Acep Purqon

First Principles Study of Molybdenum Disulfide Electronic Structure

The study of two dimensional material has gain interest due to unique properties which are different from the bulk precursors. Mono- and few-layered of Transition metal dichalcogenides (TMDCs) has band gap properties between 1-2 eV that suitable of FET devices or any optoelectronic devices. Among TMDCs, Molybdenum Disulfide (MoS2) has gain interest due to its promising band gap-tuning and transition between direct to indirect band gap properties depends on its thickness. First principles calculation by Density Functional Theory has been performed to study the characteristic of MoS2 electronic structure. Indirect band gap of MoS2 lies between point Γ to Γ-K in first brillouine zone, while the direct bandgap lies in point-K. The indirect band gap became larger while the number of layer decreased due to quantum confinement effect in c axis direction. In monolayer MoS2, the indirect band gap become larger than direct one, band gap properties transitioned from indirect to direct. The unique bandgap properties of MoS2 can lead into better application in energy devices such as solar cell [11], FET [10], and photoluminescence device.

Accuracy and Numerical Stabilty Analysis of Lattice Boltzmann Method with Multiple Relaxation Time for Incompressible Flows

Lattice Boltzmann Method (LBM) is the novel method for simulating fluid dynamics. Nowadays, the application of LBM ranges from the incompressible flow, flow in the porous medium, until microflows. The common collision model of LBM is the BGK with a constant single relaxation time τ. However, BGK suffers from numerical instabilities. These instabilities could be eliminated by implementing LBM with multiple relaxation time. Both of those scheme have implemented for incompressible 2 dimensions lid-driven cavity. The stability analysis has done by finding the maximum Reynolds number and velocity for converged simulations. The accuracy analysis is done by comparing the velocity profile with the benchmark results from Ghia, et al and calculating the net velocity flux. The tests concluded that LBM with MRT are more stable than BGK, and have a similar accuracy. The maximum Reynolds number that converges for BGK is 3200 and 7500 for MRT respectively.

Prediction of Dried Durian Moisture Content Using Artificial Neural Networks

Moisture content has a crucial issue in post-harvest processing since it plays main role to estimate a quality of dried product. However, estimating the moisture content is difficult since it shows mathematically nonlinear systems and complex physical processes. We investigate the prediction of moisture content of dried product by using Artificial Neural Networks (ANN). Our sample is a Bengkulus local durian that is dried using a microwave oven. Our results show that ANN can predict the moisture content by performing with R2 value is 98.47%. Moreover, the RMSE values is 3.97% and MSE values is 0.16%. Our results indicate that ANN model have high capability for predicting moisture content and it is potentially applied in post-harvest product, especially in drying product quality control.

Study of budding yeast colony formation and its characterizations by using circular granular cell

Budding yeast can exhibit colony formation in solid substrate. The colony of pathogenic budding yeast can colonize various surfaces of the human body and medical devices. Furthermore, it can form biofilm that resists drug effective therapy. The formation of the colony is affected by the interaction between cells and with its growth media. The cell budding pattern holds an important role in colony expansion. To study this colony growth, the molecular dynamic method was chosen to simulate the interaction between budding yeast cells. Every cell was modelled by circular granular cells, which can grow and produce buds. Cohesion force, contact force, and Stokes force govern this model to mimic the interaction between cells and with the growth substrate. Characterization was determined by the maximum (L max) and minimum (L min) distances between two cells within the colony and whether two lines that connect the two cells in the maximum and minimum distances intersect each other. Therefore, it can be recognized the colony shape in circular, oval, and irregular shapes. Simulation resulted that colony formation are mostly in oval shape with little branch. It also shows that greater cohesion strength obtains more compact colony formation.

Study on transport properties of silicene monolayer under external field using NEGF method

We investigate the current-voltage (I-V) characteristics of a pristine monolayer silicene using non-equilibrium Green function (NEGF) method combining with density functional theory (DFT). This method succeeded in showing the relationship of I and V on silicene corresponding to the electronic characteristics such as density of states. The external field perpendicular to the silicene monolayer affects in increasing of the current. Under 0.2 eV external field, the current reaches the maximum peak at Vb = 0.3 eV with the increase is about 60% from what it is in zero external field.

Geometrical Classification of Spaghetti‐Like Nanoclusters

Spaghetti‐like nanoclusters show irregular shapes. We investigate their shapes by using the concept of symmetry and isotropy. The Symmetry‐S evaluates the degree of symmetry of a cluster implying aggregate orderness, while, the Isotropy‐I evaluates the degree of parallelism of a cluster. To investigate cluster dynamics in detail, we perform molecular dynamics simulation for POPC and POPE lipids for 300 K and 340 K.>From the simulations, the clusters are not easy to configure S≈0; which implies that the cluster shapes are neither sphere nor rod shapes; simply disorder shapes. However, at some times, the clusters show similar shapes with definite shapes implying some regions or classifications. For the reasons, we classify the irregular shapes in spaghetti‐like nanoclusters by using geometrical classification as physical meaning of the concepts of symmetry and isotropy. We find, at least, four cluster modes: sphere‐like, rod‐like, cone‐like, and monolayer‐like. We also use geometrical classification as diag...

Molecular Dynamics Study of Hydration Water Behavior in Blue Copper Protein

We carry out the molecular dynamics(MD) simulation of type 1 blue copper protein azurin in room and some lower temperatures to investigate the behavior of hydration water molecules in the protein surface. In this study, we find the anomalous behavior of the water molecules , which depend on the system temperatures. These water molecules have hydrogen bond to the protein surface residues. We specify the residues type, being classified as the hydration donor and the hydration acceptor of water molecules. We analyze the residue type, and the bond length and bond strength between solvent water molecules in each temperature. Moreover, we estimate the B‐factor of these residues which indicates the fluctuation of hydration residues in each temperature. B‐factor values depend on the system temperatue althought the number of hydration residue do not depend on the temperature.

Electronic Properties of Rare-Earth Doped α-GaN

We carry out DFT calculation to study electronic properties of rare-earth (RE) doped α-GaN. GGA approximation and ultrasoft pseudopotential used in this calculation. The bond length and tetrahedral angle of pristine α-GaN are slightly changed. The direct band gap of α-GaN was detected at 2.56 eV, this is 1 eV lower from experiment. Electronic structure measurement is also performed for RE doped GaN (RE = Pr, Eu, Er, Gd and Tm), which the configuration is Ga(1-x)NREx (x=0.125). The bond length of Ga-RE is vary from 2.12-2.23 A. The impurity energy is found relative between conduction bands and valence bands of host materials.

Random Matrix Theory Approach to Indonesia Energy Portfolio Analysis

In a few years, Indonesia experienced difficulties in maintaining energy security, the problem is the decline in oil production from 1.6 million barrels per day to 861 thousand barrels per day in 2012. However, there is a difference condition in 2015 until the third week in 2016, world oil prices actually fell at the lowest price level since last 12 years. The decline in oil prices due to oversupply of oil by oil-producing countries of the world due to the instability of the world economy. Wave of layoffs in Indonesia is a response to the decline in oil prices, this led to the energy and mines portfolios Indonesia feared would not be more advantageous than the portfolio in other countries. In this research, portfolio analysis will be done on energy and mining in Indonesia by using stock price data of energy and mines in the period 26 November 2010 until April 1, 2016. It was found that the results have a wide effect of the market potential is high in the determination of the return on the portfolio energy and mines. Later, it was found that there are eight of the thirty stocks in the energy and mining portfolio of Indonesia which have a high probability of return relative to the average return of stocks in a portfolio of energy and mines.

Simulation of Fluid Flow and Heat Transfer in Porous Medium Using Lattice Boltzmann Method

Fluid flow and heat transfer in porous medium are an interesting phenomena to study. One kind example of porous medium is geothermal reservoir. By understanding the fluid flow and heat transfer in porous medium, it help us to understand the phenomena in geothermal reservoir, such as thermal change because of injection process. Thermal change in the reservoir is the most important physical property to known since it has correlation with performance of the reservoir, such as the electrical energy produced by reservoir. In this simulation, we investigate the fluid flow and heat transfer in geothermal reservoir as a simple flow in porous medium canal using Lattice Boltzmann Method. In this simulation, we worked on 2 dimension with nine vectors velocity (D2Q9). To understand the fluid flow and heat transfer in reservoir, we varied the fluid temperature that inject into the reservoir and set the heat source constant at 410°C. The first variation we set the fluid temperature 45°C, second 102.5°C, and the last 307.5°C. Furthermore, we also set the parameter of reservoir such as porosity, density, and injected fluid velocity are constant. Our results show that for the first temperature variation distribution between experiment and simulation is 92.86% match. From second variation shows that there is one pick of thermal distribution and one of turbulence zone, and from the last variation show that there are two pick of thermal distribution and two of turbulence zone.