Judul: Invers dari Matriks Circulant
Abstrak: Matriks circulant adalah matriks yang entrinya bergeser satu kolom ke kanan secara berurutan, sehingga untuk mengetahui entri dari matriks circulant dapat dilihat dari kolom pertama ataupun baris pertama. Salah satu sifat yang dimiliki matriks circulant, yaitu inversnya juga berupa circulant. Sehingga, untuk mencari invers matriks dari circulant dapat dilakukan dengan mencari entri di baris pertama atau di kolom pertama. Pada karya ilmiah ini ditentukan invers matriks circulant dengan menggunakan metode discrete Fourier transform dan sifat-sifat kenormalan pada matriks circulant.
Keyword: Matriks circulant, discrete Fourier transform, kenormalan matriks

Judul: Determinan dan Invers Matriks Circulant dengan entri Jacobsthal Numbers.
Abstrak: Matriks circulant adalah matriks yang entrinya bergeser satu kolom ke kanan secara berurutan, sehingga untuk mengetahui entri dari matriks circulant dapat dilihat dari satu kolom ataupun satu baris dari matriks tersebut. Salah satu sifat yang dimiliki matriks circulant, yaitu inversnya juga berupa circulant. Entrientri dari matriks circulant dapat diisi dengan berbagai entri, salah satunya adalah bilangan-bilangan yang membentuk suatu barisan bilangan. Salah satu barisan bilangan adalah Jacobsthal Number. Pada karya ilmiah ini ditentukan determinan matriks circulant dengan entri Jacobsthal Number menggunakan sifat determinan ketika matriks tersebut sudah dibentuk menjadi matriks segitiga atas dan mencari invers matriks tersebut cukup dengan mencari entri-entri pada baris terakhir dari matriks invers tersebut dengan memanfaatkan teorema invers dari matriks direct sum.
Keyword: bilangan Jacobsthal, determinan, inverse, matriks circulant

Judul: Pengaruh Jumlah Bahan Pretanning dan Minyak Biji Karet (Hevea brasiliensis) Terhadap Mutu Kulit Samoa. Di
Abstrak: Animal hides or skins are the most valuable by product of the meat industry. Most of those hides are converted into leather by leather tanning process. Chrome based tanning is the most popular tanning process. At the chrome based tanning process, a lot of amount chrome are throw away into the environment that make a significant effect to the biological and ecological environment damaged. Due to concerns over the use and disposal of chromed tanned leather, the leather industry is now facing increasing scrutiny over its use of chrome as tanning agent. The use of non-chrome tannages has gradually become pre-eminent to producing leather, particularly in the European automotive leather markets. Chamois leather is one of leather product. It is produced from animal hides/skins by oil tanning process, usually with fish oil. High price and odour problems to the chamois leather that produced using fish oil motivate to do some research to solve that problems. Rubber seed oil is an oil that predicted can substitute fish oil. Pretanning process is needed to increase the oil penetration and protects the pelt from putrefying during oxidation periods (Khrisnan et al., 2005). Relugan GT 50 is the agent that used on this research. Relugan GT 50 is an aldehyde tanning agent, produced by BASF. This research was aimed to find out the effects of Relugan GT 50 concentration (offer) and rubber seeds (Hevea brasiliensis) oil to the chamois leather’s quality. Beside that, this research is also aimed to decide the best combination of the factors to produce chamois leather also to know the chamois leather characteristics. The preliminary research was carried out by analyzing the rubber seed’s kernel and eggshell as well as physico-chemical properties of the rubber seed oil. The main research was done by tanning the skin with Relugan GT 50 in concentrations of 1.5, 3.0 and 4.5% followed by rubber seed oil concentrations of 10, 20, and 30%. The experimental design used was completely randomize factorial design. The preliminary research shows that rubber seed’s kernel was 49% and rubber seed’s eggshell was 51%. The rubber seed’s oil characterstics were density of 0.94 (g/cm3), viscosity of 48,4 centistokes, colour of 2713 PtCo units, inodine value 113 g iod/ 100 g, peroxide value of 24 miliequivalent/1000 gram oil, acid value of 15 mg KOH/g oil and FFA content of 5.8%. The research shows that Relugan GT 50 concentration significantly affected shrinkage temperature (Ts) and pH; rubber seed oil concentration significantly affect the organoleptic properties of the leather. The optimum conditions for the tanning were Relugan GT of 3.0% concentration and 10% rubber seeds oil. The physical properties of the leather were shrinkage temperature of 75oC, thickness of 0.92 mm, tensile strength of 21.50 N/mm2, elongation at break of 144%, tear strength of 55.77 N/mm, water absorption of 266% (2 hours) and 299% (24 hours). The chemical properties were oil content of 2.5%, ash content of 1.2% and pH of 8. The organoleptic properties were softness of 7–8, colour of 8-9, and odour of 8-9.
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