} DBR, deposited by electron beam evaporation. Optical characterization reveals an improvement in the cavity emission spectral purity of approximately one order of magnitude due to resonance effects. The combination of spectrophotometric and micro-reflectivity measurements confirms the strong quality (Q)-factor dependence on the excitation spot size. We derive simple analytical formulas to estimate leak and residual absorption losses and propose a simple approach to model the Q-factor and to give a quantitative estimation of the weight of cavity disorder. The model is in good agreement with both transfer-matrix simulation and the experimental findings. We point out that the realization of high Q-factor (In,Ga)N containing microcavities on GaN pseudo-substrates is likely to be limited by the cavity disorder.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Modeling a planar sheath in dust-containing plasmas

One-dimensional fluid model is utilized to describe the sheath at a dust-containing plasma-wall boundary. The model equations are solved on the scale of the electron Debye length. The spatial distributions of electric potential and of the velocities and densities of charged species are calculated in a wide range of control parameters. The dust charge number, electric force, and ion drag force are also investigated. The impacts of Havnes parameter, the electron to ion temperature ratio, the ion collisionality, and the ionization on the spatial distributions of the plasma species and the incident fluxes of the ions to the wall (or to the probe) are investigated. With increase of Havnes parameter, the sheath thickness and the ion flux to the wall are reduced, whereas the ion drift velocity is increased. Enhanced ion thermal motion causes the ion flux to the wall to increase. An increase in ion collisionality with neutrals causes both the sheath thickness and the ion flux to the wall to decrease. With increase of the ionization rate, the sheath thickness is found to decrease and the ion flux collected by a probe increases. The localization of dust particles above the electrode is intensified by the increases in Havnes parameter, the electron to ion temperature ratio, collisionality, and ionization rate.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Properties of polycarbonate containing BaTiO{sub 3} nanoparticles

The real part of the relative permittivity, ε′, and dielectric loss, tan δ, have been determined at audio frequencies at temperatures from about 5 K to 350 K for nano-composites composed of BaTiO{sub 3} nanoparticles and polycarbonate. The room temperature breakdown strength was also measured and thermal analysis, nuclear magnetic resonance and scanning electron microscopy studies were carried out. For some films the nanoparticles were surface-treated (STNP) while for others they were not (UNP). For concentrations of UNP greater than about 3.4 vol. %, ε′ is much larger than expected on the basis of laws of mixing. On the other hand, ε′ for materials made using STNP is well-behaved. Correspondingly, increased loss (ε″ or tan δ) in the vicinity of room temperature is observed for the materials made from UNP. The anomalously large values of relative permittivity and increased loss are attributed to the presence of large aggregates in the materials made using the UNP. For both UNP-and STNP-based materials, the breakdown strength is found to decrease as nanoparticle concentration increases. The breakdown strength for the materials made using STNP is found to be larger for all concentrations than for those containing UNP despite the presence of large aggregates in some of the STNP-based materials. This shows that breakdown is strongly affected by the nanoparticle surfaces and/or the interface layer. It is also found that the breakdown strength for materials made using UNP increases as particle size increases. Finally, variable temperature and pressure proton nuclear magnetic resonance relaxation measurements were made to assess the effect of nanoparticle inclusion on polymer motion, and the effects were found to be very minor.

36 MATERIALS SCIENCE↗
DOE OSTI2014

High temperature oxidation behavior of austenitic stainless steel AISI 304 in steam of nanofluids contain nanoparticle ZrO2

The objective of this study is to evaluate high temperature oxidation behavior of austenitic stainless steel SS 304 in steam of nanofluids contain nanoparticle ZrO{sub 2}. The oxidation was performed at high temperatures ranging from 600 to 800°C. The oxidation time was 60 minutes. After oxidation the surface of the samples was analyzed by different methods including, optical microscope, scanning electron microscope (SEM) and X-ray diffraction (XRD). X-ray diffraction examination show that the oxide scale formed during oxidation of stainless steel AISI 304 alloys is dominated by iron oxide, Fe{sub 2}O{sub 3}. Minor element such as Cr{sub 2}O{sub 3} is also appeared in the diffraction pattern. Characterization by optical microscope showed that cross section microstructure of stainless steel changed after oxidized with the oxide scale on the surface stainless steels. SEM and x-ray diffraction examination show that the oxide of ZrO{sub 2} appeared on the surface of stainless steel. Kinetic rate of oxidation of austenite stainless steel AISI 304 showed that increasing oxidation temperature and time will increase oxidation rate.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Electron spin resonance study of Er-concentration effect in GaAs;Er,O containing charge carriers

Er-concentration effect in GaAs;Er,O containing charge carriers (n-type, high resistance, p-type) has been studied by X-band Electron spin resonance (ESR) at low temperature (4.7 K < T < 18 K). Observed A, B, and C types of ESR signals were identical to those observed previously in GaAs:Er,O without carrier. The local structure around Er-2O centers is not affected by carriers because similar angular dependence of g-values was observed in both cases (with/without carrier). For temperature dependence, linewidth and lineshape analysis suggested the existence of Er dimers with antiferromagnetic exchange interaction of about 7 K. Moreover, drastic decrease of ESR intensity for C signal in p-type sample was observed and it correlates with the decrease of photoluminescence (PL) intensity. Possible model for the Er-2O trap level in GaAs:Er,O is discussed from the ESR and PL experimental results.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

New nanocomposites based on layered aluminosilicate and guanidine containing polyelectrolytes

The new functional nanomaterials based on layered aluminosilicate and guanidine containing polyelectrolytes combining high bactericidal activity with an increased ability to bind to heavy metals and organic pollutants were received. To prove the chemical structure of the model compounds (zwitterionic delocalized resonance structures AG/MAG and PAG/PMAG), as well as the presence of such structures in nanocomposites received on their basis and the MMT, IR, {sup 1}H NMR spectroscopy, X-ray diffraction studies and nanoindentation/sclerometry followed by scanning the surface in the area of the indentation were used.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Correlation of anomalous write error rates and ferromagnetic resonance spectrum in spin-transfer-torque-magnetic-random-access-memory devices containing in-plane free layers

In a small fraction of magnetic-tunnel-junction-based magnetic random-access memory devices with in-plane free layers, the write-error rates (WERs) are higher than expected on the basis of the macrospin or quasi-uniform magnetization reversal models. In devices with increased WERs, the product of effective resistance and area, tunneling magnetoresistance, and coercivity do not deviate from typical device properties. However, the field-swept, spin-torque, ferromagnetic resonance (FS-ST-FMR) spectra with an applied DC bias current deviate significantly for such devices. With a DC bias of 300 mV (producing 9.9 × 10{sup 6} A/cm{sup 2}) or greater, these anomalous devices show an increase in the fraction of the power present in FS-ST-FMR modes corresponding to higher-order excitations of the free-layer magnetization. As much as 70% of the power is contained in higher-order modes compared to ≈20% in typical devices. Additionally, a shift in the uniform-mode resonant field that is correlated with the magnitude of the WER anomaly is detected at DC biases greater than 300 mV. These differences in the anomalous devices indicate a change in the micromagnetic resonant mode structure at high applied bias.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Li{sub 4}FeH{sub 6}: Iron-containing complex hydride with high gravimetric hydrogen density

Li{sub 4}FeH{sub 6}, which has the highest gravimetric hydrogen density of iron-containing complex hydrides reported so far, is synthesized by hydrogenation of a powder mixture of iron and LiH above 6.1 GPa at 900 °C. In situ synchrotron radiation X-ray diffraction measurements reveal that while kinetics require high temperature and thus high pressure for the synthesis, Li{sub 4}FeH{sub 6} is expected to be thermodynamically stable slightly below room temperature at ambient pressure; further synthetic studies to suppress the kinetic effects may enable us to synthesize Li{sub 4}FeH{sub 6} at moderate pressures. Li{sub 4}FeH{sub 6} can be recovered at ambient conditions where Li{sub 4}FeH{sub 6} is metastable.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Fine tunable red-green upconversion luminescence from glass ceramic containing 5%Er{sup 3+}:NaYF{sub 4} nanocrystals under excitation of two near infrared femtosecond lasers

In this paper, we report fine tunable red-green upconversion luminescence of glass ceramic containing 5%Er{sup 3+}: NaYF{sub 4} nanocrystals excited simultaneously by two near infrared femtosecond lasers. When the glass ceramic was irradiated by 800 nm femtosecond laser, weak red emission centered at 670 nm was detected. Bright red light was observed when the fs laser wavelength was tuned to 1490 nm. However, when excited by the two fs lasers simultaneously, the sample emitted bright green light centered at 550 nm, while the red light kept the same intensity. The dependences of the red and the green light intensities on the two pump lasers are much different, which enables us to manipulate the color emission by adjusting the two pump laser intensities, respectively. We present a theoretical model of Er{sup 3+} ions interacting with two fs laser fields, and explain well the experimental results.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Collision dynamics of polyatomic molecules containing carbon rings at low temperatures

We explore the collision dynamics of complex hydrocarbon molecules (benzene, coronene, adamantane, and anthracene) containing carbon rings in a cold buffer gas of {sup 3}He. For benzene, we present a comparative analysis of the fully classical and fully quantum calculations of elastic and inelastic scattering cross sections at collision energies between 1 and 10 cm{sup −1}. The quantum calculations are performed using the time-independent coupled channel approach and the coupled-states approximation. We show that the coupled-states approximation is accurate at collision energies between 1 and 20 cm{sup −1}. For the classical dynamics calculations, we develop an approach exploiting the rigidity of the carbon rings and including low-energy vibrational modes without holonomic constraints. Our results illustrate the effect of the molecular shape and the vibrational degrees of freedom on the formation of long-lived resonance states that lead to low-temperature clustering.

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

Mesoporous organosilica nanotubes containing a chelating ligand in their walls

We report the synthesis of organosilica nanotubes containing 2,2′-bipyridine chelating ligands within their walls, employing a single-micelle-templating method. These nanotubes have an average pore diameter of 7.8 nm and lengths of several hundred nanometers. UV-vis absorption spectra and scanning transmission electron microscopy observations of immobilized nanotubes with an iridium complex on the bipyridine ligands showed that the 2,2′-bipyridine groups were homogeneously distributed in the benzene-silica walls. The iridium complex, thus, immobilized on the nanotubes exhibited efficient catalytic activity for water oxidation using Ce{sup 4+}, due to the ready access of reactants to the active sites in the nanotubes.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Synthesis and characterization of new class of ionic liquids containing phenolate anion

In these manuscript novel ionic liquids containing a new class of 'phenolate' anions was synthesized and characterized. 1-methylmidazole with different alkyl chains such as butyl, hexyl and octyl groups was used as the cationic part. All the ionic liquids were obtained as liquids at room temperature. The synthesized ionic liquids were characterized using {sup 1}H NMR and {sup 13}C NMR spectroscopy. The thermal stability of the ionic liquids was studied using thermo gravimetric analysis (TGA). The effect of temperature on the density and viscosity of the ionic liquids were studied over a temperature range from 293.15 K to 373.15K at atmospheric pressure. From the experimental values of density, the molecular volume, standard molar entropy and the lattice energy of the ionic liquids were calculated.

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

Influence of stress on optical transitions in GaN nanorods containing a single InGaN/GaN quantum disk

Cathodoluminescence (CL) hyperspectral imaging has been performed on GaN nanorods containing a single InGaN quantum disk (SQD) with controlled variations in excitation conditions. Two different nanorod diameters (200 and 280 nm) have been considered. Systematic changes in the CL spectra from the SQD were observed as the accelerating voltage of the electron beam and its position of incidence are varied. It is shown that the dominant optical transition in the SQD varies across the nanorod as a result of interplay between the contributions of the deformation potential and the quantum-confined Stark effect to the transition energy as consequence of radial variation in the pseudomorphic strain.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Electrooptical properties of hybrid liquid crystalline systems containing CdSe quantum dots

In this paper, we present electrooptical properties of hybrid liquid crystalline systems, which contained CdSe quantum dots (QDs). We have shown by experiments of degenerated two-wave mixing and transverse conductivity measurements that liquid crystal cells filled with nematic and doped with semiconductor nanoparticles exhibit photorefractive effect associated with photoconductivity appearing in the system. We also present the mathematical model, which explains the relationship between the photoconductivity of the layer on which the QDs reside and the generation of holographic gratings. Our research may help to develop better understanding of processes observed in such systems and create more efficient materials for holographic data storage.

77 NANOSCIENCE AND NANOTECHNOLOGY↗