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This paper reports the results of a series of experiments carried out to determine the precision of soil trace comparisons based on elemental peak height ratios determined by energy-dispersive X-ray analysis (EDXRA) in a variable pressure scanning electron microscope (VP-SEM). Experiments were conducted on 'bulk' soil aggregates, ground powders prepared from the <150 microm soil fractions and on smears of both the bulk soil and <150 microm material placed on cotton cloth. X-ray count data were obtained using area scans and spot analyses at different magnifications. The effects on elemental peak height ratios of varying the SEM chamber pressure, beam spot size, emission current and accelerating voltage were also examined. The peak height ratios for oxygen, silicon, aluminium, potassium, calcium and iron were found to show little variation as a function of chamber pressure, spot size and emission current over the ranges examined, but a strong dependency on accelerating voltage was observed. Within-sample variation in results, expressed by the percentage coefficient of variation, was found to be lowest for area scan analyses of the ground <150 microm fractions and greatest for the spot analyses of the bulk soil aggregates and the <150 microm fractions. We conclude that comparison of elemental peak height ratios determined by EDXRA can be a useful tool for rapid screening of soil samples, especially when combined with investigation of other attributes of the soil traces such as colour, fabric and the composition, shapes and surface textures of individual particles or aggregates within the soil traces. If sufficient material is available and can be readily separated without contamination or loss, higher resolution and more precise elemental data should be obtained by methods such as inductively coupled plasma atomic-emission spectrometry (ICP-AES) or mass-spectrometry (ICP-MS). 相似文献
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Advertising is the most visible element of modern marketing, and an important component of trading. It is also an activity often accused by its critics of being intrusive and pervasive. Such accusations are not easily refuted by a worldwide industry which spends billions of dollars each year reaching and persuading its target markets through daily bombardment of thousands of ads in most developed countries. When advertising does offend, mislead, or is untruthful, a structure needs to be in place in order to provide protection to all parties and, in most cases, a country's legal system is complemented by a self‐regulatory scheme. Self‐regulation is a common approach to controlling conduct or behaviour in society and, indeed, Australian advertisers have opted for this system of control for more than 60 years. 相似文献
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Debra A. Murphy Mary-Lynn Brecht Diane M. Herbeck David Huang 《Journal of youth and adolescence》2009,38(9):1226-1239
This study utilized data from the National Longitudinal Survey of Youth to investigate youth risk trajectories for HIV and
factors associated with different trajectories. The sample (N = 8,208) was 49.2% female, with a mean age of 14.31 (SD = 1.48). A group-based trajectory model was applied, which identified four distinct trajectories for both males and females:
(1) consistently higher sexual risk levels, increasing to early adulthood followed by some decrease (“high”); (2) a short
period of increase to late teens, followed by a longer period of decrease (“decreased”); (3) an initially slow increase, with
the increase accelerating by late teens, and a slight decline beginning in early adulthood (“increased”); and (4) consistently
lowest levels of sexual risk (“low”). More African Americans were found among the decreased trajectory group; among the low
risk group a higher number of youth came from families with parents who spoke a language other than English. The high-risk
group had a higher percentage of subjects in non-metropolitan areas and highest alcohol use. Among males, being employed and
being in the military were associated with inclusion in the high-risk group. Results have implications for specializing prevention
strategies for youth with different patterns of sexual risk.
相似文献
Debra A. MurphyEmail: |
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Courts that perform well are the cornerstone of the rule of law and democratic development. When courts are perceived as legalistic, fair, impartial, and independent of the influence of extrajudicial actors, aggrieved individuals are more likely to pursue litigation over other, potentially unlawful, alternatives. Using original data from surveys of more than 1,800 randomly sampled lawyers in 12 Russian cities, we investigate the effects of perceived government funding and power diversification on a variety of indicators of perceived judicial performance. We find that, according to lawyers, financial dependence on the national government has no independent effect on judicial performance, but financial dependence on local governments has consistently significant negative effects. We also find that diversified political power has consistently significant positive effects on perceived judicial performance, probably because the diversification makes courts seem less vulnerable to unified pressure from political actors. 相似文献
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