Local delivery of nanoparticles holds promise for colorectal cancer(CRC)therapy.However,the presence of the mucus layer on the epithelium poses a significant challenge to drug delivery,thereby adversely affecting trea...Local delivery of nanoparticles holds promise for colorectal cancer(CRC)therapy.However,the presence of the mucus layer on the epithelium poses a significant challenge to drug delivery,thereby adversely affecting treatment efficiency.It is crucial to develop efficient drug delivery carriers that can effectively overcome mucus barriers to treat colorectal cancer.Herein,we utilized poly(1,4-butadiene)-b-poly(ethylene oxide)polymers to prepare four distinct geometries of polymeric micelles,namely linear micelles(LMs),worm-like micelles(WLMs),large spherical micelles(LSMs),and small spherical micelles(SSMs)to investigate the influence of shape effects on overcoming colonic mucosal barrier.We found that the carriers exhibited diverse shapes while maintaining comparable physicochemical properties.Of these,WLMs had an aspect ratio similar to segmented filamentous bacteria,which exhibited superior mucus penetration ability,leading to prolonged drug release kinetics and faster entry into epithelial cells compared to LSMs.Furthermore,rectally administrated 10-hydroxycamptothecin-loaded WLMs traversed the colorectal mucus in orthotopic CRC nude mice model,penetrated and accumulated within tumor tissue,and effectively aggregated within cancer cells,thereby inducing significantly robust antitumor outcomes in vivo.These findings underscore the significance of shape design in overcoming colonic mucosal absorption barriers,offering a novel approach for the development of drug delivery carriers tailored for effective tumor therapy.展开更多
A new method for characterizing fiber bending flexibility was developed by worm-like chain model proposed by Kratky-Porod,[1]which was first introduced to the pulp and paper field in this study.For the three types of ...A new method for characterizing fiber bending flexibility was developed by worm-like chain model proposed by Kratky-Porod,[1]which was first introduced to the pulp and paper field in this study.For the three types of pulps,the experimental results were compared with the KP chain model,and the resulting determination coefficients were all above 0.95,which proved that the model was feasible to be applied to these three fibers.The relation between fiber bending rigidity and that of cellulosic chains inside was discussed to deduce the fiber bending flexibility.The flexibility of an individual fiber can be approximated as the contribution of that of all the cellulose chains inside.By this method,the fiber flexibility values were determined to be in the range of 0.6×10^(11)-3.5×10^(11)N^(-1)·m^(-2),which was comparable to that of the conventional methods recorded in the literature.展开更多
The worm-like AlN nanowires are fabricated by the plasma-enhanced chemical vapor deposition(PECVD)on Si substrates through using Al powder and N2 as precursors,CaF2 as fluxing medium,Au as catalyst,respectively.The as...The worm-like AlN nanowires are fabricated by the plasma-enhanced chemical vapor deposition(PECVD)on Si substrates through using Al powder and N2 as precursors,CaF2 as fluxing medium,Au as catalyst,respectively.The as-grown worm-like AlN nanowires each have a polycrystalline and hexagonal wurtzite structure.Their diameters are about 300 nm,and the lengths are over 10μm.The growth mechanism of worm-like AlN nanowires is discussed.Hydrogen plasma plays a very important role in forming the polycrystalline structure and rough surfaces of worm-like AlN nanowires.The worm-like AlN nanowires exhibit an excellent field-emission(FE)property with a low turn-on field of 4.5 V/μm at a current density of 0.01 mA/cm^(2) and low threshold field of 9.9 V/μm at 1 mA/cm^(2).The emission current densities of worm-like AlN nanowires each have a good stability.The enhanced FE properties of worm-like AlN nanowires may be due to their polycrystalline and rough structure with nanosize and high aspect ratio.The excellent FE properties of worm-like AlN nanowires can be explained by a grain boundary conduction mechanism.The results demonstrate that the worm-like AlN nanowires prepared by the proposed simple and the PECVD method possesses the potential applications in photoelectric and field-emission devices.展开更多
The morphological stability of vesicles consisting of an amphiphilic poly(methacrylic acid)- block-poly(methyl methacrylate-random-methacrylic acid) diblock copolymer, PMAA-b-P(MMA-r-MAA), was investigated against the...The morphological stability of vesicles consisting of an amphiphilic poly(methacrylic acid)- block-poly(methyl methacrylate-random-methacrylic acid) diblock copolymer, PMAA-b-P(MMA-r-MAA), was investigated against the external stresses of pH, salt concentration and polyamine. The worm-like vesicles underwent a partial fusion at pH 12, however, they retained the worm-like shape at pH 13 due to electrostatic repulsion. On the other hand, the spherical vesicles were completely fused at pH 12, transformed into a sheet and did not retain their shape under the higher basic condition. Similarly, the worm-like vesicles retained their morphology in 0.1 mol% solutions of sodium chloride and sodium dodecyl sulfate, while the spherical vesicles caused division and fusion even at much lower concentrations. Poly(2-dimethylaminoethyl methacrylate)(PDMAEMA) transformed the worm-like vesicle into a cleavable sheet, while it changed the spherical vesicles into a sheet without a specific form. It was found that this transformation based on the acid-base interaction between the carboxylic acid of the MAA block and the amine of the PDMAEMA was dependent on the molecular weight of the PDMAEMA. The short PDMAEMA retarded the fusion of the vesicles.展开更多
Inspired by the morphology characteristics and the locomotion mechanisms of the earthworm,and the snakes’morphology characteristics and motivated by the demands for multi-modal locomotion robots in variable working e...Inspired by the morphology characteristics and the locomotion mechanisms of the earthworm,and the snakes’morphology characteristics and motivated by the demands for multi-modal locomotion robots in variable working environments,this paper presents a novel bi-modal robot named as Snake-Worm Locomotion Robot(SWL-Robot).Two fundamentally different locomotion mechanisms,the earthworm’s peristaltic rectilinear locomotion and the snake’s lateral undulation,are synthesized in the SWL-Robot design.In detail,the SWL-Robot consists of six earthworm-like body segments interconnected by rotational joints and a head segment equipped with a couple of independently driven wheels.By actuating the segments following a peristaltic wave-like gait,the robot as a whole could perform earthworm-like rectilinear crawling.The robot could also perform snake-like undulatory locomotion driven by differential motions of the wheels at the head segment.To understand the relationship between the design parameters and the robotic locomotion performance,kinematic models of the SWL-Robot corresponding to the two locomotion modes are developed.Rich locomotion behaviors of the SWL-Robot are achieved,including the peristaltic locomotion inside a tube,multiple planar motions on a flat surface,and a hybrid motion that switches between the tube and the flat surface.It shows that the measured trajectories of the SWL-Robot agree well with the theoretical predictions.The SWL-Robot is promising to be implemented in tasks where both tubular and flat environments may be encountered.展开更多
Two triblock polymers, tetraaniline-block-poly（N-isopropyl acrylamide）-block-poly（hydroxyethyl acrylate） （TA-b-PNIPAM-b-PHEA） and TA-b-PHEA-b-PNIPAM, were synthesized with unambiguous structure by a two step met...Two triblock polymers, tetraaniline-block-poly（N-isopropyl acrylamide）-block-poly（hydroxyethyl acrylate） （TA-b-PNIPAM-b-PHEA） and TA-b-PHEA-b-PNIPAM, were synthesized with unambiguous structure by a two step method. The difference of these two diblock polymers is the connection order of carboxyl group to block, e.g., carboxyl group to PNIPAM block for PNIPAM-b-PHEA and to PHEA block for PHEA-b-PNIPAM. Secondly, block tetraaniline was linked to the diblock polymer through amidation to yield the corresponding triblock copolymer. Both of them have almost the identical chemical compositions. The only difference is the connection order of each block in the triblock polymers. When they were self-assembled at 45℃ in a suitable solution, both of their aggregates have spherical shape with slight defects on their surface with the average diameter of about 400 nm. However, when their aggregate dispersion was cooled down to 20 ℃, only TA-b-PHEA-b-PNIPAM＇s morphology changed, forming worm-like aggregates with the diameter of about 100-200 nm transformed from spherical ag- gregates. Both amphiphilic property and position of each block in this triblock copolymer are very essential for this morphology transformation. Since the worm-like aggregates presented here by our group have hollow structure in- side, its controlled release properties for doxorubicin were evaluated. Drug release experiment indicated that along with the temperature changes, the rearrangement of the intermediate layer structure caused morphology change in aggregate, thus accelerating the speed of drug release.展开更多
Semi-rigid liquid crystal polymer is a class of liquid crystal polymers different from long rigid rod liquid crystal polymer to which the well-known Onsager and Flory theories are applied. In this paper, three statist...Semi-rigid liquid crystal polymer is a class of liquid crystal polymers different from long rigid rod liquid crystal polymer to which the well-known Onsager and Flory theories are applied. In this paper, three statistical models for the semi-rigid nematic polymer were addressed. They are the elastically jointed rod model, worm-like chain model, and non-homogeneous chain model. The nematic-isotropic transition temperature was examined. The pseudo-second transition temperature is expressed analytically. Comparisons with the experiments were made and the agreements were found.展开更多
The cationic amphiphilic lipid type compound 1,1’-{[3,5-bis(dodecyloxycarbonyl)-4-phenyl-1,4- dihydropyridin-2,6-diyl]dimethylene} bispyridinium dibromide (1,4-DHP lipid) (charge +2), is a gene transfection agent. Th...The cationic amphiphilic lipid type compound 1,1’-{[3,5-bis(dodecyloxycarbonyl)-4-phenyl-1,4- dihydropyridin-2,6-diyl]dimethylene} bispyridinium dibromide (1,4-DHP lipid) (charge +2), is a gene transfection agent. The electronic structure of 1,4-DHP lipid molecule was investigated by ab initio quantum mechanics, the charges were derived, and the supramolecular structure formed by 1,4-DHP lipid molecules in water was investigated by means of molecular dynamics simulation, f99 force field, version AMBER 8.0. During the molecular dynamics simulations of 10 ns of MD 1,4-DHP lipid formed a worm-like micellae, which was preserved during the time course of 300 ns of MD simulations. Result was confirmed with the electron microscopy showing extended, rod-like structures as one of the 1,4-DHP lipid supramolecular structures, which are expected to be formed at high 1,4-DHP lipid concentrations.展开更多
A kind of worm-like aggregates, consisting of very tiny curving tubes, was first found in a residual kaolin deposit at mine 414, Jiangxi Province. The results of several mineralogical analyses show that the single cur...A kind of worm-like aggregates, consisting of very tiny curving tubes, was first found in a residual kaolin deposit at mine 414, Jiangxi Province. The results of several mineralogical analyses show that the single curving tube is composed of gibbsite and metahalloysite minerals. This particular shape of mineral aggregates has not been reported before.展开更多
Swirl-like nanospiral is a common structure found in free-swimming biological systems,such as microtubules and actin filaments or slender bacteria.It is desired for artificially designed dynamic nanomaterials.However,...Swirl-like nanospiral is a common structure found in free-swimming biological systems,such as microtubules and actin filaments or slender bacteria.It is desired for artificially designed dynamic nanomaterials.However,the spiral formation has rarely been reported in both engineered peptides and regenerated proteins.Herein,we report that such a unique assembly behavior can be achieved by using a fusion peptide consisting of a silk-derived peptide(i.e.,GAGAGAGY)and a hydrophobic,photoresponsive azobenzene(Azo)segment.In this fusion structure,GAGAGAGY acts as a domain that spontaneously forms an elongated filament in an aqueous solution,while Azo acts as a"light-operated switch"that can undergo photoinduced isomerization to modulate the self-propulsion forces and assembly behavior.With this design,the critical factors that affect the assembly of Azo-GAGAGAGY filament,including(i)length and flexibility of filaments;(ii)propulsion,and(iii)excluded volume interactions force the tip of the filament to wind up,can be regulated to realize the spiral formation.In addition,the configurations of Azo-GAGAGAGY filaments,such as straight nanoribbons,wavy nanoribbons,single-circle spiral,and multiple-circle spiral,can be facilely mediated by changing the preparation procedure,concentration,and pH value of Azo-GAGAGAGY solution,as these changes have significant influences on self-propulsion forces.Our findings can help in the better understanding of nonequilibrium thermodynamics and collective behavior of biological systems.The findings can be used as a guideline for the designs of nanoactuators,microswimmers,transformable microrobots,and intelligent drug carriers.展开更多
Direct numerical simulation(DNS)of incompressible flows in a zeropressure gradient turbulent boundary layer(TBL)is conducted by a finite difference method in which a fourth order upwind scheme is applied to discretize...Direct numerical simulation(DNS)of incompressible flows in a zeropressure gradient turbulent boundary layer(TBL)is conducted by a finite difference method in which a fourth order upwind scheme is applied to discretize the convective terms while a re-scaling approach is used to set inlet flow conditions.The Reynolds numbers based on free flow velocity and momentum thickness at the recycle section are respectively 687,1074,and 1430.The DNS has obtained favorable results indicating that the turbulence statistics is quite satisfactory as compared with the existing numerical and experimental results.The three dimensional turbulent structures at the momentum thickness Reynolds number of 1430 in several different instants are illustrated by the iso-surface of swirl strength square(the square of imaginary part of the complex eigenvalue of velocity gradient tensor)together with velocity vectors in three different cross sections.It is found that there are three kinds of vortical structures:quasi-symmetrical and asymmetrical hairpin vortices,and worm-like vortices.The DNS based on the numerical method can certainly reveal the main characteristics of the TBL flows at the given Reynolds numbers.展开更多
Recently Hari Shroff and his collaborators[Nano Letters 5(2005)]developed a nanoscopic force sensor,but the force which they measured in their single molecular experiment was much lower than the theoretical critical v...Recently Hari Shroff and his collaborators[Nano Letters 5(2005)]developed a nanoscopic force sensor,but the force which they measured in their single molecular experiment was much lower than the theoretical critical value.In order to fix this problem,we investigate the micromechanics of dsDNA based on the worm-like chain model and flexible hinge model by using Monte Carlo algorithm.The simulation results not only address Hari Shroff’s experiment difficulty reasonably,but also provide strong support for flexible hinge mechanism put forward recently by Yan and Marko[Phys.Rev.Lett.93(2004)].展开更多
基金the financial support from the National Natural Science Foundation of China(Nos.82003678,82222066,82025032)Chinese Pharmacopoeia Commission(No.2021Y30)。
文摘Local delivery of nanoparticles holds promise for colorectal cancer(CRC)therapy.However,the presence of the mucus layer on the epithelium poses a significant challenge to drug delivery,thereby adversely affecting treatment efficiency.It is crucial to develop efficient drug delivery carriers that can effectively overcome mucus barriers to treat colorectal cancer.Herein,we utilized poly(1,4-butadiene)-b-poly(ethylene oxide)polymers to prepare four distinct geometries of polymeric micelles,namely linear micelles(LMs),worm-like micelles(WLMs),large spherical micelles(LSMs),and small spherical micelles(SSMs)to investigate the influence of shape effects on overcoming colonic mucosal barrier.We found that the carriers exhibited diverse shapes while maintaining comparable physicochemical properties.Of these,WLMs had an aspect ratio similar to segmented filamentous bacteria,which exhibited superior mucus penetration ability,leading to prolonged drug release kinetics and faster entry into epithelial cells compared to LSMs.Furthermore,rectally administrated 10-hydroxycamptothecin-loaded WLMs traversed the colorectal mucus in orthotopic CRC nude mice model,penetrated and accumulated within tumor tissue,and effectively aggregated within cancer cells,thereby inducing significantly robust antitumor outcomes in vivo.These findings underscore the significance of shape design in overcoming colonic mucosal absorption barriers,offering a novel approach for the development of drug delivery carriers tailored for effective tumor therapy.
基金financially supported by the National Natural Science Foundation of China (No. 21534002)National Key R&D Program of China (No. 2019YFC1520402)
文摘A new method for characterizing fiber bending flexibility was developed by worm-like chain model proposed by Kratky-Porod,[1]which was first introduced to the pulp and paper field in this study.For the three types of pulps,the experimental results were compared with the KP chain model,and the resulting determination coefficients were all above 0.95,which proved that the model was feasible to be applied to these three fibers.The relation between fiber bending rigidity and that of cellulosic chains inside was discussed to deduce the fiber bending flexibility.The flexibility of an individual fiber can be approximated as the contribution of that of all the cellulose chains inside.By this method,the fiber flexibility values were determined to be in the range of 0.6×10^(11)-3.5×10^(11)N^(-1)·m^(-2),which was comparable to that of the conventional methods recorded in the literature.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11774017 and 51761135129).
文摘The worm-like AlN nanowires are fabricated by the plasma-enhanced chemical vapor deposition(PECVD)on Si substrates through using Al powder and N2 as precursors,CaF2 as fluxing medium,Au as catalyst,respectively.The as-grown worm-like AlN nanowires each have a polycrystalline and hexagonal wurtzite structure.Their diameters are about 300 nm,and the lengths are over 10μm.The growth mechanism of worm-like AlN nanowires is discussed.Hydrogen plasma plays a very important role in forming the polycrystalline structure and rough surfaces of worm-like AlN nanowires.The worm-like AlN nanowires exhibit an excellent field-emission(FE)property with a low turn-on field of 4.5 V/μm at a current density of 0.01 mA/cm^(2) and low threshold field of 9.9 V/μm at 1 mA/cm^(2).The emission current densities of worm-like AlN nanowires each have a good stability.The enhanced FE properties of worm-like AlN nanowires may be due to their polycrystalline and rough structure with nanosize and high aspect ratio.The excellent FE properties of worm-like AlN nanowires can be explained by a grain boundary conduction mechanism.The results demonstrate that the worm-like AlN nanowires prepared by the proposed simple and the PECVD method possesses the potential applications in photoelectric and field-emission devices.
文摘The morphological stability of vesicles consisting of an amphiphilic poly(methacrylic acid)- block-poly(methyl methacrylate-random-methacrylic acid) diblock copolymer, PMAA-b-P(MMA-r-MAA), was investigated against the external stresses of pH, salt concentration and polyamine. The worm-like vesicles underwent a partial fusion at pH 12, however, they retained the worm-like shape at pH 13 due to electrostatic repulsion. On the other hand, the spherical vesicles were completely fused at pH 12, transformed into a sheet and did not retain their shape under the higher basic condition. Similarly, the worm-like vesicles retained their morphology in 0.1 mol% solutions of sodium chloride and sodium dodecyl sulfate, while the spherical vesicles caused division and fusion even at much lower concentrations. Poly(2-dimethylaminoethyl methacrylate)(PDMAEMA) transformed the worm-like vesicle into a cleavable sheet, while it changed the spherical vesicles into a sheet without a specific form. It was found that this transformation based on the acid-base interaction between the carboxylic acid of the MAA block and the amine of the PDMAEMA was dependent on the molecular weight of the PDMAEMA. The short PDMAEMA retarded the fusion of the vesicles.
基金This research is supported by the National Natural Science Foundation of China under Grant no.11932015the Major Research Plan of the National Natural Science Foundation of China under Grant no.91748203.
文摘Inspired by the morphology characteristics and the locomotion mechanisms of the earthworm,and the snakes’morphology characteristics and motivated by the demands for multi-modal locomotion robots in variable working environments,this paper presents a novel bi-modal robot named as Snake-Worm Locomotion Robot(SWL-Robot).Two fundamentally different locomotion mechanisms,the earthworm’s peristaltic rectilinear locomotion and the snake’s lateral undulation,are synthesized in the SWL-Robot design.In detail,the SWL-Robot consists of six earthworm-like body segments interconnected by rotational joints and a head segment equipped with a couple of independently driven wheels.By actuating the segments following a peristaltic wave-like gait,the robot as a whole could perform earthworm-like rectilinear crawling.The robot could also perform snake-like undulatory locomotion driven by differential motions of the wheels at the head segment.To understand the relationship between the design parameters and the robotic locomotion performance,kinematic models of the SWL-Robot corresponding to the two locomotion modes are developed.Rich locomotion behaviors of the SWL-Robot are achieved,including the peristaltic locomotion inside a tube,multiple planar motions on a flat surface,and a hybrid motion that switches between the tube and the flat surface.It shows that the measured trajectories of the SWL-Robot agree well with the theoretical predictions.The SWL-Robot is promising to be implemented in tasks where both tubular and flat environments may be encountered.
基金This study was supported by the National Natural Science Foundation of China （No. 50903096）.
文摘Two triblock polymers, tetraaniline-block-poly（N-isopropyl acrylamide）-block-poly（hydroxyethyl acrylate） （TA-b-PNIPAM-b-PHEA） and TA-b-PHEA-b-PNIPAM, were synthesized with unambiguous structure by a two step method. The difference of these two diblock polymers is the connection order of carboxyl group to block, e.g., carboxyl group to PNIPAM block for PNIPAM-b-PHEA and to PHEA block for PHEA-b-PNIPAM. Secondly, block tetraaniline was linked to the diblock polymer through amidation to yield the corresponding triblock copolymer. Both of them have almost the identical chemical compositions. The only difference is the connection order of each block in the triblock polymers. When they were self-assembled at 45℃ in a suitable solution, both of their aggregates have spherical shape with slight defects on their surface with the average diameter of about 400 nm. However, when their aggregate dispersion was cooled down to 20 ℃, only TA-b-PHEA-b-PNIPAM＇s morphology changed, forming worm-like aggregates with the diameter of about 100-200 nm transformed from spherical ag- gregates. Both amphiphilic property and position of each block in this triblock copolymer are very essential for this morphology transformation. Since the worm-like aggregates presented here by our group have hollow structure in- side, its controlled release properties for doxorubicin were evaluated. Drug release experiment indicated that along with the temperature changes, the rearrangement of the intermediate layer structure caused morphology change in aggregate, thus accelerating the speed of drug release.
基金The work was supported by the Foundation of State Education Committee of China
文摘Semi-rigid liquid crystal polymer is a class of liquid crystal polymers different from long rigid rod liquid crystal polymer to which the well-known Onsager and Flory theories are applied. In this paper, three statistical models for the semi-rigid nematic polymer were addressed. They are the elastically jointed rod model, worm-like chain model, and non-homogeneous chain model. The nematic-isotropic transition temperature was examined. The pseudo-second transition temperature is expressed analytically. Comparisons with the experiments were made and the agreements were found.
文摘The cationic amphiphilic lipid type compound 1,1’-{[3,5-bis(dodecyloxycarbonyl)-4-phenyl-1,4- dihydropyridin-2,6-diyl]dimethylene} bispyridinium dibromide (1,4-DHP lipid) (charge +2), is a gene transfection agent. The electronic structure of 1,4-DHP lipid molecule was investigated by ab initio quantum mechanics, the charges were derived, and the supramolecular structure formed by 1,4-DHP lipid molecules in water was investigated by means of molecular dynamics simulation, f99 force field, version AMBER 8.0. During the molecular dynamics simulations of 10 ns of MD 1,4-DHP lipid formed a worm-like micellae, which was preserved during the time course of 300 ns of MD simulations. Result was confirmed with the electron microscopy showing extended, rod-like structures as one of the 1,4-DHP lipid supramolecular structures, which are expected to be formed at high 1,4-DHP lipid concentrations.
基金Project supported by the National Natural Science Foundation of China
文摘A kind of worm-like aggregates, consisting of very tiny curving tubes, was first found in a residual kaolin deposit at mine 414, Jiangxi Province. The results of several mineralogical analyses show that the single curving tube is composed of gibbsite and metahalloysite minerals. This particular shape of mineral aggregates has not been reported before.
基金This work is supported by the National Natural Science Foundation of China(No.21935002).
文摘Swirl-like nanospiral is a common structure found in free-swimming biological systems,such as microtubules and actin filaments or slender bacteria.It is desired for artificially designed dynamic nanomaterials.However,the spiral formation has rarely been reported in both engineered peptides and regenerated proteins.Herein,we report that such a unique assembly behavior can be achieved by using a fusion peptide consisting of a silk-derived peptide(i.e.,GAGAGAGY)and a hydrophobic,photoresponsive azobenzene(Azo)segment.In this fusion structure,GAGAGAGY acts as a domain that spontaneously forms an elongated filament in an aqueous solution,while Azo acts as a"light-operated switch"that can undergo photoinduced isomerization to modulate the self-propulsion forces and assembly behavior.With this design,the critical factors that affect the assembly of Azo-GAGAGAGY filament,including(i)length and flexibility of filaments;(ii)propulsion,and(iii)excluded volume interactions force the tip of the filament to wind up,can be regulated to realize the spiral formation.In addition,the configurations of Azo-GAGAGAGY filaments,such as straight nanoribbons,wavy nanoribbons,single-circle spiral,and multiple-circle spiral,can be facilely mediated by changing the preparation procedure,concentration,and pH value of Azo-GAGAGAGY solution,as these changes have significant influences on self-propulsion forces.Our findings can help in the better understanding of nonequilibrium thermodynamics and collective behavior of biological systems.The findings can be used as a guideline for the designs of nanoactuators,microswimmers,transformable microrobots,and intelligent drug carriers.
文摘Direct numerical simulation(DNS)of incompressible flows in a zeropressure gradient turbulent boundary layer(TBL)is conducted by a finite difference method in which a fourth order upwind scheme is applied to discretize the convective terms while a re-scaling approach is used to set inlet flow conditions.The Reynolds numbers based on free flow velocity and momentum thickness at the recycle section are respectively 687,1074,and 1430.The DNS has obtained favorable results indicating that the turbulence statistics is quite satisfactory as compared with the existing numerical and experimental results.The three dimensional turbulent structures at the momentum thickness Reynolds number of 1430 in several different instants are illustrated by the iso-surface of swirl strength square(the square of imaginary part of the complex eigenvalue of velocity gradient tensor)together with velocity vectors in three different cross sections.It is found that there are three kinds of vortical structures:quasi-symmetrical and asymmetrical hairpin vortices,and worm-like vortices.The DNS based on the numerical method can certainly reveal the main characteristics of the TBL flows at the given Reynolds numbers.
基金This research was supported by the Young Investigator Award received by Yan in 2006 and the Foundation for the Visiting PhD Candidate of the Chinese Academy of Science received by Liu in 2006Liu is also supported by the Innovation Foundation for Graduate Students of Guizhou University(2007022).
文摘Recently Hari Shroff and his collaborators[Nano Letters 5(2005)]developed a nanoscopic force sensor,but the force which they measured in their single molecular experiment was much lower than the theoretical critical value.In order to fix this problem,we investigate the micromechanics of dsDNA based on the worm-like chain model and flexible hinge model by using Monte Carlo algorithm.The simulation results not only address Hari Shroff’s experiment difficulty reasonably,but also provide strong support for flexible hinge mechanism put forward recently by Yan and Marko[Phys.Rev.Lett.93(2004)].
