Chemisorption and reaction of NH3 on Ni(111)

The chemisorption of ammonia on Ni(111) has been investigated using LEED, thermal desorption, and angle-resolved photoemission. For exposures at 200 K, thermal desorption shows a coverage-dependent binding energy associated with dipole-dipole interactions. A (2 × 2) LEED pattern occurs at 2–4 L exposure. Time dependence of the LEED pattern and changes in the thermal desorption induced by the LEED beam indicate that the (2 × 2) pattern is due to a stable intermediate decomposition species. Using synchrotron radiation photoemission all three valence orbitals of ammonia have been observed for the first time. The energies of the ammonia-induced features in the photoemission (?22.0, ?11.0 and ?6.7 eV below the Fermi energy) and the observed symmatries positively identify the absorbed species as molecular ammonia. Additional structure observed in the photoemission spectra after electron bombardment is associated with the stable adsorbed intermediate.     

Measurement of alligator (Alligator mississippiensis) serum angiotensin converting enzyme (ACE) using a miniaturized colorimetric assay

Oftentimes enzyme assays can be difficult when utilizing tissues from rare, endangered or exotic animals due to limited tissue supplies. We have miniaturized a common assay for angiotensin converting enzyme (ACE) to a microtiter plate format. The assay is based on the reduction of the optical density at 340 nm when the substrate 2-furanacryloyl-l-phenylalanylglycylglycine (FAPGG) is enzymatically-converted to the product 2-furanacryloyl-l-phenylalanine (FAP). The assay was used to measure ACE activity in alligator serum. The optimal pH for this assay was 7, while the ionic strength-dependence was optimal at 25–50 mM NaCl. ACE enzyme activity requires zinc, and thus the assay was sensitive to the presence of EDTA. Inclusion of only 0.2 mM EDTA-inhibited ACE activity by more than 70%. The assay only required the use of only 10 μL of sample for measurable activity, and maximal activity was recorded using 60–65 μL of serum, making it ideal for use with small amounts of blood or tissue extract.     

Characterization of mannitol in Curvularia protuberata hyphae by FTIR and Raman spectromicroscopy

FTIR and Raman spectromicroscopy were used to characterize the composition of Curvularia protuberata hyphae, and to compare a strain isolated from plants inhabiting geothermal soils with a non-geothermal isolate. Thermal IR source images of hyphae have been acquired with a 64 × 64 element focal plane array detector; single point IR spectra have been obtained with synchrotron source light. In some C. protuberata hyphae, we have discovered the spectral signature of crystalline mannitol, a fungal polyol with complex protective roles. With FTIR-FPA imaging, we have determined that the protein content in cells remains fairly constant throughout the length of a hypha, whereas the mannitol is found at discrete, irregular locations. This is the first direct observation of mannitol in intact fungal hyphae. Since the concentration of mannitol in cells varies with respect to position and is not present in all hyphae, this discovery may be related to habitat adaptation, fungal structure and growth stages.     

Mechanically robust 3D graphene macroassembly with high surface area

We report the synthesis of a three-dimensional (3D) macroassembly of graphene sheets with electrical conductivity (～10(2) S m(-1)) and Young's modulus (～50 MPa) orders of magnitude higher than those previously reported, super-compressive deformation behavior (～60% failure strain), and surface areas (>1300 m(2) g(-1)) approaching theoretically maximum values.     

Intrinsically linked signed graphs in projective space

We define a signed embedding of a signed graph into real projective space to be an embedding such that an embedded cycle is 0-homologous if and only if it is balanced. We characterize signed graphs that have a linkless signed embedding. In particular, we exhibit 46 graphs that form the complete minor-minimal set of signed graphs that contain a non-split link for every signed embedding. With one trivial exception, these graphs are derived from different signings of the seven Petersen family graphs.     

In‐plane structure of ferecrystalline compounds

This work provides a review on the in‐plane structure of a recently established subgroup of misfit layer compounds, namely ferecrystals. While misfit layer compounds can be described as layered intergrowths of two distinct substructures in which only one axis of the subunits remains incommensurate, for ferecrystals both constituents retain independent in‐plane crystalline structures. This is accompanied by extensive rotational disorder, a key feature of ferecrystals. Our comparison of the in‐plane structures of misfit layer compounds and ferecrystals suggests that the weaker registration between the subunits in ferecrystals allows the synthesis of a wider variety of compounds, varying both the range of constituents, their mismatch and their thicknesses. The in‐plane structures of the individual constituents in ferecrystalline compounds exhibit interesting features such as 2D‐symmetry, size induced structural transformation, misfit parameters that depend on the component thicknesses, and pairing distortions of constituent layers.     

Porosity measurements in natural porous rocks using magnetic resonance imaging

A magnetic resonance imaging (MRI) method is presented to measure localized porosity values inside natural porous rocks for the purpose of obtaining frequency distributions of the porosity (porosity distributions). The method is applied to study six different cores, including three Berea sandstone samples, Casper sandstone, Indiana limestone, and San Andres dolomite. An image of the porosity is shown for a transverse and a longitudinal slice in order to show qualitative variations of the porosity within each core sample. The porosity distribution for the entire core has been acquired, and it is shown with a Gaussian fit to the data. In addition, for cores known to have a layered structure, a bimodal distribution is fit to the data, and the fit is used to estimate the value of the porosity for two characteristic types of layers within the core sample.