Biological clocks

Circadian rhythms describe biological phenomena that oscillate with an ≈24-hour cycle. These rhythms include blood pressure, body temperature, hormone levels, the number of immune cells in blood, and the sleep-wake cycle. In this paper, we will focus on common genes between species that are responsible for determining the circadian behavior, especially some transcription factors (i.e., switch genes) that serve to regulate many circadian rhythm genes. The intent of this summary is to introduce the common molecular mechanism of biological clocks between flies and humans and then to describe the research from three laboratories that was presented in the session.

Important XVIII century American furniture, rare tall-case banjo & shelf clocks, early American silver and glass, old English porcelain, glass paperweights, primitive & other American paintings, from the collection of Maurice Rubin, sold by his order, public auction sale, Saturday, Oct. 9 [1954]

Mode of access: Internet.

Old clocks and watches and their makers; being an historical and descriptive account of the different styles of clocks and watches of the past, in England and abroad, to which is added a list of eight thousand makers;

Mode of access: Internet.

Lectures on church-building: with some practical remarks on bells and clocks,

Mode of access: Internet.

A rudimentary treatise on clock and watch making : with a chapter ou church clocks... /

Mode of access: Internet.

The clocks of Rondaine, and other stories,

The clocks of Rondaine.--The curious history of a message.--A fortunate opening.--The Christmas truants.--The tricycle of the future.--The accommodating circumstance.--The great show in Kobol-land.

Atomic clocks of the National Bureau of Standards.

Mode of access: Internet.

Clocks in the Evangeline and Benjamin F. Hunter Collection,

Bibliography: p. 63.

Some considerations on the subject of public clocks, particularly church clocks with hints for their improvement ...

Mode of access: Internet.

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.

Comparing lock-in ranges and transient responses of second- and third-order phase-locked loops in master-slave clock distribution networks

The distribution of clock signals throughout the nodes of a network is essential for several applications. in control and communication with the phase-locked loop (PLL) being the component for electronic synchronization process. In systems with master-slave (MS) strategies, the PLLs are the slave nodes responsible for providing reliable clocks in all nodes of the network. As PLLs have nonlinear phase detection, double-frequency terms appear and filtering becomes necessary. Imperfections in filtering process cause oscillations around the synchronous state worsening the performance of the clock distribution process. The behavior of one-way master-slave (OWMS) clock distribution networks is studied and performances of first- and second-order filter processes are compared, concerning lock-in ranges and responses to perturbations of the synchronous state. (c) 2007 Elsevier GmbH. All rights reserved.

Cyclopropyl fatty acids implicate a radical but not a cation as an intermediate in P450(BM3)-catalysed hydroxylations

Novel cyclopropyl containing fatty acids are good substrates for P450(BM3) catalysed hydroxylation and analysis of their oxidation products indicates the presence of a radical intermediate (maximum rebound rate 2.6x10(10) s(-1)) and the absence of any cationic intermediate.

Testing the link between the latitudinal gradient in species richness and rates of molecular evolution

Numerous hypotheses have been proposed to explain latitudinal gradients in species richness, but all are subject to ongoing debate. Here we examine Rohde's (1978, 1992) hypothesis, which proposes that climatic conditions at low latitudes lead to elevated rates of speciation. This hypothesis predicts that rates of molecular evolution should increase towards lower latitudes, but this prediction has never been tested. We discuss potential links between rates of molecular evolution and latitudinal diversity gradients, and present the first test of latitudinal variation in rates of molecular evolution. Using 45 phylogenetically independent, latitudinally separated pairs of bird species and higher taxa, we compare rates of evolution of two mitochondrial genes and DNA-DNA hybridization distances. We find no support for an effect of latitude on rate of molecular evolution. This result casts doubt on the generality of a key component of Rohde's hypothesis linking climate and speciation.

Delay-bounded medium access for unidirectional wireless links

Consider a wireless network where links may be unidirectional, that is, a computer node A can broadcast a message and computer node B will receive this message but if B broadcasts then A will not receive it. Assume that messages have deadlines. We propose a medium access control (MAC) protocol which replicates a message in time with carefully selected pauses between replicas, and in this way it guarantees that for every message at least one replica of that message is transmitted without collision. The protocol ensures this with no knowledge of the network topology and it requires neither synchronized clocks nor carrier sensing capabilities. We believe this result is significant because it is the only MAC protocol that offers an upper bound on the message queuing delay for unidirectional links without relying on synchronized clocks.

Collision-free prioritized medium access in the presence of hidden nodes without relying on out-of-band signaling

Consider the problem of sharing a wireless channel between a set of computer nodes. Hidden nodes exist and there is no base station. Each computer node hosts a set of sporadic message streams where a message stream releases messages with real-time deadlines. We propose a collision-free wireless medium access control (MAC) protocol which implements staticpriority scheduling. The MAC protocol allows multiple masters and is fully distributed. It neither relies on synchronized clocks nor out-of-band signaling; it is an adaptation to a wireless channel of the dominance protocol used in the CAN bus. But unlike that protocol, our protocol does not require a node having the ability to receive an incoming bit from the channel while transmitting to the channel. Our protocol has the key feature of not only being prioritized and collision-free but also dealing successfully with hidden nodes. This key feature enables schedulability analysis of sporadic message streams in multihop networks.