The use of carbon nanomaterials in membrane distillation membranes: a review

Membrane distillation (MD) is a thermal-based separation technique with the potential to treat a wide range of water types for various applications and industries. Certain challenges remain however, which prevent it from becoming commercially widespread including moderate permeate flux, decline in separation performance over time due to pore wetting and high thermal energy requirements. Nevertheless, its attractive characteristics such as high rejection (ca. 100%) of non-volatile species, its ability to treat highly saline solutions under low operating pressures (typically atmospheric) as well as its ability to operate at low temperatures, enabling waste-heat integration, continue to drive research interests globally. Of particular interest is the class of carbon-based nanomaterials which includes graphene and carbon nanotubes, whose wide range of properties have been exploited in an attempt to overcome the technical challenges that MD faces. These low dimensional materials exhibit properties such as high specific surface area, high strength, tuneable hydrophobicity, enhanced vapour transport, high thermal and electrical conductivity and others. Their use in MD has resulted in improved membrane performance characteristics like increased permeability and reduced fouling propensity. They have also enabled novel membrane capabilities such as in-situ fouling detection and localised heat generation. In this review we provide a brief introduction to MD and describe key membrane characteristics and fabrication methods. We then give an account of the various uses of carbon nanomaterials for MD applications, focussing on polymeric membrane systems. Future research directions based on the findings are also suggested.     

A new hybrid method for optimal circuit design using semi-definite programming

In this article a new method for yield optimization (design centring) is introduced. The method has a statistical-geometrical nature, hence it is called hybrid. The method exploits the semi-definite programming applications in approximating the feasible region with two bounding ellipsoids. These ellipsoids are obtained using a two phase algorithm. In the first phase, the minimum volume ellipsoid enclosing the feasible region is obtained. The largest ellipsoid that can be inscribed inside the feasible region is obtained in the second phase. The centres of these bounding ellipsoids are used as design centres. In the second phase, an additional polytopic region approximation is constructed. A comparison between the obtained region approximations is given. Saving in the number of circuit simulations needed for yield optimization is also considered. Practical examples are given to show the effectiveness of the new method.     

A CMOS current-mode log(x) and log(1/x) functions generator

A novel Complementary Metal Oxide Semiconductor (CMOS) current-mode low-voltage and low-power controllable logarithmic function circuit is presented. The proposed design utilises one Operational Transconductance Amplifier (OTA) and two PMOS transistors biased in weak inversion region. The proposed design provides high dynamic range, controllable amplitude, high accuracy and is insensitive to temperature variations. The circuit operates on a ±0.6 V power supply and consumes 0.3 μW. The functionality of the proposed circuit was verified using HSPICE with 0.35 μm 2P4M CMOS process technology.     

Studying the conversion of graphite into nanographene sheets using supercritical phase exfoliation method

Abstract

This work studies the application of supercritical-phase exfoliation method to produce 100% yield of high-quality graphene. This simple and cost-effective method utilizes supercritical carbon dioxide and ultrasonication to produce pure and defect-free mono-, few- and multi-layer graphene sheets. The process parameters such as pressure, sonication time, sonication amplitude and the amount of starting graphite were examined. The production of defect-free single-, few- and multi-layer graphene sheets was confirmed using atomic force microscopy and Raman spectroscopy. The Fourier-transform infrared spectroscopy confirms that our method does not cause any oxidation to the synthesized graphene. The conductivity of the best yield graphene sample has been tested by four-point probe method and high electrical conductivity of 8.5?×?10⁴ S/m was recorded. The synthesized graphene can be used in many applications such as supercapacitors, batteries, composites and conductive inks.     

Computerized System for Application of Value Engineering Methodology

This paper aims to present an easy, quick, and accurate way of implementing value engineering (VE) studies by introducing an integrated computerized system for the VE technique and life-cycle cost as a checkout system. The VE computer program was designed using a database computer program, FoxPro Window. The computerized version of the VE study consists of several interactive panels, representing the systematic approach (job plan) of a VE study, through which all the information and data of the VE study will be input. The program will help the user to come up with the best selected idea, based on certain calculations that will be done automatically by the VE program. Moreover, the VE case studies that will be investigated by the program will be stored, and thus the program will also serve as a data bank for these case studies as references for future studies. The objective of this paper is not to create a smart VE system, but it can be considered a major step toward this objective.     

Design and experimental investigation of portable solar thermoelectric refrigerator

The main objective of this study is to design and build an affordable solar thermoelectric refrigerator for the Bedouin people (e.g. deserts) living in remote parts of Oman where electricity is still not available. The refrigerator could be used to store perishable items and facilitate the transportation of medications as well as biological material that must be stored at low temperatures to maintain effectiveness. The design of the solar-powered refrigerator is based on the principles of a thermoelectric module (i.e., Peltier effect) to create a hot side and a cold side. The cold side of the thermoelectric module is utilized for refrigeration purposes; provide cooling to the refrigerator space. On the other hand, the heat from the hot side of the module is rejected to ambient surroundings by using heat sinks and fans. The designed solar thermoelectric refrigerator was experimentally tested for the cooling purpose. The results indicated that the temperature of the refrigeration was reduced from 27 °C to 5 °C in approximately 44 min. The coefficient of performance of the refrigerator (COP_R) was calculated and found to be about 0.16.     

Normed Distances and Their Applications in Optimal Circuit Design

A new geometric method for optimal circuit design is presented. The method treats the optimal design problem through the concept of normed distances from a feasible point to the feasible region boundaries in a norm related to the probability distribution of the circuit parameters. The method treats directly the nonlinear feasible region boundaries without any region approximation. The normed distances are found through the solution of a nonlinear optimization problem. The sufficient optimality conditions for this optimization problem are established and an ordinary explicit formula for the normed distance is also derived. An iterative boundary search technique is used to solve the nonlinear optimization problem concerning the normed distances. The convergence of this technique is proved. Practical circuit examples are given to test the method.     

Machine learning in information systems - a bibliographic review and open research issues

Electronic Markets - Artificial Intelligence (AI) and Machine Learning (ML) are currently hot topics in industry and business practice, while management-oriented research disciplines seem reluctant...     

A novel surrogate-based approach for optimal design of electromagnetic-based circuits

A new geometric design centring approach for optimal design of central processing unit-intensive electromagnetic (EM)-based circuits is introduced. The approach uses norms related to the probability distribution of the circuit parameters to find distances from a point to the feasible region boundaries by solving nonlinear optimization problems. Based on these normed distances, the design centring problem is formulated as a max–min optimization problem. A convergent iterative boundary search technique is exploited to find the normed distances. To alleviate the computation cost associated with the EM-based circuits design cycle, space-mapping (SM) surrogates are used to create a sequence of iteratively updated feasible region approximations. In each SM feasible region approximation, the centring process using normed distances is implemented, leading to a better centre point. The process is repeated until a final design centre is attained. Practical examples are given to show the effectiveness of the new design centring method for EM-based circuits.     

A state-of-the-art review of the sustainability and energy efficiency of buildings in Saudi Arabia

Sustainable buildings have an important role in achieving sustainable development by improving energy utilization and environmental performance. Buildings are considered as the biggest single contributor to world energy consumption and greenhouse gas emissions. In Saudi Arabia, the significance of the building sector can be described on the basis of per capita electricity consumption, per capita carbon dioxide emissions, and the increasing number of buildings because of economic and population growth. Therefore, the country should consider establishing energy-efficient buildings to promote sustainable development. Efforts in developing energy-efficient technologies should increase for the national energy policy. This article comprehensively describes the current challenges and opportunities of energy consumption and various energy conservation options that are viable for the Saudi building sector. Current policy efforts for improving energy efficiency in Saudi buildings have been analyzed to enhance the sustainable development in the country. The study reveals that the energy conservation policy of the country has fairly improved in the past decades. However, the country has to focus on this area and perform urgent measures to adopt energy-efficient technologies in the building sector.