Double helix DNAs become intertwined around one another during replication and recombination.Here we used magnetic tweezers to make braided DNA molecules and measured their torques under various catenations(Ca)at forc...Double helix DNAs become intertwined around one another during replication and recombination.Here we used magnetic tweezers to make braided DNA molecules and measured their torques under various catenations(Ca)at forces ranging from 0.3 to 8 pN.Images of braided DNA constructs under tensions were captured by scanning electron microscopy which showed major and minor grooves of DNAs and plectonemes of the braids.When the two DNA molecules were braided,the extension decreased as the catenation increased from 0 to 50 turns.We used a thermodynamic Maxwell relation to deduce the torque by integrating the change in the braid extension as a function of the force.The torque increased with the catenation,force and intertether distance until the catenation reached a buckling point.Under the condition of 2 pN force and Ca=20,the torque was computed to be 31,21 and 15 pN nm for the braids of which the intertether distances were 54%,31%and 26%of the DNA contour length,respectively.At an 8.03 pN holding force,the torque was computed to be 76 pN nm as the catenation increased from 0 to 30 turns,or as the catenation density varied from 0 to 0.053.The torque reached a plateau when the catenation increased above 20,indicating formation of braid-plectonemes.The twist modulus increased with the catenation prior to reaching a peak.Before reaching the peak,the moduli were higher than those of a single twisted DNA under the same catenation and applied force.Our experimental data agrees well with the calculation results by a recently developed semiflexible polymer model.Our measurements of the nonlinear torque of the braid establish new fundamental properties of DNA intertwining,which is key to understanding DNA replication and gene expression.The speaker will also introduce briefly other projects in the Xiao group including direct measurements of theforce spectrum of single unlabeled proteins such as adhesive nano-fibers for biofilm,the screening of integrin-targeted peptides drugs by single cell approaches,and the micromechanical approach for determining the survival rate of stem cells.展开更多
Compression performance of 5-axial braided composites is observed through compression tests.A mixed model of micro-buckling shear with braided tows web is set up to predict compression stress of braided composite thro...Compression performance of 5-axial braided composites is observed through compression tests.A mixed model of micro-buckling shear with braided tows web is set up to predict compression stress of braided composite through analyzing three broken modes.Using this mixed model,data from tests indicated that the main parameters effecting the compression properties of braided composite are fiber volume fraction,directional angle,axial-tow volume fraction and diameter of tow.Contributing rate of tows is proposed to describe the compression properties of fibre composites.Optimization geometrical structure of braids can optimize composite properties.展开更多
To develop electromagnetic protection composites with integrated structure -function properties, the three-dimension (3D) braided nickel plated carbon fiber/epoxy resin (Ni-CF3D/EP) composites were prepared based on 3...To develop electromagnetic protection composites with integrated structure -function properties, the three-dimension (3D) braided nickel plated carbon fiber/epoxy resin (Ni-CF3D/EP) composites were prepared based on 3D five-directional braiding, unitary nickel plating and mold compression shaping. The electromagnetic protection properties of Ni-CF3D/EP composites including shielding effective- ness (SE) and reflection loss against plane electromagnetic wave, shielding properties against electromagnetic pulse (EMP) were investigated. The test results show that the novel composites have good electromagnetic protection properties in a wide frequency range of 14 kHz～18 GHz with SE of 42 dB～95 dB, the absorption bandwidth of –5 dB in 2 GHz～18 GHz can reach 10 GHz and the pulse peak SE against EMP is 43.7 dB which can reduce the electromagnetic energy greatly. Meanwhile, the mechanic properties were also investi- gated and the results indicate that the Ni-CF3D/EP composites can replace metal materials for loading-bearing structural applications because of their excellent mechanic properties.展开更多
基金supported by the National Science Foundation of China ( 11772133, 11372116)the Fundamental Research Funds for the Central Universities ( HUST 0118012051)supported by the NIH through grants ( R01-GM105847,U54-CA193419)
文摘Double helix DNAs become intertwined around one another during replication and recombination.Here we used magnetic tweezers to make braided DNA molecules and measured their torques under various catenations(Ca)at forces ranging from 0.3 to 8 pN.Images of braided DNA constructs under tensions were captured by scanning electron microscopy which showed major and minor grooves of DNAs and plectonemes of the braids.When the two DNA molecules were braided,the extension decreased as the catenation increased from 0 to 50 turns.We used a thermodynamic Maxwell relation to deduce the torque by integrating the change in the braid extension as a function of the force.The torque increased with the catenation,force and intertether distance until the catenation reached a buckling point.Under the condition of 2 pN force and Ca=20,the torque was computed to be 31,21 and 15 pN nm for the braids of which the intertether distances were 54%,31%and 26%of the DNA contour length,respectively.At an 8.03 pN holding force,the torque was computed to be 76 pN nm as the catenation increased from 0 to 30 turns,or as the catenation density varied from 0 to 0.053.The torque reached a plateau when the catenation increased above 20,indicating formation of braid-plectonemes.The twist modulus increased with the catenation prior to reaching a peak.Before reaching the peak,the moduli were higher than those of a single twisted DNA under the same catenation and applied force.Our experimental data agrees well with the calculation results by a recently developed semiflexible polymer model.Our measurements of the nonlinear torque of the braid establish new fundamental properties of DNA intertwining,which is key to understanding DNA replication and gene expression.The speaker will also introduce briefly other projects in the Xiao group including direct measurements of theforce spectrum of single unlabeled proteins such as adhesive nano-fibers for biofilm,the screening of integrin-targeted peptides drugs by single cell approaches,and the micromechanical approach for determining the survival rate of stem cells.
文摘Compression performance of 5-axial braided composites is observed through compression tests.A mixed model of micro-buckling shear with braided tows web is set up to predict compression stress of braided composite through analyzing three broken modes.Using this mixed model,data from tests indicated that the main parameters effecting the compression properties of braided composite are fiber volume fraction,directional angle,axial-tow volume fraction and diameter of tow.Contributing rate of tows is proposed to describe the compression properties of fibre composites.Optimization geometrical structure of braids can optimize composite properties.
基金Project supported by Equipment Pre-research Foundation of China (9140A31030110JB3403)
文摘To develop electromagnetic protection composites with integrated structure -function properties, the three-dimension (3D) braided nickel plated carbon fiber/epoxy resin (Ni-CF3D/EP) composites were prepared based on 3D five-directional braiding, unitary nickel plating and mold compression shaping. The electromagnetic protection properties of Ni-CF3D/EP composites including shielding effective- ness (SE) and reflection loss against plane electromagnetic wave, shielding properties against electromagnetic pulse (EMP) were investigated. The test results show that the novel composites have good electromagnetic protection properties in a wide frequency range of 14 kHz～18 GHz with SE of 42 dB～95 dB, the absorption bandwidth of –5 dB in 2 GHz～18 GHz can reach 10 GHz and the pulse peak SE against EMP is 43.7 dB which can reduce the electromagnetic energy greatly. Meanwhile, the mechanic properties were also investi- gated and the results indicate that the Ni-CF3D/EP composites can replace metal materials for loading-bearing structural applications because of their excellent mechanic properties.
