In Situ ATR-SEIRAS of Carbon Dioxide Reduction at a Plasmonic Silver Cathode.

Illumination of a voltage-biased plasmonic Ag cathode during CO2 reduction results in a suppression of the H2 evolution reaction while enhancing CO2 reduction. This effect has been shown to be photonic rather than thermal, but the exact plasmonic mechanism is unknown. Here, we conduct an in situ ATR-SEIRAS (attenuated total reflectance-surface-enhanced infrared absorption spectroscopy) study of a sputtered thin film Ag cathode on a Ge ATR crystal in CO2-saturated 0.1 M KHCO3 over a range of potentials under both dark and illuminated (365 nm, 125 mW cm-2) conditions to elucidate the nature of this plasmonic enhancement. We find that the onset potential of CO2 reduction to adsorbed CO on the Ag surface is -0.25 VRHE and is identical in the light and the dark. As the production of gaseous CO is detected in the light near this onset potential but is not observed in the dark until -0.5 VRHE, we conclude that the light must be assisting the desorption of CO from the surface. Furthermore, the HCO3- wavenumber and peak area increase immediately upon illumination, precluding a thermal effect. We propose that the enhanced local electric field that results from the localized surface plasmon resonance (LSPR) is strengthening the HCO3- bond, further increasing the local pH. This would account for the decrease in H2 formation and increase the CO2 reduction products in the light

Metal Cooling in Simulations of Cosmic Structure Formation

The addition of metals to any gas can significantly alter its evolution by increasing the rate of radiative cooling. In star-forming environments, enhanced cooling can potentially lead to fragmentation and the formation of low-mass stars, where metal-free gas-clouds have been shown not to fragment. Adding metal cooling to numerical simulations has traditionally required a choice between speed and accuracy. We introduce a method that uses the sophisticated chemical network of the photoionization software, Cloudy, to include radiative cooling from a complete set of metals up to atomic number 30 (Zn) that can be used with large-scale three-dimensional hydrodynamic simulations. Our method is valid over an extremely large temperature range (10 K < T < 10^8 K), up to hydrogen number densities of 10^12 cm^-3. At this density, a sphere of 1 Msun has a radius of roughly 40 AU. We implement our method in the adaptive mesh refinement (AMR) hydrodynamic/N-body code, Enzo. Using cooling rates generated with this method, we study the physical conditions that led to the transition from Population III to Population II star formation. While C, O, Fe, and Si have been previously shown to make the strongest contribution to the cooling in low-metallicity gas, we find that up to 40% of the metal cooling comes from fine-structure emission by S, when solar abundance patterns are present. At metallicities, Z > 10^-4 Zsun, regions of density and temperature exist where gas is both thermally unstable and has a cooling time less than its dynamical time. We identify these doubly unstable regions as the most inducive to fragmentation. At high redshifts, the CMB inhibits efficient cooling at low temperatures and, thus, reduces the size of the doubly unstable regions, making fragmentation more difficult.Comment: 19 pages, 12 figures, significant revision, including new figure

Laser-Induced Fluorescence of Singly-Charged Xenon in a 6-kW Hall Thruster Plume

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76708/1/AIAA-2008-5102-585.pd

Evaluation of Scents Attractants for Baiting Wild Pigs

Lethal removal by trapping is one of the most cost- and time-effective means for managing wild pigs (Sus scrofa). Scent attractants are frequently used to lure wild pigs to camera stations for scouting or monitoring wild pig populations or at trap sites to reduce the amount of time for pigs to locate the trap. However, the effectiveness of scents to attract and increase wild pig visitation to camera stations or traps is debatable. Therefore, our objective was to determine if wild pigs visited camera stations sooner and more frequently when scents were used in addition to whole kernel corn. We conducted our study on portions of the state-owned Lowndes County Wildlife Management Area (5,650 ha) and on privately owned property (1,820 ha) in Lowndes and Macon counties, AL, respectively, during 2014-2016. We selected portions within these study areas where active, premeditated wild pig removal (trapping, shooting) had not occurred for at least 1 year in order to minimize biases associated with trap shy pig behavior. We sectioned each study area into 1km2 grids and assigned a camera station to each grid cell overlapping the study area. Within each grid cell, the camera station was subjectively placed in forest cover near water. We then assigned randomly treatments of corn (11.3 kg), corn and a molasses-based attractant (0.23 L), or corn and a pig urine attractant (15 ml) to each of 66 camera stations. Corn and attractants were replenished after 7 days. We then used motion-sensitive game cameras to record the time (in min) from the initial placement of bait and scent at each station until the first wild pig was captured on camera images. Cameras remained active on each station for 14 days and were set to capture 3-picture bursts with a 10-second delay among pictures and 1-minute delay between bursts. Camera stations were distributed within each study area at a density of approximately one station per 100-250 ha. We recorded the time of first detection, frequency of visits, and identifying characteristics of pigs and sounders. We used a Χ2 test to determine if frequency of visits differed among treatments and an ANOVA to determine differences in time until first visit differed among treatments. Wild pigs visited 23 of 66 (35%) bait stations which did not differ among treatment sites (P=0.231). Of these 23 active camera stations, time until first visit did not differ among treatments (P=0.599). Mean time until first visit to a station was approximately 62.0 hours (about 2.6 days). Scent attractants did not have a noticeable effect on increasing wild pig visitation to baited camera stations suggesting managers 28 should focus on proper placement of bait stations or traps in areas frequented by wild pigs rather than relying on scents to lure pigs to desired locations

Likert Items: Should(n’t) We Really Care?

One of the controversial methodological topics in the social and behavioral sciences is the (ab)use of Likert Scale items, Likert-type items and ranked ordered response categories. The debate is whether parametric tests can be legitimately conducted on technically ordinal response categories that are represented with numbers. Participants answered survey questions on moral disengagement, where we changed the intervals of seven response categories and tested whether assigning numbers made any difference in two separate studies. The results showed that participants’ ratings were not significantly different with or without numbers. Participants tend to covertly superimpose numbers where none were provided. Also, there were no significant interactions between assignment of numbers and ‘intervalness’. However, ratings were significantly different between two key interval groups. Knowing the assumptions of respondents to these Likert items even without numbers could inform researchers especially if parametric tests are to be conducted

Numerical Simulations of Supernova Dust Destruction. II. Metal-Enriched Ejecta Knots

Following our previous work, we investigate through hydrodynamic simulations the destruction of newly-formed dust grains by sputtering in the reverse shocks of supernova remnants. Using an idealized setup of a planar shock impacting a dense, spherical clump, we implant a population of Lagrangian particles into the clump to represent a distribution of dust grains in size and composition. We vary the relative velocity between the reverse shock and ejecta clump to explore the effects of shock-heating and cloud compression. Because supernova ejecta will be metal-enriched, we consider gas metallicities from Z/Zsun = 1 to 100 and their influence on cooling properties of the cloud and the thermal sputtering rates of embedded dust grains. We post-process the simulation output to calculate grain sputtering for a variety of species and size distributions. In the metallicity regime considered in this paper, the balance between increased radiative cooling and increased grain erosion depends on the impact velocity of the reverse shock. For slow shocks (velocity less than or equal to 3000 km/s), the amount of dust destruction is comparable across metallicities, or in some cases is decreased with increased metallicity. For higher shock velocities (velocity greater than or equal to 5000 km/s), an increase in metallicity from Z/Zsun = 10 to 100 can lead to an additional 24% destruction of the initial dust mass. While the total dust destruction varies widely across grain species and simulation parameters, our most extreme cases result in complete destruction for some grain species and only 44% dust mass survival for the most robust species. These survival rates are important in understanding how early supernovae contribute to the observed dust masses in high-redshift galaxies.Comment: 10 pages, 6 figures, 2 tables, changes made to the text and figures as suggested by the anonymous referee, accepted by the Astrophysical Journa