Sensors and actuators constructed from freestanding tantalum thin films show promise for micromachining applications and for the study of thin film mechanical behavior. To assess this promise, it is necessary to gain further understanding of the performance of Ta as a structural material. We first study the coefficient of thermal expansion, αTa, using micromachined bent beams, which amplify displacement compared to linear expansion. The value for αTa is 6.8•10−6 m/m°C, in good agreement with the bulk value. This validation enables the study of interstitial oxygen diffusion in Ta, for which literature values of activation energy vary widely, from 0.60 to 1.98 eV. Displacement in air due to oxygen diffusion becomes measurable after 30 min exposure at 180°C. We extract an activation energy for interstitial oxygen in Ta of 0.53 eV/atom. Analysis indicates that lattice rather than grain boundary diffusion is the associated mechanism. To inhibit the oxidation, we construct a thermal stage that controls specimen temperature in 10−5 Pa vacuum. Then, after a 24 h hold, oxidation is suppressed up to 400°C. This result is discussed in terms of O dissolution from its native oxide, coupled with further absorption from background gases.
An enzyme activity that catalyzes the hydrolysis of phosphate from the C-2 position of fructose 2,6-bisphosphate has been detected in rat liver cytoplasm. The S0.5 for fructose 2,6-bisphosphate was about 15 microM and the enzyme was inhibited by fructose 6-phosphate (Ki 40 microM) and activated by Pi (KA 1 mM). Fructose 2,6-bisphosphatase activity was purified to homogeneity by specific elution from phosphocellulose with fructose by specific elution from phosphocellulose with fructose 6-phosphate and had an apparent molecular weight of about 100,000, 6-phosphofructo 2-kinase activity copurified with fructose 2,6-bisphosphatase activity at each step of the purification scheme. Incubation of the purified protein with [gamma-32P]ATP and the catalytic subunit of the cAMP-dependent protein kinase resulted in the incorporation of 1 mol of 32P/mol of enzyme subunit (Mr = 50,000). Concomitant with this phosphorylation was an activation of the fructose 2,6-bisphosphatase and an inhibition of the 6-phosphofructo 2-kinase activity. Glucagon addition to isolated hepatocytes also resulted in an inhibition of 6-phosphofructo 2-kinase and activation of fructose 2,6-bisphosphatase measured in cell extracts, suggesting that the hormone regulates the level of fructose 2,6-bisphosphate by affecting both synthesis and degradation of the compound. These findings suggest that this enzyme has both phosphohydrolase and phosphotransferase activities i.e. that it is bifunctional, and that both activities can be regulated by cAMP-dependent phosphorylation.
The inhibition of hepatocyte 6-phosphofructo-1-kinase by glucagon was suppressed by insulin when the enzyme was measured in crude extracts. However, no effect of either hormone was observed after the removal of allosteric effectors from the enzyme, suggesting that the alterations in activity may be due to changes in the level of fructose 2,6-bisphosphate, a potent allosteric activator of the enzyme. Insulin opposed the action of both glucagon and exogenous cyclic AMP to lower fructose 2,6-bisphosphate levels. The concentration of glucagon and of cyclic AMP that gave a half-maximal decrease in fructose 2,6-bisphosphate levels was increased in the presence of 10 nM insulin from 0.03 to 0.09 nM and from 12 to 36 microM, respectively. Insulin also counteracted the effect of maximal concentrations of epinephrine on fructose 2,6-bisphosphate levels. In the presence of 0.02 nM glucagon or 10 microM epinephrine, 10 nM insulin enhanced 6-phosphofructo-2-kinase and decreased fructose 2,6-bisphosphatase activity in (NH4)2SO4-treated hepatocyte extracts. The bifunctional enzyme 6-phosphofructo-2-kinase/fructose 2,6-bisphosphatase was shown to be a substrate for the cAMP-dependent protein kinase but not for phosphorylase kinase. It was concluded that insulin opposed the action of glucagon and epinephrine by affecting the phosphorylation state of 6-phosphofructo-2-kinase/fructose 2,6-bisphosphatase. Fructose 2,6-bisphosphate levels were decreased in liver cells from diabetic rats. Addition of 30 mM glucose elevated fructose 2,6-bisphosphate levels in cells from fed and 24-h-starved rats but not in cells from diabetic rats. This was probably due to decreases in both 6-phosphofructo-2-kinase and glucokinase activity in the diabetic state. These results show that insulin has both short and long term effects on fructose 2,6-bisphosphate metabolism in liver.
The purpose of this Cooperative Research and Development Agreement (CRADA) between UT-Battelle, LLC (herein referred to as the “Contractor”) and General Motors Corporation (herein referred to as “Sponsor”) is to study efficiency benefits and materials issues associated with a diesel particulate filter (DPF) device developed by the Sponsor that is regenerated electrically. The Electrically-Assisted DPF (EADPF) technology was evaluated on a GM 1.9-liter 4- cylinder diesel engine and baselined against conventional DPF regeneration strategies which utilize exothermic heating from additional fuel oxidized over an upstream diesel oxidation catalyst (DOC). In the comparison, the EADPF technology demonstrated 50% less fuel use than the conventional approach and also reduced the amount of time required for regeneration by 60%. Both benefits are dramatic improvements over the conventional technique. Although the regeneration effectiveness was limited to 85-90% for the EADPF technique, post-study analysis of the DPF substrate indicated this limitation was due to heater element cross sectional area coverage which is a limitation that can be alleviated in future designs. A fiber optic probe technique for measuring the substrate temperature during regeneration via collection and analysis of blackbody radiation spectra was successfully employed to understand substrate vs. gas temperatures (as measured by thermocouples). While substrate temperatures were found to be 15-300ºC higher than the gas temperatures, the dominant parameter dictating the range of temperatures experienced by the substrate was the soot loading prior to regeneration. Thus, control of start of regeneration is a critical parameter for successful implementation. A secant elastic modulus (ESEC) in the range of 1 - 2 GPa consistently results in analytical (FEA or numerical) and experimental correlation for deformations of DPF cordierite ceramic equibiaxial flexure, sectored flexure, and o-ring flexure specimens and for three different DPF diameters. That range of ESEC is about 4-12 times lower than reported elastic modulus for cordierite ceramics sonically and dynamically measured. As a consequence of that lower elastic modulus, the actual stresses in a DPF during regeneration will be much lower than those predicted using sonically or dynamically measured elastic modulus, and simple heater patterning (of at least two zones of annular heating), probably can be successfully employed without creating sufficiently high stresses in cordierite DPFs to initiate fracture in them. Lastly, owing to the non-linearity of stress-strain response of the cordierite material in these DPFs, a strain-based failure criterion is more appropriate for design than the herein described (and DPF-community used) stress-based criterion and the DPF community would be better served to pursue that in the future.
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)
