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Metal‐insulator‐insulator‐metal (MIIM) diodes with thickness‐gradient films for the insulator layers are fabricated for the first time. Spatially varying atmospheric‐pressure chemical vapor deposition is used to deposit ZnO and Al2O3 films with orthogonal gradient directions, producing 414 MIIM diodes with 414 different ZnO/Al2O3 film‐thickness combinations on a single substrate for combinatorial and high‐throughput optimization. The nm‐scale ZnO/Al2O3 films are printed in only 2 min and the entire device fabrication takes 7 h, which is much less than conventional approaches for investigating many insulator‐thickness combinations. Rapid identification of the optimal thickness combination is demonstrated; high‐performance diodes (asymmetry = 227, nonlinearity = 13.1, and responsivity = 12 A/W) are observed when a trap‐assisted tunneling mechanism is dominant for insulator thicknesses of 3.4–4.4 nm (ZnO) and 7.4 nm (Al2O3). [ABSTRACT FROM AUTHOR]

Solidification of a liquid in motion driven by shear and pressure gradients occurs in many natural settings and technological applications. When the liquid is electrically conducting, its solidification rates can potentially be modulated by an imposed magnetic field. The shearing motion results in viscous dissipation and the Lorentz force induced by the magnetic field causes Joule heating of the fluid, which can influence the structure of the flow, thermal fields, and thereby the solidification process. In this study, a mathematical model is developed to study the combined effects of shear and pressure gradients in the presence of a magnetic field on the solidification of a liquid between two parallel plates, with one of them being insulated and under constant motion, and the other being cooled convectively and at rest. Under the quasi‐steady assumption, closed‐form semianalytical solutions are obtained for the instantaneous location of the solid–liquid interface, Nusselt number, and dimensionless power density as a function of various characteristic parameters such as the Hartmann number, pressure gradient parameter, Brinkman number, and Biot number. Furthermore, an interesting remelt or steady‐state condition for the interfacial location is derived as arising from the competing effects of the solid side heat flux and viscous dissipation and Joule heating on the liquid side. The newly derived analytical results are shown to reduce to the various classical results in the limiting cases. A detailed systematic study is performed by the numerical solution of the semianalytical formulation, and the effects of different characteristic parameters on the solidification process are discussed. [ABSTRACT FROM AUTHOR]

The problem of freshwater shortage is increasing a day after day. Solar distillers are suitable devices to overcome this problem for remote areas and small families. However, these devices suffer from their low productivities. Here, two different modified designs for the distillers of rotating wick types were tested. One distiller contained a rotating wick belt with a path of "L" character shape (l -RWSS), and the other with a path of "LC" shape (LC-RWSS). In addition, the wick type was investigated for black jute and cotton wicks. Moreover, the effect of belt-rotation direction (clockwise and counterclockwise) on the still performance has been studied. The period of wick belt rotation was tested (ON = 5 min and OFF = zero, 10, 20, 30, 40, 50, and 60 min). Also, the impact of using graphene quantum dots nanofluid on the distiller performance was investigated. Experimental results obtained that the jute wick obtained more distillate than the cotton cloth. Furthermore, the productivity of LC-RWSS with counterclockwise movement of wick belt was always larger than that with clockwise direction under all different OFF times. Also, the LC-RWSS (jute wick-counterclockwise-0.1 rpm) increased the freshwater productivity by about 17 % over l -RWSS. Besides, the LC-RWSS provided higher accumulated daily productivity than l -RWSS by 19 % and 17 % with and without nanofluid, respectively. Also, the cost of freshwater obtained is 0.018 and 0.021 $/L for LC-RWSS with and without nanofluids, respectively. [ABSTRACT FROM AUTHOR]