Application of colloidal gas aphrons for pollution remediation

Colloidal gas aphrons (CGAs), first described by Felix Sebba in his book Foams and Biliquid Foams—Aphrons in 1987, consist of a system of spherical microbubbles with diameters mostly above 25 µm and classified as kugelschaums (ball foam). They possess some colloidal properties and can be pumped at uniform rate through pipes and channels, much like liquids. Also, they have high stability due to very small size and thick surfactant shells. Research work published over the past two decades indicate effective applications of CGAs for clarification of particles and microorganisms, protein separation, gas and nutrient transfer and pollutant separation from water and soil matrices. In this review paper, the techniques for generating CGAs and their application to pollution abatement are discussed. Some mineral separation processes by CGA flotation have also been reviewed because of their relevance to contaminant removal processes. The CGAs were found to function on the principles of bubble entrained floc flotation, electrostatic and ionic interaction, diffusion of entrapped gas and hydrophobicity of the pollutant particles. Two tables have also been provided to present a comparative overview of the generation technologies and the effectiveness of pollution remediation techniques. Copyright © 2012 Society of Chemical Industry     

Performance analysis of MIMO–OFDM in various outdoor fading environments

Multiple-input Multiple-output (MIMO) technology is being combined with Orthogonal Frequency Division Multiplexing (OFDM) for use in next generation broadband wireless communication systems, and there has been an increase in the study of MIMO–OFDM systems. IEEE 802.11n specification uses MIMO–OFDM system to improve network throughput and coverage over the two previous standards, 802.11a and 802.11g, in indoor and outdoor environments, respectively. With an extended range of about two hundred meters in the outdoor environment, the use of 802.11n has increased. This paper analyzes the effect of shadowing, moving user and foliage in outdoor environment. There is a special need to analyze performance measures such as Spectral Efficiency and Bit Error Rate (BER), and this is the subject matter of interest in this paper.     

Influence of State of Stress on Dynamic Recrystallization in a Titanium-Modified Austenitic Stainless Steel

The influence of the state of stress on the microstructure and dynamic recrystallization (DRX) in a titanium-modified austenitic stainless steel is assessed by performing plane-strain and uniaxial hot compression studies. Although the state of stress does not alter the mechanisms of DRX nucleation, the kinetics of DRX is hindered during plane-strain deformation vis-à-vis uniaxial deformation.     

Performance of Punctured Convolutional Codes in A-CDMA Systems with Accurately Modelled Multiple Access Interference Under Perfect Phase Tracking Conditions

In this paper, a simplified expression for Improved Gaussian Approximation is considered to model multiple access interference in an A-CDMA system. Punctured convolutional codes, which are one of the subclasses of convolutional codes, are employed to provide error protection to the information transmitted over the wireless channel. A detailed theoretical analysis is made initially and then compared with the simulated results for various code rates. The simulated performance of the codes is then compared for different power levels and different number of interferers of the desired user. A perfect phase reference is assumed to be available for the information signal of the desired user throughout this paper.     

Performance modeling of finite state Markov chains for Nakagami-q and α–μ distributions over adaptive modulation and coding schemes

In this paper, performance modeling of finite state Markov chain (FSMC) for Nakagami-q and α–μ fading distributions over adaptive modulation and coding (AMC) schemes at the physical layer are discussed in detail, assuming that sufficient data is present to be transmitted continuously during the adaptive transmission period. However, this assumption is not always valid when queuing effects are taken into account at the data link layer. The received SNR obtained from a coded multiuser wireless system in the presence of a heavily shadowed environment is assumed to undergo a Nakagami-q (Hoyt distribution. Performance measures like level crossing rate, steady state probability, state transition probability and state time duration for Nakagami-q distribution and α–μ distribution are derived, plotted and analyzed. The BER for non-coherent FSK is shown to be much better than coherent FSK and PSK in the presence of Nakagami-q fading.     

Fabrication of novel poly(lactic acid)/amorphous magnesium phosphate bionanocomposite fibers for tissue engineering applications via electrospinning

Fibrous bionanocomposites consisting of amorphous magnesium phosphate (AMP) nanospheres and polylactic acid (PLA) were fabricated by electrospinning. There are two important signatures of this paper. First, AMP, as an alternative to well-known calcium phosphate (CaP) materials, is added to PLA as the second phase. To the best of our knowledge, it is the first attempt to fabricate magnesium phosphate (MgP)/biopolymer composite. This is made possible by our previously reported research on the successful synthesis of AMP nanospheres via microwave processing. Second, the sustained release of magnesium and phosphate ions from PLA matrix can stimulate a series of cell responses. The structure of the composites and their bone-like apatite-forming abilities in simulated body fluid (SBF) were examined. Additionally, the effects on the proliferation and differentiation of preosteoblast cells were evaluated by performing in vitro cell culture and monitoring markers such as Osteocalcin (OCN), Osteopontin (OPN), Alkaline phosphatase (ALP) and Collagen type-I (Col I) using real-time polymerase chain reaction (PCR). For better dispersion of AMP in the fibers, a surfactant, 12-hydroxysteric acid (HSA), as previously reported in the literature, was used. However, HSA significantly inhibited the proliferation and differentiation of preosteoblast cells, indicating the potential risk in using HSA in the combination of AMP or MgP in tissue engineering applications.     

Status of groundwater arsenic contamination in Bangladesh: A 14-year study report

Since 1996, 52,202 water samples from hand tubewells were analyzed for arsenic (As) by flow injection hydride generation atomic absorption spectrometry (FI-HG-AAS) from all 64 districts of Bangladesh; 27.2% and 42.1% of the tubewells had As above 50 and 10 μg/l, respectively; 7.5% contained As above 300 μg/l, the concentration predicting overt arsenical skin lesions. The groundwater of 50 districts contained As above the Bangladesh standard for As in drinking water (50 μg/l), and 59 districts had As above the WHO guideline value (10 μg/l). Water analyses from the four principal geomorphological regions of Bangladesh showed that hand tubewells of the Tableland and Hill tract regions are primarily free from As contamination, while the Flood plain and Deltaic region, including the Coastal region, are highly As-contaminated. Arsenic concentration was usually observed to decrease with increasing tubewell depth; however, 16% of tubewells deeper than 100 m, which is often considered to be a safe depth, contained As above 50 μg/l. In tubewells deeper than 350 m, As >50 μg/l has not been found. The estimated number of tubewells in 50 As-affected districts was 4.3 million. Based on the analysis of 52,202 hand tubewell water samples during the last 14 years, we estimate that around 36 million and 22 million people could be drinking As-contaminated water above 10 and 50 μg/l, respectively. However for roughly the last 5 years due to mitigation efforts by the government, non-governmental organizations and international aid agencies, many individuals living in these contaminated areas have been drinking As-safe water. From 50 contaminated districts with tubewell As concentrations >50 μg/l, 52% of sampled hand tubewells contained As <10 μg/l, and these tubewells could be utilized immediately as a source of safe water in these affected regions provided regular monitoring for temporal variation in As concentration. Even in the As-affected Flood plain, sampled tubewells from 22 thanas in 4 districts were almost entirely As-safe. In Bangladesh and West Bengal, India the crisis is not having too little water to satisfy our needs, it is the challenge of managing available water resources. The development of community-specific safe water sources coupled with local participation and education are required to slow the current effects of widespread As poisoning and to prevent this disaster from continuing to plague individuals in the future.     

Robust control of discrete minimum and non-minimum phase systems via data-driven virtual reference feedback tuning and IMC

In this paper, we develop a novel robust control approach for discrete minimum and non-minimum phase systems via a combined data-driven virtual reference feedback tuning ($\text{VRFT}$) and internal model control (IMC) scheme. The first step in the conventional $\text{VRFT}$ method controller design is the selection of the closed-loop reference model ($M\left(z\right)$), and $M\left(z\right)$ selection is still an open problem. The integration of the $\mathrm{IMC}$ scheme and the VRFT method provides the advantage of flexibility in controller design due to the incorporation of the $\mathrm{IMC}$ filter. As a result, the proposed design method begins with the selection of $M\left(z\right)$ and $\mathrm{IMC}$ filter. Unlike the standard $\text{VRFT}$ method, the proposed combined $\text{VRFT}$ and $\mathrm{IMC}$ design approach has the unique feature of taking into account a robustness property of dynamics, namely, maximum sensitivity ($M_{\mathrm{s}}$) as the design specification for the $M\left(z\right)$ and IMC filter selection. Moreover, the proposed approach includes a robustness specification that resolves the trade-off between performance and robustness in real-time controller design. Furthermore, the robustness guarantee with plant uncertainties and controller fragility is elucidated. The proposed approach is validated using numerical simulations and experimental validation through the temperature control process. Compared to conventional $\text{VRFT}$ controllers, experimental and simulation results show that the proposed controllers have less tracking error, minimize control effort, and improve robustness.