Testing primitivity on partial words

Primitive words, or strings over a finite alphabet that cannot be written as a power of another string, play an important role in numerous research areas including formal language theory, coding theory, and combinatorics on words. Testing whether or not a word is primitive can be done in linear time in the length of the word. Indeed, a word is primitive if and only if it is not an inside factor of its square. In this paper, we describe a linear time algorithm to test primitivity on partial words which are strings that may contain a number of “do not know” symbols. Our algorithm is based on the combinatorial result that under some condition, a partial word is primitive if and only if it is not compatible with an inside factor of its square. The concept of special, related to commutativity on partial words, is foundational in the design of our algorithm. A World Wide Web server interface at http://www.uncg.edu/mat/primitive/ has been established for automated use of the program.     

Compatibility and universality of the retention prediction system for polycyclic aromatic hydrocarbons in reversed-phase liquid chromatography

Summary System-compatibility and universality of the retention prediction concept has been investigated for polycyclic aromatic hydrocarbons in reversed-phase liquid chromatography. The results clearly indicate that the retention prediction approach has a very high potential for optimization of separation conditions in almost all reversed-phase systems, and allows more precise and rapid analysis. This approach may be one of the best optimization techniques, because the system does not require any standard materials.     

端不饱和羧基环氧丙烷聚醚与苯乙烯共聚物的微相分离

用端乙烯基液体聚合物作单体可制得各种多嵌段多相聚合物.本文在端不饱和羧基环氧丙烷液体聚醚与苯乙烯共聚物互溶性研究的基础上,对分子运动进行了进一步的研究.用膨胀仪、红外、应力-应变和DSC确定和测定其中的组分分离运动,阐述组分分离对互溶性的影响.     

NMR STUDY ON THE COMPATIBILITY OF ACR/PVC BLENDS

A 300MHz solid NMR study on the compatibility of ACR (poly (methyl methacrylate-co-methacrylate), in the ratio of 1:1)-PVC (poly (vinyl chloride)) blends is reported. Spin-lattice (T_1) and spin-spin (T_2) relaxation time of ACR, PVC and their blends are recorded in the temperature range from 215K to 355K. Experimental results indicate that ACR and PVC are compatible with each other and the domain size is smaller than 25 nm, but heterogeneit(?)s of molecular dimensions still exist. Some problems of mechanism of compatibility and data analysis are also discussed.     

VISCOMETRIC STUDY OF POLY(METHYL METHACRYLATE) AND POLYSTYRENE BLENDS IN DIFFERENT SOLVENTS

The intermolecular interaction between poly(methyl methacrylate) (PMMA) and polystyrene (PS) intetrahydrofuran (THF) and N,N'-dimethyl formamide (DMF) solvents was studied at 28℃ using a dilute solution viscometrymethod. Solvent is believed to play a key role in characterizing the viscosity behavior of the polymer solution. The intrinsicviscosity and viscosity interaction parameter were experimentally measured for the binary (solvent/polymer) and for theternary systems in two solvents. The compatibility of the polymer mixture was discussed in terms of the sign of △b_m. Theresults show that the compatibility of PMMA/PS blend in DMF is larger than that in THF.     

聚氧化乙烯-聚苯乙烯-聚氧化乙烯三嵌段共聚物/聚苯醚共混物的相容性和结晶行为

本工作对聚氧化乙烯-聚苯乙烯-聚氧化乙烯(PEO-PS-PEO)三嵌段共聚物与聚苯醚(PPO)均聚物共混物的相容性及结晶行为进行了研究。结果表明,共混体系的相容性与嵌段共聚物中苯乙烯段的含量有关,PS含量越高,PPO与共聚物PS段的相容性越好。共混体系的结晶行为也明显不同于一般均聚物共混体系。在DSC降温结晶过程中最多可出现三个结晶峰。     

COMPATIBILITY AND PHASE BEHAVIOR OF PS/SBR BLENDS H. TORSIONAL BRAID ANALYSIS

The compatibility and phase behavior of PS/SBR blends was studied with torsional braid analysis technique. The technique used in this study for preparation of braids was first developed by one of the authors, which gives more precise phase diagram as compared to other conventional methods. The results obtained are in good agreement with those obtained in our previous work.     

Effect of P(MMA-co-MAA) compatibilizer on the miscibility of nylon 6/PVDF blends

With the ultimate objective of enhancing the impact strength and weatherability of nylon 6 engineering plastic, blending with poly(vinylidene fluoride) (PVDF) was studied. In the absence of a compatibilizer the two polymers phase separate, resulting in a deterioration of the properties. Since poly(methyl methacrylate) is known to be miscible with PVDF, we evaluated poly(methyl methacrylate-co-methacrylic acid) (P(MMA-co-MAA)) of low methacrylic acid content as the compatibilizer. The carboxylic acid groups in the MAA units were expected to react with the end amino groups of nylon 6 forming block or graft copolymers, P(MMA-co-MAA)-g-nylon 6, in situ, which will function as the actual compatibilizer. The amount of P(MMA-co-MAA) added, the MMA/MAA composition and heat treatment time were varied to study their effects on the miscibility, morphology, and mechanical properties of nylon 6/PVDF blends. The enhancement of the compatibility of nylon 6 and PVDF by addition of P(MMA-co-MAA) and the partial miscibility of nylon 6 and PVDF has been confirmed through DSC, dynamic mechanical testing, SEM of fracture surfaces, and tensile testing. The decrease in the crystallization temperatures on addition of compatibilizer in DSC experiments suggests that the compatibilizer enhances the interaction between the two components and retards the crystallization. The dynamic mechanical thermal analysis experiments suggest that the compatibility in the amorphous regions of nylon 6 and PVDF in particular has been enhanced. The increase in the heat treatment time in the molten state resulted in further enhancement of the miscibility. The enhancement of compatibility by addition of a reactive compatibilizer and heat treatment resulted in a significant increase in the energy of rupture in tensile testing.     

紫外光同步固化合成互穿聚合物网络研究

互穿聚合物网络是研制高阻尼材料的理想结构,但从目前国内外文献报道的同步法互穿网络体系来看,由于在制备中采用了两种不同的聚合方法,实际上在形成网络结构的过程中都不是十分理想的同步反应,其反应速度均存在着一定程度的差别。     

Interfacial effect on photo-oxidation of PP via model blends

The interface in multiphase material plays an important role not only in mechanical properties, but also in aging behavior. This article uses polypropylene/polymethyl methacrylate (PP/PMMA) and polypropylene/polystyrene (PP/PS) blends (PMMA and PS as dispersion phase) as models to investigate the interfacial effect on the photo-oxidative aging of PP. The chemical property and stability of dispersed phase could make big difference on aging behavior of PP. PMMA, with polar functional group at the interface, accelerated the photo-oxidation of PP, while PS, with inert functional group at the interface, had little influence. Both the dispersion phases have little effects on crystallization of PP and the oxygen diffusion. The photo degradation product of PMMA could help to initiate or accelerate aging of PP mainly via free radicals transfer. Grafting reaction happened in the interface and the interfacial cohesion of PP and PMMA enhanced thereby.