5-Methylcytosine (m.sup.5C) is a type of chemical modification on the nucleotides and is widespread in both DNA and RNA. Although the DNA m.sup.5C has been extensively studied over the past years, ...the distribution and biological function of RNA m.sup.5C still remain to be elucidated. Here, I explored the profiles of RNA m.sup.5C in four mouse tissues by applying a RNA cytosine methylation data analysis tool to public mouse RNA m.sup.5C data. I found that the methylation rates of cytosine were the same with the averages of methylation level at single-nucleotide level. Furthermore, I gave a mathematical formula to describe the observed relationship and analyzed it deeply. The sufficient necessary condition for the given formula suggests that the methylation levels at most m.sup.5C sites are the same in four mouse tissues. Therefore, I proposed a hypothesis that the m.sup.5C formation catalyzed by RNA methyltransferase is random and with the same probability at most m.sup.5C sites, which is the methylation rate of cytosine. My hypothesis can be used to explain the observed profiles of RNA m.sup.5C in four mouse tissues and will be benefit to future studies of the distribution and biological function of RNA m.sup.5C in mammals.
Increasing demands for power supplies have contributed to the population of high-frequency ac (HFAC) power distribution system (PDS), and in order to increase the power capacity, multilevel inverters ...(MLIs) frequently serving as the high-frequency (HF) source-stage have obtained a prominent development. Existing MLIs commonly use more than one voltage source or a great number of power devices to enlarge the level numbers, and HF modulation (HFM) methods are usually adopted to decrease the total harmonic distortion (THD). All of these have increased the complexity and decreased the efficiency for the conversion from dc to HF ac. In this paper, a nine-level inverter employing only one input source and fewer components is proposed for HFAC PDS. It makes full use of the conversion of series and parallel connections of one voltage source and two capacitors to realize nine output levels, thus lower THD can be obtained without HFM methods. The voltage stress on power devices is relatively relieved, which has broadened its range of applications as well. Moreover, the proposed nine-level inverter is equipped with the inherent self-voltage balancing ability, thus the modulation algorithm gets simplified. The circuit structure, modulation method, capacitor calculation, loss analysis, and performance comparisons are presented in this paper, and all the superior performances of the proposed nine-level inverter are verified by simulation and experimental prototypes with rated output power of 200 W. The accordance of theoretical analysis, simulation, and experimental results confirms the feasibility of proposed nine-level inverter.
Composites incorporating nanoparticles （NPs） within metal-organic frameworks （MOFs） find applications in many different fields.In particular,using MOF layers as molecular sieves built on the NPs ...could enable selectivity in heterogeneous catalysis.However,such composites typically exhibit low catalytic efficiency,due to the slow diffusion of the reactants in the long and narrow channels of the MOF shell.In order to improve the catalytic efficiency of these systems,here we report the fabrication of NPs incorporated in nanosized MOFs （NPs@nano-MOFs）,obtained by reducing the size of the MOF crystals grown around the NPs.The crystal size of the composites was controlled by modulating the nucleation rate of the MOFs during the encapsulation of pre-synthesized and catalytically active NPs;in this way,NPs@MOF crystals smaller than 50 nm were synthesized and subsequently used as highly efficient catalysts.Due to the shorter path from the MOF surface to the active sites,the obtained Pt@nano-MOFs composites showed a higher conversion rate than their larger-sized counterparts in the synthesis of imines via cascade reaction of nitrobenzene and in the hydrogenation of olefins,while retaining the excellent size and shape selectivity associated with the molecular sieving effect of the MOF layer.The present strategy can also be applied to prepare other encapsulated nanostructures combining various types of NPs and nano-MOFs,thus highlighting the broad potential of this approach for developing optimized catalysts with high reactivity and selectivity.
Hollow metal–organic frameworks (MOFs) are promising materials with sophisticated structures, such as multiple shells, that cannot only enhance the properties of MOFs but also endow them with new ...functions. Herein, we show a rational strategy to fabricate multi‐shelled hollow chromium (III) terephthalate MOFs (MIL‐101) with single‐crystalline shells through step‐by‐step crystal growth and subsequent etching processes. This strategy relies on the creation of inhomogeneous MOF crystals in which the outer layer is chemically more robust than the inner layer and can be selectively etched by acetic acid. The regulation of MOF nucleation and crystallization allows the tailoring of the cavity size and shell thickness of each layer. The resultant multi‐shelled hollow MIL‐101 crystals show significantly enhanced catalytic activity during styrene oxidation. The insight gained from this systematic study will aid in the rational design and synthesis of other multi‐shelled hollow structures and the further expansion of their applications.
Promising MOF structures: Single‐crystalline multi‐shelled hollow metal–organic frameworks (MSHMs) were synthesized through step‐by‐step crystal growth and subsequent etching processes. The cavity size and shell thickness of each layer in the MSHMs was regulated through careful nucleation and crystallization of the metal–organic frameworks. The MSHM crystals show significantly increased catalytic activity.
The objective of this paper is to propose a new inverter topology for a multilevel voltage output. This topology is designed based on a switched capacitor (SC) technique, and the number of output ...levels is determined by the number of SC cells. Only one dc voltage source is needed, and the problem of capacitor voltage balancing is avoided as well. This structure is not only very simple and easy to be extended to a higher level, but also its gate driver circuits are simplified because the number of active switches is reduced. The operational principle of this inverter and the targeted modulation strategies are presented, and power losses are investigated. Finally, the performance of the proposed multilevel inverter is evaluated with the experimental results of an 11-level prototype inverter.
In this paper, a quasi-resonant switched-capacitor (QRSC) multilevel inverter (MLI) is proposed with self-voltage balancing for single-phase high-frequency ac (HFAC) microgrids. It is composed of a ...QRSC circuit (QRSCC) in the frontend and an H-bridge circuit in the backend. The input voltage is divided averagely by the series-connected capacitors in QRSCC, and any voltage level can be obtained by increasing the capacitor number. The different operational mechanism and the resulting different application make up for the deficiency of the existing switched-capacitor topologies. The capacitors are connected in parallel partially or wholly when discharging to the load, thus the self-voltage balancing is realized without any high-frequency balancing algorithm. In other words, the proposed QRSC MLI is especially adapted for HFAC fields, where fundamental frequency modulation is preferred when considering the switching frequency and the resulting loss. The quasi-resonance technique is utilized to suppress the current spikes that emerge from the instantaneous parallel connection of the series-connected capacitors and the input source, decreasing the capacitance, increasing their lifetimes, and reducing the electromagnetic interference, simultaneously. The circuit analysis, power loss analysis, and comparisons with typical switched-capacitor topologies are presented. To evaluate the superior performances, a nine-level prototype is designed and implemented in both simulation and experiment, whose results confirm the feasibility of the proposed QRSC MLI.
Exposure to elevated concentrations of surface ozone (O
3) causes substantial reductions in the agricultural yields of many crops. As emissions of O
3 precursors rise in many parts of the world over ...the next few decades, yield reductions from O
3 exposure appear likely to increase the challenges of feeding a global population projected to grow from 6 to 9 billion between 2000 and 2050. This study estimates year 2000 global yield reductions of three key staple crops (soybean, maize, and wheat) due to surface ozone exposure using hourly O
3 concentrations simulated by the Model for Ozone and Related Chemical Tracers version 2.4 (MOZART-2). We calculate crop losses according to two metrics of ozone exposure – seasonal daytime (08:00–19:59) mean O
3 (M12) and accumulated O
3 above a threshold of 40 ppbv (AOT40) – and predict crop yield losses using crop-specific O
3 concentration:response functions established by field studies. Our results indicate that year 2000 O
3-induced global yield reductions ranged, depending on the metric used, from 8.5–14% for soybean, 3.9–15% for wheat, and 2.2–5.5% for maize. Global crop production losses totaled 79–121 million metric tons, worth $11–18 billion annually (USD
2000). Our calculated yield reductions agree well with previous estimates, providing further evidence that yields of major crops across the globe are already being substantially reduced by exposure to surface ozone – a risk that will grow unless O
3-precursor emissions are curbed in the future or crop cultivars are developed and utilized that are resistant to O
3.
► Surface O
3 is having a substantial impact on the yields of key crops. ► Yields of wheat, soybean, and maize were reduced by up to 15% globally in 2000. ► Global year 2000 crop production losses totaled 79–121 million metric tons. ► Agricultural losses are estimated to be worth $11–18 billion USD
2000 annually.
Abstract
Developing active single-atom-catalyst (SAC) for alkaline hydrogen evolution reaction (HER) is a promising solution to lower the green hydrogen cost. However, the correlations are not clear ...between the chemical environments around the active-sites and their desired catalytic activity. Here we study a group of SACs prepared by anchoring platinum atoms on NiFe-layered-double-hydroxide. While maintaining the homogeneity of the Pt-SACs, various axial ligands (−F, −Cl, −Br, −I, −OH) are employed
via
a facile irradiation-impregnation procedure, enabling us to discover definite chemical-environments/performance correlations. Owing to its high first-electron-affinity, chloride chelated Pt-SAC exhibits optimized bindings with hydrogen and hydroxide, which favor the sluggish water dissociation and further promote the alkaline HER. Specifically, it shows high mass-activity of 30.6 A mgPt
−1
and turnover frequency of 30.3 H
2
s
−1
at 100 mV overpotential, which are significantly higher than those of the state-of-the-art Pt-SACs and commercial Pt/C catalyst. Moreover, high energy efficiency of 80% is obtained for the alkaline water electrolyser assembled using the above catalyst under practical-relevant conditions.
Abstract
Economic globalization and concomitant growth in international trade since the late 1990s have profoundly reorganized global production activities and related CO
2
emissions. Here we show ...trade among developing nations (i.e., South–South trade) has more than doubled between 2004 and 2011, which reflects a new phase of globalization. Some production activities are relocating from China and India to other developing countries, particularly raw materials and intermediate goods production in energy-intensive sectors. In turn, the growth of CO
2
emissions embodied in Chinese exports has slowed or reversed, while the emissions embodied in exports from less-developed regions such as Vietnam and Bangladesh have surged. Although China’s emissions may be peaking, ever more complex supply chains are distributing energy-intensive industries and their CO
2
emissions throughout the global South. This trend may seriously undermine international efforts to reduce global emissions that increasingly rely on rallying voluntary contributions of more, smaller, and less-developed nations.
In this study, we examine a supply-chain approach to more effectively mitigate primary PM2.5 emissions in China from the perspectives of production, consumption and their linkages using structural ...path analysis. We identify the pattern of all supply chain paths using principal component analysis. To address the severe haze problems in China, it is important to understand how final demand purchase initiates production processes and ultimately leads to primary PM2.5 emission. We found that consumers' demands on power and transportation mainly induce direct emissions, quite different from the demands on construction, industry and service products which largely drive emissions in upstream activities. We also found that nearly 80% of the economic sectors in China follow a similar pattern in generating primary PM2.5 emissions in electricity, cement and the ferrous metal industries; but only the construction sector increases the release of PM2.5 due to the production of non-metallic mineral products. These findings indicate that further reduction of end-of-pipe emissions in the power and transportation sectors will facilitate cleaner production in almost all the economic sectors. However, for urbanization induced emissions, China should mitigate PM2.5 emissions through the supply chain of construction, either severely reducing its life-cycle intensity or carefully planning to avoid extensive, unnecessary building activity.
PDF
