Introduction to the use of activity cycles as a basis for system's decomposition and simulation

1975 ◽  
Vol 7 (1) ◽  
pp. 15-20 ◽  
Author(s):  
George K. Hutchinson
Keyword(s):  
Activity Cycles

Land, People and Power in Early Medieval Wales: The cantref of Cemais in comparative perspective

2020 ◽  
Author(s):  
Rhiannon Comeau
Keyword(s):  
Comparative Analysis ◽  
Urban Society ◽  
Comparative Perspective ◽  
Seasonal Activity ◽  
Early Medieval ◽  
Habitual Activity ◽  
Activity Cycles

A study of seasonal activity cycles in a pre-urban society, examined through the lens of an early medieval Welsh case study. It examines how these cycles shaped patterns of power and habitual activity, defining spaces and structuring lives. Its multidisciplinary, comparative analysis identifies focal zones and challenges commonly applied interpretations.

scholarly journals Stellar Surface Convection, Line Asymmetries, and Wavelength Shifts

1999 ◽  
Vol 170 ◽  
pp. 268-277 ◽  
Author(s):  
Dainis Dravins
Keyword(s):  
Adaptive Optics ◽  
Temporal Variability ◽  
Stellar Surface ◽  
Time Variability ◽  
The Sun ◽  
Atmospheric Physics ◽  
Spatially Resolved ◽  
Activity Cycles ◽  
To Come ◽  
Surface Convection

AbstractWavelength positions of photospheric absorption lines may be affected by surface convection (stellar granulation). Asymmetries and wavelength shifts originate from correlated velocity and brightness patterns: rising (blueshifted) elements are hot (bright), and convective blueshifts result from a larger contribution of such blueshifted photons than of redshifted ones from the sinking and cooler (darker) gas. For the Sun, the effect is around 300 m s−1, expected to increase in F-type stars, and in giants. Magnetic fields affect convection and induce lineshift variations over stellar activity cycles. A sufficient measuring precision reveals also the temporal variability of line wavelengths (due to the evolution of granules on the stellar surface). A major future development to come from adaptive optics and optical interferometry will be the study of wavelength variations across spatially resolved stars, together with their spatially resolved time variability. Thus, precise radial velocities should soon open up new vistas in stellar atmospheric physics.

scholarly journals Enhanced stability and polyadenylation of select mRNAs support rapid thermogenesis in the brown fat of a hibernator

eLife ◽  
2015 ◽  
Vol 4 ◽  
Author(s):  
Katharine R Grabek ◽  
Cecilia Diniz Behn ◽  
Gregory S Barsh ◽  
Jay R Hesselberth ◽  
Sandra L Martin
Keyword(s):  
Mathematical Modeling ◽  
Low Temperatures ◽  
Temperature Sensitive ◽  
Molecular Pathways ◽  
Physiological Regulation ◽  
Brown Adipose ◽  
Activity Cycles ◽  
Intense Activity ◽  
Enhanced Stability ◽  
Periodic Arousal

During hibernation, animals cycle between torpor and arousal. These cycles involve dramatic but poorly understood mechanisms of dynamic physiological regulation at the level of gene expression. Each cycle, Brown Adipose Tissue (BAT) drives periodic arousal from torpor by generating essential heat. We applied digital transcriptome analysis to precisely timed samples to identify molecular pathways that underlie the intense activity cycles of hibernator BAT. A cohort of transcripts increased during torpor, paradoxical because transcription effectively ceases at these low temperatures. We show that this increase occurs not by elevated transcription but rather by enhanced stabilization associated with maintenance and/or extension of long poly(A) tails. Mathematical modeling further supports a temperature-sensitive mechanism to protect a subset of transcripts from ongoing bulk degradation instead of increased transcription. This subset was enriched in a C-rich motif and genes required for BAT activation, suggesting a model and mechanism to prioritize translation of key proteins for thermogenesis.

scholarly journals Heliospheric modulation of cosmic rays: model and observation

2017 ◽  
Vol 3 (1) ◽  
pp. 63-78
Author(s):  
Сардаана Герасимова ◽  
Sardaana Gerasimova ◽  
Петр Гололобов ◽  
Peter Gololobov ◽  
Владислав Григорьев ◽  
...  
Keyword(s):  
Cosmic Ray ◽  
Wide Energy Range ◽  
Interstellar Gas ◽  
Cosmic Ray Intensity ◽  
Basic Model ◽  
Electrical Neutrality ◽  
Cosmic Ray Modulation ◽  
Wide Energy ◽  
Activity Cycles ◽  
Zero Potential

This paper presents the basic model of cosmic ray modulation in the heliosphere, developed in Yu.G. Shafer Institute of Cosmophysical Research and Aeronomy of the Siberian Branch of RAS. The model has only one free modulation parameter: the ratio of the regular magnetic field to the turbulent one. It may also be applied to the description of cosmic ray intensity variations in a wide energy range from 100 MeV to 100 GeV. Possible mechanisms of generation of the mentioned turbulence field are considered. The primary assumption about the electrical neutrality of the heliosphere appears to be wrong, and the zero potential needed to match the model with observations in the plane of the solar equator can be achieved if the frontal point of the heliosphere, which is flowed around by interstellar gas, lies near the mentioned plane. We have revealed that the abnormal rise of cosmic ray intensity at the end of solar cycle 23 is related to the residual modulation produced by the subsonic solar wind behind the front of a standing shock wave. The model is used to describe features of cosmic ray intensity variations in several solar activity cycles.

scholarly journals Solar spectral irradiance variability of some chromospheric emission lines through the solar activity cycles 21-23

2017 ◽  
pp. 71-86
Author(s):  
Ü.D. Göker ◽  
M.Sh. Gigolashvili ◽  
N. Kapanadze
Keyword(s):  
Solar Activity ◽  
Chemical Elements ◽  
Wave Length ◽  
Spectral Lines ◽  
Spectral Irradiance ◽  
Close Connection ◽  
Solar Chromosphere ◽  
Solar Spectral Irradiance ◽  
Activity Cycles ◽  
Solar Activity Cycles

A study of variations of solar spectral irradiance (SSI) in the wave-length ranges 121.5 nm-300.5 nm for the period 1981-2009 is presented. We used various data for ultraviolet (UV) spectral lines and international sunspot number (ISSN) from interactive data centers such as SME (NSSDC), UARS (GDAAC), SORCE (LISIRD) and SIDC, respectively. We reduced these data by using the MATLsoftware package. In this respect, we revealed negative correlations of intensities of UV (289.5 nm-300.5 nm) spectral lines originating in the solar chromosphere with the ISSN index during the unusually prolonged minimum between the solar activity cycles (SACs) 23 and 24. We also compared our results with the variations of solar activity indices obtained by the ground-based telescopes. Therefore, we found that plage regions decrease while facular areas are increasing in SAC 23. However, the decrease in plage regions is seen in small sunspot groups (SGs), contrary to this, these regions in large SGs are comparable to previous SACs or even larger as is also seen in facular areas. Nevertheless, negative correlations between ISSN and SSI data indicate that these variations are in close connection with the classes of sunspots/SGs, faculae and plage regions. Finally, we applied the time series analysis of spectral lines corresponding to the wavelengths 121.5 nm-300.5 nm and made comparisons with the ISSN data. We found an unexpected increase in the 298.5 nm line for the Fe II ion. The variability of Fe II ion 298.5 nm line is in close connection with the facular areas and plage regions, and the sizes of these solar surface indices play an important role for the SSI variability, as well. So, we compared the connection between the sizes of faculae and plage regions, sunspots/SGs, chemical elements and SSI variability. Our future work will be the theoretical study of this connection and developing of a corresponding model.

scholarly journals Rest-activity cycles and melatonin phase angle of circadian entrainment in people without cone-mediated vision

2020 ◽  
Author(s):  
Manuel Spitschan ◽  
Corrado Garbazza ◽  
Susanne Kohl ◽  
Christian Cajochen
Keyword(s):  
Ganglion Cells ◽  
Light Exposure ◽  
Activity Patterns ◽  
External World ◽  
Circadian Phase ◽  
Cone System ◽  
Retinohypothalamic Tract ◽  
Activity Cycles ◽  
Phase Angles ◽  
Rest Activity

AbstractLight is strong zeitgeber to the human circadian system, entraining internal rhythms in physiology and behaviour to the external world. This is mediated by the melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs), which sense light in addition to the classical photoreceptors, the cones and rods. Circadian responses depend on light intensity, with exposure to brighter light leading to bigger circadian phase shifts and melatonin suppression. In congenital achromatopsia (prevalence 1 in 30,000 to 50,000 people), the cone system is non-functional, resulting in light avoidance and photophobia at light levels which are tolerable and habitual to individuals with a normal, trichromatic retina. Here, we examined chronotype and self-reported sleep, actigraphy-derived rest-activity cycles and increases melatonin in the evening in a group of genetically confirmed congenital achromats. We found normal rest-activity patterns in all participants, and normal melatonin phase angles of entrainment in 2/3 of our participants. Our results suggest that a functional cone system and exposure to daytime light intensities are not necessary for regular behavioural and hormonal entrainment. This may point to a compensation mechanism in circadian photoreception, which in conjunction with non-photic zeitgebers, ensures synchronisation of activity to the external world.Significance statementRhythms in physiology and behaviour are synchronised to the external cycle of light exposure. This is mediated by the retinohypothalamic tract, which connects the photoreceptors in the eye with the “circadian pacemaker” in our brain, the suprachiasmatic nucleus. What happens to our circadian rhythm when we lack the cone photoreceptors in the eye that enable us to see in daylight? We examined this question in a group of rare congenital achromats. Our work reveals that normal rhythms in rest and activity, and production of hormones, does not require a functional cone system.

scholarly journals A highly tunable dopaminergic oscillator generates ultradian rhythms of behavioral arousal

eLife ◽  
2014 ◽  
Vol 3 ◽  
Author(s):  
Ian D Blum ◽  
Lei Zhu ◽  
Luc Moquin ◽  
Maia V Kokoeva ◽  
Alain Gratton ◽  
...  
Keyword(s):  
Mammalian Species ◽  
Dopamine Neurons ◽  
Mammalian Brain ◽  
Behavioral Arousal ◽  
Dopaminergic Tone ◽  
Activity Cycles ◽  
Midbrain Dopamine ◽  
Locomotor Rhythms ◽  
Underlying Mechanisms ◽  
Period Lengthening

Ultradian (∼4 hr) rhythms in locomotor activity that do not depend on the master circadian pacemaker in the suprachiasmatic nucleus have been observed across mammalian species, however, the underlying mechanisms driving these rhythms are unknown. We show that disruption of the dopamine transporter gene lengthens the period of ultradian locomotor rhythms in mice. Period lengthening also results from chemogenetic activation of midbrain dopamine neurons and psychostimulant treatment, while the antipsychotic haloperidol has the opposite effect. We further reveal that striatal dopamine levels fluctuate in synchrony with ultradian activity cycles and that dopaminergic tone strongly predicts ultradian period. Our data indicate that an arousal regulating, dopaminergic ultradian oscillator (DUO) operates in the mammalian brain, which normally cycles in harmony with the circadian clock, but can desynchronize when dopamine tone is elevated, thereby producing aberrant patterns of arousal which are strikingly similar to perturbed sleep-wake cycles comorbid with psychopathology.

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