Illuminated Surface Area Research Articles

Improved biomass production of cyanobacteria by reutilization of the culture medium

The biomass production of a cyanobacterium (Nostoc sp.) in a photoreactor with a low illuminated surface area to volume ratio was improved by the reutilization of the culture medium. After six succesive utilizations the growth ofNostoc sp. amounted to 2.15 g/l with an average content in phycobiliproteins of 14.4% on dry weight basis. The procedure reported allowed an 80% increase in biomass. The cellular self-sedimentation proved to be effective for biomass separation between reutilization steps.

Short pulse photoemission from a dispenser cathode under the 2nd, 3rd and 4th harmonics of a picosecond Nd: YAG laser

We present new results concerning the photoemissive properties of a standard thermionic dispenser cathode, B type, a porous tungsten matrix impregnated with barium calcium aluminate, 5 BaO-3 CaO, 2 Al 2O 3, working in ultra-short pulses at a temperature far below the measurable thermoemission threshold thanks to a picosecond frequency doubled-tripled or quadrupled Nd: YAG laser delivering 35 ps pulses and a continuous electrical accelerating field applied to the cathode plane surface. Our experiments have shown that the maximum emitted charge in each current pulse corresponds to the maximum available superficial charge of the cathode and that the emitted charge is proportional to the illuminated surface area. The quantum yield values measured at low laser energy are about: η = 2.5 × 10 −5, η = 1 × 10 −4 and η = 3.5 × 10 −4 at the three photon energies h ̵ ω 3 = 2.34 eV, h ̵ ω 3 = 3.51 EV and h ̵ ω 4 = 4.68 eV respectively. Poisoning effectsdue to some residual gas molecules like O 2-H 2O existing in the vacuum cell modify the composition of the surface Ba-O monolayer and are at the origin of a decrease of the photoemitted current about 3.6% per hour. Heating slightly and permanently the cathode permits to limit these effects.

Estimation of electromagnetic scattering patterns from sinusoidal surfaces using FFT

The scattering of electromagnetic waves from perfectly conducting sinusoidal surfaces as prototypes of periodic rough surfaces is studied. Physical optics and Fourier methods are used to calculate the scattered far field at a function of the observation angle. The patterns for several surface parameters are evaluated and plotted. The size of the illuminated surface area is varied. Homogeneous and Gaussian field amplitude perturbation of a laser beam in TEM/sub 00/-mode is considered. The results are compared with other methods and show a rather good agreement. Therefore, the method may be used for far-field computation if several criteria for the validity of the Kirchhoff approximation are not violated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Raman spectroscopy of the liquid-solid interface: monolayer and bilayer adsorption of pyridine on silica

Abstract : Raman spectra of pyridine adsorbed at a silica-solution interface are reported. A flow-through sample cell is employed to control the illuminated surface area of the particulate sample and to minimize background from solution phase species. The technique is applied to study the adsorption of pyridine onto silica gel from carbon tetrachloride solution. Spectroscopic adsorption isotherms are acquired with sufficient precision to allow monolayer and bilayer forms of adsorbed pyridine to be distinguished and quantified. The monolayer form adsorbs with proton transfer decreases uniformly with increasing surface coverage. A Frumkin model fits the monolayer isotherm data and provides an estimate of the decrease in free energy of adsorption with increasing surface coverage. The bilayer isotherm exhibits a concentration threshold which could only be fit by assuming that its energy of adsorption depends strongly on monolayer coverage. The accumulation of this pyridine bilayer appears to play a role in stabilizing the charge density of ion pairs in the monolayer.