Unilateral interactions in granular packings: A model for the anisotropy modulus

Unilateral interparticle interactions have an effect on the elastic response of granular materials due to the opening and closing of contacts during quasi-static shear deformations. A simplified model is presented, for which constitutive relations can be derived. For biaxial deformations the elastic behavior in this model involves three independent elastic moduli: bulk, shear, and anisotropy modulus. The bulk and the shear modulus, when scaled by the contact density, are independent of the deformation. However, the magnitude of the anisotropy modulus is proportional to the ratio between shear and volumetric strain. Sufficiently far from the jamming transition, when corrections due to non-affine motion become weak, the theoretical predictions are qualitatively in agreement with simulation results.Comment: 6 pages, 5 figure

Isolation and cloning of the β subunit of human follicle stimulating Hormone (hFSHβ) with its native gene's signal sequence in methylotroph yeast Pichia pastoris pPIC9 shuttle vector

Introduction: Follicle Stimulating Hormone (FSH) is one of the pituitary glycoproteines that it consists of two subunits; alpha and beta. The beta subunit is responsible for the biological activity of FSH. The aim of present study was isolation of the β subunit coding sequence containing its signal sequence from human genome and then cloning of the isolated sequence in pPIC9 shuttle vector under the control of AOX1 promoter and α factor signal sequence. Material and Methods: the gene sequence of interest was isolated as a 2kb DNA fragment and cloned in pTZ57R vector resulting to pTV-2019 plasmid. The construct was used as template for modification of 5΄ region of gene upstream to ATG codon using PCR. Finally, amplicon was cloned in pPIC9 and the new construct named pPIC9F1. Results: The sequence of FSHβ gene in pTV-2019 was confirmed by restriction analysis and DNA sequencing. In addition, restriction analysis and AOX1 primer-mediated PCR showed that pPIC9F1 has correct construction. Conclusion: The new construct, pPIC9F1, contains the coding sequence of FSHβ gene and its signal sequence (E2-IVS2-E3). Therefore, this construct can be used for integration of FSHβ gene into yeast genome exactly downstream to AOX1 promoter. Under this condition, a fusion protein is produced that it contains two signal peptides, α factor and FSH signal peptides. Yeast expression system is able to cleavage α factor. It seems this is the first attempt for cloning of human FSHβ in yeast expression system

Effect of size polydispersity on micromechanical properties of static granular materials

We analytically investigate the influence of particle size polydispersity on the micromechanical properties of granular packings. In order to approximate the macroscopic quantities in terms of the microscale details, we develop a meanfield approach. It is shown that the trace of the fabric and stress tensors, and the elements of the stiffness tensor can be expressed in terms of dimensionless correction factors (which depend only on the moments of the size distribution), besides the average packing properties such as packing fraction, mean coordination number, and mean normal force. The results of numerical simulations confirm the validity of our analytical predictions, as long as the size distribution is not too wide

Effect of size polydispersity on micromechanical properties of static granular materials

We analytically investigate the influence of particle size polydispersity on the micromechanical properties of granular packings. In order to approximate the macroscopic quantities in terms of the microscale details, we develop a meanfield approach. It is shown that the trace of the fabric and stress tensors, and the elements of the stiffness tensor can be expressed in terms of dimensionless correction factors (which depend only on the moments of the size distribution), besides the average packing properties such as packing fraction, mean coordination number, and mean normal force. The results of numerical simulations confirm the validity of our analytical predictions, as long as the size distribution is not too wide