Removal of Trace Metal Contaminants from Potable Water by Electrocoagulation

This study investigated the effects of four operational and environmental variables on the removal of trace metal contaminants from drinking water by electrocoagulation (EC). Removal efficiencies for five metals (arsenic, cadmium, chromium, lead and nickel) were compared under varying combinations of electrode material, post-treatment, water composition and pH. Iron electrodes out-performed aluminum electrodes in removing chromium and arsenic. At pH 6.5, aluminum electrodes were slightly more effective at removing nickel and cadmium, while at pH 8.5, iron electrodes were more effective for these metals. Regardless of electrode, cadmium and nickel removal efficiencies were higher at pH 8.5 than at pH 6.5. Post-EC treatment using membrane filtration (0.45 μm) enhanced contaminant removal for all metals but nickel. With the exception of lead, all metals exhibited poorer removal efficiencies as the ionic strength of the background electrolyte increased, particularly in the very high-solids synthetic groundwaters. Residual aluminum concentrations were lowest at pH 6.5, while iron residuals were lowest in low ionic strength waters. Both aluminum and iron residuals required post-treatment filtration to meet drinking water standards. EC with post-treatment filtration appears to effectively remove trace metal contaminants to potable water standards, but both reactor and source water parameters critically impact removal efficiency

The iron K line complex in NGC1068: implications for X-ray reflection in the nucleus

We report a new analysis of ASCA data on the iron K line complex in NGC1068. The line complex basically consists of three components, as previously reported. A weak red wing of the 6.4 keV fluoresence iron K line is found. A plausible explanation is Compton scattering in optically thick, cold matter which can be identified with an obscuring torus or cold gas in the host galaxy. We also show that this `Compton shoulder' should be observable with ASCA using a simulated reflection spectrum. In order to explain the two higher energy lines as well as the cold 6.4 keV line, we fit the ASCA data with a composite model of cold and warm reflection. This shows that cold reflection dominates the observed X-ray emission above 4 keV. The two higher energy lines have large equivalent width with respect to the warm-scattered continuum, suggesting that efficient resonant scattering operates. The line energies are systematically lower than those expected from resonant lines for FeXXV and FeXXVI by 100 eV. The redshifts may be due to either the ionized gas of the warm mirror receding at a radial velocity of 4000-5000 km/s, or effects of Compton scattering in a complicated geometry.Comment: 7 pages, 4 figures, to appear in MNRA

Effect of Particle Shape and Charge on Bulk Rheology of Nanoparticle Suspensions

The rheology of nanoparticle suspensions for nanoparticles of various shapes with equal mass is studied using molecular dynamics simulations. The equilibrium structure and the response to imposed shear are analyzed for suspensions of spheres, rods, plates, and jacks in an explicit solvent for both charged and uncharged nanoparticles. For the volume fraction studied, ?$\phi_{vf}=0.075$, the uncharged systems are all in their isotropic phase and the viscosity is only weakly dependent on shape for spheres, rods, and plate whereas for the jacks the viscosity is an order of magnitude larger than for the other three shapes. The introduction of charge increases the viscosity for all four nanoparticle shapes with the increase being the largest for rods and plates. The presence of a repulsive charge between the particles decreases the amount of stress reduction that can be achieved by particle reorientation.Comment: 15 pages, 9 figures, in pres

Fourier Series Formalization in ACL2(r)

We formalize some basic properties of Fourier series in the logic of ACL2(r), which is a variant of ACL2 that supports reasoning about the real and complex numbers by way of non-standard analysis. More specifically, we extend a framework for formally evaluating definite integrals of real-valued, continuous functions using the Second Fundamental Theorem of Calculus. Our extended framework is also applied to functions containing free arguments. Using this framework, we are able to prove the orthogonality relationships between trigonometric functions, which are the essential properties in Fourier series analysis. The sum rule for definite integrals of indexed sums is also formalized by applying the extended framework along with the First Fundamental Theorem of Calculus and the sum rule for differentiation. The Fourier coefficient formulas of periodic functions are then formalized from the orthogonality relations and the sum rule for integration. Consequently, the uniqueness of Fourier sums is a straightforward corollary. We also present our formalization of the sum rule for definite integrals of infinite series in ACL2(r). Part of this task is to prove the Dini Uniform Convergence Theorem and the continuity of a limit function under certain conditions. A key technique in our proofs of these theorems is to apply the overspill principle from non-standard analysis.Comment: In Proceedings ACL2 2015, arXiv:1509.0552

Suzaku observation of the Phoenix Galaxy

In recent years, several Seyfert 2 galaxies have been discovered that change state when observed in X-rays a few years apart, switching from Compton-thin to reflection-dominated or viceversa. We observed a member of this class of "Changing-look" sources, the Phoenix Galaxy, with Suzaku, with the aim of better understanding the nature of the variations. The Suzaku spectrum was analyzed, and the results compared with previous ASCA and XMM-Newton observations. The source was caught in a Compton-thin state, as in XMM-Newton, but differently from ASCA. Comparing the Suzaku and XMM-Newton observations, a variation in the column density of the absorber on a time scale of years is discovered. A similar change, but on much shorter time scales (i.e. ks) may also explain the count-rate variations during the Suzaku observations. A soft excess is also present, likely due to continuum and line emission from photoionized circumnuclear matter.Comment: Accepted for publication in Astronomy & Astrophysic

Thermal Conductance Measurement and Flexibility Enhancement of Flexible Thermal Links

Introduction • Flexible thermal links provide a thermally conductive path with low mechanical stiffness • Scope of this work is to characterize – Uncertainty in thermal conductance measurements – Compliance improvements gained by slitting foil