Relationship between tensile properties and ballistic performance of poly(ethylene naphthalate) woven and nonwoven fabrics

In this study, we investigated the effect of tensile properties of poly(ethylene naphthalate) (PEN) yarns on the ballistic performance of woven and nonwoven soft and composite armors. The results of ballistic tests of PEN armors were compared with Kevlar 49 armors as a reference. Based on these results, the Cunniff's equation was revised by removing the fiber elongation at break to predict the relationship between tensile properties and ballistic performances of PEN fibers. The calculations showed that by increasing tenacity of PEN fibers from 8.5 g/den (commercial product) to 12.5 g/den (strongest up to date PEN fibers produced by a novel melt spinning process discovered by our research group), the weight ratio of PEN to Kevlar 49 decreased from 1.8 to 1.35 with the same ballistic performance. Contrary to the results of the soft armors, composite armors made of high modulus PEN woven fabric showed a 17% lower ballistic resistance compared to the composite armor made of low modulus PEN woven fabric. The results of ballistic tests indicated that high tenacity PEN fibers produced in this research could have potential in soft and composite armors, and high velocity impact applications or improve performance of PEN in its current applications. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Development of pH-sensitive and antibacterial gelatin/citric acid/Ag nanocomposite hydrogels with potential for biomedical applications

This work aimed to prepare pH-sensitive and antibacterial drug releasing systems through a completely green route. To achieve this, the gelatin natural biopolymer was crosslinked with citric acid in the presence of Ag nanoparticles (NPs). Interestingly, Ag NPs formation and gelatin crosslinking were simultaneously occurred during annealing of samples without need for any toxic chemicals, which were confirmed by FTIR, UV-vis spectra, SEM and TEM observations. In addition, potential of the citric acid crosslinked-gelatin/Ag nanocomposite hydrogels was successfully explored for drug delivery applications using cefixime as a model drug. It was found that these hydrogels have pH-dependent swelling and drug release behavior with higher drug release at pH 7.4 compared to pH 1.2. Also, an antibacterial effect against the E. coli and S. aureus microorganisms was achieved by incorporation of Ag NPs into hydrogels. These hydrogels can be considered as stimuli responsive materials for oral drug delivery and wound dressing applications.     

Predicting breakage behavior and particle size of bronze and cast iron machining chips pulverized by jet milling

It has been proposed that the breakage behavior of particulate materials can be described by two material parameters f_mat and W_min. f_mat describes the resistance of the material to fracture in impact pulverization and W_min characterizes the specific energy which a particle can absorb without fracture. It is shown in this study that this concept can be used to quantify breakage behavior of bronze and cast iron chips in jet milling process and also to predict particle size of the jet milled product. Different tin bronze and cast iron chips with varying initial size were pulverized in a target plate jet mill with different velocity. f_mat was found to be in the range of 0.06–0.09 and 0.18–0.25 for bronze and cast iron alloys, respectively. For the cast iron alloys f_mat increased with increasing content of carbon and silicon. Similarly, for the bronze alloys, f_mat increased with increasing tin content. An equation was developed to predict mean particle size of the jet milled chips as a function of the kinetic energy, initial chip size and material parameters. The experimental results of various alloys confirmed that the mean particle size after single and multiple impacts were accurately predicted.     

Security of Internet of Things using RC4 and ECC Algorithms (Case Study: Smart Irrigation Systems)

Internet of Things (IoT) deploys a wide range of technologies including wireless sensor networks, machine-to-machine communication, robots, internet technologies, and smart devices. IoT is a novel phenomenon in the IT world wherein objects can transmit data, and interact through the internet or intranet networks. But the most important and crucial issue on the IoT is privacy and data security. The objective of this paper is to create a new encryption model for data storage servers in an IoT-based irrigation systems. Thus, a hybrid encryption algorithm based on Elliptic Curve Cryptography (ECC), RC4, and SHA-256 is proposed to protect sensitive data of IoT-based irrigation systems. The proposed model uses ECC to improve RC4. In RC4, XOR operation is performed using a key encrypted by ECC and shift-right, and then the resulting data are transformed to SHA-256 to ensure security. Simulation results indicate that encryption and decryption time in the proposed model are shorter than other models like XXTEA & ECC, XXTEA & RSA, ECC&3DES&SHA-256, RC4&3DES&SHA-256, AES&RC4&SHA-256, AES&3DES &SHA-256, RC4&AES&SHA-256, RC2&3DES&SHA-256, and ECC&RC2&SHA-256 with, 43.39%, 66.03%, 45.28%, 54.71%, 50.94%, 33.96%, 33.62%, 24.52%, and, 15.09% respectively.

     

Characterization of asphalt fume composition under simulated road paving conditions by GC/MS and microflow LC/quadrupole time-of-flight MS

A highly sensitive, selective, and reliable analytical method has been developed and validated for characterization of asphalt fume generated under simulated road paving conditions. A dynamic asphalt fume generation system was modified to provide consistent test atmospheres at simulated asphalt road paving conditions. In the process of fume generation, asphalt was initially preheated in an oven to 170 degrees C, pumped to a large kettle, which maintained the asphalt temperature between 150 and 170 degrees C, and then transferred to the generator. The fume was conducted from the generator to an exposure chamber through a heated transfer line. Characterization of the asphalt fume test atmospheres included the following: (1) determination of the consistency of the asphalt aerosol composition within the generation system; (2) quantification of total organic matter of the asphalt fume by electron impact ionization of isotope dilution gas chromatography/ mass spectrometry); and (3) identification of individual priority polycyclic aromatic hydrocarbons (PAHs) in asphalt fume by selected ion monitoring. With the developed method, asphalt fumes could be characterized into three fractions: (1) filter collection of a large molecular size fraction over a range of mass-to-charge (m/z) ratios of 173-309; (2) XAD-2 trapping of a medium molecular size fraction over a range of m/z ratios of 121-197; and (3) charcoal trapping of a small molecular size fraction that contained mainly the volatile vapor fraction over a range of m/z ratios of 57-141. Total organic matter of the asphalt fume was quantified over the 5 exposure days. Sixteen specific priority PAHs were monitored and identified. These PAHs were determined at trace levels on the filter fraction. A novel approach, which utilizes collision-induced dissociation of fragmentation pathway leading to a characteristic fragmentation pattern by coupling microflow liquid chromatography to atmospheric pressure chemical ionization of quadrupole time-of-flight mass spectrometry, was used to further clarify the trace amount of key components present in simulated road paving asphalt fumes. These results demonstrate that asphalt fume composition could be characterized and specific priority PAHs could be identified by this method. The major advantages of this method are its highly sensitivity, selectivity, and reliability for chemical hazard characterization in a complex mixture. This method is suitable for support toxicity studies using simulated occupational exposure to asphalt fumes.     

Experimental and Modelling Investigations of Asphaltene Precipitation During Pressure Depletion and Gas Injection Operations

Asphaltene precipitation problems manifest themselves in different stages of oil reservoirs production. Experimental and modeling investigations are, therefore, employed as promising tools to assist in predictions of asphaltene precipitation problems and selection of proper production facilities. This study concerns experimental and modeling investigations of asphaltene precipitation during natural production and gas injection operations for a heavy Iranian crude oil at reservoir conditions. First, with design and performance of high pressure–high temperature experiments, asphaltene precipitation behavior is comprehensively investigated; the effects of pressure and temperature are fully studied during pressure depletion tests and the role of injection gas composition on precipitation is described in gas injection experiments. In the next stage, the obtained experimental results are fed into a commercial simulator to develop the asphaltene precipitation model. The results for the pressure depletion experiments indicate that the maximum amount of asphaltene precipitation takes place at fluid bubble point pressure. Increase in the temperature, as seen, causes to reduce the amount of precipitation for the entire range of pressures. For gas injection experiments, the onset of precipitation for CO₂, associated, and N₂ gases takes place at around 0.20, 0.28, and 0.50 gas to mixture mole ratios, respectively. Carbon dioxide shows the highest asphaltene precipitation values and nitrogen has the lowest amounts for the whole range of gas mole fractions. Finally, the results for modeling indicate successful asphaltene precipitation predictions for both pressure depletion and gas injection processes.     

On Residual Stresses in Resistance Spot-Welded Aluminum Alloy 6061-T6: Experimental and Numerical Analysis

In this study, an electro-thermal-structural-coupled finite element (FE) model and x-ray diffraction residual stress measurements have been utilized to analyze distribution of residual stresses in an aluminum alloy 6061-T6 resistance spot-welded joint with 2-mm-thickness sheet. Increasing the aluminum sheet thickness to more than 1 mm leads to creating difficulty in spot-welding process and increases the complexity of the FE model. The electrical and thermal contact conductances, as mandatory factors are applied in contact areas of electrode-workpiece and workpiece-workpiece to resolve the complexity of the FE model. The physical and mechanical properties of the material are defined as thermal dependent to improve the accuracy of the model. Furthermore, the electrodes are removed after the holding cycle using the birth-and-death elements method. The results have a good agreement with experimental data obtained from x-ray diffraction residual stress measurements. However, the highest internal tensile residual stress occurs in the center of the nugget zone and decreases toward nugget edge; surface residual stress increases toward the edge of the welding zone and afterward, the area decreases slightly.     

A coloured polyester fabric with antimicrobial properties conferred by copper nanoparticles

In this study, we aimed to produce a coloured polyester fabric through the in situ sonosynthesis of copper nanoparticles using copper sulphate, hydrazine, sodium hydroxide and polyvinylpyrrolidone. The treated fabrics were characterised by X‐ray diffraction, field emission scanning electron microscopy, energy‐dispersive X‐ray spectroscopy and elemental mapping. Moreover, mechanical properties, wettability and antibacterial/antifungal activities of the treated fabrics were evaluated. Central composite design based on the response surface methodology was used to study the effect of copper sulphate, hydrazine hydrate and sodium hydroxide on the weight gain and colour of the treated fabrics. In addition to their roles as reducing agents, hydrazine and sodium hydroxide were responsible for the simultaneous aminolysis and hydrolysis of polyester, increasing the adsorption of nanoparticles on the surface. According to the results, the reddish brown samples treated with copper nanoparticles showed excellent antibacterial and antifungal efficiencies, improved tensile strength and decreased wettability.