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Founding level variations

A study of mercury in Lake Michigan found levels near 1.6 pM (1.6 X 10 12 M), which is two orders of magnitude below concentrations observed in many earlier studies.5 Previous investigators apparently unknowingly contaminated their samples. A study of handling techniques for the analysis of lead in rivers investigated variations in sample collection, sample containers, protection during transportation from the field to the lab, filtration techniques, chemical preservatives, and preconcentration procedures.6 Each individual step that deviated from best practice doubled the apparent concentration of lead in stream water. Clean rooms with filtered air supplies are essential in trace analysis. Even with the best precautions, the precision of trace analysis becomes poorer as the concentration of analyte decreases (Box 5-2). [Pg.645]

No significant difference in the degradation rate of tensile properties for either uncoated or coated silk was found on variation of the irradiance level of the xenon lamp from 0.28 W/m2 to 0.42 W/m (340 nm) for a constant total energy input of 86 kj (340 nm). Apparently, reciprocity holds in this range of irradiances. [Pg.123]

Combined exposures have also been documented for surface waters. An example includes the Swiss river Aa, where mixtures of 5 herbicides comprising triazine and phenylureas were found. Seasonal variations in pollution levels were expected to lead to considerable combination effects in aquatic organisms (Chevre et al. 2006). [Pg.116]

Relatively high conformation to acceptable standards was found for coenzyme QIO (of Japanese origin), but poor conformation was found with lycopene. Nurmi et al. found wide variations in 15 soy isoflavone products examined. In their report, individual isoflavone levels were not claimed, but levels of three individual compounds, daidzein, genistein, and glycitein, fluctuated... [Pg.2446]

The ternary Ti4AlN3 is somewhat unique, in that not only is it nonstoichiometric (its actual chemistry is Ti4AlN2.9), but it also behaves more as a semi-metal than a metal [85]. Consistent with these results are ah initio predictions which show that, if stoichiometric, the Fermi level of this compound falls in a small gap (see Figure 7.2a) [38]. Interestingly, when the resistivity of two nominally identical samples were measured, a significant difference between their room-temperature resistivities was found these variations were attributed to slight variations in... [Pg.312]

Actually in each run one measures the rate of level variation of the water contained in each semicell. Constant rates have always been found within the first 120 minutes of running. Since apparatus geometry is well defined (see Fig.l) from these constant rates, the water flux can be immediately calculated. These fluxes are plotted in the figure against AT for various average temperatures T over the range between + 18°C and + 40°C. Water is always observed to flow from the warm to the cold semicell. Various interesting features are discernible in these plots ... [Pg.148]

Watt et al. (2000). One study of Glasgow women, conducted after the lime dosing began, found that variation in water-lead levels in Glasgow homes could not explain the variation in neural tube defects across the city. See MacDonell, Campbell, and Stone (2000). [Pg.280]

Chone (2000) analyzed Cabernet Sauvignon musts in 1997 and found significant variations in nitrogen levels, from 95 to 218 mg/1. [Pg.87]

Figure Bl.22.10. Carbon K-edge near-edge x-ray absorption (NEXAFS) speetra as a fiinotion of photon ineidenee angle from a submonolayer of vinyl moieties adsorbed on Ni(lOO) (prepared by dosing 0.2 1 of ethylene on that surfaee at 180 K). Several eleetronie transitions are identified in these speetra, to both the pi (284 and 286 eV) and the sigma (>292 eV) imoeeupied levels of the moleeule. The relative variations in the intensities of those peaks with ineidenee angle ean be easily eonverted into adsorption geometry data the vinyl plane was found in this ease to be at a tilt angle of about 65° from the surfaee [71], Similar geometrieal detenninations using NEXAFS have been earried out for a number of simple adsorbate systems over the past few deeades. Figure Bl.22.10. Carbon K-edge near-edge x-ray absorption (NEXAFS) speetra as a fiinotion of photon ineidenee angle from a submonolayer of vinyl moieties adsorbed on Ni(lOO) (prepared by dosing 0.2 1 of ethylene on that surfaee at 180 K). Several eleetronie transitions are identified in these speetra, to both the pi (284 and 286 eV) and the sigma (>292 eV) imoeeupied levels of the moleeule. The relative variations in the intensities of those peaks with ineidenee angle ean be easily eonverted into adsorption geometry data the vinyl plane was found in this ease to be at a tilt angle of about 65° from the surfaee [71], Similar geometrieal detenninations using NEXAFS have been earried out for a number of simple adsorbate systems over the past few deeades.
Unesterified tocopherols are found in a variety of foods however, concentration and isomer distribution of tocopherols vary gready with source. Typically, meat, fish, and dairy contain <40 mg/100 g of total tocopherols. Almost all (>75%) of this is a-tocopherol for most sources in this group. The variation in the content of meat and dairy products can be related to the content of the food ingested by the animal. A strong seasonal variation can also be observed. Vegetable oils contain significant levels of y-, P-, and 5-tocopherol, along with a-tocopherol (Table 3). [Pg.145]


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See also in sourсe #XX -- [ Pg.53 ]




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