The catalytic epoxidation of olefin was investigated on two copper complex-modified molybdenum oxides with a 3D supramolecular structure, [Cu(bipy)]4[Mo15O47].2H2O (1) and [Cu1(bix)][(Cu1bix) (δ-MoVl8O26)0....The catalytic epoxidation of olefin was investigated on two copper complex-modified molybdenum oxides with a 3D supramolecular structure, [Cu(bipy)]4[Mo15O47].2H2O (1) and [Cu1(bix)][(Cu1bix) (δ-MoVl8O26)0.5] (2) (bipy = 4,4'-bipyridine, bix = 1,4-bis(imidazole-1-ylmethyl)benzene). Both compounds were catalytically active and stable for the epoxidation of cyclooctene, 1-octene, and styrene with tert-butyl hydroperoxide (t-BuOOH) as oxidant. The excellent catalytic performance was attributed to the presence of stable coordination bonds between the molybdenum oxide and copper complex, which resulted in the formation of easily accessible Mo species with high electropositivity. In addition, the copper complex also acted as an active site for the activation of t-BuOOH, thus im- proving these copper complex-modified polyoxometalates.展开更多
A cross point assignment algorithm is proposed under consideration of very long nets (LCPA).It is to consider not only the cost of connection between cross points and pins and the exclusive cost among cross points on ...A cross point assignment algorithm is proposed under consideration of very long nets (LCPA).It is to consider not only the cost of connection between cross points and pins and the exclusive cost among cross points on the boundary of a global routing cell,but also the cost of displacement among cross points of the same net.The experiment results show that the quality and speed in the following detailed routing are improved obviously,especially for very long nets.展开更多
Speckle degrades severely the quality of medical B-scan ultrasonic images, especiallyit blurs edges and details of images. An adaptive speckle suppression and edge enhancementmethod based on Nakagami distribution is p...Speckle degrades severely the quality of medical B-scan ultrasonic images, especiallyit blurs edges and details of images. An adaptive speckle suppression and edge enhancementmethod based on Nakagami distribution is presented. The statistics of log-compressed echo im-ages is derived for Nakagami distribution. An adaptive filter based on local statistical propertyof speckle is designed. The stick technique that utilizes sticks with different sizes and variousorientations is applied to locally approximate certain linear features of image. The local regionis a stick instead of a usual window, the orientation of sticks is decided by hypothesis test op-timizing method and the length of sticks is obtained by region growing technique. Performanceof the new method has been tested on the phantom and ultrasound images of pig muscle andechocardiographic. The results show that the technique effectively reduces the speckle noise whilepreserving and enhancing the tissue edge and resolvable details.展开更多
Using state assignment to minimize power dissipation and area for finite state ma-chines is computationally hard. Most of published results show that the reduction of switchingactivity often trades with area penalty. ...Using state assignment to minimize power dissipation and area for finite state ma-chines is computationally hard. Most of published results show that the reduction of switchingactivity often trades with area penalty. In this paper, a new approach is proposed. Experimentalresults show a significant reduction of switching activity without area penalty compared withprevious publications.展开更多
A new cadmium(II) coordination polymer with benzenetricarboxylate{Cd2- (Htma)2(H2O)2}}n 1 (Htma = 1-carboxybenzene-2,4-dicarboxylate) has been synthesized by hydro- thermal reaction. 1 crystallizes in triclinic, space...A new cadmium(II) coordination polymer with benzenetricarboxylate{Cd2- (Htma)2(H2O)2}}n 1 (Htma = 1-carboxybenzene-2,4-dicarboxylate) has been synthesized by hydro- thermal reaction. 1 crystallizes in triclinic, space group P?with a = 6.9990(8), b = 7.0564(8), c = 10.096(1) ? = 83.438(1), = 86.357(2), = 69.233(2)? V = 463.02(9) 3, Dc = 2.428 g/cm3, F(000) = 328, Mr = 677.08, m(MoKa) = 2.382 mm-1, Z = 1, the final R = 0.0284 and wR = 0.0772 for 1540 observed reflections (I≥2s(I)). The structure of 1 consists of centrosymmetric dinuclear units with all metal centers being six-coordinated, which adopt a distorted octahedral configuration and lead to the formation of three-dimensional microporous framework with size of about 3 ??8 ? Fluoerescent measurement showed that 1 exhibits intense fluorescent emission.展开更多
Overmodulation is frequently required during the transient interval at high speed operations of IPMSMs (interior permanent magnet synchronous motors). In this work, an overmodulation method is developed in the synch...Overmodulation is frequently required during the transient interval at high speed operations of IPMSMs (interior permanent magnet synchronous motors). In this work, an overmodulation method is developed in the synchronous reference frame with a provision of assigning different priorities to d- and q-axes currents. During the current boosting in motoring, the d-axis current is increased by priority for a fast current response, and to minimize the overmodulation period. However in the regeneration process, the q-axis current is decreased by priority during a load reduction. Simulation and experimental results show that the proposed method, compared with the existing minimum-phase error method, is better for a fast current response, and in shortening the overmodulation period.展开更多
The theoretical calculation and spectroscopic experiments indicate a kind of triangular three bonding supramolecular complexes CBr4…X^-…-H-C, which consist of carbon tetrabromide, halide, and protic solvent molecule...The theoretical calculation and spectroscopic experiments indicate a kind of triangular three bonding supramolecular complexes CBr4…X^-…-H-C, which consist of carbon tetrabromide, halide, and protic solvent molecule (referring to dichloromethane, chloroform and acetonitrile), can be formed in solution. The strength of halogen and hydrogen bonds in the triangular complexes using halide as common acceptor obeys the order of iodide〉bromide〉chloride. The halogen and hydrogen bonds work weak-cooperatively. Charge transfer bands of halogen bonding complexes between CBra and halide are observed in UV-Vis absorption spectroscopy in three solvents, and then the stoichiometry of 1:1, formation constants K and molar extinction coefficients ε of the halogen bonding complexes are obtained by Benesi-Hildebrand method. The K and ε show a dependence on the solvent dielectric constant and, on the whole, obey an order of iodide〉bromide〉chloride in the same solvents. Furthermore, the C-H vibrational frequencies of solvent molecules vary obviously with the addition of halide, which indicates the C-H…X- interaction. The experimental data indicate that the halogen bond and hydrogen bond coexist by sharing a common halide acceptor as predicted by calculation.展开更多
Supramolecular polymer complexes with small molecules are self-assembled through non-covalent interactions and have been proposed for a wide variety of applications in materials science and nanoscience.Our research gr...Supramolecular polymer complexes with small molecules are self-assembled through non-covalent interactions and have been proposed for a wide variety of applications in materials science and nanoscience.Our research group has recently shown the possibility of forming highly ordered nanofibers of supramolecular complexes in their thermodynamically stable state using the electrospinning technique.The ultrafast solvent evaporation rate of electrospinning made possible the in-depth characterization of complexes that had never been prepared in their pure state before because of kinetic issues associated with their formation by conventional approaches.The improved understanding of the formation mechanism allowed us to extend the concept to other techniques featuring a fast solvent evaporation rate,such as electrospray and spin-coating.In this article,we review our most significant contributions in this research field.展开更多
When the shoot apical meristem of plants is damaged or removed,fecundity and/or plant growth may suffer(under-compensation),remain unaffected(compensation)or increase(overcompensation).The latter signifies a potential...When the shoot apical meristem of plants is damaged or removed,fecundity and/or plant growth may suffer(under-compensation),remain unaffected(compensation)or increase(overcompensation).The latter signifies a potential‘cost’of apical dominance.Using natural populations of 19 herbaceous angiosperm species with a conspicuously vertical,apically dominant growth form,we removed(clipped)the shoot apical meristem for replicate plants early in the growing season to test for a potential cost of apical dominance.Clipped and unclipped(control)plants had their near neighbours removed,and were harvested after flowering production had finished but before seed dispersal.Dry mass was measured separately for aboveground body size(shoots),leaves,seeds and fruits;and number of leaves,fruits and seeds per plant were counted.We predicted that:(i)our study species(because of their strong apically dominant growth form)would respond to shoot apical meristem removal with greater branching intensity,and thus overcompensation in terms of fecundity and/or biomass;and(ii)overcompensation is particularly enabled for species that produce smaller but more leaves,and hence with a larger bud bank of axillary meristems available for deployment in branching and/or fruit production.Widely variable compensatory capacities were recorded,and with no significant between-species relationship with leaf size or leafing intensity—thus indicating no generalized potential cost of apical dominance.Overall,the results point to species-specific treatment effects on meristem allocation patterns,and suggest importance for effects involving local variation in resource availability,and between-species variation in phenology,life history traits and susceptibility to herbivory.展开更多
A peptide nucleic acid (PNA)-peptide conjugated molecule, T'3(AKAE)2, was designed to have both a PNA segment for oligo- nucleotide binding and an ionic self-complementary peptide sequence for self-association. T...A peptide nucleic acid (PNA)-peptide conjugated molecule, T'3(AKAE)2, was designed to have both a PNA segment for oligo- nucleotide binding and an ionic self-complementary peptide sequence for self-association. T'3(AKAE)2 could co-assemble with oligoadenines (d(A)x) to form virus-like supramolecular structures whose morphology showed dependence on the chain length and rigidity of the d(A)x molecules. Smaller nanospheres with diameters of 13.0±2.0 nm were produced in the case of d(A)6. Wormlike aggregates with lengths of 20-50 nm and diameters of 15.0±2.5 nm were found in the cases of d(A)12, d(A)ls, d(A)24 and d(A)30. And larger spherical aggregates with diameters of 18±5 nm came into presence in the cases of d(A)36 and d(A)42+. These nanostructures were suggested to be formed under a cooperative effect of base pair recognition and peptidic association. The study provides insights into the programmed assembly of a multi-components system as well as control of the size and shade of the co-assembled structures, which is of great significance in develouing gene/drug deliverv systems.展开更多
A single stage ultra micro centrifugal compressor constituting ultra micro gas turbine is required to operate at high rotational speed in order to achieve the pressure ratio which establishes the gas turbine cycle. As...A single stage ultra micro centrifugal compressor constituting ultra micro gas turbine is required to operate at high rotational speed in order to achieve the pressure ratio which establishes the gas turbine cycle. As a conse- quence, the aerodynamic losses can be increased by the interaction of a shock wave with the boundary layer on the blade surface. Moreover, the centrifugal force which exceeds the allowable s^ress of the impeller material can act on the root of blades. On the other hand, the restrictions of processing technology for the downsizing of im- peller not only relatively enlarge the size of tip clearance but also make it difficult to shape the impeller with the i three-dimensional blade. Therefore, it is important to establish the design technology for the impeller with the two-dimensional blade which possesses the sufficient aerodynamic performance and enough strength to bear the centrifugal force caused by the high rotational speed. In this study, the flow in two types of impeller with the two-dimensional blade which have different meridional configuration was analyzed numerically, The computed results clarified the influence of the meridional configuration on the loss generations in the impeller passage.展开更多
基金supported by the National Natural Science Foundation of China(21173100 and 21320102001)~~
文摘The catalytic epoxidation of olefin was investigated on two copper complex-modified molybdenum oxides with a 3D supramolecular structure, [Cu(bipy)]4[Mo15O47].2H2O (1) and [Cu1(bix)][(Cu1bix) (δ-MoVl8O26)0.5] (2) (bipy = 4,4'-bipyridine, bix = 1,4-bis(imidazole-1-ylmethyl)benzene). Both compounds were catalytically active and stable for the epoxidation of cyclooctene, 1-octene, and styrene with tert-butyl hydroperoxide (t-BuOOH) as oxidant. The excellent catalytic performance was attributed to the presence of stable coordination bonds between the molybdenum oxide and copper complex, which resulted in the formation of easily accessible Mo species with high electropositivity. In addition, the copper complex also acted as an active site for the activation of t-BuOOH, thus im- proving these copper complex-modified polyoxometalates.
文摘A cross point assignment algorithm is proposed under consideration of very long nets (LCPA).It is to consider not only the cost of connection between cross points and pins and the exclusive cost among cross points on the boundary of a global routing cell,but also the cost of displacement among cross points of the same net.The experiment results show that the quality and speed in the following detailed routing are improved obviously,especially for very long nets.
文摘Speckle degrades severely the quality of medical B-scan ultrasonic images, especiallyit blurs edges and details of images. An adaptive speckle suppression and edge enhancementmethod based on Nakagami distribution is presented. The statistics of log-compressed echo im-ages is derived for Nakagami distribution. An adaptive filter based on local statistical propertyof speckle is designed. The stick technique that utilizes sticks with different sizes and variousorientations is applied to locally approximate certain linear features of image. The local regionis a stick instead of a usual window, the orientation of sticks is decided by hypothesis test op-timizing method and the length of sticks is obtained by region growing technique. Performanceof the new method has been tested on the phantom and ultrasound images of pig muscle andechocardiographic. The results show that the technique effectively reduces the speckle noise whilepreserving and enhancing the tissue edge and resolvable details.
基金Supported by NNSF of China(Key International Cooperative Project No.60010121219)
文摘Using state assignment to minimize power dissipation and area for finite state ma-chines is computationally hard. Most of published results show that the reduction of switchingactivity often trades with area penalty. In this paper, a new approach is proposed. Experimentalresults show a significant reduction of switching activity without area penalty compared withprevious publications.
基金This research was supported by the Ministry of Science and Technology of China (001CB1089) the National Natural Science Foundation of China (20273073 90206040) and Natural Science Foundation of Fujian Province (2002F014)
文摘A new cadmium(II) coordination polymer with benzenetricarboxylate{Cd2- (Htma)2(H2O)2}}n 1 (Htma = 1-carboxybenzene-2,4-dicarboxylate) has been synthesized by hydro- thermal reaction. 1 crystallizes in triclinic, space group P?with a = 6.9990(8), b = 7.0564(8), c = 10.096(1) ? = 83.438(1), = 86.357(2), = 69.233(2)? V = 463.02(9) 3, Dc = 2.428 g/cm3, F(000) = 328, Mr = 677.08, m(MoKa) = 2.382 mm-1, Z = 1, the final R = 0.0284 and wR = 0.0772 for 1540 observed reflections (I≥2s(I)). The structure of 1 consists of centrosymmetric dinuclear units with all metal centers being six-coordinated, which adopt a distorted octahedral configuration and lead to the formation of three-dimensional microporous framework with size of about 3 ??8 ? Fluoerescent measurement showed that 1 exhibits intense fluorescent emission.
文摘Overmodulation is frequently required during the transient interval at high speed operations of IPMSMs (interior permanent magnet synchronous motors). In this work, an overmodulation method is developed in the synchronous reference frame with a provision of assigning different priorities to d- and q-axes currents. During the current boosting in motoring, the d-axis current is increased by priority for a fast current response, and to minimize the overmodulation period. However in the regeneration process, the q-axis current is decreased by priority during a load reduction. Simulation and experimental results show that the proposed method, compared with the existing minimum-phase error method, is better for a fast current response, and in shortening the overmodulation period.
基金ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (No.20675009 and No. 90922023). The basis set aug-cc-pVDZ-PP for iodine atom is downloaded at the website http://bse.pnl.gov/ bse/portal.
文摘The theoretical calculation and spectroscopic experiments indicate a kind of triangular three bonding supramolecular complexes CBr4…X^-…-H-C, which consist of carbon tetrabromide, halide, and protic solvent molecule (referring to dichloromethane, chloroform and acetonitrile), can be formed in solution. The strength of halogen and hydrogen bonds in the triangular complexes using halide as common acceptor obeys the order of iodide〉bromide〉chloride. The halogen and hydrogen bonds work weak-cooperatively. Charge transfer bands of halogen bonding complexes between CBra and halide are observed in UV-Vis absorption spectroscopy in three solvents, and then the stoichiometry of 1:1, formation constants K and molar extinction coefficients ε of the halogen bonding complexes are obtained by Benesi-Hildebrand method. The K and ε show a dependence on the solvent dielectric constant and, on the whole, obey an order of iodide〉bromide〉chloride in the same solvents. Furthermore, the C-H vibrational frequencies of solvent molecules vary obviously with the addition of halide, which indicates the C-H…X- interaction. The experimental data indicate that the halogen bond and hydrogen bond coexist by sharing a common halide acceptor as predicted by calculation.
基金supported by a grant and a graduate scholarship (MRL)from the Natural Sciences and Engineering Research Council of Canada(NSERC)
文摘Supramolecular polymer complexes with small molecules are self-assembled through non-covalent interactions and have been proposed for a wide variety of applications in materials science and nanoscience.Our research group has recently shown the possibility of forming highly ordered nanofibers of supramolecular complexes in their thermodynamically stable state using the electrospinning technique.The ultrafast solvent evaporation rate of electrospinning made possible the in-depth characterization of complexes that had never been prepared in their pure state before because of kinetic issues associated with their formation by conventional approaches.The improved understanding of the formation mechanism allowed us to extend the concept to other techniques featuring a fast solvent evaporation rate,such as electrospray and spin-coating.In this article,we review our most significant contributions in this research field.
基金This work was supported by a Natural Sciences and Engineering Research Council of Canada research grant to L.W.A.
文摘When the shoot apical meristem of plants is damaged or removed,fecundity and/or plant growth may suffer(under-compensation),remain unaffected(compensation)or increase(overcompensation).The latter signifies a potential‘cost’of apical dominance.Using natural populations of 19 herbaceous angiosperm species with a conspicuously vertical,apically dominant growth form,we removed(clipped)the shoot apical meristem for replicate plants early in the growing season to test for a potential cost of apical dominance.Clipped and unclipped(control)plants had their near neighbours removed,and were harvested after flowering production had finished but before seed dispersal.Dry mass was measured separately for aboveground body size(shoots),leaves,seeds and fruits;and number of leaves,fruits and seeds per plant were counted.We predicted that:(i)our study species(because of their strong apically dominant growth form)would respond to shoot apical meristem removal with greater branching intensity,and thus overcompensation in terms of fecundity and/or biomass;and(ii)overcompensation is particularly enabled for species that produce smaller but more leaves,and hence with a larger bud bank of axillary meristems available for deployment in branching and/or fruit production.Widely variable compensatory capacities were recorded,and with no significant between-species relationship with leaf size or leafing intensity—thus indicating no generalized potential cost of apical dominance.Overall,the results point to species-specific treatment effects on meristem allocation patterns,and suggest importance for effects involving local variation in resource availability,and between-species variation in phenology,life history traits and susceptibility to herbivory.
基金the National Natural Science Foundation of China (21473255, 21003160)the Fundamental Research Funds for the Central Universities (14CX05040A, 15CX05017A)
文摘A peptide nucleic acid (PNA)-peptide conjugated molecule, T'3(AKAE)2, was designed to have both a PNA segment for oligo- nucleotide binding and an ionic self-complementary peptide sequence for self-association. T'3(AKAE)2 could co-assemble with oligoadenines (d(A)x) to form virus-like supramolecular structures whose morphology showed dependence on the chain length and rigidity of the d(A)x molecules. Smaller nanospheres with diameters of 13.0±2.0 nm were produced in the case of d(A)6. Wormlike aggregates with lengths of 20-50 nm and diameters of 15.0±2.5 nm were found in the cases of d(A)12, d(A)ls, d(A)24 and d(A)30. And larger spherical aggregates with diameters of 18±5 nm came into presence in the cases of d(A)36 and d(A)42+. These nanostructures were suggested to be formed under a cooperative effect of base pair recognition and peptidic association. The study provides insights into the programmed assembly of a multi-components system as well as control of the size and shade of the co-assembled structures, which is of great significance in develouing gene/drug deliverv systems.
文摘A single stage ultra micro centrifugal compressor constituting ultra micro gas turbine is required to operate at high rotational speed in order to achieve the pressure ratio which establishes the gas turbine cycle. As a conse- quence, the aerodynamic losses can be increased by the interaction of a shock wave with the boundary layer on the blade surface. Moreover, the centrifugal force which exceeds the allowable s^ress of the impeller material can act on the root of blades. On the other hand, the restrictions of processing technology for the downsizing of im- peller not only relatively enlarge the size of tip clearance but also make it difficult to shape the impeller with the i three-dimensional blade. Therefore, it is important to establish the design technology for the impeller with the two-dimensional blade which possesses the sufficient aerodynamic performance and enough strength to bear the centrifugal force caused by the high rotational speed. In this study, the flow in two types of impeller with the two-dimensional blade which have different meridional configuration was analyzed numerically, The computed results clarified the influence of the meridional configuration on the loss generations in the impeller passage.