WorldWideScience

Sample records for biological clocks

  1. Biological Clocks & Circadian Rhythms

    Science.gov (United States)

    Robertson, Laura; Jones, M. Gail

    2009-01-01

    The study of biological clocks and circadian rhythms is an excellent way to address the inquiry strand in the National Science Education Standards (NSES) (NRC 1996). Students can study these everyday phenomena by designing experiments, gathering and analyzing data, and generating new experiments. As students explore biological clocks and circadian…

  2. The circadian clock and cell cycle: Interconnected biological circuits

    OpenAIRE

    Masri, Selma; Cervantes, Marlene; Sassone-Corsi, Paolo

    2013-01-01

    The circadian clock governs biological timekeeping on a systemic level, helping to regulate and maintain physiological processes, including endocrine and metabolic pathways with a periodicity of 24-hours. Disruption within the circadian clock machinery has been linked to numerous pathological conditions, including cancer, suggesting that clock-dependent regulation of the cell cycle is an essential control mechanism. This review will highlight recent advances on the ‘gating’ controls of the ci...

  3. The Bird of Time: Cognition and the Avian Biological Clock

    OpenAIRE

    Vincent Michael Cassone; David F Westneat

    2012-01-01

    Avian behavior and physiology are embedded in time at many levels of biological organization. Biological clock function in birds is critical for sleep/wake cycles, but may also regulate the acquisition of place memory, learning of song from tutors, social integration and time-compensated navigation. This relationship has two major implications. First, mechanisms of the circadian clock should be linked in some way to the mechanisms of all these behaviors. How is not yet clear, and evidence tha...

  4. The bird of time: cognition and the avian biological clock

    OpenAIRE

    Cassone, Vincent M.; David F Westneat

    2012-01-01

    Avian behavior and physiology are embedded in time at many levels of biological organization. Biological clock function in birds is critical for sleep/wake cycles, but may also regulate the acquisition of place memory, learning of song from tutors, social integration, and time-compensated navigation. This relationship has two major implications. First, mechanisms of the circadian clock should be linked in some way to the mechanisms of all these behaviors. How is not yet clear, and evidence th...

  5. The role of biological clock in glucose homeostasis 

    Directory of Open Access Journals (Sweden)

    Piotr Chrościcki

    2013-06-01

    Full Text Available The mechanism of the biological clock is based on a rhythmic expression of clock genes and clock-controlled genes. As a result of their transcripto-translational associations, endogenous rhythms in the synthesis of key proteins of various physiological and metabolic processes are created. The major timekeeping mechanism for these rhythms exists in the central nervous system. The master circadian clock, localized in suprachiasmatic nucleus (SCN, regulates multiple metabolic pathways, while feeding behavior and metabolite availability can in turn regulate the circadian clock. It is also suggested that in the brain there is a food entrainable oscillator (FEO or oscillators, resulting in activation of both food anticipatory activity and hormone secretion that control digestion processes. Moreover, most cells and tissues express autonomous clocks. Maintenance of the glucose homeostasis is particularly important for the proper function of the body, as this sugar is the main source of energy for the brain, retina, erythrocytes and skeletal muscles. Thus, glucose production and utilization are synchronized in time. The hypothalamic excited orexin neurons control energy balance of organism and modulate the glucose production and utilization. Deficiency of orexin action results in narcolepsy and weight gain, whereas glucose and amino acids can affect activity of the orexin cells. Large-scale genetic studies in rodents and humans provide evidence for the involvement of disrupted clock gene expression rhythms in the pathogenesis of obesity and type 2 diabetes. In general, the current lifestyle of the developed modern societies disturbs the action of biological clock

  6. The Bird of Time: Cognition and the Avian Biological Clock

    Directory of Open Access Journals (Sweden)

    Vincent Michael Cassone

    2012-03-01

    Full Text Available Avian behavior and physiology are embedded in time at many levels of biological organization. Biological clock function in birds is critical for sleep/wake cycles, but may also regulate the acquisition of place memory, learning of song from tutors, social integration and time-compensated navigation. This relationship has two major implications. First, mechanisms of the circadian clock should be linked in some way to the mechanisms of all these behaviors. How is not yet clear, and evidence that the central clock has effects is piecemeal. Second, selection acting on characters that are linked to the circadian clock should influence aspects of the clock mechanism itself. Little evidence exists for this in birds, but there have been few attempts to assess this idea. At its core, the avian circadian clock is a multi-oscillator system comprising the pineal gland, the retinae and the avian homologues of the suprachiasmatic nuclei, whose mutual interactions ensure coordinated physiological functions, which are in turn synchronized to ambient light cycles via encephalic, pineal and retinal photoreceptors. At the molecular level, avian biological clocks comprise a genetic network of positive elements clock and bmal1 whose interactions with the negative elements period2, period3 and the cryptochromes form an oscillatory feedback loop that circumnavigates the 24 hrs of the day. We assess the possibilities for dual integration of the clock with time-dependent cognitive processes. Closer examination of the molecular, physiological, and behavioral elements of the circadian system would place birds at a very interesting fulcrum in the neurobiology of time in learning, memory and navigation. 

  7. Positive temporal dependence of the biological clock implies hyperbolic discounting

    Directory of Open Access Journals (Sweden)

    PeterBossaerts

    2011-01-01

    Full Text Available Temporal preferences of animals and humans often exhibit inconsistencies, whereby an earlier, smaller reward may be preferred when it occurs immediately but not when it is delayed. Such choices reflect hyperbolic discounting of future rewards, rather than the exponential discounting required for temporal consistency. Simultaneously, however, evidence has emerged that suggests that animals and humans have an internal representation of time that often differs from the calendar time used in detection of temporal inconsistencies. Here, we prove that temporal inconsistencies emerge if fixed durations in calendar time are experienced as positively related (positive quadrant dependent. Hence, what are time-consistent choices within the time framework of the decision maker appear as time-inconsistent to an outsider who analyzes choices in calendar time. As the biological clock becomes more variable, the fit of the hyperbolic discounting model improves. A recent alternative explanation for temporal choice inconsistencies builds on persistent under-estimation of the length of distant time intervals. By increasing the expected speed of our stochastic biological clock for time farther into the future, we can emulate this explanation. Ours is therefore an encompassing theoretical framework that predicts context-dependent degrees of intertemporal choice inconsistencies, to the extent that context can generate changes in autocorrelation, variability, and expected speed of the biological clock. Our finding should lead to novel experiments that will clarify the role of time perception in impulsivity, with critical implications for, among others, our understanding of aging, drug abuse and pathological gambling.

  8. Peripheral Skin Temperature and Circadian Biological Clock in Shift Nurses after a Day off

    OpenAIRE

    Massimo Bracci; Veronica Ciarapica; Alfredo Copertaro; Mariella Barbaresi; Nicola Manzella; Marco Tomasetti; Simona Gaetani; Federica Monaco; Monica Amati; Matteo Valentino; Venerando Rapisarda; Lory Santarelli

    2016-01-01

    The circadian biological clock is essentially based on the light/dark cycle. Some people working with shift schedules cannot adjust their sleep/wake cycle to the light/dark cycle, and this may result in alterations of the circadian biological clock. This study explored the circadian biological clock of shift and daytime nurses using non-invasive methods. Peripheral skin temperature, cortisol and melatonin levels in saliva, and Per2 expression in pubic hair follicle cells were investigated for...

  9. Peripheral Skin Temperature and Circadian Biological Clock in Shift Nurses after a Day off.

    Science.gov (United States)

    Bracci, Massimo; Ciarapica, Veronica; Copertaro, Alfredo; Barbaresi, Mariella; Manzella, Nicola; Tomasetti, Marco; Gaetani, Simona; Monaco, Federica; Amati, Monica; Valentino, Matteo; Rapisarda, Venerando; Santarelli, Lory

    2016-01-01

    The circadian biological clock is essentially based on the light/dark cycle. Some people working with shift schedules cannot adjust their sleep/wake cycle to the light/dark cycle, and this may result in alterations of the circadian biological clock. This study explored the circadian biological clock of shift and daytime nurses using non-invasive methods. Peripheral skin temperature, cortisol and melatonin levels in saliva, and Per2 expression in pubic hair follicle cells were investigated for 24 h after a day off. Significant differences were observed in peripheral skin temperature and cortisol levels between shift and daytime nurses. No differences in melatonin levels were obtained. Per2 maximum values were significantly different between the two groups. Shift nurses exhibited lower circadian variations compared to daytime nurses, and this may indicate an adjustment of the circadian biological clock to continuous shift schedules. Non-invasive procedures, such as peripheral skin temperature measurement, determination of cortisol and melatonin in saliva, and analysis of clock genes in hair follicle cells, may be effective approaches to extensively study the circadian clock in shift workers. PMID:27128899

  10. Peripheral Skin Temperature and Circadian Biological Clock in Shift Nurses after a Day off

    Directory of Open Access Journals (Sweden)

    Massimo Bracci

    2016-04-01

    Full Text Available The circadian biological clock is essentially based on the light/dark cycle. Some people working with shift schedules cannot adjust their sleep/wake cycle to the light/dark cycle, and this may result in alterations of the circadian biological clock. This study explored the circadian biological clock of shift and daytime nurses using non-invasive methods. Peripheral skin temperature, cortisol and melatonin levels in saliva, and Per2 expression in pubic hair follicle cells were investigated for 24 h after a day off. Significant differences were observed in peripheral skin temperature and cortisol levels between shift and daytime nurses. No differences in melatonin levels were obtained. Per2 maximum values were significantly different between the two groups. Shift nurses exhibited lower circadian variations compared to daytime nurses, and this may indicate an adjustment of the circadian biological clock to continuous shift schedules. Non-invasive procedures, such as peripheral skin temperature measurement, determination of cortisol and melatonin in saliva, and analysis of clock genes in hair follicle cells, may be effective approaches to extensively study the circadian clock in shift workers.

  11. Phase Resetting Light Pulses Induce Per1 and Persistent Spike Activity in a Subpopulation of Biological Clock Neurons

    OpenAIRE

    Kuhlman, Sandra J.; Silver, Rae; Le Sauter, Joseph; Bult-Ito, Abel; McMahon, Douglas G.

    2003-01-01

    The endogenous circadian clock of the mammalian suprachiasmatic nucleus (SCN) can be reset by light to synchronize the biological clock of the brain with the external environment. This process involves induction of immediate-early genes such as the circadian clock gene Period1 (Per1) and results in a stable shift in the timing of behavioral and physiological rhythms on subsequent days. The mechanisms by which gene activation permanently alters the phase of clock neuron activity are unknown. T...

  12. Molecular Approach to the Nyctinastic Movement of the Plant Controlled by a Biological Clock

    Directory of Open Access Journals (Sweden)

    Shosuke Yamamura

    2001-10-01

    Full Text Available Most leguminous plants close their leaves in the evening, as if to sleep, and open them early in the morning. This circadian rhythm is known to be controlled by the biological clock of such plants. Extensive studies on other nyctinastic plants led to the isolation of a variety of leaf-closing and leaf-opening substances. And, we found that the circadian rhythmic leaf-movement of these plants is controlled by a biological clock that regulates the balance of concentration between leaf-opening and -closing substances.

  13. Extreme violation of sleep hygiene: sleeping against the biological clock during a multiday relay event

    NARCIS (Netherlands)

    A. van Maanen; B. Roest; M. Moen; F. Oort; P. Vergouwen; I Paul; P. Groenenboom; M. Smits

    2015-01-01

    Background: Sleep hygiene is important for sleep quality and optimal performance during the day. However, it is not always possible to follow sleep hygiene requirements. In multiday relay events, athletes have to sleep immediately after physical exertion and sometimes against their biological clock.

  14. Diurnal rhythms in neurexins transcripts and inhibitory/excitatory synapse scaffold proteins in the biological clock.

    Directory of Open Access Journals (Sweden)

    Mika Shapiro-Reznik

    Full Text Available The neurexin genes (NRXN1/2/3 encode two families (α and β of highly polymorphic presynaptic proteins that are involved in excitatory/inhibitory synaptic balance. Recent studies indicate that neuronal activation and memory formation affect NRXN1/2/3α expression and alternative splicing at splice sites 3 and 4 (SS#3/SS#4. Neurons in the biological clock residing in the suprachiasmatic nuclei of the hypothalamus (SCN act as self-sustained oscillators, generating rhythms in gene expression and electrical activity, to entrain circadian bodily rhythms to the 24 hours day/night cycles. Cell autonomous oscillations in NRXN1/2/3α expression and SS#3/SS#4 exons splicing and their links to rhythms in excitatory/inhibitory synaptic balance in the circadian clock were explored. NRXN1/2/3α expression and SS#3/SS#4 splicing, levels of neurexin-2α and the synaptic scaffolding proteins PSD-95 and gephyrin (representing excitatory and inhibitory synapses, respectively were studied in mRNA and protein extracts obtained from SCN of C3H/J mice at different times of the 24 hours day/night cycle. Further studies explored the circadian oscillations in these components and causality relationships in immortalized rat SCN2.2 cells. Diurnal rhythms in mNRXN1α and mNRXN2α transcription, SS#3/SS#4 exon-inclusion and PSD-95 gephyrin and neurexin-2α levels were found in the SCN in vivo. No such rhythms were found with mNRXN3α. SCN2.2 cells also exhibited autonomous circadian rhythms in rNRXN1/2 expression SS#3/SS#4 exon inclusion and PSD-95, gephyrin and neurexin-2α levels. rNRXN3α and rNRXN1/2β were not expressed. Causal relationships were demonstrated, by use of specific siRNAs, between rNRXN2α SS#3 exon included transcripts and gephyrin levels in the SCN2.2 cells. These results show for the first time dynamic, cell autonomous, diurnal rhythms in expression and splicing of NRXN1/2 and subsequent effects on the expression of neurexin-2α and postsynaptic

  15. Extreme Violation of Sleep Hygiene: Sleeping Against the Biological Clock During a Multiday Relay Event

    Directory of Open Access Journals (Sweden)

    van Maanen

    2015-12-01

    Full Text Available Background Sleep hygiene is important for sleep quality and optimal performance during the day. However, it is not always possible to follow sleep hygiene requirements. In multiday relay events, athletes have to sleep immediately after physical exertion and sometimes against their biological clock. Objectives In this pilot study we investigated the effect of having to sleep at an abnormal circadian time on sleep duration. Patients and Methods Eight runners and two cyclists performing a 500 km relay race were followed. They were divided into two groups that took turns in running and resting. Each group ran four times for approximately five hours while the other group slept. As a result, sleep times varied between normal and abnormal times. All athletes wore actigraphs to record the duration and onset of sleep. Results Linear mixed model analyses showed that athletes slept on average 43 minutes longer when they slept during usual (night times than during abnormal (day times. In general, sleep duration decreased during the race with on average 18 minutes per period. Conclusions This pilot study shows that, even under extreme violation of sleep hygiene rules, there still is an apparent effect of circadian rhythm on sleep duration in relay race athletes.

  16. Circadian rhythms of cyanobacteria: monitoring the biological clocks of individual colonies by bioluminescence.

    OpenAIRE

    Kondo, T.; Ishiura, M

    1994-01-01

    Reproducible circadian rhythms of bioluminescence from individual colonies of cyanobacteria (Synechococcus sp. strain PCC 7942) has been observed. Phenotypic monitoring of colonies on agar plates will enable us to genetically analyze the molecular mechanism of the circadian clock of cyanobacteria by screening for clock mutants. By the introduction of a bacterial luciferase gene, we previously developed a transformed cyanobacterial strain (AMC149) that expresses luciferase as a bioluminescent ...

  17. Phase Resetting Light Pulses Induce Per1 and Persistent Spike Activity in a Subpopulation of Biological Clock Neurons

    Science.gov (United States)

    Kuhlman, Sandra J.; Silver, Rae; Le Sauter, Joseph; Bult-Ito, Abel; McMahon, Douglas G.

    2012-01-01

    The endogenous circadian clock of the mammalian suprachiasmatic nucleus (SCN) can be reset by light to synchronize the biological clock of the brain with the external environment. This process involves induction of immediate-early genes such as the circadian clock gene Period1 (Per1) and results in a stable shift in the timing of behavioral and physiological rhythms on subsequent days. The mechanisms by which gene activation permanently alters the phase of clock neuron activity are unknown. To study the relationship between acute gene activation and persistent changes in the neurophysiology of SCN neurons, we recorded from SCN neurons marked with a dynamic green fluorescent protein (GFP) reporter of Per1 gene activity. Phase-resetting light pulses resulted in Per1 induction in a distinct subset of SCN neurons that also exhibited a persistent increase in action potential frequency 3–5 hr after a light pulse. By simultaneously quantifying Per1 gene activation and spike frequency in individual neurons, we found that the degree of Per1 induction was highly correlated with neuronal spike frequency on a cell-by-cell basis. Increased neuronal activity was mediated by membrane potential depolarization as a result of a reduction in outward potassium current. Double-label immunocytochemistry revealed that vasoactive intestinal peptide (VIP)-expressing cells, but not arginine vasopressin (AVP)-expressing cells, exhibited significant Per1 induction by light pulses. Rhythmic GFP expression occurred in both VIP and AVP neurons. Our results indicate that the steps that link acute molecular events to permanent changes in clock phase involve persistent suppression of potassium current, downstream of Per1 gene induction, in a specific subset of Per1-expressing neurons enriched for VIP. PMID:12598633

  18. Body Clock

    Institute of Scientific and Technical Information of China (English)

    刘洪毓

    2000-01-01

    “Body clocks” are biological methods of controling body activities.Every living thing has one. In humans, a body clock controls normal periods of sleeping and waking. It controls the time swhen you are most likely to feel pain.Eating, sleeping and exercising at about the same time each day will help keep body activities normal. But changes in your life, a new job, for example, destroy the balance and thus cause health problems.

  19. The circadian clock goes genomic

    OpenAIRE

    Staiger, D; Shin, J; Johansson, M; Davis, S

    2013-01-01

    Large-scale biology among plant species, as well as comparative genomics of circadian clock architecture and clock-regulated output processes, have greatly advanced our understanding of the endogenous timing system in plants.

  20. Synchronization of Biological Clock Neurons by Light and Peripheral Feedback Systems Promotes Circadian Rhythms and Health

    OpenAIRE

    Ramkisoensing, Ashna; Meijer, Johanna H.

    2015-01-01

    In mammals, the suprachiasmatic nucleus (SCN) functions as a circadian clock that drives 24-h rhythms in both physiology and behavior. The SCN is a multicellular oscillator in which individual neurons function as cell-autonomous oscillators. The production of a coherent output rhythm is dependent upon mutual synchronization among single cells and requires both synaptic communication and gap junctions. Changes in phase-synchronization between individual cells have consequences on the amplitude...

  1. Beyond fossil calibrations: Realities of molecular clock practices in evolutionary biology

    Directory of Open Access Journals (Sweden)

    Christy Anna Hipsley

    2014-05-01

    Full Text Available Molecular-based divergence dating methods, or molecular clocks, are the primary neontological tool for estimating the temporal origins of clades. While the appropriate use of vertebrate fossils as external clock calibrations has stimulated heated discussions in the paleontological community, less attention has been given to the quality and implementation of other calibration types. In lieu of appropriate fossils, many studies rely on alternative sources of age constraints based on geological events, substitution rates and heterochronous sampling, as well as dates secondarily derived from previous analyses. To illustrate the breadth and frequency of calibration types currently employed, we conducted a literature survey of over 600 articles published from 2007 to 2013. Over half of all analyses implemented one or more fossil dates as constraints, followed by geological events and secondary calibrations (15% each. Vertebrate taxa were subjects of nearly half of all studies, while invertebrates and plants together accounted for 43%, followed by viruses, protists and fungi (3% each. Current patterns in calibration practices were disproportionate to the number of discussions on their proper use, particularly regarding plants and secondarily derived dates, which are both relatively neglected. Based on our survey, we provide a comprehensive overview of the latest approaches in clock calibration, and outline strengths and weaknesses associated with each. This critique should serve as a call to action for researchers across multiple communities, particularly those working on clades for which fossil records are poor, to develop their own guidelines regarding selection and implementation of alternative calibration types. This issue is particularly relevant now, as time-calibrated phylogenies are used for more than dating evolutionary origins, but often serve as the backbone of investigations into biogeography, diversity dynamics and rates of phenotypic

  2. Synchronization of Biological Clock Neurons by Light and Peripheral Feedback Systems Promotes Circadian Rhythms and Health.

    Science.gov (United States)

    Ramkisoensing, Ashna; Meijer, Johanna H

    2015-01-01

    In mammals, the suprachiasmatic nucleus (SCN) functions as a circadian clock that drives 24-h rhythms in both physiology and behavior. The SCN is a multicellular oscillator in which individual neurons function as cell-autonomous oscillators. The production of a coherent output rhythm is dependent upon mutual synchronization among single cells and requires both synaptic communication and gap junctions. Changes in phase-synchronization between individual cells have consequences on the amplitude of the SCN's electrical activity rhythm, and these changes play a major role in the ability to adapt to seasonal changes. Both aging and sleep deprivation negatively affect the circadian amplitude of the SCN, whereas behavioral activity (i.e., exercise) has a positive effect on amplitude. Given that the amplitude of the SCN's electrical activity rhythm is essential for achieving robust rhythmicity in physiology and behavior, the mechanisms that underlie neuronal synchronization warrant further study. A growing body of evidence suggests that the functional integrity of the SCN contributes to health, well-being, cognitive performance, and alertness; in contrast, deterioration of the 24-h rhythm is a risk factor for neurodegenerative disease, cancer, depression, and sleep disorders. PMID:26097465

  3. Synchronization of biological clock neurons by light and peripheral feedback systems promotes circadian rhythms and health

    Directory of Open Access Journals (Sweden)

    Ashna eRamkisoensing

    2015-06-01

    Full Text Available In mammals, the suprachiasmatic nucleus (SCN functions as a circadian clock that drives 24-hour rhythms in both physiology and behavior. The SCN is a multicellular oscillator in which individual neurons function as cell-autonomous oscillators. The production of a coherent output rhythm is dependent upon mutual synchronization among single cells and requires both synaptic communication and gap junctions. Changes in phase synchronization between individual cells have consequences on the amplitude of the SCN’s electrical activity rhythm, and these changes play a major role in the ability to adapt to seasonal changes. Both aging and sleep deprivation negatively affect the circadian amplitude of the SCN, whereas behavioral activity (i.e., exercise has a positive effect on amplitude. Given that the amplitude of the SCN’s electrical activity rhythm is essential for achieving robust rhythmicity in physiology and behavior, the mechanisms that underlie neuronal synchronization warrant further study. A growing body of evidence suggests that the functional integrity of the SCN contributes to health, well-being, cognitive performance, and alertness; in contrast, deterioration of the 24-hour rhythm is a risk factor for neurodegenerative disease, cancer, depression, and sleep disorders.

  4. Introduction: Finding new clock components; past and future

    OpenAIRE

    Takahashi, Joseph S.

    2004-01-01

    The molecular mechanism of circadian clocks has been unraveled primarily by the use of phenotype-driven (forward) genetic analysis in a number of model systems. We are now in a position to consider what constitutes a clock component, whether we can establish criteria for clock components, and whether we have found most of the primary clock components? This perspective discusses clock genes and how genetics, molecular biology and biochemistry have been used to find clock gene...

  5. Transcripts from the Circadian Clock: Telling Time and Season

    NARCIS (Netherlands)

    K. Brand (Karl)

    2011-01-01

    textabstractWe all know it when we wake mere moments before an alarm clock is scheduled to wake us: our body clock made the alarm clock redundant. This phenomenon is driven by an endogenous timer known as the biological, or circadian clock. Each revolution of the Earth about its own axis produces pe

  6. cGMP-phosphodiesterase inhibition enhances photic responses and synchronization of the biological circadian clock in rodents.

    Directory of Open Access Journals (Sweden)

    Santiago A Plano

    Full Text Available The master circadian clock in mammals is located in the hypothalamic suprachiasmatic nuclei (SCN and is synchronized by several environmental stimuli, mainly the light-dark (LD cycle. Light pulses in the late subjective night induce phase advances in locomotor circadian rhythms and the expression of clock genes (such as Per1-2. The mechanism responsible for light-induced phase advances involves the activation of guanylyl cyclase (GC, cGMP and its related protein kinase (PKG. Pharmacological manipulation of cGMP by phosphodiesterase (PDE inhibition (e.g., sildenafil increases low-intensity light-induced circadian responses, which could reflect the ability of the cGMP-dependent pathway to directly affect the photic sensitivity of the master circadian clock within the SCN. Indeed, sildenafil is also able to increase the phase-shifting effect of saturating (1200 lux light pulses leading to phase advances of about 9 hours, as well as in C57 a mouse strain that shows reduced phase advances. In addition, sildenafil was effective in both male and female hamsters, as well as after oral administration. Other PDE inhibitors (such as vardenafil and tadalafil also increased light-induced phase advances of locomotor activity rhythms and accelerated reentrainment after a phase advance in the LD cycle. Pharmacological inhibition of the main downstream target of cGMP, PKG, blocked light-induced expression of Per1. Our results indicate that the cGMP-dependent pathway can directly modulate the light-induced expression of clock-genes within the SCN and the magnitude of light-induced phase advances of overt rhythms, and provide promising tools to design treatments for human circadian disruptions.

  7. Effect and Regulatory Mechanism of Clock Gene Per1 on Biological Behaviors of Human Oral Squamous Carcinoma Cell.

    Science.gov (United States)

    Han-Xue, L I; Kai, Yang; Xiao-Juan, F U; Qin, Zhao

    2016-04-10

    Objective To investigate the effect and regulatory mechanism of clock gene Per1 on the proliferation,apoptosis,migration,and invasion of human oral squamous carcinoma SCC15 cells. Methods RNA interference was used to knock down Per1 gene in human oral squamous cell carcinoma SCC15 cell line. Changes of cell proliferation and apoptosis were analyzed by flow cytometry. Transwell assay was carried out to assess cell migration and invasion. Real-time polymerase chain reaction was used to detect the mRNA expressions of Ki-67,murine double minute 2(MDM2),c-Myc,p53,Bax,Bcl-2,metalloproteinase (MMP)2,MMP9,and vascular endothelial growth factor (VEGF). Results shRNA-mediated knockdown of Per1 promoted the proliferation,migration and invasion capacity,and inhibited cell apoptosis capacity of SCC15 cells (all PKi-67,MDM2,Bcl-2,MMP2,and MMP9 and decreased the mRNA expressions of c-Myc,p53,and Bax (all P0.05). Conclusions Clock gene Perl can regulate important tumor-related genes downstream such as Ki-67,MDM2,c-Myc,p53,Bax,Bcl-2,MMP2,and MMP9,and the aberrant expression of Per1 can affect tumor cell proliferation,apoptosis,migration and invasion. An in-depth study of Per1 may further clarify the mechanism of tumorigenesis and tumor development and thus provides new effective molecular targets for cancer treatment. PMID:27181891

  8. Unraveling the circadian clock in Arabidopsis

    OpenAIRE

    Wang, Xiaoxue; Ma, Ligeng

    2012-01-01

    The circadian clock is an endogenous timing system responsible for coordinating an organism’s biological processes with its environment. Interlocked transcriptional feedback loops constitute the fundamental architecture of the circadian clock. In Arabidopsis, three feedback loops, the core loop, morning loop and evening loop, comprise a network that is the basis of the circadian clock. The components of these three loops are regulated in distinct ways, including transcriptional, post-transcri...

  9. Atomic Clocks

    Science.gov (United States)

    Wynands, Robert

    Time is a strange thing. On the one hand it is arguably the most inaccessible physical phenomenon of all: both in that it is impossible to manipulate or modify—for all we know—and in that even after thousands of years mankind's philosophers still have not found a fully satisfying way to understand it. On the other hand, no other quantity can be measured with greater precision. Today's atomic clocks allow us to reproduce the length of the second as the SI unit of time with an uncertainty of a few parts in 1016—orders of magnitude better than any other quantity. In a sense, one can say [1

  10. "Molecular Clock" Analogs: A Relative Rates Exercise

    Science.gov (United States)

    Wares, John P.

    2008-01-01

    Although molecular clock theory is a commonly discussed facet of evolutionary biology, undergraduates are rarely presented with the underlying information of how this theory is examined relative to empirical data. Here a simple contextual exercise is presented that not only provides insight into molecular clocks, but is also a useful exercise for…

  11. Network properties of the mammalian circadian clock

    NARCIS (Netherlands)

    Rohling, Johannes Hermanus Theodoor

    2009-01-01

    The biological clock regulates daily and seasonal rhythms in mammals. This clock is located in the suprachiasmatic nuclei (SCN), which are two small nuclei each consisting of 10,000 neurons. The neurons of the SCN endogenously generate a rhythm of approximately 24 hours. Under the influence of the l

  12. The circadian clock coordinates ribosome biogenesis.

    Directory of Open Access Journals (Sweden)

    Céline Jouffe

    Full Text Available Biological rhythms play a fundamental role in the physiology and behavior of most living organisms. Rhythmic circadian expression of clock-controlled genes is orchestrated by a molecular clock that relies on interconnected negative feedback loops of transcription regulators. Here we show that the circadian clock exerts its function also through the regulation of mRNA translation. Namely, the circadian clock influences the temporal translation of a subset of mRNAs involved in ribosome biogenesis by controlling the transcription of translation initiation factors as well as the clock-dependent rhythmic activation of signaling pathways involved in their regulation. Moreover, the circadian oscillator directly regulates the transcription of ribosomal protein mRNAs and ribosomal RNAs. Thus the circadian clock exerts a major role in coordinating transcription and translation steps underlying ribosome biogenesis.

  13. Avian Circadian Organization: A Chorus of Clocks

    OpenAIRE

    Cassone, Vincent M.

    2013-01-01

    In birds, biological clock function pervades all aspects of biology, controlling daily changes in sleep: wake, visual function, song, migratory patterns and orientation, as well as seasonal patterns of reproduction, song and migration. The molecular bases for circadian clocks are highly conserved, and it is likely the avian molecular mechanisms are similar to those expressed in mammals, including humans. The central pacemakers in the avian pineal gland, retinae and SCN dynamically interact to...

  14. Lego clocks : building a clock from parts

    NARCIS (Netherlands)

    Brunner, Michael; Simons, Mirre J. P.; Merrow, Martha

    2008-01-01

    A new finding opens up speculation that the molecular mechanism of circadian clocks in Synechococcus elongatus is composed of multiple oscillator systems (Kitayama and colleagues, this issue, pp. 1513-1521), as has been described in many eukaryotic clock model systems. However, an alternative intepr

  15. Optical Clocks in Space

    CERN Document Server

    Schiller, S; Nevsky, A; Koelemeij, J C J; Wicht, A; Gill, P; Klein, H A; Margolis, H S; Mileti, G; Sterr, U; Riehle, F; Peik, E; Tamm, C; Ertmer, W; Rasel, E; Klein, V; Salomon, C; Tino, G M; Lemonde, P; Holzwarth, R; Hänsch, T W; Tamm, Chr.

    2007-01-01

    The performance of optical clocks has strongly progressed in recent years, and accuracies and instabilities of 1 part in 10^18 are expected in the near future. The operation of optical clocks in space provides new scientific and technological opportunities. In particular, an earth-orbiting satellite containing an ensemble of optical clocks would allow a precision measurement of the gravitational redshift, navigation with improved precision, mapping of the earth's gravitational potential by relativistic geodesy, and comparisons between ground clocks.

  16. The Glyoxal Clock Reaction

    Science.gov (United States)

    Ealy, Julie B.; Negron, Alexandra Rodriguez; Stephens, Jessica; Stauffer, Rebecca; Furrow, Stanley D.

    2007-01-01

    Research on the glyoxal clock reaction has led to adaptation of the clock reaction to a general chemistry experiment. This particular reaction is just one of many that used formaldehyde in the past. The kinetics of the glyoxal clock makes the reaction suitable as a general chemistry lab using a Calculator Based Laboratory (CBL) or a LabPro. The…

  17. Changes of biological clock protein in neonatal rats with hypoxic-ischemic brain damage%缺氧缺血性脑损伤新生大鼠松果体钟基因表达的变化

    Institute of Scientific and Technical Information of China (English)

    李永富; 金美芳; 孙斌; 冯星

    2013-01-01

    Objective To study the effects of biological clock protein on circadian disorders in hypoxic-ischemic brain damage ( HIBD) by examining levels of CLOCK and BMAL1 proteins in the pineal gland of neonatal rats. Methods Seventy-two 7-day-old Sprague-Dawley (SD) rats were randomly divided into sham-operated and HIBD groups. HIBD model was prepared according to the modified Levine method. Western blot analysis was used to measure the levels of CLOCK and BMAL1 in the pineal gland at 0, 2, 12, 24, 36 and 48 hours after operation. Results Both CLOCK and BMAL levels in the pineal gland increased significantly 48 hours after HIBD compared with the sham-operated group ( P 0. 05 ) . Conclusions Levels of CLOCK and BMAL1 proteins in the pineal gland of rats increase significantly 48 hours after HIBD, suggesting that both CLOCK and BMAL1 may be involved the regulatory mechanism of circadian disorders in rats with HIBD.%目的 观察缺氧缺血性脑损伤(hypoxic-ischemic brain damage,HIBD)新生大鼠松果体中CLOCK、BMAL1蛋白表达的变化,探讨钟基因表达异常在HIBD导致的昼夜节律紊乱中的作用.方法 72只7日龄新生Sprague-Dawley大鼠随机分为假手术组与HIBD模型组,每组36只.采用改良Levine法建立HIBD模型,用Western blot方法测定两组新生大鼠术后0、2、12、24、36、48 h松果体中CLOCK、BMAL1蛋白水平.结果 HIBD模型组松果体的CLOCK及BMAL1蛋白表达水平在HIBD后48 h高于假手术组(P<0.05),在0、2、12、24、36 h CLOCK及BMAL1蛋白表达水平与假手术组相比差异均无统计学意义(P>0.05).结论 HIBD新生大鼠松果体中CLOCK和BMAL1蛋白在损伤48 h后有显著升高,提示两者可能共同参与缺氧缺血时昼夜节律紊乱的发生.

  18. The intrinsic circadian clock within the cardiomyocyte directly regulates myocardial gene expression, metabolism, and contractile function

    Science.gov (United States)

    Virtually every mammalian cell, including cardiomyocytes, possesses an intrinsic circadian clock. The role of this transcriptionally based molecular mechanism in cardiovascular biology remains unknown. We hypothesized that circadian clock within the cardiomyocyte plays a role in regulating myocardia...

  19. Precision Clock Evaluation Facility

    Data.gov (United States)

    Federal Laboratory Consortium — FUNCTION: Tests and evaluates high-precision atomic clocks for spacecraft, ground, and mobile applications. Supports performance evaluation, environmental testing,...

  20. Circadian clock genes universally control key agricultural traits

    Science.gov (United States)

    Circadian clocks are endogenous timers that enable plants to synchronize biological processes with daily and seasonal environmental conditions in order to allocate resources during the most beneficial times of day and year. The circadian clock regulates a number of central plant activities, includin...

  1. Transcripts from the Circadian Clock: Telling Time and Season

    OpenAIRE

    Brand, Karl

    2011-01-01

    textabstractWe all know it when we wake mere moments before an alarm clock is scheduled to wake us: our body clock made the alarm clock redundant. This phenomenon is driven by an endogenous timer known as the biological, or circadian clock. Each revolution of the Earth about its own axis produces periods of light and dark which define what we all experience as a ‘day’. This profound cyclic variation in solar energy is responsible for driving the evolution of adaptive responses as early as 3.8...

  2. Design of Alarm Clock

    OpenAIRE

    Budík, Marek

    2015-01-01

    The goal of this thesis is to create alarm clock, which respect the functional, technical and aesthetic requirements of this device and attain an attractive design of this product. The final draft should be innovative, original and user attractive alarm clock.

  3. Active optical clock

    Institute of Scientific and Technical Information of China (English)

    CHEN JingBiao

    2009-01-01

    This article presents the principles and techniques of active optical clock, a special laser combining the laser physics of one-atom laser, bad-cavity gas laser, super-cavity stabilized laser and optical atomic clock together. As a simple example, an active optical clock based on thermal strontium atomic beam shows a quantum-limited linewidth of 0.51 Hz, which is insensitive to laser cavity-length noise, and may surpass the recorded narrowest 6.7 Hz of Hg ion optical clock and 1.5 Hz of very recent optical lattice clock. The estimated 0.1 Hz one-second instability and 0.27 Hz uncertainty are limited only by the rela-tivistic Doppler effect, and can be improved by cold atoms.

  4. On-chip clock error characterization for clock distribution system

    OpenAIRE

    Shan, Chuan; Galayko, Dimitri; Anceau, François

    2013-01-01

    In this paper, we investigate a test strategy for characterization of clock error statistics between two clock domains in high-speed clocking systems (gigahertz and more). The method allows an indirect measurement (not based on time interval measurement) of clock error distribution by observing the integrity of a periodic sequence transmitted between two clocking domains. The method is compatible with fully on-chip implementation, and the readout of result to off-chip signals is cadenced at l...

  5. Stable clocks and general relativity

    CERN Document Server

    Will, C M

    1995-01-01

    We survey the role of stable clocks in general relativity. Clock comparisons have provided important tests of the Einstein Equivalence Principle, which underlies metric gravity. These include tests of the isotropy of clock comparisons (verification of local Lorentz invariance) and tests of the homogeneity of clock comparisons (verification of local position invariance). Comparisons of atomic clocks with gravitational clocks test the Strong Equivalence Principle by bounding cosmological variations in Newton's constant. Stable clocks also play a role in the search for gravitational radiation: comparision of atomic clocks with the binary pulsar's orbital clock has verified gravitational-wave damping, and phase-sensitive detection of waves from inspiralling compact binaries using laser interferometric gravitational observatories will facilitate extraction of useful source information from the data. Stable clocks together with general relativity have found important practical applications in navigational systems s...

  6. Subtleties of the clock retardation

    OpenAIRE

    Redzic, D. V.

    2015-01-01

    For a simple electromagnetic model of a clock introduced by Jefimenko (clock $\\#$ 1 in 1996 {\\it Am. J. Phys.} {\\bf 64} 812), a change of the rate of the clock when it is set in uniform motion is calculated exactly, employing the correct equation of motion of a charged particle in the electromagnetic field and the universal boostability assumption. Thus, for the clock under consideration, a dynamical content of the clock retardation is demonstrated. Somewhat surprisingly, the analysis present...

  7. The Regulation of Segmentation Clock Period in Zebrafish

    OpenAIRE

    Herrgen, Leah

    2008-01-01

    Oscillations are present at many different levels of biological organization. The cell cycle that directs the division of individual cells, the regular depolarization of neurons in the sinu-atrial node which underlies the regular beating of the heart, the circadian rhythms that govern the daily activity cycles of virtually all organisms, and the clocks that make entire populations of fireflies flash on and off in unison feature as prominent examples of biological clocks. During development, b...

  8. Circadian Clock Control of Liver Metabolic Functions.

    Science.gov (United States)

    Reinke, Hans; Asher, Gad

    2016-03-01

    The circadian clock is an endogenous biological timekeeping system that synchronizes physiology and behavior to day/night cycles. A wide variety of processes throughout the entire gastrointestinal tract and notably the liver appear to be under circadian control. These include various metabolic functions such as nutrient uptake, processing, and detoxification, which align organ function to cycle with nutrient supply and demand. Remarkably, genetic or environmental disruption of the circadian clock can cause metabolic diseases or exacerbate pathological states. In addition, modern lifestyles force more and more people worldwide into asynchrony between the external time and their circadian clock, resulting in a constant state of social jetlag. Recent evidence indicates that interactions between altered energy metabolism and disruptions in the circadian clock create a downward spiral that can lead to diabetes and other metabolic diseases. In this review, we provide an overview of rhythmic processes in the liver and highlight the functions of circadian clock genes under physiological and pathological conditions; we focus on their roles in regulation of hepatic glucose as well as lipid and bile acid metabolism and detoxification and their potential effects on the development of fatty liver and nonalcoholic steatohepatitis. PMID:26657326

  9. Short-term influence of cataract surgery on circadian biological rhythm and related health outcomes (CLOCK-IOL trial): study protocol for a randomized controlled trial

    OpenAIRE

    Saeki, Keigo; Obayashi, Kenji; Nishi, Tomo; Miyata, Kimie; Maruoka, Shinji; Ueda, Tetsuo; OKAMOTO, Masahiro; Hasegawa, Taiji; Matsuura, Toyoaki; Tone, Nobuhiro; Ogata, Nahoko; Kurumatani, Norio

    2014-01-01

    Background Light information is the most important cue of circadian rhythm which synchronizes biological rhythm with external environment. Circadian misalignment of biological rhythm and external environment is associated with increased risk of depression, insomnia, obesity, diabetes, cardiovascular disease, and cancer. Increased light transmission by cataract surgery may improve circadian misalignment and related health outcomes. Although some observational studies have shown improvement of ...

  10. On clocks and clouds

    Directory of Open Access Journals (Sweden)

    M. K. Witte

    2013-09-01

    Full Text Available Cumulus clouds exhibit a life cycle that consists of: (a the growth phase (increasing size, most notably in the vertical direction; (b the mature phase (growth ceases; any precipitation that develops is strongest during this period; and (c the dissipation phase (cloud dissipates because of precipitation and/or entrainment; no more dynamical support. Although radar can track clouds over time and give some sense of the age of a cloud, most aircraft in situ measurements lack temporal context. We use large eddy simulations of trade wind cumulus cloud fields from cases during the Barbados Oceanographic and Meteorological Experiment (BOMEX and Rain In Cumulus over the Ocean (RICO campaigns to demonstrate a potential cumulus cloud "clock". We find that the volume-averaged total water mixing ratio rt is a useful cloud clock for the 12 clouds studied. A cloud's initial rt is set by the subcloud mixed-layer mean rt and decreases monotonically from the initial value due primarily to entrainment. The clock is insensitive to aerosol loading, environmental sounding and extrinsic cloud properties such as lifetime and volume. In some cases (more commonly for larger clouds, multiple pulses of buoyancy occur, which complicate the cumulus clock by replenishing rt. The clock is most effectively used to classify clouds by life phase.

  11. Optical atomic clocks

    International Nuclear Information System (INIS)

    In the last ten years extraordinary results in time and frequency metrology have been demonstrated. Frequency-stabilization techniques for continuous-wave lasers and femtosecond optical frequency combs have enabled a rapid development of frequency standards based on optical transitions in ultra-cold neutral atoms and trapped ions. As a result, today’s best performing atomic clocks tick at an optical rate and allow scientists to perform high-resolution measurements with a precision approaching a few parts in 1018. This paper reviews the history and the state of the art in optical-clock research and addresses the implementation of optical clocks in a possible future redefinition of the SI second as well as in tests of fundamental physics.

  12. Optical atomic clocks

    CERN Document Server

    Poli, N; Gill, P; Tino, G M

    2014-01-01

    In the last ten years extraordinary results in time and frequency metrology have been demonstrated. Frequency-stabilization techniques for continuous-wave lasers and femto-second optical frequency combs have enabled a rapid development of frequency standards based on optical transitions in ultra-cold neutral atoms and trapped ions. As a result, today's best performing atomic clocks tick at an optical rate and allow scientists to perform high-resolution measurements with a precision approaching a few parts in $10^{18}$. This paper reviews the history and the state of the art in optical-clock research and addresses the implementation of optical clocks in a possible future redefinition of the SI second as well as in tests of fundamental physics.

  13. Optical atomic clocks

    Science.gov (United States)

    Poli, N.; Oates, C. W.; Gill, P.; Tino, G. M.

    2013-12-01

    In the last ten years extraordinary results in time and frequency metrology have been demonstrated. Frequency-stabilization techniques for continuous-wave lasers and femtosecond optical frequency combs have enabled a rapid development of frequency standards based on optical transitions in ultra-cold neutral atoms and trapped ions. As a result, today's best performing atomic clocks tick at an optical rate and allow scientists to perform high-resolution measurements with a precision approaching a few parts in 1018. This paper reviews the history and the state of the art in optical-clock research and addresses the implementation of optical clocks in a possible future redefinition of the SI second as well as in tests of fundamental physics.

  14. Clocking in the face of unpredictability beyond quantum uncertainty

    Science.gov (United States)

    Madjid, F. Hadi; Myers, John M.

    2015-05-01

    In earlier papers we showed unpredictability beyond quantum uncertainty in atomic clocks, ensuing from a proven gap between given evidence and explanations of that evidence. Here we reconceive a clock, not as an isolated entity, but as enmeshed in a self-adjusting communications network adapted to one or another particular investigation, in contact with an unpredictable environment. From the practical uses of clocks, we abstract a clock enlivened with the computational capacity of a Turing machine, modified to transmit and to receive numerical communications. Such "live clocks" phase the steps of their computations to mesh with the arrival of transmitted numbers. We lift this phasing, known in digital communications, to a principle of logical synchronization, distinct from the synchronization defined by Einstein in special relativity. Logical synchronization elevates digital communication to a topic in physics, including applications to biology. One explores how feedback loops in clocking affect numerical signaling among entities functioning in the face of unpredictable influences, making the influences themselves into subjects of investigation. The formulation of communications networks in terms of live clocks extends information theory by expressing the need to actively maintain communications channels, and potentially, to create or drop them. We show how networks of live clocks are presupposed by the concept of coordinates in a spacetime. A network serves as an organizing principle, even when the concept of the rigid body that anchors a special-relativistic coordinate system is inapplicable, as is the case, for example, in a generic curved spacetime.

  15. Circadian clock and the onset of cardiovascular events.

    Science.gov (United States)

    Takeda, Norihiko; Maemura, Koji

    2016-06-01

    The onset of cardiovascular diseases often shows time-of-day variation. Acute myocardial infarction or ventricular arrhythmia such as ventricular tachycardia occurs mainly in the early morning. Multiple biochemical and physiological parameters show circadian rhythm, which may account for the diurnal variation of cardiovascular events. These include the variations in blood pressure, activity of the autonomic nervous system and renin-angiotensin axis, coagulation cascade, vascular tone and the intracellular metabolism of cardiomyocytes. Importantly, the molecular clock system seems to underlie the circadian variation of these parameters. The center of the biological clock, also known as the central clock, exists in the suprachiasmatic nucleus. In contrast, the molecular clock system is also activated in each cell of the peripheral organs and constitute the peripheral clock. The biological clock system is currently considered to have a beneficial role in maintaining the homeostasis of each organ. Discoordination, however, between the peripheral clock and external environment could potentially underlie the development of cardiovascular events. Therefore, understanding the molecular and cellular pathways by which cardiovascular events occur in a diurnal oscillatory pattern will help the establishment of a novel therapeutic approach to the management of cardiovascular disorders. PMID:26888119

  16. Decamp Clock Board Firmware

    International Nuclear Information System (INIS)

    Decamp (Dark Energy Survey Camera) is a new instrument designed to explore the universe aiming to reveal the nature of Dark Energy. The camera consists of 72 CCDs and 520 Mpixels. The readout electronics of DECam is based on the Monsoon system. Monsoon is a new image acquisition system developed by the NOAO (National Optical Astronomical Observatory) for the new generation of astronomical cameras. The Monsoon system uses three types of boards inserted in a Eurocard format based crate: master control board, acquisition board and clock board. The direct use of the Monsoon system for DECam readout electronics requires nine crates mainly due to the high number of clock boards needed. Unfortunately, the available space for DECam electronics is constrained to four crates at maximum. The major drawback to achieve such desired compaction degree resides in the clock board signal density. This document describes the changes performed at CIEMAT on the programmable logic of the Monsoon clock board aiming to meet such restricted space constraints. (Author) 5 refs

  17. Clock Reaction: Outreach Attraction

    Science.gov (United States)

    Carpenter, Yuen-ying; Phillips, Heather A.; Jakubinek, Michael B.

    2010-01-01

    Chemistry students are often introduced to the concept of reaction rates through demonstrations or laboratory activities involving the well-known iodine clock reaction. For example, a laboratory experiment involving thiosulfate as an iodine scavenger is part of the first-year general chemistry laboratory curriculum at Dalhousie University. With…

  18. Decamp Clock Board Firmware

    Energy Technology Data Exchange (ETDEWEB)

    Vicente, J. de; Castilla, J.; Martinez, G.

    2007-09-27

    Decamp (Dark Energy Survey Camera) is a new instrument designed to explore the universe aiming to reveal the nature of Dark Energy. The camera consists of 72 CCDs and 520 Mpixels. The readout electronics of DECam is based on the Monsoon system. Monsoon is a new image acquisition system developed by the NOAO (National Optical Astronomical Observatory) for the new generation of astronomical cameras. The Monsoon system uses three types of boards inserted in a Eurocard format based crate: master control board, acquisition board and clock board. The direct use of the Monsoon system for DECam readout electronics requires nine crates mainly due to the high number of clock boards needed. Unfortunately, the available space for DECam electronics is constrained to four crates at maximum. The major drawback to achieve such desired compaction degree resides in the clock board signal density. This document describes the changes performed at CIEMAT on the programmable logic of the Monsoon clock board aiming to meet such restricted space constraints. (Author) 5 refs.

  19. Conveyor belt clock synchronization

    CERN Document Server

    Giovannetti, V; Maccone, L; Shapiro, J H; Wong, F N C; Giovannetti, Vittorio; Lloyd, Seth; Maccone, Lorenzo; Shapiro, Jeffrey H.; Wong, Franco N. C.

    2004-01-01

    A protocol for synchronizing distant clocks is proposed that does not rely on the arrival times of the signals which are exchanged, and an optical implementation based on coherent-state pulses is described. This protocol is not limited by any dispersion that may be present in the propagation medium through which the light signals are exchanged. Possible improvements deriving from the use of quantum-mechanical effects are also addressed.

  20. Synchronization of clocks

    International Nuclear Information System (INIS)

    In this report we recall the famous Huygens’ experiment which gave the first evidence of the synchronization phenomenon. We consider the synchronization of two clocks which are accurate (show the same time) but have pendula with different masses. It has been shown that such clocks hanging on the same beam can show the almost complete (in-phase) and almost antiphase synchronizations. By almost complete and almost antiphase synchronization we defined the periodic motion of the pendula in which the phase shift between the displacements of the pendula is respectively close (but not equal) to 0 or π. We give evidence that almost antiphase synchronization was the phenomenon observed by Huygens in XVII century. We support our numerical studies by considering the energy balance in the system and showing how the energy is transferred between the pendula via oscillating beam allowing the pendula’s synchronization. Additionally we discuss the synchronization of a number of different pendulum clocks hanging from a horizontal beam which can roll on the parallel surface. It has been shown that after a transient, different types of synchronization between pendula can be observed; (i) the complete synchronization in which all pendula behave identically, (ii) pendula create three or five clusters of synchronized pendula. We derive the equations for the estimation of the phase differences between phase synchronized clusters. The evidence, why other configurations with a different number of clusters are not observed, is given.

  1. Prediction of GNSS satellite clocks

    International Nuclear Information System (INIS)

    This thesis deals with the characterisation and prediction of GNSS-satellite-clocks. A prerequisite to develop powerful algorithms for the prediction of clock-corrections is the thorough study of the behaviour of the different clock-types of the satellites. In this context the predicted part of the IGU-clock-corrections provided by the Analysis Centers (ACs) of the IGS was compared to the IGS-Rapid-clock solutions to determine reasonable estimates of the quality of already existing well performing predictions. For the shortest investigated interval (three hours) all ACs obtain almost the same accuracy of 0,1 to 0,4 ns. For longer intervals the individual predictions results start to diverge. Thus, for a 12-hours- interval the differences range from nearly 10 ns (GFZ, CODE) until up to some 'tens of ns'. Based on the estimated clock corrections provided via the IGS Rapid products a simple quadratic polynomial turns out to be sufficient to describe the time series of Rubidium-clocks. On the other hand Cesium-clocks show a periodical behaviour (revolution period) with an amplitude of up to 6 ns. A clear correlation between these amplitudes and the Sun elevation angle above the orbital planes can be demonstrated. The variability of the amplitudes is supposed to be caused by temperature-variations affecting the oscillator. To account for this periodical behaviour a quadratic polynomial with an additional sinus-term was finally chosen as prediction model both for the Cesium as well as for the Rubidium clocks. The three polynomial-parameters as well as amplitude and phase shift of the periodic term are estimated within a least-square-adjustment by means of program GNSS-VC/static. Input-data are time series of the observed part of the IGU clock corrections. With the estimated parameters clock-corrections are predicted for various durations. The mean error of the prediction of Rubidium-clock-corrections for an interval of six hours reaches up to 1,5 ns. For the 12-hours

  2. Microchip-Based Trapped-Atom Clocks

    OpenAIRE

    Vuletic, Vladan; Leroux, Ian D.; Schleier-Smith, Monika H.

    2011-01-01

    This is a chapter of a recently published book entitled Atom Chips, edited by Jakob Reichel and Vladan Vuletic. The contents of this chapter include: Basic Principles; Atomic-Fountain versus Trapped-Atom Clocks; Optical-Transition Clocks versus Microwave Clocks; Clocks with Magnetically Trapped Atoms--Fundamental Limits and Experimental Demonstrations; Readout in Trapped-Atom Clocks; and Spin Squeezing.

  3. Optical atomic clocks and metrology

    Science.gov (United States)

    Ludlow, Andrew

    2014-05-01

    The atomic clock has long demonstrated the capability to measure time or frequency with very high precision. Consequently, these clocks are used extensively in technological applications such as advanced synchronization or communication and navigation networks. Optical atomic clocks are next- generation timekeepers which reference narrowband optical transitions between suitable atomic states. Many optical time/frequency standards utilize state-of-the-art quantum control and precision measurement. Combined with the ultrahigh quality factors of the atomic resonances at their heart, optical atomic clocks have promised new levels of timekeeping precision, orders of magnitude higher than conventional atomic clocks based on microwave transitions. Such measurement capability enables and/or enhances many of the most exciting applications of these clocks, including the study of fundamental laws of physics through the measurement of time evolution. Here, I will highlight optical atomic clocks and their utility, as well as review recent advances in their development and performance. In particular, I will describe in detail the optical lattice clock and the realization of frequency measurement at the level of one part in 1018. To push the performance of these atomic timekeepers to such a level and beyond, several key advances are being explored worldwide. These will be discussed generally, with particular emphasis on our recent efforts at NIST in developing the optical lattice clock based on atomic ytterbium.

  4. A Light Clock Satisfying the Clock Hypothesis of Special Relativity

    Science.gov (United States)

    West, Joseph

    2007-01-01

    The design of the FMEL, a floor-mirrored Einstein-Langevin "light clock", is introduced. The clock provides a physically intuitive manner to calculate and visualize the time dilation effects for a spatially extended set of observers (an accelerated "frame") undergoing unidirectional acceleration or observers on a rotating cylinder of constant…

  5. Maximum-Likelihood Estimator of Clock Offset between Nanomachines in Bionanosensor Networks

    Directory of Open Access Journals (Sweden)

    Lin Lin

    2015-12-01

    Full Text Available Recent advances in nanotechnology, electronic technology and biology have enabled the development of bio-inspired nanoscale sensors. The cooperation among the bionanosensors in a network is envisioned to perform complex tasks. Clock synchronization is essential to establish diffusion-based distributed cooperation in the bionanosensor networks. This paper proposes a maximum-likelihood estimator of the clock offset for the clock synchronization among molecular bionanosensors. The unique properties of diffusion-based molecular communication are described. Based on the inverse Gaussian distribution of the molecular propagation delay, a two-way message exchange mechanism for clock synchronization is proposed. The maximum-likelihood estimator of the clock offset is derived. The convergence and the bias of the estimator are analyzed. The simulation results show that the proposed estimator is effective for the offset compensation required for clock synchronization. This work paves the way for the cooperation of nanomachines in diffusion-based bionanosensor networks.

  6. Maximum-Likelihood Estimator of Clock Offset between Nanomachines in Bionanosensor Networks

    Science.gov (United States)

    Lin, Lin; Yang, Chengfeng; Ma, Maode

    2015-01-01

    Recent advances in nanotechnology, electronic technology and biology have enabled the development of bio-inspired nanoscale sensors. The cooperation among the bionanosensors in a network is envisioned to perform complex tasks. Clock synchronization is essential to establish diffusion-based distributed cooperation in the bionanosensor networks. This paper proposes a maximum-likelihood estimator of the clock offset for the clock synchronization among molecular bionanosensors. The unique properties of diffusion-based molecular communication are described. Based on the inverse Gaussian distribution of the molecular propagation delay, a two-way message exchange mechanism for clock synchronization is proposed. The maximum-likelihood estimator of the clock offset is derived. The convergence and the bias of the estimator are analyzed. The simulation results show that the proposed estimator is effective for the offset compensation required for clock synchronization. This work paves the way for the cooperation of nanomachines in diffusion-based bionanosensor networks. PMID:26690173

  7. Simulating Future GPS Clock Scenarios with Two Composite Clock Algorithms

    Science.gov (United States)

    Suess, Matthias; Matsakis, Demetrios; Greenhall, Charles A.

    2010-01-01

    Using the GPS Toolkit, the GPS constellation is simulated using 31 satellites (SV) and a ground network of 17 monitor stations (MS). At every 15-minutes measurement epoch, the monitor stations measure the time signals of all satellites above a parameterized elevation angle. Once a day, the satellite clock estimates the station and satellite clocks. The first composite clock (B) is based on the Brown algorithm, and is now used by GPS. The second one (G) is based on the Greenhall algorithm. The composite clock of G and B performance are investigated using three ground-clock models. Model C simulates the current GPS configuration, in which all stations are equipped with cesium clocks, except for masers at USNO and Alternate Master Clock (AMC) sites. Model M is an improved situation in which every station is equipped with active hydrogen masers. Finally, Models F and O are future scenarios in which the USNO and AMC stations are equipped with fountain clocks instead of masers. Model F is a rubidium fountain, while Model O is more precise but futuristic Optical Fountain. Each model is evaluated using three performance metrics. The timing-related user range error having all satellites available is the first performance index (PI1). The second performance index (PI2) relates to the stability of the broadcast GPS system time itself. The third performance index (PI3) evaluates the stability of the time scales computed by the two composite clocks. A distinction is made between the "Signal-in-Space" accuracy and that available through a GNSS receiver.

  8. Controllable clock circuit design in PEM system

    International Nuclear Information System (INIS)

    A high-precision synchronized clock circuit design will be presented, which can supply steady, reliable and anti-jamming clock signal for the data acquirement (DAQ) system of Positron Emission Mammography (PEM). This circuit design is based on the Single-Chip Microcomputer and high-precision clock chip, and can achieve multiple controllable clock signals. The jamming between the clock signals can be reduced greatly with the differential transmission. Meanwhile, the adoption of CAN bus control in the clock circuit can prompt the clock signals to be transmitted or masked simultaneously when needed. (authors)

  9. Circadian clock components in the rat neocortex

    DEFF Research Database (Denmark)

    Rath, Martin Fredensborg; Rohde, Kristian; Fahrenkrug, Jan;

    2013-01-01

    The circadian master clock of the mammalian brain resides in the suprachiasmatic nucleus (SCN) of the hypothalamus. At the molecular level, the clock of the SCN is driven by a transcriptional/posttranslational autoregulatory network with clock gene products as core elements. Recent investigations...... have shown the presence of peripheral clocks in extra-hypothalamic areas of the central nervous system. However, knowledge on the clock gene network in the cerebral cortex is limited. We here show that the mammalian clock genes Per1, Per2, Per3, Cry1, Cry2, Bmal1, Clock, Nr1d1 and Dbp are expressed...

  10. 'The clocks that time us'-circadian rhythms in neurodegenerative disorders

    NARCIS (Netherlands)

    Videnovic, A.; Lazar, A.S.; Barker, R.A.; Overeem, S.

    2014-01-01

    Circadian rhythms are physiological and behavioural cycles generated by an endogenous biological clock, the suprachiasmatic nucleus. The circadian system influences the majority of physiological processes, including sleep-wake homeostasis. Impaired sleep and alertness are common symptoms of neurodeg

  11. Circadian Clocks, Stress, and Immunity

    Science.gov (United States)

    Dumbell, Rebecca; Matveeva, Olga; Oster, Henrik

    2016-01-01

    In mammals, molecular circadian clocks are present in most cells of the body, and this circadian network plays an important role in synchronizing physiological processes and behaviors to the appropriate time of day. The hypothalamic–pituitary–adrenal endocrine axis regulates the response to acute and chronic stress, acting through its final effectors – glucocorticoids – released from the adrenal cortex. Glucocorticoid secretion, characterized by its circadian rhythm, has an important role in synchronizing peripheral clocks and rhythms downstream of the master circadian pacemaker in the suprachiasmatic nucleus. Finally, glucocorticoids are powerfully anti-inflammatory, and recent work has implicated the circadian clock in various aspects and cells of the immune system, suggesting a tight interplay of stress and circadian systems in the regulation of immunity. This mini-review summarizes our current understanding of the role of the circadian clock network in both the HPA axis and the immune system, and discusses their interactions. PMID:27199894

  12. Circadian clock, cell cycle and cancer

    OpenAIRE

    Cansu Özbayer; İrfan Değirmenci

    2011-01-01

    There are a few rhythms of our daily lives that we are under the influence. One of them is characterized by predictable changes over a 24-hour timescale called circadian clock. This cellular clock is coordinated by the suprachiasmatic nucleus in the anterior hypothalamus. The clock consist of an autoregulatory transcription-translation feedback loop compose of four genes/proteins; BMAL1, Clock, Cyrptochrome, and Period. BMAL 1 and Clock are transcriptional factors and Period and Cyrptochrome ...

  13. Gravitomagnetism and Relative Observer Clock Effects

    OpenAIRE

    Bini, Donato; Jantzen, Robert T; Mashhoon, Bahram

    2000-01-01

    The gravitomagnetic clock effect and the Sagnac effect for circularly rotating orbits in stationary axisymmetric spacetimes are studied from a relative observer point of view, clarifying their relationships and the roles played by special observer families. In particular Semer\\'ak's recent characterization of extremely accelerated observers in terms of the two-clock clock effect is shown to be complemented by a similarly special property of the single-clock clock effect.

  14. Variable molecular clocks in hominoids

    OpenAIRE

    Elango, Navin; Thomas, James W.; Yi, Soojin V.

    2006-01-01

    Generation time is an important determinant of a neutral molecular clock. There are several human-specific life history traits that led to a substantially longer generation time in humans than in other hominoids. Indeed, a long generation time is considered an important trait that distinguishes humans from their closest relatives. Therefore, humans may exhibit a significantly slower molecular clock as compared to other hominoids. To investigate this hypothesis, we performed a large-scale anal...

  15. The circadian clock in mammals

    OpenAIRE

    Zordan, Mauro; Kyriacou, Charalambos P

    2000-01-01

    The basic physiological and anatomical basis for circadian rhythms in mammalian behaviour and physiology is introduced. The pathways involved in photic entrainment of the circadian clock are discussed in relation of new findings that identify the molecules that are involved in signalling between the environment and the clock. The molecular basis of endogenous cycles is described in the mouse, and compared to the mechanism that is present in the fly. Finally we speculate on the relationship be...

  16. The circadian clock in mammals

    OpenAIRE

    Zordan, M. A.; Kyriacou, C P

    2005-01-01

    The basic physiological and anatomical basis for circadian rhythms in mammalian behaviour and physiology is introduced. The pathways involved in photic entrainment of the circadian clock are discussed in relation of new findings that identify the molecules that are involved in signalling between the environment and the clock. The molecular basis of endogenous cycles is described in the mouse, and compared to the mechanism that is present in the fly. Finally we speculate on the relationship be...

  17. Molecular cloning and bioinformatic analysis of biological clock genes Bmcry1 and Bmcry2 in Bombyx mori%家蚕生物钟基因Bmcryl与Bmcry2的克隆及生物信息学分析

    Institute of Scientific and Technical Information of China (English)

    王文栋; 梁辉; 朱晓苏; 陶卉; 徐丽; 司马杨虎; 徐世清

    2011-01-01

    隐花色素基因(cryptochrome gene,Cry)是已确认的主要生物钟基因之一,它广泛分布于细菌和真核生物中.昆虫Cry基因分为Cry1,和Cry2两类,果蝇只有Cry1,蜜蜂等膜翅目昆虫只有Cry2.为了研究鳞翅目模式昆虫家蚕Bombyx mori的昼夜生物钟分子调控机制和昆虫CRY蛋白的进化,本研究克隆了家蚕Bmcry1与Bmcry2基因的全长cDNA序列,长度分别为2 166 bp和2 389 bp(GenBank登录号分别为HM747059和HM747060),拼接了全基因序列(GenBank 登录号分别为HM747057和HM747058).Bmcry1基因具有12个外显子和11个内含子,Bmcry2具有9个外显子,8个内含子.染色体定位表明Bmcry1和8mcry2分别位于第17号和15号染色体.通过同源建模获得了Bmcry1和Bmcry2蛋白的三维结构,其FAD入口大而深,这与CRY不与嘧啶二聚体结合相符;Bmcry1和Bmcry2表面多为负电荷,只在FAD人口位置有正电荷富集.多序列比对、蛋白质基序和功能域分析、聚类分析等结果显示,Bmcry1和Bmcry2分属昆虫的CRY1和CRY2,与柞蚕Antheraea pernyi等鳞翅目昆虫中CRY蛋白的亲缘关系最近.家蚕的两类CRY与其他昆虫CRY相似,也都具有DNA光解酶和FAD结合功能域,但保守位点和蛋白基序位点不同.本实验为进一步研究家蚕CRY1和CRY2的分子进化机制和功能创造了条件.%Cryptochrome gene (Cry) is one of the major biological clock genes which were widely distributed in bacteria and eukaryotes. Cry genes of insect species are clearly divided into two types, Cry1 and Cry2. Only Cry1 is expressed in Drosophila, while only Cry2 was expressed in bees and other hymenopteran insects. In order to explore the molecular mechanism of circadian clock in lepidopteran model insect Bombyx mori and the evolution of CRY proteins in insect species, we cloned the eDNA sequences of Bmcryl (2 166 bp, GenBank accession no. HM747059) and Bmcry2 (2 389 bp, GenBank accession no.HM747060), and obtained their gene sequences (Gen

  18. Somitogenesis clock-wave initiation requires differential decay and multiple binding sites for clock protein.

    Directory of Open Access Journals (Sweden)

    Mark Campanelli

    2010-04-01

    Full Text Available Somitogenesis is a process common to all vertebrate embryos in which repeated blocks of cells arise from the presomitic mesoderm (PSM to lay a foundational pattern for trunk and tail development. Somites form in the wake of passing waves of periodic gene expression that originate in the tailbud and sweep posteriorly across the PSM. Previous work has suggested that the waves result from a spatiotemporally graded control protein that affects the oscillation rate of clock-gene expression. With a minimally constructed mathematical model, we study the contribution of two control mechanisms to the initial formation of this gene-expression wave. We test four biologically motivated model scenarios with either one or two clock protein transcription binding sites, and with or without differential decay rates for clock protein monomers and dimers. We examine the sensitivity of wave formation with respect to multiple model parameters and robustness to heterogeneity in cell population. We find that only a model with both multiple binding sites and differential decay rates is able to reproduce experimentally observed waveforms. Our results show that the experimentally observed characteristics of somitogenesis wave initiation constrain the underlying genetic control mechanisms.

  19. Atomic clock ensemble in space

    International Nuclear Information System (INIS)

    Atomic Clock Ensemble in Space (ACES) is a mission using high-performance clocks and links to test fundamental laws of physics in space. Operated in the microgravity environment of the International Space Station, the ACES clocks, PHARAO and SHM, will generate a frequency reference reaching instability and inaccuracy at the 1 · 10−16 level. A link in the microwave domain (MWL) and an optical link (ELT) will make the ACES clock signal available to ground laboratories equipped with atomic clocks. Space-to-ground and ground-to-ground comparisons of atomic frequency standards will be used to test Einstein's theory of general relativity including a precision measurement of the gravitational red-shift, a search for time variations of fundamental constants, and Lorentz Invariance tests. Applications in geodesy, optical time transfer, and ranging will also be supported. ACES has now reached an advanced technology maturity, with engineering models completed and successfully tested and flight hardware under development. This paper presents the ACES mission concept and the status of its main instruments.

  20. Circadian clocks, epigenetics, and cancer

    KAUST Repository

    Masri, Selma

    2015-01-01

    The interplay between circadian rhythm and cancer has been suggested for more than a decade based on the observations that shift work and cancer incidence are linked. Accumulating evidence implicates the circadian clock in cancer survival and proliferation pathways. At the molecular level, multiple control mechanisms have been proposed to link circadian transcription and cell-cycle control to tumorigenesis.The circadian gating of the cell cycle and subsequent control of cell proliferation is an area of active investigation. Moreover, the circadian clock is a transcriptional system that is intricately regulated at the epigenetic level. Interestingly, the epigenetic landscape at the level of histone modifications, DNA methylation, and small regulatory RNAs are differentially controlled in cancer cells. This concept raises the possibility that epigenetic control is a common thread linking the clock with cancer, though little scientific evidence is known to date.This review focuses on the link between circadian clock and cancer, and speculates on the possible connections at the epigenetic level that could further link the circadian clock to tumor initiation or progression.

  1. Interactions of polymorphisms in different clock genes associated with circadian phenotypes in humans

    Directory of Open Access Journals (Sweden)

    Mario Pedrazzoli

    2010-01-01

    Full Text Available Several studies have shown that mutations and polymorphisms in clock genes are associated with abnormal circadian parameters in humans and also with more subtle non-pathological phenotypes like chronotypes. However, there have been conflicting results, and none of these studies analyzed the combined effects of more than one clock gene. Up to date, association studies in humans have focused on the analysis of only one clock gene per study. Since these genes encode proteins that physically interact with each other, combinations of polymorphisms in different clock genes could have a synergistic or an inhibitory effect upon circadian phenotypes. In the present study, we analyzed the combined effects of four polymorphisms in four clock genes (Per2, Per3, Clock and Bmal1 in people with extreme diurnal preferences (morning or evening. We found that a specific combination of polymorphisms in these genes is more frequent in people who have a morning preference for activity and there is a different combination in individuals with an evening preference for activity. Taken together, these results show that it is possible to detect clock gene interactions associated with human circadian phenotypes and bring an innovative idea of building a clock gene variation map that may be applied to human circadian biology.

  2. Colloquium: Physics of optical lattice clocks

    International Nuclear Information System (INIS)

    Recently invented and demonstrated optical lattice clocks hold great promise for improving the precision of modern time keeping. These clocks aim at the 10-18 fractional accuracy, which translates into a clock that would neither lose nor gain a fraction of a second over an estimated age of the Universe. In these clocks, millions of atoms are trapped and interrogated simultaneously, dramatically improving clock stability. Here the principles of operation of these clocks are discussed and, in particular, a novel concept of magic trapping of atoms in optical lattices. Recently proposed microwave lattice clocks are also highlights and several applications that employ the optical lattice clocks as a platform for precision measurements and quantum information processing.

  3. Acting with the Clock: Clocking Practices in Early Childhood

    Science.gov (United States)

    Pacini-Ketchabaw, Veronica

    2012-01-01

    In this article, the author addresses intra-actions that take place among humans and non-human others--the physical world, the materials--in early childhood education's everyday practices. Her object of study is the clock. Specifically, she provides an example of what it might mean to account for the intra-activity of the material-discursive…

  4. [Cognitive Function and Calcium. Ca2+-dependent regulatory mechanism of circadian clock oscillation and its relevance to neuronal function].

    Science.gov (United States)

    Kon, Naohiro; Fukada, Yoshitaka

    2015-02-01

    Circadian clock generates a variety of biological rhythms such as sleep/wake cycles and blood hormone rhythms. The circadian clock also bolsters daily mental activities. In fact, abnormalities of the circadian rhythms are found in several neurological disorders. The circadian clock has two important functions: (i) a cell-autonomous oscillatory function and (ii) a phase-adjusting function that synchronizes the clock oscillation with environmental cycling conditions such as light/dark cycle. Behavioral rhythms are controlled by the central clock in hypothalamic suprachiasmatic nucleus (SCN). The central clock orchestrates peripheral clocks in the other tissues via neuronal connection and/or actions of humoral factors. The molecular mechanism of the cell-autonomous clock is based on transcriptional feedback regulation of clock genes by their encoded products. Ca2+ is essential for not only the light response of the clock but also the cell autonomous oscillation mechanism. This article provides an overview of recent progress in studies of Ca2+-dependent regulatory mechanism of the molecular clockwork. PMID:25634045

  5. Identifying Nonstationary Clock Noises in Navigation Systems

    OpenAIRE

    Patrizia Tavella; Lorenzo Galleani

    2008-01-01

    The stability of the atomic clocks on board the satellites of a navigation system should remain constant with time. In reality there are numerous physical phenomena that make the behavior of the clocks a function of time, and for this reason we have recently introduced the dynamic Allan variance (DAVAR), a measure of the time-varying stability of an atomic clock. In this paper we discuss the dynamic Allan variance for phase and frequency jumps, two common nonstationarities of atomic clocks. T...

  6. Single-transistor-clocked flip-flop

    Science.gov (United States)

    Zhao, Peiyi; Darwish, Tarek; Bayoumi, Magdy

    2005-08-30

    The invention provides a low power, high performance flip-flop. The flip-flop uses only one clocked transistor. The single clocked transistor is shared by the first and second branches of the device. A pulse generator produces a clock pulse to trigger the flip-flop. In one preferred embodiment the device can be made as a static explicit pulsed flip-flop which employs only two clocked transistors.

  7. 47 CFR 80.935 - Station clock.

    Science.gov (United States)

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false Station clock. 80.935 Section 80.935... MARITIME SERVICES Compulsory Radiotelephone Installations for Small Passenger Boats § 80.935 Station clock. Each station subject to this subpart must have a working clock or timepiece readily available to...

  8. Collisionally induced atomic clock shifts and correlations

    International Nuclear Information System (INIS)

    We develop a formalism to incorporate exchange symmetry considerations into the calculation of collisional frequency shifts for atomic clocks using a density-matrix formalism. The formalism is developed for both fermionic and bosonic atomic clocks. Numerical results for a finite-temperature 87Sr 1S0 (F=9/2) atomic clock in a magic wavelength optical lattice are presented.

  9. CLOCK and NPAS2 have overlapping roles in the suprachiasmatic circadian clock

    OpenAIRE

    DeBruyne, Jason P.; Weaver, David R.; Reppert, Steven M.

    2007-01-01

    Heterodimers of CLOCK and BMAL1, bHLH-PAS transcription factors, are believed to be the major transcriptional regulators of the circadian clock mechanism in mammals. However, a recent study shows that CLOCK-deficient mice continue to exhibit robust behavioral and molecular rhythms. Here we report that the transcription factor NPAS2 (MOP4) is able to functionally substitute for CLOCK in the master brain clock in mice to regulate circadian rhythmicity.

  10. Clock Drawing in Developmental Dyslexia.

    Science.gov (United States)

    Eden, Guinevere F.; Wood, Frank B.; Stein, John F.

    2003-01-01

    A study involving 93 children (ages 10-12), 295 with poor reading skills, found many children with dyslexia and some garden-variety poor readers showed significant left neglect on the Clock Drawing Test. In poor readers with dyslexia, spatial construction deficits were observed like those of parents with acquired right-hemisphere lesions.…

  11. A quantum network of clocks

    Science.gov (United States)

    Komar, Peter; Kessler, Eric; Bishof, Michael; Jiang, Liang; Sorensen, Anders; Ye, Jun; Lukin, Mikhail

    2014-05-01

    Shared timing information constitutes a key resource for positioning and navigation with a direct correspondence between timing accuracy and precision in applications such as the Global Positioning System (GPS). By combining precision metrology and quantum networks, we propose here a quantum, cooperative protocol for the operation of a network consisting of geographically remote optical atomic clocks. Using non-local entangled states, we demonstrate an optimal utilization of the global network resources, and show that such a network can be operated near the fundamental limit set by quantum theory yielding an ultra-precise clock signal. Furthermore, the internal structure of the network, combined with basic techniques from quantum communication, guarantees security both from internal and external threats. Realization of such a global quantum network of clocks may allow construction of a real-time single international time scale (world clock) with unprecedented stability and accuracy. See also: Komar et al. arXiv:1310.6045 (2013) and Kessler et al. arXiv:1310.6043 (2013).

  12. Clock gene expression during development

    Czech Academy of Sciences Publication Activity Database

    Sumová, Alena; Bendová, Zdeňka; Sládek, Martin; Kováčiková, Zuzana; El-Hennamy, Rehab; Laurinová, Kristýna; Illnerová, Helena

    2007-01-01

    Roč. 191, Suppl.658 (2007), s. 18-18. ISSN 1748-1708. [Joint meeting of The Slovak Physiological Society, The Physiological Society and The Federation of European Physiological Societies. 11.09.2007-14.09.2007, Bratislava] Institutional research plan: CEZ:AV0Z50110509 Keywords : cpr1 * clock genes * suprachiasmatic nucleus * rat Subject RIV: FB - Endocrinology, Diabetology, Metabolism, Nutrition

  13. Interactions between circadian clocks and photosynthesis for the temporal and spatial coordination of metabolism

    OpenAIRE

    Dodd, Antony N; Belbin, Fiona E.; Frank, Alexander; Webb, Alex A. R.

    2015-01-01

    All plant productivity, including the food that we eat, arises from the capture of solar energy by plants. At most latitudes sunlight is available for only part of the 24 h day due to the rotation of the planet. This rhythmic and predictable alteration in the environment has driven the evolution of the circadian clock, which has an extremely pervasive influence upon plant molecular biology, physiology and phenology. A number of recent studies have demonstrated that the circadian clock is inte...

  14. Biologic

    CERN Document Server

    Kauffman, L H

    2002-01-01

    In this paper we explore the boundary between biology and the study of formal systems (logic). In the end, we arrive at a summary formalism, a chapter in "boundary mathematics" where there are not only containers but also extainers ><, entities open to interaction and distinguishing the space that they are not. The boundary algebra of containers and extainers is to biologic what boolean algebra is to classical logic. We show how this formalism encompasses significant parts of the logic of DNA replication, the Dirac formalism for quantum mechanics, formalisms for protein folding and the basic structure of the Temperley Lieb algebra at the foundations of topological invariants of knots and links.

  15. Automatic control of clock duty cycle

    Science.gov (United States)

    Feng, Xiaoxin (Inventor); Roper, Weston (Inventor); Seefeldt, James D. (Inventor)

    2010-01-01

    In general, this disclosure is directed to a duty cycle correction (DCC) circuit that adjusts a falling edge of a clock signal to achieve a desired duty cycle. In some examples, the DCC circuit may generate a pulse in response to a falling edge of an input clock signal, delay the pulse based on a control voltage, adjust the falling edge of the input clock signal based on the delayed pulse to produce an output clock signal, and adjust the control voltage based on the difference between a duty cycle of the output clock signal and a desired duty cycle. Since the DCC circuit adjusts the falling edge of the clock cycle to achieve a desired duty cycle, the DCC may be incorporated into existing PLL control loops that adjust the rising edge of a clock signal without interfering with the operation of such PLL control loops.

  16. Circadian clock, cell cycle and cancer

    Directory of Open Access Journals (Sweden)

    Cansu Özbayer

    2011-12-01

    Full Text Available There are a few rhythms of our daily lives that we are under the influence. One of them is characterized by predictable changes over a 24-hour timescale called circadian clock. This cellular clock is coordinated by the suprachiasmatic nucleus in the anterior hypothalamus. The clock consist of an autoregulatory transcription-translation feedback loop compose of four genes/proteins; BMAL1, Clock, Cyrptochrome, and Period. BMAL 1 and Clock are transcriptional factors and Period and Cyrptochrome are their targets. Period and Cyrptochrome dimerize in the cytoplasm to enter the nucleus where they inhibit Clock/BMAL activity.It has been demonstrate that circadian clock plays an important role cellular proliferation, DNA damage and repair mechanisms, checkpoints, apoptosis and cancer.

  17. Expression conservation within the circadian clock of a monocot: natural variation at barley Ppd-H1 affects circadian expression of flowering time genes, but not clock orthologs

    Directory of Open Access Journals (Sweden)

    Campoli Chiara

    2012-06-01

    Full Text Available Abstract Background The circadian clock is an endogenous mechanism that coordinates biological processes with daily changes in the environment. In plants, circadian rhythms contribute to both agricultural productivity and evolutionary fitness. In barley, the photoperiod response regulator and flowering-time gene Ppd-H1 is orthologous to the Arabidopsis core-clock gene PRR7. However, relatively little is known about the role of Ppd-H1 and other components of the circadian clock in temperate crop species. In this study, we identified barley clock orthologs and tested the effects of natural genetic variation at Ppd-H1 on diurnal and circadian expression of clock and output genes from the photoperiod-response pathway. Results Barley clock orthologs HvCCA1, HvGI, HvPRR1, HvPRR37 (Ppd-H1, HvPRR73, HvPRR59 and HvPRR95 showed a high level of sequence similarity and conservation of diurnal and circadian expression patterns, when compared to Arabidopsis. The natural mutation at Ppd-H1 did not affect diurnal or circadian cycling of barley clock genes. However, the Ppd-H1 mutant was found to be arrhythmic under free-running conditions for the photoperiod-response genes HvCO1, HvCO2, and the MADS-box transcription factor and vernalization responsive gene Vrn-H1. Conclusion We suggest that the described eudicot clock is largely conserved in the monocot barley. However, genetic differentiation within gene families and differences in the function of Ppd-H1 suggest evolutionary modification in the angiosperm clock. Our data indicates that natural variation at Ppd-H1 does not affect the expression level of clock genes, but controls photoperiodic output genes. Circadian control of Vrn-H1 in barley suggests that this vernalization responsive gene is also controlled by the photoperiod-response pathway. Structural and functional characterization of the barley circadian clock will set the basis for future studies of the adaptive significance of the circadian clock in

  18. Circadian Rhythms: Hijacking the Cyanobacterial Clock

    Science.gov (United States)

    Hoyle, Nathaniel P.; O’Neill, John S

    2016-01-01

    The production of limitless carbon-free energy is a long-sought dream of scientists and politicians alike. One strategy for achieving this aim is the production of hydrogen by photosynthetic microorganisms – harnessing the effectively limitless power of the sun to power our cars, toasters and PCR machines. It may be tempting to think of host expression systems as miniature factories given over entirely to the production our molecule of interest. However, the biological nature of the host must be taken into account if we are to maximize productivity. The circadian rhythm, an organism’s entrainable oscillation of biological processes with a period of around 24 hours, is one such aspect that has received scant attention but is likely to be of particular importance to photosynthetic host systems. In this issue of current biology Xu et al. describe how our knowledge of the Synechococcus elongatus circadian clock can be leveraged to improve the production of exogeneous proteins, including those involved in the production of hydrogen [1]. PMID:24309283

  19. Mitigating aliasing in atomic clocks

    Science.gov (United States)

    Uys, Hermann; Akhalwaya, Ismail; Sastrawan, Jarrah; Biercuk, Michael

    2015-05-01

    Passive atomic clocks periodically calibrate a classical local oscillator against an atomic quantum reference through feedback. The periodic nature of this correction leads to undesirable aliasing noise. The Dick Effect, is a special case of aliasing noise consisting of the down-conversion of clock noise at harmonics of the correction frequency to a frequency of zero. To combat the Dick effect and aliasing noise in general, we suggest an extension to the usual feedback protocol, in which we incorporate information from multiple past measurements into the correction after the most recent measurement, approximating a crude low pass anti-aliasing filter of the noise. An analytical frequency domain analysis of the approach is presented and supported by numerical time domain simulations.

  20. Hanle detection for optical clocks

    CERN Document Server

    Zhang, Xiaogang; Pan, Duo; Chen, Peipei; Xue, Xiaobo; Zhuang, Wei; Chen, Jingbiao

    2014-01-01

    Considering the strong inhomogeneous spatial polarization and intensity distribution of spontaneous decay fluorescence due to the Hanle effect, we propose and demonstrate a universe Hanle detection configuration of electron-shelving method for optical clocks. Experimental results from Ca atomic beam optical frequency standard with 423 nm electron-shelving method show that a designed Hanle detection geometry with optimized magnetic field direction, detection laser beam propagation and polarization direction, and detector position can improve the fluorescence collection rate by more than one order of magnitude comparing with that of inefficient geometry. With the fixed 423 nm fluorescence, the improved 657 nm optical frequency standard signal intensity is presented. And the potential application of the Hanle detection geometry designed for facilitating the fluorescence collection for optical lattice clock with a limited solid angle of the fluorescence collection has been discussed. This Hanle detection configur...

  1. Signal processing in cellular clocks

    OpenAIRE

    Forger, Daniel B.

    2011-01-01

    Many biochemical events within a cell need to be timed properly to occur at specific times of day, after other events have happened within the cell or in response to environmental signals. The cellular biochemical feedback loops that time these events have already received much recent attention in the experimental and modeling communities. Here, we show how ideas from signal processing can be applied to understand the function of these clocks. Consider two signals from the network s(t) and r(...

  2. Gaming in Combinatorial Clock Auctions

    OpenAIRE

    Janssen, Maarten; Karamychev, Vladimir

    2013-01-01

    textabstractIn recent years, Combinatorial Clock Auctions (CCAs) have been used around the world to allocate frequency spectrum for mobile telecom licenses. CCAs are claimed to significantly reduce the scope for gaming or strategic bidding. In this paper, we show, however, that CCAs significantly enhance the possibilities for strategic bidding. Real bidders in telecom markets are not only interested in the spectrum they win themselves and the price they pay for that, but also in the price com...

  3. Design principles underlying circadian clocks.

    OpenAIRE

    Rand, D.A.; Shulgin, B. V.; D. Salazar; Millar, A. J.

    2004-01-01

    A fundamental problem for regulatory networks is to understand the relation between form and function: to uncover the underlying design principles of the network. Circadian clocks present a particularly interesting instance, as recent work has shown that they have complex structures involving multiple interconnected feedback loops with both positive and negative feedback. While several authors have speculated on the reasons for this, a convincing explanation is still lacking.We analyse both t...

  4. Hanle Detection for Optical Clocks

    Directory of Open Access Journals (Sweden)

    Xiaogang Zhang

    2015-01-01

    Full Text Available Considering the strong inhomogeneous spatial polarization and intensity distribution of spontaneous decay fluorescence due to the Hanle effect, we propose and demonstrate a universe Hanle detection configuration of electron-shelving method for optical clocks. Experimental results from Ca atomic beam optical frequency standard with electron-shelving method show that a designed Hanle detection geometry with optimized magnetic field direction, detection laser beam propagation and polarization direction, and detector position can improve the fluorescence collection rate by more than one order of magnitude comparing with that of inefficient geometry. With the fixed 423 nm fluorescence, the improved 657 nm optical frequency standard signal intensity is presented. The potential application of the Hanle detection geometry designed for facilitating the fluorescence collection for optical lattice clock with a limited solid angle of the fluorescence collection has been discussed. The Hanle detection geometry is also effective for ion detection in ion optical clock and quantum information experiments. Besides, a cylinder fluorescence collection structure is designed to increase the solid angle of the fluorescence collection in Ca atomic beam optical frequency standard.

  5. Hanle detection for optical clocks.

    Science.gov (United States)

    Zhang, Xiaogang; Zhang, Shengnan; Pan, Duo; Chen, Peipei; Xue, Xiaobo; Zhuang, Wei; Chen, Jingbiao

    2015-01-01

    Considering the strong inhomogeneous spatial polarization and intensity distribution of spontaneous decay fluorescence due to the Hanle effect, we propose and demonstrate a universe Hanle detection configuration of electron-shelving method for optical clocks. Experimental results from Ca atomic beam optical frequency standard with electron-shelving method show that a designed Hanle detection geometry with optimized magnetic field direction, detection laser beam propagation and polarization direction, and detector position can improve the fluorescence collection rate by more than one order of magnitude comparing with that of inefficient geometry. With the fixed 423 nm fluorescence, the improved 657 nm optical frequency standard signal intensity is presented. The potential application of the Hanle detection geometry designed for facilitating the fluorescence collection for optical lattice clock with a limited solid angle of the fluorescence collection has been discussed. The Hanle detection geometry is also effective for ion detection in ion optical clock and quantum information experiments. Besides, a cylinder fluorescence collection structure is designed to increase the solid angle of the fluorescence collection in Ca atomic beam optical frequency standard. PMID:25734183

  6. Rate variation and estimation of divergence times using strict and relaxed clocks

    Directory of Open Access Journals (Sweden)

    Yang Ziheng

    2011-09-01

    Full Text Available Abstract Background Understanding causes of biological diversity may be greatly enhanced by knowledge of divergence times. Strict and relaxed clock models are used in Bayesian estimation of divergence times. We examined whether: i strict clock models are generally more appropriate in shallow phylogenies where rate variation is expected to be low, ii the likelihood ratio test of the clock (LRT reliably informs which model is appropriate for dating divergence times. Strict and relaxed models were used to analyse sequences simulated under different levels of rate variation. Published shallow phylogenies (Black bass, Primate-sucking lice, Podarcis lizards, Gallotiinae lizards, and Caprinae mammals were also analysed to determine natural levels of rate variation relative to the performance of the different models. Results Strict clock analyses performed well on data simulated under the independent rates model when the standard deviation of log rate on branches, σ, was low (≤0.1, but were inappropriate when σ>0.1 (95% of rates fall within 0.0082-0.0121 subs/site/Ma when σ = 0.1, for a mean rate of 0.01. The independent rates relaxed clock model performed well at all levels of rate variation, although posterior intervals on times were significantly wider than for the strict clock. The strict clock is therefore superior when rate variation is low. The performance of a correlated rates relaxed clock model was similar to the strict clock. Increased numbers of independent loci led to slightly narrower posteriors under the relaxed clock while older root ages provided proportionately narrower posteriors. The LRT had low power for σ = 0.01-0.1, but high power for σ = 0.5-2.0. Posterior means of σ2 were useful for assessing rate variation in published datasets. Estimates of natural levels of rate variation ranged from 0.05-3.38 for different partitions. Differences in divergence times between relaxed and strict clock analyses were greater in two

  7. Optical to microwave clock frequency ratios with a nearly continuous strontium optical lattice clock

    CERN Document Server

    Lodewyck, Jérôme; Bookjans, Eva; Robyr, Jean-Luc; Shi, Chunyan; Vallet, Grégoire; Targat, Rodolphe Le; Nicolodi, Daniele; Coq, Yann Le; Guéna, Jocelyne; Abgrall, Michel; Rosenbusch, Peter; Bize, Sébastien

    2016-01-01

    Optical lattice clocks are at the forefront of frequency metrology. Both the instability and systematic uncertainty of these clocks have been reported to be two orders of magnitude smaller than the best microwave clocks. For this reason, a redefinition of the SI second based on optical clocks seems possible in the near future. However, the operation of optical lattice clocks has not yet reached the reliability that microwave clocks have achieved so far. In this paper, we report on the operation of a strontium optical lattice clock that spans several weeks, with more than 80% uptime. We make use of this long integration time to demonstrate a reproducible measurement of frequency ratios between the strontium clock transition and microwave Cs primary and Rb secondary frequency standards.

  8. Atomic clocks: A mathematical physics perspective

    International Nuclear Information System (INIS)

    Full text: Accuracy of atomic clocks (since their introduction in 50's) is increasing by roughly one order per decade. A natural theoretical problem posed by this development is to seek the ultimate accuracy of atomic clocks and means to achieve it. This problem was indeed extensively studied and various bounds on the accuracy are well understood, e.g. shot noise limit. I would present a mathematical minded (but simple) model of atomic clocks and discuss accuracy bounds within the model. (author)

  9. The Square Light Clock and Special Relativity

    Science.gov (United States)

    Galli, J. Ronald; Amiri, Farhang

    2012-01-01

    A thought experiment that includes a square light clock is similar to the traditional vertical light beam and mirror clock, except it is made up of four mirrors placed at a 45[degree] angle at each corner of a square of length L[subscript 0], shown in Fig. 1. Here we have shown the events as measured in the rest frame of the square light clock. By…

  10. Performance Evaluation of Clock Synchronization Algorithms

    OpenAIRE

    Anceaume, Emmanuelle; Puaut, Isabelle

    1998-01-01

    Clock synchronization algorithms ensure that physically dispersed processors have a common knowledge of time. This report proposes a survey of software fault-tolerant clock synchronization algorithms: deterministic, probabilistic and statistical ; internal and external ; and resilient from crash to Byzantine failures. Our survey is based on a classification of clock synchronization algorithms (according to their internal structure and to three orthogonal and independent basic building blocks ...

  11. Interaction of circadian clock proteins PER2 and CRY with BMAL1 and CLOCK

    OpenAIRE

    Bordon Alain; Tallone Tiziano; Langmesser Sonja; Rusconi Sandro; Albrecht Urs

    2008-01-01

    Abstract Background Circadian oscillation of clock-controlled gene expression is mainly regulated at the transcriptional level. Heterodimers of CLOCK and BMAL1 act as activators of target gene transcription; however, interactions of PER and CRY proteins with the heterodimer abolish its transcriptional activation capacity. PER and CRY are therefore referred to as negative regulators of the circadian clock. To further elucidate the mechanism how positive and negative components of the clock int...

  12. Robustness of circadian clocks to daylight fluctuations: hints from the picoeucaryote Ostreococcus tauri.

    Directory of Open Access Journals (Sweden)

    Quentin Thommen

    Full Text Available The development of systemic approaches in biology has put emphasis on identifying genetic modules whose behavior can be modeled accurately so as to gain insight into their structure and function. However, most gene circuits in a cell are under control of external signals and thus, quantitative agreement between experimental data and a mathematical model is difficult. Circadian biology has been one notable exception: quantitative models of the internal clock that orchestrates biological processes over the 24-hour diurnal cycle have been constructed for a few organisms, from cyanobacteria to plants and mammals. In most cases, a complex architecture with interlocked feedback loops has been evidenced. Here we present the first modeling results for the circadian clock of the green unicellular alga Ostreococcus tauri. Two plant-like clock genes have been shown to play a central role in the Ostreococcus clock. We find that their expression time profiles can be accurately reproduced by a minimal model of a two-gene transcriptional feedback loop. Remarkably, best adjustment of data recorded under light/dark alternation is obtained when assuming that the oscillator is not coupled to the diurnal cycle. This suggests that coupling to light is confined to specific time intervals and has no dynamical effect when the oscillator is entrained by the diurnal cycle. This intriguing property may reflect a strategy to minimize the impact of fluctuations in daylight intensity on the core circadian oscillator, a type of perturbation that has been rarely considered when assessing the robustness of circadian clocks.

  13. Global synchronization of parallel processors using clock pulse width modulation

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Dong; Ellavsky, Matthew R.; Franke, Ross L.; Gara, Alan; Gooding, Thomas M.; Haring, Rudolf A.; Jeanson, Mark J.; Kopcsay, Gerard V.; Liebsch, Thomas A.; Littrell, Daniel; Ohmacht, Martin; Reed, Don D.; Schenck, Brandon E.; Swetz, Richard A.

    2013-04-02

    A circuit generates a global clock signal with a pulse width modification to synchronize processors in a parallel computing system. The circuit may include a hardware module and a clock splitter. The hardware module may generate a clock signal and performs a pulse width modification on the clock signal. The pulse width modification changes a pulse width within a clock period in the clock signal. The clock splitter may distribute the pulse width modified clock signal to a plurality of processors in the parallel computing system.

  14. Progress of the ~(87)Rb Fountain Clock

    Institute of Scientific and Technical Information of China (English)

    ZHOU Zi-Chao; WEI Rong; SHI Chun-Yan; LV De-Sheng; LI Tang; WANG Yu-Zhu

    2009-01-01

    A fountain atomic clock based on cold ~(87)Rb atoms has been in operation in our laboratory for several months.We therefore report the design of the rubidium fountain clock including its physical package,optical system and daily operation.Ramsey fringes have been attained with the signal to noise ratio of about 100.

  15. Could Atomic clocks be affected by neutrinos?

    CERN Document Server

    Hanafi, Hanaa

    2016-01-01

    An atomic clock is a clock device that uses an electronic transition frequency of the electromagnetic spectrum of atoms as a frequency standard in order to derive a time standard since time is the reciprocal of frequency. If the electronic transition frequencies are in an "optical region", we are talking in this case about optical atomic clocks. If they are in an "microwave region" these atomic clocks are made of the metallic element cesium so they are called Cesium atomic clocks. Atomic clocks are the most accurate time and frequency standards known despite the different perturbations that can affect them, a lot of researches were made in this domain to show how the transitions can be different for different type of perturbations..Since atomic clocks are very sensitive devices, based on coherent states (A coherent state tends to loose coherence after interacting). One question can arise (from a lot of questions) which is why cosmic neutrinos are not affecting these clocks? The answer to this question requir...

  16. Fast Clock Recovery for Digital Communications

    Science.gov (United States)

    Tell, R. G.

    1985-01-01

    Circuit extracts clock signal from random non-return-to-zero data stream, locking onto clock within one bit period at 1-gigabitper-second data rate. Circuit used for synchronization in opticalfiber communications. Derives speed from very short response time of gallium arsenide metal/semiconductor field-effect transistors (MESFET's).

  17. Temperature influences in receiver clock modelling

    Science.gov (United States)

    Wang, Kan; Meindl, Michael; Rothacher, Markus; Schoenemann, Erik; Enderle, Werner

    2016-04-01

    In Precise Point Positioning (PPP), hardware delays at the receiver site (receiver, cables, antenna, …) are always difficult to be separated from the estimated receiver clock parameters. As a result, they are partially or fully contained in the estimated "apparent" clocks and will influence the deterministic and stochastic modelling of the receiver clock behaviour. In this contribution, using three years of data, the receiver clock corrections of a set of high-precision Hydrogen Masers (H-Masers) connected to stations of the ESA/ESOC network and the International GNSS Service (IGS) are firstly characterized concerning clock offsets, drifts, modified Allan deviations and stochastic parameters. In a second step, the apparent behaviour of the clocks is modelled with the help of a low-order polynomial and a known temperature coefficient (Weinbach, 2013). The correlations between the temperature and the hardware delays generated by different types of antennae are then analysed looking at daily, 3-day and weekly time intervals. The outcome of these analyses is crucial, if we intend to model the receiver clocks in the ground station network to improve the estimation of station-related parameters like coordinates, troposphere zenith delays and ambiguities. References: Weinbach, U. (2013) Feasibility and impact of receiver clock modeling in precise GPS data analysis. Dissertation, Leibniz Universität Hannover, Germany.

  18. Progress of the 87Rb Fountain Clock

    International Nuclear Information System (INIS)

    A fountain atomic clock based on cold 87 Rb atoms has been in operation in our laboratory for several months. We therefore report the design of the rubidium fountain clock including its physical package, optical system and daily operation. Ramsey fringes have been attained with the signal to noise ratio of about 100

  19. A colorful model of the circadian clock.

    Science.gov (United States)

    Reppert, Steven M

    2006-01-27

    The migration of the colorful monarch butterfly provides biologists with a unique model system with which to study the cellular and molecular mechanisms underlying a sophisticated circadian clock. The monarch circadian clock is involved in the induction of the migratory state and navigation over long distances, using the sun as a compass. PMID:16439193

  20. Internal Clock Drift Estimation in Computer Clusters

    Directory of Open Access Journals (Sweden)

    Hicham Marouani

    2008-01-01

    Full Text Available Most computers have several high-resolution timing sources, from the programmable interrupt timer to the cycle counter. Yet, even at a precision of one cycle in ten millions, clocks may drift significantly in a single second at a clock frequency of several GHz. When tracing the low-level system events in computer clusters, such as packet sending or reception, each computer system records its own events using an internal clock. In order to properly understand the global system behavior and performance, as reported by the events recorded on each computer, it is important to estimate precisely the clock differences and drift between the different computers in the system. This article studies the clock precision and stability of several computer systems, with different architectures. It also studies the typical network delay characteristics, since time synchronization algorithms rely on the exchange of network packets and are dependent on the symmetry of the delays. A very precise clock, based on the atomic time provided by the GPS satellite network, was used as a reference to measure clock drifts and network delays. The results obtained are of immediate use to all applications which depend on computer clocks or network time synchronization accuracy.

  1. Tectonic blocks and molecular clocks

    Science.gov (United States)

    2016-01-01

    Evolutionary timescales have mainly used fossils for calibrating molecular clocks, though fossils only really provide minimum clade age constraints. In their place, phylogenetic trees can be calibrated by precisely dated geological events that have shaped biogeography. However, tectonic episodes are protracted, their role in vicariance is rarely justified, the biogeography of living clades and their antecedents may differ, and the impact of such events is contingent on ecology. Biogeographic calibrations are no panacea for the shortcomings of fossil calibrations, but their associated uncertainties can be accommodated. We provide examples of how biogeographic calibrations based on geological data can be established for the fragmentation of the Pangaean supercontinent: (i) for the uplift of the Isthmus of Panama, (ii) the separation of New Zealand from Gondwana, and (iii) for the opening of the Atlantic Ocean. Biogeographic and fossil calibrations are complementary, not competing, approaches to constraining molecular clock analyses, providing alternative constraints on the age of clades that are vital to avoiding circularity in investigating the role of biogeographic mechanisms in shaping modern biodiversity. This article is part of the themed issue ‘Dating species divergences using rocks and clocks’. PMID:27325840

  2. Cold atom Clocks and Applications

    CERN Document Server

    Bize, S; Abgrall, M; Marion, H; Maksimovic, I; Cacciapuoti, L; Gruenert, J; Vian, C; Dos Santos, F P; Rosenbusch, P; Lemonde, P; Santarelli, G; Wolf, P; Clairon, A; Luiten, A; Tobar, M; Salomon, C

    2005-01-01

    This paper describes advances in microwave frequency standards using laser-cooled atoms at BNM-SYRTE. First, recent improvements of the $^{133}$Cs and $^{87}$Rb atomic fountains are described. Thanks to the routine use of a cryogenic sapphire oscillator as an ultra-stable local frequency reference, a fountain frequency instability of $1.6\\times 10^{-14}\\tau^{-1/2}$ where $\\tau $ is the measurement time in seconds is measured. The second advance is a powerful method to control the frequency shift due to cold collisions. These two advances lead to a frequency stability of $2\\times 10^{-16}$ at $50,000s for the first time for primary standards. In addition, these clocks realize the SI second with an accuracy of $7\\times 10^{-16}$, one order of magnitude below that of uncooled devices. In a second part, we describe tests of possible variations of fundamental constants using $^{87}$Rb and $^{133}$Cs fountains. Finally we give an update on the cold atom space clock PHARAO developed in collaboration with CNES. This ...

  3. Single electron relativistic clock interferometer

    CERN Document Server

    Bushev, Pavel; Sholokhov, Dmitry; Kukharchyk, Nadezhda; Zych, Magdalena

    2016-01-01

    Although time is one of the fundamental notions in physics, it does not have a unique description. In quantum theory time is a parameter ordering the succession of the probability amplitudes of a quantum system, while according to relativity theory each system experiences in general a different proper time, depending on the system's world line, due to time to time dilation. It is therefore of fundamental interest to test the notion of time in the regime where both quantum and relativistic effects play a role, for example, when different amplitudes of a single quantum clock experience different magnitudes of time dilation. Here we propose a realization of such an experiment with a single electron in a Penning trap. The clock can be implemented in the electronic spin precession and its time dilation then depends on the radial (cyclotron) state of the electron. We show that coherent manipulation and detection of the electron can be achieved already with present day technology. A single electron in a Penning trap...

  4. A low maintenance Sr optical lattice clock

    CERN Document Server

    Hill, Ian R; Bowden, William; Bridge, Elizabeth M; Donnellan, Sean; Curtis, E Anne; Gill, Patrick

    2016-01-01

    We describe the Sr optical lattice clock apparatus at NPL with particular emphasis on techniques used to increase reliability and minimise the human requirement in its operation. Central to this is a clock-referenced transfer cavity scheme for the stabilisation of cooling and trapping lasers. We highlight several measures to increase the reliability of the clock with a view towards the realisation of an optical time-scale. The clock contributed 502 hours of data over a 25 day period (84% uptime) in a recent measurement campaign with several uninterrupted periods of more than 48 hours. An instability of $2\\times10^{-17}$ was reached after $10^5$ s of averaging in an interleaved self-comparison of the clock.

  5. Phase locking and multiple oscillating attractors for the coupled mammalian clock and cell cycle

    Science.gov (United States)

    Feillet, Céline; Krusche, Peter; Tamanini, Filippo; Janssens, Roel C.; Downey, Mike J.; Martin, Patrick; Teboul, Michèle; Saito, Shoko; Lévi, Francis A.; Bretschneider, Till; van der Horst, Gijsbertus T. J.; Delaunay, Franck; Rand, David A.

    2014-01-01

    Daily synchronous rhythms of cell division at the tissue or organism level are observed in many species and suggest that the circadian clock and cell cycle oscillators are coupled. For mammals, despite known mechanistic interactions, the effect of such coupling on clock and cell cycle progression, and hence its biological relevance, is not understood. In particular, we do not know how the temporal organization of cell division at the single-cell level produces this daily rhythm at the tissue level. Here we use multispectral imaging of single live cells, computational methods, and mathematical modeling to address this question in proliferating mouse fibroblasts. We show that in unsynchronized cells the cell cycle and circadian clock robustly phase lock each other in a 1:1 fashion so that in an expanding cell population the two oscillators oscillate in a synchronized way with a common frequency. Dexamethasone-induced synchronization reveals additional clock states. As well as the low-period phase-locked state there are distinct coexisting states with a significantly higher period clock. Cells transition to these states after dexamethasone synchronization. The temporal coordination of cell division by phase locking to the clock at a single-cell level has significant implications because disordered circadian function is increasingly being linked to the pathogenesis of many diseases, including cancer. PMID:24958884

  6. Dilatation effect of ''quantum clocks''

    International Nuclear Information System (INIS)

    The relativistic dilatation effect of the life-time of unstable microparticles combined with quantum symmetry of their description results in the ''quantum-dilatation'' dilemma. It is due to the classical character of the relativity theory which here reveals itself in the classical world-line of the clock necessary in order to deduce the dilatation effect from the Lorentz transformation. It is shown how to solve this dilemma, basing on the relation continuum C4. Two types of measurements of time intervals, the direct and indirect one, are analyzed. The former type corresponds to the external space-time continuum, where any direct measurement takes place, and the latter, to the internal relation continuum C4, where the internal structures of isolated micro-systems are sunk. (author)

  7. Circadian clocks are designed optimally

    CERN Document Server

    Hasegawa, Yoshihiko

    2014-01-01

    Circadian rhythms are acquired through evolution to increase the chances for survival by synchronizing to the daylight cycle. Reliable synchronization is realized through two trade-off properties: regularity to keep time precisely, and entrainability to synchronize the internal time with daylight. Since both properties have been tuned through natural selection, their adaptation can be formalized in the framework of mathematical optimization. By using a succinct model, we found that simultaneous optimization of regularity and entrainability entails inherent features of the circadian mechanism irrespective of model details. At the behavioral level we discovered the existence of a dead zone, a time during which light pulses neither advance nor delay the clock. At the molecular level we demonstrate the role-sharing of two light inputs, phase advance and delay, as is well observed in mammals. We also reproduce the results of phase-controlling experiments and predict molecular elements responsible for the clockwork...

  8. Ontogenesis of the circadian clock within the rat liver

    Czech Academy of Sciences Publication Activity Database

    Sládek, Martin; Sumová, Alena; Jindráková, Zuzana; Bendová, Zdeňka; Illnerová, Helena

    Florida : Sage Publications, 2006. s. 89-90. [Meeting of Society for Research on Biological Rhythms /10./. 21.05.2006-25.05.2006, Sandestin] R&D Projects: GA ČR(CZ) GA309/05/0350; GA AV ČR(CZ) IAA500110605; GA MŠk(CZ) LC554 Grant ostatní: EU 6th Framework Project EUCLOCK(XE) 018741 Institutional research plan: CEZ:AV0Z50110509 Keywords : circadian clock * liver * ontogenesis Subject RIV: FH - Neurology

  9. [Circadian clock and non-visual functions: the role of light in humans].

    Science.gov (United States)

    Gronfier, Claude

    2014-01-01

    Hormonal secretion, cognitive performance, motor activity, metabolic processes, the sleep wake cycle and, most recently shown, cell division and ADN repair show a 24 h rhythmicity that is driven by the circadian timing system (the biological clock). Their appropriate activity over the 24 h requires appropriate entrainment of the circadian clock, which is achieved through the synchronizing effects of ocular light exposure. The activation of melanopsin-expressing ganglion cells in the retina depends on timing, quality, intensity, and history of light exposure. Inappropriate lighting leads to inappropriate synchronization of the clock, and activation of non-visual functions (mood, wakefulness, cognition, etc.). In turn, a deficit of circadian entrainment to the 24 h is responsible for alterations of a large number of functions, and leads to altered sleep, wake, mood, neurobehavioral processes and cell division, but also to pathologies. The crucial role of the circadian clock and the nature of the non-visual functions activated by light give rise to the concept that light is a biological need fundamental to health. Without an appropriate light hygiene, the clock receives an odd tempo, and it is cacophony! PMID:25840452

  10. Entrainment Dissociates Transcription and Translation of a Circadian Clock Gene in Neurospora

    NARCIS (Netherlands)

    Tan, Ying; Dragovic, Zdravko; Roenneberg, Till; Merrow, Martha

    2004-01-01

    Circadian systems coordinate the daily sequence of events in cells, tissues, and organisms. In constant conditions, the biological clock oscillates with its endogenous period, whereas it is synchronized to the 24 hr light:dark cycle in nature. Here, we investigate light entrainment of Neurospora cra

  11. Selective Inhibition of Casein Kinase 1 epsilon Minimally Alters Circadian Clock Period

    Czech Academy of Sciences Publication Activity Database

    Walton, K. M.; Fisher, K.; Rubitski, D.; Marconi, M.; Meng, Q.-J.; Sládek, Martin; Adams, J.; Bass, M.; Chandrasekaran, R.; Butler, T.; Griffor, M.; Rajamohan, F.; Serpa, M.; Chen, Y.; Claffey, M.; Hastings, M.; Loudon, A.; Maywood, E.; Ohren, J.; Doran, A.; Wager, T. T.

    2009-01-01

    Roč. 330, č. 2 (2009), s. 430-439. ISSN 0022-3565 Institutional research plan: CEZ:AV0Z50110509 Keywords : circadian clock * casein kinase 1 epsilon * inhibitor Subject RIV: EB - Genetics ; Molecular Biology Impact factor: 4.093, year: 2009

  12. Iterative quantum algorithm for distributed clock synchronization

    International Nuclear Information System (INIS)

    Clock synchronization is a well-studied problem with many practical and scientific applications. We propose an arbitrary accuracy iterative quantum algorithm for distributed clock synchronization using only three qubits. The n bits of the time difference Δ between two spatially separated clocks can be deterministically extracted by communicating only O(n) messages and executing the quantum iteration process n times based on the classical feedback and measurement operations. Finally, we also give the algorithm using only two qubits and discuss the success probability of the algorithm

  13. Using Atomic Clocks to Detect Gravitational Waves

    CERN Document Server

    Loeb, Abraham

    2015-01-01

    Atomic clocks have recently reached a fractional timing precision of $<10^{-18}$. We point out that an array of atomic clocks, distributed along the Earth's orbit around the Sun, will have the sensitivity needed to detect the time dilation effect of mHz gravitational waves (GWs), such as those emitted by supermassive black hole binaries at cosmological distances. Simultaneous measurement of clock-rates at different phases of a passing GW provides an attractive alternative to the interferometric detection of temporal variations in distance between test masses separated by less than a GW wavelength, currently envisioned for the eLISA mission.

  14. The circadian clock in cancer development and therapy

    Science.gov (United States)

    Most aspects of mammalian function display circadian rhythms driven by an endogenous clock. The circadian clock is operated by genes and comprises a central clock in the brain that responds to environmental cues and controls subordinate clocks in peripheral tissues via circadian output pathways. The...

  15. Draper Clock-Synchronization Protocol in SAL

    Data.gov (United States)

    National Aeronautics and Space Administration — In 1973, Daly, Hpokins, and McKenna (from Draper Lab.) presented a fault-tolerant digital clocking system at the FTCS conference. This is probably one of the first...

  16. The Mechanics of Mechanical Watches and Clocks

    CERN Document Server

    Du, Ruxu

    2013-01-01

    "The Mechanics of Mechanical Watches and Clocks" presents historical views and mathematical models of mechanical watches and clocks. Although now over six hundred years old, mechanical watches and clocks are still popular luxury items that fascinate many people around the world. However few have examined the theory of how they work as presented in this book. The illustrations and computer animations are unique and have never been published before. It will be of significant interest to researchers in mechanical engineering, watchmakers and clockmakers, as well as people who have an engineering background and are interested in mechanical watches and clocks. It will also inspire people in other fields of science and technology, such as mechanical engineering and electronics engineering, to advance their designs. Professor Ruxu Du works at the Chinese University of Hong Kong, China. Assistant Professor Longhan Xie works at the South China University of Technology, China.

  17. Entrainment of the Neurospora circadian clock

    NARCIS (Netherlands)

    Merrow, M; Boesl, C; Ricken, J; Messerschmitt, M; Goedel, M; Roenneberg, T

    2006-01-01

    Neurospora crassa has been systematically investigated for circadian entrainment behavior. Many aspects of synchronization can be investigated in this simple, cellular system, ranging from systematic entrainment and drivenness to masking. Clock gene expression during entrainment and entrainment with

  18. Programmable Clock Waveform Generation for CCD Readout

    Energy Technology Data Exchange (ETDEWEB)

    Vicente, J. de; Castilla, J.; Martinez, G.; Marin, J.

    2006-07-01

    Charge transfer efficiency in CCDs is closely related to the clock waveform. In this paper, an experimental framework to explore different FPGA based clock waveform generator designs is described. Two alternative design approaches for controlling the rise/fall edge times and pulse width of the CCD clock signal have been implemented: level-control and time-control. Both approaches provide similar characteristics regarding the edge linearity and noise. Nevertheless, dissimilarities have been found with respect to the area and frequency range of application. Thus, while the time-control approach consumes less area, the level control approach provides a wider range of clock frequencies since it does not suffer capacitor discharge effect. (Author) 8 refs.

  19. Micro Mercury Ion Clock (MMIC) Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Demonstrate micro clock based on trapped Hg ions with more than 10x size reduction and power; Fractional frequency stability at parts per 1014 level, adequate for...

  20. High-Accuracy Microwave Atomic Clock via Magic Optical Lattice

    OpenAIRE

    Zhou, Xiaoji; Chen, Xuzong; Chen, Jingbiao

    2005-01-01

    A microwave atomic clock scheme based on Rb and Cs atoms trapped in optical lattice with magic wavelength for clock transition is proposed. The ac Stark shift of clock transition due to trapping laser can be canceled at some specific laser wavelengths. Comparing with in fountain clock, the cavity related shifts, the collision shift, and the Doppler effect are eliminated or suppressed dramatically in atomic clock when the magic optical lattice is exploited. By carefully analyzing various sourc...

  1. Automated Synthesis of Skew-Based Clock Distribution Networks

    OpenAIRE

    José Luis Neves; Eby G. Friedman

    1998-01-01

    In this paper a top-down methodology is presented for synthesizing clock distribution networks based on application-dependent localized clock skew. The methodology is divided into four phases: 1) determination of an optimal clock skew schedule for improving circuit performance and reliability; 2) design of the topology of the clock tree based on the circuit hierarchy and minimum clock path delays; 3) design of circuit structures to implement the delay values associated with the branches of th...

  2. Working around the clock: circadian rhythms and skeletal muscle

    OpenAIRE

    ZHANG, XIPING; Dube, Thomas J.; Esser, Karyn A.

    2009-01-01

    The study of the circadian molecular clock in skeletal muscle is in the very early stages. Initial research has demonstrated the presence of the molecular clock in skeletal muscle and that skeletal muscle of a clock-compromised mouse, Clock mutant, exhibits significant disruption in normal expression of many genes required for adult muscle structure and metabolism. In light of the growing association between the molecular clock, metabolism, and metabolic disease, it will also be important to ...

  3. Clock genes, hair growth and aging

    OpenAIRE

    Geyfman, Mikhail; Andersen, Bogi

    2010-01-01

    Hair follicles undergo continuous cycles of growth, involution and rest. This process, referred to as the hair growth cycle, has a periodicity of weeks to months. At the same time, skin and hair follicles harbor a functional circadian clock that regulates gene expression with a periodicity of approximately twenty four hours. In our recent study we found that circadian clock genes play a role in regulation of the hair growth cycle during synchronized hair follicle cycling, uncovering an unexpe...

  4. Expression of Clock Proteins in Developing Tooth

    OpenAIRE

    Zheng, Li; Papagerakis, Silvana; Schnell, Santiago D.; Hoogerwerf, Willemijntje A; Papagerakis, Petros

    2010-01-01

    Morphological and functional changes during ameloblast and odontoblast differentiation suggest that enamel and dentin formation is under circadian control. Circadian rhythms are endogenous self-sustained oscillations with periods of 24 hours that control diverse physiological and metabolic processes. Mammalian clock genes play a key role in synchronizing circadian functions in many organs. However, close to nothing is known on clock genes expression during tooth development. In this work, we ...

  5. Circadian Clock Proteins in Mood Regulation

    OpenAIRE

    Partonen, Timo

    2015-01-01

    Mood regulation is known to be affected by the change of seasons. Recent research findings have suggested that mood regulation may be influenced by the function of circadian clocks. In addition, the activity of brown adipocytes has been hypothesized to contribute to mood regulation. Here, the overarching link to mood disorders might be the circadian clock protein nuclear receptor subfamily 1, group D, member 1.

  6. Circadian clock proteins in mood regulation

    Directory of Open Access Journals (Sweden)

    Timo ePartonen

    2015-01-01

    Full Text Available Mood regulation is known to be affected by the change of seasons. Recent research findings have suggested that mood regulation may be influenced by the function of circadian clocks. In addition, the activity of brown adipocytes has been hypothesized to contribute to mood regulation. Here, the overarching link to mood disorders might be the circadian clock protein NR1D1 (nuclear receptor subfamily 1, group D, member 1.

  7. Reduced Kalman Filters for Clock Ensembles

    Science.gov (United States)

    Greenhall, Charles A.

    2011-01-01

    This paper summarizes the author's work ontimescales based on Kalman filters that act upon the clock comparisons. The natural Kalman timescale algorithm tends to optimize long-term timescale stability at the expense of short-term stability. By subjecting each post-measurement error covariance matrix to a non-transparent reduction operation, one obtains corrected clocks with improved short-term stability and little sacrifice of long-term stability.

  8. Optical lattice clock with Strontium atoms

    International Nuclear Information System (INIS)

    This thesis presents the latest achievements regarding the optical lattice clock with Strontium atoms developed at LNE-SYRTE. After a review of the different types of optical clocks that are currently under development, we stress on the concept of optical lattice clock which was first imagined for Sr87 using the 1S0 → 3P0 transition. We exhibit the features of this atom, in particular the concept of magic wavelength for the trap, and the achievable performances for this kind of clock. The second part presents the experimental aspects, insisting particularly on the ultra-stable laser used for the interrogation of the atoms which is a central part of the experiment. Among the latest improvements, an optical pumping phase and an interrogation phase using a magnetic field have been added in order to refine the evaluation of the Zeeman effect. Finally, the last part presents the experimental results. The last evaluation of the clock using Sr87 atoms allowed us to reach a frequency accuracy of 2.6*10-15 and a measurement in agreement with the one made at JILA (Tokyo university) at the 10-15 level. On another hand, thanks to recent theoretical proposals, we made a measurement using the bosonic isotope Sr88 by adapting the experimental setup. This measurement represents the first evaluation for this type of clock, with a frequency accuracy of 7*10-14. (author)

  9. Circadian clock manipulation for cancer prevention and control and the relief of cancer symptoms.

    Science.gov (United States)

    Hrushesky, William J M; Grutsch, James; Wood, Patricia; Yang, Xiaoming; Oh, Eun-Young; Ansell, Christine; Kidder, Stephanie; Ferrans, Carol; Quiton, Dinah Faith T; Reynolds, Justin; Du-Quiton, Jovelyn; Levin, Robert; Lis, Christopher; Braun, Donald

    2009-12-01

    Life has evolved on this planet with regular daily spans of direct solar energy availability alternating with nocturnal spans of dark. Virtually every earth-borne life form has factored this circadian pattern into its biology to ensure the temporal coordination with its resonating environment, a task essential for its individual survival and that of its species. The first whole genome inspections of mutations in human colon and breast cancer have observed specific retained clock gene mutations. Single nucleotide polymorphisms within the genes of clock, clock-controlled, and melatonin pathways have been found to confer excess cancer risk or protection from cancer. Experimental studies have shown that specific core clock genes (Per2 and Per1) are tumor suppressors because their genetic absence doubles tumor numbers, and decreasing their expression in cancer cells doubles cancer growth rate, whereas their overexpression decreases cancer growth rate and diminishes tumor numbers. Experimental interference with circadian clock function increases cancer growth rate, and clinical circadian disruption is associated with higher cancer incidence, faster cancer progression, and shorter cancer patient survival. Patients with advanced lung cancer suffering greater circadian activity/sleep cycle disruption suffer greater interference with function, greater anxiety and depression, poorer nighttime sleep, greater daytime fatigue, and poorer quality of life than comparable patients who maintain good circadian integration. We must now determine whether strategies known to help synchronize the circadian clocks of normal individuals can do so in advanced cancer patients and whether doing so allows cancer patients to feel better and/or live longer. Several academic laboratories and at least 2 large pharmaceutical firms are screening for small molecules targeting the circadian clock to stabilize its phase and enhance its amplitude and thereby consolidate and coordinate circadian

  10. Effects of different per translational kinetics on the dynamics of a core circadian clock model.

    Directory of Open Access Journals (Sweden)

    Paula S Nieto

    Full Text Available Living beings display self-sustained daily rhythms in multiple biological processes, which persist in the absence of external cues since they are generated by endogenous circadian clocks. The period (per gene is a central player within the core molecular mechanism for keeping circadian time in most animals. Recently, the modulation PER translation has been reported, both in mammals and flies, suggesting that translational regulation of clock components is important for the proper clock gene expression and molecular clock performance. Because translational regulation ultimately implies changes in the kinetics of translation and, therefore, in the circadian clock dynamics, we sought to study how and to what extent the molecular clock dynamics is affected by the kinetics of PER translation. With this objective, we used a minimal mathematical model of the molecular circadian clock to qualitatively characterize the dynamical changes derived from kinetically different PER translational mechanisms. We found that the emergence of self-sustained oscillations with characteristic period, amplitude, and phase lag (time delays between per mRNA and protein expression depends on the kinetic parameters related to PER translation. Interestingly, under certain conditions, a PER translation mechanism with saturable kinetics introduces longer time delays than a mechanism ruled by a first-order kinetics. In addition, the kinetic laws of PER translation significantly changed the sensitivity of our model to parameters related to the synthesis and degradation of per mRNA and PER degradation. Lastly, we found a set of parameters, with realistic values, for which our model reproduces some experimental results reported recently for Drosophila melanogaster and we present some predictions derived from our analysis.

  11. Temperature compensation model for the circadian clock of Neurospora crassa

    Science.gov (United States)

    Tang, Xiaojia; Schüttler, Heinz-Bernd; Arnold, Jonathan

    2008-03-01

    In the lowly bread mould, Neurospora crassa, biomolecular reactions involving the white-collar-1 (wc-1), white-colloar-2 (wc2), and frequency (frq) genes and their products constitute building blocks of the biological clock that would response to temperature as well as light. The period of the biological clock remains stable in response to variation in ambient temperature, which is called a compensation phenomenon. Recent experimental results show evidences that the temperature compensation could be explained by the temperature sensitive translational control of production of two isoforms of the main oscillator protein FRQ: a long form FRQ^1-989 which is more abundantly produced at higher temperature; and a short from FRQ^100-989, more abundantly produced at lower temperature. With our recently developed method of genetic network identification, we are now simulating the network's temperature response based on published experimental data. These will serve as the starting point for a simulation-prediction-experiment-simulation workflow cycle. In this cycle, the maximally informative next experiment (MINE) technology will be employed to select the best experimental control parameters specifying the temperature response to be used in the next step of the workflow cycle.

  12. On the Evolution of Memory: A Time for Clocks

    Directory of Open Access Journals (Sweden)

    Jason Robert Gerstner

    2012-02-01

    Full Text Available What was the earliest engram? Biology has evolved to encode representations of past events, and in neuroscience, we are attempting to link experience-dependent changes in molecular signaling with cellular processes that ultimately lead to behavioral output. The theory of evolution has guided biological research for decades, and since phylogenetically conserved mechanisms drive circadian rhythms, these processes may serve as common predecessors underlying more complex behavioral phenotypes. For example, the cAMP/MAPK/CREB cascade is interwoven with the clock to trigger circadian output, and is also known to affect memory formation. Time-of-day dependent changes have been observed in long-term potentiation (LTP within the mammalian suprachiasmatic nucleus and hippocampus, along with light-induced circadian phase resetting and fear conditioning behaviors. Together this suggests during evolution, similar processes underlying metaplasticity in more simple circuits may have been redeployed in higher-order brain regions. Therefore, this notion predicts a model that LTP and metaplasticity may exist in clock-forming circuits of lower-order species, through phylogenetically conserved pathways, leading to several testable hypotheses.

  13. Coupling between the Circadian Clock and Cell Cycle Oscillators: Implication for Healthy Cells and Malignant Growth

    Science.gov (United States)

    Feillet, Celine; van der Horst, Gijsbertus T. J.; Levi, Francis; Rand, David A.; Delaunay, Franck

    2015-01-01

    Uncontrolled cell proliferation is one of the key features leading to cancer. Seminal works in chronobiology have revealed that disruption of the circadian timing system in mice, either by surgical, genetic, or environmental manipulation, increased tumor development. In humans, shift work is a risk factor for cancer. Based on these observations, the link between the circadian clock and cell cycle has become intuitive. But despite identification of molecular connections between the two processes, the influence of the clock on the dynamics of the cell cycle has never been formally observed. Recently, two studies combining single live cell imaging with computational methods have shed light on robust coupling between clock and cell cycle oscillators. We recapitulate here these novel findings and integrate them with earlier results in both healthy and cancerous cells. Moreover, we propose that the cell cycle may be synchronized or slowed down through coupling with the circadian clock, which results in reduced tumor growth. More than ever, systems biology has become instrumental to understand the dynamic interaction between the circadian clock and cell cycle, which is critical in cellular coordination and for diseases such as cancer. PMID:26029155

  14. Coupling between the circadian clock and cell cycle oscillators: implication for healthy cells and malignant growth

    Directory of Open Access Journals (Sweden)

    Celine eFeillet

    2015-05-01

    Full Text Available Uncontrolled cell proliferation is one of the key features leading to cancer. Seminal works in chronobiology have revealed that disruption of the circadian timing system in mice, either by surgical, genetic or environmental manipulation, increased tumor development. In humans, shift work is a risk factor for cancer. Based on these observations, the link between the circadian clock and cell cycle has become intuitive. But despite identification of molecular connections between the two processes, the influence of the clock on the dynamics of the cell cycle has never been formally observed. Recently, two studies combining single live cell imaging with computational methods have shed light on robust coupling between clock and cell cycle oscillators. We recapitulate here these novel findings and integrate them with earlier results in both healthy and cancerous cells. Moreover, we propose that the cell cycle may be synchronized or slowed down through coupling with the circadian clock, which results in reduced tumour growth. More than ever, systems biology has become instrumental to understand the dynamic interaction between the circadian clock and cell cycle, which is critical in cellular coordination and for diseases such as cancer.

  15. Mass spectrometry-based absolute quantification reveals rhythmic variation of mouse circadian clock proteins.

    Science.gov (United States)

    Narumi, Ryohei; Shimizu, Yoshihiro; Ukai-Tadenuma, Maki; Ode, Koji L; Kanda, Genki N; Shinohara, Yuta; Sato, Aya; Matsumoto, Katsuhiko; Ueda, Hiroki R

    2016-06-14

    Absolute values of protein expression levels in cells are crucial information for understanding cellular biological systems. Precise quantification of proteins can be achieved by liquid chromatography (LC)-mass spectrometry (MS) analysis of enzymatic digests of proteins in the presence of isotope-labeled internal standards. Thus, development of a simple and easy way for the preparation of internal standards is advantageous for the analyses of multiple target proteins, which will allow systems-level studies. Here we describe a method, termed MS-based Quantification By isotope-labeled Cell-free products (MS-QBiC), which provides the simple and high-throughput preparation of internal standards by using a reconstituted cell-free protein synthesis system, and thereby facilitates both multiplexed and sensitive quantification of absolute amounts of target proteins. This method was applied to a systems-level dynamic analysis of mammalian circadian clock proteins, which consist of transcription factors and protein kinases that govern central and peripheral circadian clocks in mammals. Sixteen proteins from 20 selected circadian clock proteins were successfully quantified from mouse liver over a 24-h time series, and 14 proteins had circadian variations. Quantified values were applied to detect internal body time using a previously developed molecular timetable method. The analyses showed that single time-point data from wild-type mice can predict the endogenous state of the circadian clock, whereas data from clock mutant mice are not applicable because of the disappearance of circadian variation. PMID:27247408

  16. Robustness from flexibility in the fungal circadian clock

    Directory of Open Access Journals (Sweden)

    Akman Ozgur E

    2010-06-01

    Full Text Available Abstract Background Robustness is a central property of living systems, enabling function to be maintained against environmental perturbations. A key challenge is to identify the structures in biological circuits that confer system-level properties such as robustness. Circadian clocks allow organisms to adapt to the predictable changes of the 24-hour day/night cycle by generating endogenous rhythms that can be entrained to the external cycle. In all organisms, the clock circuits typically comprise multiple interlocked feedback loops controlling the rhythmic expression of key genes. Previously, we showed that such architectures increase the flexibility of the clock's rhythmic behaviour. We now test the relationship between flexibility and robustness, using a mathematical model of the circuit controlling conidiation in the fungus Neurospora crassa. Results The circuit modelled in this work consists of a central negative feedback loop, in which the frequency (frq gene inhibits its transcriptional activator white collar-1 (wc-1, interlocked with a positive feedback loop in which FRQ protein upregulates WC-1 production. Importantly, our model reproduces the observed entrainment of this circuit under light/dark cycles with varying photoperiod and cycle duration. Our simulations show that whilst the level of frq mRNA is driven directly by the light input, the falling phase of FRQ protein, a molecular correlate of conidiation, maintains a constant phase that is uncoupled from the times of dawn and dusk. The model predicts the behaviour of mutants that uncouple WC-1 production from FRQ's positive feedback, and shows that the positive loop enhances the buffering of conidiation phase against seasonal photoperiod changes. This property is quantified using Kitano's measure for the overall robustness of a regulated system output. Further analysis demonstrates that this functional robustness is a consequence of the greater evolutionary flexibility conferred on

  17. Interaction of circadian clock proteins PER2 and CRY with BMAL1 and CLOCK

    Directory of Open Access Journals (Sweden)

    Bordon Alain

    2008-04-01

    Full Text Available Abstract Background Circadian oscillation of clock-controlled gene expression is mainly regulated at the transcriptional level. Heterodimers of CLOCK and BMAL1 act as activators of target gene transcription; however, interactions of PER and CRY proteins with the heterodimer abolish its transcriptional activation capacity. PER and CRY are therefore referred to as negative regulators of the circadian clock. To further elucidate the mechanism how positive and negative components of the clock interplay, we characterized the interactions of PER2, CRY1 and CRY2 with BMAL1 and CLOCK using a mammalian two-hybrid system and co-immunoprecipitation assays. Results Both PER2 and the CRY proteins were found to interact with BMAL1 whereas only PER2 interacts with CLOCK. CRY proteins seem to have a higher affinity to BMAL1 than PER2. Moreover, we provide evidence that PER2, CRY1 and CRY2 bind to different domains in the BMAL1 protein. Conclusion The regulators of clock-controlled transcription PER2, CRY1 and CRY2 differ in their capacity to interact with each single component of the BMAL1-CLOCK heterodimer and, in the case of BMAL1, also in their interaction sites. Our data supports the hypothesis that CRY proteins, especially CRY1, are stronger repressors than PER proteins.

  18. DESIGN OF TWO-PHASE SINUSOIDAL POWER CLOCK AND CLOCKED TRANSMISSION GATE ADIABATIC LOGIC CIRCUIT

    Institute of Scientific and Technical Information of China (English)

    Wang Pengjun; Yu Junjun

    2007-01-01

    First the research is conducted on the design of the two-phase sinusoidal power clock generator in this paper. Then the design of the new adiabatic logic circuit adopting the two-phase sinusoidal power clocks-Clocked Transmission Gate Adiabatic Logic (CTGAL) circuit is presented. This circuit makes use of the clocked transmission gates to sample the input signals, then the output loads are charged and discharged in a fully adiabatic manner by using bootstrapped N-Channel Metal Oxide Semiconductor (NMOS) and Complementary Metal Oxide Semiconductor (CMOS) latch structure.Finally, with the parameters of Taiwan Semiconductor Manufacturing Company (TSMC) 0.25 μm CMOS device, the transient energy consumption of CTGAL, Bootstrap Charge-Recovery Logic (BCRL)and Pass-transistor Adiabatic Logic (PAL) including their clock generators is simulated. The simulation result indicates that CTGAL circuit has the characteristic of remarkably low energy consumption.

  19. Microwave Atomic Clock in the Optical Lattice with Specific Frequency

    International Nuclear Information System (INIS)

    A scheme for a microwave atomic clock is proposed for Cs or Rb atoms trapped in a blue detuned optical lattice. The ac Stark shift of the clock transition due to a trapping laser is calculated. We analyze it at some specific laser wavelength. Compared with the case of the fountain clock, the cavity related shifts, the collision shift and the Doppler effect are eliminated or suppressed dramatically in an atomic lattice clock. By analyzing various sources of clock uncertainty, a microwave atomic lattice clock with a high accuracy and small volume is feasible

  20. Compact, Highly Stable Ion Atomic Clock

    Science.gov (United States)

    Prestage, John

    2008-01-01

    A mercury-ion clock now at the breadboard stage of development (see figure) has a stability comparable to that of a hydrogen-maser clock: In tests, the clock exhibited an Allan deviation of between 2 x 10(exp -13) and 3 x 10(exp -13) at a measurement time of 1 second, averaging to about 10(exp -15) at 1 day. However, the clock occupies a volume of only about 2 liters . about a hundredth of the volume of a hydrogen-maser clock. The ion-handling parts of the apparatus are housed in a sealed vacuum tube, wherein only a getter pump is used to maintain the vacuum. Hence, this apparatus is a prototype of a generation of small, potentially portable high-precision clocks for diverse ground- and space-based navigation and radio science applications. Furthermore, this new ion-clock technology is about 100 times more stable and precise than the rubidium atomic clocks currently in use in the NAV STAR GPS Earth-orbiting satellites. In this clock, mercury ions are shuttled between a quadrupole and a 16-pole linear radio-frequency trap. In the quadrupole trap, the ions are tightly confined and optical state selection from a Hg-202 radio-frequency-discharge ultraviolet lamp is carried out. In the 16-pole trap, the ions are more loosely confined and atomic transitions resonant at frequency of about 40.507 GHz are interrogated by use of a microwave beam at that frequency. The trapping of ions effectively eliminates the frequency pulling caused by wall collisions inherent to gas-cell clocks. The shuttling of the ions between the two traps enables separation of the state-selection process from the clock microwave- resonance process, so that each of these processes can be optimized independently of the other. The basic ion-shuttling, two-trap scheme as described thus far is not new: it has been the basis of designs of prior larger clocks. The novelty of the present development lies in major redesigns of its physics package (the ion traps and the vacuum and optical subsystems) to effect

  1. Dual-wavelength active optical clock

    CERN Document Server

    Xu, Zhichao; Zhuang, Wei; Chen, Jingbiao

    2014-01-01

    We experimentally realize the dual-wavelength active optical clock for the first time. As the Cs cell temperature is kept between 118 $^{\\circ }C$ and 144 $^{\\circ }C$, both the 1359 nm and the 1470 nm stimulated emission output of Cs four-level active optical clock are detected. The 1470 nm output linewidth of each experimental setup of Cs four-level active optical clock is measured to be 590 Hz with the main cavity length unstabilized. To stabilize the cavity length of active optical clock, the experimental scheme of 633 nm and 1359 nm good-bad cavity dual-wavelength active optical clock is proposed, where 633 nm and 1359 nm stimulated emission is working at good-cavity and bad-cavity regime respectively. The cavity length is stabilized by locking the 633 nm output frequency to a super-cavity with the Pound-Drever-Hall (PDH) technique. The frequency stability of 1359 nm bad-cavity stimulated emission output is then expected to be further improved by at least 1 order of magnitude than the 633 nm PDH system d...

  2. Direct laser cooling Al+ ions optical clocks

    CERN Document Server

    Zhang, J; Luo, J; Lu, Z H

    2016-01-01

    Al$^+$ ions optical clock is a very promising optical frequency standard candidate due to its extremely small blackbody radiation shift. It has been successfully demonstrated with indirect cooled, quantum-logic-based spectroscopy technique. Its accuracy is limited by second-order Doppler shift, and its stability is limited by the number of ions that can be probed in quantum logic processing. We propose a direct laser cooling scheme of Al$^+$ ions optical clocks where both the stability and accuracy of the clocks are greatly improved. In the proposed scheme, two Al$^+$ ions traps are utilized. The first trap is used to trap a large number of Al$^+$ ions to improve the stability of the clock laser, while the second trap is used to trap a single Al$^+$ ions to provide the ultimate accuracy. Both traps are cooled with a continuous wave 167 nm laser. The expected clock laser stability can reach $9.0\\times10^{-17}/\\sqrt{\\tau}$. For the second trap, in addition to 167 nm laser Doppler cooling, a second stage pulsed ...

  3. Susceptibility of Redundant Versus Singular Clock Domains Implemented in SRAM-Based FPGA TMR Designs

    Science.gov (United States)

    Berg, Melanie D.; LaBel, Kenneth A.; Pellish, Jonathan

    2016-01-01

    We present the challenges that arise when using redundant clock domains due to their clock-skew. Radiation data show that a singular clock domain (DTMR) provides an improved TMR methodology for SRAM-based FPGAs over redundant clocks.

  4. Quantum clock: A critical discussion on spacetime

    Science.gov (United States)

    Burderi, Luciano; Di Salvo, Tiziana; Iaria, Rosario

    2016-03-01

    We critically discuss the measure of very short time intervals. By means of a Gedankenexperiment, we describe an ideal clock based on the occurrence of completely random events. Many previous thought experiments have suggested fundamental Planck-scale limits on measurements of distance and time. Here we present a new type of thought experiment, based on a different type of clock, that provide further support for the existence of such limits. We show that the minimum time interval Δ t that this clock can measure scales as the inverse of its size Δ r . This implies an uncertainty relation between space and time: Δ r Δ t >G ℏ/c4, where G , ℏ, and c are the gravitational constant, the reduced Planck constant, and the speed of light, respectively. We outline and briefly discuss the implications of this uncertainty conjecture.

  5. Which came first, spacetime or clocks?

    International Nuclear Information System (INIS)

    Emergent quantum mechanics seeks a deeper level theory, anticipating that such a theory will provide a clearer picture of the relation between the quantum and classical worlds. In this work we show that the quantum-classical divide is a manifestation of the transition from Newton's absolute time to relativity's path-dependent time. The prior theory in this case is that particles are intrinsic clocks. The emergence of separate classical and quantum behaviour is seen by considering different continuum limits in a single digital clock model. A continuum limit that constructs a continuous worldline provides a simple basis for Minkowski spacetime. An alternative limit in which the clock itself contains boost information leads to the Dirac equation.

  6. Quantum clock: A critical discussion on spacetime

    CERN Document Server

    Burderi, Luciano; Iaria, Rosario

    2016-01-01

    We critically discuss the measure of very short time intervals. By means of a Gedankenexperiment, we describe an ideal clock based on the occurrence of completely random events. Many previous thought experiments have suggested fundamental Planck-scale limits on measurements of distance and time. Here we present a new type of thought experiment, based on a different type of clock, that provide further support for the existence of such limits. We show that the minimum time interval $\\Delta t$ that this clock can measure scales as the inverse of its size $\\Delta r$. This implies an uncertainty relation between space and time: $\\Delta r$ $\\Delta t$ $> G \\hbar / c^4$; where G, $\\hbar$ and c are the gravitational constant, the reduced Planck constant, and the speed of light, respectively. We outline and briefly discuss the implications of this uncertainty conjecture.

  7. Models of the Primordial Standard Clock

    CERN Document Server

    Chen, Xingang; Wang, Yi

    2014-01-01

    Oscillating massive fields in the primordial universe can be used as Standard Clocks. The ticks of these oscillations induce features in the density perturbations, which directly record the time evolution of the scale factor of the primordial universe, thus if detected, provide a direct evidence for the inflation scenario or the alternatives. In this paper, we construct a full inflationary model of primordial Standard Clock and study its predictions on the density perturbations. This model provides a full realization of several key features proposed previously. We compare the theoretical predictions from inflation and alternative scenarios with the Planck 2013 temperature data on Cosmic Microwave Background (CMB), and identify a statistically marginal but interesting candidate. We discuss how future CMB temperature and polarization data, non-Gaussianity analysis and Large Scale Structure data may be used to further test or constrain the Standard Clock signals.

  8. The Deep Space Atomic Clock Mission

    Science.gov (United States)

    Ely, Todd A.; Koch, Timothy; Kuang, Da; Lee, Karen; Murphy, David; Prestage, John; Tjoelker, Robert; Seubert, Jill

    2012-01-01

    The Deep Space Atomic Clock (DSAC) mission will demonstrate the space flight performance of a small, low-mass, high-stability mercury-ion atomic clock with long term stability and accuracy on par with that of the Deep Space Network. The timing stability introduced by DSAC allows for a 1-Way radiometric tracking paradigm for deep space navigation, with benefits including increased tracking via utilization of the DSN's Multiple Spacecraft Per Aperture (MSPA) capability and full ground station-spacecraft view periods, more accurate radio occultation signals, decreased single-frequency measurement noise, and the possibility for fully autonomous on-board navigation. Specific examples of navigation and radio science benefits to deep space missions are highlighted through simulations of Mars orbiter and Europa flyby missions. Additionally, this paper provides an overview of the mercury-ion trap technology behind DSAC, details of and options for the upcoming 2015/2016 space demonstration, and expected on-orbit clock performance.

  9. Sample-Clock Phase-Control Feedback

    Science.gov (United States)

    Quirk, Kevin J.; Gin, Jonathan W.; Nguyen, Danh H.; Nguyen, Huy

    2012-01-01

    To demodulate a communication signal, a receiver must recover and synchronize to the symbol timing of a received waveform. In a system that utilizes digital sampling, the fidelity of synchronization is limited by the time between the symbol boundary and closest sample time location. To reduce this error, one typically uses a sample clock in excess of the symbol rate in order to provide multiple samples per symbol, thereby lowering the error limit to a fraction of a symbol time. For systems with a large modulation bandwidth, the required sample clock rate is prohibitive due to current technological barriers and processing complexity. With precise control of the phase of the sample clock, one can sample the received signal at times arbitrarily close to the symbol boundary, thus obviating the need, from a synchronization perspective, for multiple samples per symbol. Sample-clock phase-control feedback was developed for use in the demodulation of an optical communication signal, where multi-GHz modulation bandwidths would require prohibitively large sample clock frequencies for rates in excess of the symbol rate. A custom mixedsignal (RF/digital) offset phase-locked loop circuit was developed to control the phase of the 6.4-GHz clock that samples the photon-counting detector output. The offset phase-locked loop is driven by a feedback mechanism that continuously corrects for variation in the symbol time due to motion between the transmitter and receiver as well as oscillator instability. This innovation will allow significant improvements in receiver throughput; for example, the throughput of a pulse-position modulation (PPM) with 16 slots can increase from 188 Mb/s to 1.5 Gb/s.

  10. Clocks, cryptochromes and Monarch migrations

    OpenAIRE

    Kyriacou, Charalambos P.

    2009-01-01

    The annual migration of the Monarch butterfly (Danaus plexippus) from eastern North America to central Mexico is one of nature's most inspiring spectacles. Recent studies including one in BMC Biology, have begun to dissect the molecular and neurogenetic basis for this most complex behavior.

  11. Clocks, cryptochromes and Monarch migrations.

    Science.gov (United States)

    Kyriacou, Charalambos P

    2009-01-01

    The annual migration of the Monarch butterfly (Danaus plexippus) from eastern North America to central Mexico is one of nature's most inspiring spectacles. Recent studies including one in BMC Biology, have begun to dissect the molecular and neurogenetic basis for this most complex behavior. PMID:19591650

  12. The development of clocks into the eighteenth century

    OpenAIRE

    Dugan, David

    2004-01-01

    The advantages of clocks with escapements over water clocks, that they can be miniaturized. The superb chronometers of the seventeenth century onwards, Harrison and others. The emergence of clockmakers and precise engineering. Superb luxury goods. Simon Schaffer explains.

  13. Clocking Scheme for Switched-Capacitor Circuits

    DEFF Research Database (Denmark)

    Steensgaard-Madsen, Jesper

    A novel clocking scheme for switched-capacitor (SC) circuits is presented. It can enhance the understanding of SC circuits and the errors caused by MOSFET (MOS) switches. Charge errors, and techniques to make SC circuits less sensitive to them are discussed.......A novel clocking scheme for switched-capacitor (SC) circuits is presented. It can enhance the understanding of SC circuits and the errors caused by MOSFET (MOS) switches. Charge errors, and techniques to make SC circuits less sensitive to them are discussed....

  14. Caring around the Clock: rounding in practice.

    Science.gov (United States)

    Hutchings, Marie

    A large acute trust in the East Midlands looked to the US to inform its implementation of hourly rounding, otherwise known as intentional rounding. A combination of transformational leadership and meaningful interactions form the basis of a new approach to rounding--Caring around the Clock. The trust piloted the concept on 10 wards with results showing a 32% reduction in call lights. The successful change in practice required an investment in staff education to equip staff with the necessary skills. The trust is currently rolling out Caring around Hourly rounding can reducethe Clock to 79 inpatient wards. PMID:23342834

  15. Clocking Scheme for Switched-Capacitor Circuits

    DEFF Research Database (Denmark)

    Steensgaard-Madsen, Jesper

    1998-01-01

    A novel clocking scheme for switched-capacitor (SC) circuits is presented. It can enhance the understanding of SC circuits and the errors caused by MOSFET (MOS) switches. Charge errors, and techniques to make SC circuits less sensitive to them are discussed.......A novel clocking scheme for switched-capacitor (SC) circuits is presented. It can enhance the understanding of SC circuits and the errors caused by MOSFET (MOS) switches. Charge errors, and techniques to make SC circuits less sensitive to them are discussed....

  16. Entangling the lattice clock: Towards Heisenberg-limited timekeeping

    OpenAIRE

    Weinstein, Jonathan D.; Beloy, Kyle; Derevianko, Andrei

    2009-01-01

    We present a scheme for entangling the atoms of an optical lattice to reduce the quantum projection noise of a clock measurement. The divalent clock atoms are held in a lattice at a ``magic'' wavelength that does not perturb the clock frequency -- to maintain clock accuracy -- while an open-shell J=1/2 ``head'' atom is coherently transported between lattice sites via the lattice polarization. This polarization-dependent ``Archimedes' screw'' transport at magic wavelength takes advantage of th...

  17. 47 CFR 80.865 - Radiotelephone station clock.

    Science.gov (United States)

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false Radiotelephone station clock. 80.865 Section 80.865 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES... W § 80.865 Radiotelephone station clock. A clock having a face of at least 12.7 cm (5 in.)...

  18. On synchronization of clocks in general space-times

    Directory of Open Access Journals (Sweden)

    M. R. H Khajehpour

    2005-09-01

    Full Text Available   Einstein and transport synchronizations of infinitesimally spaced and distant clocks are considered in a general Riemannian space-time. It is shown that infinitesimally spaced clocks can always be synchronized. In general one can not find observers for whom distant clock are Einstein synchronized but transport synchronized observers do always exit. Whenever both procedures are possible, they are equivalent.

  19. Vasopressin and the Output of the Hypothalamic Biological Clock

    NARCIS (Netherlands)

    A. Kalsbeek; E. Fliers; M.A. Hofman; D.F. Swaab; R.M. Buijs

    2010-01-01

    The physiological effects of vasopressin as a peripheral hormone were first reported more than 100 years ago. However, it was not until the first immunocytochemical studies were carried out in the early 1970s, using vasopressin antibodies, and the discovery of an extensive distribution of vasopressi

  20. Probing entrainment of Ostreococcus tauri circadian clock by blue and green light through a mathematical modeling approach

    Directory of Open Access Journals (Sweden)

    Quentin eThommen

    2015-02-01

    Full Text Available Most organisms anticipate daily environmental variations and orchestrate cellular functions thanks to a circadian clock which entrains robustly to the day/night cycle, despite fluctuations in light intensity due to weather or seasonal variations. Marine organisms are also subjected to fluctuations in light spectral composition as their depth varies, due to differential absorption of different wavelengths by sea water. Studying how light input pathways contribute to circadian clock robustness is therefore important.Ostreococcus tauri, a unicellular picoplanktonic marine green alga with low genomic complexity and simple cellular organization, has become a promising model organism for systems biology. Functional and modeling approaches have shown that a core circadian oscillator based on orthologs of Arabidopsis TOC1 and CCA1 clock genes accounts for most experimental data acquired under a wide range of conditions. Some evidence points at putative light input pathway(s consisting of a two-component signaling system (TCS controlled by the only two histidine kinases (HK of O. tauri. LOVHK is a blue light photoreceptor under circadian control, that is required for circadian clock function. An involvement of Rhodopsin-HK (RhodHK is also conceivable since rhodopsin photoreceptors mediate blue to green light input in animal circadian clocks.Here, we probe the role of LOVHK and RhodHK in mediating light input to the TOC1-CCA1 oscillator using a mathematical model incorporating the TCS hypothesis. This model agrees with clock gene expression time series representative of multiple environmental conditions in blue or green light, characterizing entrainment by light/dark cycles, free-running in constant light, and resetting. Experimental and theoretical results indicate that both blue and green light can reset O. tauri circadian clock. Moreover, our mathematical analysis suggests that Rhod-HK is a blue-green light receptor and drives the clock together with

  1. The peripheral clock regulates human pigmentation.

    Science.gov (United States)

    Hardman, Jonathan A; Tobin, Desmond J; Haslam, Iain S; Farjo, Nilofer; Farjo, Bessam; Al-Nuaimi, Yusur; Grimaldi, Benedetto; Paus, Ralf

    2015-04-01

    Although the regulation of pigmentation is well characterized, it remains unclear whether cell-autonomous controls regulate the cyclic on-off switching of pigmentation in the hair follicle (HF). As human HFs and epidermal melanocytes express clock genes and proteins, and given that core clock genes (PER1, BMAL1) modulate human HF cycling, we investigated whether peripheral clock activity influences human HF pigmentation. We found that silencing BMAL1 or PER1 in human HFs increased HF melanin content. Furthermore, tyrosinase expression and activity, as well as TYRP1 and TYRP2 mRNA levels, gp100 protein expression, melanocyte dendricity, and the number gp100+ HF melanocytes, were all significantly increased in BMAL1 and/or PER1-silenced HFs. BMAL1 or PER1 silencing also increased epidermal melanin content, gp100 protein expression, and tyrosinase activity in human skin. These effects reflect direct modulation of melanocytes, as BMAL1 and/or PER1 silencing in isolated melanocytes increased tyrosinase activity and TYRP1/2 expression. Mechanistically, BMAL1 knockdown reduces PER1 transcription, and PER1 silencing induces phosphorylation of the master regulator of melanogenesis, microphthalmia-associated transcription factor, thus stimulating human melanogenesis and melanocyte activity in situ and in vitro. Therefore, the molecular clock operates as a cell-autonomous modulator of human pigmentation and may be targeted for future therapeutic strategies. PMID:25310406

  2. Analytic clock frequency selection for global DVFS

    NARCIS (Netherlands)

    Gerards, Marco E.T.; Hurink, Johann L.; Hölzenspies, Philip K.F.; Kuper, Jan; Smit, Gerard J.M.

    2014-01-01

    Computers can reduce their power consumption by decreasing their speed using Dynamic Voltage and Frequency Scaling (DVFS). A form of DVFS for multicore processors is global DVFS, where the voltage and clock frequency is shared among all processor cores. Because global DVFS is efficient and cheap to

  3. Circadian Clock Regulates Bone Resorption in Mice.

    Science.gov (United States)

    Xu, Cheng; Ochi, Hiroki; Fukuda, Toru; Sato, Shingo; Sunamura, Satoko; Takarada, Takeshi; Hinoi, Eiichi; Okawa, Atsushi; Takeda, Shu

    2016-07-01

    The circadian clock controls many behavioral and physiological processes beyond daily rhythms. Circadian dysfunction increases the risk of cancer, obesity, and cardiovascular and metabolic diseases. Although clinical studies have shown that bone resorption is controlled by circadian rhythm, as indicated by diurnal variations in bone resorption, the molecular mechanism of circadian clock-dependent bone resorption remains unknown. To clarify the role of circadian rhythm in bone resorption, aryl hydrocarbon receptor nuclear translocator-like (Bmal1), a prototype circadian gene, was knocked out specifically in osteoclasts. Osteoclast-specific Bmal1-knockout mice showed a high bone mass phenotype due to reduced osteoclast differentiation. A cell-based assay revealed that BMAL1 upregulated nuclear factor of activated T cells, cytoplasmic, calcineurin-dependent 1 (Nfatc1) transcription through its binding to an E-box element located on the Nfatc1 promoter in cooperation with circadian locomotor output cycles kaput (CLOCK), a heterodimer partner of BMAL1. Moreover, steroid receptor coactivator (SRC) family members were shown to interact with and upregulate BMAL1:CLOCK transcriptional activity. Collectively, these data suggest that bone resorption is controlled by osteoclastic BMAL1 through interactions with the SRC family and binding to the Nfatc1 promoter. © 2016 American Society for Bone and Mineral Research. PMID:26841172

  4. The salient features of the clock

    DEFF Research Database (Denmark)

    Ebbesen, Toke Riis

    2005-01-01

    functional semiotics is explained in short terms and then further demonstrated in the analysis of a basic mechanical alarm clock. On this ground, the digital watch and digital design products in general are characterised and three possible avenues for the interpretation of the interactive possibilities of...

  5. An Iodine Fluorescence Quenching Clock Reaction

    Science.gov (United States)

    Weinberg, Richard B.; Muyskens, Mark

    2007-01-01

    Clock reactions based upon competing oxidation and reduction reactions of iodine and starch as the most popular type of chemistry example is presented to illustrate the redox phenomena, reaction kinetics, and principles of chemical titration. The examination of the photophysical principles underlying the iodine fluorescence quenching clock…

  6. On accelerated clocks and the quantum theory

    International Nuclear Information System (INIS)

    It is shown that the locality hypothesis of relativity breaks down for large proper accelerations which are relevant to semiclassical phenomena. A general modification for the rate of accelerated clocks incorporating the effect of proper acceleration is thus proposed. Connection is made with Caianiello's quantum line element

  7. Clock Synchronization for Multihop Wireless Sensor Networks

    Science.gov (United States)

    Solis Robles, Roberto

    2009-01-01

    In wireless sensor networks, more so generally than in other types of distributed systems, clock synchronization is crucial since by having this service available, several applications such as media access protocols, object tracking, or data fusion, would improve their performance. In this dissertation, we propose a set of algorithms to achieve…

  8. Suppression of clock shifts at field-insensitive transitions

    CERN Document Server

    Arnold, Kyle J

    2016-01-01

    We show that it is possible to significantly reduce quadrupole and tensor polarizability shifts of a clock transition by operating at a judiciously chosen field-insensitive point. In some cases shifts are almost completely eliminated making the transition an effective J = 0 to J = 0 candidate. This significantly improves the feasibility of a recent proposal for clock operation with large ion crystals. For such multi-ion clocks, geometric constraints and selection rules naturally divide clock operation into two categories based on the orientation of the magnetic field. We discuss the limitations imposed on each type and how calibrations might be carried out for clock operation.

  9. Atomic clocks: the atoms as primary time and frequency standards

    International Nuclear Information System (INIS)

    In this article, we present the atomic clock as time and frequency standard and as one of the peaceful uses of atoms for development. In the first part, we present the general principles of time and frequency metrology and the key role of the caesium atom in this field as well as the main applications of atomic clocks. In the second part we introduce the different clock technologies based on Ramsey method, with a focus on atomic beam clocks and atomic fountain clocks. (author)

  10. Next Generation JPL Ultra-Stable Trapped Ion Atomic Clocks

    Science.gov (United States)

    Burt, Eric; Tucker, Blake; Larsen, Kameron; Hamell, Robert; Tjoelker, Robert

    2013-01-01

    Over the past decade, trapped ion atomic clock development at the Jet Propulsion Laboratory (JPL) has focused on two directions: 1) new atomic clock technology for space flight applications that require strict adherence to size, weight, and power requirements, and 2) ultra-stable atomic clocks, usually for terrestrial applications emphasizing ultimate performance. In this paper we present a new ultra-stable trapped ion clock designed, built, and tested in the second category. The first new standard, L10, will be delivered to the Naval Research Laboratory for use in characterizing DoD space clocks.

  11. S-Wave Collisional Frequency Shift of a Fermion Clock

    CERN Document Server

    Hazlett, Eric L; Stites, Ronald W; Gibble, Kurt; O'Hara, Kenneth M

    2012-01-01

    We report an s-wave collisional frequency shift of an atomic clock based on fermions. In contrast to bosons, the fermion clock shift is insensitive to the population difference of the clock states, set by the first pulse area in Ramsey spectroscopy, \\theta_1. The fermion shift instead depends strongly on the second pulse area \\theta_2. It allows the shift to be canceled, nominally at \\theta_2 = \\pi/2, but correlations shift the null to slightly larger \\theta_2. The shift applies to optical lattice clocks and increases with the spatial inhomogeneity of the clock excitation field, naturally large at optical frequencies.

  12. Study on the Distribution of Networked Devices’ Clock Skew

    Directory of Open Access Journals (Sweden)

    Jiao Chengbo

    2011-08-01

    Full Text Available Clock skews of devices on the Internet are viewed as one way delay noise, but their distribution is unknown. We explore the distribution of clock skews to see the conflict probability. In this paper, we introduce an accurate clock skew estimation algorithm to filter inaccurate clock skew estimation by comparing the results between linear programming method and least square fitting. Delay jitter and other noises affect the estimation result. When the difference of two methods is large, the estimation result is unstable and inaccurate, so the estimation result should be dropped. Based on this algorithm, we use traces of real Internet measurements to collect 1825 accurate clock skews of different devices to establish a fingerprint database. Furthermore, we show the distribution of clock skews and comparing conflict probability with different number of devices. The distribution shows that clock skews are diverse, and most of clock skews are in the region of [-100, 100] PPM. The results indicate that when the number of devices is small (<5, clock skews won’t be conflict with each other, so clock skews are good tools to detect faked devices or NAT; When the number of devices increases, the conflict probability increases linearly, so clock skews of different devices can not distinguish each devices effectively.

  13. Expression of clock genes /period/ and /timeless /in the central nervous system of the mediterranean flour moth, Ephestia kuehniella

    Czech Academy of Sciences Publication Activity Database

    Kobelková, Alena; Závodská, Radka; Šauman, Ivo; Bazalová, Olga; Doležel, David

    2015-01-01

    Roč. 30, č. 2 (2015), s. 104-116. ISSN 0748-7304 R&D Projects: GA ČR GC14-32654J Institutional support: RVO:60077344 Keywords : circadian clock * activity rhythms * eclosion rhythm Subject RIV: EB - Genetics ; Molecular Biology Impact factor: 2.774, year: 2014

  14. Intergeneric complementation of a circadian rhythmicity defect : phylogenetic conservation of structure and function of the clock gene frequency

    NARCIS (Netherlands)

    Merrow, Martha W.; Dunlap, Jay C.; Dover, G.

    1994-01-01

    The Neurospora crassa frequency locus encodes a 989 amino acid protein that is a central component, a state variable, of the circadian biological clock. We have determined the sequence of all or part of this protein and surrounding regulatory regions from additional fungi representing three genera a

  15. Clock distribution system for large high altitude air shower observatory

    International Nuclear Information System (INIS)

    In this paper, we report a clock distribution system for Water Cherenkov Detector Arrays (WCDAs) in Large High Altitude Air Shower Observatory (LHAASO) project. The designed electronics system is of high performance in implementing the clock distribution among detectors of a large scale of dimension. Based on Serializer/Deserializer (SerDes) and fiber transmission, the clock distribution system is the modules of central back end to distributed front end. The clock distribution system has been evaluated with a two modules system. While all the four SerDes candidates for clock transmission with jitters below 17 ps, the DS92LV16 has a fixed phase relationship between transmission clock and recovered clock, hence its use in LHAASO WCDAs. (authors)

  16. Satellite virtual atomic clock with pseudorange difference function

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Satellite atomic clocks are the basis of GPS for the control of time and frequency of navigation signals. In the Chinese Area Positioning System (CAPS), a satellite navigation system without the satellite atomic clocks onboard is successfully developed. Thus, the method of time synchronization based on satellite atomic clocks in GPS is not suitable. Satellite virtual atomic clocks are used to implement satellite navigation. With the satellite virtual atomic clocks, the time at which the signals are transmitted from the ground can be delayed into the time that the signals are transmitted from the satellites and the pseudorange measuring can be fulfilled as in GPS. Satellite virtual atomic clocks can implement the navigation, make a pseudorange difference, remove the ephemeris error, and improve the accuracy of navigation positioning. They not only provide a navigation system without satellite clocks, but also a navigation system with pseudorange difference.

  17. Entangling the lattice clock: Towards Heisenberg-limited timekeeping

    CERN Document Server

    Weinstein, Jonathan D; Derevianko, Andrei

    2009-01-01

    We present a scheme for entangling the atoms of an optical lattice to reduce the quantum projection noise of a clock measurement. The divalent clock atoms are held in a lattice at a ``magic'' wavelength that does not perturb the clock frequency -- to maintain clock accuracy -- while an open-shell J=1/2 ``head'' atom is coherently transported between lattice sites via the lattice polarization. This polarization-dependent ``Archimedes' screw'' transport at magic wavelength takes advantage of the vanishing vector polarizability of the scalar, J=0, clock states of bosonic isotopes of divalent atoms. The on-site interactions between the clock atoms and the head atom are used to engineer entanglement and for clock readout.

  18. Optimal implementations for reliable circadian clocks.

    Science.gov (United States)

    Hasegawa, Yoshihiko; Arita, Masanori

    2014-09-01

    Circadian rhythms are acquired through evolution to increase the chances for survival through synchronizing with the daylight cycle. Reliable synchronization is realized through two trade-off properties: regularity to keep time precisely, and entrainability to synchronize the internal time with daylight. We find by using a phase model with multiple inputs that achieving the maximal limit of regularity and entrainability entails many inherent features of the circadian mechanism. At the molecular level, we demonstrate the role sharing of two light inputs, phase advance and delay, as is well observed in mammals. At the behavioral level, the optimal phase-response curve inevitably contains a dead zone, a time during which light pulses neither advance nor delay the clock. We reproduce the results of phase-controlling experiments entrained by two types of periodic light pulses. Our results indicate that circadian clocks are designed optimally for reliable clockwork through evolution. PMID:25238386

  19. Supporting Family Awareness with the Whereabouts Clock

    Science.gov (United States)

    Sellen, Abigail; Taylor, Alex S.; Kaye, Joseph ‘Jofish'; Brown, Barry; Izadi, Shahram

    We report the results of a field trial of a situated awareness device for families called the “Whereabouts Clock”. The Clock displays the location of family members using cellphone data as one of four privacy-preserving, deliberately coarse-grained categories ( HOME, WORK, SCHOOL or ELSEWHERE). The results show that awareness of others through the Clock supports not only family communication and coordination but also more emotive aspects of family life such as reassurance, connectedness, identity and social touch. We discuss how the term “awareness” means many things in practice and highlight the importance of designing not just for family activities, but in order to support the emotional, social and even moral aspects of family life.

  20. The suprachiasmatic nuclei as a seasonal clock.

    Science.gov (United States)

    Coomans, Claudia P; Ramkisoensing, Ashna; Meijer, Johanna H

    2015-04-01

    In mammals, the suprachiasmatic nucleus (SCN) contains a central clock that synchronizes daily (i.e., 24-h) rhythms in physiology and behavior. SCN neurons are cell-autonomous oscillators that act synchronously to produce a coherent circadian rhythm. In addition, the SCN helps regulate seasonal rhythmicity. Photic information is perceived by the SCN and transmitted to the pineal gland, where it regulates melatonin production. Within the SCN, adaptations to changing photoperiod are reflected in changes in neurotransmitters and clock gene expression, resulting in waveform changes in rhythmic electrical activity, a major output of the SCN. Efferent pathways regulate the seasonal timing of breeding and hibernation. In humans, seasonal physiology and behavioral rhythms are also present, and the human SCN has seasonally rhythmic neurotransmitter levels and morphology. In summary, the SCN perceives and encodes changes in day length and drives seasonal changes in downstream pathways and structures in order to adapt to the changing seasons. PMID:25451984

  1. The Large Built Water Clock Of Amphiaraeion.

    Science.gov (United States)

    Theodossiou, E.; Katsiotis, M.; Manimanis, V. N.; Mantarakis, P.

    A very well preserved ancient water clock was discovered during excavations at the Amphiaraeion, in Oropos, Greece. The Amphiaraeion, a famous religious and oracle center of the deified healer Amphiaraus, was active from the pre-classic period until the replacement of the ancient religion by Christianity in the 5th Century A.D.. The foretelling was supposedly done through dreams sent by the god to the believers sleeping in a special gallery. In these dreams the god suggesting to them the therapy for their illness or the solution to their problems. The patients, then threw coins into a spring of the sanctuary. In such a place, the measurement of time was a necessity. Therefore, time was kept with both a conical sundial and a water clock in the form of a fountain. According to archeologists, the large built structure that measured the time for the sanctuary dates from the 4th Century B.C.

  2. Clock drawing performance in cognitively normal elderly

    OpenAIRE

    Hubbard, E J; Santini, V; Blankevoort, C.G.; Volkers, K.M.; Barrup, M.S.; Byerly, L; Chaisson, C.; Jefferson, A.L.; Kaplan, E; Green, R.C.; Stern, R. A.

    2008-01-01

    The Clock Drawing Test (CDT) is a common neuropsychological measure sensitive to cognitive changes and functional skills (e.g., driving test performance) among older adults. However, normative data have not been adequately developed. We report the distribution of CDT scores using three common scoring systems (Mendez, Ala, and Underwood, 1992; Freund, Gravenstein, Ferris, Burke, & Shaheen, 2005; and Cahn, Salmon, Monsch, Butters, Wiederholt, & Corey-Bloom, 1996), among 207 cognitively normal e...

  3. The circadian clock, reward and memory

    OpenAIRE

    Urs eAlbrecht

    2011-01-01

    During our daily activities, we experience variations in our cognitive performance, which is often accompanied by cravings for small rewards, such as consuming coffee or chocolate. This indicates that the time of day, cognitive performance, and reward may be related to one another. This review will summarize data that describe the influence of the circadian clock on addiction and mood-related behavior and put the data into perspective in relation to memory processes.

  4. Absolute clock synchronisation and special relativity paradoxes

    OpenAIRE

    Ciborowski, Jacek; Wlodarczyk, Marta

    2012-01-01

    Solving special relativity paradoxes requires rigorous analysis of event timing, due to relative simultaneity in consequence of the Lorentz transformation. Since clock synchronisation is a convention in special theory of relativity, instead of the Einstein's procedure one may choose such that offers absolute simultaneity. We present in short the corresponding formalism in one spatial dimension. We show that paradoxes do not arise with this choice of synchronisation and descriptions of these i...

  5. Molecular clock in neutral protein evolution

    Directory of Open Access Journals (Sweden)

    Wilke Claus O

    2004-08-01

    Full Text Available Abstract Background A frequent observation in molecular evolution is that amino-acid substitution rates show an index of dispersion (that is, ratio of variance to mean substantially larger than one. This observation has been termed the overdispersed molecular clock. On the basis of in silico protein-evolution experiments, Bastolla and coworkers recently proposed an explanation for this observation: Proteins drift in neutral space, and can temporarily get trapped in regions of substantially reduced neutrality. In these regions, substitution rates are suppressed, which results in an overall substitution process that is not Poissonian. However, the simulation method of Bastolla et al. is representative only for cases in which the product of mutation rate μ and population size Ne is small. How the substitution process behaves when μNe is large is not known. Results Here, I study the behavior of the molecular clock in in silico protein evolution as a function of mutation rate and population size. I find that the index of dispersion decays with increasing μNe, and approaches 1 for large μNe . This observation can be explained with the selective pressure for mutational robustness, which is effective when μNe is large. This pressure keeps the population out of low-neutrality traps, and thus steadies the ticking of the molecular clock. Conclusions The molecular clock in neutral protein evolution can fall into two distinct regimes, a strongly overdispersed one for small μNe, and a mostly Poissonian one for large μNe. The former is relevant for the majority of organisms in the plant and animal kingdom, and the latter may be relevant for RNA viruses.

  6. Regulated DNA Methylation and the Circadian Clock: Implications in Cancer

    Directory of Open Access Journals (Sweden)

    Tammy M. Joska

    2014-09-01

    Full Text Available Since the cloning and discovery of DNA methyltransferases (DNMT, there has been a growing interest in DNA methylation, its role as an epigenetic modification, how it is established and removed, along with the implications in development and disease. In recent years, it has become evident that dynamic DNA methylation accompanies the circadian clock and is found at clock genes in Neurospora, mice and cancer cells. The relationship among the circadian clock, cancer and DNA methylation at clock genes suggests a correlative indication that improper DNA methylation may influence clock gene expression, contributing to the etiology of cancer. The molecular mechanism underlying DNA methylation at clock loci is best studied in the filamentous fungi, Neurospora crassa, and recent data indicate a mechanism analogous to the RNA-dependent DNA methylation (RdDM or RNAi-mediated facultative heterochromatin. Although it is still unclear, DNA methylation at clock genes may function as a terminal modification that serves to prevent the regulated removal of histone modifications. In this capacity, aberrant DNA methylation may serve as a readout of misregulated clock genes and not as the causative agent. This review explores the implications of DNA methylation at clock loci and describes what is currently known regarding the molecular mechanism underlying DNA methylation at circadian clock genes.

  7. Photoperiodic plasticity in circadian clock neurons in insects

    Directory of Open Access Journals (Sweden)

    Sakiko eShiga

    2013-08-01

    Full Text Available Since Bünning’s observation of circadian rhythms and photoperiodism in the runner bean Phaseolus multiflorus in 1936, many studies have shown that photoperiodism is based on the circadian clock system. In insects, involvement of circadian clock genes or neurons has been recently shown in the photoperiodic control of developmental arrests, diapause. Based on molecular and neuronal studies in Drosophila melanogaster, photoperiodic changes have been reported for expression patterns of the circadian clock genes, subcellular distribution of clock proteins, fiber distribution, or the number of plausible clock neurons in different species. Photoperiod sets peaks of per or tim mRNA abundance at lights-off in Sarcophaga crassipalpis, Chymomyza costata and Protophormia terraenovae. Abundance of per and Clock mRNA changes by photoperiod in Pyrrhocoris apterus. Subcellular Per distribution in circadian clock neurons changes with photoperiod in P. terraenovae. Although photoperiodism is not known in Leucophaea maderae, under longer day length, more stomata and longer commissural fibers of circadian clock neurons have been found. These plastic changes in the circadian clock neurons could be an important constituent for photoperiodic clock mechanisms to integrate repetitive photoperiodic information and produce different outputs based on day length.

  8. Clock drawing performance in cognitively normal elderly.

    Science.gov (United States)

    Hubbard, Emily J; Santini, Veronica; Blankevoort, Christiaan G; Volkers, Karin M; Barrup, Melissa S; Byerly, Laura; Chaisson, Christine; Jefferson, Angela L; Kaplan, Edith; Green, Robert C; Stern, Robert A

    2008-05-01

    The Clock Drawing Test (CDT) is a common neuropsychological measure sensitive to cognitive changes and functional skills (e.g., driving test performance) among older adults. However, normative data have not been adequately developed. We report the distribution of CDT scores using three common scoring systems [Mendez, M. F., Ala, T., & Underwood, K. L. (1992). Development of scoring criteria for the Clock Drawing Task in Alzheimer's Disease. Journal of the American Geriatrics Society, 40, 1095-1099; Cahn, D. A., Salmon, D. P., Monsch, A. U., Butters, N., Wiederholt, W. C., & Corey-Bloom, J. (1996). Screening for dementia of the Alzheimer type in the community: The utility of the Clock Drawing Test. Archives of Clinical Neuropsychology, 11(6), 529-539], among 207 cognitively normal elderly. The systems were well correlated, took little time to use, and had high inter-rater reliability. We found statistically significant differences in CDT scores based on age and WRAT-3 Reading score, a marker of education quality. We present means, standard deviations, and t- and z-scores based on these subgroups. We found that "normal" CDT performance includes a wider distribution of scores than previously reported. Our results may serve as useful comparisons for clinicians wishing to know whether their patients perform in the general range of cognitively normal elderly. PMID:18243644

  9. A microresonator frequency comb optical clock

    CERN Document Server

    Papp, Scott B; DelHaye, Pascal; Quinlan, Franklyn; Lee, Hansuek; Vahala, Kerry J; Diddams, Scott A

    2013-01-01

    Optical-frequency combs enable measurement precision at the 20th digit, and accuracy entirely commensurate with their reference oscillator. A new direction in experiments is the creation of ultracompact frequency combs by way of nonlinear parametric optics in microresonators. We refer to these as microcombs, and here we report a silicon-chip-based microcomb optical clock that phase-coherently converts an optical-frequency reference to a microwave signal. A low-noise comb spectrum with 25 THz span is generated with a 2 mm diameter silica disk and broadening in nonlinear fiber. This spectrum is stabilized to rubidium frequency references separated by 3.5 THz by controlling two teeth 108 modes apart. The optical clocks output is the electronically countable 33 GHz microcomb line spacing, which features an absolute stability better than the rubidium transitions by the expected factor of 108. Our work demonstrates the comprehensive set of tools needed for interfacing microcombs to state-of-the-art optical clocks.

  10. Quantum mechanics, matter waves, and moving clocks

    CERN Document Server

    Mueller, Holger

    2013-01-01

    This paper is divided into three parts. In the first (section 1), we demonstrate that all of quantum mechanics can be derived from the fundamental property that the propagation of a matter wave packet is described by the same gravitational and kinematic time dilation that applies to a clock. We will do so in several steps, first deriving the Schroedinger equation for a nonrelativistic particle without spin in a weak gravitational potential, and eventually the Dirac equation in curved space-time describing the propagation of a relativistic particle with spin in strong gravity. In the second part (sections 2-4), we present interesting consequences of the above quantum mechanics: that it is possible to use wave packets as a reference for a clock, to test general relativity, and to realize a mass standard based on a proposed redefinition of the international system of units, wherein the Planck constant would be assigned a fixed value. The clock achieved an absolute accuracy of 4 parts per billion (ppb). The exper...

  11. Atomic Clocks with Suppressed Blackbody Radiation Shift

    International Nuclear Information System (INIS)

    We develop a concept of atomic clocks where the blackbody radiation shift and its fluctuations can be suppressed by 1-3 orders of magnitude independent of the environmental temperature. The suppression is based on the fact that in a system with two accessible clock transitions (with frequencies ν1 and ν2) which are exposed to the same thermal environment, there exists a 'synthetic' frequency νsyn ∝ (ν1-ε12ν2) largely immune to the blackbody radiation shift. For example, in the case of 171Yb+ it is possible to create a synthetic-frequency-based clock in which the fractional blackbody radiation shift can be suppressed to the level of 10-18 in a broad interval near room temperature (300±15 K). We also propose a realization of our method with the use of an optical frequency comb generator stabilized to both frequencies ν1 and ν2, where the frequency νsyn is generated as one of the components of the comb spectrum.

  12. Characterization and modeling of intermittent locomotor dynamics in clock gene-deficient mice.

    Directory of Open Access Journals (Sweden)

    Toru Nakamura

    Full Text Available The scale-invariant and intermittent dynamics of animal behavior are attracting scientific interest. Recent findings concerning the statistical laws of behavioral organization shared between healthy humans and wild-type mice (WT and their alterations in human depression patients and circadian clock gene (Period 2; Per2 mutant mice indicate that clock genes play functional roles in intermittent, ultradian locomotor dynamics. They also claim the clinical and biological importance of the laws as objective biobehavioral measures or endophenotypes for psychiatric disorders. In this study, to elucidate the roles of breakdown of the broader circadian regulatory circuit in intermittent behavioral dynamics, we studied the statistical properties and rhythmicity of locomotor activity in Per2 mutants and mice deficient in other clock genes (Bmal1, Clock. We performed wavelet analysis to examine circadian and ultradian rhythms and estimated the cumulative distributions of resting period durations during which locomotor activity levels are continuously lower than a predefined threshold value. The wavelet analysis revealed significant amplification of ultradian rhythms in the BMAL1-deficient mice, and instability in the Per2 mutants. The resting period distributions followed a power-law form in all mice. While the distributions for the BMAL1-deficient and Clock mutant mice were almost identical to those for the WT mice, with no significant differences in their parameter (power-law scaling exponent, only the Per2 mutant mice showed consistently and significantly lower values of the scaling exponent, indicating the increased intermittency in ultradian locomotor dynamics. Furthermore, based on a stochastic priority queuing model, we explained the power-law nature of resting period distributions, as well as its alterations shared with human depressive patients and Per2 mutant mice. Our findings lead to the development of a novel mathematical model for abnormal

  13. Telomere biology in healthy aging and disease

    NARCIS (Netherlands)

    Oeseburg, Hisko; de Boer, Rudolf A.; van Gilst, Wiek H.; van der Harst, Pim

    2010-01-01

    Aging is a biological process that affects most cells, organisms and species. Telomeres have been postulated as a universal biological clock that shortens in parallel with aging in cells. Telomeres are located at the end of the chromosomes and consist of an evolutionary conserved repetitive nucleoti

  14. The functional interplay between protein kinase CK2 and CCA1 transcriptional activity is essential for clock temperature compensation in Arabidopsis.

    Directory of Open Access Journals (Sweden)

    Sergi Portolés

    2010-11-01

    Full Text Available Circadian rhythms are daily biological oscillations driven by an endogenous mechanism known as circadian clock. The protein kinase CK2 is one of the few clock components that is evolutionary conserved among different taxonomic groups. CK2 regulates the stability and nuclear localization of essential clock proteins in mammals, fungi, and insects. Two CK2 regulatory subunits, CKB3 and CKB4, have been also linked with the Arabidopsis thaliana circadian system. However, the biological relevance and the precise mechanisms of CK2 function within the plant clockwork are not known. By using ChIP and Double-ChIP experiments together with in vivo luminescence assays at different temperatures, we were able to identify a temperature-dependent function for CK2 modulating circadian period length. Our study uncovers a previously unpredicted mechanism for CK2 antagonizing the key clock regulator CIRCADIAN CLOCK-ASSOCIATED 1 (CCA1. CK2 activity does not alter protein accumulation or subcellular localization but interferes with CCA1 binding affinity to the promoters of the oscillator genes. High temperatures enhance the CCA1 binding activity, which is precisely counterbalanced by the CK2 opposing function. Altering this balance by over-expression, mutation, or pharmacological inhibition affects the temperature compensation profile, providing a mechanism by which plants regulate circadian period at changing temperatures. Therefore, our study establishes a new model demonstrating that two opposing and temperature-dependent activities (CCA1-CK2 are essential for clock temperature compensation in Arabidopsis.

  15. On the clock paradox in the case of circular motion of the moving clock

    International Nuclear Information System (INIS)

    Very often in many textbooks the formalism of the general theory of relativity is applied to gravitational problems. We think that it would be didactically useful to show how it can be adopted also for describing physical situations in accelerated frames of reference by working out in detail a particular case. This choice will also offer an opportunity to discuss a classical topic of relativistic physics. Indeed, we deal analytically with a version of the so-called clock paradox in which the moving clock performs a circular motion. The rest clock is denoted as (1), the rotating clock is (2), the inertial frame in which (1) is at rest and (2) moves is I and, finally, the accelerated frame in which (2) is at rest and (1) rotates is A. By using the general theory of relativity in order to describe the motion of (1) as seen in A we will show the following features. (I) A differential ageing between (1) and (2) occurs at their reunion and it has an absolute character, i.e. the proper time interval measured by a given clock is the same both in I and in A. (II) From a quantitative point of view, the magnitude of the differential ageing between (1) and (2) does depend on the kind of rotational motion performed by A. Indeed, if it is uniform there is no tangential force in the direction of motion of (2) but only normal to it. In this case, the proper time interval reckoned by (2) does depend only on its constant velocity v = rω. In contrast, if the rotational motion is uniformly accelerated, i.e. a constant force acts tangentially along the direction of motion, the proper time intervals do depend on the angular acceleration α. (III) Finally, in regard to the sign of the ageing, the moving clock (2) always measures a shorter interval of proper time with respect to (1)

  16. α1B-Adrenergic receptor signaling controls circadian expression of Tnfrsf11b by regulating clock genes in osteoblasts

    Directory of Open Access Journals (Sweden)

    Takao Hirai

    2015-11-01

    Full Text Available Circadian clocks are endogenous and biological oscillations that occur with a period of <24 h. In mammals, the central circadian pacemaker is localized in the suprachiasmatic nucleus (SCN and is linked to peripheral tissues through neural and hormonal signals. In the present study, we investigated the physiological function of the molecular clock on bone remodeling. The results of loss-of-function and gain-of-function experiments both indicated that the rhythmic expression of Tnfrsf11b, which encodes osteoprotegerin (OPG, was regulated by Bmal1 in MC3T3-E1 cells. We also showed that REV-ERBα negatively regulated Tnfrsf11b as well as Bmal1 in MC3T3-E1 cells. We systematically investigated the relationship between the sympathetic nervous system and the circadian clock in osteoblasts. The administration of phenylephrine, a nonspecific α1-adrenergic receptor (AR agonist, stimulated the expression of Tnfrsf11b, whereas the genetic ablation of α1B-AR signaling led to the alteration of Tnfrsf11b expression concomitant with Bmal1 and Per2 in bone. Thus, this study demonstrated that the circadian regulation of Tnfrsf11b was regulated by the clock genes encoding REV-ERBα (Nr1d1 and Bmal1 (Bmal1, also known as Arntl, which are components of the core loop of the circadian clock in osteoblasts.

  17. The Effects of Clock Drift on the Mars Exploration Rovers

    Science.gov (United States)

    Ali, Khaled S.; Vanelli, C. Anthony

    2012-01-01

    All clocks drift by some amount, and the mission clock on the Mars Exploration Rovers (MER) is no exception. The mission clock on both MER rovers drifted significantly since the rovers were launched, and it is still drifting on the Opportunity rover. The drift rate is temperature dependent. Clock drift causes problems for onboard behaviors and spacecraft operations, such as attitude estimation, driving, operation of the robotic arm, pointing for imaging, power analysis, and telecom analysis. The MER operations team has techniques to deal with some of these problems. There are a few techniques for reducing and eliminating the clock drift, but each has drawbacks. This paper presents an explanation of what is meant by clock drift on the rovers, its relationship to temperature, how we measure it, what problems it causes, how we deal with those problems, and techniques for reducing the drift.

  18. Synthetic Spin-Orbit Coupling in an Optical Lattice Clock

    Science.gov (United States)

    Wall, Michael L.; Koller, Andrew P.; Li, Shuming; Zhang, Xibo; Cooper, Nigel R.; Ye, Jun; Rey, Ana Maria

    2016-01-01

    We propose the use of optical lattice clocks operated with fermionic alkaline-earth atoms to study spin-orbit coupling (SOC) in interacting many-body systems. The SOC emerges naturally during the clock interrogation, when atoms are allowed to tunnel and accumulate a phase set by the ratio of the "magic" lattice wavelength to the clock transition wavelength. We demonstrate how standard protocols such as Rabi and Ramsey spectroscopy that take advantage of the sub-Hertz resolution of state-of-the-art clock lasers can perform momentum-resolved band tomography and determine SOC-induced s -wave collisions in nuclear-spin-polarized fermions. With the use of a second counterpropagating clock beam, we propose a method for engineering controlled atomic transport and study how it is modified by p - and s -wave interactions. The proposed spectroscopic probes provide clean and well-resolved signatures at current clock operating temperatures.

  19. Realization of a time-scale with an optical clock

    CERN Document Server

    Grebing, C; Dörscher, S; Häfner, S; Gerginov, V; Weyers, S; Lipphardt, B; Riehle, F; Sterr, U; Lisdat, C

    2015-01-01

    Optical clocks are not only powerful tools for prime fundamental research, but are also deemed for the re-definition of the SI base unit second as they surpass the performance of caesium atomic clocks in both accuracy and stability by more than an order of magnitude. However, an important obstacle in this transition has so far been the limited reliability of the optical clocks that made a continuous realization of a time-scale impractical. In this paper, we demonstrate how this dilemma can be resolved and that a time-scale based on an optical clock can be established that is superior to one based on even the best caesium fountain clocks. The paper also gives further proof of the international consistency of strontium lattice clocks on the $10^{-16}$ accuracy level, which is another prerequisite for a change in the definition of the second.

  20. Clock Auto-synchronizing Method for BES III ETOF Upgrade

    CERN Document Server

    Si-Yu, Wang; Shu-Bin, Liu; Qi, An

    2015-01-01

    An automatic clock synchronizing method implemented in field programmable gate array (FPGA) is proposed in this paper. It is developed for the clock system which will be applied in the end-cap time of flight (ETOF) upgrade of the Beijing Spectrometer (BESIII). In this design, an FPGA is used to automatically monitor the synchronization circuit and deal with signals coming from external clock synchronization circuit. By testing different delay time of the detection signal and analyzing state signals returned, the synchronization windows will be found automatically in FPGA. The new clock system not only retains low clock jitter which is less than 20ps root mean square (RMS), but also demonstrates automatic synchronization to the beam bunches. So far, the clock auto-synchronizing function has been working successfully under a series of tests. It will greatly simplify the system initialization and maintenance in the future.

  1. A clock network for geodesy and fundamental science

    CERN Document Server

    Lisdat, C; Quintin, N; Shi, C; Raupach, S M F; Grebing, C; Nicolodi, D; Stefani, F; Al-Masoudi, A; Dörscher, S; Häfner, S; Robyr, J -L; Chiodo, N; Bilicki, S; Bookjans, E; Koczwara, A; Koke, S; Kuhl, A; Wiotte, F; Meynadier, F; Camisard, E; Abgrall, M; Lours, M; Legero, T; Schnatz, H; Sterr, U; Denker, H; Chardonnet, C; Coq, Y Le; Santarelli, G; Amy-Klein, A; Targat, R Le; Lodewyck, J; Lopez, O; Pottie, P -E

    2015-01-01

    Leveraging the unrivaled performance of optical clocks in applications in fundamental physics beyond the standard model, in geo-sciences, and in astronomy requires comparing the frequency of distant optical clocks truthfully. Meeting this requirement, we report on the first comparison and agreement of fully independent optical clocks separated by 700 km being only limited by the uncertainties of the clocks themselves. This is achieved by a phase-coherent optical frequency transfer via a 1415 km long telecom fiber link that enables substantially better precision than classical means of frequency transfer. The fractional precision in comparing the optical clocks of three parts in $10^{17}$ was reached after only 1000 s averaging time, which is already 10 times better and more than four orders of magnitude faster than with any other existing frequency transfer method. The capability of performing high resolution international clock comparisons paves the way for a redefinition of the unit of time and an all-optic...

  2. Electromagnetic synchronisation of clocks with finite separation in a rotating system

    International Nuclear Information System (INIS)

    For clocks on the vertices of a triangle, it is shown that clock synchronisation using electromagnetic signals between finitely spaced clocks in a rotating frame leads to the same synchronisation error as a closely spaced band of clocks along the same light path. In addition, the above result is generalised to n equally spaced clocks. (author)

  3. A Blind Circadian Clock in Cavefish Reveals that Opsins Mediate Peripheral Clock Photoreception

    OpenAIRE

    Cavallari, N; E.Frigato; Vallone, D.; N.Fröhlich; J.F. Lopez-Olmeda; A.Foà; R.De Berti; Sánchez-Vázquez, F. J.; C.Bertolucci; Foulkes, N S

    2011-01-01

    The circadian clock is a physiological timing mechanism that allows organisms to anticipate and adapt to the day-night cycle. Since it ticks with a period that is not precisely 24 h, it is vital that it is reset on a daily basis by signals such as light to ensure that it remains synchronized with the day-night cycle. The molecular mechanisms whereby light regulates the clock remain incompletely understood. Here we have studied a cavefish that has evolved for millions of years in the perpetual...

  4. Clock rates, clock settings and the physics of the space-time Lorentz transformation

    CERN Document Server

    Field, J H

    2006-01-01

    A careful study is made of the operational meaning of the time symbols appearing in the space-time Lorentz transformation. Four distinct symbols, with different physical meanings, are needed to describe reciprocal measurements involving stationary and uniformly-moving clocks. Physical predictions concern only the observed rate of a clock as a function of its relative speed, not its setting. How the failure to make this distinction leads to the conventional predictions of spurious `relativity of simultaneity' and `length contraction' effects in special relativity is explained.

  5. Atomic fountains and optical clocks at SYRTE: status and perspectives

    CERN Document Server

    Abgrall, M; De Sarlo, L; Guéna, J; Laurent, Ph; Coq, Y Le; Targat, R Le; Lodewyck, J; Lours, M; Rosenbusch, P; Rovera, D; Bize, S

    2015-01-01

    In this article, we report on the work done with the LNE-SYRTE atomic clock ensemble during the last 10 years. We cover progress made in atomic fountains and in their application to timekeeping. We also cover the development of optical lattice clocks based on strontium and on mercury. We report on tests of fundamental physical laws made with these highly accurate atomic clocks. We also report on work relevant to a future possible redefinition of the SI second.

  6. Clocks and dynamics in quantum models of gravity

    OpenAIRE

    Malkiewicz, Przemyslaw

    2016-01-01

    We investigate how the quantum dynamics of gravitational models depend on the clocks employed in quantization procedure. Our previous result demonstrates that almost all physical features of quantum cosmological bounces depend on the choice of clock. The vital question whether all the quantum (or, semiclassical) solutions admit, away from the quantum interaction region in the far past and future, invariant asymptotic limits irrespectively of the clock's choice is addressed herein. We analyze ...

  7. The Clock-Proxy Auction: A Practical Combinatorial Auction Design

    OpenAIRE

    Lawrence M. Ausubel; Peter Cramton; Paul Milgrom

    2004-01-01

    We propose the clock-proxy auction as a practical means for auctioning many related items. A clock auction phase is followed by a last-and-final proxy round. The approach combines the simple and transparent price discovery of the clock auction with the efficiency of the proxy auction. Linear pricing is maintained as long as possible, but then is abandoned in the proxy round to improve efficiency and enhance seller revenues. The approach has many advantages over the simultaneous ascending auct...

  8. Gated Clock Implementation of Arithmetic Logic Unit (ALU)

    OpenAIRE

    Dr. Neelam R. Prakash; Akash

    2013-01-01

    Low power design has emerged as one of the challenging area in today’s ASIC (Application specific integrated circuit) design. With continuous decrease in transistor size, power density is increasing and there is an urgent need for reduction in total power consumption. Clock gating is one most effective technique for low power synchronous circuit design. Clock gating technique in low power design is used to reduce the dynamic power consumption. Clock signal in a synchronous circuit is used for...

  9. Relativity theory and time perception: single or multiple clocks?

    Directory of Open Access Journals (Sweden)

    Catalin V Buhusi

    Full Text Available BACKGROUND: Current theories of interval timing assume that humans and other animals time as if using a single, absolute stopwatch that can be stopped or reset on command. Here we evaluate the alternative view that psychological time is represented by multiple clocks, and that these clocks create separate temporal contexts by which duration is judged in a relative manner. Two predictions of the multiple-clock hypothesis were tested. First, that the multiple clocks can be manipulated (stopped and/or reset independently. Second, that an event of a given physical duration would be perceived as having different durations in different temporal contexts, i.e., would be judged differently by each clock. METHODOLOGY/PRINCIPAL FINDINGS: Rats were trained to time three durations (e.g., 10, 30, and 90 s. When timing was interrupted by an unexpected gap in the signal, rats reset the clock used to time the "short" duration, stopped the "medium" duration clock, and continued to run the "long" duration clock. When the duration of the gap was manipulated, the rats reset these clocks in a hierarchical order, first the "short", then the "medium", and finally the "long" clock. Quantitative modeling assuming re-allocation of cognitive resources in proportion to the relative duration of the gap to the multiple, simultaneously timed event durations was used to account for the results. CONCLUSIONS/SIGNIFICANCE: These results indicate that the three event durations were effectively timed by separate clocks operated independently, and that the same gap duration was judged relative to these three temporal contexts. Results suggest that the brain processes the duration of an event in a manner similar to Einstein's special relativity theory: A given time interval is registered differently by independent clocks dependent upon the context.

  10. AMPK at the crossroads of circadian clocks and metabolism

    OpenAIRE

    Jordan, Sabine D.; Lamia, Katja A.

    2012-01-01

    Circadian clocks coordinate behavior and physiology with daily environmental cycles and thereby optimize the timing of metabolic processes such as glucose production and insulin secretion. Such circadian regulation of metabolism provides an adaptive advantage in diverse organisms. Mammalian clocks are primarily based on a transcription and translation feedback loop in which a heterodimeric complex of the transcription factors CLOCK (circadian locomotor output cycles kaput) and BMAL1 (brain an...

  11. Molecular clocks and the human condition: approaching their characterization in human physiology and disease.

    Science.gov (United States)

    Fitzgerald, G A; Yang, G; Paschos, G K; Liang, X; Skarke, C

    2015-09-01

    Molecular clockworks knit together diverse biological networks and compelling evidence from model systems infers their importance in metabolism, immunological and cardiovascular function. Despite this and the diurnal variation in many aspects of human physiology and the phenotypic expression of disease, our understanding of the role and importance of clock function and dysfunction in humans is modest. There are tantalizing hints of connection across the translational divide and some correlative evidence of gene variation and human disease but most of what we know derives from forced desynchrony protocols in controlled environments. We now have the ability to monitor quantitatively ex vivo or in vivo the genome, metabolome, proteome and microbiome of humans in the wild. Combining this capability, with the power of mobile telephony and the evolution of remote sensing, affords a new opportunity for deep phenotyping, including the characterization of diurnal behaviour and the assessment of the impact of the clock on approved drug function. PMID:26332979

  12. Power and Skew Aware Point Diffusion Clock Network

    Science.gov (United States)

    Jung, Gunok; Kim, Chunghee; Chae, Kyoungkuk; Park, Giho; Park, Sung Bae

    This letter presents point diffusion clock network (PDCN) with local clock tree synthesis (CTS) scheme. The clock network is implemented with ten times wider metal line space than typical mesh networks for low power and utilized to nine times smaller area CTS execution for minimized clock skew amount. The measurement results show that skew amount of PDCN with local CTS is reduced to 36% and latency is shrunk to 45% of the amount in a 4.81mm2 CortexA-8 core with 65nm Samsung process.

  13. Real-time geopotentiometry with synchronously linked optical lattice clocks

    CERN Document Server

    Takano, Tetsushi; Ushijima, Ichiro; Ohmae, Noriaki; Akatsuka, Tomoya; Yamaguchi, Atsushi; Kuroishi, Yuki; Munekane, Hiroshi; Miyahara, Basara; Katori, Hidetoshi

    2016-01-01

    According to the Einstein's theory of relativity, the passage of time changes in a gravitational field. On earth, raising a clock by one centimetre increases its tick rate by 1.1 parts in 10$^{18}$, enabling optical clocks to perform precision geodesy. Here, we demonstrate geopotentiometry by determining the height difference of master and slave clocks separated by 15 km with uncertainty of 5 cm. The subharmonic of the master clock is delivered through a telecom fibre to phase-lock and synchronously interrogate the slave clock. This protocol rejects laser noise in the comparison of two clocks, which improves the stability of measuring the gravitational red shift. Such phase-coherently operated clocks facilitate proposals for linking clocks and interferometers. Over half a year, 11 measurements determine the fractional frequency difference between the two clocks to be $1,652.9(5.9)\\times 10^{-18}$, or a height difference of 1,516(5) cm, consistent with an independent measurement by levelling and gravimetry. Ou...

  14. Temperature regulates transcription in the zebrafish circadian clock.

    Directory of Open Access Journals (Sweden)

    2005-11-01

    Full Text Available It has been well-documented that temperature influences key aspects of the circadian clock. Temperature cycles entrain the clock, while the period length of the circadian cycle is adjusted so that it remains relatively constant over a wide range of temperatures (temperature compensation. In vertebrates, the molecular basis of these properties is poorly understood. Here, using the zebrafish as an ectothermic model, we demonstrate first that in the absence of light, exposure of embryos and primary cell lines to temperature cycles entrains circadian rhythms of clock gene expression. Temperature steps drive changes in the basal expression of certain clock genes in a gene-specific manner, a mechanism potentially contributing to entrainment. In the case of the per4 gene, while E-box promoter elements mediate circadian clock regulation, they do not direct the temperature-driven changes in transcription. Second, by studying E-box-regulated transcription as a reporter of the core clock mechanism, we reveal that the zebrafish clock is temperature-compensated. In addition, temperature strongly influences the amplitude of circadian transcriptional rhythms during and following entrainment by light-dark cycles, a property that could confer temperature compensation. Finally, we show temperature-dependent changes in the expression levels, phosphorylation, and function of the clock protein, CLK. This suggests a mechanism that could account for changes in the amplitude of the E-box-directed rhythm. Together, our results imply that several key transcriptional regulatory elements at the core of the zebrafish clock respond to temperature.

  15. The role of the mechanical clock in medieval science.

    Science.gov (United States)

    Álvarez, Víctor Pérez

    2015-03-01

    The invention and spread of the mechanical clock is a complex and multifaceted historical phenomenon. Some of these facets, such as its social impact, have been widely studied, but their scientific dimensions have often been dismissed. The mechanical clock was probably born as a scientific instrument for driving a model of the universe, and not only natural philosophers but also kings, nobles and other members of the social elites showed an interest in clocks as scientific instruments. Public clocks later spread a new way of telling time based on equal hours, laying the foundations for changes in time consciousness that would accelerate scientific thinking. PMID:25802023

  16. The Space Optical Clocks Project: Development of high-performance transportable and breadboard optical clocks and advanced subsystems

    CERN Document Server

    Schiller, S; Nevsky, A; Alighanbari, S; Vasilyev, S; Abou-Jaoudeh, C; Mura, G; Franzen, T; Sterr, U; Falke, S; Lisdat, Ch; Rasel, E; Kulosa, A; Bize, S; Lodewyck, J; Tino, G M; Poli, N; Schioppo, M; Bongs, K; Singh, Y; Gill, P; Barwood, G; Ovchinnikov, Y; Stuhler, J; Kaenders, W; Braxmaier, C; Holzwarth, R; Donati, A; Lecomte, S; Calonico, D; Levi, F

    2012-01-01

    The use of ultra-precise optical clocks in space ("master clocks") will allow for a range of new applications in the fields of fundamental physics (tests of Einstein's theory of General Relativity, time and frequency metrology by means of the comparison of distant terrestrial clocks), geophysics (mapping of the gravitational potential of Earth), and astronomy (providing local oscillators for radio ranging and interferometry in space). Within the ELIPS-3 program of ESA, the "Space Optical Clocks" (SOC) project aims to install and to operate an optical lattice clock on the ISS towards the end of this decade, as a natural follow-on to the ACES mission, improving its performance by at least one order of magnitude. The payload is planned to include an optical lattice clock, as well as a frequency comb, a microwave link, and an optical link for comparisons of the ISS clock with ground clocks located in several countries and continents. Undertaking a necessary step towards optical clocks in space, the EU-FP7-SPACE-2...

  17. Clocks underneath: the role of peripheral clocks in the timing of female reproductive physiology

    Directory of Open Access Journals (Sweden)

    MichaelTSellix

    2013-07-01

    Full Text Available The central circadian pacemaker in the suprachiasmatic nucleus (SCN is a critical component of the neuroendocrine circuit controlling gonadotropin secretion from the pituitary gland. The SCN conveys photic information to hypothalamic targets including the gonadotropin releasing hormone (GnRH neurons. Many of these target cells are also cell autonomous clocks. It has been suggested that, rather then being singularly driven by the SCN, the timing of gonadotropin secretion depends on the activity of multiple hypothalamic oscillators. While this view provides a novel twist to an old story, it does little to diminish the central role of rhythmic hypothalamic output in this system. It is now clear that the pituitary, ovary, uterus and oviduct have functional molecular clocks. Evidence supports the notion that the clocks in these tissues contribute to the timing of events in reproductive physiology. The goal of this review is to highlight the current evidence for molecular clock function in the peripheral components of the female hypothalamo-pituitary-gonadal (HPG axis as it relates to the timing of gonadotropin secretion, ovulation and parturition.

  18. An association between clock genes and clock-controlled cell cycle genes in murine colorectal tumors

    Czech Academy of Sciences Publication Activity Database

    Soták, Matúš; Polidarová, Lenka; Ergang, Peter; Sumová, Alena; Pácha, Jiří

    2013-01-01

    Roč. 132, č. 5 (2013), s. 1032-1041. ISSN 0020-7136 R&D Projects: GA MZd(CZ) NS9982 Institutional research plan: CEZ:AV0Z50110509 Keywords : cancer * circadian rhythm * peripheral circadian clock Subject RIV: FE - Other Internal Medicine Disciplines Impact factor: 5.007, year: 2013

  19. Polarizabilities of the beryllium clock transition

    International Nuclear Information System (INIS)

    The polarizabilities of the three lowest states of the beryllium atom are determined from a large basis configuration interaction calculation. The polarizabilities of the 2s21Se ground state (37.73a03) and the 2s2p 3P0o metastable state (39.04a03) are found to be very similar in size and magnitude. This leads to an anomalously small blackbody radiation shift at 300 K of -0.018(4) Hz for the 2s21Se-2s2p 3P0o clock transition. Magic wavelengths for simultaneous trapping of the ground and metastable states are also computed.

  20. Grand-mother clocks and quiet lasers

    OpenAIRE

    Arnaud, Jacques; Chusseau, Laurent; Philippe, Fabrice

    2009-01-01

    7 pages Galileo noted in the 16th century that the period of oscillation of a pendulum is almost independent of the amplitude. However, such a pendulum is damped by air friction. The latter may be viewed as resulting from air molecules getting in contact with the pendulum. It follows that air friction, not only damps the oscillation, but also introduces randomness. In the so-called ``grand-mother'' clock, discovered by Huygens in the 18th century, damping is compensated for, on the average...

  1. A precise clock distribution network for MRPC-based experiments

    Science.gov (United States)

    Wang, S.; Cao, P.; Shang, L.; An, Q.

    2016-06-01

    In high energy physics experiments, the MRPC (Multi-Gap Resistive Plate Chamber) detectors are widely used recently which can provide higher-resolution measurement for particle identification. However, the application of MRPC detectors leads to a series of challenges in electronics design with large number of front-end electronic channels, especially for distributing clock precisely. To deal with these challenges, this paper presents a universal scheme of clock transmission network for MRPC-based experiments with advantages of both precise clock distribution and global command synchronization. For precise clock distributing, the clock network is designed into a tree architecture with two stages: the first one has a point-to-multipoint long range bidirectional distribution with optical channels and the second one has a fan-out structure with copper link inside readout crates. To guarantee the precision of clock frequency or phase, the r-PTP (reduced Precision Time Protocol) and the DDMTD (digital Dual Mixer Time Difference) methods are used for frequency synthesis, phase measurement and adjustment, which is implemented by FPGA (Field Programmable Gate Array) in real-time. In addition, to synchronize global command execution, based upon this clock distribution network, synchronous signals are coded with clock for transmission. With technique of encoding/decoding and clock data recovery, signals such as global triggers or system control commands, can be distributed to all front-end channels synchronously, which greatly simplifies the system design. The experimental results show that both the clock jitter (RMS) and the clock skew can be less than 100 ps.

  2. Dopamine receptor-mediated regulation of neuronal "clock" gene expression.

    Science.gov (United States)

    Imbesi, M; Yildiz, S; Dirim Arslan, A; Sharma, R; Manev, H; Uz, T

    2009-01-23

    Using a transgenic mice model (i.e. "clock" knockouts), clock transcription factors have been suggested as critical regulators of dopaminergic behaviors induced by drugs of abuse. Moreover, it has been shown that systemic administration of psychostimulants, such as cocaine and methamphetamine regulates the striatal expression of clock genes. However, it is not known whether dopamine receptors mediate these regulatory effects of psychostimulants at the cellular level. Primary striatal neurons in culture express dopamine receptors as well as clock genes and have been successfully used in studying dopamine receptor functioning. Therefore, we investigated the role of dopamine receptors on neuronal clock gene expression in this model using specific receptor agonists. We found an inhibitory effect on the expression of mClock and mPer1 genes with the D2-class (i.e. D2/D3) receptor agonist quinpirole. We also found a generalized stimulatory effect on the expression of clock genes mPer1, mClock, mNPAS2 (neuronal PAS domain protein 2), and mBmal1 with the D1-class (i.e. D1) receptor agonist SKF38393. Further, we tested whether systemic administration of dopamine receptor agonists causes similar changes in striatal clock gene expression in vivo. We found quinpirole-induced alterations in mPER1 protein levels in the mouse striatum (i.e. rhythm shift). Collectively, our results indicate that the dopamine receptor system may mediate psychostimulant-induced changes in clock gene expression. Using striatal neurons in culture as a model, further research is needed to better understand how dopamine signaling modulates the expression dynamics of clock genes (i.e. intracellular signaling pathways) and thereby influences neuronal gene expression, neuronal transmission, and brain functioning. PMID:19017537

  3. NPAS2 Compensates for Loss of CLOCK in Peripheral Circadian Oscillators

    OpenAIRE

    Landgraf, Dominic; Wang, Lexie L.; Diemer, Tanja; Welsh, David K.

    2016-01-01

    Heterodimers of CLOCK and BMAL1 are the major transcriptional activators of the mammalian circadian clock. Because the paralog NPAS2 can substitute for CLOCK in the suprachiasmatic nucleus (SCN), the master circadian pacemaker, CLOCK-deficient mice maintain circadian rhythms in behavior and in tissues in vivo. However, when isolated from the SCN, CLOCK-deficient peripheral tissues are reportedly arrhythmic, suggesting a fundamental difference in circadian clock function between SCN and periph...

  4. Oscillation of Clock and Clock Controlled Genes Induced by Serum Shock in Human Breast Epithelial and Breast Cancer Cells: Regulation by Melatonin

    OpenAIRE

    S. Xiang; Mao, L; T. Duplessis; Yuan, L.; R. Dauchy; Dauchy, E.; D.E. Blask,; T. Frasch; Hill, S M

    2012-01-01

    This study investigates differences in expression of clock and clock-controlled genes (CCGs) between human breast epithelial and breast cancer cells and breast tumor xenografts in circadian intact rats and examines if the pineal hormone melatonin influences clock gene and CCG expression. Oscillation of clock gene expression was not observed under standard growth conditions in vitro, however, serum shock (50% horse serum for 2 h) induced oscillation of clock gene and CCG expression in MCF-10A ...

  5. Real-time estimation of satellite clock offset using adaptively robust Kalman filter with classified adaptive factors

    OpenAIRE

    G Huang; Q. Zhang;  

    2012-01-01

    In order to estimate the satellite clock offset in a real-time mode, a new algorithm of adaptively robust Kalman filter with classified adaptive factors for clock offset estimation is proposed. Compared with standard Kalman filter clock offset model, the new method can detect and control outliers and clock jumps automatically in real-time. Moreover, the clock model parameters, which contain the clock offset, clock speed and clock shift, are classified to decide the adaptive factors in the new...

  6. Limits to clock synchronization induced by completely dephasing communication channels

    International Nuclear Information System (INIS)

    Clock synchronization procedures are analyzed in the presence of imperfect communications. In this context we show that there are physical limitations, which prevent one from synchronizing distant clocks when the intervening medium is completely dephasing, as in the case of a rapidly varying dispersive medium

  7. Atomic clocks: new prospects in metrology and geodesy

    CERN Document Server

    Delva, Pacôme

    2013-01-01

    We present the latest developments in the field of atomic clocks and their applications in metrology and fundamental physics. In the light of recent advents in the accuracy of optical clocks, we present an introduction to the relativistic modelization of frequency transfer and a detailed review of chronometric geodesy.

  8. Molecular clock integration of brown adipose tissue formation and function

    Science.gov (United States)

    Nam, Deokhwa; Yechoor, Vijay K.; Ma, Ke

    2016-01-01

    Abstract The circadian clock is an essential time-keeping mechanism that entrains internal physiology to environmental cues. Despite the well-established link between the molecular clock and metabolic homeostasis, an intimate interplay between the clock machinery and the metabolically active brown adipose tissue (BAT) is only emerging. Recently, we came to appreciate that the formation and metabolic functions of BAT, a key organ for body temperature maintenance, are under an orchestrated circadian clock regulation. Two complementary studies from our group uncover that the cell-intrinsic clock machinery exerts concerted control of brown adipogenesis with consequent impacts on adaptive thermogenesis, which adds a previously unappreciated temporal dimension to the regulatory mechanisms governing BAT development and function. The essential clock transcriptional activator, Bmal1, suppresses adipocyte lineage commitment and differentiation, whereas the clock repressor, Rev-erbα, promotes these processes. This newly discovered temporal mechanism in fine-tuning BAT thermogenic capacity may enable energy utilization and body temperature regulation in accordance with external timing signals during development and functional recruitment. Given the important role of BAT in whole-body metabolic homeostasis, pharmacological interventions targeting the BAT-modulatory activities of the clock circuit may offer new avenues for the prevention and treatment of metabolic disorders, particularly those associated with circadian dysregulation.

  9. The Circadian Clock-Controlled Transcriptome of Developing Soybean Seeds.

    Science.gov (United States)

    A number of metabolic and physiological processes in plants are controlled by the circadian clock, which enables the plant to anticipate daily changes in the environment. Microarray expression profiling was used to identify circadian clock controlled genes expressed in developing soybean seeds. 1.8...

  10. Optimal Infinite Runs in One-Clock Priced Timed Automata

    DEFF Research Database (Denmark)

    David, Alexandre; Ejsing-Duun, Daniel; Fontani, Lisa; Larsen, Kim Guldstrand; Popescu, Vasile; Haubach Smedegård, Jacob

    We address the problem of finding an infinite run with the optimal cost-time ratio in a one-clock priced timed automaton and pro- vide an algorithmic solution. Through refinements of the quotient graph obtained by strong time-abstracting bisimulation partitioning, we con- struct a graph with time...... of the one-clock priced timed automaton....

  11. Verge and Foliot Clock Escapement: A Simple Dynamical System

    Science.gov (United States)

    Denny, Mark

    2010-01-01

    The earliest mechanical clocks appeared in Europe in the 13th century. From about 1250 CE to 1670 CE, these simple clocks consisted of a weight suspended from a rope or chain that was wrapped around a horizontal axle. To tell time, the weight must fall with a slow uniform speed, but, under the action of gravity alone, such a suspended weight would…

  12. Development and entrainment of the colonic circadian clock during ontogenesis

    Czech Academy of Sciences Publication Activity Database

    Polidarová, Lenka; Olejníková, Lucie; Paušlyová, Lucia; Sládek, Martin; Soták, Matúš; Pácha, Jiří; Sumová, Alena

    2014-01-01

    Roč. 306, č. 4 (2014), G346-G356. ISSN 0193-1857 R&D Projects: GA ČR(CZ) GAP303/12/1108 Institutional support: RVO:67985823 Keywords : circadian clock * clock gene * ontogenesis * circadian entrainment Subject RIV: ED - Physiology Impact factor: 3.798, year: 2014

  13. The circadian clock regulates auxin signaling and responses in Arabidopsis.

    Directory of Open Access Journals (Sweden)

    Michael F Covington

    2007-08-01

    Full Text Available The circadian clock plays a pervasive role in the temporal regulation of plant physiology, environmental responsiveness, and development. In contrast, the phytohormone auxin plays a similarly far-reaching role in the spatial regulation of plant growth and development. Went and Thimann noted 70 years ago that plant sensitivity to auxin varied according to the time of day, an observation that they could not explain. Here we present work that explains this puzzle, demonstrating that the circadian clock regulates auxin signal transduction. Using genome-wide transcriptional profiling, we found many auxin-induced genes are under clock regulation. We verified that endogenous auxin signaling is clock regulated with a luciferase-based assay. Exogenous auxin has only modest effects on the plant clock, but the clock controls plant sensitivity to applied auxin. Notably, we found both transcriptional and growth responses to exogenous auxin are gated by the clock. Thus the circadian clock regulates some, and perhaps all, auxin responses. Consequently, many aspects of plant physiology not previously thought to be under circadian control may show time-of-day-specific sensitivity, with likely important consequences for plant growth and environmental responses.

  14. A Novel Method of Clock Synchronization in Distributed System

    Science.gov (United States)

    Li, G.; Niu, M. J.; Cai, Y. S.; Chen, X.; Ren, Y. Q.

    2016-03-01

    Time synchronization plays an important role in application of aircraft flying formation and constellation autonomous navigation, etc. In application of clock synchronization in the network system, it is not always true that each observed node may be interconnected, therefore, it is difficult to achieve time synchronization of network system with high precision in the condition that a certain node can only obtain the measurement information of clock from one of its corresponding neighbors, and cannot obtain from other nodes. According to this special problem, a novel method of high precision time synchronization of network system has been proposed. In this paper, we regard each clock as a node in the network system, and based on different distributed topology definition, the following three control algorithms of time synchronization under three circumstances have been designed: without a master clock (reference clock), with a master clock (reference clock), and with a fixed communication delay in the network system. The validity of the designed clock synchronization protocol has been proved both theoretically and through numerical simulation.

  15. From atomic clocks to coordinate times

    Science.gov (United States)

    Petit, G.

    2006-08-01

    The IAU'1991 Resolution A4, complemented by IAU'2000 Resolution B1.3-4, provide rigorous definitions for barycentric and geocentric reference systems in a relativistic framework and define the coordinate times of these systems as TCB and TCG, respectively. Other coordinate times in use are TT, defined from TCG through IAU'2000 Resolution B1.9, and TDB, whose rigorous definition from TCB is now proposed. For practical use, these coordinate times must be realized and the proper time provided by atomic clocks (Atomic time AT) is used to generate all coordinate times. The present sequence is AT => TT ||> TCG -> TCB ||> TDB, where the sign => indicates the complex series of operations involved in generating International atomic time TAI and where ||> is an exact transformation. The paper examines the uncertainty of realization of TAI and the uncertainty brought by the transformation TCG -> TCB. On-going and future evolutions of atomic clocks are reviewed along with their impact on the diagram of time transformations.

  16. Animal clocks: when science meets nature.

    Science.gov (United States)

    Kronfeld-Schor, Noga; Bloch, Guy; Schwartz, William J

    2013-08-22

    Daily rhythms of physiology and behaviour are governed by an endogenous timekeeping mechanism (a circadian 'clock'), with the alternation of environmental light and darkness synchronizing (entraining) these rhythms to the natural day-night cycle. Our knowledge of the circadian system of animals at the molecular, cellular, tissue and organismal levels is remarkable, and we are beginning to understand how each of these levels contributes to the emergent properties and increased complexity of the system as a whole. For the most part, these analyses have been carried out using model organisms in standard laboratory housing, but to begin to understand the adaptive significance of the clock, we must expand our scope to study diverse animal species from different taxonomic groups, showing diverse activity patterns, in their natural environments. The seven papers in this Special Feature of Proceedings of the Royal Society B take on this challenge, reviewing the influences of moonlight, latitudinal clines, evolutionary history, social interactions, specialized temporal niches, annual variation and recently appreciated post-transcriptional molecular mechanisms. The papers emphasize that the complexity and diversity of the natural world represent a powerful experimental resource. PMID:23825215

  17. The clock ambiguity: Implications and new developments

    CERN Document Server

    Albrecht, Andreas

    2008-01-01

    We consider the ambiguity associated with the choice of clock in time reparameterization invariant theories. This arbitrariness undermines the goal of prescribing a fixed set of physical laws, since a change of time variable can completely alter the predictions of the theory. We review the main features of the clock ambiguity and our earlier work on its implications for the emergence of physical laws in a statistical manner. We also present a number of new results: We show that (contrary to suggestions in our earlier work) time independent Hamiltonians may quite generally be assumed for laws of physics that emerge in this picture. We also further explore the degree to which the observed Universe can be well approximated by a random Hamiltonian. We discuss the possibility of predicting the dimensionality of space, and also relate the 2nd derivative of the density of states to the heat capacity of the Universe. This new work adds to the viability of our proposal that strong predictions for physical laws may eme...

  18. An Integrated Architectural Clock Implemented Memory Design Analysis

    Directory of Open Access Journals (Sweden)

    Ravi Khatwal

    2015-07-01

    Full Text Available Recently Low power consumption and Custom Memory design is major issue for embedded designer. Micro wind and Xilinx simulator implements SRAM design architecture and performs efficient simulation. These simulators implements high performances and low power consumption of SRAM design. SRAM efficiency analyzed with 6-T architecture design and row/column based architectural design. We have analyzed clock implemented memory design and simulated with specific application. We have implemented clock based SRAM architecture that improves the internal clock efficiency of SRAM. Architectural Clock implemented memory design reduces the propagation delay and access time. Internal semiconductor material design implemented technique also improves the SRAM data transitions scheme. Semiconductor material and clock implemented design improve simulation performance of SRAM and these design implements for recently developed Application Specific Memory Design Architecture and mobile devices.

  19. The quantum beat principles and applications of atomic clocks

    CERN Document Server

    Major, F

    2007-01-01

    This work attempts to convey a broad understanding of the physical principles underlying the workings of these quantum-based atomic clocks, with introductory chapters placing them in context with the early development of mechanical clocks and the introduction of electronic time-keeping as embodied in the quartz-controlled clocks. While the book makes no pretense at being a history of atomic clocks, it nevertheless takes a historical perspective in its treatment of the subject. Intended for nonspecialists with some knowledge of physics or engineering, The Quantum Beat covers a wide range of salient topics relevant to atomic clocks, treated in a broad intuitive manner with a minimum of mathematical formalism. Detailed descriptions are given of the design principles of the rubidium, cesium, hydrogen maser, and mercury ion standards; the revolutionary changes that the advent of the laser has made possible, such as laser cooling, optical pumping, the formation of "optical molasses," and the cesium "fountain" stand...

  20. Multiple-bit-rate clock recovery circuit: theory

    International Nuclear Information System (INIS)

    The multiple-bit-rate clock recovery circuit has been recently proposed as a part of the communications packet switch. All packets must be the same length and be preceded by the frequency header, which is a number of consecutive ones (return-to-zero mode). The header is compared with the internal clock, and the result is used to set output clock frequency. The clock rate is defined by a number of fluxons propagating in ring oscillator, which is a close circular Josephson transmission line. The theory gives a bit rate bandwidth as a function of internal clock frequency, header length and silence time (maximum number of consecutive zeros in the packet). (author)

  1. Standard Clock in primordial density perturbations and cosmic microwave background

    International Nuclear Information System (INIS)

    Standard Clocks in the primordial epoch leave a special type of features in the primordial perturbations, which can be used to directly measure the scale factor of the primordial universe as a function of time a(t), thus discriminating between inflation and alternatives. We have started to search for such signals in the Planck 2013 data using the key predictions of the Standard Clock. In this Letter, we summarize the key predictions of the Standard Clock and present an interesting candidate example in Planck 2013 data. Motivated by this candidate, we construct and compute full Standard Clock models and use the more complete prediction to make more extensive comparison with data. Although this candidate is not yet statistically significant, we use it to illustrate how Standard Clocks appear in Cosmic Microwave Background (CMB) and how they can be further tested by future data. We also use it to motivate more detailed theoretical model building

  2. Clock-turning gait synthesis for humanoid robots

    Institute of Scientific and Technical Information of China (English)

    Zhe TANG; Zengqi SUN; Hongbo LIU; Meng Joo ER

    2007-01-01

    Turning gait is a basic motion for humanoid robots.This paper presents a method for humanoid turning.i.e.clock-turning.The objective of clock-turning is to change robot direction at a stationary spot.The clock-turning planning consists of four steps:ankle trajectory generation,hip trajectory generation,knee trajectory generation,and inverse kinematics calculation.Our proposed method is based on a typical humanoid structure with 12 DOFs(degrees of freedom).The final output of clock-turning planning is 12 reference trajectories.which are used to control a humanoid robot wim 12 DOFs.ZMP(zero moment point)is used as stability criterion for the planning.Simulation experiments are conducted to verify the effectiveness of our proposed clock-turning method.

  3. A self-interfering clock as a "which path" witness.

    Science.gov (United States)

    Margalit, Yair; Zhou, Zhifan; Machluf, Shimon; Rohrlich, Daniel; Japha, Yonathan; Folman, Ron

    2015-09-11

    In Einstein's general theory of relativity, time depends locally on gravity; in standard quantum theory, time is global-all clocks "tick" uniformly. We demonstrate a new tool for investigating time in the overlap of these two theories: a self-interfering clock, comprising two atomic spin states. We prepare the clock in a spatial superposition of quantum wave packets, which evolve coherently along two paths into a stable interference pattern. If we make the clock wave packets "tick" at different rates, to simulate a gravitational time lag, the clock time along each path yields "which path" information, degrading the pattern's visibility. In contrast, in standard interferometry, time cannot yield "which path" information. This proof-of-principle experiment may have implications for the study of time and general relativity and their impact on fundamental effects such as decoherence and the emergence of a classical world. PMID:26249229

  4. Geophysical applicability of atomic clocks: direct continental geoid mapping

    CERN Document Server

    Bondarescu, Ruxandra; Hetényi, György; Boschi, Lapo; Jetzer, Philippe; Balakrishna, Jayashree; 10.1111/j.1365-246X.2012.05636.x

    2012-01-01

    The geoid is the true physical figure of the Earth, a particular equipotential surface of the gravity field of the Earth that accounts for the effect of all subsurface density variations. Its shape approximates best (in the sense of least squares) the mean level of oceans, but the geoid is more difficult to determine over continents. Satellite missions carry out distance measurements and derive the gravity field to provide geoid maps over the entire globe. However, they require calibration and extensive computations including integration, which is a non-unique operation. Here we propose a direct method and a new tool that directly measures geopotential differences on continents using atomic clocks. General Relativity Theory predicts constant clock rate at sea level, and faster (resp. slower) clock rate above (resp. below) sea level. The technology of atomic clocks is on the doorstep of reaching an accuracy level in clock rate that is equivalent to 1 cm in determining equipotential surface (including geoid) he...

  5. The Retina and Other Light-sensitive Ocular Clocks.

    Science.gov (United States)

    Besharse, Joseph C; McMahon, Douglas G

    2016-06-01

    Ocular clocks, first identified in the retina, are also found in the retinal pigment epithelium (RPE), cornea, and ciliary body. The retina is a complex tissue of many cell types and considerable effort has gone into determining which cell types exhibit clock properties. Current data suggest that photoreceptors as well as inner retinal neurons exhibit clock properties with photoreceptors dominating in nonmammalian vertebrates and inner retinal neurons dominating in mice. However, these differences may in part reflect the choice of circadian output, and it is likely that clock properties are widely dispersed among many retinal cell types. The phase of the retinal clock can be set directly by light. In nonmammalian vertebrates, direct light sensitivity is commonplace among body clocks, but in mice only the retina and cornea retain direct light-dependent phase regulation. This distinguishes the retina and possibly other ocular clocks from peripheral oscillators whose phase depends on the pace-making properties of the hypothalamic central brain clock, the suprachiasmatic nuclei (SCN). However, in mice, retinal circadian oscillations dampen quickly in isolation due to weak coupling of its individual cell-autonomous oscillators, and there is no evidence that retinal clocks are directly controlled through input from other oscillators. Retinal circadian regulation in both mammals and nonmammalian vertebrates uses melatonin and dopamine as dark- and light-adaptive neuromodulators, respectively, and light can regulate circadian phase indirectly through dopamine signaling. The melatonin/dopamine system appears to have evolved among nonmammalian vertebrates and retained with modification in mammals. Circadian clocks in the eye are critical for optimum visual function where they play a role fine tuning visual sensitivity, and their disruption can affect diseases such as glaucoma or retinal degeneration syndromes. PMID:27095816

  6. Post-transcriptional control of the mammalian circadian clock: implications for health and disease.

    Science.gov (United States)

    Preußner, Marco; Heyd, Florian

    2016-06-01

    Many aspects of human physiology and behavior display rhythmicity with a period of approximately 24 h. Rhythmic changes are controlled by an endogenous time keeper, the circadian clock, and include sleep-wake cycles, physical and mental performance capability, blood pressure, and body temperature. Consequently, many diseases, such as metabolic, sleep, autoimmune and mental disorders and cancer, are connected to the circadian rhythm. The development of therapies that take circadian biology into account is thus a promising strategy to improve treatments of diverse disorders, ranging from allergic syndromes to cancer. Circadian alteration of body functions and behavior are, at the molecular level, controlled and mediated by widespread changes in gene expression that happen in anticipation of predictably changing requirements during the day. At the core of the molecular clockwork is a well-studied transcription-translation negative feedback loop. However, evidence is emerging that additional post-transcriptional, RNA-based mechanisms are required to maintain proper clock function. Here, we will discuss recent work implicating regulated mRNA stability, translation and alternative splicing in the control of the mammalian circadian clock, and its role in health and disease. PMID:27108448

  7. The eCDR-PLL, a radiation-tolerant ASIC for clock and data recovery and deterministic phase clock synthesis

    International Nuclear Information System (INIS)

    A radiation-tolerant CDR/PLL ASIC has been developed for the upcoming LHC upgrades, featuring clock Frequency Multiplication (FM) and Clock and Data Recovery (CDR), showing deterministic phase and low jitter. Two FM modes have been implemented: either generating 40, 60, 120 and 240 MHz clock outputs for GBT-FPGA applications or providing 40, 80, 160 and 320 MHz clocks for TTC and e-link applications. The CDR operates with 40, 80, 160 or 320 Mbit/s data rates while always generating clocks at 40, 80, 160 and 320 MHz, regardless of the data rate. All the outputs are phase programmable with a resolution of 195 ps or 260 ps, depending on the selected mode. The ASIC has been designed using radiation-tolerant techniques in a 130 nm CMOS technology and operates at a 1.2 V supply voltage

  8. Clocks for quaternary environments in Australia

    International Nuclear Information System (INIS)

    The Australian continent offers a variety of natural systems where records of the Earth's past environment have been stored, including sediment cores, tree rings, rock surfaces and corals. Rock varnish, mud-wasp nests and pack-rat middens provide alternative archives for vegetation and environmental change in arid areas, where continuous sedimentary sequences or trees are not available. Each of these media contain specific information on past climatic conditions but we must determine their chronology and decipher the relevant environmental parameters. Cosmogenic radionuclides, such as 14C, 10Be, 26Al and 36Cl, analysed by accelerator mass spectrometry, provide valuable radiometric clocks to establish an absolute time scale for the environmental events of the Quaternary. U-series, potassium-argon, argonargon and optically stimulated luminescence are other dating methods used in palaeoenvironmental studies. ANSTO supports the Quaternary science community in Australia providing the analysis of long-lived radionuclides: some significant projects from this program will be illustrated. (author)

  9. The Information Flow Problem on Clock Networks

    OpenAIRE

    Atkins, Ross

    2016-01-01

    The information flow problem on a network asks whether $r$ senders, $v_1,v_2, \\ldots ,v_r$ can each send messages to $r$ corresponding receivers $v_{n+1}, \\ldots ,v_{n+r}$ via intermediate nodes $v_{r+1}, \\ldots ,v_n$. For a given finite $R \\subset \\mathbb{Z}^+$, the clock network $N_n(R)$ has edge $v_iv_k$ if and only if $k>r$ and $k-i \\in R$. We show that the information flow problem on $N_n(\\{1,2, \\ldots ,r\\})$ can be solved for all $n \\geq r$. We also show that for any finite $R$ such tha...

  10. Diurnal oscillations of soybean circadian clock and drought responsive genes.

    Directory of Open Access Journals (Sweden)

    Juliana Marcolino-Gomes

    Full Text Available Rhythms produced by the endogenous circadian clock play a critical role in allowing plants to respond and adapt to the environment. While there is a well-established regulatory link between the circadian clock and responses to abiotic stress in model plants, little is known of the circadian system in crop species like soybean. This study examines how drought impacts diurnal oscillation of both drought responsive and circadian clock genes in soybean. Drought stress induced marked changes in gene expression of several circadian clock-like components, such as LCL1-, GmELF4- and PRR-like genes, which had reduced expression in stressed plants. The same conditions produced a phase advance of expression for the GmTOC1-like, GmLUX-like and GmPRR7-like genes. Similarly, the rhythmic expression pattern of the soybean drought-responsive genes DREB-, bZIP-, GOLS-, RAB18- and Remorin-like changed significantly after plant exposure to drought. In silico analysis of promoter regions of these genes revealed the presence of cis-elements associated both with stress and circadian clock regulation. Furthermore, some soybean genes with upstream ABRE elements were responsive to abscisic acid treatment. Our results indicate that some connection between the drought response and the circadian clock may exist in soybean since (i drought stress affects gene expression of circadian clock components and (ii several stress responsive genes display diurnal oscillation in soybeans.

  11. Automatic minimisation of micromotion in a 88Sr+ optical clock

    International Nuclear Information System (INIS)

    Optical clocks based on narrow linewidth transitions in single cold ions confined in RF traps are being developed at a number of laboratories worldwide. For these ion clock systems, excess micromotion can cause both Stark and Doppler frequency shifts and also a degradation of frequency stability as a result of a reduced excitation rate to the clock transition. At NPL, we detect micromotion in our 88Sr+ optical clocks by observing the correlation between photon arrival times and the zero crossing of the RF trap drive signal. Recently, two nominally identical 88Sr+ optical clocks have been operated over several days and their frequencies compared against one another. During this time the dc voltages on the endcap and compensation voltage electrodes required to minimise the micromotion can change significantly, particularly following the loading of an ion. This paper describes an automatic method to monitor and minimise micromotion applicable to single ion clocks and which we demonstrate using our two NPL 88Sr+ ion clocks. (paper)

  12. Caenorhabditis elegans opens up new insights into circadian clock mechanisms.

    Science.gov (United States)

    Hasegawa, Kenji; Saigusa, Tetsu; Tamai, Yoichi

    2005-01-01

    The roundworm, Caenorhabditis elegans, is known to carry homologues of clock genes such as per (=period) and tim (=timeless), which constitute the core of the circadian clock in Drosophila and mammals: lin-42 and tim-1. Analyses using WormBase (C. elegans gene database) have identified with relatively high identity analogous of the clock genes recognized in Drosophila and mammals, with the notable exception of cry (=cryptochrome), which is lacking in C. elegans. All of these C. elegans cognates of the clock genes appear to belong to members of the PAS-superfamily and to participate in development or responsiveness to the environment but apparently are not involved in the C. elegans circadian clock. Nevertheless, C. elegans exhibits convincing circadian rhythms in locomotor behavior in the adult stage and in resistance to hyperosmotic stress in starved larvae (L1) after hatching, indicating that it has a circadian clock with a core design entirely different from that of Drosophila and mammals. Here two possibilities are considered. First, the core of the C. elegans circadian clock includes transcriptional/translational feedback loops between genes and their protein products that are entirely different from those of Drosophila and mammals. Second, a more basic principle such as homeostasis governs the circadian cellular physiology, and was established primarily to minimize the accumulation of DNA damage in response to an environment cycling at 24 h intervals. PMID:15865318

  13. A molecular clock regulates angiopoietin-like protein 2 expression.

    Directory of Open Access Journals (Sweden)

    Tsuyoshi Kadomatsu

    Full Text Available Various physiological and behavioral processes exhibit circadian rhythmicity. These rhythms are usually maintained by negative feedback loops of core clock genes, namely, CLOCK, BMAL, PER, and CRY. Recently, dysfunction in the circadian clock has been recognized as an important foundation for the pathophysiology of lifestyle-related diseases, such as obesity, cardiovascular disease, and some cancers. We have reported that angiopoietin-like protein 2 (ANGPTL2 contributes to the pathogenesis of these lifestyle-related diseases by inducing chronic inflammation. However, molecular mechanisms underlying regulation of ANGPTL2 expression are poorly understood. Here, we assess circadian rhythmicity of ANGPTL2 expression in various mouse tissues. We observed that ANGPTL2 rhythmicity was similar to that of the PER2 gene, which is regulated by the CLOCK/BMAL1 complex. Promoter activity of the human ANGPTL2 gene was significantly induced by CLOCK and BMAL1, an induction markedly attenuated by CRY co-expression. We also identified functional E-boxes in the ANGPTL2 promoter and observed occupancy of these sites by endogenous CLOCK in human osteosarcoma cells. Furthermore, Cry-deficient mice exhibited arrhythmic Angptl2 expression. Taken together, these data suggest that periodic expression of ANGPTL2 is regulated by a molecular clock.

  14. Automatic minimisation of micromotion in a 88Sr+ optical clock

    Science.gov (United States)

    Barwood, G. P.; Huang, G.; Klein, H. A.; Gill, P.

    2015-07-01

    Optical clocks based on narrow linewidth transitions in single cold ions confined in RF traps are being developed at a number of laboratories worldwide. For these ion clock systems, excess micromotion can cause both Stark and Doppler frequency shifts and also a degradation of frequency stability as a result of a reduced excitation rate to the clock transition. At NPL, we detect micromotion in our 88Sr+ optical clocks by observing the correlation between photon arrival times and the zero crossing of the RF trap drive signal. Recently, two nominally identical 88Sr+ optical clocks have been operated over several days and their frequencies compared against one another. During this time the dc voltages on the endcap and compensation voltage electrodes required to minimise the micromotion can change significantly, particularly following the loading of an ion. This paper describes an automatic method to monitor and minimise micromotion applicable to single ion clocks and which we demonstrate using our two NPL 88Sr+ ion clocks.

  15. Using a transportable optical clock for chronometric levelling

    Science.gov (United States)

    Lisdat, Christian; Sterr, Uwe; Koller, Silvio; Grotti, Jacopo; Vogt, Stefan; Häfner, Sebastian; Herbers, Sofia; Al-Masoudi, Ali

    2016-07-01

    With their supreme accuracy and precision, optical clocks in combination with new methods of long-distance frequency transfer can be used to determine height differences by measuring the gravitational red shift between two clocks without accumulation of measurement errors, as in classical levelling. We are developing transportable optical clocks for this purpose that will also serve for the technology development regarding optical clocks in Space and for international comparisons between optical clocks that cannot be linked with sufficient accuracy otherwise. In this talk we will focus on the transportable strontium lattice clock that we are developing and its first evaluation. Presently, we achieve a fractional frequency instability of 3 × 10^{-17} after 1000 s averaging time, which is equivalent to a height resolution of 30 cm. The first uncertainty evaluation of the system yielded 7 × 10^{-17}. We expect rapid improvements to an uncertainty of a few parts in 10^{17}. The clock is now located within a car trailer, which requires compact and rugged lasers systems and physics package. Special care has been taken in the design of the ultra-frequency stable interrogation laser that has to achieve fractional frequency instabilities of considerably below 10^{-15}. Typical laboratory constructions of the reference resonator system used to pre-stabilize the laser frequency are not compatible with the requirement of transportability. In an actual levelling campaign, this clock will be connected via a stabilized optical fibre link with another, stationary frequency standard. The measured gravitational red shift will be compared with the ones calculated from potential differences derived with state of the art geodetic data and models. We will discuss the status of measurements of geodetic relevance with optical clocks and give an outlook on our next steps. This work is supported by QUEST, DFG (RTG 1729, CRC 1128), EU-FP7 (FACT) and EMRP (ITOC). The EMRP is jointly funded

  16. Time in the 10,000-Year Clock

    OpenAIRE

    Hillis, Danny; Seaman, Rob; Allen, Steve; Giorgini, Jon

    2011-01-01

    The Long Now Foundation is building a mechanical clock that is designed to keep time for the next 10,000 years. The clock maintains its long-term accuracy by synchronizing to the Sun. The 10,000-Year Clock keeps track of five different types of time: Pendulum Time, Uncorrected Solar Time, Corrected Solar Time, Displayed Solar Time and Orrery Time. Pendulum Time is generated from the mechanical pendulum and adjusted according to the equation of time to produce Uncorrected Solar Time, which is ...

  17. Progress Towards a Compact Optical Clock at JPL

    Science.gov (United States)

    Sullivan, Scott; Rellergert, Wade; Grudinin, Ivan; Baumgartel, Lukas; Yu, Nan

    2014-05-01

    The unprecedented stability and accuracy provided by optical clocks allows improved navigation and planetary science in space applications as well as more precise tests of fundamental laws of physics. However, technological advances towards the miniaturization of the physical volume and reduced power consumption of these clocks must be made to suit space-based application. We will describe JPL's effort towards the development of a compact, low-power optical clock based on 171Yb+. This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Partial support from NASA Fundamental Physics Program is acknowledged.

  18. Relativistic effects for the JUICE on‐board clock

    OpenAIRE

    S. Bauer; Hussmann, H.; J. Mueller; Oberst, J.

    2014-01-01

    We studied relativistic effects on spacecraft clock rates for ESA’s JUICE mission and derived a relationship between dynamical time TDB and on‐board time. We analysed the S/C on‐board clock rate by using the JUICE mission nominal trajectory. We identify significant changes in the rate of the clock due to large changes of the S/C velocity and its distance to the solar system bodies during the various spacecraft operational phases. After ≈ 11.5 years, at the end of the mission, the offset in ti...

  19. Stimulated Raman clock transition without a differential ac Stark

    International Nuclear Information System (INIS)

    We considered a stimulated Raman clock transition between the ground hyperfine states of an alkali atom by using the second-order perturbation theory and the spherical tensor formalism. When the light fields are circularly polarized and properly detuned, the differential ac Stark shift of the clock transition vanishes with non-vanishing transition amplitude. With a two-zone Raman Ramsey method and a slow atomic beam, the proposed scheme should result in a clock with a systematic shift of the order of a few mHz for the case of cesium. (author)

  20. Magic Wavelength of an Optical Clock Transition of Barium

    International Nuclear Information System (INIS)

    Similar to most of the other alkaline earth elements, barium atoms can be candidates for optical clocks, thus the magic wavelength for an optical lattice is important for the clock transition. We calculate the magic wavelength of a possible clock transition between 6s21S0 and 6s5d3 D2 states of barium atoms. Our theoretical result shows that there are three magic wavelengths 615.9nm, 641.2nm and 678.8nm for a linearly polarized optical lattice laser for barium. (atomic and molecular physics)

  1. Circadian Clocks as Modulators of Metabolic Comorbidity in Psychiatric Disorders.

    Science.gov (United States)

    Barandas, Rita; Landgraf, Dominic; McCarthy, Michael J; Welsh, David K

    2015-12-01

    Psychiatric disorders such as schizophrenia, bipolar disorder, and major depressive disorder are often accompanied by metabolic dysfunction symptoms, including obesity and diabetes. Since the circadian system controls important brain systems that regulate affective, cognitive, and metabolic functions, and neuropsychiatric and metabolic diseases are often correlated with disturbances of circadian rhythms, we hypothesize that dysregulation of circadian clocks plays a central role in metabolic comorbidity in psychiatric disorders. In this review paper, we highlight the role of circadian clocks in glucocorticoid, dopamine, and orexin/melanin-concentrating hormone systems and describe how a dysfunction of these clocks may contribute to the simultaneous development of psychiatric and metabolic symptoms. PMID:26483181

  2. High speed fiber-based clock enhancement of NRZ data

    Institute of Scientific and Technical Information of China (English)

    Tong Wu; Kun Qiu

    2005-01-01

    A scheme for all-fiber clock enhancement of non-return-to-zero (NRZ) data based on cross-phase modulation (XPM) effect in nonlinear fibers is proposed and demonstrated in simulation. The simulation results indicate that the clock-to-data ratio of NRZ signals at 64 Gb/s can be increased to 22.94 dB by using this scheme, and the pattern effect in clock enhanced signals is very weak. The ability of high speed operation up to 140 Gb/s of this scheme is also proved in our simulation.

  3. Regulation of behavioral circadian rhythms and clock protein PER1 by the deubiquitinating enzyme USP2

    DEFF Research Database (Denmark)

    Yang, Yaoming; Duguay, David; Bédard, Nathalie;

    2012-01-01

    Endogenous 24-hour rhythms are generated by circadian clocks located in most tissues. The molecular clock mechanism is based on feedback loops involving clock genes and their protein products. Post-translational modifications, including ubiquitination, are important for regulating the clock...

  4. Optical lattice clocks: Hz-level spectral width with sub-Hz reproducibility

    International Nuclear Information System (INIS)

    State-of-the-art optical clocks have surpassed microwave clocks in this century, causing discussions to redefine the SI second based on an optical transition. The superiority of optical standards was clearly revealed by two of optical-optical comparisons, one of which is a remote comparison of two strontium lattice clocks, and the other is a characterization of a single Ca+ ion clock using a Sr lattice clock as a frequency reference. The former for the first time demonstrated the frequency reproducibility of physically separated clocks at the 10−16 level. The latter has confirmed the capability of single Ca+ clocks to reach the ∼10−16 instability.

  5. Toward A Neutral Mercury Optical Lattice Clock: Determination of the Magic Wavelength for the Ultraviolet clock Transition

    International Nuclear Information System (INIS)

    A lattice clock combines the advantages of ion and neutral atom based clocks, namely the recoil and first order Doppler free spectroscopy allowed by the Lamb-Dicke regime. This lattice light field shifts the energy levels of the clock transition. However a wavelength can be found where the light-shift of the clock states cancelled to first order. In this thesis, we present the latest advances in optical lattice clock with mercury atoms developed at LNE-SYRTE. After a review of the current performances of different optical clock are currently under development, we focus on the concept of optical lattice clock and the features of the mercury that make him an excellent candidate for the realization of an optical lattice clock achievement the uncertainty of the level of 10-17. The second part is devoted to the characterization of the mercury MOT, using a sensitive detection system, which allowed us to evaluate the temperature of different isotopes present in the MOT and have a good evidence of sub-Doppler cooling for the fermionic isotopes. The third part of this these, present the experimental aspects of the implementation and the development of the laser source required for trapping mercury atoms operating near the predicted magic wavelength. Finally, we report on the Lamb-Dicke spectroscopy of the 1S0 →3 P0 clock transition in the 199Hg atoms confined in lattice trap. With use of the ultra-stable laser system, linked to LNE-SYRTE primary frequency reference, we have determined the center frequency of the transition for a range of lattice wavelengths and different lattice depths. Analyzing these measurement, we have carried out the first experimental determination of the magic wavelength, which is the crucial step towards achieving a highly accurate frequency standard using mercury. (author)

  6. Recent progress of neutral mercury lattice clock in SIOM

    Science.gov (United States)

    Zhao, R. C.; Fu, X. H.; Liu, K. K.; Gou, W.; Sun, J. F.; Xu, Z.; Wang, Y. Z.

    2016-06-01

    Neutral mercury atom is one of good candidates of optical lattice clock. Due to its large atomic number, mercury atom is insensitive to black body radiation, which is the severe limitation for the development of optical clocks. However, the challenge of neutral mercury lattice clock is the requirement of high power deep-UV lasers, especially for both the cooling laser and the lattice laser. Here, we report the recent progress of neutral mercury lattice clock in SIOM, including the development for laser cooling of mercury atom and the cooling laser system with fiber laser amplifier. We have realized the magneto-optical trap of mercury atoms and measured the parameters of cold mercury atoms. A home-made external cavity diode laser works as a seed laser for a room temperature 1014.8 nm fiber laser amplifier. A new efficient frequency-doubling cavity from 1015 nm to 507 nm has been developed.

  7. Two-photon assisted clock comparison to picosecond precision

    CERN Document Server

    Zhang, Shi-Wei; Yao, Yin-Ping; Wan, Ren-Gang; Zhang, Tong-Yi

    2015-01-01

    We have experimentally demonstrated a clock comparison scheme utilizing time-correlated photon pairs generated from the spontaneous parametric down conversion process of a laser pumped beta-barium borate crystal. The coincidence of two-photon events are analyzed by the cross correlation of the two time stamp sequences. Combining the coarse and fine part of the time differences at different resolutions, a 64 ps precision for clock synchronization has been realized. We also investigate the effects of hardware devices used in the system on the precision of clock comparison. The results indicate that the detector's time jitter and the background noise will degrade the system performance. With this method, comparison and synchronization of two remote clocks could be implemented with a precision at the level of a few tens of picoseconds.

  8. Atomic Clocks and Variations of the FIne Structure Constant

    Science.gov (United States)

    Prestage, John D.; Tjoelker, Robert L.; Maleki, Lute

    1995-01-01

    We describe a new test for possible variations of the fine structure constant alpha by comparisons of rates between clocks based on hyperfine transitions in alkali atoms with different atomic number Z. H-maser, Cs, and Hg(+) clocks have a different dependence on alpha via relativistic contributions of order (Z-alpha)(sup 2). Recent H-maser vs Hg(+) clock comparison data improve laboratory limits on a time variation by 100-fold to give dot-alpha less than or equal to 3.7 x 10(exp -14)/yr. Future laser cooled clocks (Be(+), Rb, Cs, Hg(+), etc.), when compared, will yield the most sensitive of all tests for dot-alpha/alpha.

  9. Measurement of Magic Wavelengths for the ^{40}Ca^{+} Clock Transition.

    Science.gov (United States)

    Liu, Pei-Liang; Huang, Yao; Bian, Wu; Shao, Hu; Guan, Hua; Tang, Yong-Bo; Li, Cheng-Bin; Mitroy, J; Gao, Ke-Lin

    2015-06-01

    We demonstrate experimentally the existence of magic wavelengths and determine the ratio of oscillator strengths for a single trapped ion. For the first time, two magic wavelengths near 396 nm for the ^{40}Ca^{+} clock transition are measured simultaneously with high precision. By tuning the applied laser to an intermediate wavelength between transitions 4s_{1/2}→4p_{1/2} and 4s_{1/2}→4p_{3/2}, the sensitivity of the clock transition Stark shift to the oscillator strengths is greatly enhanced. Furthermore, with the measured magic wavelengths, we determine the ratio of the oscillator strengths with a deviation of less than 0.5%. Our experimental method may be applied to measure magic wavelengths for other ion clock transitions. Promisingly, the measurement of these magic wavelengths paves the way to building all-optical trapped ion clocks. PMID:26196619

  10. Complementary approaches to understanding the plant circadian clock

    CERN Document Server

    Akman, Ozgur E; Loewe, Laurence; Troein, Carl; 10.4204/EPTCS.19.1

    2010-01-01

    Circadian clocks are oscillatory genetic networks that help organisms adapt to the 24-hour day/night cycle. The clock of the green alga Ostreococcus tauri is the simplest plant clock discovered so far. Its many advantages as an experimental system facilitate the testing of computational predictions. We present a model of the Ostreococcus clock in the stochastic process algebra Bio-PEPA and exploit its mapping to different analysis techniques, such as ordinary differential equations, stochastic simulation algorithms and model-checking. The small number of molecules reported for this system tests the limits of the continuous approximation underlying differential equations. We investigate the difference between continuous-deterministic and discrete-stochastic approaches. Stochastic simulation and model-checking allow us to formulate new hypotheses on the system behaviour, such as the presence of self-sustained oscillations in single cells under constant light conditions. We investigate how to model the timing of...

  11. A Simple Loop for Simultaneous OTDM Demultiplexing and Clock Recovery

    International Nuclear Information System (INIS)

    A simple and stable loop consisting of a pair of concatenated electroabsorption modulators (EAMs) and 10 GHz clock recovery module is presented and demonstrated experimentally for simultaneous demultiplexing and clock recovery for OTDM networks. The 10Gb/s demultiplexed signal and 10 GHz recovered clock are successfully implemented from 80 Gbit/s and 160 Gbit/s OTDM signals utilizing the loop. The loop based on EAM-PLL can provide excellent tolerance range (> 5 dB) of the OSCR of the source laser, and the recovered clock signal exhibits low rms jitter over a dynamic input optical power range of 15 dB. (fundamental areas of phenomenology (including applications))

  12. Speed of light as measured by two terrestrial stable clocks

    International Nuclear Information System (INIS)

    It is shown that despite the recent criticism within the special theory of relativity there exists an arrangement of stable clocks rotating with the earth which predicts diurnal variations of the one-way speed of light, as suggested previously

  13. Speed of light as measured by two terrestrial stable clocks

    Science.gov (United States)

    Hsu, J. P.; Sherry, T. N.; Chiu, C. B.

    1977-01-01

    Despite the recent criticism within the special theory of relativity, there exists an arrangement of stable clocks rotating with the earth which predicts diurnal variations of the one-way speed of light, as suggested previously.

  14. Clocks and dynamics in quantum models of gravity

    CERN Document Server

    Malkiewicz, Przemyslaw

    2016-01-01

    We investigate how the quantum dynamics of gravitational models depend on the clocks employed in quantization procedure. Our previous result demonstrates that almost all physical features of quantum cosmological bounces depend on the choice of clock. The vital question whether all the quantum (or, semiclassical) solutions admit, away from the quantum interaction region in the far past and future, invariant asymptotic limits irrespectively of the clock's choice is addressed herein. We analyze the semiclassical dynamics of the Bianchi Type I model undergoing a quantum bounce. Our result follows from the universal principle of the free choice of clock and thus, it applies to all quantum gravity models based on the concept of the physical Hilbert space and inner dynamics. Then we propose a suitable interpretation of quantum models of gravity. As a by-product of the pursuit of our main goal, we elaborate the semiclassical description of anisotropic singularity resolution.

  15. An atomic clock with $10^{-18}$ instability

    CERN Document Server

    Hinkley, N; Phillips, N B; Schioppo, M; Lemke, N D; Beloy, K; Pizzocaro, M; Oates, C W; Ludlow, A D

    2013-01-01

    Atomic clocks have been transformational in science and technology, leading to innovations such as global positioning, advanced communications, and tests of fundamental constant variation. Next-generation optical atomic clocks can extend the capability of these timekeepers, where researchers have long aspired toward measurement precision at 1 part in $\\bm{10^{18}}$. This milestone will enable a second revolution of new timing applications such as relativistic geodesy, enhanced Earth- and space-based navigation and telescopy, and new tests on physics beyond the Standard Model. Here, we describe the development and operation of two optical lattice clocks, both utilizing spin-polarized, ultracold atomic ytterbium. A measurement comparing these systems demonstrates an unprecedented atomic clock instability of $\\bm{1.6\\times 10^{-18}}$ after only $\\bm{7}$ hours of averaging.

  16. Clock synchronization of a broadband seismometer through IEEE-1588 protocol

    OpenAIRE

    Pallares, Oriol; Río Fernandez, Joaquín del; Shariat Panahi, Shahram

    2010-01-01

    In seismology, the time of the signal acquisition is highly important in order to know the magnitude and location of the earthquake. This paper presents the tests carried out to synchronize the seismometer clock through the IEEE-1588 protocol.

  17. Quantum Atomic Clock Synchronization: An Entangled Concept of Nonlocal Simultaneity

    Science.gov (United States)

    Abrams, D.; Dowling, J.; Williams, C.; Jozsa, R.

    2000-01-01

    We demonstrate that two spatially separated parties (Alice and Bob) can utilize shared prior quantum entanglement, as well as a classical information channel, to establish a synchronized pair of atomic clocks.

  18. Superradiance on the milliHertz linewidth strontium clock transition

    CERN Document Server

    Norcia, Matthew A; Cline, Julia R K; Thompson, James K

    2016-01-01

    Today's best atomic clocks are limited by frequency noise on the lasers used to interrogate the atoms. 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. Here, we demonstrate and characterize superradiant emission from the mHz linewidth clock transition in an ensemble of laser-cooled $^{87}$Sr 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 sub-ensembles.

  19. Novel putative mechanisms to link circadian clocks to healthy aging.

    Science.gov (United States)

    Popa-Wagner, Aurel; Catalin, Bogdan; Buga, Ana-Maria

    2015-08-01

    The circadian clock coordinates the internal physiology to increase the homeostatic capacity thereby providing both a survival advantage to the system and an optimization of energy budgeting. Multiple-oscillator circadian mechanisms are likely to play a role in regulating human health and may contribute to the aging process. Our aim is to give an overview of how the central clock in the hypothalamus and peripheral clocks relate to aging and metabolic disorders, including hyperlipidemia and hyperglycemia. In particular, we unravel novel putative mechanisms to link circadian clocks to healthy aging. This review may lead to the design of large-scale interventions to help people stay healthy as they age by adjusting daily activities, such as feeding behavior, and or adaptation to age-related changes in individual circadian rhythms. PMID:24297467

  20. A Low-jitter 2.5-to-10 GHz Clock Multiplier Unit in CMOS

    OpenAIRE

    Beek, van, P.; Vaucher, C.S.; Leenaerts, D. M. W.; Klumperink, E.A.M.; Nauta, B.

    2003-01-01

    This paper demonstrates a low-jitter clock multiplier unit [1] that generates a 10 GHz output clock from a 2.5 GHz reference clock. An integrated 10 GHz LCoscillator is locked to the input clock, using a simple and fast phase detector circuit. This phase detector overcomes the speed limitation of a conventional tri-state Phase Frequency Detector, by eliminating an internal feedback loop. A frequency detector guarantees PLL locking without degenerating jitter performance. The clock multiplier ...

  1. CLOCK:BMAL1 is a pioneer-like transcription factor

    OpenAIRE

    Menet, Jerome S.; Pescatore, Stefan; Rosbash, Michael

    2014-01-01

    The mammalian circadian clock requires the master transcription factors CLOCK and BMAL1 to drive rhythmic gene expression. Here, Menet et al. report that rhythmic binding of CLOCK:BMAL1 on DNA promotes rhythmic chromatin opening. Mechanisms include CLOCK:BMAL1 binding to nucleosomes and chromatin modifications such as incorporation of histone variant H2A.Z. The data indicate that clock regulation of transcription relies on rhythmic regulation of chromatin accessibility, thus extending the con...

  2. Low Power at Different levels of VLSI Design an clock Distribution Schemes

    OpenAIRE

    Chetan Sharma

    2011-01-01

    Low power chip requirement in the VLSI industry is main considerable field due to the reduction of chip dimension day by day and environmental factors. In this paper various low power techniques at Gate level, Architecture level and different tradeoffs between different clock distribution schemes like as single driver clock scheme and distributed buffers clock scheme are reviewed. Here it is also tried to showing various effects of particular clock distribution scheme such as clock skew, cloc...

  3. Design of Resonant Clock Distribution Networks for 3-D Integrated Circuits

    OpenAIRE

    Rahimian Omam, Somayyeh; Pavlidis, Vasileios; De Micheli, Giovanni

    2011-01-01

    Designing a low power clock network in synchronous circuits is an important task. This requirement is stricter for 3-D circuits due to the increased power densities. Resonant clock networks are considered efficient low-power alternatives to conventional clock distribution schemes. These networks utilize additional inductive circuits to reduce the power consumption while delivering a full swing clock signal to the sink nodes. A design method for 3-D resonant clock networks is presented. The p...

  4. SpiraClock: a continuous and non-intrusive display for upcoming events

    OpenAIRE

    Dragicevic, Pierre; Huot, Stéphane

    2002-01-01

    In this paper, we present SpiraClock, a new visualization technique for nearby events. SpiraClock fills a gap between static calendar displays and pop-up reminders by giving the user a continuous and non-intrusive feedback on nearby events. Events are displayed inside an analog clock that can be used as a regular computer clock. We used SpiraClock for displaying bus schedules, and collected user feedback.

  5. Clock is important for food and circadian regulation of macronutrient absorption in mice

    OpenAIRE

    Pan, Xiaoyue; Hussain, M. Mahmood

    2009-01-01

    Clock genes respond to external stimuli and exhibit circadian rhythms. This study investigated the expression of clock genes in the small intestine and their contribution in the regulation of nutrient absorption by enterocytes. We examined expression of clock genes and macronutrient transport proteins in the small intestines of wild-type and Clock mutant (Clkmt/mt) mice with free or limited access to food. In addition, we studied absorption of macronutrients in these mice. Intestinal clock ge...

  6. Improving X10 Program Performances by Clock Removal

    OpenAIRE

    Feautrier, Paul; Violard, Eric; Ketterlin, Alain

    2014-01-01

    X10 is a promising recent parallel language designed specifically to address the challenges of productively programming a wide variety of target platforms. The sequential core of X10 is an object-oriented language in the Java family. This core is augmented by a few parallel constructs that create activities as a generalization of the well known fork/join model. Clocks are a generalization of the familiar barriers. Synchronization on a clock is specified by the advance() method call. Activitie...

  7. Motion and gravity effects in the precision of quantum clocks

    OpenAIRE

    Lindkvist, Joel; Sabín, Carlos; Johansson, Göran; Fuentes, Ivette

    2014-01-01

    We show that motion and gravity affect the precision of quantum clocks. We consider a localised quantum field as a fundamental model of a quantum clock moving in spacetime and show that its state is modified due to changes in acceleration. By computing the quantum Fisher information we determine how relativistic motion modifies the ultimate bound in the precision of the measurement of time. While in the absence of motion the squeezed vacuum is the ideal state for time estimation, we find that...

  8. When the circadian clock meets the melanin pigmentary system.

    Science.gov (United States)

    Slominski, Andrzej T; Hardeland, Rüdiger; Reiter, Russel J

    2015-04-01

    Silencing of BMAL1 and PER1 stimulates melanogenic activity of follicular and epidermal melanocytes, indicating a novel role for peripheral circadian clock processes in the regulation of melanin pigmentation. Linking the expression levels of BMAL1/PER1 with changes in melanogenesis opens exciting opportunities to study the role of the local molecular clock in modulation of melanocyte functions in the hair follicle and the epidermis with attendant effects on epidermal barrier functions in general. PMID:25785947

  9. Interpretable Machine Learning Models for the Digital Clock Drawing Test

    OpenAIRE

    Souillard-Mandar, William; Davis, Randall; Rudin, Cynthia; Au, Rhoda; Penney, Dana

    2016-01-01

    The Clock Drawing Test (CDT) is a rapid, inexpensive, and popular neuropsychological screening tool for cognitive conditions. The Digital Clock Drawing Test (dCDT) uses novel software to analyze data from a digitizing ballpoint pen that reports its position with considerable spatial and temporal precision, making possible the analysis of both the drawing process and final product. We developed methodology to analyze pen stroke data from these drawings, and computed a large collection of featu...

  10. The clock ambiguity and the emergence of physical laws

    OpenAIRE

    Albrecht, Andreas; Iglesias, Alberto

    2007-01-01

    The process of identifying a time variable in time reparameterization invariant theories results in great ambiguities about the actual laws of physics described by a given theory. A theory set up to describe one set of physical laws can equally well be interpreted as describing any other laws of physics by making a different choice of time variable or ``clock''. In this article we demonstrate how this ``clock ambiguity'' arises and then discuss how one might still hope to extract specific pre...

  11. An Integrated Architectural Clock Implemented Memory Design Analysis

    OpenAIRE

    Ravi Khatwal; Manoj Kumar Jain

    2015-01-01

    Recently Low power consumption and Custom Memory design is major issue for embedded designer. Micro wind and Xilinx simulator implements SRAM design architecture and performs efficient simulation. These simulators implements high performances and low power consumption of SRAM design. SRAM efficiency analyzed with 6-T architecture design and row/column based architectural design. We have analyzed clock implemented memory design and simulated with specific application. We have implemented clock...

  12. A mercury optical lattice clock at LNE-SYRTE

    Science.gov (United States)

    De Sarlo, L.; Favier, M.; Tyumenev, R.; Bize, S.

    2016-06-01

    We describe the development of an optical lattice clock based on mercury and the results obtained since the 7 th SFSM. We briefly present a new solution for the cooling laser system and an improved lattice trap that allows us to interrogate a few thousand atoms in parallel. This translates into a fractional short term stability of 1.2 x 10-15 at the clock frequency of 1.129 PHz.

  13. Consistency Models in Distributed Systems with Physical Clocks

    OpenAIRE

    Du, Jiaqing

    2014-01-01

    Most existing distributed systems use logical clocks to order events in the implementation of various consistency models. Although logical clocks are straightforward to implement and maintain, they may affect the scalability, availability, and latency of the system when being used to totally order events in strong consistency models. They can also incur considerable overhead when being used to track and check the causal relationships among events in some weak consistency models. In this thesi...

  14. Master Clock and Time-Signal-Distribution System

    Science.gov (United States)

    Tjoelker, Robert; Calhoun, Malcolm; Kuhnle, Paul; Sydnor, Richard; Lauf, John

    2007-01-01

    A timing system comprising an electronic master clock and a subsystem for distributing time signals from the master clock to end users is undergoing development to satisfy anticipated timing requirements of NASA s Deep Space Network (DSN) for the next 20 to 30 years. This system has a modular, flexible, expandable architecture that is easier to operate and maintain than the present frequency and timing subsystem (FTS).

  15. Methylphenidate Modifies the Motion of the Circadian Clock

    OpenAIRE

    Antle, Michael C.; van Diepen, Hester C; Deboer, Tom; Pedram, Pardis; Pereira, Rob Rodrigues; Meijer, Johanna H.

    2012-01-01

    People with attention-deficit/hyperactivity disorder (ADHD) often experience sleep problems, and these are frequently exacerbated by the methylphenidate they take to manage their ADHD symptoms. Many of the changes to sleep are consistent with a change in the underlying circadian clock. The present study was designed to determine if methylphenidate alone could alter properties of the circadian clock. Young male mice were examined in light–dark cycles and in constant darkness and recordings wer...

  16. Clocks, computers, black holes, spacetime foam, and holographic principle

    OpenAIRE

    Ng, Y. Jack

    2000-01-01

    What do simple clocks, simple computers, black holes, space-time foam, and holographic principle have in common? I will show that the physics behind them is inter-related, linking together our concepts of information, gravity, and quantum uncertainty. Thus, the physics that sets the limits to computation and clock precision also yields Hawking radiation of black holes and the holographic principle. Moreover, the latter two strongly imply that space-time undergoes much larger quantum fluctuati...

  17. Clocking In Turbines: Remarks On Physical Nature And Geometric Requirements

    Directory of Open Access Journals (Sweden)

    Swirydczuk Jerzy

    2015-04-01

    Full Text Available The article discusses two issues relating to the clocking phenomenon in turbines, which are the physical course of stator wake deformation in rotor passages and its further interaction with downstream stator blades, and turbine geometry parameters which are believed to be most favourable for clocking. In both cases, the results presented in the article have made it possible to verify and reformulate the previously accepted opinions.

  18. Adrenergic regulation of clock gene expression in mouse liver

    OpenAIRE

    Terazono, Hideyuki; Mutoh, Tatsushi; Yamaguchi, Shun; Kobayashi, Masaki; Akiyama, Masashi; Udo, Rhyuta; Ohdo, Shigehiro; Okamura, Hitoshi; Shibata, Shigenobu

    2003-01-01

    A main oscillator in the suprachiasmatic nucleus (SCN) conveys circadian information to the peripheral clock systems for the regulation of fundamental physiological functions. Although polysynaptic autonomic neural pathways between the SCN and the liver were observed in rats, whether activation of the sympathetic nervous system entrains clock gene expression in the liver has yet to be understood. To assess sympathetic innervation from the SCN to liver tissue, we investigated whether inj...

  19. Clock Face Drawing Test Performance in Children with ADHD

    Directory of Open Access Journals (Sweden)

    Ahmad Ghanizadeh

    2013-01-01

    Full Text Available  Introduction: The utility and discriminatory pattern of the clock face drawing test in ADHD is unclear. This study therefore compared Clock Face Drawing test performance in children with ADHD and controls.   Material & methods: 95 children with ADHD and 191 school children were matched for gender ratio and age. ADHD symptoms severities were assessed using DSM-IV ADHD checklist and their intellectual functioning was assessed. The participants completed three clock-drawing tasks, and the following four functions were assessed: Contour score, Numbers score, Hands setting score, and Center score    Results: All the subscales scores of the three clock drawing tests of the ADHD group were lower than that of the control group. In ADHD children, inattention and hyperactivity/impulsivity scores were not related with free drawn clock test scores. When pre-drawn contour test was performed, inattentiveness score was statistically associated with Number score. None of the other variables of age, gender, intellectual functioning, and hand use preference were associated with Numbers score. In pre-drawn clock, no association of ADHD symptoms with any CDT subscales was significant. In addition, more errors are observed with free drawn clock and Pre-drawn contour than pre-drawn clock.    Conclusion: Putting Numbers and Hands setting are more sensitive measures to screen ADHD than Contour and Center drawing. Test performance, except Hands setting, may have already reached a developmental plateau. It is probable that Hand setting deficit in children with ADHD may not decrease from age 8 to 14 years. Performance of children with ADHD is associated with the complexity of CDT.

  20. Gravitational wave detection with optical lattice atomic clocks

    OpenAIRE

    Kolkowitz, Shimon; Pikovski, Igor; Langellier, Nicholas; Lukin, Mikhail D.; Walsworth, Ronald L.; Ye, Jun

    2016-01-01

    We propose a space-based gravitational wave detector consisting of two spatially separated, drag-free satellites sharing ultra-stable optical laser light over a single baseline. Each satellite contains an optical lattice atomic clock, which serves as a sensitive, narrowband detector of the local frequency of the shared laser light. A synchronized two-clock comparison between the satellites will be sensitive to the effective Doppler shifts induced by incident gravitational waves (GWs) at a lev...

  1. General relativistic effects in quantum interference of "clocks"

    CERN Document Server

    Zych, Magdalena; Costa, Fabio; Brukner, Časlav

    2016-01-01

    Quantum mechanics and general relativity have been each successfully tested in numerous experiments. However, the regime where both theories are jointly required to explain physical phenomena remains untested by laboratory experiments, and is also not fully understood by theory. This contribution reviews recent ideas for a new type of experiments: quantum interference of "clocks", which aim to test novel quantum effects that arise from time dilation. "Clock" interference experiments could be realised with atoms or photons in near future laboratory experiments.

  2. A Clock Enhanced Loop for Simultaneous Error-Free Demultiplexing and Clock Recovery of 160 Gb/s OTDM Signal Single-Channel Transmission over 100 km

    Institute of Scientific and Technical Information of China (English)

    JIA Nan; LI Tang-Jun; ZHONG Kang-Ping; WANG Mu-Guang; CHEN Ming; LI Jing; CHI Jian-Feng

    2010-01-01

    @@ A simple clock enhanced loop of cascaded electro-absorption modulators(EAMs)and 10GHz clock recovery modules is presented.The intensity of harmonic of clock-frequency component is analyzed theoretically and verified experimentally in a 160Gb/s OTDM 100km transmission system.The 10GHz clock component is enhanced obviously before launching into the clock recovery module and the recovered clock signal exhibits low rms jitter of < 400 fs.Moreover,completely error-free(10-12)transmission is observed for more than two hours without using forward error correction technology.The power penalty is about 3.6dB.The proposed loop has merits of enhancing base clock component,simultaneously de-multiplexing and clock recovery,which make the performance of this loop more stable and high suppression of non-target channels.

  3. A clock network for geodesy and fundamental science.

    Science.gov (United States)

    Lisdat, C; Grosche, G; Quintin, N; Shi, C; Raupach, S M F; Grebing, C; Nicolodi, D; Stefani, F; Al-Masoudi, A; Dörscher, S; Häfner, S; Robyr, J-L; Chiodo, N; Bilicki, S; Bookjans, E; Koczwara, A; Koke, S; Kuhl, A; Wiotte, F; Meynadier, F; Camisard, E; Abgrall, M; Lours, M; Legero, T; Schnatz, H; Sterr, U; Denker, H; Chardonnet, C; Le Coq, Y; Santarelli, G; Amy-Klein, A; Le Targat, R; Lodewyck, J; Lopez, O; Pottie, P-E

    2016-01-01

    Leveraging the unrivalled performance of optical clocks as key tools for geo-science, for astronomy and for fundamental physics beyond the standard model requires comparing the frequency of distant optical clocks faithfully. Here, we report on the comparison and agreement of two strontium optical clocks at an uncertainty of 5 × 10(-17) via a newly established phase-coherent frequency link connecting Paris and Braunschweig using 1,415 km of telecom fibre. The remote comparison is limited only by the instability and uncertainty of the strontium lattice clocks themselves, with negligible contributions from the optical frequency transfer. A fractional precision of 3 × 10(-17) is reached after only 1,000 s averaging time, which is already 10 times better and more than four orders of magnitude faster than any previous long-distance clock comparison. The capability of performing high resolution international clock comparisons paves the way for a redefinition of the unit of time and an all-optical dissemination of the SI-second. PMID:27503795

  4. Dark energy from quantum uncertainty of distant clock

    Science.gov (United States)

    Luo, M. J.

    2015-06-01

    The observed cosmic acceleration was attributed to an exotic dark energy in the framework of classical general relativity. The dark energy behaves very similar with vacuum energy in quantum mechanics. However, once the quantum effects are seriously taken into account, it predicts a completely wrong result and leads to a severe fine-tuning. To solve the problem, the exact meaning of time in quantum mechanics is reexamined. We abandon the standard interpretation of time in quantum mechanics that time is just a global parameter, replace it by a quantum dynamical variable playing the role of physical clock. We find that synchronization of two spatially separated clocks can not be precisely realized at quantum level. There is an intrinsic quantum uncertainty of distant clock time, which implies an apparent vacuum energy fluctuation and gives an observed dark energy density at tree level approximation, where L P and L H are the Planck and Hubble scale cutoffs. The fraction of the dark energy is given by , which does not evolve with the internal clock time. The "dark energy" as a quantum cosmic variance is always seen comparable with the matter energy density by an observer using the internal clock time. The corrected distance-redshift relation of cosmic observations due to the distant clock effect are also discussed, which again gives a redshift independent fraction . The theory is consistent with current cosmic observations.

  5. The Molecular Circadian Clock and Alcohol-Induced Liver Injury

    Science.gov (United States)

    Udoh, Uduak S.; Valcin, Jennifer A.; Gamble, Karen L.; Bailey, Shannon M.

    2015-01-01

    Emerging evidence from both experimental animal studies and clinical human investigations demonstrates strong connections among circadian processes, alcohol use, and alcohol-induced tissue injury. Components of the circadian clock have been shown to influence the pathophysiological effects of alcohol. Conversely, alcohol may alter the expression of circadian clock genes and the rhythmic behavioral and metabolic processes they regulate. Therefore, we propose that alcohol-mediated disruption in circadian rhythms likely underpins many adverse health effects of alcohol that cut across multiple organ systems. In this review, we provide an overview of the circadian clock mechanism and showcase results from new studies in the alcohol field implicating the circadian clock as a key target of alcohol action and toxicity in the liver. We discuss various molecular events through which alcohol may work to negatively impact circadian clock-mediated processes in the liver, and contribute to tissue pathology. Illuminating the mechanistic connections between the circadian clock and alcohol will be critical to the development of new preventative and pharmacological treatments for alcohol use disorders and alcohol-mediated organ diseases. PMID:26473939

  6. The Molecular Circadian Clock and Alcohol-Induced Liver Injury

    Directory of Open Access Journals (Sweden)

    Uduak S. Udoh

    2015-10-01

    Full Text Available Emerging evidence from both experimental animal studies and clinical human investigations demonstrates strong connections among circadian processes, alcohol use, and alcohol-induced tissue injury. Components of the circadian clock have been shown to influence the pathophysiological effects of alcohol. Conversely, alcohol may alter the expression of circadian clock genes and the rhythmic behavioral and metabolic processes they regulate. Therefore, we propose that alcohol-mediated disruption in circadian rhythms likely underpins many adverse health effects of alcohol that cut across multiple organ systems. In this review, we provide an overview of the circadian clock mechanism and showcase results from new studies in the alcohol field implicating the circadian clock as a key target of alcohol action and toxicity in the liver. We discuss various molecular events through which alcohol may work to negatively impact circadian clock-mediated processes in the liver, and contribute to tissue pathology. Illuminating the mechanistic connections between the circadian clock and alcohol will be critical to the development of new preventative and pharmacological treatments for alcohol use disorders and alcohol-mediated organ diseases.

  7. Serum factors in older individuals change cellular clock properties

    Science.gov (United States)

    Pagani, Lucia; Schmitt, Karen; Meier, Fides; Izakovic, Jan; Roemer, Konstanze; Viola, Antoine; Cajochen, Christian; Wirz-Justice, Anna; Brown, Steven A.; Eckert, Anne

    2011-01-01

    Human aging is accompanied by dramatic changes in daily sleep–wake behavior: Activity shifts to an earlier phase, and the consolidation of sleep and wake is disturbed. Although this daily circadian rhythm is brain-controlled, its mechanism is encoded by cell-autonomous circadian clocks functioning in nearly every cell of the body. In fact, human clock properties measured in peripheral cells such as fibroblasts closely mimic those measured physiologically and behaviorally in the same subjects. To understand better the molecular mechanisms by which human aging affects circadian clocks, we characterized the clock properties of fibroblasts cultivated from dermal biopsies of young and older subjects. Fibroblast period length, amplitude, and phase were identical in the two groups even though behavior was not, thereby suggesting that basic clock properties of peripheral cells do not change during aging. Interestingly, measurement of the same cells in the presence of human serum from older donors shortened period length and advanced the phase of cellular circadian rhythms compared with treatment with serum from young subjects, indicating that a circulating factor might alter human chronotype. Further experiments demonstrated that this effect is caused by a thermolabile factor present in serum of older individuals. Thus, even though the molecular machinery of peripheral circadian clocks does not change with age, some age-related circadian dysfunction observed in vivo might be of hormonal origin and therefore might be pharmacologically remediable. PMID:21482780

  8. Frequency noise processes in a strontium ion optical clock

    International Nuclear Information System (INIS)

    A recent comparison of the frequencies of a pair of optical clocks based on the 674 nm 2S1/2–2D5/2 optical clock transition in 88Sr+ has highlighted the need to understand factors affecting frequency instability. We have developed statistical models to show that our clock is capable of reaching the quantum projection noise limit; for our clock using 100 ms probe pulses, this is ∼3 × 10−15/√τ. However, this optical clock uses atomic transitions with a linear Zeeman shift, which can lead to a degradation in stability in the presence of magnetic field noise. We show that this generally leads to an increase in white frequency noise, even in cases dominated by magnetic field flicker or random walk noise. By taking into account both the quantum projection and magnetic field noise we are able to explain our observed frequency instabilities. This analysis will relate to any optical clock with a linear Zeeman shift where cancellation of this shift is achieved by interrogating pairs of components. Furthermore, implementing automatic control of lasers and minimization of micromotion requires pausing of the frequency servo occasionally; this leads to only a small degradation of frequency stability. (paper)

  9. Quantum arrival and dwell times via idealized clocks

    International Nuclear Information System (INIS)

    A number of approaches to the problem of defining arrival- and dwell-time probabilities in quantum theory makes use of idealized models of clocks. An interesting question is the extent to which the probabilities obtained in this way are related to standard semiclassical results. In this paper, we explore this question using a reasonably general clock model, solved using path-integral methods. We find that, in the weak-coupling regime, where the energy of the clock is much less than the energy of the particle it is measuring, the probability for the clock pointer can be expressed in terms of the probability current in the case of arrival times, and the dwell-time operator in the case of dwell times, the expected semiclassical results. In the regime of strong system-clock coupling, we find that the arrival-time probability is proportional to the kinetic-energy density, consistent with an earlier model involving a complex potential. We argue that, properly normalized, this may be the generically expected result in this regime. We show that these conclusions are largely independent of the form of the clock Hamiltonian.

  10. Inexpensive Clock for Displaying Planetary or Sidereal Time

    Science.gov (United States)

    Lux, James

    2007-01-01

    An inexpensive wall clock has been devised for displaying solar time or sidereal time as it would be perceived on a planet other than the Earth, or for displaying sidereal time on the Earth. The concept of a wall clock synchronized to a period other than the terrestrial mean solar day is not new in itself. What is new here is that the clock is realized through a relatively simple electronic modification of a common battery-powered, quartz-crystal-oscillator-driven wall clock. The essence of the modification is to shut off the internal oscillator of the clock and replace the internal-oscillator output signal with a signal of the required frequency generated by an external oscillator. The unmodified clock electronic circuitry includes a quartz crystal connected to an integrated circuit (IC) that includes, among other parts, a buffer amplifier that conditions the oscillator output. The modification is effected by removing the quartz crystal and connecting the output terminal of the external oscillator, via a capacitor, to the input terminal of the buffer amplifier

  11. Mercury Ion Clock for a NASA Technology Demonstration Mission.

    Science.gov (United States)

    Tjoelker, Robert L; Prestage, John D; Burt, Eric A; Chen, Pin; Chong, Yong J; Chung, Sang K; Diener, William; Ely, Todd; Enzer, Daphna G; Mojaradi, Hadi; Okino, Clay; Pauken, Mike; Robison, David; Swenson, Bradford L; Tucker, Blake; Wang, Rabi

    2016-07-01

    There are many different atomic frequency standard technologies but only few meet the demanding performance, reliability, size, mass, and power constraints required for space operation. The Jet Propulsion Laboratory is developing a linear ion-trap-based mercury ion clock, referred to as DSAC (Deep-Space Atomic Clock) under NASA's Technology Demonstration Mission program. This clock is expected to provide a new capability with broad application to space-based navigation and science. A one-year flight demonstration is planned as a hosted payload following an early 2017 launch. This first-generation mercury ion clock for space demonstration has a volume, mass, and power of 17 L, 16 kg, and 47 W, respectively, with further reductions planned for follow-on applications. Clock performance with a signal-to-noise ratio (SNR)*Q limited stability of 1.5E-13/τ(1/2) has been observed and a fractional frequency stability of 2E-15 at one day measured (no drift removed). Such a space-based stability enables autonomous timekeeping of with a technology capable of even higher stability, if desired. To date, the demonstration clock has been successfully subjected to mechanical vibration testing at the 14 grms level, thermal-vacuum operation over a range of 42(°)C, and electromagnetic susceptibility tests. PMID:27019481

  12. Influence of relativistic effects on satellite-based clock synchronization

    Science.gov (United States)

    Wang, Jieci; Tian, Zehua; Jing, Jiliang; Fan, Heng

    2016-03-01

    Clock synchronization between the ground and satellites is a fundamental issue in future quantum telecommunication, navigation, and global positioning systems. Here, we propose a scheme of near-Earth orbit satellite-based quantum clock synchronization with atmospheric dispersion cancellation by taking into account the spacetime background of the Earth. Two frequency entangled pulses are employed to synchronize two clocks, one at a ground station and the other at a satellite. The time discrepancy of the two clocks is introduced into the pulses by moving mirrors and is extracted by measuring the coincidence rate of the pulses in the interferometer. We find that the pulses are distorted due to effects of gravity when they propagate between the Earth and the satellite, resulting in remarkably affected coincidence rates. We also find that the precision of the clock synchronization is sensitive to the source parameters and the altitude of the satellite. The scheme provides a solution for satellite-based quantum clock synchronization with high precision, which can be realized, in principle, with current technology.

  13. Clock auto-synchronization method for BESIII ETOF upgrade

    Science.gov (United States)

    Wang, Si-Yu; Cao, Ping; Liu, Shu-Bin; An, Qi

    2015-12-01

    An automatic clock synchronization method implemented in a field programmable gate array (FPGA) is proposed in this paper. It is developed for the clock system which will be applied in the end-cap time of flight (ETOF) upgrade of the Beijing Spectrometer (BESIII). In this design, an FPGA is used to automatically monitor the synchronization circuit and deal with signals coming from the external clock synchronization circuit. By testing different delay time of the detection signal and analyzing the signal state returned, the synchronization windows can be found automatically by the FPGA. The new clock system not only retains low clock jitter which is less than 20ps root mean square (RMS), but also demonstrates automatic synchronization to the beam bunches. So far, the clock auto-synchronizing function has been working successfully under a series of tests. It will greatly simplify the system initialization and maintenance in the future. Supported by National Natural Science Foundation of China (10979003, 11005107), CAS Center for Excellence in Particle Physics (CCEPP)

  14. Reduced Voltage Scaling in Clock Distribution Networks

    Directory of Open Access Journals (Sweden)

    Khader Mohammad

    2009-01-01

    Full Text Available We propose a novel circuit technique to generate a reduced voltage swing (RVS signals for active power reduction on main buses and clocks. This is achieved without performance degradation, without extra power supply requirement, and with minimum area overhead. The technique stops the discharge path on the net that is swinging low at a certain voltage value. It reduces active power on the target net by as much as 33% compared to traditional full swing signaling. The logic 0 voltage value is programmable through control bits. If desired, the reduced-swing mode can also be disabled. The approach assumes that the logic 0 voltage value is always less than the threshold voltage of the nMOS receivers, which eliminate the need of the low to high voltage translation. The reduced noise margin and the increased leakage on the receiver transistors using this approach have been addressed through the selective usage of multithreshold voltage (MTV devices and the programmability of the low voltage value.

  15. Cardiovascular tissues contain independent circadian clocks

    Science.gov (United States)

    Davidson, A. J.; London, B.; Block, G. D.; Menaker, M.

    2005-01-01

    Acute cardiovascular events exhibit a circadian rhythm in the frequency of occurrence. The mechanisms underlying these phenomena are not yet fully understood, but they may be due to rhythmicity inherent in the cardiovascular system. We have begun to characterize rhythmicity of the clock gene mPer1 in the rat cardiovascular system. Luciferase activity driven by the mPer1 gene promoter is rhythmic in vitro in heart tissue explants and a wide variety of veins and arteries cultured from the transgenic Per1-luc rat. The tissues showed between 3 and 12 circadian cycles of gene expression in vitro before damping. Whereas peak per1-driven bioluminescence consistently occurred during the late night in the heart and all arteries sampled, the phases of the rhythms in veins varied significantly by anatomical location. Varying the time of the culture procedure relative to the donor animal's light:dark cycle revealed that, unlike some other rat tissues such as liver, the phases of in vitro rhythms of arteries, veins, and heart explants were affected by culture time. However, phase relationships among tissues were consistent across culture times; this suggests diversity in circadian regulation among components of the cardiovascular system.

  16. Chemical clocks for early-type galaxies

    CERN Document Server

    Carretero, C; Beckman, J E

    2007-01-01

    We present a detailed stellar population analysis of 27 massive elliptical galaxies within 4 very rich clusters at redshift z~0.2. We obtained accurate estimates of the mean luminosity-weighted ages and relative abundances of CN, Mg and Fe as functions of the galaxy velocity dispersion, sigma. Our results are compatible with a scenario in which the stellar populations of massive elliptical galaxies, independently of their environment and mass, had formation timescales shorter than ~1 Gyr. This result implies that massive elliptical galaxies have evolved passively since, at least, as long ago as z~2. For a given galaxy mass the duration of star formation is shorter in those galaxies belonging to more dense environments. Finally, we show that the abundance ratios [CN/Fe] and [Mg/Fe] are the key "chemical clocks" to infer the star formation history timescales in ellipticals. In particular, [Mg/Fe] provides an upper limit for those formation timescales, while [CN/Fe] apperars to be the most suitable parameter to ...

  17. Development of a strontium optical lattice clock for space applications

    Science.gov (United States)

    Singh, Yeshpal

    2016-07-01

    With timekeeping being of paramount importance for modern life, much research and major scientific advances have been undertaken in the field of frequency metrology, particularly over the last few years. New Nobel-prize winning technologies have enabled a new era of atomic clocks; namely the optical clock. These have been shown to perform significantly better than the best microwave clocks reaching an inaccuracy of 1.6x10-18 [1]. With such results being found in large lab based apparatus, the focus now has shifted to portability - to enable the accuracy of various ground based clocks to be measured, and compact autonomous performance - to enable such technologies to be tested in space. This could lead to a master clock in space, improving not only the accuracy of technologies on which modern life has come to require such as GPS and communication networks. But also more fundamentally, this could lead to the redefinition of the second and tests of fundamental physics including applications in the fields of ground based and satellite geodesy, metrology, positioning, navigation, transport and logistics etc. Within the European collaboration, Space Optical Clocks (SOC2) [2-3] consisting of various institutes and industry partners across Europe we have tried to tackle this problem of miniaturisation whilst maintaining stability, accuracy (5x10-17) and robustness whilst keeping power consumption to a minimum - necessary for space applications. We will present the most recent results of the Sr optical clock in SOC2 and also the novel compact design features, new methods employed and outlook. References [1] B. J. Bloom, T. L. Nicholson, J. R. Williams, S. L. Campbell, M. Bishof, X. Zhang, W. Zhang, S. L. Bromley, and J. Ye, "An optical lattice clock with accuracy and stability at the 10-18 level," Nature 506, 71-75 (2014). [2] S. Schiller et al. "Towards Neutral-atom Space Optical Clocks (SOC2): Development of high-performance transportable and breadboard optical clocks and

  18. British domestic synchronous clocks 1930-1980 the rise and fall of a technology

    CERN Document Server

    Pook, Leslie Philip

    2015-01-01

    This book complements available one-make books on domestic synchronous clocks. It is also a history of science book that sets British domestic synchronous clocks, their manufacturers and technology in their social context. Part I covers the historical background, British domestic synchronous clock manufacturers and brands, how synchronous clocks work, domestic synchronous clock cases, practical advice on the servicing of domestic synchronous clocks, and analysis of the marketing and reliability of British domestic synchronous clocks. This analysis provides an explanation of the rise and eventual fall of their technology. Part II contains galleries of a selection of British domestic synchronous clocks, and of the movements with which they are fitted. There is a front and back view of each clock, together with a brief description. Views of each movement include views with the movement partly dismantled, together with a brief technical description of the movement. This profusely illustrated book is primarily fo...

  19. Functional Implications of the CLOCK 3111T/C Single-Nucleotide Polymorphism.

    Science.gov (United States)

    Ozburn, Angela R; Purohit, Kush; Parekh, Puja K; Kaplan, Gabrielle N; Falcon, Edgardo; Mukherjee, Shibani; Cates, Hannah M; McClung, Colleen A

    2016-01-01

    Circadian rhythm disruptions are prominently associated with bipolar disorder (BD). Circadian rhythms are regulated by the molecular clock, a family of proteins that function together in a transcriptional-translational feedback loop. The CLOCK protein is a key transcription factor of this feedback loop, and previous studies have found that manipulations of the Clock gene are sufficient to produce manic-like behavior in mice (1). The CLOCK 3111T/C single-nucleotide polymorphism (SNP; rs1801260) is a genetic variation of the human CLOCK gene that is significantly associated with increased frequency of manic episodes in BD patients (2). The 3111T/C SNP is located in the 3'-untranslated region of the CLOCK gene. In this study, we sought to examine the functional implications of the human CLOCK 3111T/C SNP by transfecting a mammalian cell line (mouse embryonic fibroblasts isolated from Clock(-/-) knockout mice) with pcDNA plasmids containing the human CLOCK gene with either the T or C SNP at position 3111. We then measured circadian gene expression over a 24-h time period. We found that the CLOCK3111C SNP resulted in higher mRNA levels than the CLOCK 3111T SNP. Furthermore, we found that Per2, a transcriptional target of CLOCK, was also more highly expressed with CLOCK 3111C expression, indicating that the 3'-UTR SNP affects the expression, function, and stability of CLOCK mRNA. PMID:27148095

  20. Strontium Optical Lattice Clock: In Quest of the Ultimate Performance

    International Nuclear Information System (INIS)

    This thesis presents the latest achievements regarding the Sr optical lattice clock experiment at LNESYRTE, Observatoire de Paris. After having described the general principles for optical lattice clocks and the operation of the clock in question, the emphasis is put on the features that have been added to the experiment since 2007. The most important new elements are an ultra-stable reference cavity for the clock laser, the development of a non-destructive detection technique, and the construction of a second Sr lattice clock. The ultra-stable cavity is constructed from a ULE spacer and fused silica mirrors and has shown a thermal noise floor at 6.5 * 10-16, placing it among the best in the world. The non-destructive detection is effectuated by a phase measurement of a weak probe beam that traverses the atoms placed in one arm of a Mach-Zender interferometer. The non-destructive aspect enables a recycling of the atoms from cycle to cycle which consequently increases the duty cycle, allowing for an increase of the stability of the clock. With these new tools the frequency stability is expected to be 2.2 * 10-16/√τ for an optimized sequence. The most recent comparisons between the two Sr clocks reach an accuracy level of 10-16 after about 1000 s, and this way we have been able to characterize lattice related frequency shifts with an unprecedented accuracy. The measurements ensure a control of lattice related effects at the 10-18 level even for trap depths as large as 50Er. (authors)

  1. Pacemaker-neuron-dependent disturbance of the molecular clockwork by a Drosophila CLOCK mutant homologous to the mouse Clock mutation.

    Science.gov (United States)

    Lee, Euna; Cho, Eunjoo; Kang, Doo Hyun; Jeong, Eun Hee; Chen, Zheng; Yoo, Seung-Hee; Kim, Eun Young

    2016-08-16

    Circadian clocks are composed of transcriptional/translational feedback loops (TTFLs) at the cellular level. In Drosophila TTFLs, the transcription factor dCLOCK (dCLK)/CYCLE (CYC) activates clock target gene expression, which is repressed by the physical interaction with PERIOD (PER). Here, we show that amino acids (AA) 657-707 of dCLK, a region that is homologous to the mouse Clock exon 19-encoded region, is crucial for PER binding and E-box-dependent transactivation in S2 cells. Consistently, in transgenic flies expressing dCLK with an AA657-707 deletion in the Clock (Clk(out)) genetic background (p{dClk-Δ};Clk(out)), oscillation of core clock genes' mRNAs displayed diminished amplitude compared with control flies, and the highly abundant dCLKΔ657-707 showed significantly decreased binding to PER. Behaviorally, the p{dClk-Δ};Clk(out) flies exhibited arrhythmic locomotor behavior in the photic entrainment condition but showed anticipatory activities of temperature transition and improved free-running rhythms in the temperature entrainment condition. Surprisingly, p{dClk-Δ};Clk(out) flies showed pacemaker-neuron-dependent alterations in molecular rhythms; the abundance of dCLK target clock proteins was reduced in ventral lateral neurons (LNvs) but not in dorsal neurons (DNs) in both entrainment conditions. In p{dClk-Δ};Clk(out) flies, however, strong but delayed molecular oscillations in temperature cycle-sensitive pacemaker neurons, such as DN1s and DN2s, were correlated with delayed anticipatory activities of temperature transition. Taken together, our study reveals that the LNv molecular clockwork is more sensitive than the clockwork of DNs to dysregulation of dCLK by AA657-707 deletion. Therefore, we propose that the dCLK/CYC-controlled TTFL operates differently in subsets of pacemaker neurons, which may contribute to their specific functions. PMID:27489346

  2. A high-precision synchronization circuit for clock distribution

    International Nuclear Information System (INIS)

    In this paper, a novel structure of a high-precision synchronization circuit, HPSC, using interleaved delay units and a dynamic compensation circuit is proposed. HPSCs are designed for synchronization of clock distribution networks in large-scale integrated circuits, where high-quality clocks are required. The application of a hybrid structure of a coarse delay line and dynamic compensation circuit performs roughly the alignment of the clock signal in two clock cycles, and finishes the fine tuning in the next three clock cycles with the phase error suppressed under 3.8 ps. The proposed circuit is implemented and fabricated using a SMIC 0.13 μm 1P6M process with a supply voltage at 1.2 V. The allowed operation frequency ranges from 200 to 800 MHz, and the duty cycle ranges between [20%, 80%]. The active area of the core circuits is 245 × 134 μm2, and the power consumption is 1.64 mW at 500 MHz. (paper)

  3. 2e-18 total uncertainty in an atomic clock

    CERN Document Server

    Nicholson, T L; Hutson, R B; Marti, G E; Bloom, B J; McNally, R L; Zhang, W; Barrett, M D; Safronova, M S; Strouse, G F; Tew, W L; Ye, J

    2014-01-01

    The pursuit of better atomic clocks has advanced many research areas, providing better quantum state control, new insights in quantum science, tighter limits on fundamental constant variation, and improved tests of relativity. The record for the best stability and accuracy is currently held by optical lattice clocks. This work takes an important step towards realizing the full potential of a many-particle clock with a state-of-the-art stable laser. Here, we achieve fractional stability of 2.2e-16 at 1 s by using seconds-long coherent interrogations of our clock transition in a low-density system not limited by atomic interactions. With this better stability, we perform a new accuracy evaluation of our clock, improving many systematic uncertainties that limited our previous measurements, such as the lattice ac Stark and blackbody radiation (BBR) shifts. For the lattice ac Stark systematic, we identify the lattice laser frequency where the scalar and tensor components of the shift cancel, allowing for state ind...

  4. Progress Toward a Compact, Highly Stable Ion Clock

    Science.gov (United States)

    Prestage, John; Chung, Sang

    2009-01-01

    There was an update on the subject of two previous NASA Tech Briefs articles: Compact, Highly Stable Ion Clock (NPO-43075), Vol. 32, No. 5 (May 2008), page 63; and Neon as a Buffer Gas for a Mercury-Ion Clock (NPO-42919), Vol. 32, No. 7 (July 2008), page 62. To recapitulate: A developmental miniature mercury-ion clock has stability comparable to that of a hydrogen-maser clock. The ion-handling components are housed in a sealed vacuum tube, wherein a getter pump maintains the partial vacuum, and the evacuated tube is backfilled with mercury vapor in a neon buffer gas. There was progress in the development of the clock, with emphasis on the design, fabrication, pump-down, and bake-out of the vacuum tube (based on established practice in the travelingwave- tube-amplifier industry) and the ability of the tube to retain a vacuum after a year of operation. Other developments include some aspects of the operation of mercury-vapor source (a small appendage oven containing HgO) so as to maintain the optimum low concentration of mercury vapor, and further efforts to miniaturize the vacuum and optical subsystems to fit within a volume of 2 L.

  5. Atomic clocks as a tool to monitor vertical surface motion

    CERN Document Server

    Bondarescu, Ruxandra; Lundgren, Andrew; Hetényi, György; Houlié, Nicolas; Jetzer, Philippe; Bondarescu, Mihai

    2015-01-01

    Atomic clock technology is advancing rapidly, now reaching stabilities of $\\Delta f/f \\sim 10^{-18}$, which corresponds to resolving $1$ cm in equivalent geoid height over an integration timescale of about 7 hours. At this level of performance, ground-based atomic clock networks emerge as a tool for monitoring a variety of geophysical processes by directly measuring changes in the gravitational potential. Vertical changes of the clock's position due to magmatic, volcanic, post-seismic or tidal deformations can result in measurable variations in the clock tick rate. As an example, we discuss the geopotential change arising due to an inflating point source (Mogi model), and apply it to the Etna volcano. Its effect on an observer on the Earth's surface can be divided into two different terms: one purely due to uplift and one due to the redistribution of matter. Thus, with the centimetre-level precision of current clocks it is already possible to monitor volcanoes. The matter redistribution term is estimated to b...

  6. Energy Efficient Global Clock Synchronization for Wireless Sensor Networks

    Directory of Open Access Journals (Sweden)

    Vinod Namboodiri

    2010-05-01

    Full Text Available Clock synchronization is critical to many sensor networks for the success of the application as well as energyefficiency. Achieving a global time frame through localized averaging of clock values for multiple rounds till convergenceis a promising approach to clock synchronization due to the decentralized nature of computation coupled withscalability. However, it is not clear what power levels for all nodes would make the synchronization process energyefficient.Large power levels lead to faster convergence but consume a lot of energy per round of synchronization.On the other hand, smaller powers consume little energy per round, but convergence is very slow requiring a lotof rounds to achieve synchronization. In this paper we look at the problem of finding a power assignment thatachieves global clock synchronization in the most energy-efficient manner possible. We look at the problem throughtwo dimensions; rate of convergence and energy consumed per round of synchronization. A centralized algorithm ispresented that uses the path congestion of the induced communication graph to estimate which power assignmentshave good convergence properties and find one that minimizes the total energy to achieve clock synchronization.Our evaluation demonstrates that the power assignment derived from this algorithm is very energy-efficient and isapplicable for wireless communication environments with various distance-power gradients. Further, we present asimple distributed algorithm which nodes can execute locally to derive energy-efficient power levels for global clocksynchronization, and is especially useful in large-scale deployments.

  7. A Movable-Cavity Cold Atom Space Clock

    Institute of Scientific and Technical Information of China (English)

    BIAN Feng-Gang; WEI Rong; JIANG Hai-Feng; WANG Yu-Zhu

    2005-01-01

    @@ We present an experimental scheme of a cold atom space clock with a movable cavity. By using a single microwave cavity, we find that the clock has a significant advantage, i.e. the longitudinal cavity phase shift is eliminated. A theoretical analysis has been carried out in terms of the relation between the atomic transition probability and the velocity of the moving cavity by taking into account the velocity distribution of cold atoms. The requirements for the microwave power and its stability for atomic πr /2 excitation at different moving velocities of the cavity lead to the determination of the proper working parameters of the rubidium clock in frequency accuracy 10-17. Finally,the mechanical stability for the scheme is analysed and the ways of solving the possible mechanical instability of the device are proposed.

  8. Tests of local position invariance using continuously running atomic clocks

    CERN Document Server

    Peil, Steven; Hanssen, James L; Swanson, Thomas B; Ekstrom, Christopher R; 10.1103/PhysRevA.87.010102

    2013-01-01

    Tests of local position invariance (LPI) made by comparing the relative redshift of atomic clocks based on different atoms have been carried out for a variety of pairs of atomic species. In most cases, several absolute frequency measurements per year are used to look for an annual signal, resulting in tests that can span on order of a decade. By using the output of continuously running clocks, we carry out LPI tests with comparable or higher precision after less than 1.5 years. These include new measurements of the difference in redshift anomalies \\beta\\ for hyperfine transitions in Rb87 and Cs133 and in H and Cs133 and a measurement comparing Rb87 and H, resulting in a stringent limit on LPI, \\beta(Rb) - \\beta(H)=(-2.7 +/- 4.9) x 10^(-7). The method of making these measurements for continuous clocks is discussed.

  9. Searching for dark matter with optical atomic clocks

    CERN Document Server

    Wcislo, Piotr; Bober, Marcin; Cygan, Agata; Lisak, Daniel; Ciurylo, Roman; Zawada, Michal

    2016-01-01

    One of the most fundamental questions of modern physics is the existence of yet unknown forms of matter and interactions. The total mass density of the Universe appears to be dominated by some hypothetical dark matter (DM). However, beyond its gravitational interaction at galactic scale, little is known about the DM nature and properties. One possibility is that it has a form of stable topological defects built from light scalar fields which, for nonzero DM-SM coupling, would result in transient variations of fundamental constants. Optical atomic clocks, highly sensitive to variations of the fine-structure constant, seem to be natural candidates for such searches. Here we demonstrate the first experimental constraint on the strength of transient DM-SM coupling determined with optical atomic clocks. Instead of measuring the phase difference between two distant clocks we determine a common component of their readouts. We show that our constraint, even for one-day measurement, greatly exceeds previous laboratory...

  10. An alternative derivation of the gravitomagnetic clock effect

    International Nuclear Information System (INIS)

    The possibility of detecting the gravitomagnetic clock effect using artificial Earth satellites provides the incentive to develop a more intuitive approach to its derivation. We first consider two test electric charges moving on the same circular orbit but in opposite directions in orthogonal electric and magnetic fields and show that the particles take different times in describing a full orbit. The expression for the time difference is completely analogous to that of the general relativistic gravitomagnetic clock effect in the weak-field and slow-motion approximation. The latter is obtained by considering the gravitomagnetic force as a small classical non-central perturbation of the main central Newtonian monopole force. A general expression for the clock effect is given for a spherical orbit with an arbitrary inclination angle. This formula differs from the result of the general relativistic calculations by terms of order c-4

  11. Performance of a 229Thorium solid-state nuclear clock

    International Nuclear Information System (INIS)

    The 7.8 eV nuclear isomer transition in 229thorium has been suggested as a clock transition in a new type of optical frequency standard. Here we discuss the construction of a ‘solid-state nuclear clock’ from thorium nuclei implanted into single crystals transparent in the vacuum ultraviolet range. We investigate crystal-induced line shifts and broadening effects for the specific system of calcium fluoride. At liquid nitrogen temperatures, the clock performance will be limited by decoherence due to magnetic coupling of the thorium nuclei to neighboring nuclear moments, ruling out the commonly used Rabi or Ramsey interrogation schemes. We propose clock stabilization based on a fluorescence spectroscopy method and present optimized operation parameters. Taking advantage of the large number of quantum oscillators under continuous interrogation, a fractional instability level of 10−19 might be reached within the solid-state approach. (paper)

  12. Jitter impact on clock distribution in LHC experiments

    International Nuclear Information System (INIS)

    The LHC Bunch Clock is one of the most important accelerator signals delivered to the experiments. Being directly derived from the Radio Frequency driving the beams in the accelerator by a simple division of its frequency by a factor of 10, the Bunch Clock signal represents the frequency at which the bunches are crossing each other at each experiment. It is thus used to synchronize all the electronics systems in charge of event detection. Its frequency is around 40.079 MHz, but varies with beam parameters (energy, particle type, etc) by a few hundreds of Hz. The present paper discusses the quality of this Bunch Clock signal in terms of jitter. It is in particular compared to typical requirements of electronic components of the LHC detectors and put in perspective with the intrinsic jitter of the beam itself, to which this signal is related.

  13. General relativistic effects in quantum interference of ''clocks''

    International Nuclear Information System (INIS)

    Quantum mechanics and general relativity have been extensively and independently confirmed in many experiments. However, all experiments that measured the influence of gravity on quantum systems are still fully consistent with non-relativistic, Newtonian gravity. Here we discuss a novel effect in quantum interference experiments that can probe the interplay between quantum mechanics and general relativity. We consider interference of a ''clock'' - a particle with some evolving degrees of freedom - placed in a superposition of two different gravitational potentials. According to general relativity each amplitude of the superposition will experience a different gravitational time dilation. Due to quantum complementarity the visibility of quantum interference will thus drop to the extent to which the information about the location becomes available from the ''clock''. The clock can be implemented in an internal degree of freedom of a massive particle or in the position of a photon. The proposed experiment would thus provide the first test of quantum mechanics in curved background.

  14. The Kitaev–Feynman clock for open quantum systems

    International Nuclear Information System (INIS)

    We show that Kitaev's construction of Feynman's clock, in which the time-evolution of a closed quantum system is encoded as a ground state problem, can be extended to open quantum systems. In our formalism, the ground states of an ensemble of non-Hermitian Kitaev–Feynman clock Hamiltonians yield stochastic trajectories, which unravel the evolution of a Lindblad master equation. In this way, one can use the Kitaev–Feynman clock not only to simulate the evolution of a quantum system, but also its interaction with an environment such as a heat bath or measuring apparatus. A simple numerical example of a two-level atom undergoing spontaneous emission is presented and analyzed. (paper)

  15. Fault Secure Encoder and Decoder with Clock Gating

    Directory of Open Access Journals (Sweden)

    N.Kapileswar

    2012-04-01

    Full Text Available This paper presents circuit design for a low power fault secure encoder and decoder system. Memory cells in logic circuits have been protected from soft errors for more than a decade due to increase in soft error rates. In this paper the circuitry around the memory block have been susceptible to soft errors and must be protected from faults. The proposed design uses error correcting codes and ring counter addressing scheme. In the ring counter several new clock gating techniques are proposed to reduce power consumption. A fault secure Encoder and Decoder error free low power logic circuits can be achieved by the proposed design. Simulation results show great improvement in power consumption. Fault secure Encoder and Decoder with clock gated by CG-element consumes approximately half the power of that consumed by the fault free circuit which doesn’t employ clock gating technique

  16. Fault-tolerant clock synchronization validation methodology. [in computer systems

    Science.gov (United States)

    Butler, Ricky W.; Palumbo, Daniel L.; Johnson, Sally C.

    1987-01-01

    A validation method for the synchronization subsystem of a fault-tolerant computer system is presented. The high reliability requirement of flight-crucial systems precludes the use of most traditional validation methods. The method presented utilizes formal design proof to uncover design and coding errors and experimentation to validate the assumptions of the design proof. The experimental method is described and illustrated by validating the clock synchronization system of the Software Implemented Fault Tolerance computer. The design proof of the algorithm includes a theorem that defines the maximum skew between any two nonfaulty clocks in the system in terms of specific system parameters. Most of these parameters are deterministic. One crucial parameter is the upper bound on the clock read error, which is stochastic. The probability that this upper bound is exceeded is calculated from data obtained by the measurement of system parameters. This probability is then included in a detailed reliability analysis of the system.

  17. ‘Leading clocks lag’ and the de Broglie wavelength

    Science.gov (United States)

    Shuler, Robert L., Jr.

    2016-03-01

    The forgotten history of de Broglie waves as themselves artifacts of a Lorentz transform, not physical lengths and frequencies to be transformed, causes confusion for students and others. In this paper the de Broglie wavelength is derived and dependence of de Broglie frequency on velocity explained in terms of Einstein synchronized reference frame measurements of a single clock (2-on-1) versus measurements of an Einstein reference frame by an observer with a single clock (1-on-2). A new memory aid for the relativity of simultaneity, ‘leading clocks lag,’ is introduced that puts it on a par with the heuristics ‘time dilation’ and ‘length contraction’ for quick and easy problem visualization.

  18. Circadian clocks optimally adapt to sunlight for reliable synchronization

    CERN Document Server

    Hasegawa, Yoshihiko

    2014-01-01

    Circadian oscillation provides selection advantages through synchronization to the daylight cycle. However, a reliable clock must be designed through two conflicting properties: entrainability to properly respond to external stimuli such as sunlight, and regularity to oscillate with a precise period. These two aspects do not easily coexist because better entrainability favors higher sensitivity, which may sacrifice the regularity. To investigate conditions for satisfying the two properties, we analytically calculated the optimal phase-response curve with a variational method. Our result indicates an existence of a dead zone, i.e., a time during which external stimuli neither advance nor delay the clock. This result is independent of model details and a dead zone appears only when the input stimuli obey the time course of actual insolation. Our calculation demonstrates that every circadian clock with a dead zone is optimally adapted to the daylight cycle. Our result also explains the lack of a dead zone in osc...

  19. Event-Clock Automata: From Theory to Practice

    CERN Document Server

    Geeraerts, Gilles; Sznajder, Nathalie

    2011-01-01

    Event clock automata (ECA) are a model for timed languages that has been introduced by Alur, Fix and Henzinger as an alternative to timed automata, with better theoretical properties (for instance, ECA are determinizable while timed automata are not). In this paper, we revisit and extend the theory of ECA. We first prove that no finite time abstract language equivalence exists for ECA, thereby disproving a claim in the original work on ECA. This means in particular that regions do not form a time abstract bisimulation. Nevertheless, we show that regions can still be used to build a finite automaton recognizing the untimed language of an ECA. Then, we extend the classical notions of zones and DBMs to let them handle event clocks instead of plain clocks (as in timed automata) by introducing event zones and Event DBMs (EDBMs). We discuss algorithms to handle event zones represented as EDBMs, as well as (semi-) algorithms based on EDBMs to decide language emptiness of ECA.

  20. Mapping Out Atom-Wall Interaction with Atomic Clocks

    International Nuclear Information System (INIS)

    We explore the feasibility of probing atom-wall interaction with atomic clocks based on atoms trapped in engineered optical lattices. Optical lattice is normal to the wall. By monitoring the wall-induced clock shift at individual wells of the lattice, one would measure the dependence of the atom-wall interaction on the atom-wall separation. We find that the induced clock shifts are large and observable at already experimentally demonstrated levels of accuracy. We show that this scheme may uniquely probe the long-range atom-wall interaction in all three qualitatively distinct regimes of the interaction: van der Waals (image-charge interaction), Casimir-Polder (QED vacuum fluctuations), and Lifshitz (thermal-bath fluctuations) regimes.

  1. A Two-Photon E1-M1 Optical Clock

    CERN Document Server

    Alden, E A; Leanhardt, A E

    2014-01-01

    An allowed E1-M1 excitation scheme creates optical access to the ${^1S_0} \\rightarrow {^3P_0}$ clock transition in group II type atoms. This method does not require the hyperfine mixing or application of an external magnetic field of other optical clock systems. The advantages of this technique include a Doppler-free excitation scheme and increased portability with the use of vapor cells. We will discuss technical mechanisms of a monochromatic excitation scheme for a hot E1-M1 clock and briefly discuss a bichromatic scheme to eliminate light shifts. We determine the optimal experimental parameters for Hg, Yb, Ra, Sr, Ba, Ca, Mg, and Be and calculate that neutral Hg has ideal properties for a hot, portable frequency standard.

  2. Synchronizing computer clocks using a local area network

    Science.gov (United States)

    Levine, Judah

    1990-01-01

    Researchers completed the first tests of a method to synchronize the clocks of networked computers to the National Institute of Standards and Technology (NIST) time scale. The method uses a server computer to disseminate the time to other clients on the same local-area network. The server is synchronized to NIST using the ACTS protocol over a dial-up telephone line. The software in both the server and the parameters of this model are used to adjust the time of the local clock and the interval between calibration requests in a statistically optimum way. The algorithm maximizes the time between calibrations while at the same time keeping the time of the local clock correct within a specific tolerance. The method can be extended to synchronize computers linked over wide-area networks, and an experiment to test the performance of the algorithms over such networks is being planned.

  3. Late Glacial Demographic Expansion Motivates a Clock Overhaul for Population Genetics.

    Science.gov (United States)

    Hoareau, Thierry B

    2016-05-01

    The molecular clock hypothesis is fundamental in evolutionary biology as by assuming constancy of the molecular rate it provides a timeframe for evolution. However, increasing evidence shows time dependence of inferred molecular rates with inflated values obtained using recent calibrations. As recent demographic calibrations are virtually non-existent in most species, older phylogenetic calibration points (>1 Ma) are commonly used, which overestimate demographic parameters. To obtain more reliable rates of molecular evolution for population studies, I propose the calibration of demographic transition (CDT) method, which uses the timing of climatic changes over the late glacial warming period to calibrate expansions in various species. Simulation approaches and empirical data sets from a diversity of species (from mollusk to humans) confirm that, when compared with other genealogy-based calibration methods, the CDT provides a robust and broadly applicable clock for population genetics. The resulting CDT rates of molecular evolution also confirm rate heterogeneity over time and among taxa. Comparisons of expansion dates with ecological evidence confirm the inaccuracy of phylogenetically derived divergence rates when dating population-level events. The CDT method opens opportunities for addressing issues such as demographic responses to past climate change and the origin of rate heterogeneity related to taxa, genes, time, and genetic information content. PMID:26683588

  4. Low-jitter on-chip clock for RSFQ circuit applications

    International Nuclear Information System (INIS)

    The ultra-narrow linewidth of a long Josephson junction (LJJ) oscillator offers low timing jitter as a clock source. In this paper, we will discuss the improvement of an LJJ clock by using an annular geometry. We demonstrate the integration of an annular LJJ with a clock decimator which consists of a serial chain of toggle-flip-flops (TFFs). Each TFF divides its input frequency by a factor of 2. We have also developed a clock frequency selector. The clock selector circuit can choose either the master clock fm or one of its sub-harmonics (fm/2m, m=1 to n), based on the select inputs. The generation of a set of clocks will enable us to integrate the on-chip LJJ clock with a flash analogue-to-digital converter. (author)

  5. Generating clock signals for a cycle accurate, cycle reproducible FPGA based hardware accelerator

    Science.gov (United States)

    Asaad, Sameth W.; Kapur, Mohit

    2016-01-05

    A method, system and computer program product are disclosed for generating clock signals for a cycle accurate FPGA based hardware accelerator used to simulate operations of a device-under-test (DUT). In one embodiment, the DUT includes multiple device clocks generating multiple device clock signals at multiple frequencies and at a defined frequency ratio; and the FPG hardware accelerator includes multiple accelerator clocks generating multiple accelerator clock signals to operate the FPGA hardware accelerator to simulate the operations of the DUT. In one embodiment, operations of the DUT are mapped to the FPGA hardware accelerator, and the accelerator clock signals are generated at multiple frequencies and at the defined frequency ratio of the frequencies of the multiple device clocks, to maintain cycle accuracy between the DUT and the FPGA hardware accelerator. In an embodiment, the FPGA hardware accelerator may be used to control the frequencies of the multiple device clocks.

  6. Blackbody radiation shift of the Ga+ clock transition

    International Nuclear Information System (INIS)

    The blackbody radiation shift of the Ga+ clock transition is computed to be −0.0140 ± 0.0062 Hz at 300 K. The small shift is consistent with the blackbody radiation shifts of the clock transitions of other group III ions which are of a similar size. The polarizabilities of the Ga+ states were computed using the configuration interaction method with an underlying semi-empirical core potential. Quadrupole and non-adiabatic dipole polarizabilities were also computed. A byproduct of the analysis involved calculations of the low-lying spectrum and oscillator strengths, including polarizabilities, of the Ga2+ ion. (paper)

  7. Absolute simultaneity: Special relativity without light signals or synchronised clocks

    CERN Document Server

    Field, J H

    2006-01-01

    Using only the reciprocity postulate, it is demonstrated that the spatial separation of two objects, at rest in some inertial frame, is invariant. This result holds in both Galilean and special relativity. A corollary is that there are no `length contraction' or associated 'relativity of simultaneity' effects in the latter theory. A thought experiment employing four unsynchronised clocks and a single measuring rod provides a demonstration of the time dilatation effect. This effect, which is universal for all synchronised clocks at rest in any inertial frame, is the unique space-time phenomenon discriminating Galilean and special relativity.

  8. General flat four-dimensional world pictures and clock systems

    Science.gov (United States)

    Hsu, J. P.; Underwood, J. A.

    1978-01-01

    We explore the mathematical structure and the physical implications of a general four-dimensional symmetry framework which is consistent with the Poincare-Einstein principle of relativity for physical laws and with experiments. In particular, we discuss a four-dimensional framework in which all observers in different frames use one and the same grid of clocks. The general framework includes special relativity and a recently proposed new four-dimensional symmetry with a nonuniversal light speed as two special simple cases. The connection between the properties of light propagation and the convention concerning clock systems is also discussed, and is seen to be nonunique within the four-dimensional framework.

  9. Reference clock parameters for digital communications systems applications

    Science.gov (United States)

    Kartaschoff, P.

    1981-01-01

    The basic parameters relevant to the design of network timing systems describe the random and systematic time departures of the system elements, i.e., master (or reference) clocks, transmission links, and other clocks controlled over the links. The quantitative relations between these parameters were established and illustrated by means of numerical examples based on available measured data. The examples were limited to a simple PLL control system but the analysis can eventually be applied to more sophisticated systems at the cost of increased computational effort.

  10. UML MARTE Time Model and Its Clock Constraint Specification Language

    OpenAIRE

    Mallet, Frédéric; Peraldi-Frati, Marie-Agnès; Deantoni, Julien; De Simone, Robert

    2014-01-01

    The UML Profile for MARTE extends the UML with constructs dedicated to the modeling and analysisof real-time and embedded systems. Its time profile provides a rich model of time based on the notionof logical clocks that can be used consistently through all modeling elements/diagrams. The MARTEtime profile comes with a companion language, called CCSL. CCSL is a formal declarative languageused to handle the MARTE logical clocks and schedule the execution of the different parts of a model.This c...

  11. Accuracy Evaluation of NIM5 Cesium Fountain Clock

    International Nuclear Information System (INIS)

    The NIM5 fountain clock is the second fountain clock built at NIM (National Institute of Metrology, China), and has been operating stably and sub-continually since 2008. The fountain operates with a simple one-stage optical molasses to collect cold atoms, which reduces the collisional frequency shift dramatically. The fractional frequency uncertainty is estimated to be 2 × 10−15. The typical frequency instability of 2.5 × 10−14 is obtained at 10 s. Comparisons with other fountain frequency standards worldwide demonstrate agreement within the stated uncertainties

  12. CLOCK SYNCHRONIZATION: ESTIMATION OF NONDETERMINISTIC DELAYS IN WIRELESS MESSAGE DELIVERY

    Directory of Open Access Journals (Sweden)

    Shiu Kumar

    2015-01-01

    Full Text Available Clock synchronization is significantly essential as they require universal time on WSN nodes for time measurement, event ordering and coordinated actions, and power management. This paper gives an insight of solving the problem of the non-deterministic delays that exist in the wireless message delivery. Sensor nodes consisting of Arduino Mega and 2.4 GHz nRF24L01+ radio modules are used, and based on the estimation of non-deterministic delays a clock synchronization protocol for WSN is proposed. The results obtained are quiet promising compared to the existing synchronization protocols for WSNs.

  13. Illuminating the circadian clock in monarch butterfly migration.

    Science.gov (United States)

    Froy, Oren; Gotter, Anthony L; Casselman, Amy L; Reppert, Steven M

    2003-05-23

    Migratory monarch butterflies use a time-compensated Sun compass to navigate to their overwintering grounds in Mexico. Here, we report that constant light, which disrupts circadian clock function at both the behavioral and molecular levels in monarchs, also disrupts the time-compensated component of flight navigation. We further show that ultraviolet light is important for flight navigation but is not required for photic entrainment of circadian rhythms. Tracing these distinct light-input pathways into the brain should aid our understanding of the clock-compass mechanisms necessary for successful migration. PMID:12764200

  14. THE STOCHASTIC ESTIMATION OF SATELLITE CLOCK CORRECTION INFORMATION IN WADGPS

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Using autocorrelation information of the pseudorange errors generated by se lective availability (SA) frequency dithering, we have constructed a simple first order stochas tic model for SA effects. This model has been used in a Kalman filter to account for the stochastic behavior of SA dithering in estimating satellite clock information in wide area dif ferential GPS. We have obtained fifteen percent improvement in the user positioning using the correlation information on the satellite clock information in a Kalman filter, when comparing the results obtained using a regular least square estimation.

  15. Nuclear clocks based on resonant excitation of gamma-transitions

    CERN Document Server

    Peik, Ekkehard

    2015-01-01

    We review the ideas and concepts for a clock that is based on a radiative transition in the nucleus rather than in the electron shell. This type of clock offers advantages like an insensitivity against field-induced systematic frequency shifts and the opportunity to obtain high stability from interrogating many nuclei in the solid state. Experimental work concentrates on the low-energy (about 8 eV) isomeric transition in Th-229. We review the status of the experiments that aim at a direct optical observation of this transition and outline the plans for high-resolution laser spectroscopy experiments.

  16. Nuclear clocks based on resonant excitation of gamma-transitions

    OpenAIRE

    Peik, Ekkehard; Okhapkin, Maxim

    2015-01-01

    We review the ideas and concepts for a clock that is based on a radiative transition in the nucleus rather than in the electron shell. This type of clock offers advantages like an insensitivity against field-induced systematic frequency shifts and the opportunity to obtain high stability from interrogating many nuclei in the solid state. Experimental work concentrates on the low-energy (about 8 eV) isomeric transition in Th-229. We review the status of the experiments that aim at a direct opt...

  17. Circadian Clock genes Per2 and clock regulate steroid production, cell proliferation, and luteinizing hormone receptor transcription in ovarian granulosa cells

    International Nuclear Information System (INIS)

    Highlights: → Treatment with Per2 and Clock siRNAs decreased the number of granulosa cells and LHr expression. →Per2 siRNA treatment did not stimulate the production of estradiol and expression of P450arom. → Clock siRNA treatment inhibited the production of estradiol and expression of P450arom mRNA. →Per2 and Clock siRNA treatment increased and unchanged, respectively, progesterone production in FSH-treated granulosa cells. → The expression of StAR mRNA was increased by Per2 siRNA and unchanged by Clock siRNA. -- Abstract: Circadian Clock genes are associated with the estrous cycle in female animals. Treatment with Per2 and Clock siRNAs decreased the number of granulosa cells and LHr expression in follicle-stimulating hormone FSH-treated granulosa cells. Per2 siRNA treatment did not stimulate the production of estradiol and expression of P450arom, whereas Clock siRNA treatment inhibited the production of estradiol and expression of P450arom mRNA. Per2 and Clock siRNA treatment increased and unchanged, respectively, progesterone production in FSH-treated granulosa cells. Similarly, expression of StAR mRNA was increased by Per2 siRNA and unchanged by Clock siRNA. Our data provide a new insight that Per2 and Clock have different action on ovarian granulosa cell functions.

  18. CRY Drives Cyclic CK2-Mediated BMAL1 Phosphorylation to Control the Mammalian Circadian Clock

    OpenAIRE

    Tamaru, Teruya; Hattori, Mitsuru; Honda, Kousuke; Nakahata, Yasukazu; Sassone-Corsi, Paolo; van der Horst, Gijsbertus T. J.; Ozawa, Takeaki; Takamatsu, Ken

    2015-01-01

    Intracellular circadian clocks, composed of clock genes that act in transcription-translation feedback loops, drive global rhythmic expression of the mammalian transcriptome and allow an organism to anticipate to the momentum of the day. Using a novel clock-perturbing peptide, we established a pivotal role for casein kinase (CK)-2-mediated circadian BMAL1-Ser90 phosphorylation (BMAL1-P) in regulating central and peripheral core clocks. Subsequent analysis of the underlying mechanism showed a ...

  19. Oscillating perceptions: the ups and downs of the CLOCK protein in the mouse circadian system

    Indian Academy of Sciences (India)

    Jason P. Debruyne

    2008-12-01

    A functional mouse CLOCK protein has long been thought to be essential for mammalian circadian clockwork function, based mainly on studies of mice bearing a dominant negative, antimorphic mutation in the Clock gene. However, new discoveries using recently developed Clock-null mutant mice have shaken up this view. In this review, I discuss how this recent work impacts and alters the previous view of the role of CLOCK in the mouse circadian clockwork.

  20. System and method for clock synchronization and position determination using entangled photon pairs

    Science.gov (United States)

    Shih, Yanhua (Inventor)

    2010-01-01

    A system and method for clock synchronization and position determination using entangled photon pairs is provided. The present invention relies on the measurement of the second order correlation function of entangled states. Photons from an entangled photon source travel one-way to the clocks to be synchronized. By analyzing photon registration time histories generated at each clock location, the entangled states allow for high accuracy clock synchronization as well as high accuracy position determination.

  1. A mathematical model for the atomic clock error in case of jumps

    International Nuclear Information System (INIS)

    We extend the mathematical model based on stochastic differential equations describing the error gained by an atomic clock to the cases of anomalous behavior including jumps and an increase of instability. We prove an exact iterative solution that can be useful for clock simulation, prediction, and interpretation, as well as for the understanding of the impact of clock error in the overall system in which clocks may be inserted as, for example, the Global Satellite Navigation Systems. (authors)

  2. Timing Jitter Analysis for Clock recovery Circuits Based on an Optoelectronic Phase-Locked Loop (OPLL)

    DEFF Research Database (Denmark)

    Zibar, Darko; Mørk, Jesper; Oxenløwe, Leif Katsuo; Galili, Michael; Clausen, Anders

    2005-01-01

    Timing jitter of an OPLL based clock recovery is investigated. We demonstrate how loop gain, input and VCO signal jitter, loop filter bandwidth and a loop time delay influence jitter of the extracted clock signal......Timing jitter of an OPLL based clock recovery is investigated. We demonstrate how loop gain, input and VCO signal jitter, loop filter bandwidth and a loop time delay influence jitter of the extracted clock signal...

  3. All-optical clock recovery of NRZ-DPSK signals using optical resonator-type filters

    DEFF Research Database (Denmark)

    Peucheret, Christophe; Seoane, Jorge; Ji, Hua

    It is shown how introducing a limited rise time to the driving signal enables all-optical clock recovery of NRZ-DPSK signals generated using a phase modulator. A Fabry-Perot filter is used to generate the optical clock.......It is shown how introducing a limited rise time to the driving signal enables all-optical clock recovery of NRZ-DPSK signals generated using a phase modulator. A Fabry-Perot filter is used to generate the optical clock....

  4. CRY Drives Cyclic CK2-Mediated BMAL1 Phosphorylation to Control the Mammalian Circadian Clock

    NARCIS (Netherlands)

    T. Tamaru (Teruya); M. Hattori (Mitsuru); K. Honda (Kousuke); Y. Nakahata (Yasukazu); P. Sassone-Corsi (Paolo); G.T.J. van der Horst (Gijsbertus); T. Ozawa (Takeaki); K. Takamatsu (Ken)

    2015-01-01

    textabstractIntracellular circadian clocks, composed of clock genes that act in transcription-translation feedback loops, drive global rhythmic expression of the mammalian transcriptome and allow an organism to anticipate to the momentum of the day. Using a novel clock-perturbing peptide, we establi

  5. Regulation of behavioral circadian rhythms and clock protein PER1 by the deubiquitinating enzyme USP2

    Directory of Open Access Journals (Sweden)

    Yaoming Yang

    2012-06-01

    Endogenous 24-hour rhythms are generated by circadian clocks located in most tissues. The molecular clock mechanism is based on feedback loops involving clock genes and their protein products. Post-translational modifications, including ubiquitination, are important for regulating the clock feedback mechanism. Previous work has focused on the role of ubiquitin ligases in the clock mechanism. Here we show a role for the rhythmically-expressed deubiquitinating enzyme ubiquitin specific peptidase 2 (USP2 in clock function. Mice with a deletion of the Usp2 gene (Usp2 KO display a longer free-running period of locomotor activity rhythms and altered responses of the clock to light. This was associated with altered expression of clock genes in synchronized Usp2 KO mouse embryonic fibroblasts and increased levels of clock protein PERIOD1 (PER1. USP2 can be coimmunoprecipitated with several clock proteins but directly interacts specifically with PER1 and deubiquitinates it. Interestingly, this deubiquitination does not alter PER1 stability. Taken together, our results identify USP2 as a new core component of the clock machinery and demonstrate a role for deubiquitination in the regulation of the circadian clock, both at the level of the core pacemaker and its response to external cues.

  6. Frequency Ratio of ${}^{199}$Hg and ${}^{87}$Sr Optical Lattice Clocks beyond the SI Limit

    CERN Document Server

    Yamanaka, Kazuhiro; Ushijima, Ichiro; Takamoto, Masao; Katori, Hidetoshi

    2015-01-01

    We report on a frequency ratio measurement of a ${}^{199}$Hg-based optical lattice clock referencing a ${}^{87}$Sr-based clock. Evaluations of lattice light shift, including atomic-motion-dependent shift, enable us to achieve a total systematic uncertainty of $7.2 \\times 10^{-17}$ for the Hg clock. The frequency ratio is measured to be $\

  7. Dual modes of CLOCK:BMAL1 inhibition mediated by Cryptochrome and Period proteins in the mammalian circadian clock

    OpenAIRE

    Ye, Rui; Selby, Cristopher P.; Chiou, Yi-Ying; Ozkan-Dagliyan, Irem; Gaddameedhi, Shobhan; Sancar, Aziz

    2014-01-01

    The mammalian circadian clock is based on a transcription–translation feedback loop in which CLOCK and BMAL1 proteins act as transcriptional activators of Cryptochrome and Period genes, which encode proteins that repress CLOCK–BMAL1 with a periodicity of ∼ 24 h. Ye et al. show that CRY binds to CLOCK–BMAL1 at the promoter and inhibits CLOCK–BMAL1-dependent transcription without dissociating the complex. PER alone has no effect on CLOCK–BMAL1-activated transcription, but in the presence of CRY...

  8. The effect of white light on normal and malignant murine melanocytes: A link between opsins, clock genes, and melanogenesis.

    Science.gov (United States)

    de Assis, L V M; Moraes, M N; da Silveira Cruz-Machado, S; Castrucci, A M L

    2016-06-01

    The skin possesses a photosensitive system comprised of opsins whose function is not fully understood, and clock genes which exert an important regulatory role in skin biology. Here, we evaluated the presence of opsins in normal (Melan-a cells) and malignant (B16-F10 cells) murine melanocytes. Both cell lines express Opn2, Opn4 - for the first time reported in these cell types - as well as S-opsin. OPN4 protein was found in a small area capping the cell nuclei of B16-F10 cells kept in constant dark (DD); twenty-four hours after the white light pulse (WLP), OPN4 was found in the cell membrane. Despite the fact that B16-F10 cells expressed less Opn2 and Opn4 than Melan-a cells, our data indicate that the malignant melanocytes exhibited increased photoresponsiveness. The clock gene machinery is also severely downregulated in B16-F10 cells as compared to Melan-a cells. Per1, Per2, and Bmal1 expression increased in B16-F10 cells in response to WLP. Although no response in clock gene expression to WLP was observed in Melan-a cells, gene correlational data suggest a minor effect of WLP. In contrast to opsins and clock genes, melanogenesis is significantly upregulated in malignant melanocytes in comparison to Melan-a cells. Tyrosinase expression increased after WLP only in B16-F10 cells; however no increase in melanin content after WLP was seen in either cell line. Our findings may prove useful in the treatment and the development of new pharmacological approaches of depigmentation diseases and skin cancer. PMID:26947915

  9. Modeling pharmacological clock and memory patterns of interval timing in a striatal beat-frequency model with realistic, noisy neurons

    Directory of Open Access Journals (Sweden)

    Sorinel A. Oprisan

    2011-09-01

    Full Text Available In most species, the capability of perceiving and using the passage of time in the seconds-to-minutes range (interval timing is not only accurate but also scalar: errors in time estimation are linearly related to the estimated duration. The ubiquity of scalar timing extends over behavioral, lesion, and pharmacological manipulations. For example, in mammals, dopaminergic drugs induce an immediate, scalar change in the perceived time (clock pattern, whereas cholinergic drugs induce a gradual, scalar change in perceived time (memory pattern. How do these properties emerge from unreliable, noisy neurons firing in the milliseconds range? Neurobiological information relative to the brain circuits involved in interval timing provide support for an Striatal Beat Frequency (SBF model, in which time is coded by the coincidental activation of striatal spiny neurons by cortical neural oscillators. While biologically plausible, the impracticality of perfect oscillators, or their lack thereof, questions this mechanism in a brain with noisy neurons. We explored the computational mechanisms required for the clock and memory patterns in an SBF model with biophysically realistic and noisy Morris-Lecar neurons (SBF-ML. Under the assumption that dopaminergic drugs modulate the firing frequency of cortical oscillators, and that cholinergic drugs modulate the memory representation of the criterion time, we show that our SBF-ML model can reproduce the pharmacological clock and memory patterns observed in the literature. Numerical results also indicate that parameter variability (noise – which is ubiquitous in the form of small fluctuations in the intrinsic frequencies of neural oscillators within and between trails, and in the errors in recording/retrieving stored information related to criterion time – seems to be critical for the time-scale invariance of the clock and memory patterns.

  10. Altered circadian clock gene expression in patients with schizophrenia.

    Science.gov (United States)

    Johansson, Anne-Sofie; Owe-Larsson, Björn; Hetta, Jerker; Lundkvist, Gabriella B

    2016-07-01

    Impaired circadian rhythmicity has been reported in several psychiatric disorders. Schizophrenia is commonly associated with aberrant sleep-wake cycles and insomnia. It is not known if schizophrenia is associated with disturbances in molecular rhythmicity. We cultured fibroblasts from skin samples obtained from patients with chronic schizophrenia and from healthy controls, respectively, and analyzed the circadian expression during 48h of the clock genes CLOCK, BMAL1, PER1, PER2, CRY1, CRY2, REV-ERBα and DBP. In fibroblasts obtained from patients with chronic schizophrenia, we found a loss of rhythmic expression of CRY1 and PER2 compared to cells from healthy controls. We also estimated the sleep quality in these patients and found that most of them suffered from poor sleep in comparison with the healthy controls. In another patient sample, we analyzed mononuclear blood cells from patients with schizophrenia experiencing their first episode of psychosis, and found decreased expression of CLOCK, PER2 and CRY1 compared to blood cells from healthy controls. These novel findings show disturbances in the molecular clock in schizophrenia and have important implications in our understanding of the aberrant rhythms reported in this disease. PMID:27132483

  11. Chaotic map based key agreement with/out clock synchronization

    International Nuclear Information System (INIS)

    In order to address Bergamo et al.'s attack, Xiao et al. proposed a key agreement protocol using chaotic maps. Han then presented three attacks on Xiao et al.'s protocol. To enhance the security of key agreement based on chaotic maps, Chang et al. proposed a new key agreement using passphrase, which works in clock synchronization environment. However, their protocol still has some issues: one is its passphrase is not easy to remember and much longer than password; the second one is it cannot resist guessing attack if the constructed passphrase is easy to remember and also has already existed in some rational dictionaries; the third one is it cannot work without clock synchronization. In this paper, we will present two different key agreement protocols, which can resist guessing attack. The first one works in clock synchronization environment. The second one can work without clock synchronization. They both use authenticated password for secure communications. The protocols are secure against replaying attacks and a shared session key can be established.

  12. The AGS Ggamma Meter and Calibrating the Gauss Clock

    Energy Technology Data Exchange (ETDEWEB)

    Ahrens, Leif [Brookhaven National Laboratory (BNL), Upton, NY (United States). Collider-Accelerator Dept.

    2014-03-31

    During AGS Polarized Proton acceleration periods, one output from the AGS Ggamma Meter, namely the energy (or Ggamma) calculated from the magnetic field in the AGS main magnets and the beam radius- both measured in particular instant, is used to figure out the times in the AGS magnet acceleration cycle when the beam passes through a particular set of depolarizing resonances. The resonance set occur whenever a particle’s Ggamma (energy*(G/m) becomes nearly equal to n*Qx (i.e. any integer multiplied by the horizontal betatron tune). This deliverable is why the machinery is referred to as the ''Ggamma Meter'' rather than the AGS energy meter. The Ggamma Meter takes as inputs a set of measurements of frequency (F(t)), radius (r(t)), and gauss clock counts (GCC(t)). The other energy (GgammaBr) assumes the field when the gauss clock starts counting is known. The change in field to time t is given by the measured accumulated gauss clock counts multiplied by the gauss clock calibration (gauss/GCC). In order to deal with experimental data, this calibration factor gets an added ad hoc complication, namely a correction dependent on the rate of change the counting rate. The Ggamma meter takes GCC(t) and together with the past history for this cycle calculates B(t).

  13. Clock ambiguity and the emergence of physical laws

    International Nuclear Information System (INIS)

    The process of identifying a time variable in time-reparameterization invariant theories results in great ambiguities about the actual laws of physics described by a given theory. A theory set up to describe one set of physical laws can equally well be interpreted as describing any other laws of physics by making a different choice of time variable or clock. In this article we demonstrate how this 'clock ambiguity' arises and then discuss how one might still hope to extract specific predictions about the laws of physics even when the clock ambiguity is present. We argue that a requirement of quasiseparability should play a critical role in such an analysis. As a step in this direction, we compare the Hamiltonian of a local quantum field theory with a completely random Hamiltonian. We find that any random Hamiltonian (constructed in a sufficiently large space) can yield a 'good enough' approximation to a local field theory. Based on this result we argue that theories that suffer from the clock ambiguity may in the end provide a viable fundamental framework for physics in which locality can be seen as a strongly favored (or predicted) emergent behavior. We also speculate on how other key aspects of known physics such as gauge symmetries and Poincare invariance might be predicted to emerge in this framework.

  14. Nanomagnetic logic with non-uniform states of clocking

    Science.gov (United States)

    Puliafito, Vito; Giordano, Anna; Azzerboni, Bruno; Finocchio, Giovanni

    2016-04-01

    Nanomagnetic logic transmits information along a path of nanomagnets. The basic mechanism to drive such a transmission, known as clocking, can be achieved by exploiting the spin-Hall effect (SHE), as recently observed in experiments on Ta/CoFeB/MgO multilayers (Bhowmik et al 2014 Nat. Nano 9 59). This paper shows the fundamental mechanism of the spin-Hall driven clocking by using a full micromagnetic framework and considering two different devices, Ta/CoFeB/MgO and Pt/CoFeB/MgO. The former is used for a direct comparison of the numerical results with the experiments while the latter permits the effect of the Dzyaloshinskii-Moriya interaction (DMI) in the clocking mechanism to be predicted. Results show that the clocking state is non-uniform and it is characterized by the presence of domains separated by Bloch (Néel) domain walls depending on the absence (presence) of the DMI. Our findings point out that for the design of nanomagnetic logic a full micromagnetic approach is necessary.

  15. The Chemical and Educational Appeal of the Orange Juice Clock.

    Science.gov (United States)

    Kelter, Paul B.; And Others

    1996-01-01

    Describes the recent history, chemistry, and educational uses of the Orange Juice Clock demonstration in which a galvanic cell is made from the combination of a magnesium strip, a copper strip, and juice in a beaker. Discusses the chemistry basics, extensions for more advanced students, questions for student/teacher workshop participants, and…

  16. The AGS Ggamma Meter and Calibrating the Gauss Clock

    International Nuclear Information System (INIS)

    During AGS Polarized Proton acceleration periods, one output from the AGS Ggamma Meter, namely the energy (or Ggamma) calculated from the magnetic field in the AGS main magnets and the beam radius- both measured in particular instant, is used to figure out the times in the AGS magnet acceleration cycle when the beam passes through a particular set of depolarizing resonances. The resonance set occur whenever a particle's Ggamma (energy*(G/m) becomes nearly equal to n*Qx (i.e. any integer multiplied by the horizontal betatron tune). This deliverable is why the machinery is referred to as the ''Ggamma Meter'' rather than the AGS energy meter. The Ggamma Meter takes as inputs a set of measurements of frequency (F(t)), radius (r(t)), and gauss clock counts (GCC(t)). The other energy (GgammaBr) assumes the field when the gauss clock starts counting is known. The change in field to time t is given by the measured accumulated gauss clock counts multiplied by the gauss clock calibration (gauss/GCC). In order to deal with experimental data, this calibration factor gets an added ad hoc complication, namely a correction dependent on the rate of change the counting rate. The Ggamma meter takes GCC(t) and together with the past history for this cycle calculates B(t).

  17. A Medieval Clock Made out of Simple Materials

    Science.gov (United States)

    Danese, B.; Oss, S.

    2008-01-01

    A cheap replica of the verge-and-foliot clock has been built from simple materials. It is a didactic tool of great power for physics teaching at every stage of schooling, in particular at university level. An account is given of its construction and its working principles, together with motivated examples of a few activities. (Contains 3 tables…

  18. Educational Technology Classics: The Computer versus the Clock

    Science.gov (United States)

    Slack, Charles W.

    2010-01-01

    It is no accident that the first use of computers in school systems was to arrange schedules for students and teachers. The proper use of the computer in the classroom is as a replacement for the clock and its strict temporal schedule. By conveying information through self-instructional content, the computer can schedule work for pupils in…

  19. Range Estimation for Indoor Positioning via Drifting Clocks

    DEFF Research Database (Denmark)

    Bagdonas, Kazimieras; Schiøler, Henrik; Borre, Kai

    accuracy for a Time Of Arrival (TOA) based ranging system. We presume a system equipped with low resolution clocks featuring a constant drift. We propose a methodology how to infer accurate TOA from aliased measurements. Additionally, results obtained via simulation and extensive experimental campaigns are...

  20. Clock Reading: An Underestimated Topic in Children with Mathematics Difficulties

    Science.gov (United States)

    Burny, Elise; Valcke, Martin; Desoete, Annemie

    2012-01-01

    Recent studies have shown that children with mathematics difficulties (MD) have weaknesses in multiple areas of mathematics. Andersson, for example, recently found that children with MD perform significantly worse than other children on clock reading tasks. The present study builds on this recent finding and aims at a more profound understanding…

  1. A bi-directional fixed-latency clock distribution system

    International Nuclear Information System (INIS)

    The Askar'yan Radio Array (ARA) Collaboration is constructing a giant array of radio-frequency antennas deployed in the ice near the geographic South Pole. This experiment aims at detecting the extremely weak signal of neutrinos with energies in excess of 100 PeV from ultrahigh-energy cosmic ray interactions with the cosmic microwave background radiation. The antennas are located in shallow holes drilled to depths of 200 m and need high fidelity RF signal transmission over extended lengths to the data acquisition logic at the surface. We report on a transmission scheme whereby signals are digitized in the ice and the waveforms are digitally sent via high-speed serial links. Reconstruction algorithms require distribution of a low-jitter clock from the surface down to the digitization boards in the holes with knowledge of the overall time delay between the two clock domains. Previously, we designed a clock synchronization system using electrical signaling over CAT5. This year we have updated our solution to optical fibers using high speed transceiver blocks in Spartan-6 FPGAs. This note describes our improvements on the latter solution: technical details as well as methods of maintaining a fixed phase between two clocks after power cycles and resets

  2. The NIST 27 Al+ quantum-logic clock

    Science.gov (United States)

    Leibrandt, David; Brewer, Samuel; Chen, Jwo-Sy; Hume, David; Hankin, Aaron; Huang, Yao; Chou, Chin-Wen; Rosenband, Till; Wineland, David

    2016-05-01

    Optical atomic clocks based on quantum-logic spectroscopy of the 1 S0 3 P0 transition in 27 Al+ have reached a systematic fractional frequency uncertainty of 8 . 0 ×10-18 , enabling table-top tests of fundamental physics as well as measurements of gravitational potential differences. Currently, the largest limitations to the accuracy are second order time dilation shifts due to the driven motion (i.e., micromotion) and thermal motion of the trapped ions. In order to suppress these shifts, we have designed and built new ion traps based on gold-plated, laser-machined diamond wafers with differential RF drive, and we have operated one of our clocks with the ions laser cooled to near the six mode motional ground state. We present a characterization of the time dilation shifts in the new traps with uncertainties near 1 ×10-18 . Furthermore, we describe a new protocol for clock comparison measurements based on synchronous probing of the two clocks using phase-locked local oscillators, which allows for probe times longer than the laser coherence time and avoids the Dick effect. This work is supported by ARO, DARPA, and ONR.

  3. Special Relativity in Week One: 2) All Clocks Run Slow

    Science.gov (United States)

    Huggins, Elisha

    2011-01-01

    In our initial article on teaching special relativity in the first week of an introductory physics course, we used the principle of relativity and Maxwell's theory of light to derive Einstein's second postulate (that the speed of light is the same to all observers). In this paper we study thought experiments involving a light pulse clock moving…

  4. Methylphenidate modifies the motion of the circadian clock.

    Science.gov (United States)

    Antle, Michael C; van Diepen, Hester C; Deboer, Tom; Pedram, Pardis; Pereira, Rob Rodrigues; Meijer, Johanna H

    2012-10-01

    People with attention-deficit/hyperactivity disorder (ADHD) often experience sleep problems, and these are frequently exacerbated by the methylphenidate they take to manage their ADHD symptoms. Many of the changes to sleep are consistent with a change in the underlying circadian clock. The present study was designed to determine if methylphenidate alone could alter properties of the circadian clock. Young male mice were examined in light-dark cycles and in constant darkness and recordings were performed on behavioral activity, sleep, and electrical activity in the suprachiasmatic nucleus (SCN) of freely moving mice. Methylphenidate in the drinking water (0.08%) significantly increased activity in the mid-to-late night, and led to a delay in the onset of activity and sleep relative to the light-dark cycle. While locomotor levels returned to baseline after treatment ended, the phase angle of entrainment required at least a week to return to baseline levels. In constant darkness, the free-running period of both wheel-running and general locomotor rhythms was lengthened by methylphenidate. When the treatment ended, the free-running period either remained stable or only partially reverted to baseline levels. Methylphenidate also altered the electrical firing rate rhythms in the SCN. It induced a delay in the trough of the rhythm, an increment in rhythm amplitude, and a reduction in rhythm variability. These observations suggest that methylphenidate alters the underlying circadian clock. The observed changes are consistent with clock alterations that would promote sleep-onset insomnia. PMID:22763623

  5. Charge domain filter operating up to 20 MHz clock frequency

    OpenAIRE

    Gal, R.A.J.; Wallinga, H.

    1983-01-01

    An analog sampled data low pass third order Butterworth filter has been realised in a buried channel CCD technology. This Charge Domain Filter, composed of transversal and recursive CCD filter sections, has been tested at clock frequencies up to 20 MHz.

  6. Phase resetting of the mammalian circadian clock by DNA damage

    NARCIS (Netherlands)

    Oklejewicz, Malgorzata; Destici, Eugin; Tamanini, Filippo; Hut, Roelof A.; Janssens, Roel; van der Horst, Gijsbertus T. J.

    2008-01-01

    To anticipate the momentum of the day, most organisms have developed an internal clock that drives circadian rhythms in metabolism, physiology, and behavior [1]. Recent studies indicate that cell-cycle progression and DNA-damage-response pathways are under circadian control [2-4]. Because circadian

  7. One-Way Speed of Light Measurements without Clock Synchronisation

    Directory of Open Access Journals (Sweden)

    Cahill R. T.

    2012-07-01

    Full Text Available The 1991 DeWitte double one-way 1st order in v= c experiment successfully measured the anisotropy of the speed of light using clocks at each end of the RF coaxial cables. However Spavieri et al. , Physics Letters A (2012, have reported that (i clock effects caused by clock transport should be included, and (ii that this additional effect cancels the one-way light speed timing effect, implying that one-way light speed experiments “do not actually lead to the measurement of the one-way speed of light or determination of the absolute velocity of the preferred frame”. Here we explain that the Spavieri et al. derivation makes an assumption that is not always valid: that the propagation is subject to the usual Fresnel drag effect, which is not the case for RF coaxial cables. As well DeWitte did take account of the clock transport effect. The Spavieri et al. paper has prompted a clarification of these issues.

  8. Insight Into the Circadian Clock Within Rat Colonic Epithelial Cells

    Czech Academy of Sciences Publication Activity Database

    Sládek, Martin; Rybová, Markéta; Jindráková, Zuzana; Zemanová, Zdeňka; Polidarová, Lenka; Mrnka, Libor; O´Neill, J.; Pácha, Jiří; Sumová, Alena

    2007-01-01

    Roč. 133, č. 4 (2007), s. 1240-1249. ISSN 0016-5085 R&D Projects: GA AV ČR(CZ) IAA500110605 Institutional research plan: CEZ:AV0Z50110509 Keywords : cirkadian clock * colon * NHE3 Subject RIV: FH - Neurology Impact factor: 11.673, year: 2007

  9. Clock Synchronisation in the Vicinity of the Earth

    OpenAIRE

    Goy, Francois

    1997-01-01

    The transmission time of an electromagnetic signal in the vicinity of the earth is calculated to c-2 and contains an orbital Sagnac term. On earth, the synchronisation of the Barycentric Coordinate Time (TCB) can be realised by atomic clocks, but not the one of Geocentric Coordinate Time (TCG). The principle of equivalence is discussed.

  10. Mapping the magnetic field vector in a fountain clock

    International Nuclear Information System (INIS)

    We show how the mapping of the magnetic field vector components can be achieved in a fountain clock by measuring the Larmor transition frequency in atoms that are used as a spatial probe. We control two vector components of the magnetic field and apply audio frequency magnetic pulses to localize and measure the field vector through Zeeman spectroscopy.

  11. New methods to assess circadian clocks in humans

    Czech Academy of Sciences Publication Activity Database

    Nováková, Marta; Sumová, Alena

    2014-01-01

    Roč. 52, č. 5 (2014), s. 404-412. ISSN 0019-5189 R&D Projects: GA MZd(CZ) NT11474 Grant ostatní: Univerzita Karlova(CZ) 22810 Institutional research plan: CEZ:AV0Z50110509 Institutional support: RVO:67985823 Keywords : circadian * clock gene * melatonin * human Subject RIV: ED - Physiology Impact factor: 0.835, year: 2014

  12. Open Core Protocol (OCP) Clock Domain Crossing Interfaces

    DEFF Research Database (Denmark)

    Herlev, Mathias; Poulsen, Christian Keis; Sparsø, Jens

    2014-01-01

    The open core protocol (OCP) is an openly licensed configurable and scalable interface protocol for on-chip subsystem communications. The protocol defines read and write transactions from a master towards a slave across a point-to-point connection and the protocol assumes a single common clock. T...

  13. Conceptual Design of a Micron-Scale Atomic Clock

    CERN Document Server

    Hannah, Eric C

    2007-01-01

    A theoretical proposal for reducing an entire atomic clock to micron dimensions. A phosphorus or nitrogen atom is introduced into a fullerene cage. This endohedral fullerene is then coated with an insulating shell and a number of them are deposited as a thin layer on a silicon chip. Next to this layer a GMR sensor is fabricated which is close to the endohedral fullerenes. This GMR sensor measures oscillating magnetic fields on the order of micro-gauss from the nuclear spins varying at the frequency of the hyperfine transition (413 MHz frequency). Given the micron scale and simplicity of this system only a few transistors are needed to control the waveforms and to perform digital clocking. This new form of atomic clock exhibits extremely low power (nano watts), high vibration and shock resistance, stability on the order of 10^{-9}, and is compatible with MEMS fabrication and chip integration. As GMR sensors continue to improve in sensitivity the stability of this form of atomic clock will increase proportionat...

  14. Photoperiodic entrainment of the circadian molecular clock in the mice

    Czech Academy of Sciences Publication Activity Database

    Sosniyenko, Serhiy; Hut, R.; Matějů, Kristýna; Sládek, Martin; Illnerová, Helena; Sumová, Alena

    Praha : The Czech Neuroscience Society, 2007. s. 92-92. [Conference of the Czech Neuroscience Society /6./. 19.11.2007-20.11.2007, Praha] Grant ostatní: 6th Framework project EUCLOCK(XE) 18741 Institutional research plan: CEZ:AV0Z50110509 Keywords : spo2 * photoperiod * clock genes * mice Subject RIV: FH - Neurology

  15. Photoperiodic entrainment of the circadian molecular clock in the mice

    Czech Academy of Sciences Publication Activity Database

    Sosniyenko, Serhiy; Laurinová, Kristýna; Sládek, Martin; Sumová, Alena

    Brno : Fyziologický ústav LF MU, 2007. [Fyziologické dny /83./. 06.02.2007-08.02.2007, Brno] Grant ostatní: 6th Framework project EUCLOCK(XE) 18741 Institutional research plan: CEZ:AV0Z50110509 Keywords : spo2 * photoperiod * clock genes * mice Subject RIV: FH - Neurology

  16. Metrological characterization of the pulsed Rb clock with optical detection

    CERN Document Server

    Micalizio, Salvatore; Godone, Aldo; Levi, Filippo

    2011-01-01

    We report on the implementation and the metrological characterization of a vapor-cell Rb frequency standard working in pulsed regime. The three main parts that compose the clock, physics package, optics and electronics, are described in detail in the paper. The prototype is designed and optimized to detect the clock transition in the optical domain. Specifically, the reference atomic transition, excited with a Ramsey scheme, is detected by observing the interference pattern on a laser absorption signal. \\ The metrological analysis includes the observation and characterization of the clock signal and the measurement of frequency stability and drift. In terms of Allan deviation, the measured frequency stability results as low as $1.7\\times 10^{-13} \\ \\tau^{-1/2}$, $\\tau$ being the averaging time, and reaches the value of few units of $10^{-15}$ for $\\tau=10^{4}$ s, an unprecedent achievement for a vapor cell clock. We discuss in the paper the physical effects leading to this result with particular care to laser...

  17. Suppressing Loss of Ions in an Atomic Clock

    Science.gov (United States)

    Prestage, John; Chung, Sang

    2010-01-01

    An improvement has been made in the design of a compact, highly stable mercury- ion clock to suppress a loss of ions as they are transferred between the quadrupole and higher multipole ion traps. Such clocks are being developed for use aboard spacecraft for navigation and planetary radio science. The modification is also applicable to ion clocks operating on Earth: indeed, the success of the modification has been demonstrated in construction and operation of a terrestrial breadboard prototype of the compact, highly stable mercury-ion clock. Selected aspects of the breadboard prototype at different stages of development were described in previous NASA Tech Briefs articles. The following background information is reviewed from previous articles: In this clock as in some prior ion clocks, mercury ions are shuttled between two ion traps, one a 16- pole linear radio-frequency trap, while the other is a quadrupole radio-frequency trap. In the quadrupole trap, ions are tightly confined and optical state selection from a 202Hg lamp is carried out. In the 16-pole trap, the ions are more loosely confined and atomic transitions are interrogated by use of a microwave beam at approximately 40.507 GHz. The trapping of ions effectively eliminates the frequency pulling that would otherwise be caused by collisions between clock atoms and the wall of a gas cell. The shuttling of the ions between the two traps enables separation of the state-selection process from the clock microwave-resonance process, so that each of these processes can be optimized independently of the other. This is similar to the operation of an atomic beam clock, except that with ions the beam can be halted and reversed as ions are shuttled back and forth between the two traps. When the two traps are driven at the same radio frequency, the strength of confinement can be reduced near the junction between the two traps, depending upon the relative phase of the RF voltage used to operate each of the two traps, and

  18. Time-of-day- and light-dependent expression of ubiquitin protein ligase E3 component N-recognin 4 (UBR4 in the suprachiasmatic nucleus circadian clock.

    Directory of Open Access Journals (Sweden)

    Harrod H Ling

    Full Text Available Circadian rhythms of behavior and physiology are driven by the biological clock that operates endogenously but can also be entrained to the light-dark cycle of the environment. In mammals, the master circadian pacemaker is located in the suprachiasmatic nucleus (SCN, which is composed of individual cellular oscillators that are driven by a set of core clock genes interacting in transcriptional/translational feedback loops. Light signals can trigger molecular events in the SCN that ultimately impact on the phase of expression of core clock genes to reset the master pacemaker. While transcriptional regulation has received much attention in the field of circadian biology in the past, other mechanisms including targeted protein degradation likely contribute to the clock timing and entrainment process. In the present study, proteome-wide screens of the murine SCN led to the identification of ubiquitin protein ligase E3 component N-recognin 4 (UBR4, a novel E3 ubiquitin ligase component of the N-end rule pathway, as a time-of-day-dependent and light-inducible protein. The spatial and temporal expression pattern of UBR4 in the SCN was subsequently characterized by immunofluorescence microscopy. UBR4 is expressed across the entire rostrocaudal extent of the SCN in a time-of-day-dependent fashion. UBR4 is localized exclusively to arginine vasopressin (AVP-expressing neurons of the SCN shell. Upon photic stimulation in the early subjective night, the number of UBR4-expressing cells within the SCN increases. This study is the first to identify a novel E3 ubiquitin ligase component, UBR4, in the murine SCN and to implicate the N-end rule degradation pathway as a potential player in regulating core clock mechanisms and photic entrainment.

  19. A Study on the Steering Strategy for the Master Clock

    Science.gov (United States)

    Zhao, Shu-Hong; Wang, Zheng-Ming; Yin, Dong-Shan

    2015-01-01

    A physical realization of UTC (Coordinated Universal Time) by the master clock system in a time laboratory is named UTC(k). In order to make the deviation of UTC(k) from UTC as small as possible, and keep high short-term and long-term frequency stabilities as well, a new steering algorithm is proposed, and the detailed algorithm is as follows: Firstly, a stable reference time scale (TA) for real-time monitoring UTC(NTSC) is introduced. The time scale algorithm for generating TA, which is computed as a weighted average of about 22 free-running atomic clocks at the National Time Service Center (NTSC), is based on the ALGOS algorithm. And the weighting procedure is designed to optimize the short-term frequency stability of the scale. Secondly, the frequency offset is calculated. (1) The frequency of the master clock in the next time interval is calculated; (2) The phase difference between TA and UTC(NTSC) is deducted; (3) The final frequency offset is generated on the basis of above steps. A software is compiled according to this algorithm. The results calculated with the software are sent to the microphase stepper automatically, so that the time signal derived from the steered master clock can be accurate, meanwhile its stability is not influenced. Finally, the experimental result shows that the new master clock steering strategy can control the phase offset within ±15 ns, meanwhile it can also improve its short-term stability on the condition that its long-term one is not influenced.

  20. CULLIN-3 controls TIMELESS oscillations in the Drosophila circadian clock.

    Directory of Open Access Journals (Sweden)

    Brigitte Grima

    Full Text Available Eukaryotic circadian clocks rely on transcriptional feedback loops. In Drosophila, the PERIOD (PER and TIMELESS (TIM proteins accumulate during the night, inhibit the activity of the CLOCK (CLK/CYCLE (CYC transcriptional complex, and are degraded in the early morning. The control of PER and TIM oscillations largely depends on post-translational mechanisms. They involve both light-dependent and light-independent pathways that rely on the phosphorylation, ubiquitination, and proteasomal degradation of the clock proteins. SLMB, which is part of a CULLIN-1-based E3 ubiquitin ligase complex, is required for the circadian degradation of phosphorylated PER. We show here that CULLIN-3 (CUL-3 is required for the circadian control of PER and TIM oscillations. Expression of either Cul-3 RNAi or dominant negative forms of CUL-3 in the clock neurons alters locomotor behavior and dampens PER and TIM oscillations in light-dark cycles. In constant conditions, CUL-3 deregulation induces behavioral arrhythmicity and rapidly abolishes TIM cycling, with slower effects on PER. CUL-3 affects TIM accumulation more strongly in the absence of PER and forms protein complexes with hypo-phosphorylated TIM. In contrast, SLMB affects TIM more strongly in the presence of PER and preferentially associates with phosphorylated TIM. CUL-3 and SLMB show additive effects on TIM and PER, suggesting different roles for the two ubiquitination complexes on PER and TIM cycling. This work thus shows that CUL-3 is a new component of the Drosophila clock, which plays an important role in the control of TIM oscillations.

  1. Clock recovering characteristics of adaptive finite-impulse-response filters in digital coherent optical receivers.

    Science.gov (United States)

    Kikuchi, Kazuro

    2011-03-14

    We analyze the clock-recovery process based on adaptive finite-impulse-response (FIR) filtering in digital coherent optical receivers. When the clock frequency is synchronized between the transmitter and the receiver, only five taps in half-symbol-spaced FIR filters can adjust the sampling phase of analog-to-digital conversion optimally, enabling bit-error rate performance independent of the initial sampling phase. Even if the clock frequency is not synchronized between them, the clock-frequency misalignment can be adjusted within an appropriate block interval; thus, we can achieve an asynchronous clock mode of operation of digital coherent receivers with block processing of the symbol sequence. PMID:21445201

  2. Byzantine-fault tolerant self-stabilizing protocol for distributed clock synchronization systems

    Science.gov (United States)

    Malekpour, Mahyar R. (Inventor)

    2010-01-01

    A rapid Byzantine self-stabilizing clock synchronization protocol that self-stabilizes from any state, tolerates bursts of transient failures, and deterministically converges within a linear convergence time with respect to the self-stabilization period. Upon self-stabilization, all good clocks proceed synchronously. The Byzantine self-stabilizing clock synchronization protocol does not rely on any assumptions about the initial state of the clocks. Furthermore, there is neither a central clock nor an externally generated pulse system. The protocol converges deterministically, is scalable, and self-stabilizes in a short amount of time. The convergence time is linear with respect to the self-stabilization period.

  3. The clock distribution system for the ATLAS Liquid Argon Calorimeter Phase-I Upgrade Demonstrator

    International Nuclear Information System (INIS)

    A prototype Liquid-argon Trigger Digitizer Board (LTDB), called the LTDB Demonstrator, has been developed to demonstrate the functions of the ATLAS Liquid Argon Calorimeter Phase-I trigger electronics upgrade. Forty Analog-to-Digital converters and four FPGAs with embedded multi-gigabit-transceivers on each Demonstrator need high quality clocks. A clock distribution system based on commercial components has been developed for the Demonstrator. The design of the clock distribution system is presented. The performance of the clock distribution system has been evaluated. The components used in the clock distribution system have been qualified to meet radiation tolerance requirements of the Demonstrator

  4. Deep RNA profiling identified CLOCK and molecular clock genes as pathophysiological signatures in collagen VI myopathy.

    Science.gov (United States)

    Scotton, Chiara; Bovolenta, Matteo; Schwartz, Elena; Falzarano, Maria Sofia; Martoni, Elena; Passarelli, Chiara; Armaroli, Annarita; Osman, Hana; Rodolico, Carmelo; Messina, Sonia; Pegoraro, Elena; D'Amico, Adele; Bertini, Enrico; Gualandi, Francesca; Neri, Marcella; Selvatici, Rita; Boffi, Patrizia; Maioli, Maria Antonietta; Lochmüller, Hanns; Straub, Volker; Bushby, Katherine; Castrignanò, Tiziana; Pesole, Graziano; Sabatelli, Patrizia; Merlini, Luciano; Braghetta, Paola; Bonaldo, Paolo; Bernardi, Paolo; Foley, Reghan; Cirak, Sebahattin; Zaharieva, Irina; Muntoni, Francesco; Capitanio, Daniele; Gelfi, Cecilia; Kotelnikova, Ekaterina; Yuryev, Anton; Lebowitz, Michael; Zhang, Xiping; Hodge, Brian A; Esser, Karyn A; Ferlini, Alessandra

    2016-04-15

    Collagen VI myopathies are genetic disorders caused by mutations in collagen 6 A1, A2 and A3 genes, ranging from the severe Ullrich congenital muscular dystrophy to the milder Bethlem myopathy, which is recapitulated by collagen-VI-null (Col6a1(-/-)) mice. Abnormalities in mitochondria and autophagic pathway have been proposed as pathogenic causes of collagen VI myopathies, but the link between collagen VI defects and these metabolic circuits remains unknown. To unravel the expression profiling perturbation in muscles with collagen VI myopathies, we performed a deep RNA profiling in bothCol6a1(-/-)mice and patients with collagen VI pathology. The interactome map identified common pathways suggesting a previously undetected connection between circadian genes and collagen VI pathology. Intriguingly,Bmal1(-/-)(also known asArntl) mice, a well-characterized model displaying arrhythmic circadian rhythms, showed profound deregulation of the collagen VI pathway and of autophagy-related genes. The involvement of circadian rhythms in collagen VI myopathies is new and links autophagy and mitochondrial abnormalities. It also opens new avenues for therapies of hereditary myopathies to modulate the molecular clock or potential gene-environment interactions that might modify muscle damage pathogenesis. PMID:26945058

  5. Turning Back the Clock: Inferring the History of the Eight O'clock Arc

    CERN Document Server

    Finkelstein, Steven L; Rudnick, Gregory; Egami, Eiichi; Floc'h, Emeric Le; Rieke, Marcia J; Rigby, Jane; Willmer, Christopher N A

    2009-01-01

    We present the results from an optical and near-infrared spectroscopic study of the ultraviolet-luminous z = 2.73 galaxy, the 8 o'clock arc. Due to gravitational lensing, this galaxy is magnified by a factor of > 10, allowing in-depth measurements which are usually unfeasible at such redshifts. In the optical spectra, we measured the systemic redshift of the galaxy, z = 2.7322 +/- 0.0012, using stellar photospheric lines. This differs from the redshift of absorption lines in the interstellar medium, z = 2.7302 +/- 0.0006, implying gas outflows on the order of 160 km/s. With H and K-band near-infrared spectra, we have measured nebular emission lines of Halpha, Hbeta, Hgamma, [N II] and [O III], which have a redshift z = 2.7333 +/- 0.0001, consistent with the derived systemic redshift. From the Balmer decrement, we measured the dust extinction to be A_5500 = 0.53 +/- 0.16 mag. Correcting Halpha for dust extinction and the assumed lensing factor, we measure a star-formation rate of ~ 90 Msol/yr, which is higher ...

  6. Frequency ratios of Sr, Yb and Hg based optical lattice clocks and their applications

    CERN Document Server

    Takamoto, Masao; Das, Manoj; Nemitz, Nils; Ohkubo, Takuya; Yamanaka, Kazuhiro; Ohmae, Noriaki; Takano, Tetsushi; Akatsuka, Tomoya; Yamaguchi, Atsushi; Katori, Hidetoshi

    2015-01-01

    This article describes the recent progress of optical lattice clocks with neutral strontium ($^{87}$Sr), ytterbium ($^{171}$Yb) and mercury ($^{199}$Hg) atoms. In particular, we present frequency comparison between the clocks locally via an optical frequency comb and between two Sr clocks at remote sites using a phase-stabilized fibre link. We first review cryogenic Sr optical lattice clocks that reduce the room-temperature blackbody radiation shift by two orders of magnitude and serve as a reference in the following clock comparisons. Similar physical properties of Sr and Yb atoms, such as transition wavelengths and vapour pressure, have allowed our development of a compatible clock for both species. A cryogenic Yb clock is evaluated by referencing a Sr clock. We also report on a Hg clock, which shows one order of magnitude less sensitivity to blackbody radiation, while its large nuclear charge makes the clock sensitive to the variation of fine-structure constant. Connecting all three types of clocks by an o...

  7. Osmotic stress at the barley root affects expression of circadian clock genes in the shoot.

    Science.gov (United States)

    Habte, Ermias; Müller, Lukas M; Shtaya, Munqez; Davis, Seth J; von Korff, Maria

    2014-06-01

    The circadian clock is an important timing system that controls physiological responses to abiotic stresses in plants. However, there is little information on the effects of the clock on stress adaptation in important crops, like barley. In addition, we do not know how osmotic stress perceived at the roots affect the shoot circadian clock. Barley genotypes, carrying natural variation at the photoperiod response and clock genes Ppd-H1 and HvELF3, were grown under control and osmotic stress conditions to record changes in the diurnal expression of clock and stress-response genes and in physiological traits. Variation at HvELF3 affected the expression phase and shape of clock and stress-response genes, while variation at Ppd-H1 only affected the expression levels of stress genes. Osmotic stress up-regulated expression of clock and stress-response genes and advanced their expression peaks. Clock genes controlled the expression of stress-response genes, but had minor effects on gas exchange and leaf transpiration. This study demonstrated that osmotic stress at the barley root altered clock gene expression in the shoot and acted as a spatial input signal into the clock. Unlike in Arabidopsis, barley primary assimilation was less controlled by the clock and more responsive to environmental perturbations, such as osmotic stress. PMID:24895755

  8. Design and Analysis of Sequential Elements for Low Power Clocking System with Low Power Techniques

    Directory of Open Access Journals (Sweden)

    S.Sasidhar Reddy

    2014-09-01

    Full Text Available This paper proposed the design of sequential elements for low power clocking system with low low power techniques for saving the power. Power consumption is a major bottleneck of system performance and is listed as one of the top three challenges in International Technology Roadmap for Semiconductor 2008. In practice, a large portion of the on chip power is consumed by the clock system which is made of the clock distribution network and flop-flops. In this paper, various design techniques for a low power clocking system are surveyed. Among them is an effective way to reduce capacity of the clock load by minimizing number of clocked transistors. To approach this, proposed a novel clocked pair shared flip-flop which reduces the number of local clocked transistors by approximately 40%. A 24% reduction of clock driving power is achieved. In addition, low swing and double edge clocking, can be easily incorporated into the new flip-flop to build clocking systems. As the feature size becomes smaller, shorter channel lengths result in increased sub-threshold leakage current through a transistor when it is off. Dual sleep and sleepy stack methods are proposed to avoid static power consumption; the flip flops are simulated using HSPICE.

  9. Entanglement and spin squeezing in a network of distant optical lattice clocks

    Science.gov (United States)

    Polzik, Eugene S.; Ye, Jun

    2016-02-01

    We propose an approach for the collective enhancement of precision for remote optical lattice clocks and a way of generating the Einstein-Podolsky-Rosen (EPR) state of remote clocks. In the first scenario, a distributed spin-squeezed state (SSS) of M clocks is generated by a collective optical quantum nondemolition measurement on clocks with parallel Bloch vectors. Surprisingly, optical losses, which usually present the main limitation to SSS, can be overcome by an optimal network design which provides close to Heisenberg scaling of the time precision with the number of clocks M . We provide an optimal network solution for distant clocks as well as for clocks positioned within close proximity of each other. In the second scenario, we employ collective dissipation to drive two clocks with oppositely oriented Bloch vectors into a steady-state entanglement. The corresponding EPR state provides secret time sharing beyond the projection noise limit between the two quantum synchronized clocks protected from eavesdropping. An important application of the EPR-entangled clock pair is the remote sensing of, for example, gravitational effects and other disturbances to which clock synchronization is sensitive.

  10. NPAS2 Compensates for Loss of CLOCK in Peripheral Circadian Oscillators.

    Directory of Open Access Journals (Sweden)

    Dominic Landgraf

    2016-02-01

    Full Text Available Heterodimers of CLOCK and BMAL1 are the major transcriptional activators of the mammalian circadian clock. Because the paralog NPAS2 can substitute for CLOCK in the suprachiasmatic nucleus (SCN, the master circadian pacemaker, CLOCK-deficient mice maintain circadian rhythms in behavior and in tissues in vivo. However, when isolated from the SCN, CLOCK-deficient peripheral tissues are reportedly arrhythmic, suggesting a fundamental difference in circadian clock function between SCN and peripheral tissues. Surprisingly, however, using luminometry and single-cell bioluminescence imaging of PER2 expression, we now find that CLOCK-deficient dispersed SCN neurons and peripheral cells exhibit similarly stable, autonomous circadian rhythms in vitro. In CLOCK-deficient fibroblasts, knockdown of Npas2 leads to arrhythmicity, suggesting that NPAS2 can compensate for loss of CLOCK in peripheral cells as well as in SCN. Our data overturn the notion of an SCN-specific role for NPAS2 in the molecular circadian clock, and instead indicate that, at the cellular level, the core loops of SCN neuron and peripheral cell circadian clocks are fundamentally similar.

  11. Analysis of a clock-aided global navigation satellite system (GNSS)

    International Nuclear Information System (INIS)

    This paper presents a dilution of precision (DOP) analysis of a clock-aided global navigation satellite system (GNSS). Firstly, the analysis shows that a best linear unbiased estimator should be used in the clock-aided GNSS to get the best improvements in accuracy. Secondly, the influence of the clock on vertical DOP (VDOP) and horizontal DOP (HDOP) is analysed by using the clock characteristics as a weighting matrix. The analysis highlights quantitative improvements in the VDOP and HDOP and explains why improvements in the VDOP are superior to those of the HDOP in the clock-aided GNSS. Finally, the paper analyses how incorrectly known a priori clock variances degrade the level of accuracy and offers guidelines for determining a weighting matrix in the cases where the clock characteristics are not clearly known

  12. Expression of core clock genes in colorectal tumour cells compared with normal mucosa

    DEFF Research Database (Denmark)

    Fonnes, S; Donatsky, A M; Gögenur, I

    2015-01-01

    AIM: Experimental studies have shown that some circadian core clock genes may act as tumour suppressors and have an important role in the response to oncological treatment. This study investigated the evidence regarding modified expression of core clock genes in colorectal cancer and its...... expression of colorectal cancer cells compared with healthy mucosa cells from specimens analysed by real-time or quantitative real-time polymer chain reaction. The expression of the core clock genes Period, Cryptochrome, Bmal1 and Clock in colorectal tumours were compared with healthy mucosa and correlated...... of Clock. Other core clock genes did not appear to be differentially expressed. Decreased Period gene expression was correlated to some clinicopathological features. CONCLUSION: The Period genes seemed to be modified in colorectal tumour cells compared with normal mucosa. Core clock genes might be...

  13. Interactions between the circadian clock and metabolism: there are good times and bad times

    Institute of Scientific and Technical Information of China (English)

    Mi Shi; Xiangzhong Zheng

    2013-01-01

    An endogenous circadian (~24 h) clock regulates rhythmic processes of physiology,metabolism and behavior in most living organisms.While able to free-run under constant conditions,the circadian clock is coupled to day:night cycles to increase its amplitude and align the phase of circadian rhythms to the right time of the day.Disruptions of the circadian clock are correlated with brain dysfunctions,cardiovascular diseases and metabolic disorders.In this review,we focus on the interactions between the circadian clock and metabolism.We discuss recent findings on circadian clock regulation of feeding behavior and rhythmic expression of metabolic genes,and present evidence of metabolic input to the circadian clock.We emphasize how misalignment of circadian clocks within the body and with environmental cycles or daily schedules leads to the increasing prevalence of metabolic syndromes in modern society.

  14. Divergent roles of clock genes in retinal and suprachiasmatic nucleus circadian oscillators.

    Directory of Open Access Journals (Sweden)

    Guo-Xiang Ruan

    Full Text Available The retina is both a sensory organ and a self-sustained circadian clock. Gene targeting studies have revealed that mammalian circadian clocks generate molecular circadian rhythms through coupled transcription/translation feedback loops which involve 6 core clock genes, namely Period (Per 1 and 2, Cryptochrome (Cry 1 and 2, Clock, and Bmal1 and that the roles of individual clock genes in rhythms generation are tissue-specific. However, the mechanisms of molecular circadian rhythms in the mammalian retina are incompletely understood and the extent to which retinal neural clocks share mechanisms with the suprachiasmatic nucleus (SCN, the central neural clock, is unclear. In the present study, we examined the rhythmic amplitude and period of real-time bioluminescence rhythms in explants of retina from Per1-, Per2-, Per3-, Cry1-, Cry2-, and Clock-deficient mice that carried transgenic PERIOD2::LUCIFERASE (PER2::LUC or Period1::luciferase (Per1::luc circadian reporters. Per1-, Cry1- and Clock-deficient retinal and SCN explants showed weakened or disrupted rhythms, with stronger effects in retina compared to SCN. Per2, Per3, and Cry2 were individually dispensable for sustained rhythms in both tissues. Retinal and SCN explants from double knockouts of Cry1 and Cry2 were arrhythmic. Gene effects on period were divergent with reduction in the number of Per1 alleles shortening circadian period in retina, but lengthening it in SCN, and knockout of Per3 substantially shortening retinal clock period, but leaving SCN unaffected. Thus, the retinal neural clock has a unique pattern of clock gene dependence at the tissue level that it is similar in pattern, but more severe in degree, than the SCN neural clock, with divergent clock gene regulation of rhythmic period.

  15. Genome increase as a clock for the origin and evolution of life

    Directory of Open Access Journals (Sweden)

    Sharov Alexei A

    2006-06-01

    Full Text Available Abstract Background The size of non-redundant functional genome can be an indicator of biological complexity of living organisms. Several positive feedback mechanisms including gene cooperation and duplication with subsequent specialization may result in the exponential growth of biological complexity in macro-evolution. Results I propose a hypothesis that biological complexity increased exponentially during evolution. Regression of the logarithm of functional non-redundant genome size versus time of origin in major groups of organisms showed a 7.8-fold increase per 1 billion years, and hence the increase of complexity can be viewed as a clock of macro-evolution. A strong version of the exponential hypothesis is that the rate of complexity increase in early (pre-prokaryotic evolution of life was at most the same (or even slower than observed in the evolution of prokaryotes and eukaryotes. Conclusion The increase of functional non-redundant genome size in macro-evolution was consistent with the exponential hypothesis. If the strong exponential hypothesis is true, then the origin of life should be dated 10 billion years ago. Thus, the possibility of panspermia as a source of life on earth should be discussed on equal basis with alternative hypotheses of de-novo life origin. Panspermia may be proven if bacteria similar to terrestrial ones are found on other planets or satellites in the solar system. Reviewers This article was reviewed by Eugene V. Koonin, Chris Adami and Arcady Mushegian.

  16. The Chemical and Educational Appeal of the Orange Juice Clock

    Science.gov (United States)

    Kelter, Paul B.; Carr, James D.; Johnson, Tanya; Mauricio Castro-Acuña, Carlos

    1996-12-01

    The Orange Juice Clock, in which a galvanic cell is made from the combination of a magnesium strip, a copper strip, and juice in a beaker, has been a popular classroom, conference, and workshop demonstration for nearly 10 years. It is widely enjoyed because it shows visually how chemistry - or more precisely, electrochemistry - is responsible for the very common phenomenon of a clock ticking. The chemistry of the process can also be understood on a variety of levels, from middle school (simple electron flow in a circuit, Ohm's law) and high school (reduction/oxidation and standard cell potentials) to first-year college (cell potential at nonideal conditions) and graduate school courses (overpotential and charge transfer across interfaces.) The discussion that follows considers the recent history, chemistry, and educational uses of the demonstration. The History The demonstration was devised by one of us (PK) in 1986, after reading an activity in Hubert Alyea's 1947 compendium of chemical demonstrations from this Journal (1). In that activity, Alyea hooked a magnesium strip to the negative battery terminal of an electric bell and hooked a copper strip to the positive terminal. He placed the loose ends of the strips into a 1M 2SO4 solution and the bell rang. After trying the demonstration, it seemed to make sense to modify the electrolyte to orange juice because it is safe, readily available, and would be a mixture in which the magnesium would oxidize more slowly than in sulfuric acid. Further, a clock was substituted for the bell because a clock is easier on the ears than a bell. A video of the orange-juice clock setup is given as Figure 1. Figure 1.The orange juice clock set up. Video of orange juice clock was filmed and editted by Jerry Jacobson at the University of Wisconsin - Madison. The apparatus was presented in 1987 as part of a teacher workshop led by Irwin Talesnick, then of Queen's University in Canada. Talesnick, whose distinguished career has been

  17. Synchronization of Distant Optical Clocks at the Femtosecond Level

    CERN Document Server

    Deschenes, Jean-Daniel; Giorgetta, Fabrizio R; Swann, William C; Baumann, Esther; Bergeron, Hugo; Cermak, Michael; Coddington, Ian; Newbury, Nathan R

    2015-01-01

    The use of optical clocks/oscillators in future ultra-precise navigation, gravitational sensing, and relativity experiments will require time comparison and synchronization over terrestrial or satellite free-space links. Here we demonstrate full unambiguous synchronization of two optical timescales across a free-space link. The time deviation between synchronized timescales is below 1 fs over durations from 0.1 s to 6500 s, despite atmospheric turbulence and kilometer-scale path length variations. Over several days, the time wander is below +/-20 fs. Our approach relies on the two-way reciprocity of a single-spatial-mode optical link, valid to below 225 attoseconds across a turbulent 4-km path. This femtosecond level of time-frequency transfer should enable optical networks using state-of-the-art optical clocks/oscillators.

  18. Atomic Clock Ensemble in Space: Scientific Objectives and Mission Status

    Energy Technology Data Exchange (ETDEWEB)

    Cacciapuoti, L. [European Space Agency, ESTEC, Keplerlaan 1 - P.O. Box 299, 2200 AG Noordwijk ZH (Netherlands)], E-mail: Luigi.Cacciapuoti@esa.int; Dimarcq, N.; Santarelli, G.; Laurent, P.; Lemonde, P.; Clairon, A. [SYRTE-CNRS UMR8630, Observatoire de Paris, 61, avenue de l' Observatoire 75014 Paris (France); Berthoud, P.; Jornod, A. [Observatoire de Neuchatel, 58, rue de l' Observatoire, CH-2000 Neuchatel (Switzerland); Reina, F.; Feltham, S. [European Space Agency, ESTEC, Keplerlaan 1 - P.O. Box 299, 2200 AG Noordwijk ZH (Netherlands); Salomon, C. [Laboratoire Kastler Brossel, ENS, 24, rue Lhomond, 75005 Paris (France)

    2007-04-15

    Atomic Clock Ensemble in Space (ACES) is a mission in fundamental physics that will operate a new generation of atomic clocks in the microgravity environment of the International Space Station. Fractional frequency instability and inaccuracy at the 10{sup -16} level will be achieved. The on-board time base, distributed on Earth via a microwave link, will be used for space-to-ground as well as ground-to-ground comparisons of atomic frequency standards. Based on these comparisons, ACES will perform fundamental physics tests and develop applications in time and frequency metrology, universal time scales, global positioning and navigation, geodesy, and gravimetry. After a general overview of the mission concept and its scientific objectives, the present status of ACES instruments and sub-systems will be discussed.

  19. Thermally reliable clocked non-volatile spin wave logic device

    Science.gov (United States)

    Dutta, Sourav; Nikonov, Dmitri; Manipatruni, Sasikanth; Young, Ian; Naeemi, Azad

    The possibility of utilizing spin waves for information transmission and computation has been an area of active research due to the unique ability to manipulate the amplitude and phase of the spin waves for building complex logic circuits. Here, we present a comprehensive scheme for building a thermally reliable clocked non-volatile spin wave logic device (SWLD) by introducing a charge-to-spin converter that translates information from electrical domain to spin domain, exploiting the magneto-electric effect for spin wave transmission, detection and non-volatile memory, utilizing the phase of the spin wave as information token, ensuring phase-dependent deterministic switching of the magnetoelectric spin wave detector in the presence of thermal noise via compensation of demagnetization and a novel clocking scheme that ensures sequential transmission of information in a cascaded SWLD and non- reciprocity

  20. Spin-orbit coupled fermions in an optical lattice clock

    CERN Document Server

    Kolkowitz, S; Bothwell, T; Wall, M L; Marti, G E; Koller, A P; Zhang, X; Rey, A M; Ye, J

    2016-01-01

    Engineered spin-orbit coupling (SOC) in cold atom systems can aid in the study of novel synthetic materials and complex condensed matter phenomena. Despite great advances, alkali atom SOC systems are hindered by heating from spontaneous emission, which limits the observation of many-body effects. Here we demonstrate the use of optical lattice clocks (OLCs) to engineer and study SOC with metrological precision and negligible heating. We show that clock spectroscopy of the ultra-narrow transition in fermionic 87Sr represents a momentum- and spin-resolved in situ probe of the SOC band structure and eigenstates, providing direct access to the SOC dynamics and control over lattice band populations, internal electronic states, and quasimomenta. We utilize these capabilities to study Bloch oscillations, spin-momentum locking, and van Hove singularities in the transition density of states. Our results lay the groundwork for the use of OLCs to probe novel SOC phases including magnetic crystals, helical liquids, and to...

  1. Constructive polarization modulation for coherent population trapping clock

    International Nuclear Information System (INIS)

    We propose a constructive polarization modulation scheme for atomic clocks based on coherent population trapping (CPT). In this scheme, the polarization of a bichromatic laser beam is modulated between two opposite circular polarizations to avoid trapping the atomic populations in the extreme Zeeman sublevels. We show that if an appropriate phase modulation between the two optical components of the bichromatic laser is applied synchronously, the two CPT dark states which are produced successively by the alternate polarizations add constructively. Measured CPT resonance contrasts up to 20% in one-pulse CPT and 12% in two-pulse Ramsey-CPT experiments are reported, demonstrating the potential of this scheme for applications to high performance atomic clocks

  2. Timing of Photoperiodic Flowering:Light Perception and Circadian Clock

    Institute of Scientific and Technical Information of China (English)

    Yun Zhou; Xiao-Dong Sun; Min Ni

    2007-01-01

    Flowering symbolizes the transition of a plant from vegetative phase to reproductive phase and is controlled by fairly complex and highly coordinated regulatory pathways. Over the last decade, genetic studies in Arabidopsis have aided the discovery of many signaling components involved in these pathways. In this review, we discuss how the timing of flowering is regulated by photoperiod and the involvement of light perception and the circadian clock in this process. The specific regulatory mechanisms on CONSTANS expression and CONSTANS stability by the circadian clock and photoreceptors are described in detail. In addition, the roles of CONSTANS, FLOWERING LOCUS T, and several other light signaling and circadiandependent components in photoperiodic flowering are also highlighted.

  3. Gravitational wave detection with optical lattice atomic clocks

    CERN Document Server

    Kolkowitz, Shimon; Langellier, Nicholas; Lukin, Mikhail D; Walsworth, Ronald L; Ye, Jun

    2016-01-01

    We propose a space-based gravitational wave detector consisting of two spatially separated, drag-free satellites sharing ultra-stable optical laser light over a single baseline. Each satellite contains an optical lattice atomic clock, which serves as a sensitive, narrowband detector of the local frequency of the shared laser light. A synchronized two-clock comparison between the satellites will be sensitive to the effective Doppler shifts induced by incident gravitational waves (GWs) at a level competitive with other proposed space-based GW detectors, while providing complementary features. The detected signal is a differential frequency shift of the shared laser light due to the relative velocity of the satellites, rather than a phase shift arising from the relative satellite positions, and the detection window can be tuned through the control sequence applied to the atoms' internal states. This scheme enables the detection of GWs from continuous, spectrally narrow sources, such as compact binary inspirals, ...

  4. Planar transformers for column parallel CCD clock drive

    International Nuclear Information System (INIS)

    The LCFI Collaboration is developing the sensors, readout electronics and mechanical support structures for the Vertex Detector (VXD) of the International Linear Collider (ILC). High-speed readout is needed to ensure that the occupancy due to the pair production background at the ILC is kept below 1% level. In order to satisfy this requirement, Column Parallel CCDs (CPCCDs) and Column Parallel Readout chips (CPRs) have been developed. The CPCCD has to operate at a clock frequency of 50 MHz, which represents a difficult technical challenge due to the relatively large sensor capacitance. The design and performance of planar transformers, which can be used to provide the required 20 A clock current, are described.

  5. Clockscalpel: Understanding Root Causes of Internet Clock Synchronization Inaccuracy

    Science.gov (United States)

    Hong, Chi-Yao; Lin, Chia-Chi; Caesar, Matthew

    Synchronizing clocks is an integral part of modern network and security architectures. However, the ability to synchronize clocks in modern networks is not well-understood. In this work, we use testbeds equipped with a high-accuracy GPS receiver to acquire ground truth, to study the accuracy of probe-based synchronization techniques to over 1861 public time servers. We find that existing synchronization protocols provide a median error of 2 - 5 ms, but suffer from a long-tail. We analyze sources of inaccuracy by decoupling and quantifying different network factors. We found that most inaccuracies stem from asymmetry of propagation delay and queueing delay. We discuss possible schemes to compensate these errors to improve synchronization accuracy.

  6. PPARs Integrate the Mammalian Clock and Energy Metabolism

    Directory of Open Access Journals (Sweden)

    Lihong Chen

    2014-01-01

    Full Text Available Peroxisome proliferator-activated receptors (PPARs are a group of nuclear receptors that function as transcription factors regulating the expression of numerous target genes. PPARs play an essential role in various physiological and pathological processes, especially in energy metabolism. It has long been known that metabolism and circadian clocks are tightly intertwined. However, the mechanism of how they influence each other is not fully understood. Recently, all three PPAR isoforms were found to be rhythmically expressed in given mouse tissues. Among them, PPARα and PPARγ are direct regulators of core clock components, Bmal1 and Rev-erbα, and, conversely, PPARα is also a direct Bmal1 target gene. More importantly, recent studies using knockout mice revealed that all PPARs exert given functions in a circadian manner. These findings demonstrated a novel role of PPARs as regulators in correlating circadian rhythm and metabolism. In this review, we summarize advances in our understanding of PPARs in circadian regulation.

  7. Motion and gravity effects in the precision of quantum clocks

    CERN Document Server

    Lindkvist, Joel; Johansson, Göran; Fuentes, Ivette

    2014-01-01

    We show that motion and gravity affect the precision of quantum clocks. We consider a localised quantum field as a fundamental model of a quantum clock moving in spacetime and show that its state is modified due to changes in acceleration. By computing the quantum Fisher information we determine how relativistic motion modifies the ultimate bound in the precision of the measurement of time. While in the absence of motion the squeezed vacuum is the ideal state for time estimation, we find that it is highly sensitive to the motion-induced degradation of the quantum Fisher information. We show that coherent states are generally more resilient to this degradation and that in the case of very low initial number of photons, the optimal precision can be even increased by motion. These results can be tested with current technology by using superconducting resonators with tunable boundary conditions.

  8. Motion and gravity effects in the precision of quantum clocks.

    Science.gov (United States)

    Lindkvist, Joel; Sabín, Carlos; Johansson, Göran; Fuentes, Ivette

    2015-01-01

    We show that motion and gravity affect the precision of quantum clocks. We consider a localised quantum field as a fundamental model of a quantum clock moving in spacetime and show that its state is modified due to changes in acceleration. By computing the quantum Fisher information we determine how relativistic motion modifies the ultimate bound in the precision of the measurement of time. While in the absence of motion the squeezed vacuum is the ideal state for time estimation, we find that it is highly sensitive to the motion-induced degradation of the quantum Fisher information. We show that coherent states are generally more resilient to this degradation and that in the case of very low initial number of photons, the optimal precision can be even increased by motion. These results can be tested with current technology by using superconducting resonators with tunable boundary conditions. PMID:25988238

  9. Activity clocks: spreading dynamics on temporal networks of human contact

    CERN Document Server

    Gauvin, Laetitia; Cattuto, Ciro; Barrat, Alain

    2013-01-01

    Dynamical processes on time-varying complex networks are key to un- derstanding and modeling a broad variety of processes in socio-technical systems. Here we focus on empirical temporal networks of human proxim- ity and we aim at understanding the factors that, in simulation, shape the arrival time distribution of simple spreading processes. Abandoning the notion of wall-clock time in favour of node-specific clocks based on activ- ity exposes robust statistical patterns in the arrival times across different social contexts. Using randomization strategies and generative models constrained by data, we show that these patterns can be understood in terms of heterogeneous inter-event time distributions coupled with hetero- geneous numbers of events per edge. We also show, both empirically and by using a synthetic dataset, that significant deviations from the above behavior can be caused by the presence of edge classes with strong activity correlations.

  10. C-terminal binding protein (CtBP activates the expression of E-box clock genes with CLOCK/CYCLE in Drosophila.

    Directory of Open Access Journals (Sweden)

    Taichi Q Itoh

    Full Text Available In Drosophila, CLOCK/CYCLE heterodimer (CLK/CYC is the primary activator of circadian clock genes that contain the E-box sequence in their promoter regions (hereafter referred to as "E-box clock genes". Although extensive studies have investigated the feedback regulation of clock genes, little is known regarding other factors acting with CLK/CYC. Here we show that Drosophila C-terminal binding protein (dCtBP, a transcriptional co-factor, is involved in the regulation of the E-box clock genes. In vivo overexpression of dCtBP in clock cells lengthened or abolished circadian locomotor rhythm with up-regulation of a subset of the E-box clock genes, period (per, vrille (vri, and PAR domain protein 1ε (Pdp1ε. Co-expression of dCtBP with CLK in vitro also increased the promoter activity of per, vri, Pdp1ε and cwo depending on the amount of dCtBP expression, whereas no effect was observed without CLK. The activation of these clock genes in vitro was not observed when we used mutated dCtBP which carries amino acid substitutions in NAD+ domain. These results suggest that dCtBP generally acts as a putative co-activator of CLK/CYC through the E-box sequence.

  11. Optimal and Robust Saturated Control for a Clock Generator

    OpenAIRE

    Albea-Sanchez, Carolina; Lesecq, Suzanne; Puschini, Diego

    2011-01-01

    Fine-grain Dynamic Voltage and Fre- quency Scaling (DVFS) is becoming a requirement for Globally-Asynchronous Locally-Synchronous (GALS) architectures. However, the area overhead of adding voltage and frequency control engines in each volt- age/frequency island must be taken into account to optimize the circuit. This paper focuses on the control for the frequency actuator. An optimal and robust saturated control law, with a minimum hardware implementation area is proposed for a Clock Gen- era...

  12. Circadian Rhythms, the Molecular Clock, and Skeletal Muscle

    OpenAIRE

    Lefta, Mellani; Wolff, Gretchen; Esser, Karyn A

    2011-01-01

    Almost all organisms ranging from single cell bacteria to humans exhibit a variety of behavioral, physiological, and biochemical rhythms. In mammals, circadian rhythms control the timing of many physiological processes over a 24-h period, including sleep-wake cycles, body temperature, feeding, and hormone production. This body of research has led to defined characteristics of circadian rhythms based on period length, phase, and amplitude. Underlying circadian behaviors is a molecular clock me...

  13. Explaining the imperfection of the molecular clock of hominid mitochondria.

    Directory of Open Access Journals (Sweden)

    Eva-Liis Loogväli

    Full Text Available The molecular clock of mitochondrial DNA has been extensively used to date various genetic events. However, its substitution rate among humans appears to be higher than rates inferred from human-chimpanzee comparisons, limiting the potential of interspecies clock calibrations for intraspecific dating. It is not well understood how and why the substitution rate accelerates. We have analyzed a phylogenetic tree of 3057 publicly available human mitochondrial DNA coding region sequences for changes in the ratios of mutations belonging to different functional classes. The proportion of non-synonymous and RNA genes substitutions has reduced over hundreds of thousands of years. The highest mutation ratios corresponding to fast acceleration in the apparent substitution rate of the coding sequence have occurred after the end of the Last Ice Age. We recalibrate the molecular clock of human mtDNA as 7990 years per synonymous mutation over the mitochondrial genome. However, the distribution of substitutions at synonymous sites in human data significantly departs from a model assuming a single rate parameter and implies at least 3 different subclasses of sites. Neutral model with 3 synonymous substitution rates can explain most, if not all, of the apparent molecular clock difference between the intra- and interspecies levels. Our findings imply the sluggishness of purifying selection in removing the slightly deleterious mutations from the human as well as the Neandertal and chimpanzee populations. However, for humans, the weakness of purifying selection has been further exacerbated by the population expansions associated with the out-of Africa migration and the end of the Last Ice Age.

  14. CONTANGO: Integrated Optimization of SoC Clock Networks

    OpenAIRE

    Markov, Igor L.; Dong-Jin Lee

    2011-01-01

    On-chip clock networks are remarkable in their impact on the performance and power of synchronous circuits, in their susceptibility to adverse effects of semiconductor technology scaling, as well as in their strong potential for improvement through better CAD algorithms and tools. Existing literature is rich in ideas and techniques but performs large-scale optimization using analytical models that lost accuracy at recent technology nodes and have rarely been validated by realistic SPICE simul...

  15. Atomic clocks comparison by means of television chain

    International Nuclear Information System (INIS)

    The various methods and techniques of time and frequency dissemination are presented. One of them, the Line 10 Method, was used to compare two atomic clocks, localized in different places is a distance of more or less four-hundred kilometers. The results are compared with parallel results obtained with another method, physical transport, giving the necessary experimental basis of the applicability of the Line 10 Method in Brazil

  16. Research of a long distance clock distribution system

    International Nuclear Information System (INIS)

    Ultrahigh-energy neutrinos with energies in excess of 100 PeV from the GZK effect will be studied using a new detector at the South Pole called the Askaryan Radio Array (ARA). The radiofrequency emission which occurs when these particles interact in the glacial ice is detected by an array of antennas spread out over an enormous area, over 100 km2 and embedded in the ice at depths of 200 m to increase sensitivity. Signals from the antennas are digitized by specialized electronics and must be time synchronized with accuracies of order 50 ps or less for event reconstruction to function properly. A system has been proposed which digitizes the impulse waveforms in situ in the ice and sends the data to the surface using high-speed serial links. This requires distribution of a low-jitter clock to each hole but has substantial advantages in cost and power which drive our development effort to realize this technology. Last year we implemented a first version of a long distance clock synchronization system using electrical signaling over CAT5. This year we have updated our solution to optical fiber using high speed transceiver blocks in Spartan 6 FPGAs. The master clock is embedded into the data stream and distributed to the various holes where a phase-locked derivative is recovered. In this way, we have implemented a 1.25 Gbps data link over a bi-directional communication system fulfilling the requirements of the project. This note describes our efforts on the latter solution: technical details as well as methods of maintaining fixed phase difference between two clocks after power cycle and reset.

  17. Coordination of the maize transcriptome by a conserved circadian clock

    Directory of Open Access Journals (Sweden)

    Harmon Frank G

    2010-06-01

    Full Text Available Abstract Background The plant circadian clock orchestrates 24-hour rhythms in internal physiological processes to coordinate these activities with daily and seasonal changes in the environment. The circadian clock has a profound impact on many aspects of plant growth and development, including biomass accumulation and flowering time. Despite recent advances in understanding the circadian system of the model plant Arabidopsis thaliana, the contribution of the circadian oscillator to important agronomic traits in Zea mays and other cereals remains poorly defined. To address this deficit, this study investigated the transcriptional landscape of the maize circadian system. Results Since transcriptional regulation is a fundamental aspect of circadian systems, genes exhibiting circadian expression were identified in the sequenced maize inbred B73. Of the over 13,000 transcripts examined, approximately 10 percent displayed circadian expression patterns. The majority of cycling genes had peak expression at subjective dawn and dusk, similar to other plant circadian systems. The maize circadian clock organized co-regulation of genes participating in fundamental physiological processes, including photosynthesis, carbohydrate metabolism, cell wall biogenesis, and phytohormone biosynthesis pathways. Conclusions Circadian regulation of the maize genome was widespread and key genes in several major metabolic pathways had circadian expression waveforms. The maize circadian clock coordinated transcription to be coincident with oncoming day or night, which was consistent with the circadian oscillator acting to prepare the plant for these major recurring environmental changes. These findings highlighted the multiple processes in maize plants under circadian regulation and, as a result, provided insight into the important contribution this regulatory system makes to agronomic traits in maize and potentially other C4 plant species.

  18. Estimating metazoan divergence times with a molecular clock

    OpenAIRE

    Peterson, Kevin J.; Lyons, Jessica B.; Nowak, Kristin S.; Takacs, Carter M.; Wargo, Matthew J.; McPeek, Mark A.

    2004-01-01

    Accurately dating when the first bilaterally symmetrical animals arose is crucial to our understanding of early animal evolution. The earliest unequivocally bilaterian fossils are ≈555 million years old. In contrast, molecular-clock analyses calibrated by using the fossil record of vertebrates estimate that vertebrates split from dipterans (Drosophila) ≈900 million years ago (Ma). Nonetheless, comparative genomic analyses suggest that a significant rate difference exists between vertebrates a...

  19. Fine tuning GPS clock estimation in the MCS

    Science.gov (United States)

    Hutsell, Steven T.

    1995-01-01

    With the completion of a 24 operational satellite constellation, GPS is fast approaching the critical milestone, Full Operational Capability (FOC). Although GPS is well capable of providing the timing accuracy and stability figures required by system specifications, the GPS community will continue to strive for further improvements in performance. The GPS Master Control Station (MCS) recently demonstrated that timing improvements are always composite Clock, and hence, Kalman Filter state estimation, providing a small improvement to user accuracy.

  20. Photoperiodic entrainment of the circadian clock in the mice SCN

    Czech Academy of Sciences Publication Activity Database

    Sosniyenko, Serhiy; Matějů, Kristýna; Sládek, Martin; Illnerová, Helena; Sumová, Alena

    Praha : FgÚ AV ČR, 2008. ---. [PhD Student Workshop of Institute of Physiology. 02.06.2008-04.06.2008, Seč] Grant ostatní: EUCLOCK(XE) 018741 Institutional research plan: CEZ:AV0Z50110509 Source of funding: R - rámcový projekt EK Keywords : spo2 * photoperiod * mice * circadian clock Subject RIV: FH - Neurology

  1. Clock synchronization design and evaluation for trigger-less data acquisition system

    International Nuclear Information System (INIS)

    For modern particle physics experiments, trigger-less data acquisition (DAQ) system has been put into practice because of the need of reaction multiplicity and trigger flexibility. In such new DAQ systems, global synchronized clock plays an important role because it affects the granularity of time slice and precision of reference clock. In this paper, a novel synchronized clock distribution method is proposed. With the help of modulation technique, master clock module distributes system clock to each slave module. To synchronize slave clocks, the propagation delay is adjusted and the clock phase is aligned by an FPGA chip automatically. Furthermore, an ADC- based method is proposed to evaluate the performance of multi-module clock synchronization simultaneously. The experiments of a prototype system show that slave clocks can be synchronized less than 100 ps over 150 m range. The proposed method is simple and flexible, and it can be used in trigger-less DAQ system and other applications of clock distribution preciously. (authors)

  2. Newly Described Components and Regulatory Mechanisms of Circadian Clock Function in Arabidopsis thaliana

    Institute of Scientific and Technical Information of China (English)

    Manuel Adrián Troncoso-Ponce; Paloma Mas

    2012-01-01

    The circadian clock temporally coordinates plant growth and metabolism in close synchronization with the diurnal and seasonal environmental changes.Research over the last decade has identified a number of clock components and a variety of regulatory mechanisms responsible for the rhythmic oscillations in metabolic and physiological activities.At the core of the clock,transcriptional/translational feedback loops modulate the expression of a significant proportion of the genome.In this article,we briefly describe some of the very recent advances that have improved our understanding of clock organization and function in Arabidopsis thaliana.The new studies illustrate the role of clock protein complex formation on circadian gating of plant growth and identify alternative splicing as a new regulatory mechanism for clock function.Examination of key clock properties such as temperature compensation has also opened new avenues for functional research within the plant clockwork.The emerging connections between the circadian clock and metabolism,hormone signaling and response to biotic and abiotic stress also add new layers of complexity to the clock network and underscore the significance of the circadian clock regulating the daily life of plants.

  3. Compact atomic clock prototype based on coherent population trapping

    Directory of Open Access Journals (Sweden)

    Danet Jean-Marie

    2014-01-01

    Full Text Available Toward the next generations of compact atomic clocks, clocks based on coherent population trapping (CPT offer a very interesting alternative. Thanks to CPT, a quantum interfering process, this technology has made a decisive step in the miniaturization direction. Fractional frequency stability of 1.5x10-10 at 1 s has been demonstrated in commercial devices of a few cm3. The laboratory prototype presented here intends to explore what could be the ultimate stability of a CPT based device. To do so, an original double-Λ optical scheme and a pulsed interrogation have been implemented in order to get a good compromise between contrast and linewidth. A study of two main sources of noise, the relative intensity and the local oscillator (LO noise, has been performed. By designing simple solutions, it led to a new fractional frequency limitation lower than 4x10-13 at 1 s integration. Such a performance proves that such a technology could rival with classical ones as double resonance clocks.

  4. Clock rate comparison in a uniform gravitational field

    CERN Document Server

    Alberici, M

    2004-01-01

    A partially alternative derivation of the expression for the time dilation effect in a uniform static gravitational field is obtained by means of a thought experiment in which rates of clocks at rest at different heights are compared using as reference a clock bound to a free falling reference system (FFRS). Derivations along these lines have already been proposed, but generally introducing some shortcut in order to make the presentation elementary. The treatment is here exact: the clocks whose rates one wishes to compare are let to describe their world lines (Rindler's hyperbolae) with respect to the FFRS, and the result is obtained by comparing their lengths in space-time. The exercise may nonetheless prove pedagogically instructive insofar as it shows that the exact result of General Relativity (GR) can be obtained in terms of physical and geometrical reasoning without having recourse to the general formalism. It also compels to deal with a few subtle points inherent in the very foundations of GR.

  5. Colour as a signal for entraining the mammalian circadian clock.

    Directory of Open Access Journals (Sweden)

    Lauren Walmsley

    2015-04-01

    Full Text Available Twilight is characterised by changes in both quantity ("irradiance" and quality ("colour" of light. Animals use the variation in irradiance to adjust their internal circadian clocks, aligning their behaviour and physiology with the solar cycle. However, it is currently unknown whether changes in colour also contribute to this entrainment process. Using environmental measurements, we show here that mammalian blue-yellow colour discrimination provides a more reliable method of tracking twilight progression than simply measuring irradiance. We next use electrophysiological recordings to demonstrate that neurons in the mouse suprachiasmatic circadian clock display the cone-dependent spectral opponency required to make use of this information. Thus, our data show that some clock neurons are highly sensitive to changes in spectral composition occurring over twilight and that this input dictates their response to changes in irradiance. Finally, using mice housed under photoperiods with simulated dawn/dusk transitions, we confirm that spectral changes occurring during twilight are required for appropriate circadian alignment under natural conditions. Together, these data reveal a new sensory mechanism for telling time of day that would be available to any mammalian species capable of chromatic vision.

  6. Suppression of collisional shifts in a strongly interacting lattice clock

    CERN Document Server

    Swallows, Matthew D; Lin, Yige; Blatt, Sebastian; Martin, Michael J; Rey, Ana Maria; Ye, Jun

    2010-01-01

    Atomic clocks based on neutral atoms confined in optical lattices provide a unique opportunity for precise studies of quantum many-body systems. The 87Sr optical lattice clock at JILA has reached an overall fractional frequency uncertainty of 1x10^-16 [1, 2]. This uncertainty is dominated by two contributions: atomic collisions and frequency shifts due to room-temperature blackbody radiation. The density-dependent frequency shift arises from collisions between fermionic atoms that are subject to slightly inhomogeneous optical excitation [3, 4]. Several theories of the underlying frequency shift mechanism have been proposed [5-7]. A three-dimensional optical lattice clock, where each lattice site contains at most one atom, has been reported [8], and its collisional shift has been characterized with an uncertainty of 7x10^-16. Here we present a different and seemingly paradoxical solution to the problem: by strongly confining atoms in an array of quasi-one-dimensional potentials formed by a two-dimensional opti...

  7. A new clocking method for a charge coupled device

    International Nuclear Information System (INIS)

    We propose and demonstrate a new clocking method for a charge-coupled device (CCD). When a CCD is used for a photon counting detector of X-rays, its weak point is a limitation of its counting rate, because high counting rate makes non-negligible pile-up of photons. In astronomical usage, this pile-up is especially severe for an observation of a bright point-like object. One typical idea to reduce the pile-up is a parallel sum (P-sum) mode. This mode completely loses one-dimensional information. Our new clocking method, panning mode, provides complementary properties between the normal mode and the P-sum mode. We performed a simple simulation in order to investigate a pile-up probability and compared the simulated result and actual obtained event rates. Using this simulation and the experimental results, we compared the pile-up tolerance of various clocking modes including our new method and also compared their other characteristics

  8. Causes and consequences of hyperexcitation in central clock neurons.

    Directory of Open Access Journals (Sweden)

    Casey O Diekman

    Full Text Available Hyperexcited states, including depolarization block and depolarized low amplitude membrane oscillations (DLAMOs, have been observed in neurons of the suprachiasmatic nuclei (SCN, the site of the central mammalian circadian (~24-hour clock. The causes and consequences of this hyperexcitation have not yet been determined. Here, we explore how individual ionic currents contribute to these hyperexcited states, and how hyperexcitation can then influence molecular circadian timekeeping within SCN neurons. We developed a mathematical model of the electrical activity of SCN neurons, and experimentally verified its prediction that DLAMOs depend on post-synaptic L-type calcium current. The model predicts that hyperexcited states cause high intracellular calcium concentrations, which could trigger transcription of clock genes. The model also predicts that circadian control of certain ionic currents can induce hyperexcited states. Putting it all together into an integrative model, we show how membrane potential and calcium concentration provide a fast feedback that can enhance rhythmicity of the intracellular circadian clock. This work puts forward a novel role for electrical activity in circadian timekeeping, and suggests that hyperexcited states provide a general mechanism for linking membrane electrical dynamics to transcription activation in the nucleus.

  9. Probing many-body interactions in an optical lattice clock

    International Nuclear Information System (INIS)

    We present a unifying theoretical framework that describes recently observed many-body effects during the interrogation of an optical lattice clock operated with thousands of fermionic alkaline earth atoms. The framework is based on a many-body master equation that accounts for the interplay between elastic and inelastic p-wave and s-wave interactions, finite temperature effects and excitation inhomogeneity during the quantum dynamics of the interrogated atoms. Solutions of the master equation in different parameter regimes are presented and compared. It is shown that a general solution can be obtained by using the so called Truncated Wigner Approximation which is applied in our case in the context of an open quantum system. We use the developed framework to model the density shift and decay of the fringes observed during Ramsey spectroscopy in the JILA 87Sr and NIST 171Yb optical lattice clocks. The developed framework opens a suitable path for dealing with a variety of strongly-correlated and driven open-quantum spin systems. -- Highlights: •Derived a theoretical framework that describes many-body effects in a lattice clock. •Validated the analysis with recent experimental measurements. •Demonstrated the importance of beyond mean field corrections in the dynamics

  10. Direct detection of the 229Th nuclear clock transition

    Science.gov (United States)

    von der Wense, Lars; Seiferle, Benedict; Laatiaoui, Mustapha; Neumayr, Jürgen B.; Maier, Hans-Jörg; Wirth, Hans-Friedrich; Mokry, Christoph; Runke, Jörg; Eberhardt, Klaus; Düllmann, Christoph E.; Trautmann, Norbert G.; Thirolf, Peter G.

    2016-05-01

    Today’s most precise time and frequency measurements are performed with optical atomic clocks. However, it has been proposed that they could potentially be outperformed by a nuclear clock, which employs a nuclear transition instead of an atomic shell transition. There is only one known nuclear state that could serve as a nuclear clock using currently available technology, namely, the isomeric first excited state of 229Th (denoted 229mTh). Here we report the direct detection of this nuclear state, which is further confirmation of the existence of the isomer and lays the foundation for precise studies of its decay parameters. On the basis of this direct detection, the isomeric energy is constrained to between 6.3 and 18.3 electronvolts, and the half-life is found to be longer than 60 seconds for 229mTh2+. More precise determinations appear to be within reach, and would pave the way to the development of a nuclear frequency standard.

  11. Temporal Regulation of Cytokines by the Circadian Clock

    Directory of Open Access Journals (Sweden)

    Atsuhito Nakao

    2014-01-01

    Full Text Available Several parameters of the immune system exhibit oscillations with a period of approximately 24 hours that refers to “circadian rhythms.” Such daily variations in host immune system status might evolve to maximize immune reactions at times when encounters with pathogens are most likely to occur. However, the mechanisms behind circadian immunity have not been fully understood. Recent studies reveal that the internal time keeping system “circadian clock” plays a key role in driving the daily rhythms evident in the immune system. Importantly, several studies unveil molecular mechanisms of how certain clock proteins (e.g., BMAL1 and CLOCK temporally regulate expression of cytokines. Since cytokines are crucial mediators for shaping immune responses, this review mainly summarizes the new knowledge that highlights an emerging role of the circadian clock as a novel regulator of cytokines. A greater understanding of circadian regulation of cytokines will be important to exploit new strategies to protect host against infection by efficient cytokine induction or to treat autoimmunity and allergy by ameliorating excessive activity of cytokines.

  12. Synchronization of Active Atomic Clocks via Quantum and Classical Channels

    CERN Document Server

    Roth, Alexander

    2016-01-01

    Superradiant lasers based on atomic ensembles exhibiting ultra-narrow optical transitions can emit light of unprecedented spectral purity and may serve as active atomic clocks. We consider two frequency-detuned active atomic clocks, which are coupled in a cascaded setup, i.e. as master & slave lasers, and study the synchronization of the slave to the master clock. In a setup where both atomic ensembles are coupled to a common cavity mode such synchronization phenomena have been predicted by Xu et al. [Phys. Rev. Lett. 113, 154101 (2014)] and experimentally observed by Weiner et al. [arXiv:1503.06464 (2015)]. Here we demonstrate that synchronization still occurs in cascaded setups but exhibits distinctly different phase diagrams. We study the characteristics of synchronization in comparison to the case of coupling through a common cavity. We also consider synchronization through a classical channel where light of the master laser is measured phase sensitively and the slave laser is injection locked by feed...

  13. Individual Optical Addressing of Atomic Clock Qubits With Stark Shifts

    Science.gov (United States)

    Lee, Aaron; Smith, Jacob; Richerme, Phillip; Neyenhuis, Brian; Hess, Paul; Zhang, Jiehang; Monroe, Chris

    2016-05-01

    In recent years, trapped ions have proven to be a versatile quantum information platform, enabled by their long lifetimes and high gate fidelities. Some of the most promising trapped ion systems take advantage of groundstate hyperfine ``clock'' qubits, which are insensitive to background fields to first order. This same insensitivity also makes σz manipulations of the qubit impractical, eliminating whole classes of operations. We prove there exists a fourth-order light shift, or four-photon Stark shift, of the clock states derived from two coherent laser beams whose beatnote is close to the qubit splitting. Using a mode-locked source generates a large light shift with only modest laser powers, making it a practical σz operation on a clock qubit. We experimentally verify and measure the four-photon Stark shift and demonstrate its use to coherently individually address qubits in a chain of 10 Yb 171 ions with low crosstalk. We use this individual addressing to prepare arbitrary product states with high fidelity and also to apply independent σz terms transverse to an Ising Hamiltonian. This work is supported by the ARO Atomic Physics Program, the AFOSR MURI on Quantum Measurement and Verification, and the NSF Physics Frontier Center at JQI.

  14. Using Clocks and Atomic Interferometry for Gravity Field Observations

    Science.gov (United States)

    Müller, Jürgen

    2016-07-01

    New technology developed in the frame of fundamental physics may lead to enhanced capabilities for geodetic applications such as refined observations of the Earth's gravity field. Here, we will present new sensor measurement concepts that apply atomic interferometry for gravimetry and clock measurements for observing potential values. In the first case, gravity anomalies can be determined by observing free-falling atoms (quantum gravimetry). In the second case, highly precise optical clocks can be used to measure differences of the gravity potential over long distances (relativistic geodesy). Principally, also inter-satellite ranging between test masses in space with nanometer accuracy belongs to these novel developments. We will show, how the new measurement concepts are connected to classical geodetic concepts, e.g. geopotential numbers and clock readings. We will illustrate the application of these new methods and their benefit for geodesy, where local and global mass variations can be observed with unforeseen accuracy and resolution, mass variations that reflect processes in the Earth system. We will present a few examples where geodesy will potentially benefit from these developments. Thus, the novel technologies might be applied for defining and realizing height systems in a new way, but also for fast local gravimetric surveys and exploration.

  15. An In Vitro ES Cell-Based Clock Recapitulation Assay Model Identifies CK2α as an Endogenous Clock Regulator

    OpenAIRE

    Umemura, Yasuhiro; Yoshida, Junko; Wada, Masashi; Tsuchiya, Yoshiki; Minami, Yoichi; Watanabe, Hitomi; Kondoh, Gen; Takeda, Junji; Inokawa, Hitoshi; Horie, Kyoji; Yagita, Kazuhiro

    2013-01-01

    We previously reported emergence and disappearance of circadian molecular oscillations during differentiation of mouse embryonic stem (ES) cells and reprogramming of differentiated cells, respectively. Here we present a robust and stringent in vitro circadian clock formation assay that recapitulates in vivo circadian phenotypes. This assay system first confirmed that a mutant ES cell line lacking Casein Kinase I delta (CKIδ) induced ∼3 hours longer period-length of circadian rhythm than the w...

  16. Immunoreactivities to three circadian clock proteins in two ground crickets suggest interspecific diversity of the circadian clock structure

    Czech Academy of Sciences Publication Activity Database

    Shao, Q. M.; Sehadová, H.; Ichihara, N.; Sehnal, František; Takeda, M.

    2006-01-01

    Roč. 21, č. 2 (2006), s. 118-131. ISSN 0748-7304 Grant ostatní: Japan Society for the Promotion of Science(JP) JSPS 99L01205; Japan Society for the Promotion of Science(JP) ID No. P 04197 Institutional research plan: CEZ:AV0Z50070508 Keywords : circadian rhythm * photoperiodic clock * cryptochrome (CRY) Subject RIV: ED - Physiology Impact factor: 4.633, year: 2006

  17. Regulation of clock-controlled genes in mammals.

    Directory of Open Access Journals (Sweden)

    Katarzyna Bozek

    Full Text Available The complexity of tissue- and day time-specific regulation of thousands of clock-controlled genes (CCGs suggests that many regulatory mechanisms contribute to the transcriptional output of the circadian clock. We aim to predict these mechanisms using a large scale promoter analysis of CCGs.Our study is based on a meta-analysis of DNA-array data from rodent tissues. We searched in the promoter regions of 2065 CCGs for highly overrepresented transcription factor binding sites. In order to compensate the relatively high GC-content of CCG promoters, a novel background model to avoid a bias towards GC-rich motifs was employed. We found that many of the transcription factors with overrepresented binding sites in CCG promoters exhibit themselves circadian rhythms. Among the predicted factors are known regulators such as CLOCKratioBMAL1, DBP, HLF, E4BP4, CREB, RORalpha and the recently described regulators HSF1, STAT3, SP1 and HNF-4alpha. As additional promising candidates of circadian transcriptional regulators PAX-4, C/EBP, EVI-1, IRF, E2F, AP-1, HIF-1 and NF-Y were identified. Moreover, GC-rich motifs (SP1, EGR, ZF5, AP-2, WT1, NRF-1 and AT-rich motifs (MEF-2, HMGIY, HNF-1, OCT-1 are significantly overrepresented in promoter regions of CCGs. Putative tissue-specific binding sites such as HNF-3 for liver, NKX2.5 for heart or Myogenin for skeletal muscle were found. The regulation of the erythropoietin (Epo gene was analysed, which exhibits many binding sites for circadian regulators. We provide experimental evidence for its circadian regulated expression in the adult murine kidney. Basing on a comprehensive literature search we integrate our predictions into a regulatory network of core clock and clock-controlled genes. Our large scale analysis of the CCG promoters reveals the complexity and extensiveness of the circadian regulation in mammals. Results of this study point to connections of the circadian clock to other functional systems including

  18. An in vitro ES cell-based clock recapitulation assay model identifies CK2α as an endogenous clock regulator.

    Science.gov (United States)

    Umemura, Yasuhiro; Yoshida, Junko; Wada, Masashi; Tsuchiya, Yoshiki; Minami, Yoichi; Watanabe, Hitomi; Kondoh, Gen; Takeda, Junji; Inokawa, Hitoshi; Horie, Kyoji; Yagita, Kazuhiro

    2013-01-01

    We previously reported emergence and disappearance of circadian molecular oscillations during differentiation of mouse embryonic stem (ES) cells and reprogramming of differentiated cells, respectively. Here we present a robust and stringent in vitro circadian clock formation assay that recapitulates in vivo circadian phenotypes. This assay system first confirmed that a mutant ES cell line lacking Casein Kinase I delta (CKIδ) induced ∼3 hours longer period-length of circadian rhythm than the wild type, which was compatible with recently reported results using CKIδ null mice. In addition, this assay system also revealed that a Casein Kinase 2 alpha subunit (CK2α) homozygous mutant ES cell line developed significantly longer (about 2.5 hours) periods of circadian clock oscillations after in vitro or in vivo differentiation. Moreover, revertant ES cell lines in which mutagenic vector sequences were deleted showed nearly wild type periods after differentiation, indicating that the abnormal circadian period of the mutant ES cell line originated from the mutation in the CK2α gene. Since CK2α deficient mice are embryonic lethal, this in vitro assay system represents the genetic evidence showing an essential role of CK2α in the mammalian circadian clock. This assay was successfully applied for the phenotype analysis of homozygous mutant ES cells, demonstrating that an ES cell-based in vitro assay is available for circadian genetic screening. PMID:23840637

  19. Variation in candidate genes CLOCK and ADCYAP1 does not consistently predict differences in migratory behavior in the songbird genus Junco [v1; ref status: indexed, http://f1000r.es/11p

    Directory of Open Access Journals (Sweden)

    Mark P Peterson

    2013-04-01

    Full Text Available Recent studies exploring the molecular genetic basis for migratory variation in animals have identified polymorphisms in two genes (CLOCK and ADCYAP1 that are linked to circadian rhythms and correlate with migratory propensity and phenology among individuals and populations. Results from these initial studies are mixed, however, and additional data are needed to assess the generality and diversity of the molecular mechanisms that regulate the biology of migration. We sequenced CLOCK and ADCYAP1 in 15 populations across the two species of the avian genus Junco, a North American lineage in which multiple recently diverged subspecies and populations range from sedentary to long-distance migrants. We found no consistent associations between allele length and migratory status across the genus for either CLOCK or ADCYAP1. However, within two subspecies groups, populations that migrate longer distances have longer CLOCK alleles on average. Additionally, there was a positive relationship between ADCYAP1 allele length and migratory restlessness (zugunruhe among individuals within one of two captive populations studied—a result similar to those reported previously within captive blackcaps (Sylvia atricapilla. We conclude that, while both ADCYAP1 and CLOCK may correlate with migratory propensity within or among certain populations or species, previously identified relationships between migratory behavior and sequence variants cannot be easily generalized across taxa.

  20. Design and Construction of an Atomic Clock on an Atom Chip

    International Nuclear Information System (INIS)

    We describe the design and construction of an atomic clock on an atom chip, intended as a secondary standard, with a stability in the range of few 10-13 at 1 s. This clock is based on a two-photon transition between the hyperfine states |F = 1; mF = -1> and |2; 1> of the electronic ground state of the 87Rb atom. This transition is interrogated using a Ramsey scheme, operating on either a cloud of thermal atoms or a Bose-Einstein condensate. In contrast to atomic fountain clocks, this clock is magnetically trapped on an atom chip. We describe a theoretical model of the clock stability and the design and construction of a dedicated apparatus. It is able to control the magnetic field at the relative 10-5 level and features a hybrid atom chip, containing DC conductors as well as a microwave transmission line for the clock interrogation. (author)

  1. Ultra-stable optical clock with two cold-atom ensembles

    CERN Document Server

    Schioppo, M; McGrew, W F; Hinkley, N; Fasano, R J; Beloy, K; Yoon, T H; Milani, G; Nicolodi, D; Sherman, J A; Phillips, N B; Oates, C W; Ludlow, A D

    2016-01-01

    Atomic clocks based on optical transitions are the most stable, and therefore precise, timekeepers available. These clocks operate by alternating intervals of atomic interrogation with dead time required for quantum state preparation and readout. This non-continuous interrogation of the atom system results in the Dick effect, an aliasing of frequency noise of the laser interrogating the atomic transition. Despite recent advances in optical clock stability achieved by improving laser coherence, the Dick effect has continually limited optical clock performance. Here we implement a robust solution to overcome this limitation: a zero-dead-time optical clock based on the interleaved interrogation of two cold-atom ensembles. This clock exhibits vanishingly small Dick noise, thereby achieving an unprecedented fractional frequency instability of $6 \\times 10^{-17} / \\sqrt{\\tau}$ for an averaging time $\\tau$ in seconds. We also consider alternate dual-atom-ensemble schemes to extend laser coherence and reduce the stan...

  2. Towards a Re-definition of the Second Based on Optical Atomic Clocks

    CERN Document Server

    Riehle, Fritz

    2015-01-01

    The rapid increase in accuracy and stability of optical atomic clocks compared to the caesium atomic clock as primary standard of time and frequency asks for a future re-definition of the second in the International System of Units (SI). The status of the optical clocks based on either single ions in radio-frequency traps or on neutral atoms stored in an optical lattice is described with special emphasis of the current work at the Physikalisch-Technische Bundesanstalt (PTB). Besides the development and operation of different optical clocks with estimated fractional uncertainties in the 10^-18 range, the supporting work on ultra-stable lasers as core elements and the means to compare remote optical clocks via transportable standards, optical fibers, or transportable clocks is reported. Finally, the conditions, methods and next steps are discussed that are the prerequisites for a future re-definition of the second.

  3. Biological Threats

    Science.gov (United States)

    ... Workplace Plans School Emergency Plans Main Content Biological Threats Biological agents are organisms or toxins that can ... for Disease Control and Prevention . Before a Biological Threat Unlike an explosion, a biological attack may or ...

  4. Design and implementation of a clock recovery circuit for fast Ethernet applications

    Institute of Scientific and Technical Information of China (English)

    朱全庆; 邹雪城; 沈绪榜

    2004-01-01

    A circuit architechure to realize clock recovery for fast Ethernet applications is presented, whick includies system architecture, modified Mueller Muller algorithm for 100BASE-TX, phase detector for 100BASE-TX and multiple output charge pump PLL. The clock recovery circuit is verified by TSMC 0.35um 1P5M CMOS process. The results show that this clock recovery circuit exactly extracts the timing information. It has advantages over others for simple and easy implementation.

  5. Balance equations can buffer noisy and sustained environmental perturbations of circadian clocks

    OpenAIRE

    Domijan, Mirela; Rand, David A.

    2010-01-01

    We present a new approach to understanding how regulatory networks such as circadian clocks might evolve robustness to environmental fluctuations. The approach is in terms of new balance equations that we derive. We use it to describe how an entrained clock can buffer the effects of daily fluctuations in light and temperature levels. We also use it to study a different approach to temperature compensation where instead of considering a free-running clock, we study temperature buffering of the...

  6. A New Method to Minimize the Clock Skew to Enhance Performance of Digital System

    OpenAIRE

    N. Suresh Kumar,; J. Anitha; M.S.S. Praveen,; N. Asok Kumar,; R. Ajay Suresh Babu

    2010-01-01

    A Pipe line technology is used in any digital system to perform multiple tasks simultaneously and to reduce the data losses in data transactions. But the conventional pipeline system is facing problems due to improper synchronization of clock pulses. This is a universal problem in all the digital systems mostly called jitter or skew. Inmost of the digital systems the propagation of information mainly controlled on the basis of clock pulses. In most of the digital systems the clock skew decrea...

  7. Entrainment of the circadian clock in humans: mechanism and implications for sleep disorders.

    OpenAIRE

    David Metcalfe

    2007-01-01

    Humans exhibit behaviour and physiology controlled by a circadian clock. The circadian period is genetically determined and administered by a series of interlocked autoregulatory feedback loops largely in the suprachiasmatic nuclei of the hypothalamus. The phase of the clock is, however, synchronised by a number of external environmental cues such as light. A failure or change in any one of the requisite clock components may result in the onset of a long-term sleep disorder. This review discu...

  8. Influence Factors of an All-Optical Recovered Clock from Two-Section DFB Lasers

    International Nuclear Information System (INIS)

    All-optical clock recovery by a two-section DFB laser with different injection wavelengths is demonstrated experimentally at 38.5 GHz. An optical clock with a root-mean-square timing jitter of 250 fs and an extinction ratio of 12.1 dB is obtained with 1551 nm injection. The timing jitter of the recovered clock is further investigated for various intensity ratios of the two DFB emission modes. (fundamental areas of phenomenology(including applications))

  9. System and method for adaptively deskewing parallel data signals relative to a clock

    Science.gov (United States)

    Jenkins, Philip Nord; Cornett, Frank N.

    2011-10-04

    A system and method of reducing skew between a plurality of signals transmitted with a transmit clock is described. Skew is detected between the received transmit clock and each of received data signals. Delay is added to the clock or to one or more of the plurality of data signals to compensate for the detected skew. The delay added to each of the plurality of delayed signals is updated to adapt to changes in detected skew.

  10. The clock and control system for the ATLAS Liquid Argon Calorimeter Phase-I upgrade

    International Nuclear Information System (INIS)

    A Liquid-argon Trigger Digitizer Board (LTDB) is being developed to upgrade the ATLAS Liquid Argon Calorimeter Phase-I trigger electronics. The LTDB located at the front end needs to obtain the clock signals and be configured and monitored remotely from the back end. A clock and control system is being developed for the LTDB and the major functions of the system have been evaluated. The design and evaluation of the clock and control system are presented in this paper

  11. The expression of melanopsin and clock genes in Xenopus laevis melanophores and their modulation by melatonin

    International Nuclear Information System (INIS)

    Vertebrates have a central clock and also several peripheral clocks. Light responses might result from the integration of light signals by these clocks. The dermal melanophores of Xenopus laevis have a photoreceptor molecule denominated melanopsin (OPN4x). The mechanisms of the circadian clock involve positive and negative feedback. We hypothesize that these dermal melanophores also present peripheral clock characteristics. Using quantitative PCR, we analyzed the pattern of temporal expression of Opn4x and the clock genes Per1, Per2, Bmal1, and Clock in these cells subjected to a 14-h light:10-h dark (14L:10D) regime or constant darkness (DD). Also, in view of the physiological role of melatonin in the dermal melanophores of X. laevis, we determined whether melatonin modulates the expression of these clock genes. These genes show a time-dependent expression pattern when these cells are exposed to 14L:10D, which differs from the pattern observed under DD. Cells kept in DD for 5 days exhibited overall increased mRNA expression for Opn4x and Clock, and a lower expression for Per1, Per2, and Bmal1. When the cells were kept in DD for 5 days and treated with melatonin for 1 h, 24 h before extraction, the mRNA levels tended to decrease for Opn4x and Clock, did not change for Bmal1, and increased for Per1 and Per2 at different Zeitgeber times (ZT). Although these data are limited to one-day data collection, and therefore preliminary, we suggest that the dermal melanophores of X. laevis might have some characteristics of a peripheral clock, and that melatonin modulates, to a certain extent, melanopsin and clock gene expression

  12. Interfacing Of PIC 18F252 Microcontroller with Real Time Clock via I2C Protocol

    Directory of Open Access Journals (Sweden)

    Arnab G. Samanta

    2014-09-01

    Full Text Available This paper describes a microcontroller based digital clock which can be used in real time systems. The system is constructed using PIC18F252 (microcontroller, DS1307 (real time clock IC and its software program is written with C programming language. A 3v battery backup is provided to real time clock IC. Communication between PIC microcontroller and DS1307 takes place through I²C Bus protocol.

  13. Frequency ratios of optical lattice clocks at the 17th decimal place

    Science.gov (United States)

    Katori, Hidetoshi

    2016-05-01

    Optical lattice clocks benefit from a low quantum-projection noise by simultaneously interrogating a large number of atoms, which are trapped in an optical lattice tuned to the ``magic wavelength'' to largely cancel out light shift perturbation in the clock transition. About a thousand atoms enable the clocks to achieve 10-18 instability in a few hours of operation, allowing intensive investigation and control of systematic uncertainties. As optical lattice clocks have reached inaccuracies approaching 10-18, it is now the uncertainty of the SI second (~ 10-16) itself that restricts the measurement of the absolute frequencies of such optical clocks. Direct comparisons of optical clocks are, therefore, the only way to investigate and utilize their superb performance beyond the SI second. In this presentation, we report on frequency comparisons of optical lattice clocks with neutral strontium (87 Sr), ytterbium (171 Yb) and mercury (199 Hg) atoms. By referencing cryogenic Sr clocks, we determine frequency ratios, νYb/νSr and νHg/νSr, of a cryogenic Yb clock and a Hg clock with uncertainty at the mid 10-17 level. Such ratios provide an access to search for temporal variation of the fundamental constants. We also present remote comparisons between cryogenic Sr clocks located at RIKEN and the University of Tokyo over a 30-km-long phase-stabilized fiber link. The gravitational red shift Δν /ν0 ~ 1.1× 10-18 Δh cm-1 reads out the height difference of Δh ~ 15 m between the two clocks with uncertainty of 5 cm, which demonstrates a step towards relativistic geodesy. ERATO, JST.

  14. The expression of melanopsin and clock genes in Xenopus laevis melanophores and their modulation by melatonin

    Energy Technology Data Exchange (ETDEWEB)

    Bluhm, A.P.C.; Obeid, N.N.; Castrucci, A.M.L.; Visconti, M.A. [Departamento de Fisiologia, Instituto de Biociências, Universidade de São Paulo, São Paulo, SP (Brazil)

    2012-05-25

    Vertebrates have a central clock and also several peripheral clocks. Light responses might result from the integration of light signals by these clocks. The dermal melanophores of Xenopus laevis have a photoreceptor molecule denominated melanopsin (OPN4x). The mechanisms of the circadian clock involve positive and negative feedback. We hypothesize that these dermal melanophores also present peripheral clock characteristics. Using quantitative PCR, we analyzed the pattern of temporal expression of Opn4x and the clock genes Per1, Per2, Bmal1, and Clock in these cells subjected to a 14-h light:10-h dark (14L:10D) regime or constant darkness (DD). Also, in view of the physiological role of melatonin in the dermal melanophores of X. laevis, we determined whether melatonin modulates the expression of these clock genes. These genes show a time-dependent expression pattern when these cells are exposed to 14L:10D, which differs from the pattern observed under DD. Cells kept in DD for 5 days exhibited overall increased mRNA expression for Opn4x and Clock, and a lower expression for Per1, Per2, and Bmal1. When the cells were kept in DD for 5 days and treated with melatonin for 1 h, 24 h before extraction, the mRNA levels tended to decrease for Opn4x and Clock, did not change for Bmal1, and increased for Per1 and Per2 at different Zeitgeber times (ZT). Although these data are limited to one-day data collection, and therefore preliminary, we suggest that the dermal melanophores of X. laevis might have some characteristics of a peripheral clock, and that melatonin modulates, to a certain extent, melanopsin and clock gene expression.

  15. Strontium optical lattice clocks for practical realization of the metre and secondary representation of the second

    CERN Document Server

    Bober, M; Cygan, A; Lisak, D; Masłowski, P; Prymaczek, M; Wcisło, P; Ablewski, P; Piwiński, M; Wójtewicz, S; Bielska, K; Bartoszek-Bober, D; Trawiński, R; Zawada, M; Ciuryło, R; Zachorowski, J; Piotrowski, M; Gawlik, W; Ozimek, F; Radzewicz, C

    2015-01-01

    We present a system of two independent strontium optical lattice standards probed with a single shared ultra-narrow laser. The absolute frequency of the clocks can be verified by the use of Er:fiber optical frequency comb with the GPS-disciplined Rb frequency standard. We report hertz-level spectroscopy of the clock line and measurements of frequency stability of the two strontium optical lattice clocks.

  16. The Drosophila circadian clock is a variably coupled network of multiple peptidergic units

    OpenAIRE

    Z. Yao; Shafer, O.T.

    2014-01-01

    Daily rhythms in behavior emerge from networks of neurons that express molecular clocks. Drosophila’s clock neuron network consists of a diversity of cell types, yet is modeled as two hierarchically organized groups, one of which serves as a master pacemaker. Here we establish that the fly’s clock neuron network consists of multiple units of independent neuronal oscillators, each unified by its neuropeptide transmitter and mode of coupling to other units. Our work reveals that the circadian c...

  17. Diurnal regulation of MTP and plasma triglyceride by CLOCK is mediated by SHP

    OpenAIRE

    Pan, Xiaoyue; Zhang, Yuxia; Wang, Li; Hussain, M. Mahmood

    2010-01-01

    We examined the role of clock genes in the diurnal regulation of plasma triglyceride-rich apolipoprotein B-lipoproteins and their biosynthetic chaperone, microsomal triglyceride transfer protein (MTP). Clock mt/mt mice showed sustained hypertriglyceridemia and high MTP expression. CLOCK knockdown activated MTP promoter, and reduced small heterodimer partner (SHP, NROB2). CLOCK up-regulated SHP by binding to its E-box. SHP suppressed MTP expression by binding to the HNF4α/LRH-1 at the MTP prom...

  18. New experiments on the effect of clock shifts on homing in pigeons

    Science.gov (United States)

    Schmidt-Koenig, K.

    1972-01-01

    The effect of clock shifts as an experimental tool for predictably interfering with the homing ability of birds is discussed. Clock shifts introduce specific errors in the birds' sun azimuth compass, resulting in corresponding errors during initial orientation and possibly during orientation enroute. The effects of 6 hour and 12 hour clock shifts resulted in a 90 degree deviation and a 180 degree deviation from the initial orientation, respectively. The method for conducting the clock shift experiments and results obtained from previous experiments are described.

  19. The clock modules in TOF readout system for heavy ion experiments at IMP

    International Nuclear Information System (INIS)

    This paper describes two clock modules in the time-of-flight readout systems, which are applied in the Cold Target Recoil Ion Momentum Spectrometer(COLTRIMS) system and the Cooler Storage Ring (CSRm) at Institute of Modern Physics, Chinese Academy of Sciences.The two clock modules are designed on 3U PXI module and 6U PXI module. With high precision crystal oscillators and clock distribution, these two modules offer clock signal to the TOF readout electronics modules with low jitter less than 11 ps(RMS) and 12 ps(RMS). (authors)

  20. Study of laser-pumped double-resonance clock signals using a microfabricated cell

    International Nuclear Information System (INIS)

    We present our microwave spectroscopic studies on laser-microwave double-resonance (DR) signals obtained from a micro-fabricated Rb vapor cell. This study focuses on the characteristics and systematic shifts of the ground-state 'clock transition' in 87Rb (| Fg = 1,mF = 0) → | Fg = 2, mF = 0)) used in Rb atomic clocks, and represents a first step toward a miniature atomic clock based on the DR scheme. A short-term clock instability below 2 × 1011τ-1/2 is demonstrated, staying below 10-11 up to τ = 104 s.