We describe the design and implementation of a bit-serial, four-bit, binary optical counter. The counter was designed and simulated using a digital optical simulation program developed for this purpose. It consists of five switches, a 4-bit fiber loop memory to store the count, four splitters, and fibers to interconnect the components. The counter is presently limited to a clock rate of 50 MHz because of the propagation delay in the single-bit time feedback loop. As designed, the same hardware may be used to count any even number of bits simply by changing the lengths of two fiber loops. The counter is unique in that it does not employ latches or other synchronizing memory elements, rather relying on a time-of-flight architecture. We describe the system issues involved in construction of the counter as well as the novel requirements on the switch drive electronics. We then outline the issues still to be addressed for the current counter and conclude with suggested design alternatives to improve its operation and increase its clock rate.
Objective: The objective of this study was to determine clinical rates and correlations of postoperative urinary retention (POUR) in elective spine decompression and fusion procedures.Summary of Background Data: POUR is a common postoperative complication that often has a major adverse impact on a patient's recovery from elective lumbar spine surgery. The etiology of POUR in most cases is unknown. Patients undergoing lumbar spine surgery are considered to be at increased risk for POUR due to prone positioning during surgery and intraoperative cauda equina nerve root manipulation. Current studies reporting on POUR after elective spine surgery provide limited insight regarding risk factors and effective prevention strategies for this at-risk population. The purpose of this study is to identify risk factors for POUR after elective lumbar spine surgery and strategies for reducing its incidence.Materials and Methods: Two hundred consecutive patients aged 50 years or older undergoing combined lumbar decompression and fusion procedures over a 5-month period at a single institution were prospectively observed. Demographic and clinical data were prospectively recorded, including: medical history, surgical data, medications administered, complications, and postoperative hospital course. Factors correlating with POUR through a univariate analysis with P ≤ 0.20 were considered for multivariate analysis.Results: POUR occurred in 19 of 200 patients. Those with POUR were more likely to be male (20% vs. 4%, odds ratio = 6.2). Administration of scopolamine (P = 0.02), neostigmine (P = 0.01), and the total number of levels operated on (P = 0.02) were found to be independent risk factors for the development of POUR. Length of surgery, surgical level, the performance of an interbody fusion did not have a bearing on the development of POUR (P > 0.05).Discussion: We describe a single institution's experience of POUR incidence in 200 consecutive patients aged 50 years or older undergoing single or multilevel lumbar spine fusion procedures by 1 of 4 surgeons. Specific demographic and clinical risk factors were identified and a codified classification for POUR in a surgical population is presented. The results of this study will help clinicians appropriately counsel patients undergoing elective lumbar fusion about the potential development of POUR. The perioperative administration of scopolamine and neostigmine should be cautiously considered in men over 50 years of age due to the increased POUR risk.Conclusions: Perioperative scopolamine and neostigmine administration in men over 50 should be avoided when possible to minimize the risk of POUR.
Approximate expressions are derived for the high-frequency electromagnetic backscattering from an absorbing infinite strip on which an impedance boundary condition is imposed. Each face of the strip is assumed to possess an arbitrary constant surface impedance not necessarily equal to that of the other face. The problem is treated by a method of successive approximations based on known half-plane solutions; secondary (and in some cases, tertiary) diffraction effects are thereby included. Particularly important is the special case of a perfectly-conducting strip coated on one side with thin layers of highly refractive absorbing materials. Some experimental results of backscattering from an absorber-coated rectangular plate are presented and discussed in the light of the theoretical model.
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