State Transitions and the Continuum Limit for a 2D Interacting, Self-Propelled Particle System

We study a class of swarming problems wherein particles evolve dynamically via pairwise interaction potentials and a velocity selection mechanism. We find that the swarming system undergoes various changes of state as a function of the self-propulsion and interaction potential parameters. In this paper, we utilize a procedure which, in a definitive way, connects a class of individual-based models to their continuum formulations and determine criteria for the validity of the latter. H-stability of the interaction potential plays a fundamental role in determining both the validity of the continuum approximation and the nature of the aggregation state transitions. We perform a linear stability analysis of the continuum model and compare the results to the simulations of the individual-based one

Weight loss, quality of life and employment status after Roux-en-Y gastric bypass: 5-year analysis.

BACKGROUND: Obesity can have a tremendous impact on the psychosocial, physical, and economic health of those afflicted by it. We hypothesized that if surgery results in significant weight loss and improves quality of life, those unemployed and disabled as a result of their morbid obesity might be more likely to become gainfully employed after Roux-en-Y gastric bypass (RYGBP). METHODS: We reviewed the medical charts of all patients who underwent RYGBP from April 1998 to December 1999. Demographics and employment status were obtained, along with preoperative weight, body mass index, Short Form 36 Health Survey and Beck Depression Inventory-II scores. For those employed, the recuperation time was also analyzed. Statistical analysis was performed using Student\u27s t test and analysis of variance. RESULTS: Fifty-seven patients underwent RYGBP. Of the 57 patients, 41 were selected for analysis, 34% of whom were employed, with a mean recuperation time of 3.5 weeks. Their mean age was 32.4 years. The mean body mass index was 53.4 kg/m(2) preoperatively and 31.2 kg/m(2) at 5 years. Of the 41 patients, 27 (66%) were receiving disability and 25 (61%) attributed their disability to their morbidly obese state. At 5 years, 4 (16%) of the 25 were gainfully employed and no longer receiving public assistance. CONCLUSION: Despite successful long-term weight loss and improvement in quality of life, many morbid obesity patients do not return to gainful employment in the workforce after RYGBP. The mean body mass index was greater in the unemployed group at both 1 and 5 years, but the difference was not statistically significant. The socioeconomic impact of morbid obesity persists long after a reduction in weight and improvement in quality of life