Use Of Longer Wavelengths Research Articles

Photosynthesis: A Simple Demonstration of the Emerson Enhancement Effect

Photosynthesis is perhaps the single most important living process. However, the rapid advances within the last 25 years have resulted in a dearth of simple experiments that can demonstrate the basis of our present understanding. The experiment described here illustrates the operation of two separate light reactions in photosynthesis by showing the Emerson enhancement effect. The efficiency of photosynthesis has been found to vary as plants are illuminated with monochromatic light of different wavelengths. One common finding has been that the efficiency of photosynthesis decreases with the use of longer wavelengths of light. The decline in photosynthetic rate occurs in spite of strong light-absorption by chlorophyll. Robert Emerson (1957) and his colleagues discovered that the low rate of photosynthesis in long-wavelength light could be overcome, or even surpassed, by simultaneously illuminating the plants with a second beam of shorter-wavelength light. The rate of photosynthesis in the combined light beams was greater than could be expected by adding the rates found when either beam was provided alone. This relative excess of photosynthesis is known as the Emerson enhancement effect. One conclusion that Emerson reached on the basis of his discovery was that photosynthesis involves two photochemical processes. The exact, detailed explanations of how these two processes are achieved by the chlorophyll and accessory pigments have been modified considerably since Emerson published his work. Howevrer,

Particle Size Determination by Soft X-Ray Scattering

Small angle x-ray scattering measurements are made on samples of colloidal gold of radius from 50 to 400 angstroms. Copper (1.54 angstrom wave-length) and aluminum (8.32 angstrom wave-length) radiation are used. The usual method of analysis is shown to be valid only for particles of radius less than 120 wave-lengths. Extension of the method to larger particles is achieved, giving improved electron microscope correlation. The use of longer wave-lengths and optimum shaped slits are shown to reduce geometry errors sufficiently to give clear evidence of predicted intensity maxima. The first three secondary shape function maxima are observed. An additional interference maximum attributable to particle-to-particle interference is observed. The position and magnitude of this maximum are correctly predicted by an expression based on earlier fluid scattering theory.