A measurement of the ^235U prompt fission neutron spectrum (PFNS) by the recoil proton method was performed at the Institute of Nuclear Physics and Chemistry, China. Details of the method, which include the calculatio...A measurement of the ^235U prompt fission neutron spectrum (PFNS) by the recoil proton method was performed at the Institute of Nuclear Physics and Chemistry, China. Details of the method, which include the calculation and validation of the response matrix, are presented. The PFNS for ^235U in the energy range 1–12 MeV, induced by thermal neutrons, was obtained. The measured spectrum in the low-energy region was in good agreement with previous work and the ENDF/B-VII library, except for minor differences. In the high-energy region, however, the relative height of the measured spectrum was greater, and an analysis of the experiment indicated uncertainties of 13% at 10 MeV and 24% at 12 MeV. Experimental results showed that the recoil proton method could be used to measure prompt fission neutron spectra. Some directions for future work are included.展开更多
This paper reviewed studies on remote sensing of water depth retrieval. Four water depth retrieval models （single-band, dou- ble-ratio-band, multi-band, and BP network models） were evaluated using TM image and water...This paper reviewed studies on remote sensing of water depth retrieval. Four water depth retrieval models （single-band, dou- ble-ratio-band, multi-band, and BP network models） were evaluated using TM image and water data from Bangong Co Lake, which is located in China＇s Tibet Autonomous Region and Indian Kashmir. Tested by independent data, comparison of these four models demonstrates that BP network model performed better than the multi-band model, with the single-band model performing the worst. To sum up, this study demonstrates that first, BP network model performed better than the traditional model; second, precise atmospheric correction and radiation study, affected by different water level sand sediment, could improve the precision of water depth retrieval.展开更多
The cross sections of the^(169)Tm(n,2n)^(168)Tm reaction have been measured at incident energies of 12 to 19.8 MeV using the activation technique,relative to the^(93)Nb(n,2n)^(92)mNb reaction.Thulium(Tm)samples were i...The cross sections of the^(169)Tm(n,2n)^(168)Tm reaction have been measured at incident energies of 12 to 19.8 MeV using the activation technique,relative to the^(93)Nb(n,2n)^(92)mNb reaction.Thulium(Tm)samples were irradiated on the surface of a two-ring orientation assembly with neutrons produced from the^(3)H(d,n)^(4)He reaction at the 5SDH-21.7-MV Tandem accelerator in China.Theoretical model calculations were performed.The present data were then compared with previous experimental data and available evaluated data.This study provides more precise nuclear data for improvement of future evaluations.展开更多
【目的】研究低出生体重儿在生后24月龄内发生追赶性生长时其体质量指数(body mass index,BMI)的变化规律。【方法】采用出生队列方法,选择嘉定区2016年1月—2016年12月出生的户籍和常住儿童中自愿加入0~24月龄随访研究中的低出生体重儿...【目的】研究低出生体重儿在生后24月龄内发生追赶性生长时其体质量指数(body mass index,BMI)的变化规律。【方法】采用出生队列方法,选择嘉定区2016年1月—2016年12月出生的户籍和常住儿童中自愿加入0~24月龄随访研究中的低出生体重儿(出生体重<2500 g)126人,根据出生体重和孕周分为早产适于胎龄儿组73人、足月小于胎龄儿组53人;选择同地区、孕周37~41周、出生体重2500~3999 g 105人为对照组。比较3组婴幼儿生后0~24月龄间BMI均数、标准差的差异,分析男女婴幼儿在0~24月龄间BMI曲线的变化。【结果】①共纳入231人,男童111人,女童120人;②2组低出生体重儿在出生和2月龄阶段BMI均值均低于对照组,早产适于胎龄儿从4月龄开始BMI与对照组无明显差异,但是足月小于胎龄儿组BMI指数在4~18月龄间始终低于早产适于胎龄儿组别和对照组,差异有统计学意义(P<0.05);③3组婴幼儿BMI指数在生后均呈现快速上升,在4~6月龄时达高峰,7~9月龄BMI数值开始下降,早产适于胎龄儿在6月龄BMI的比较中便赶上正常体重儿童的BMI值,而足月小于胎龄儿一直到24月龄仍与正常体重儿童的BMI值有差异,但是3组间的差值有缩小。男女性别间BMI上升曲线相似,但早产适于胎龄儿女童组别高峰值延长。【结论】低出生体重儿的BMI存在追赶性增长现象,其后期变化趋势与正常出生体重儿相似。在儿童早期生长发育阶段,应给予低出生体重儿喂养方面的合理指导和干预。展开更多
Glucose oxidase(GOD)has many practical applications,but its poor thermostability limits its broader use.In this research,three primary mutants of wild-type GOD were designed using rational mutagenesis,and the GODm mut...Glucose oxidase(GOD)has many practical applications,but its poor thermostability limits its broader use.In this research,three primary mutants of wild-type GOD were designed using rational mutagenesis,and the GODm mutant was constructed by combinatorial design.The expression,purifcation,and enzymatic properties of the mutants were studied.The specifc enzyme activity of GODm was 2.10-fold higher than that of wild type,and the(k_(cat)/K_(m))value was increased by 1.45-fold.After treatment at 55℃for 3 h,GODm retained 37.5%of its enzymatic activity,and the half-life(t_(1/2))of GODm at 55℃and 65℃was 2.28-fold and 3.36-fold higher than that of wild type,respectively.By analyzing the three-dimensional structure of wild type and the GODm mutant,it was found that T30V formed a new hydrogen bond with FAD and strengthened the hydrophobic interaction,D315K optimized the surface electrostatic interaction,and A162T improved the efciency of the electron pathway.Thus,a novel mutant with improved thermostability and catalytic efciency was obtained in this research.展开更多
(2S)-Sakuranetin is a 7-O-methylflavonoid that has anticancer,antiviral,and antimicrobial activities.Methylation process is involved in biosynthesizing(2S)-sakuranetin from(2S)-naringenin,in which S-adenosylmethionine...(2S)-Sakuranetin is a 7-O-methylflavonoid that has anticancer,antiviral,and antimicrobial activities.Methylation process is involved in biosynthesizing(2S)-sakuranetin from(2S)-naringenin,in which S-adenosylmethionine(SAM)serves as the methyl donor.In this study,after methyl donor and substrate inhibition were identified as limiting factors for(2S)-sakuranetin biosynthesis,an efficient(2S)-sakuranetin-producing strain was constructed by enhancing methyl donor supply and cell tolerance to(2S)-naringenin.Firstly,PfOMT3 from Perilla frutescens was selected as the optimal flavonoid 7-O-methyltransferase(F7-OMT)for the conversion of(2S)-naringenin to(2S)-sakuranetin.Then,the methylation process was upregulated by regulating pyridoxal 5′-phosphate(PLP)content,key enzymes in methionine synthesis pathway,and the availability of ATP.Furthermore,genes that can enhance cell resistance to(2S)-naringenin were identified from molecular chaperones and sRNAs.Finally,by optimizing the fermentation process,681.44 mg/L of(2S)-sakuranetin was obtained in 250-mL shake flasks.The titer of(2S)-sakuranetin reached 2642.38 mg/L in a 5-L bioreactor,which is the highest titer ever reported.This work demonstrates the importance of cofactor PLP in methylation process,and provides insights to biosynthesize other O-methylated flavonoids efficiently in E.coli.展开更多
The glutamate decarboxylase(Gad)system is an important amino acid-dependent acid resistance system commonly found in microorganisms.Actinobacillus succinogenes is one of the best natural producers of succinic acid(SA)...The glutamate decarboxylase(Gad)system is an important amino acid-dependent acid resistance system commonly found in microorganisms.Actinobacillus succinogenes is one of the best natural producers of succinic acid(SA)but lacks glutamate decarboxylase.This study assessed the efects of Gad system introduction into A.succinogenes.The recombinant strains gadB-SW and gadBC-SW were constructed by heterologous expression of gadB alone,or gadB together with gadC,respectively.After 1.0 and 1.5 h of acid stress at pH 4.6,cell survival of gadBC-SW was greater than gadB-SW.The growth of gadB-SW and gadBC-SW was both afected by the expression of heterologous proteins and byγ-aminobutyric acid,with gadBC-SW growth reduced at a neutral pH.SA production in acidic conditions was evaluated by a shake fask and by 3-L bioreactor fermentation.The results showed gadBC-SW to increase SA production by 8.4%in shake fask compared to the parent strain,SW.For a 3-L bioreactor batch fermentation under acidic environment,the highest conversion rate of sugar to SA was observed for gadBC-SW,reaching 96%.However,SA concentration by gadBC-SW was only 47 g/L and 31 g/L at pH 6.5 and pH 6.0,respectively.In summary,the introduction of heterologous gadB and gadC into A.succinogenes not only improved acid tolerance but also infuenced the synthesis of SA and added a metabolic burden.展开更多
基金supported by the National Natural Science Foundation of China(No.11775196)the Chinese Special Project for ITER(No.2015GB108006)
文摘A measurement of the ^235U prompt fission neutron spectrum (PFNS) by the recoil proton method was performed at the Institute of Nuclear Physics and Chemistry, China. Details of the method, which include the calculation and validation of the response matrix, are presented. The PFNS for ^235U in the energy range 1–12 MeV, induced by thermal neutrons, was obtained. The measured spectrum in the low-energy region was in good agreement with previous work and the ENDF/B-VII library, except for minor differences. In the high-energy region, however, the relative height of the measured spectrum was greater, and an analysis of the experiment indicated uncertainties of 13% at 10 MeV and 24% at 12 MeV. Experimental results showed that the recoil proton method could be used to measure prompt fission neutron spectra. Some directions for future work are included.
基金supported by the projection of China Geographic Survey (12120113099800)the projection of "863" (2012AA062601)
文摘This paper reviewed studies on remote sensing of water depth retrieval. Four water depth retrieval models （single-band, dou- ble-ratio-band, multi-band, and BP network models） were evaluated using TM image and water data from Bangong Co Lake, which is located in China＇s Tibet Autonomous Region and Indian Kashmir. Tested by independent data, comparison of these four models demonstrates that BP network model performed better than the multi-band model, with the single-band model performing the worst. To sum up, this study demonstrates that first, BP network model performed better than the traditional model; second, precise atmospheric correction and radiation study, affected by different water level sand sediment, could improve the precision of water depth retrieval.
基金Supported by the National Natural Science Foundation of China(12075216)。
文摘The cross sections of the^(169)Tm(n,2n)^(168)Tm reaction have been measured at incident energies of 12 to 19.8 MeV using the activation technique,relative to the^(93)Nb(n,2n)^(92)mNb reaction.Thulium(Tm)samples were irradiated on the surface of a two-ring orientation assembly with neutrons produced from the^(3)H(d,n)^(4)He reaction at the 5SDH-21.7-MV Tandem accelerator in China.Theoretical model calculations were performed.The present data were then compared with previous experimental data and available evaluated data.This study provides more precise nuclear data for improvement of future evaluations.
文摘【目的】研究低出生体重儿在生后24月龄内发生追赶性生长时其体质量指数(body mass index,BMI)的变化规律。【方法】采用出生队列方法,选择嘉定区2016年1月—2016年12月出生的户籍和常住儿童中自愿加入0~24月龄随访研究中的低出生体重儿(出生体重<2500 g)126人,根据出生体重和孕周分为早产适于胎龄儿组73人、足月小于胎龄儿组53人;选择同地区、孕周37~41周、出生体重2500~3999 g 105人为对照组。比较3组婴幼儿生后0~24月龄间BMI均数、标准差的差异,分析男女婴幼儿在0~24月龄间BMI曲线的变化。【结果】①共纳入231人,男童111人,女童120人;②2组低出生体重儿在出生和2月龄阶段BMI均值均低于对照组,早产适于胎龄儿从4月龄开始BMI与对照组无明显差异,但是足月小于胎龄儿组BMI指数在4~18月龄间始终低于早产适于胎龄儿组别和对照组,差异有统计学意义(P<0.05);③3组婴幼儿BMI指数在生后均呈现快速上升,在4~6月龄时达高峰,7~9月龄BMI数值开始下降,早产适于胎龄儿在6月龄BMI的比较中便赶上正常体重儿童的BMI值,而足月小于胎龄儿一直到24月龄仍与正常体重儿童的BMI值有差异,但是3组间的差值有缩小。男女性别间BMI上升曲线相似,但早产适于胎龄儿女童组别高峰值延长。【结论】低出生体重儿的BMI存在追赶性增长现象,其后期变化趋势与正常出生体重儿相似。在儿童早期生长发育阶段,应给予低出生体重儿喂养方面的合理指导和干预。
基金The authors are grateful for the fnancial support from the National First-class Discipline Program of Light Industry Technology and Engineering(Grant No.LITE2018-04)the Topnotch Academic Programs Project of Jiangsu Higher Education Institutions(TAPP),and the National Natural Science Foundation of China(NSFC)(32072162).
文摘Glucose oxidase(GOD)has many practical applications,but its poor thermostability limits its broader use.In this research,three primary mutants of wild-type GOD were designed using rational mutagenesis,and the GODm mutant was constructed by combinatorial design.The expression,purifcation,and enzymatic properties of the mutants were studied.The specifc enzyme activity of GODm was 2.10-fold higher than that of wild type,and the(k_(cat)/K_(m))value was increased by 1.45-fold.After treatment at 55℃for 3 h,GODm retained 37.5%of its enzymatic activity,and the half-life(t_(1/2))of GODm at 55℃and 65℃was 2.28-fold and 3.36-fold higher than that of wild type,respectively.By analyzing the three-dimensional structure of wild type and the GODm mutant,it was found that T30V formed a new hydrogen bond with FAD and strengthened the hydrophobic interaction,D315K optimized the surface electrostatic interaction,and A162T improved the efciency of the electron pathway.Thus,a novel mutant with improved thermostability and catalytic efciency was obtained in this research.
基金This work was supported by the National Key Research and Development Program of China(2019YFA0904800)the National Natural Science Foundation of China(21908078).
文摘(2S)-Sakuranetin is a 7-O-methylflavonoid that has anticancer,antiviral,and antimicrobial activities.Methylation process is involved in biosynthesizing(2S)-sakuranetin from(2S)-naringenin,in which S-adenosylmethionine(SAM)serves as the methyl donor.In this study,after methyl donor and substrate inhibition were identified as limiting factors for(2S)-sakuranetin biosynthesis,an efficient(2S)-sakuranetin-producing strain was constructed by enhancing methyl donor supply and cell tolerance to(2S)-naringenin.Firstly,PfOMT3 from Perilla frutescens was selected as the optimal flavonoid 7-O-methyltransferase(F7-OMT)for the conversion of(2S)-naringenin to(2S)-sakuranetin.Then,the methylation process was upregulated by regulating pyridoxal 5′-phosphate(PLP)content,key enzymes in methionine synthesis pathway,and the availability of ATP.Furthermore,genes that can enhance cell resistance to(2S)-naringenin were identified from molecular chaperones and sRNAs.Finally,by optimizing the fermentation process,681.44 mg/L of(2S)-sakuranetin was obtained in 250-mL shake flasks.The titer of(2S)-sakuranetin reached 2642.38 mg/L in a 5-L bioreactor,which is the highest titer ever reported.This work demonstrates the importance of cofactor PLP in methylation process,and provides insights to biosynthesize other O-methylated flavonoids efficiently in E.coli.
基金The authors are grateful for the fnancial support from the National First-class Discipline Program of Light Industry Technology and Engineering(Grant No.LITE2018-04)the Topnotch Academic Programs Project of Jiangsu Higher Education Institutions(TAPP).
文摘The glutamate decarboxylase(Gad)system is an important amino acid-dependent acid resistance system commonly found in microorganisms.Actinobacillus succinogenes is one of the best natural producers of succinic acid(SA)but lacks glutamate decarboxylase.This study assessed the efects of Gad system introduction into A.succinogenes.The recombinant strains gadB-SW and gadBC-SW were constructed by heterologous expression of gadB alone,or gadB together with gadC,respectively.After 1.0 and 1.5 h of acid stress at pH 4.6,cell survival of gadBC-SW was greater than gadB-SW.The growth of gadB-SW and gadBC-SW was both afected by the expression of heterologous proteins and byγ-aminobutyric acid,with gadBC-SW growth reduced at a neutral pH.SA production in acidic conditions was evaluated by a shake fask and by 3-L bioreactor fermentation.The results showed gadBC-SW to increase SA production by 8.4%in shake fask compared to the parent strain,SW.For a 3-L bioreactor batch fermentation under acidic environment,the highest conversion rate of sugar to SA was observed for gadBC-SW,reaching 96%.However,SA concentration by gadBC-SW was only 47 g/L and 31 g/L at pH 6.5 and pH 6.0,respectively.In summary,the introduction of heterologous gadB and gadC into A.succinogenes not only improved acid tolerance but also infuenced the synthesis of SA and added a metabolic burden.
