Quantum effects in chemistry: seven sample situations

Significant quantum effects in chemistry range from static structure (electronic and geometrical) through dynamical behavior, including optical properties, conductance, relaxation, decoherence, and thermalization. We outline seven situations in which molecular systems exhibit ineluctably quantum behavior. These range from situations in which the community can understand the problem quantitatively and conceptually (for example for dilute sets of spins in NMR) to femtosecond/attosecond situations, which the community understands only primitively. In condensed phase, the dynamics will always evolve in a system/bath environment, and we discuss here how to pose, and to start understanding, problems of that sort.     

Ueber eine Eigenschaft gewisser linearer irreductibler Differentialgleichungen

Ohne Zusammenfassung     

Singlet fission for dye-sensitized solar cells: can a suitable sensitizer be found?

We discuss possible improvements in the efficiency of dye-sensitized photovoltaic cells using dyes capable of singlet fission into two triplets, thus producing two electron-hole pairs from a single photon. It is pointed out that, in addition to derivatives of large alternant hydrocarbons, those of biradicals are also likely candidates for a favorable ordering of excited-state energy levels, E(T2), E(S1) > 2E(T1). A large number of potentially favorable structures has been examined by the semiempirical Pariser-Parr-Pople method and some also by the time-dependent density functional theory method. Several likely candidates have been identified for experimental examination.     

Poly(vinyl alcohol)-Amino Acid Hydrogels Fabricated into Tissue Engineering Scaffolds by Colloidal Gas Aphron Technology

A new class of hydrogels made from poly(vinyl alcohol) (PVA) and amino acid was formed into porous tissue engineering scaffolds by the colloidal gas aphron (CGA) method. CGA microfoams are formed using high speed stirring to generate uniform, micrometer scale bubbles. CGAs offer several advantages over conventional scaffold fabrication techniques including room temperature processing, aqueous conditions and utilization of air bubbles to create uniform pores. This technique eliminates the need for toxic solvents and salt templates. In addition, the novel poly(vinyl alcohol) hydrogels are inherently strong, eliminating the need for crosslinkers.     

Self-heating of plastics during cyclic defformation

Analysis of the phenomenon of self-heating as a result of competition between hysteresis heating and heat losses to the ambient medium shows that for polymers two zones of steady-state heating are possible: a low-temperature zone, corresponding to a high endaurace limit, and a high-temperature zone, corresponding to low endurance. Between these zones is a temperature region in which steady-state heating is impossible. The high-temperature steady-state zone is frequently not realized as a consequence of the sharp drop in strength at high temperatures. The transition from one steady-state zone to the other is discontinuous, the occurrence of one or the other zone being determined by the deformation conditions (stress, cycling speed, size of specimen, heat conductivity, etc.). However, the self-heating temperature at which this transition takes place does not depend on the deformation conditions, but is determined only by the properties of the material. These conclusions have been confirmed experimentally.Mekhanika Polimerov, Vol. 1, No. 3, pp. 93–100, 1965     

Structure changes in glassforming liquids upon cooling and compression

Upon cooling and compression, both the thermodynamic and the kinetic properties of glassformers change. In fragile glassformers, these changes suggest changes in the local structure of the liquid. Thermodynamic data may then provide a measure of structure changes. Special criteria for structure changes in terms of energy and pressure fluctuations in the isochoric system are proposed; recent theoretical results allow one to rewrite the criteria in terms of long- and short-time thermodynamic characteristics of the liquid. Based on the proposed criteria, we discuss the changes in the local structure due to temperature and pressure variations.     

Capillary force on a nanoscale tip in dip-pen nanolithography

Monte Carlo simulation has been used to characterize the capillary force due to the condensation of a liquid meniscus between a tip with a nanoscale asperity and a flat surface. To consider both hydrophobic and hydrophilic molecules coating the tip as a model of dip-pen nanolithography, tips with various wettabilities are studied. The capillary force due to the meniscus is calculated for various saturations (humidities). We have implemented a thermodynamic integration technique that can project the force into energetic and entropic contributions. In most cases, the force is mainly energetic in origin. At the snap-off separation where the meniscus disappears, the tip feels a significant entropic force at high saturation. Our calculation shows nonmonotonic behavior of the pull-off force as a function of saturation, which is in qualitative accord with experiments.     

Markov partitions for anosov flows onn-dimensional manifolds

In this work we construct a Markov partition for transitive Anosov flows, such that the measure of the boundary of the partition is zero. Symbolic dynamics for these flows is also developed.