Nowadays, water pollution has become a global issue affecting most countries in the world. Water quality should be monitored to alert authorities on water pollution, so that action can be taken quickly. The objective of the review is to study various conventional and modern methods of monitoring water quality to identify the strengths and weaknesses of the methods. The methods include the Internet of Things (IoT), virtual sensing, cyber-physical system (CPS), and optical techniques. In this review, water quality monitoring systems and process control in several countries, such as New Zealand, China, Serbia, Bangladesh, Malaysia, and India, are discussed. Conventional and modern methods are compared in terms of parameters, complexity, and reliability. Recent methods of water quality monitoring techniques are also reviewed to study any loopholes in modern methods. We found that CPS is suitable for monitoring water quality due to a good combination of physical and computational algorithms. Its embedded sensors, processors, and actuators can be designed to detect and interact with environments. We believe that conventional methods are costly and complex, whereas modern methods are also expensive but simpler with real-time detection. Traditional approaches are more time-consuming and expensive due to the high maintenance of laboratory facilities, involve chemical materials, and are inefficient for on-site monitoring applications. Apart from that, previous monitoring methods have issues in achieving a reliable measurement of water quality parameters in real time. There are still limitations in instruments for detecting pollutants and producing valuable information on water quality. Thus, the review is important in order to compare previous methods and to improve current water quality assessments in terms of reliability and cost-effectiveness.

Driven primarily by scientific curiosity, but also by the potential applications of intense sources of coherent sound, researchers have targeted the phonon laser (saser) since the invention of the optical laser over 50 years ago. Here we fabricate a vertical cavity structure designed to operate as a saser oscillator device at a frequency of 325 GHz. It is based on a semiconductor superlattice gain medium, inside a multimode cavity between two acoustic Bragg reflectors. We measure the acoustic output of the device as a function of time after applying electrical pumping. The emission builds in intensity reaching a steady state on a timescale of order 0.1 μs. We show that the results are consistent with a model of the dynamics of a saser cavity exactly analogous to the models used for describing laser dynamics. We also obtain estimates for the gain coefficient, steady-state acoustic power output and efficiency of the device.

In this paper, RF sputtered magnesium oxide (MgO) thin films (225 nm) on Aluminum (Al6061) grade and Copper substrates were used as thermal interface materials for high-power LED. X-ray diffraction spectra showed the presence of polycrystalline MgO with (200) and (220) oriented cubic MgO (c-MgO) phase as preferred. Thermal conductivity measurement showed an improvement from 17.26 to 22.63 W/mK for Al6061 substrates and from 15.04 to 20.18 W/mK for Cu substrates, respectively. An impressive decrease in junction temperature (Tj) was recorded for MgO thin films interfaced LED on both substrates, especially 2 h annealed MgO on Cu and Al6061 showed a noticeable difference in junction temperatures Δ _Tj of 32.91 °C and 23.08 °C, respectively. Consequently, the difference in total thermal resistance (ΔR _th-tot ) of 5.15 and 3.69 K/W were recorded for MgO film coated Cu and Al6061 substrates, respectively, when compared to their values of bare substrates measured at 700 mA. From surface analysis by atomic force microscope, smooth surfaces for annealed MgO thin films were evidenced when compared to the unannealedfilms and bare substrates, which was making the LED package with low junction temperature and thermal resistance. Overall, MgO thin film synthesized over Cu substrates showed good performance on reducing T _j and Rth of LED at higher driving currents when compared to that of LED on MgO coated Al6061 substrates.