Variable remanence acquisition efficiency in sediments containing biogenic and detrital magnetites: Implications for relative paleointensity signal recording

Widespread geological preservation of biogenic magnetite makes it important to assess how such particles contribute to sedimentary paleomagnetic signals. We studied a sediment core from the South China Sea that passes the strict empirical criteria for magnetic "uniformity" used in relative paleointensity studies. Such assessments are based routinely on bulk magnetic parameters that often fail to enable identification of mixed magnetic mineral assemblages. Using techniques that enable component-specific magnetic mineral identification, we find that biogenic and detrital magnetites occur in approximately equal concentrations within the studied sediments. We analyzed normalized remanence signals associated with the two magnetite components to assess whether co-occurring biogenic and detrital magnetites record geomagnetic information in the same way and with the same efficiency. Paleomagnetic directions for the two components have no phase lag, which suggests that the biogenic and detrital magnetites acquired their magnetizations at equivalent times. However, we find that the biogenic magnetite is generally 2-4 times more efficient as the detrital magnetite in contributing to the natural remanent magnetization (NRM) despite their approximately equal magnetic contributions. Variations in the concentration and efficiency of remanence acquisition of the two components suggest that a significant part of the NRM is controlled by nongeomagnetic factors that will affect relative paleointensity recording. We recommend that methods suited to the detection of variable recording efficiency associated with biogenic and detrital magnetites should be used on a routine basis in relative paleointensity studies

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6′-O-galloylpaeoniflorin (GPF), a galloylated derivative of paeoniflorin isolated from peony root, has been proven to possess antioxidant potential. In this present study, we revealed that GPF treatment exerted significant neuroprotection of PC12 cells following OGD, as evidenced by a reduction of oxidative stress, inflammatory response, cellular injury, and apoptosis in vitro. Furthermore, treatment with GPF increased the levels of phosphorylated Akt (p-Akt) and nuclear factor-erythroid 2-related factor 2 (Nrf2), as well as promoted Nrf2 translocation in PC12 cells, which could be inhibited by Ly294002, an inhibitor of phosphoinositide 3-kinase (PI3K). In addition, Nrf2 knockdown or Ly294002 treatment significantly attenuated the antioxidant, anti-inflammatory, and antiapoptotic activities of GPF in vitro. In vivo studies indicated that GPF treatment significantly reduced infarct volume and improved neurological deficits in rats subjected to CIRI, as well as decreased oxidative stress, inflammation, and apoptosis, which could be inhibited by administration of Ly294002. In conclusion, these results revealed that GPF possesses neuroprotective effects against oxidative stress, inflammation, and apoptosis after ischemia-reperfusion insult via activation of the PI3K/Akt/Nrf2 pathway

Direct transformation of-alkane into all-conjugated polyene via cascade dehydrogenation

Selective C(sp$^{3}$) −H activation is of fundamental importance in processing alkane feedstocks to produce high-value-added chemical products. By virtue of an on-surface synthesis strategy, we report selective cascade dehydrogenation of n-alkane molecules under surface constraints, which yields monodispersed all-trans conjugated polyenes with unprecedented length controllability. We are also able to demonstrate the generality of this concept for alkyl-substituted molecules with programmable lengths and diverse functionalities, and more importantly its promising potential in molecular wiring

Role of humidity on the structures and properties of regenerated silk fibers

Silk fiber was processed from highly concentrated spinning dope to solid fibers along with water removal. To understand the mechanism of water removal during silk fiber spinning process, a microfluidic chip was designed and applied to investigate the structures and mechanical properties of two kinds of regenerated silk fibroin fibers dry-spun at different relative humidity. The experimental results showed that the diameters of the fibers spun at 40% RH are always larger than the fibers spun at 50% RH due to different removal rates of water. The fibers spun at low humidity contain more β-sheet structure and lower degree of chain orientation and crystalline orientation. These results indicate that the fast phase transition of silk fibroin from sol–gel to silk fiber undergoes with rapid water removal and higher fiber orientation relates to more residue water and drawing force

Mid-infrared 2D Photodetector based on bilayer PtSe2

In this work, large crystal atomic layer PtSe2 with a narrow band gap is synthesized by chemical transfer method. We then demonstrated, for the first time, mid-infrared photodetectors based on bilayer PtSe2 with fast response time and high responsivity up to 4.5 A/W under mid-infrared illumination (10 μm) at room temperature.MOE (Min. of Education, S’pore)Accepted versio

Pore-neck resistance to light gases in a microporous BTESE-derived silica: A comparison of membrane and xerogel powder

A supported membrane and a xerogel derived from 1,2-bis(triethoxysilyl)ethane (BTESE) under the same conditions were characterized by a gas uptake technique and membrane permeation method, respectively, to investigate the transport mechanism inside the pores. The results indicated that the transport in both materials was governed by repulsive necks, with more adsorptive gases experiencing stronger restrictions. Furthermore, on the basis of a comparison between the two samples, the similarity of activation energies for spherical gases provided positive evidence for the commonly used assumption of pore network equivalence between xerogels and membranes derived under the same conditions. Finally, the neck dimensions in both materials were evaluated by the GT-based model, and a mean value of approximately 2.90 angstrom (center-to-center distance) was obtained

Modelling of disjoining pressure for Lennard-Jones free thin films

Development of disjoining pressure was performed to study the symmetric, Lennard-Jones (LJ) free thin films using molecular modelling. A methodology rooted from film thermodynamics was established to derive the disjoining pressure isotherm (II - h), which is based on the surface tension at varied film thicknesses and can be viewed as a post-processing technique. The results showed that the disjoining pressure of LJ fluid is purely attractive. Compared with the complicated method reported previously, this methodology is demonstrated to be more convenient and readily applicable for other liquid films (e.g. aqueous thin films containing electrolyte or surfactants) meanwhile it can be applied at both low and high temperatures

Relationship and driving factors between urbanization and natural ecosystem health in China

Sustainable urban development is one of the most urgent problems worldwide, especially in China, which is in rapid urbanization. Reducing the negative impacts of urbanization and improving the relationship between the two have become research priorities. Using 260 cities in China as the research object, this study evaluated the level and temporal and spatial variation of urbanization and natural ecosystem health, explored the relationships between them, and influence mechanism of urbanization on natural ecosystem health. The results showed that the level of population urbanization, social urbanization, economic urbanization and land urbanization was significantly improved in 2000 compared to 2015, and the spatial distribution was higher in the east of China than in the west. The overall level of ecosystem health improved slightly throughout the same period, and its spatial distribution was higher in the north of China than in the south. In terms of the four dimensions of ecosystem health, the ecosystem services and organization were improved, and the ecological environment and elasticity were decreased. Urbanization mainly affected ecosystem health by changing the demand for the quantity and type of ecosystem services through the growth and aggregation of population. However, under the comprehensive effect of the four dimensions of urbanization on natural ecosystem health, the overall constraint intensity of urbanization on natural ecosystem health was relatively stable. The coupling and coordination level between urbanization and natural ecosystem health showed improvement from 2000 to 2015, and the social and economic factors were highly influential. According to the level of urbanization and natural ecosystem health, all cities were classified, which showed the urban development was mainly the medium-level balanced. On this basis, management suggestions were put forward for each type of city. By analyzing the action process and mechanism between urban development and natural ecosystem health, it provides a theoretical basis for in-depth understanding and coordinating the relationship of the urban ecological economy

Critical pore dimensions for gases in a BTESE-derived organic-inorganic hybrid silica: A theoretical analysis

This work studied the critical pore dimensions for different light gases in disordered microporous hybrid silica which was derived from 1,2-bis(triethoxysilyl)ethane (BTESE) precursor. The Lennard-Jones (LJ) parameters of the material, obtained from high pressure isotherms of light gases, were employed to evaluate dispersive interaction, diffusivity and adsorption coefficient in the nanopores of the hybrid silica, and the results demonstrated that the entrance barrier was the key factor to break down the separation limits confining the Graham law and the Knudsen model by gas kinetic theory. Finally, the critical pore dimensions for different resistance dominated regions were evaluated, which theoretically explained why the separation capacity of the hybrid silica was less promising than pure silica for the purpose of gas separation

Rare earth element fractionations of the northwestern South China Sea sediments, and their implications for East Asian monsoon reconstruction during the last 36 kyr

Rare earth elements (REEs) fractionations in siliciclastic marine sediments are related to the parent rock properties, weathering degree, grain size, and heavy minerals. The relations between marine sediment REE compositions and regional paleoclimate are not fully understood. Here, the REEs for detrital components of a core retrieved from the northwestern South China Sea (SCS) were measured. Results show the REE (LREE/HREE, (La/Yb)(N)) and Light REE ((La/Sm)(N)) fractionation degrees have good responses to the regional paleoclimate over the past 36 kyr. Sea level played a key role in REE fractionations during similar to 36-24 kyr BP, manifesting as lower REE and LREE fractionation degrees correspond to the decreased sea level. The entire trends for LREE/HREE, (La/Yb)(N) and (La/Sm)(N) over the past 20.5 kyr are almost in phase with the regional East Asian summer monsoon (EASM) records. Because REEs are mainly concentrated in heavy minerals, the density difference of heavy minerals is probably the main controlling factor on REE fractionations. Clay minerals and feldspars released during the weathering process have a high content of Light REEs (LREEs). In the warm, wet periods (Holocene Optimum, and Bolling-Allerod), more precipitation promoted weathering and strengthened the estuarine hydrodynamic force, which respectively resulted in high content of clay minerals and feldspars, and high-density heavy minerals (e.g., monazite). The process led to LREE enrichment because the enriched minerals contain higher contents of the LREEs. In contrast, the dry, cold climate conditions during the periods Heinrich 1, Younger Dryas, and Last Glacial Maximum resulted in the reversed REE fractionations, as the weak hydrodynamic force can only carry the low-density heavy minerals (e.g., zircon) that are enriched in HREEs. This model does not seem to apply to 36- 24 kyr BP, probably because of the re-transport of ancient shelf sediments. The study facilitates the understanding of REE application in paleoclimate reconstruction within slope sediments