铜镍双金属催化剂上糠醛水相选择性偶联加氢-重排制环戊酮

生物质资源高效催化转化制备高附加值化学品具有重要的科学意义与工业应用潜力.生物质基糠醛催化加氢-重排制备环戊酮是一条具有吸引力的“非石油”制备路线,但该过程面临副产物多、环戊酮选择性难以提高等难题,除糠醛外,中间物种也很容易发生多种聚合副反应.因此,探索中间物种聚合副反应的条件和作用机制,是提高目标产物环戊酮的选择性和收率的关键.本文制备了CuNi/Al-MCM-41双金属纳米过渡金属催化剂,通过精确调控介质水的pH值和原料浓度,实现了糠醛加氢-重排耦合制备环戊酮的高选择性和高收率.在2.0 MPa H_(2),160℃和近中性条件下反应5 h,糠醛的转化率为99.0%,环戊酮的选择性达到97.7%;其催化性能远远高于单组份铜或镍催化剂以及其它分子筛载体(MCM-41,SBA-15,HY,ZSM-5)负载的CuNi双金属催化剂.研究结果表明,高度分散在MCM-41上的少量Al组分,有利于Cu,Ni金属组分相互均匀分散.XPS结果表明,双金属催化剂CuNi/Al-MCM-41中Cu和Ni具有明显的电子结合能偏移,表明Ni向Cu转移电子;耦合催化反应性能的提高可能与CuNi双金属协同作用及电荷转移效应有关.傅立叶变换红外光谱和质谱结果表明,聚合副反应对反应体系的pH值敏感.在酸性条件下,中间产物糠醇在反应体系中容易发生聚合,导致糠醇重排生成3-羟基环戊烯酮的选择性降低;在碱性条件下,3-羟基环戊烯酮转化为4-羟基-环戊-2-烯酮后,容易进一步发生聚合副反应.在近中性条件下可有效避免中间体的聚合,提高加氢重排生成环戊酮的选择性.此外,降低原料糠醛的初始浓度,有利于降低聚合等副反应,能够进一步提高目标产物环戊酮的收率.本文为研制双金属纳米过渡金属催化剂以及利用双金属协同作用等方面提供新的启示,为解决生物质原料转化过程中普遍存在的聚合副反应和碳平衡降低等问题提供了新思路.

导热型芳纶纳米纸基绝缘材料的制备及性能

研究了氮化硼(BN)导热填料的种类、添加量及成形方式对导热型芳纶纳米(ANFs)纸基绝缘材料的绝缘、导热及力学性能的影响。研究结果表明,溶胶凝胶法(Sol-gel)使得ANFs之间形成的交织网络结构可改善BN填料在纸张中的分布均匀性,解决了纸张"两面差"问题,减小了填料聚集现象从而实现均匀传热,制备的20%BN@ANFs绝缘纸导热系数达到0.125 W/(m·K),比空白ANFs绝缘纸提高了3.7倍。当添加经过功能化改性的BN-OH时,可提高ANFs与BN之间的界面结合力从而降低界面热阻,绝缘纸的导热系数高达0.144 W/(m·K),比空白纸提高了4.2倍,同时具有优异的力学性能(拉伸强度145 MPa)与绝缘强度(耐压强度25.3 kV/mm),有望满足未来小型化、轻质化、集成化的电气绝缘设备对绝缘材料性能不断的升级要求。

Contingency management strategies of the Nursing Department in centralized rescue of patients with coronavirus disease 2019

Objectives:This article aims to summarize a series of contingency management strategies of the Nursing Department in the centralized treatment of patients with coronavirus disease 2019(COVID-19).Methods:The strategies of the Nursing Department included an early warning for prevention and control,taking functions of vertically commanding and horizontally coordinating,and reasonably allocating nursing workforce,to facilitate centralized treatment work in the in-hospital fever clinic,isolation wards and ICU,and referral and admission of critical patients.Five special groups were established in charge of training and examination,management and supervision,psychological support,logistical support,and reporting and publicity,respectively.Results:It was achieved that no deaths from critical patients and no medical staff,no other patients were infected.Conclusion:Through the implementation of these strategies,safe and efficient centralized treatment was ensured timely,orderly and sustainably.

Multi-scale phase average waveform of electroencephalogram signals in childhood absence epilepsy using wavelet transformation

BACKGROUND： Recent studies have focused on various methods of wavelet transformation for electroencephalogram （EEG） signals. However, there are very few studies reporting characteristics of multi-scale phase waves during epileptic discharge.OBJECTIVE： To extract multi-scale phase average waveforms from childhood absence epilepsy EEG signals between time and frequency domains using wavelet transformation, and to compare EEG signals of absence seizure with pre-epileptic seizure and normal children, and to quantify multi-scale phase average waveforms from childhood absence epilepsy EEG signals. DESIGN, TIME AND SETTING： The case-comparative experiment was performed at the Department of Neuroelectrophysiology, Tianjin Medical University from August 2002 to May 2005. PARTICIPANTS： A total of 15 patients with childhood absence epilepsy from the General Hospital of Tianjin Medical University were enrolled in the study. The patients were not administered anti-epileptic drugs or sedatives prior to EEG testing. In addition, 12 healthy, age- and gender-matched children were also enrolled.METHODS： EEG signals were tested on 15 patients with childhood absence epilepsy and 12 normal children. Epileptic discharge signals during clinical and subclinical seizures were collected 10 and 20 times, respectively. The collected EEG signals were treated with wavelet transformation to extract multi-scale characteristics during absence epilepsy seizure using a conditional sampling method. Multi-scale phase average waveforms were collected using a conditional phase averaging technique. Amplitude of phase average waveform from EEG signals of epilepsy seizure, subclinical epileptic discharge, and EEG signals of normal children were compared and statistically analyzed in the first half-cycle.MAIN OUTCOME MEASURES： Multi-scale wavelet coefficient and the evolution of EEG signals were observed during childhood absence epilepsy seizures using wavelet transformation. Multi-scale phase average waveforms from EEG signals were observed using a conditional sampling method and phase averaging technique.RESULTS： Multi-scale characteristics of EEG signals demonstrated that 12-scale （3 Hz） rhythmical activity was significantly enhanced during childhood absence epilepsy seizure and co-existed with background structure （〈1 Hz, low frequency discharge）. The phase average wave exhibited opposed phase abnormal rhythm at 3 Hz. Prior to childhood absence epilepsy seizure, EEG detected opposed abnormal a rhythm and 3 Hz composition, which were not detected with traditional EEG. Compared to EEG signals from normal children, epileptic discharges from clinical and subclinical childhood absence epilepsy seizures were positive and amplitude was significantly greater （P〈0.05）.CONCLUSION： Wavelet transformation was used to analyze EEG signals from childhood absence epilepsy to obtain multi-scale quantitative characteristics and phase average waveforms. Multi-scale wavelet coefficients of EEG signals correlated with childhood absence epilepsy seizure, and multi-scale waveforms prior to epilepsy seizure were similar to characteristics during the onset period. Compared to normal children, EEG signals during epilepsy seizure exhibited an opposed phase model.

Natural Polysaccharide:Modification and Application

Natural polysaccharides are synthetic macromolecules located in the cell wall and intracellular,intercellular,and secretory cells.These are essential components of life activities.Cellulose and its derivatives,chitosan,alginic acid,starch,and other natural polymer materials that exist in nature are polysaccharides.This article briefly reviews the structure and sources of several natural polysaccharides,focusing on the modification design strategies of polysaccharides such as graft polymerization,oxidation,etherification,and esterification on cellulose(mainly cellulose nanocrystals,CNC),chitosan(CTS),and other polysaccharides and derivatives in the fields of biomass energy,composite materials,wastewater treatment,and biomedicine.Based on the theory of modification and application of polysaccharides at the present stage,future research goals and modification strategy design are prospected.

Highly Improved Microstructure and Properties of Poly(p-phenylene terephthalamide) Paper-based Materials via Hot Calendering Process

In this study,the effect of hot calendering process on the microstructure and properties of poly(p-phenylene terephthalamide)(PPTA) paper-based materials was investigated.The microstructures of the fracture surface,crystalline structure,and single fiber strength of the PPTA paperbased materials as well as the different bonding behaviors between the PPTA fibers and PPTA fibrids obtained before and after the hot calendering process were examined.The results indicated that a high linear pressure would result in a limited improvement of the strength owing to the unimproved paper structure.The optimal values of tensile index and dielectric strength of 56.6 N·m/g and 27.6 kV/mm,respectively,could only be achieved with a synergistic effects of hot calendering temperature and linear pressure(240℃ and 110 k N/m,respectively).This result suggested it was possible to achieve a significant reinforcement and improvement in the interfacial bonding of functional PPTA paper-based materials,and avoid the formation of unexpected pleats and cracks in PPTA paper-based materials during the hot calendering process.

Preparation of Highly Crystalline Microcrystalline Cellulose by Hydrolysis of Cellulose with Phosphotungstic Acid

Phosphotungstic acid(H_3PW_(12)O_(40), HPW), a kind of solid acid, is widely used for hydrolyzing cellulose to prepare microcrystalline cellulose(MCC). MCC is usually used in food, synthetic leather, chemical and pharmaceutical industries. The use of response surface methodology(RSM)can help avoid the random error caused by single factor experimental design,reduce test times and cost, and improve quality. The RSM was used in this study to determine the following optimal process conditions: H^+ molar quantity, 31 mmol/L; reaction temperature, 93℃; reaction time, 2 h; and solid to liquid ratio, 1∶38. Under these conditions, the crystallinity of MCC was77.4%. Thus, the use of RSM allows the preparation of MCC with higher performance and increased crystallinity.

Coaxing Polysaccharide Granules into Supramolecular Biocolloidal Additives for Papermaking

In light of developments in polysaccharide-based sustainable processes involving supramolecular interactions,we herein present our findings pertaining to coaxing polysaccharide granules into functional supramolecular biocolloids.Translucent biocolloidal dispersions containing various forms of starch are facilely designable,essentially built upon complexation between disassembled native cornstarch granules and amphiphilic ligands.Oily moieties of guest molecules are dynamically attractable into cavities of helical structures,with cationic groups pointing toward the bulk phase.This noncovalent attraction can generate core-shell biocolloidal particles.The significantly higher gelatinizability of freeze-dried biocolloids in contrast to native cornstarch granules is attributable to complex formation,and a homogenous dispersion is readily formable at room temperature.Our results also show biocolloids'ligand-related antibacterial activity.The use of biocolloids as wet-end additives for biofiber assemblies(cellulosic paper)can enhance mechanical strength,fines retention,and filler bondability.Supramolecular biocolloids with positively charged,translucent,easily gelatinizable,antibacterial,and polysaccharide-bondable functionalities would find tailorable use in the paper industry.

Foam Forming: An Effective Method to Prepare Polyimide Fiber-based Paper

Well-dispersed fiber suspension is the precondition of good paper formation. Compared with cellulosic fibers, synthetic fibers are prone to flocculate because of their long length and hydrophobic nature, resulting in poor paper formation. To solve this problem, dispersants and extremely low forming consistency are typically adopted during the traditional wet-forming process, which cause a large amount of water consumption and treatment cost. Therefore, increasing forming consistency without compromising paper formation remains a challenge for papermakers. In this work, foam forming was adopted to disperse polyimide fibers (PI) with high forming consistency. The results showed that the formation index of handsheets increased when the bubble size and distribution became small and narrow. Compared with traditional wet-forming process with the same consistency (0.4%), the formation index of handsheets by foam forming increased by approximately 100% when C8 alkyl glucoside (APG08) concentration reached 16 g/L. Notably, forming consistency could increase by eight times while keeping the same level of paper formation. Overall, foam forming exhibits great advantages in dispersing long fiber and reducing water consumption and environmental pressure, and has potential applications in specialty paper made of long fibers.

An overview of the switching parameter variation of RRAM

Resistive random access memory(RRAM) has been considered as one of the most promising candidates for next-generation nonvolatile memory, due to its advantages of simple device structure, excellent scalability, fast operation speed and low power consumption. Deeply understanding the physical mechanism and effectively controlling the statistical variation of switching parameters are the basis of fostering RRAM into commercial application. In this paper, based on the deep understanding on the mechanism of the formation and rupture of conductive filament, we summarize the methods of analyzing and modeling the statistics of switching parameters such as SET/RESET voltage, current, speed or time. Then, we analyze the distributions of switching parameters and the influencing factors. Additionally, we also sum up the analytical model of resistive switching statistics composed of the cell-based percolation model and SET/RESET switching dynamics. The results of the model can successfully explain the experimental distributions of switching parameters of the Ni O- and Hf O2-based RRAM devices. The model also provides theoretical guide on how to improve the uniformity and reliability such as disturb immunity. Finally, some experimental approaches to improve the uniformity of switching parameters are discussed.

CMOS兼容的晶圆级硅锥阵列局域化细丝形成以实现极佳阻变存储器均一性

具有高密度三维集成特点的阻变存储器(RRAM)是下一代非易失性存储技术的有利竞争者之一.然而,导电细丝形成和断裂的随机性导致了RRAM均一性差的问题,这严重阻碍了RRAM芯片的大规模商用.目前,已有部分研究通过引入锥形结构,减少RRAM中导电细丝形成和断裂的随机性.但是,这些方法往往步骤繁琐、成本较高或分辨率有限,限制了这些技术的大规模推广.本研究提出了一种CMOS兼容的、可在纳米尺度调控的晶圆级硅锥阵列(SSA)制备方法.该方法可制备不同曲率半径的SSA,用于调控RRAM中的导电细丝.高分辨率透射电子显微镜和能量色散谱表征结果表明,SSA结构诱导器件在尖端区域形成准单根或少量的导电细丝,显著改善了器件转变参数的均一性.此外,减小尖端区域的曲率半径可显著提升器件转变电压和高/低阻态的分布均一性及器件阻态的保持特性等.器件转变参数均一性的改善归因于尖端区域内的局域电场增强效应.本研究所提出的SSA方法具备低成本、CMOS兼容且纳米尺度可控的特点,为高均一性RRAM器件的大规模集成提供了一种参考策略.