Local higher integrability for parabolic quasiminimizers in metric spaces

Using purely variational methods, we prove in metric measure spaces local higher integrability for minimal p-weak upper gradients of parabolic quasiminimizers related to the heat equation. We assume the measure to be doubling and the underlying space to be such that a weak Poincaré inequality is supported. We define parabolic quasiminimizers in the general metric measure space context, and prove an energy type estimate. Using the energy estimate and properties of the underlying metric measure space, we prove a reverse Hölder inequality type estimate for minimal $p$ -weak upper gradients of parabolic quasiminimizers. Local higher integrability is then established based on the reverse Hölder inequality, by using a modification of Gehring’s lemma.     

Electro-oxidation of ethanol using PtSnRh/C electrocatalysts prepared by an alcohol-reduction process

PtRh/C (90:10), PtRh/C (50:50), PtSn/C (50:50), and PtSnRh/C (50:40:10) electrocatalysts were prepared by an alcohol-reduction process using ethylene glycol as solvent and reduction agent and Vulcan Carbon XC72 as supports. The electrocatalysts were characterized by energy-dispersive X-ray analysis, X-ray diffraction, and transmission electron microscopy. The electro-oxidation of ethanol was studied by cyclic voltammetry chronoamperometry at room temperature and on a single cell of a direct ethanol fuel cell at 100 °C. Cyclic voltammetry and chronoamperometry experiments showed that PtSnRh/C and PtSn/C electrocatalysts have similar performance for ethanol oxidation at room temperature, while the activity of PtRh/C electrocatalysts was very low. At 100 °C on a single cell, PtSnRh/C showed superior performance compared to PtSn/C and PtRh/C electrocatalysts.     

Rembrandt's Old Woman Praying, 1629/30: A look below the surface using X-ray fluorescence mapping

Rembrandt's painting Old Woman Praying, 1629/30, is the most valuable and exceptional work of art of the Residenzgalerie Salzburg (RGS). It is painted on a gilded copper plate with dimensions of only approximately 15 × 12 cm. The painting probably belongs to a series of three small-scale tronies, all executed on gilded copper plates. This particular picture preparation, which represents a special feature in Rembrandt's work, is quite unusual in the history of art. Previous investigations on the comparable paintings The Laughing Man, 1629/30, in the Mauritshuis, The Hague and the Self Portrait, 1630, in the National Museum, Stockholm showed that the gilding of the copper plate was applied over a lead white ground. To characterize the painting in the RGS, X-ray fluorescence (XRF) mapping was performed in a collaboration between the Research Office Residenzgalerie, Land Salzburg, the XGLab S.R.L, Milan, and the Conservation Science Department of the Kunsthistorische Museum Vienna (KHM). The results indicate a different structure for this painting than that used for The Laughing Man and the Self Portrait. The gilding was applied directly onto the copper plate, but with three areas with the gilding missing. It seems likely that in these sections, the gold was purposely removed to provide a different darker effect. XRF mapping yielded valuable insights into the structure of the painting and its technique as well as the principal pigments used for its composition.     

Role and effective treatment of dispersive forces in materials: Polyethylene and graphite crystals as test cases

A semiempirical addition of dispersive forces to conventional density functionals (DFT-D) has been implemented into a pseudopotential plane-wave code. Test calculations on the benzene dimer reproduced the results obtained by using localized basis set, provided that the latter are corrected for the basis set superposition error. By applying the DFT-D/plane-wave approach a substantial agreement with experiments is found for the structure and energetics of polyethylene and graphite, two typical solids that are badly described by standard local and semilocal density functionals.     

The Gaussian and augmented-plane-wave density functional method for ab initio molecular dynamics simulations

A new algorithm for density-functional-theory-based ab initio molecular dynamics simulations is presented. The Kohn–Sham orbitals are expanded in Gaussian-type functions and an augmented-plane-wave-type approach is used to represent the electronic density. This extends previous work of ours where the density was expanded only in plane waves. We describe the total density in a smooth extended part which we represent in plane waves as in our previous work and parts localised close to the nuclei which are expanded in Gaussians. Using this representation of the charge we show how the localised and extended part can be treated separately, achieving a computational cost for the calculation of the Kohn–Sham matrix that scales with the system size N as O(NlogN). Furthermore, we are able to reduce drastically the size of the plane-wave basis. In addition, we introduce a multiple-cutoff method that improves considerably the performance of this approach. Finally, we demonstrate with a series of numerical examples the accuracy and efficiency of the new algorithm, both for electronic structure calculations and for ab initio molecular dynamics simulations. Received: 15 December 1998 /Accepted: 18 February 1999 /Published online: 14 July 1999     

Wetting behavior of porous silicon surfaces functionalized with a fulleropyrrolidine

We report the immobilization of a fulleropyrrolidine, bearing a dec-9-ynyl functionality, on silicon surfaces through a thermal hydrosilylation protocol. Contact angle measurements on porous silicon (PS) surfaces reveal an unusual dependence of the angle with the PS roughness that apparently contradicts Wenzel's formula. This result has been explained by an extension of Wenzel's model in which the critical angle, which discriminates between the hydrophilic/hydrophobic character of a solid material, is substantially reduced below 90 degrees by surface roughness.     

Solid-state NMR studies of weak interactions in supramolecular systems

The field of application of solid-state NMR to the study of supramolecular systems is growing rapidly, with many research groups involved in the development of techniques for the study of crystalline and amorphous phases. This Feature Article aims to provide an overview of the recent contributions of our research group to this field, paying particular attention to the study of the weak interactions such as hydrogen bonds in supramolecular systems through solid-state NMR investigations. The structure and dynamic behaviour of selected host-guest systems will be also discussed.     

Enumeration procedure for monitoring test microbe populations on inoculated carriers in AOAC use-dilution methods

The AOAC Use-Dilution methods do not provide procedures to enumerate the test microbe on stainless steel carriers (penicylinders) or guidance on the expected target populations of the test microbe (i.e., a performance standard). This report describes the procedures used by the U.S. Environmental Protection Agency to enumerate the test microbe (carrier counts) associated with conducting the Use-Dilution method with Staphylococcus aureus (Method 955.15) and Pseudomonas aeruginosa (Method 964.02) and the examination of historical data. The carrier count procedure involves the random selection of carriers, shearing bacterial cells from the carrier surface through sonication, and plating of serially diluted inoculum on trypticase soy agar. For each Use-Dilution test conducted, the official AOAC method was strictly followed for carrier preparation, culture initiation, test culture preparation, and carrier inoculation steps. Carrier count data from 78 Use-Dilution tests conducted over a 6-year period were compiled and analyzed. A mean carrier count of 6.6 logs (approximately 4.0 x 10(6) colony-forming units/carrier) was calculated for both S. aureus and P. aeruginosa. Of the mean values, 95% fell within +/- 2 repeatability standard deviations. The enumeration procedure and target carrier counts are desirable for standardizing the Use-Dilution methods, increasing their reproducibility, and ensuring the quality of the data.     

The role of the atomic charges on the ligands and platinum(II) in affecting the cis and trans influences in [PtXL(PPh3)2]+ complexes (X = NO3, Cl, Br, I; L = 4-substituted pyridines, amines, PPh3). A 31P NMR and DFT investigation

One bond Pt-P coupling constants (1)J(PtP) of a series of cationic complexes [PtXL(PPh(3))(2)](+) (X = NO(3), Cl, Br, I; L = 4-Z-pyridines, Z = electron withdrawing or releasing groups, 4a-k; or X = Cl, L = NH(3), PhCH(2)NH(2) and (i)PrNH(2), 5a-c) have been used to establish the trans and cis influence sequences of X and pyridines. The crystal structure of compound 4f(BF(4)) with Z = (t)Bu has been resolved. In the pyridine complexes 4a-d (Z = H, variable X), both the trans and cis influence series of the anionic ligands X decrease along the same sequence I > Br > Cl > NO(3), as previously found for [PtX(PPh(3))(3)](+) (X = NO(3), Cl, Br, I, 3a-d), however in 4a-d the cis influence turns out to be more important than the trans. On the contrary, in [PtCl(4-Z-py)(PPh(3))(2)](+) (4b,e-k) the sequence of the trans influence of the 4-Z-pyridines is opposite to that of the cis, the latter being Z = CN > CHO > Br > PhCO > H > Me > (t)Bu > NH(2), i.e. the most basic pyridine gives rise to the lowest cis influence. This correlation was found to hold also for complexes 5a-c (L = amines). All the observed trends have been fully reproduced by B3LYP/def2-SVP DFT calculations, by looking at the relevant optimized bond lengths of selected complexes of type 3, 4 and 5. Subsequent evaluation of the atomic charges, by resorting to two independent methods, i.e., the Natural Bond Order analysis of the wavefunction and the Bader's Quantum Theory of Atoms in Molecules, allowed for rationalization of the origin of the cis and trans influences. The negative charge on the nitrogen atoms of free pyridines becomes more negative upon protonation and even more so when coordinated to the [PtCl(PPh(3))(2)](+) moiety. The least negatively charged nitrogen atom of coordinated pyridines is that of 4-CN-py (the highest cis influencing pyridine derivative), which gives rise to the lowest positive charge on Pt, confirming the relationship between the lowering of the charge on the metal ion and a high cis influence. The trans influence can be described in terms of competition between the charges on the two trans donor atoms. In contrast with the behaviour of pyridines, the positive charge on the phosphorous atom of free PPh(3) increases upon coordination to Pt(II), moreover the PPh(3) ligands acquire a substantial positive charge, thus efficiently delocalising the charge of the cationic complex.     

Mononuclear heterocyclic rearrangements. Part 4 Synthesis and characterization of the E-isomer phenylhydrazone of 3-benzoyl-5-phenyl-1,2,4-oxadiazole

3-Benzoyl-5-phenyl-1,2,4-oxadiazole (I) with phenylhydrazine in acetic acid gives the two geometrical isomers, phenylhydrazones II-Z and II-E, which have been characterized by uv-visible, ir, and nmr spectra. The possible II-E ? II-Z isomerization as well as the rearrangement of II-Z and of II-E into 2,5-diphenyl-4-benzoylamino-1,2,3-triazole (III) has been pointed out.