Fabrication and mechanical properties of metakaolin-based geopolymer composites reinforced with auxetic fabrics

This work presents a novel experimental study on the use of auxetic fabrics as the main reinforcement in geopolymer composites, aiming at higher energy dissipation in impact demanding applications. For this, a potassium-based geopolymer was reinforced with an auxetic fabric consisting of basalt fiber fillings positioned between helical auxetic yarns (HAY) made of a thermoplastic polyester core, and a stiffer liquid-crystal polymer wrap, which dispersed the load demands into several single elements having different capabilities. The composites were investigated under quasi-static flexural and tensile loadings, in both longitudinal and transverse directions. The latter showed increased mechanical strengths, up to 26 MPa in tension, and 12.8 MPa in flexural strength. Each fiber portion was tested in tension separately, reaching flexible (core) and stiffer (wrap and basalt) responses, whereas HAYs displayed combined performances due to a suitable auxeticity effect, that is, a negative Poisson's ratio. The pullout investigation justified the cracking and delamination of the composites, due to its cyclic lateral area modification, which created a load demand much higher than what the brittle geopolymer can sustain in this type of solicitation. Thermogravimetric analyses helped to predict the use of such configurations under thermal exposure, pointing out that the geopolymer material could be a suitable thermal barrier to prevent sudden degradation of the fabric under these conditions.     

Physics & Modeling of Ambipolar Snapback Behavior in Gate Grounded NMOS

Silicon - This paper models first snapback ambipolar action in NMOS, when subjected to high current stress across the drain terminal. We analyze 2 − D ambipolar current in Gate Grounded NMOS...     

Stable Graphene Membranes for Selective Ion Transport and Emerging Contaminants Removal in Water

Carbon-based materials, such as graphene oxide and reduced graphene oxide membranes have been recently used to fabricate ultrathin, high-flux, and energy-efficient membranes for ionic and molecular sieving in aqueous solution. However, these membranes appeared rather unstable during long-term operation in water with a tendency to swell over time. Membranes produced from pristine, stable, layered graphene materials may overcome these limitations while providing high-level performance. In this paper, an efficient and “green” strategy is proposed to fabricate µm-thick, graphene-based laminates by liquid phase exfoliation in Cyrene and vacuum filtration on a PVDF support. The membranes appear structurally robust and mechanically stable, even after 90 days of operation in water. In ion transport studies, the membranes show size selection (>3.3 Å) and anion-selectivity via the positively charged nanochannels forming the graphene laminate. In antibiotic (tetracycline) diffusion studies under dynamic conditions, the membrane achieve rejection rates higher than 95%. Sizable antibacterial properties are demonstrated in contact method tests with Staphylococcus aureus and Escherichia coli bacteria. Overall, these “green” graphene-based membranes represent a viable option for future water management applications.     

Wireless Sensor Network-based Detection of Poisonous Gases Using Principal Component Analysis

This work utilizes a statistical approach of Principal Component Analysis (PCA) towards the detection of Methane (CH₄)-Carbon Monoxide (CO) Poisoning occurring in coal mines, forest fires, drainage systems etc. where the CH₄ and CO emissions are very high in closed buildings or confined spaces during oxidation processes. Both methane and carbon monoxide are highly toxic, colorless and odorless gases. Both of the gases have their own toxic levels to be detected. But during their combined presence, the toxicity of the either one goes unidentified may be due to their low levels which may lead to an explosion. By using PCA, the correlation of CO and CH₄ data is carried out and by identifying the areas of high correlation (along the principal component axis) the explosion suppression action can be triggered earlier thus avoiding adverse effects of massive explosions. Wireless Sensor Network is deployed and simulations are carried with heterogeneous sensors (Carbon Monoxide and Methane sensors) in NS-2 Mannasim framework. The rise in the value of CO even when CH₄ is below the toxic level may become hazardous to the people around. Thus our proposed methodology will detect the combined presence of both the gases (CH₄ and CO) and provide an early warning in order to avoid any human losses or toxic effects.     

Fatigue crack propagation of sheet molding compounds in various evironments

The effect of the absorption of water and isooctane on the rate of fatigue crack propagation of sheet molding compounds (SMC-R30 and SMC-R65) was investigated. A crack extension gage was used to measure the crack length. Results show that the absorption of water decreases the rate of fatigue crack propagation in the initial cycles but increases the rate of propagation in the final cycle. The absorption of isooctane into SMC-R65 tends to decrease the rate of fatigue crack propagation. Microscopic observation shows considerable swelling of the polyester matrix due to the absorption of water and no significant apparent effect due to the absorption of isooctane.     

Upconversion of NaYF4: Yb,Er Nanoparticles Co-doped with Zr 4+ for Magnetic Phase Transition and Biomedical Imaging Applications

Tracking of cancer cells and cytotoxicity of normal tissue are the leading problem in cancer treatment. The magnetic and fluorescent multifunctional particles evolve as an emerging alternative for future target recognition. The ferromagnetic materials potentially treat the defects in the gene. Hence, ferromagnetic materials are the best for the treatment of cancer using gene therapy. Here, β-NaYF₄: Yb, Er compounds doped with 10%, 20% and 30% Zirconium (Zr) are prepared through hydrothermal technique. Citrate itself is a highly biocompatible surface ligand that labels the imaging probe. The X-ray diffraction analysis is evident for transforming hexagonal to cubic phase via Zr doping in NaYF₄: Yb, Er compounds. The electron microscopic images identify the hexagonal plates. This compound can emit visible light in response to infrared (IR) light irradiation. Especially β-NaYF₄: Yb, Er, and 10% of Zr, Yb, Er tridoped NaYF₄ compounds show enhanced red emission exploited in bioimaging applications. Insignificantly, 30% of Zr, Yb, Er tridoped NaYF₄ concentration exhibit hexagonal and dominating cubic (α) phase, could decrease red emissions intensity and magnetisation value. This Zr material reveals peculiar magnetic properties, especially ferromagnetism at a lower magnetic field and produces paramagnetism at a higher magnetic field. Here, 10–20% Zr, Yb, Er tridoped NaYF₄ concentrations exhibit better magnetic properties. The resultant compound is viable for the VERO cells.