An analysis of contributing mining factors in coal workers' pneumoconiosis prevalence in the United States coal mines,1986-2018

In the United States,an unexpected and severe increase in coal miners' lung diseases in the late 1990s prompted researchers to investigate the causes of the dis...     

A broadband out‐of‐phase gysel power divider based on a dual‐band circuit with a single fixed isolation resistor

Based on the double‐sided parallel‐strip lines with an inserted conductor as a virtual ground, a high power divider with dual‐band/broadband response and frequency‐independent 180° phase difference between the output ports is implemented in this paper. The circuit topology employs a single commercially available external isolation resistor as well as moderate line impedances (15–100 ohm), making it suitable for high‐power applications. Precise closed‐form design equations on the basis of even‐ and odd‐mode analysis are derived. In addition to the wide range of frequency band ratios from 1 to 2.65, broadband response is also obtained by selecting the proper value of frequency band ratios. To substantiate the design equations and theory, a circuit with 2:1 frequency ratio and 84.5% bandwidth referring to 16 dB isolation and 12 dB return loss values is developed. To the authors' knowledge, this is the widest bandwidth reported for out‐of‐phase high power dividers. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2016.     

Performance evaluation of single stand and hybrid solar water heaters: a comprehensive review

In this review, flat plate and concentrate-type solar collectors, integrated collector–storage systems, and solar water heaters combined with photovoltaic–thermal modules, solar-assisted heat pump solar water heaters, and solar water heaters using phase change materials are studied based on their thermal performance, cost, energy, and exergy efficiencies. The maximum water temperature and thermal efficiencies are enlisted to evaluate the thermal performance of the different solar water heaters. It is found that the solar water heaters’ performance is considerably improved by boosting water flow rate and tilt angle, modification of the shape and number of collectors, using wavy diffuse and electrodepositioned reflector coating, application of the corrugated absorber surface and coated absorber, use of turbulent enhancers, using thermal conductive working fluid and nanofluid, the inclusion of the water storage tank, and tank insulation. These items increase the heat transfer area and coefficient, thermal conductivity, the Reynolds and Nusselt numbers, heat transfer rate, and energy and exergy efficiencies. The evacuated tube heaters have a higher temperature compared to the collectors with a plane surface. Their thermal performance increases by using all-glass active circulation and heat pipe integration. The concentrative type of solar water heaters is superior to other solar heaters, particularly in achieving higher water temperatures. Their performance improves by using a rotating mirror concentrator. The integration of the system with energy storage components, phase change materials, or a heat pump provides a satisfactory performance over conventional solar water heaters.

Graphical abstract

Modification of solar water heaters

     

Dryland river regime shifts in Iran: Drivers and feedbacks

In the Anthropocene, human activities have created unprecedented changes and nonlinear relationships between humans and nature. These changes can be much faster and more intense in arid and semiarid areas that have been affected by intense human activities. Iran has climates from very humid to very dry, but arid and semiarid climates cover the country's largest area. Many of these arid areas have undergone severe changes in their surface and groundwater ecosystems in recent years, which have caused severe damage to humans and the environment in the area and surrounding areas. Therefore, in this study, using the theory of regime shifts, the time series of the Zayandeh-Rud River Basin in the center of Iran were analyzed. First, the data of the desired time series in the period of 1986–2018 was arranged seasonally. Then, using the sequential t-test method, regime shifts in these time series were identified, and then, causal loop diagrams of these shifts and their drivers and feedbacks were interpreted. The results showed that in the time series of quantity and quality of surface water and groundwater level in the studied stations and aquifers, regime shifts can be identified. Regime shifts were also identified in the time series of agricultural land area. These shifts have occurred with the increase in human activities since the early 1950s in the metropolis of Isfahan, the increase in agricultural and industrial exploitation, and consequently, the increase in population. When this reinforcing feedback loop becomes dominant, the Zayandeh-Rud River system has shifted from a regime of rich water resources to a regime of poor water resources. However, by recognizing and systematically analyzing these shifts, the Zayandeh-Rud River system can be directed toward a sustainable system through structural reform, negotiation, and redefining goals.     

Comparative study of one-pot and facile methods to synthesize codoped CQDs with low band gap and photovoltaic properties

Three different one-pot methods of electrochemical, solvothermal, and pyrolysis were applied for the synthesis of nitrogen-doped carbon quantum dots (N-CQDs), N-F codoped carbon quantum dots (CQDs), and N-S codoped CQDs from monoethanolamine and citric acid precursors. Ammonium fluoride and/or thiourea were used as the precursors of the second dopant corporation. The effective synthesis parameters were studied on the basis of the factorial experimental design methodology to maximize absorption edge and reduce band gap in UV-visible spectroscopy. Among the best results, the synthesized N-F/CQDs prepared from ammonium fluoride and citric acid in monoethanolamine revealed the highest absorption edge of 650 nm, the band gap of 1.91 eV, and the particle size of 24 ± 7 nm using the pyrolysis method. The X-ray photoelectron spectroscopy (XPS) analysis indicated simultaneous doping of F and N atoms in the CQDs structure, and the photoluminescence (PL) analysis revealed excitation-dependent properties, which are effective for optical sensor and solar cell applications.     

Investigation of mixing performance in a semi-active T-micromixer actuated by magnetic nanoparticles: Characterization via Villermaux–Dushman reaction

A semi-active T-type micromixer is designed to intensify micromixing by actuating magnetic nanoparticles (MNPs). Five permanent magnets in a zig-zag arrangement are located next to the mixing channel of the micromixer to apply the magnetic field to the fluid flow. Micromixing performance is considered in terms of the segregation index (X_S) by the Villermaux/Dushman reaction test. The effects of magnetic flux intensity (B = 380–500 mT), the concentration of MNPs (φ = 0.002–0.01 [w/v]), and flow rate ratios on X_S and pressure drop are investigated. By increasing MNPs concentration from φ = 0.002–0.008 (w/v), X_S decreased and the rise in φ up to 0.008 (w/v) has not been significant on X_S. Maximum mixing efficiency (i.e., minimum X_S = 0.0088) is achieved for B = 500 mT and φ = 0.01 (w/v). By applying the magnetic field, the mixing performance increased due to the motion of MNPs, but its negative effect is an increase in the pressure drop along the micromixer reactor. Generally, with the formation of MNPs barriers inside the mixing channel, the main fluid flows through these layers and creates the sinusoidal flow paths compared to no magnetic field conditions, and thus, a superior mixing efficiency could be attained.     

Challenges and Strategies for Optimizing Corrosion and Biodegradation Stability of Biomedical Micro- and Nanoswimmers: A Review

The last two decades have witnessed the emergence of micro- and nanoswimmers (MNSs). Researchers have invested significant efforts in engineering motile micro- and nanodevices to address current limitations in minimally invasive medicine. MNSs can move through complex fluid media by using chemical fuels or external energy sources such as magnetic fields, ultrasound, or light. Despite significant advancements in their locomotion and functionalities, the gradual deterioration of MNSs in human physiological media is often overlooked. Corrosion and biodegradation caused by chemical reactions with surrounding medium and the activity of biological agents can significantly affect their chemical stability and functional properties during their lifetime performance. It is therefore essential to understand the degradation mechanisms and factors that influence them to design ideal biomedical MNSs that are affordable, highly efficient, and sufficiently resistant to degradation (at least during their service time). This review summarizes recent studies that delve into the physicochemical characteristics and complex environmental factors affecting the corrosion and biodegradation of MNSs, with a focus on metal-based devices. Additionally, different strategies are discussed to enhance and/or optimize their stability. Conversely, controlled degradation of non-toxic MNSs can be highly advantageous for numerous biomedical applications, allowing for less invasive, safer, and more efficient treatments.