Hybrid inorganic perovskites (HIPs) have been developed in recent years as new high-efficiency semiconductors with a wide range of uses in various optoelectronic applications such as solar cells and light-emitting diodes (LEDs). In this work, we used a first-principles theoretical study to investigate the effects of phase transition on the electronic and optical properties of CsPbI3 pure inorganic perovskites. The results showed that at temperatures over 300 °C, the structure of CsPbI3 exhibits a cube phase (pm3m) with no tilt of PbI6 octahedra (distortion index = 0 and bond angle variance = 0). As the temperature decreases (approximately to room temperature), the PbI6 octahedra is tilted, and the distortion index and bond angle variance increase. Around room temperature, the CsPbI3 structure enters an orthorhombic phase with two tilts PbI6 octahedra. It was found that changing the halogens in all structures reduces the volume of PbI6 octahedra. The tilted PbI6 octahedra causes the distribution of interactions to vary drastically, which leads to a change in band gap energy. This is the main reason for the red and blue shifts in the absorption spectrum of CsPbI3. In general, it can be said that the origin of all changes in the structural, electronic, and optical properties of HIPs is the changes in the volume, orientation, and distortion index of PbI6 octahedra.

Friction Stir Welding (FSW) is a solid-state bonding technique. There are many direct and indirect factors affecting the mechanical and microstructural properties of the FSW joints. Tool offset, tilt angle, and plunge depth are determinative tool positioning in the FSW process. Investigating the effect of these factors simultaneously with other parameters such as process speeds (rotational speed and translational speed) and tool geometry leads to a poor understanding of the impact of these factors on the FSW process. Because the three mentioned parameters have the same origin, they should be studied separately from other process parameters. This paper investigates the effects of tilt angle, plunge depth, and tool offset on Ultimate Tensile Stress (UTS) of joints between AA6061-T6 and AA7075-T6. To design the experiments, optimization, and statistical analysis, Response Surface Methodology (RSM) has been used. Experimental tests were carried out to find the maximum achievable UTS of the joint. The optimum values were determined based on the optimization procedure as 0.7 mm of tool offset, 2.7 degrees of tilt angle, and 0.1 mm of plunge depth. These values resulted in a UTS of 281 MPa. Compared to the UTS of base metals, the joint efficiency of the optimized welded sample was nearly 90 percent.

Thermal conductivity (TC) of a phase change material (PCM) may be enhanced by distributing nanostructured materials (NSMs) termed nano-PCM. It is critical to accurately estimate the TC of nano-PCM to assess heat transfer during phase transition processes, namely, solidification and melting. Here, we propose Gaussian process regression (GPR) strategies involving four various kernel functions (KFs) (including exponential (E), squared exponential (SE), rational quadratic (RQ), and matern (M)) to predict TC of n-octadecane as a PCM. The accessible computational techniques indicate the accuracy of our proposed GPR model compared to the previously proposed methods. In this research, the foremost forecasting strategy has been considered as a GPR method. This model consists of the matern KF whose R2 values of training and testing phases are 1 and 1, respectively. In the following, a sensitivity analysis (SA) is used to explore the effectiveness of variables in terms of outputs and shows that the temperature (T) of nanofluid (NF) is the most efficient input parameter. The work describes the physical properties of NFs and the parameters that should be determined to optimize their efficiency.