Characteristics and microstructure of aqueous colloidal dispersions of graphite oxide

A highly oxidized graphite oxide was synthesized from natural graphite powder by oxidation with KMnO₄ in concentrated H₂SO₄ followed by hydrolysis, washing and centrifugation. Concentrated gel-like colloidal dispersions were obtained. The corresponding filtrates, supernatants, GO dispersions, and solid GO films obtained from them, were investigated by various chemical analyses, small angle X-ray scattering, X-ray diffraction, light scattering (LS), Scanning Electron Microscopy, Fourier Transform Infrared Spectroscopy, ¹³C Nuclear Magnetic Resonance and Thermo-Gravimetric Analysis. The spectroscopic analysis shows besides the common peaks assigned to water molecules, hydroxyl and carboxyl groups, elimination of CC bonds due to strong oxidation and presence of bands assigned to sulfate. Data of Gas Chromatography/Mass Spectrometry experiments confirm the presence in GO of water and an abundance of carboxyl groups. Scattering measurements confirm that the structure of the GO colloids consists of plate-like objects, mostly containing only a few layers, with a small population of thicker aggregates. SEM images of cross sections of dried GO film, obtained by freeze fracture, demonstrate that a continuous film-like structure was successfully achieved by elimination of water localized within exfoliated GO particles in the swelled GO aqueous colloidal dispersions.     

Cardenolide sequestration by the dogbane tiger moth (Cycnia tenera; Arctiidae)

Cycnia tenera adults, reared as larvae onAsclepias humistrata, had 10 times higher cardenolide concentrations, and contained 15 times more total cardenolide, than did moths reared onA. tuberosa. Thin-layer chromatography confirmed that each individual cardenolide visualized in the adult moths reared on the former host plant corresponds to one present in the plant, thus demonstrating that the insects' cardenolides are indeed derived from the larval food. Adult weights were significantly greater when the larvae had been fed upon the higher cardenolide plant species,A. humistrata. Similar results for other milkweed-feeding insects have been interpreted by some authors as evidence against a metabolic cost of handling cardenolides. However, such interpretations confound cardenolide differences among milkweed species with other differences in plant primary and secondary chemistry that affect insect growth and development. While the cooccurrence inC. tenera of other noxious chemicals (e.g., alkaloids) is not precluded, cardenolides sequestered from larval host plants have probably contributed to the evolution of visual and auditory aposematism in this species. As the eggs are laid in large clutches and larvae are gregarious, such aposematism may have evolved via kin selection.     

Methods of reducing loss of efficiency due to discreteness of distributions

All models of this paper involve R x C contingency tables in which the total frequency is fixed (full multinomial model), or in which the row totals are fixed (product multinomial model). For the most part, we assume that the column categories are ordered. For the full multinomial model the null hypothesis of interest is independence, i.e., the (ij)th cell probability is the product of the marginal probabilities of the ith row and jth column. In the product multinomial model the null hypothesis is that the R multinomial distributions have the same vector of cell probabilities. Our review includes (1) a careful listing of two-sided and one-sided alternatives, and (2) methodology to reduce the loss of efficiency of tests because of the discreteness of the model (The methodologies discussed are efficient in several senses. Tests are exact. Tests have very favorable and robust power properties. Tests make use of back-up statistics, thereby providing a finer grid of p-values. In some special cases, e.g., a 2 x C table and a one-sided alternative, conditional p-values are found, within seconds, simply by entering row frequencies into a given website. Thus, computational efficiency is exceptional.), and (3) a critique of some exact linear permutation tests (that are conditional on row and column margins) for both two-sided and some one-sided alternatives. Furthermore, recommendations as to which tests to use for specific alternatives are made.     

New intermediates in the conversion of stigmasterol to cholestanol in the Mexican bean beetle

Three intermediates involved in the conversion of stigmasterol to cholestanol in the Mexican bean beetle,Epilachna varivestis, were isolated and identified from an insect for the first time. The three new insect sterols, 22-stigmastenol, 22,24-cholestadienol and 24-cholestenol, were shown to be metabolites of [³H]stigmasterol and accumulated in insect tissues when larvae were fed lima bean leaves coated with azasteroid inhibitors. The side chain metabolism of the ubiquitous phytosterol stigmasterol in the Mexican bean beetle is similar to that in other species that produce cholesterol from C₂₈ and C₂₉ phytosterols; however, the Mexican bean beetle initially reduces the Δ⁵-bond and produces mainly cholestanol and lesser amounts of lathosterol as dealkylation products.     

Sterol metabolism studies in rats: Effects of taurodeoxycholic acid feeding on sterol metabolism

Sterol metabolism studies using isotopic and chromatographic techniques were carried out in: (a) control rats fed stock chow +0.1% cholesterol (control group), and (b) rats fed stock chow +0.1% cholesterol and supplemented with 0.5% sodium taurodeoxycholate (taurodeoxycholate group). Feeding the bile acid enriched diet led to decreased acidic steroid synthesis, decreased cholesterol turnover, and cholesterol balance compared to nonsupplemented controls. There were no significant differences in fecal neutral sterol output, endogenous neutral sterol output, or cholesterol absorption between bile acid fed animals and controls. Tissue cholesterol levels (liver, plasma, and bile) in the two groups were also similar.     

Detergency of binary mixtures of LAS/STPP and LAS/Zeolites: influence of (Ca++) on the washing liquor

The influence of sodium tripolyphosphate (STPP) or zeolites on the detergency performance of linear alkylbenzene sulfonate (LAS) has been evaluated at different water hardness levels. This study demonstrates that STPP or zeolite behaves either as a sequestrant or through an important synergism with LAS, showing a minimum and a maximum in detergency performance, depending on the water hardness level. There is an optimum LAS/builder ratio for each individual water hardness level. This optimum has to be determined experimentally as it will not always necessarily coincide with the highest surfactant and/or builder concentrations.     

Volume strain measurements on CACO3/polypropylene particulate composites: The effect of particle size

The use of rigid fillers to toughen polymers has received considerable attention in recent years. The role of the rigid particle here is that of debonding, at some stage, from the matrix, thus triggering dilatational processes similar to those observed in rubber‐toughened polymers. The role of particle size in these rigid filled composites has not been studied in great detail. In this work, volume strain measurements were carried out on a series of particulate composites based on polypropylene filled with calcium carbonate (CC) particles with average diameters of 0.07, 0.7, and 3.5 μm and filler volume fractions ranging from 0.05 to 0.30. The experimental results have shown a strong particle size effect. A model is proposed to take this effect into account, based upon the formation of an immobilized layer of polymer on the surface of the filler particles. The experimental results are consistent with a surface layer of 15–25 nm. The results are discussed in relation to the fracture behavior of these composites reported earlier. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 925–935, 2004     

Surface modifications of polymers with fluorine-containing plasmas: Deposition versus replacement reactions

Surfaces of polyethylene; poly(vinyl fluoride), poly(vinylidene fluoride), poly(tetrafluoroethylene), cellulose acetate butyrate, and polyoxymethylene were modified in various cold plasma reactions; feed gases to the plasma reactor were trifluoromethane, hexafluoroethane, and tetrafluoromethane. Using X-ray photoelectron spectroscopy (ESCA) to characterize the surfaces, it was established that the plasma reactions lead to fluorinated surfaces containing ? CF₃, ? CF₂, and ? CF groups, All of these fluorinated surfaces exhibit advancing contact angles (with water) larger than 900. However, differences in the ESCA spectra, weight-gain/-loss measurements and scanning-electron-microscopy (SEM) photographs reveal that the mechanisms of fluorination in the various plasma environments are markedly different. The CF₃H gas polymerizes in the gas phase of the plasma and deposits a smooth, fluorinated film on polymers and other substrates. The C₂F₆ plasma simultaneously etches polymers and polymerizes onto polymer surfaces. The CF₄ plasma etches and reacts with the polymer surface but does not polymerize. For polyoxymethylene, the combined roughening (by etching) and fluorination of the surfaces lead to completely non-wettable surfaces (water contact angle approximately 180°). The highly non-wettable surfaces of these two polymers are believed to result from the physical etching and roughening at a very fine scale (approximately five micrometers) while the outermost surfaces are reacting to become highly fluorinated.     

An Optimal Transport Approach to Robust Reconstruction and Simplification of 2D Shapes

We propose a robust 2D shape reconstruction and simplification algorithm which takes as input a defect‐laden point set with noise and outliers. We introduce an optimal‐transport driven approach where the input point set, considered as a sum of Dirac measures, is approximated by a simplicial complex considered as a sum of uniform measures on 0‐ and 1‐simplices. A fine‐to‐coarse scheme is devised to construct the resulting simplicial complex through greedy decimation of a Delaunay triangulation of the input point set. Our method performs well on a variety of examples ranging from line drawings to grayscale images, with or without noise, features, and boundaries.