Mahler measure and entropy for commuting automorphisms of compact groups

We compute the joint entropy ofd commuting automorphisms of a compact metrizable group. LetR _d = [u ₁ ^±1 ,...,[d ₁ ^±1 ] be the ring of Laurent polynomials ind commuting variables, andM be anR _d -module. Then the dual groupX _M ofM is compact, and multiplication onM by each of thed variables corresponds to an action _M of ^d by automorphisms ofX _M . Every action of ^d by automorphisms of a compact abelian group arises this way. IffR _d , our main formula shows that the topological entropy of is given by

A three-dimensional model of tongue movement based on ultrasound and x-ray microbeam data

Point-tracking techniques provide timing information about structural movements of the tongue. Imaging techniques provide information about cross-sectional and pharyngeal tongue shape and movement. This study joined these techniques in a single subject. Five pellets on the tongue surface were tracked using x-ray microbeam, and the midsagittal and coronal planes of the tongue were imaged using real-time ultrasound. The speech materials were the consonants [s] and [l] and the vowels [i], [a], and [o] combined in VCVCe utterances. Analyses concentrated on the difference in tongue movements related to the two consonants. A model of tongue movement was developed, in which critical features of consonant shape and position dominated the tongue opening movement. In this model, the tongue is divided into subdivisions termed "functional segments" in both the sagittal and coronal planes. Movements of the functional segments created observable opening movement patterns.     

Self-assembly of gears at a fluid/air interface

This paper describes a dynamic system-a system that develops order only when dissipating energy-comprising millimeter to centimeter scale gears that self-assemble into a simple machine at a fluid/air interface. The gears are driven externally and indirectly by magnetic interactions; they are made of poly(dimethylsiloxane) (PDMS) or magnetically doped PDMS, and fabricated by soft lithography. Transfer of torque between gears can take place through three different mechanisms: mechanical interaction, hydrodynamic shear, and capillarity/overlap of menisci. Interplay between these forces allows interactions and motions that are not possible with conventional systems of gears.     

Wetting of structured hydrophobic surfaces by water droplets

Super-hydrophobic surfaces may arise due to an interplay between the intrinsic, relatively high, contact angle of the more or less hydrophobic solid surface employed and the geometric features of the solid surface. In the present work, this relationship was investigated for a range of different surface geometries, making use of surface free energy minimization. As a rule, the free energy minima (and maxima) occur when the Laplace and Young conditions are simultaneously fulfilled. Special effort has been devoted to investigating the free energy barriers present between the Cassie-Baxter (heterogeneous wetting) and Wenzel (homogeneous wetting) modes. The predictions made on the basis of the model calculations compare favorably with experimental results presented in the literature.     

A mechanistic evaluation of the amperometric response of reduced thiols in quinone mediated systems

The specificity of the reaction of benzoquinone with reduced thiol species has been investigated and the nature of the amperometric electrode response elucidated. The analytical applicability of the methodology has been assessed and it has been shown that through appropriate selection of the redox properties of the indicating quinone, interference from other electroactive species can be minimised. A discrepancy in the reaction stoichiometry has however been found between the glutathione and cysteine quinone adducts and the implications in interpreting the resulting sensor response are rationalised. The adaptation of the approach to disposable, screen printed electrode assemblies has been investigated.     

Self-assembled aggregates of the carotenoid zeaxanthin: Time-resolved study of excited states

In this study, we present a way of controlling the formation of the two types of zeaxanthin aggregates in hydrated ethanol: J-zeaxanthin (head-to-tail aggregate, characteristic absorption band at 530 nm) and H-zeaxanthin (card-pack aggregate, characteristic absorption band at 400 nm). To control whether J- or H- zeaxanthin is formed, three parameters are important: (1) pH, that is, the ability to form a hydrogen bond; (2) the initial concentration of zeaxanthin, that is, the distance between zeaxanthin molecules; and (3) the ratio of ethanol/water. To create H-aggregates, the ability to form hydrogen bonds is crucial, while J-aggregates are preferentially formed when hydrogen-bond formation is prevented. Further, the formation of J-aggregates requires a high initial zeaxanthin concentration and a high ethanol/water ratio, while H-aggregates are formed under the opposite conditions. Time-resolved experiments revealed that excitation of the 530-nm band of J-zeaxanthin produces a different relaxation pattern than excitation at 485 and 400 nm, showing that the 530-nm band is not a vibrational band of the S2 state but a separate excited state formed by J-type aggregation. The excited-state dynamics of zeaxanthin aggregates are affected by annihilation that occurs in both J- and H-aggregates. In H-aggregates, the dominant annihilation component is on the subpicosecond time scale, while the main annihilation component for the J-aggregate is 5 ps. The S(1) lifetimes of aggregates are longer than in solution, yielding 20 and 30 ps for H- and J-zeaxanthin, respectively. In addition, H-type aggregation promotes a new relaxation channel that forms the zeaxanthin triplet state.