The Experts below are selected from a list of 174 Experts worldwide ranked by ideXlab platform

Frauke Grater - One of the best experts on this subject based on the ideXlab platform.

  • viscous friction between crystalline and amorphous phase of dragline silk
    PLOS ONE, 2014
    Co-Authors: Sandeep P Patil, Senbo Xiao, Konstantinos Gkagkas, Bernd Markert, Frauke Grater
    Abstract:

    The hierarchical structure of spider dragline silk is composed of two major constituents, the amorphous phase and crystalline units, and its mechanical response has been attributed to these prime constituents. Silk mechanics, however, might also be influenced by the resistance against sliding of these two phases relative to each other under load. We here used atomistic molecular dynamics (MD) simulations to obtain friction forces for the relative sliding of the amorphous phase and crystalline units of Araneus diadematus spider silk. We computed the Coefficient of Viscosity of this interface to be in the order of 102 Ns/m2 by extrapolating our simulation data to the viscous limit. Interestingly, this value is two orders of magnitude smaller than the Coefficient of Viscosity within the amorphous phase. This suggests that sliding along a planar and homogeneous surface of straight polyalanine chains is much less hindered than within entangled disordered chains. Finally, in a simple finite element model, which is based on parameters determined from MD simulations including the newly deduced Coefficient of Viscosity, we assessed the frictional behavior between these two components for the experimental range of relative pulling velocities. We found that a perfectly relative horizontal motion has no significant resistance against sliding, however, slightly inclined loading causes measurable resistance. Our analysis paves the way towards a finite element model of silk fibers in which crystalline units can slide, move and rearrange themselves in the fiber during loading.

  • rate dependent behavior of the amorphous phase of spider dragline silk
    Biophysical Journal, 2014
    Co-Authors: Sandeep P Patil, Bernd Markert, Frauke Grater
    Abstract:

    The time-dependent stress-strain behavior of spider dragline silk was already observed decades ago, and has been attributed to the disordered sequences in silk proteins, which compose the soft amorphous matrix. However, the actual molecular origin and magnitude of internal friction within the amorphous matrix has remained inaccessible, because experimentally decomposing the mechanical response of the amorphous matrix from the embedded crystalline units is challenging. Here, we used atomistic molecular dynamics simulations to obtain friction forces for the relative sliding of peptide chains of Araneus diadematus spider silk within bundles of these chains as a representative unit of the amorphous matrix in silk fibers. We computed the friction Coefficient and Coefficient of Viscosity of the amorphous phase to be in the order of 10−6 Ns/m and 104 Ns/m2, respectively, by extrapolating our simulation data to the viscous limit. Finally, we used a finite element method for the amorphous phase, solely based on parameters derived from molecular dynamics simulations including the newly determined Coefficient of Viscosity. With this model the time scales of stress relaxation, creep, and hysteresis were assessed, and found to be in line with the macroscopic time-dependent response of silk fibers. Our results suggest the amorphous phase to be the primary source of Viscosity in silk and open up the avenue for finite element method studies of silk fiber mechanics including viscous effects.

Bernhard Jakoby - One of the best experts on this subject based on the ideXlab platform.

  • a differential pressure wave based sensor setup for the acoustic Viscosity of liquids
    IEEE Sensors Journal, 2016
    Co-Authors: H Antlinger, Stefan Clara, R Beigelbeck, S Cerimovic, F Keplinger, Bernhard Jakoby
    Abstract:

    We investigate a differential sensor setup utilizing acoustic pressure waves, which aims at the determination of the acoustic Viscosity (or the second Coefficient of Viscosity) of highly viscous liquids with shear viscosities in the range of several 100 mPa $\cdot $ s and above. The whole setup is modeled in PSPICE and investigated experimentally. The presented approach is suitable for further miniaturization and is based on a differential configuration, such that spurious effects associated with the parameter spread of the used lead-zirconate-titanate transducers ideally cancel out. We demonstrate the operation in time domain (avoiding spurious interference effects), present an according calibration procedure with a known reference liquid, and discuss the effects of diffraction. Finally, the experimental results demonstrate the applicability of the setup.

  • an acoustic transmission sensor for the longitudinal Viscosity of fluids
    Sensors and Actuators A-physical, 2013
    Co-Authors: H Antlinger, Stefan Clara, R Beigelbeck, S Cerimovic, F Keplinger, Bernhard Jakoby
    Abstract:

    Physical fluid parameters like Viscosity, mass density and sound velocity can be determined utilizing ultrasonic sensors. We introduce the concept of a recently devised transmission based sensor utilizing pressure waves to determine the longitudinal Viscosity, bulk Viscosity, and second Coefficient of Viscosity of a sample fluid in a test chamber. A model is presented which allows determining these parameters from measurement values by means of a fit. The setup is particularly suited for liquids featuring higher viscosities for which measurement data are scarcely available to date. The setup can also be used to estimate the sound velocity in a simple manner from the phase of the transfer function.

Sandeep P Patil - One of the best experts on this subject based on the ideXlab platform.

  • viscous friction between crystalline and amorphous phase of dragline silk
    PLOS ONE, 2014
    Co-Authors: Sandeep P Patil, Senbo Xiao, Konstantinos Gkagkas, Bernd Markert, Frauke Grater
    Abstract:

    The hierarchical structure of spider dragline silk is composed of two major constituents, the amorphous phase and crystalline units, and its mechanical response has been attributed to these prime constituents. Silk mechanics, however, might also be influenced by the resistance against sliding of these two phases relative to each other under load. We here used atomistic molecular dynamics (MD) simulations to obtain friction forces for the relative sliding of the amorphous phase and crystalline units of Araneus diadematus spider silk. We computed the Coefficient of Viscosity of this interface to be in the order of 102 Ns/m2 by extrapolating our simulation data to the viscous limit. Interestingly, this value is two orders of magnitude smaller than the Coefficient of Viscosity within the amorphous phase. This suggests that sliding along a planar and homogeneous surface of straight polyalanine chains is much less hindered than within entangled disordered chains. Finally, in a simple finite element model, which is based on parameters determined from MD simulations including the newly deduced Coefficient of Viscosity, we assessed the frictional behavior between these two components for the experimental range of relative pulling velocities. We found that a perfectly relative horizontal motion has no significant resistance against sliding, however, slightly inclined loading causes measurable resistance. Our analysis paves the way towards a finite element model of silk fibers in which crystalline units can slide, move and rearrange themselves in the fiber during loading.

  • rate dependent behavior of the amorphous phase of spider dragline silk
    Biophysical Journal, 2014
    Co-Authors: Sandeep P Patil, Bernd Markert, Frauke Grater
    Abstract:

    The time-dependent stress-strain behavior of spider dragline silk was already observed decades ago, and has been attributed to the disordered sequences in silk proteins, which compose the soft amorphous matrix. However, the actual molecular origin and magnitude of internal friction within the amorphous matrix has remained inaccessible, because experimentally decomposing the mechanical response of the amorphous matrix from the embedded crystalline units is challenging. Here, we used atomistic molecular dynamics simulations to obtain friction forces for the relative sliding of peptide chains of Araneus diadematus spider silk within bundles of these chains as a representative unit of the amorphous matrix in silk fibers. We computed the friction Coefficient and Coefficient of Viscosity of the amorphous phase to be in the order of 10−6 Ns/m and 104 Ns/m2, respectively, by extrapolating our simulation data to the viscous limit. Finally, we used a finite element method for the amorphous phase, solely based on parameters derived from molecular dynamics simulations including the newly determined Coefficient of Viscosity. With this model the time scales of stress relaxation, creep, and hysteresis were assessed, and found to be in line with the macroscopic time-dependent response of silk fibers. Our results suggest the amorphous phase to be the primary source of Viscosity in silk and open up the avenue for finite element method studies of silk fiber mechanics including viscous effects.

P. Ramakrishnan - One of the best experts on this subject based on the ideXlab platform.

  • Viscous flow during sintering of attrition milled nanocrystalline titanium powders
    Materials Research Bulletin, 2007
    Co-Authors: Vikram V. Dabhade, T.r. Rama Mohan, P. Ramakrishnan
    Abstract:

    Nanocrystalline powders are expected to exhibit viscous flow during sintering due to presence of substantial amount of quasi-amorphous layers at the grain boundaries. The present investigation attempts to determine the contribution of viscous flow during sintering of nanocrystalline titanium powders. Model equations originally suggested by Frenkel are applied on the shrinkage data to determine the activation energy for viscous flow, frequency factor and the Coefficient of Viscosity. Nanocrystalline titanium powders were found to exhibit lower activation energy for viscous flow, higher frequency factor and higher Coefficient of Viscosity as compared to micron sized titanium powders.

Elin Yusibani - One of the best experts on this subject based on the ideXlab platform.

  • A Review on Viscometer Devices for Gas Phase
    Aceh International Journal of Science and Technology, 2012
    Co-Authors: Elin Yusibani
    Abstract:

    Abstract -Viscosity, one of the transport properties, is a basic property required for developing any device in which fluid flows. In the present paper, major gas viscometers devices are reviewed. The review is covering to the pressures and the temperatures ranges, methods and accuracy of the instruments, and the Coefficient of Viscosity-range of the sample. This study is expected become useful information for any researcher who wants to develop a gas viscometer apparatus in a near future. By identifying the Coefficient of Viscosity-range and the  easurement-range of temperatures and pressures, then we can choose the effective and efficient method to be developed.