Lattice models and Landau theory for type II incommensurate crystals

Ground state properties and phonon dispersion curves of a classical linear chain model describing a crystal with an incommensurate phase are studied. This model is the DIFFOUR (discrete frustrated phi4) model with an extra fourth-order term added to it. The incommensurability in these models may arise if there is frustration between nearest-neighbor and next-nearest-neighbor interactions. We discuss the effect of the additional term on the phonon branches and phase diagram of the DIFFOUR model. We find some features not present in the DIFFOUR model such as the renormalization of the nearest-neighbor coupling. Furthermore the ratio between the slopes of the soft phonon mode in the ferroelectric and paraelectric phase can take on values different from -2. Temperature dependences of the parameters in the model are different above and below the paraelectric transition, in contrast with the assumptions made in Landau theory. In the continuum limit this model reduces to the Landau free energy expansion for type II incommensurate crystals and it can be seen as the lowest-order generalization of the simplest Lifshitz-point model. Part of the numerical calculations have been done by an adaption of the Effective Potential Method, orginally used for models with nearest-neighbor interaction, to models with also next-nearest-neighbor interactions.Comment: 33 pages, 7 figures, RevTex, submitted to Phys. Rev.

The effects of acute exercise on subsequent cigarette smoking

The present study was conducted to examine the effects of acute aerobic exercise on smoking behavior. On alternate days, 10 healthy young smokers were subjected to half an hour of sustained high exercise (about 56% of maximum work capacity) or of low exercise (about 28% of maximum, simulating normal daytime activity). During the high-exercise condition, there were pronounced increases in physiological markers of physical activity such as mean work, heart rate, and lactic acid as well as elevations in circulating hormones (norepinephrine, epinephrine, and immunoreactive beta-endorphin and cortisol) known to be affected by vigorous exercise. Despite a trend toward decreased desire for cigarettes after the high exercise condition, there were no differences in plasma nicotine levels following the smoking of a usual-brand cigarette 35 min later. The sustained effects of the two exercise conditions were also similar: plasma cotinine levels 24 hr later (reflecting nicotine intake over the entire exercise day) revealed no significant differences between hight and low exercise.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44810/1/10865_2004_Article_BF00846420.pd

Bronsted acid catalyzed tandem defunctionalization of biorenewable ferulic acid and derivates into bio-catechol

An efficient conversion of biorenewable ferulic acid into bio-catechol has been developed. The transformation comprises two consecutive defunctionalizations of the substrate, that is, C-O (demethylation) and C-C (de-2-carboxyvinylation) bond cleavage, occurring in one step. The process only requires heating of ferulic acid with HCl (or H2SO4) as catalyst in pressurized hot water (250 degrees C, 50 bar N-2). The versatility is shown on a variety of other (biorenewable) substrates yielding up to 84% di-(catechol, resorcinol, hydroquinone) and trihydroxybenzenes (pyrogallol, hydroxyquinol), in most cases just requiring simple extraction as work-up