High-quality and high-efficiency processing of gallium nitride (GaN) crystals is urgently required for optoelectronic communications and other major industries. This study proposes a novel high-efficiency non-damage magnetorheological chemical polishing (MCP) process to overcome the existing problems of low efficiency and lattice distortion during processing. The effects of the MCP fluid composition and key processing parameters on the surface roughness and material removal rate (MRR）of GaN crystals were studied experimentally. The results showed that a compounded abrasive containing silica fluid exhibited better polishing effects than a single abrasive. The polishing efficiency could be improved by adding NaOH solid particles, and the MRR reached 13.19 nm min-1 when the pH of the MCP fluid was 10. The MRR increased gradually with an increase in the pole rotation speed and worktable speed and a decrease in the polishing gap. The surface roughness of the GaN crystals was improved from Ra 115 nm to Ra 0.375 nm after polishing for 4 h. The surface and sub-surface damage of the polished GaN crystals was analyzed using scanning electron microscope (SEM) and transmission electron microscope (TEM). The results confirmed that the MCP process can realize the non-damage polishing of GaN crystals. Moreover, a prediction model for the surface roughness of GaN crystals in the MCP process was constructed. The overall difference between the actual and predicted surface roughness values for the model was 11.6%.

Cylinder bore honing is a finishing process that generates a crosshatch pattern with alternate valleys and plateaus responsible for enhancing lubrication and preventing gas and oil leakage in the engine cylinder bore. The required functional surface in the cylinder bore is generated by a sequential honing process and is characterized by Rk roughness parameters (Rk, Rvk, Rpk, Mr1, Mr2). Predicting the desired surface roughness relies primarily on two techniques: (i) analytical models (AM) and (ii) machine learning (ML) models. Both of these techniques offer certain advantages and limitations. AM's are interpretable as they indicate distinct mapping relation between input variables and honed surface texture. However, AM's are usually based on simplified assumptions to ensure the traceability of multiple variables. Consequently, their prediction accuracy is adversely impacted when these assumptions are not satisfied. However, ML models accurately predict the surface texture but their prediction mechanism is challenging to interpret. Furthermore, the ML models' performance relies heavily on the representativeness of data employed in developing them. Thus, either prediction accuracy or model interpretability suffers when AM and ML models are implemented independently. This study proposes a hybrid model framework to incorporate the benefits of AM and ML simultaneously. In the hybrid model, an Artificial neural network (ANN) compensates the AM by correcting its error. This retains the physical understanding built into the model while simultaneously enhancing the prediction accuracy. The proposed approach resulted in a hybrid model that significantly improved the prediction accuracy of the AM and additionally provided superior performance compared to independent ANN.

Background: The study was done on various concrete Cubes, Beams and cylinders that were made by using different compositions of unconventional materials. The strength measurements were done at different intervals. A strong correlation between strength parameters of concrete with respect to its composition, age and economy was found. Aim: To study economical and strength characteristics of different mould shapes of concrete made by using various compositions of unconventional materials like marble powder , fly ash etc. The characteristics were than compared with regular conventional concrete. Methods: We performed a prospective study for a total period of 3 months on a total of 72 moulds of concrete. These 72 moulds of concrete were moulded in 3 different shapes (24 moulds in cube shape, 24 moulds in beam shape, and 24 moulds in cylindrical shape). A particular concrete mix was used for a set of three shapes of concrete moulds (3 cube shaped, 3 beam shaped, and 3 cylindrical shaped). 8 such sets were made using 8 different compositions of concrete mix. These 8 compositions were achieved by either partially of fully replacing coarse aggregate or sand or cement. A) By replacing coarse aggregate: 75% fresh aggregate +25 % recycled aggregate 1 , 100% recycled aggregate 2 .B) By replacing cement: 95% cement +3% marble powder +2% flyash 3 , 85% cement +10% marble powder +5% flyash 4 , 75% cement +15% marble powder +10% flyash 5. C) By replacing sand : 75% sand +25% brick dust 6 , 50% sand +50% brick dust 7. The 8 th composition was regular concrete mix and was used for reference purposes. Note: M20 grade of concrete having ratio 1:1.5:3 (1 cement: 1 fine aggregate: 1 coarse aggregate) was considered for this research. Compressive strength of concrete cubes was tested after 7 days, 21 days and 28 days of moulding. Flexural strength of beams and split tensile strength of concrete cylinders were also calculated. Results: Economy and strength properties of a concrete mix are a function of its components and their respective percentage. It is inferred that concrete mix constituents could be partially replaced by less expensive or waste materials, thus providing less expensive mortar. Although the resultant mix has degraded strength characteristics, it can still be used at places where strength requirements of concrete are fulfilled at less value. Conclusion: Calculated partial replacement of constituents of concrete mixes by unconventional; less expensive and waste materials can be a useful method for reducing the cost of mortar. It can be possible for a concrete mix to meet strength requirements and be less expensive by using unconventional materials. It can also be possible to reflect certain properties of unconventional materials into the concrete. This is only possible after extensive research.

Portland cement is used by the construction industries, which is known to be a heavy contributor of carbon dioxide emissions and environmental damage. Adding of industrial wastes like demolished old concrete OF structures, silica fume (SF) fly ash (FA) as additional cementing materials (SCMs) could result in a substantial reduction of the overall Carbon dioxide trace marks of the final concrete product. Use of these additional materials in construction industry especially in the making of concrete is highly challenging. Remarkable research efforts are needed to study about the engineering properties of concrete incorporating such industrial wastes. Present research is an effort to study the properties of concrete adding industrial wastes such as demolished concrete, FA and SF The improvement of properties of RCA concrete with the incorporation of two ureolytic-type bacteria, Bacillus subtilis and Bacillus sphaericus to improve the properties of RCA concrete. The experimental investigations are carried out by experts evaluate the improvement of the compressive strength, capillary water absorption and drying shrinkage of RCA concrete adding bacteria. Seven concrete mixes are manufactured using Portland slag cement (PSC) partially changed with SF ranging from 0 to 30%. The mix proportions were obtained as per Indian standard IS: 10262-2009 with 10% extra cement when SF is taken as per the above the construction practice by experts. Optimal dosages of SF for maximum values of compressive strength, tensile splitting strength and flexural strength at 28 days are determined. Keywords: Bacillus subtilis, Bacillus sphaericus, RCA, PSC, Silica Fume.