A valence bond liquid on the honeycomb lattice

The honeycomb lattice material Li2RuO3 undergoes a dimerization of Ru4+ cations on cooling below 270C, where the magnetic susceptibility vanishes. We use density functional theory calculations to show that this reflects the formation of a 'valence bond crystal', with a strong bond disproportionation. On warming, x-ray diffraction shows that discrete three-fold symmetry is regained on average, and the dimerization apparently disappears. In contrast, local structural measurements using high-energy x-rays, show that disordered dimers survive at the nanoscale up to at least 650C. The high temperature phase of Li2RuO3 is thus an example of a valence bond liquid, where thermal fluctuations drive resonance between different dimer coverages, a classic analogue of the resonating valence bond state often discussed in connection with high T$_c$ cuprates.Comment: 5 pages, 4 figures, References correcte

Quasiparticle interference in antiferromagnetic parent compounds of Fe-based superconductors

Recently reported quasiparticle interference imaging in underdoped Ca(Fe{1-x}Co{x})_2As{2} shows pronounced C{2} asymmetry that is interpreted as an indication of an electronic nematic phase with a unidirectional electron band, dispersive predominantly along the $b$-axis of this orthorhombic material. On the other hand, even more recent transport measurements on untwinned samples show near isotropy of the resistivity in the $ab$ plane, with slightly larger conductivity along a (and not b). We show that in fact both sets of data are consistent with the calculated ab initio Fermi surfaces, which has a decisively broken C_{4}, and yet similar Fermi velocity in both directions. This reconciles completely the apparent contradiction between the conclusions of the STM and the transport experiments.Comment: A version of this work was posted (arXiv:1005.1761) as a comment on a Science paper entitled "Nematic Electronic Structure in the Parent State of the Iron-Based Superconductor Ca(Fe1-xCox)2As2". The comment was rejected by Science on account of it being posted on the ArXiv. This is a version published in PRB as a research pape

Development and Testing of Relative Risk-based Health Messages for Electronic Cigarette Products

Background: Health messages on e-cigarette packs emphasise nicotine addiction or harms using similar wording to warnings on cigarette packs. These may not be appropriate for e-cigarettes which constitute a reduced risk alternative for smokers. This research aimed to (1) develop and test a selection of relative risk messages for e-cigarette products; (2) compare these to the two current EU Tobacco Products Directive (TPD) nicotine addiction messages; and (3) explore differences between smokers, non-smokers and dual users. Method: Twenty-six messages focusing on either harm-reduction or cessation were developed and rated by multidisciplinary experts for accuracy, persuasiveness and clarity. The eight highest ranking messages were compared alongside the TPD messages in a sample of 983 European residents (316 smokers, 327 non-smokers, 340 dual users) on understandability, believability and convincingness. Results: On all three constructs combined, the two TPD messages rated the highest, closely followed by four relative risk messages “Completely switching to e-cigarettes lowers your risk of smoking related diseases”, “Use of this product is much less harmful than smoking”, “Completely switching to e-cigarettes is a healthier alternative to smoking”, and “This product presents substantially lower risks to health than cigarettes” which did not differ statistically from the TPD messages. Non-smokers rated TPD1 significantly higher overall than dual users. Dual users rated “This product is a safer alternative to smoking” significantly higher than non-smokers. Messages did not differ on understandability. Conclusions: These alternative messages provide a useful resource for future research and for policy makers considering updating e-cigarette product labelling

Perceptions of neighborhood social environment and drug dependence among incarcerated women and men: a cross-sectional analysis

Abstract Background Perception of neighborhood social environment can influence an individual’s susceptibility to drug dependence. However, this has never been examined with a jailed sample, where frequent transitions between local jails and disadvantaged neighborhoods are common. Understanding these associations could aid in the design of targeted programs to decrease drug dependence and recidivism among the incarcerated. Methods For this study, 596 women and men from three Kansas City jails were surveyed over the course of six months in 2010. Drug dependence was assessed with DSM-IV criteria. Independent variables included fear of one’s neighborhood, perceived level of neighborhood violence, and social capital. All data were self-reported and were analyzed using logistic regression. Results Controlling for gender and age, fear of neighborhood violence was associated with increased odds of having drug dependence (OR = 1.27, CI 1.02, 1.58) and a higher level of social capital prior to incarceration was associated with lower odds of drug dependence (OR = 0.65, CI 0.44, 0.96). Mental health problem diagnosis and past year intimate partner violence were significant mediating factors. Gender and race/ethnicity were significant moderating factors between neighborhood disadvantage and drug dependence. Conclusions Our study suggests that drug dependence programs for women and men who cycle between jails and communities require both individual- and community-level interventions. To be most effective, programs at the community-level should focus on helping specific groups navigate their communities, as well as address individual health needs associated with drug dependence.Peer Reviewe