Comparison of three wet-alkaline methods of digestion of biogenic silica in water

Methods for determination of low levels of biogenic silica (0.2–0.4 mg SiO 2 ) in aqueous samples after digestion with three wetalkaline extraction procedures compared favourably in both precision of replicates and recovery of silica utilized by diatoms in budgeted cultures. Leaching samples with 0.2 M NaOH for 10–15 min at 100°C was the least time consuming procedure. Also interference from silicate minerals was lower for this method than leaching with either 0.5 or 5% Na 2 CO 3 for 2 h at 85°C. The use of filters to concentrate samples enables detection of low levels of biogenic silica with colorimetric procedures. Polycarbonate filters are recommended in preference to cellulose acetate or polyvinyl chloride filters for sample collection. Time-course experiments are recommended for establishing digestion times and determining the presence of mineral silicate interference. Wet-alkaline digestion methods are recommended for routine analysis of biogenic silica in suspended matter in preference to infra-red analysis, alkaline fusion and hydrofluoric acid/nitric acid methods.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74725/1/j.1365-2427.1983.tb00658.x.pd

Walking rover trafficability - Presenting a comprehensive analysis and prediction tool

Although walking rovers perform well in rocky terrain, their performance over sands and other deformable materials has not been well studied. A better understanding of walking rover terramechanics will be essential if they are to be actually deployed on a space mission. This paper presents a comprehensive walking rover terramechanics model incorporating slip and sinkage dependencies. In addition to quantifying the leg / soil forces, the superior trafficability potential of a walking rover in deformable terrain is demonstrated, and a control approach is described which can reduce the risk inherent in traversing soils with unknown physical parameters. This work enhances the state of the art of legged rover trafficability and highlights some potential benefits from deploying micro-legged rovers for future surface exploration missions