OPERATIONAL ANALYSIS OF QUEUEING PHENOMENA

Operational analysis provides a framework for studying queueing phenomena during finite time periods. There are two sources of error in using operational formulas for performance prediction: parameter estimation error and assumption violation. This thesis investigates how these errors affect the estimates of performance quantities. Different operational assumptions are used to derive several formulas for the mean queue length and response time of an isolated service center. One formula is analogous to the stochastic Pollaczck-Khinchine formula for an M/G/1 queue. If the necessary assumptions are not satisfied, the formulas are only estimators. The error in each estimator is expressed in terms of the assumption errors. An analysis of the error expressions reveals a common term that can be used to detect ill-conditioned problems. A flow balance assumption is used in the derivation of many operational formulas. We demonstrate that violation of this assumption can lead to large errors in state occupancies. A flow balanced portion of an observation period can be used to approximate the state occupancies. The errors are shown to be no larger than the proportion of the observation period that is discarded

Systematics of a Neotropical clade of dead-leaf-foraging antwrens (Aves: Thamnophilidae; Epinecrophylla)

© 2020 Elsevier Inc. The stipple-throated antwrens of the genus Epinecrophylla (Aves: Thamnophilidae) are represented by eight species primarily found in the lowlands of the Amazon Basin and the Guiana Shield. The genus has a long and convoluted taxonomic history, with many attempts made to address the taxonomy and systematics of the group. Here we employ massively parallel sequencing of thousands of ultraconserved elements (UCEs) to provide both the most comprehensive subspecies-level phylogeny of Epinecrophylla antwrens and the first population-level genetic analyses for most species in the genus. Most of our results are robust to a diversity of phylogenetic and population genetic methods, but we show that even with thousands of loci we are unable to fully resolve the relationships between some western Amazonian species in the haematonota group. We uncovered phylogenetic relationships between taxa and patterns of population structure that are discordant with both morphology and current taxonomy. For example, we found deep genetic breaks between taxa in the ornata group that are currently regarded as species, and in the haematonota and leucophthalma groups we found paraphyly at the species and subspecies levels, respectively. As has been found in many Amazonian taxa, our phylogenetic results show that the major river systems of the Amazon Basin appear to have an effect on the genetic structure and range limits within Epinecrophylla. Our population genetics analyses showed extensive admixture between some taxa despite their deep genetic divergence. We present a revised taxonomy for the group and suggest areas for further study