A study of fucoidan from the brown seaweed Chorda filum

Fucoidan fractions from the brown seaweed Chorda filum were studied using solvolytic desulfation.Methylation analysis and NMR spectroscopy were applied for native and desulfated polysaccharides.Homefucan sulfate from C.filum was shown to contain poly-a-(1-3)-fucopyranoside backbone with a high degree of branching,mainly of a-(1-2)-linked single units.Some fucopyranose residues are sulfated at O-4(mainly) and O-2 positions.Some a-(1-3)-linked fucose residues were shown by NMR to be 2-O-acetylated.The 1H and 13C NMR spectra of desulfated,deaceylated fucan were complerely assigned.THe spectral data obtained correspond to a quasiregular polysaccharide structure with a branched hexasaccharide repeating unit.Other fucoidan frations from C.filum have more complex carbohydrate composition and give rather complex methvlation patterns.

两种施氮水平下不同基因型冬小麦叶片光合特性与形态差异的研究

田间试验研究不施N和施N(90kg/hm2)条件下“NR9405”、“9430”、“偃师9号”、“小偃6号”、“陕229”、“西农2208”、“矮丰3号”和“商188”等8种不同基因型冬小麦中后期生理特性及其叶片形态的差异结果表明,抽穗期倒二叶和灌浆期旗叶的净光合速率、气孔导度、蒸腾速率及瞬时水分利用效率在不同基因型间存在显著差异,施N仅能显著降低抽穗期倒二叶的蒸腾速率,而对功能叶的其他生理指标无明显影响。小麦成熟期旗叶和倒二叶的长度、宽度及叶面积在不同基因型间也存在极显著差异,施N对这些叶片形态指标有极显著地促进作用,基因型和N肥同时影响灌浆期旗叶的SPAD值,而叶片衰老指数主要受基因型调控。总体上看,冬小麦叶片形态指标同时受施N和基因型影响,而生理指标主要受基因型影响,N肥的影响相对较小。

基于分支时序逻辑的编译优化测试用例自动生成方法的研究与实现

编译器是软件产业中重要的工具，对它的质量保证非常重要。编译优化是编译器的重要功能，它的质量对于编译器质量有重大影响。可采用软件测试的方法进行编译器优化模块的质量保证。测试需要测试用例。编译优化的测试用例必须触发编译器的优化功能，是具有可被优化特征的源程序。对不同的编译优化，该特征各不相同。需要将不同优化所对应的特征加入到源程序中以构造编译优化测试用例程序。 TRANS语言结合了时序逻辑，描述了不同的编译优化，包括优化前后的代码特征、优化执行的条件及方法。优化前的代码特征和执行优化的条件可被用作构造编译优化测试用例程序所需的特征。一种基于时序逻辑的编译优化测试用例程序生成方法的框架已被提出。该方法从TRANS描述的某种变体生成编译优化测试用例程序。但是该框架并未完善，面临多方面的问题。本文参考该框架的思想，设计了编译优化测试用例程序生成方法，解决了算法框架的部分问题。该方法可以适应复杂描述的情况；公式的合法性及语义得以保持；具体化并完整化了原有框架。该方法是具有针对性的编译优化测试用例程序自动生成方法。本文对该方法作了原型系统实现，并从中得到测试用例程序。本文设计并进行针对GCC的优化模块测试实验，以覆盖率为评价指标检验了测试用例程序的质量。实验表明该方法生成的测试用例程序具有针对性。对编译优化模块的测试，该方法是一种行之有效的办法。并且该方法仍有更多的应用空间，加以改进后可用于优化组合测试、优化正确性检测等。

Characterization of the Microstructure of Bimodal HDPE Resin

In this work, two industrial bimodal high density polyethylene resins, resin A and resin B having similar molecular weight (M-w), molecular weight distribution (M-wD), and short-chain branching (SCB) content but different mechanical properties, were fractionated through cross-fractionation. The fractions were further, characterized by GPC, C-13 NMR, DSC AND FT IR techniques. These two resins were firstly fractionated into two franctions, i.e. high-temperature and low temperature fractions, via preparative solution crystallization fractionation. Resin A with much better mechanical properties contains more high-temperature fractions with longer crystalizable sequences. The SCB content in the low temperature fraction of resin A is lower than the of resin B. Both low-temperature fractions were then further fractionated using solvent gradient fractionation (SGF). The characterization of SGF fraction indicates that most of the branches fall into the high molecular weight chain in both low-temperature fractions.

A Novel Strategy to Branched Polyacrylonitrile Via One-Pot RAFT Copolymerization of Acrylonitrile and an Asymmetrical Divinyl Monomer

Branched polyacrylonitriles were prepared via the one-pot radical copolymerization of acrylonitirle and an asymmetric divinyl monomer (allyl methacrylate) that possesses both a higher reactive methacrylate and a lower reactive allyl. RAFT technique was used to keep a low-propagation chain concentration via a fast reversible chain transfer euilibration and thus the cross-linking was prevented until a high level of monomer conversions. This novel strategy was demonstrated to engenerate a branched architecture with abundant pendant functional vinyl and nitrile groups, and controlled molecular weight as a behavior of controlled/living radical polymerization characteristics. The effect of the various experimental parameters, including temperature, brancher to monomer molar ratio, and chain transfer agent to initiator molar ratio, on the control Of moleculer dimension (molecular weight and polydispersity indices) and the degree of branching were investigated in detail. Moreover, H-1 NMR and gel permeation chromatography confirm the branched architecture of the resultant polymer. The intrinsic viscosity of the copolymer is also lower than the linear counterpart.

Syntheses and ethylene polymerization behavior of supported salicylaldimine-based neutral nickel(II) catalysts

Two novel salicylaldimine-based neutral nickel(II) complexes, [(2,6-iPr(2)C(6)H(3))NCH(2-ArC6H3O)]Ni(PPh3)Ph (6, Ar = 2-(OH)C6H4; 8, Ar = 2-OH-3-(2,6-iPr(2)C(6)H(3)NCH)C6H3), have been synthesized, and their structures have also been confirmed by X-ray crystallography, elemental analysis, and H-1 and C-13 NMR spectra. An important structural feature of the two complexes is the free hydroxyl group, which allows them to react with silica pretreated with trimethylaluminum under immobilization by the formation of a covalent bond between the neutral nickel(II) complex and the pretreated silica. As active single-component catalysts, the two complexes exhibited high catalytic activities up to 1.14 and 1.47 x 10(6) g PE/mol(Ni)center dot h for ethylene polymerization, respectively, and yielded branched polymers. Requiring no cocatalyst, the two supported catalysts also showed relatively high activities up to 4.0 x 10(5) g PE/mol(Ni)center dot h and produced polyethylenes with high weight-average molecular weights of up to 120 kg/mol and a moderate degree of branching (ca. 13-26 branches per 1000 carbon atoms).

Reversible addition-fragmentation chain transfer mediated radical polymerization of asymmetrical divinyl monomers targeting hyperbranched vinyl polymers

Reversible addition-fragmentation chain transfer (RAFT) mediated radical polymerizations of allyl methacrylate and undecenyl methacrylate, compounds containing two types of vinyl groups with different reactivities, were investigated to provide hyperbranched polymers. The RAFT agent benzyl dithiobenzoate was demonstrated to be an appropriate chain-transfer agent to inhibit crosslinking and obtain polymers with moderate-to-high conversions. The polymerization of allyl methacrylate led to a polymer without branches but with five- or six-membered rings. However, poly(undecenyl methacrylate) showed an indication of branching rather than intramolecular cycles. The hyperbranched structure of poly(undecenyl methacrylate) was confirmed by a combination of H-1, C-13, H-1-H-1 correlation spectroscopy, and distortionless enhancement by polarization transfer 135 NMR spectra. The branching topology of the polymers was controlled by the variation of the reaction temperature, chain-transfer-agent concentration, and monomer conversion. The significantly lower inherent viscosities of the resulting polymers, compared with those of linear analogues, demonstrated their compact structure,

Facile syntheses and characterization of hyperbranched poly(ester-amide)s from commercially available aliphatic carboxylic anhydride and multihydroxyl primary amine

A new method for synthesis of novel hyperbranched poly(ester-amide)s from commercially available AA' and CBx type monomers has been developed on the basis of a series of model reactions. The hyperbranched poly(ester-amide)s with multihydroxyl end groups are prepared by thermal polycondensation of carboxyl anhydrides (AA') and multihydroxyl primary amine (CBx) without any catalyst and solvent. The reaction mechanism in the initial stage of polymerization was investigated with in situ H-1 NMR. In the initial stage of the reaction, primary amino groups of 2-amino-2-ethyl-1,3-propanediol (AEPO) or tris(hydroxymethyl)aminomethane (THAM) react rapidly with anhydride, forming an intermediate which can be considered as a new AB(x) type monomer. Further self-polycondensation reactions of the AB. molecules produce hyperbranched polymers. Analysis using H-1 and C-13 NMR spectroscopy revealed the degree of branching of the resulting polymers ranging from 0.36 to 0.55. These hyperbranched poly(ester-amide)s contain configurational isomers observed by C-13 and DEPT C-13 NMR spectroscopy, possess high molecular weights with broad distributions and display glass-transition temperatures (T(g)s) between 7 and 96 degreesC.

Synthesis and characterization of hyperbranched poly(ester-amide)s based on gallic acid and DL-2-aminobutyric acid

A novel AB(3)-type monomer was prepared from gallic acid and DL-2-aminobutyric acid, and used for the synthesis of the biocompatible hyperbranched poly(ester-amide)s by self-polycondensation. The polymers were characterized via FTIR and NMR spectroscopy and thermal analysis, and the average degree of branching of the polymers was estimated to be 0.75. The polymers with abundant acetyl end groups were found to be amorphous with lower intrinsic viscosity, better thermal stability and excellent solubility.

Structural analysis of saponins from medicinal herbs using electrospray ionization tandem mass spectrometry

The underivatized saponins from Tribulus terrestris and Panax ginseng have been investigated by electrospray ionization multi-stage tandem mass spectrometry (ESI-MSn). In ESI-MS spectra, a predominant [M + Na](+) ion in positive mode and [M - H](-) ion in negative mode were observed for molecular mass information. Multi-stage tandem mass spectrometry of the molecular ions was used for detailed structural analysis. Fragment ions from glycoside cleavage can provide information on the mass of aglycone and the primary sequence and branching of oligosaccharide chains in terms of classes of monosaccharides. Fragment ions from cross-ring cleavages of sugar residues can give some information about the linkages between sugar residues. It was found that different alkali metal-cationized adducts with saponins have different degrees of fragmentation, which may originate from the different affinity of a saponin with each alkali metal in the gas phase. ESI-MSn has been proven to be an effective tool for rapid determination of native saponins in extract mixtures, thus avoiding tedious derivatization and separation steps.

Seed-mediated synthesis of branched gold nanoparticles with the assistance of citrate and their surface-enhanced Raman scattering properties

We report an easy synthesis of highly branched gold particles through a seed-mediated growth approach in the presence of citrate. The addition of citrate in the growth solution is found to be crucial for the formation of these branched gold particles. Their size can be varied from 47 to 185 nm. The length of the thumb-like branch is estimated to be between about 5 and 20 nm, and changes slightly as the particle size increases. Owing to these obtuse and short branches, their surface plasmon resonance displays a marked red-shift with respect to the normal spherical particles. These branched gold particles exhibit stronger SERS activity than the non-branched ones, which is most likely related to these unique branching features.

Synthesis and characterization of hyperbranched aromatic poly(ether imide)s

The four AB(2) monomers, N-[3- or 4-bis(4-hydroxyphenyl)toluoyl]-4-chlorophthalimide and N-{3- or 4-[1,1-bis(4-hydroxyphenyl)]ethylphenyl}-4-chlorophthalimides, were prepared and used for synthesis of hyperbranched poly(ether imide)s bearing hydroxyl end groups. These hyperbranched poly(ether imide)s had moderate molecular weights with broad distributions and showed glass-transition temperatures (Tgs) between 177 and 230 degreesC. The thermogravimetric analytic measurement revealed the decomposition temperature at 5% weight-loss temperatures (T-d(5%)) ranging from 240 to 281 degreesC. Analysis using H-1 NMR spectroscopy revealed the four types of hyperbranched poly(ether imide)s to have similar degrees of branching (ca. 60%). These polymers were modified by acylation or nucleophilic substitution reaction at the hydroxyl end groups. The conversion effectiveness depended on the type of modification reaction, modifier, and reaction conditions. The thermal stability and solubility of hyperbranched poly(ether imide)s were improved by the modification of the end groups.

Characterization of the microstructure of biaxially oriented polypropylene using preparative temperature-rising elution fractionation

Two commercial biaxially oriented polypropylene (BOPP) resins, resin A and resin B, having different processing properties, were fractionated by preparative temperature-rising elution fractionation (TREF). The TREF fractions were further characterized by gel permeation chromatography (GPC), gel permeation chromatography coupled with light scattering (GPC-LS), wide-angle X-ray diffraction (WAXD), and differential scanning calorimetry (DSC). GPC-LS did not find visible long-chain branching in either resin A or B. The results from TREF and DSC indicate that the fractional melting parameter f(T) may be used to predict the profile of the TREF cumulative weight distribution curve. GPC results show that the molecular weights of the fractions tend to increase with elution temperature. WAXD and DSC data show that the crystallinity of fractions does not increase monotonically with increase of elution temperature. There appears to be a maximum in the plot of crystallinity versus elution temperature. The high-speed BOPP resin A has a lower isotacticity but a homogeneous isotacticity distribution and a higher molecular weight but a broader molecular weight distribution than resin B.

Non-isothermal crystallization behavior and kinetics of metallocene short chain branched polyethylene

The non-isothermal crystallization behavior and kinetics of metallocene short chain branched polyethylene were investigated via DSC at cooling rates from 2.5 to 20 degreesC/min, and subsequent heating at rate of 10 degreesC/min. To verify the effect of molecular weight and branching content on crystallization, three group samples were chosen: (1) linear polyethylene with low molecular weight and high molecular weight; (2) low molecular weight polyethylene with low branching content and high branching content; (3) high molecular weight polyethylene with low branching content and high branching content. The results show that crystallization temperature, crystallinity, melting temperature and crystallization rate are highly branching content-dependent. Molecular weight effect is less important, compared to branching content. A dramatic decrease of crystallization temperature, crystallinity, crystallization rate and melting temperature was observed for branched samples. The non-isothermal kinetics was analyzed via the methods, developed by Gupta and Mo Zhi-shen, and good agreement was obtained.

Polydispersity of ethylene sequence length in metallocene ethylene/alpha-olefin copolymers. I. Characterized by thermal-fractionation technique

In this article, the polydispersity of the ethylene sequence length (ESL) in ethylene/alpha-olefin copolymers was studied by atomic force microscopy (AFM) and the thermal-fractionation technique. The crystal morphology observation by AFM showed that morphology changed gradually with decreasing average ESL from complete lamellae over shorter and more curved lamellae to a granular-like morphology, and the mixed morphology was observed after stepwise crystallization from phase-separated melt. This result indicated that the ethylene sequence with different lengths crystallized into a crystalline phase with a different size and stability at the copolymer systems. The thermal-fractionation technique was used to characterize the polydispersity of ESL. Three of the following statistical terms were introduced to describe the distribution of ESL and the lamellar thickness: the arithmetic mean (L) over bar (n), the weight mean (L) over bar (w), and the broadness index I = (L) over bar (w)/(L) over bar (n). It was concluded that the polydispersity of ESL could be quantitatively characterized by the thermal-fractionation technique. The effects of temperature range, temperature-dependent specific heat capacity C-p of copolymer, and the molecular weight on the results of thermal fractionation were discussed,