Judul: Water Quality of River Inside and Outside the Sibual – Buali Nature Reserve Area, South Tapanuli
Abstrak: Cagar Alam (CA) Sibual – buali merupakan kawasan hutan konservasi yang berfungsi sebagai perlindungan sistem hidrologi, salah satunya yaitu aliran Sungai Aek Nabara dan Sungai Aek Sitandiang supaya tetap terjaga kualitas airnya dari kerusakan. Penggunaan lahan sempadan sungai di luar kawasan CA akan berpengaruh terhadap perubahan kualitas perairan dibawahnya. Penelitian ini bertujuan untuk mengkaji status kualitas air Sungai Aek Nabara, dan Sungai Aek Sitandiang di dalam kawasan dan perubahannya di luar kawasan Cagar Alam Sibual – buali. Penelitian dilakukan di Sungai Aek Nabara dan Sungai Aek Sitandiang. Metode pengumpulan data berupa data fisik kualitas air, pengambilan spesimen makrozoobenthos, dan data beban pencemaran. Pencemaran di dalam kawasan cagar alam lebih rendah dibandingkan dengan di luar kawasan cagar alam dan pengaruh potensi beban pencemaran Sungai Aek Nabara dan Aek Sitandiang masih relatif kecil pada masing – masing sumber pencemar. Beban pencemaran total masing – masing sungai tergolong rendah sehingga mendukung status pencemaran kedua sungai pada kategori rendah. Kata kunci: Aek Nabara, Aek Sitandiang, Cagar Alam Sibual – buali, kualitas air, The Sibual - Buali Nature Reserve (CA) is a conservation forest area that functions as a protection for the hydrological system, one of which is the Aek Nabara River and Aek Sitandiang River to maintain its water quality from damage. Use of riparian land outside the CA area will affect changes in the quality of the waters below. This study aims to assess the water quality status of the Aek Nabara River and Aek Sitandiang River in the area and its changes outside the Sibual - Buali Nature Reserve. The research was conducted in the Aek Nabara River and Aek Sitandiang River. The data collection methods are physical water data, water quality data, macrozoobenthos specimen collection, and pollution load data. Pollution inside the nature reserve area is lower than that outside the nature reserve area and the effect of the potential pollution load of the Aek Nabara and Aek Sitandiang rivers is still relatively small at each pollutant source. The total pollution load of each river is classified as low so that it supports the pollution status of the two rivers in the low category. Keywords: Aek Nabara, Aek Sitandiang, Sibual – buali nature reserve, water quality
Keyword: Aek Nabara, Aek Sitandiang, Sibual – buali nature reserve, water quality

Judul: Effect of Land Use and Rainfall on Water Quality of the Cimandiri River, Sukabumi, Indonesia
Abstrak: Penurunan kualitas air di Sungai Cimandiri merupakan isu penting yang perlu diidentifikasi penyebabnya. Penggunaan lahan dan curah hujan di Daerah Aliran Sungai (DAS) diduga mempengaruhi kualitas air sungai. Penelitian bertujuan mengidentifikasi dampak penggunaan lahan dan curah hujan terhadap kualitas air Sungai Cimandiri. Metode penelitian dibuat menggunakan model regresi linear berganda (RLB) dan linear mixed method (LMM). Proporsi penggunaan lahan dan rata-rata curah hujan harian sebagai variabel bebas dan parameter kualitas air sebagai variabel terikat. Data penggunaan lahan, curah hujan, dan kualitas air yang digunakan adalah data periode 2017–2023. Parameter kualitas air yang digunakan, meliputi; total suspended solid (TSS), dissolved oxygen (DO), biochemical oxygen demand (BOD), chemical oxygen demand (COD), fosfat, dan fecal coliform. Hasil penelitian menunjukkan bahwa penggunaan lahan dan curah hujan memiliki hubungan terhadap parameter kualitas air. Penggunaan lahan memiliki pengaruh nyata (p < 0,05) terhadap parameter kualitas air, sedangkan curah hujan tidak berpengaruh nyata (p > 0,05) terhadap kualitas air secara statistik. Model regresi linear berganda untuk setiap segmen DAS memiliki kekuatan model yang bervariasi. Segmen tengah memiliki kekuatan model yang lebih baik dalam menjelaskan hubungan penggunaan lahan dan curah hujan terhadap parameter kualitas air dibandingkan segmen lain dengan nilai R2adj berkisar antara 51,32–96,05%. Linear mixed method mampu menjelaskan pengaruh segmen pada model hubungan seluruh DAS Cimandiri untuk parameter TSS (95,45%) dan DO (42,28%)., Water quality decreased in the Cimandiri River has become an important issue that requires identification of its root causes. Land use and rainfall patterns within the watershed (DAS) are presumed to influence river water quality. This study aims to identify the impacts of land use and rainfall on water quality in the Cimandiri River. The study methodology utilized multiple linear regression (MLR) and linear mixed model (LMM). The proportion of land use and average daily rainfall were utilized as independent variables, while water quality parameters served as dependent variables. The study utilized land use, rainfall, and water quality data from the period of 2017–2023. The water quality parameters assessed include total suspended solids (TSS), dissolved oxygen (DO), biochemical oxygen demand (BOD), chemical oxygen demand (COD), phosphate, and fecal coliform. The study findings indicate a correlation between land use and rainfall patterns and water quality parameters. Land use had a significant effect (p < 0.05) on water quality parameters, while rainfall did not have a statistically significant (p > 0.05) effect on water quality. The strength of the multiple linear regression models varied across watershed segments. The middle segment exhibited a better model fit in explaining the relationship between land use and rainfall with water quality parameters compared to other segments, with R2 adj values ranging from 51.32–96.05%. The linear mixed method effectively explained the influence of segments on the relationship model for the entire Cimandiri watershed for TSS (95.45%) and DO (42.28%) parameters
Keyword: Kualitas air sungai, Model campuran linear, Regresi linear berganda, linear mixed methods, multiple linear regression, water river quality

Judul: Penentuan Nilai Eigen dan Vektor Eigen dari Matriks Tridiagonal 2-Toeplitz dengan Pendekatan Polinomial Chebyshev
Abstrak: The eigenvalues and eigenvectors of a matrix can be determined by finding its characteristic polynomials. The characteristic polynomials of a tridiagonal 2-Toeplitz matrix is shown to be closely connected to polynomials which satisfy the Chebyshev recurrence relationship. If the order of the matrix is odd, then the eigenvalues are found explicitly in terms of the Chebyshev zeros and the eigenvectors are found in terms of the polynomials satisfying the recurrence relationship. For even ordered matrices, the situation is more complicated. The problem in these cases is that although the Chebyshev recurrence formula is still applied, its initial values are not generating Chebyshev polynomials
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