Application of response surface methodology to laser-induced breakdown spectroscopy : influences of hardware configuration

Response Surface Methodology (RSM) was employed to optimise LIBS analysis of single crystal silicon at atmospheric pressure and under vacuum conditions (pressure ~10-6mbar). Multivariate analysis software (StatGraphics 5.1) was used to design and analyse several multi-level, full factorial RSM experiments. A Quality Factor (QF) was conceived as the response parameter for the experiments, representing the quality of the LIBS spectrum captured for a given hardware configuration. The QF enabled the hardware configuration to be adjusted so that a best compromise between resolution, signal intensity and signal noise could be achieved. The effect on the QF of simultaneously adjusting spectrometer gain, gate delay, gate width, lens position and spectrometer slit width was investigated, and the conditions yielding the best QF determined

Sex Segregation and Salary Structure in Academia

This article reports a study of aggregate unit salary levels, within a major research university. We analyze these salary levels, as they are influenced by unit sex composition, and modified by unit attainment levels—where unit refers to the departments, colleges and schools, and other academic divisions of the university. We investigate three central issues of sex and salary, previously overlooked in salary studies of academic employees: Do high proportions of women depress men's unit salary levels ("competition" hypothesis)? Are women's salary levels higher in male-dominated, and lower in female-dominated, units ("concentration" hypothesis)? Are men salary-compensated for working with women ("compensation" hypothesis)? The findings support none of these hypotheses. Rather, the relationship between unit sex composition and salary rests upon the connection between units' composition and attainment levels.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69126/2/10.1177_073088848100800103.pd

Hardness determination of bio-ceramics using laser-induced breakdown spectroscopy.

Laser-Induced Breakdown Spectroscopy (LIBS) was applied to the analysis of bioceramic samples. The relationship between sample hardness and LIBS plasma properties was investigated, with comparison to conventional Vickers hardness measurements. The plasma excitation temperature Te was determined using the lineto- continuum ratio for the Si (I) 288.16 nm emission line; we have demonstrated a linear relationship between sample surface hardness and plasma temperature. Results indicate that hardness determination based on measurements of Te offers greater reproducibility than Vickers hardness measurements, under the conditions considered here. The validity of spectroscopic diagnostics based on LTE was confirmed

The effect of ambient pressure on laserinduced silicon plasma temperature, density and morphology.

Laser-induced breakdown spectroscopy of silicon was performed using a nanosecond pulsed frequency doubled Nd :YAG (532 nm) laser. The temporal evolution of the laser ablation plumes was characterized under a range of low pressures. Electron densities were determined from the Stark broadening of the Si (I) 288.16 nm emission line and were found to be in the range 2.79 × 1016 cm−3 to 5.59 × 1019 cm−3. Excitation temperatures of 9000–21 000K were calculated using the Si (I) 288.16 nm emission line to continuum ratio. The morphology of the laser plume, observed with respect to time, was seen to be strongly dependent on the ambient pressure. The density and temperature of the plasma were also found to vary critically with plasma morphology. Three ambient pressure regimes were identified where the plasma evolution was observed to differ markedly. Requirements for the existence of local thermal equilibrium conditions in the laser-induced plasmas are discussed with respect to these results