Studying the Dynamical Properties of 20 Nearby Galaxy Clusters

Using SDSS-DR7, we construct a sample of 42382 galaxies with redshifts in the region of 20 galaxy clusters. Using two successive iterative methods, the adaptive kernel method and the spherical infall model, we obtained 3396 galaxies as members belonging to the studied sample. The 2D projected map for the distribution of the clusters members is introduced using the 2D adaptive kernel method to get the clusters centers. The cumulative surface number density profile for each cluster is fitted well with the generalized King model. The core radii of the clusters' sample are found to vary from 0.18 Mpc \mbox{h}^{-1} (A1459) to 0.47 Mpc \mbox{h}^{-1} (A2670) with mean value of 0.295 Mpc \mbox{h}^{-1}. The infall velocity profile is determined using two different models, Yahil approximation and Praton model. Yahil approximation is matched with the distribution of galaxies only in the outskirts (infall regions) of many clusters of the sample, while it is not matched with the distribution within the inner core of the clusters. Both Yahil approximation and Praton model are matched together in the infall region for about 9 clusters in the sample but they are completely unmatched for the clusters characterized by high central density. For these cluster, Yahil approximation is not matched with the distribution of galaxies, while Praton model can describe well the infall pattern of such clusters.Comment: 16 pages, 8 figure

Corrosion study of pipeline material for seabed sediment in tropical climate

Corrosive environments such as marine sediments can cause corrosion to steel pipelines at any time when certain conditions are met. Seabed sediment could cause severe corrosion damage due to its corrosiveness to the pipelines buried under it. Many consequences could take place in case if there is incident in oil/gas pipelines. Successfully identifying elements of corrosion in marine sediment would enhance the future of steel structure protection and monitoring systems. This article focuses on the behaviour of corrosion rate of steel located near shore environment and the aim is to determine the effect of sediment on corrosion of steel. To investigate that, simulated near shore sediment conditions have been used where the steel coupons buried in sediments which have different characteristics. Weight loss technique has been implemented to determine the weight loss rate of the steel specimens. Based on the results of this study, metal weight loss increases as the duration of exposure to seabed sediment environment become longer. The sea sediment simulated condition has given significant levels of corrosion. Conclusively, the corrosion rate of steel in seabed sediment located in tropical region is complicated and further studies are suggested

Penerapan Strategi Belajar Aktif Learning Start With A Question (Lsq) untuk Meningkatkan Prestasi Belajar Siswa pada Pokok Bahasan Hidrokarbon di Kelas X SMA Negeri 10 Pekanbaru

Research on the application of active learning strategy type Learning Start With A Question (LSQ)) has been done to improve student's achievement on the subject of hydrocarbon in class X of SMAN 10 Pekanbaru. Form of the research is experiment research with pretest-posttest design. The sample consisted of two classes, X.5 class as experiment class and X.7 class as control class that randomly selected after testing normality and homogeneity. Experiment class was given by implementing active learning strategy type LSQ and the control class was given by conventional method. Analysis of data used t-test. Data of research obtained tcount > ttable (5,78 > 1,67). It means that using active learning strategy type LSQ can improve student's achievement on the subject of hydrocarbon in class X of SMAN 10 Pekanbaru. The category improvement of student's achievement in experiment class was high category (N-Gain =0,71) and in control class was medium category (N-Gain =0,51)

Penerapan Metode Pembelajaran Aktif Cooperative Script untuk Meningkatkan Prestasi Belajar Siswa pada Pokok Bahasan Struktur Atom di Kelas X Mia SMA Negeri 1 Kepenuhan Kabupaten Rokan Hulu

Research on the application of active learning Cooperative Script method has been done in class X of SMAN Kepenuhan Kabupaten Rokan Hulu on the subject of atomic structure. Based on the results of observations conducted by researchers at the SMAN1Kepenuhan Kabupaten Rokan Hulu do known that learning is teacher centered, so that students become less active and negatively affect student achievement. The objective was to determine the increase in student achievement and increase student achievement category. The research form is an experimental research with pretest-posttest design. The sample consisted of two classes, namely class X MIA1 as the experimental group and the class X MIA2 as the control group. The experimental group is the group of students who were treated by applying the active learning of Cooperative Script method, while the control group was treated with information discussion methods. Data analysis technique used is the t-test. The results showed tarithmetic>ttable (2,07 > 1,68) and N-gain of the experimental group is 0,754 which includes the high category. Therefore, it can be concluded that the application for active learning Cooperative Script method can increase student achievement in the subject of anatomic structure in SMAN 1 Kepenuhan Kabupaten Rokan Hulu