A fundamental study of chitosan/PEO electrospinning

A highly deacetylated (97.5%) chitosan in 50% acetic acid was electrospun at moderate temperatures (25-70 °C) in the presence of a low content of polyethylene oxide (10 wt% PEO) to beadless nanofibers of 60-80 nm in diameter. A systematic quantitative analysis of the solution properties such as surface tension, conductivity, viscosity and acid concentration was conducted in order to shed light on the electrospinnability of this polysaccharide. Rheological properties of chitosan and PEO solutions were studied in order to explain how PEO improves the electrospinnability of chitosan. Positive charges on the chitosan molecule and its chain stiffness were considered as the main limiting factors for electrospinability of neat chitosan as compared to PEO, since surface tension and viscosity of the respective solutions were similar. Various blends of chitosan and PEO solutions with different component ratios were prepared (for 4 wt% total polymer content). A significant positive deviation from the additivity rule in the zero shear viscosity of chitosan/PEO blends was observed and believed to be a proof for strong hydrogen bonding between chitosan and PEO chains, making their blends electrospinnable. The impact of temperature and blend composition on the morphology and diameter of electrospun fibers was also investigated. Electrospinning at moderate temperatures (40-70 °C) helped to obtain beadless nanofibers with higher chitosan content. Additionally, it was found that higher chitosan content in the precursor blends led to thinner nanofibers. Increasing chitosan/PEO ratio from 50/50 to 90/10 led to a diameter reduction from 123 to 63 nm. Producing defect free nanofibrous mats from the electrospinning process and with high chitosan content is particularly promising for antibacterial film packaging and filtration applications.     

A Comprehensive Analysis of Macrosegregation Formation During Twin-Roll Casting

Metallurgical and Materials Transactions B - A two-phase Eulerian–Eulerian volume-averaged model is used to predict the formation of macrosegregation during the twin-roll casting of...     

Nonlinear output feedback control of V2G single‐phase on‐board BEV charger

In this work, we consider the problem of controlling a single‐phase on‐board battery electric vehicle (BEV) charger with vehicle‐to‐grid (V2G) technology. The BEV charger consists of a bidirectional ac‐dc power converter connected to the single‐phase power grid, followed by a bidirectional dc‐dc power converter interfacing an EV battery pack. The main control objectives are fourfold: (i) Unitary Power Factor (UPF) in grid‐side; (ii) tight dc‐bus voltage regulation; (iii) safety battery charge and battery discharge during the grid‐to‐vehicle (G2V) mode and V2G mode, respectively; and (iv) asymptotic stability of the closed loop system. After an accurate system modelling, a nonlinear controller is designed using a backstepping design technique. The point is that the battery inner voltage is not accessible to measurement. Therefore, a nonlinear observer is invoked in order to estimate all non‐measured variables making the solution cheaper and noiseless. It is shown using a formal analysis and numerical simulations, that the proposed output feedback controller (combining a nonlinear controller and a nonlinear observer) meets all control objectives.     

Enhanced electroactive β phase in three phase PVDF/CaCO3/nanoclay composites: Effect of micro‐CaCO3 and uniaxial stretching

In this study, electroactive polar phase transformation and crystallinity of poly(vinylidene fluoride) (PVDF)‐based composites, such as PVDF/CaCO₃/nanoclay, is explored as a function of micro‐CaCO₃ fraction and draw ratio (R) of uniaxial stretching. Composites including PVDF/clay, PVDF/CaCO₃ and most importantly PVDF/CaCO₃/clay with varying fraction of micro‐CaCO₃ were extruded into homogenous and flexible cast films. Characterization via Fourier transform infrared spectroscopy, X‐ray diffraction, and differential scanning calorimetry (DSC) confirmed the presence of β phase in all the composites incorporated with micro‐CaCO₃ and nanoclay either individually (i.e., PVDF/CaCO₃ and PVDF/clay films, respectively) or together (i.e., PVDF/CaCO₃/nanoclay composites). Interestingly, a gradual but significant improvement in this electroactive phase (β phase) was obtained with successive increment in CaCO₃ content into a fixed composition of PVDF and nanoclay (PVDF/CaCO₃/clay composites). Further increment in β phase content was obtained via uniaxial stretching to different draw ratios and at a temperature of 90 °C, where for PVDF/CaCO₃/clay (especially, 100–35‐3 and 100–40‐3) samples almost no α phase was observed irrespective of R. Conversely, the crystallinity of melt extruded samples decreased gradually all the way with CaCO₃ concentration in PVDF/CaCO₃/clay composites compared to the neat PVDF while increased gradually with increasing draw ratio. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44940.     

The bond and flexural strengthening of reinforced concrete elements strengthened with near surface mounted prestressing steel (PS) bars

Abstract

The main objective of this work is to study the performance of prestressing steel (PS) bars as reinforcements in the reinforced concrete (RC) elements strengthened by the near-surface mounted method (NSM). The work includes two parts. In the first part, direct pull-out tests are performed in order to study the bond performance between PS reinforcement and concrete. The influences of groove sizes and PS surface conditions (smooth and sand coated) are evaluated. The results show that the sand coated PS (PS-Sc) reinforcement has the best adhesion behavior compared with the smooth bar, and its pull-out force is increased by 48%. For this reason, the PS-Sc bars are used in the second part of this work as NSM reinforcement to strengthen RC beams subjected to bending forces. Then, four-point bending tests are carried out to understand the flexural behavior of strengthened RC beams with PS-Sc reinforcements of different lengths and ratios. The obtained results demonstrate that the use of NSM-PS-Sc bars strengthening technique leads to important enhancement in the load carrying capacity of the RC beams. The first crack load and ultimate load of the strengthened RC beams attain 71.41 and 65.67%, respectively, which are higher than those of the control beam. Furthermore, the experimental values show a good agreement with the analytical values in both the ultimate deflection and the ultimate load. This proves that the NSM-PS-Sc bars studied in this work are promising reinforcement of the RC beams.     

Delay-dependent Stabilization Conditions of Controlled Positive Continuous-time Systems

The stabilization problem for a class of linear continuous-time systems with time-varying non differentiable delay is solved while imposing positivity in closed-loop. In particular, the synthesis of state-feedback controllers is studied by giving sufficient conditions in terms of linear matrix inequalities(LMIs). The obtained results are then extended to systems with non positive delay matrix by applying a memory controller. The effectiveness of the proposed method is shown by using numerical examples.     

Using genetic algorithm for lot sizing and scheduling problem with arbitrary job volumes and distinct job due date considerations

This paper considers an integrated lot sizing and scheduling problem for a production–distribution environment with arbitrary job volumes and distinct due dates considerations. In the problem, jobs are firstly batch processed on a batching machine at production stage and then delivered to a pre-specified customer at the subsequent delivery stage by a capacitated vehicle. Each job is associated with a distinct due date and a distinct volume, and has to be delivered to the customer before its due date, i.e. delay is not allowed. The processing time of a batch is a constant independent of the jobs it contains. In production, a constant set-up time as well as a constant set-up cost is required before the first job of this batch is processed. In delivery, a constant delivery time as well as a constant delivery cost is needed for each round-trip delivery between the factory and the customer. Moreover, it is supposed that a job that arrives at the customer before its due date will incur a customer inventory cost. The objective is to find a coordinated lot sizing and scheduling scheme such that the total cost is minimised while guaranteeing a certain customer service level. A mixed integer formulation is proposed for this problem, and then a genetic algorithm is developed to solve it. To evaluate the performance of the proposed genetic algorithm, a lower bound on the objective value is established. Computational experiments show that the proposed genetic algorithm performs well on randomly generated problem instances.     

Biaxial orientation behavior of polystyrene: Orientation and properties

Square sheets of extrusion grade polystyrene (PS) were biaxially stretched using a laboratory biaxial stretcher. The effects of process parameters such as stretch ratio, drawing sequence, drawing speed, and temperature were studied. Birefringence, mechanical properties, and thermal shrinkage of the stretched sheets were the focus of this study. A high orientation was achieved at high stretch ratio, and orientations from uniaxial to equi‐biaxial were obtained by controlling the relative magnitude of stretch ratio in machine (MD) and transverse (TD) directions. Stretching increased tensile strength and elongation at break significantly, which indicated an improvement in the toughness of the oriented PS sheets. Those properties were correlated with biaxial orientation factors: a rapid increase was observed for both tensile strength and elongation at break for birefringence levels above ?0.005, and below, a plateau was observed. The shrinkage strain and stress were found to correlate well with the biaxial orientation factors. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 487–496, 2003     

A New Approach in Optimizing the Induction Heating Process Using Flux Concentrators: Application to 4340 Steel Spur Gear

The beneficial effects of using flux concentrators during induction heat treatment process of spur gears made of 4340 high strength steel is demonstrated using 3D finite element model. The model is developed by coupling electromagnetic field and heat transfer equations and simulated by using Comsol software. Based on an adequate formulation and taking into account material properties and process parameters, the model allows calculating temperature distribution in the gear tooth. A new approach is proposed to reduce the electromagnetic edge effect in the gear teeth which allows achieving optimum hardness profile after induction heat treatment. In the proposed method, the principal gear is positioned in sandwich between two other gears having the same geometry that act as flux concentrators. The gap between the gear and the flux concentrators was optimized by studying temperature variation between the tip and root regions of gear teeth. Using the proposed model, it was possible identifying processing conditions that allow for quasi-uniform final temperature profile in the medium and high frequency conditions during induction hardening of spur gears.