Preparation of syndiotacticity-rich high molecular weight poly(vinyl alcohol) microfibrillar fiber by photoinitiated bulk polymerization and saponification

Vinyl pivalate (VPi) was polymerized in bulk by ultraviolet-ray initiation at low temperatures using 2,2′-azobis(2,4-dimethylvaleronitrile) (ADMVN) and 2,2'-azobis(isobutyronitrile) (AIBN) as photoinitiators. High molecular weight (HMW) poly(vinyl pivalate) (PVPi), having a number-average degree of polymerization (P_n) of 13,000–28,000, was obtained at conversions below 30% and converted by saponification to a syndiotacticity-rich HMW poly(vinyl alcohol) (PVA) microfibrillar fiber with P_n of 7300–18,300, syndiotactic diad (S-diad) and triad contents of ∼ 64% and ∼ 39%, respectively, and crystal melting temperature (T_m) of ∼ 249°C. ADMVN gave higher P_n than AIBN. On the other hand, conversion was smaller with the former than with the latter, and it was found that the initiation rate of ADMVN was lower than that of AIBN. P_n of PVA was constant while P_n of the precursor PVPi increased with increasing conversion. The syndiotacticity, T_m and thermal stability of PVA obtained from PVPi were much superior to those of PVA derived from poly(vinyl acetate) prepared under the same polymerization conditions. Polymerization of VPi at lower temperatures gave PVA with higher syndiotacticity. © 1997 John Wiley & Sons, Inc.     

The Structures of Colour String for e+e－→qqg and γ→3g

In Lund model,the explanation of e⁺e^－→qqg→3 jets and γ→3g→h's is based on applying Lund string fragmentation model to their assumed structures of colour string for qqg and 3g systems.In this paper,starting from the colour wave functions of qqg and 3g systems,we study these colour string structures by QCD directly.The results reveal the reasonableness and accuracy of Lund string pictures.     

STUDY OF QUASI-MOLECULE RESONANCE OF CHAIN CONFIGURATION INDUCED BY 6Li(d,dd) α REACTION AT LOW ENERGY

⁶Li(d,dd) α reaction induced by 7.3—10.6MeV deuterons was studied under collinear condition.An enhancement in differential cross section beyond the well known QFS and FSI contribution was observed at incident energy of 9MeV.It is the state of quasi-molecule resonance of chain configuration.     

Highly Fluorinated and Crosslinkable Dendritic Polymer for Photonic Applications

Summary: A novel crosslinkable dendritic polymer has been synthesized by the thermal polymerization of peripheral aryl trifluorovinyl ether moieties of a highly fluorinated dendrimer. The resulting perfluorocyclobutane(PFCB)‐containing dendritic polymer exhibited excellent processability, low optical loss (0.36 dB · cm⁻¹ at 1 310 nm with 1% dye doping), high thermal stability, and good solvent resistance for waveguide‐based photonic applications.

Structure of the crosslinkable fluorinated dendrimer synthesized.     

Synthesis and properties of new Si?H-containing polymers

Poly[(methylsilylene)ethynylene] ( 1 ) and poly[2,5-thiophenediyl(methylsilylene)] ( 2 ) are prepared in good yields. Thermogravimetric analysis and differential scanning calorimetry indicate the Si H group to increase the pyrolysis residue yields. Gelation was achieved from polymer 1 to get improved preceramic materials. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2275–2282, 1998     

邻近基坑开挖顺序对既有隧道的变形影响分析

以邻近轨道交通2号线鼓外区间隧道的宁波绿地中心项目基坑为案例, 研究了基坑开挖对隧道水平位移、结构沉降、道床沉降的影响规律, 并利用PLAXIS程序分析了基坑分坑、分块开挖顺序对隧道变形的影响. 结果表明: 对隧道变形影响较大的是基坑与隧道之间的距离以及基坑分坑面积的大小, 两者呈线性关系; 开挖面积越大, 隧道变形越大; 基坑与隧道之间的距离越大, 变形越小. 邻近轨道交通的基坑开挖时, 应先远坑后近坑, 先小坑后大坑, 并采取跳挖的施工顺序. 具体研究成果可以为类似工程提供借鉴.     

微波消解ICP-AES法同时测定蒙药新-Ⅱ中多种微量元素及Ca/Mg,Cu/Zn比值的分析

采用微波消解ICP—AES法同时测定蒙药新-Ⅱ中Ca、Mg、Fe、Zn、Ni、Mn、Cu、Pb等15种微量元素,并对蒙药新-Ⅱ中Ca／Mg,Cu／Zn比值进行了初步的分析。结果表明,蒙药新-Ⅱ中含有多种微量元素,其中人体有益的微量元素Ca、Mg、Fe、Cu、Ni、Zn、Mn的量相对高,即Ca〉Mg〉Fe〉Mn〉Zn〉Ni〉Cu,而人体有害微量元素Cd、Pb、Ag的量相对较低,Ca／Mg和Cu／Zn比值分别为4．1760、0．6077。加标回收率在97．5％～105．5％之间,相对标准偏差RSD≤2．7％,检出限≤0．008μg／mL。     

Dissecting single-cell genomes through the clonal organoid technique

The revolution in genome sequencing technologies has enabled the comprehensive detection of genomic variations in human cells, including inherited germline polymorphisms, de novo mutations, and postzygotic mutations. When these technologies are combined with techniques for isolating and expanding single-cell DNA, the landscape of somatic mosaicism in an individual body can be systematically revealed at a single-cell resolution. Here, we summarize three strategies (whole-genome amplification, microdissection of clonal patches in the tissue, and in vitro clonal expansion of single cells) that are currently applied for single-cell mutational analyses. Among these approaches, in vitro clonal expansion, particularly via adult stem cell-derived organoid culture technologies, yields the most sensitive and precise catalog of somatic mutations in single cells. Moreover, because it produces living mutant cells, downstream validation experiments and multiomics profiling are possible. Through the synergistic combination of organoid culture and genome sequencing, researchers can track genome changes at a single-cell resolution, which will lead to new discoveries that were previously impossible.Subject terms: Genomic analysis, Genomics, Adult stem cells, Genetic techniques     

Post‐exposure delay stability for 193 nm single‐layer photoresist: Solvent effect

We investigated the effect of post‐exposure delay (PED) for poly[2‐(2‐hydroxyethyl)carboxylate‐5‐norbornene‐co‐2‐t‐butylcarboxylate‐5‐norborene‐co‐2‐carboxylic acid‐5‐norborene‐co‐maleic anhydride] [poly(HNC/BNC/NC/MA)] resist film, which formulated with photoacid generator (PAG) under the several solvents. The solvents used in this study were propylene glycol methyl ether acetate (PGMEA), isobutyl methyl ketone (IBMK), 2‐heptanone (2‐H), and (2‐methoxy)ethyl acetate (MEA). We have introduced a new concept of rheological approach to explain the solvent effect for PED by using rheometer and light scattering equipment. In the PGMEA solvent, the resist solution shows Newtonian behavior, but the other resist solutions show shear‐thinning behavior. The resist film prepared by the shear‐thinning solvent exhibited good PED stability. In order to explain these results, we conjectured that the resist polymer existed in long‐rod shape under the specific solvent and high shear rate. Also, we could obtain 0.16 μm L/S patterns in a severely amine‐contaminated environment (about 35 ppb) after 30 min PED by using this method. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 148–153, 2000     

电解二氧化锰在MgSO4溶液中的电化学行为

应用循环伏安法、恒流充放电、X射线衍射研究了电解二氧化锰在MgSO4溶液中的可充性和充放电过程晶体结构的变化.结果表明:电解二氧化锰具有一定的电化学循环性能;经过初始几次充放电循环后,达到稳定状态;充放电过程电解二氧化锰的γ-MnO2晶体结构可逆地发生变化,保证了电解二氧化锰的可充性.