Polar optical phonons in core-shell semiconductor nanowires

We obtain the the long-wavelength polar optical vibrational modes of semiconductor core-shell nanowires by means of a phenomenological continuum model. A basis for the space of solutions is derived, and by applying the appropriate boundary conditions, the transcendental equations for the coupled and uncoupled modes are attained. Our results are applied to the study of the GaAs-GaP core-shell nanowire, for which we calculate numerically the polar optical modes, analyzing the role of strain in the vibrational properties of this nanosystem

What underpins the decline in syphilis in Southern and Eastern Africa? An exploratory ecological analysis.

BACKGROUND: AIDS mortality played an important role in the decline in syphilis prevalence in the USA, but its effect on the dramatic reduction in syphilis prevalence in Southern and Eastern Africa has not been explored. In this ecological study, we investigated the extent to which the relationship between syphilis and HIV prevalence at a population level varied between the early and late periods of the HIV epidemic. METHODS: We performed linear regression analysis to measure the association between the national prevalence of syphilis and the peak-HIV prevalence in the early and late phases of the HIV epidemic in 11 countries of Southern and Eastern Africa. RESULTS: Our analysis showed a strong positive association between peak-HIV prevalence and syphilis prevalence early in the HIV epidemic (R(2)=0.59; p=0.006). Although only of borderline statistical significance, this linear relationship between HIV prevalence and syphilis prevalence switched to a negative direction late in the HIV epidemic (R(2)=0.32; p=0.07). CONCLUSIONS: AIDS mortality may have played an important role in the decline in syphilis in this region. Consequently, with AIDS deaths declining in Sub-Saharan Africa, vigilant surveillance of syphilis prevalence will be necessary to detect a potential re-emergence, as has occurred in high-income countries, and to render a timely public health response

Exóstosis cartilaginosas múltiples como causa de compresión medular en un husky de 6 meses

Se describe un raro caso de Exóstosis Cartilaginosas Múltiples en una localización poco frecuente como es la lámina dorsal vertebral, produciendo una mielopatía comprensiva. La paresia posterior progresiva resultante fue tratada con éxito quirúrgicamente mediante una laminectomía. El animal recuperó el estado neurológico normal en el postoperatorio inmediato, manteniéndolo a lo largo de un periodo de seguimiento de un año y medio

Fijación de la no-unión del proceso ancóneo mediante tornillo. Estudio retrospectivo en 13 casos clínicos

En este estudio se hace una evaluación retrospectiva de la técnica de fijación con tornillo del proceso ancóneo no unificado en una serie de 13 casos. Los resultados de la cirugía (con un seguimiento de 2 años de media) fueron considerados "excelentes" o "buenos" en 12 o 13 casos, y todos los animales mejoraron el grado de cojera. En el 92% de los codos se consiguió una unión ósea completa del proceso ancóneo, y en el 70%, un estancamiento de la artrosis. La tasa de complicaciones fue del 15%, todas ellas de carácter muy leve.

Low-frequency phonons in carbon nanotubes: A continuum approach

7 págs.; 6 figs.; 2 apéndices ; PACS number s : 68.65. k, 63.22. mLow-frequency phonons in carbon nanotubes are studied using a continuum model which allows consideration of an arbitrary wall thickness for the nanotube. Phonon dispersion relations are calculated for two archetypal examples of carbon nanotubes, the (5,5) and (10,10) tubes. The dependence of the radial breathing mode frequency at Γ on the inverse nanotube diameter is verified within this model; furthermore, we prove it to hold for all pure modes within the thin-shell approximation. The effect of the nanotube wall thickness on the eigenfrequencies of carbon nanotubes is also analyzed, and a criterion to fix this parameter within a continuum model is presented. We compare our results to other continuum approaches, and show that by choosing the appropriate parameters, excellent agreement with recent first-principles calculations can be achieved. © 2006 The American Physical Society.This work has been partly supported by the Spanish DGES Grant No. MAT 2002-04540-C05-03 and the Vicerrectorado de Relaciones Internacionales UCLM.Peer Reviewe