FINITE ELEMENT ANALYSIS FOR DYNAMIC RESPONSE OF VISCOELASTIC SANDWICHED STRUCTURES INTEGRATED WITH ALUMINUM SHEETS

Passive vibration attenuation of modern mechanical structures is one of the most essential technologies applied to the arsenal of modern mechanical structures. In this work, dynamics analysis is performed on viscoelastic (VE) sandwich beam and plate by using finite element method. The proposed structure is composed of a VE core and aluminum face sheets as substrate layers on both sides of the structure. Small-strain VE material is modeled based on complex constant moduli model and numerical method is used to develop the finite element (FE) shear model based on first-order shear deformation theory (FSDT) and Hamilton principle. In modal analysis, model-effective mass analysis is performed to investigate its dominant mode shape and sweet spot at resonance using C3D20 and CPS8 elements. The former is indicated as a 3-D element with 20 nodes while the latter is indicated as a 2-D plane strain element with eight nodes. In harmonic analysis, resonance frequency is obtained based on mode superposition method to evaluate the steady-state response of VE sandwich beam via maximum deformation. Thereafter, the results are compared against analytical solutions from the literature. Moreover, a parametric study shows that the natural frequency of the beam did not change with the increase in core thickness. However, normalized loss factor of VE sandwich beam  is directly proportional to VE damping factor  and the thickness of VE core layer. Based on frequency response function, the results of resonance frequencies for VE beam are in the range of modal natural frequency

In silico analysis of Brucella abortus Omp2b and in vitro expression of SOmp2b

Purpose At present, there is no vaccine available for the prevention of human brucellosis. Brucella outer membrane protein 2b (Omp2b) is a 36 kD porin existed in common Brucella pathogens and it is considered as priority antigen for designing a new subunit vaccine. Materials and Methods In the current study, we aimed to predict and analyze the secondary and tertiary structures of the Brucella abortus Omp2b protein, and to predict T-cell and B-cell epitopes with the help of bioinformatics tools. Subsequently, cloning and expression of the short form of Omp2b (SOmp2b) was performed using pET28a expression vector and Escherichia coli BL21 host, respectively. The recombinant SOmp2b (rSOmp2b) was purified with Ni-NTA column. Results The recombinant protein was successfully expressed in E. coli host and purified under denaturation conditions. The yield of the purified rSOmp2b was estimated by Bradford method and found to be 220 µg/mL of the culture. Conclusion Our results indicate that Omp2b protein has a potential to induce both B-cell– and T-cell–mediated immune responses and it can be evaluated as a new subunit vaccine candidate against brucellosis. Keywords: Brucella; Omp2b; In silico approach; Epitope prediction; Protein expressio

Correlation between Methylation and Expression Level of P15 and P16 Genes during Differentiation of Cord Blood Stem Cells into Erythroid Lineage Mediated by Erythropoietin

Background: Several influential factors such as transcription factors and intracellular signaling components are involved in differentiation of stem cells into a specific lineage. P15 and p16 proteins are among these factors. Accumulating evidences has introduced the epigenetic as a master regulator of these factors during lineage specification. The main objective of this study is to determine the correlation between the expression level and methylation pattern of P15 and P16 genes in erythroid lineage after in vitro differentiation by erythropoietin (EPO).Materials and Methods: The purified and expanded CD34+ cord blood stem cells were differentiated into erythroid lineage in the presence of EPO. DNA was isolated from both cord blood stem cells and differentiated cells. The Real-Time PCR performed using cDNA and the isolated DNA was used in methylation Specific PCR (MSP) reaction for methylation pattern analysis in both pre and post differentiation stages.Results: The study demonstrated that P15 and P16 genes have partial methylation after erythroid differentiation by EPO. The Expression of P15 gene was higher after differentiation and the expression of P16 gene had a slightly decreased level in post differentiation stage.Conclusion: Significant increase in P15 gene expression after differentiation to erythroid lineage, suggests the remarkable efficacy of this gene in erythroid function. According to upregulation of P15 gene after differentiation despite unchanged methylation status and slight down regulation of P16 gene with slight hyper-methylation of the gene it can be suggested that although the methylation can affects the expression level of P16 gene, the P15 gene is not affected by this mechanism during erythroid differentiation mediated by EPO

Size-dependent nonlinear secondary resonance of micro-/nano-beams made of nano-porous biomaterials including truncated cube cells

© 2018, Springer-Verlag GmbH Austria, part of Springer Nature. Porous biomaterials have been utilized in cellular structures in order to mimic the function of bone as a branch of tissue engineering approach. With the aid of nano-porous biomaterials in which the pore size is at nanoscale, the capability of biological molecular isolation becomes more efficient. In the present study, first the mechanical properties of nano-porous biomaterials are estimated on the basis of a truncated cube cell model including a refined hyperbolic shear deformation for the associated lattice structure. After that, based upon a nonlocal strain gradient beam model, the size-dependent nonlinear secondary resonance of micro-/nano-beams made of the nano-porous biomaterial is predicted corresponding to both subharmonic and superharmonic excitations. The nonclassical governing differential equation of motion is constructed via Hamilton’s principle. By employing the Galerkin technique together with the multiple-timescale method, the nonlocal strain gradient frequency response and amplitude response of the nonlinear oscillation of micro-/nano-beams made of a nano-porous biomaterial under hard excitation are achieved. It is shown that in the superharmonic case, increasing the pore size leads to an enhancement of the nonlinear hardening spring-type behavior of the jump phenomenon and the height of limit point bifurcations. In the subharmonic case, higher pore size causes an increase in the gap between two branches associated with the high-frequency and low-frequency solutions