Judul: Synthesis and characterization of hydroxyapatite from seashell wastes of anadara granosa
Abstrak: Hidroksiapatit merupakan senyawa kalsium fosfat yang merupakan komponen utama dari tulang dan gigi yang mempunyai sifat dapat berikatan dengan tulang alami. Hidroksiapatit merupakan senyawa mineral dari kelompok mineral apatit dengan rumus kimia Ca10(PO4)6(OH)2 dan mempunyai struktur heksagonal dengan parameter kisi a = 9.443 Ǻ dan c = 6.875Ǻ serta nisbah Ca/P sekitar 1.67. Kristal apatit banyak mengandung gugus karbon dalam bentuk karbonat. Pada struktur hidroksiapatit, karbon dapat menggantikan ion OH- membnetuk kristal apatit karbonat tipe A, dan bila menggantikan ion PO43- Sintesis serbuk hidroksiapatit telah dilakukan dengan berbagai sumber Ca dan P, diantaranya kalsium nitrat (Ca(NO membentuk kristal apatit karbonat tipe B.
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Judul: Sintesis dan Pencirian Hidroksiapatit dari Limbah Cangkang Kerang Hijau dengan Metode Kering
Abstrak: Hydroxyapatite (HAp) is a calcium phosphate biomaterial utilized in medicine as bone implant and dental fillings. HAp has been synthesized from green mussel shells with dry method. Calcination of green mussel shells at 1100 oC for 18 hours produced CaO with 97.83% crystallinity. Contact of CaO with the air for a night produced Ca(OH)2 with 85.45% crystallinity. Heating of CaO and Ca(OH)2 as the starting materials at 900 and 1100 °C for 2 hours produced HAp as characterized by using X-ray diffractometer (XRD), Fourier transform infrared (FTIR) spectrophotometer, and scanning electron microscope (SEM). The best HAp result was obtained from CaO material. The XRD diffractogram showed the formation of HAp phase accompanied by other calcium phosphate phase at 2θ angles matched with Joint Crystal Powder Diffraction Standard data. The FTIR spectra showed the presence of PO4 3– and OH– groups of the HAp and the SEM picture showed homogenous HAp crystal granule size. With additional treatments, the HAp pore size can be adjusted to be applied as bone implant or dental fillings.
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Judul: A Continuous Vaccination Strategy in the SVIR Epidemic Model
Abstrak: Vaccination is conducted to minimize the spread of a disease. The vaccination is usually done several times within a fixed time interval. In the SVIR model, it is assumed that individuals do not get immediate immunity following a vaccination program. So according to process of vaccination on SVIR model, there are two strategies, i.e. the continuous vaccination strategy (CVS) and the pulse vaccination strategy (PVS). In this study, only the CVS strategy in epidemic model SVIR is considered. Results of the study indicate that dynamics of the CVS system depends on the basic reproductive number. If the basic reproductive number is less than one, then the disease-free fixed point is asymptotically stable. It means that the disease will eventually disappear from the population. Conversely, if the basic reproductive number is greater than one, then the endemic fixed point is asymptotically stable, which means that the disease will remain exist in the population. Simulation result shows that the vaccination would minimize the spread of disease by reducing the basic reproductive number. If the time for the vaccinated recipients to obtain the immunity, as well as a possibility of vaccinated recipients to be infected are neglected, then the disease will be eradicated. This condition is called an over-evaluating effect of vaccination.
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