Using bifurcations in the determination of lock-in ranges for third-order phase-locked loops

Transmission and switching in digital telecommunication networks require distribution of precise time signals among the nodes. Commercial systems usually adopt a master-slave (MS) clock distribution strategy building slave nodes with phase-locked loop (PLL) circuits. PLLs are responsible for synchronizing their local oscillations with signals from master nodes, providing reliable clocks in all nodes. The dynamics of a PLL is described by an ordinary nonlinear differential equation, with order one plus the order of its internal linear low-pass filter. Second-order loops are commonly used because their synchronous state is asymptotically stable and the lock-in range and design parameters are expressed by a linear equivalent system [Gardner FM. Phaselock techniques. New York: John Wiley & Sons: 1979]. In spite of being simple and robust, second-order PLLs frequently present double-frequency terms in PD output and it is very difficult to adapt a first-order filter in order to cut off these components [Piqueira JRC, Monteiro LHA. Considering second-harmonic terms in the operation of the phase detector for second order phase-locked loop. IEEE Trans Circuits Syst [2003;50(6):805-9; Piqueira JRC, Monteiro LHA. All-pole phase-locked loops: calculating lock-in range by using Evan`s root-locus. Int J Control 2006;79(7):822-9]. Consequently, higher-order filters are used, resulting in nonlinear loops with order greater than 2. Such systems, due to high order and nonlinear terms, depending on parameters combinations, can present some undesirable behaviors, resulting from bifurcations, as error oscillation and chaos, decreasing synchronization ranges. In this work, we consider a second-order Sallen-Key loop filter [van Valkenburg ME. Analog filter design. New York: Holt, Rinehart & Winston; 1982] implying a third order PLL The resulting lock-in range of the third-order PLL is determined by two bifurcation conditions: a saddle-node and a Hopf. (C) 2008 Elsevier B.V. All rights reserved.

The John Dewey`s epistemology and informational literacy

The `reflexive thinking` concept is discussed in this article as a means of contextualizing John Dewey`s intellectual legacy. `Reflection` represents a fundamental element for the construction of the necessary competences to information seeking and use, and consequently to individual and collective development. Since the reflexive thinking habit in information literacy is a way of learning, some questions concerning teaching and learning processes are also investigated. The discussion is, therefore, supported by the supposition that reflexive thinking is a cognitive strategy that allows a deeper comprehension of related problems, phenomena, and processes by means of the perception of the relations and the identification of involved elements, as well as the analysis and interpretation of meanings, empowering the information literacy process.

The Genome Sequence of Taurine Cattle: A Window to Ruminant Biology and Evolution

To understand the biology and evolution of ruminants, the cattle genome was sequenced to about sevenfold coverage. The cattle genome contains a minimum of 22,000 genes, with a core set of 14,345 orthologs shared among seven mammalian species of which 1217 are absent or undetected in noneutherian (marsupial or monotreme) genomes. Cattle-specific evolutionary breakpoint regions in chromosomes have a higher density of segmental duplications, enrichment of repetitive elements, and species-specific variations in genes associated with lactation and immune responsiveness. Genes involved in metabolism are generally highly conserved, although five metabolic genes are deleted or extensively diverged from their human orthologs. The cattle genome sequence thus provides a resource for understanding mammalian evolution and accelerating livestock genetic improvement for milk and meat production.

Holt-Oram syndrome: novel TBX5 mutation and associated anomalous right coronary artery

The Holt-Oram syndrome was confirmed in an asymptomatic 36-year-old man by a novel TBX5-gene mutation (exon 8 acceptor splicing site, c.663-1G greater than A). Computed tomography showed an atrial septal defect and an anomalous right coronary artery crossing between the aorta and pulmonary arteries. Surgery corrected the septal defect and the initial segment of the anomalous vessel was unroofed and enlarged. Anomalous coronary arteries were not previously described in the Holt-Oram syndrome patients and should be added to the list of possible associated cardiac defects.