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Spektra: Jurnal Fisika dan Aplikasinya

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Published by Universitas Negeri Jakarta

ISSN : 25413384 EISSN : 25413392 DOI : -

Core Subject : Science, Engineering,

Aerospace Engineering Electrical & Electronics Engineering Energy Materials Science & Nanotechnology Physics

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Articles 264 Documents

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Pre-selection of Globular Clusters for Detecting Intermediate-Mass Black Holes via Microlensing Zahra, Fatimah; Jaelani, Anton Timur
Spektra: Jurnal Fisika dan Aplikasinya Vol. 11 No. 1 (2026): SPEKTRA: Jurnal Fisika dan Aplikasinya, Volume 11 Issue 1, April 2026
Publisher : Program Studi Fisika Universitas Negeri Jakarta

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.21009/SPEKTRA.111.02

Intermediate-mass black holes (IMBHs) are the key to understanding the formation of supermassive black holes (SMBHs) that are typically found in centers of massive galaxies. In general definition, IMBHs are black holes masses ranging from 102 M⨀ to 105 M⨀. Black hole seeding theory suggests that IMBHs formed at high redshifts (z ≥ 0) through gravitational collapse of Population III stars, direct collapse of protogalaxy clouds, or stellar collisions inside high-density clusters. These IMBHs evolve into SMBHs through accretion and mergers. However, not all of these IMBHs are successful in forming SMBHs. Those that fail are hypothesized to be observable in the local universe, particularly in globular clusters and dwarf galaxies. IMBHs have yet to be definitively detected, however several strong candidates have been located in the cores of globular clusters. This study describes the preliminary selection stage of globular cluster candidates with the aim to look further into the possibility of detecting IMBHs via microlensing. The selection process was based on several physical properties of the globular clusters including mass, metallicity, and central velocity dispersion. Since background star density strongly affects microlensing detection probability, we restricted the sample to clusters located in the direction of the Galactic center. We utilized Gaia DR3 data to estimate background star density for selected globular clusters using proper motion filtering and Theil-Sen regression method. These estimates provide the foundation for further subsequent simulations of microlensing detection probabilities associated with central IMBHs.

Tunning Surface Hydrophilicity of PVA Nanofiber Bone Scaffolds Via Amino Acid and Nanohydroxyapatite Incorporation: Hartman, Rohul Rizki Mubaroq; Sari, Yessie Widya; Yusuf , Yusril
Spektra: Jurnal Fisika dan Aplikasinya Vol. 11 No. 1 (2026): SPEKTRA: Jurnal Fisika dan Aplikasinya, Volume 11 Issue 1, April 2026
Publisher : Program Studi Fisika Universitas Negeri Jakarta

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.21009/SPEKTRA.111.03

Polyvinyl alcohol (PVA) is a biodegradable and biocompatible polymer with potential use in bone tissue engineering. However, its excessively high hydrophilicity led to poor cell adhesion, limiting its suitability as a bone scaffold. This study investigates the modification of PVA nanofibers through the incorporation of negatively charged amino acids (aspartic acid, glutamic acid) and nano-hydroxyapatite (nHA) to tailor surface hydrophilicity. Electrospun nanofiber composites of Asp/PVA/nHA and Glu/PVA/nHA were fabricated with varying nHA concentrations. Higher nHA content was found to decrease hydrophilicity, whereby Asp/PVA/nHA and Glu/PVA/nHA with nHA concentration of 3.5% were within the ideal range for optimal cell adhesion and proliferation characterized by contact angle between 40o – 70o. Samples containing Asp exhibited a lower hydrophilicity compared to their respective Glu-containing counterparts, which may correlated to the difference side chain of Asp and Glu structure. Statistically significant differences (p ≤0.05) suggest that nHA and amino acids effectively modulate surface characteristics, supporting the potential of fine-tuning PVA hydrophilicity via nHA and amino incorporation for improved performance in bone tissue engineering applications.

Integrating Time-Dependent and Time-Independent Earthquake Recurrence Models for Fault-Based Seismic Hazard Assessment in the Lampung Region, Southern Sumatra Wulandari, Rizki; Styawan, Yudha; Prabowo, Satria Bagus
Spektra: Jurnal Fisika dan Aplikasinya Vol. 11 No. 1 (2026): SPEKTRA: Jurnal Fisika dan Aplikasinya, Volume 11 Issue 1, April 2026
Publisher : Program Studi Fisika Universitas Negeri Jakarta

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.21009/SPEKTRA.111.05

The Lampung region in southern Sumatra is exposed to significant seismic hazard due to its proximity to the Sunda megathrust and multiple active crustal faults. This study integrates time-independent (Poissonian) and time-dependent (Brownian Passage Time/BPT) earthquake recurrence models to evaluate fault-specific rupture probabilities and their implications for probabilistic seismic hazard assessment (PSHA). This approach systematically bridges the gap between traditional stationary models and the physical reality of seismic cycles, ensuring that the resulting hazard estimates reflect the current elapsed time since the last major rupture. Earthquake catalogs from USGS, BMKG, and historical sources were compiled for shallow events ( 50 km) between 1900–2023, and fault parameters were derived from national hazard maps and published geological studies. Recurrence intervals were estimated for 28 major fault segments across Sumatra, the Sunda Strait, and western Java. Results show strong temporal variability in seismic potential, with the Kumering South segment exhibiting the highest 50-year rupture probability (>50%) due to its elapsed time nearing the estimated recurrence interval. In contrast, segments such as Semangko West-A show markedly reduced short-term probability under the BPT model. PSHA simulations using OpenQuake reveal peak ground acceleration (PGA) values of 0.6–1.5 g for 2% exceedance in 50 years, indicating very high hazard levels in areas adjacent to the Sumatra Fault System. Incorporating time-dependent recurrence provides a more cycle-consistent spatial pattern compared to Poissonian results, reducing overestimation in early-cycle segments and enhancing hazard representation in late-cycle faults. While this study is constrained by uncertainties in historical recurrence intervals and fault slip-rates, these findings provide a more refined academic contribution to regional hazard characterization, supporting more robust risk mitigation strategies in Lampung Province.

Shakemap and Focal Mechanism Analysis of the December 2024 Gresik Earthquake Zaman, Mochamad Tanwiruz; Suprianto, Agus; Rohman, Lutfi; Cahyono, Eko
Spektra: Jurnal Fisika dan Aplikasinya Vol. 11 No. 1 (2026): SPEKTRA: Jurnal Fisika dan Aplikasinya, Volume 11 Issue 1, April 2026
Publisher : Program Studi Fisika Universitas Negeri Jakarta

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.21009/SPEKTRA.111.04

An earthquake that occurred on December 30, 2024 in Gresik Regency, located at 7.05° S and 112.62° E with a focal depth of 14 km and magnitude M3.3, was a shallow earthquake felt with an intensity of II–III MMI. This study aims to analyze the earthquake shaking intensity map (Shakemap), determine the earthquake source mechanism, and perform earthquake scenario modeling using the maximum magnitude based on the Indonesian Earthquake Source and Hazard Map (PUSGEN). Shakemap analysis was carried out using the BMKG Shakemap server based on accelerograph network data. Fault mechanism analysis was performed using focal mechanism software with P-wave polarity input obtained from waveform signal picking using SeisGram2K software. Meanwhile, the Shakemap scenario was generated using the ShakeMap application available at the Pasuruan Geophysical Station. The results show that the distribution of Peak Ground Acceleration (PGA) and shaking intensity is influenced not only by the distance from the epicenter but also by local geological conditions that contribute to ground-motion amplification. Source mechanism analysis indicates that the Gresik earthquake was dominated by a strike-slip faulting mechanism with a weak oblique component, interpreted as sinistral strike-slip motion along the RMKS–Tuban 3 fault zone. Scenario earthquake modeling with a magnitude of M 6.2 indicates that Gresik Regency has the potential to experience strong ground shaking with maximum intensities reaching VI–VII MMI, while surrounding areas such as Surabaya City, eastern Lamongan Regency, and western Bangkalan Regency may experience intensities up to VI MMI. These findings indicate that although the Gresik earthquake had a relatively small magnitude, the potential earthquake impact in Gresik and surrounding areas could become significant if a maximum-magnitude earthquake occurs, therefore, this study provides important information for earthquake disaster mitigation efforts.

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