Domains in CoCr investigated by neutron depolarization

Polarized neutrons (λ = 0.47 nm) are transmitted through RF and magnetron sputtered CoCr films (0.3-5 μm thick) with the polarization vector in the plane or perpendicular to the plane of the film. In the former case we can deduce from the depolarization the effective height heffof the domains and from the angular dependence of the depolarization the section width δ (which is proportional to the domain width) in the remanent states after perpendicular and after in-plane saturation. As expected, heffappears to be larger after perpendicular saturation and for a film thickness h ∼ 400 nm, heffapproaches h. This is attributed to the disappearance of reversed spike domains in the thinnest films. The lower hefffound in magnetron films with a lower surface/bulk coercivity ratio is also consistent with spike domain theory. The section width δ is found to he proportional to hx with x depending on the preparation or magnetic history of the film between 0.6 and 0.8. For magnetron films δ is ∼ 1.5 as large as in RF films of equal thickness, in qualitative agreement only with the fact that K1is twice as large as for RF films

Surface and bulk magnetic behaviour of sputtered CoCr films

The magnetic hysteresis curve at the surface of RF- and magnetron-sputtered CoCr (81/19 at.%), in the thickness range of 20-2500 nm, was measured with a rotating-analyser apparatus using the magneto-optic Kerr effect. The Kerr rotation of CoCr films (13-19 at.% Cr) decreases with increasing Cr content, and depends slightly on wavelength, showing a faint minimum between 550 and 600 nm. The surface hysteresis is compared with the bulk hysteresis as measured with a VSM. For RF films the maximum surface coercivity is higher than the bulk coercivity, being 120 and 95 kA m-1 respectively for 80 nm thick films but an abrupt decrease in only the surface coercivity was found at t=125 nm. The coercivity of magnetron-sputtered CoCr deviates from that of RF-sputtered films. Until a maximum coercivity is reached at approximately=1 mu m, the surface coercivity is about 20% higher, but at approximately=2 mu m both coercivities decrease strongly. The existence of reversed domains within the main domains of CoCr is proposed, and the reversal mechanism is thought to be one in which the reversed domains grow at the expense of the main domain

Superconducting and structural properties of plasma sprayed YBaCuO layers deposited on metallic substrates

The properties of plasma sprayed Y-Ba-Cu-O coatings deposited on metallic substrates are studied. Stainless steel, nickel steels and pure nickel are used as substrate. Y-Ba-Cu-O deposited on stainless steel and nickel steel reacts with the substrate. This interaction can be suppressed by using an yttria-stabilized zirconia (YsZ) diffusion barrier. However, after heat treatment the Y-Ba-Cu-O layers on YsZ show cracks perpendicular to the surface. As a result the critical current density is very low. The best results are obtained for Y-Ba-Cu-O deposited on pure nickel; here no cracks perpendicular to the surface are observed. The critical current increases with the anneal temperature but annealing for longer than 10 h does not seem to improve the superconducting properties any further

First principles modelling of magnesium titanium hydrides

Mixing Mg with Ti leads to a hydride Mg(x)Ti(1-x)H2 with markedly improved (de)hydrogenation properties for x < 0.8, as compared to MgH2. Optically, thin films of Mg(x)Ti(1-x)H2 have a black appearance, which is remarkable for a hydride material. In this paper we study the structure and stability of Mg(x)Ti(1-x)H2, x= 0-1 by first-principles calculations at the level of density functional theory. We give evidence for a fluorite to rutile phase transition at a critical composition x(c)= 0.8-0.9, which correlates with the experimentally observed sharp decrease in (de)hydrogenation rates at this composition. The densities of states of Mg(x)Ti(1-x)H2 have a peak at the Fermi level, composed of Ti d states. Disorder in the positions of the Ti atoms easily destroys the metallic plasma, however, which suppresses the optical reflection. Interband transitions result in a featureless optical absorption over a large energy range, causing the black appearance of Mg(x)Ti(1-x)H2.Comment: 22 pages, 9 figures, 4 table

Echocardiography of isolated subacute left heart tamponade in a patient with cor pulmonale and circumferential pericardial effusion

Patients with advanced idiopathic pulmonary artery hypertension have often a chronic pericardial effusion. It is the result of increased transudation and impaired re-absorption due to elevated venous pressure. These patients have pre-existent symptoms and signs of chronic right heart failure. High degree of suspicion is required to detect of development of an atypical form of tamponade with isolated compression of left heart chambers as shown in present case report. Transthoracic echocardiography provides a rapid access to the correct diagnosis, a prompt relief of symptoms following the ultrasound guided pericardiocentesis and important diagnostic tool for regular follow up of patients thereafter as shown in our case report

MODELING OF A METHANE FUELLED DIRECT CARBON FUEL CELL SYSTEM

ABSTRACT Energy conversion today is subject to high thermodynamic losses. About 50 to 90 % of the exergy of primary fuels is lost during conversion into power or heat. The fast increasing world energy demand makes a further increase of conversion efficiencies inevitable. The substantial thermodynamic losses (exergy losses of 20 to 30 %) of thermal fuel conversion will limit future improvements of power plant efficiencies. Electrochemical conversion of fuel enables fuel conversion with minimum losses. Various fuel cell systems have been investigated at the Delft University of Technology during the past twenty years. It appeared that exergy analyses can be very helpful in understanding the extent and causes of thermodynamic losses in fuel cell systems. More than 50 % of the losses in high temperature fuel cell (MCFC and SOFC) systems can be caused by heat transfer. Therefore system optimisation must focus on reducing the need for heat transfer as well as improving the conditions for the unavoidable heat transfer. Various options for reducing the need for heat transfer are discussed in this paper. High temperature fuel cells, eventually integrated into gas turbine processes, can replace the combustion process in future power plants. High temperature fuel cells will be necessary to obtain conversion efficiencies up to 80 % in case of large scale electricity production in the future. The introduction of fuel cells is considered to be a first step in the integration of electrochemical conversion in future energy conversion systems. Keywords: Fuel cell systems; Exergy analysis; Thermodynamic analysis; System modelling; Cycle Tempo; PEMFC; MCFC; SOFC; Applications INTRODUCTION Today our world strongly depends on the availability of energy for almost all of their activities. Total energy demand is growing fast, in particular due to the development of the large Asian countries. To ensure our future energy supply the losses of energy conversion have to be reduced and the utilisation of available sources, in particular renewable sources, should be stimulated. Conversion of primary fuels into electricity, power, heat or secondary fuels is necessary to fulfil our energy demands. These conversions are involved with substantial thermodynamic losses. These losses should be presented as exergy losses to get a true representation of the thermodynamic performance of conversion systems. Exergy is the potential to obtain work from an amount of energy or from an energy flow; exergy values do represent a true yardstick for all relevant thermodynamic characteristics Exergy efficiencies are some percentage points lower than thermal efficiencies (based on the lower heating value of the fuel) in case of the conversion of primary energy into power. As thermal efficiencies of less than 50 % are normal practice exergy losses will on average be higher than 50 %. Thermal efficiencies are in general high (around 90 % or more) in case of heat generating systems, but exergy efficiencies are much lower depending on the temperature level at which i