The development of the concept of spring and damping coefficients for journal bearings is briefly reviewed. Methods for computing the coefficients are described, and their use in rotor dynamics calculations (unbalance response, stability) is discussed. The limitations imposed by nonlinearities on the application of the coefficients is illustrated by examples.

One hundred and forty-four cases of aneurysms of the ductus arteriosus (DAA) have been reported in the literature of which 106 appeared spontaneously and 38 followed surgical treatment of a patent ductus arteriosus (PDA). Within the last few years there has been an increasing number of reported spontaneous DAA. However, the real incidence is presumably still underestimated. Aortography is a well established diagnostic method. In neonates, transthoracic echocardiography has shown convincing potential, whereas in older children and adults, transoesophageal echocardiography has yielded very promising results. Serious complications following spontaneous DAA are rupture, erosion, infection and thromboembolism. In infants younger than 2 months of age, the complication rate is 31%, in children between 2 months and 15 years, 66%, in adults, 47%. The rate of complications following postoperative DAA is even higher: 91% of the unoperated cases died due to rupture or infection. The operative mortality in children older than 2 months and adults is low. In the neonate group, 2 of 8 died during operation. The operative mortality in patients with postoperative DAA was 26%. Based on information from the literature, we suggest prompt surgical treatment of all spontaneous DAA in patients older than 2 months of age, and in all patients with postoperative DAA. In infants, a DAA should be closely followed with echocardiography, as spontaneous regression has been reported in this age group. If no regression is seen within a few days, it should be surgically corrected.

No abstract

A method is described for calculating the threshold speed of instability and the damped critical speeds of a general flexible rotor in fluid-film journal bearings. It is analogous to the Myklestad-Prohl method for calculating critical speeds and is readily programmed for numerical computation. The rotor model can simulate any practical shaft geometry and support configuration. The bearings are represented by their linearized dynamic properties, also known as the stiffness and damping coefficients of the bearing, and the calculation includes hysteretic internal damping in the shaft and destabilizing aerodynamic forces. To demonstrate the application of the method, results are shown for an industrial, multistage compressor.

Background-Off-pump coronary artery bypass grafting compared with coronary revascularization with cardiopulmonary bypass seems safe and results in about the same outcome in low-risk patients. Observational studies indicate that off-pump surgery may provide more benefit in high-risk patients. Our objective was to compare 30-day outcomes in high-risk patients randomized to coronary artery bypass grafting without or with cardiopulmonary bypass. Methods and Results-We randomly assigned 341 patients with a EuroSCORE Ն5 and 3-vessel coronary disease to undergo coronary artery bypass grafting without or with cardiopulmonary bypass. Patients were followed through the Danish National Patient Registry. The primary outcome was a composite of adverse cardiac and cerebrovascular events (ie, all-cause mortality, acute myocardial infarction, cardiac arrest with successful resuscitation, low cardiac output syndrome/cardiogenic shock, stroke, and coronary reintervention). An independent adjudication committee blinded to treatment allocation assessed the outcomes. Baseline characteristics were well balanced between groups. The mean number of grafts per patient did not differ significantly between groups (3.22 in off-pump group and 3.34 in on-pump group; Pϭ0.11). Fewer grafts were performed to the lateral part of the left ventricle territory during off-pump surgery (0.97 versus 1.14 after on-pump surgery; Pϭ0.01). No significant differences in the composite primary outcome (15% versus 17%; Pϭ0.48) or the individual components were found at 30-day follow-up. Conclusions-Both off-and on-pump coronary artery bypass grafting can be performed in high-risk patients with low short-term complications.