A geometrical approach to the integrability of soliton equations

A separability criterion in one-degree-of-freedom dynamics, suitable for soliton equations, is given in terms of a geometrical structure on the phase manifold. For solitonic degrees of freedom, i.e., those corresponding to the discrete spectrum of the associated Lax operator, integrability is a priori proved.     

Optical properties of Cu nanoclusters supported on MgO(100)

The vertical transitions of Cu atoms, dimers, and tetramers deposited on the MgO surface have been investigated by means of ab initio calculations based either on complete active space second-order perturbation theory or on time-dependent density functional theory. Three adsorption sites have been considered as representative of the complexity of the MgO surface: regular sites at flat (100) terraces, extended defects such as monoatomic steps, and point defects such as neutral oxygen vacancies (F or color centers). The optical properties of the supported Cu clusters have been compared with those of the corresponding gas-phase units. Upon deposition a substantial modification of the energy levels of the supported cluster is induced by the Pauli repulsion with the substrate. This causes shifts in the optical transitions going from free to supported clusters. The changes in cluster geometry induced by the substrate have a much smaller effect on the optical absorption bands. On F centers the presence of filled impurity levels in the band gap of MgO results in a strong mixing with the empty levels of the Cu atoms and clusters with consequent deep changes in the optical properties of the color centers. The results allow to interpret electron energy loss spectra of Cu atoms deposited on MgO thin films.     

Gold atoms and dimers on amorphous SiO(2): calculation of optical properties and cavity ringdown spectroscopy measurements

We report on the optical absorption spectra of gold atoms and dimers deposited on amorphous silica in size-selected fashion. Experimental spectra were obtained by cavity ringdown spectroscopy. Issues on soft-landing, fragmentation, and thermal diffusion are discussed on the basis of the experimental results. In parallel, cluster and periodic supercell density functional theory (DFT) calculations were performed to model atoms and dimers trapped on various defect sites of amorphous silica. Optically allowed electronic transitions were calculated, and comparisons with the experimental spectra show that silicon dangling bonds [[triple bond]Si(.-)], nonbridging oxygen [[triple bond]Si-O(.-)], and the silanolate group [[triple bond]Si-O(-)] act as trapping centers for the gold particles. The results are not only important for understanding the chemical bonding of atoms and clusters on oxide surfaces, but they will also be of fundamental interest for photochemical studies of size-selected clusters on surfaces.     

Quality control in hair analysis: A systematic study on washing procedures for trace element determinations

Trace element analysis of human hair is widely used to provide an indicator of body burden, but there is a major problem associated with preparation. The washing procedure adopted before analysis represents still a critical point which deserves particular attention. This study aimed at comparing the efficiency of the most commonly used washing methods to identify the procedure which allows for satisfactory removal of external contamination alone. As results depend strongly on the element, toxic (Cd and Pb), essential trace (Cr, Cu, Se and Zn) and major (Ca, K and Mg) elements were tested. The comparison was carried out with six different methods which include use of ionic and non-ionic detergents, organic solvents, chelating agents and sonication. Removal efficiency varied according to the element and pretreatment, the highest being observed for EDTA and the lowest for sonication. Unsatisfactory results were found using an acetone/methanol mixture for the potential contamination caused by it. Organic solvents showed the highest removal efficiency for K and toxic elements, and seemed to be effective in removing a limited but significant fraction of element incorporated in the lipid matter of hair. The ionic detergent Na lauryl sulphate, instead, was more effective for essential elements, but also triggered a higher analytic variability. As detergents appear to remove only external contamination, a non-ionic detergent such as Triton X-100 is proposed as a reliable alternative to the acetone method recommended by IAEA. Practical advantages are safe working conditions, rapidity of application and reduction in costs.     

Gagliardo-Nirenberg inequalities for differential forms in Heisenberg groups

The \(L^1\)-Sobolev inequality states that for compactly supported functions u on the Euclidean n-space, the \(L^{n/(n-1)}\)-norm of a compactly supported function is controlled by the \(L^1\)-norm of its gradient. The generalization to differential forms (due to Lanzani and Stein and Bourgain and Brezis) is recent, and states that a the \(L^{n/(n-1)}\)-norm of a compactly supported differential h-form is controlled by the \(L^1\)-norm of its exterior differential du and its exterior codifferential \(\delta u\) (in special cases the \(L^1\)-norm must be replaced by the \(\mathcal H^1\)-Hardy norm). We shall extend this result to Heisenberg groups in the framework of an appropriate complex of differential forms.     

Design of a Novel Composite H2S‐Releasing Hydrogel for Cardiac Tissue Repair

The design of 3D scaffolds is a crucial step in the field of regenerative medicine. Scaffolds should be degradable and bioresorbable as well as display good porosity, interconnecting pores, and topographic features; these properties favour tissue integration and vascularization. These requirements could be fulfilled by hybrid hydrogels using a combination of natural and synthetic components. Here, the mechanical and biological properties of a polyethylene glycol‐fibrinogen hydrogel (PFHy) are improved in order to favour the proliferation and differentiation of human Sca‐1^pos cardiac progenitor cells (hCPCs). PFHys are modified by embedding air‐ or perfluorohexane‐filled bovine serum albumin microbubbles (MBs) and characterized. Changes in cell morphology are observed in MBs–PFHys, suggesting that MBs could enhance the formation of bundles of cells and influence the direction of the spindle growth. The properties of MBs as carriers of active macromolecules are also exploited. For the first time, enzyme‐coated MBs have been used as systems for the production of hydrogen sulfide (H₂S)‐releasing scaffolds. Novel H₂S‐releasing PFHys are produced, which are able to improve the growth of hCPCs. This novel 3D cell–scaffold system will allow the assessment of the effects of H₂S on the cardiac muscle regeneration with its potential applications in tissue repair.

     

Cold denaturation of yeast frataxin offers the clue to understand the effect of alcohols on protein stability

Although alcohols are well-known to be protein denaturants when present at high concentrations, their effect on proteins at low concentrations is much less well characterized. In this paper, we present a study of the effects of alcohols on protein stability using Yfh1, the yeast ortholog of the human protein frataxin. Exploiting the unusual property of this protein of undergoing cold denaturation around 0 degrees C without any ad hoc destabilization, we determined the stability curve on the basis of both high and low temperature unfolding in the presence of three commonly used alcohols: trifluoroethanol, ethanol, and methanol. In all cases, we observed an extended temperature range of protein stability as determined by a modest increase of the high temperature of unfolding but an appreciable decrease in the low temperature of unfolding. On the basis of simple thermodynamic considerations, we are able to interpret the literature on the effects of alcohols on proteins and to generalize our findings. We suggest that alcohols, at low concentration and physiological pH, stabilize proteins by greatly widening the range of temperatures over which the protein is stable. Our results also clarify the molecular mechanism of the interaction and validate the current theoretical interpretation of the mechanism of cold denaturation.     

Rapid access to 1,6-anhydro-beta-L-hexopyranose derivatives via domino reaction: synthesis of L-allose and L-glucose

An expeditious and efficient synthesis of 1,6-anhydro-beta-L-hexopyranosyl derivatives 3 as valuable building blocks for the preparation of L-sugars is herein reported. This route relies upon the use of a domino reaction involving five synthetic steps from the 5,6-dihydro-1,4-dithiin 4. As 1,6-anhydro derivatives 3 are obtained, dithioethylene bridge removal and double-bond dihydroxylation give access to protected L-allose and L-glucose in stereoselective fashion and high yields.     

Compensated compactness for differential forms in Carnot groups and applications

In this paper we prove a compensated compactness theorem for differential forms of the intrinsic complex of a Carnot group. The proof relies on an Ls-Hodge decomposition for these forms. Because of the lack of homogeneity of the intrinsic exterior differential, Hodge decomposition is proved using the parametrix of a suitable 0-order Laplacian on forms.