The rollup and the drilldown are quite frequent based on dimension hierarchies in on-line analytical processing (OLAP), but prefixCube does not directly support dimension hierarchies. The PrefixCube is extended for ...The rollup and the drilldown are quite frequent based on dimension hierarchies in on-line analytical processing (OLAP), but prefixCube does not directly support dimension hierarchies. The PrefixCube is extended for incorporating hierarchical data cubes, i.e. cubes with hierarchical dimensions ,thus obtaining HierPrefixCube. HierPrefixCube retains advantages on computation and organization of PrefixCube, and it can directly support aggregate queries on levels of the dimension hierarchy.展开更多
Assembling of a few particles into a cluster commonly occurs in many systems.However,it is still challenging to precisely control particle assembling,due to the various amorphous structures induced by thermal fluctuat...Assembling of a few particles into a cluster commonly occurs in many systems.However,it is still challenging to precisely control particle assembling,due to the various amorphous structures induced by thermal fluctuations during cluster formation.Although these structures may have very different degrees of aggregation,a quantitative method is lacking to describe them,and how these structures evolve remains unclear.Therefore a significant step towards precise control of particle self-assembly is to describe and analyze various aggregation structures during cluster formation quantitatively.In this work,we are motivated to propose a method to directly count and quantitatively compare different aggregated structures.We also present several case studies to evaluate how the aggregated structures during cluster formation are affected by external controlling factors,e.g.,different interaction ranges,interaction strengths,or anisotropy of attraction.展开更多
Mesoporous nanocrystal clusters of anatase TiO2 with large surface area and enhanced photocatalytic activity have been successfully synthesized. The synthesis involves the self-assembly of hydrophobic TiO2 nanocrystal...Mesoporous nanocrystal clusters of anatase TiO2 with large surface area and enhanced photocatalytic activity have been successfully synthesized. The synthesis involves the self-assembly of hydrophobic TiO2 nanocrystals into submicron clusters, coating of these clusters with a silica layer, thermal treatment to remove organic ligands and improve the crystallinity of the clusters, and finally removing silica to expose the mesoporous catalysts. With the help of the silica coating, the clusters not only maintain their small grain size but also keep their mesoporous structure after calcination at high temperatures (with BET surface area as high as 277 m2/g). The etching of SiO2 also results in the clusters having high dispersity in water. We have been able to identify the optimal calcination temperature to produce TiO2 nanocrystal clusters that possess both high crystallinity and large surface area, and therefore show excellent catalytic efficiency in the decomposition of organic molecules under illumination by UV light. Convenient doping with nitrogen converts these nanocrystal clusters into active photocatalysts in both visible light and natural sunlight. The strategy of forming well-defined mesoporous clusters using nanocrystals promises a versatile and useful method for designing photocatalysts with enhanced activity and stability.展开更多
Ultrathin nanostructures have attracted much attention in recent years due to their predictable novel properties and various potential applications. The improvement in synthetic skills has led to many successful synth...Ultrathin nanostructures have attracted much attention in recent years due to their predictable novel properties and various potential applications. The improvement in synthetic skills has led to many successful syntheses of nanostructures including zerodimensional (0D) nanoclusters, one-dimensional (1D) nanowires, two-dimensional (2D) nanosheets and other higher-level complex nanostructures, where cluster-assembly of primary nanocrystals is a common process. In this review, progress in ultrathin nanocrystals in the last decade and several important factors in the growth mechanisms are covered. By giving examples of cluster assembly from 1D to 3D nanostructures, the utility of cluster assembly in the synthesis of new materials has been demonstrated.展开更多
An ideal surrogate host for heterologous production of various natural products is expected to have efficient nutrient utilization,fast growth,abundant precursors and energy supply,and a pronounced gene expression.Str...An ideal surrogate host for heterologous production of various natural products is expected to have efficient nutrient utilization,fast growth,abundant precursors and energy supply,and a pronounced gene expression.Streptomyces albus BK3-25 is a high-yield industrial strain producing type-Ⅰ polyketide sahnomycin,with a unique ability of bean oil utilization.Its potential of being a surrogate host for heterologous production of PKS was engineered and evaluated herein.Firstly,introduction of a three-gene cassette for the biosynthesis of ethylmalonyl-CoA resulted in accumulation of ethylmalonyl-CoA precursor and sahnomycin,and subsequent deletion of the sahnomycin biosynthetic gene cluster resulted in a host with rich supplies of common polyketide precursors,including malonyl-CoA,methylmalonyl-CoA,and ethylmalonyl-CoA.Secondly,the energy and reducing force were measured,and the improved accumulation of ATP and NADPH was observed in the mutant.Furthermore,the strength of a series of selected endogenous promoters based on microarray data was assessed at different growth phases,and a strong constitutive promoter was identified,providing a useful tool for further engineered gene expression.Finally,the potential of the BK3-25 derived host ZXJ-6 was evaluated with the introduction of the actinorhodin biosynthetic gene cluster from Streptomyces coelicolor,and the heterologous production of actinorhodin was obtained.This work clearly indicated the potential of the high-yield sahnomycin producer as a surrogate host for heterologous production of polyketides,although more genetic manipulation should be conducted to streamline its performance.展开更多
Streptothricins (STs) are used commercially to treat bacterial and fungal diseases in agriculture. Mining of the sequenced microbial genomes uncovered two cryptic ST clusters from Streptomyces sp. C and Streptomyces s...Streptothricins (STs) are used commercially to treat bacterial and fungal diseases in agriculture. Mining of the sequenced microbial genomes uncovered two cryptic ST clusters from Streptomyces sp. C and Streptomyces sp. TP-A0356. The ST cluster from S. sp. TP-A0356 was verified by successful heterologous expression in Streptomyces coelicolor M145. Two new ST analogs were produced together with streptothricin F and streptothricin D in the heterologous host. The ST cluster was further confirmed by inactivation of gene stnO, which was proposed encoding an aminomutase supplying -lysines for the poly-β-Lys chain formation. A putative biosynthetic pathway for STs is proposed based on bioinformatics analyses of the ST genes and experimental evidence.展开更多
The complete mitochondrial genome of Nanorana pleskei from the Qinghai-Tibet Plateau was sequenced. It includes 17,660 base pairs, containing 13 protein-coding genes, two rRNAs and 23 tRNAs. A tandem duplication of tR...The complete mitochondrial genome of Nanorana pleskei from the Qinghai-Tibet Plateau was sequenced. It includes 17,660 base pairs, containing 13 protein-coding genes, two rRNAs and 23 tRNAs. A tandem duplication of tRNAu^t gene was found in this mitochondrial genome, and the similarity between the two tRNAMet genes is 85.8%, being the highest in amphibian mitochondrial genomes sequenced thus far. Based on gene organization, 24 types were found from 145 amphibian mitochondrial genomes. Type 1 was present in 108 species, type 11 in 11 species, types 5, 16, 17, and 20 each in two species, and the others each present in one species. Fifteen types were found in Anura, being the most diversity in three orders of the Lissamphibia. Our phylogenetic results using 11 protein-coding gene sequences of 145 amphibian mitochondrial genomes strongly support the mo- nophyly of the Lissamphibia, as well as its three orders, the Gymnophiona, Caudata, and Anura, among which the relationships were ((Gymnophiona (Caudata, Anura)). Based on the phylogenetic trees, type 1 was recognized as the ancestral type for am- phibians, and type 11 was the synapomorphic type for the Neobatrachia. Gene rearrangements among lineages provide meaning- ful phylogenetic information. The rearrangement of the LTPF tRNA gene cluster and the translocation of the ND5 gene only found in the Neobatrachia support the monophyly of this group; similarly, the tandem duplication of the tRNAMet genes only found in the Dicroglossidae support the monophyly of this family展开更多
文摘The rollup and the drilldown are quite frequent based on dimension hierarchies in on-line analytical processing (OLAP), but prefixCube does not directly support dimension hierarchies. The PrefixCube is extended for incorporating hierarchical data cubes, i.e. cubes with hierarchical dimensions ,thus obtaining HierPrefixCube. HierPrefixCube retains advantages on computation and organization of PrefixCube, and it can directly support aggregate queries on levels of the dimension hierarchy.
文摘Assembling of a few particles into a cluster commonly occurs in many systems.However,it is still challenging to precisely control particle assembling,due to the various amorphous structures induced by thermal fluctuations during cluster formation.Although these structures may have very different degrees of aggregation,a quantitative method is lacking to describe them,and how these structures evolve remains unclear.Therefore a significant step towards precise control of particle self-assembly is to describe and analyze various aggregation structures during cluster formation quantitatively.In this work,we are motivated to propose a method to directly count and quantitatively compare different aggregated structures.We also present several case studies to evaluate how the aggregated structures during cluster formation are affected by external controlling factors,e.g.,different interaction ranges,interaction strengths,or anisotropy of attraction.
文摘Mesoporous nanocrystal clusters of anatase TiO2 with large surface area and enhanced photocatalytic activity have been successfully synthesized. The synthesis involves the self-assembly of hydrophobic TiO2 nanocrystals into submicron clusters, coating of these clusters with a silica layer, thermal treatment to remove organic ligands and improve the crystallinity of the clusters, and finally removing silica to expose the mesoporous catalysts. With the help of the silica coating, the clusters not only maintain their small grain size but also keep their mesoporous structure after calcination at high temperatures (with BET surface area as high as 277 m2/g). The etching of SiO2 also results in the clusters having high dispersity in water. We have been able to identify the optimal calcination temperature to produce TiO2 nanocrystal clusters that possess both high crystallinity and large surface area, and therefore show excellent catalytic efficiency in the decomposition of organic molecules under illumination by UV light. Convenient doping with nitrogen converts these nanocrystal clusters into active photocatalysts in both visible light and natural sunlight. The strategy of forming well-defined mesoporous clusters using nanocrystals promises a versatile and useful method for designing photocatalysts with enhanced activity and stability.
基金supported by the National Natural Science Foundation of China (91127040, 20921001)the National Basic Research Program of China (973 Program, 2011CB932402)
文摘Ultrathin nanostructures have attracted much attention in recent years due to their predictable novel properties and various potential applications. The improvement in synthetic skills has led to many successful syntheses of nanostructures including zerodimensional (0D) nanoclusters, one-dimensional (1D) nanowires, two-dimensional (2D) nanosheets and other higher-level complex nanostructures, where cluster-assembly of primary nanocrystals is a common process. In this review, progress in ultrathin nanocrystals in the last decade and several important factors in the growth mechanisms are covered. By giving examples of cluster assembly from 1D to 3D nanostructures, the utility of cluster assembly in the synthesis of new materials has been demonstrated.
基金supported by grants from the National Natural Science Foundation of China(21661140002 and 31470157)the Ministry of Science and Technology of China(2012CB721005 and 2012AA022107)
文摘An ideal surrogate host for heterologous production of various natural products is expected to have efficient nutrient utilization,fast growth,abundant precursors and energy supply,and a pronounced gene expression.Streptomyces albus BK3-25 is a high-yield industrial strain producing type-Ⅰ polyketide sahnomycin,with a unique ability of bean oil utilization.Its potential of being a surrogate host for heterologous production of PKS was engineered and evaluated herein.Firstly,introduction of a three-gene cassette for the biosynthesis of ethylmalonyl-CoA resulted in accumulation of ethylmalonyl-CoA precursor and sahnomycin,and subsequent deletion of the sahnomycin biosynthetic gene cluster resulted in a host with rich supplies of common polyketide precursors,including malonyl-CoA,methylmalonyl-CoA,and ethylmalonyl-CoA.Secondly,the energy and reducing force were measured,and the improved accumulation of ATP and NADPH was observed in the mutant.Furthermore,the strength of a series of selected endogenous promoters based on microarray data was assessed at different growth phases,and a strong constitutive promoter was identified,providing a useful tool for further engineered gene expression.Finally,the potential of the BK3-25 derived host ZXJ-6 was evaluated with the introduction of the actinorhodin biosynthetic gene cluster from Streptomyces coelicolor,and the heterologous production of actinorhodin was obtained.This work clearly indicated the potential of the high-yield sahnomycin producer as a surrogate host for heterologous production of polyketides,although more genetic manipulation should be conducted to streamline its performance.
基金supported in part by the National Natural Science Foundation of China (31170037)Ministry of Science and Technology of China (2013CB734003)the China Postdoctoral Science Foundation (2013M530755)
文摘Streptothricins (STs) are used commercially to treat bacterial and fungal diseases in agriculture. Mining of the sequenced microbial genomes uncovered two cryptic ST clusters from Streptomyces sp. C and Streptomyces sp. TP-A0356. The ST cluster from S. sp. TP-A0356 was verified by successful heterologous expression in Streptomyces coelicolor M145. Two new ST analogs were produced together with streptothricin F and streptothricin D in the heterologous host. The ST cluster was further confirmed by inactivation of gene stnO, which was proposed encoding an aminomutase supplying -lysines for the poly-β-Lys chain formation. A putative biosynthetic pathway for STs is proposed based on bioinformatics analyses of the ST genes and experimental evidence.
文摘The complete mitochondrial genome of Nanorana pleskei from the Qinghai-Tibet Plateau was sequenced. It includes 17,660 base pairs, containing 13 protein-coding genes, two rRNAs and 23 tRNAs. A tandem duplication of tRNAu^t gene was found in this mitochondrial genome, and the similarity between the two tRNAMet genes is 85.8%, being the highest in amphibian mitochondrial genomes sequenced thus far. Based on gene organization, 24 types were found from 145 amphibian mitochondrial genomes. Type 1 was present in 108 species, type 11 in 11 species, types 5, 16, 17, and 20 each in two species, and the others each present in one species. Fifteen types were found in Anura, being the most diversity in three orders of the Lissamphibia. Our phylogenetic results using 11 protein-coding gene sequences of 145 amphibian mitochondrial genomes strongly support the mo- nophyly of the Lissamphibia, as well as its three orders, the Gymnophiona, Caudata, and Anura, among which the relationships were ((Gymnophiona (Caudata, Anura)). Based on the phylogenetic trees, type 1 was recognized as the ancestral type for am- phibians, and type 11 was the synapomorphic type for the Neobatrachia. Gene rearrangements among lineages provide meaning- ful phylogenetic information. The rearrangement of the LTPF tRNA gene cluster and the translocation of the ND5 gene only found in the Neobatrachia support the monophyly of this group; similarly, the tandem duplication of the tRNAMet genes only found in the Dicroglossidae support the monophyly of this family