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Han, S.

Publications and source records attributed to Han, S..

285 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Eliminating Voltage Decay of Lithium-Rich Li 1.14 Mn 0.54 Ni 0.14 Co 0.14 O 2 Cathodes by Controlling the Electrochemical Process

Lithium-rich material owns a particularly high capacity owing to the activation of electrochemical inactive Li 2 MnO 3 phase. But at the same time, MnO 2 phase formed after Li 2 MnO 3 activation confronts a severe problem of converting to spinel phase, and resulting in voltage decay. To our knowledge, this phenomenon is inherent property of layered manganese oxide materials and can hardly be overcome. Based on this, unlike previous reports, herein we design a method for the first time to accelerate the phase transformation by tuning the charge upper-limit voltage at a high value, so the phase transformation process can be finished in a few cycles. Then material structure remains stable while cycling at a low upper-limit voltage. By this novel method voltage decay is eliminated significantly.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Ferromagnetic-organic interfacial states and their role on low voltage current injection in tris-8-hydroxyquinloline (Alq{sub 3}) organic spin valves

Organic Spin Valves (OSVs) operate at small bias (<100 mV) when carrier injection should not occur due to injection barriers and in built potentials. We explore the consequences of hybrid-interface states between a ferromagnetic electrode and an organic semiconductor in OSV carrier injection. By temperature-dependent Dark Injection measurements, we observe hole trapping due to these filled states and measure a low thermal activation energy (∼100 meV) of the carrier density within OSVs. The small injection barrier is consistent with a significant interfacial potential, due to hybrid-interface state filling, overcoming the injection barrier due to the electrode work function—transport level mismatch.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2001

Simulated microgravity upregulates an endothelial vasoconstrictor prostaglandin

Endothelial nitric oxide contributes to the vascular hyporesponsiveness to norepinephrine (NE) observed in carotid arteries from rats exposed to simulated microgravity. The goal of the present study was to determine whether a cyclooxygenase product of arachidonic acid also influences vascular responsiveness in this setting. Microgravity was simulated in rats by hindlimb unweighting (HU). After 20 days of HU, carotid arteries were isolated from control and HU-treated rats, and vascular rings were mounted in tissue baths for the measurement of isometric contraction. Two cyclooxygenase inhibitors, indomethacin and ibuprofen, and the selective thromboxane A(2) prostanoid-receptor antagonist, SQ-29548, had no effect on the contraction to NE in control vessels but markedly reduced contraction to NE in HU vessels. When the endothelium was removed, indomethacin no longer had any effect on the NE-induced contraction in HU vessels. In endothelium-intact vessels in the presence of indomethacin, the addition of the nitric oxide synthase inhibitor, N(G)-L-nitro-arginine methyl ester, to the medium bathing HU vessels increased the contraction to NE to the level of that of the control vessels. These results indicate that HU treatment induced two endothelial changes in carotid artery that opposed each other. Nitric oxide activity was increased and was responsible for the vascular hyporesponsiveness to NE. The activity of a vasoconstrictor prostaglandin was also increased, and attenuated the vasodilating effect of nitric oxide.

Non-NASA Center↗
NASA NTRS2000

Radial Flows in Supergranules

We determine the radial component of the supergranular flow velocity by examining the center-to-limb variation of the Doppler velocity signal. We acquire individual Doppler images obtained with the MDI instrument on the SOHO spacecraft and process them to remove the p-mode oscillation signal, the axisymmetric flows, the convective blueshift signal, and instrumental artifacts. The remaining Doppler signal contains only cellular flow structures. The Doppler signal from the horizontal flows in these cells varies like sin p, where p is the heliocentric angle from disk center. The Doppler signal from radial flows varies like cos p. We fit the center-to-limb variation of the mean squared velocity signal to a straight line in sin(exp 2) rho over the central portion of the disk. The intercept of this line at disk center gives the amplitude of the radial component of the flow. The slope of the line gives the amplitude of the horizontal component. We find that the radial flows for typical supergranules have speeds about 10% that of their associated horizontal flows or about 30 m/s. The ratio of the radial to horizontal flow speed increases from 9% to about 18% as the size of the cells decreases from > 60 Mm to approximately 5 Mm. We use data simulations to check these results and find a ratio that increases from 5% to only about 12% over the same range of cell sizes. These smaller ratios are attributed to an underestimation of the horizontal flow speeds due to the fact that, the transverse component of the horizontal flow is not detected by the Doppler measurements.

Hathaway, D. H.↗
NASA NTRS2000

Evidence that simulated microgravity may alter the vascular nonreceptor tyrosine kinase second messenger pathway

Simulated microgravity (hind limb unweighting; HU) reduces maximal contractile capacity to norepinephrine (NE) but not 5-hydroxytryptamine (5-HT) in the rat abdominal aorta of male Wistar rats. Our earlier study showed that voltage-operated calcium channels, the MAPK pathway [1], and vasoconstrictive prostaglandins contribute to the NE-induced contraction of control (C) but not HU, aorta rings. Genistein, a general tyrosine kinase inhibitor, caused a significant reduction in vascular contractility in C but not HU arteries. The present study explored the role of protein kinase C (PKC) and extracellular receptor-activated kinase 1 and 2 (ERK1/2) in the HU-induced vascular hyporesponsiveness to NE. Microgravity was simulated in Wistar rats by 20 day HU. The abdominal aorta was removed from control and HU rats, cut into 3 mm rings, and mounted in tissue baths to measure isometric contraction. Protein levels were determined using Western blot analysis. PD98059, a selective MAPKK inhibitor, caused a marked inhibition of NE-induced contraction in both C and HU arteries. Calphostin C, a PKC inhibitor, completely abolished the contractile response to NE in both C and HU tissues. Phosphorylated (activated) ERK1/2 protein mass was greater in C, compared to HU, aortas, and was reduced by genistein only in C tissues. MAPK total protein levels in the rat aorta were increased in the HU-treated, compared to C, animals. These results indicate that PKC represents an early transduction step in the contractile response to NE in the rat abdominal aorta. That inhibition of the step immediately before activation of MAPK reduced contraction in both C and HU tissues, while general tyrosine kinase inhibition with genistein blocked only the control responses, suggests that a nonreceptor tyrosine kinase may be involved in HU-induced vascular hyporesponsiveness to NE.

Non-NASA Center↗
NASA NTRS1999

The Photospheric Convection Spectrum

Spectra of the cellular photospheric flows are determined from observations acquired by the MDI instrument on the SOHO spacecraft. Spherical harmonic spectra are obtained from the full-disk observations. Fourier spectra are obtained from the high-resolution observations. The p-mode oscillation signals and instrumental artifacts are reduced by temporal filtering of the Doppler data. The resulting spectra give power (kinetic energy) per wavenumber for effective spherical harmonic degrees from 1 to over 3000. The spectra show distinct peaks representing granules and supergranules but no distinct features at wavenumbers representative of mesogranu;es or giant cells. The observed cellular patterns and spectra are well represented by a model that only includes granules and supergranules.

Hathaway, D. H.↗
NASA NTRS1993

Numerical study of 1-D, 3-vector component, thermally-conductive MHD solar wind

In the present study, transient, 1-dimensional, 3-vector component MHD equations are used to simulate steady and unsteady, thermally conductive MHD solar wind expansions between the solar surface and 1 AU (astronomical unit). A variant of SIMPLE numerical method was used to integrate the equations. Steady state solar wind properties exhibit qualitatively similar behavior with the known Weber-Davies Solutions. Generation of Alfven shock, in addition to the slow and fast MHD shocks, was attempted by the boundary perturbations at the solar surface. Property changes through the disturbance were positively correlated with the fast and slow MHD shocks. Alfven shock was, however, not present in the present simulations.

Han, S.↗