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All Journal E-Jurnal Matematika Journal of the Indonesian Mathematical Society Communication in Biomathematical Sciences Enthusiastic : International Journal of Applied Statistics and Data Science
ZAI, FIDELIS NOFERTINUS
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Computer Science & IT Decision Sciences, Operations Research & Management Economics, Econometrics & Finance Engineering Mathematics Social Sciences

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ANALISIS KESTABILAN MODEL MATEMATIKA JUMLAH PEROKOK PENGARUH KENAIKAN HARGA ROKOK DENGAN DINAMIKA AKAR KUADRAT FIDELIS NOFERTINUS ZAI; ARYL ZULDAUS SEMBIRING; ARDINAL VANBASTEN; ANGGI NOVITA NASUTION; LASKER PANGARAPAN SINAGA
E-Jurnal Matematika Vol 9 No 4 (2020)
Publisher : Mathematics Department, Faculty of Mathematics and Natural Sciences, Udayana University

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.24843/MTK.2020.v09.i04.p310

Abstract

Consumption of cigarettes in large quantities by the public is one of the main concerns in every country because cigarettes contain harmful ingredients that can trigger various diseases. This journal will explain the mathematical model of the number of smokers affected by rising prices of cigarettes with square root dynamics. The population is divided into four, composed of potential smokers, occasionally smokers, heavy smokers, and ex-smokers. The results of the model analysis are that there is a single point of smoker’s endemic equilibrium. If conditions are met, then the endemic equilibrium point of smokers will be asymptotically stable, and over a long period of time there will always be a spread of smokers.
Model Populasi Pongo abelii dengan Perubahan Daya Dukung Lingkungan Jabriel, Karsten Maynard; Jamaludin, Muhamad; Zai, Fidelis Nofertinus
Communication in Biomathematical Sciences Vol. 6 No. 1 (2023)
Publisher : The Indonesian Bio-Mathematical Society

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5614/cbms.2023.6.1.3

Abstract

Pongo abelii is an endangered orangutan species. The reduction of Pongo abelii can be caused by the removal or loss of orangutans from the population and habitat loss. In general, research on population dynamics with changing carrying capacity is rarely done and it is simulated in this study. We adopted the Verhulst logistic model to model the population dynamics of Pongo abelii. This study aimed to see the effect of increasing the carrying capacity on the population of the endangered Pongo abelii species. From the results of this study, it is concluded that for areas other than Tripa Swamp, Siranggas/Batu Ardan, and East Batang Toru (Sarulla), the addition of carrying capacity is one of the effective options that is urgently needed to maintain a large population of orangutans. For the Tripa Swamp, Siranggas/Batu Ardan, and East Batang Toru (Sarulla) areas, suppressing the number of orangutans loss population is needed to maintain the population, which consists of poaching as trade, conflict killing, hunting/food, wounding, and fire. The results of this study can provide suggestions for tackling the declining population of Pongo abelii species by prohibiting the expansion of the species’ habitat
Effects of Inversion Layer on The Atmospheric Pollutant Dispersion from A High Chimney Zai, Fidelis Nofertinus; Gunawan, Agus Yodi
Journal of the Indonesian Mathematical Society VOLUME 29 NUMBER 3 (NOVEMBER 2023)
Publisher : IndoMS

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.22342/jims.29.3.1597.299-310

Abstract

An inversion layer is a layer in the lower atmosphere at a certain height through which there is no transport of pollutants. It plays as a significant factor in the formation of air pollutants where they are trapped. In this paper, a mathematical model describing an atmospheric pollutant dispersion from a high chimney in the presence of an inversion layer is constructed. The aim of the model is to predict the concentration of pollutants at ground level. The advection-diffusion equation governs the concentration of a pollutant released into the air. An analytical solution procedure via the integral transforms is presented for the steady-state case. Solutions are entirely determined by two parameters, i.e., the source strength emanating from the chimney and the height of the inversion layer. The pollutant concentration on the ground level with some multiple source formations will be explored, and also for various values of inversion layer height. Results show that the lower the inversion layer, the higher the pollutant concentration on the ground level is.
Spatio-Temporal Modeling of Crime Rates Using Geographically and Temporally Weighted Regression Putra, Robiansyah Putra; Zai, Fidelis Nofertinus
Enthusiastic : International Journal of Applied Statistics and Data Science Volume 5 Issue 2, October 2025
Publisher : Universitas Islam Indonesia

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.20885/enthusiastic.vol5.iss2.art4

Abstract

This study analyzes the spatio-temporal modeling of crime rates in 35 regencies and cities in Central Java using the geographically and temporally weighted regression (GTWR) method. The objective is to investigate how socio-economic factors, including the open unemployment rate, percentage of the poor population, population density, average years of schooling, job vacancies, labor force participation rate, and labor wage, influence crime rates across different regions and periods. The goodness-of-fit test results indicateed that the GTWR model had an R-squared value of 93.51%, higher than the 88.64% of the geographically weighted regression (GWR) model, demonstrating GTWR’s ability to explain crime data variations that were heterogeneous both spatially and temporally. Partial significance tests and mapping results showed that the influence of variables differed across years and regions, with population density and labor-related factors consistently being the main predictors. These findings highlight the importance of designing crime prevention policies that are locally tailored and based on spatio-temporal evidence.  
Co-Authors Agus Yodi Gunawan ANGGI NOVITA NASUTION ARDINAL VANBASTEN ARYL ZULDAUS SEMBIRING Jabriel, Karsten Maynard Jamaludin, Muhamad Lasker Pangarapan Sinaga Lisa Damayanti Ningrum Noval Putra Ramadhani Putra, Robiansyah Putra