22 research outputs found
Free serum cortisol during the postoperative acute phase response determined by equilibrium dialysis liquid chromatography-tandem mass spectrometry
In severely ill patients low concentrations of the corticosteroid binding globulin are typically found; the aim of this study was to quantify directly free bioactive cortisol concentrations in the sera of postoperative cardiosurgical patients. Serum samples of 12 consecutive patients undergoing aortocoronary bypass surgery taken preoperatively and on the postoperative days 1 to 4 were analyzed. Total serum cortisol was quantified using liquid chromatographytandem mass spectrometry with an online sample extraction system and trideuterated cortisol as the internal standard, and free serum cortisol was measured after overnight equilibrium dialysis. Whereas on the first postoperative day, the median total serum cortisol concentration was approximately twofold increased compared to preoperative samples (preoperatively, 245 nmol/l (interquartile range (IQR) 203293 nmol/l); first postoperative day, 512 nmol/l (IQR 410611 nmol/l)), median dialyzable free cortisol concentration was almost sevenfold increased (preoperatively, 14.2 nmol/l (IQR 10.920.7 nmol/l); first postoperative day, 98.3 nmol/l (IQR 81.3134 nmol/l)). On the fourth postoperative day, median free cortisol was still significantly increased compared to baseline sampling (p < 0.05), whereas median total cortisol was not. A median of 5.7% (IQR 5.47.0%) of total cortisol was found as free cortisol on the preoperative day, 21.2% (IQR 18.9 23.5%) on the first postoperative day and 10.5% (IQR 9.814.0%) on the fourth postoperative day. It is concluded that during the postoperative period the freeto bound ratio of cortisol is highly variable and that during the acute phase response direct quantification of free bioactive cortisol concentrations seems to be biologically more appropriate than the measurement of total cortisol concentrations
Revisiting the Corrosion of the Aluminum Current Collector in Lithium-Ion Batteries
The
corrosion of aluminum current collectors and the oxidation
of solvents at a relatively high potential have been widely investigated
with an aim to stabilize the electrochemical performance of lithium-ion
batteries using such components. The corrosion behavior of aluminum
current collectors was revisited using a home-build high-precision
electrochemical measurement system, and the impact of electrolyte
components and the surface protection layer on aluminum foil was systematically
studied. The electrochemical results showed that the corrosion of
aluminum foil was triggered by the electrochemical oxidation of solvent
molecules, like ethylene carbonate, at a relative high potential.
The organic radical cations generated from the electrochemical oxidation
are energetically unstable and readily undergo a deprotonation reaction
that generates protons and promotes the dissolution of Al<sup>3+</sup> from the aluminum foil. This new reaction mechanism can also shed
light on the dissolution of transitional metal at high potentials
Ultrafast growth of single-crystal graphene assisted by a continuous oxygen supply
Graphene has a range of unique physical properties(1,2) and could be of use in the development of a variety of electronic, photonic and photovoltaic devices(3-5). For most applications, large-area high-quality graphene films are required and chemical vapour deposition (CVD) synthesis of graphene on copper surfaces has been of particular interest due to its simplicity and cost effectiveness(6-15). However, the rates of growth for graphene by CVD on copper are less than 0.4 mu m s(-1), and therefore the synthesis of large, single-crystal graphene domains takes at least a few hours. Here, we show that single-crystal graphene can be grown on copper foils with a growth rate of 60 mu m s(-1). Our high growth rate is achieved by placing the copper foil above an oxide substrate with a gap of similar to 15 mu m between them. The oxide substrate provides a continuous supply of oxygen to the surface of the copper catalyst during the CVD growth, which significantly lowers the energy barrier to the decomposition of the carbon feedstock and increases the growth rate. With this approach, we are able to grow single-crystal graphene domains with a lateral size of 0.3 mm in just 5 s.ope