Judul: Freeze Drying Characteristics of Strawberry  (Fragaria virginiana)
Abstrak: Buah stroberi yang kaya akan karbohidrat dan vitamin C, biasanya dikonsumsi segar atau diolah menjadi selai, jus, manisan dan sirop. Namun stroberi merupakan produk hortikultura yang mudah rusak (perishable) dan sangat rentan terhadap serangan hama/penyakit. Oleh karena itu perlu dilakukan penanganan pascapanen agar kualitas dapat dipertahankan. Salah satu teknik pengolahan untuk memperpanjang masa simpan stroberi adalah dengan pengeringan beku (freeze drying). Penelitian ini bertujuan untuk mengetahui karakterisitik pengeringan beku dan pengaruh teknik pengeringan beku terhadap mutu stroberi kering beku. Penelitian dilakukan di Laboratorium Departemen Teknik Mesin dan Biosistem dan Pilot Plant STP IPB Taman Kencana Bogor. Bahan yang digunakan adalah stroberi yang diperoleh dari petani di Lembang, Kabupaten Bandung Barat, Bandung. Umur petik 14 – 16 hari setelah awal pembentukan buah (HSPB). Tahapan penelitian terdiri dari persiapan sampel, pembekuan, pengeringan beku, dan pengamatan mutu. Pembekuan dilakukan selama 110 hingga 120 menit hingga suhu bahan mencapai kisaran -12°C hingga -15 °C. Pengeringan beku dilakukan selama 12 jam, 24 jam, dan 36 jam. Rancangan percobaan yang digunakan adalah Rancangan Faktorial yang disusun secara Acak Lengkap (Faktorial RAL) dengan faktor pertama tekanan (0,5 mbar dan 0,1 mbar) dan faktor kedua lama pengeringan (12 jam, 24 jam dan 36 jam) dengan 2 kali ulangan. Parameter mutu yang diamati meliputi laju pengeringan, susut bobot, kekerasan, total padatan terlarut, rasio rehidrasi dan nilai kesukaan/hedonik. Hasil penelitian menunjukkan tekanan berpengaruh nyata terhadap laju pengeringan, kadar air, susut bobot, kekerasan, total padatan terlarut, rasio rehidrasi dan uji organoleptik rasa dan tekstur, tetapi tidak berpengaruh nyata terhadap uji organoleptik warna dan aroma. Lama pengeringan berpengaruh nyata terhadap laju pengeringan, susut bobot, kekerasan, total padatan terlarut, rasio rehidrasi dan uji organoleptik rasa, warna, dan tekstur, tetapi tidak berpengaruh nyata terhadap uji organoleptik aroma. Pengeringan beku pada tekanan 0,1 mbar dan lama pengeringan 36 jam menghasilkan stroberi kering beku yang paling baik dengan laju pengeringan 9,90 %bk/jam, kadar air 9,64 %bb, penurunan susut bobot 81%, TPT 13,51 °Brix, dan kekerasan 7,47 kgf . Penilaian terhadap organoleptik menunjukkan bahwa tekanan 0,1 mbar dan lama pengeringan 36 jam menghasilkan produk stroberi kering beku dengan tingkat penerimaan panelis yang lebih baik berdasarkan penilaian terhadap rasa dan warna dengan skor 5 (agak suka)
Keyword: Strawberry, freeze drying, physical propesties, product quality

Judul: Manufacture of dried strawberry (Fragaria sp)and quality changes during storage
Abstrak: Strawberries are one of the fruits are perishable, this is because the smooth texture of strawberry skin’s so easily scratched and then it will decay, apart from that the water content in strawberries is very high. So that needs to be done to improve the shelf life handling of fruit, one of the means used for curing is the drying of fruit. Dried Strawberries are one of the processed products are preferred by consumers, this is because the strawberries that have a sour taste will be reduced due to the addition of sugar during the drying process. In addition it will be more chewy texture of the fruit because decrease water content in strawberries. Making dried strawberries has two factors that influence the concentration of preservatives and long soaking the fruit in sugar solution. Preservatives used in the manufacture of dried strawberries is sodium metabisulfite. The selection of sodium metabisulfite is because compared with other sulfite compounds, sodium metabisulfite most stable. In addition sulfite salt is a material that is not harmful to the body, because these compounds can be oxidized to sulfate which can be excreted with urine. From the results of preference tests with three parameters: taste, color, and texture of the resulting rank of 30 panelists most preferred is the interaction between sodium metabisulfite 300 ppm and 72 hours immersion. Test the quality changes during the four weeks that the water content of the above also shows that the interaction does not change significantly.
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Judul: Hamiltonian formulation for linear waves motion in two layers fluid
Abstrak: The surface wave could be considered as a wave that separates two fluids, namely water and air. Based on this assumption, it is introduced the interfacial wave, a wave between two layers of fluid with different density. The formulation of interfacial waves motion begins with deriving the base equation of irrotational ideal fluid. Furthermore, according to irrotational fluid assumption, the base equation can be stated in velocity potential. In this derivation, the fluids domain is assumed to be restricted by rigid lid boundary conditions, both at the upper and lower limit. Therefore, the interfacial waves motion can be explained in a hamiltonian formulation. In the hamiltonian formulation, total energy is defined as the sum of kinetic and potential energy. The hamiltonian system is obtained from reduction of kinetic energy by using the Dirichlet Neumann Operator. The resulted kinetic energy equation is nonlinear. Therefore, this form is linearized by first part of the Taylor expansion. This linearization gives a dispersion relation of linear wave. Based on this dispersion relation, the phase speed of the linear wave depends on the density ratio of the two layers fluid.
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