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Impact of Polymerization Protocol on Structure-Property Relationships of Entirely Lipid-Derived Poly(ester urethane)s
Get PDFThe impact of polymerization protocol on phase structure and properties of entirely lipid-derived thermoplastic poly(ester urethane)s (TPEU)s was investigated. The TPEUs were synthesized from 1,7-heptamethylene diisocyanate, polyester diols and 1,9-nonanediol (ND) as chain extender. A two-stage polymerization method was used to prepare two TPEUs; one in which ND was added in the first stage of polymerization as part of the prepolymer and another in the second stage after the prepolymer was formed. Two very different morphologies exhibiting different degrees of phase separation were obtained, driven by the sequence of addition of the chain extender. The incorporation of the chain extender in the prepolymer resulted in a TPEU with a narrow hard segment distribution, enhanced urethane-urethane hydrogen bonding and higher molecular weight. The hydrogen bond density, degree of crystallinity, glass transition temperature and mechanical properties of the TPEUs were directly related to the degree of phase separation and hence polymerization protocol
Soil Microbial Dynamics Modeling in Fluctuating Ecological Situations by Using Subtractive Clustering and Fuzzy Rule-Based Inference Systems
Get PDFMicrobial population and enzyme activities are the significant indicators of soil strength. Soil microbial dynamics characterize microbial population and enzyme activities. The present study explores the development of efficient predictive modeling systems for the estimation of specific soil microbial dynamics, like rock phosphate solubilization, bacterial population, and ACC-deaminase activity. More specifically, optimized subtractive clustering (SC) and Wang and Mendel's (WM) fuzzy inference systems (FIS) have been implemented with the objective to achieve the best estimation accuracy of microbial dynamics. Experimental measurements were performed using controlled pot experiment using minimal salt media with rock phosphate as sole carbon source inoculated with phosphate solubilizing microorganism in order to estimate rock phosphate solubilization potential of selected strains. Three experimental parameters, including temperature, pH, and incubation period have been used as inputs SC-FIS and WM-FIS. The better performance of the SC-FIS has been observed as compared to the WM-FIS in the estimation of phosphate solubilization and bacterial population with the maximum value of the coefficient of determination in the estimation of previous microbial dynamics
Modeling and Analysis of Novel Multilevel Inverter Topology with Minimum Number of Switching Components
Get PDFThis paper proposes a novel single phase symmetrical and asymmetrical type extendable multilevel inverter topology with minimum number of switches. The basic circuit of the proposed inverter topology consist of four dc voltage sources and 10 main switches which synthesize 9-level output voltage during symmetrical operation and 17-level output voltage during asymmetrical operation. The comparison between the proposed topology with conventional and other existing inverter topologies is presented in this paper. The advantages of the proposed inverter topology includes minimum switches, less harmonic distortion and minimum switching losses. The performance of the proposed multilevel inverter topology has been analyzed in both symmetrical and asymmetrical conditions. The simulation model is developed using MATLAB/SIMULINK software to verify the performance of the proposed inverter
Deformation and failure analysis of river levee induced by coal mining and its influence factor
Get PDFTo study the influence of coal mining on the stability of river levees, a mechanical model of mining-induced river levee deformation was established. This was based on the mining-induced deformation characteristics of river levees and the application of a typical surface subsidence function. Meanwhile, a failure criterion was proposed for river levees. Using some examples, the deformation of, and stress distribution through, river levees under the influence of mining were obtained: the maximum tensile stress on the bottom of the river levee was less than the tensile strength, under which circumstance the river levee remained undamaged. Meanwhile, this research analyzed the influence of three factors including the maximum surface subsidence wmax, half-length of surface subsidence basin L, and foundation coefficient k on the stability of river levees. Results showed that reducing the mining height of the working face and the foundation coefficient, and increasing the strike length of the working face could reduce the influence of mining on river levees. These results provided a theoretical basis for predicting the mining-induced deformation and failure of river levees
Local and biglobal linear stability analysis of parallel
Get PDFLinear Stability Analysis (LSA) of parallel shear flows, v ia local and global approaches, is presented. The local analysis is carried out by solving the Orr-Sommerfeld (OS) equation using a spectral-collocation method based on Chebyshev polynomials. A stabilized finite element formulation is employed to carry out the global analysis using the linearized disturbance equations in primitive variables. The local and global analysis are compared. As per the Squires theorem, the two-dimensional disturbance has the largest growth rate. Therefore, only two-dimensional disturbances are considered. By its very nature, the local analysis assumes the disturbance field to be spatially periodic in the streamwise direction. The global analysis permits a more general disturbance. However, to enable a comparison with the local analysis, periodic boundary conditions, at the inlet and exit of the domain, are imposed on the disturbance. Computations are carried out for the LSA of the Plane Poiseuille Flow (PPF). The relationship between the wavenumber, α, of the disturbance and the streamwise extent of the domain, L, in the global analysis is explored for Re = 7000. It is found that α and L are related by L = 2πn/α, where n is the number of cells of the instability along the streamwise direction within the domain length, L. The procedure to interpret the results from the global analysis, for comparison with local analysis, is described
Axisymmetric Slow Motion of a Prolate Particle in a Circular Capillary with Slip Surfaces
Get PDFThe problem of the steady migration of an axially symmetric prolate particle along its axis of revolution coinciding with the centerline of a circular capillary is investigated semi-analytically in the limit of low Reynolds number, where the viscous fluid may slip at the solid surfaces. A method of distribution of spherical singularities along the axis inside the particle is employed to establish the general solution of the fluid velocity satisfying the boundary conditions at the capillary wall and infinity. The slip condition at the particle surface is then satisfied by using a boundary collocation method to determine the unknown constants in this solution. The hydrodynamic drag force acting on the particle is obtained with good convergence for the cases of a prolate spheroid and a prolate Cassini oval with various values of the slip parameter of the particle, slip parameter of the capillary wall, aspect ratio or shape parameter of the particle, and spacing parameter between the particle and the wall. For the axially symmetric migrations of a spheroid and a Cassini oval in a capillary with no-slip surfaces and of a sphere in a capillary with slip surfaces, our results agree excellently with the numerical solutions obtained earlier. The capillary wall affects the particle migration significantly when the solid surfaces get close to each other. For a specified particle-in-capillary configuration, the normalized drag force exerted on the particle in general decreases with increasing slippage at the solid surfaces, except when the fluid slips little at the capillary wall and the particle-wall spacing parameter is relatively large. For fixed spacing parameter and slip parameters, the drag force increases with an increase in the axial-to-radial aspect ratio (or surface area effective for viscous interaction with the capillary wall) of the particle, but this tendency can be reversed when the particle is highly slippery
3D Bio-Plotted Tricalcium Phosphate/Zirconia Composite Scaffolds to Heal Large Size Bone Defects
Get PDFβ-TCP-Zirconia scaffolds with different architectures were fabricated by means of 3D-Bioplotting in order to enhance the mechanical and in-vitro ability of the scaffold to heal large size bone defects. In the present study scaffold architecture with different strand orientations (0°-90°, 0°-45°-135°-180°, 0°-108°-216° and 0°-72°-144°-36°-108°) were fabricated, characterized and evaluated for mechanical strength and cell proliferation ability. β-TCP powder (25 µm) and PVA (Polyvinyl Alcohol) was acquired from Fisher Scientific, India. Zirconia (18 to 32 µm) was procured from Lobachemie, India. In brief 7.5%, PVA in distilled water was used as a binder and was mixed with 10 grams of (70/30) TCP-Zirconia ratio to make the ceramic paste. The paste was further sieved through a 100-micron sieve and was filled in a 30 ml syringe. With 400 microns needle, the scaffold architectures were printed layer by layer and were allowed to dry at room temperature. The dried samples were sintered at 1500oC in a silicon carbide furnace and were allowed to remain at this temperature for 5 hours. The sintered samples were then characterized by X-Ray Diffraction, Scanning Electron Microscopy, Uniaxial Compression Tests, Fourier transform infrared spectroscopy and cell proliferation by XTT assay using MG-63 human osteosarcoma cell line. It was revealed that all samples maintained their structure and functional groups after sintering. Also, it was found that the architecture with (0°-72°-144°-36°-108°) strand orientation had the best strength and cell proliferation ability. Jointly these properties are required for scaffold fabrication in the field of bone tissue engineering
Effects of Simulated Microgravity on Vascular Development in Zebrafish
Get PDFResearch in microgravity is of utmost importance for disclosing the impact of gravity on biological processes and organisms. With the development of space technology, scientists pay more attention to cardiovascular diseases associated with microgravity. However, up to date only sparse data exist on microgravity and cardiovascular development mechanisms. In this study, zebrafish was chosen as the model organism. Zebrafish embryos were exposed to microgravity using a ground-based simulation microgravity (SM) bioreactor. The effects of SM on the development of early embryonic vascular system were studied in vivo in real-time. Zebrafish embryos were selected and divided into two groups at 12 hpf. One group was cultured in the MG-IIA bioreactor whereas the control group was cultured under normal gravity conditions. SM did not affect the number of live zebrafish and there were nonspecific developmental phenotypes in two groups. The heart rate in SM zebrafish embryos was significantly decreased. Then the vascular development differences between two groups were analyzed by qPCR and whole mount in situ hybridization. The effect of SM on zebrafish vascular development was not evident at 12 hpf - 24 hpf stage, but it had significant influences at 24 hpf-36 hpf stage.We also found that nos2b expression was up-regulated in the SM group both at 24 hpf and 36 hpf, interesting, all nos2b expression was observed in the hypothalamus at 24 hpf, it was no difference in the hypothalamus but significantly increased in the dorsal near the vascular at 36 hpf. These data suggested that the effect of SM on vasculogenesis stage is not obvious, but it has significant influences on angiogenesis, which maybe has relationship with the expression of nos2b
Impact of Coronary Tortuosity on Coronary Pressure and Wall Shear Stress: an Experimental Study
Get PDFCoronary tortuosity is a common angiographic finding, but the hemodynamic significance of coronary tortuosity is largely unknown. The impact of coronary tortuosity on coronary pressure and wall shear stress is still unclear. We addressed this issue in the present experimental study. A distorted tube model connected to heart pumping machine was established to simulate the coronary circulation. The pressure of each point was measured with a coronary pressure guidewire. Influence of tortuosity angle and tortuosity number on local pressure was measured. Wall shear stress was calculated accordingly to the pressure of each point. Pressure distribution in this system was affected both by tortuosity angle and tortuosity number. Driving pressure for the coronary tortuosity was positively related with tortuosity number while negatively linked with tortuosity angle. Wall shear stress was higher in proportion to the severity of coronary tortuosity. Coronary tortuosity can lead to more decrease of coronary blood pressure in dependence on the severity of tortuosity, and driving pressure for the coronary tortuosity increased accordingly. Tortuous artery has higher wall shear stress in dependent on the severity of coronary tortuosity, indicated that coronary tortuosity may be a factor for delaying the formation and progression of atherosclerotic plaque
Durability of Thermally Modified Wood of Gmelina arborea and Tectona grandis Tested under Field and Accelerated Conditions
Get PDFThis study evaluated the durability in terms of decay and mechanical resistance of thermally modified (TM) wood of Tectona grandis and Gmelina arborea treated at 160, 180, 200 and 220 °C. The TM wood of both species treated above 200 °C and 180 °C respectively presents lower weight loss (WL) after 300 days exposure in field and accelerated testing. It was also found that in field testing over 180 °C, the module of elasticity (MOE) and module of rupture (MOR) of the exposed and unexposed stakes of TM wood were not affected. Accelerated tests showed that the loss in flexural resistance was reflected more in the MOR than in the MOE. Finally, the accelerated and field tests showed that G. arborea and T. grandis TM wood treated at 180, 200 and 220 °C present statistically similar values of WL and flexural mechanical resistance