在2003年制定的H.264/AVC视频编码标准获得巨大的成功后,新一代视频编码国际标准HEVC(High Ef-ficiency Video Coding)在ITU-T的VCEG和ISO/IEC的MPEG通力合作下已经开发成功。HEVC提供了多项先进的视频编码技术。尽管HEVC的视频编码层...在2003年制定的H.264/AVC视频编码标准获得巨大的成功后,新一代视频编码国际标准HEVC(High Ef-ficiency Video Coding)在ITU-T的VCEG和ISO/IEC的MPEG通力合作下已经开发成功。HEVC提供了多项先进的视频编码技术。尽管HEVC的视频编码层结构仍然是常见的基于块运动补偿的混合视频编码模式,但是和先前的标准相比具有多处重要改进。文中对HEVC标准的技术的主要特点和性能进行了综述。展开更多
Ascorbyl octyl aldehyde acetals are prepared from the reaction of ascorbic acid with octyl aldehyde using p-toluene sulfonic acid as catalyst,dimethyl acetamide as solvent,cyclohexane as dehydration agent. The acetals...Ascorbyl octyl aldehyde acetals are prepared from the reaction of ascorbic acid with octyl aldehyde using p-toluene sulfonic acid as catalyst,dimethyl acetamide as solvent,cyclohexane as dehydration agent. The acetals are obtained as a mixt. of two diastereomers(ratio,0.46∶0.54) based on the results of 1H-NMR spectroscopic analysis. The antioxidation activity of ascorbyl octyl aldehyde acetals in fresh tea seed oil is evaluated by peroxide value(POV) determination. The POV data show that ascorbyl octyl aldehyde acetals exhibits signifcant dose-effect relationship. The antioxidation activity of ascorbyl octyl aldehyde acetals is stronger than that of VC or PG but weaker than that of TBHQ,when their amount in fresh tea seed oil is respectively added according to the maximum allowed concentration as food additives in China.展开更多
D-isoascorbyl myristate is synthesized by direct esterification from myristic acid and by transesterification from methyl myristate in the presence of con.H2SO4.The structure of the title compound is characterized by ...D-isoascorbyl myristate is synthesized by direct esterification from myristic acid and by transesterification from methyl myristate in the presence of con.H2SO4.The structure of the title compound is characterized by FT-IR and 1H-NMR.展开更多
Cyclohexanone L-ascorbic acid ketal is synthesized from the reaction of L-isoascorbic acid and cyclohexanone with p-toluene sulfonic acid as catalyst,N,N-dimethyl acetamide(DMAc) as solvent and cyclohexane as water ca...Cyclohexanone L-ascorbic acid ketal is synthesized from the reaction of L-isoascorbic acid and cyclohexanone with p-toluene sulfonic acid as catalyst,N,N-dimethyl acetamide(DMAc) as solvent and cyclohexane as water carrying agent.The optimal reaction conditions determined by orthogonal experiment are as follows:L-ascorbic acid 1.76 g(10 mmol),cyclohexanone 1.57 g(16 mmol),p-toluene sulfonic acid 0.38 g(2 mmol),DMAc 6 mL,cyclohexane 9 mL,reaction temperature 120～125℃ and reation time 2.5 h.The yield is 85.8% under these optimal conditions.The title compound is characterized by 1H NMR,FTIR and EI-MS.展开更多
文摘在2003年制定的H.264/AVC视频编码标准获得巨大的成功后,新一代视频编码国际标准HEVC(High Ef-ficiency Video Coding)在ITU-T的VCEG和ISO/IEC的MPEG通力合作下已经开发成功。HEVC提供了多项先进的视频编码技术。尽管HEVC的视频编码层结构仍然是常见的基于块运动补偿的混合视频编码模式,但是和先前的标准相比具有多处重要改进。文中对HEVC标准的技术的主要特点和性能进行了综述。
文摘Ascorbyl octyl aldehyde acetals are prepared from the reaction of ascorbic acid with octyl aldehyde using p-toluene sulfonic acid as catalyst,dimethyl acetamide as solvent,cyclohexane as dehydration agent. The acetals are obtained as a mixt. of two diastereomers(ratio,0.46∶0.54) based on the results of 1H-NMR spectroscopic analysis. The antioxidation activity of ascorbyl octyl aldehyde acetals in fresh tea seed oil is evaluated by peroxide value(POV) determination. The POV data show that ascorbyl octyl aldehyde acetals exhibits signifcant dose-effect relationship. The antioxidation activity of ascorbyl octyl aldehyde acetals is stronger than that of VC or PG but weaker than that of TBHQ,when their amount in fresh tea seed oil is respectively added according to the maximum allowed concentration as food additives in China.
文摘D-isoascorbyl myristate is synthesized by direct esterification from myristic acid and by transesterification from methyl myristate in the presence of con.H2SO4.The structure of the title compound is characterized by FT-IR and 1H-NMR.
文摘Cyclohexanone L-ascorbic acid ketal is synthesized from the reaction of L-isoascorbic acid and cyclohexanone with p-toluene sulfonic acid as catalyst,N,N-dimethyl acetamide(DMAc) as solvent and cyclohexane as water carrying agent.The optimal reaction conditions determined by orthogonal experiment are as follows:L-ascorbic acid 1.76 g(10 mmol),cyclohexanone 1.57 g(16 mmol),p-toluene sulfonic acid 0.38 g(2 mmol),DMAc 6 mL,cyclohexane 9 mL,reaction temperature 120～125℃ and reation time 2.5 h.The yield is 85.8% under these optimal conditions.The title compound is characterized by 1H NMR,FTIR and EI-MS.
