A de novo designed four-helix bundle polypeptide with a modeled three-dimensional structure has been studied by chemical kinetics and Brownian dynamics simulations as an application of the diffusion-collision model. The complementary studies give information on kinetic pathways in the folding of the peptide and on the statistical propensities and time histories of the positions and orientations of the four helices.

A simplified model of a polypeptide chain is used to study the dynamics of the beta-sheet-coil transition. Each amino acid residue is treated as a single quasiparticle in an effective potential that approximates the potential of mean force in solution. The model is used to study the equilibrium and dynamic aspects of the sheet-coil transition. Systems studied include ones with both strands free to move (two-strand sheet), and ones with either strand fixed in position (multistrand sheet). The equilibrium properties examined include sheet-coil equilibrium constants and their dependence on chain position. Dynamic properties are investigated by a stochastic simulation of the Brownian motion of the chain in its solvent surroundings. Time histories of the dihedral angles and residue-residue cross-strand distances are used to study the behavior of the sheet structure. Auto- and cross-correlation functions are calculated from the time histories with relaxation times of tens to hundreds of picoseconds. Sheet-coil rate constants of tens of ns-1 were found for the fixed strand cases.

A folding algorithm is described, based on the diffusion-collision model, combining static and dynamic calculational methods. The algorithm is applied to predict the basic structure and schematic folding pathways of an artificial four-helix bundle.

Variability of chlorophyll-a concentration and sea surface temperature (SST) in Natuna waters were analyzed using satellite data Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and the National Oceanic and Atmospheric Administration-Advanced Very High Resolution Radiometer (NOAA-AVHRR). SeaWiFS data with a resolution of 9×9 km 2 and AVHRR with a resolution of 4×4 km 2 were the monthly average data downloaded from NASA website. Chlorophyll-a concentrations and SST were estimated using OC4v4 and MCSST algorithms. In general, the concentration of chlorophyll-a in Natuna waters ranged between 0.11-4.92 mg/m 3 with an average of 0.56 mg/m 3 during the west season and 0.09-2.93 mg/m 3 with an average of 0.66 mg/m 3 during the east season. Chlorophyll-a concentrations were relatively high seen in coastal areas, especially around the mouth of the Kapuas, Musi, and Batang Hari rivers allegedly caused by the high nutrient intake from the mainland. SST variability in Natuna waters ranged from 23.46-30.88 °C during the west season and tended to be lower than that the east season (27.91-31.95 °C). In addition, the SST values tended to be lower in the offshore than that inshore. During the west season (Nov-Feb) and the transitional season (Apr) in the years of Elnino Southern Oscillation (ENSO), the concentration of chlorophyll-a and the SST in Natuna waters was generally higher than that in non-ENSO years. The results of wind analyses showed that ENSO caused the change of direction and speed of wind from its normal conditions. ABSTRAK Variabilitas konsentrasi klorofil-a dan suhu permukaan laut (SPL) di perairan Natuna dianalisis dari data satelit Sea-viewing Wide Field-of-view Sensor (SeaWiFS) dan National Oceanic and Atmospheric Administration-Advanced Very High Resolution Radiometer (NOAA-AVHRR). Data SeaWiFS dengan resolusi 9×9 km 2 dan AVHRR dengan resolusi 4×4 km 2 merupakan data rata-rata bulanan yang diunduh dari situs NASA. Konsentrasi klorofil-a diestimasi dengan menggunakan algoritma OC4v4 dan nilai SPL diestimasi berdasarkan algoritma MCSST. Secara umum, konsentrasi klorofil-a di Perairan Natuna berkisar antara 0.11-4.92 mg/m 3 dengan rata-rata 0.56 mg/m 3 pada musim barat dan 0.09-2.93 mg/m 3 dengan rata-rata 0.66 mg/m 3 pada musim timur. Konsentrasi klorofil-a relatif tinggi terlihat pada daerah pesisir khususnya di sekitar muara Sungai Kapuas, Sungai Musi, dan Sungai Batanghari yang diduga akibat asupan zat hara yang cukup tinggi dari daratan. Variabilitas SPL di Perairan Natuna berkisar antara 23.46-30.88 °C pada musim barat dan cenderung lebih rendah dibandingkan dengan musim timur yang berkisar antara 27.91-31.95 °C. Selain itu, nilai SPL cenderung lebih rendah pada daerah offshore dan menigkat menuju perairan pantai. Pada musim barat (Nop-Feb) dan musim peralihan (Apr) tahun ElNino Southern Oscillation (ENSO), konsentrasi klorofil-a dan nilai SPL di Perairan Natuna secara umum lebih tinggi dibandingkan pada tahun non-ENSO. Hasil analisis data angin juga menunjukkan bahwa ENSO menyebabkan perobahan pergeraka...