Karakterisasi Batuan Reservouir Pasir dengan Menggunakan Metode Hydraulic Flow Unit pada Sumur X

Pada ilmu logging, untuk mencari parameter berupa permeabilitas terdapat berbagai metode yangdinilai cukup akurat. Metode-metode yang biasa digunakan dalam mencari nilai permeabilitas antaralain adalah Timur, Tixier, Coates, dan Wylie-Rose. Pada perkembangannya terdapat metode baruyaitu metode Kozeny-Carman.Dengan metode Kozeny-Carman ini maka dikembangkan lagi suatumetode yang bernama HydraulicFlowUnit.Metode Hydraulic Flow Unit sendiri adalah suatu metodeyang menggabungkan antara atribut geologi batuan dengan data petrofisik yang ada sehingga akanmenghasilkan flow unit yang berbeda pada tiap batuan bergantung dari tekstur ataupunmineraloginya. Secara singkat HydraulicFlowUnit adalah pengelompokan batuan berdasar padaprinsip geologi dalam atribut aliran yang mengalir didalamnya. Pada tulisan ini perhitungan parameterpermeabilitas pada sumur “X” dengan Formasi Plover (gambar 1) menggunakan salah satu teoriberupa HydraulicFlowUnit. Dalam menentukan permeabilitas dengan menggunakan metodeHydraulic Flow Unit ini diperlukan data core yang berasal dari analisa core. Namun seperti yangdiketahui analisa core sendiri memakan biaya yang cukup banyak sehingga tidak setiap intervaldilakukan analisa core, oleh karena itu perlu dilakukan perhitungan permeabilitas pada intervalkedalaman yang tidak memiliki core. Untuk dapat menentukan permeabilitas pada interval kedalamanyang tidak memiliki core pada sumur “X”, terdapat metode statistik seperti Artificial NeuralNetwork.Metode ini tersedia pada software Interactive Petropyhsics. Dengan input data yang baikmaka perhitungan permeabilitas dapat dilakukan. Pada tulisan ini metode yang digunakan untukmencari parameter permeabilitas pada interval tidak ada core adalah metode Hydraulic Flow Unityang dibantu dengan metode statistik Artificial Neural Network. Penggunaan metode perhitunganpermeabilitas lainnya yaitu Timur dan Tixier dilakukan pula pada sumur “X”. Kedua metode empiris ininantinya akan di komparasi dengan metode Hydraulic Flow Unit terhadap sampel data core yangtersedia pada sumur “X”. Komparasi yang dilakukan memperlihatkan metode perhitunganpermeabilitas Hydraulic Flow Unit memiliki tingkat keakuratan yang lebih baik daripada metode Timurdan Tixier pada sumur “X

Spin-transfer switching and low-field precession in exchange-biased spin valve nano-pillars

Using a three-dimensional focused-ion beam lithography process we have fabricated nanopillar devices which show spin transfer torque switching at zero external magnetic fields. Under a small in-plane external bias field, a field-dependent peak in the differential resistance versus current is observed similar to that reported in asymmetrical nanopillar devices. This is interpreted as evidence for the low-field excitation of spin waves which in our case is attributed to a spin-scattering asymmetry enhanced by the IrMn exchange bias layer coupled to a relatively thin CoFe fixed layer.Comment: 11 pages, 4 figures. To appear in APL, April 200

On the biology and bioacoustic characteristic of spotted catfish arius maculatus (Thunberg 1792) from the Malaysian Estuary.

Estuaries of Matang mangrove reserves in Perak provide an ideal habitat for Arius maculatus population. Results of our survey showed that most of the fish species caught were in their sub-adult stages with size ranged between 11 – 21 cm SL as shown in length frequency analysis. The relative growth condition of the fish population was allometrically negative with “b” value < 3.0 (W = 0.040L2.78) respectively. Study on reproductive biology of the species showed that almost half of the specimens caught were comprised of maturing males and female’s gonad development attained stage II – III. Stomach content analysis demonstrated that A. maculatus was an excellent benthic feeder in muddy water environment. Three major food items have been listed and dominated by zoobenthos and benthic crustacean. Meanwhile bioacoustic study showed that the fish produced a distinct sound resulted from stridulation of pectoral fins. The roles played by Matang mangrove systems as an integral breeding and nursery ground for this particular species was also discussed

Surface Modification of an Experimental Silicone Rubber Maxillofacial Material to Improve Wettability

OBJECTIVES: Good wettability of maxillofacial prosthetic materials is important so hat a lubricating layer is formed with supporting tissues thus reducing patient discomfort. The purpose of the study was to surface modify an experimental silicone rubber material in order to improve wettability. METHODS : Samples of experimental silicone rubber were surface modified by first argon plasma treatment followed by chemisorption of ethyleneoxy functional silanes. These were compared with the same silicone rubber which had ethyleneoxy functional surfactants incorporated into the polymer matrix. In all cases contact angles, tear strength and water uptake were measured. RESULTS: Surface modified materials had comparable contact angles to surfactant modified silicone rubber, all being significantly lower than the unmodified material. Surface modified materials however had a significantly higher tear strength and lower water uptake in comparison to surfactant modified materials. CONCLUSION: Argon plasma treatment followed by chemisorption of ethyleneoxy functional silanes proved an effective way of improving the wettability of an experimental silicone rubber maxillofacial prosthetic material without altering bulk properties

Effective Fokker-Planck Equation for Birhythmic Modified van der Pol Oscillator

We present an explicit solution based on the phase-amplitude approximation of the Fokker-Planck equation associated with the Langevin equation of the birhythmic modified van der Pol system. The solution enables us to derive probability distributions analytically as well as the activation energies associated to switching between the coexisting different attractors that characterize the birhythmic system. Comparing analytical and numerical results we find good agreement when the frequencies of both attractors are equal, while the predictions of the analytic estimates deteriorate when the two frequencies depart. Under the effect of noise the two states that characterize the birhythmic system can merge, inasmuch as the parameter plane of the birhythmic solutions is found to shrink when the noise intensity increases. The solution of the Fokker-Planck equation shows that in the birhythmic region, the two attractors are characterized by very different probabilities of finding the system in such a state. The probability becomes comparable only for a narrow range of the control parameters, thus the two limit cycles have properties in close analogy with the thermodynamic phases

Global stability analysis of birhythmicity in a self-sustained oscillator

We analyze global stability properties of birhythmicity in a self-sustained system with random excitations. The model is a multi-limit cycles variation of the van der Pol oscillatorintroduced to analyze enzymatic substrate reactions in brain waves. We show that the two frequencies are strongly influenced by the nonlinear coefficients $\alpha$ and $\beta$. With a random excitation, such as a Gaussian white noise, the attractor's global stability is measured by the mean escape time $\tau$ from one limit-cycle. An effective activation energy barrier is obtained by the slope of the linear part of the variation of the escape time $\tau$ versus the inverse noise-intensity 1/D. We find that the trapping barriers of the two frequencies can be very different, thus leaving the system on the same attractor for an overwhelming time. However, we also find that the system is nearly symmetric in a narrow range of the parameters.Comment: 17 pages, 8 figures, to appear on Choas, 201

Power-dependent nonlinear optical behaviours of ponceau bs chromophore at 532 nm via z-scan technique

This paper reports on the power-dependent nonlinear optical (NLO) attributes for both nonlinear refractive index, n2 and nonlinear absorption coefficient, β of Ponceau BS (PBS) chromophore, a synthetic organic compound that falls under azo family. Single-beam Z-scan technique was utilized for the nonlinear measurement. Dominant absorption peak is observed in the visible region due to the high conjugation of diazene functional group absorption. The existence of vital vibrational bonds e.g. the azo bond (1576 cm−1) was confirmed via Fourier Transform Infrared Spectroscopy (FTIR). The intermolecular charge transfer (ICT) of delocalized electrons is responsible for the quick nonlinear response of the sample under intense laser excitation. Response from the closed and open aperture Z-scan technique indicates that PBS chromophore exhibits self-defocusing effects with negative sign of n2 and reverse saturable absorption (RSA) in the order of 10−9 and 10−4 respectively. The real and imaginary components of third order susceptibility, χ3 are relatively high in the order of 10−8 and 10-5 respectively under different laser powers (0.12, 0.14, 0.16, 0.18 & 0.20 W). In short, PBS chromophore shows promising features and can be considered as a potential candidate for various NLO applications under low-power laser operation

Quasi one dimensional 4^4He inside carbon nanotubes

We report results of diffusion Monte Carlo calculations for both $^4$He absorbed in a narrow single walled carbon nanotube (R = 3.42 \AA) and strictly one dimensional $^4$He. Inside the tube, the binding energy of liquid $^4$He is approximately three times larger than on planar graphite. At low linear densities, $^4$He in a nanotube is an experimental realization of a one-dimensional quantum fluid. However, when the density increases the structural and energetic properties of both systems differ. At high density, a quasi-continuous liquid-solid phase transition is observed in both cases.Comment: 11 pages, 3ps figures, to appear in Phys. Rev. B (RC

Classification of Spherically Symmetric Static Spacetimes according to their Matter Collineations

The spherically symmetric static spacetimes are classified according to their matter collineations. These are studied when the energy-momentum tensor is degenerate and also when it is non-degenerate. We have found a case where the energy-momentum tensor is degenerate but the group of matter collineations is finite. For the non-degenerate case, we obtain either {\it four}, {\it five}, {\it six} or {\it ten} independent matter collineations in which four are isometries and the rest are proper. We conclude that the matter collineations coincide with the Ricci collineations but the constraint equations are different which on solving can provide physically interesting cosmological solutions.Comment: 15 pages, no figure, Late