Judul: Sintesis Hidroksiapatit Berpori dari Cangkang Telur Ayam dengan Matriks Selulosa Nata De Coco dan Natrium Alginat
Abstrak: This research has been done on the synthesis of porous hydroxyapatite from hen eggshells with nata de coco cellulose and Na-alginate matrix. The method used for synthesis of HAp powder is wise drop precipitation, whereas for synthesis of HAp/cellulose and HAp/alginate composites, cellulose immersion and phase separation method were used. The products are HAp powder, scaffold shaped HAp/alginate, and sheet shaped HAp/cellulose composites. XRD characterization results have shown a diffarction pattern that indicated HAp phase with degree of crystallinity more than 80% for HAp powder and more than 50% for composite of HAp/cellulose. FTIR characterization results have shown an absorption spectral clusters of constituent HAp compound and composite of HAp/algiate compound. Scan results using SEM showed that composite of HAp/alginate has porosity structure with enough regularity and size variation start from 93 μm until 182 μm. EDX analysis produced a spectrum of element which present in the composites. The Ca/P ratios based on mass percentage from EDX analysis of HAp/alginate composite are 1.84 and 1.86, while for HAp/cellulose composite are 1.43 and 1.45. The used of CaCl2 as corsslink agent were thought to be the factor that increase the Ca/P ratio in HAp/alginate composite.
Keyword: nata de coco cellulose., Na-alginate, composite, porous hydroxyapatite

Judul: Sintesis Hidroksiapatit Berpori dari Cangkang Telur Ayam dan Porogen dari Kitosan
Abstrak: This research had been done the synthesis of porous hydroxyapatite (HA) by presipitasi method. The precusor calcium using come from eggshells and (NH4)2HPO4 as phosphate source. The ratio of HA-chitosan to synthesize porous HA are 90:10, 80:20, 70:30, 60:40, and 50:50 and variation of chitosan size are 0.26 μm and 625.45 μm. The phase and crystaline structure of sample characterized by X-Ray Diffractometer. For sample with chitosan size 100% HA phase obtained. The biggest size of chrystaline gotten of HA_X60 sample by 63,83 nm. The functional groups of HA identified by Fourier Transform Infrared Spectroscopy. The functional groups of HA which detected by are OH-, PO4 3-, and CO3 2-. The morphological structure of sample analyzed by Scanning Electron Microscopy. The result of sampel HA had shown the porouses structure with chitosan as porogen however its size is quite small. In the order of about 0.2 – 1.6 μm in the form of cyrcle and the ditribution of porouses is smooth. Variation of chitosan size as porogen is not significant and has no effect to the crystal size.
Keyword: presipitasi., porous, hydroxyapatite, eggshells, Chitosan

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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