In most glaciological and hydrological models, surface roughness of snow and ice is an important parameter. However, roughness is generally used only as an estimated parameter for lack of available observations. In this paper, we present a method to collect and analyze ice-surface-roughness data using a specially designed instrument for survey and geostatistical methods for analysis. The glacier-roughness sensor (GRS), built at the University of Trier, records variations in microtopography at 0.2 m × 0.1 m resolution when pulled across an ice surface. Global positioning system data are used for location. After several processing steps, the data are analyzed using geostatistical methods. The mathematical tool used to achieve a morphological characterization of ice-surface types is the variogram. GRS data, variograms and surface roughness analysis are ideal matches for morphological characterization, because none of them requires or provides absolute elevation values. Morphology is described not by absolute elevation values, but by the change of elevation in space which is the derivative of elevation (surface-roughness values). The variogram is calculated from incremental values. Parameters extracted from variograms of GRS data serve to distinguish lake surfaces, wind structures, ridge-and- vaUey systems, melting structures and blue-ice areas. Examples are from Jakobshavn Isbræ drainage basin, West Greenland.
Synchronous cells of the green alga, Scenedesmus obliquus, cultured in a 14‐h/10‐h light/dark regime, contain a peak of ribonucleoside‐diphosphate reductase activity and maximum deoxyribonucleoside 5′‐triphosphate concentrations at the 12th hour of the cell cycle, coinciding with DNA synthesis and preceding the formation of eight daughter cells. The intracellular dTTP pool reaches 4.5 pmol and the other pools 2–3 pmol/106 cells. Algal reductase activity is sensitive to cycloheximide, but not to lincomycin. These correlations demonstrate the functioning of the NDP → dNDP → dNTP pathway of DNA precursor biosynthesis in plant cells.
In the presence of 20 μg 5‐fluorodeoxyuridine/ml, an inhibitor of thymidylate synthesis, the dTTP pool is rapidly depleted and DNA synthesis ceases. 5‐Fluorouracil and methotrexate produce similar effects. At the same time the ribonucleotide reductase activity and also the dATP pool are greatly increased, especially when fluorodeoxyuridine treatment is combined with continued illumination of the algae. In contrast, arabinosylcytosine, an inhibitor of DNA replication, has no effect on ribonucleotide reduction. The control of de novo enzyme synthesis in the eucaryotic algae therefore appears to depend on the presence of dTTP (or a related nucleotide), but not directly coupled to DNA synthesis. This interdependence resembles the situation observed in HeLa cells, while it may differ in detail from control mechanisms of ribonucleotide reductase studied in bacteria.
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