Browsing by Author "Zhou, Jing"
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Item Dynamics of Some Fermi Acceleration Models(2020) Zhou, Jing; Dolgopyat, Dmitry; Mathematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In the thesis we describe the dynamics of two variations of the Fermi acceleration models. The first model consists of a rectangular billiard with two periodically vertically oscillating slits. A point particle bounces elastically against the billiard table and the slits. We assume that the horizontal motion of the particle is in resonance with those of the slits. In this case, we have found a mechanism of trapping regions which provides the exponential acceleration for almost all initial conditions with sufficiently high initial energy. Under an additional hyperbolicity assumption on the parameters of the system, we estimate the waiting time after which most high-energy orbits start to gain energy exponentially fast. The second model depicts a point particle bouncing elastically against a periodically oscillating platform in a gravity field. We assume that the platform motion is piecewise smooth with one singularity. If the second derivative of the platform motion behaves well, i.e. it is either always positive or always less than the negative of the gravitational constant, then the escaping orbits constitute a null set and the system is recurrent. However, under these assumptions, escaping orbits coexist with bounded orbits at arbitrarily high energy levels.Item Racial variation in breast cancer treatment among department of defense beneficiaries(2011) Enewold, Lindsey; Zhou, Jing; McGlynn, Katherine A.; Anderson, William F.; Shriver, Craig D.; Potter, John F.; Zahm, Shelia H.; Zhu, KangminBACKGROUND: Although the overall age-adjusted incidence rates for female breast cancer are higher among whites than blacks, mortality rates are higher among blacks. Many attribute this discrepancy to disparities in health care access and to blacks presenting with later stage disease. Within the Department of Defense (DoD) Military Health System, all beneficiaries have equal access to health care. The aim of this study was to determine whether female breast cancer treatment varied between white and black patients in the DoD system. METHODS: The study data were drawn from the DoD cancer registry and medical claims databases. Study subjects included 2308 white and 391 black women diagnosed with breast cancer between 1998 and 2000. Multivariate logistic regression analyses that controlled for demographic factors, tumor characteristics, and comorbidities were used to assess racial differences in the receipt of surgery, chemotherapy, and hormonal therapy. RESULTS: There was no significant difference in surgery type, particularly when mastectomy was compared with breast-conserving surgery plus radiation (blacks vs whites: odds ratio [OR], 1.1; 95% confidence interval [CI], 0.8-1.5). Among those with local stage tumors, blacks were as likely as whites to receive chemotherapy (OR, 1.2; 95% CI, 0.9-1.7) and hormonal therapy (OR, 1.0; 95% CI, 0.6-1.4). Among those with regional stage tumors, blacks were significantly less likely than whites to receive chemotherapy (OR, 0.4; 95% CI, 0.2-0.7) and hormonal therapy (OR, 0.5; 95% CI, 0.3-0.8). CONCLUSIONS: Even within an equal access health care system, stage-related racial variations in breast cancer treatment are evident. Studies that identify driving factors behind these within-stage racial disparities are warranted. Cancer 2011;. © 2011 American Cancer Society.