NMR Analysis of the Water-Soluble Fraction of Airborne Pollen Particles

The analysis of ambient organic aerosols by nuclear magnetic resonance (NMR) spectroscopy is limited because of the large number of organic compounds present at low concentrations. Here, we demonstrate the integrative analysis of NMR spectra of airborne pollen particles using reference spectra, spectral similarity metrics, principal components analysis (PCA), and a chemical mass balance model to determine the predominant types of organic compounds. Strong associations among glucose, fucose, specific amino acids, and airborne pollen particles were observed by spectral similarity metrics and PCA. Carbohydrates accounted for about 51 % of the airborne pollen particles in the spectrum followed by amino acids (42 %) and other compounds (7 %). Overall, our investigations showed that analysis of NMR spectral data of mixtures of environmental organic compounds with pattern recognition methods may generate information on the chemical characteristics of the mixture.     

On Abrikosov Lattice Solutions of the Ginzburg-Landau Equations

We prove existence of Abrikosov vortex lattice solutions of the Ginzburg-Landau equations of superconductivity, with multiple magnetic flux quanta per fundamental cell. We also revisit the existence proof for the Abrikosov vortex lattices, streamlining some arguments and providing some essential details missing in earlier proofs for a single magnetic flux quantum per a fundamental cell.     

Goethals–Seidel Difference Families with Symmetric or Skew Base Blocks

We single out a class of difference families which is widely used in some constructions of Hadamard matrices and which we call Goethals–Seidel (GS) difference families. They consist of four subsets (base blocks) of a finite abelian group of order v, which can be used to construct Hadamard matrices via the well-known Goethals–Seidel array. We consider the special class of these families in cyclic groups, where each base block is either symmetric or skew. We omit the well-known case where all four blocks are symmetric. By extending previous computations by several authors, we complete the classification of GS-difference families of this type for odd \(v<50\). In particular, we have constructed the first examples of so called good matrices, G-matrices and best matrices of order 43, and good matrices and G-matrices of order 45. We also point out some errors in one of the cited references.     

Time-dependent Cu-induced gelation of poly(ethylene-alt-maleic acid) in aqueous solution

The complexation of Cu²⁺ ions with an alternating copolymer of maleic acid (MAc) and ethylene in aqueous solution was followed through turbidimetry and absorption spectrophotometry as a function of the polymer concentration and the metal ion-to-polymer molar ratio, r. The introduction of Cu²⁺ ions was performed in aqueous solution through neutralization of the polyacid with Cu(OH)₂ powder. A gelation window between homogeneous and phase-separated solutions was observed in the phase diagram of the polymer/Cu²⁺ mixture and the viscoelastic properties of the hydrogels were evaluated through rheology measurements. It is found that the stiffness of the hydrogels can be tuned by the polymer concentration and the mixing ratio r. Moreover, the stiffness of the hydrogels increases substantially with time. In fact, this time evolution may be as long as one month or longer if the composition of the aqueous solution is close to the gelation threshold. The gelation properties can be qualitatively explained from the possible formation of binuclear polymer/Cu²⁺ complexes in aqueous solutions, as indicated from the absorption spectroscopy results.     

Caccioppoli’s inequalities on constant mean curvature hypersurfaces in Riemannian manifolds

We prove some Caccioppoli’s inequalities for the traceless part of the second fundamental form of a complete, noncompact, finite index, constant mean curvature hypersurface of a Riemannian manifold, satisfying some curvature conditions. This allows us to unify and clarify many results scattered in the literature and to obtain some new results. For example, we prove that there is no stable, complete, noncompact hypersurface in ${{\mathbb R}^{n+1}, n \leq 5}$ , with constant mean curvature ${H \not=0}$ , provided that, for suitable p, the L ^p norm of the traceless part of second fundamental form satisfies some growth condition.     

Doubly responsive polymer-microgel composites: rheology and structure

Mixtures of alkali swellable microgels and linear PNIPAm chains exhibit doubly responsive properties both with pH and temperature. Below the lower critical solution temperature (LCST), the linear chains of PNIPAm are soluble and increase the osmotic pressure outside the microgels, which causes them to deswell. Above the LCST, the PNIPAm chains become insoluble and form spherical colloidal particles confined between the microgels that subsequently reswell. The swelling and deswelling of the microgels change the rheological properties of the composites, providing a unique way to tune the elasticity of the composites with temperature. The structure of the composites above the LCST is studied using multiple light scattering and fluorescence confocal microscopy. The phase separation of PNIPAm above the LCST is strongly affected by the confinement of the PNIPAm chains between the microgels.     

pH/Thermosensitive Hydrogels Formed at Low pH by a PMMA‐PAA‐P2VP‐PAA‐PMMA Pentablock Terpolymer

A poly(methyl methacrylate)‐block‐poly(acrylic acid)‐block‐poly(2‐vinyl pyridine)‐block‐poly(acrylic acid)‐block‐poly(methyl methacrylate) (PMMA‐PAA‐P2VP‐PAA‐PMMA), pentablock terpolymer has been synthesized by anionic polymerization with sequential addition of monomers and studied in aqueous media at low pH. The system exhibits combined properties and adopts the behavior of ‘telechelic’ polyelectrolytes and that of double hydrophilic polyampholytes. This complex behavior leads to the pentablock terpolymer forming a pH and temperature sensitive reversible hydrogel at very low polymer concentration.

     

Global sensitivity analysis for the design of nonlinear identification experiments

Nonlinear Dynamics - Bayesian inference techniques have been used extensively in recent years for parameter estimation in nonlinear systems. Despite the many advances made in the field, highly...     

Adsorption and aggregation of cationic amphiphilic polyelectrolytes on silica

The adsorption of two cationic amphiphilic polyelectrolytes, which are copolymers of two charged monomers, triethyl(vinylbenzyl)ammonium chloride and dimethyldodecyl(vinylbenzyl)ammonium chloride (which is the amphiphilic one) with different contents of amphiphilic groups (40% (40DT) and 80% (80DT)), onto the hydrophilic silica-aqueous solution interface has been studied by in situ null ellipsometry and tapping mode atomic force microscopy (AFM). Adsorption isotherms for both polyelectrolytes were obtained at 25 degrees C and at different ionic strengths, and the adsorption kinetics was also investigated. At low ionic strength, thin adsorbed layers were observed for both polyelectrolytes. The adsorption increases with polymer concentration and reaches, in most cases, a plateau at a concentration below 50 ppm. For the 80DT polymer, at higher ionic strength, an association into aggregates occurs at concentrations at and above 50 ppm. The aggregates were observed directly by AFM at the surface, and by dynamic light scattering in the solution. The adsorption data for this case demonstrated multilayer formation, which correlates well with the increase in viscosity with the ionic strength observed for 80DT.