54 resultados para Shi san jing.
em Chinese Academy of Sciences Institutional Repositories Grid Portal
Resumo:
Novel biodegradable poly(carbonate ester)s with photolabile protecting groups were synthesized by ring-opening copolymerization Of L-lactide (LA) with 5-methyl-5-(2-nitro-benzoxycarbonyl)-1,3-dioxan-2-one (MNC) with diethyl zinc (Et2Zn) as catalyst. The poly(L-lactide-co-5-methyl-5-carboxyl-1,3-dioxan-2-one) (P(LA-co-MCC)) was obtained by UV irradiation Of poly(L-lactide acid-co-5-methyl-5-(2-nitro-benzoxycarbonyl)-1,3-dioxan-2-one) (P(LA-co-MNC)) to remove the protective 2-nitrobenzyl group.
Resumo:
A series of novel poly(ester-carbonate)s bearing pendant allyl ester groups P(LA-co-MAC)s were prepared by ring-opening copolymerization Of L-lactide (LA) and 5-methyl-5-allyloxycarbonyl-1,3-dioxan-2-one (MAC) with diethyl zinc (ZnEt2) as initiator. NMR analysis investigated the microstructure of the copolymer. DSC results indicated that the copolymers displayed a single glass-transition temperature (T-g), which was indicative of a random copolymer, and the Tg decreased with increasing carbonate content in the copolymer.
Resumo:
A novel biodegradable poly(epsilon-caprolactone)-poly(ethylene glycol)-based polyurethanes (PCL-PEG-PU) with pendant amino groups was synthesized by direct coupling of PEG ester of NH2-protected-(aspartic acid) (PEG-Asp-PEG diols) and poly(epsilon-caprolactone) (PCL) diols with hexamethylene dissocyanate (HDI) under mild reaction conditions and by subsequent deprotection of benzyloxycarbonyl (Cbz) groups. GPC, H-1 NMR, and C-13 NMR studies confirmed the polymer structures and the complete deprotection. DSC and WXRD results indicated that the crystallinity of the copolymer was enhanced with increasing PCL diols in the copolymer. The content of amino group in the polymer could be adjusted by changing the molar ratio of PEG-Asp-PEG diols to PCL diols. Thus the results of this study provide a good way to prepare polyurethanes bearing hydrophilic PEG segments and reactive amino groups without complicated synthesis.
Resumo:
Novel poly(ester carbonate)s were synthesized by the ring-opening polymerization Of L-lactide and functionalized carbonate monomer 9-phenyl-2,4,8,10-tetraoxaspiro[5,5]undecan-3-one derived from pentaerythritol with diethyl zinc as an initiator. H-1 NMR analysis revealed that the carbonate content in the copolymer was almost equal to that in the feed. DSC results indicated that T-g of the copolymer increased with increasing carbonate content in the copolymer. Moreover, the protecting benzylidene groups in the copolymer poly(L-lactide-co-9-phenyl-2,4,8,10-tetraoxaspiro[5,5]undecan-3-one) were removed by hydrogenation with palladium hydroxide on activated charcoal as a catalyst to give a functional copolymer, poly(L-lactide-co-2,2-dihydroxylmethyl-propylene carbonate), containing pendant primary hydroxyl groups. Complete deprotection was confirmed by H-1 NMR and FTIR spectroscopy. The in vitro degradation rate of the deprotected copolymers was faster than that of the protected copolymers in the presence of proteinase K. The cell morphology and viability on a copolymer film evaluated with ECV-304 cells showed that poly(ester carbonate)s derived from pentaerythritol are good biocompatible materials suitable for biomedical applications.
Resumo:
Polymer blends of poly(methyl methacrylate) (PMMA) and poly(styrene-co-acrylonitrile) (SAN) with an acrylonitrile content of about 30 wt % were prepared by means of solution-casting and characterized by virtue of pressure-volume-temperature (PVT) dilatometry. The Sanchez-Lacombe (SL) lattice fluid theory was used to calculate the spinodals, the binodals, the Flory-Huggins (FH) interaction parameter, the enthalpy of the mixing, the volume change of the mixing, and the combinatorial and vacancy entropies of the mixing for the PMMA/SAN system. A new volume-combining rule was used to evaluate the close-packed volume per mer, upsilon*, of the PMMA/SAN blends. The calculated results showed that the new and the original volume-combining rules had a slight influence on the FH interaction parameter, the enthalpy of the mixing, and the combinatorial entropy of the mixing. Moreover, the spinodals and the binodals calculated with the SL theory by means of the new volume-combining rule could coincide with the measured data for the PMMA/SAN system with a lower critical solution temperature, whereas those obtained by means of the original one could not.
Resumo:
The phylogenetic relationships among 12 genera of treefrogs (Family, Rhacophoridae), were investigated based on a large sequence data set, including five nuclear (brain-derived neurotrophic factor, proopiomelanocortin, recombination activating gene 1, tyr
Resumo:
The evolution of flight is the most important feature of birds, and this ability has helped them become one of the most successful groups of vertebrates. However, some species have independently lost their ability to fly. The degeneration of flight abilit
Resumo:
Using next-generation sequencing technology alone, we have successfully generated and assembled a draft sequence of the giant panda genome. The assembled contigs (2.25 gigabases (Gb)) cover approximately 94% of the whole genome, and the remaining gaps (0.05 Gb) seem to contain carnivore-specific repeats and tandem repeats. Comparisons with the dog and human showed that the panda genome has a lower divergence rate. The assessment of panda genes potentially underlying some of its unique traits indicated that its bamboo diet might be more dependent on its gut microbiome than its own genetic composition. We also identified more than 2.7 million heterozygous single nucleotide polymorphisms in the diploid genome. Our data and analyses provide a foundation for promoting mammalian genetic research, and demonstrate the feasibility for using next-generation sequencing technologies for accurate, cost-effective and rapid de novo assembly of large eukaryotic genomes.
Resumo:
In this paper we report, to the best of our knowledge, the first experimental realization of distributed feedback (DFB) semiconductor lasers based on reconstruction-equivalent-chirp (REC) technology. Lasers with different lasing wavelengths are achieved simultaneously on one chip, which shows a potential for the REC technology in combination with the photonic integrated circuits (PIC) technology to be a possible method for monolithic integration, in that its fabrication is as powerful as electron beam technology and the cost and time-consuming are almost the same as standard holographic technology. (C) 2009 Optical Society of America
Resumo:
This paper presents a detailed study on the effects of carbon incorporation and substrate temperature on structural, optical, and electrical properties of p-type nanocrystalline amorphous silicon films. A p-nc-SiC: H thin film with optical gap of 1.92 eV and activation energy of 0.06 eV is obtained through optimizing the plasma parameters. By using this p-type window layer, single junction diphasic nc-SiC : H/a-Si : H solar cells have been successfully prepared with a V-oc of 0.94 eV.
Cloning and Characterization of an RNase-Related Protein Gene Preferentially Expressed in Rice Stems
Resumo:
本工作采用DSC方法、红外光谱方法、光学显微镜方法、小角激光光散射方法及X射线衍射和散射方法研究了聚(ε-已内酯)(PCL)/苯乙烯-丙烯腈共聚物(SAN)共混物的相容性、熔融行为、结晶过程及结晶形态。观察到PCL/SAN共混物在0~30%wt PCL组成范围内,表现出单一的玻璃化转变,这个转变界于两个纯组合的玻璃化转变之间。在红外光谱上观察到PCL的羰基峰随着SAN的混入移向低频率。说明PCL分子与SAN分子之间存在着特殊的相互作用。从熔点下降计算的相互作用参数结果表明,PCL/SAN共混物在热力学上是相容的。共混物中PCL的熔点下降表明SAN分子对于PCL熔融行为是有影响的,同时不同的退火条件对于PCL/SAN共混物的PCL熔点也是有影响的,退火温度越高相应的PCL熔点越高。在PPCL/SAN共混物体中,PCL的球晶生长速率类似于均聚物,并且随着SAN含量的增加球晶生长速率下降,说明SAN分子阻碍了PCL分子链段的迁移,并且可以从理论上模拟共物混物中PCL的线性生长速率。在结晶性的PCL/SAN共混物中,PCL是以球晶形式存在的,在不同的结晶条件下,产生不同的球晶形态。在慢速降温结晶条件,SAN的加入促使PCL片晶发生扭曲形成环状球晶,通过光学显微镜方法和光散射方法计算出扭曲周期,结果表明扭曲周期随着SAN含量的增加而减少,同时也表明球晶半径随着SAN含量的增加而减小。在等温结晶条件下,SAN的加入,使得PCL的球晶半径减小。X射线衍射结果表明SAN分子并不存在PCL晶体中,而小角X射线散射结果表明在共混物中,随着SAN含量的增加,PCL片晶中心之间距离(长周期)逐渐增加,而且片晶与无定形片层的界面是分明的。指出无定形相是存在在PCL的片晶之间。
Resumo:
本论文主要借助原子力显微镜(AFM)、X-射线光电子能谱(XPS)等实验手段,纳米尺度上在线原位地研究了高温临界组成PMMMA/SAN(50/50,w/w)共混薄膜体系,分析并探讨了此共混薄膜表面相分离及其超薄膜体系的润湿/去润湿和相分离行为。首先,从敲击式AFM中相位图的成像原理出发,建立了一个高温下用原位AFM定性鉴别不同聚合物的纳米尺寸微区的方法,即:先在基底(硅)上铺展一层非常平坦的单一组分(SAN)薄膜,再在此千膜上,通过旋涂由选择性溶剂(冰醋酸)配制的另一组分(PMMA)的极稀溶液,使之不能形成一层连续的完整膜,最后在高温(175℃)下用敲击模式的原子力显微镜(TM-AFM)检测相位图随退火时间的变化。得到在175℃的相位图中,PMMA富相比SAN的富相显得更暗,这为后续工作提供了定性鉴别相区的方法。其次,高温下用原位AFM研究了PMMA/SAN薄膜表面相分离过程,在线观察了相分离的归并过程,定量地得到了临界相分离温度,并给出了特征波矢对时间依赖关系的标度指数,划分了相分离动力学演变的不同阶段。对于膜厚约为130nm的体系,表面相分离的临界温度大约为165℃,其表面相分离的特征波矢与时间的标度关系q+(t)-t-n,在整个实验时间内,随时间的演变过程中,显示了两个不同的指数变化区,即前期很慢的n=0.13和后期的n=1/3。0.13的指数关系可能是由于表面聚合物链的几何受限及表面富集相把部分新生成的另一相覆盖所致,1/3的指数关系可以认为是由普遍的Brownian扩散所致。而对于膜厚为50曲的此组成共混薄膜,得到的标度关系与C汕n线性理论吻合得非常好的Spinodal Deposition(SD)表面相分离的初期,即n=0,这是由于降低膜厚 增加了共混物的相容性,提高了临界温度,从而减缓了相分离过程,使得在我 们观测的时间范围内更易观察到表面相分离的初期。再次,用阶梯式降温的好M和XPS,发现了PMMA/SAN体系原位和离位实验结果存在巨大差别的主要原因之一—润湿温度的存在。对PMMA/SAN(50/50,w/w,-130nm)共混薄膜体系,原位AFM的退火和准淬火实验表明, 虽然在高温和室温、真空和常态、原位和离位,相分离的聚合物共混薄膜表面 形貌变化不大,但是表面物理性质却有很大的区别。原位XPS实验表明,未经 任何处理的样品在185℃退火时,很快在离表面很薄的下面形成一层PMMA含 量远低于本体值的薄层,之后最表面的PMMA也往本体迁移,直至表面SAN 的含量远高于它的本体值。对已在175℃退火20hr的此样品,逐渐降温退火过 程的原位XPS表明,当退火温度降至145oC时,样品表面几乎完全被PMMA覆盖,很好地验证了Conlposto等提出的润湿温度的假设,即对此体系,润湿温 度是原位和离位存在巨大的差异的主要因素之一,这与原位AFM的实验结果也,存在很好的一致性。最后,高温下原位观察了硅基底上PMMA/SAN超薄膜(膜厚-Rg)的去润湿、相分离过程和PMMA在基底上的润湿过程,以及云母基底上的该体系高温下的稳定润湿行为。以硅为基底的PMM刀sAN共混超薄膜在155”c下发生了类 似sPinodal dewetting的去润湿,其原因可能是在垂直于基底的浓度梯度引起的表面组成的涨落,对这种去润湿的动力学还进行了探讨。以硅为基底的PMMA/SAN共混超薄膜在175℃下不仅发生了类似spinodal dewetting的去润 湿,而且还发生了去润湿液滴内部的相分离以及相分离析出的PMMA润湿硅基底的过程,提出了一个简单的模型描述了这种复杂的过程。此外,还研究了不同基底对此共混超薄膜体系的润湿行为进行了研究,以云母为基底的此共混体系在175℃下长时间内是稳定的,其原因可能是云母与PMMA和SAN均有很强的作用力,足于补偿聚合物链在构象嫡上的损失。