D-葡萄糖酸衍生物C5和C6羟基保护基迁移现象研究

2-O-甲基-3,4-O-丙酮叉基-D-葡萄糖酸甲酯(6)的C6羟基用乙酰基保护、C5仲羟基用TBS保护得到化合物8,碳酸钾脱除C6-O-乙酰基时,C5-O-TBS迁移到C6羟基得到了化合物9(74%收率),没有得到目标产物12;将化合物6的C6羟基用TBS保护、C5羟基乙酰基保护的化合物10,四丁基氟化铵脱除C6-O...     

A Cost‐effective Nafion Composite Membrane as an Effective Vanadium‐Ion Barrier for Vanadium Redox Flow Batteries

Ion exchange membranes play a key role in all vanadium redox flow batteries (VRFBs). The mostly available commercial membrane for VRFBs is Nafion. However, its disadvantages, such as high cost and severe vanadium‐ion permeation, become obstacles for large‐scale energy storage. It is thus crucial to develop an efficient membrane with low permeability of vanadium ions and low cost to promote commercial applications of VRFBs. In this study, graphene oxide (GO) has been employed as an additive to the Nafion 212 matrix and a composite membrane named rN212/GO obtained. The thickness of rN212/GO has been reduced to only 41 μm (compared with 50 μm Nafion 212), which indicates directly lower cost. Meanwhile, rN212/GO shows lower permeability of vanadium ions and area‐specific resistance compared to the Nafion 212 membrane due to the abundant oxygen‐containing functional groups of GO additives. The VRFB cells with the rN212/GO membrane show higher Coulombic efficiencies and lower capacity decay than those of VRFB cells with the Nafion 212 membrane. Therefore, the cost‐effective rN212/GO composite membrane is a promising alternative to suppress migration of vanadium ions across the membrane to set up VRFB cells with better performances.     

A pair of solar spike emissions

Using the 2.6–3.8 GHz solar radio spectrometer of the National Astronomical Observatories of China (NAOC), a pair of microwave millisecond spike (MMS) emissions were observed, and their frequency drift rate was measured. The separatrix frequency of the MMS pair was at 2900 MHz. Its emission layer was about 2×10⁴km above the photosphere. The polarization degree was wave-like variation with an average value of about 25% in LCP. An MMS pair differs greatly from the type III bursts pair. For the latter, in a certain frequency range, there is no emission around separatrix frequency. This phenomenon may help better understand the mechanism of MMS.     

Na2PO3F对LiNi0.83Co0.11Mn0.06O2材料的复合改性及机理分析

采用湿化学法使用Na₂PO₃F对LiNi_0.83Co_0.11Mn_0.06O₂进行表面改性, 得到F^–掺杂和LiF包覆的正极材料. X射线衍射谱(XRD)结果显示(003)衍射峰向高角度偏移, 结合X射线光电子能谱(XPS)及透射电子显微镜(TEM)证明F^–进入到材料晶格内部; 扫描电镜(SEM)、TEM及XPS结果显示, 改性后材料表面存在均匀LiF包覆层, 可提高电极/电解液界面稳定性, 改善循环稳定性; 通过计算锂离子扩散系数, 证明Li⁺传输速率得到提升, 倍率性能改善. 电化学性能测试结果显示, 材料的循环稳定性和倍率性能均得到显著提高: 在2.75~4.3 V电压窗口下, 材料1 C循环200周后容量保持率由32.2%提高到65.2%, 10 C条件下放电比容量由145.7 mAh/g提高到161.5 mAh/g. 对循环后极片进行XPS分析, 正极-电解质界面(CEI层)层中的LiF, Li_xPO_yF_z, NiF₂减少, 有利于提高材料稳定性及循环性能.     

Entropy-Regularized Optimal Transport on Multivariate Normal and q-normal Distributions

The distance and divergence of the probability measures play a central role in statistics, machine learning, and many other related fields. The Wasserstein distance has received much attention in recent years because of its distinctions from other distances or divergences. Although computing the Wasserstein distance is costly, entropy-regularized optimal transport was proposed to computationally efficiently approximate the Wasserstein distance. The purpose of this study is to understand the theoretical aspect of entropy-regularized optimal transport. In this paper, we focus on entropy-regularized optimal transport on multivariate normal distributions and q-normal distributions. We obtain the explicit form of the entropy-regularized optimal transport cost on multivariate normal and q-normal distributions; this provides a perspective to understand the effect of entropy regularization, which was previously known only experimentally. Furthermore, we obtain the entropy-regularized Kantorovich estimator for the probability measure that satisfies certain conditions. We also demonstrate how the Wasserstein distance, optimal coupling, geometric structure, and statistical efficiency are affected by entropy regularization in some experiments. In particular, our results about the explicit form of the optimal coupling of the Tsallis entropy-regularized optimal transport on multivariate q-normal distributions and the entropy-regularized Kantorovich estimator are novel and will become the first step towards the understanding of a more general setting.     

河滩相软土试验工程观测成果分析

以河滩相软土为研究对象,利用沉降板、测斜管、孔隙水压力计等多种测试仪器,选取有代表性的观测断面,进行了一年多的沉降与稳定观测。通过观测数据对河滩相软土的沉降规律进行了分析,同时推算了河滩相软土的沉降系数ms,这对今后在河南省河滩相软土地基上修筑高等级公路具有重要的参考价值。     

Biodegradable CuI/BCNF composite thermoelectric film for wearable energy harvesting

Cellulose - Cellulose is the most widely distributed polymer material in nature and is considered a low-cost, green and recyclable material. Because of its excellent mechanical, optical and thermal...     

The fluorine-free coating has excellent hydrophobic and oleophobic properties for porous cellulose-based materials

Cellulose - Nanofibrillated cellulose is obtained from cellulose resources (e.g., Natural cellulose, bacterial cellulose) and is deemed to be environmentally friendly, green, and inexhaustible....     

The oxidase-like activity of iridium nanoparticles,and their application to colorimetric determination of dissolved oxygen

Iridium nanoparticles (IrNPs) with intrinsic oxidase-like activity were synthesized by using sodium citrate as the stabilizer and NaBH₄ as the reducing agent. The IrNPs have an average diameter of 2.5 ± 0.5 nm and exhibit excellent oxidase-like property. Under the catalytic action of the IrNPs, 3,3′,5,5′-tetramethylbenzidine (TMB) is oxidized by dissolved oxygen (DO) to form a blue product with an absorption maximum at 652 nm. The catalytic activity is ascribed to the production of superoxide anion radical (O₂ˉ?). The chromogenic reaction is exploited for the determination of DO. The method exhibits a wide calibration range from 12.5 to 257.5 μM of DO and a limit of detection as low as 4.7 μM. Compared to other methods, this method presented here shows improved precision and faster response time.

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Graphic abstract Iridium nanoparticles (IrNPs) stabilized by sodium citrate exhibit oxidase-like activity and can effectively catalyze dissolved oxygen (DO) by oxidizing 3,3′,5,5′-tetramethylbenzidine (TMB) to form a blue product.