Judul: Correlation between Digit Ratio (2D:4D) with Hand Grip Strength in Indonesian Adult Men
Abstrak: Rasio digit jari 2D:4D merupakan biomarker alami yang telah banyak digunakan untuk mengetahui paparan hormon testosteron prenatal yang dapat berpengaruh terhadap tingginya peforma kekuatan seseorang. Rasio ini juga mempengaruhi hal- hal lain seperti tinggi badan dan kekuatan tangan. Namun, di Indonesia penelitian mengenai keterkaitan ini masih sedikit dilaporkan. Oleh karena itu, penelitian ini bertujuan mengetahui pengaruh rasio digit jari 2D:4D terhadap kekuatan genggaman tangan (Hand Grip Strength) pada laki-laki dewasa Indonesia. Hasil penelitian menunjukkan rasio digit jari (2D:4D) memiliki korelasi negatif terhadap kekuatan genggaman pada kedua tangan, yang dapat diartikan semakin rendah rasio digit jari maka semakin tinggi kekuatan genggaman. Beberapa faktor lain seperti tinggi badan, berat badan serta BMI juga memiliki korelasi positif yang signifikan terhadap kekuatan genggaman. Namun, hanya faktor umur yang tidak memiliki pengaruh yang signifikan dikarenakan tidak meratanya kisaran umur sampel yang diambil., The 2D:4D digit ratio is a natural biomarker that has been widely used to determine prenatal testosterone exposure, which can affect a person's high strength performance. This ratio also affects other factors, such as height and hand strength. However, research on this linkage in Indonesia is still limited. Therefore, this study aims to determine the effect of the 2D:4D digit ratio on hand grip strength in Indonesian adult men. The results showed a negative correlation between the finger digit ratio (2D:4D) and grip strength in both hands, indicating that a lower finger digit ratio corresponds to higher grip strength. Several other factors, including height, weight, and BMI, also showed a significant positive correlation with grip strength. However, the age factor had no significant effect due to the uneven age range of the sampled individuals.
Keyword: biomarkers, finger digit ratio, hand grip strength, testosterone

Judul: Prenatal Testosterone Exposure to Socio-Cognitive Ability and Digit Ratio (2D:4D) in IPB University Students
Abstrak: According to the Empathizing-Systemizing Theory, higher levels of prenatal testosterone improve the ability to analyze complex systems while in the other hand inhibiting empathy (socio-cognition). Effect of prenatal testosterone exposure also expressed in finger (2D:4D) digit ratio, resulting in male have smaller digit ratio than female. This research was aimed to investigate differences between sexes in socio-cognitive ability, digit ratio and their relationship among IPB University Students. Consistent with previous studies, male achieved lower score than female in cognitive empathy task (Reading the Mind in the Eyes test), with average correct answer 19.83 and 21.33 respectively. However no significant difference between sexes on self-report on empathy (Fisher Temperamental Inventory) is found. In case of digit ratio, the average digit ratio of male participant is 0.963 while female is 0.981. Even though the result shows decrement of socio-cognitive ability parallels to decrement of digit ratio, no statistical correlation is found between these parameters.
Keyword: empathy, prenatal testosterone, digit ratio

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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