Rheological and thermal properties of agarose aqueous solutions and hydrogels

In this article, we report on the rheological properties of agarose aqueous solutions and gels. Viscosity curves were determined for homogeneous agarose aqueous solutions at different temperatures (from 68 to 38 °C) to study the viscosity behavior as the systems undergo gelation. The gelation phenomenon of agarose solutions was also investigated by shear oscillation experiments and differential scanning calorimetry. The gelation and melting temperature as a function of agarose concentration were determined together with the gelation and melting enthalpies. The results obtained were interpreted using the two‐step model describing the gelation of agarose in water. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 322–328, 2008     

The catwalk task: Reflections and synthesis: Part 2

In this article we recount our experiences with a series of encounters with the catwalk task and reflect on the professional growth that these opportunities afforded. First, we individually reflect on our own mathematical work on the catwalk task. Second, we reflect on our experiences working with a group of community college students on the catwalk task and our interpretations of their mathematical thinking. In so doing we also detail a number of innovative and novel student-generated representations of the catwalk photos. Finally, we each individually reflect on the entire experience with the catwalk problem, as mathematics learners, as teachers, and as professionals.     

Crucigasterins A-E, antimicrobial amino alcohols from the Mediterranean colonial ascidian Pseudodistoma crucigaster

Five new unsaturated 2-amino-3-alcohols, crucigasterins A-E (2-6), were isolated together with known related compound 7 from the Mediterranean ascidian Pseudodistoma crucigaster and characterised as diacetyl derivatives (2a-6a) by spectroscopic methods. The threo-relative configuration of the amino alcohol portion was inferred by NOE analysis of the oxazolidinone derivative of crucigasterin A (2) as well as by ¹³C NMR comparison with synthetic threo and erythro model compounds. The co-occurring metabolites were assumed to have the same relative configuration as 2 by comparison of the diagnostic carbon value of C-1. The absolute stereochemistry of compound 7 that had not been previously reported was determined by applying the modified Mosher’s method on the corresponding N-acetyl derivative. The same absolute configuration was suggested for the other co-occurring crucigasterins by biogenetic considerations. Antibacterial and antifungal activities of selected crucigasterins were also evaluated.     

New hydrogels from interpenetrated physical gels of agarose and chemical gels of polyacrylamide: Effect of relative concentration and crosslinking degree on the viscoelastic and thermal properties

In this article, we report on the viscoelastic and thermal properties of agarose–polyacrylamide (PAAm) interpenetrating polymer hydrogels (IPHs) and semi‐IPHs as a function of agarose concentration and PAAm crosslinking degree. The results demonstrated that the agarose is able to gel in the presence of crosslinked and linear IPHs. In addition, the reticulation of PAAm in the presence of agarose is confirmed for the case of IPHs giving rise to systems with dimensional stability at high temperatures. The formation of a fully IPH was ascertained at low agarose concentrations. A study of the morphology and nanoscale elasticity of the different systems has been carried out with atomic force microscopy/ultrasonic force microscopy (UFM). UFM data provide further evidence of interpenetration, allowing us to visualize—if present—phase‐separated domains with nanoscale resolution for the various crosslinking degrees and PAAm and agarose concentrations used during the formation of the IPHs. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

A version of Stöber synthesis enabling the facile prediction of silica nanospheres size for the fabrication of opal photonic crystals

A sol-gel synthesis procedure based on the method proposed by Stöber et al. (J Colloid Interface Sci 26:302–315, 1968) has been adopted for the one-step preparation of mono-dispersed silica nanospheres. An excellent control of the particle diameter over a wide range is obtained by varying the amount of silicon alkoxide only, while the concentration of all other components is kept fixed: this allows the fabrication of artificial opals with a finely tuned and precisely predictable lattice parameter.     

Structure and Dynamics of Oligonucleotides in the Gas Phase

By combining ion‐mobility mass spectrometry experiments with sub‐millisecond classical and ab initio molecular dynamics we fully characterized, for the first time, the dynamic ensemble of a model nucleic acid in the gas phase under electrospray ionization conditions. The studied oligonucleotide unfolds upon vaporization, loses memory of the solution structure, and explores true gas‐phase conformational space. Contrary to our original expectations, the oligonucleotide shows very rich dynamics in three different timescales (multi‐picosecond, nanosecond, and sub‐millisecond). The shorter timescale dynamics has a quantum mechanical nature and leads to changes in the covalent structure, whereas the other two are of classical origin. Overall, this study suggests that a re‐evaluation on our view of the physics of nucleic acids upon vaporization is needed.     

Automatic Dantzig–Wolfe reformulation of mixed integer programs

Mathematical Programming - Dantzig–Wolfe decomposition (or reformulation) is well-known to provide strong dual bounds for specially structured mixed integer programs (MIPs). However, the...     

Cement: a two thousand year old nano-colloid

Since Roman times, cement is one of the synthetic materials with the largest production and usage by mankind. Its properties allowed the expansion of the Roman Empire and the building of still fascinating works. In spite of the diverse use of cement and the abundant literature accumulated during a century of systematic scientific research on this material, the understanding of its properties is still far from complete. Several issues are still open, ranging from the understanding of the hydration kinetics and the influence of the modern industrial additives, to the deep comprehension of the atomic arrangement and nanostructure of disordered hydrated calcium silicate phase (C-S-H) formed by hydration. This feature article briefly summarizes recent results in the field, highlighting the necessity for a colloidal model of the cement microstructure that, combined with the layer-like structure of the colloidal units, is the most effective approach to fully describe the characteristics of this peculiar material.     

The continuous-flow cycloaddition of azomethine ylides to carbon nanotubes

This communication demonstrates a straightforward continuous-flow method for efficient exohedral functionalisation of carbon nanotubes which affords soluble samples in a much shorter time over conventional batch processing.     

DIFFERENT CHROMATOGRAPHIC BEHAVIOR OF A THYMINE-CONTAINING NEW ULTRAVIOLET PHOTOPRODUCT AND SPORE PHOTOPRODUCT

Abstract— One- and two-dimensional cochromatography in five different solvents of a near UV photo-product induced by 365 nm irradiation of DNA in aqueous solution and the 'spore photoproduct', 5-thyminyl-5,6-dihydrothymine, produced by 254 nm irradiation of dry DNA, indicate that the two photoproducts seem to have related structures but are different.