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A MATHEMATICAL MODEL OF GPS SATELLITE TIME AND FREQUENCY BASED ON THE SPECIAL THEORY OF RELATIVITY Endah Purnomosari; Siska Astari Dewi; Wiwiek Eka Mulyani; Valentinus Galih Vidia Putra; Fadil Abdullah
INKOFAR Vol. 9 No. 2 (2025)
Publisher : Politeknik META Industri Cikarang

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Abstract

The Global Positioning System (GPS) relies on highly precise atomic clocks in satellites and ground stations to determine global time and position accurately. Relativistic effects, including gravitational fields and satellite orbital motion, induce frequency shifts in these clocks, necessitating corrections for accurate navigation. This study developed a novel approach to integrate general coordinates into GPS, emphasizing implementation simplicity. We investigated the application of special relativity to calculate time and frequency shifts in GPS satellites. Our analysis estimated a daily relativistic correction of approximately 21.6 microseconds, with a positional imprecision of 6.48 km per day if uncorrected. By employing a general time-space coordinate system, we calculated position4 and velocity-4 vectors, accounting for special relativistic effects on GPS time and frequency. The proposed method simplifies relativistic corrections while enhancing their conceptual clarity. Results demonstrate improved precision and efficiency in GPS positioning through the integration of general coordinates with a streamlined approach. This research offers valuable insights for international engineering communities, scholars, and practitioners, advancing the understanding of relativity’s impact on GPS satellite operations.
STUDI KARAKTERISTIK DAN KENYAMANAN KAIN RAJUT UNTUK SPORTWEAR Liana Dwi Fitrianti; Assyfa Kusumaningsih; Siska Astari Dewi; Witri Aini Salis; Uni Kusyanti
Texere Online First
Publisher : Politeknik STTT Bandung

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.53298/texere.v24i2.05

Abstract

Exercise is now a routine part of daily life for most people, valued for its direct contribution to physical and mental health. This has driven a marked rise in demand for sportswear, and market growth needs to be matched by comparable gains in the quality and volume of production. This study evaluates the structural characteristics of four polyester Single Jersey Mesh knitted fabrics together with their thermophysiological and tactile comfort performance, with the aim of classifying their suitability by exercise intensity. Samples were tested using a Fabric Touch Tester (FTT), a Moisture Management Tester (MMT), and a Sweating Guarded Hot Plate (SGHP). Sample B recorded the highest Permeability Index (PI = 1.9214), pointing to a greater capacity for heat and moisture dissipation than sample D (PI = 0.5010). Sample D, however, performed best for softness, smoothness, and low evaporative resistance. Taken together, these results support samples B and C for high-intensity sportswear, while samples A and D are better suited to low-to-moderate intensity sportswear and casual wear.
STUDI KARAKTERISTIK DAN KENYAMANAN KAIN RAJUT UNTUK SPORTWEAR Liana Dwi Fitrianti; Assyfa Kusumaningsih; Siska Astari Dewi; Witri Aini Salis; Uni Kusyanti
Texere Vol 24, No 2 (2026): Texere Volume 24 Nomor 2 Tahun 2026
Publisher : Politeknik STTT Bandung

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.53298/texere.v24i2.05

Abstract

Kebanyakan orang saat ini menganggap olahraga merupakan bagian penting dari aktivitas keseharian mereka, karena secara langsung membantu menjaga kesehatan fisik dan mental. Hal ini menyebabkan konsumsi pakaian olahraga meningkat secara signifikan. Meningkatnya permintaan pasar harus berbanding lurus dengan kualitas dan kuantitas pakaian olahraga yang diproduksi. Tujuan utama penelitian ini adalah untuk mengevaluasi secara kuantitatif dan sistematis hubungan antara diferensiasi mikro-struktur jeratan (technical face dan technical back) empat varian kain rajut Single Jersey Mesh poliester dengan performa kenyamanan taktil (FTT), manajemen kelembapan (MMT), serta resistansi termal-evaporatif (SGHP), guna menyusun matriks klasifikasi objektif kesesuaian bahan terhadap tingkat intensitas aktivitas olahraga. Sifat kenyamanan diuji menggunakan instrumen Fabric Touch Tester (FTT), Moisture Management Tester (MMT), dan Sweating Guarded Hot Plate (SGHP). Hasil pengujian menunjukkan bahwa sampel B memiliki nilai Permeability Index (PI) paling tinggi (1,9214) yang berbanding terbalik dengan sampel D yang memiliki nilai PI paling rendah (0,5010). Namun, sampel D memiliki hasil uji kelembutan, kehalusan, dan resistansi evaporasi yang baik. Berdasarkan evaluasi komprehensif, sampel C dan B sangat direkomendasikan untuk high-intensity sportswear, sedangkan sampel A dan D lebih ideal untuk low-to-moderate intensity sportswear dan pakaian harian.
Co-Authors Assyfa Kusumaningsih Endah Purnomosari Fadil Abdullah Liana Dwi Fitrianti Uni Kusyanti Valentinus Galih Vidia Putra WITRI AINI SALIS Wiwiek Eka Mulyani