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The rotor thermal bending due to the rotor-to-stator rubbing can lead to one of three types of observed rotor lateral motion: (1) spiral with increasing amplitude, (2) oscillating between rub]no-rub conditions, and (3) asymptotical approach to the rotor limit cycle. Based on the machinery observations, it is assumed in the analytical part of the paper that the speed scale of transient thermal effects is considerably lower than that of rotor vibrations, and that the thermal effect reflects only on the rotor steady-state vibrational response. This response would change due to thermally induced bow of the rotor, which can be considered to slowly vary in timefor the purpose of rotor vibration calculations. Thus uncoupled from the thermal problem, the rotor vibration is analyzed. The major consideration is given to the rotor which experiences intermittent contact with the stator, due to predetermined thermal bow, unbalance force, and radial constant load force. In the case of inelastic impact, it causes an on/off, step-change in the stiffness of the system. Using a specially developed variable transformation for the system with discontinuities, and averaging technique the resonance regimes of motion are obtained. These regimes are used to calculate the heat generated during contact stage, as a function of thermal bow modal parameters, which is used as a boundary condition for the rotor heat transfer problem. The latter is treated as quasi-static, which reduces the problem to an ordinary differential equation for the thermal bow vector. It is investigated from the stability standpoint.

Background. Self-expanding metal stents can alleviate malignant colonic obstruction in incurable patients and avoid palliative stoma surgery. Objective. Evaluate stent effectiveness and safety on palliation of patients with malignant colorectal strictures. Design. Two prospective, one Spanish and one global, multicenter studies. Settings. 39 centers (22 academic, 17 community hospitals) from 13 countries. Patients. A total of 257 patients were enrolled, and 255 patients were treated with a WallFlex uncovered enteral colonic stent. Follow-up was up to 12 months or until death or retreatment. Interventions(s). Self-expanding metal stent placement. Main Outcome Measures. Procedural success, clinical success, and safety. Results. Procedural success was 98.4% (251). Clinical success rates were 87.8% at 30 days, 89.7% at 3 months, 92.8% at 6 months, and 96% at 12 months. Overall perforation rate was 5.1%. Overall migration rate was 5.5%. Overall death rate during follow-up was 48.6% (124), with 67.7% of deaths related to the patient’s colorectal cancer, unrelated in 32.3%. Only 2 deaths were related to the stent or procedure. Limitations. No control group. Conclusions. The primary palliative option for patients with malignant colonic obstruction should be self-expanding metal stent placement due to high rates of technical success and efficacy in symptom palliation and few complications.