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Results for “PHASE STABILITY”

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 1,549 records · Page 86
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Characterization of the bistable wideband optical filter on the basis of nonlinear 2D photonic crystal

In our work, we investigated the wideband optical filter on the basis of nonlinear photonic crystal. The all-optical flip-flop using ultra-short pulses with duration lower than 200 fs is obtained in such filters. Here we pay special attention to the stability problem of the nonlinear element. To investigate this problem, the temporal response demonstrating the flip-flop have been computed within the certain range of the wavelengths as well as at different input power.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Surface oxidation energetics and kinetics on MoS{sub 2} monolayer

In this work, surface oxidation of monolayer MoS{sub 2} (one of the representative semiconductors in transition-metal dichalcogenides) has been investigated using density functional theory method. Oxygen interaction with MoS{sub 2} shows that, thermodynamically, the surface tends to be oxidized. However, the dissociative absorption of molecular oxygen on the MoS{sub 2} surface is kinetically limited due to the large energy barrier at low temperature. This finding elucidates the air stability of MoS{sub 2} surface in the atmosphere. Furthermore, the presence of defects significantly alters the surface stability and adsorption mechanisms. The electronic properties of the oxidized surface have been examined as a function of oxygen adsorption and coverage as well as substitutional impurities. Our results on energetics and kinetics of oxygen interaction with the MoS{sub 2} monolayer are useful for the understanding of surface oxidation, air stability, and electronic properties of transition-metal dichalcogenides at the atomic scale.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Specific features of ZnCdS nanoparticles synthesized in different solvents

Stable colloidal solutions of ZnCdS nanoparticles (3–6 nm in diameter) in polyvinyl alcohol, polyethylene glycol, and H{sub 2}O are produced. The size of the synthesized nanoparticles is independent of the relation between precursors. It is shown that stabilization of the particles is defined by the charge-stability factor and can be attained without any additional stabilizing additives. The ZnCdS quantum dots synthesized emit in a wide spectral range from 450 to 600 nm.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Long-term stability assessment of AlGaN/GaN field effect transistors modified with peptides: Device characteristics vs. surface properties

AlGaN/GaN Field Effect Transistors (FETs) are promising biosensing devices. Functionalization of these devices is explored in this study using an in situ approach with phosphoric acid etchant and a phosphonic acid derivative. Devices are terminated on peptides and soaked in water for up to 168 hrs to examine FETs for both device responses and surface chemistry changes. Measurements demonstrated threshold voltage shifting after the functionalization and soaking processes, but demonstrated stable FET behavior throughout. X-ray photoelectron spectroscopy and atomic force microscopy confirmed peptides attachment to device surfaces before and after water soaking. Results of this work point to the stability of peptide coated functionalized AlGaN/GaN devices in solution and support further research of these devices as disposable, long term, in situ biosensors.

36 MATERIALS SCIENCE↗
NASA NTRS1992

Particle scattering and current sheet stability in the geomagnetic tail during the substorm growth phase

The particle scattering and current sheet stability features in the geomagnetic tail during the phase of substorm growth were investigated using Tsyganenko's (1989) magnetic field model. In a study of four substorm events which were observed both in the high-altitude nightside tail and in the auroral ionosphere, the model magnetic field was adjusted to each case so as to represent the global field development during the growth phase of the substorms. The model results suggest that the auroral brightenings are connected with processes taking place in the near-earth region inside about 15 earth radii. The results also suggest that there is a connection between the chaotization of the electrons and the auroral brightenings at substorm onset.

Pulkkinen, T. I.↗
DOE OSTI2016

Neutron diffraction analysis and electrochemical performance of spinel Ni(Mn{sub 2−x}Co{sub x})O{sub 4} as anode materials for lithium ion battery

Highlights: • The reversible capacity and cyclability of Ni(Mn{sub 2−x}Co{sub x})O{sub 4} first increases and then decreases with increasing Co content. • Neutron diffraction and Rielveld refinements are applied to analyze the site occupancies of Mn, Co, O and Ni. • Excessive Co ions in 8a and 16d sites reduce the structure stability leading to poor electrochemical performance. - Abstract: The effects of Co substitution on the structure and electrochemical performances of spinel Ni(Mn{sub 2−x}Co{sub x})O{sub 4} (x = 0, 0.5, and 1.0) have been investigated. With the increase of Co content the lattice parameters decrease owing to the smaller ion radius of Co than Mn. The reversible capacity and cyclability of Ni(Mn{sub 2−x}Co{sub x})O{sub 4} first increase and then decrease with the increase of Co content and NiMn{sub 1.5}Co{sub 0.5}O{sub 4} shows the best electrochemical performance in compared to the other two samples. Neutron diffraction and Rielveld refinement are further applied to analyze the site occupancies of the elements of Mn, Co, O and Ni. A certain amount of Co ions substitution are favorable to enhance the electrochemical performance, but excessive Co ions in 8a and 16d sites reduce the stability of host structure which leads to the poor electrochemical performance.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Development of a dipodal Schiff base ligand with N-imine and O-naphtholate donors: A potential chelator towards Cu(II) metal ion established through potentiometric and spectrophotometric studies

A novel hydroxynaphthaldehyde derived Schiff base ligand N,N’-bis-[2-[(2-hydroxy-1-naphthyl)methyleneamino]ethyl]propanediamide (DOTA2HNAP) containing nitrogen and oxygen donor atoms has been developed. The lowest energy molecular structure of DOTA2HNAP and its complexes with Cu (II) metal ion were examined by molecular mechanics using MM+ force which later was re-optimized by semi-empirical method. The theoretical IR and UV spectra of the ligand were obtained using semi empirical/ZINDO/PM3 and were compared with the experimental ones. The coordinating ability of DOTA2HNAP with H{sup +} and Cu(II) ions was investigated in 1:99 (DMSO: water) binary solvent mixture at 25±1°C by potentiometric and spectrophotometric method. The electronic spectra of the ligand show three distinct peaks (253nm, 320nm and 360nm) implicating existence of the Schiff base in quinone form that was well supported by theoretical spectral studies. Out of various complex species forming in solution, all the metal ions show higher stability of complexes when in 1:1 metal-ligand stoichiometry, binding through two N-imine and two O-naphtholate groups.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Nanostructured Cu-Cr alloy with high strength and electrical conductivity

The influence of nanostructuring by high pressure torsion (HPT) on strength and electrical conductivity in the Cu-Cr alloy has been investigated. Microstructure of HPT samples was studied by transmission electron microscopy with special attention on precipitation of small chromium particles after various treatments. Effect of dynamic precipitation leading to enhancement of strength and electrical conductivity was observed. It is shown that nanostructuring leads to combination of high ultimate tensile strength of 790–840 MPa, enhanced electrical conductivity of 81%–85% IACS and thermal stability up to 500 °C. The contributions of grain refinement and precipitation to enhanced properties of nanostructured alloy are discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

H-treatment impact on conductive-filament formation and stability in Ta{sub 2}O{sub 5}-based resistive-switching memory cells

In this article, we evidence the lower formation energy and improved stability of the conductive filament (CF) formed in TiN\Ta{sub 2}O{sub 5}\Ta resistive-switching memory cells treated in NH{sub 3} atmosphere at 400 °C. This annealing treatment results in (i) lower forming voltage, (ii) lower CF resistance, and (iii) longer retention lifetime of the oxygen-vacancy (V{sub o}) chain constituting the CF. Atomistic insights into these processes are provided by ab initio calculations performed for hydrogen (H) species incorporated in non-stoichiometric Ta{sub 2}O{sub 5} supercells: (i) V{sub o} formation energy is reduced by the presence of H, (ii) V{sub o}-chain CF conductivity is increased by V{sub o} + OH complex formation, and (iii) V{sub o}-chain retention is strengthened by the stable V{sub o} + OH complex. As a result, efficient CF formation and excellent state stability are obtained after 15 days at 250 °C.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Synthesis of ruthenium metal doped titanium dioxide nanoparticles for CO{sub 2} hydrogenation

Two different types of Ru metal doped TiO{sub 2} nanoparticles were synthesized using a sole gel method with and without ionic liquid. It was clearly observed during characterizing the Ru-TiO{sub 2}-IL catalyst with respect to Ru-TiO{sub 2} catalyst that Ru metal is dispersed while using ionic liquid as reaction medium for catalyst synthesis. TEM image also reveals the presence of agglomeration free, stable and well dispersed Ru metal doped TiO{sub 2} nanoparticles in Ru-TiO{sub 2}-IL over a Ru-TiO{sub 2} catalyst. Such unique feature of the Ru-TiO{sub 2}-IL catalyst reflected in terms of high TON /TOF value of formic acid during the hydrogenation reaction of CO{sub 2} in task specific ionic liquid medium. Low catalysts loading, moisture/air stability, high selectivity, an easy reaction protocol for catalyst synthesis as well as stress-free reaction condition along with 6 times catalysts recycling is the major outcomes of the proposed protocol.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

TPCPF: Three-Phase Continuation Power Flow Tool for Voltage Stability Assessment of Distribution Networks With Distributed Energy Resources

This article presents a three-phase unbalanced continuation power flow algorithm for voltage stability assessment of distribution systems with high penetration of distributed energy resources (DERs). Analyzing distribution system voltage stability with DER will allow high penetration of renewable energy necessary for the sustainability goals. The developed algorithm can analyze voltage stability for both the meshed and radial systems and the balanced and unbalanced three-phase distribution systems. The developed tool allows the voltage stability analysis to facilitate the planning, operation, control, and distribution system management. The impact of DER on the voltage stability of several test cases has been analyzed considering constant power (P Q) and regulated-voltage (P V ) modes of operation for DER units. Moreover, different voltage stability case studies are presented to demonstrate the impact of unbalance, load increment, and network topology on the maximum loading capacity. Finally, results using the IEEE 13-node feeder, the 18-bus balanced shipboard system, the 13-node CIGRE benchmark system, and the 136-bus redial distribution feeder demonstrate that the developed continuation power flow tool can efficiently perform voltage stability analysis for active distribution systems.

42 ENGINEERING↗
DOE OSTI2012

Photocatalytic activity and stability of TiO{sub 2} and WO{sub 3} thin films

Photocatalysis represents a viable option for complete degrading the dye molecules resulted in the textile industry, up to products that do not represent environmental threats. The photocatalytic degradation of methyl orange has been investigated using TiO{sub 2}, WO{sub 3} and mixed thin films. The photodegradation efficiency is examined in correlation with the experimental parameters (irradiation time, H{sub 2}O{sub 2} addition and stability), along with the morphology and crystallinity data. The H{sub 2}O{sub 2} addition increases the photodegradation efficiency by providing additional hydroxyl groups and further reducing the recombination of the electron-hole pairs by reacting with the electrons at the catalyst interface. To test the stability of the photocatalytic films in long time running processes, batch series of experiments were conducted using contact periods up to 9 days. The results show that the thin films maintained their photocatalytic properties confirming their stability and viability for up-scaling. Highlights: Black-Right-Pointing-Pointer TiO{sub 2}, WO{sub 3} and mixed thin films Black-Right-Pointing-Pointer We tested the photocatalytic activity and photocatalyst stability over a period up to 9 days of continuous irradiation. Black-Right-Pointing-Pointer The influence of medium pH and oxidizing agent (H{sub 2}O{sub 2}) was analyzed.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Magnetization stability analysis of the Stoner-Wohlfarth model under a spin-polarized current with a tilted polarization

The stationary-state solutions of magnetization dynamics under a spin-polarized current that was polarized in an arbitrary direction were investigated by solving the Landau-Lifshitz-Gilbert-Slonczewski equation for a single-domain magnet. Taking into consideration the uniaxial magnetic anisotropy, the equilibrium directions of the magnetization vectors were analytically obtained by solving an algebraic cubic equation. It was found that one to three pairs of magnetization equilibrium states existed, depending on the current intensity and the direction of the spin polarization. By numerically analyzing the stabilities of these equilibrium states, the threshold switching current for the reversing the magnetic vector was obtained under different current polarization configurations, which may be useful for use in future spintronics devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Multilevel characteristics and memory mechanisms for nonvolatile memory devices based on CuInS{sub 2} quantum dot-polymethylmethacrylate nanocomposites

Nonvolatile memory devices based on CuInS{sub 2} (CIS) quantum dots (QDs) embedded in a polymethylmethacrylate (PMMA) layer were fabricated using spin-coating method. The memory window widths of the capacitance-voltage (C-V) curves for the Al/CIS QDs embedded in PMMA layer/p-Si devices were 0.3, 0.6, and 1.0 V for sweep voltages of ±3, ±5, and ±7 V, respectively. Capacitance-cycle data demonstrated that the charge-trapping capability of the devices with an ON/OFF ratio value of 2.81 × 10{sup −10} was maintained for 8 × 10{sup 3} cycles without significant degradation and that the extrapolation of the ON/OFF ratio value to 1 × 10{sup 6} cycles converged to 2.40 × 10{sup −10}, indicative of the good stability of the devices. The memory mechanisms for the devices are described on the basis of the C-V curves and the energy-band diagrams.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Computational study of AuSi{sub n} (n=1-9) nanoalloy clusters invoking DFT based descriptors

Nanoalloy clusters formed between Au and Si are topics of great interest today from both scientific and technological point of view. Due to its remarkable catalytic, electronic, mechanical and magnetic properties Au-Si nanoalloy clusters have extensive applications in the field of microelectronics, catalysis, biomedicine, and jewelry industry. Density Functional Theory (DFT) is a new paradigm of quantum mechanics, which is very much popular to study the electronic properties of materials. Conceptual DFT based descriptors have been invoked to correlate the experimental properties of nanoalloy clusters. In this venture, we have systematically investigated AuSi{sub n} (n=1-9) nanoalloy clusters in the theoretical frame of the B3LYP exchange correlation. The experimental properties of AuSi{sub n} (n=1-9) nanoalloy clusters are correlated in terms of DFT based descriptors viz. HOMO-LUMO gap, Electronegativity (χ), Global Hardness (η), Global Softness (S) and Electrophilicity Index (ω). The calculated HOMO-LUMO gap exhibits interesting odd-even alteration behaviour, indicating that even numbered clusters possess higher stability as compare to their neighbour odd numbered clusters. This study also reflects a very well agreement between experimental bond length and computed data.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Theoretical investigation of the atomic and electronic structure of Li{sub x}BC{sub 3} intercalated compounds

Li{sub x}BC{sub 3} intercalated compounds with various configurations are studied for their possible application as electrode materials for lithium current sources. For this purpose, the band structure and the density of states were calculated for each structure, and energy stability and possible deformations due to a change in the unit cell volume during intercalation are investigated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Electronic structure, elasticity, bonding features and mechanical behaviour of zinc intermetallics: A DFT study

The structural stability, electronic structure, elastic and mechanical properties of TiZn and ZrZn intermetallics have been studied using ab-initio full potential linearized augmented plane wave (FP-LAPW) method within generalized gradient approximation for exchange and correlation potentials. The various structural parameters, such as lattice constant (a{sub 0}), bulk modulus (B), and its pressure derivative (B’) are analysed and compared. The investigation of elastic constants affirm that both TiZn and ZrZn are elastically stable in CsCl (B{sub 2} phase) structure. The electronic structures have been analysed quantitatively from the band structure which reveals the metallic nature of these compounds. To better illustrate the nature of bonding and charge transfer, we have also studied the Fermi surfaces. The three well known criterion of ductility namely Pugh’s rule, Cauchy’s pressure and Frantsevich rule elucidate the ductile nature of these compounds.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗