Investigating denitrification from two Missouri claypan soils

Includes vita.Denitrification in agricultural soils is responsible for a majority of anthropogenic nitrous oxide (N2O) production, and N2O is a major greenhouse gas with a global warming potential [approximately] 300 times that of carbon dioxide. The objectives of this research were to: 1) compare multiple RNA-based sequencing methods for quantifying denitrification genes in soil; 2) relate denitrification gene abundance in soil to actual and potential denitrification rates in claypan soils; 3) measure actual and potential soil denitrification rates from claypan soils and understand how landscape position influences denitrification; and 4) upscale the estimates of denitrification to the field scale to understand its importance to the N budget in row crop fields. The research sites consisted of two claypan soil fields in Central Missouri. Several sets of soil cores were collected in triplicate in two landscape transects across both fields and N2 and N2O production were measured using a gas flow soil core incubation system. In addition, soil denitrification potential, under non-limiting conditions, was determined on 90 m-grid samples collected from the fields. Potential and actual denitrification rates were not significantly different between fields, but potential denitrification rates were greater by almost two-fold in the toeslope position (p [less than] 0.10) compared to the backslope and summit positions across, fields. In one field, actual denitrification rates were greater in the summit landscape position while rates were greater in the backslope position in the other field. Actual denitrification in these fields predominantly resulted in N2 emissions and N2O accounted for a minor portion of the total flux. Although the high smectitic clay content of upland soils provides environmental conditions suitable for high N2O flux rates, these results suggested that denitrification rates are higher in the toe-slope position due to accumulation of soil C from long-term sediment deposition. Therefore, long-term erosion patterns rather than current or recent crop management systems controlled observed spatial patterns of denitrification on these claypan fields. One set of cores was analyzed for extractable soil RNA, and nosZ gene abundance using three methods: real-time quantitative polymerase chain reaction (RT-qPCR); droplet digital polymerase chain reaction (ddPCR); and nanostring sequencing techniques at two depths (0-15 cm and 15-30 cm). There were significant differences in soil RNA quantities between the two depths, with an average of 54.51 mg RNA kg soil-1 at 0-15 cm and 14.20 mg kg-1 at 15-30 cm. The low soil RNA concentrations in the subsoil prevented quantification of the nosZ gene abundance, and suggested low overall microbial activity below 15 cm depth in these claypan soils. Abundance of nosZ in the surface soil showed that ddPCR resulted in significantly greater gene copy estimates than those of RT-qPCR and nanostring sequencing (p [less than] 0.10). There were no statistical differences between nosZ abundance when comparing RT-qPCR and nanostring sequencing. Variability of nosZ abundance was very minimal in both RT-qPCR and nanostring technologies. Landscape variability of the gene copy estimates in these two fields were not similar to the actual denitrification measurement pattern. These results suggest more research should be conducted to establish the molecular sequencing technique best suited to measure genes involved in denitrification from soil samples or that gene prevalence may not effectively predict denitrification, and on these two Missouri claypan soils, most of the biological community and activity are in the top 15 cm of the soil profile. Actual denitrification, along with other parameters for soil volumetric water content, and soil temperature were used to model and upscale estimates for denitrification at the field scale. Soil O2, temperature, and volumetric water content (VWC) were measured at a depth of 10 cm depth at three landscape positions within each field and were used to establish a relationship between VWC and soil O2 content. It was assumed conditions for denitrification were a soil O2 content [less than or equal to] 5 [percent] and a soil temperature ≥15oC, and flux estimates were corrected using a Q10 value of 2. For each field, daily and annual denitrification estimates were calculated for years grown under corn or wheat, due to N fertilizer application. Daily total denitrification (N2O+N2) estimates ranged from 0.39 kg N ha-1d-1 to 0.87 kg N ha-1d-1. The highest annual denitrification estimates were for Field 1 in 2016, in which 9.26 kg N ha-1 were estimated. Denitrification accounted for up to 7.6 [percent] of total applied N. There are many facets to denitrification. This study highlights the complex relationship between denitrification and other soil characteristics. Denitrification was more strongly related to differences in soils across landscape position rather than crop management, and served as a major N-loss pathway in both fields. These results will aid in our understanding of denitrification and demonstrates the need for denitrification mitigation strategies.Includes bibliographical reference

Perigree Propulsion for Orbital Launch of Nuclear Rockets

A thrust program called perigee propulsion which minimizes gravity loss is analyzed. Thrust is applied intermittently in regions of high velocity (near successive perigees). The increased energy-addition efficiency yields mass ratios approaching those for impulsive velocity change. Corresponding times to reach desired energy are in days but are still small relative to mission times. For specified orbital-launch missions, perigee- propulsion nuclear-rocket systems are shown to equal continuous-thrust performance with reactor powers an order of magnitude less than those of continuous-thrust systems. Application and operational aspects of perigee propulsion are discussed

Enhancing of catalytic properties of vanadia via surface doping with phosphorus using atomic layer deposition

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in J. Vac. Sci. Technol. A 34, 01A135 (2016) and may be found at https://doi.org/10.1116/1.4936390.Atomic layer deposition is mainly used to deposit thin films on flat substrates. Here, the authors deposit a submonolayer of phosphorus on V2O5 in the form of catalyst powder. The goal is to prepare a model catalyst related to the vanadyl pyrophosphate catalyst (VO)2P2O7 industrially used for the oxidation of n-butane to maleic anhydride. The oxidation state of vanadium in vanadyl pyrophosphate is 4+. In literature, it was shown that the surface of vanadyl pyrophosphate contains V5+ and is enriched in phosphorus under reaction conditions. On account of this, V2O5 with the oxidation state of 5+ for vanadium partially covered with phosphorus can be regarded as a suitable model catalyst. The catalytic performance of the model catalyst prepared via atomic layer deposition was measured and compared to the performance of catalysts prepared via incipient wetness impregnation and the original V2O5 substrate. It could be clearly shown that the dedicated deposition of phosphorus by atomic layer deposition enhances the catalytic performance of V2O5 by suppression of total oxidation reactions, thereby increasing the selectivity to maleic anhydride.DFG, 53182490, EXC 314: Unifying Concepts in Catalysi

South Asian monsoon history over the past 60 kyr recorded by radiogenic isotopes and clay mineral assemblages in the Andaman Sea

The Late Quaternary variability of the South Asian (or Indian) monsoon has been linked with glacial‐interglacial and millennial scale climatic changes but past rainfall intensity in the river catchments draining into the Andaman Sea remains poorly constrained. Here we use radiogenic Sr, Nd, and Pb isotope compositions of the detrital clay‐size fraction and clay mineral assemblages obtained from sediment core NGHP Site 17 in the Andaman Sea to reconstruct the variability of the South Asian monsoon during the past 60 kyr. Over this time interval εNd values changed little, generally oscillating between −7.3 and −5.3 and the Pb isotope signatures are essentially invariable, which is in contrast to a record located further northeast in the Andaman Sea. This indicates that the source of the detrital clays did not change significantly during the last glacial and deglaciation suggesting the monsoon was spatially stable. The most likely source region is the Irrawaddy river catchment including the Indo‐Burman Ranges with a possible minor contribution from the Andaman Islands. High smectite/(illite + chlorite) ratios (up to 14), as well as low 87Sr/86Sr ratios (0.711) for the Holocene period indicate enhanced chemical weathering and a stronger South Asian monsoon compared to marine oxygen isotope stages 2 and 3. Short, smectite‐poor intervals exhibit markedly radiogenic Sr isotope compositions and document weakening of the South Asian monsoon, which may have been linked to short‐term northern Atlantic climate variability on millennial time scales

Inward Leakage in Tight-Fitting PAPRs

A combination of local flow measurement techniques and fog flow visualization was used to determine the inward leakage for two tight-fitting powered air-purifying respirators (PAPRs), the 3M Breathe-Easy PAPR and the SE 400 breathing demand PAPR. The PAPRs were mounted on a breathing machine head form, and flows were measured from the blower and into the breathing machine. Both respirators leaked a little at the beginning of inhalation, probably through their exhalation valves. In both cases, the leakage was not enough for fog to appear at the mouth of the head form

Effects of lateral diffusion on morphology and dynamics of a microscopic lattice-gas model of pulsed electrodeposition

The influence of nearest-neighbor diffusion on the decay of a metastable low-coverage phase (monolayer adsorption) in a square lattice-gas model of electrochemical metal deposition is investigated by kinetic Monte Carlo simulations. The phase-transformation dynamics are compared to the well-established Kolmogorov-Johnson-Mehl-Avrami theory. The phase transformation is accelerated by diffusion, but remains in accord with the theory for continuous nucleation up to moderate diffusion rates. At very high diffusion rates the phase-transformation kinetic shows a crossover to instantaneous nucleation. Then, the probability of medium-sized clusters is reduced in favor of large clusters. Upon reversal of the supersaturation, the adsorbate desorbs, but large clusters still tend to grow during the initial stages of desorption. Calculation of the free energy of subcritical clusters by enumeration of lattice animals yields a quasi-equilibrium distribution which is in reasonable agreement with the simulation results. This is an improvement relative to classical droplet theory, which fails to describe the distributions, since the macroscopic surface tension is a bad approximation for small clusters.Comment: Minor corrections and modifications. 15 pages with 10 figures. Accepted for publication in the Journal of Chemical Physics, see http://jcp.aip.org/jcp

Precise Measures of Orbital Period, Before and After Nova Eruption for QZ Aurigae

For the ordinary classical nova QZ Aurigae (which erupted in 1964), we report 1317 magnitudes from 1912--2016, including four eclipses detected on archival photographic plates from long before the eruption. We have accurate and robust measures of the orbital period both pre-eruption and post-eruption, and we find that the orbital period decreased, with a fractional change of -290.71+-0.28 parts-per-million across the eruption, with the orbit necessarily getting smaller. Further, we find that the light curve outside of eclipses and eruption is flat at near B=17.14 from 1912--1981, whereupon the average light curve starts fading down to B=17.49 with large variability. QZ Aur is a robust counter-example against the Hibernation model for the evolution of cataclysmic variables, where the model requires that all novae have their period increase across eruptions. Large period decreases across eruptions can easily arise from mass imbalances in the ejecta, as are commonly seen in asymmetric nova shells.Comment: MNRAS in press, 24 pages, 5 tables, 6 figure

Using CO2 to Determine Inhaled Contaminant Volumes and Blower Effectiveness in Several Types of Respirators

This experiment was conducted to determine how much contaminant could be expected to be inhaled when overbreathing several different types of respirators. These included several tight-fitting and loose-fitting powered air-purifying respirators (PAPRs) and one air-purifying respirator (APR). CO2 was used as a tracer gas in the ambient air, and several loose-and tight-fitting respirators were tested on the head form of a breathing machine. CO2 concentration in the exhaled breath was monitored as well as CO2 concentration in the ambient air. This concentration ratio was able to give a measurement of protection factor, not for the respirator necessarily, but for the wearer. Flow rates in the filter/blower inlet and breathing machine outlet were also monitored, so blower effectiveness (defined as the blower contribution to inhaled air) could also be determined. Wearer protection factors were found to range from 1.1 for the Racal AirMate loose-fitting PAPR to infinity for the 3M Hood, 3M Breath-Easy PAPR, and SE 400 breath-responsive PAPR. Inhaled contaminant volumes depended on tidal volume but ranged from 2.02 L to 0 L for the same respirators, respectively. Blower effectiveness was about 1.0 for tight-fitting APRs, 0.18 for the Racal, and greater than 1.0 for two of the loose-fitting PAPRs. With blower effectiveness greater than 1.0, some blower flow during the exhalation phase contributes to the subsequent inhalation. Results from this experiment point to different ways to measure respirator efficacy