Solid flow drives surface nanopatterning by ion-beam irradiation

Ion Beam Sputtering (IBS) is known to produce surface nanopatterns over macroscopic areas on a wide range of materials. However, in spite of the technological potential of this route to nanostructuring, the physical process by which these surfaces self-organize remains poorly under- stood. We have performed detailed experiments of IBS on Si substrates that validate dynamical and morphological predictions from a hydrodynamic description of the phenomenon. Our results elucidate flow of a nanoscopically thin and highly viscous surface layer, driven by the stress created by the ion-beam, as a description of the system. This type of slow relaxation is akin to flow of macroscopic solids like glaciers or lead pipes, that is driven by defect dynamics.Comment: 12 pages, 4 figure

Expansion of non-native brown trout in South Europe may be inadvertently driven by stocking: Molecular and social survey in the North Iberian Narcea River

The biological and anthropogenic (management) factors that may contribute to the expansion of non-native lineages in managed fish have been studied in this work taking brown trout (Salmo trutta) as a model species. The changes of users’ opinion about stocking was studied employing social science methodology (surveys). The evolution of hatchery stocks together with the outcome of stocking were analysed with two genetic tools: the LDH-C1* locus (marker of non-native stocks) and six microsatellite loci (for assignment of wild trout to the natural population or putative hatchery stocks). Consulted stakeholders were convinced of the correctness of releasing only native stocks, although in practice the hatcheries managed by them contained important proportions of non-native gene carriers. Our results suggest that allochthonous individuals perform better and grow faster in hatchery conditions than the native ones. We also find a dilution of the impact of this kind of suplementation in wild conditions. The use of only native individuals as hatchery breeders tested for the presence of non-native alleles previously to the artificial crosses must be a priority. Surveys can help steer policy making toward decisions that will be followed by the public, but they should not be used to justify science

Los tornillos como método suplementario de fijación de las cúpulas acetabulares: Utilidad de la digitalización de imágenes

La fijación suplementaria con tornillos de los componentes acetabulares hemisféricos no cementados es utilizada para proporcionar estabilidad primaria al implante. No obstante su empleo se asocia a un mayor riesgo de lesiones neurovasculares, complicaciones propias de los tornillos e incremento de osteolisis. Se han estudiado retrospectivamente las radiografías de 30 cúpulas cotiloideas no cementadas modelo Bihapro, suplementadas con tornillos, con un seguimiento mínimo de 5 años. Se utilizó, además, un programa de análisis y procesamiento de imágenes por ordenador. No se produjeron lesiones neurovasculares o viscerales, no se apreció ninguna movilización de la cúpula y sólo se observó un caso e osteolisis alrededor de un tornillo en un paciente sometido a cirugía de revisión. La digitalización de imágenes es una técnica que permite entre otras ventajas graduar densidades óseas periprotésicas facilitando un diagnóstico precoz de zonas líticas y microdeslizamientos protésicos, eliminando la subjetividad del observador.The supplementary fixation with screws non-cemented acetabular hemispheric components is used to provide primary stability to the implants. However, their use has been associated to a bigger risk of neurological and vascular damage, characteristic complications of the screws and osteolysis. The X-rays of 30 non-cemented acetabular cups model Bihapro supplemented with screws have been studied retrospectively with a 5 year-old minimum follow-up. It was also used an analysis program and computer store of images. No neurological or vascular damage took place. Any mobilization of the cup was not appreciated and only in one case of an osteolytic area was observed around a screw in a patient who unfderwent revision surgery. The digitalization of images is a technique that allows among other advantages to graduate periprosthetic bone densities facilitating an early diagnose of lytic areas and prosthetic micromovements eliminating the observer's subjectivity

Unveiling the structure of the planetary nebula M 2-48: Kinematics and physical conditions

The kinematics and physical conditions of the bipolar planetary nebula M 2-48 are analysed from high and low dispersion long-slit spectra. Previous CCD narrow-band optical observations have suggested that this nebula is mainly formed by a pair of symmetric bow-shocks, an off-center semi-circular shell, and an internal bipolar structure. The bipolar outflow has a complex structure, characterised by a series of shocked regions located between the bright core and the polar tips. There is an apparent kinematic discontinuity between the bright bipolar core and the outer regions. The fragmented ring around the bright bipolar region presents a low expansion velocity and could be associated to ejection in the AGB-PN transition phase, although its nature remains unclear. The chemical abundances of the central region are derived, showing that M 2-48 is a Type I planetary nebula (PN)

Coulomb explosion sputtering of selectively oxidized Si

We have studied multiply charged Arq+ ion induced potential sputtering of a unique system comprising of coexisting Silicon and Silicon oxide surfaces. Such surfaces are produced by oblique angle oxygen ion bombardment on Si(100), where ripple structures are formed and one side of each ripple gets more oxidized. It is observed that higher the potential energy of Arq+ ion, higher the sputtering yield of the non conducting (oxide) side of the ripple as compared to the semiconducting side. The results are explained in terms of Coulomb explosion model where potential sputtering depends on the conductivity of the ion impact sites.Comment: 9 pages and 3 figure

The physical structure of the point-symmetric and quadrupolar planetary nebula NGC 6309

We analyse the point-symmetric planetary nebula NGC 6309 in terms of its three-dimensional structure and of internal variations of the physical conditions to deduce the physical processes involved in its formation. We used VLA-D 3.6-cm continuum, ground-based, and HST-archive imaging as well as long slit high- and low-dispersion spectroscopy. The low-dispersion spectra indicate a high excitation nebula, with low to medium variations of its internal physical conditions. In the optical images, the point-symmetric knots show a lack of [NII] emission as compared with similar features previously known in other PNe. A rich internal structure of the central region is seen in the HST images, resembling a deformed torus. Long slit high-dispersion spectra reveal a complex kinematics in the central region. The spectral line profiles from the external regions of NGC 6309 indicate expanding lobes (~40 km/s) as those generally found in bipolar nebulae. Finally, we have found evidence for the presence of a faint halo, possibly related to the envelope of the AGB-star progenitor. Our data indicate that NGC 6309 is a quadrupolar nebula with two pairs of bipolar lobes whose axes are oriented PA=40 and PA=76. Equatorial and polar velocities for these two pairs of lobes are 29 and 86 km/s for the bipolar system at PA=40 and 25 and 75 km/s for the bipolar system at PA=76. There is also a central torus that is expanding at 25 km/s. Kinematical age for all these structures is around 3700 to 4000 yr. We conclude that NGC 6309 was formed by a set of well-collimated bipolar outflows (jets), which were ejected in the initial stages of its formation as a planetary nebula. These jets carved the bipolar lobes in the previous AGB wind and their remnants are now observed as the point-symmetric knots tracing the edges of the lobes.Comment: To be published in Astronomy & Astrophysics; 11 pages, 8 figures, 4 table

Caracterización arqueomética de azulejos sevillanos

El estudio e investigación que se presenta se corresponde a una caracteriza ción realizada sobre piezas cerámicas vidriadas que, procedentes de distintos edi ficios de Sevilla, se encuentran almacenadas en la actualidad, en los Reales Al cázares de Sevilla. La metodología seguida ha consistido en el estudio de propiedades físicas determinantes del estado de conservación, análisis químico y mineralógico de las pastas y estudio por microscopía electrónica de las caracte rísticas de los vidriados e interfases. El estudio ha permitido establecer diferen cias de acuerdo con la época de fabricación, así como con relación a la conser vación de las piezas