Search results for "clock"
showing 10 items of 230 documents
Quaternary diversification in European alpine plants: pattern and process
2004
Molecular clock approaches applied previously to European alpine plants suggest that Primula sect. Auricula , Gentiana sect. Ciminalis and Soldanella diversified at the beginning of the Quaternary or well within this period, whereas Globularia had already started diversifying in the (Late–)Tertiary. In the first part of this paper we present evidence that, in contrast to Globularia and Soldanella , the branching patterns of the molecular internal transcribed spacer phylogenies of both Primula and Gentiana are incompatible with a constant–rates birth–death model. In both of these last two taxa, speciation probably decreased through Quaternary times, perhaps because of some niche–filling pro…
Metazoan Circadian Rhythm: Toward an Understanding of a Light-Based Zeitgeber in Sponges
2013
In all eukaryotes, the 24-h periodicity in the environment contributed to the evolution of the molecular circadian clock. We studied some elements of a postulated circadian clock circuit in the lowest metazoans, the siliceous sponges. First, we identified in the demosponge Suberites domuncula the enzyme luciferase that generates photons. Then (most likely), the photons generated by luciferase are transmitted via the biosilica glass skeleton of the sponges and are finally harvested by cryptochrome in the same individual; hence, cryptochrome is acting as a photosensor. This information-transduction system, generation of light (luciferase), photon transmission (through the siliceous spicules),…
Phylogenetic analysis of the isopenicillin-N-synthetase horizontal gene transfer.
1996
A phylogenetic study of the isopenicillin-N-synthetase (IPNS) gene sequence from prokaryotic and lower eukaryotic producers of beta-lactam antibiotics by means of a maximum-likelihood approach has been carried out. After performing an extensive search, rather than invoking a global molecular clock, the results obtained are best explained by a model with three rates of evolution. Grouped in decreasing order, these correspond to A. nidulans and then to the rest of the eukaryotes and prokaryotes, respectively. The estimated branching date between prokaryotic and fungal IPNS sequences (852 +/- 106 MY) strongly supports the hypothesis that the IPNS gene was horizontally transferred from bacteria…
Retinal image quality and visual stimuli processing by simulation of partial eye cataract
2016
Visual stimuli were demonstrated on a 4.3’’ mobile phone screen inside a “Virtual Reality” adapter that allowed separation of the left and right eye visual fields. Contrast of the retina image thus can be controlled by the image on the phone screen and parallel to that at appropriate geometry by the AC voltage applied to scattering PDLC cell inside the adapter. Such optical pathway separation allows to demonstrate to both eyes spatially variant images, that after visual binocular fusion acquire their characteristic indications. As visual stimuli we used grey and different color (two opponent components to vision – red-green in L*a*b* color space) spatially periodical stimuli for left and ri…
Totally asymmetric exclusion process fed by using a non-Poissonian clock
2015
In this article we consider the one-dimensional totally asymmetric open-boundary exclusion process fed by a process with power-law-distributed waiting times. More specifically, we use a modified Pareto distribution to define the jump rate for jumps into the system. We then characterize the propagation of fluctuations through the system by kinetic Monte Carlo simulations and by numerical evaluation of the steady-state partition function. peerReviewed
The diversity and evolution of chelicerate hemocyanins
2012
Abstract Background Oxygen transport in the hemolymph of many arthropod species is facilitated by large copper-proteins referred to as hemocyanins. Arthropod hemocyanins are hexamers or oligomers of hexamers, which are characterized by a high O2 transport capacity and a high cooperativity, thereby enhancing O2 supply. Hemocyanin subunit sequences had been available from horseshoe crabs (Xiphosura) and various spiders (Araneae), but not from any other chelicerate taxon. To trace the evolution of hemocyanins and the emergence of the large hemocyanin oligomers, hemocyanin cDNA sequences were obtained from representatives of selected chelicerate classes. Results Hemocyanin subunits from a sea s…
Noise characterization of analog to digital converters for amplitude and phase noise measurements
2017
International audience; Improvements on electronic technology in recent years have allowed the application of digital techniques in phase noise metrology where low noise and high accuracy are required, yielding flexibility in systems implementation and setup. This results in measurement systems with extended capabilities, additional functionalities and ease of use. In most digital schemes the Analog to Digital Converters (ADCs) set the ultimate performance of the system, therefore the proper selection of this component is a critical issue. Currently, the information available in literature describes in depth the ADC features only at frequency offsets far from the carrier. However, the perfo…
Residual Phase Noise Measurement of Optical Second Harmonic Generation in PPLN Waveguides
2017
We report on the characterization, including residual phase noise and fractional frequency instability, of fiber-coupled PPLN non-linear crystals. These components are devoted to frequency doubling 871 nm light from an extended-cavity diode laser to produce a 435.5 nm beam, corresponding to the ytterbium ion electric quadrupole clock transition. We measure doubling efficiencies of up to 117.5 %/W. Using a Mach-Zehnder interferometer and an original noise rejection technique, the residual phase noise of the doublers is estimated to be lower than ${\rm -35\, dBrad^2/Hz}$ at 1 Hz, making these modules compatible with up-to-date optical clocks and ultra-stable cavities. The influence of externa…
Esteve Graset. Una dramaturgia interdisciplinaria. Materiales del discurso escénico en Esteve Graset
2016
Esteve Graset es uno de los artistas españoles más desconocidos y a la vez interesantes de la escena nacional e internacional de las últimas décadas. Es autor de textos, instalaciones escénicas, importantes trabajos sobre la voz humana (conciertos) y muchas producciones escénicas con actores y bailarines en las que se pone en práctica la suma de todos sus conocimientos e inquietudes. Con los materiales de sus propias representaciones organiza instalaciones en las que da vida a los objetos. Su personalidad independiente y evolutiva, su discurso como actor, director, autor, creador y pedagogo, así como la gran variedad de disciplinas artísticas que contempla su obra, y su compromiso con el ti…
Microstructures in shells of the freshwater gastropod Viviparus viviparus: a potential sensor for temperature change?
2013
Abstract Mollusk shells contain a plethora of information on past climate variability. However, only a limited toolkit is currently available to reconstruct such data from the shells. The environmental data of some proxies (e.g. Sr/Ca ratios) is obscured by physiological effects, whereas other proxies, such as δ 18 O, simultaneously provide information on two or more different environmental variables. The present study investigates whether microstructures of the freshwater gastropod Viviparus viviparus provide an alternative means to reconstruct past water temperature. Cold and highly variable temperature regimes resulted in the precipitation of highly unordered first-order lamellae of simp…