Articles de revues : « Clock-transitions »

1

Jukes, Thomas H. « Transitions, transversions, and the molecular evolutionary clock ». Journal of Molecular Evolution 26, n^o 1-2 (novembre 1987) : 87–98. http://dx.doi.org/10.1007/bf02111284.

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Wynands, R., R. Schroder et S. Weyers. « Majorana Transitions in an Atomic Fountain Clock ». IEEE Transactions on Instrumentation and Measurement 56, n^o 2 (avril 2007) : 660–63. http://dx.doi.org/10.1109/tim.2007.891116.

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Wolfowicz, Gary, Alexei M. Tyryshkin, Richard E. George, Helge Riemann, Nikolai V. Abrosimov, Peter Becker, Hans-Joachim Pohl, Mike L. W. Thewalt, Stephen A. Lyon et John J. L. Morton. « Atomic clock transitions in silicon-based spin qubits ». Nature Nanotechnology 8, n^o 8 (23 juin 2013) : 561–64. http://dx.doi.org/10.1038/nnano.2013.117.

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BENDIX, CLAIRE, JUAN M. MENDOZA, DESIREE N. STANLEY, ROBERT MEELEY et FRANK G. HARMON. « The circadian clock-associated genegigantea1affects maize developmental transitions ». Plant, Cell & ; Environment 36, n^o 7 (28 février 2013) : 1379–90. http://dx.doi.org/10.1111/pce.12067.

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GIRAUD, MATHIEU, PHILLIPE VEBER et DOMINIQUE LAVENIER. « PATH-EQUIVALENT DEVELOPMENTS IN ACYCLIC WEIGHTED AUTOMATA ». International Journal of Foundations of Computer Science 18, n^o 04 (août 2007) : 799–811. http://dx.doi.org/10.1142/s012905410700498x.

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Weighted finite automata (WFA) are used with FPGA accelerating hardware to scan large genomic banks. Hardwiring such automata raises surface area and clock frequency constraints, requiring efficient ∊-transitions-removal techniques. In this paper, we present bounds on the number of new transitions for the development of acyclic WFA, which is a special case of the ∊-transitions-removal problem. We introduce a new problem, a partial removal of ∊-transitions while accepting short chains of ∊-transitions.

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Vuilleumier, Robin, Laurence Besseau, Gilles Boeuf, Aurélien Piparelli, Yoav Gothilf, Walter G. Gehring, David C. Klein et Jack Falcón. « Starting the Zebrafish Pineal Circadian Clock with a Single Photic Transition ». Endocrinology 147, n^o 5 (1 mai 2006) : 2273–79. http://dx.doi.org/10.1210/en.2005-1565.

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The issue of what starts the circadian clock ticking was addressed by studying the developmental appearance of the daily rhythm in the expression of two genes in the zebrafish pineal gland that are part of the circadian clock system. One encodes the photopigment exorhodopsin and the other the melatonin synthesizing enzyme arylalkylamine N-acetyltransferase (AANAT2). Significant daily rhythms in AANAT2 mRNA abundance were detectable for several days after fertilization in animals maintained in a normal or reversed lighting cycle providing 12 h of light and 12 h of dark. In contrast, these rhythms do not develop if animals are maintained in constant lighting or constant darkness from fertilization. In contrast to exorhodopsin, rhythmicity of AANAT2 can be initiated by a pulse of light against a background of constant darkness, by a pulse of darkness against a background of constant lighting, or by single light-to-dark or dark-to-light transitions. Accordingly, these studies indicate that circadian clock function in the zebrafish pineal gland can be initiated by minimal photic cues, and that single photic transitions can be used as an experimental tool to dissect the mechanism that starts the circadian clock in the pineal gland.

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Lewis, Sina G., Kori E. Smyser et Joel D. Eaves. « Clock transitions guard against spin decoherence in singlet fission ». Journal of Chemical Physics 155, n^o 19 (21 novembre 2021) : 194109. http://dx.doi.org/10.1063/5.0069344.

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Wolfowicz, Gary, Alexei M. Tyryshkin, Richard E. George, Helge Riemann, Nikolai V. Abrosimov, Peter Becker, Hans-Joachim Pohl, Mike L. W. Thewalt, Stephen A. Lyon et John J. L. Morton. « Erratum : Atomic clock transitions in silicon-based spin qubits ». Nature Nanotechnology 8, n^o 11 (novembre 2013) : 881. http://dx.doi.org/10.1038/nnano.2013.218.

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Yudin, V. I., A. V. Taichenachev, M. Yu Basalaev, T. Zanon-Willette, T. E. Mehlstäubler, R. Boudot, J. W. Pollock, M. Shuker, E. A. Donley et J. Kitching. « Combined error signal in Ramsey spectroscopy of clock transitions ». New Journal of Physics 20, n^o 12 (18 décembre 2018) : 123016. http://dx.doi.org/10.1088/1367-2630/aaf47c.

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Siegert, M., et H. U. Everts. « Layering transitions in the chiral clock model : Bethe approximation ». Journal of Physics A : Mathematical and General 22, n^o 1 (7 janvier 1989) : 117–28. http://dx.doi.org/10.1088/0305-4470/22/1/018.

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Camparo, James, John Coffer et Jeremy Townsend. « Laser-pumped atomic clock exploiting pressure-broadened optical transitions ». Journal of the Optical Society of America B 22, n^o 3 (1 mars 2005) : 521. http://dx.doi.org/10.1364/josab.22.000521.

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Rubín-Osanz, Marcos, François Lambert, Feng Shao, Eric Rivière, Régis Guillot, Nicolas Suaud, Nathalie Guihéry et al. « Chemical tuning of spin clock transitions in molecular monomers based on nuclear spin-free Ni(ii) ». Chemical Science 12, n^o 14 (2021) : 5123–33. http://dx.doi.org/10.1039/d0sc05856d.

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Najafian, Kaveh, Ziv Meir et Stefan Willitsch. « From megahertz to terahertz qubits encoded in molecular ions : theoretical analysis of dipole-forbidden spectroscopic transitions in N2+ ». Physical Chemistry Chemical Physics 22, n^o 40 (2020) : 23083–98. http://dx.doi.org/10.1039/d0cp03906c.

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Aharon, Nati, Nicolas Spethmann, Ian D. Leroux, Piet O. Schmidt et Alex Retzker. « Robust optical clock transitions in trapped ions using dynamical decoupling ». New Journal of Physics 21, n^o 8 (28 août 2019) : 083040. http://dx.doi.org/10.1088/1367-2630/ab3871.

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Yamagata, A., et I. Ono. « Phase transitions of the 6-clock model in two dimensions ». Journal of Physics A : Mathematical and General 24, n^o 1 (7 janvier 1991) : 265–75. http://dx.doi.org/10.1088/0305-4470/24/1/033.

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Shiddiq, Muhandis, Dorsa Komijani, Yan Duan, Alejandro Gaita-Ariño, Eugenio Coronado et Stephen Hill. « Enhancing coherence in molecular spin qubits via atomic clock transitions ». Nature 531, n^o 7594 (mars 2016) : 348–51. http://dx.doi.org/10.1038/nature16984.

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Matsuo, Haruhiko, et Kiyohide Nomura. « Berezinskii–Kosterlitz–Thouless transitions in the six-state clock model ». Journal of Physics A : Mathematical and General 39, n^o 12 (8 mars 2006) : 2953–64. http://dx.doi.org/10.1088/0305-4470/39/12/006.

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Sasai, Masaki. « Role of the reaction-structure coupling in temperature compensation of the KaiABC circadian rhythm ». PLOS Computational Biology 18, n^o 9 (6 septembre 2022) : e1010494. http://dx.doi.org/10.1371/journal.pcbi.1010494.

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When the mixture solution of cyanobacterial proteins, KaiA, KaiB, and KaiC, is incubated with ATP in vitro, the phosphorylation level of KaiC shows stable oscillations with the temperature-compensated circadian period. Elucidating this temperature compensation is essential for understanding the KaiABC circadian clock, but its mechanism has remained a mystery. We analyzed the KaiABC temperature compensation by developing a theoretical model describing the feedback relations among reactions and structural transitions in the KaiC molecule. The model showed that the reduced structural cooperativity should weaken the negative feedback coupling among reactions and structural transitions, which enlarges the oscillation amplitude and period, explaining the observed significant period extension upon single amino-acid residue substitution. We propose that an increase in thermal fluctuations similarly attenuates the reaction-structure feedback, explaining the temperature compensation in the KaiABC clock. The model explained the experimentally observed responses of the oscillation phase to the temperature shift or the ADP-concentration change and suggested that the ATPase reactions in the CI domain of KaiC affect the period depending on how the reaction rates are modulated. The KaiABC clock provides a unique opportunity to analyze how the reaction-structure coupling regulates the system-level synchronized oscillations of molecules.

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Chan, Catherine S. « Belonging to the City : Representations of a Colonial Clock Tower in British Hong Kong ». Journal of Urban History 45, n^o 2 (19 avril 2018) : 321–32. http://dx.doi.org/10.1177/0096144218769894.

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This study interprets the transformation of a European clock tower that was built in British Hong Kong. By examining its purpose and life in the nineteenth and twentieth centuries, I focus on the voices that spoke for the clock tower in times of crisis and change. Through a combination of government documents, newspaper articles, editorial letters, historical narratives, travel guides, and photographs, this study aims to show the transitions of the clock tower in line with the development of local identity in Hong Kong during the colonial era. It highlights the shift in colonial society from a racially segregated city to a cosmopolitan city shared, to a certain extent, by urban elites, foreign settlers, and local Chinese residents.

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Loriani, Sina, Alexander Friedrich, Christian Ufrecht, Fabio Di Pumpo, Stephan Kleinert, Sven Abend, Naceur Gaaloul et al. « Interference of clocks : A quantum twin paradox ». Science Advances 5, n^o 10 (octobre 2019) : eaax8966. http://dx.doi.org/10.1126/sciadv.aax8966.

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The phase of matter waves depends on proper time and is therefore susceptible to special-relativistic (kinematic) and gravitational (redshift) time dilation. Hence, it is conceivable that atom interferometers measure general-relativistic time-dilation effects. In contrast to this intuition, we show that (i) closed light-pulse interferometers without clock transitions during the pulse sequence are not sensitive to gravitational time dilation in a linear potential. (ii) They can constitute a quantum version of the special-relativistic twin paradox. (iii) Our proposed experimental geometry for a quantum-clock interferometer isolates this effect.

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SHAKER, MOHAMED O., et MAGDY A. BAYOUMI. « A CLOCK GATED SUCCESSIVE APPROXIMATION REGISTER FOR A/D CONVERSIONS ». Journal of Circuits, Systems and Computers 23, n^o 02 (février 2014) : 1450023. http://dx.doi.org/10.1142/s0218126614500236.

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A novel low power clock gated successive approximation register (SAR) is proposed. The new register is based on gating the clock signal when there is no data switching activity. It operates with fewer transistors and no redundant transitions which makes it suitable for low power applications. The proposed register consisting of 8 bits has been designed up to the layout level with 1 V power supply in 90 nm CMOS technology and has been simulated using SPECTRE. Simulation results have shown that the proposed register saves up to 75% of power consumption.

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Collett, Charles, Kai-Isaak Ellers, Nicholas Russo, Kevin Kittilstved, Grigore Timco, Richard Winpenny et Jonathan Friedman. « A Clock Transition in the Cr7Mn Molecular Nanomagnet ». Magnetochemistry 5, n^o 1 (14 janvier 2019) : 4. http://dx.doi.org/10.3390/magnetochemistry5010004.

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A viable qubit must have a long coherence time T 2 . In molecular nanomagnets, T 2 is often limited at low temperatures by the presence of dipole and hyperfine interactions, which are often mitigated through sample dilution, chemical engineering and isotope substitution in synthesis. Atomic-clock transitions offer another route to reducing decoherence from environmental fields by reducing the effective susceptibility of the working transition to field fluctuations. The Cr7Mn molecular nanomagnet, a heterometallic ring, features a clock transition at zero field. Both continuous-wave and spin-echo electron-spin resonance experiments on Cr7Mn samples, diluted via co-crystallization, show evidence of the effects of the clock transition with a maximum T 2 ∼ 390 ns at 1.8 K. We discuss improvements to the experiment that may increase T 2 further.

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NIKOLAIDIS, S., et E. D. KYRIAKIS-BITZAROS. « A CHARGE RECYCLING TECHNIQUE FOR THE DESIGN OF LOW POWER CMOS CLOCK DRIVERS ». Journal of Circuits, Systems and Computers 09, n^o 03n04 (juin 1999) : 169–80. http://dx.doi.org/10.1142/s0218126699000153.

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The design of low power CMOS clock drivers using a charge recycling technique is introduced in this paper. Considering a clock signal and its complement, the half of the charge stored in the load capacitances is reused in every clock edge. The proposed circuit exploits the inherent input-output delay of the driver for the generation of all necessary control signals, using fully digital logic and conventional technology. Extensive simulations of the circuit have been performed and the influence of various design parameters on its response has been studied. Compared to traditional taper buffers, power savings over 45% are obtained for the output load transitions whereas the total power reduction decreases by 10% to 35% due to control overhead. Moreover, no speed degradation is observed but almost a duplication of the silicon area is required.

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Yu, Geng-Hua, Ying-Ge Geng, Long Li, Chao Zhou, Cheng-Bo Duan, Rui-Peng Chai et Yong-Ming Yang. « The ac Stark shifts of the terahertz clock transitions of barium ». Chinese Physics B 24, n^o 10 (29 septembre 2015) : 103201. http://dx.doi.org/10.1088/1674-1056/24/10/103201.

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Külske, C., et P. Schriever. « Non-robust Phase Transitions in the Generalized Clock Model on Trees ». Journal of Statistical Physics 170, n^o 1 (21 novembre 2017) : 1–21. http://dx.doi.org/10.1007/s10955-017-1919-3.

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Krčmár, R., A. Gendiar et T. Nishino. « Entanglement-Entropy Study of Phase Transitions in Six-State Clock Model ». Acta Physica Polonica A 137, n^o 5 (mai 2020) : 598–600. http://dx.doi.org/10.12693/aphyspola.137.598.

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Bauch, Andreas, et Roland Schröder. « Frequency shifts in a cesium atomic clock due to Majorana transitions ». Annalen der Physik 505, n^o 5 (1993) : 421–49. http://dx.doi.org/10.1002/andp.19935050502.

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Adams, Sally, et Isabelle A. Carré. « Downstream of the plant circadian clock : output pathways for the control of physiology and development ». Essays in Biochemistry 49 (30 juin 2011) : 53–69. http://dx.doi.org/10.1042/bse0490053.

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The plant circadian clock controls many aspects of growth and development, allowing an individual to adapt its physiology and metabolism in anticipation of diurnal and seasonal environmental changes. Circadian regulation of hormone levels and hormonal signalling modulates many features of development, including daily growth patterns and the breaking of seed dormancy. The clock also plays a role in seasonal day-length perception, allowing plants to optimally time key development transitions, such as reproduction. Moreover, the clock restricts (gates) the sensitivity of a plant's response to environmental cues, such as light and stress, to specific times of the day, ensuring that the plant can distinguish between normal fluctuations and longer-term changes. The central oscillator controls many of these output pathways via rhythmic gene expression, with several of the core clock components encoding transcription factors. Post-transcriptional processes are also likely to make an important contribution to the circadian regulation of output pathways. The plant circadian clock plays a role in regulating fitness, hybrid vigour and numerous stress responses. Thus elucidating the complexities of the circadian output mechanisms and their regulation may provide new avenues for crop enhancement.

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Norcia, Matthew A., Matthew N. Winchester, Julia R. K. Cline et James K. Thompson. « Superradiance on the millihertz linewidth strontium clock transition ». Science Advances 2, n^o 10 (octobre 2016) : e1601231. http://dx.doi.org/10.1126/sciadv.1601231.

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Laser frequency noise contributes a significant limitation to today’s best atomic clocks. A proposed solution to this problem is to create a superradiant laser using an optical clock transition as its gain medium. This laser would act as an active atomic clock and would be highly immune to the fluctuations in reference cavity length that limit today’s best lasers. We demonstrate and characterize superradiant emission from the millihertz linewidth clock transition in an ensemble of laser-cooled 87Sr atoms trapped within a high-finesse optical cavity. We measure a collective enhancement of the emission rate into the cavity mode by a factor of more than 10,000 compared to independently radiating atoms. We also demonstrate a method for seeding superradiant emission and observe interference between two independent transitions lasing simultaneously. We use this interference to characterize the relative spectral properties of the two lasing subensembles.

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Huang, Yi Sheng, et Ho Shan Chiang. « Enhancement of a Fault Measure for AMSs Using Probabilistic Timed Automata ». Advanced Materials Research 317-319 (août 2011) : 681–84. http://dx.doi.org/10.4028/www.scientific.net/amr.317-319.681.

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A novel approach for probabilistic timed structure that is based on combining the formalisms of timed automata and probabilistic automata representation of the system is proposed. Due to their real-valued clocks can measure the passage of time and transitions can be probabilistic such that it can be expressed as a discrete probability distribution on the set of target states. The usage of clock variables and the specification of state space are illustrated with real value time applications. The transitions between states are probabilistic by events which describe either the occurrence of faults or normal working conditions. Additionally, the passage of discrete time and transitions can be probabilistic by mean of the theory of expectation sets to obtain a unified measure reasoning strategy.

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Flambaum, V. V., et V. A. Dzuba. « Search for variation of the fundamental constants in atomic, molecular, and nuclear spectra ». Canadian Journal of Physics 87, n^o 1 (1 janvier 2009) : 25–33. http://dx.doi.org/10.1139/p08-072.

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The search for variation of the fundamental constants such as the fine-structure constant α (α = e2/hc) and the ratios of fundamental masses (for example, electron-to-proton mass ratio μ = me/mp) is reviewed. Strong emphasis is given to establishing the relationships between the change in the measured frequencies of atomic, molecular, or nuclear transitions and the corresponding change of the fundamental constants. Transitions in which the sensitivity of the frequency change to the variation of the fine-structure constant is strongly enhanced are discussed and most recent experimental results are presented. Most attention is given to the use of atomic, molecular, and nuclear transitions in the study of quasar absorption spectra and in atomic clock experiments.PACS Nos.: 31.25.Eb, 31.25.Jf

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Das, Arghya, Anal Bhowmik, Narendra Nath Dutta et Sonjoy Majumder. « Two-Photon Polarizability of Ba+ Ion : Control of Spin-Mixing Processes in an Ultracold 137Ba+—87Rb Mixture ». Atoms 10, n^o 4 (3 octobre 2022) : 109. http://dx.doi.org/10.3390/atoms10040109.

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In this work, we present a scheme of a two-photon interaction to calculate magic wavelengths for the 62S12− 52D32,52 clock transitions of Ba+ ion employing the relativistic coupled-cluster method. These magic wavelengths can be essential inputs to achieve better accuracy in the future ionic clock experiments. In this paper, we further show an application of a two-photon interaction to the spin-mixing processes, |0,0⟩↔|+1,−1⟩ and |0,0⟩↔|−1,+1⟩, of an ultra-cold spin-1 mixture of 137Ba+ ions and 87Rb atoms. We determine the protocols for selecting these spin-mixing oscillations by changing the strength and frequencies of the externally applied magnetic field and laser beams, respectively.

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Liu, Junjie, Jakub Mrozek, Aman Ullah, Yan Duan, José J. Baldoví, Eugenio Coronado, Alejandro Gaita-Ariño et Arzhang Ardavan. « Quantum coherent spin–electric control in a molecular nanomagnet at clock transitions ». Nature Physics 17, n^o 11 (14 octobre 2021) : 1205–9. http://dx.doi.org/10.1038/s41567-021-01355-4.

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Deng, Yuangang, Tao Shi et Su Yi. « Motional n-phonon bundle states of a trapped atom with clock transitions ». Photonics Research 9, n^o 7 (28 juin 2021) : 1289. http://dx.doi.org/10.1364/prj.427062.

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Chen, Yong, Zhi-Yuan Xie et Ji-Feng Yu. « Phase transitions of the five-state clock model on the square lattice ». Chinese Physics B 27, n^o 8 (août 2018) : 080503. http://dx.doi.org/10.1088/1674-1056/27/8/080503.

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Yamagata, A., et I. Ono. « Phase transitions of the ferromagnetic 6-clock model on the square lattice ». Journal of Magnetism and Magnetic Materials 90-91 (décembre 1990) : 293–95. http://dx.doi.org/10.1016/s0304-8853(10)80105-2.

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Asorey, M., J. G. Esteve et J. Salas. « Exact renormalization-group analysis of first-order phase transitions in clock models ». Physical Review B 48, n^o 6 (1 août 1993) : 3626–32. http://dx.doi.org/10.1103/physrevb.48.3626.

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Giménez-Santamarina, Silvia, Salvador Cardona-Serra, Juan M. Clemente-Juan, Alejandro Gaita-Ariño et Eugenio Coronado. « Exploiting clock transitions for the chemical design of resilient molecular spin qubits ». Chemical Science 11, n^o 39 (2020) : 10718–28. http://dx.doi.org/10.1039/d0sc01187h.

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Duraivel, A. N., B. Paulchamy et K. Mahendrakan. « Proficient Technique for High Performance Very Large-Scale Integration System to Amend Clock Gated Dual Edge Triggered Sense Amplifier Flip-Flop with Less Dissipation of Power Leakage ». Journal of Nanoelectronics and Optoelectronics 16, n^o 4 (1 avril 2021) : 602–11. http://dx.doi.org/10.1166/jno.2021.2984.

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Clocked flip flops are used to memory in synchronous or clocked series networks, adjusting the individual clock signal status. Therefore, at these times of clock signal transfer, the state of the memory unit and the state of the whole electrical structure change. It’s only during signal transfer that the key to a flip-flop being correctly operated. Two transitions from 0 and 1 are followed by a clock pulse, and 1 to 0. The pulse shift is defined by the positive and negative sides of the pulse. The data on or off the clock cycle edges are recorded by a single-edge trigger flip flop (SETFF), but the flip flop with the double-edge sensor amplifier (DETSAFF). Another common technique for dynamic energy consumption reduced when the device is idle is the clock gating. In this document. Sleep is used to reduce the power of the leakage Here are the following: High threshold voltages sleep transistors are used. Among the supply voltage and VDD the sleep pMOS transistor and the pull-up system and between the network and the ground GND a sleep NMOs Transistor is located. With sleep transistors, CG-SAFF can save up to 30% of its power during zero input switching operation. For different sequential device architecture, the proposed flip-flop may be used.

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Nowrousian, Minou, Giles E. Duffield, Jennifer J. Loros et Jay C. Dunlap. « The frequency Gene Is Required for Temperature-Dependent Regulation of Many Clock-Controlled Genes in Neurospora crassa ». Genetics 164, n^o 3 (1 juillet 2003) : 923–33. http://dx.doi.org/10.1093/genetics/164.3.923.

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Abstract The circadian clock of Neurospora broadly regulates gene expression and is synchronized with the environment through molecular responses to changes in ambient light and temperature. It is generally understood that light entrainment of the clock depends on a functional circadian oscillator comprising the products of the wc-1 and wc-2 genes as well as those of the frq gene (the FRQ/WCC oscillator). However, various models have been advanced to explain temperature regulation. In nature, light and temperature cues reinforce one another such that transitions from dark to light and/or cold to warm set the clock to subjective morning. In some models, the FRQ/WCC circadian oscillator is seen as essential for temperature-entrained clock-controlled output; alternatively, this oscillator is seen exclusively as part of the light pathway mediating entrainment of a cryptic “driving oscillator” that mediates all temperature-entrained rhythmicity, in addition to providing the impetus for circadian oscillations in general. To identify novel clock-controlled genes and to examine these models, we have analyzed gene expression on a broad scale using cDNA microarrays. Between 2.7 and 5.9% of genes were rhythmically expressed with peak expression in the subjective morning. A total of 1.4-1.8% of genes responded consistently to temperature entrainment; all are clock controlled and all required the frq gene for this clock-regulated expression even under temperature-entrainment conditions. These data are consistent with a role for frq in the control of temperature-regulated gene expression in N. crassa and suggest that the circadian feedback loop may also serve as a sensor for small changes in ambient temperature.

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Cornwall Scoones, Jake, Deb Sankar Banerjee et Shiladitya Banerjee. « Size-Regulated Symmetry Breaking in Reaction-Diffusion Models of Developmental Transitions ». Cells 9, n^o 7 (9 juillet 2020) : 1646. http://dx.doi.org/10.3390/cells9071646.

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The development of multicellular organisms proceeds through a series of morphogenetic and cell-state transitions, transforming homogeneous zygotes into complex adults by a process of self-organisation. Many of these transitions are achieved by spontaneous symmetry breaking mechanisms, allowing cells and tissues to acquire pattern and polarity by virtue of local interactions without an upstream supply of information. The combined work of theory and experiment has elucidated how these systems break symmetry during developmental transitions. Given that such transitions are multiple and their temporal ordering is crucial, an equally important question is how these developmental transitions are coordinated in time. Using a minimal mass-conserved substrate-depletion model for symmetry breaking as our case study, we elucidate mechanisms by which cells and tissues can couple reaction–diffusion-driven symmetry breaking to the timing of developmental transitions, arguing that the dependence of patterning mode on system size may be a generic principle by which developing organisms measure time. By analysing different regimes of our model, simulated on growing domains, we elaborate three distinct behaviours, allowing for clock-, timer- or switch-like dynamics. Relating these behaviours to experimentally documented case studies of developmental timing, we provide a minimal conceptual framework to interrogate how developing organisms coordinate developmental transitions.

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Lan, Shau-Yu, Pei-Chen Kuan, Brian Estey, Damon English, Justin M. Brown, Michael A. Hohensee et Holger Müller. « A Clock Directly Linking Time to a Particle's Mass ». Science 339, n^o 6119 (10 janvier 2013) : 554–57. http://dx.doi.org/10.1126/science.1230767.

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Historically, time measurements have been based on oscillation frequencies in systems of particles, from the motion of celestial bodies to atomic transitions. Relativity and quantum mechanics show that even a single particle of mass m determines a Compton frequency ω0 = mc2/ℏ, where c is the speed of light and ℏ is Planck's constant h divided by 2π. A clock referenced to ω0 would enable high-precision mass measurements and a fundamental definition of the second. We demonstrate such a clock using an optical frequency comb to self-reference a Ramsey-Bordé atom interferometer and synchronize an oscillator at a subharmonic of ω0. This directly demonstrates the connection between time and mass. It allows measurement of microscopic masses with 4 × 10−9 accuracy in the proposed revision to SI units. Together with the Avogadro project, it yields calibrated kilograms.

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Shen, Jizhong, Liang Geng et Xuexiang Wu. « Low Power Pulse-Triggered Flip-Flop Based on Clock Triggering Edge Control Technique ». Journal of Circuits, Systems and Computers 24, n^o 07 (17 juin 2015) : 1550094. http://dx.doi.org/10.1142/s0218126615500942.

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Flip-flop is an important unit in digital integrated circuits, whose characteristics have a deep impact on the performance of the circuits. To reduce the power dissipation of flip-flops, clock triggering edge control technique is proposed, which is feasible to block one or two triggering edges of a clock cycle if they are redundant in dual-edge pulse-triggered flip-flops (DEPFFs). Based on this technique, redundant pulses can be suppressed when the input stays unchanged, and all the redundant triggerings are eliminated to reduce redundant transitions at the internal nodes of the flip-flop, so the power dissipation can be decreased. Then a novel DEPFF based on clock triggering edge control (DEPFF-CEC) technique is proposed. Based on the SMIC 65-nm technology, the post layout simulation results show that the proposed DEPFF-CEC gains an improvement of 8.03–39.83% in terms of power dissipation when the input switching activity is 10%, as compared with its counterparts. Thus, it is suitable for energy-efficient designs whose input data switching activity is low.

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Jorba, Jaume, Ray Campagnoli, Lina De et Olen Kew. « Calibration of Multiple Poliovirus Molecular Clocks Covering an Extended Evolutionary Range ». Journal of Virology 82, n^o 9 (20 février 2008) : 4429–40. http://dx.doi.org/10.1128/jvi.02354-07.

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ABSTRACT We have calibrated five different molecular clocks for circulating poliovirus based upon the rates of fixation of total substitutions (K t ), synonymous substitutions (K s ), synonymous transitions (A s ), synonymous transversions (B s ), and nonsynonymous substitutions (K a ) into the P1/capsid region (2,643 nucleotides). Rates were determined over a 10-year period by analysis of sequences of 31 wild poliovirus type 1 isolates representing a well-defined phylogeny derived from a common imported ancestor. Similar rates were obtained by linear regression, the maximum likelihood/single-rate dated-tip method, and Bayesian inference. The very rapid K t [(1.03 ± 0.10) × 10−2 substitutions/site/year] and K s [(1.00 ± 0.08) × 10−2] clocks were driven primarily by the A s clock [(0.96 ± 0.09) × 10−2], the B s clock was ∼10-fold slower [(0.10 ± 0.03) × 10−2], and the more stochastic K a clock was ∼30-fold slower [(0.03 ± 0.01) × 10−2]. Nonsynonymous substitutions at all P1/capsid sites, including the neutralizing antigenic sites, appeared to be constrained by purifying selection. Simulation of the evolution of third-codon positions suggested that saturation of synonymous transitions would be evident at 10 years and complete at ∼65 years of independent transmission. Saturation of synonymous transversions was predicted to be minimal at 20 years and incomplete at 100 years. The rapid evolution of the K t , K s , and A s clocks can be used to estimate the dates of divergence of closely related viruses, whereas the slower B s and K a clocks may be used to explore deeper evolutionary relationships within and across poliovirus genotypes.

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Armitstead, K., et J. M. Yeoman. « A series approach to wetting and layering transitions. III. The chiral clock model ». Journal of Physics A : Mathematical and General 21, n^o 1 (7 janvier 1988) : 173–95. http://dx.doi.org/10.1088/0305-4470/21/1/023.

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Taichenachev, A. V., V. I. Yudin, C. W. Oates, Z. W. Barber, N. D. Lemke, A. D. Ludlow, U. Sterr, Ch Lisdat et F. Riehle. « Compensation of field-induced frequency shifts in Ramsey spectroscopy of optical clock transitions ». JETP Letters 90, n^o 11 (février 2010) : 713–17. http://dx.doi.org/10.1134/s0021364009230052.

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Gao Feng, Wang Ye-Bing, Tian Xiao, Xu Peng et Chang Hong. « Observation of transitions in strontium triplet state and its application in optical clock ». Acta Physica Sinica 61, n^o 17 (2012) : 173201. http://dx.doi.org/10.7498/aps.61.173201.

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Ueno, Yohtaro, et Katsumi Kasono. « Incompletely ordered phases and phase transitions in the three-dimensional general clock model ». Physical Review B 48, n^o 22 (1 décembre 1993) : 16471–83. http://dx.doi.org/10.1103/physrevb.48.16471.

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Lodewyck, Jérôme. « On a definition of the SI second with a set of optical clock transitions ». Metrologia 56, n^o 5 (16 septembre 2019) : 055009. http://dx.doi.org/10.1088/1681-7575/ab3a82.

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Udem, Th, S. A. Diddams, K. R. Vogel, C. W. Oates, E. A. Curtis, W. D. Lee, W. M. Itano, R. E. Drullinger, J. C. Bergquist et L. Hollberg. « Absolute Frequency Measurements of theHg+and Ca Optical Clock Transitions with a Femtosecond Laser ». Physical Review Letters 86, n^o 22 (28 mai 2001) : 4996–99. http://dx.doi.org/10.1103/physrevlett.86.4996.

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