An Integrated Model for Tension Stiffening and Reinforcement Corrosion of RC Flexural Members

An integrated model is proposed to describe tension stiffening in reinforced concrete (RC) flexural members that are undergoing uniform corrosion of reinforcement. The tension stiffening model is taken as base to incorporate the effects of reinforcement corrosion. The model is developed in two steps. In the first step, tension stiffening of concrete is modelled using an exponential stress-strain curve defined as function of a decay parameter. Modular ratio and reinforcement ratio are considered in the definition of the decay parameter. In the second step, the effects of uniform corrosion of reinforcement are integrated with the tension stiffening model. For this, fractional reduction in bar diameter is included as an additional parameter in the model. Later, global damage indicator of a structure is defined based on the secant stiffness calculated from its nonlinear load-displacement response. Performance of the proposed model is demonstrated through numerical studies using two RC beams whose details as well as responses are available in literature. Subsequently, the calculated values of damage indicator are shown useful to quantify reduction in load-carrying capacity of the beams. Based on such quantification, effect of assumed corrosion rates of reinforcement bar on capacity loss of the beam is studied in detail.     

Dehydration of ethanol through blend membranes of chitosan and sodium alginate by pervaporation

Polyion complex membranes made by blending 84% deacetylated chitosan and sodium alginate biopolymers followed by crosslinking with glutaraldehyde were tested for the separation of ethanol–water mixtures. The membranes were characterized by FTIR to verify the formation of the polyion complex, X-ray diffraction (XRD) to observe the effects of blending on crystallinity, DSC, and TGA to investigate the thermal stability, and tensile testing to assess their mechanical stability. The effect of experimental parameters such as feed composition, membrane thickness and permeate pressure on separation performance of the crosslinked membranes was determined. Sorption studies were carried out to evaluate the extent of interaction and degree of swelling of the blend membranes, in pure as well as mixtures of the two liquids. Crosslinked blend membranes were found to have good potential for breaking the azeotrope of 0.135 mol fraction of water and a high selectivity of 436 was observed at a reasonable flux of 0.22 kg/(m² 10 μm h). Membrane selectivities were found to improve with decreasing membrane pressure but remained relatively constant for variable membrane thickness. Increasing membrane thickness decreased the flux and higher permeate pressure caused a reduction in both flux and selectivity.     

Outer approximation algorithm with physical domain reduction for computer‐aided molecular and separation process design

Integrated approaches to the design of separation systems based on computer‐aided molecular and process design (CAMPD) can yield an optimal solvent structure and process conditions. The underlying design problem, however, is a challenging mixed integer nonlinear problem, prone to convergence failure as a result of the strong and nonlinear interactions between solvent and process. To facilitate the solution of this problem, a modified outer‐approximation (OA) algorithm is proposed. Tests that remove infeasible regions from both the process and molecular domains are embedded within the OA framework. Four tests are developed to remove subdomains where constraints on phase behavior that are implicit in process models or explicit process (design) constraints are violated. The algorithm is applied to three case studies relating to the separation of methane and carbon dioxide at high pressure. The process model is highly nonlinear, and includes mass and energy balances as well as phase equilibrium relations and physical property models based on a group‐contribution version of the statistical associating fluid theory (SAFT‐γ Mie) and on the GC⁺ group contribution method for some pure component properties. A fully automated implementation of the proposed approach is found to converge successfully to a local solution in 30 problem instances. The results highlight the extent to which optimal solvent and process conditions are interrelated and dependent on process specifications and constraints. The robustness of the CAMPD algorithm makes it possible to adopt higher‐fidelity nonlinear models in molecular and process design. © 2016 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 62: 3484–3504, 2016     

On Uniqueness of Moving Average Representations of Heavy‐tailed Stationary Processes

The paper solves the open problem of identification of two‐sided moving average representations with i.i.d. summands, for stationary processes in non‐Gaussian domains of attraction of α‐stable laws. This shows the possibility to identify nonparametrically both the sequence of two‐sided moving average coefficients and the distribution of the underlying heavy‐tailed i.i.d. process.     

Novel electrospun poly(vinylidene fluoride-co-hexafluoropropylene)–in situ SiO2 composite membrane-based polymer electrolyte for lithium batteries

Composite membranes of poly(vinylidene fluoride-co-hexafluoropropylene) {P(VdF-HFP)} and different composition of silica have been prepared by electrospinning polymer solution containing in situ generated silica. These membranes are made up of fibers of 1–2 μm diameters. These fibers are stacked in layers to produce fully interconnected pores that results in high porosity. Polymer electrolytes were prepared by immobilizing 1 M LiPF₆ in ethylene carbonate (EC)/dimethyl carbonate (DMC) in the membranes. The composite membranes exhibit a high electrolyte uptake of 550–600%. The optimum electrochemical properties have been observed for the polymer electrolyte containing 6% in situ silica to show ionic conductivity of 8.06 mS cm⁻¹ at 20 °C, electrolyte retention ratio of 0.85, anodic stability up to 4.6 V versus Li/Li⁺, and a good compatibility with lithium metal resulting in low interfacial resistance. A first cycle specific capacity of 170 mAh g⁻¹ was obtained when the polymer electrolyte was evaluated in a Li/lithium iron phosphate (LiFePO₄) cell at 0.1 C-rate at 25 °C, corresponding to 100% utilization of the cathode material. The properties of composite membrane prepared with in situ silica were observed to be comparatively better than the one prepared by direct addition of silica.     

Effect of fixed horizontal louver shading devices on thermal perfomance of building by TRNSYS simulation

Buildings in most countries around the world require large amounts of energy both for cooling and heating. In fact cooling loads due to solar gains represent about half of global cooling loads for residential as well as non-residential buildings. While solar gains through windows contribute largely to these loads, any method of decreasing these gains through shading should be applied with caution, since a balance is required; decreasing cooling loads by shading may increase heating loads drastically and vice versa. So the overall energy requirements both for heating and cooling should be considered. With this in mind a study was done on the thermal performance of a building by TRNSYS simulation, and a shading model for windows was incorporated in it. The shading devices adopted were external fixed horizontal louvers with different slat lengths and tilts. The study was conducted for four different cities in Italy. The optimization of the shading devices was done with respect to primary energy loads for the whole year, and the optimum design was found to depend on location and weather conditions. It was also found that shading factor varies with time of day and is different for summer and winter. For example, for Milan it was found that 70% of gain is cut off in summer, while only 40% is cut off in winter by using optimum shading, which is desirable.     

Rigorous mathematical modeling techniques for optimal delivery of macromolecules to the brain

Several treatment modalities for neurodegenerative diseases or tumors of the central nervous system involve invasive delivery of large molecular weight drugs to the brain. Despite the ample record of experimental studies, accurate drug targeting for the human brain remains a challenge. This paper proposes a systematic design method of administering drugs to specific locations in the human brain based on first principles transport in porous media. The proposed mathematical framework predicts achievable treatment volumes in target regions as a function of brain anatomy and infusion catheter position. A systematic procedure to determine the optimal infusion and catheter design parameters that maximize the penetration depth and volumes of distribution will be discussed. The computer simulations are validated with agarose gel phantom experiments and rat data. The rigorous computational approach will allow physicians and scientists to better plan the administration of therapeutic drugs to the central nervous system.      

Microwave absorption properties of FSS-impacted composites as a broadband microwave absorber

The development of a cost-effective microwave absorber with wide bandwidth corresponding to reflection loss (RL)?≤??10 dB is still a very challenging task. A sugarcane bagasse-based agricultural waste composite has been analyzed for its elemental contents. The combination of elements is suitable for its possible usage as a cost-effective microwave absorbing material. Therefore, this composite has been subjected to morphological and electromagnetic studies to analyze its microwave absorbing behavior. The frequency dependent complex dielectric permittivity and complex magnetic permeability values were obtained using a transmission/reflection waveguide approach in the X-band. Furthermore, the effect of the Minkowski loop frequency selective surface (FSS) was studied over the absorption capability of the composite. It was found that the application of FSS leads to a reduction in thickness up to 2.9 mm and an enhancement in absorption bandwidth up to 3.6 GHz. The FSS patterned composite shows a remarkable performance with peak RL of ?28.4 dB at 10.7 GHz and absorption bandwidth of 3.6 GHz.     

Rechargeable lithium/sulfur battery with suitable mixed liquid electrolytes

The suitability of some single/binary liquid electrolytes and polymer electrolytes with a 1 M solution of LiCF₃SO₃ was evaluated for discharge capacity and cycle performance of Li/S cells at room temperature. The liquid electrolyte content in the cell was found to have a profound influence on the first discharge capacity and cycle property. The optimum, stable cycle performance at about 450 mAh g⁻¹ was obtained with a medium content (12 μl) of electrolyte. Comparison of cycle performance of cells with tetra(ethylene glycol)dimethyl ether (TEGDME), TEGDME/1,3-dioxolane (DIOX) (1:1, v/v) and 1,2-dimethoxyethane (DME)/di(ethylene glycol)dimethyl ether (DEGDME) (1:1, v/v) showed better results with the mixed electrolytes based on TEGDME. The addition of 5 vol.% of toluene in TEGDME had a remarkable effect of increasing the initial discharge capacity from 386 to 736 mAh g⁻¹ (by >90%) and stabilizing the cycle properties, attributed to the reduced lithium metal interfacial resistance obtained for the system. Polymer electrolyte based on microporous poly(vinylidene fluoride) (PVdF) membrane and TEGDME/DIOX was evaluated for ionic conductivity at room temperature, lithium metal interfacial resistance and cycle performance in room-temperature Li/S cells. A comparison of the liquid electrolyte and polymer electrolyte showed a better performance of the former.     

Tribochemistry of MoS3 Nanoparticle Coatings

The tribology of nanoparticles based on transition metal dichalcogenides has been studied extensively. However, evaluation of metal chalcogenides with other stoichiometries has been lacking. We have studied the friction, endurance, and tribochemistry of bonded molybdenum trisulfide (MoS₃) nanoparticle-based coatings for the first time. A facile aqueous chemistry method was used to fabricate the MoS₃ nanoparticles. Pin-on-disk tribometry of an MoS₃ coating using phenolic resin as the binder was conducted in a dry N₂ atmosphere (0.06 % RH, using normal loads of 5 N and 10 N). The results were compared with two types of commercial bonded coatings based on the solid lubricant molybdenum disulfide (MoS₂), as well as a bonded coating we formulated with commercial MoS₂ nanoparticles. Surprisingly, the MoS₃ coating showed similar lubricating ability to the MoS₂-based coatings, exhibiting average μ _k < 0.05 and endurance greater than a million cycles. To evaluate the tribochemistry occurring in the contact region, tribotesting of an MoS₃ coating was halted when steady-state low friction was achieved (i.e., prefailure). Raman spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction on the surface of this wear track showed that the MoS₃ had undergone a tribochemical reaction to form the solid lubricant MoS₂, which explains the excellent lubricity of the coating. This result opens up the possibility of developing MoS₃ nanoparticle-based solid lubricant coatings and MoS₃ nanoparticle additives for oils and greases that are synthetically easier and lower cost than formulations based on MoS₂ nanoparticles.