Synthesis and characterization of efficient polyamide thin film nanocomposite membranes

The availability of fresh water is directly associated with accessible natural resources. However, 2.5 billion of the world\u27s population (around 40%) does not have access to proper sanitation systems, with 6 to 8 million annual deaths related to inadequate water supply, sanitation and hygiene in 2013. Currently, sea water desalination offers a feasible strategy to face global water challenge. Different water desalination techniques were developed and membrane desalination is currently the highest cost effective technique. Reverse osmosis (RO) system is by far considered the least expensive membrane process. Typically, RO system uses the thin film composite (TFC) membranes. A typical TFC membrane consists of two layers: a top dense polyamide (PA) skin layer (responsible for salt rejection) applied on an underlying support layer (responsible for mechanical support of the thin PA layer). Recently, a new category of membranes has emerged known as thin film nanocomposite membranes (TFNC) where nanoparticles (NPs) are incorporated into the support layer to enhance its properties. The support layer surface pore diameters are quite crucial in supporting and preserving the integrity of the PA layer. Thus, the ideal support layer shall comprise a non-porous to slightly porous top surface. However, a support layer with non-porous surface would resist the water flow. Consequently, the main target of the work represented was to fabricate a highly porous membrane that could still support a PA layer on top of it. Membranes with symmetric cross section have high permeability due to the highly interconnected porous structure. Yet, the surface of the symmetric membranes is also highly porous; and hence, serving as a TFNC support is challenging. Thus, this study focuses on tailoring symmetric TFNC support membranes to effectively support the PA layer. Firstly, we investigated the influence of different fabrication parameters on the support membrane properties. This entailed the understanding of the thermodynamic behavior of the cast solution during fabrication till the final precipitation of the support membrane. TFNC support membranes were prepared using cast solution of Polyethersulfone (PES) polymer in N-methyl-2-pyrrolidone (NMP) as a solvent. Afterwards, the effect of non-solvent addition was investigated using Triethylene Glycol (TEG). Furthermore, Pluronic® (Plu) and Titanium dioxide (TiO2) NPs were incorporated in two different sets of experiments to compare the enhancement of support membrane hydrophilicity and mechanical stability. Support membranes were fabricated using two consecutive phase separation processes, namely: Vapor-Induced Phase Separation (VIPS) followed by Liquid-Induced Phase Separation (LIPS). Various conditions were tested during the VIPS process, including relative humidity degree (RH) at exposure, exposure time and the effect of air convection during the exposure period. The cast solutions were prepared under 30% and 80% RH for exposure time ranging from 1 to 5 minutes. Forced convection condition was applied to the cast solutions whereas compressed dry air was introduced to the cast solution during the exposure period. On the other hand, free convection condition was defined in terms of the absence of compressed dry air introduction during VIPS process. Solution composition was systematically changed to further understand its influence on the thermodynamic behavior under VIPS process. This entailed studying the change in PES content ranging from 10 to 15 wt%, as well as the TEG (0 to 60 wt%), Plu (0 to 5 wt%) and TiO2 (0 to 1 wt%). This variability in cast solution composition clarified the influences of the solution viscosity and hygroscopicity on the thermodynamic behavior of the cast solution, which in turns, reflected on the support membrane final morphology. Afterwards, support membranes were characterized for their cross-sectional morphology using scanning electron microscopy, pore size distribution using the capillary flow porometer, hydrophilicity using contact angle method, surface charge using surface charge analyzer and chemical composition using Fourier transform infrared spectroscopy and proton nuclear magnetic resonance. Also, membranes hydraulic permeability and wettability were tested. Membranes fabricated under different conditions showed various structures including asymmetric and symmetric cross section morphologies. The effect of air convection was significantly important and in some cases even switched the cross section structure from asymmetric to completely symmetric. Interestingly, at low RH value (30%) and under free convection condition, membranes with semi-symmetric structure were successfully produced. This novel structure holds the privileges of both symmetric and asymmetric membranes. It showed high water permeability and mechanical stability due to the highly interconnected pores structure, as well as, having a very thin skin surface to support the PA layer on top of it. Furthermore, the semi-symmetric membrane showed higher compaction resistance (91.3%) and recovery (94%) as compared to the asymmetric membrane. As a consequence, the semi-symmetric morphology was considered as the structure of our interest as a TFNC support membrane. Support membrane hydrophilicity, water permeability, mechanical stability and morphology are known to have high contribution to the overall TFNC membrane performance. Thus, the developed semi-symmetric structure was then reproduced using cast solutions containing the hydrophilic additives Plu and TiO2. Results showed that the addition of TiO2 had increased both the membrane hydrophilicity and compaction resistance. However, semi-symmetric supports were only achievable with 0.05 and 0.1 wt% TiO2 concentrations. As a concluding step, polyamide (PA) top skin layer was fabricated on semi-symmetric support membranes of different compositions. The final TFNC showed the higher permeability values when semi-symmetric supports were compared to asymmetric support of same composition. Furthermore, the highest TFC permeability was for support membrane containing 1 wt% Plu and that containing 0.1 wt% TiO2

Routing in Sensor Networks: Performance and Security in clustered networks

© ASEE 2008Due to high restrictions in sensor network, where the resources are limited, clustering protocols for routing organization have been proposed in much research for increasing system throughput, decreasing system delay and saving energy. Even these algorithms have proposed some levels of security, but because of their dynamic nature of communication, most of their security solutions are not suitable. In this paper we focus on how to apply the highest possible level of security to sensor networks and at the same time increase the performance of these networks by changing the way that sensors communicate with each other

Using Available Wireless/Wired Network Infrastructure for Public Safety and Emergency Early Response

© ASEE 2008After September eleven the idea of Public Safety became a key policy goal for every governmental, education and commercial institute. Currently, most of the buildings are equipped with infrastructure for internal and external communication and networking. By being able to utilize the existing infrastructure of wireless / wired network in a building, we can have in place an early response system to disasters. This is important to save lives and get resolution for a disaster sooner. The idea here is to eliminate or reduce additional cost for a dedicated infrastructure for early response system. Due to the growth for the need of internetworking, most of the buildings have already a good base for such a system. This article contributes to the solution of the problem by specifying a novel solution for integration WLAN and existing infrastructure to the system of public safety and emergency early response

Multi-generations Key Pre-distribution's Technique in Wireless Sensor Networks

Network future relies nowadays on producing a low-cost and effective network in less cost. One of the most effective network solutions is the Wireless Sensor Networks (WSN). Security is the main challenge of this kind of networks where the nodes in such network are restricted by the power consumption due to limited power source. The main factor of WSN security is the key management part which consists of creating, distributing, and using the keys in the network lifecycle. Key Pre-distribution technique is approved to work efficiently to support WSN security. One of the drawbacks of this technique is that it is not supporting renewing and refreshing keys to support multi-generations sensors. In this work we present a novel technique to reproduce new keys from old pre-distributed keys in efficient way to save the power

Modified LEACH – Energy Efficient Wireless Networks Communication

The final publication is available at www.springerlink.comMany algorithms and techniques were proposed to increase the efficiency of Sensor Networks. Due to high restrictions of this kind of networks, where the resources are limited, many factors may affect its work. Theses factors are: System throughput, system delay, and energy. Clustering protocols have been propose to decrease system throughput and system delay, and increase energy saving. In this paper, we propose a new technique that can be applied to sensor networks to produce high performance and stable Sensor Networks.http://link.springer.com/chapter/10.1007%2F978-90-481-3662-9_2

Covering Materials Incorporating Radiation-Preventing Techniques to Meet Greenhouse Cooling Challenges in Arid Regions: A Review

Cooling greenhouses is essential to provide a suitable environment for plant growth in arid regions characterized by brackish water resources. However, using conventional cooling methods are facing many challenges. Filtering out near infra-red radiation (NIR) at the greenhouse cover can significantly reduce the heating load and can solve the overheating problem of the greenhouse air. This paper is to review (i) the problems of using conventional cooling methods and (ii) the advantages of greenhouse covers that incorporate NIR reflectors. This survey focuses on how the cover type affects the transmittance of photosynthetically active radiation (PAR), the reflectance or absorptance of NIR and the greenhouse air temperature. NIR-reflecting plastic films seem to be the most suitable, low cost and simple cover for greenhouses under arid conditions. Therefore, this review discusses how various additives should be incorporated in plastic film to increase its mechanical properties, durability and ability to stand up to extremely harsh weather. Presently, NIR-reflecting covers are able to reduce greenhouse air temperature by no more than 5°C. This reduction is not enough in regions where the ambient temperature may exceed 45°C in summer. There is a need to develop improved NIR-reflecting plastic film covers

Investigating the Performance of Apodized Fiber Bragg Gratings for Sensing Applications

Fiber Bragg gratings (FBGs) technology has demonstrated its suitability for many applications in recent fiber technologies. Sensing application is one of the main applications of FBGs. In this work, we present a comprehensive investigation for using apodized FBGs in sensing applications. Different evaluation parameters such as, reflectivity, sidelobes, and fullwidth-half-maximum (FWHM) are tested in order to determine the most proper apodization profile for sensors. According to our study, the Blackman apodization gives the best profile that can be used in sensing applications. The reflectivity of Blackman apodization is nearly unity with minimum sidelobes level, -60.3 dB, and narrow FWHM. The length of Blackman apodized FBG is 0.33 cm and Δn = 14.4 x 10‒4 and maximum reflectivity is 99.44%

Automated Adaptive Mobile Learning System using Shortest Path Algorithm and Learning Style

A directed graph represents an accurate picture of course descriptions for online courses through computer-based implementation of various educational systems. E-learning and m-learning systems are modeled as a weighted, directed graph where each node represents a course unit. The Learning Path Graph (LPG) represents and describes the structure of domain knowledge, including the learning goals, and all other available learning paths. In this paper, we propose a system prototype that implements a propose adaptive learning path algorithms that uses the student’s information from their profile and their learning style in order to improve the students’ learning performances through an m-learning system that provides a suitable course content sequence in a personalized manner.https://doi.org/10.3991/ijim.v12i5.818

The cientificWorldJOURNAL Review Article Covering Materials Incorporating Radiation-Preventing Techniques to Meet Greenhouse Cooling Challenges in Arid Regions: A Review

Cooling greenhouses is essential to provide a suitable environment for plant growth in arid regions characterized by brackish water resources. However, using conventional cooling methods are facing many challenges. Filtering out near infra-red radiation (NIR) at the greenhouse cover can significantly reduce the heating load and can solve the overheating problem of the greenhouse air. This paper is to review (i) the problems of using conventional cooling methods and (ii) the advantages of greenhouse covers that incorporate NIR reflectors. This survey focuses on how the cover type affects the transmittance of photosynthetically active radiation (PAR), the reflectance or absorptance of NIR and the greenhouse air temperature. NIR-reflecting plastic films seem to be the most suitable, low cost and simple cover for greenhouses under arid conditions. Therefore, this review discusses how various additives should be incorporated in plastic film to increase its mechanical properties, durability and ability to stand up to extremely harsh weather. Presently, NIR-reflecting covers are able to reduce greenhouse air temperature by no more than 5 • C. This reduction is not enough in regions where the ambient temperature may exceed 45 • C in summer. There is a need to develop improved NIR-reflecting plastic film covers

An efficient multi-time step FEM–SFEM iterative coupling procedure for elastic–acoustic interaction problems

An iterative coupling methodology between the Finite Element Method (FEM) and the Spectral Finite Element Method (SFEM) for the modeling of coupled elastic-acoustic problems in the time domain is presented here. Since the iterative coupling procedure allows the use of a nonconforming mesh at the interface between the subdomains, the difference in the element sizes concerning the FEM and SFEM is handled in a straightforward and efficient manner, thereby retaining all the advantages of the SFEM. By means of the HHT time integration method, controllable numerical damping can be introduced in one of the subdomains, increasing the robustness of the method and improving the accuracy of the results; besides, independent time-step sizes can be considered within each subdomain, resulting in a more efficient algorithm. In this work, a modification in the subcycling procedure is proposed, ensuring not only an efficient and accurate methodology but also avoiding the computation of a relaxation parameter. Numerical simulations are presented in order to illustrate the accuracy and potential of the proposed methodology.CAPES, UFJF, UFSJ, FAPEMIG and CNP