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Activity Cycle (activity + cycle)
Selected AbstractsThe cofilin activity cycle in lamellipodia and invadopodiaJOURNAL OF CELLULAR BIOCHEMISTRY, Issue 6 2009Matthew Oser Abstract The actin severing protein cofilin is essential for directed cell migration and chemotaxis, in many cell types and is also important for tumor cell invasion during metastasis. Through its severing activity, cofilin increases the number of free barbed ends to initiate actin polymerization for actin-based protrusion in two distinct subcellular compartments in invasive tumor cells: lamellipodia and invadopodia. Cofilin severing activity is tightly regulated and multiple mechanisms are utilized to regulate cofilin activity. In this prospect, we have grouped the primary on/off regulation into two broad categories, both of which are important for inhibiting cofilin from binding to F-actin or G-actin: (1) Blocking cofilin activity by the binding of cofilin to either PI(4,5)P2 at lamellipodia, or cortactin at invadopodia. (2) Blocking cofilin's ability to bind to actin via serine phosphorylation. Although the literature suggests that these cofilin regulatory mechanisms may be cell-type dependent, we propose the existence of a common cofilin activity cycle in which both operate. In this common cycle, the mechanism used to initiate cofilin activity is determined by the starting point in the cycle in a given subcellular compartment. J. Cell. Biochem. 108: 1252,1262, 2009. © 2009 Wiley-Liss, Inc. [source] Robust circadian rhythm in heart rate and its variability: influence of exogenous melatonin and photoperiodJOURNAL OF SLEEP RESEARCH, Issue 2 2007GILLES VANDEWALLE Summary Heart rate (HR) and heart rate variability (HRV) undergo marked fluctuations over the 24-h day. Although controversial, this 24-h rhythm is thought to be driven by the sleep,wake/rest,activity cycle as well as by endogenous circadian rhythmicity. We quantified the endogenous circadian rhythm of HR and HRV and investigated whether this rhythm can be shifted by repeated melatonin administration while exposed to an altered photoperiod. Eight healthy males (age 24.4 ± 4.4 years) participated in a double-blind cross-over design study. In both conditions, volunteers were scheduled to 16 h,8 h rest : wake and dark : light cycles for nine consecutive days preceded and followed by 29-h constant routines (CR) for assessment of endogenous circadian rhythmicity. Melatonin (1.5 mg) or placebo was administered at the beginning of the extended sleep opportunities. For all polysomnographically verified wakefulness periods of the CR, we calculated the high- (HF) and low- (LF) frequency bands of the power spectrum of the R,R interval, the standard deviation of the normal-to-normal (NN) intervals (SDNN) and the square root of the mean-squared difference of successive NN intervals (rMSSD). HR and HRV variables revealed robust endogenous circadian rhythms with fitted maxima, respectively, in the afternoon (16:36 hours) and in the early morning (between 05:00 and 06:59 hours). Melatonin treatment phase-advanced HR, HF, SDNN and rMSSD, and these shifts were significantly greater than after placebo treatment. We conclude that endogenous circadian rhythmicity influences autonomic control of HR and that the timing of these endogenous rhythms can be altered by extended sleep/rest episodes and associated changes in photoperiod as well as by melatonin treatment. [source] Changes in convective properties over the solar cycle: effect on p-mode damping ratesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2001G. Houdek Measurements of both solar irradiance and p-mode oscillation frequencies indicate that the structure of the Sun changes with the solar cycle. Balmforth, Gough & Merryfield investigated the effect of symmetrical thermal disturbances on the solar structure and the resulting pulsation frequency changes. They concluded that thermal perturbations alone cannot account for the variations in both irradiance and p-mode frequencies, and that the presence of a magnetic field affecting acoustical propagation is the most likely explanation of the frequency change, in the manner suggested earlier by Gough & Thompson and by Goldreich et al. Numerical simulations of Boussinesq convection in a magnetic field have shown that at high Rayleigh number the magnetic field can modify the preferred horizontal length scale of the convective flow. Here, we investigate the effect of changing the horizontal length scale of convective eddies on the linewidths of the acoustic resonant mode peaks observed in helioseismic power spectra. The turbulent fluxes in these model computations are obtained from a time-dependent, non-local generalization of the mixing-length formalism. The modelled variations are compared with p-mode linewidth changes revealed by the analysis of helioseismic data collected by the Birmingham Solar-Oscillations Network (BiSON); these low-degree (low- l) observations cover the complete falling phase of solar activity cycle 22. The results are also discussed in the light of observations of solar-cycle variations of the horizontal size of granules and with results from 2D simulations by Steffen of convective granules. [source] The Big Bear Solar Observatory Ca II K-line index for solar cycle 23ASTRONOMISCHE NACHRICHTEN, Issue 7 2010M.F. Naqvi Abstract We present an analysis of 2634 Ca II K-line full-disk filtergrams obtained with the 15-cm aperture photometric full-disk telescope at Big Bear Solar Observatory during the period from 1996 January 1 to 2005 October 24. Using limb darkening corrected and contrast enhanced filtergrams, solar activity indices were derived, which are sensitive to the 11-year solar activity cycle and 27-day rotational period of plages around active regions and the bright chromospheric network. The present work extends an earlier study (solar cycle 22), which was based on video data. The current digital data are of much improved quality with higher spatial resolution and a narrower passband ameliorating photometric accuracy. The time series of chromospheric activity indices cover most of solar cycle 23. One of the most conspicuous features of the Ca II K indices is the secondary maximum in late 2001/early 2002 after an initial decline of chromospheric activity during the first half of 2001. We conclude that a secular trend exists in the Ca II K indices, which has its origin in the bright chromospheric network and brightenings related to decaying active regions. Superposed on this secular trend are the signatures of recurring, long-lived active regions, which are clusters of persistent and continuously emerging magnetic flux. Such features are less visible, when the activity belts on both side of the equator are devoid of the brightenings related to decaying active regions as was the case in October/November 2003 at a time when a superactivity complex including several naked-eye sunspots emerged (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Four-colour photometry of EY Dra: A study of an ultra-fast rotating active dM1-2e starASTRONOMISCHE NACHRICHTEN, Issue 3 2010K. Vida Abstract We present more than 1000-day long photometry of EY Draconis in BV (RI)C passbands. The changes in the light curve are caused by the spottedness of the rotating surface. Modelling of the spotted surface shows that there are two large active regions present on the star on the opposite hemispheres. The evolution of the surface patterns suggests a flip-flop phenomenon. Using Fourier analysis, we detect a rotation period of Prot = 0.45875 d, and an activity cycle with P , 350 d, similar to the 11-year long cycle of the Sun. This cycle with its year-long period is the shortest one ever detected on active stars. Two bright flares are also detected and analysed (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The chromospherically active binary star EI Eridani: II.ASTRONOMISCHE NACHRICHTEN, Issue 4 2009Long-term Doppler imaging Abstract Data from 11 years of continuous spectroscopic observations of the active RS CVn-type binary star EI Eridani , gained at NSO/McMath-Pierce, KPNO/Coudé Feed and during the MUSICOS 98 campaign , were used to obtain 34 Doppler maps in three spectroscopic lines for 32 epochs, 28 of which are independent of each other. Various parameters are extracted from our Doppler maps: average temperature, fractional spottedness, and longitudinal and latitudinal spot-occurrence functions. We find that none of these parameters show a distinct variation nor a correlation with the proposed activity cycle as seen from photometric long-term observations. This suggests that the photometric brightness cycle may not necessarily be due to just a cool spot cycle. The general morphology of the spot pattern remains persistent over the whole period of 11 years. A large cap-like polar spot was recovered from all our images. A high degree of variable activity was noticed near latitudes of ,60,70° where the appendages of the polar spot emerged and dissolved (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Magnetic activity on 12 Cam and 29 Dra from long-term photometryASTRONOMISCHE NACHRICHTEN, Issue 4 2009M. Zboril Abstract We present newly discovered magnetic cycles of two late-type and long-period SB1 systems: 12 Cam and 29 Dra. The long-term photometry study revealed the presence of magnetic multiperiodic cycles on both stars, namely 14.8 and 8.5 yr for 12 Cam and 20.3, 11.1, and 7.6 yr for 29 Dra. Furthermore, the modelling of the V -band light curves revealed the existence of two active longitudes on 12 Cam and probably on 29 Dra as well. Both stars show changes of rotational period. The 12 Cam is the slowest rotating star whose activity cycle has been determined. The activity cycles determined by us allow us to extend to the slower rotation regime and to improve the significance of the empirical relation between rotation period and magnetic cycle length (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Towards using modern data assimilation and weather forecasting methods in solar physicsASTRONOMISCHE NACHRICHTEN, Issue 3-4 2007A. S. BrunArticle first published online: 7 MAR 200 Abstract We discuss how data assimilation and forecasting methods developed in Earth's weather prediction models could be used to improve our capability to anticipate solar dynamical phenomena and assimilate the huge amount of data that new solar satellites, such as SDO or Hinode, will provide in the coming years. We illustrate with some simple examples such as the solar magnetic activity cycle, the eruption of CMEs, the real potential of such methods for solar physics. We believe that we now need to jointly develop solar forecasting models, whose purpose are to assimilate observational data in order to improve our predictability power, with "first principle" solar models, whose purpose is to understand the underpinning physical processes behind the solar dynamics. These two complementary approaches should lead to the development of a solar equivalent of Earth's general circulation model. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Short-period near-contact binary systems at the beginning of the overcontact phaseMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2002Shengbang Qian Abstract A detailed analysis of orbital period changes of seven near-contact binary stars (NCBs) (BL And, V473 Cas, XZ CMi, BV Eri, RU Eri, UU Lyn and GR Tau) with period less than 1 d has been performed and their respective O,C diagrams are formed and discussed. It is found that all systems analysed show secular period decreasing. For V473 Cas, the analysis of the period change was performed based on data collected by Moschner, Frank & Bastian. For XZ CMi, its period shows some complex changes, a possible cyclic oscillation is discovered to superpose on the secular decrease that can be explained either by the presence of a third body or by magnetic activity cycles of the components. Since the third-body assumption is consistent with the photometric solution of Rafert, XZ CMi may be a truly triple system. For BV Eri, the period decrease is only supported by weak evidence. All the seven systems are short-period NCBs with AF-type primary components where both components are filling or nearly filling the critical Roche lobe. As the period decreases, the separation between both components will be reducing and thus these systems will evolve into A-type overcontact binaries. The period decrease may be caused by mass transfer or/and by angular momentum loss via magnetic braking. Combined with the published data on the other systems of the same type, a possible statistical connection between orbital period P and its rate of decrease dP/dt is obtained: dP/dt=,5.3 × 10,7×P+ 1.3 × 10,7 d yr,1. This correlation indicates that the smaller the orbital period P is, the smaller its rate of change dP/dt will be. The correlation found in this paper indicates that there may be a smooth transition from A- and F-type NCBs with period decreases to the A- and F-type overcontact binaries that have period increases, and in that sense one may postulate that the NCBs may be the progenitors of the A-type W UMa systems and will be oscillating around a marginal-contact state as predicted by thermal relaxation oscillation (TRO) theory. [source] ACCOUNTING FOR TEMPERATURE IN PREDATOR FUNCTIONAL RESPONSESNATURAL RESOURCE MODELING, Issue 4 2007J. DAVID LOGAN ABSTRACT. A rational mechanism that integrates temperature-mediated activity cycles into standard predator functional responses is presented. Daily temperature variations strongly influence times that predators can search for prey, and they affect the activity periods of prey, thereby modifying their detection by predators. Thus, key parameters in the functional response, the search time and the detection, become temperature-dependent. These temperature mediated responses are included in discrete-time population growth models, and it is shown how environmental temperature variations, such as those that may occur under global climate change, can affect population levels. As an illustration, a logistic growth model with a stochastic, temperature-dependent predation term is examined, and the response to both average temperature levels and temperature variability is quantified. We infer, through simulations, that predation and prey abundance are strongly affected by mean temperature, temperature amplitudes, and increasing uncertainty in predicting temperature levels and variation, thus confirming many qualitative conclusions in the ecological literature. In particular, we show that increased temperature variability increases oscillations in the system and leads to increased probability of extinction of the prey. [source] | |||||||||||||