42 research outputs found
Eine verbesserte Anpassung von Südamerika an Afrika : Ergebnisse einer Rekonstruktion der ursprünglichen Form von Rift-Becken
A method for palinspastic reconstruction of
rift basins is described here. It is based on the
assumption of isostatic equilibrium and calculated from the present topography and sediment
thickness in a rift basin. Passive continental
margins along eastern South America
and western Africa were moved landward from
the ocean-continent boundary approximately
100 km. When South America is rotated to
Africa, a tight fit with Africa results along the
northern and central margins of South America.
The southern part of South America was rotated
to fit against Africa based on the palinspastic reconstruction of the San Jorge,
Colorado and Salado marginal rift basins in
Argentina. The method could also be applied
to passive margins to calculate the total amount
of crustal stretching that occurred during
continental extension and rifting. The pre-rift
condition of passive margins could then be
calculated for more accurate initial fits between conjugate passive margins
Preliminary reconstruction of the salinity of the ocean in the Cenozoic and Mesozoic
The salinity of the ocean in the past can be reconstructed by using knowledge of the existing evaporite deposits on land and in the offshore. We assume that evaporites on land follow the same rates of sedimentary cycling as other sedimentary materials to determine the flux of salts to the sea. However, the salt can be stored in the ocean until conditions appropriate for deposition occur. We assume that salt removals into the deep offshore, continental margin and marginal sea deposits, are not yet part of the recycling system. We conclude that during most of the Cenozoic salinities have been higher than they are today. Each of the major salt extractions into the offshore has caused a rapid decrease of oceanic salinity by a few per mille. In the Early Cretaceous mean ocean salinities ranged between 38 and 42‰, and the Jurassic and Triassic they were between 43 and 53‰
Results of a climate model for Triassic Pangaea
We have used a new General Circulation Model, GENESIS Version
1.02, derived from the U. S. National Center for Atmospheric Research
Community Climate Model I (NCAR-CCM I) to simulate the climate of
an Earth with realistic Pangaean geography. The climate model was run
assuming that the ocean heat flux was similar to that of today, atmospheric
C02 content was four times that of today, the solar constant was
2 % less than today, and the Earth's orbit was circular, with mean obliquity
23.4°. Models were run for paleogeographies at 245 Ma (Scythian)
and 225 Ma (Carnian).
The results indicate that no ice cap would develop over the land, and
there is no permanent sea ice. The seasonal temperature Variation in the
interior of the continent is in the order of 50 °C. The Continental areas
are very dry except for a few Coastal areas and along uplifts. The models
both suggest an extreme seasonal monsoonal circulation, with strong
westerly winds parallel to the entire coast of Gondwana and the east
coast of Laurasia during the northern hemisphere summet. In both hemispheres,
the effect is to cause coastal upwelling. The model also predicts
permafrost in the deeper soil layers poleward of 50° N and S. The effects
of topographic uplifts on the atmospheric circulation are pervasive. Topography
strongly affects the monsoonal circulation causing major deviations
of the wind Systems suggested in model runs with idealized geographies.
Topography also plays a crucial role in concentrating rainfall in a few
small areas.
It is evident that in order to have a realistic Simulation of paleoclimate,
an accurate representation of the paleotopography is essential.
It is also evident that the paleoclimate models may be useful in suggesting
geological criteria that can confirm or reject the predicted paleoclimatic
conditions
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The AEPEX Mission: Imaging Energetic Particle Precipitation in the Atmosphere through its Bremsstrahlung X-ray Signatures
The Atmospheric Effects of Precipitation through Energetic X-rays (AEPEX) mission is a 6U CubeSat that will monitor energetic electron precipitation from the radiation belts into the upper atmosphere. The primary instrument will image energetic (50–300 keV) X-rays produced in the atmosphere by bremsstrahlung, providing a near-direct signature of electron precipitation. An energetic electron detector will measure the precipitating electron spectrum, while the X-ray observations will be used to determine the absolute flux. X-ray images will be produced with 10-s time resolution and 50–100 km spatial resolution. The 6U spacecraft uses flight heritage spacecraft bus subsystems, including the attitude determination and control, electrical power, and command & data handling systems. AEPEX is designed to be operated from low-Earth orbit at ~500 km altitude with a high inclination in order to cover the outer radiation belt. AEPEX will be the first spacecraft mission to measure X-rays in the 50–300 keV energy range emitted by Earth’s atmosphere in response to radiation belt precipitation, and the first to image that precipitation from above.</p
Possible origins of macroscopic left-right asymmetry in organisms
I consider the microscopic mechanisms by which a particular left-right (L/R)
asymmetry is generated at the organism level from the microscopic handedness of
cytoskeletal molecules. In light of a fundamental symmetry principle, the
typical pattern-formation mechanisms of diffusion plus regulation cannot
implement the "right-hand rule"; at the microscopic level, the cell's
cytoskeleton of chiral filaments seems always to be involved, usually in
collective states driven by polymerization forces or molecular motors. It seems
particularly easy for handedness to emerge in a shear or rotation in the
background of an effectively two-dimensional system, such as the cell membrane
or a layer of cells, as this requires no pre-existing axis apart from the layer
normal. I detail a scenario involving actin/myosin layers in snails and in C.
elegans, and also one about the microtubule layer in plant cells. I also survey
the other examples that I am aware of, such as the emergence of handedness such
as the emergence of handedness in neurons, in eukaryote cell motility, and in
non-flagellated bacteria.Comment: 42 pages, 6 figures, resubmitted to J. Stat. Phys. special issue.
Major rewrite, rearranged sections/subsections, new Fig 3 + 6, new physics in
Sec 2.4 and 3.4.1, added Sec 5 and subsections of Sec
Occupancy maps of 208 chromatin-associated proteins in one human cell type
Transcription factors are DNA-binding proteins that have key roles in gene regulation. Genome-wide occupancy maps of transcriptional regulators are important for understanding gene regulation and its effects on diverse biological processes. However, only a minority of the more than 1,600 transcription factors encoded in the human genome has been assayed. Here we present, as part of the ENCODE (Encyclopedia of DNA Elements) project, data and analyses from chromatin immunoprecipitation followed by high-throughput sequencing (ChIP–seq) experiments using the human HepG2 cell line for 208 chromatin-associated proteins (CAPs). These comprise 171 transcription factors and 37 transcriptional cofactors and chromatin regulator proteins, and represent nearly one-quarter of CAPs expressed in HepG2 cells. The binding profiles of these CAPs form major groups associated predominantly with promoters or enhancers, or with both. We confirm and expand the current catalogue of DNA sequence motifs for transcription factors, and describe motifs that correspond to other transcription factors that are co-enriched with the primary ChIP target. For example, FOX family motifs are enriched in ChIP–seq peaks of 37 other CAPs. We show that motif content and occupancy patterns can distinguish between promoters and enhancers. This catalogue reveals high-occupancy target regions at which many CAPs associate, although each contains motifs for only a minority of the numerous associated transcription factors. These analyses provide a more complete overview of the gene regulatory networks that define this cell type, and demonstrate the usefulness of the large-scale production efforts of the ENCODE Consortium
Metabolomic Profiling Reveals Mitochondrial-Derived Lipid Biomarkers That Drive Obesity-Associated Inflammation
Obesity has reached epidemic proportions worldwide. Several animal models of obesity exist, but studies are lacking that compare traditional lard-based high fat diets (HFD) to “Cafeteria diets" (CAF) consisting of nutrient poor human junk food. Our previous work demonstrated the rapid and severe obesogenic and inflammatory consequences of CAF compared to HFD including rapid weight gain, markers of Metabolic Syndrome, multi-tissue lipid accumulation, and dramatic inflammation. To identify potential mediators of CAF-induced obesity and Metabolic Syndrome, we used metabolomic analysis to profile serum, muscle, and white adipose from rats fed CAF, HFD, or standard control diets. Principle component analysis identified elevations in clusters of fatty acids and acylcarnitines. These increases in metabolites were associated with systemic mitochondrial dysfunction that paralleled weight gain, physiologic measures of Metabolic Syndrome, and tissue inflammation in CAF-fed rats. Spearman pairwise correlations between metabolites, physiologic, and histologic findings revealed strong correlations between elevated markers of inflammation in CAF-fed animals, measured as crown like structures in adipose, and specifically the pro-inflammatory saturated fatty acids and oxidation intermediates laurate and lauroyl carnitine. Treatment of bone marrow-derived macrophages with lauroyl carnitine polarized macrophages towards the M1 pro-inflammatory phenotype through downregulation of AMPK and secretion of pro-inflammatory cytokines. Results presented herein demonstrate that compared to a traditional HFD model, the CAF diet provides a robust model for diet-induced human obesity, which models Metabolic Syndrome-related mitochondrial dysfunction in serum, muscle, and adipose, along with pro-inflammatory metabolite alterations. These data also suggest that modifying the availability or metabolism of saturated fatty acids may limit the inflammation associated with obesity leading to Metabolic Syndrome
Systematic assessment of long-read RNA-seq methods for transcript identification and quantification
The Long-read RNA-Seq Genome Annotation Assessment Project (LRGASP) Consortium was formed to evaluate the effectiveness of long-read approaches for transcriptome analysis. The consortium generated over 427 million long-read sequences from cDNA and direct RNA datasets, encompassing human, mouse, and manatee species, using different protocols and sequencing platforms. These data were utilized by developers to address challenges in transcript isoform detection and quantification, as well as de novo transcript isoform identification. The study revealed that libraries with longer, more accurate sequences produce more accurate transcripts than those with increased read depth, whereas greater read depth improved quantification accuracy. In well-annotated genomes, tools based on reference sequences demonstrated the best performance. When aiming to detect rare and novel transcripts or when using reference-free approaches, incorporating additional orthogonal data and replicate samples are advised. This collaborative study offers a benchmark for current practices and provides direction for future method development in transcriptome analysis