Synchronous and Sequential Strategies in the Process Design of Cascade Equipment

Cascade or multistage equipment is characterized by the repetition of similar equipment elements in series. Process design, resulting into the main geometric and kinematic dimensions of the equipment, makes use of different strategies. These strategies, based on a process description, the (equality- and inequality) constraints and the number of degrees of freedom of the mathematical system, which describes the process, can be divided in synchronous- and sequential procedures. In a synchronous strategy no a priori requirements are made as to the distribution of a given process variable over the stages, so that the equipment dimensions are obtained simultaneously. In contrast to this a sequential strategy makes use of a priori statements resulting into stage-to-stage calculations and a decreasing number of degrees of freedom. The general theory presented with detailed information on process description, constraints and degrees of freedom, has been applied to the process design of a multi-stage centrifugal compressor

Evidence for multiple steps in the pre-steady-state electron transfer reaction of nitrogenase from Azotobacter vinelandii

AbstractThe effect of the NaCl concentration and the reaction temperature on the MgATP-dependent pre-steady-state electron transfer reaction (from the Fe protein to the MoFe protein) of nitrogenase from Azotobacter vinelandii was studied by stopped-flow spectrophotometry and rapid-freeze EPR spectroscopy. Besides lowering the reaction temperature, also the addition of NaCl decreased the observed rate constant and the amplitude of the absorbance increase (at 430 nm) which accompanies pre-steady-state electron transfer. The diminished absorbance increase observed at 5°C (without NaCl) can be explained by assuming reversible electron transfer, which was revealed by rapid-freeze EPR experiments that indicated an incomplete reduction of the FeMo cofactor. This was not the case with the salt-induced decrease of the amplitude of the stopped-flow signal: the observed absorbance amplitude of the electron transfer reaction predicted only 35% reduction of the MoFe protein, whereas rapid-freeze EPR showed 80% reduction of the FeMo cofactor. In the presence of salt, the kinetics of the reduction of the FeMo cofactor showed a lag period which was not observed in the absorbance changes. It is proposed that the pre-steady-state electron transfer reaction is not a single reaction but consists of two steps: electron transfer from the Fe protein to a still unidentified site on the MoFe protein, followed by the reduction of the FeMo cofactor. The consequences of our finding that the pre-steady-state FeMo cofactor reduction does not correlate with the amplitude and kinetics of the pre-steady-state absorbance increase will be discussed with respect to the present model of the kinetic cycle of nitrogenase

Aldosterone, atherosclerosis and vascular events in patients with stable coronary artery disease

AbstractBackground and aimsPlasma aldosterone has been associated with all-cause and cardiovascular mortality in high-risk cardiovascular populations, including patients with heart failure, myocardial infarction and high-risk coronary artery disease (CAD) patients. In the present study, we evaluated the association of plasma aldosterone levels with vascular events in a large prospective cohort of stable CAD patients recruited in an outpatient setting. Moreover, we investigated the relationship between aldosterone and atherosclerotic burden.Methods and resultsBaseline plasma aldosterone levels were measured in 2699 subjects with CAD (mean age 60±10years, 82% male). During a median follow-up of 4.7years, 308 (11%) patients died, of which 203 were from a vascular cause. Vascular endpoints of myocardial infarction, ischemic stroke or vascular death occurred in 355 (13%) patients. Multivariable Cox regression analysis was performed, adjusting for multiple confounders. Aldosterone (median 96pg/mL, interquartile range 70–138pg/mL, normal range 58–362pg/mL) was independently associated with major vascular events (hazard ratio (HR) 1.56, 95% confidence interval (CI) 1.13–2.15) and vascular mortality (HR 1.95, 95% CI 1.27–3.00). By multivariable regression analysis, aldosterone was also associated with the presence of atherosclerosis in additional vascular territories (cerebrovascular disease and/or peripheral artery disease) (p=0.026).ConclusionsIn patients with stable coronary artery disease, plasma aldosterone is independently associated with the risk of major vascular events and vascular mortality and with atherosclerotic burden