我国人工皮革发展机遇的探讨

介绍了国外超细纤维人工皮革的产销与应用情况．追溯了国际上这一领域最新技术的进展．通过对国内未来几年市场需求的分析与预测，提出了应在高起点上发展我国人工皮革的思路。     

Biomimetic strain hardening in interpenetrating polymer network hydrogels

In this paper, we present the systematic development of mechanically enhanced interpenetrating polymer network (IPN) hydrogels with Young's moduli rivaling those of natural load-bearing tissues. The IPNs were formed by synthesis of a crosslinked poly(acrylic acid) (PAA) network within an end-linked poly(ethylene glycol) (PEG) macromonomer network. The strain-hardening behavior of these PEG/PAA IPNs was studied through uniaxial tensile testing and swelling measurements. The interaction between the independently crosslinked networks within the IPN was varied by (1) changing the molecular weight of the PEG macromonomer, (2) controlling the degree of PAA ionization by changing pH, and (3) increasing the polymer content in the PAA network. Young's moduli and the maximum stress-at-break of the swollen hydrogels were normalized on the basis of their polymer content. Strain hardening in the IPNs exhibited a strong dependence on the molecular weight of the first network macromonomer, the pH of the swelling buffer, as well as the polymer content of the second network. The results indicate that the mechanical enhancement of these IPNs is mediated by the strain-induced intensity of physical entanglements between the two networks. The strain can be applied either by mechanical deformation or by changing the pH to modulate the swelling of the PAA network. At pHs below the pK_a of PAA (4.7), entanglements between PEG and PAA are reinforced by interpolymer hydrogen bonds, yielding IPNs with high fracture strength. At pHs above 4.7, a “pre-stressed” IPN with dramatically enhanced modulus is formed due to ionization-induced swelling of the PAA network within a static PEG network. The modulus enhancement ranged from two-fold to over 10-fold depending on the synthesis conditions used. Variation of the network parameters and swelling conditions enabled “tuning” of the hydrogels' physical properties, yielding materials with water content between 58% and 90% water, tensile strength between 2.0 MPa and 12.0 MPa, and initial Young's modulus between 1.0 MPa and 19.0 MPa. Under physiologic pH and salt concentration, these materials attain “biomimetic” values for initial Young's modulus in addition to high tensile strength and water content. As such, they are promising new candidates for artificial replacement of natural tissues such as the cornea, cartilage, and other load-bearing structures.     

Activities of MFI-Supported Rhenium Catalysts for the Aromatization of Methane: Effect of Cationic Form of the Inorganic Carrier

MFI type inorganic carrier was used in two different cationic forms, hydrogen and calcium respectively. MFI-supported molybdenum and rhenium catalysts were prepared. The activities of the catalysts were compared for the aromatization reaction of methane. Higher activity values were attained with the catalysts supported on HZSM-5. Aromatics were also observed with the catalysts supported on CaZSM-5, despite their deficiency in acid sites. Highly dispersed rhenium is expected to be formed with the use of the inorganic carrier in calcium form. On the other hand, lower reaction rates were observed with rhenium supported on CaZSM-5, in spite of the improved dispersion of the active rhenium species on this catalyst. This was interpreted in terms of the critical role of the acid sites in the conversion of methane to aromatics, compared to the improved dispersion of the active metal.     

An improved technique for exfoliating and dispersing nanoclay particles into polymer matrices using supercritical carbon dioxide

An environmentally benign process, which uses supercritical carbon dioxide (sc-CO₂) as a processing aid, is developed in this work to help exfoliate and disperse nanoclay into the polymer matrices. The process relies on rapid expansion of the clay followed by direct injection into the extruder where the mixture is dispersed into the polymer melt. Results from the mechanical properties, rheological studies, and X-ray diffraction (XRD) show that this method represents a significant improvement relative to direct melt blending in single or twin-screw extruders or other methods using sc-CO₂. The greatest mechanical property response was a result of directly injecting pre-mixed sc-CO₂ and nanoclay into the polypropylene melt during extrusion. It was observed that for concentrations as high as 6.6 wt% (limited only by present process capabilities), XRD peaks were eliminated, suggesting a high degree of exfoliation. Mechanical properties such as modulus increased by as much as 54%. The terminal region of the dynamic mechanical spectrum was similar to that of the base polymer, contrary to what is frequently reported in the literature.     

Illumination invariant object tracking with adaptive sparse representation

Since the introduction of the sparse representation-based tracking method named ?₁ tracker, there have been further studies into this tracking framework with promised results in challenging video sequences. However, in the situation of large illumination changes and shadow casting, the tracked object cannot be modeled efficiently by sparse representation templates. To overcome this problem, we propose a new illumination invariant tracker based on photometric normalization techniques and the sparse representation framework. With photometric normalization methods, we designed a new illumination invariant template presentation for tracking that eliminates the illumination influences, such as brightness variation and shadow casting. For a higher tracking accuracy, we introduced a strategy that adaptively selects the optimum template presentation at the update step of the tracking process. The experiments show that our approach outperforms the previous ?₁ and some state-of-the-art algorithms in tracking sequences with severe illumination effects.     

The role of electrostatic interactions in the mechanism of peptide bond hydrolysis by a Ser-Lys catalytic dyad

General-base catalysis in the active site of serine proteasesis carried out by the imidazole side chain of a histidine. Duringformation of the transition state, an adjacent carboxylic acidgroup stabilizes the positive charge that forms on the general-basecatalyst and as a result contributes several orders of magnitudeto the catalytic efficiency of these enzymes. In the recentlydiscovered family of self-cleaving proteins exemplified by theLexA repressor of Escherichia coli, instead of the imidazoleof a histidine, the active-site general-base catalyst was foundto be the -amino of a lysine. The considerably higher capacityof the lysine side chain for proton acceptance raises interestingquestions concerning the role of electrostatic interactionsin the mechanism of proton transfer by this highly basic group.The negative charge elimination studies described here and theireffects on the k_max and pK of LexA self-cleavage are consistentwith a model in which electrostatic interactions between anacidic side chain and the general-base catalyst form a barrierto proton transfer. The implications are that the -amino group,unlike the imidazole group, is capable of effecting proton transferwithout the intervention of a countercharge.     

Application of Fuzzy Moving Sliding Surface Approach for Container Cranes

International Journal of Control, Automation and Systems - In this paper, we consider the fuzzy moving sliding surface anti-sway control problem for container cranes. We first introduce the dynamic...     

Phase evolution,crystal structure,and microwave dielectric properties of gillespite-type ceramics

A gillespite-structured MCuSi₄O₁₀ (M = Ba_1-xSr_x, Sr_1-xCa_x) ceramics with tetrahedral structure (P4/ncc) were prepared by solid-state reaction method. X-ray diffraction and thermogravimetry with differential scanning calorimetry (TG-DSC) were employed to study the phase synthesis process of BaCuSi₄O₁₀. Pure BaCuSi₄O₁₀ phase was obtained at 1075°C and decomposed into BaSiO₃, BaCuSi₂O₆, and SiO₂ when calcined at 1200°C. The relationships between the crystal structure and microwave dielectric properties of MCuSi₄O₁₀ ceramics were revealed based on the Rietveld refinement and P-V-L complex chemical bond theory. The dielectric constant (ε_r) decreased linearly with decreasing total bond susceptibility and ionic polarizability. Quality factor (Q × f) was closely dependent on bond strength and lattice energy. The temperature coefficient of resonant frequency (τ_f) was controlled by the stability of [CuO₄]⁶⁻ plane in MCuSi₄O₁₀. Optimum microwave dielectric properties were obtained for SrCuSi₄O₁₀ when sintered at 1100°C for 3 hours with a ε_r of 5.59, a Q × f value of 82 252 GHz, and a τ_f of −41.34 ppm/°C. Thus, SrCuSi₄O₁₀ is a good candidate for millimeter-wave devices.     

Near infrared light-induced disassembly of polymeric micelles based on methylene blue conjugated polyethylene glycol

Light-sensitive drug delivery systems are considered ideal for applications in the biomedical fields for their ability to release the payload in an on-demand spatiotemporal controlled manner through the manipulation of the light source. Among the broad radiation spectrum, near infrared (NIR) light is considered advantageous compared to UV and visible light, due to its inherently lower photodamage to normal tissues and deeper penetration to lesion areas. In this study, we report a successful synthesis of a polymer capable of undergoing partial degradation upon irradiation with NIR light by conjugating 10-N-carbamoyl linkage methylene blue (MB) moiety, a NIR photocleavable ligand, with polyethylene glycol (PEG). Through effective coupling of MB, a hydrophobic moiety, to the hydrophilic PEG molecule, an amphiphilic polymer was synthesized, as demonstrated by a lowered surface tension (55 mN/m at 0.1% wt/vol). Subsequently, photo-induced reversal of surface activity associated with self-assembled structure disruption, was displayed by surface tension measurements, size distribution analysis, and burst release profile of paclitaxel (PTX) from polymeric micelles upon the exposure to NIR irradiation.