Dephasing of Local Vibrations in a Planar Lattice of Adsorbed Molecules

We investigate anharmonically coupled high- and low-frequency excitations in a planar lattice of adsorbed molecules interacting with phonons of a crystal. Dephasing of high-frequency local vibrations by low-frequency resonance modes is described in terms of temperature Green's function. The equations obtained are solved, first, with a small ratio of the anharmonic coupling coefficient for high- and low-frequency modes to the resonance width, and second, in the low-temperature limit. High-frequency spectral line positions and widths depend on dispersion laws and resonance mode lifetimes. It is shown that lateral interactions of low-frequency modes of adsorbed molecules can lead to a significant narrowing of high-frequency spectral lines, which is consistent with experimental data.Comment: REVTeX, 11 pages, no figure

Dipolar ground state of planar spins on triangular lattices

An infinite triangular lattice of classical dipolar spins is usually considered to have a ferromagnetic ground state. We examine the validity of this statement for finite lattices and in the limit of large lattices. We find that the ground state of rectangular arrays is strongly dependent on size and aspect ratio. Three results emerge that are significant for understanding the ground state properties: i) formation of domain walls is energetically favored for aspect ratios below a critical valu e; ii) the vortex state is always energetically favored in the thermodynamic limit of an infinite number of spins, but nevertheless such a configuration may not be observed even in very large lattices if the aspect ratio is large; iii) finite range approximations to actual dipole sums may not provide the correct ground sta te configuration because the ferromagnetic state is linearly unstable and the domain wall energy is negative for any finite range cutoff.Comment: Several short parts have been rewritten. Accepted for publication as a Rapid Communication in Phys. Rev.

Cost-effectiveness of rotavirus immunization in Vietnam:Results and challenges

OBJECTIVES: To assess the cost-effectiveness of universal rotavirus immunization, explicitly the use of Rotateq® and affordability of implementing rotavirus immunization based on the Global Alliance for Vaccines and Immunization (GAVI)-subsidized vaccine price in the context of Vietnamese health care system for the next 5 years. METHODS: An age-structured cohort model was developed for the 2009 Vietnamese birth cohort and applied a 5-year time horizon with time cycle of 1 month for <1-year-old children and annually thereafter. Results from no vaccination and vaccination were compared. Outcomes included rotavirus episodes requiring home-treatment, outpatient visits, hospitalizations and deaths. Multiple outcomes per rotavirus infection are possible in the model. Acceptability and affordability analyses were done using Monte Carlo simulations. Costs were expressed in 2009 US$. RESULTS: Rotavirus immunization would not completely protect under-five-year-old children against rotavirus infection due to partial nature of vaccine immunity, however, would effectively reduce rotavirus severe cases by ∼55$1.6 million annually. In the base-case, the incremental cost per quality- adjusted-life-year (QALY) was US$665 from health care perspective,-Vietnamese per-capita-GDP in 2009. Affordability results showed that at the GAVI-subsidized vaccine price, rotavirus vaccination could be affordable in Vietnam. CONCLUSIONS: Rotavirus immunization in Vietnam would be a cost-effective health intervention. However, it only becomes affordable under the GAVI's financial support. Vaccine price is the most crucial factor to decision-makers regarding introducing this vaccine into the country's immunization. Given the high underfive mortality rate, results showed that rotavirus immunization is the “best hope” for prevention of rotavirus-related diarrhoeal disease in Vietnam. In the next five years, Vietnam is definitely in debt to external financial support in implementing rotavirus vaccination. It is recommended that new and cheaper rotavirus vaccine candidates be developed to speed up rotavirus vaccines introduction in the developing world

Interacting circular nanomagnets

Regular 2D rectangular lattices of permalloy nanoparticles (40 nm in diameter) were prepared by the method of the electron lithography. The magnetization curves were studied by Hall magnetometry with the compensation technique for different external field orientations at 4.2K and 77K. The shape of hysteresis curves indicates that there is magnetostatic interaction between the particles. The main peculiarity is the existence of remanent magnetization perpendicular to easy plain. By numerical simulation it is shown, that the character of the magnetization reversal is a result of the interplay of the interparticle interaction and the magnetization distribution within the particles (vortex or uniform).Comment: 16 pages, 8 figure