bluuebunny/crossref_metadata_2025 huggingface dataset:
Launching a solidarity campaign: Technology-enhanced project-based language learning to promote entrepreneurial education and social awareness
Authors: Dooly Melinda , Masats Dolors , Mont Maria
Published: April 2021

To promote social consciousness and a sense of responsibility, educational proposals organised around the principles of technology-enhanced project-based language learning (Dooly & Sadler,2016) should engage students in a process of reflecting upon and responding to crucial social issues. Thus, in this paper we will present a project carried out by two groups of primary students who launched a solidarity campaign to collect money for four Syrian children living in a refugee camp in Greece. The project was implemented in a cross-disciplinary Arts and Crafts class taught through English and resulted in significant outputs in English (those addressed to the Syrian children) and in Catalan (those targeted at the local community). First, we outline the student-led project and then we analyse some fragments of student plurilingual practices during the project development that demonstrate their learning gains. Our findings reveal that our meaningful contextualised cross-disciplinary project favoured the natural integration of multiple skills, competences, and field knowledge form various disciplines while promoting a sense of social consciousness and empathy. First, it enabled children to put their plurilingual competence into play and take decisions regarding language choices to meet particular communicative objectives. Second, it contributed to the acquisition of 21st century knowledge, competence, and skills, while helping the learners gain social values. Third, it engaged learners in processes of problem solving, decision making and creative thinking that lead to the development of entrepreneurial competencies. To conclude we argue that when young learners are given responsibilities and opportunities to take up socially relevant challenges learning becomes meaningful for them and those around them.
Optimal distributed control for a coupled phase-field system
Authors: Chen Bosheng , Li Huilai , Liu Changchun
Published: April 2021

Our aim is to consider a distributed optimal control problem for a coupled phase-field system which was introduced by Cahn and Novick-Cohen. First, we establish that the existence of a weak solution, in particular, we also obtain that a strong solution is uniqueness. Then the existence of optimal controls is proved. Finally we derive that the control-to-state operator is Fréchet differentiable and the first-order necessary optimality conditions involving the adjoint system are discussed as well.
A competition model in the chemostat with allelopathy and substrate inhibition
Authors: Dellal Mohamed , Bar Bachir , Lakrib Mustapha
Published: April 2021

A model of two microbial species in a chemostat competing for a single resource is considered, where one of the competitors that produces a toxin, which is lethal to the other competitor (allelopathic inhibition), is itself inhibited by the substrate. Using general growth rate functions of the species, necessary and sufficient conditions of existence and local stability of all equilibria of the four-dimensional system are determined according to the operating parameters represented by the dilution rate and the input concentration of the substrate. With Michaelis-Menten or Monod growth functions, it is well known that the model can have a unique positive equilibrium which is unstable as long as it exists. If a non monotonic growth rate is considered (which is the case when there is substrate inhibition), it is shown that a new positive equilibrium point exists which can be stable according to the operating parameters of the system. We describe its operating diagram, which is the bifurcation diagram giving the behavior of the system with respect to the operating parameters. By means of this bifurcation diagram, we show that the general model presents a set of fifteen possible behaviors: washout, competitive exclusion of one species, coexistence, multi-stability, occurrence of stable limit cycles through a super-critical Hopf bifurcations, homoclinic bifurcations and flip bifurcation. This diagram is very useful to understand the model from both the mathematical and biological points of view.
Global solvability to a singular chemotaxis-consumption model with fast and slow diffusion and logistic source
Authors: Zhou Langhao , Wang Liangwei , Jin Chunhua
Published: April 2021

In this paper, we consider the following chemotaxis-consumption model with porous medium diffusion and singular sensitivity

   \begin{document}$ \begin{align*} \left\{ \begin{aligned} &u_{t} = \Delta u^{m}-\chi \mathrm{div}(\frac{u}{v}\nabla v)+\mu u(1-u), \\ &v_{t} = \Delta v-u^{r}v, \end{aligned}\right. \end{align*} $\end{document}

in a bounded domain \begin{document}$ \Omega\subset\mathbb R^N $\end{document} (\begin{document}$ N\ge 2 $\end{document}) with zero-flux boundary conditions. It is shown that if \begin{document}$ r<\frac{4}{N+2} $\end{document}, for arbitrary case of fast diffusion (\begin{document}$ m\le 1 $\end{document}) and slow diffusion \begin{document}$ (m>1) $\end{document}, this problem admits a locally bounded global weak solution. It is worth mentioning that there are no smallness restrictions on the initial datum and chemotactic coefficient.
An efficient multi-grid method for TV minimization problems
Authors: Zhang Zhenwei , Li Xue , Duan Yuping , Yin Ke , Tai Xue-Cheng
Published: April 2021

We propose an efficient multi-grid domain decomposition method for solving the total variation (TV) minimization problems. Our multi-grid scheme is developed based on the piecewise constant function spanned subspace correction rather than the piecewise linear one in [17], which ensures the calculation of the TV term only occurs on the boundaries of the support sets. Besides, the domain decomposition method is implemented on each layer to enable parallel computation. Comprehensive comparison results are presented to demonstrate the improvement in CPU time and image quality of the proposed method on medium and large-scale image denoising and reconstruction problems.
A linear sampling method for inverse acoustic scattering by a locally rough interface
Authors: Li Jianliang , Yang Jiaqing , Zhang Bo
Published: April 2021

This paper is concerned with the inverse problem of time-harmonic acoustic scattering by an unbounded, locally rough interface which is assumed to be a local perturbation of a plane. The purpose of this paper is to recover the local perturbation of the interface from the near-field measurement given on a straight line segment with a finite distance above the interface and generated by point sources. Precisely, we propose a novel version of the linear sampling method to recover the location and shape of the local perturbation of the interface numerically. Our method is based on a modified near-field operator equation associated with a special rough surface, constructed by reformulating the forward scattering problem into an equivalent integral equation formulation in a bounded domain, leading to a fast imaging algorithm. Numerical experiments are presented to illustrate the effectiveness of the imaging method.
Constructing “Pure” and “Applied” Science in Early Francoism
Authors: Nieto-Galan Agustí
Published: April 2021

The paper discusses several appropriations of the categories of “pure” and “applied” science (mainly in chemistry) in early Francoism. At the height of a crusade that criminalized “pure” science as inherently attached to the culture of the Second Spanish Republic, the category of “pure” assumed spiritual, religious and anti-materialist values in the early education policies of the new regime, in the context of the newly founded national research centre, the Consejo Superior de Investigaciones Científicas (CSIC). At the same time, relevant Francoist scientists stressed the high moral status of a new utilitarian, “applied” science, to efficiently serve the material needs of the country. As a result, the categories of “pure” and “applied” science, and their rhetorical use in public addresses and propaganda, became useful tools for building a strong alliance between science and power that cemented the dictatorship.
Deans of humanitarianism and perfidy. The collaboration of the Diplomatic Missions of Argentina and Chile with the Francoist cause during the Spanish Civil War (and after), 1936-1969
Authors: Píriz Carlos
Published: April 2021

During the Spanish Civil War of 1936-1939, some thirty Diplomatic Missions opened their doors and create new sites for the reception of persecution victims under the protection of the right of asylum. However, beyond the humanitarian role, a tendentious collaboration of some of their delegates with the rebels could be seen from the beginning. Argentina and Chile, which held the Diplomatic Deanship in those years, were two prime examples of this. A good number of their representatives used various strategies to help the coup plotters of 1936, such as the refuge, care and irregular extraction of people or espionage. At the same time, they played a role that alternated between searching for consensus with other Diplomatic Missions (mainly the Latin American ones), which really meant demanding that those other legations follow their lead, and denouncing the excesses of the consolidated republican rearguard, especially on the international scene. A situation which tarnishes the image of the legitimate Spanish governments. Once the contest ended, many of those collaborators were praised and rewarded by the Franco regime, and other fascists regimes. This research focuses on demonstrating, based on original documentation and providing new and compelling data, that close (and proven) relationship.
An Exploration of Esports Consumer Consumption Patterns, Fandom, and Motives
Authors: Anderson Devin , Sweeney Kevin , Pasquini Erica , Estes Brent , Zapalac Ryan
Published: April 2021

Esports, or competitive gaming, has become a large market in the entertainment industry, with a total market value approaching $1 billion USD in 2019. An understanding of esports consumers has become increasingly important as the industry continues to grow and evolve. Using a sample of 374 university students at a large public university, this study examines the motivations and fandom of esports consumers using a modified version of the Sport Fandom Questionnaire (SFQ) and the Motivation Scale for Sports Consumption (MSSC). Survey respondents were asked about their consumption of esports in relation to viewership, event attendance, social media usage, and spending. Three stepwise regression analyses were employed to examine the predictive capabilities of esports fandom and esports motivations on esports consumption variables. The results reveal a wide variety of relationships between esports fandom, motivation for consumption, and consumption behaviors.
Characteristics of Ni-Zn Rechargeable Batteries with Zn Anode Prepared by Using Nano-Cellulose as its Binder Agent
Authors: Shelni Rofika Rida Nurul , Mardiyati Mardiyati , Hidayat Rahmat
Published: April 2021

While the operating voltages of Ni-Zn batteries are smaller than Li-ion batteries, Ni-Zn batteries offer some advantages, such as high specific energy and low cost. Ni-Zn batteries use green materials as they use aqueous electrolytes and do not need hazardous organic solvents. Both Ni and Zn are abundant and much less expensive in comparison to lithium. Therefore, Ni-Zn batteries are more suitable as secondary batteries for applications that do not need mobility, such as for storing electricity from solar panels at home or office building. At present, large scale usage of Ni-Zn batteries is hindered by their low life cycle due to Zn anode degradation during the operation. The Zn anode deteriorates as dendrite and passivation growth causing self-discharge at the Zn anode. Many efforts have been tried to solve those problems by adding additives in the electrode or electrolyte and a specific binder in the Zn anode. In the present work, in addition to standard CMC and PTFE as the binder in Zn anode, we also added nano-cellulose as its binder agent as the host matrix may be formed with a much smaller void, providing much more dispersion of ZnO nanoparticles and better reduction on Zn dendrite formation. The battery structures in this work were Zn-anode | electrolytes (KOH, aqueous) | Ni-cathode. Ni cathode used in this work is similar to those found in commercial Ni-Zn batteries. The Zn anode was prepared with various compositions of binder and hydroxides, such as Ca(OH)2, and ZnO nanoparticles as the active materials. The characteristics of the batteries are largely affected by the composition of the binder and other substances forming the Zn anode, particularly the proportion of the hydroxide. However, in general, the present result shows the potential of this modified Ni-Zn battery as an alternative to supersede expensive Li-ion batteries for low-cost and stationary applications.
The Effect of Static Electric Field and Nucleator Agent on the Solidification of CaCl2·6H2O and Ca(NO3)2·4H2O
Authors: Putri Risky Afandi , Rahman Annisa , Yusuf Akhmad , Kurnia Daniel , Sutjahja Inge Magdalena
Published: April 2021

The addition of energy from the electric field is one way in the active method to overcome the nucleation barriers of inorganic phase change materials (PCM) e.g. salt hydrate. The effort is to aim at improving the performance of PCM as a thermal energy storage system. Moreover, the passive method commonly uses a chemical substance called nucleator agent to induce the nucleation and to reduce the phase separation that typically occurs during the freezing-thawing cycle of salt hydrate PCM. In this paper, we report an experimental study to conduct the effect of the static electric field (DC voltage) and nucleator agent as a combination of passive and active methods on the nucleation of salt hydrates consisting of CaCl2·6H2O and Ca(NO3)2·4H2O. In general, the nucleation temperature of CaCl2·6H2O and CaCl2·6H2O+BaSO4 (0.1 wt%) become higher with the increase of the intensity of the electric field, leading to the decreases of supercooling degree. Besides that, the electric field also induces the increase in the nucleation rate, as measured by the shorter induction time. Meanwhile, the case for Ca(NO3)2·4H2O and Ca(NO3)2·4H2O+Ba(OH)2·8H2O (1 wt%) show that the nucleation temperature tends to become smaller with increase the intensity of the electric field, leading to increases the supercooling degree. However, the addition of the nucleator agent, Ba(OH)2·8H2O (1 wt%) to Ca(NO3)2·4H2O has not provided a significant result in terms of nucleation probability.
The Effect of Partial Substitution of Non-Magnetic Impurity Zn on the Magnetic Moments of Eu1.88Ce0.12Cu1-yZnyO4+α-δ
Authors: Syakuur Muhammad Abdan , Maryati Yati , Saragi Togar , Risdiana Risdiana
Published: April 2021

Structure and magnetic properties of electron-doped superconducting cuprates have been investigated in order to study the effect of magnetic impurity to its physical properties. Here, we reported structure and magnetic properties of Eu1.88Ce0.12Cu1-yZnyO4+α-δ (ECCZO) with y = 0 and 0.03. The properties of ECCZO have been studied from X-ray diffraction data and temperature dependence of magnetic susceptibility data, to elucidate the effect of partial substitution of non-magnetic impurity Zn for Cu to its structure, Tc and the value of magnetic moments per unit volume extracted from susceptibility data in normal state. Magnetic-susceptibility measurements were carried out down to 2 K on-field cooling at 5 Oe for Eu1.88Ce0.12Cu1-yZnyO4+a-d with y = 0 and 0.03. For ECCZO sample with y = 0 and d = 0.0669 indicated the change of magnetic behavior from paramagnetic to diamagnetic below 12 K which is addressed to the Tc onset of this samples. Diamagnetic behavior is observed starting from about 12 K. Above 12 K, all samples show paramagnetic behavior with the values of the magnetic moment in every volume unit increased with increasing Zn.
Synthesis of TiO2-rGO Nanocomposite and its Application as Photoanode of Dye-Sensitized Solar Cell (DSSC)
Authors: Celline Ayunita Chintia , Subagja Astria Yuliani , Suryaningsih Sri , Aprilia Annisa , Safriani Lusi
Published: April 2021

Dye-sensitized solar cells (DSSC) are solar cells that has a great potential to be applied as renewable energy conversion. The major advantages of DSSC are the ease of fabrication process and low cost of production. Despite of these advantages, the efficiency of DSSC for converting light into electricity is still low. It is due to charge recombination in DSSC which limits the photoanode performance. Numerous efforts has been carried out to increase the efficiency of DSSC, one of which is by adding reduced graphene oxide (rGO) to titanium oxide (TiO2) to obtain TiO2-rGO nanocomposite. In this study, the synthesis of TiO2-rGO nanocomposites was carried out with concentration of rGO are 0.6, 0.8, and 1.0 wt% to amount of TiO2. We have done some characterizations to confirm the result of synthesized TiO2-rGO. UV-Vis measurement shows the addition of rGO has widened the absorption up to 400 nm. The FT-IR spectrum confirms that the rGO peaks appears at wavelength of 1400, 1600, dan 1700 cm-1 which exhibited the vibration C-O, C=C, and C=O stretching from COOH groups, respectively. The highest efficiency of DSSC with photoanode TiO2-rGO nanocomposite is 0.09% which was obtained from 0.8 wt% of rGO.
Effect of Growth Time on the Structural and Morphological Properties of MoS2 Synthesized via Hydrothermal Method
Authors: Emrinaldi Tengku , Imawan Cuk , Ginting Riski Titian , Fauzia Vivi
Published: April 2021

Recently, molybdenum disulfide (MoS2), have been explored as photothermal materials for solar evaporation. However, the optimum phase for photothermal material, 1T-MoS2 or 2H-MoS2, is still debatable. In this work, we observed the morphological and structural properties of MoS2 prepared by a simple hydrothermal process at 200 °C in three different growth times (16, 20, and 24 hours) using Na2MoO4·2H2O (sodium molybdate) as a Mo precursor, and CS(NH2)2 (thiourea) as S precursor. MoS2 nanoflowers were successfully prepared with nanosheets petals and its diameter increased from 0.4 to 2.8 and 4.5 as the growth time increased from 16 to 20 and 24 hours. The increase in growth time also led to improve the Mo:S ratio from 1:8 to 1:5 and facilitate the phase transformation from 1T to 2H as indicated by the shifting of (002) diffraction peak from 9.25° to higher degrees (12.98°, and 14.12°).
Facile Synthesis of 1T-MoS2 Nanoflowers Using Hydrothermal Method
Authors: Fareza Ananta Rizki , Nugroho Ferry Anggoro Ardy , Fauzia Vivi
Published: April 2021

Molybdenum disulfide (MoS2) is one of the promising 2D materials thanks to its outstanding physicochemical properties and therefore is predicted to play a key role in optoelectronics devices and energy applications. MoS2 exhibits three phases with distinctive crystal structure depending on its stacking order: 1T (metallic), 2H (semiconducting), and 3R (semiconducting). Among all of them, 1T-MoS2 has become the center of interest due to its e.g., high catalytic activity. However, most of the methods to obtain 1T-MoS2 are complex and costly, for example strain engineering, electron beam treatment, and plasmonic hot electron injection. As response, we here demonstrate a facile and cost-efficient hydrothermal route at 200 °C to synthesize MoS2 with high content of 1T phase. MoS2-200 °C nanoflowers has an average diameter of 2.96 µm with the S/Mo atomic ratio of 1.50 and the band gap of 1.39 eV. It has an additional diffraction peak at 2θ = 9.22o, indicating the transformation of semiconducting 2H into metallic 1T. Higher concentration of 1T phase in MoS2-200 °C is also indicated by high intensity of the E1g Raman peak.
The Effects of Carbon Coating on the Structure and Electrical Conductivity of LiFeSi0.03P0.97O4/ c Cathode Material via Solid State Process
Authors: Az-Zahra Pelangi , Zainuri Mochammad , Della Hafizhah Ellora , Widya Putri May Shela , Subagyo Bintoro Anang
Published: April 2021

The synthesis of LiFeSi0.03P0.97O4/C (LFSP/C) composites have been done by solid state method. This study investigates the effects of carbon coating on the structure, microstructure and electrical conductivity of LFSP/C cathode materials. The carbon coating on Lithium Ferro Phosphate (LFP) plays a crucial role in determining its electrical conductivity. The variation of carbon content is 0wt.%; 6wt.%; 7wt.%; 8wt.% (LFP-0%, LFP-6%, LFP-7% and LFP-8%). The characterization was performed using X-Ray Diffraction (XRD), Scanning Electron Microscopy - Energy Dispersive X-ray (SEM-EDX), HighResolution-Transmission Electron Microscopy (HR-TEM) and LCR Meter tests. The XRD result have shown single-phase olivine (LiFePO4) in all samples. The analysis microstructure using SEM have shown increasing carbon content can reduce agglomeration. The particles size of LFSP is 845.570 nm, and after coating carbon the particles size decreased up to 457.191 nm. The EDX results showed that the amount of atomic percentage for carbon tends to increase as the amount of carbon content increased. HR-TEM images indicates that the formation of carbon layer have formed, but not perfectly coat the LFP particle. The average carbon layer size is 78,31 nm with the size of LFSP particle is 352.82 nm. The LCR Meter result showed that LFP-7% had the largest electronic conductivity (2,275x10-7 S/cm). The carbon coating led to significant enhancement in electronic conductivity from ~10-9-10-10 S/cm to ~10-7 S/cm.
Nano-Goethite (α-FeOOH) Magnetic Structure Investigated Using Ising Core-Shell Model: Preliminary Study
Authors: Adiperdana Budi , Kartika Nadya Larasati , Risdiana Risdiana
Published: April 2021

Ising core-shell model was proposed to reconstruct superparamagnetism hysteresis in nano-goethite (α-FeOOH). Core and shell set as antiferromagnetic and paramagnetic state respectively. Core and shell radius varies until the theoretical hysteresis fit with experiment hysteresis. At low temperature, the hysteresis reconstructed nicely with 55% antiferromagnetic core contribution and 45% paramagnetic shell contribution. At high temperature, the core-shell model show unrealistic result compared to the pure paramagnetic state.
Density Functional Theory Approach for Muon Sites Estimation in Mn3Sn
Authors: Murdaka Fiqhri Heda , Suprayoga Edi , Pradipto Abdul Muizz , Nakamura Kohji , Nugroho Agustinus Agung
Published: April 2021

We report the estimation of muon sites inside Mn3Sn using density functional theory based on the full-potential linearized augmented plane wave (FLAPW) calculation. Our calculation shows that the Perdew–Burke–Ernzerhof (PBE) Generalized-Gradient Approximation (GGA) functional is closer to the experimental structure compared to the von Barth-Hedin Local Density Approximation (LDA)-optimized geometry. The PBE GGA is therefore subsequently used in FLAPW post-calculation for the electrostatic potential calculation to find the local minima position as a guiding strategy for estimating the muon site. Our result reveals at least two muon sites of which one is placed at the center between two Mn-Sn triangular layers (A site) and the other at the trigonal prismatic site of Sn atom (B site). The total energy of Mn3Sn system in the presence of muon at A site or B site are compared and we find that A site is a more favorable site for muon to stop.
Investigation of CO Adsorption on Hydroxyapatite (001) Surface Using Density Functional Theory
Authors: Hamzah Liza Saharani , Juliandri Juliandri , Noviyanti Atiek Rostika , Adiperdana Budi , Risdiana Risdiana
Published: April 2021

Hydroxyapatite (HA) is a phosphate mineral with the chemical formula of Ca10(PO4)6(OH)2. The presence of pores in HA allows easy interaction with other compounds, so it can be used to detect the CO gas. Other than that, the hydroxyl group in hydroxyapatite allows the ion exchange process, a significant reaction in a gas sensor. The interaction of hydroxyapatite with CO gas has been studied using density functional theory. The HA adsorption potential energy surface was investigated using slab model with (001) expansion and 10 Å vacuum. CO gas kept fixed 1.0 Å above the HA surface and traced along the surface with grid 10×10. The result shows that the surface is divided into two main potentials that more likely and unlikely for CO to stay. The CO gas is most likely to stay between two oxygen from (PO3) tetrahedral that pointing down.
The Effect of Accelerated Salt Spray Exposure on Mechanical Properties of Glass Fiber Reinforced Polyester Composite
Authors: Farishi Salman , Wulandari Retno , Rifathin Annisa , Rusmana Dasep , Jamilah Nurul
Published: April 2021

This paper presents the effect of accelerated salt spray (fog) exposure on commercially glass fiber reinforced polyester composite to determine the durability of the material. Aging behavior after exposure in the salt-spray environment was studied by mechanical properties i.e. flexural stress and flexural modulus. The accelerated salt spray exposure was conducted by Copper-Accelerated Acetic Acid Salt Spray (CASS) Test according to ASTM B368. The CASS exposure was carried out for 120 hours and observed every 24 hours. The flexural modulus results tend to be constant up to 4 days and more significant change on 5th day of measurement. Furthermore, the morphology of specimens investigated by a Scanning Electron Microscopy (SEM). The SEM results also showed that only scratch occurred on the surface of the specimens test. The longer of the CASS exposure time, the higher the number of scratches. From this study, it could be concluded that Glass Fiber Reinforced Polyester Composite has slightly damage for 120 hours CASS test exposure.
Tensile Strength of PMMA/n-ZrSiO4 Composites Using Dynamic Mechanical Analyzer (DMA)
Authors: Dona Rama , Purnamasari Novita Dwi , Wulandari Wiwit , Hilmi Allif Rosyidy , Fauziyah Nur Aini , Pratapa Suminar
Published: April 2021

This study aimed to determine the tensile strength and strain properties of poly(methyl methacrylate) (PMMA)/nano-zircon (n-ZrSiO4) composites with various nano-zircon sizes. Wet milling method for 5 and 15 h without annealing treatment was used to obtain the nano-zircon powders. Results showed that milling for 15 hours can reduce zircon size up to 93 nm. Meanwhile, the composites were synthesized with zircon compositions of 1, 2.5, and 5 wt.%. Dynamic Mechanical Analyzer (DMA) measurement were carried out to characterize the tensile-strain dependence on filler compositions of the PMMA/n-ZrSiO4 composites. The PMMA/n-ZrSiO4 composite with 5 wt.% and 15h milling zircon exhibited the highest tensile strength, ca. 10.02 MPa or 2 times of the pure PMMA. The tensile strength of the composites can be explained from the mean size and size distribution of the filler.
Influence of Zinc Oxide Addition on Azodicarbonamide Thermal Decomposition in the Polyethylene/Ethylene Vinyl Acetate Foaming Release
Authors: Afrinaldi Bambang , Vicarneltor David Natanael , Rudianto Reza Pahlevi , Hakim Arif Rachman , Muslim Opa Fajar
Published: April 2021

Thermal properties, i.e. melting point and decomposition temperature of polymers, azodicarbonamide (ADC), and other additives mixture, are the most important information to determine the appropriate foaming process parameters. ADC has been widely used as a blowing agent for foam fabrication. Here, ADC will decompose and release gas which will be trapped in the melting polymer to make a foamed product. Originally, ADC has a decomposition temperature at around 220°C. In this study, the effect of Zinc Oxide (ZnO) addition on the thermal properties of intermediate product and Polyethylene/Ethylene Vinyl Acetate (PE/EVA) foam with ADC as the blowing agent was investigated. ZnO addition decreased the decomposition temperature of ADC. The thermal properties were characterized by Differential Scanning Calorimetry (DSC). The result showed that the decomposition temperature of ADC significantly decreased from the temperature of 220°C to 170°C with the increment of the ZnO.
Effect of Filler Concentration and Time Sonication of ZnO Composite for Radar Absorbing Material Applications
Authors: Denny Yus Rama , Trenggono Adhitya , Firmansyah Teguh , Revaldi Irvan , Taryana Yana , Aritonang Sovian
Published: April 2021

Effects of filler concentration and sonication time on the structure, morphology, reflection loss and absorption percentage of ZnO composite was investigated. The structure, morphology, reflection loss and absorption percentage of the composite was investigated using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Vector Network Analyzer (VNA). The ZnO composite was made by solution mixing method with the epoxy resin as a filler varied of 10 wt%, 20 wt%, and 30 wt%. The hardener was mixed to the ZnO composite by the composition of 2: 1. The sonication time was varied of 30, 45 and 60 minutes. The XRD showed that the crystal structure of ZnO composite was confirmed as a hexagonal structure and the structure was not change for all composite. The VNA results showed that the optimum reflection loss value was-9.37042 dB at the frequency of 12.3 GHz for the filler composition of 20 wt% and sonification time of 45 minutes. On the other hand, the minimum reflection loss value was-6.86845 dB at the frequency of 12.3 GHz for the filler composition of 10 wt% and sonification time of 45 minutes. In addition, the optimum absorption percentage was 18 % at a filler composition of 10 wt% with 60 minutes sonication time. This study demonstrates a promising method to improve a microwave absorption of ZnO composites.
Physical Properties of Polyethylene and Ethylene Vinyl Acetate Foam Mixtures
Authors: Muslim Opa Fajar , Juwono Ariadne Lakshmidevi , Novriadi Dwi , Tulus Tulus
Published: April 2021

Previous studies on the physical properties of each Polyethylene (PE) or Ethylene Vinyl Acetate (EVA) foam have been widely reported. The current challenge is how to understand the combination of PE and EVA foam in order to obtain appropriate properties in various applications. Therefore, an experimental breakthrough in order to understand the physical mechanism on the PE:EVA mixed foam in order to maintain many appropriate properties due to their applications was studied. The physical properties of a combination of PE and EVA foam with Azodicarbonamide (ADC) as blowing agent and the addition of Zinc Oxide (ZnO) as accelerated agent in foaming process have been investigated in this study. The foams were prepared via two steps. Firstly, the various content of PE and EVA resins with combination of various content of ZnO and the addition of ADC, stearic acids and antioxidants were mixed by a single screw extrusion as the results of pellets. Furthermore, this intermediate product was pressed by compression moulding at the temperature of 175 °C and pressure of 30 bar for 5 minutes, then the pressure was released for the foaming process. The effect of the addition of ZnO were observed on the density and the mechanical properties of the foams. The density decreased with increasing of ZnO content up to 4 per hundred resin (phr) on the foam with PE content maximum of 20 phr. Interestingly the density of the foam increased with the addition of 6 phr of ZnO. Due to the increasing number of ZnO, we found the formation of foams completely. We observed the approval of the hardness, tensile and compression properties of each formulation, respectively. Furthermore, the morphology observation of the foams was conducted by scanning electron microscopy (SEM) to measure the size and homogeneous of the cells. We observed large size of cells at low density of foams, meanwhile uniform of cell was obtained at the high density of foams. Finally, the Fourier transform infrared (FTIR) spectroscopy confirmed that in general the intensity of the absorption peak at around 2216 cm-1 - 2223 cm-1 of each formulation decreased with the addition of ZnO up to 4 phr of ZnO and increased again at 6 phr of ZnO.
Refining Process and Identifying Content of Local Iron Sand
Authors: Saragi Togar , Pramesti Gustiani A. , Syakuur Muhammad Abdan , Syakir Norman , Hidayat Sahrul , Manawan Maykel , Risdiana Risdiana
Published: April 2021

We reported simple processing of local iron sand in order to increase the purity of magnetic phase. The refining process of iron sand is carried out in two stages, namely the iron sand extract using a permanent magnet and the purification process. The purification process was carried out by co-precipitation method in varying of the dissolving temperatures and volume of HCl. The iron salt solution formed is then precipitated using NH4OH solution and then sintered at 100 °C and 1000 °C, respectively. All samples are characterized by X-ray fluorescence (XRF) and X-ray diffraction (XRD) to identify the elemental content and the crystal structure. From the XRF measurements, it was found that the Fe content before purification process was 32.68 %, increasing to 33.12 % after purification process with HCL volume of 75 ml and sintered at 100 °C. From XRD measurement, it was found that the crystal structure of iron sand before purification process was dominated by magnesioferrite (33.2 %), and magnetite (20.2 %). After purification process at 1000 °C, the magnesioferrite phase increased to 80.2 % and 50.2 % for HCl volume of 50 ml and 75 ml, respectively, while the magnetite phase increase to become 34.5 % for 100 ml of HCl.
Magnetic Characteristics of Graphene Oxide and Reduced Graphene Oxide
Authors: Syakir Norman , Saragi Togar , Fitrilawati Fitrilawati , Maryati Yati , Widyaiswari Utami , Sari Dita Puspita , Risdiana Risdiana
Published: April 2021

Graphene oxide (GO) is 2D material made of honey comb carbon structure as backbone and decorated by oxygen functional groups in both sides. These functional groups have role to the GO properties, such as magnetic susceptibility, band gap, conductivity. There are several processes to reduce its oxygen content, such as chemical, photo and thermal reduction, resulted reduced graphene oxide (rGO). Several studies reported the magnetic properties of GO and rGO correlating with the process of synthesis and reducing oxygen contents. We report the magnetic characteristic of a commercial GO 0.5 mg/ml dispersed in H2O from Graphenia and RGO that were synthesized through thermal reduction process of GO precursor. In this process, we use oven vacuum system at 200 °C for 1 hour. All samples were prepared as GO and rGO thick films. The GO and rGO samples structure were indentified from XRD data and SQUID data for magnetic characteristics. We explored the temperature dependence of magnetic susceptibility by applying magnetic field of 500 Oe in Zero Field Cooling (ZFC) and Field Cooling (FC). The result shows different susceptibility behavior of GO and rGO samples in all wide range of temperature between 0 to 300 Kelvin. The value of magnetic susceptibility rGO is higher than that of GO and has splitting curve of ZFC and FC at low temperatures below 200 Kelvin. However, GO has the splitting curve of ZFC and FC occurred at high temperatures above 200 Kelvin.
Characteristics of Barium M-Hexaferrite with Doping Mn and Ni in X-Band Frequency for Microwave Absorption
Authors: Susilawati Susilawati , Doyan Aris
Published: April 2021

Synthesis of Barium M-Hexaferrite samples based on natural iron sand at Ketapang beach, Pringgabaya District, East Lombok with Mn-Ni doping (BaFe12-xMnxNixO19) has been successfully carried out using the coprecipitation method. The synthesis aims to determine the characteristics of the electrical properties of the Reflection Loss sample of BaFe12-xMnxNixO19 doped with Mn-Ni metal. The basic materials used in this study were natural iron sand and Barium Carbonate (BaCO3) powder, while the doping materials used were Nickel (II) Chloride Hexahydrate (NiCl2.6H2O) and Manganese(II) chloride (MnCl2) powder with a variety of mole fraction (X = 0, 2; 0 ‚4; 0‚6 and 0.8). The solvent uses distilled water, 37% hydrochloric acid (HCl), and 25% NH4OH solution. The samples were then calcined at 25 °C, 400 °C, and 600 °C. The obtained samples show that the higher the Mn-Ni doping ion content and the calcination temperature, the smaller the resulting Reflection Loss value and the greater the absorption rate of microwaves.
Characterization of Mesoporous Biphasic Calcium Phosphate Synthesized Using Chitosan and Aloe Vera Template
Authors: Tasomara Riesma , Herdianto Nendar , Gustiono Dwi , Rahmania Adita Wardani , Hakim Hanan , Lukmana Lukmana
Published: April 2021

Biphasic calcium phosphate (BCP) is a bonegraft material which is a mixture of hydroxyapatite (Ca10(PO4)6(OH)2, HA) and betatricalcium phosphate (Ca3(PO4)2, β-TCP). The combination of HA and β-TCP provides faster osseointegration, compared to HA, into parent bone so it can accelerate the bone recovery process. The mesoporous structure of bone graft material is suitable for drug delivery purpose. In order to study the mesoporous structure of BCP, the BCPs were prepared by precipitation method using chitosan, aloe vera, and chitosan-aloe vera hybrid as templates. A solution containing Ca(NO3)2·4H2O and template and a solution containing (NH4)2HPO4 and NH4HCO3 were used as starting materials. All prepared samples were calcined at 900°C for 1 hour. The identification of phases and functional groups of obtained BCP powders were characterized by X-Ray Diffraction technique and Fourier Transform Infrared (FTIR) spectroscopy, repectively. The XRD patterns show typical peaks of both HA and β-TCP crystal phases. FTIR spectra confirm the presence of phosphate functional groups. Morphological analysis using Scanning Electron Microscope (SEM) observed the presence of regular porous structure, however, the mesoporous structure was not seen. Particle size distribution and pore size analysis were analyzed by Particle Size Analyzer and Brunauer–Emmett–Teller (BET) method, respectively.
Synthesis and Characterization of Polydimethylsiloxane (PDMS) with Medium Viscosity via Ring-Opening Polymerization
Authors: Setiadji Soni , Agasa Zulfi Mofa , Auliya Diba Grace , Fitrilawati Fitrilawati , Syakir Norman , Noviyanti Atiek Rostika , Rahayu Iman , Supriadin Asep , Risdiana Risdiana
Published: April 2021

Duration of use and injectability are external factors for Polydimethylsiloxane (PDMS) that needs to be considered when PDMS utilized as a vitreous substituted liquid in vitreoretinal surgery. In general, PDMS which has been used as a substitute for vitreous humour is PDMS with a low viscosity in the value about 1000 cSt and a high viscosity at a value of about 5000 cSt. Various deficiencies have been encountered from low and high viscosity of PDMS, causing research to be continued to obtain PDMS which has suitable properties as a substitute for vitreous humour. One of them is research to obtain medium viscosity of PDMS with a viscosity value of about 2000 cSt. Here, we reported synthesis and characterization of PDMS with medium viscosity in ranges from 1800 to 2600 mPas. PDMS was synthesized through Ring-Opening Polymerization (ROP) pathway using the monomer of Octamethylcyclotetrasiloxane (D4) and the chain terminator of Hexamethyldisiloxane (MM). Various concentrations of potassium hydroxide (KOH) of 3, 4, 6 and 8 %(w/v) were applied as initiator to form gel of PDMS. All synthesized PDMS samples were identified to have viscosity values of 1800-2600 mPas, refractive index values of 1.4042-1.4044 and surface tension values of 22-23 mN/m. Meanwhile, the results of Fourier-Transform Infrared (FTIR) measurement showed that the absorption peaks were similar to that of our previous report.
Initial Study of Magnetic Characterization of Barium Hexaferrite with the Addition of Cobalt Oxide Prepared by Powder Metallurgy Process
Authors: Wibowo Trie Joko Satrio , Dwiwanto Supono A. , Kristiantoro Tony , Saragi Togar , Risdiana Risdiana
Published: April 2021

Co3O4 powder was added to barium hexaferrite by powder metallurgy process to determine its effect on the magnetic properties. The variation of the addition of Co3O4 are 0.0, 0.5, 1.0, 2.0, 3.0, and 5.0 wt%. Characterization and magnetic testing included density calculation, Permagraph test, and XRD were performed in order to elucidate the effect of Co3O4 addition to its structure and magnetic properties of barium hexaferrite. The magnetic density obtained was in the ranges of 3.2 - 4.35 g/cm3. From the permagraph test, it is found that the value of remanence (Br) was in between 1.18 and 1.5 kG. The value of coercivity (Hc) was in the range of 0.594 - 3.366 kOe, and the maximum product energy (BHmax) was found to be in between 0.07 and 0.48 MGOe. From the XRD analysis, it was found that two types of barium hexaferrite were formed, namely barium hexaferrite type M(BaFe12O19) and X(Ba2Fe30O46). It is concluded that the addition of the Co3O4 compound increased the value of magnetic density and decreased magnetic properties.
The Effect of Acid Solution on Dental Magnetic Attachment
Authors: Kusumadewi An-Nissa , Damayanti Lisda , Rukiah Rukiah , Risdiana Risdiana
Published: April 2021

Dental magnetic attachments used as a retainer for overdentures are encapsulated with a corrosion resistant casing to prevent corrosion of magnets. However, some studies reported that the casing still has a risk of corrosion. This study aims to determine the effect of acid solutions on magnetic attractive force, dissolving metal ions and corrosion of magnetic attachment surfaces. The dental magnetic attachment material used is Magfit DX 600 (Aichi, Japan). It consists of assembly and keeper. The assembly and keeper immersed in acid solutions with a pH of 3.8 and 5.8 for 7 and 14 days. After immersion, the assembly and keeper were analyzed using SEM, universal testing machine, and the atomic absorption spectrophotometry to determine the surface corrosion, the magnetic attractive force, and dissolved metal ions, respectively. It is found that all assemblies showed signs of corrosion and reduction of magnetic attractive force after immersed in acid solutions with a pH of 3.8 and 5.8 for 7 and 14 days. A greater decrease in magnetic attraction was obtained at 14 days immersion in an acid solution with a pH of 3.8. Fe ion dissolution in the assembly and keeper was found to increase at 14 days of immersion. The lower the pH of the acid solution and the longer the immersion time, the signs of corrosion on the surface of dental magnetic attachment are clearly observed. The magnetic attraction force also decreased with decreasing the value of pH as well as the increase of the content of Fe ion in immersed solution.
Parameter Design of EDM Process to Optimize Surface Roughness and Material Removal Rate Using Taguchi Method
Authors: Firmansyah Muhammad Firly , Suwarno Suwarno , Pradana Yanuar Rohmat Aji , Suprayitno Suprayitno
Published: April 2021

Electrical discharge machining (EDM) is a non-conventional process that is widely used for high-precision machining, complex product shapes, and high hardness materials. The EDM mechanism is based on the thermoelectric energy between the electrode and the workpiece. The EDM process has many parameters that can be adjusted, such as discharge current, voltage, pulse on time, pulse off time, electrode polarity, workpiece material, electrode material, dielectric fluid type, flushing pressure, flushing direction and flushing method. This study aims to find the parameters of the EDM process to optimize its productivity indicated by material removal rate (MRR) and its quality indicated by surface roughness of SS-316 material. The varied parameters were discharge current, pulse on time, and pulse off time with 3 levels for each parameter. Fractional orthogonal array L9 were applied for three 3-level variables. Performance fluctuation due to noise factors were simply approximated by 3 replicating measurements to estimate mean and standard deviation. Taguchi S/N ratio were adopted as robustness index for the optimum parameter design. The optimization results show that the discharge current 30A, pulse on time 100μs, and pulse off time 8μs are the optimum for MRR. As for surface roughness, the discharge current is 10A, pulse on time is 100μs, and pulse off time is 8μs. The only different of EDM parameter for optimum MRR and optimum Ra is discharge current.
The Effect of Variation Concentration Cristobalite Silica from Natural Silica Sand to Hydrophobicity on Steel Plate Surface
Authors: Zainuri Mochammad , Awathifi Lana , Silvia Linda , Triwikantoro Triwikantoro , Subagyo Bintoro Anang
Published: April 2021

In this research, pure silica powder has been synthesized from the sand of the Bangka-Belitung Islands. Natural sand is extracted with permanent magnets and immersed with HCl to obtain pure silica, followed by coprecipitation and calcination processes at a temperature of 900 °C for 10 hours. The final result of the synthesis process is pure silica powder in the cristobalite phase (83.03% wt) and the tridymite phase (16.97% wt). The synthesized silica powder is used as a modification on topcoat of steel to increase the hydrophobicity of steel plate surface so that it can reduce the rate of corrosion. Steel plate has been painted by using the brush painting method and consists of three layers, namely the primary layer, midcoat and topcoat. The variation in this research is the concentration of silica powder on the topcoat of steel such as 0% wt (sample 1), 3% wt (sample 2), 6% wt (sample 3), 9% wt (sample 4), and 12% wt. (sample 5). These variations have an effect on the surface geometry of the steel plate, namely the surface gets rougher as the concentration of silica powder is mixed. The hydrophobicity of the steel plate can be seen from the measurement Water Contact Angle (WCA). The WCA using fresh water in sample first until five’th are 75,828 ̊, 90 ̊, 91,397 ̊ 96,520 ̊, and 104 ̊, respectively. While the WCA using seawater in sample first, second and fourth are 80.618 ̊, 102 ̊, and 104.56 ̊, respectively.
Possible Defect Recovery in T’-Pr2-xCexCuO4 with x = 0.10 Nanoparticles Analyzed by Neutron Diffraction
Authors: Putra Putu Eka Dharma , Insani A. , Irfanita Resky , Baqiya Malik Anjelh , Darminto Darminto
Published: April 2021

We report the possible existence of defect recovery and the magnetic behavior in the T’-Pr2-xCexCuO4 (T’-PCCO) with x = 0.10 nanoparticles through the partially reduction annealing process. The powders of T’-PCCO nanoparticles were synthesized by using the chemically dissolved method followed by partially reduction annealing at 700 °C for 5 h in argon atmosphere. The high-resolution neutron powder diffraction (HRPD) technique has been employed to study the nuclear structure, vacancy, and the magnetic properties of the T’-PCCO nanoparticles. It is found that there is an increase of oxygen occupancy at the in-plane oxygen, O(1), and the apical oxygen, O(3), which signifies the decrease of the number of the vacancy on their sites. Meanwhile, the out plane oxygen, O(2), seems to be unchanged in the partially reduced samples. The Fourier difference profile shows an enhancement of the neutron scattering density at all the critical sites of O(1), O(3), and the Cu site. This may lead to the idea of the defect recovery affecting the whole magnetic moments which is responsible for the absence of weak ferromagnetism in the T’-PCCO nanoparticles.