Stories of the Proterozoic earth: Paleoproterozoic Chuanlinggou arcitarchs and Neoproterozoic ¹⁷O-depleted Barite

This dissertation consists of two independent topics, both critical to understanding Earth history during the Proterozoic Eon. (1) Paleoproterozoic Chuanlinggou Acritarchs: The eukaryotic affinity of acritarchs from the Chuanlinggou Formation has been questioned because of lack of indisputable morphological evidence. In this study, Chuanlinggou acritarchs were examined by jointly using optical microscopy, scanning electron microscopy, and transmission electron microscopy. In most cases, an ovoidal group of acritarchs represents a half-vesicle following a complete longitudinal rupture, which is a morphological model different from a whole envelope with medial splits, as proposed by earlier studies. This ovoidal group displays a bipolar morphology, longitudinal rupture, and occasionally striated wall structures that are consistent with a eukaryotic affinity. Thus, the Chuanlinggou ovoidal acritarchs probably extend the eukaryotic body fossil record into the Paleoproterozoic, circa 200 million years earlier than the morphologically more complex acritarchs from the Mesoproterozoic Roper Group. (2) Neoproterozoic 17O-depleted Barite: Distinct, non-mass-dependent 17O depletion was reported in barite from Marinoan cap dolostones, and has been interpreted as an indication of an extremely high-pCO2 atmosphere. Understanding the origins of this barite — and particularly the source of sulfate — is critical to interpreting the anomalous 17O signature and its implications for sulfur and oxygen cycles after Marinoan glaciation. In this study, together with field, petrographic, and Sr isotope data, the expanded dataset (1) confirms large variability in ∆17O, δ18O, and δ34S of barite; (2) demonstrates a hyperbolic relationship between the ∆17O and δ34S; (3) reveals that individual barite crystal fans and fans of the same generation possess well-clustered sets of δ18O, Δ17O, and δ34S values; and (4) shows that barite crystal fans of different layers bear different sets of Δ17O, δ18O, and δ34S values. The study suggests that 17O-depleted barite crystals were formed under supersaturation when Ba2+ from sulfate-free deepwater came to mix with sulfate-bearing shallow water. The large variability in sulfur and triple-oxygen isotope composition and the high 87Sr/86Sr ratios indicate that the two sites were sufficiently close to continents so that the isotopic composition of sulfate was easily influenced by changes in riverine flux

Reliability based optimization for semi-actively controlled seismic structures

A stochastic semi-active control strategy for the MR damping controlled structure is provided in this paper. The integrated optimization of the weighting matrices pertaining to the active optimal control and the MR parameters pertaining to the semi-active optimal control is implemented. In order to reveal the advantages of this strategy, comparative studies on two aspects are involved, i.e. optimization schemes and probabilistic criteria. The comparison between the integrated and the separated schemes based on the probabilistic criteria in terms of statistical moments shows that the integrated scheme exhibits a better control effectiveness. While the comparison between the probabilistic criteria in terms of statistical moments and the reliability used for the integrated scheme shows that the probabilistic criteria in terms of reliability attains a more safe structure

Reliability of base-isolated structures with sliding hydromagnetic bearings considering stochastic ground motions

Stochastic seismic response analysis and reliability assessment of a base-isolated structure with sliding hydro-magnetic bearings are performed combining the probability density evolution method and the stochastic func-tion model of seismic ground motions. The reliability assessments are based on the extreme value distribution of the inter-story drifts of the base-isolated structure. Compared with the responses of the base-fixed struc-ture, the superstructure of the base-isolated structure almost behaves like a rigid body. The sliding hydromag-netic bearing is efficient in reducing the responses by one degree of seismic intensity. Finally, the dynamic re-liability of the base-isolated structure is evaluated, which provides an index for decision making in practice

Feedback between carbon and nitrogen cycles during the Ediacaran Shuram excursion

This research is supported by the National Natural Science Foundation of China (41872032, 41830215, 41930320) and the Chinese ‘111’ project (B20011).The middle Ediacaran Period records one of the deepest negative carbonate carbon isotope (δ13Ccarb) excursions in Earth history (termed the Shuram excursion). This excursion is argued by many to represent a large perturbation of the global carbon cycle. If true, this event may also have induced significant changes in the nitrogen cycle, because carbon and nitrogen are intimately coupled in the global ocean. However, the response of the nitrogen cycle to the Shuram excursion remains ambiguous. Here, we reported high resolution bulk nitrogen isotope (δ15N) and organic carbon isotope (δ13Corg) data from the upper Doushantuo Formation in two well-preserved sections (Jiulongwan and Xiangerwan) in South China. The Shuram-equivalent excursion is well developed in both localities, and our results show a synchronous decrease in δ15N across the event. This observation is further supported by bootstrapping simulations taking into account all published δ15N data from the Doushantuo Formation. Isotopic mass balance calculations suggest that the decrease in δ15N during the Shuram excursion is best explained by the reduction of isotopic fractionation associated with water column denitrification (εwd) in response to feedbacks between carbon and nitrogen cycling, which were modulated by changes in primary productivity and recycled nutrient elements through remineralization of organic matter. The study presented here thus offers a new perspective for coupled variations in carbon and nitrogen cycles and sheds new light on this critical time in Earth history.Publisher PDFPeer reviewe

Two-dimensional simulation of large-scale wind field via a joint wavenumber-frequency power spectrum

The demand of large span spatial structures is booming in developing countries as their urbanization processes keep steady pace. These structures are characterized with long-span roofs, which probably will suffer wind-induced damages in their lifecycles because of their flexible natures and harmful aerodynamic actions caused by complicated forms of roof surface and stochastic wind field around them. Relevant studies are yet relatively rare in history. The recently proposed wavenumberfrequency joint PSD based spectral representation method (WN-SRM) has greatly reduced the computational burden of traditional wind field simulation methods, which makes possible for performing stochastic wind field simulation for large size structures. This paper presents a two-dimensional, homogeneous wind field simulation for a long-span, unevenly curved roof structure. The results show that the improved spectral representation method, i.e. WN-SRM works well in wind field simulation for flexible, long-span roof structure in terms of efficiency and effectiveness

Simulation of Fluctuating Wind Speed Fields by Stochastic Harmonic Function Representation Method Based on Joint Wavenumber-Frequency Power Spectrum

Simulation of wind speed fields usually plays a crucial role in the reliability analysis of large-size and high-rise structures such as tall buildings, long-span bridges and offshore wind turbines. To simulate a fluctuating wind speed field by the spectral representation method (SRM), two schemes can be adopted: (1) the conventional SRM, involving the decomposition of the cross power spectrum density (XPSD) matrix of fluctuating wind speed inevitablyand (2) the joint wavenumber-frequency spectrum based SRM, where a series of trigonometric functions are directly superimposed without any decompositions of XPSD matrix. However, both the two approaches involve large amounts of random variables, which hinder the reliability analysis of structures. In this paper, the stochastic harmonic function (SHF) representation method is extended and integrated with the joint wavenumber-frequency power spectrum to simulate fluctuating wind speed fields in one spatial dimension. Further, an efficient non-uniformly discretized scheme in wavenumber and frequency directions is suggested such that the number of random variables is dramatically reduced. Simulation results demonstrate the efficiency and validity of the proposed method.Financial supports from the National Natural Science Foundation of China (Grant Nos. 51725804, 11672209, and 11761131014) and the International Joint Research Program of Shanghai Municipal Government (Grant No. 18160712800) are highly appreciated

A productivity collapse to end earth's great oxidation

Author Posting. © National Academy of Sciences, 2019. This article is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences 116 (35), (2019): 17207-17212, doi:10.1073/pnas.1900325116.It has been hypothesized that the overall size of—or efficiency of carbon export from—the biosphere decreased at the end of the Great Oxidation Event (GOE) (ca. 2,400 to 2,050 Ma). However, the timing, tempo, and trigger for this decrease remain poorly constrained. Here we test this hypothesis by studying the isotope geochemistry of sulfate minerals from the Belcher Group, in subarctic Canada. Using insights from sulfur and barium isotope measurements, combined with radiometric ages from bracketing strata, we infer that the sulfate minerals studied here record ambient sulfate in the immediate aftermath of the GOE (ca. 2,018 Ma). These sulfate minerals captured negative triple-oxygen isotope anomalies as low as ∼ −0.8‰. Such negative values occurring shortly after the GOE require a rapid reduction in primary productivity of >80%, although even larger reductions are plausible. Given that these data imply a collapse in primary productivity rather than export efficiency, the trigger for this shift in the Earth system must reflect a change in the availability of nutrients, such as phosphorus. Cumulatively, these data highlight that Earth’s GOE is a tale of feast and famine: A geologically unprecedented reduction in the size of the biosphere occurred across the end-GOE transition.Olivia M. J. Dagnaud assisted during fieldwork. S. V. Lalonde and E. A. Sperling provided helpful comments on an early version of the manuscript. We thank N. J. Planavsky and an anonymous reviewer for their constructive feedback. M.S.W.H. was supported by an NSERC PGS-D and student research grants from National Geographic, the APS Lewis and Clark Fund, Northern Science Training Program, McGill University Graduate Research Enhancement and Travel Awards, Geological Society of America, Mineralogical Association of Canada, and Stanford University. P.W.C. acknowledges support from the University of Colorado Boulder, the Agouron Institute Geobiology postdoctoral Fellowship program, a Natural Sciences and Engineering Council of Canada Postgraduate Scholarship–Doctoral Program scholarship, and the NSTP. Y.P. was supported by the Strategic Priority Research Program of CAS (XDB26000000). T.J.H. thanks Maureen E. Auro for laboratory assistance and the NSF for supporting isotope research in the NIRVANA Labs.2020-02-1

Silica nanoparticles enhance autophagic activity, disturb endothelial cell homeostasis and impair angiogenesis

BACKGROUND: Given that the effects of ultrafine fractions (<0.1 μm) on ischemic heart diseases (IHD) and other cardiovascular diseases are gaining attention, this study is aimed to explore the influence of silica nanoparticles (SiNPs)-induced autophagy on endothelial cell homeostasis and angiogenesis. METHODS AND RESULTS: Ultrastructural changes of autophagy were observed in both vascular endothelial cells and pericytes in the heart of ICR mice by TEM. Autophagic activity and impaired angiogenesis were further confirmed by the immunohistochemistry staining of LC3 and VEGFR2. In addition, the immunohistochemistry results showed that SiNPs had an inhibitory effect on ICAM-1 and VCAM-1, but no obvious effect on E-selectin in vivo. The disruption of F-actin cytoskeleton occurred as an initial event in SiNPs-treated endothelial cells. The depolarized mitochondria, autophagic vacuole accumulation, LC3-I/LC3-II conversion, and the down-regulation of cellular adhesion molecule expression were all involved in the disruption of endothelial cell homeostasis in vitro. Western blot analysis indicated that the VEGFR2/PI3K/Akt/mTOR and VEGFR2/MAPK/Erk1/2/mTOR signaling pathway was involved in the cardiovascular toxicity triggered by SiNPs. Moreover, there was a crosstalk between the VEGFR2-mediated autophagy signaling and angiogenesis signaling pathways. CONCLUSIONS: In summary, the results demonstrate that SiNPs induce autophagic activity in endothelial cells and pericytes, subsequently disturb the endothelial cell homeostasis and impair angiogenesis. The VEGFR2-mediated autophagy pathway may play a critical role in maintaining endothelium and vascular homeostasis. Our findings may provide experimental evidence and explanation for cardiovascular diseases triggered by nano-sized particles. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12989-014-0050-8) contains supplementary material, which is available to authorized users

Toxic Effects of Silica Nanoparticles on Zebrafish Embryos and Larvae

Silica nanoparticles (SiNPs) have been widely used in biomedical and biotechnological applications. Environmental exposure to nanomaterials is inevitable as they become part of our daily life. Therefore, it is necessary to investigate the possible toxic effects of SiNPs exposure. In this study, zebrafish embryos were treated with SiNPs (25, 50, 100, 200 μg/mL) during 4-96 hours post fertilization (hpf). Mortality, hatching rate, malformation and whole-embryo cellular death were detected. We also measured the larval behavior to analyze whether SiNPs had adverse effects on larvae locomotor activity. The results showed that as the exposure dosages increasing, the hatching rate of zebrafish embryos was decreased while the mortality and cell death were increased. Exposure to SiNPs caused embryonic malformations, including pericardial edema, yolk sac edema, tail and head malformation. The larval behavior testing showed that the total swimming distance was decreased in a dose-dependent manner. The lower dose (25 and 50 μg/mL SiNPs) produced substantial hyperactivity while the higher doses (100 and 200 μg/mL SiNPs) elicited remarkably hypoactivity in dark periods. In summary, our data indicated that SiNPs caused embryonic developmental toxicity, resulted in persistent effects on larval behavior. © 2013 Duan et al.published_or_final_versio