TAILIEUCHUNG - The Self-Made Tapestry Phần 3

Ý tưởng rằng các phản ứng hóa học có thể phát triển các sóng đi du lịch đi lại một waybefore dài, thậm chí, lý thuyết các phản ứng dao động (trong đó, như chúng ta đã thấy, bắt đầu với Lotka trong năm 1910). | The idea that chemical reactions can develop travelling waves goes back a long waybefore even the theory of oscillating reactions which as we saw started with Lotka in 1910 . At a meeting of German chemists in Dresden in 1906 Robert Luther director of the Physical Chemistry Laboratory in Leipzig presented a paper on the discovery and analysis of propagating chemical wavefronts in autocatalytic reactions. Sceptics were apparently quelled by Luther s demonstration of the phenomenon before their very eyeshe showed chemical waves in a reaction between oxalic acid and permanganate ions projected onto a screen in front of the audience. Luther suggested that the waves arose from a competition between an autocatalytic reaction and the process of diffusion that transports the chemical reagents through the reaction medium. Diffusion is a random processmolecules of the reacting molecules are buffeted from all directions by collisions with molecules of the surrounding solvent generally water and as a result they execute a convoluted meandering path often likened to a drunkard s walk. Despite this randomness the molecules do actually get somewhere rather than just meandering a little around their initial positionsbut the direction they take is random and the distance travelled from some initial location increases only rather slowly as time progresses. Whereas the distance covered by walking along a straight path at constant speed increases in direct proportion to the time elapsed the distance travelled by a random walker is proportional to the square root of the elapsed time. Random walks owing to diffusion were much studied at the beginning of the century notably by Albert Einstein. When a chemical reaction is conducted under conditions where the concentrations are not maintained uniformly throughout the medium by vigorous mixing diffusion becomes important since it limits the rate at which a reagent that has become used up in one region can be replenished from elsewhere to .

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