设计了一种新型高能量密度化合物2,6-双(二硝基亚甲基)-1,3,4,5,7,8-六硝基十二氢二咪唑[4,5-b:4',5'-e]吡嗪(DNNIP)。首先在B3PW91/6-31G++(d,p)水平下对目标分子进行优化,通过键长和键级的比较分析,判断母环的五元环侧链处N—...设计了一种新型高能量密度化合物2,6-双(二硝基亚甲基)-1,3,4,5,7,8-六硝基十二氢二咪唑[4,5-b:4',5'-e]吡嗪(DNNIP)。首先在B3PW91/6-31G++(d,p)水平下对目标分子进行优化,通过键长和键级的比较分析,判断母环的五元环侧链处N—NO2键为分解引发键,其键解离能是96.40 k J/mol;然后,基于静电势改进的蒙特卡洛法推测出该化合物的理论密度为2.07 g/cm3,采用等键反应计算出生成热为1 907.33 k J/mol,并进一步计算出DNNIP的爆速为10.35 km/s,爆压为51.47 GPa,爆轰性能明显优于现有常见含能材料。DNNIP的撞击感度为12 cm,与CL-20接近;能级差为0.158 78 a.u.(4.32 e V),光热稳定性较高,并且通过态密度分析认为硝基是分子中相对敏感位置。展开更多
以2,3,5,6-四氨基吡啶三盐酸盐一水合物(TAP·3HCl·H2O)和2,5-二羟基对苯二甲酸(DHTA)为单体,合成聚[2,5-二羟基-1,4-苯撑吡啶并二咪唑](PIPD),并采用干喷湿纺法制备了PIPD初生纤维,初生纤维在温度400℃,张力33 c N/dtex的条...以2,3,5,6-四氨基吡啶三盐酸盐一水合物(TAP·3HCl·H2O)和2,5-二羟基对苯二甲酸(DHTA)为单体,合成聚[2,5-二羟基-1,4-苯撑吡啶并二咪唑](PIPD),并采用干喷湿纺法制备了PIPD初生纤维,初生纤维在温度400℃,张力33 c N/dtex的条件下进行热处理得到PIPD纤维,研究了PIPD纤维的结构与性能。结果表明:PIPD初生纤维的线密度为959.6 tex,拉伸强度为2.15 GPa,拉伸模量为154.2 GPa;热处理后的PIPD纤维较初生纤维致密程度有所提高,线密度和拉伸强度有所下降,拉伸模量提高,热稳定性较好;纺丝原液脱泡良好、提高纺丝组件的温度均一性以及降低纤维中残酸量可进一步提高PIPD纤维的性能。展开更多
A repeated sequence DNA fragment, L5B-4, was cloned from the 5 kb BamHI DNA fragments of rat genomic DNA. The expressions of the L5B-4 DNA fragment are different in liver and hepatoma cells. The amounts of transcripts...A repeated sequence DNA fragment, L5B-4, was cloned from the 5 kb BamHI DNA fragments of rat genomic DNA. The expressions of the L5B-4 DNA fragment are different in liver and hepatoma cells. The amounts of transcripts in hepatoma cells are lower in nucleus and higher in cytoplasm, especially in polysomal RNA, as compared with that in liver cells. The alteration shown in polysomal RNA of hepatoma cells seems to be specific. These results are discussed with respect to the possible function of this repeated DNA and its variation in hepatoma cells.展开更多
A group of the mesogen jacketed liquid crystal polymers based on the monomers 2,5-bis (4-substituted benzoyl)oxystyrenes are synthesized. The substituents include alkoxy, alkyl, and cyano groups. The synthesis and the...A group of the mesogen jacketed liquid crystal polymers based on the monomers 2,5-bis (4-substituted benzoyl)oxystyrenes are synthesized. The substituents include alkoxy, alkyl, and cyano groups. The synthesis and the primary characterization of the liquid crystal phase of the monomers and the polymers are described. While some of the monomers give smectic textures the polymers are found to be nematic above their melting or glass transition temperatures. Interestingly the unsubstituted monomer and its polymer poly 2,5-di( benzoyloxy ) styrene are also liquid crystalline. The single crystal structure of one of the monomers is also discussed.展开更多
The high melting point and strong chemical bonding of NbB_(2)pose a great challenge to the preparation of high-density nanostructured NbB_(2)composite coating.Herein,we report a novel,simple,and efficient method to fa...The high melting point and strong chemical bonding of NbB_(2)pose a great challenge to the preparation of high-density nanostructured NbB_(2)composite coating.Herein,we report a novel,simple,and efficient method to fabricate in-situ NbB_(2)–NbC–Al_(2)O_(3)composite coating by plasma spraying Nb_(2)O_(5)–B_(4)C–Al composite powder,aiming at realizing the higher densification and ultra-fine microstructure of NbB_(2)composite coating.The microstructure and properties of in-situ NbB_(2)–NbC–Al_(2)O_(3)composite coating were studied comparatively with ex-situ NbB_(2)–NbC–Al_(2)O_(3)composite coating(plasma spraying NbB_(2)–NbC–Al_(2)O_(3)composite powder).The reaction mechanism of Nb_(2)O_(5)–B_(4)C–Al composite powder in plasma jet was analyzed in detail.The results showed that the in-situ nanostructured NbB_(2)–NbC–Al_(2)O_(3)composite coating presented a lower porosity and superior performance including higher microhardness,toughness and wear resistance compared to the plasma sprayed ex-situ NbB_(2)–NbC–Al_(2)O_(3)coating and other boride composite coatings.Densification of the in-situ NbB_(2)–NbC–Al_(2)O_(3)coating was attributed to the low melting point of Nb_(2)O_(5)–B_(4)C–Al composite powder and the exothermic effect of in-situ reaction.The superior performance was ascribed to the density improvement and the strengthening and toughening effect of the nanosized phases.The in-situ reaction path could be expressed as:Nb_(2)O_(5)+Al®Nb+Al_(2)O_(3),and Nb+B_(4)C®NbB_(2)+NbC.展开更多
文摘设计了一种新型高能量密度化合物2,6-双(二硝基亚甲基)-1,3,4,5,7,8-六硝基十二氢二咪唑[4,5-b:4',5'-e]吡嗪(DNNIP)。首先在B3PW91/6-31G++(d,p)水平下对目标分子进行优化,通过键长和键级的比较分析,判断母环的五元环侧链处N—NO2键为分解引发键,其键解离能是96.40 k J/mol;然后,基于静电势改进的蒙特卡洛法推测出该化合物的理论密度为2.07 g/cm3,采用等键反应计算出生成热为1 907.33 k J/mol,并进一步计算出DNNIP的爆速为10.35 km/s,爆压为51.47 GPa,爆轰性能明显优于现有常见含能材料。DNNIP的撞击感度为12 cm,与CL-20接近;能级差为0.158 78 a.u.(4.32 e V),光热稳定性较高,并且通过态密度分析认为硝基是分子中相对敏感位置。
文摘A repeated sequence DNA fragment, L5B-4, was cloned from the 5 kb BamHI DNA fragments of rat genomic DNA. The expressions of the L5B-4 DNA fragment are different in liver and hepatoma cells. The amounts of transcripts in hepatoma cells are lower in nucleus and higher in cytoplasm, especially in polysomal RNA, as compared with that in liver cells. The alteration shown in polysomal RNA of hepatoma cells seems to be specific. These results are discussed with respect to the possible function of this repeated DNA and its variation in hepatoma cells.
文摘A group of the mesogen jacketed liquid crystal polymers based on the monomers 2,5-bis (4-substituted benzoyl)oxystyrenes are synthesized. The substituents include alkoxy, alkyl, and cyano groups. The synthesis and the primary characterization of the liquid crystal phase of the monomers and the polymers are described. While some of the monomers give smectic textures the polymers are found to be nematic above their melting or glass transition temperatures. Interestingly the unsubstituted monomer and its polymer poly 2,5-di( benzoyloxy ) styrene are also liquid crystalline. The single crystal structure of one of the monomers is also discussed.
基金The authors gratefully acknowledge the financial supports of the National Natural Science Foundation of China(No.52072110)the Natural Science Foundation of Hebei Province(No.E2018202034).
文摘The high melting point and strong chemical bonding of NbB_(2)pose a great challenge to the preparation of high-density nanostructured NbB_(2)composite coating.Herein,we report a novel,simple,and efficient method to fabricate in-situ NbB_(2)–NbC–Al_(2)O_(3)composite coating by plasma spraying Nb_(2)O_(5)–B_(4)C–Al composite powder,aiming at realizing the higher densification and ultra-fine microstructure of NbB_(2)composite coating.The microstructure and properties of in-situ NbB_(2)–NbC–Al_(2)O_(3)composite coating were studied comparatively with ex-situ NbB_(2)–NbC–Al_(2)O_(3)composite coating(plasma spraying NbB_(2)–NbC–Al_(2)O_(3)composite powder).The reaction mechanism of Nb_(2)O_(5)–B_(4)C–Al composite powder in plasma jet was analyzed in detail.The results showed that the in-situ nanostructured NbB_(2)–NbC–Al_(2)O_(3)composite coating presented a lower porosity and superior performance including higher microhardness,toughness and wear resistance compared to the plasma sprayed ex-situ NbB_(2)–NbC–Al_(2)O_(3)coating and other boride composite coatings.Densification of the in-situ NbB_(2)–NbC–Al_(2)O_(3)coating was attributed to the low melting point of Nb_(2)O_(5)–B_(4)C–Al composite powder and the exothermic effect of in-situ reaction.The superior performance was ascribed to the density improvement and the strengthening and toughening effect of the nanosized phases.The in-situ reaction path could be expressed as:Nb_(2)O_(5)+Al®Nb+Al_(2)O_(3),and Nb+B_(4)C®NbB_(2)+NbC.
