Well-conditioned computation for H ∞ controller near the optimum

The present paper gives a procedure for determining a H optimal controller in the assumption that the game Riccati equations have stabilizing positive definite solutions at the optimum value. A specific feature of the construction is its first step consisting in balancing with respect to the positive definite stabilizing solutions of the Riccati equations. The justification is based on singular perturbations reduction.     

Selective synthesis of double temperature-sensitive polymer-peptide conjugates

A novel synthetic route has been developed to couple selectively a modified octa-peptide, that is able to gel at low temperature, to the prototypical thermoresponsive polymer poly(N-isopropylacrylamide) to give a bioconjugate that exhibits double thermoresponsiveness.     

Hydrogen‐bonded supramolecular polymers containing dimethylsilane groups: Synthesis,crystal structure,and characterization

Bis[N‐(4‐carboxyphenyl)phtalimidyl]dimethylsilane prepared by the reaction between bis(3,4‐dicarboxyphenyl)dimethylsilane anhydride and p‐aminobenzoic acid has been used to built three novel hydrogen‐bonded supramolecular polymers as a result of cocrystallization with pyridine derivatives: 4,4′‐bipyridyl ( SP1 ), 1,2‐bis(4‐pyridyl)ethylene ( SP2 ), and 4,4′‐azopyridine ( SP3 ). The structures of the dianhydride, diacid, and derived supramolecular polymers were investigated by Fourier transform infrared (FTIR) and proton magnetic resonance (¹H NMR) spectroscopy. Self‐assembling was proved by the presence of the IR absorption bands around 1900 and 2400 cm^?1 specific for hydrogen bond. The association constant values were estimated by using FTIR spectroscopy in solid state. According to X‐ray diffraction study, the bis(3,4‐dicarboxyphenyl)dimethylsilane anhydride ( 1 ) has an isolated molecular structure. Bis[N‐(4‐carboxyphenyl)phtalimidyl]dimethylsilane ( 2 ) molecules are associated in the crystal structure via dimeric O? H … O hydrogen bonds resulting in the wavy 1D supramolecular chain. The main packing motif for SP1 and SP3 is represented by wavy chain formed by alternating sequences of 4,4′‐bipyridyl or 4,4′‐azopyridine and bis[N(4‐carboxyphenyl)phtalimidyl]dimethylsilane molecules linked by O? H … N hydrogen bonds. Thermal behavior was studied by differential scanning calorimetry and thermogravimetric analysis. The ability for the structuration in film was emphasized by atomic force microscopy. The molecular transport ability of the reversible associations was estimated by dynamic water vapor sorption (DVS) analysis. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Poly(Azomethine Sulfones). I. Synthesis and Characterization of New Poly(Azomethine Sulfones) Containing Ortho/Para Aromatic Moieties

Abstract

New poly(azomethine sulfones) with linear structures containing methylene bis(2-oxobenzylidene aniline), methylene bis(4-oxobenzylidene aniline), 1,4-bis(4-oxobenzylidene amino)phenylene and 1,4-bis(2-oxobenzylidene amino)phenylene units were prepared in the conventional literature manner by the reaction of azomethine bisphenols (M 1–4) with 4,4′-sulfonyl bischlorobenzene. The resulting polymers were confirmed by IR, ¹H-NMR and elemental analysis, and were characterized by UV measurements, viscosities, solubilities, DSC and thermo-gravimetric analysis (TGA) in air. A difference in the solubility and thermal behavior between the polymers with ortho- and para- chains was observed. The hydrolitic stability of the polymers in 10% wt aqueous sulfuric acid was reasonable     

Polydimethylsiloxane/silica/titania composites prepared by solvent-free sol–gel technique

Composites based on polydimethylsiloxane incorporating silica and titania were prepared by mixing polydimethylsiloxane with proper oxides precursors, tetraethyl-orthosilicate and tetrabutyl-orthotitanate. In the presence of environmental humidity and in acid catalysis, hydrolysis/condensation processes take place with formation of oxides and concomitantly polymer crosslinking. Partial replacement of SiO₂ in a polydimethylsiloxane/silica composite with titania (both generated in situ by sol–gel process) affects surface hydrophilicity (evaluated by dynamic contact angle), water vapor sorption ability (determined by dynamic vapor sorption) and thermal stability. The dielectric properties are also controlled by composition.     

Reactivity of Mg–Al hydrotalcites in solid and delaminated forms in ammonium carbonate solutions

Treatment of Mg–Al hydrotalcites (LDHs, layered double hydroxides) in aqueous (NH₄)₂CO₃ at 298 K leads to composites of dawsonite, hydrotalcite, and magnesium ammonium carbonate. The mechanism and kinetics of this transformation, ultimately determining the relative amounts of these components in the composite, depend on the treatment time (from 1 h to 9 days), the Mg/Al ratio in the hydrotalcite (2-4), and on the starting layered double hydroxide (solid or delaminated form). The materials at various stages of the treatment were characterized by inductive coupled plasma-optical emission spectroscopy, X-ray diffraction, transmission electron microscopy, infrared spectroscopy, thermogravimetry, and nitrogen adsorption at 77 K. The progressive transformation of hydrotalcite towards crystalline dawsonite and magnesium ammonium carbonate phases follows a dissolution–precipitation mechanism. A gradual decrease of the Mg/Al ratio in the resulting solids was observed in time due to magnesium leaching in the reacting medium. Dawsonite–hydrotalcite composite formation is favored at high aluminum contents in the starting hydrotalcite, while the formation of magnesium ammonium carbonate is favored at high Mg/Al ratios. The synthetic strategy comprising hydrotalcite delamination in formamide prior to aqueous (NH₄)₂CO₃ treatment is more reactive towards composite formation than starting from the bulk solid hydrotalcite.     

Latent heat nano composite building materials

Heat storage for heating and cooling of buildings reduces the conventional energy consumption with a direct impact on CO₂ emissions. The goal of this study was to find the physico-chemical fundamentals for tailoring phase change material (PCM)-epoxy composites as building materials depending on phase change temperature and latent heat using the optimal geometry for each application. Thus, some nano-composite materials were prepared by mixing a PCM with large latent heats with epoxy resin and Al powder. Some polyethylene glycols of different molecular weights (1000, 1500, and 2000) were used as PCMs. Subsequently these PCM-epoxy composites were thermo-physically characterized by DSC measurements and found to be suitable for building applications due to their large latent heat, appropriate phase change temperature and good performance stability. Moreover these cross-linked three dimensional structures are able to reduce the space and costs for encapsulation.     

Silver nanoparticles obtained with a glucose modified siloxane surfactant

Journal of Nanoparticle Research - Silver nanoparticles were obtained in aqueous medium, at room temperature, by redox reactions, with or without glucose, in the presence of a glucose-containing...     

Linear bounds for Calderón–Zygmund operators with even kernel on UMD spaces

It is well-known that several classical results about Calderón–Zygmund singular integral operators can be extended to X-valued functions if and only if the Banach space X has the UMD property. The dependence of the norm of an X-valued Calderón–Zygmund operator on the UMD constant of the space X is conjectured to be linear. We prove that this is indeed the case for sufficiently smooth Calderón–Zygmund operators with cancellation, associated to an even kernel. Our method uses the Bellman function technique to obtain the right estimates for the norm of dyadic Haar shift operators. We then apply the representation theorem of T. Hytönen to extend the result to general Calderón–Zygmund operators.