Sepuluh Nopember Institute of Technology

The concept of a circular economy for rare earth elements (REEs) is being developed. The circular economy involves optimising the lifecycle of products to achieve sustainable and efficient consumption. REEs are considered critical elements of high economic value. Considering limited rare earth reserves, secondary source REEs are very important to sustainable use. Spent nickel-metal hydride (Ni-MH) batteries are electronic waste containing valuable REEs. Ni-MH batteries that have reached their age limit, if thrown away, will become hazardous waste. Recycling Ni-MH battery waste efficiently enables REEs to be recovered and reused. The REE recovery process has challenges that must be considered such as efficiency, low REE concentration, environmental concerns and scalability, thus requiring the development of new, efficient recovery methods and processes for REE. Currently the hydrometallurgical method is preferred for REE recovery from Ni-MH batteries because it has high yields, low energy requirements, ease of separation from base metals and low greenhouse gas emissions. One such REE recovery using hydrochloric acid on a pilot scale yielded 91.6% lanthanum.

Neodymium-iron-boron is a rare earth element (REE)-based permanent magnet material. Its main magnetic phase is Nd 2 Fe 14 B and it has minor phase neodymium-rich or α-iron. The neodymium-iron-boron permanent magnet has a remarkable maximum energy product ((BH) Max ) reaching 474 kJ m ⁻³ or nearly 60 mega-gauss-oersteds (MGOe), making neodymium-iron-boron magnets highly suitable for wide use in various technological applications. A commercial neodymium-iron-boron magnet contains 22–32 wt% of REEs such as neodymium, dysprosium, praseodymium and lanthanum. As a result of increasing demand for these materials, the availability of REE from natural resources are decreasing and several REEs such as neodymium, dysprosium and praseodymium are in the critical category. Recycling neodymium-iron-boron magnet waste to recover the REEs is one possible solution to provide raw materials for the permanent magnet industry while minimising electronic device waste. Pyrometallurgical and hydrometallurgical metal extraction processes are commonly used for REE recovery. These two methods are excellent for REE recovery and relatively easy to conduct, allowing pyrometallurgical and hydrometallurgical methods to be adopted on industrial scale to benefit the availability of raw materials for the neodymium-iron-boron magnet industry.

Permanent magnets are crucial materials for the development of electronics and telecommunications technology. During the early modern era, the development of permanent magnet materials focused on finding new materials to meet maximum energy product ((BH) Max ) criteria. Currently, rare earth-based alloy permanent magnet materials, such as samarium-cobalt and neodymium-iron-boron, are the most advanced permanent magnet materials and have superior magnetic properties compared to other magnetic materials. Research and development in permanent magnets currently focuses more on engineering existing magnetic materials to develop a sustainable and environmentally friendly rare earth permanent magnet production system, in order to realise a circular economy system in the permanent magnet industry.

The shear capacity of reinforced beam concrete was designed to resist the stirrup reinforcement, Vs, and by the concrete itself, Vc. Previous studies of geopolymer concrete show the mechanical properties of this proposed green concrete, yet the structural investigation is infrequently investigated. These studies mostly observed the impact of using alternative binder resources that affect the workability, setting time, compressive strength, split tensile strength, and drying shrinkage. Therefore, this study aims to observe the structural behavior of geopolymer concrete, precisely its shear capacity. Four geopolymer concrete beam types were designed to have shear failure mode when tested using a Universal Testing Machine by four-point load bending method. The results showed that geopolymer concrete has ductile behavior. Comparison between the Vu value of the test results with Vn calculation of nominal cross-sectional capacity according to standard concrete rules in an average of 2.11 higher than the nominal capacity conventionally calculated according to SNI. Two models of linear regression equations for concrete Vc values were created to explore this further. It was found that the presence of a constant increases the value of the coefficient of determination by up to 29% for the Vc equation in geopolymer concrete. In addition, cracking patterns observed with the DIC method using GOM Correlate software also showed that all the beam specimens had failure both in flexure and shear, even though they all are designed in a shear failure state.

In recent years, alternative energy has become one of the concerns of the Indonesian government due to the increase in energy demand and the decrease in fuel oil reserves. Liquid natural gas (LNG) can be used as an alternative fuel with green energy considerations. LNG in Indonesia has not been used optimally and massively, so the government encourages the regulation of the Minister of Energy and Mineral Resources of Indonesia number 13 of 2020. The existence of a separate LNG source from the receiving terminal makes LNG distribution more difficult. The aim of this paper is to design a mini LNG vessel with a capacity of 10.000 cb m that is capable of distributing LNG in the Papua region, considering that the construction of gas pipeline installations is not possible due to geographical conditions and the high economic investment. A parametric design approach with a linear regression method is used to determine the ship’s principal dimensions. The design of a type C independent LNG tank is calculated by the principle of two-dimensionality based on the IGC code and obtained by pressure vessel standards. This study’s conceptual design consists of a lines plan, general arrangement, intact stability, the design of a type C independent LNG tank, and an economic analysis.

The offshore converter platform (OCP) functions as a substation to transfer energy generated by offshore wind turbines to an onshore substation to be widely distributed. This paper focuses on the temporary stools and upper grillages that structurally support the OCP topside during the fabrication stage. At the yard, one of the issues is temporary stools exposed of buckling and settlement, which will affect the structural integrity of the temporary stool in supporting the weight of the topside. Therefore, this analysis aims to determine the correct configuration and dimension of the temporary stools to function as an effective support for the topside. By utilizing the SACS software to conduct global structural analysis, the stress of each temporary stool and topside member is found, and the critical temporary stool location is analyzed further with ANSYS for finite element analysis to locate the local stress and deformation with a non-linear approach. Static analysis results in normal and settlement conditions indicate overstress as the UC member and deflections on the structure surpass the allowable criteria. Therefore, there are three modification iterations for the temporary stool, in which the third modification with the temporary stool dimension of OD323.9 × 17.48 obtained a maximum stress of 302.58 MPa and maximum deformation of 5.705 mm. To conclude, this temporary stool configuration and dimension is able to support the fabrication process of the topside structure and can replace the OD323.9 × 12.70 temporary stool, especially in critical locations.

Enhancing the diesel generator’s fuel efficiency is a result of the DC distribution system. Thus, the aim is optimizing the diesel generator’s fuel in accordance with its specific fuel requirements. This study focuses on the comparative analysis of the fuel oil consumption (FOC) of diesel generators employing the particle swarm optimization (PSO) technique in two distinct configurations: a radial DC distribution system and a zonal type. These configurations are specifically designed for trimaran vessels that are powered by hybrid electricity. Simulations are conducted to assess the ship’s operation during sailing. The PSO optimization approach was employed to simulate a DC distribution system, encompassing both radial and zonal kinds. Load factors were assigned to each generator based on their respective classifications. The application of particle swarm optimization (PSO) has proven to be effective in optimizing fuel oil consumption on both radial and zonal types of DC distribution systems. The findings indicate that the zonal distribution system exhibits superior fuel efficiency compared to the radial distribution system.

Berthing ships safely is crucial in maritime transport, as it involves maneuvering vessels alongside structures. This interaction produces complex forces, stressing both the ship and the dock. The Ship berthing force varies with vessel characteristics, which is essential for port dock design. This study investigates these forces using the Lagrangian particle method, specifically the smoothed particle hydrodynamics (SPH), and empirical equations. Using DualSPHysics, ship and dock models were analyzed at various berthing velocities (0.2, 0.3, 0.5, 0.6, and 0.8 m/s). Sea level data from the north coast of Java were utilized. Results reveal a correlation between berthing velocity and force received by the dock, consistent across SPH and empirical methods.

This study investigates the interplay between price promotions and the level of safety stocks. We propose a framework where both price promotions and improved service levels, operationalized through higher safety stocks, can affect sales. We treat the annual number of promotions as a decision variable and the cycle service level as a strategic parameter. For annual planning purposes, we identify the market conditions where the relationship between the number of promotions and safety stocks is antagonistic and synergistic. We show that higher safety stocks, leading to improved service levels and sales, can “replace” price promotions. This antagonistic relationship is observed in markets with high pre-promotion sales, less reactive to price promotions, and more responsive to product availability. The synergistic relationship implies that these two sales-stimulating tools can simultaneously be used to increase sales. It appears in “anemic” and underdeveloped markets, where the combined contribution of a higher number of price promotions and safety stocks “fuels” the increase in sales, and makes the promotional and operational efforts financially viable to support. We also show that higher values of the ordering cost, inventory holding cost, and lead time, negatively affect the optimal annual number of price promotions adopted by the firm.

Point processes are stochastic models generating interacting points or events in time and/or space. Among characteristics of these models, first-order intensity and conditional intensity functions are often considered. We focus on inhomogeneous parametric forms of these functions assumed to depend on a certain number of spatial covariates. When this number of covariates is large, we are faced with a high-dimensional problem. This paper provides an overview of these questions and existing solutions based on regularizations.

Phantom materials with acoustic and mechanical characteristics resembling tissues are essential for ensuring ultrasound device quality. This study aimed to evaluate the biomechanical and acoustic properties of polyvinyl chloride plastisol (PVCP) modified with glycerol at various concentrations to mimic the mechanical properties of human soft tissues used in ultrasonic elastography. Four types of phantoms were made with 0, 3, 5, and 10% glycerol added to the PVCP solution. Furthermore, the mixture of each phantom composition was stirred at a speed of 350 rpm and temperature of 180°C until homogeneous. The mixture was poured into three types of molds for each test. Finally, each phantom sample was evaluated using the density, sound speed, attenuation, viscoelasticity, and shear elasticity parameters from shear wave elastography. This study showed that the density of the PVCP phantom ranged from 1.058 to 1.088 g/cm3, the speed of sound was 1562.86 ± 14.99 to 1609.70 ± 13.91 m/s, and attenuation coefficient was 1.29 ± 0.054 to 2.97 ± 0.108 dB/cm at a frequency of 5 MHz. These values are within the range of liver and glandular breast tissue properties with variations below 6.87%. The Kelvin–Voigt model shows that the phantom with 5% glycerol has shear modules and viscosity equivalent to glandular breast tissue. The addition of glycerol allows the regulation of the acoustic and viscoelastic properties of the PVCP phantom in line with soft tissues, both healthy and pathological, making it ideal for ultrasound simulation and elastography. This study successfully created a phantom for ultrasound elastography imaging.

PDAM Surya Sembada, a clean water provider in Surabaya, faces challenges in managing databases and water assets. Geographic Information Systems (GIS) and low-cost Global Navigation Satellite Systems (GNSS) offer solutions to enhance asset monitoring. However, integrating low-cost GNSS with PDAM databases on Android applications is still not optimal, as it functions only as a receiver, not as base station. This study develops low-cost GNSS tool and Android application to integrate SMART GEO-PD ITS with PDAM databases using NTRIP (Network Transport of RTCM via IP) to distribute corrections, Bluetooth for Android integration, and API (Application Programming Interface) for PDAM database access. SMART GEO-PD ITS is a low-cost GNSS receiver developed through collaboration between ITS and PDAM Surya Sembada, designed for high-precision positioning and easy smartphone integration. Testing is conducted to assess the accuracy, consistency, and level of correction of low-cost GNSS. The corrections provided by low-cost GNSS are compared with those from InaCORS, an Indonesian Continuously Operating Reference Station (CORS) managed by the Badan Informasi Geospasial (BIG), Indonesia's geospatial information agency. Accuracy and consistency of PDAM asset geolocation measurement compared to geodetic GNSS. Results indicate that the low-cost GNSS base station can broadcast correction signals via NTRIP and is publicly accessible. The integration of the Android application and SMART GEO-PD ITS enables near real-time PDAM asset geolocation and management. Tests show that the InaCORS correction is not equivalent to low-cost GNSS correction. Accuracy and consistency testing has shown that geodetic GNSS does not offer the same level of accuracy and consistency as low-cost GNSS. In geolocation tests, the difference distance ranged from 0.017 to 0.29 m, whereas with low-cost GNSS it ranged from 0.005 to 0.111 m. Users have rated this application highly for recording PDAM customer water asset data.

Composite beam-column connection offers several advantages compared to conventional concrete beam-column connection. As instance, high load-bearing capacity, good serviceability, high stiffness, drift capacity, minimized energy displacement, practical fabrication, high efficiency, high deformation capacity, high durability, and cost-effectiveness, as well as a reduction in structural loads and element dimensions. In high-seismic areas, the use of composite steel-reinforced concrete (SRC) structures has been observed to exhibit ductile behaviour. This research investigates several aspects of the criteria required for the structural elements of composite beam-column connections integrated with WF and H-beam profiles. That study compares five beam-column joint models consisting of RC and four SRC developments use the Finite Element Method with the ABAQUS program to obtain the behaviour under cyclic loading. Based on several obtained results and parameters, it can be concluded that All models showed failure in the beam elements, confirming the strong column-weak beam principle. Composite SRC beam-column joints produced higher moments than the RC model, but SRC models experienced less beam rotation. SRC-01 was identified as the most ideal model with superior structural performance in resisting seismic forces.

Market fluctuations in the stock sector are common. The possible loss that investors may incur because of their investment activity is referred to as investment risk. Returns on investments may fall short of expectations due to a variety of circumstances. Fit of the model to the data; performance in representing volatility, prediction, stability, and analysis; and interpretation goals are all factors to consider. This study investigates the volatility of the Indonesian composite index (ICI) using the GARCH-MIDAS model, integrating daily ICI returns with monthly macroeconomic indicators: Indonesian bank interest rates (BIIR), consumer price index (CPI), effective federal fund rate (EFFR), and inflation rate (IR). We begin by graphically analysing the trends in ICI returns and macroeconomic variables to identify potential patterns and shifts. Descriptive statistics offer a detailed numerical summary, setting the stage for in-depth empirical analysis. The long-run component of stock market volatility is estimated using the GARCH-MIDAS model, with macroeconomic variables included to capture their impact on market fluctuations. Maximum likelihood estimation (MLE) is employed to estimate the model parameters, ensuring a robust fit to the observed data. Our findings indicate that the EFFR has the most significant impact on ICI volatility, contrary to previous studies. Forecasting performance is evaluated using mean squared error (MSE) and mean absolute error (MAE), confirming the superior predictive capability of the EFFR variable. The study assesses risk using value at risk (VaR) for the ICI, incorporating the EFFR to account for macroeconomic influences on market volatility. VaR values at 99% and 95% confidence levels provide insights into potential maximum losses, aiding in informed investment decision-making. This research enhances knowledge of the relationship between macroeconomic variables and stock market volatility, providing investors and policymakers with important information for risk management and investment strategy optimization in the Indonesian equity market.

Fire safety signage icons have become extremely important in visual communication, conveying critical information with precision to prevent fire disasters. This study investigates the causal relationships among five cognitive constructs—semantic distance, communicativeness, complexity, layout, and perceived quality—of fire safety signage icons presented in four distinct formats: image-related, concept-related, semi-abstract (ISO 7010:2019), and combined. Thirty participants evaluated 12 pairs of semantic differential scales derived from these constructs. Structural equation modeling revealed that communicativeness exerted the most significant influence on perceived quality, followed by layout and semantic distance, while complexity indirectly affected perceived quality. This pioneering study is the first to uncover and analyze the causal relationships between cognitive factors and an icon's perceived quality. The proposed dimensions and semantic differential scales can also be applied and extended to evaluate other icons beyond fire safety signage.

Agricultural practices such as conventional (CN) and conservation agriculture (CA) influence the composition and structure of soil microorganisms. We used short reads and genome-resolved metagenomic-based dual sequencing approaches to create a profile of bacterial and archaeal communities in hyperthermic Typic Haplustepts soil after seven years of CA and CN. The most differences in the physico-chemical and biological properties of soil were higher pH, organics carbon, available nitrogen and microbial biomass contents, activities of dehydrogenase, β-glucosidase, and arylsulfatase, found in CA soil. The dominant bacterial taxa under both management types were Pseudomonadota (46–48%), Acidobacteriota (12–13%), Planctomycetota (8–10%), Bacteroidota (7–8%), and Actinomycetota (6–7%). Nitrososphaerota (1.1–1.5%) was the predominant archaeal phyla in CA and CN soils. The alpha diversity was 1.5 times higher in CA compared to CN soils. Fourteen high-quality (HQ) metagenomic-assembled genomes (MAGs) were recovered from both groups. Four HQ metagenome-assembled genomes (MAGs) from the Pseudomonadota phylum were exclusively recovered from the CA soil. The dominance of this phylum in the CA soil might be correlated with its nutrient richness, as certain classes of Pseudomonadota, such as Alpha, Beta-, Gamma-, and Deltaproteobacteria, are known to be copiotrophic. Copiotrophic organisms thrive in nutrient-rich environments, which could explain their prevalence in the CA soil. CAZyme gene analysis showed that Glycoside Hydrolases (GH) and GlycosylTransferases (GT) classes are dominant in the CA group, possibly due to higher substrate availability from the application of crop residues, which provide a rich source of complex carbohydrates. Several biogeochemical gene families related to C1 compounds, hydrogen, oxygen, and sulfur metabolism were enriched in CA soils, suggesting these practices may contribute to a soil environment with increased organic matter content, microbial diversity, and nutrient availability. Overall, CA practices seemed to improve soil health by supporting soil microbial communities abundance.

This study aims to improve the purity of bioethanol produced from Bioethanol Recycle of Enzyme Fermentation (BR-EF) by employing batch distillation and absorption techniques. A distillation column with raschig rings and molecular sieve was used, with an initial BR-EF volume of 1 L and concentrations ranging from 15% to 35% (v/v). The distillation process, conducted at 78°C using microwave heating, lasted between 2–6 h. The optimal bioethanol concentration of 97.72% (v/v) was achieved with a 30% (v/v) BR-EF concentration and a 4-hour distillation time. Optimal response with a bioethanol concentration of 99.824% (v/v). The ideal conditions for Multiple Response Prediction were determined to be flow rate of adsorption and weight of silica gel are 0.116 and 58.295. Further optimization was performed using MATLAB (Matrix Laboratory) and Differential Expert (DE) to assess the impact of BR-EF concentration and distillation time on bioethanol yield, with results visualized in a 3D response surface graph. This study offers valuable insights into optimizing bioethanol production, enhancing its purity and market potential.

This study introduces a Takagi-Sugeno (T-S) fuzzy modeling framework for kinematic modeling of mecanum wheeled mobile robot (MWMR). T-S fuzzy systems are particularly effective in capturing complex nonlinear dynamics and unmodeled subsystems inherent to MWMR architectures. Optimization of parameters within the T-S structure is achieved through a genetic algorithm (GA), enabling precise alignment between the T-S derived model and physical system behavior. Notably, the proposed methodology achieves convergence to optimal T-S model within 200 generations of the GA, without necessitating an explicit analytical formulation of the complete MWMR dynamics. Validation experiments reveal the optimized T-S model achieves 0.015 m/s a mean squared error (MSE) difference relative to empirical velocity profiles from the MWMR platform. Rigorous numerical assessment demonstrates the formulated T-S model achieves exceptional dynamic congruence with the physical MWMR platform, manifesting peak velocity discrepancies of 57 × 10−4 m/s accompanied by standard deviations of 0.027 m/s across experimental trials. Comparative evaluation against conventional probabilistic modeling techniques highlights superior predictive accuracy and dynamic fidelity of the proposed T-S framework. Observed results substantiate the model’s capacity to replicate nonlinear kinematic interactions and transient velocity characteristics under experimentally validated boundary conditions, corroborating theoretical expectations through empirical system identification.

This study aimed to determine the effect of concentration and immersion time of Salak (Salacca zalacca) Seed extract as a green inhibitor on the corrosion inhibition efficiency and corrosion rate of AISI 1040 steel in a 1M HCl environment. The chemical composition of AISI 1040 steel was confirmed using OES testing to verify its compliance with AISI 1040 chemical standards. The antioxidant activity of the salak (Salacca zalacca) seed extract was determined through the 1,1-Diphenyl-2-Picrylhydrazyl (DPPH) test yielding an IC50 value of 192.55 ppm, indicating weak antioxidant activity. Qualitative phytochemical analysis confirmed the presence of flavonoids and tannins in the extract, as verified by Fourier Transform Infrared (FTIR) testing. The study explored concentration variations ranging from 100 to 500 ppm and immersion time variations of 10 to 30 days were used. The highest inhibition efficiency was obtained at 500 ppm concentration, while the lowest was at 100 ppm, with values of 40.26% and 18.90% respectively. Additionally, the corrosion rate was reduced to 0.035 mm/year at the highest concentration of 500 ppm. These findings demonstrated the potential of salak (Salacca zalacca) seed extract as an eco-friendly, effective corrosion inhibitor for AISI 1040 steel.