Accurate and precise measurements of light scattering and extinction by atmospheric particulate matter aid understanding of tropospheric photochemistry and are required for estimates of the direct climate effects of aerosols. In this work, we report on a second generation instrument to simultaneously measure light scattering (b(scat)) and extinction (b(ext)) coefficient by dispersed aerosols. The ratio of scattering to extinction is known as the single scatter albedo (SSA); thus, the instrument is referred to as the albedometer. Extinction is measured with the well-established cavity ring-down (CRD) technique, and the scattering coefficient is determined through collection of light scattered from the CRD beam. The improved instrument allows reduction in sample volume to <1% of the original design, and a reduction in response time by a factor of >30. Through using a commercially available condensation particle counter (CPC), we have measured scattering (σ(scat)) and extinction (σ(ext)) cross sections for size-selected ammonium sulfate and nigrosin aerosols. In most cases, the measured scattering and extinction cross section were within 1 standard deviation of the accepted values generated from Mie theory suggesting accurate measurements are made. While measurement standard deviations for b(ext) and b(scat) were generally <1 Mm(-1) when the measurement cell was sealed or purged with filtered air, relative standard deviations >0.1 for these variables were observed when the particle number density was low. It is inferred that statistical fluctuations of the absolute number of particles within the probe beam leads to this effect. However, measured relative precision in albedo is always superior to that which would be mathematically propagated assuming independent measurements of b(scat) and b(ext). Thus, this report characterizes the measurement precision achieved, evaluates the potential for systematic error to be introduced through light absorption by gases, presents comparisons with Mie theory, and provides ambient monitoring data collected on a mineral dust dominated aerosol at our location.
A microfluidic system for cell culture and drug response studies was developed to elucidate the effects of hypoxia on drug susceptibility. Drug response studies were performed in prostate cancer cells and Ramos B cells under normoxic and hypoxic conditions. A vacuum actuated microfluidic culture device was used for cell culture and PC3 cells were cultured in the chip up to 16 hours. Cells were treated with several concentrations of staurosporine and apoptosis was assayed using the fluorescent probes MitoTracker Red and Annexin-V. For hypoxic samples, the chip was placed in a hypoxia chamber and pre-conditioned at <1% oxygen before inducing the cells with staurosporine. Cells exposed to 2 μM staurosporine were 32% ± 10% apoptotic under normoxic conditions but only 1.5% ± 12% apoptotic under hypoxic conditions. As little as 1 hour of hypoxic preconditioning increased drug resistance. Cell apoptosis correlated with drug dose, although in each case hypoxia reduced the apoptotic fraction significantly. Given the rapid nature of cell adaptation to hypoxia, this chip and analysis approach can be used to identify compounds that can induce cell death in hypoxic tumor cells rapidly.
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