Analysis of a lateral-directional airframe/propulsion system interaction of a Mach 3 cruise aircraft.
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Gilyard, G. B.↗
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Influence of Terminal Carboxyl Groups on the Structure and Reactivity of Functionalized m-Carboranethiolate Self-Assembled Monolayers
The structure and function of self-assembled monolayers (SAMs) at the nanoscale are determined by the steric and electronic effects of their building blocks. Carboranethiol molecules form pristine monolayers that provide tunable two-dimensional systems to probe lateral and interfacial interactions. Additional ω-functionality, such as carboxyl groups, can be introduced to change the properties of the exposed surfaces. Here, two geometrically similar isomeric m-carborane analogues of m-mercaptobenzoic acid, 1-COOH-7-SH-1,7-C 2 B 10 H 10 and racem-1-COOH-9-SH-1,7-C 2 B 10 H 10 , are characterized and their SAMs on Au{111} are examined. The latter isomer belongs to the rare group of chiral cage molecules and becomes, to our knowledge, the first example assembled on Au{111}. Although different in symmetry, molecules of both isomers assemble into similar hexagonal surface patterns. The nearest-neighbor spacing of 8.4 ± 0.4 Å is larger than that of non-carboxylated isomers, consistent with the increased steric demands of the carboxyl groups. Computational modeling reproduced this spacing and suggests a tilt relative to the surface normal. However, tilt domains are not observed experimentally, suggesting the presence of strong lateral interactions. Analyses of the influence of the functional groups through the pseudo-aromatic m-carborane skeleton showed that the thiol group attached to either carbon or boron atoms increases the carboxyl group acidity in solution. In contrast, the acidity of the exposed carboxyl group in the SAMs decreases upon surface attachment; computational analyses suggest that the driving force of this shift is the dielectric of the environment in the monolayer as a result of confined intermolecular interactions, proximity to the Au surface, and partial desolvation.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Interaction position, time, and energy resolution in organic scintillator bars with dual-ended readout
We report on the position, timing, and energy resolution of a range of plastic scintillator bars and reflector treatments using dual-ended silicon photomultiplier readout. These measurements are motivated by the upcoming construction of an optically segmented single-volume neutron scatter camera, in which neutron elastic scattering off of hydrogen is used to kinematically reconstruct the location and energy of a neutron-emitting source. For this application, interaction position resolutions of about 10 mm and timing resolutions of about 1 ns are necessary to achieve the desired efficiency for fission-energy neutrons. The results presented here indicate that this is achievable with an array of 5 x 5 x 190 mm 3 bars of EJ-204 scintillator wrapped in Teflon tape, read out with SensL’s J-series 6 x 6 mm 2 silicon photomultipliers. With two independent setups, we also explore the systematic variability of the position resolution, and show that, in general, using the difference in the pulse arrival time at the two ends is less susceptible to systematic variation than using the log ratio of the charge amplitude of the two ends. Finally, we measure a bias in the absolute time of interactions as a function of position along the bar: the measured interaction time for events at the center of the bar is 100 ps later than interactions near the SiPM.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Aerodynamic interactions from reaction controls for lateral control of the M2-F2 lifting-body entry configuration at transonic and supersonic and supersonic Mach numbers
Tests were conducted in the Ames 6 by 6 foot wind tunnel to determine the interaction of reaction jets for roll control on the M2-F2 lifting-body entry vehicle. Moment interactions are presented for a Mach number range of 0.6 to 1.7, a Reynolds number range of 1.2 x 10 to the 6th power to 1.6 x 10 to the 6th power (based on model reference length), an angle-of-attack range of -9 deg to 20 deg, and an angle-of-sideslip range of -6 deg to 6 deg at an angle of attack of 6 deg. The reaction jets produce roll control with small adverse yawing moment, which can be offset by horizontal thrust component of canted jets.
Bailey, R. O.↗
Topographically driven crustal flow and its implication to the development of pinned oroclines
Pinned oroclines, a type of curved orogen which results from lateral pinning of a growing fold-thrust belt, tend to resemble parabolic Newtonian curvature modified by different degrees of flattening at the flow front. It is proposed that such curves can be generated by Newtonian crustal flow driven by topographic variations. In this model, regional topographic differences create a regional flow which produces a parabolic flow front on interaction with lateral bounding obstacles. Local topographic variations modify the parabolic curves and yield more flat-crested, non-Newtonian-type curvatures. A finite-difference thin-skin tectonic simulation demonstrates that both Newtonian and non-Newtonian curved orogens can be produced within a Newtonian crust.
Hsui, Albert T.↗
The Influence of Contrasting Microbial Lifestyles on the Pre-symbiotic Metabolite Responses of Eucalyptus grandis Roots
Plant roots co-inhabit the soil with a diverse consortium of microbes of which a number attempt to enter symbiosis with the plant. These microbes may be pathogenic, mutualistic, or commensal. Hence, the health and survival of plants is heavily reliant on their ability to perceive different microbial lifestyles and respond appropriately. Emerging research suggests that there is a pivotal role for plant root secondary metabolites in responding to microbial colonization. However, it is largely unknown if plants are able to differentiate between microbes of different lifestyles and respond differently during the earliest stages of pre-symbiosis (i.e., prior to physical contact). In studying plant responses to a range of microbial isolates, we questioned: (1) if individual microbes of different lifestyles and species caused alterations to the plant root metabolome during pre-symbiosis, and (2) if these early metabolite responses correlate with the outcome of the symbiotic interaction in later phases of colonization. We compared the changes of the root tip metabolite profile of the model tree Eucalyptus grandis during pre-symbiosis with two isolates of a pathogenic fungus (Armillaria luteobubalina), one isolate of a pathogenic oomycete (Phytophthora cinnamomi), two isolates of an incompatible mutualistic fungus (Suillus granulatus), and six isolates of a compatible mutualistic fungus (Pisolithus microcarpus). Untargeted metabolite profiling revealed predominantly positive root metabolite responses at the pre-symbiosis stage, prior to any observable phenotypical changes of the root tips. Metabolite responses in the host tissue that were specific to each microbial species were identified. A deeper analysis of the root metabolomic profiles during pre-symbiotic contact with six strains of P. microcarpus showed a connection between these early metabolite responses in the root with later colonization success. Further investigation using isotopic tracing revealed a portion of metabolites found in root tips originated from the fungus. RNA-sequencing also showed that the plant roots undergo complementary transcriptomic reprogramming in response to the fungal stimuli. Taken together, our results demonstrate that the early metabolite responses of plant roots are partially selective toward the lifestyle of the interacting microbe, and that these responses can be crucial in determining the outcome of the interaction.
59 BASIC BIOLOGICAL SCIENCES↗
Interaction Effects Produced by Jet Exhausting Laterally Near Base of Ogive-Cylinder Model in Supersonic Main Stream
The experimentally determined interaction effects of a side jet exhausting near the base of an ogive-cylinder model are presented and discussed. The interaction force appears to be independent of main-stream Mach number, boundary-layer condition (laminar or turbulent), angle of attack, and forebody length. The ratio of interaction force to jet force is found to be inversely proportional to the square root of the product of jet stagnation-to-free-stream pressure ratio and jet-to-body diameter ratio.
Vinson, P. W.↗
Thermodynamics of amyloid formation and the role of intersheet interactions
The self-assembly of proteins into β-sheet-rich amyloid fibrils has been observed to occur with sigmoidal kinetics, indicating that the system initially is trapped in a metastable state. Here, we use a minimal lattice-based model to explore the thermodynamic forces driving amyloid formation in a finite canonical (NVT) system. By means of generalized-ensemble Monte Carlo techniques and a semi-analytical method, the thermodynamic properties of this model are investigated for different sets of intersheet interaction parameters. When the interactions support lateral growth into multi-layered fibrillar structures, an evaporation/condensation transition is observed, between a supersaturated solution state and a thermodynamically distinct state where small and large fibril-like species exist in equilibrium. Intermediate-size aggregates are statistically suppressed. These properties do not hold if aggregate growth is one-dimensional.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Atomically Resolved Elucidation of the Electrochemical Covalent Molecular Grafting Mechanism of Single Layer Graphene
Engineering graphene at the atomic level via chemical doping, substrate interactions or lateral confinement opens up avenues for precise tuning of its electronic and magnetic properties. Chemical doping by covalent modification routes using electrochemical tools offers rich opportunities that are yet to be fully explored. The key to controlling graphene's physicochemical properties requires a detailed atomistic understanding of the geometry and mechanism of the covalent attachment process. By employing diaryliodonium salts instead of the commonly used diazonium salts, precise molecular grafting onto epitaxial graphene is achieved. Using atomically resolved imaging via scanning tunneling microscopy it is shown that for single layer, high quality, low defect graphene, the functionalization process is controlled by kinetics rather than thermodynamics in accord with Marcus–Gerisher theory. The predominance of the preferential pairwise attachment of molecular grafts specifically on the same graphene sublattice gives rise to ferromagnetic properties previously observed in nitrophenyl modified graphene. Furthermore, p-type doping has been quantified by electrical measurements and angle resolved photoelectron spectroscopy. Overall this electrochemical route for precise covalent functionalization of single layer graphene is general and can be straightforwardly extended to other 2D few-layer confined materials such as transition metal chalcogenides.
36 MATERIALS SCIENCE↗
Investigation of the reaction mechanism of the hydrodeoxygenation of propionic acid over a Rh(1 1 1) surface: A first principles study
Microkinetic models based on first principles calculations have been used to study the vapor and liquid phase hydrodeoxygenation of propionic acid on a Rh(111) surface. Calculations suggest that both decarboxylation and decarbonylation do not occur at an appreciable rate under all reaction environments. Propanol and propionaldehyde are the main products on this surface and they are produced at similar rates in both vapor and liquid phase environments. While a condensed phase can shift the reaction rate, the dominant pathways and selectivity towards the various products are hardly affected. At 473 K, the turnover frequency is increased by about a factor of 1.5 in liquid water relative to the gas phase. In liquid 1,4-dioxane, the turnover frequency is also slightly increased relative to the gas phase. Here, given the uncertainty in Rh cavity radius in the liquid phase calculations, computations with different cavity radii have been performed. With larger Rh cavity radius, the promotional effect of the solvents on the turnover frequency becomes more significant, while practically no changes are observed for a smaller cavity radius.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Direct Observations of Ion Densities at Functionalized Interfaces to Test Hypotheses Regarding the Origin of Specific Ion Effects
Interactions of anions with protonatable groups were investigated using X-ray fluorescence near total reflection (XFNTR) on floating monolayers at the surface of water. The number of ions attracted to the interfacial region, which XFNTR measures directly, is ion-specific as well as monolayer-specific. Our observation of the distinctly different behaviors of ClO 4 – and ReO 4 – , two ions with the same tetrahedral structure and almost the same sizes and hydration enthalpies, challenges current theories of ion specificity. Our observations are inconsistent with not only the Gouy–Chapman model (as expected) but also size-modified Poisson–Boltzmann theory and the “law of matching water affinity”. Furthermore, we suggest that factors other than ion size and ion–water interactions, including possibly ion–ion interactions and lateral ordering at the interface, must be considered to account for specific ion effects.
36 MATERIALS SCIENCE↗
Microscopic insights into long-range 1D ordering in a dense semi-disordered molecular overlayer
In this work, the formation of a two-phase surface molecular overlayer that transitions from isolated propene molecules to a highly ordered 1D chain structure on Cu(111) is elucidated through combined high-resolution STM imaging and DFT-based calculations. These models reveal how disordered molecules present in-between the 1D chains stabilizes the system as a whole.
09 BIOMASS FUELS↗
THE ACS LCID PROJECT: ON THE ORIGIN OF DWARF GALAXY TYPES—A MANIFESTATION OF THE HALO ASSEMBLY BIAS?
We discuss how knowledge of the whole evolutionary history of dwarf galaxies, including details on the early star formation events, can provide insight on the origin of the different dwarf galaxy types. We suggest that these types may be imprinted by the early conditions of formation rather than only being the result of a recent morphological transformation driven by environmental effects. We present precise star formation histories of a sample of Local Group dwarf galaxies, derived from color–magnitude diagrams reaching the oldest main-sequence turnoffs. We argue that these galaxies can be assigned to two basic types: fast dwarfs that started their evolution with a dominant and short star formation event and slow dwarfs that formed a small fraction of their stars early and have continued forming stars until the present time (or almost). These two different evolutionary paths do not map directly onto the present-day morphology (dwarf spheroidal versus dwarf irregular). Slow and fast dwarfs also differ in their inferred past location relative to the Milky Way and/or M31, which hints that slow dwarfs were generally assembled in lower-density environments than fast dwarfs. We propose that the distinction between a fast and slow dwarf galaxy primarily reflects the characteristic density of the environment where they form. At a later stage, interaction with a large host galaxy may play a role in the final gas removal and ultimate termination of star formation.
79 ASTRONOMY AND ASTROPHYSICS↗
Vibration and buckling studies of pretensioned structures
Results of analyses and tests of a simple pretensional structure are presented. Linear finite element analysis correlated well with experimental small amplitude vibration data. The buckling and vibration behavior of a pretensional stayed column was studied in detail. The bifurcation buckling load was also predicted accurately. Postbuckling behavior of the column was unusual and results in a post buckling restoring force of only 1/64 the bifurcation buckling load. Interaction between lateral accelerations and compressive load creates isolated stay slackening at loads above 50 percent of the buckling load. Further research will be required to fully understand their impact on the use of pretensioned structures as large space structures.
Belvin, W. K.↗
Basin-wide gradients in dolomite d26Mg and 87Sr/86Sr identify the structural centre of the Williston Basin as a source of magnesium for dolomitization of the Middle Devonian Winnipegosis Formation
Dolomitized carbonates in the Williston Basin are common below the Middle Devonian Prairie Evaporite Formation, indicating a plausible role for brine-reflux as the source of Mg for dolomitization. However, the Lower Member Winnipegosis Formation, which directly underlies the evaporite sequence, exhibits dolomite 87Sr/86Sr ratios that are higher than expected for Middle Devonian seawater, instead suggesting that the dolomitizing fluids ascended from the deep basin where present-day formation waters are known to be more radiogenic. This interpretation is supported in this study by Mg isotope data showing a basin-scale gradient of increasing d26Mg values from the deep center (–2.03‰) to the edge (–1.34‰) of the Williston Basin along the lower Member Winnipegosis bed. Dolomite favors light isotopes of Mg when it forms, thus driving dolomitizing solutions, and the produced dolomite, towards heavier isotopic compositions in the direction of fluid flow. However, dolomite is also Mg-deficient when it forms, and its initial Mg isotope composition is susceptible to alteration by fluid-rock interactions occurring later in the depositional history of the deposit. We argue that the Mg isotope gradient in the Lower Member Winnipegosis was created by an ascending flow of isotopically light Mg-bearing fluid that differentially altered an earlier formed brine-reflux dolomite, with more alteration occurring deeper in the basin and less towards to edges. Alteration of pre-existing dolomite by an Mg isotope exchange mechanism requires large supplies of Mg. This fact, and the direction of fluid flow point to the underlying crystalline basement as an important Mg source for dolomitization in the Williston Basin. We speculate that ultramafic rocks supplied the Mg when they were hydrothermally altered during an anomalous heating event that affected the Williston Basin in the Late Devonian / Early Carboniferous. Seismic pumping drove these fluids upwards through fracture networks in the crust, and eventually into the deep center of the Williston Basin along vertically-oriented down-to-the-basement faults, pressuring deep aquifers like the Winnipegosis, which resulted in fluids migrating up the stratigraphic dip of the beds towards the edges of the basin. Plotting and contouring the dolomite d26Mg data on a map of the Williston Basin reveals the pathways taken by the migrating fluids. One prominent pathway extending outwards from the center of the basin towards the northeast bears a strong resemblance to petroleum migration fairways deduced for the underlying Late Ordovician Red River Formation. This study demonstrates that Mg isotopic mapping of large dolomite bodies is a useful tool for deciphering fluid flow histories in sedimentary basins and may assist in locating migrated petroleum and Mississippi Valley Type ore deposits.
Magnesium Isotopes, Strontium Isotopes, Dolomitiza↗
Atomistic mechanisms for bilayer growth of graphene on metal substrates
Epitaxial growth on metal substrates has been shown to be the most powerful approach in producing large-scale high-quality monolayer graphene, yet it remains a major challenge to realize uniform bilayer graphene growth. Here we carry out a comparative study of the atomistic mechanisms for bilayer graphene growth on the (111) surfaces of Cu and Ni, using multiscale approaches combining first-principles calculations and rate-equation analysis. We first show that the relatively weak graphene-Cu interaction enhances the lateral diffusion and effective nucleation of C atoms underneath the graphene island, thereby making it more feasible to grow bilayer graphene on Cu. In contrast, the stronger graphene-Ni interaction suppresses the lateral mobility and dimerization of C atoms underneath the graphene, making it unlikely to achieve controlled growth of bilayer graphene on Ni. We then determine the critical graphene size beyond which nucleation of the second layer will take place. Intriguingly, the critical size exhibits an effective inverse "Ehrlich-Schwoebel barrier" effect, becoming smaller for faster C migration from the Cu surface to the graphene-Cu interface sites across the graphene edge. Lastly, these findings allow us to propose a novel alternating growth scheme to realize mass production of bilayer graphene.
36 MATERIALS SCIENCE↗
Organic molecules deposited on graphene: A computational investigation of self-assembly and electronic structure
We use ab initio simulations to investigate the adsorption and the self-assembly processes of tetracyanoquinodimethane (TCNQ), tetrafluoro-tetracyanoquinodimethane (F4-TCNQ), and tetrasodium 1,3,6,8-pyrenetetrasulfonic acid (TPA) on the graphene surface. We find that there are no chemical bonds at the molecule–graphene interface, even at the presence of grain boundaries on the graphene surface. The molecules bond to graphene through van der Waals interactions. In addition to the molecule–graphene interaction, we performed a detailed study of the role played by the (lateral) molecule–molecule interaction in the formation of the, experimentally verified, self-assembled layers of TCNQ and TPA on graphene. Regarding the electronic properties, we calculate the electronic charge transfer from the graphene sheet to the TCNQ and F4-TCNQ molecules, leading to a p-doping of graphene. Meanwhile, such charge transfer is reduced by an order of magnitude for TPA molecules on graphene. In this case, it is not expected a significant doping process upon the formation of self-assembled layer of TPA molecules on the graphene sheet.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
An Analytical Model for Non-Uniform Magnetic Field Effects on Two-Dimensional Laminar Jet Diffusion Flames
In 1846, Michael Faraday found that permanent magnets could cause candle flames to deform into equatorial disks. He believed that the change in flame shape was caused by the presence of charged particles within the flames interacting with the magnetic fields. Later researchers found that the interaction between the flame ions and the magnetic fields were much too small to cause the flame deflection. Through a force analysis, von Engel and Cozens showed that the change in the flame shape could be attributed to the diamagnetic flame gases in the paramagnetic atmosphere. Paramagnetism occurs in materials composed of atoms with permanent magnetic dipole moments. In the presence of magnetic field gradients, the atoms align with the magnetic field and are drawn into the direction of increasing magnetic field. Diamagnetism occurs when atoms have no net magnetic dipole moment. In the presence of magnetic gradient fields, diamagnetic substances are repelled towards areas of decreasing magnetism. Oxygen is an example of a paramagnetic substance. Nitrogen, carbon monoxide and dioxide, and most hydrocarbon fuels are examples of diamagnetic substances. In order to evaluate the usefulness of these magnets in altering flame behavior, a study has been undertaken to develop an analytical model to describe the change in the flame length of a laminar diffusion jet in the presence of a nonuniform magnetic field.
Calvert, M. E.↗