10,479 research outputs found
Computation of the equilibrium composition of reacting gas-solid mixtures with material and energy balance constraints Status report
Equilibrium composition computed for reacting- gas-solid composite materials using material and energy constraint
Experimental verification of the non-equilibrium model for predicting behavior in the char zone of a charring ablator Status report
Experimental simulation to establish accuracy of nonequilibrium flow model with system simulating charring during ablatio
Solution of the Frozen Flow Momentum Equation Status Report
Momentum equation solved for frozen flow in char zone of charring ablato
One-watt fiber-based power-by-light system for satellite applications
In this work, a fiber-based optical powering (or power-by-light) system capable of providing more than 1 W is developed. The prototype was used in order to power a shunt regulator for controlling the activation and deactivation of solar panels in satellites. The work involves the manufacture of a light receiver (a GaAs multiple photovoltaic converter (MPC)), a power conditioning block, and a regulator and the implementation and characterization of the whole system. The MPC, with an active area of just 3.1 mm2, was able to supply 1 W at 5 V with an efficiency of 30%. The maximum measured device efficiency was over 40% at an input power (Pin) of 0.5 W. Open circuit voltage over 7 V was measured for Pin over 0.5 W. A system optoelectronic efficiency (including the optical fiber, connectors, and MPC) of 27% was measured at an output power (Pout) of 1 W. At Pout = 0.2 W, the efficiency was as high as 36%. The power conditioning block and the regulator were successfully powered with the system. The maximum supplied power in steady state was 0.2 W, whereas in transient state, it reached 0.44 W. The paper also describes the characterization of the system within the temperature range going from -70 to +100?°C
Self-fields in thin superconducting tapes: implications to the thickness effect in coated conductors
Most applications of superconductors, such as power transmission lines,
motors, generators, and transformers, require long cables through which large
currents circulate. Impressive progress has recently been achieved in the
current-carrying capability in conductors based on high-temperature
superconductors. Coated conductors are likely the best examples, consisting of
very good quality thin layers of YBCO superconductor grown on top of a metallic
tape with some intermediate layers. However, there is an important problem for
achieving large currents: a large decrease in transport critical-current
density Jc when increasing film thickness has been observed in coated
conductors made by all available techniques. Here, we theoretically explain the
nature and the ubiquitous presence of this so-called thickness effect by
analyzing the self-field created by the transport currents in the
superconductor, assuming a realistic field-dependent Jc. This knowledge can
help finding new ways to improve transport current in thick superconducting
films.Comment: 7 pages, 3 figure
Submarine Accumulations of Methane Hydrates in Adjacences of Marambio Island (Seymour Island), Antarctica and Its Probable Environmental Incident
The presence of aliphatic hydrocarbons in sediments at the bottom of the platform and the continental margin of the northeastern tip of the Antarctic Peninsula and its natural escapes, leads us to infer about the likely effects they may have on the Antarctic environment, particularly on changes off average in surface temperatures and seawater. Methane leaks recorded in shallow waters of the region are compatible with the destabilization of gas hydrates in the marine substrate and with changes in average surface temperatures and seawater, suggesting a probable environmental impact such as a consequence of this process, based on the hypothesis of the “clathrate rifle”, the scientific theory of Gerry Dickens and James Kennet, which argues that the rise in sea temperature can lead to a sudden release of methane from the clathrate deposits located in the ocean bottoms, as happened in the Eocene
Superconducting/magnetic three state nanodevice for memory and reading applications
We present a simple nanodevice that can operate in two modes: i) three-state
memory and ii) reading device. The nanodevice is fabricated with an array of
ordered triangular-shaped nanomagnets embedded in a superconducting thin film.
The input signal is ac current and the output signal is dc voltage. Vortex
ratchet effect in combination with out of plane magnetic anisotropy of the
nanomagnets is the background physics which governs the nanodevice performance.Comment: 10 pages, 4 figure
Scaling of the conductance in gold nanotubes
A new form of gold nanobridges has been recently observed in ultrahigh-vacuum
experiments, where the gold atoms rearrange to build helical nanotubes, akin in
some respects to carbon nanotubes. The good reproducibility of these wires and
their unexpected stability will allow for conductance measurements and make
them promising candidates for future applications . We present here a study of
the transport properties of these nanotubes in order to understand the role of
chirality and of the different orbitals in quantum transport observables. The
conductance per atomic row shows a light decreasing trend as the diameter
grows, which is also shown through an analytical formula based on a one-orbital
model.Comment: 5 pages, 6 figure
Reliability evaluation of III-V concentrator solar cells
Concentrator solar cells have been proposed as an interesting way of reducing the cost of photovoltaic electricity. However, in order to compete with conventional solar modules it is necessary not only to reduce costs but also to evaluate and increase the present reliability. Concentrator solar cells work at higher temperature, solar radiation and current stress than conventional solar cells and a carefully reliability analysis is needed. In this paper a reliability analysis procedure, that is being developed, is presented
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