High State (high + state)

Distribution by Scientific Domains

Selected Abstracts

FLOX® Steam Reforming for PEM Fuel Cell Systems,

FUEL CELLS, Issue 4 2004
H.-P. Schmid
Abstract Primary energy savings and CO2 reduction is one of the key motivations for the use of fuel cell systems in the energy sector. A benchmark of domestic cogeneration by PEMFC with existing large scale power production systems such as combined steam-gas turbine cycle, clearly reveals that only fuel cell systems optimising overall energy efficiency (>,85%) and electrical efficiencies (>,35%) show significant primary energy savings, about 10%, compared with the best competing technology. In this context, fuel processing technology plays a dominant role. A comparison of autothermal and steam reforming concepts in a PEMFC system shows inherent advantages in terms of efficiency at low complexity for the latter. The main reason for this is that steam reforming allows for the straightforward and effective use of the anode-off gas energy in the reformer burner. Consequently, practical electrical system efficiencies over 40% seem to be achievable, most likely by steam reformers. FLOX®-steam reforming technology has reached a high state of maturity, offering diverse advantages including: compact design, stable anode off-gas usage, high efficiency, as well as simple control behaviour. Scaling of the concept is straightforward and offers an opportunity for efficient adaptation to smaller (1,kW) and larger (50,kW) units. [source]

Chandra monitoring observations of the ultraluminous X-ray source NGC 5204 X-1

T. P. Roberts
ABSTRACT We report the results of a two-month campaign conducted with the Chandra X-ray observatory to monitor the ultraluminous X-ray source (ULX) NGC 5204 X-1. This was composed of a 50-ks observation, followed by ten 5-ks follow-ups spaced initially at ,3, then at ,10-d intervals. The ULX flux is seen to vary by factors ,5 on time-scales of a few days, but no strong variability is seen on time-scales shorter than an hour. There is no evidence for a periodic signal in the X-ray data. An examination of the X-ray colour variations over the period of the campaign shows the ULX emission consistently becomes spectrally harder as its flux increases. The X-ray spectrum from the 50-ks observation can be fitted by a number of disparate spectral models, all of which describe a smooth continuum with, unusually for a ULX, a broad emission feature evident at 0.96 keV. The spectral variations, both within the 50-ks observation and over the course of the whole campaign, can then be explained solely by variations in the continuum component. In the context of an optically thick corona model (as found in other recent results for ULXs) the spectral variations can be explained by the heating of the corona as the luminosity of the ULX increases, consistent with the behaviour of at least one Galactic black hole system in the strongly Comptonized very high state. We find no new evidence supporting the presence of an intermediate-mass black hole in this ULX. [source]

The X-ray/,-ray spectrum of XTE J1550,564 in the very high state

Marek Gierli
ABSTRACT We fit the broad-band X-ray/,-ray spectrum (0.8,1000 keV) of the accreting black hole XTE J1550,564 in the very high state. The quasi-simultaneous data from ASCA, RXTE and OSSE (on CGRO) show that the disc is strongly Comptonized, with a high-energy tail extending out to several hundred keV. However, inverse Compton scattering by a purely thermal or purely power-law electron distribution cannot explain the observed spectrum. Instead, the data require a hybrid distribution, with both thermal and non-thermal electrons scattering the disc photons. This is very similar to the electron distribution inferred for other high and very high state black hole binaries, showing that it is a generic feature of high mass accretion rate black holes. [source]

Spin-filtering effect in a two-dimensional electron gas under a local fringe field

Seon-Gu Huh
Abstract We fabricated a spin-filtering device which consists of InAs based two-dimensional electron gas and two ferromagnetic pads. A fringe field at the edge of a ferromagnetic pad was used to induce spin polarization of the moving electrons in a two-dimensional electron gas. The direction of the fringe field was determined by the magnetization of the ferromagnetic pad, which was switched by using the external magnetic field. A current of which spins were aligned by one fringe field (polarizer) was filtered by the other fringe field (analyzer). The resistance of the device was in either a high state or a low state depending on the alignment of the fringe fields. The spin-filtering effect diminishes rapidly as the thermal energy exceeds the Zeeman splitting. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Formulation of aqueous concentrated alumina suspensions.

Influence of a disaccharide: trehalose
Abstract Trehalose, a disaccharide, is very well known to protect living cells efficiently from dehydration and has been tested in the formulation of aqueous alumina suspensions. It has been added into slurries stabilized with Tiron®, (HO)2C6H2(SO3Na)2, which permits a high state of dispersion by creating repulsive potential between particles. Trehalose added into such suspensions acts as a lubricant and enhances flowing properties of suspensions because of its strong interaction with water which breaks the hydrogen-bonded network of the solvent. Trehalose addition is beneficial for carrying out shaping methods of alumina components by coagulation as it increases solid concentration in the suspension, which facilitates pouring the suspension into a mould. Unfortunately this addition hinders coagulation of particles. © 2003 Society of Chemical Industry [source]