GREGORY ET AL-CO2 AND PHOTOPERIODISM metabolism and photoperiodism. Thesis In the course of experiments on the effect of radioactive elements on the growth of Chlorella pyrenoidosa, Porter and Knauss (9), determinations were made of the content of a radioactive element in algal cells when the ratio of that element to its stable isotope was kept constant, but the total concentration of the two isotopes in the solution was varied. Calculations were then made, assuming no isotope effect, of the total contents of the two isotopes in the algal cells. These determinations were made for the elements P, S, Ca, Fe, Mn, Zn, Cu, and Sr.A limited amount of information is available on the effect of the nutrient concentration of an element on the uptake of that element by algae. Scott (11) has reported that the ratio of uptake of calcium and magnesium by Chlorella depends upon the ratio of these two elements in the nutrient solution. Scott (12) has also studied the behavior of phosphatedeficient cells during a restoration period when adequate phosphate was supplied to the nutrient medium. He found the phosphate uptake to be proportional to the nutrient concentration only at levels that were limiting for growth.More information on the effect of nutrient concentration of an element on its uptake has been obtained through studies with higher plants and diatoms. Beckenbach et al (1), in making a statistical analysis of the relationship between the ionic content of the culture solution and the element content in corn plant tissues, found the most important single factor affecting the absorption and accumulation of an element in plant tissues to be its absolute concentration in the nutrient solution. Similar results were reported by Tidmore (14) on corn, sorghum, and tomatoes, and by Beeson et al (2) on tomato plants. Recently, Rediske and Selders (10) reported the uptake of strontium by plants to be proportional to the concentration of this element in the nutrient solution. Goldberg et al (5), working with diatoms, found the phosphate uptake to be proportional to the concentration in the medium over the range 0.5 to 3.5 ,ug/l. Similar findings were reported by Ketchum (7). Seven and one half ml of nutrient solution (KNO3, 3.0 gm/l; MgSO4 * 7 H20, 4.8 gm/l; Ca(NO3)2, 1.0 gm/l; KH2PO4, 3.0 gm/l; MnSO4 * H20, 2.0 mg/l; H3BO3, 2.0 mg/l; CUSO4-5 H20, 0.2 mg/l, and ZnSO4-7 H20, 0.2 mg/l), less the element being investigated, were added to 20 x 150 mm culture tubes. Varying amounts of the element being studied and the appropriate amounts of water were added to each tube. After sterilization each tube received 0.2 ml of a sterile iron solution (1 gm FeSO4 -7 H20/500 ml), 1.0 ml of inoculum (an optical density of 0.60 at 660 mnA/18 mm tube, approximately 17 x 106 cells/ ml) and amounts of a solution containing a radioactive isotope of the element under study to yield a final specific activity of one mc/gm of that element.In experiments on the absorption of copper the specific activity was 3 to 8 mc/gm of element. Radioisotopes used were p3...
We present results on back contact buried contact solar cells based on the Metallization Wrap Around (MWA) concept. In this cell design the current is conducted over metallized edges of the solar cell to the rear side busbar. The applied processing sequence is almost identical to the one of conventional buried contact cells and is based on pln-contact isolation by mechanical abrasion. One major problem of MWA solar cells seems to be the long current paths in the fingers to the collecting busbar on the rear side. Therefore device simulations were carried out in order to find the optimum grid desi n for different cell sizes (10x10 cm2 and 12.5x12.5 cm ). The device simulations showed that the MWA solar cell concept leads to higher efficiencies as compared to conventional cells. Best efficiencies obtained in this study are q=17.5 YO (cell area 25 cm2) and q=16.6 % (100 cm2) on Cz-Si. For mc-Si efficiencies of q=15.7 % (25 cm2) and q=14.4 % (100 cm2) were reached.
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