Prediction of tensile modulus of nanocomposites based on polymeric blends

A simple model was proposed for predicting the Young’s modulus of nanocomposites based on polymeric blends. First, a simple model was derived for binary blends containing only two polymers. This model is more useful for those blends with high degree of continuity. Therefore, the morphology of the blend is divided into parallel and series regions and the percolation theory is used to calculate the volume fraction of these phases. In the next step, the addition of nanoclay, as a third component, is being considered. These nanoparticles may possibly find locations at the matrix, minor or interface. In the latter case, the model was expanded into a three-phase model including the matrix, dispersed and a third phase containing nanoclay which itself was split into series and parallel sections. A model related to the reinforcing effect of nanoclay was employed and combined with the above model to estimate the modulus of this ternary nanocomposite. The experimental data which is obtained from nanocomposite based on low-density polyethylene/thermoplastic starch/Cloisite 30B were compared with the model results and revealed a good agreement with each other. Also, the model predictions were compared with other experimental data from literature sources to verify the model accuracy. The comparison showed that the model predictions can predict the experimental data rationally. This model can be used to determine the structure of a nanocomposite without any other expensive tests.     

Design of a dual function buried channel waveguide for pulse compression and dispersion compensation in two different wavelengths for the purpose of optical integration

Silicon - Optical pulse compression and dispersion compensation are two important applications in optical systems. The present paper proposes a dual function buried channel waveguide to be used in...     

Glassy carbon electrodes modified with a film of nanodiamond-graphite/chitosan: Application to the highly sensitive electrochemical determination of Azathioprine

A novel modified glassy carbon electrode with a film of nanodiamond-graphite/chitosan is constructed and used for the sensitive voltammetric determination of azathioprine (Aza). The surface morphology and thickness of the film modifier are characterized using atomic force microscopy. The electrochemical response characteristics of the electrode toward Aza are investigated by means of cyclic voltammetry. The modified electrode showed an efficient catalytic role for the electrochemical reduction of Aza, leading to a remarkable decrease in reduction overpotential and enhancement of the kinetics of the electrode reaction with a significant increase of peak current. The effects of experimental variables, such as the deposited amount of modifier suspension, the pH of the supporting electrolyte, the accumulation potential and time were investigated. Under optimal conditions, the modified electrode showed a wide linear response to the concentration of Aza in the range of 0.2-100 μM with a detection limit of 65 nM. The prepared modified electrode showed several advantages: simple preparation method, high stability and uniformity in the composite film, high sensitivity, excellent catalytic activity in physiological conditions and good reproducibility. The modified electrode can be successfully applied to the accurate determination of trace amounts of Aza in pharmaceutical and clinical preparations.     

Synthesis,characterization and adsorption studies of h-BN crystal for efficient removal of Cd2+ from aqueous solution

In the present study, hexagonal boron nitride (h-BN) was synthesized from boric acid and melamine by thermal annealing method in a nitrogen atmosphere. The pure h-BN was used as an efficient sorbent for the uptake of Cd²⁺ ions from the solution phase. The kinetics and sorption studies of metal ions onto the h-BN were carried out in batch adsorption experiments at different temperature, time, pH, sorbent dosage, and concentration of metal ions. The optimum pH for the removal of the Cd²⁺ ions was found to be pH 7. The effect of temperature showed that the process of Cd²⁺ sorption remained endothermic in the range of 298 K–328 K. The Lagergren's first and Ho's second kinetic models were tested to interpret the adsorption kinetic data, however the present data was explained well by Ho's model for kinetics. The thermodynamic perameters ΔG, ΔS and ΔH were determined using the available adsorption data at different temperatures. The physicochemical properties of the synthesized product were also characterized before and after adsorption by different analytical techniques like FT-IR, TGA, XRD and Point of Zero Charge (PZC). The morphology of the surface was analyzed with the help of Scanning Electron Microscopy. The h-BN proved to be an efficient adsorbent for the uptake of the Cd²⁺ ions from aqueous media.     

Effect of process integration on the reduction of fuel consumption

From the process design, demand for utilities can be estimated. The utility system is then designed with respect to the process design. Energy-integrated process design can be introduced at this stage to seek the design that requires the minimum energy, and the corresponding levels at which the utility should enter the process can also be determined. The interaction between process design and the utility system is a further step of energy integration. This step is usually considered after the process design is energy-integrated and targets for minimum hot and cold utilities identified.

When hot and cold utilities are specified, it is possible to deal with these utilities as normal process streams to be presented on a grid diagram with the rest of the process streams. The objective of this simultaneous approach for the interaction between utilities and process design is to assign the most efficient way for the utility to be introduced to the process. Consequently, the synthesis of the heat-exchanger network design should become more effective, thereby resulting in a reduced demand for utility import.     

Ecological Regime versus Minimum Environmental Flow:Comparison of Results for a River in a Semi Mediterranean Region

Water Resources Management - Maintaining Environmental Flow (EF) plays a critical role in protecting rivers and their ecosystems. Because of shortage of data and limited financial resources in...     

Physical mechanisms of heat transfer during single bubble nucleate boiling of FC-72 under saturation conditions. II: Theoretical analysis

This paper is the second part of a two-part study concerning the dynamics of heat transfer during the nucleation process of FC-72 liquid. The experimental findings on the nature of different heat transfer mechanisms involved in the nucleation process were discussed in part I. In this paper, the experimental results are compared with the existing boiling models. The boiling models based on dominance of a single mechanism of heat transfer did not match the experimental results. However, the Rohsenow model was found to closely predict the heat transfer through the microconvection mechanism that is primarily active outside the bubble/surface contact area. An existing transient conduction model was modified to predict the surface heat transfer during the rewetting process (i.e. transient conduction mechanism). This model takes into account the gradual rewetting of the surface during the transient conduction process rather than a simple sudden surface coverage assumption commonly used in the boiling literature. The initial superheat energy of the microlayer (i.e. microlayer sensible energy) was accurately calculated and found to significantly contribute in microlayer evaporation. This even exceeded the direct wall heat transfer to microlayer at high surface superheat temperatures. A composite model was introduced that closely matches our experimental results. It incorporates models for three mechanisms of heat transfer including microlayer evaporation, transient conduction, microconvection, as well as their influence area and activation time. The significance of this development is that, for the first time, all submodels of the composite correlation were independently verified using experimental results.     

Multi-Reservoir System Optimization Based on Hybrid Gravitational Algorithm to Minimize Water-Supply Deficiencies

The growing prevalence of droughts and water scarcity have increased the importance of operating dam and reservoir systems efficiently. Several methods based on algorithms have been developed in recent years in a bid to optimize water release operation policy, in order to overcome or minimize the impact of droughts. However, all of these algorithms suffer from some weaknesses or drawbacks – notably early convergence, a low rate of convergence, or trapping in local optimizations – that limit their effectiveness and efficiency in seeking to determine the global optima for the operation of water systems. Against this background, the present study seeks to introduce and test a Hybrid Algorithm (HA) which integrates the Gravitational Search Algorithm (GSA) with the Particle Swarm Optimization Algorithm (PSOA) with the goal of minimizing irrigation deficiencies in a multi-reservoir system. The proposed algorithm was tested for a specific important multi-reservoir system in Iran: namely the Golestan Dam and Voshmgir Dam system. The results showed that applying the HA could reduce average irrigation deficiencies for the Golestan Dam substantially, to only 2 million cubic meters (MCM), compared to deficiency values for the Genetic Algorithm (GA), PSOA and GSA of 15.1, 6.7 and 5.8 MCM respectively. In addition, the HA performed very efficiently, reducing substantially the computational time needed to achieve the global optimal when compared with the other algorithms tested. Furthermore, the HA showed itself capable of assuring a high volumetric reliability index (VRI) to meet the pattern of water demand downstream from the dams, as well as clearly outperforming the other algorithms on other important indices. In conclusion, the proposed HA seems to offer considerable potential as an optimizer for dam and reservoir operations world-wide.