Centrally symmetric polytopes with many faces

We present explicit constructions of centrally symmetric polytopes with many faces: (1) we construct a d-dimensional centrally symmetric polytope P with about 3 ^d/4 ≈ (1.316) ^d vertices such that every pair of non-antipodal vertices of P spans an edge of P, (2) for an integer k ≥ 2, we construct a d-dimensional centrally symmetric polytope P of an arbitrarily high dimension d and with an arbitrarily large number N of vertices such that for some 0 < δ _k < 1 at least (1 ? (δ _k ) ^d )( _k ^N ) k-subsets of the set of vertices span faces of P, and (3) for an integer k ≥ 2 and α > 0, we construct a centrally symmetric polytope Q with an arbitrarily large number of vertices N and of dimension d = k ^1+o(1) such that at least $(1 - k^{ - \alpha } )(_k^N )$ k-subsets of the set of vertices span faces of Q.     

X-ray absorption study of Cu,Zn SOD under high pressure

Abstract

We have investigated Cu, Zn Superoxide Dismutase (Cu, Zn SOD) metal sites at high pressure using X-ray absorption. XAS (X-ray Absorption Spectroscopy) gives information on local structure and it is particularly suited to metal site investigation. To the best of our knowledge, this is the first time that protein conformational states have been investigated using the high pressure XAS technique. Cu, Zn SOD catalyses the dismutation of toxic oxygen radicals produced in cells; this reaction occurs at the copper metal site. Structural changes around the copper, induced by pressure, can be directly related to protein substates. Their characterisation is thus important in the understanding of protein activity.

The high-pressure device was a Paris-Edinburgh large volume cell.

Experiments were performed on lyophilised Cu, Zn SOD between 0 and 48 kbar at the copper and zinc K-edges. The two metal local atomic environments have a different behaviour as pressure increases: copper exhibits a more flexible environment; on the contrary, zinc shows small structural modifications. We have identified a state, formed between 3 and 8 kbar, which is stable up to 48 kbar.     

A sensitive fluorimetric assay for cationic surfactants

Summary A new fluorimetric assay for cationic surfactants is based on their capability of quenching the fluorescence of 8-octadecyloxypyrene-1,3,6-trisulfonate (PTS-18). It is specific for cationic surfactants which can be determined in the 40–400 g concentration range. The method is considered to be advantageous over former methods in that it only requires addition of the sample solution to the fluorophore solution, followed by measurement of fluorescence intensity of the probe. This is in contrast to existing methods where the detergent/dye ion pair has to be extracted before measurement.     

Environmental exposure assessment framework for nanoparticles in solid waste

Information related to the potential environmental exposure of engineered nanomaterials (ENMs) in the solid waste management phase is extremely scarce. In this paper, we define nanowaste as separately collected or collectable waste materials which are or contain ENMs, and we present a five-step framework for the systematic assessment of ENM exposure during nanowaste management. The framework includes deriving EOL nanoproducts and evaluating the physicochemical properties of the nanostructure, matrix properties and nanowaste treatment processes as well as transformation processes and environment releases, eventually leading to a final assessment of potential ENM exposure. The proposed framework was applied to three selected nanoproducts: nanosilver polyester textile, nanoTiO₂ sunscreen lotion and carbon nanotube tennis racquets. We found that the potential global environmental exposure of ENMs associated with these three products was an estimated 0.5–143 Mg/year, which can also be characterised qualitatively as medium, medium, low, respectively. Specific challenges remain and should be subject to further research: (1) analytical techniques for the characterisation of nanowaste and its transformation during waste treatment processes, (2) mechanisms for the release of ENMs, (3) the quantification of nanowaste amounts at the regional scale, (4) a definition of acceptable limit values for exposure to ENMs from nanowaste and (5) the reporting of nanowaste generation data.     

Exclusively Heteronuclear NMR Experiments to Obtain Structural and Dynamic Information on Proteins

Provided that ¹³C‐detected NMR experiments are either preferable or complementary to ¹H detection, we report here tools to determine C^α? C′, C′? N, and C^α? H^α residual dipolar couplings on the basis of the CON experiment. The coupling constants determined on ubiquitin are consistent with the subset measured with the ¹H‐detected HNCO sequences. Since the utilization of residual dipolar couplings may depend on the mobility of the involved nuclei, we also provide tools to measure longitudinal and transverse relaxation rates of N and C′. This new set of experiments is a further development of a whole strategy based on ¹³C direct‐detection NMR spectroscopy for the study of biological macromolecules.     

Rheological investigation of thermal transitions in vesicular dispersion

The thermal behavior of unsonicated dispersions of a double-chained surfactant, Dioctadecyldimethylammonium bromide (DODAB), has been studied over a wide concentration range using DSC and dynamic rheology. All dispersions are characterized by the pre- and main transition peaks at 35 °C and 43 °C, respectively. But, only above 10 mM DODAB, a third endotherm at 52 °C appears which may correspond to the (ULVs + L_α fragments) → MLVs transition. The thermal-induced MLV’s size is proportionally dependent on the concentration. In addition, and in agreement with DSC data, dynamic rheology has proven to be an indirect way to elucidate the structural transitions in these DODAB vesicular dispersions.