Judul: Analisis Model Antrean Berulang M/G/1 dengan Prioritas Preemptive Resume dan Collisions pada Kerusakan Server dan Penundaan Perbaikan
Abstrak: Sistem antrean M/G/1 adalah sistem antrean dengan proses kedatangan pelanggan berdistribusi Poisson, waktu layanan pelanggan berdistribusi umum, dan server tunggal. Pada karya ilmiah ini, terdapat dua jenis pelanggan yaitu pelanggan positif dan negatif. Pelanggan positif akan dilayani seperti biasa oleh server dan diambil dari antrean sesuai dengan disiplin yang ditentukan, sedangkan pelanggan negatif yang tidak mendapat pelayanan mengakibatkan kerusakan pada server dan dapat menghapus pelanggan yang ada dalam layanan pada sistem. Disiplin antrean yang digunakan dalam model ini adalah disiplin prioritas preemptive. Dengan menyelesaikan persamaan diferensial untuk fungsi pembangkit peluang dalam kondisi steady-state, diperoleh peluang lama server sedang menganggur, sibuk melayani pelanggan, menunggu perbaikan, dan sedang dalam perbaikan, serta ukuran kinerja lainnya. Kemudian, diperoleh juga nilai harapan periode sibuk., The M/G/1 queue system is a queue system with arrival process of customers follows Poisson process, customer service time has a general distribution, and has single server. In this manuscript, there are two types of customers, namely positive and negative customers. The positive customers are treated in the normal way by a server and are taken from a queue according to the specified queueing system, while the negative customer, which does not receive service, causes the server breakdown and removes the customer being in service from the system. The queue discipline used in this model is preemptive resume priority. By solving the differential equation for the probability generating function in steady-state condition, the probability that the server is idle, busy serving a customer, waiting for repair and under repair, and other performance measure was obtained. Finally, the expected value of busy period was obtained as well.
Keyword: expected value, Poisson, probability, retrial queue

Judul: The Expected Value of the Queueing Length on the M/M/1 Queue Model Which Can be Repaired by Considering the Damage Level
Abstrak: Suatu antrean terjadi karena jumlah pelanggan yang datang melebihi jumlah fasilitas yang disediakan. Sistem dapat diandalkan saat server mungkin mengalami kegagalan atau kerusakan dan server dapat segera diperbaiki. Pada karya ilmiah ini, ditinjau sistem antrean M/M/1 yang dapat diperbaiki dengan mempertimbangkan tingkat kerusakan, dengan proses kedatangan pelanggan berdistribusi Poisson. Saat server mengalami kerusakan pada waktu kosong atau waktu sibuk, server segera menuju proses perbaikan. Setelah periode perbaikan selesai, server kembali dengan kondisi baru dan dapat melanjutkan sistem. Kemudian, dengan menyelesaikan persamaan diferensial untuk fungsi pembangkit peluang pada peluang steady-state, formulasi dari nilai harapan panjang antrean pada sistem dapat diperoleh. Simulasi numerik pengaruh parameter terhadap nilai harapan panjang antrean menunjukkan bahwa perubahan panjang antrean dan laju waktu perbaikan sensitif terhadap laju pelayanan, serta panjang antrean rata-rata dipengaruhi oleh laju tingkat kerusakan pada waktu sibuk dan laju waktu perbaikan., A queue occurs because the number of customers who come exceeds the number of provided facilities. The system can be relied on when the server may experience failure or damage, but it can be repaired immediately. In this manuscript, the M/M/1 queuing system that can be repaired by considering the level of damage is reviewed, where the customers arrival process is Poisson distributed. When the server crashes at an idle time or busy time, the server immediately goes to the repairing process. After the repairing process is over, the server returns with a new condition and the server’s operation can be continued. Furthermore, by solving the differential equation for the probability generating function at steady-state probability, the formulation of the expected value of the queue length in the system can be obtained. Numerical simulation of the effect of parameters on the expected value of queue length shows that changes in queue length and repairing time are sensitive to service rates, and the average queue lengths usually are affected by damage rates at busy times and repairing times rate.
Keyword: queue, probability generating function, expected value, repairable system

Judul: Elektrodeposisi Film Tipis Semikonduktor Cu2ZnSnS4 (CZTS) pada Substrat Kaca ITO
Abstrak: Semiconductor Cu2ZnSnS4 (CZTS) thin film that can be used as absorber layers on solar cell module was made via electrodeposition method. CZTS thin film was electrodeposited on the surface of a silicate glass coated with a thin layer of indium tin oxide (ITO). Deposition process was done using potentiostatic mode at room temperature with a potential of 1.05 V for 30, 45, and 60 minutes, followed with annealing the film at 2 different temperatures, 500 ºC using furnace and 180 ºC using hot plate, both treatments for 45 minutes in N2/H2S atmosphere. The X-ray difractograms were analyzed using Match 2 program and showed that the CZTS thin films had kesterit crystalline structure, with a low percentage of CZTS phase. The thin film also contained secondary phases such as Cu2S, ZnS, and SnS. The obtained CZTS thin films had a thickness between 1.039 and 1.676 μm. Absorption study showed that the band gap energy of CZTS thin films which was annealed using furnace ranged from 1.50 to 1.52 eV, whereas that annealed using the hot plate was not observed. The band gap energy value showed that CZTS thin films can be used as sunlight absorber layers on solar cell. The formation of CZTS crystal film on this investigation was effectively performed using furnace annealing process at a temperature of 500 ºC with deposition time of 45 minutes.
Keyword: Thin film, Electrodeposition, Cu2ZnSnS4