The Experts below are selected from a list of 222357 Experts worldwide ranked by ideXlab platform

Markus J Buehler - One of the best experts on this subject based on the ideXlab platform.

  • secondary structure transition and Critical Stress for a model of spider silk assembly
    Biomacromolecules, 2016
    Co-Authors: Tristan Giesa, Carole C Perry, Markus J Buehler
    Abstract:

    Spiders spin their silk from an aqueous solution to a solid fiber in ambient conditions. However, to date, the assembly mechanism in the spider silk gland has not been satisfactorily explained. In this paper, we use molecular dynamics simulations to model Nephila clavipes MaSp1 dragline silk formation under shear flow and determine the secondary structure transitions leading to the experimentally observed fiber structures. While no experiments are performed on the silk fiber itself, insights from this polypeptide model can be transferred to the fiber scale. The novelty of this study lies in the calculation of the shear Stress (300–700 MPa) required for fiber formation and identification of the amino acid residues involved in the transition. This is the first time that the shear Stress has been quantified in connection with a secondary structure transition. By study of molecules containing varying numbers of contiguous MaSp1 repeats, we determine that the smallest molecule size giving rise to a “silk-like”...

  • Secondary Structure Transition and Critical Stress for a Model of Spider Silk Assembly
    2016
    Co-Authors: Tristan Giesa, Carole C Perry, Markus J Buehler
    Abstract:

    Spiders spin their silk from an aqueous solution to a solid fiber in ambient conditions. However, to date, the assembly mechanism in the spider silk gland has not been satisfactorily explained. In this paper, we use molecular dynamics simulations to model Nephila clavipes MaSp1 dragline silk formation under shear flow and determine the secondary structure transitions leading to the experimentally observed fiber structures. While no experiments are performed on the silk fiber itself, insights from this polypeptide model can be transferred to the fiber scale. The novelty of this study lies in the calculation of the shear Stress (300–700 MPa) required for fiber formation and identification of the amino acid residues involved in the transition. This is the first time that the shear Stress has been quantified in connection with a secondary structure transition. By study of molecules containing varying numbers of contiguous MaSp1 repeats, we determine that the smallest molecule size giving rise to a “silk-like” structure contains six polyalanine repeats. Through a probability analysis of the secondary structure, we identify specific amino acids that transition from α-helix to β-sheet. In addition to portions of the polyalanine section, these amino acids include glycine, leucine, and glutamine. The stability of β-sheet structures appears to arise from a close proximity in space of helices in the initial spidroin state. Our results are in agreement with the forces exerted by spiders in the silking process and the experimentally determined global secondary structure of spidroin and pulled MaSp1 silk. Our study emphasizes the role of shear in the assembly process of silk and can guide the design of microfluidic devices that attempt to mimic the natural spinning process and predict molecular requirements for the next generation of silk-based functional materials

Fumihiro Wakai - One of the best experts on this subject based on the ideXlab platform.

  • strength and toughness of nanocrystalline sio 2 stishovite toughened by fracture induced amorphization
    Acta Materialia, 2017
    Co-Authors: Kimiko Yoshida, Norimasa Nishiyama, Masato Sone, Fumihiro Wakai
    Abstract:

    Abstract The finding of “fracture-induced amorphization” in nanocrystalline SiO 2 stishovite lead to a proposal of a new type of transformation toughening by the direct transition from crystal to amorphous state, which is different from the classical martensitic transformation of zirconia. Here, we investigated strength and toughness of nanocrystalline stishovite by using micro-cantilever beam specimens of different sizes. The maximum strength of 6.3 GPa gave the estimate of the lower bound of Critical Stress for amorphization, which was much higher than the Critical transformation Stress of zirconia. The crack growth resistance curve (R-curve) rose steeply with crack extension of only a few μm, and reached to a plateau value of 10.9 MPa m 1/2 . We discussed the effects of grain size, microstrain, and dislocation density on the Critical Stress, the transformation zone width, and thereby, the fracture toughness.

Wei-bin Yuan - One of the best experts on this subject based on the ideXlab platform.

  • distortional buckling of perforated cold formed steel beams subject to uniformly distributed transverse loads
    Thin-walled Structures, 2020
    Co-Authors: Boksun Kim, Weijian Hong, Wei-bin Yuan
    Abstract:

    Abstract Thin-walled channel beams are easily punched with circular holes on the web to allow the access for services such as plumbing pipes and electric wires. The presence of the holes can alter the Stress distribution in the member and reduce the cross-sectional property. Consequently, it changes its buckling mode. Since perforated cold-formed steel beams are usually placed between main structural frame and corrugated roof, the most common loading case is the uniformly distributed transverse load. Recent work by Chen and Li has given the solution for distortional buckling of channel-, zed- and sigma-sections subject to the uniformly distributed transverse load. This paper is an extension of Chen and Li's research to explore the distortional buckling behaviour of perforated cold-formed steel beams with holes. The effect of perforations on the Critical Stress is evaluated. A new model is deduced to predict the Critical Stress of distortional buckling by reducing the stiffness of the vertical spring. The Rayleigh-Ritz method is used to solve eigenvalue problems. In order to validate the analytical model, finite element analyses have been performed by using ANSYS. When the beam is longer than 3500 mm, the Critical Stress computed from the analytical model matches well with the Critical Stress acquired from the finite element analyses.

  • Distortional buckling of perforated cold-formed steel channel-section beams with circular holes in web
    International Journal of Mechanical Sciences, 2017
    Co-Authors: Wei-bin Yuan, Nan-ting Yu, Long-yuan Li
    Abstract:

    Abstract This paper presents the numerical and analytical investigations on the distortional buckling of perforated cold-formed steel channel-section beams with circular holes in web. The numerical investigation involves the use of finite element methods. In the analytical analysis the distortional buckling model recommended in EN1993-1-3 is employed. The influence of the web holes on the distortional buckling behaviour and corresponding Critical Stress and moment of perforated cold-formed steel channel-section beams are discussed. Finally, a simple analytical formulation is proposed for evaluating the effect of hole size on the reduction of Critical Stress and Critical moment of the channel-section beams with circular holes in web.

Tristan Giesa - One of the best experts on this subject based on the ideXlab platform.

  • secondary structure transition and Critical Stress for a model of spider silk assembly
    Biomacromolecules, 2016
    Co-Authors: Tristan Giesa, Carole C Perry, Markus J Buehler
    Abstract:

    Spiders spin their silk from an aqueous solution to a solid fiber in ambient conditions. However, to date, the assembly mechanism in the spider silk gland has not been satisfactorily explained. In this paper, we use molecular dynamics simulations to model Nephila clavipes MaSp1 dragline silk formation under shear flow and determine the secondary structure transitions leading to the experimentally observed fiber structures. While no experiments are performed on the silk fiber itself, insights from this polypeptide model can be transferred to the fiber scale. The novelty of this study lies in the calculation of the shear Stress (300–700 MPa) required for fiber formation and identification of the amino acid residues involved in the transition. This is the first time that the shear Stress has been quantified in connection with a secondary structure transition. By study of molecules containing varying numbers of contiguous MaSp1 repeats, we determine that the smallest molecule size giving rise to a “silk-like”...

  • Secondary Structure Transition and Critical Stress for a Model of Spider Silk Assembly
    2016
    Co-Authors: Tristan Giesa, Carole C Perry, Markus J Buehler
    Abstract:

    Spiders spin their silk from an aqueous solution to a solid fiber in ambient conditions. However, to date, the assembly mechanism in the spider silk gland has not been satisfactorily explained. In this paper, we use molecular dynamics simulations to model Nephila clavipes MaSp1 dragline silk formation under shear flow and determine the secondary structure transitions leading to the experimentally observed fiber structures. While no experiments are performed on the silk fiber itself, insights from this polypeptide model can be transferred to the fiber scale. The novelty of this study lies in the calculation of the shear Stress (300–700 MPa) required for fiber formation and identification of the amino acid residues involved in the transition. This is the first time that the shear Stress has been quantified in connection with a secondary structure transition. By study of molecules containing varying numbers of contiguous MaSp1 repeats, we determine that the smallest molecule size giving rise to a “silk-like” structure contains six polyalanine repeats. Through a probability analysis of the secondary structure, we identify specific amino acids that transition from α-helix to β-sheet. In addition to portions of the polyalanine section, these amino acids include glycine, leucine, and glutamine. The stability of β-sheet structures appears to arise from a close proximity in space of helices in the initial spidroin state. Our results are in agreement with the forces exerted by spiders in the silking process and the experimentally determined global secondary structure of spidroin and pulled MaSp1 silk. Our study emphasizes the role of shear in the assembly process of silk and can guide the design of microfluidic devices that attempt to mimic the natural spinning process and predict molecular requirements for the next generation of silk-based functional materials

Long-yuan Li - One of the best experts on this subject based on the ideXlab platform.

  • Distortional buckling of perforated cold-formed steel channel-section beams with circular holes in web
    International Journal of Mechanical Sciences, 2017
    Co-Authors: Wei-bin Yuan, Nan-ting Yu, Long-yuan Li
    Abstract:

    Abstract This paper presents the numerical and analytical investigations on the distortional buckling of perforated cold-formed steel channel-section beams with circular holes in web. The numerical investigation involves the use of finite element methods. In the analytical analysis the distortional buckling model recommended in EN1993-1-3 is employed. The influence of the web holes on the distortional buckling behaviour and corresponding Critical Stress and moment of perforated cold-formed steel channel-section beams are discussed. Finally, a simple analytical formulation is proposed for evaluating the effect of hole size on the reduction of Critical Stress and Critical moment of the channel-section beams with circular holes in web.