Micromechanical finite element analyses of fire retardant woven fabric composites at elevated temperatures using unit cells at multiple length scales

This paper presents a micromechanical Finite Element (FE) model developed to predict the effective mechanical properties of glass fibre-reinforced (woven fabric) polymer composites with/without fire retardant particulate additives at elevated temperatures. The elevated mechanical properties of glass fibre-reinforced epoxy composites with/without fire retardants were predicted using three unit cells of varying length scales in micromechanical FE analysis. Theoretically predictions of flexural behaviour of these fibre-reinforced polymer composites at elevated temperatures were satisfactorily validated against experimentally measured data. The numerical model developed herein was then used for the prediction of other mechanical properties of fibre-reinforced polymer composites that would have been difficult to collect at elevated temperatures. Micromechanical FE models such as the one contained in this paper are useful to architectural engineers as they can be used to guide the design and qualification of new engineering composites that satisfy stringent Building codes in fire prone engineering applications

Global wave loads on a damaged ship

A computational tool was applied based on a two dimensional linear method to predict the hydrodynamic loads for damaged ships. Experimental tests on a ship model have also been carried out to predict the hydrodynamic loads in various design conditions. The results of the theoretical method and experimental tests are compared to validate the theoretical method. The extreme wave induced loads have been calculated by short term prediction. For the loads in intact condition, the prediction with duration of 20 years at sea state 5 is used, while for loads in damaged conditions the prediction in 96 hours exposure time at sea 3 is used. The maximum values of the most probable extreme amplitudes of dynamic wave induced loads in damaged conditions are much less than those in intact condition because of the reduced time. An opening could change the distribution of not only stillwater bending moment but also wave-induced bending moment. It is observed that although some cross sections are not structurally damaged, the total loads acting on these cross sections after damage may be increased dramatically compared to the original design load in intact condition

Cogging torque reduction for radially laminated flux-switching permanent magnet machine with 12/14 poles

Flux-switching permanent-magnet machine (FSPMM) offers high torque density, impressive flux weakening capability and mechanical ruggedness because of its distinctive configuration, and is potentially suitable for the application in the plug-in hybrid electric vehicle (PHEV). However, the FSPMM compared with other traditional machines commonly used in the PHEV generally exhibits higher cogging torque for its double salient structures of both stator and rotor poles. Furthermore, the back EMF wave including odd harmonics especially 3rd and 5th ones are not ideally sinusoidal that could bring some extra copper loss and decrease its efficiency. Hence, how to minimize the cogging torque so to reduce the torque ripple, and how to reduce the total harmonic distortion (THD) of the back EMF wave are important issues in the field of FSPMM. Four rotor topologies in this paper are proposed to suppress the cogging torque and make the back EMF more sinusoidal for an FSPMM with 12/14 (stator/rotor) poles so as to make it more suitable to the brushless AC (BLAC) operation. Plenty of theory analysis and quantitative comparisons are made between different schemes. The validity of the proposed techniques has been confirmed by 2-D models of the finite element algorithm (FEA) executed in commercial software, Ansoft Maxwell 12

Integrated thermal, micro- and macro-mechanical modelling of post-fire flexural behaviour of flame-retarded glass/epoxy composites

This paper presents an integrated modelling approach for the post-thermal exposure flexural behaviour of glass fibre-reinforced (GFR) epoxy composites with/without flame retardants at both material and structural levels. This numerical model incorporates the outcomes from chemical kinetics and heat-mass transfer analyses. The unit cell-based micro-mesoscopic and meso-macroscopic mechanical models have been shown to accurately simulate the mechanical behaviour of GFR epoxy composites at the material level. The post-fire (e.g., composites thermally damaged by exposure to one-sided radiant heating) flexural behaviours of GFR epoxy composites were numerically modelled using finite element (FE) analyses. The predicted residual flexural stiffness for GFR epoxy composites exposed to different transient radiant heating conditions are compared with experimentally-measured post-fire flexural data in order to validate the numerical modelling approach while allowing its accuracy to be assessed. The good agreement between predicted and experimental data demonstrates the accuracy of the integrated numerical model in simulating the post-fire flexural bending of GFR epoxy composites

An injectable antibacterial hydrogel with bacterial-targeting properties for subcutaneous suppuration treatment

Purulent infections present challenges to medical procedures and burden patients with drainage procedures. An injectable antibacterial hydrogel can be directly administered to the infected tissue through a syringe, making it one of the most effective strategies for treating subcutaneous infections. In this study, we utilized an injectable hydrogel (PHP gel) with targeted bactericidal properties for surgery-free treatment of subcutaneous infections. The PHP gel was cross-linked using the Schiff base reaction between amino-functionalized polyhydromethylpyrimidine (PHP-NH2) and oxidized dextran (o-Dex). PHP-NH2 possesses the ability to kill bacteria through electrostatic interactions, while o-Dex enhances bacterial targeting by binding to lectins on the bacterial outer membrane via sugar units. In vitro experiments demonstrated that the PHP gel effectively eradicated 100 % of pathogenic bacteria within 2 h. Moreover, when used in vivo for treating purulent subcutaneous infections, the injectable PHP gel exhibited remarkable efficacy by preventing infection progression and eliminating pustule tissue within 24 h. Importantly, no significant adverse effects on blood or organ systems were observed in mice treated with PHP gel. Therefore, this polysaccharide- and polyhydropyrimidine- based hydrogel material holds immense potential as a novel antibacterial agent for managing purulent subcutaneous infections

Gabaa Receptor-Mediated Activation Of L-Type Calcium Channels Induces Neuronal Excitation In Surgically Resected Human Hypothalamic Hamartomas

Purpose: The human hypothalamic hamartoma (HH) is a rare, intrinsically epileptogenic lesion associated with gelastic seizures, but the underlying mechanisms remain unclear. Here, we examined the role of GABAA receptors in surgically resected HH tissue. Methods: HH tissue slices (350 μm) were studied using cellular electrophysiological, calcium imaging, and immunocytochemical techniques. Results: Two neuronal cell types were seen: small (10-16 μm) spontaneously firing GABAergic neurons and large (20-28 μm) quiescent neurons. In gramicidin-perforated patch recordings, muscimol (30 μM) induced membrane depolarization in 70% of large (but not small) neurons and a concomitant rise in intracellular calcium. These responses were blocked by bicuculline methiodide (50 μM). Depolarizing neurons also exhibited more positive reversal potentials (Emuscimol) and significantly higher intracellular chloride concentrations compared to those that hyperpolarized. The cation chloride co-transporters NKCC1 and KCC2 were coexpressed in the majority of large neurons, but fluorometric measurements revealed that 84% of large HH neurons expressed solely or relatively more NKCC1. Bumetanide (20 μM), a NKCC1 antagonist, partially suppressed muscimol-induced excitation in large neurons. Concordant with robust expression of CaV1.2 and CaV1.3 subunits in HH neurons, the L-type calcium channel blocker nifedipine (100 μM) prevented muscimol-induced neuronal excitation. Conclusions: GABAA receptor-mediated excitation, due in part to differential expression of NKCC1 and KCC2 and subsequent activation of L-type calcium channels, may contribute to seizure genesis in HH tissue. Given the ready availability of L-type calcium channel blockers, our results have clinical ramifications for the treatment of seizures associated with HH lesions. © 2008 International League Against Epilepsy

Enhancement of grain connectivity and critical current density in the ex-situ sintered MgB2 superconductors by doping minor Cu

The influence of Cu addition on the microstructure and superconducting performance of ex-situ sintered MgB2 is systemically studied. It is found that the critical current density (J(c)) of the Cu-doped sample is improved compared to the un-doped samples. In particular, the J(c) of the Cu-doped sample sintered at 900 degrees C for only 10 min is the best value at low fields. The reason is that Cu addition can obviously promote the decomposition of MgB2 MgB2 + Mg, which produces more Mg that can then react with Cu, forming local Mg-Cu liquid at high temperature. The presence of this local Mg-Cu liquid can significantly enhance the migration and self-sintering of MgB2, leading to the significant improvement in the grain connectivity and J(c). Our results indicate that Cu addition is a promising method to fabricate high-performance ex-situ MgB2 bulks and wires. (C) 2017 Elsevier B.V. All rights reserved