The synthesis of all-carbon tetrasubstituted olefins under mild reaction conditions is challenging because of the inevitable issues including significant steric hindrance and the uncontrolled Z/E ...stereoselectivity. In this paper, we report the synthesis of all-carbon tetrasubstituted alkenes from readily available carboxylic acids and alkenyl triflates with the synergistic catalysis of cyclo-octa-1,5-diene(tetramethyl-1,4-benzoquinone)nickel and visible light under an air atmosphere, thus avoiding the need for a glovebox or a Schlenk line. A wide range of aromatic carboxylic acids and cyclic and acyclic alkenyl triflates undergo the C-C coupling process smoothly, forming structurally diverse alkenes stereospecifically in moderate to good yields. The practicality of the method is further illustrated by the late-stage modification of complex molecules, the one pot synthesis and gram-scale applications. This is an important step towards the valuable utilization of carboxylic acids, and it also simplifies the experimental operation of metallophotoredox catalysis with moisture sensitive nickel(0) catalysis.
Whole-genome sequence data have revealed that numerous eukaryotic organisms derive from distant polyploid ancestors, even when these same organisms are genetically and karyotypically diploid. Such ...ancient whole-genome duplications (WGDs) have been important for long-term genome evolution and are often speculatively associated with important evolutionary events such as key innovations, adaptive radiations, or survival after mass extinctions. Clearly, reliable methods for unveiling ancient WGDs are key toward furthering understanding of the long-term evolutionary significance of polyploidy. In this chapter, we describe a set of basic established comparative genomics approaches for the inference of ancient WGDs from genomic data based on empirical age distributions and collinearity analyses, explain the principles on which they are based, and illustrate a basic workflow using the software "wgd," geared toward a typical exploratory analysis of a newly obtained genome sequence.
Yang, W.X.; Hu, Z.X.; Lei, H.C., and Li, B.D., 2020. Numerical simulation study on the microphysical processes of Typhoon Wipha using a new moisture conditioning method. In: Guido Aldana, P.A. and ...Kantamaneni, K. (eds.), Advances in Water Resources, Coastal Management, and Marine Science Technology. Journal of Coastal Research, Special Issue No. 104, pp. 156–159. Coconut Creek (Florida), ISSN 0749-0208. With the non-static mesoscale model ARPS (Advanced Regional Prediction System), by using the NCEP/ NCAR global final analysis data, and the global surface and sounding data under MICAPS (Meteorological Information Comprehensive Analysis and Process System) assimilated in 4 dimensions as the initial field and lateral boundary conditions, the initial moisture field is adjusted according to the surface accumulated rain of each 6 h, and the triple nested simulation is conducted to produce 3 dimensional high time -spatial (Wipha) are analysed. The results are significant for understanding the cloud structure and the precipitation forming mechanisms of the Typhoon storm. It is found that the ice phase microphysical processes are the key storm mechanisms in different periods. The melting graupel confirms that the rain is the most important mechanism. The intensity of the production of graupel varies in accordance with the Typhoon.
The presence of embedded convection in stratiform clouds strongly affects ice microphysical properties and precipitation formation. In situ aircraft measurements, including upward and downward ...spirals and horizontal penetrations, were performed within both embedded convective cells and stratiform regions of a mixed-phase stratiform cloud system on 22 May 2017. Supercooled liquid water measurements, particle size distributions, and particle habits in different cloud regions were discussed with the intent of characterizing the riming process and determining how particle size distributions vary from convective to stratiform regions. Significant amounts of supercooled liquid water, with maxima up to 0.6 g m
−3
, were observed between −3°C and −6°C in the embedded convective cells while the peak liquid water content was generally less than 0.1 g m
−3
in the stratiform regions.
There are two distinct differences in particle size distributions between convective and stratiform regions. One difference is the significant shift toward larger particles from upper −15°C to lower −10°C in the convective region, with the maximum particle dimensions increasing from less than 6000 µm to over 1 cm. The particles larger than 1 cm at −10°C are composed of dendrites and their aggregates. The other difference is the large concentrations of small particles (25–205 µm) at temperatures between −3°C and −5°C in the convective region, where rimed ice particles and needles coexist. Needle regions are observed from three of the five spirals, but only the cloud conditions within the convective region fit into the Hallett-Mossop criteria.
Three cases of microphysical characteristics and kinematic structures in the negative temperature region of summer mesoscale cloud systems over the eastern Tibetan Plateau (TP) were investigated ...using X-band dual-polarization radar. The time-height series of radar physical variables and mesoscale horizontal divergence
δ
¯
derived by quasi-vertical profiles (QVPs) indicated that the dendritic growth layer (DGL, −20°C to −10°C) was ubiquitous, with large-value zones of
K
DP
(specific differential phase), Z
DR
(differential reflectivity), or both, and corresponded to various dynamic fields (ascent or descent). Ascents in the DGL of cloud systems with vigorous vertical development were coincident with large-value zones of Z
DR
, signifying ice crystals with a large axis ratio, but with no obvious large values of
K
DP
, which differs from previous findings. It is speculated that ascent in the DGL promoted ice crystals to undergo further growth before sinking. If there was descent in the DGL, a high echo top corresponded to large values of
K
DP
, denoting a large number concentration of ice crystals; but with the echo top descending, small values of
K
DP
formed. This is similar to previous results and reveals that a high echo top is conducive to the generation of ice crystals. When ice particles fall to low levels (−10°C to 0°C), they grow through riming, aggregation, or deposition, and may not be related to the kinematic structure. It is important to note that this study was only based on a limited number of cases and that further research is therefore needed.
Data collected using the micro rain radar(MRR) situated in Jinan city, eastern China, were used to explore the altitudinal and temporal evolution of rainfall microphysical characteristics, and to ...analyze the bright band(BB) characteristics and hydrometeor classification. Specifically, a low-intensity and stable stratiform precipitation event that occurred from 0000 to0550 UTC 15 February 2015 and featured a BB was studied. During this event, the rainfall intensity was less than 2 mm h-1 at a height of 300 m, which was above the radar site level, so the errors caused by the vertical air motion could be ignored.The freezing height from the radiosonde matched well with the top of the BB observed by the MRR. It was also found that the number of 0.5–1 mm diameter drops showed no noticeable variation below the BB. The maximum fall velocity and the maximum gradient fall velocity(GFV) of the raindrops appeared at the bottom of the BB. Meanwhile, a method that uses the GFV and reflectivity to identify the altitude and the thickness of the BB was established, with which the MRR can provide a reliable and real-time estimation of the 0?C isotherm. The droplet fall velocity was used to classify the types of snow crystals above the BB. In the first 20 min of the selected precipitation event, graupel prevailed above the BB; and at an altitude of2000 m, graupel also dominated in the first 250 min. After 150 min, the existence of graupel and dendritic crystals with water droplets above the BB was inferred.
A 2D axisymmetric bin model is used to conduct idealized numerical experiments of cloud seeding. The simulations are performed for two clouds that differ in their initial wind shear. Results show ...that, although cloud seeding with an ice concentration of 1000 L−1 in a regime that has relatively high supercooled liquid water can obtain a positive effect, the rainfall enhancement seems more pronounced when the cloud develops in a wind shear environment. In no-shear environment, the change in the microphysical thermodynamic field after seeding shows that, although more graupel is produced via riming and this can increase the surface rainfall intensity, the larger drag force and cooling of melting graupel is unfavorable for the development of cloud. On the contrary, when the cloud develops in a wind shear environment, since the main downdraft is behind the direction of movement of the cloud, its negative effect on precipitation is much weaker.
摘要
本文采用二维轴对称分档云模式开展了人工催化数值试验, 对两种不同初始风切变的对流云进行了模拟.结果表明, 尽管在过冷水相对较高的区域播撒1000 L−1的冰晶可以增加地面降水, 但当云在风切变环境中发展时, 人工播撒对降雨增强的作用似乎更加明显.在无切变环境下, 微物理量,热力场的变化表明播撒后大量的霰所产生的拖曳力和融化冷却有可能切断主上升气流, 从而不利于云的发展.相反, 当云在风切变环境中发展时, 由于播撒产生的主下沉气流位于云的运动方向之后, 其对降水的负面影响要弱得多.
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Major improvements in sequencing technologies and genome sequence assembly have led to a huge increase in the number of available genome sequences. In turn, these genome sequences form an invaluable ...source for evolutionary, ecological, and comparative studies. One kind of analysis that has become routine is the search for traces of ancient polyploidy, particularly for plant genomes, where whole-genome duplication (WGD) is rampant.
Here, we present a major update of a previously developed tool wgd, namely wgd v2, to look for remnants of ancient polyploidy, or WGD. We implemented novel and improved previously developed tools to (a) construct KS age distributions for the whole-paranome (collection of all duplicated genes in a genome), (b) unravel intragenomic and intergenomic collinearity resulting from WGDs, (c) fit mixture models to age distributions of gene duplicates, (d) correct substitution rate variation for phylogenetic placement of WGDs, and (e) date ancient WGDs via phylogenetic dating of WGD-retained gene duplicates. The applicability and feasibility of wgd v2 for the identification and the relative and absolute dating of ancient WGDs is demonstrated using different plant genomes.
wgd v2 is open source and available at https://github.com/heche-psb/wgd.
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