Bacterial flagellar filaments can undergo a polymorphic phase transition in both vitro and vivo environments. Each bacterial flagellar filament has 12 different helical forms which are macroscopically represented by d...Bacterial flagellar filaments can undergo a polymorphic phase transition in both vitro and vivo environments. Each bacterial flagellar filament has 12 different helical forms which are macroscopically represented by different pitch lengths and helix radii. For external mechanical force induced filament phase transitions, there is so far only one experiment performed by Hotani in 1982, who showed a very beautiful cyclic phase transition phenomenon in his experiment on isolated flagellar filaments. In the present paper, we give a detailed mechanical analysis on Hotani＇s experiments. Through theoretical computations, we obtained a phase transition rule based on the phase transition mechanism. The theoretical analysis provides a foundation facilitating the establishment of phase transition theory for bacterial flagellar filaments.展开更多
Bacterial flagellar filament can undergo a stress-induced polymorphic phase transition in both vitro and vivo environments.The filament has 12 different helical forms(phases) characterized by different pitch lengths a...Bacterial flagellar filament can undergo a stress-induced polymorphic phase transition in both vitro and vivo environments.The filament has 12 different helical forms(phases) characterized by different pitch lengths and helix radii.When subjected to the frictional force of flowing fluid,the filament changes between a left-handed normal phase and a right-handed semi-coiled phase via phase nucleation and growth.This paper develops non-local finite element method(FEM) to simulate the phase transition under a displacement-controlled loading condition(controlled helix-twist).The FEM formulation is based on the Ginzburg-Landau theory using a one-dimensional non-convex and non-local continuum model.To describe the processes of the phase nucleation and growth,viscosity-type kinetics is also used.The non-local FEM simulation captures the main features of the phase transition:two-phase coexistence with an interface of finite thickness,phase nucleation and phase growth with interface propagation.The non-local FEM model provides a tool to study the effects of the interfacial energy/thickness and loading conditions on the phase transition.展开更多
Lead-free(K0.5-x/2Na0.5-x/2Lix)(Nb0.8Ta0.2)O3(KNLNT)and(K0.49-x/2Na0.49-x/2-LixCa0.01)(Nb0.8Ta0.2)O3(KNLNT-Ca)ceramics were prepared by a conventional ceramic processing.Structural analysis shows that the Ca^2+ doping...Lead-free(K0.5-x/2Na0.5-x/2Lix)(Nb0.8Ta0.2)O3(KNLNT)and(K0.49-x/2Na0.49-x/2-LixCa0.01)(Nb0.8Ta0.2)O3(KNLNT-Ca)ceramics were prepared by a conventional ceramic processing.Structural analysis shows that the Ca^2+ doping takes the A site of ABO3 perovskite and decreases the phase transition temperature.Property measurements reveal that as a donor dopant,the Ca^2+ doping results in higher room-temperature dielectric constant,lower dielectric loss,and lower mechanical quality factor.In addition,the Ca^2+ doping does not change the positive piezoelectric coefficient d33,but increases the converse piezoelectric coefficient d 33*significantly.This is likely due to the increase in the relaxation,as well as the appearance of(CaNa/K·-VNa/K’)defect dipoles.展开更多
基金supported by the Hong Kong University of Science and Technology and the National Natural Science Foundation of China (10902013)
文摘Bacterial flagellar filaments can undergo a polymorphic phase transition in both vitro and vivo environments. Each bacterial flagellar filament has 12 different helical forms which are macroscopically represented by different pitch lengths and helix radii. For external mechanical force induced filament phase transitions, there is so far only one experiment performed by Hotani in 1982, who showed a very beautiful cyclic phase transition phenomenon in his experiment on isolated flagellar filaments. In the present paper, we give a detailed mechanical analysis on Hotani＇s experiments. Through theoretical computations, we obtained a phase transition rule based on the phase transition mechanism. The theoretical analysis provides a foundation facilitating the establishment of phase transition theory for bacterial flagellar filaments.
基金supported by the Hong Kong University of Science and Technology and the National Natural Science Foundation of China (10902013)
文摘Bacterial flagellar filament can undergo a stress-induced polymorphic phase transition in both vitro and vivo environments.The filament has 12 different helical forms(phases) characterized by different pitch lengths and helix radii.When subjected to the frictional force of flowing fluid,the filament changes between a left-handed normal phase and a right-handed semi-coiled phase via phase nucleation and growth.This paper develops non-local finite element method(FEM) to simulate the phase transition under a displacement-controlled loading condition(controlled helix-twist).The FEM formulation is based on the Ginzburg-Landau theory using a one-dimensional non-convex and non-local continuum model.To describe the processes of the phase nucleation and growth,viscosity-type kinetics is also used.The non-local FEM simulation captures the main features of the phase transition:two-phase coexistence with an interface of finite thickness,phase nucleation and phase growth with interface propagation.The non-local FEM model provides a tool to study the effects of the interfacial energy/thickness and loading conditions on the phase transition.
文摘Lead-free(K0.5-x/2Na0.5-x/2Lix)(Nb0.8Ta0.2)O3(KNLNT)and(K0.49-x/2Na0.49-x/2-LixCa0.01)(Nb0.8Ta0.2)O3(KNLNT-Ca)ceramics were prepared by a conventional ceramic processing.Structural analysis shows that the Ca^2+ doping takes the A site of ABO3 perovskite and decreases the phase transition temperature.Property measurements reveal that as a donor dopant,the Ca^2+ doping results in higher room-temperature dielectric constant,lower dielectric loss,and lower mechanical quality factor.In addition,the Ca^2+ doping does not change the positive piezoelectric coefficient d33,but increases the converse piezoelectric coefficient d 33*significantly.This is likely due to the increase in the relaxation,as well as the appearance of(CaNa/K·-VNa/K’)defect dipoles.
