988 research outputs found
Early Triassic oceanic red beds coupled with deep sea oxidation in South Tethys
Carbonate oceanic red beds (ORBs) are unusual in Phanerozoic shelf settings but can be widespread during discrete intervals. Several scenarios have been invoked to explain the origin of these ORBs but there remains uncertainty about the process by which the red pigmentation of ORBs forms. Here, we propose that the occurrence of ORBs at intermediate water depths in shelf regions is controlled by fluctuations in the redox state of deeper waters. We have examined Early Triassic Peri-Gondwana shelf sections in South Tibet which show the development of Spathian (late Early Triassic) ORBs at intermediate water depths. The red color of these ORBs is imparted by randomly dispersed hematite crystals that are microns in size, showing weak alteration by late burial diagenesis. Widespread anoxia, in both shelf seas and the oceanic realm, was well developed in the Early Triassic. Synchronous occurrence of Spathian ORBs in deep shelf regions is closely related to the improved oxidation in deeper settings, from anoxia to dysoxia, based on changes in the redox proxy of pyrite framboid sizes. It is, therefore, inferred that prolonged deep-water anoxia might serve as source of Fe (II) for the formation of ORBs when intensified upwelling develops. The global occurrence of Early Triassic ORBs is coincident with the significant rebound of biodiversity after the Permian-Triassic mass extinction, indicating the occurrence of ORBs marks the terminal stage of an oceanic anoxic event and ORBs can serve as an indicator of the ameliorated marine ecosystem
Precipitation of high Mg-calcite and protodolomite using dead biomass of aerobic halophilic bacteria
The microbial dolomite model has been used to interpret the origin of sedimentary dolomite. In this model, the formation of low-temperature protodolomite, an important precursor to sedimentary dolomite, can be facilitated either by actively metabolizing cells of anaerobic microbes and aerobic halophilicarchaea or by their inactive biomass. Aerobic halophilic bacteria are widely distributed in (proto-)dolomite-depositing evaporitic environments and their biomass might serve as a template for the crystallization of protodolomite. To test this hypothesis, carbonation experiments were conducted using dead biomass of an aerobic halophilic bacterium (Exiguobacterium sp. strain JBHLT-3). Our results show that dead biomass of JBHLT-3 can accelerate Mg2+ uptake in carbonate mineral precipitates. In addition, the amount of Mg incorporated into Ca-Mg carbonates is proportional to the concentration of biomass. High Mg-calcite is produced with 0.25 or 0.5 g/L biomass, whereasprotodolomite forms with 1 g/L biomass. This is confirmed by the main Raman peak of Ca-Mg carbonates, which shifts towards higher wavenumbers with increased Mg substitution. Microbial cells and their imprints are preserved on the surface of high Mg-calcite and protodolomite. Hence, this study furthers our understanding of the dolomitization within buried and dead microbial mats, which provides useful insights into the origin of ancient dolomite
The catalytic role of planktonic aerobic heterotrophic bacteria in protodolomite formation: Results from Lake Jibuhulangtu Nuur, Inner Mongolia, China
Dolomite nucleation and subsequent crystallization are kinetically-controlled processes. Modern dolomite-forming environments provide clues to the trigger factors that facilitate dolomite formation under Earth surface conditions. It has been documented that certain types of benthic microorganisms promoted the precipitation of protodolomite from sediment pore waters. As protodolomite is thought to be a possible precursor of sedimentary ordered dolomite, microbial mediation has thus been suggested as one interpretation of the occurrence of dolomite in modern sediments. To date, however, it is still unclear whether planktonic microorganisms could directly initiate protodolomite crystallization in the upper water column of present dolomite depositing environments. In this study, we report on the occurrence of authigenic protodolomite in the upmost sediments of a high-sulfate, Chinese inland saline lake (Lake Jibuhulangtu Nuur). This lake was therefore considered to be a natural laboratory to test the catalytic effect of planktonic aerobic heterotrophic bacteria on protodolomite formation. Laboratory mineralization experiments were conducted in a liquid medium that mimicked the ion concentrations and pH condition of lake surface water. The incubation experiments showed that aragonite formed in the abiotic systems, while protodolomite predominantly occurred in the bioreactors using either an enrichment culture or pure isolates of aerobic heterotrophic and halophilic bacteria from lake water. The resulting microbially-induced protodolomite crystals displayed spherical morphology and had MgCO3 composition ranging from 42.7 mol% to 47.1 mol%. These protodolomite spherulites were formed by aggregation of randomly-distributed nano-crystals. Compared to synthetic abiotic protodolomite, microbially-induced protodolomite contained considerable amounts of organic matter, which might occur as intracrystalline inclusion or was located between nano-crystals of protodolomite spherulite. Our results support the emerging view that dissolved sulfate is not an inhibitor for the formation of low-temperature (proto-)dolomite. The presence of organic matter intimately associated with dolomite crystals may serve as a hallmark indicative of a biotically induced origin for some types of dolomite
Application of CRISPR/Cas9 in crop quality improvement
The various crop species are major agricultural products and play an indispensable role in sustaining human life. Over a long period, breeders strove to increase crop yield and improve quality through traditional breeding strategies. Today, many breeders have achieved remarkable results using modern molecular technologies. Recently, a new gene-editing system, named the clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 technology, has also succeeded in improving crop quality. It has become the most popular tool for crop improvement due to its versatility. It has accelerated crop breeding progress by virtue of its precision in specific gene editing. This review summarizes the current application of CRISPR/Cas9 technology in crop quality improvement. It includes the modulation in appearance, palatability, nutritional components and other preferred traits of various crops. In addition, the challenge in its future application is also discussed
A Note on Noncommutative Brane Inflation
In this paper, we investigate the noncommutative KKLMMT D3/anti-D3 brane
inflation scenario in detail. Incorporation of the brane inflation scenario and
the noncommutative inflation scenario can nicely explain the large negative
running of the spectral index as indicated by WMAP three-year data and can
significantly release the fine-tuning for the parameter . Using the WMAP
three year results (blue-tilted spectral index with large negative running), we
explore the parameter space and give the constraints and predictions for the
inflationary parameters and cosmological observables in this scenario. We show
that this scenario predicts a quite large tensor/scalar ratio and what is more,
a too large cosmic string tension (assuming that the string coupling is
in its likely range from 0.1 to 1) to be compatible with the present
observational bound. A more detailed analysis reveals that this model has some
inconsistencies according to the fit to WMAP three year results.Comment: 20 pages, 5 figures; accepted for publication in JCA
Proximity of the superconducting dome and the quantum critical point in the two-dimensional Hubbard model
We use the dynamical cluster approximation to understand the proximity of the superconducting dome to the quantum critical point in the two-dimensional Hubbard model. In a BCS formalism, Tc may be enhanced through an increase in the d-wave pairing interaction (Vd) or the bare pairing susceptibility (χ0d). At optimal doping, where Vd is revealed to be featureless, we find a power-law behavior of χ 0d(ω=0), replacing the BCS log, and strongly enhanced T c. We suggest experiments to verify our predictions. © 2011 American Physical Society
Three-dimensional parton distribution functions and in the polarized proton-antiproton Drell-Yan process
We present predictions of the unweighted and weighted double spin asymmetries
related to the transversal helicity distribution and the longitudinal
transversity distribution , two of eight leading-twist transverse
momentum dependent parton distributions (TMDs) or three-dimensional parton
distribution functions (3dPDFs), in the polarized proton-antiproton Drell-Yan
process at typical kinematics on the Facility for Antiproton and Ion Research
(FAIR). We conclude that FAIR is ideal to access the new 3dPDFs towards a
detailed picture of the nucleon structure.Comment: 6 latex pages, 5 figures, version for publication in EPJ
Search for Light Weakly-Interacting-Massive-Particle Dark Matter by Annual Modulation Analysis with a Point-Contact Germanium Detector at the China Jinping Underground Laboratory
We present results on light weakly interacting massive particle (WIMP)
searches with annual modulation (AM) analysis on data from a 1-kg mass -type
point-contact germanium detector of the CDEX-1B experiment at the China Jinping
Underground Laboratory. Datasets with a total live time of 3.2 yr within a 4.2
yr span are analyzed with analysis threshold of 250 eVee. Limits on
WIMP-nucleus (-) spin-independent cross sections as function of WIMP
mass () at 90\% confidence level (C.L.) are derived using the dark
matter halo model. Within the context of the standard halo model, the 90\% C.L.
allowed regions implied by the DAMA/LIBRA and CoGeNT AM-based analysis are
excluded at 99.99\% and 98\% C.L., respectively. These results correspond to
the best sensitivity at 6 among WIMP AM
measurements to date.Comment: 5 pages, 4 figure
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