On the nature of transverse coronal waves revealed by wavefront dislocations

Coronal waves are an important aspect of the dynamics of the plasma in the corona. Wavefront dislocations are topological features of most waves in nature and also of magnetohydrodynamic waves. Are there dislocations in coronal waves? The finding and explanation of dislocations may shed light on the nature and characteristics of the propagating waves, their interaction in the corona and in general on the plasma dynamics. We positively identify dislocations in coronal waves observed by the Coronal Multi-channel Polarimeter (CoMP) as singularities in the Doppler shifts of emission coronal lines. We study the possible singularities that can be expected in coronal waves and try to reproduce the observed dislocations in terms of localization and frequency of appearance. The observed dislocations can only be explained by the interference of a kink and a sausage wave modes propagating with different frequencies along the coronal magnetic field. In the plane transverse to the propagation, the cross-section of the oscillating plasma must be smaller than the spatial resolution, and the two waves result in net longitudinal and transverse velocity components that are mixed through projection onto the line of sight. Alfv\'en waves can be responsible of the kink mode, but a magnetoacoustic sausage mode is necessary in all cases. Higher (flute) modes are excluded. The kink mode has a pressure amplitude that is smaller than the pressure amplitude of the sausage mode, though its observed velocity is larger. This concentrates dislocations on the top of the loop. To explain dislocations, any model of coronal waves must include the simultaneous propagation and interference of kink and sausage wave modes of comparable but different frequencies, with a sausage wave amplitude much smaller than the kink one.Comment: 11 pages. 5 figures. Accepted for publication in A&

Manejo quirúrgico de la poliposis nasosinusal

Indexación: ScieloIntroducción: La poliposis nasosinusal es un proceso inflamatorio crónico de la mucosa rinosinusal, de etiología desconocida, y que requiere de tratamiento quirúrgico en más de 50% de los pacientes. Objetivo: Evaluar los resultados de la cirugía endoscópica en pacientes con poliposis nasosinusal en el Hospital Barros Luco-Trudeau. Material y método: Estudio retrospectivo de 180 fichas clínicas de pacientes operados en este hospital en el período 1999-2008. Resultados: La distribución según sexo fue de 63% varones y 37% mujeres (p <0,001) y el promedio etario, de 44,9 años. El motivo principal de consulta fue la obstrucción nasal. Un tercio de los pacientes tenía poliposis masiva. El 17% se asoció con asma. Más del 50% de los pacientes usó corticoides inhalados en el preoperatorio. En el 58% se realizó cirugía endoscópica hasta etmoides anterior. No hubo complicaciones mayores en esta serle estudiada. La recidiva global fue de 24%. El promedio de meses libres de recidiva fue 46,7 meses (IC 95%: 37,5-55,5), con una recidiva de 25% al año de seguimiento. No se encontró asociación entre recidiva y los factores de riesgo estudiados. Discusión: En comparación con la literatura, se observa similares características demográficas. Sin embargo, los factores de riesgo de recidiva no fueron significativos, aparentemente debido a una baja prevalenciay a pérdida del seguimiento. La tasa de recidiva aumenta con el tiempo, motivo por el cual se requiere un seguimiento a largo plazo. Conclusiones: No se detectó asociación entre recidiva y los factores de riesgo clásicamente descritos en la literatura. Las recidivas fueron tardías y se obtuvieron tasas de recidiva similares a lo publicado en la literatura.Introduction: Sinonasal polyposis is a chronic inflammatory process rhinosinusal mucosa of unknown etiology which in over 50% of patients requires surgical treatment. Aim: To evaluate the results of endoscopic surgery in patients with sinonasal polyposis in the Barros Luco-Trudeau Hospital. Material and method: Retrospective study of 180 medical records of patients operated at this hospital from 1999 to 2008. Results: The sexual distribution was 63% male and 37% women (p <0.001). The average age was 44.9years. The chief complaint was nasal obstruction. A third of the patients had massive polyposis. The 17% was associated with asthma. Over 50% of patients used inhaled corticosteroids preoperatively in 58% performed endoscopic surgery to anterior ethmoid. There were no major complications in these series studied. The overall recurrence was 24%. The average number of months free of recurrence was 46.7 months (95% Cl 37.5 to 55.5) with a recurrence of 25% per year of follow up. We found no association between recurrence and the risk factors studied. Discussion: Comparing with the lierature, we see the same demographic characteristics but risk factors for recurrence are not significant, apparently due to the low prevalence and loss of follow-up. The recurrence rate is increased over time and therefore requires a long-term monitoring. Conclusions: We found no association between recurrence and the risk factors classically described in literature. Recurrences were late and we had similar recurrence rates to publish in the lierature.http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-48162010000100002&nrm=is

Use of massively parallel computing to improve modelling accuracy within the nuclear sector

The extreme environments found within the nuclear sector impose large safety factors on modelling analyses to ensure components operate in their desired manner. Improving analysis accuracy has clear value of increasing the design space that could lead to greater efficiency and reliability. Novel materials for new reactor designs often exhibit non-linear behaviour; additionally material properties evolve due to in-service damage a combination that is difficult to model accurately. To better describe these complex behaviours a range of modelling techniques previously under-pursued due to computational expense are being developed. This work presents recent advancements in three techniques: Uncertainty quantification (UQ); Cellular automata finite element (CAFE); Image based finite element methods (IBFEM). Case studies are presented demonstrating their suitability for use in nuclear engineering made possible by advancements in parallel computing hardware that is projected to be available for industry within the next decade costing of the order of $100k

Understanding air release through air valves

[EN] Water transients with entrapped air can originate large pressure peaks that can severely damage distribution networks. Entrapped air can have a damping or amplifying effect on these undesirable pressure peaks. Unfortunately, the complexity of the phenomenon too often makes it difficult to obtain a fully reliable prediction about when air pockets will mitigate or accentuate water transients. Furthermore, the value of some of the parameters involved in the conventional numerical models cannot be calculated or measured and need to be determined through a calibration process. With the aim of overcoming most of the aforementioned uncertainties, this paper summarizes a complete set of tests conducted at WL | Delft Hydraulics. These tests were simulated by means of a tailored numerical model that includes a set of parameters whose values were determined by means of a calibration process. The experimental setup, a large-scale facility, consisted of a single steep pipeline with an air valve installed at its top end. Air release through different air valves was tested under different conditions. © 2011 American Society of Civil Engineers.This research has been possible thanks to the European Community Programme "Access to Major Research Infrastructure" under the Fifth Framework Growth Programme (Contract No. GIRT-CT-2002-05069).Carlos Alberola, MDM.; Arregui De La Cruz, F.; Cabrera Marcet, E.; Palau, C. (2011). Understanding air release through air valves. Journal of Urban Planning and Development. 137(4):461-469. doi:10.1061/(ASCE)HY.1943-7900.0000324S461469137

Resonantly damped surface and body MHD waves in a solar coronal slab with oblique propagation

The theory of magnetohydrodynamic (MHD) waves in solar coronal slabs in a zero-$\beta$ configuration and for parallel propagation of waves does not allow the existence of surface waves. When oblique propagation of perturbations is considered both surface and body waves are able to propagate. When the perpendicular wave number is larger than a certain value, the body kink mode becomes a surface wave. In addition, a sausage surface mode is found below the internal cut-off frequency. When non-uniformity in the equilibrium is included, surface and body modes are damped due to resonant absorption. In this paper, first, a normal-mode analysis is performed and the period, the damping rate, and the spatial structure of eigenfunctions are obtained. Then, the time-dependent problem is solved, and the conditions under which one or the other type of mode is excited are investigated.Comment: 19 pages, 9 figures, accepted for publication in Solar Physic

Ferromagnetic resonance assisted optomechanical magnetometer

The resonant enhancement of mechanical and optical interaction in optomechanical cavities enables their use as extremely sensitive displacement and force detectors. In this work we demonstrate a hybrid magnetometer that exploits the coupling between the resonant excitation of spin waves in a ferromagnetic insulator and the resonant excitation of the breathing mechanical modes of a glass microsphere deposited on top. The interaction is mediated by magnetostriction in the ferromagnetic material and the consequent mechanical driving of the microsphere. The magnetometer response thus relies on the spectral overlap between the ferromagnetic resonance and the mechanical modes of the sphere, leading to a peak sensitivity better than 900 pT Hz$^{-1/2}$ at 206 MHz when the overlap is maximized. By externally tuning the ferromagnetic resonance frequency with a static magnetic field we demonstrate sensitivity values at resonance around a few nT Hz$^{-1/2}$ up to the GHz range. Our results show that our hybrid system can be used to build high-speed sensor of oscillating magnetic fields

Inversion of physical parameters in solar atmospheric seismology

Magnetohydrodynamic (MHD) wave activity is ubiquitous in the solar atmosphere. MHD seismology aims to determine difficult to measure physical parameters in solar atmospheric magnetic and plasma structures by a combination of observed and theoretical properties of MHD waves and oscillations. This technique, similar to seismology or helio-seismology, demands the solution of two problems. The direct problem involves the computation of wave properties of given theoretical models. The inverse problem implies the calculation of unknown physical parameters, by means of a comparison of observed and theoretical wave properties. Solar atmospheric seismology has been successfully applied to different structures such as coronal loops, prominence fine structures, spicules, or jets. However, it is still in its infancy. Far more is there to come. We present an overview of recent results, with particular emphasis in the inversion procedure.Comment: 10 pages, 3 figures, review paper to appear in Astrophysics and Space Science Proceeding

Restos vegetales en muestras de subsuelo, Formación Lajas, Jurásico medio, Cuenca Neuquina, Neuquén, Argentina

Se dan a conocer restos vegetales preservados como impresiones correspondientes a diferentes órganos, tales como tallos, hojas y ramas asignables a equisetópsidas, pteridospermópsidas y coníferas respecVvamente. Los mismos fueron recuperados de muestras de tesVgos coronas de la Formación Lajas, Jurásico Medio de la cuenca Neuquina, de pozos pertenecientes al área del Engolfamiento Neuquino, al norte de la Dorsal de Huincul. La Formación Lajas se describe como depósitos marinomarginales, principalmente sistemas deltaicos, compuestos por areniscas y en menor medida pelitas oscuras y verdosas con abundantes rastros carbonosos. Además de los megafósiles mencionados, se reportan numerosos restos de fitodetritos. Los fósiles vegetales fueron hallados en los niveles carbonosos asignables a ambientes de planicie deltaica, a interbarras de frente deltaico, y a barras de frente deltaico. Los procesos depositacionales en las barras de frente deltaico están dominados por procesos tracVvos, por lo cual, se infiere que algunos de los restos (tallos y ramas), corresponden a elementos resistentes a estos procesos mientras que aquellos más delicados (frondes) a ambientes de planicie deltaica, siendo depositados por suspensión en ambientes más tranquilos. Esto podría indicar la presencia de dos poblaciones vegetales, una más aun a ambiente deltaico, ya que por la buena preservación de sus partes más delicadas no evidencia transporte, y otra que representa una comunidad vegetal más conVnental-terrígena, que hubiera sufrido algún grado de transporte debido a la acción fluvial. El material estudiado se encuentra depositado en el Repositorio de material fósil de YPF Tecnología.Facultad de Ciencias Naturales y Muse

Coronal magnetic field measurement using loop oscillations observed by Hinode/EIS

We report the first spectroscopic detection of a kink MHD oscillation of a solar coronal structure by the Extreme-Ultraviolet Imaging Spectrometer (EIS) on the Japanese Hinode satellite. The detected oscillation has an amplitude of 1 kms−1 in the Doppler shift of the FeXII 195 Å spectral line (1.3 MK), and a period of 296 s. The unique combination of EIS’s spectroscopic and imaging abilities enables us to measure simultaneously the mass density and length of the oscillating loop. This enables us to measure directly the magnitude of the local magnetic field, the fundamental coronal plasma parameter, as 39 ± 8 G, with unprecedented accuracy. This proof of concept makes EIS an exclusive instrument for the full scale implementation of the MHD coronal seismological technique