Glass fiber/carbon nanotubes/epoxy three‐component composites as radar absorbing materials

The use of micro or nano‐fillers to optimize the properties of epoxy resins has become a common practice. The Carbon nanotubes (CNT) are considered excellent fillers because of their strength, stiffness, thermal conductivity, electrical capacity, and thermal stability, along with large electromagnetic wave absorption capability in the microwave range. In this work, electromagnetic absorption properties and dynamic‐mechanical response obtained with the incorporation of CNT into glass fiber/epoxy composites have been studied. A novel procedure to disperse and deposit CNT onto glass fiber fabrics has been developed to reach high overall content of CNT in the composite (4.15 wt%). Storage modulus increased with the incorporation of CNT, especially when they had also been incorporated into the epoxy, and for higher frequency (3 Hz). The response of the composites to electromagnetic radiation has shown an increasing trend for higher CNT content (up to 2 wt%), reaching an excellent attenuation value of up to −18.3 dB (98.5% of absorption). POLYM. COMPOS., 37:2277–2284, 2016. © 2015 Society of Plastics Engineers     

The Catalytic Mechanism of Pdx2 Glutaminase Driven by a Cys-His-Glu Triad: A Computational Study

The catalytic mechanism of Pdx2 was studied with atomic detail employing the computational ONIOM hybrid QM/MM methodology. Pdx2 employs a Cys-His-Glu catalytic triad to deaminate glutamine to glutamate and ammonia – the source of the nitrogen of pyridoxal 5’-phosphate (PLP). This enzyme is, therefore, a rate-limiting step in the PLP biosynthetic pathway of Malaria and Tuberculosis pathogens that rely on this mechanism to obtain PLP. For this reason, Pdx2 is considered a novel and promising drug target to treat these diseases. The results obtained show that the catalytic mechanism of Pdx2 occurs in six steps that can be divided into four stages: (i) activation of Cys₈₇, (ii) deamination of glutamine with the formation of the glutamyl-thioester intermediate, (iii) hydrolysis of the formed intermediate, and (iv) enzymatic turnover. The kinetic data available in the literature (19.1–19.5 kcal mol⁻¹) agree very well with the calculated free energy barrier of the hydrolytic step (18.2 kcal.mol⁻¹¹), which is the rate-limiting step of the catalytic process when substrate is readily available in the active site. This catalytic mechanism differs from other known amidases in three main points: i) it requires the activation of the nucleophile Cys₈₇ to a thiolate; ii) the hydrolysis occurs in a single step and therefore does not require the formation of a second tetrahedral reaction intermediate, as it is proposed, and iii) Glu₁₉₈ does not have a direct role in the catalytic process. Together, these results can be used for the synthesis of new transition state analogue inhibitors capable of inhibiting Pdx2 and impair diseases like Malaria and Tuberculosis.     

Failure Analysis of Two Stainless Steel Based Components Used in an Oil Refinery

The petroleum industry has changed significantly over the past decades. For example, in Brazil, oil extraction under very deep sea water is growing very quickly. As a consequence, materials and components used for such applications must have properties required to withstand adverse conditions and ensure satisfactory performance and reliability in service. Nonetheless, components that normally fulfill these standard requirements can fail under severe service conditions such as high pressure and temperatures and high concentrations of H₂S and CO₂. Among the factors that can cause the premature failure in metallic components are the use of inadequate materials, the presence of defects that appeared during the production, and errors of project, assembly, or maintenance. Failure analysis allows the identification of causes and thus contributes to improvements in the operation and performance of similar equipment. In this work, light optical microscopy and scanning electron microscopy (SEM) were used to analyze the microstructure and fracture surface of two centrifugal pump shafts that failed during use in a Brazilian petroleum refinery. The results showed that one shaft, made of duplex stainless steel, failed by fatigue fracture, and the other, made of 316 austenitic stainless steel, experienced a similar fracture, which was promoted by the presence of nonmetallic inclusion particles.     

Design and development of a multipurpose utility AWD electric vehicle with a hybrid powertrain based on PEM fuel cells and batteries

This paper presents the results obtained on the research project CIT-370000-2008-11, entitled “Multi-purpose remote-controlled all-wheel-drive tool-vehicle powered by fuel cells” funded by the Spanish Ministry of Science and Technology. A new concept multipurpose electric vehicle has been designed and manufactured, based on three basic features: a hybrid power system consisting in PEM fuel cells + batteries, an all-wheel-drive traction system, and the capability of being either on-site driven or remote-controlled. The vehicle is formed by two frames connected by a two-degree of freedom joint, and is powered by two 2.5 kW DC motors, one in each axle. All the electric circuits for the suitable control of the power hybrid system have been developed in our Laboratory, allowing a large flexibility. After the different tests performed, it has been verified that the vehicle presents good maneuverability, a good traction performance in off-road driving, as well as a good slope-climbing capability. Under the experimental conditions tested, the vehicle reached a maximum speed of 11 km/h on flat surface, keeping the maximum power consumption always around 3 kW.     

Structural effects of the hydrolysis of poly(methylene oxide) and poly(glycolic acid) exposed to completion and acidizing fluids in an oil well environment

Two hydrolyzable polymers, poly(methylene oxide) (PMO) and poly(glycolic acid) (PGA), were tested for association with mechanical systems to promote diversion of formation acid treatments in oil wells. Samples were confined to chemical products commonly employed in oil well completion processes, HCl 15% w/w and NaCl 23% w/w aqueous solutions, in separate metallic cylindrical cells, under conditions observed in southeastern Brazilian offshore fields (50 and 75°C and pressure of 41.4 MPa). Pristine samples were characterized by ¹³C-NMR. Hydrolytic influences were evaluated by differential scanning calorimetry, scanning electron microscopy, wide angle X-ray diffraction, and computerized microtomography. The intense effects observed showed a specific correspondence with each tested polymer and were evidenced by postexposure analysis. The results indicate that both polymers can be used in association with mechanical diverting systems to promote chemical treatment distribution and, therefore, improve oil well productivity. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47362.     

QoS-RRC: an overprovisioning-centric and load balance-aided solution for future internet QoS-oriented routing

The concepts and designs of 4WARD project for the Future Internet involve a clean-slate architecture with various networking innovations, including a new connectivity paradigm called Generic Path (GP). In GP architecture, several facilities are designed to efficiently support complex value-added applications and services with assured Quality of Service (QoS). The GP mainly makes transparent the underlying network structure and heterogeneity, and any entities, regardless of their purpose (technology, location or architectural layer) communicate with each other in a single way via a common interface. In addition, cooperation with network-layer provisioning mechanisms is required to map data paths that are compliant with session-demanded resources (QoS requirements - minimum bandwidth and maximum delay/loss experience) in appropriate GPs. In contrast, robust and scalable QoS-provisioning facilities are urgently required as a support for efficient GP allocations. To address this need, this paper introduces the QoS-Routing and Resource Control (QoS-RRC), a set of GP-compliant facilities to meet the requirements mentioned above. QoS-RRC complements GP architecture with QoS-oriented routing, with the aid of load balancing to select paths that comply with session-demands while keeping residual bandwidth to increase user experience. To address scalability issues, QoS-RRC operates on the basis of an overprovisioning-centric approach to achieve cost-effectiveness in terms of state storage, signaling load and network operations. An initial QoS-RRC performance evaluation was carried out in Network Simulator v.2 (NS-2), which showed that there had been drastic improvements in the flow delay experience and bandwidth use among a range of relevant state-of-the-art solutions. Moreover, the impact of QoS-RRC on the user experience (compared to current IP QoS and routing standards) has been evaluated, by analyzing the main objective and subjective Quality of Experience (QoE) metrics, namely Peak Signal to Noise Ratio (PSNR), The Structural Similarity Index (SSIM), Video Quality Metric (VQM) and Mean Opinion Score (MOS).     

Glass transition and the flowability and caking of powders containing amorphous lactose

Many powders contain amorphous components, such as amorphous lactose in milk powders, which when given sufficient conditions of temperature and water content, will mobilise as a high viscosity flow making the particles sticky. This can lead to increased cohesiveness, powder caking and increased adhesion to surfaces. The transition from the glassy state is established by increasing the powder temperature to above its glass transition temperature which can be measured using differential scanning calorimetry. Exposing milk powder to over 10-20 °C above the lactose glass transition makes the powder more sticky, rendering it a lot more cohesive and also increases its adhesion to a stainless steel surface. This glass transition induced stickiness is time-dependent. Over time, crystallisation can take place converting the amorphous lactose into crystalline lactose. Furthermore, the caking behaviour of powders depends on the amount of component present in the amorphous state. Finally, this work presents an approach for applying the measured relationship between the glass transition and water content for predicting caking problems with powders containing amorphous components.     

Statistical analysis of impact-fracture characteristics and microstructure of industrial Portland cement clinkers

Impact is the dominant breakage mode in most industrial grinding mills used in cement manufacture. The physical amenability of two industrial Portland cement clinkers to size reduction was determined through measurement of their fracture strengths under impact loading. It was found that the fracture strength of clinker is strongly dependent on size, which is consistent with the increasing expenditure of energy in fine grinding. Also, it was observed that the measured fracture strengths could be well described by either single or multiple Weibull distributions. The appearance of these distributions was consistent with the variability in the composition and microstructure of the clinker nodules, observed in a detailed examination under the microscope. Possible reasons for the appearance of these populations are given. It is concluded that the fracture strength of clinker is generally determined by porosity at coarser nodule sizes and by mineralogy and texture at finer sizes.     

Particle Growth during Calcination of Polycation Oxides Synthesized by the Polymeric Precursors Method

The particle-growth kinetics of sodium niobate and zirconium titanate powders that were processed by the polymeric precursors method were studied. The growth kinetics that were studied for the particle, in the final stage of crystallization, showed that the growth process occurs in two different stages. For temperatures <800°C, the particle-growth mechanism is associated with surface diffusion, with an activation energy in the range of 40-80 kJ/mol. For temperatures >800°C, particle growth is controlled by densification of the nanometric particle clusters and by a neck-size-controlled particle-growth mechanism. The results suggest that this behavior was typical of the synthesis method, because two different polycation oxides presented the same behavior.