Ginzburg-Landau theory of crystalline anisotropy for bcc-liquid interfaces

The weak anisotropy of the interfacial free-energy $\gamma$ is a crucial parameter influencing dendritic crystal growth morphologies in systems with atomically rough solid-liquid interfaces. The physical origin and quantitative prediction of this anisotropy are investigated for body-centered-cubic (bcc) forming systems using a Ginzburg-Landau theory where the order parameters are the amplitudes of density waves corresponding to principal reciprocal lattice vectors. We find that this theory predicts the correct sign, $\gamma_{100}>\gamma_{110}$, and magnitude, $(\gamma_{100}-\gamma_{110}) / (\gamma_{100}+\gamma_{110})\approx 1$, of this anisotropy in good agreement with the results of MD simulations for Fe. The results show that the directional dependence of the rate of spatial decay of solid density waves into the liquid, imposed by the crystal structure, is a main determinant of anisotropy. This directional dependence is validated by MD computations of density wave profiles for different reciprocal lattice vectors for $\{110\}$ crystal faces. Our results are contrasted with the prediction of the reverse ordering $\gamma_{100}<\gamma_{110}$ from an earlier formulation of Ginzburg-Landau theory [Shih \emph{et al.}, Phys. Rev. A {\bf 35}, 2611 (1987)].Comment: 9 pages, 5 figure

Extended quantum critical phase in a magnetized spin-1/2 antiferromagnetic chain

Measurements are reported of the magnetic field dependence of excitations in the quantum critical state of the spin S=1/2 linear chain Heisenberg antiferromagnet copper pyrazine dinitrate (CuPzN). The complete spectrum was measured at k_B T/J <= 0.025 for H=0 and H=8.7 Tesla where the system is ~30% magnetized. At H=0, the results are in quantitative agreement with exact calculations of the dynamic spin correlation function for a two-spinon continuum. At high magnetic field, there are multiple overlapping continua with incommensurate soft modes. The boundaries of these continua confirm long-standing predictions, and the intensities are consistent with exact diagonalization and Bethe Ansatz calculations.Comment: 4 pages, 4 figure

Magnetothermal transport in the spin-1/2 chains of copper pyrazine dinitrate

We present experiments on the thermal transport in the spin-1/2 chain compound copper pyrazine dinitrate Cu(C_4 H_4 N_2)(NO_3)_2. The heat conductivity shows a surprisingly strong dependence on the applied magnetic field B, characterized at low temperatures by two main features. The first one appearing at low B is a characteristic dip located at mu_B B ~ k_B T, that may arise from Umklapp scattering. The second one is a plateau-like feature in the quantum critical regime, mu_B |B-B_c| < k_B T, where B_c is the saturation field at T=0. The latter feature clearly points towards a momentum and field independent mean free path of the spin excitations, contrary to theoretical expectations.Comment: 4 pages, 4 figure

An advance notification letter increases participation in colorectal cancer screening

© 2007 Royal Society of MedicineObjectives: To determine the impact of novel invitation strategies on population participation in faecal immunochemical test (FIT)-based colorectal cancer (CRC) screening. Setting A community screening programme in Adelaide, South Australia. Methods: In total, 2400 people aged 50–74 years were randomly allocated to one of four CRC screening invitation strategies: (a) Control: standard invitation-to-screen letter explaining risk of CRC and the concept, value and method of screening; (b) Risk: invitation with additional messages related to CRC risk; (c) Advocacy: invitation with additional messages related to advocacy for screening from previous screening programme participants and (d) Advance Notification: first, a letter introducing Control letter messages followed by the standard invitation-to-screen. Invitations included an FIT kit. Programme participation rates were determined for each strategy relative to control. Associations between participation and sociodemographic variables were explored. Results: At 12 weeks after invitation, participation was: Control: 237/600 (39.5%); Risk: 242/600 (40.3%); Advocacy: 216/600 (36.0%) and Advance Notification: 290/600 (48.3%). Participation was significantly greater than Control only in the Advance Notification group (Relative risk [RR] 1.23, 95% confidence interval [CI] 1.06–1.43). This effect was apparent as early as two weeks from date of offer; Advance Notification: 151/600 (25.2%) versus Control: 109/600 (18.2%, RR 1.38, 95% CI 1.11–1.73). Conclusions: Advance notification significantly increased screening participation. The effect may be due to a population shift in readiness to undertake screening, and is consistent with the Transtheoretical Model of behaviour change. Risk or lay advocacy strategies did not improve screening participation. Organized screening programmes should consider using advance notification letters to improve programme participation.S R Cole, A Smith, CWilson, D Turnbull, A Esterman and G P Youn

Pseudomonas aeruginosa is capable of natural transformation in biofilms

Abstract Natural transformation is a mechanism that enables competent bacteria to acquire naked, exogenous DNA from the environment. It is a key process that facilitates the dissemination of antibiotic resistance and virulence determinants throughout bacterial populations. Pseudomonas aeruginosa is an opportunistic Gram-negative pathogen that produces large quantities of extracellular DNA (eDNA) that is required for biofilm formation. P. aeruginosa has a remarkable level of genome plasticity and diversity that suggests a high degree of horizontal gene transfer and recombination but is thought to be incapable of natural transformation. Here we show that P. aeruginosa possesses homologs of all proteins known to be involved in natural transformation in other bacterial species. We found that P. aeruginosa in biofilms is competent for natural transformation of both genomic and plasmid DNA. Furthermore, we demonstrate that type IV pili (T4P) facilitate but are not absolutely essential for natural transformation in P. aeruginosa

Evaluation of the relative contribution of meteorological and oceanic forces to the drift of ice islands offshore Newfoundland

On 29 April 2015, four beacons were deployed onto an ice island in the Strait of Belle Isle to record positional data. The ice island later broke up into many fragments, four of which were tracked by the beacons. The relative influences of wind drag, current drag, Coriolis force, sea surface height gradient and sea-ice force on the drift of the tracked ice island fragments were analyzed. Using atmospheric and oceanic model outputs, the sea-ice force was calculated as the residual of the fragments' net forces and the sum of all other forces. This was compared against the force obtained through ice concentration-dependent relationships when sea ice was present. The sea-ice forces calculated from the residual approach and concentration-dependent relationships were significant only when sea ice was present at medium-high concentrations in the vicinity of the ice island fragments. The forces from ocean currents and sea surface tilt contributed the most to the drift of the