scholarly journals Long-term evolution of large-scale magnetic fields in rotating stratified convection

2014 ◽  
Vol 66 (SP1) ◽  
pp. S2 ◽  
Author(s):  
Youhei Masada ◽  
Takayoshi Sano
Keyword(s):  
Magnetic Fields ◽  
Large Scale ◽  
Long Term Evolution ◽  
Term Evolution

scholarly journals Reconstructing solar magnetic fields from historical observations

2019 ◽  
Vol 627 ◽  
pp. A11
Author(s):  
I. O. I. Virtanen ◽  
I. I. Virtanen ◽  
A. A. Pevtsov ◽  
L. Bertello ◽  
A. Yeates ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Active Regions ◽  
Long Term Evolution ◽  
Photospheric Magnetic Field ◽  
Solar Magnetic Fields ◽  
Term Evolution ◽  
Large Scale Field

Aims. The evolution of the photospheric magnetic field has only been regularly observed since the 1970s. The absence of earlier observations severely limits our ability to understand the long-term evolution of solar magnetic fields, especially the polar fields that are important drivers of space weather. Here, we test the possibility to reconstruct the large-scale solar magnetic fields from Ca II K line observations and sunspot magnetic field observations, and to create synoptic maps of the photospheric magnetic field for times before modern-time magnetographic observations. Methods. We reconstructed active regions from Ca II K line synoptic maps and assigned them magnetic polarities using sunspot magnetic field observations. We used the reconstructed active regions as input in a surface flux transport simulation to produce synoptic maps of the photospheric magnetic field. We compared the simulated field with the observed field in 1975−1985 in order to test and validate our method. Results. The reconstruction very accurately reproduces the long-term evolution of the large-scale field, including the poleward flux surges and the strength of polar fields. The reconstruction has slightly less emerging flux because a few weak active regions are missing, but it includes the large active regions that are the most important for the large-scale evolution of the field. Although our reconstruction method is very robust, individual reconstructed active regions may be slightly inaccurate in terms of area, total flux, or polarity, which leads to some uncertainty in the simulation. However, due to the randomness of these inaccuracies and the lack of long-term memory in the simulation, these problems do not significantly affect the long-term evolution of the large-scale field.

Hydrogeological simulation of sedimentary basin evolution during a glacial cycle

2021 ◽  
Author(s):  
Christian Silbermann
Keyword(s):  
Boundary Conditions ◽  
Large Scale ◽  
Sedimentary Basin ◽  
Long Term Evolution ◽  
Nuclear Waste Repository ◽  
Glacial Cycle ◽  
Thermal Problem ◽  
Term Evolution ◽  
The Impact

<p><strong>Co-authors: Francesco Parisio, Thomas Nagel</strong></p><p>Glaciation cycles affect the long-term evolution of geosystems by crustal deformation, ground freezing and thawing, as well as large-scale hydrogeological changes. In order to properly understand the present and future conditions of potential nuclear waste repository sites, we need to simulate the past history. <br>For this, a sedimentary basin is considered here as a large-scale hydrogeological benchmark study. The long-term evolution during one glacial cycle is simulated using the open-source multi-field finite element code <em>OpenGeoSys</em>. The impact of the glacial loading (weight and induced shear) is taken into account using appropriate time-dependent stress boundary conditions. As a preliminary study, the hydro-mechanically coupled problem and the thermal problem are considered separately. For comparison with a previously published study by Bense et al. (2008), the entire displacement field is prescribed and the groundwater evolution (hydraulic problem) is regarded. Then, the displacement is only prescribed by means of boundary conditions. The impact of different constitutive assumptions on the deformation and hydraulic behavior is analyzed. The thermal problem is used to simulate the evolution of frost bodies in the subsurface beneath and ahead of the glacier.</p><p>V. F. Bense and M. A. Person. Transient hydrodynamics within intercratonic sedimentary basins during glacial cycles. Journal of Geophysical Research,<br>113(F4):F04005, 10 2008.</p>

scholarly journals Polyploids increase overall diversity despite higher turnover than diploids in the Brassicaceae

2020 ◽  
Vol 287 (1934) ◽  
pp. 20200962
Author(s):  
Cristian Román-Palacios ◽  
Y. Franchesco Molina-Henao ◽  
Michael S. Barker
Keyword(s):  
Chromosome Numbers ◽  
Large Scale ◽  
Interspecific Variation ◽  
Similar Rate ◽  
Long Term Evolution ◽  
Tree Of Life ◽  
Evolutionary Significance ◽  
Single Family ◽  
Term Evolution

Although polyploidy is widespread across the plant Tree of Life, its long-term evolutionary significance is still poorly understood. Here, we examine the effects of polyploidy in explaining the large-scale evolutionary patterns within angiosperms by focusing on a single family exhibiting extensive interspecific variation in chromosome numbers. We inferred ploidy from haploid chromosome numbers for 80% of species in the most comprehensive species-level chronogram for the Brassicaceae. After evaluating a total of 94 phylogenetic models of diversification, we found that ploidy influences diversification rates across the Brassicaceae. We also found that despite diversifying at a similar rate to diploids, polyploids have played a significant role in driving present-day differences in species richness among clades. Overall, in addition to highlighting the complexity in the evolutionary consequences of polyploidy, our results suggest that rare successful polyploids persist while significantly contributing to the long-term evolution of clades. Our findings further indicate that polyploidy has played a major role in driving the long-term evolution of the Brassicaceae and highlight the potential of polyploidy in shaping present-day diversity patterns across the plant Tree of Life.

scholarly journals Multi-Temporal Variabilities of Evapotranspiration Rates and Their Associations with Climate Change and Vegetation Greening in the Gan River Basin, China

Water ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 2568 ◽  
Author(s):  
Meng Bai ◽  
Bing Shen ◽  
Xiaoyu Song ◽  
Shuhong Mo ◽  
Lingmei Huang ◽  
...  
Keyword(s):  
Climate Change ◽  
River Basin ◽  
Human Activities ◽  
Large Scale ◽  
Temporal Dynamics ◽  
Long Term Evolution ◽  
Interactive Effects ◽  
Positive Effects ◽  
Term Evolution

Understanding the spatial-temporal dynamics of evapotranspiration in relation to climate change and human activities is crucial for the sustainability of water resources and ecosystem security, especially in regions strongly influenced by human impact. In this study, a process-based evapotranspiration (ET) model in conjunction with the Global Land Surface Satellite (GLASS) LAI dataset was used to characterize the spatial-temporal pattern of evapotranspiration from 1982 to 2016 over the Gan River basin (GRB), the largest sub-basin of the Poyang Lake catchment, China. The results showed that the actual annual ET (ETa) weakly increased with an annual trend of 0.88 mm year−2 from 1982 to 2016 over the GRB, along with a slight decline in annual potential ET (ETp). On an ecosystem scale; however, only the evergreen broadleaved forest and cropland presented a positive ETa trend, while the rest of the ecosystems demonstrated negative trends of ETa. Both correlation analysis and sensitivity analysis revealed a close relationship between ETa inter-annual variability and energy availability. Attribution analysis illustrated that contributions of climate change and vegetation greening on the ETa trend were −0.48 mm year−2 and 1.36 mm year−2, respectively. Climate change had a negative impact on the ETa trend over the GRB. However, the negative effects have been offset by the positive effects of vegetation greening, which mainly resulted from the large-scale revegetation in forestland and agricultural practices in cropland. It is concluded that large-scale afforestation and agricultural management were the main drivers of the long-term evolution of water consumption over the GRB. This study can improve our understanding of the interactive effects of climate change and human activities on the long-term evolution of water cycles.

Long-term evolution of crustal neutron star magnetic fields

1994 ◽  
Vol 433 ◽  
pp. 780 ◽  
Author(s):  
V. A. Urpin ◽  
G. Chanmugam ◽  
Yeming Sang
Keyword(s):  
Neutron Star ◽  
Magnetic Fields ◽  
Long Term Evolution ◽  
Term Evolution

scholarly journals Long-term evolution of a magnetic massive merger product

2020 ◽  
Vol 495 (3) ◽  
pp. 2796-2812
Author(s):  
F R N Schneider ◽  
S T Ohlmann ◽  
Ph Podsiadlowski ◽  
F K Röpke ◽  
S A Balbus ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
White Dwarfs ◽  
Massive Stars ◽  
Thermal Relaxation ◽  
Long Term Evolution ◽  
Critical Surface ◽  
Single Star ◽  
Strong Magnetic Fields ◽  
Term Evolution

ABSTRACT About 10 per cent of stars more massive than ${\approx}1.5\, {\mathrm{M}}_{\odot }$ have strong, large-scale surface magnetic fields and are being discussed as progenitors of highly magnetic white dwarfs and magnetars. The origin of these fields remains uncertain. Recent three-dimensional (3D) magnetohydrodynamical simulations have shown that strong magnetic fields can be generated in the merger of two massive stars. Here, we follow the long-term evolution of such a 3D merger product in a 1D stellar evolution code. During a thermal relaxation phase after the coalescence, the merger product reaches critical surface rotation, sheds mass and then spins down primarily because of internal mass readjustments. The spin of the merger product after thermal relaxation is mainly set by the co-evolution of the star–torus structure left after coalescence. This evolution is still uncertain, so we also consider magnetic braking and other angular momentum-gain and -loss mechanisms that may influence the final spin of the merged star. Because of core compression and mixing of carbon and nitrogen in the merger, enhanced nuclear burning drives a transient convective core that greatly contributes to the rejuvenation of the star. Once the merger product relaxed back to the main sequence, it continues its evolution similar to that of a genuine single star of comparable mass. It is a slow rotator that matches the magnetic blue straggler τ Sco. Our results show that merging is a promising mechanism to explain some magnetic massive stars and it may also be key to understand the origin of the strong magnetic fields of highly magnetic white dwarfs and magnetars.

scholarly journals LONG TERM EVOLUTION OF MAGNETIC TURBULENCE IN RELATIVISTIC COLLISIONLESS SHOCKS

2008 ◽  
Vol 17 (10) ◽  
pp. 1769-1775 ◽  
Author(s):  
PHILIP CHANG ◽  
ANATOLY SPITKOVSKY ◽  
JONATHAN ARONS
Keyword(s):  
Magnetic Fields ◽  
Magnetic Energy ◽  
Analytic Form ◽  
Long Term Evolution ◽  
Particle Distributions ◽  
Particle In Cell ◽  
Magnetic Turbulence ◽  
Term Evolution ◽  
Simple Analytic Form

We study the long term evolution of magnetic fields generated by an initially unmagnetized collisionless relativistic e+e- shock. Our 2D particle-in-cell numerical simulations show that downstream of such a Weibel-mediated shock, particle distributions are approximately isotropic, relativistic Maxwellians, and the magnetic turbulence is highly intermittent spatially, non-propagating, and decaying. Using linear kinetic theory, we find a simple analytic form for these damping rates. Our theory predicts that the overall magnetic energy decays as (ωp t)-q with q ~ 1, which compares favorably with simulations, but predicts overly rapid damping of short-wavelength modes. The magnetic trapping of particles within the magnetic structures may be the origin of this discrepancy. We conclude that initially unmagnetized relativistic shocks in electron-positron plasmas are unable to form persistent downstream magnetic fields. These results put interesting constraints on synchrotron models for the prompt and afterglow emission from GRBs.

scholarly journals Large Chromosomal Rearrangements during a Long-Term Evolution Experiment with Escherichia coli

mBio ◽  
2014 ◽  
Vol 5 (5) ◽  
Author(s):  
Colin Raeside ◽  
Joël Gaffé ◽  
Daniel E. Deatherage ◽  
Olivier Tenaillon ◽  
Adam M. Briska ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Genome Sequencing ◽  
Large Scale ◽  
Optical Mapping ◽  
Chromosomal Rearrangements ◽  
Long Term Evolution ◽  
Whole Genome ◽  
Term Evolution ◽  
Evolution Experiment

ABSTRACTLarge-scale rearrangements may be important in evolution because they can alter chromosome organization and gene expression in ways not possible through point mutations. In a long-term evolution experiment, twelveEscherichia colipopulations have been propagated in a glucose-limited environment for over 25 years. We used whole-genome mapping (optical mapping) combined with genome sequencing and PCR analysis to identify the large-scale chromosomal rearrangements in clones from each population after 40,000 generations. A total of 110 rearrangement events were detected, including 82 deletions, 19 inversions, and 9 duplications, with lineages having between 5 and 20 events. In three populations, successive rearrangements impacted particular regions. In five populations, rearrangements affected over a third of the chromosome. Most rearrangements involved recombination between insertion sequence (IS) elements, illustrating their importance in mediating genome plasticity. Two lines of evidence suggest that at least some of these rearrangements conferred higher fitness. First, parallel changes were observed across the independent populations, with ~65% of the rearrangements affecting the same loci in at least two populations. For example, the ribose-utilization operon and themanB-cpsGregion were deleted in 12 and 10 populations, respectively, suggesting positive selection, and this inference was previously confirmed for the former case. Second, optical maps from clones sampled over time from one population showed that most rearrangements occurred early in the experiment, when fitness was increasing most rapidly. However, some rearrangements likely occur at high frequency and may have simply hitchhiked to fixation. In any case, large-scale rearrangements clearly influenced genomic evolution in these populations.IMPORTANCEBacterial chromosomes are dynamic structures shaped by long histories of evolution. Among genomic changes, large-scale DNA rearrangements can have important effects on the presence, order, and expression of genes. Whole-genome sequencing that relies on short DNA reads cannot identify all large-scale rearrangements. Therefore, deciphering changes in the overall organization of genomes requires alternative methods, such as optical mapping. We analyzed the longest-running microbial evolution experiment (more than 25 years of evolution in the laboratory) by optical mapping, genome sequencing, and PCR analyses. We found multiple large genome rearrangements in all 12 independently evolving populations. In most cases, it is unclear whether these changes were beneficial themselves or, alternatively, hitchhiked to fixation with other beneficial mutations. In any case, many genome rearrangements accumulated over decades of evolution, providing these populations with genetic plasticity reminiscent of that observed in some pathogenic bacteria.

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