Judul: Environmental conditions related to community structure of macrozoobenthos in Belumai River District of Deli Serdang, North Sumatera Province.
Abstrak: Belumai River is one of the rivers in Deli Serdang Regency, North Sumatra Province. Activity along Belumai River basin includes the activity of industrial, domestic and agricultural activities. The Belumai River used by some people for bathing, washing, toilet (MCK). People who use the river water susceptible of contracting diseases including skin irritation and eye irritation. Belumai River environment has a very important component of people lives around the river. Increasing of development activities such as input from industrial waste, urban sewage and runoff of agricultural water carried by the currents have an impact on water quality degradation Belumai River. The high activities have affected the composition and abundance of species makrozobentos in the Belumai River. Only those species that are tolerant of the environment can still survive. The purpose of this research is to analyze the relationship environmental conditions with community structure of macrozoobenthos. This research was conducted in Belumai River Deli Serdang Regency, North Sumatra Province, on 4 stations for 3 months, with a time interval of 1 month. Determination of the station, based on consideration of the different input load from any location, thus defined three sub-districts into the sampling site, which is 1 station in the district of STM Hilir, station 2 and station 3 in the District of Tanjung Morawa, and 4 station in the District of Batang Quiz. Samples collected consisted of physical parameters, namely temperature, currents, depth, turbidity, and type substrate. Chemical parameters namely pH, DO, COD and TOM. Macrozoobenthos was collected as biological parameter. Macrozoobenthos were found during research in Belumai River consists of 3 classes (gastropods, insects and Oligochaeta). Station 1 genus number obtained during the observation that there are 5 genera : Branchiura sp., Chironomus sp., Lumbricus sp., Melanoides sp., and Bellamya sp. Station 2 genus number obtained during the observation that there are 4 genera : Branchiura sp., Lumbricus sp., Limnodrilus sp., and Goniobasis sp. Station 3 genus number obtained during the observation that there are 5 genera : Branchiura sp, Lumbricus sp., Limnodrilus sp., Goniobasis sp., and Tubifex sp. Station 4 genus number obtained during the observation that there are 6 genera : Branchiura sp., Lumbricus sp. , Limnodrilus sp., Goniobasis sp., Chironomus sp., and Goniobasis sp. Type uniform distribution of each station is visible from the class Oligochaeta Branchiura sp., and Lumbricus sp. The percentage of the composition of each class is the Oligochaeta 79%, Gastropoda 17%, and Insects 4%. Oligochaeta has the highest percentage with 79%. The high percentage indicates the existence of a class Oligochaeta Belumai River has been polluted. Oligochaeta are a tolerant organisms and able to withstand environmental conditions containing high organic matter. Diversity of macrozoobenthos in Belumai River based on analysis of k-dominant curve shows that the diversity decreases in the downstream direction. seen from the station groupings based on the analysis of Bray-Curtis Dissimilarity for macrozoobenthos and Pearson for physico-chemical parameters, resulting in two dendrogram which shows similarities. Both the dendrogram showed distinct groupings that station 1 to station 2, 3, 4. The existence of these groups due to differences in the input
Keyword: Belumai River, river water quality, diversity of macrozoobenthos

Judul: Struktur Komunitas Makrozoobentos sebagai Bioindikator Kualitas Lingkungan Perairan Hilir Sungai Musi
Abstrak: One of the problems exist on this time was more decreased it water quality of Musi river especially at downstream part as consequence the increasing of various activity antropogenic and industrial activity in downstream waters of Musi river. The research was done from April to July 2007 by purposive random sampling method at 18 stations and analisys in representative laboratory. The purpose from this research can give based information about characteristics of changes structure of makrozoobenthos community was can be used as bioindicator about environmental quality in downstream waters of Musi river. Results of this research was found 25 species macrozoobenthos devided into 6 class and 3 phyllum. There is Tubifex sp, Lumbriculus sp, Haplotaxis sp, Branchiura sp, Nereis sp, Nepthys cormuta, Cossura sp, Chironomous sp, Hydropsche sp, Polycentropus sp, Palpomya sp, Gomphoides sp, Bellamya javanica, Bellamya sumatrensis, Melanoides tuberculata, Anentome sp, Pila ampullacea, Thiara sp, Corbicula javanica, Anodonta woodiana, Gammarus sp, Namalycastis sp, Cirratulus sp, and Physa sp. The highest density was dominated by class Oligochaeta that is Tubifex sp were 86.94 % in April and 87.74 % in July 2007. Based on study biology parameter showed that the environmental quality in downstream waters of the Musi river was categorized into 3 groups that is group 1 ; heavy polluted (poor water quality) the marked of existence lower diversity index, higher density and higher dominance index were dominated species Tubifex sp in April and July 2007 was found at the stations Musi Kramasan, Muara Ogan, Ampera, Wilmar, Pusri, and Hoktong, group 2 ; moderate polluted (fair water quality) was found at the stations Gandus, Pre Ogan, Sungai Kundur, Pulau Borang, PT. SAP, SST. Pulau Burung and Tanjung Buyut were the marked diversity index low to moderate, lower density and lower to moderate dominance index lower to moderate with the species marked is Hydropsche sp, group 3 ; light polluted (good water quality) was found at the stasiun Pulokerto, Upang, Pre Selat Cemara, Selat Cemara and Pulau Payung the marked with diversity index and was by moderate and lower dominance index were dominated Gammarus sp. From the results was found several tolerant species that can be used as bioindicator environmental quality in downstream waters of Musi river is Tubifex sp, Lumbriculus sp, Nereis sp and Chironomous sp was categorized as heavy pollution indicator (poor water quality), Facultative species is Hydropsche sp as indicator light to moderate pollution and Gammarus sp as indicator clean water restoration zone (self-purification).
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Judul: Invers dari Matriks Tridiagonal Jacobi
Abstrak: Suatu matriks berukuran n×n dinamakan matriks tridiagonal jika untuk . Karya ilmiah ini memberikan algoritma yang mudah untuk menemukan invers ( dari matriks tridiagonal Jacobi yang simetrik dan nonsimetrik. Setiap elemen pada matriks tridiagonal ini adalah bilangan real. Terdapat 3 lema dan 2 teorema untuk menentukan . Lema pertama menunjukkan persamaan utama dalam membuktikan lema-lema dan teorema-teorema selanjutnya. Invers dari matriks yang simetrik dibuktikan oleh lema kedua yang menunjukkan elemen-elemen baris ke- dari . Selanjutnya, lema kedua dilengkapi dengan teorema pertama yang menunjukkan elemen-elemen dengan . Invers dari matriks yang nonsimetrik dibuktikan oleh lema ketiga yang menunjukkan elemen-elemen dengan dan elemen-elemen dengan dibuktikankan oleh teorema kedua.
Keyword: symmetric, nonsymmetric, matrix