An XPS study of pulsed plasma polymerised allyl alcohol film growth on polyurethane

The growth of highly functionalised poly allyl alcohol films by pulsed plasma polymerisation of CH₂CHCH₂OH on biomedical grade polyurethane has been followed by X-ray photoelectron spectroscopy (XPS) and contact angle measurements. Film thickness is observed to increase approximately linearly with plasma modification time, suggesting a layer-by-layer growth mode of poly allyl alcohol. Water contact angle measurements reveal the change in the surface free energy of wetting decreases linearly with plasma modification up to the monolayer point after which a constant limiting value of −24 mJ m⁻² was attained. Films prepared at 20 W plasma power with a duty cycle of 10 μs:500 μs exhibit a high degree of hydroxyl (OH) retention with minimal fragmentation of the monomer observed. Increasing the plasma power up to 125 W is found to improve OH retention at the expense of ether formation generating films close to the monomer stoichiometry. Duty cycle plays an important role in controlling both film composition and thickness, with longer off times increasing OH retention, while longer on times enhance allyl alcohol film growth.     

Study on hydrophilicity of polymer surfaces improved by plasma treatment

Surface properties of polycarbonate (PC), polypropylene (PP), polyethylene terephthalate (PET) samples treated by microwave-induced argon plasma have been studied with contact angle measurement, X-ray photoelectron spectroscopy (XPS) and scanned electron microscopy (SEM). It is found that plasma treatment modified the surfaces both in composition and roughness. Modification of composition makes polymer surfaces tend to be highly hydrophilic, which mainly depended on the increase of ratio of oxygen-containing group as same as other papers reported. And this experiment further revealed that CO bond is the key factor to the improvement of the hydrophilicity of polymer surfaces. Our SEM observation on PET shown that the roughness of the surface has also been improved in micron scale and it has influence on the surface hydrophilicity.     

On the Lyapunov stability for SIRS epidemic models with general nonlinear incidence rate

We study an epidemic model for infections with non permanent acquired immunity (SIRS). The incidence rate is assumed to be a general nonlinear function of the susceptibles and the infectious classes. By using a peculiar Lyapunov function, we obtain necessary and sufficient conditions for the local nonlinear stability of equilibria. Conditions ensuring the global stability are also obtained. Unlike the recent literature on this subject, here no restrictions are required about the monotonicity and concavity of the incidence rate with respect to the infectious class. Among the applications, the noteworthy case of a convex incidence rate is provided.     

Textbook representations of radian angle measure: The need to build on the quantitative view of angle

Empirical studies of angle, angle measure, and radian angle measure have primarily focused on documenting students' and teachers' conceptions. Representations of angle measure have the potential to inform and build on these conceptions. To gain insight into the concept of radian angle measure from a curricular perspective, I investigated the representations of radian angle measure in eight widely used U.S. high school mathematics textbooks. The data for this study are the 20 figures and the 8 definitions of radian angle measure in the textbooks. Inductive content analysis was used to identify the frequency of observable characteristics in the representations. Textbook figures of radian angle measure most frequently focus on a one-radian angle. Textbook figures also demonstrated radian angle measures in terms of π, in standard position, even when the Cartesian-coordinate plane was not in the figure. The frequently used characteristics of radian representations could inadvertently reinforce a qualitative concept of angle, instead of fostering the quantitative attributes of radian angle measure. Moving forward, analyzing conceptions that are evoked by the frequently used representations of radian angle measure could build a link between evidence from this study and studies of learning.     

Global analysis for an epidemical model of vector-borne plant viruses with disease resistance and nonlinear incidence

Vector-borne disease models play an important role in understanding the mechanism of plant disease transmission. In this paper, we study a vector-borne model with plant disease resistance, disease exposed period and nonlinear incidence. We compute the basic reproduction number, determine the implicit locations of equilibria and then investigate their global stability by generalizing a classic geometric approach to higher dimensional systems. Higher dimensions cause greater difficulties such as the construction of the transformation matrix and the estimate of the $Lozinski\tilde{\iota}$ measure in this geometric approach. For a complete control of vector-borne diseases, a quantitative way is provided by the given expression of the basic reproduction number, from which we need not only increasing plant disease resistance but also decreasing the contact rate between infected plants and susceptible vectors instead of a single one of them.     

A New Green Thermoplastic Polymer with Improved Hydrophobic Character

Summary: A green thermoplastic polymer based on wheat flour was modified by the addition of a natural crosslinker genipin. Films of the polymer modified with different composition of genipin were prepared by extrusion. Free surface energy using contact angle method, moisture absorption test and hardness test were used to characterize the products. From moisture absorption and contact angle measurements, it was seen that for genipin amounts higher than 0.2% w/w, a hydrophobic character is achieved. Results obtained indicate enhancement in hydrophobic properties of the films.     

基于改进灰色关联度的IOWA算子最优组合预测模型

通过引进诱导有序加权平均(IOWA)算子和改进灰色关联度的计算式,提出了新的基于改进灰色关联度的IOWA算子的组合预测模型.方法可以克服传统的组合预测方法赋予不变的加权平均系数和以单一误差指标作为预测精度衡量的缺陷.定义基于改进灰色关联度的IOWA算子的优性组合预测的概念,最后给出实例分析表明了新模型能有效地提高组合预测精度.     

Surface structure and properties of poly-(ethylene terephthalate) hydrolyzed by alkali and cutinase

This study was aimed at comparatively investigating the hydrolysis of crystalline and amorphous poly-(ethylene terephthalate) films by alkali and cutinase. Changes of surface properties were investigated by FTIR spectroscopy (ATR mode). The A₁₃₄₁/A₁₄₁₀ and I₁₁₂₀/I₁₁₀₀ absorbance ratios, and the full width at half maximum of the carbonyl stretching band (FWHM₁₇₁₅) were used to evaluate the polymer crystallinity and its changes upon hydrolysis. The effect of different treatments on chain orientation was evaluated by calculating R ratios of appropriate bands. The spectroscopic indexes showed that both alkali and enzyme treatments induced structural and conformational rearrangements with a consequent increase in crystallinity in both amorphous and crystalline films. The crystalline PET film was modified more strongly by alkali than by cutinase, while the opposite occurred for the amorphous one. The trend of the water contact angle (WCA) clearly indicates that alkali is more effective than cutinase in enhancing hydrophilicity of PET films and that the effect is stronger on amorphous than on crystalline films. The values of WCA correlate well with the FTIR indexes calculated from the spectra of hydrolyzed crystalline PET films. The mechanism of the surface hydrolysis of PET by alkali and cutinase is discussed.     

Effect of L64 on the Phase Behavior of 1-Dodecyl-3-methylimidazolium Chloride/Water System

Phase behavior of ternary system involving surfactant‐like ionic liquid 1‐dodecyl‐3‐methylimidazolium chloride ([C₁₂mim]Cl), water, and nonionic surfactant PEO‐PPO‐PEO block copolymer (Pluronic L64) is investigated at 25°C. Hexagonal (H₁) and lamellar liquid crystal phase (Lα) are found in [C₁₂mim]Cl/H₂O/L64 system by using polarized optical microscopy (POM), small‐angle X‐ray scattering (SAXS) techniques and ²H NMR spectra. The phase structure (H₁ phase), which is formed in [C₁₂mim]Cl/H₂O binary system, is not changed when L64 with a low concentration is added. However, phase transitions will occur from hexagonal to multiphases of H₁ and cubic phases (C), then to Lα+C phases with constant [C₁₂mim]Cl/H₂O ratio and increasing L64 concentration. Moreover, at given L64 (5%, 20%) concentration, the lattice parameter of H₁ or Lα phase decreases with increasing [C₁₂mim]Cl/H₂O ratio. Fourier transform infrared (FTIR) spectra indicate that the H‐bonded network comprising an imidazolium ring, chloride ion and water formed in [C₁₂mim]Cl/H₂O binary system is disrupted upon addition of L64. This is helpful to the phase transition, due to the decreasing of interfacial curvature induced by dehydration of hydrated layer after the addition of PEO block of L64.