Judul: Disain dan kinerja pisau sadap elektrik untuk tanaman karet (hevea brasiliensis)
Abstrak: Rubber tree tapping is usually done using a manual type tapping knife. By using this knife, bark consumption and cutting depth can not be controlled. To solve the problem, it is important to develop a mechanized or electric tapping knife which can control bark consumption and cutting depth. The objectives of this study were to design and to test the working performance of an electric tapping knife. For determining the cutting power, bark cutting resistance of 5-17 years old rubber trees were measured using a tapping knife which is equipped with a ring transducer. A reciprocating chisel mechanism was chosen for cutting the bark, and was driven by an electric DC motor. The electric tapping knife was designed for downward tapping system, and equipped with rolls for controlling bark consumption and cutting depth. It was powered by a 66 Watt electric DC motor, and operated by a tapper. The prototype was tested on 5, 6 and 8 years old rubber trees. The test result showed that the bark consumption could be controlled in the range of 1.8-2.1 mm. Bark cutting depth was 0.9-1.2 mm, which was shallower than the normal cutting depth (1.5 mm from cambium). However, the bark cutting by the prototype was smooth and did not wound cambium layer and wood. The shallower cutting depth caused a lower latex yields in the range of 45- 66% lower than normal yield. Cutting duration using the prototype was 14-22 second per tree, which was longer than manual tapping duration (6-8 second). Tapping groove resulted by the electric tapping knife was tidy, uniform, and halfspiral shaped.
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Judul: Modifikasi Pisau Sadap Karet dengan Mekanisme Kontrol Ketebalan Sadapan dan Pencegahan Pelukaan Kambium pada Tanaman Karet
Abstrak: Tapping techniques determine the productivity of rubber plant. Good tapping is done at deepness of 1 mm from the cambium and thickness among 1.5-2 mm. In practice, it is difficult to prevent the wounding of cambium cause tapping too deep so the shape of recovered skin became irreguler and difficult to tap. The thickness of tapping affect the economic life of the rubber tree. If the thickness exceed 2 mm, tapping fields will quickly run out. Modified rubber tapping knife could control the thickness of tapping and prevent the wounding of cambium due to tapping. This knife tapped on the average thickness of 1.96 mm and 6.57 mm of deepness, does not exceed of the rubber skin that is 8.55 mm. Then statistical test was conducted to determine the effect of the thickness of tapping and latex production. The result showed that the thickness of tapping (above 1.5-2 mm) was not significant to amount of latex production. So tapping by using the modified rubber tapping knife can save tapping field untill 66%.
Keyword: deepness of tapping, thickness of tapping, rubber tapping knife, tapping

Judul: Approximation of the Median of Poisson Distribution Using the Relation of Poisson-Gamma Distribution
Abstrak: A major drawback of median is that median cannot usually be defined in closed form, even in the cases where their distribution functions are known. This study gives an approximation of the closed form for the median of the Poisson distribution by using the relation of Poisson-Gamma distribution. The approximation uses elementary techniques based on the monotonicity of certain sequences involving tail probabilities of the Poisson distribution and the Central Limit Theorem. Furthermore, a closed form expression for the mean absolute deviation 􀜧|􀜰􀰒 􀵆 􀜯􀝁􀝀􁈺􀜰􀰒􁈻| is also studied. The median is relevant because of the fact that it minimizes the mean absolute deviation of a Poisson random variable (􀜰􀰒􁈻 by considering median as central tendency.
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