Three model polyurethane hard segments based on dimethylol butanoic acid (DMBA) and 1,6-hexane diisocyanate (HDI), toluene diisocyanate (TDI) and 4,4'-diphenylmethane diisocyanate (MDI) were prepared by the soluti...Three model polyurethane hard segments based on dimethylol butanoic acid (DMBA) and 1,6-hexane diisocyanate (HDI), toluene diisocyanate (TDI) and 4,4'-diphenylmethane diisocyanate (MDI) were prepared by the solution method. Fourier Infrared (FTIR) spectroscopy was employed to study the H-bonds in these model polyurethanes. The model polyurethane hard segment prepared from HDI and 1,4-butanodiol (BDO) was used for comparison. It was found that the incorporation of the pendent carboxyl through DMBA into the model hard segments weakens the original NH…O = C H-bond but gives more H-bond patterns based on the two H-bond donors, urethane NH and carboxylic OH. The carboxylic dimer is one of the main H-bond types and is stronger than another main H-bond type NH…O=C. In addition, the H-bond in aromatic model hard segments is stronger than that of aliphatic hard segments. The appearance of the free C=O and the fact that almost all N—H is H-bonded suggest that there possibly exist either the third H-bond acceptor or the H-bond formed by one acceptor with two donors.展开更多
Polyester-based biodegradable polyurethane （PU） with different hard segment ratios was selected to modify the impact toughness of poly（L-lactide） （PLLA）. The influence of blending composition and hard segment ra...Polyester-based biodegradable polyurethane （PU） with different hard segment ratios was selected to modify the impact toughness of poly（L-lactide） （PLLA）. The influence of blending composition and hard segment ratio of PU on the phase morphology, crystallization behavior and mechanical properties of PLLA/PU blends has been investigated systematically. The results showed that the PU particles were uniformly dispersed in PLLA matrix at a scale from sub- microns to several microns. The glass transition temperature of PU within these blends decreased compared to that of neat PU, but rose slightly with its content and hard segment ratio. The presence of PU retarded the crystallization ability of PLLA, whereas enhanced its elongation at break and impact resistance effectively. As the PU content reaches up to 30 wt%, the phenomenon of brittle-ductile transition occurred, resulting in a rougher fracture surface with the formation of fibril-like structure. Moreover, under the same concentrations, the elongation at break and impact strength of PLLA blends decreased slightly with the increase of hard segment ratio of PU.展开更多
The thermally stimulated shape memory behavior of ethylene oxide-butylene terephthalate (EOBT) segmented copolymers with different soft segment molecular weight and hard segment content was investigated. The deformati...The thermally stimulated shape memory behavior of ethylene oxide-butylene terephthalate (EOBT) segmented copolymers with different soft segment molecular weight and hard segment content was investigated. The deformation recovery ratio R-f of the EOBT samples increases with the soft segment molecular weight and the hard segment weight content, while the average overall deformation recovery speed V-r increases with the hard segment content. The temperature of maximum deformation recovery speed (T-M) is determined by the melting temperature of the soft segment crystals and the stability of the crystallized hard segment domains.展开更多
· AIM: To describe a new surgical technique for managing dislocated sclerotic cataractous lens.· METHODS: Six patients with advanced posteriorly dislocated cataracts were operated at a tertiary care centre a...· AIM: To describe a new surgical technique for managing dislocated sclerotic cataractous lens.· METHODS: Six patients with advanced posteriorly dislocated cataracts were operated at a tertiary care centre and analyzed retrospectively. After standard 3 port23 G pars plana vitrectomy and perfluorocarbon liquid(PFCL) injection, the dislocated white cataract was held with occlusion using phaco fragmatome and then chopped into smaller pieces with a sharp tipped chopper using 25 G chandelier endoilluminator. Each piece was emulsified individually. Following aspiration of PFCL,Fluid Air Exchange was done in all the cases and surgery completed uneventfully.·RESULTS: Best corrected visual acuity(BCVA) in all the patients was better than 6/12 after one month of follow up. No serious complications were noted till minimum 6mo of follow up.·CONCLUSION: Four port posterior segment nucleotomy with a chandelier endoilluminator, fragmatome and a chopper appears to be a safe, easy and effective procedure for managing dislocated sclerotic cataractous nuclei. Ultrasonic energy used and adverse thermal effects of the fragmatome on the sclera may be lesser.展开更多
为研究曲线段大直径盾构隧道在上软下硬地层对管片上浮的影响,针对曲线段盾构隧道施工开挖面支护力、管片上浮的施工风险因素进行研究,采用极限平衡法研究开挖面支护力稳定性的影响,对开挖产生的不规则类棱台型土体进行横向竖向受力分析...为研究曲线段大直径盾构隧道在上软下硬地层对管片上浮的影响,针对曲线段盾构隧道施工开挖面支护力、管片上浮的施工风险因素进行研究,采用极限平衡法研究开挖面支护力稳定性的影响,对开挖产生的不规则类棱台型土体进行横向竖向受力分析,建立静力平衡方程,求解开挖面处于极限平衡时的极限支护力.进一步研究开挖面支护力、曲线段大直径盾构隧道在上软下硬地层掘进对管片上浮的影响,并且分析影响管片上浮的地质以及盾构掘进姿态等因素,提出相应盾构管片上浮综合控制措施.结果表明:当破裂角φ_(1)=29.0°,φ_(2)=25.5°时,极限支护力T=128.5 k Pa.应合理控制盾构掘进姿态,保证合理的支护力,防止在上软下硬地层大直径盾构盾尾注浆滞后以及浆液硬化滞后,隧道产生偏离曲线掘进轴线的上下摆动,造成管片上浮;对于上浮比较严重的区域,可以采用双液注浆法,阻止管片上浮;对于已经产生管片上浮的区域,可以采取“上压下放”的方式增加隧道的配重或采用抗拔装置施加外力来抵抗地下水上浮量.展开更多
基金This work was supported by the Natural Science Foundation of Henan Province (004030600)
文摘Three model polyurethane hard segments based on dimethylol butanoic acid (DMBA) and 1,6-hexane diisocyanate (HDI), toluene diisocyanate (TDI) and 4,4'-diphenylmethane diisocyanate (MDI) were prepared by the solution method. Fourier Infrared (FTIR) spectroscopy was employed to study the H-bonds in these model polyurethanes. The model polyurethane hard segment prepared from HDI and 1,4-butanodiol (BDO) was used for comparison. It was found that the incorporation of the pendent carboxyl through DMBA into the model hard segments weakens the original NH…O = C H-bond but gives more H-bond patterns based on the two H-bond donors, urethane NH and carboxylic OH. The carboxylic dimer is one of the main H-bond types and is stronger than another main H-bond type NH…O=C. In addition, the H-bond in aromatic model hard segments is stronger than that of aliphatic hard segments. The appearance of the free C=O and the fact that almost all N—H is H-bonded suggest that there possibly exist either the third H-bond acceptor or the H-bond formed by one acceptor with two donors.
基金financially supported by the National Natural Science Foundation of China(No.51403210)China Postdoctoral Science Foundation(No.2014M550801)President Fund of University of Chinese Academy of Sciences(No.Y35102CN00)
文摘Polyester-based biodegradable polyurethane （PU） with different hard segment ratios was selected to modify the impact toughness of poly（L-lactide） （PLLA）. The influence of blending composition and hard segment ratio of PU on the phase morphology, crystallization behavior and mechanical properties of PLLA/PU blends has been investigated systematically. The results showed that the PU particles were uniformly dispersed in PLLA matrix at a scale from sub- microns to several microns. The glass transition temperature of PU within these blends decreased compared to that of neat PU, but rose slightly with its content and hard segment ratio. The presence of PU retarded the crystallization ability of PLLA, whereas enhanced its elongation at break and impact resistance effectively. As the PU content reaches up to 30 wt%, the phenomenon of brittle-ductile transition occurred, resulting in a rougher fracture surface with the formation of fibril-like structure. Moreover, under the same concentrations, the elongation at break and impact strength of PLLA blends decreased slightly with the increase of hard segment ratio of PU.
文摘The thermally stimulated shape memory behavior of ethylene oxide-butylene terephthalate (EOBT) segmented copolymers with different soft segment molecular weight and hard segment content was investigated. The deformation recovery ratio R-f of the EOBT samples increases with the soft segment molecular weight and the hard segment weight content, while the average overall deformation recovery speed V-r increases with the hard segment content. The temperature of maximum deformation recovery speed (T-M) is determined by the melting temperature of the soft segment crystals and the stability of the crystallized hard segment domains.
文摘· AIM: To describe a new surgical technique for managing dislocated sclerotic cataractous lens.· METHODS: Six patients with advanced posteriorly dislocated cataracts were operated at a tertiary care centre and analyzed retrospectively. After standard 3 port23 G pars plana vitrectomy and perfluorocarbon liquid(PFCL) injection, the dislocated white cataract was held with occlusion using phaco fragmatome and then chopped into smaller pieces with a sharp tipped chopper using 25 G chandelier endoilluminator. Each piece was emulsified individually. Following aspiration of PFCL,Fluid Air Exchange was done in all the cases and surgery completed uneventfully.·RESULTS: Best corrected visual acuity(BCVA) in all the patients was better than 6/12 after one month of follow up. No serious complications were noted till minimum 6mo of follow up.·CONCLUSION: Four port posterior segment nucleotomy with a chandelier endoilluminator, fragmatome and a chopper appears to be a safe, easy and effective procedure for managing dislocated sclerotic cataractous nuclei. Ultrasonic energy used and adverse thermal effects of the fragmatome on the sclera may be lesser.
文摘为研究曲线段大直径盾构隧道在上软下硬地层对管片上浮的影响,针对曲线段盾构隧道施工开挖面支护力、管片上浮的施工风险因素进行研究,采用极限平衡法研究开挖面支护力稳定性的影响,对开挖产生的不规则类棱台型土体进行横向竖向受力分析,建立静力平衡方程,求解开挖面处于极限平衡时的极限支护力.进一步研究开挖面支护力、曲线段大直径盾构隧道在上软下硬地层掘进对管片上浮的影响,并且分析影响管片上浮的地质以及盾构掘进姿态等因素,提出相应盾构管片上浮综合控制措施.结果表明:当破裂角φ_(1)=29.0°,φ_(2)=25.5°时,极限支护力T=128.5 k Pa.应合理控制盾构掘进姿态,保证合理的支护力,防止在上软下硬地层大直径盾构盾尾注浆滞后以及浆液硬化滞后,隧道产生偏离曲线掘进轴线的上下摆动,造成管片上浮;对于上浮比较严重的区域,可以采用双液注浆法,阻止管片上浮;对于已经产生管片上浮的区域,可以采取“上压下放”的方式增加隧道的配重或采用抗拔装置施加外力来抵抗地下水上浮量.
