Clusters of biological organisms often show diverse collective motions. Considering the physical properties of active elements with mutual interactions, we propose a mathematical model of collective motion. Several kinds of cluster motion seen in nature, including collective rotation, chaos, and wandering, occur in computer simulations of our deterministic model. By introducing a set of dimensionless parameters, we categorize the collective motions and obtain their phase diagram. We analyze the collective motions with a disorder parameter and Lyapunov spectra to characterize their transitions. [S0031-9007(96)00218-9]
A gastric tube has been widely used for reconstruction of the esophagus after esophagectomy for esophageal cancer. Reflux esophagitis after esophagectomy is frequently observed. Therefore we retrospectively investigated the risk factors for reflux esophagitis after gastric pull-up esophagectomy in 74 outpatients with thoracic esophageal cancer. Reflux esophagitis was diagnosed endoscopically. Esophagitis was classified according to the Los Angeles classification. Reflux symptoms, medications, and the surgical procedure were reviewed. The relation between reflux symptoms and reflux esophagitis and the influence of the anastomotic site were evaluated. Reflux esophagitis was observed in 53 patients. Severe esophagitis (grade C or D) was found in 75.6% of these patients. Although all patients with esophagitis took antacid agents, histamine receptor-2 blocker was effective in only 35% of them. The correlation between reflux symptoms and reflux esophagitis was not significant. Reflux esophagitis was present in 56.4% of patients with neck anastomosis and in 88.6% of patients with intrathoracic anastomosis ( p = 0.0039). We concluded that routine endoscopic examination is necessary after gastric pull-up esophagectomy because reflux esophagitis is not diagnosed based on reflux symptoms. When a gastric tube is used for reconstruction after esophagectomy, neck anastomosis is recommended to lower the risk of reflux esophagitis.
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