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217. Near optimum digital phase locked loops.

Author

Polk, D. R and Gupta, S. C

Subjects
Electronics
Abstract

Near optimum digital phase locked loops are derived utilizing nonlinear estimation theory. Nonlinear approximations are employed to yield realizable loop structures. Baseband equivalent loop gains are derived which under high signal to noise ratio conditions may be calculated off-line. Additional simplifications are made which permit the application of the Kalman filter algorithms to determine the optimum loop filter. Performance is evaluated by a theoretical analysis and by simulation. Theoretical and simulated results are discussed and a comparison to analog results is made.

Published
1972

218. Bounds on the performance of a class of digital communication systems

Author

Polk, D. R, Gupta, S. C, and Cohn, D. L

Subjects
Communications
Abstract

Bounds on the capacity of a class of digital communication channels are derived. Equating the bounds on capacity to rate-distortion functions of (typical) sources in turn produces bounds on the performance of a class of digital communication systems. For ratios of squared quantization level to noise variance much less than one, the power requirements for this class of digital communication systems are shown to be within approximately 3 dB of the theoretical optimum.

Published
1973

219. An approach to the analysis of performance of quasi-optimum digital phase-locked loops.

Author

Polk, D. R and Gupta, S. C

Subjects
Electronics
Abstract

An approach to the analysis of performance of quasi-optimum digital phase-locked loops (DPLL's) is presented. An expression for the characteristic function of the prior error in the state estimate is derived, and from this expression an infinite dimensional equation for the prior error variance is obtained. The prior error-variance equation is a function of the communication system model and the DPLL gain and is independent of the method used to derive the DPLL gain. Two approximations are discussed for reducing the prior error-variance equation to finite dimension. The effectiveness of one approximation in analyzing DPLL performance is studied.

Published
1973

249. Predicting Persistence of Functional Abdominal Pain From Childhood Into Young Adulthood.

Author

Horst, Sara, Shelby, Grace, Anderson, Julia, Acra, Sari, Polk, D. Brent, Saville, Benjamin R., Garber, Judy, and Walker, Lynn S.

Abstract

Background & Aims Pediatric functional abdominal pain has been linked to functional gastrointestinal disorders (FGIDs) in adulthood, but little is known about patient characteristics in childhood that increase the risk for FGID in young adulthood. We investigated the contribution of gastrointestinal symptoms, extraintestinal somatic symptoms, and depressive symptoms in pediatric patients with functional abdominal pain and whether these predicted FGIDs later in life. Methods In a longitudinal study, consecutive new pediatric patients, diagnosed with functional abdominal pain in a subspecialty clinic, completed a comprehensive baseline evaluation of the severity of their physical and emotional symptoms. They were contacted 5 to 15 years later and evaluated, based on Rome III symptom criteria, for abdominal pain–related FGIDs, including irritable bowel syndrome, functional dyspepsia, functional abdominal pain syndrome, and abdominal migraine. Controlling for age, sex, baseline severity of abdominal pain, and time to follow-up evaluation, multivariable logistic regression was used to evaluate the association of baseline gastrointestinal, extraintestinal somatic, and depressive symptoms in childhood with FGID in adolescence and young adulthood. Results Of 392 patients interviewed an average of 9.2 years after their initial evaluation, 41% (n = 162) met symptom criteria for FGID; most met the criteria for irritable bowel syndrome. Extraintestinal somatic and depressive symptoms at the initial pediatric evaluation were significant predictors of FGID later in life, after controlling for initial levels of GI symptoms. Age, sex, and abdominal pain severity at initial presentation were not significant predictors of FGID later in life. Conclusions In pediatric patients with functional abdominal pain, assessment of extraintestinal and depressive symptoms may be useful in identifying those at risk for FGID in adolescence and young adulthood. [ABSTRACT FROM AUTHOR]

Published
2014
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