Physicochemical characterization of acrylamide/bisacrylamide hydrogels and their application for the conservation of easel paintings

Acrylamide chemical gels have been synthesized to obtain systems with mechanic and hydrophilic properties suitable for the cleaning of works of art. The gel characteristics were tailored by changing the polymer percentage present in the final hydrogel formulation from 2 to 10% w/w. Two different hydrogels have been selected in this interval for an in depth characterization (i.e., S 4% w/w and H 6% w/w). Water retention properties of the gels along with the free water index have been determined by the combination of standard dehydration tests and differential scanning calorimetry (DSC) measurements. The gels' structure has been determined by scanning electron microscopy (SEM) and small angle X-ray scattering (SAXS). The water retention capacity of hydrogel, H, was also determined. Cleaning tests on easel painting replicas, performed with both hydrogels loaded with an aqueous detergent system, showed good results in the removal of a widely used synthetic adhesive and hence offered these gels as a real alternative to the widely applied physical gel methodology with the advantage of being a residue-free technique. A preliminary SAXS investigation confirms the persistence of the detergent system nanostructure inside the hydrogel.     

Ultrastrong coupling regime and plasmon polaritons in parabolic semiconductor quantum wells

Ultrastrong coupling is studied in a modulation-doped parabolic potential well coupled to an inductance-capacitance resonant circuit. In this system, in accordance to Kohn's theorem, strong reduction of the energy level separation caused by the electron-electron interaction compensates the depolarization shift. As a result, a very large ratio of 27% of the Rabi frequency to the center resonance frequency as well as a polariton gap of width 2π × 670 GHz are observed, suggesting parabolic quantum wells as the system of choice in order to explore the ultrastrong coupling regime.     

Rounding-based heuristics for nonconvex MINLPs

We propose two primal heuristics for nonconvex mixed-integer nonlinear programs. Both are based on the idea of rounding the solution of a continuous nonlinear program subject to linear constraints. Each rounding step is accomplished through the solution of a mixed-integer linear program. Our heuristics use the same algorithmic scheme, but they differ in the choice of the point to be rounded (which is feasible for nonlinear constraints but possibly fractional) and in the linear constraints. We propose a feasibility heuristic, that aims at finding an initial feasible solution, and an improvement heuristic, whose purpose is to search for an improved solution within the neighborhood of a given point. The neighborhood is defined through local branching cuts or box constraints. Computational results show the effectiveness in practice of these simple ideas, implemented within an open-source solver for nonconvex mixed-integer nonlinear programs.     

Modelling of Enzyme Properties in Organic Solvents

Summary.  In this article we review how molecular modeling techniques can be used to shed some light on the influence of organic solvents on the molecular characteristics of proteins and enzymes. Molecular dynamic simulations on bovine pancreas trypsin inhibitor, chymotrypsin, and subtilisin make it possible to get a deeper understanding into how increased intramolecular interactions improve conformational rigidity, thus explaining the lower reactivity and the higher thermostability of enzymes in non-aqueous media. The application of thermodynamics-based models allows first qualitative predictions on the selectivity of many reaction types; however, the application of quantum mechanical/molecular mechanical methods is required for the development of quantitative models of actual reactivity patterns. Received November 18, 1999. Accepted (revised) February 8, 2000     

Optical Properties of M(II) Schiff-base Complexes Dispersed in Ethylene based Polymers

Summary: Several salicylaldiminate M(II) complexes of Nickel, Copper and Cobalt have been prepared and mixed with ethylene based polymers in order to prepare new composite materials with interesting morphological and optical properties by profiting of the presence of alkyl chains and push-pull substituents connected to the ligand structure. The phase dispersion behaviour of the binary films has been studied by scanning electron microscopy (SEM) and x-ray microanalysis, whereas the optical properties of the composite samples have been evaluated by UV-vis and fluorescence spectroscopy. The results in absorption have been analysed in terms of the anisotropy induced by the mechanical orientation of the polymer matrix and by the role of the metal centre according to the different strength of the complexes transition dipole moment. The luminescence behaviour have been discussed in terms of potential developments aimed at preparing polymeric supported Schiff base ligands for metal ions sensor applications.     

A remark on the finite number of particles effect in Monte Carlo methods for kinetic equations

Monte Carlo methods are the most popular methods for solving problems in kinetic theory [2, 5]. In this short remark we emphasize some of the side effects due to the use of conservative methods over a finite number of statistical samples (particles) in the simulation. The most relevant aspect is that the steady states of the system are compactly supported and thus they cannot be Maxwellian (or any other non compactly supported statistics) unless the number of particles goes to infinity. These aspects are studied numerically with the help of a simple one-dimensional space homogeneous kinetic model. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Application of calorimetry and DTA to metal systems

The calorimetric methods employed for the study of metal systems (solution, combustion, direct reaction calorimetry) are considered and briefly discussed with respect to each other.The development of apparatus for the calorimetry of metals and alloys is examined as a whole, with particular reference to the progressive increase of the maximum limit of the working temperature.The employment of calorimetric methods for the determination of equilibrium phase diagrams is described according to two different approaches: (1) corresponding to classical DTA, based on the identification of phase boundaries by the exploration of the system as a function of temperature, at constant composition; (2) corresponding to the measurement of partial and integral enthalpies of alloy formation as a function of the composition, at constant temperature.A brief report is given of the utilization of calorimetric data for the computation of equilibrium phase diagrams and equations are also given that allow the equilibrium temperature to be calculated between a liquid solution (binary or multicomponent) and a pure component (or an intermetallic compound) as a function of the thermodynamic parameters obtained by calorimetric methods.     

The effect of oxygen rf discharge on pulsed laser deposition of oxide films

In this work final results on TiO₂ film deposition by Plasma Assisted Pulsed Laser Deposition (PAPLD) with an rf biased substrate are presented. In previous work it has been shown that PAPLD is an improvement over conventional PLD for the elimination of particulates in high refractive index thin film deposition. This paper will give a comparison between conventional PLD and PAPLD on the stoichiometry, morphology, and optical properties of deposited TiO₂ films. It will be demonstrated that oxygen rf discharge during the PLD process makes incorporation of oxygen into the depositing films extremely effective. This effect of the rf discharge allows operation of the PLD process at a lower oxygen background pressure while enhancing the deposition rate. Also, the production of a good quality TiO₂ film by PAPLD using a pure metal titanium target will be shown. PACS 79.20.Ds; 52.80.Pi