Mixing in supersonic flow

Method for determining turbulent transport coefficient in supersonic flo

Predictions of axisymmetric free turbulent shear flows using a generalized eddy-viscosity approach

The generalized eddy viscosity approach is described and results are presented of test cases which show that predictions obtained by this approach are adequate for most engineering applications. Because of the importance of starting computations from the injection station where experimentally determined mean and turbulence parameters are rarely available, a very simple core model applicable to simple step-type (slug) profiles was developed. Agreement between predicted and experimental mean profiles was generally almost as good for calculations made by using this model throughout the core region and the transition model for all subsequent regions as predictions made by starting from experimental profiles in the transition region. The generalized eddy-viscosity model, which was developed in part through correlation of turbulence parameters, successfully predicted turbulent shear stress, turbulent intensity, and mean velocity profiles for a 0.040-inch-diameter microjet. Therefore, successful scaling by the model was demonstrated since data used in its development was for jet areas up to 90,000 times as large as the microjet and velocities only 1/20th as high

Supersonic mixing of hydrogen and air

Fuel injection parameter effects on mixing of gaseous hydrogen with supersonic air strea

Developing a gas rocket performance prediction technique

A simple, semi-empirical performance correlation/prediction technique applicable to gaseous and liquid propellant rocket engines is presented. Excellent correlations were attained for over 100 test firings by adjusting the computation of the gaseous mixing of an unreactive, coaxial jet using a correlation factor, F, which resulted in prediction of the experimental combustion efficiency for each firing. Static pressure, mean velocity and turbulence intensity in the developing region of non-reactive coaxial jets, typical of those of coaxial injector elements were determined. Detailed profiles were obtained at twelve axial locations (extending from the nozzle exit for a distance of five diameters) downstream from a single element of the Bell Aerospace H2/O2 19-element coaxial injector. These data are compared with analytical predictions made using both eddy viscosity and turbulence kinetic energy mixing models and available computer codes. Comparisons were disappointing, demonstrating the necessity of developing improved turbulence models and computational techniques before detailed predictions of practical coaxial free jet flows are attempted

Fibronectin-Cleaving Activity in Bronchial Secretions of Patients with Cystic Fibrosis

In cystic fibrosis, colonization of the airways with Pseudomonas aeruginosa follows colonization with Staphylococcus aureus and is related to accelerated deterioration of pulmonary function. Because P. aeruginosa adheres better to cell surfaces devoid of fibronectin, we searched for fibronectin-cleaving activity in bronchial secretions and saliva from 24 patients with cystic fibrosis who were followed up for 4.5 y and from two control groups. Proteolytic activity against 125I-labeled fibronectin wascontinuously present in cystic fibrosis bronchial secretions; significantly higher fibronectin-cleaving activity was found in older vs. younger patients, in patients with advanced disease stages determined by a five-stage scoring system, and in those colonized with P. aeruginosa. The fibronectin-cleaving activity was due to neutrophil elastase and cathepsin G. Cystic fibrosis bronchial secretions had proteolytic activity against surface fibronectin of airway mucosal cells. Thus fibronectin-cleaving activity of bronchial secretions rather than of saliva may favor P. aeruginosa colonization of the upper respiratory tract in individuals with cystic fibrosi

Post cardiac surgery vasoplegia is associated with high preoperative copeptin plasma concentration

International audienceABSTRACT: INTRODUCTION: Post cardiac surgery vasodilatation is possibly related to a vasopressin deficiency that could be related to a chronic stimulation of the adeno-hypophysis. To assess vasopressin system activation, perioperative course of copeptin and vasopressin plasma concentrations have been studied in consecutive patients operated on cardiac surgery. METHODS: 64 consecutive patients scheduled for elective cardiac surgery with cardiopulmonary bypass were studied. Haemodynamic, laboratory and clinical data were recorded before and during cardiopulmonary bypass, and at the 8th post-operative hour (H8). At the same time, point's blood was withdrawn to determine plasma concentrations of arginine-vasopressin (AVP, radioimmunoassay) and copeptin (immunoluminometric assay). Post cardiac surgery vasodilation (PCSV) was defined as a mean arterial blood pressure less than 60 mmHg with a cardiac index [equal to or greater than] 2.2 L * min^-1 * m^-2, and was treated with norepinephrine (NE) in order to restore a mean blood pressure > 60 mmHg. Patients with PCSV were compared to the other patients (controls). Student's t, Fisher's exact test, or non parametric tests (Mann Whitney, Wilkoxon) were used when appropriate. A correlation between AVP and copeptin has been evaluated and a receiver-operator characteristic (ROC) analysis was calculated to assess the utility of preoperative copeptin to distinguish between controls and PCSV patients. RESULTS: Patients who experienced a PCSV have significantly higher copeptin plasma concentration before cardiopulmonary bypass (P <0.001) but lower AVP concentrations at H8 (P <0.01) than controls. PCSV patients had preoperative hyponatremia and decreased left ventricle ejection fraction, and experienced more complex surgery (redo). The area under the ROC curve of preoperative copeptin concentration was 0.86[plus/minus]0.04 [95%CI: 0.78-0.94] (P <0.001). The best predictive value for preoperative copeptin plasma concentration was 9.43 pmol/L with a sensitivity of 90% and a specificity of 77%. CONCLUSIONS: High preoperative copeptin plasma concentration is predictive of PSCV and suggests an activation of the AVP system before surgery that may facilitate depletion of endogenous AVP stores and a relative AVP deficit after surgery

Procalcitonin guided antibiotic therapy and hospitalization in patients with lower respiratory tract infections: a prospective, multicenter, randomized controlled trial

<p>Abstract</p> <p>Background:</p> <p>Lower respiratory tract infections like acute bronchitis, exacerbated chronic obstructive pulmonary disease and community-acquired pneumonia are often unnecessarily treated with antibiotics, mainly because of physicians' difficulties to distinguish viral from bacterial cause and to estimate disease-severity. The goal of this trial is to compare medical outcomes, use of antibiotics and hospital resources in a strategy based on enforced evidence-based guidelines versus procalcitonin guided antibiotic therapy in patients with lower respiratory tract infections.</p> <p>Methods and design:</p> <p>We describe a prospective randomized controlled non-inferiority trial with an open intervention. We aim to randomize over a fixed recruitment period of 18 months a minimal number of 1002 patients from 6 hospitals in Switzerland. Patients must be >18 years of age with a lower respiratory tract infections <28 days of duration. Patients with no informed consent, not fluent in German, a previous hospital stay within 14 days, severe immunosuppression or chronic infection, intravenous drug use or a terminal condition are excluded. Randomization to either guidelines-enforced management or procalcitonin-guided antibiotic therapy is stratified by centre and type of lower respiratory tract infections. During hospitalization, all patients are reassessed at days 3, 5, 7 and at the day of discharge. After 30 and 180 days, structured phone interviews by blinded medical students are conducted. Depending on the randomization allocation, initiation and discontinuation of antibiotics is encouraged or discouraged based on evidence-based guidelines or procalcitonin cut off ranges, respectively. The primary endpoint is the risk of combined disease-specific failure after 30 days. Secondary outcomes are antibiotic exposure, side effects from antibiotics, rate and duration of hospitalization, time to clinical stability, disease activity scores and cost effectiveness. The study hypothesis is that procalcitonin-guidance is non-inferior (i.e., at worst a 7.5% higher combined failure rate) to the management with enforced guidelines, but is associated with a reduced total antibiotic use and length of hospital stay.</p> <p>Discussion:</p> <p>Use of and prolonged exposure to antibiotics in lower respiratory tract infections is high. The proposed trial investigates whether procalcitonin-guidance may safely reduce antibiotic consumption along with reductions in hospitalization costs and antibiotic resistance. It will additionally generate insights for improved prognostic assessment of patients with lower respiratory tract infections.</p> <p>Trial registration:</p> <p>ISRCTN95122877</p

Microwave Devices Employing Magnetic Waves

Contains reports on six research projects.Joint Services Electronics Program (Contract DAAG29-78-C-0020)National Science Foundation (Grant ENG76-18359