Crustal Analysis of Venus from Magellan Satellite Observations at Atalanta Planitia, Beta Regio, and Thetis Regio

As a result of NASA's Magellan satellite mission, serious questions have arisen concerning the crust of Venus. Venus is very similar to Earth in size and composition, yet different in tectonic style and internal dynamics. For example, the primary mode of heat loss appears to be hot-spot volcanism (Head et al., 1992), whereas on Earth it is plate tectonics and plate boundary volcanism. The relatively young and unmodified appearance of most Venusian craters and their largely random distribution has led some researchers to conclude that a global resurfacing event occurred between 300 to 1000 Ma (Schaber et al., 1992). The possible correlation between modified craters and low crater density with volcanically and tectonically active regions supports the notion that ongoing volcanic activity may represent the primary mode of planetary resurfacing (Phillips et al., 1992; Head et al., 1992). An alternative hypothesis suggests that perhaps volcanism is ongoing on Venus, but at a reduced rate subsequent to a global resurfacing event (Price et al., 1996). Understanding the crustal properties of the different tectonic regions, including the crustal plateaus and their relationships to cold spots and hot spots, is important for developing meaningful models of Venusian tectonics and internal dynamics. A discrete model for the structure and properties of the Venusian crust is essential in constraining models for the tectonic and resurfacing history of Venus. In this paper, I investigate an improved quantitative method for interpreting attributes of the Venusian crust from spherical harmonic topographic and gravity models. I use spectral correlation theory to compare gravity effects of topography against free-air gravity anomalies for the tectonically disparate regions of Atalanta Planitia, Beta Regio, and Thetis Regio. For all three areas, observed free-air gravity anomaly magnitudes are much smaller than the gravity effects modeled from topographic relief and there is strong positive correlation between free-air gravity anomalies, topography, and terrain gravity effects. Adjusting terrain gravity effects for correlated free-air gravity anomalies yield compensated effects that I use to estimate Moho relief and crustal thickness variations of the three study regions. For Atalanta Planitia, the crust appears to be relatively thin with peripherally thickened crust associated with concentric ridge belts and tessera terrain. Crustal thickness may increase rapidly between the interior of this lowland plain and the adjacent periphery and highlands. For Beta Regio and Thetis Regio, crustal thicknesses may approach 40 km and 50 km, respectively. Beta Regio, with its large free-air gravity anomalies and apparent structurally related terrain-decorrelated gravity component, may be a partially compensated region. The lack of anticorrelated topographic and gravity features in these disparate tectonic environments is consistent with a largely undifferentiated and dynamically supported crust, which is ubiquitously distributed over the study regions and possibly the entire planet.No embarg

Spontaneous selective deposition of iron oxide nanoparticles on graphite as model catalysts

Iron oxide nanomaterials participate in redox processes that give them ideal properties for their use as earth-abundant catalysts. Fabricating nanocatalysts for such applications requires detailed knowledge of the deposition and growth. We report the spontaneous deposition of iron oxide nanoparticles on HOPG in defect areas and on step edges from a metal precursor solution. To study the nucleation and growth of iron oxide nanoparticles, tailored defects were created on the surface of HOPG using various ion sources that serve as the target sites for iron oxide nucleation. After solution deposition and annealing, the iron oxide nanoparticles were found to nucleate and coalesce at 400 °C. AFM revealed that the particles on the sp3 carbon sites enabled the nanoparticles to aggregate into larger particles. The iron oxide nanoparticles were characterized as having an Fe3+ oxidation state and two different oxygen species, Fe–O and Fe–OH/Fe–OOH, as determined by XPS. STEM imaging and EDS mapping confirmed that the majority of the nanoparticles grown were converted to hematite after annealing at 400 °C. A mechanism of spontaneous and selective deposition on the HOPG surface and transformation of the iron oxide nanoparticles is proposed. These results suggest a simple method for growing nanoparticles as a model catalyst

Mechanical properties and characterization of epoxy composites containing highly entangled as-received and acid treated carbon nanotubes

Huntsman–Merrimack MIRALON® carbon nanotubes (CNTs) are a novel, highly entan-gled, commercially available, and scalable format of nanotubes. As-received and acid-treated CNTs were added to aerospace grade epoxy (CYCOM® 977-3), and the composites were characterized. The epoxy resin is expected to infiltrate the network of the CNTs and could improve mechanical properties. Epoxy composites were tested for flexural and viscoelastic properties and the as-re-ceived and acid treated CNTs were characterized using Field-Emission Scanning and Transmission Electron Microscopy, X-Ray Photoelectron Spectroscopy, and Thermogravimetric Analysis. Composites containing 0.4 wt% as-received CNTs showed an increase in flexural strength, from 136.9 MPa for neat epoxy to 147.5 MPa. In addition, the flexural modulus increased from 3.88 GPa for the neat epoxy to 4.24 GPa and 4.49 GPa for the 2.0 wt% and 3.0 wt% as-received CNT/epoxy compo-sites, respectively. FE-SEM micrographs indicated good dispersion of the CNTs in the as-received CNT/epoxy composites and the 10 M nitric acid 6 h treatment at 120 °C CNT/epoxy composites. CNTs treated with 10 M nitric acid for 6 h at 120 °C added oxygen containing functional groups (C– O, C=O, and O=C–O) and removed iron catalyst present on the as-received CNTs, but the flexural properties were not improved compared to the as-received CNT/epoxy composites

A multiplexed, confinable CRISPR/Cas9 gene drive can propagate in caged Aedes aegypti populations

Aedes aegypti is the main vector of several major pathogens including dengue, Zika and chikungunya viruses. Classical mosquito control strategies utilizing insecticides are threatened by rising resistance. This has stimulated interest in new genetic systems such as gene drivesHere, we test the regulatory sequences from the Ae. aegypti benign gonial cell neoplasm (bgcn) homolog to express Cas9 and a separate multiplexing sgRNA-expressing cassette inserted into the Ae. aegypti kynurenine 3-monooxygenase (kmo) gene. When combined, these two elements provide highly effective germline cutting at the kmo locus and act as a gene drive. Our target genetic element drives through a cage trial population such that carrier frequency of the element increases from 50% to up to 89% of the population despite significant fitness costs to kmo insertions. Deep sequencing suggests that the multiplexing design could mitigate resistance allele formation in our gene drive system

New Approach to Simultaneous In Situ Measurements of the air/liquid/solid interface using PM-IRRAS

Vibrational spectroscopy techniques have evolved to measure gases, liquids, and solids at surfaces and interfaces. In the field of surface-sensitive vibrational spectroscopy, infrared spectroscopy measures the adsorption on surfaces and changes from reactions. Previous polarized modulated-infrared reflection–absorption spectroscopy (PM-IRRAS) measurements at the gas/solid interface were developed to observe catalytic reactions near reaction conditions. Other PM-IRRAS measurements use liquid cells where the sample is submerged and compressed against a prism that has traditionally been used for electrochemical reactions. This article presents a new method that is used to observe in situ adsorption of molecules using PM-IRRAS at the gas/liquid/solid interface. We demonstrate the meniscus method by measuring the adsorption of octadecanethiol on gold surfaces. Characterization of self-assembled monolayers (SAMs), the “gold standard” for PM-IRRAS calibration measurements, was measured in ethanol solutions. The condensed-phase (air/liquid) interface in addition to the liquid/solid interface was measured simultaneously in solution. These are compared with liquid attenuated total reflectance (ATR)-Fourier transform infrared (FTIR) spectroscopy measurements to confirm the presence of the SAM and liquid ethanol. A model of the three-phase system is used to approximate the thickness of the liquid ethanol layer and correlate these values to signal attenuation using PM-IRRAS. This proof-of-concept study enables the measurement of reactions at the gas/liquid/solid interface that could be adapted for other reactions at the electrode and electrolyte interfaces with applications in environmental science and heterogeneous catalysis

Effects of Wet Chemical Oxidation on Surface Functionalization and Morphology of Highly Oriented Pyrolytic Graphite

The knowledge of chemical functionalization for area selective deposition (ASD) is crucial for designing the next generation heterogeneous catalysis. Surface functionalization by oxidation was studied on the surface of highly oriented pyrolytic graphite (HOPG). The HOPG surface was exposed to with various concentrations of two different acids (HCl and HNO3). We show that exposure of the HOPG surface to the acid solutions produce primarily the same -OH functional group and also significant differences the surface topography. Mechanisms are suggested to explain these strikingly different surface morphologies after surface oxidation. This knowledge can be used to for ASD synthesis methods for future graphene-based technologies

De-agglomeration of cathode composites for direct recycling of Li-ion batteries.

Direct recycling of Li-ion batteries (LIBs) reclaims electrode materials using physical separation followed by materials\u27 rejuvenation processes. The cathode composites in LIBs contain both carbon black and PVDF binders in its chemistry. For the rejuvenation process to work, an ability to remove these impurities is desirable. In the present work, de-agglomeration of individual components from the cathode composites has been carried out using a mechanical process that is developed for preserving functional integrity of the cathode active materials. It has been shown that the size of the cathode composites is effectively reduced upon a de-agglomeration process due to a liberation of PVDF binders from the cathode composites. The de-agglomeration performance has been evaluated by separating mixed materials by the degree in surface hydrophobicity using the froth flotation method. The performance improves with end-of-life (EOL) LIBs compared to new LIBs, benefiting from a degradation of PVDF binders after charging-discharging cycles. X-ray photoelectron spectra suggests that the de-agglomeration is done by breaking intermolecular bond between PVDF and cathode active materials as well as covalent bond within PVDF binders. The present work demonstrates a non-chemical method for liberating individual components from cathode composites for the direct recycling of LIBs

Influence of surface etching and oxidation on the morphological growth of Al\u3csub\u3e2\u3c/sub\u3eO\u3c/sub\u3e3\u3csub\u3e by ALD

Selective deposition using atomic layer deposition has potential as a viable method for growing patterned nanostructured materials, thus advancing the design of next-generation electronics and catalysts. This study investigated how etching HOPG produces different densities of functional groups and different morphologies that were found to influence the growth of Al2O3 structures. Hydrochloric acid produced a high density of –OH and –COOH functional sites on terrace regions on HOPG in comparison to nitric acid that produced –OH functional sites at defects. After exposure to ALD cycles of trimethylaluminum and water, different structures of Al2O3 were found to grow on the functional sites compared to defect sites. Field emission scanning electron microscopy, atomic force microscopy and Raman spectral imaging were used to characterize the changes in surface topography after etching and ALD. Vibrational spectroscopy and X-ray photoelectron spectroscopy were used to measure surface functionalization and quantify Al2O3 growth. Results suggest that the Al2O3 nucleation and growth at submonolayer coverage is affected by the surface functionalization as well as the topography and density of functional sites. This study finds that selective deposition on active areas are determined by the morphology and the functional groups that depend on the etching mechanism with the surface. These results suggest that understanding both the topography and type of functional site are necessary for designing the next-generation electronic devices and catalysts

Rapidly responsive smart adhesive-coated micropillars utilizing catechol–boronate complexation chemistry

Smart adhesive hydrogels containing 10 mol% each of dopamine methacrylamide (DMA) and 3-acrylamido phenylboronic acid (APBA) were polymerized in situ onto polydimethylsiloxane (PMDS) micropillars with different aspect ratios (AR = 0.4, 1 and 2). Using Johnson–Kendall–Roberts (JKR) contact mechanics tests, the adhesive-coated pillars demonstrated strong wet adhesion at pH 3 (Wadh = 420 mJ m−2) and can be repeatedly deactivated and reactivated by changing the pH value (pH 9 and 3, respectively). When compared to the bulk adhesive hydrogel of the same composition, the adhesive-coated pillars exhibited a significantly faster rate of transition (1 min) between strong and weak adhesion. This was attributed to an increased surface area to volume ratio of the adhesive hydrogel-coated pillars, which permitted rapid diffusion of ions into the adhesive matrix to form or break the catechol–boronate complex

Satellite Gravity Constraints on the Antarctic Moho and Its Potential Isostatic Adjustments

Abstract We investigate the impact of combining Gravity Field and Steady‐state Ocean Circulation Explorer (GOCE) satellite gravity anomaly and Bedmap2 terrain relief data to enhance Antarctic seismic Moho estimates over the satellite's coverage region south of latitude 60°S. The study considers improving the seismic surface wave‐inferred AN1 Moho (An et al., 2015a, https://doi.org/10.1002/2014JB011332) from misfits of the gravitational effects of the terrain and the seismic Moho computed at 250 km altitude. The updates also relate the GOCE gravity anomalies that correlate directly and inversely with the terrain's gravity effects as isostatic anomalies of the uncompensated mantle relief. These terrain‐correlated effects infer potential isostatic adjustments of the Moho that may help constrain the crust's stress field, track the Gamburtsev Subglacial Mountains to the Kerguelen mantle hotspot, and further test the putative Wilkes Land impact basin for its crustal attributes. Analysis of the gravity‐updated seismic AN1 Moho (sAMoho) estimates suggests that most are within the seismic errors of several kilometers or less. However, the gravity‐updated estimates that are deeper than the sAMoho estimates tend to characterize anomalously hot upper mantle where the assumed mantle‐to‐crust density contrast may be too low. These Moho difference estimates discern elevated heat flow for the Maud Rise, Kerguelen Plateau, Pacific‐Antarctic Ridge, and most of western Antarctica extending from the Pacific‐Antarctic Ridge along the Transantarctic Mountains and across the Ross Sea through Marie Byrd Land and the western margin of the Antarctic Peninsula Microplate to the Scotia Ridge. The methodology of this study also is effective in updating any Moho model for improved gravity and terrain data