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Computer-Based Modelling of Network Functions for Linear Dynamic Circuits Using Modified Nodal Approach
Get PDFIn this paper, a computer-based systematic and efficient formulation method is presented for obtaining the network functions of linear or linearized time-invariant dynamic circuits. The method employs the modified nodal approach to obtain the system equations. The technique is based on developing a matrix formulation for modelling network functions. By using both symbolic manipulation of algebraic expressions and numeric processes, the network functions are expressed with a matrix-based method. Application examples are given to illustrate the features of the method
The Effect of Posterior Pedicle Screws Biomechanical Fixation for Thoracolumbar Burst Fracture
Get PDFThe purpose of this study was to explore the clinical efficacy and safety of posterior pedicle screw fixation in the treatment of thoracolumbar burst fracture. A total of 120 patients with thoracolumbar burst fractures were selected from January 2014 to December 2016. 60 patients were divided into the study group, and 60 patients were as the control group. The patients in the study group were treated with posterior pedicle screw fixation. The control group was treated with posterior non-traumatic pedicle screw fixation. After treatment, there were six months follow up. The clinical indexes, complications, and the anterior aspect height ratio, the Cobb angle, and the numeric rating scales (NRS) score were compared between the two groups at one month, six months after the operation. Results were I incisions healed into two groups, and no infection occurred after the operation. The operation time of the study group was higher than that of the control group (p0.05). At one month and six months after the operation, the anterior vertebral height of the two groups was significantly higher than before, and the Cobb angle and NRS score were substantially lower than those before surgery, the difference was statistically significant (p0.05). Moreover, the angle of Cobb and the NRS score were lower than those of the control group (p<0.05). The occurrence of postoperative low back pain and biomechanical fixation failure in the study group were significantly lower than those in the control group (p<0.05). To conclude, through the posterior approach, the pedicle screw fixation can efficiently prevent kyphosis, correct the loss and reduce the postoperative complications. It is a useful method for the treatment of thoracolumbar burst fractures
Shear Stress and Oxidized LDL Regulates Endothelial Cell Tube Formation through VEGF Signaling
Get PDFShear stress and oxidized low-density lipoprotein (oxLDL) caused by abnormal blood is critical to angiogenesis for atherosclerosis. However, the mechanism in shear stress or ox-LDL regulated angiogenesis is still not well understood. There is the hypothesis that shear stress or oxLDL regulates angiogenesis through the vascular endothelial growth factor (VEGF) signaling pathway. It is discovered that both high shear stress and low concentration of oxLDL contribute to angiogenesis, which is inhibited once the VEGF or VEGFR expression is knocked down. The expression of p-FAK and p-paxillin is regulated by the VEGF/VEGFR signal axis. VEGFR2, p-FAK, p-paxillin and VEGFR1 are VEGF-responsive proteins, and they are also upregulated by high shear stress and low concentration of oxLDL. If the VEGF or VEGFR2 is knocked down, phosphorylation of FAK and paxillin induced by high shear stress and low concentration of oxLDL are also significantly inhibited. In summary, present studies have demonstrated that high shear stress and low concentration of oxLDL induces angiogenesis through the VEGFR2/FAK/paxillin signaling pathway
Chitin Preparation by Demineralizing Deproteinized Lobster Shells with CO2 and a Cationite
Get PDFThe inorganic components of crustacean shells are usually removed using HCl solutions. This provokes undesirable modifications in the extracted chitin. In the present procedure, deproteinized lobster shells were demineralized with CO2 and a cationic resin (cationite). The resulting chitin (CHI-CO2) is compared in terms of degree of acetylation (DA), crystallinity index (CrI) and thermal stability with chitins obtained by demineralization procedures with HCl (CHI-HCl) and ethylenediaminetetraacetic acid (CHI-EDTA). The ash content of chitins demineralized with CO2 was similar to that of chitins prepared using HCl or EDTA. However, the resultant DA and CrI of CHI-HCl and CHI-EDTA were lower than those of CHI-CO2. Thermal stability of CHI-CO2 was also higher, with maximum decomposition velocity at 360 °C, above those of CHIEDTA (348 °C) and CHI-HCl (332 °C). This indicates that the use of CO2 and a cationite for demineralizing lobster shells is a promising alternative to conventional HCl and EDTA treatments for obtaining chitin
Improvement of Natural Fiber Composite Materials by Carbon Fibers
Get PDFThe purpose of this work is the improvement of flax fiber-reinforced composites obtained by vacuum molding in order to encourage their insertion into industrial products. The relatively high degree of porosity in these kinds of composites, due to the lack of compatibility between epoxy matrix and flax fibers and the hydrophilicity of flax fiber, remains a major constraint to their use in the industrial world. Hence, we have used a combination of carbon fibers with those of flax in order to optimize the properties of the assembly. Several stacking sequences have been tested in order to analyze the influence of the addition of carbon fibers on the water recovery behavior and the mechanical tensile behavior according to their position inside the laminate. It has been shown that adding surface carbon plies presents a barrier effect for the water sorption by limiting the creation and the percolation of internal porosities. The same effect is observed on tensile behavior where stacking sequences with external carbon fiber plies are more resistant than stacking sequences with internal carbon plies
Conductive Polymer Composites Synthesized from Diacetylene-Functionalized Linseed Oil and MWCNT: Gamma Irradiation and Organic Vapor Sensing
Get PDFEpoxidized linseed oil (ELO) was synthesized and functionalized with propargylamine (PA) or 3-ethynylaniline (EA) and the products were crosslinked to obtain the diacetylene-functionalized epoxidized linseed oil polymers which were used as matrices in the preparation of the composites with multiwalled carbon nanotubes (MWCNTs). Electrical resistance at percentages between 4 and 20 wt/wt% of filler was measured and the percolation threshold was calculated, obtaining 1.2 and 1.7% for the composites with EA and PA respectively. Low critical concentration evidenced a good dispersion of the MWCNTs without necessity of any modification. The final products were used in the sensing of acetone, chloroform and ethanol. The electrical resistance changes were measured at different concentrations and the sensibility was calculated. In order to improve stability toward the vapors, composites were irradiated with gamma rays and new sensing was done and compared. The results showed differences in sensibility, selectivity and reproducibility
Valorization of Citrus Waste: Use in Catalysis for the Oxidation of Sulfides
Get PDFThe utilization and valorization of industrial waste is an effective strategy for environmental protection. Since the juice industry generates a huge amount of citrus waste, we studied the application of thermally treated orange peel in catalysis. On the other hand, Keggin heteropolyacids are excellent oxidant catalysts used as a replacement for conventional oxidants; however, their solubility in polar solvents and the low specific area limit their use as heterogeneous catalysts. The utilization of treated orange peel as heteropolyacid support for the selective oxidation of sulfides is presented here. Firstly, orange peel was thermally treated, and then it was incorporated with heteropolyacids (PMo) during the silica synthesis by the sol-gel method. Therefore, SiO2-PMo, SiO2-OP100-PMo, and SiO2-OP200-PMo were obtained, characterized by FTIR, SBET, XRD, and potentiometric titration, and were tested as heterogeneous catalysts in the selective oxidation of sulfide to sulfoxide in a greener process: H2O2 as oxidant and ethanol as solvent, at 25 °C
Beetosan-Based Hydrogels Modified with Natural Substances
Get PDFIn this study a series of hydrogels based on Beetosan® and containing natural substances, such as bee pollen and sage (Salvia officinalis), have been prepared. Beetosan is a type of chitosan that is obtained from the external skeletons of naturally occurring dead honeybees. In multistage chemical treatment, dead insect waste is converted into chitosan that is used in research as a hydrogel matrix. Prepared materials were synthesized using photopolymerization. Studies on the obtained hydrogels included determining their swelling ability and behavior in a simulated body fluid environment, as well as determining their chemical structure by Fourier transform infrared spectroscopy (FTIR). Based on the research it can be stated that all synthesized modified hydrogels are characterized by swelling ability and do not tend to degrade after immersing in solutions with a composition similar to body fluids
Effect of Cellulose Nanocrystals on Fire, Thermal and Mechanical Behavior of N,N’-Diallylphenylphosphoricdiamide Modified Poly(lactic acid)
Get PDFPresented herein is a deep investigation of the fire, mechanical and thermal performances of poly(lactic acid) (PLA)-based nanocomposites, which were obtained by combining cellulose nanocrystals (CNC) with various contents of N,N’-diallyl-phenylphosphoricdiamide (P-AA) via a two-steps masterbatch melt extrusion process (glycidyl methacrylate grafting on PLA and CNC premixing with PLA). Results have shown that the value of the limiting oxygen index (LOI) increased to 28.8% and a V-0 rating in UL94 test was obtained when 2 wt% of P-AA was added in the presence of cellulose nanocrystals (3 wt%). The incorporation of CNC induced a decrease of both PHRR and THR values in micro combustion tests; meanwhile, the nucleating and plasticization effects of CNC and P-AA were evidenced. Results from tensile tests and dynamic mechanical thermal analysis (DMA) showed that the addition of CNC importantly enhanced the mechanical performance of P-AA containing systems, while the thermal stability of the nanocomposites was slightly improved in the presence of the cellulosic nanoreinforcement
Mixed Convection of Nanofluids inside a Lid-Driven Cavity Heated by a Central Square Heat Source
Get PDFA numerical work has been performed to analyze the laminar mixed convection of nanofluids confined in a lid driven square enclosure with a central square and isotherm heat source. All the walls are cooled at constant temperature, and the top wall slides rightward at constant velocity. The simulations considered four types of nanofluids (Cu, Ag, Al2O3 and TiO2)-Water. The governing equations were solved using finite volume approach by the SIMPLER algorithm. Comparisons with previously published work are performed and found to be in good agreement. The influence of pertinent parameters such as Richardson number, size of the heat source, solid volume fraction and type of nanofluid, on the heat transfer characteristics of mixed convection is studied. For all the simulations, the Reynolds number is fixed to Re=100. The results show that a better cooling of the heat source is obtained at a size of S=0.25 for copper-water nanofluid at Ri=100 where the buoyancy is stronger. As a consequence, we can economise the lid driven energy. The results also show that adding nanoparticles into pure water improves heat transfer in the enclosure. Furthermore, Copper and Silver-water nanofluids yield the best heat transfer enhancement in comparison with the other nanofluids