Three-Dimensional Propagation of Magnetohydrodynamic Waves in Solar Coronal Arcades

We numerically investigate the excitation and temporal evolution of oscillations in a two-dimensional coronal arcade by including the three-dimensional propagation of perturbations. The time evolution of impulsively generated perturbations is studied by solving the linear, ideal magnetohydrodynamic (MHD) equations in the zero-beta approximation. As we neglect gas pressure the slow mode is absent and therefore only coupled MHD fast and Alfven modes remain. Two types of numerical experiments are performed. First, the resonant wave energy transfer between a fast normal mode of the system and local Alfven waves is analyzed. It is seen how, because of resonant coupling, the fast wave with global character transfers its energy to Alfvenic oscillations localized around a particular magnetic surface within the arcade, thus producing the damping of the initial fast MHD mode. Second, the time evolution of a localized impulsive excitation, trying to mimic a nearby coronal disturbance, is considered. In this case, the generated fast wavefront leaves its energy on several magnetic surfaces within the arcade. The system is therefore able to trap energy in the form of Alfvenic oscillations, even in the absence of a density enhancement such as that of a coronal loop. These local oscillations are subsequently phase-mixed to smaller spatial scales. The amount of wave energy trapped by the system via wave energy conversion strongly depends on the wavelength of perturbations in the perpendicular direction, but is almost independent from the ratio of the magnetic to density scale heights.Comment: 27 pages, 11 figure

Mechanical Unfolding of a Simple Model Protein Goes Beyond the Reach of One-Dimensional Descriptions

We study the mechanical unfolding of a simple model protein. The Langevin dynamics results are analyzed using Markov-model methods which allow to describe completely the configurational space of the system. Using transition path theory we also provide a quantitative description of the unfolding pathways followed by the system. Our study shows a complex dynamical scenario. In particular, we see that the usual one-dimensional picture: free-energy vs end-to-end distance representation, gives a misleading description of the process. Unfolding can occur following different pathways and configurations which seem to play a central role in one-dimensional pictures are not the intermediate states of the unfolding dynamics.Comment: 10 pages, 6 figure

Germ cell survival and differentiation after xenotransplantation of testis tissue from three endangered species: Iberian lynx (Lynx pardinus), Cuvier's gazelle (Gazella cuvieri) and Mohor gazelle (G. dama mhorr)

The use of assisted reproductive techniques for endangered species is a major goal for conservation. One of these techniques, testis tissue xenografting, allows for the development of spermatozoa from animals that die before reaching sexual maturity. To assess the potential use of this technique with endangered species, testis tissue from six Iberian lynxes (one fetus, two perinatal cubs, two 6-month-old and one 2-year-old lynx), two Cuvier's gazelle fetuses and one 8-month-old Mohor gazelle were transplanted ectopically into nude mice. Tissue from the lynx fetus, perinatal cubs and 2-year-old donors degenerated, whereas spermatogonia were present in 15% of seminiferous tubules more than 70 weeks after grafting in transplanted testis tissue from 6-month-old donors. Seminal vesicle weights (indicative of testosterone production) increased over time in mice transplanted with tissue from 6-month-old lynxes. Progression of spermatogenesis was observed in xenografts from gazelles and was donor age dependent. Tissue from Cuvier's gazelle fetuses contained spermatocytes 40 weeks after grafting. Finally, round spermatids were found 28 weeks after transplantation in grafts from the 8-month-old Mohor gazelle. This is the first time that xenotransplantation of testicular tissue has been performed with an endangered felid and the first successful xenotransplantation in an endangered species. Our results open important options for the preservation of biological diversity. Journal compilation © CSIRO 2014.This study was supported by the Spanish Ministry of Science and Innovation (grants CGL2006-13340 and CGL2009-11606).Peer Reviewe

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

Data-driven model for the assessment of mycobacterium tuberculosis transmission in evolving demographic structures

In the case of tuberculosis (TB), the capabilities of epidemic models to produce quantitatively robust forecasts are limited by multiple hindrances. Among these, understanding the complex relationship between disease epidemiology and populations’ age structure has been highlighted as one of the most relevant. TB dynamics depends on age in multiple ways, some of which are traditionally simplified in the literature. That is the case of the heterogeneities in contact intensity among different age strata that are common to all airborne diseases, but still typically neglected in the TB case. Furthermore, while demographic structures of many countries are rapidly aging, demographic dynamics are pervasively ignored when modeling TB spreading. In this work, we present a TB transmission model that incorporates country-specific demographic prospects and empirical contact data around a data-driven description of TB dynamics. Using our model, we find that the inclusion of demographic dynamics is followed by an increase in the burden levels predicted for the next decades in the areas of the world that are most hit by the disease today. Similarly, we show that considering realistic patterns of contacts among individuals in different age strata reshapes the transmission patterns reproduced by the models, a result with potential implications for the design of age-focused epidemiological interventions

Magnetohydrodynamic Waves in Partially Ionized Prominence Plasmas

Prominences or filaments are cool clouds of partially ionized plasma living in the solar corona. Ground- and space-based observations have confirmed the presence of oscillatory motions in prominences and they have been interpreted in terms of magnetohydrodynamic (MHD) waves. Existing observational evidence points out that these oscillatory motions are damped in short spatial and temporal scales by some still not well known physical mechanism(s). Since prominences are partially ionized plasmas, a potential mechanism able to damp these oscillations could be ion-neutral collisions. Here, we will review the work done on the effects of partial ionization on MHD waves in prominence plasmas.Comment: Review paper to appear in Astrophysics and Space Science Proceeding

Suppression of spermatogenesis before grafting increases survival and supports resurgence of spermatogenesis in adult mouse testis

Objective: To test whether absence of complete spermatogenesis in mature testicular tissue before grafting will increase graft survival. Design: Prospective experimental study. Setting: Laboratory. Animal(s): Donor testes were obtained from adult untreated mice, adult mice rendered cryptorchid, and adult mice treated with a GnRH antagonist (acyline). Intervention(s): Donor testes were ectopically grafted to nude mice and recovered at three time points. Main Outcome Measure(s): Most advanced germ cell type and presence of spermatogonia were assessed. Donor testes and grafts were analyzed by histology and by immunocytochemistry for ubiquitin C-terminal hydrolase-L1 to mark germ cells. Result(s): Suppression of spermatogenesis by inducing cryptorchidism or acyline treatment resulted in improved survival of grafted tissue compared with controls and recovery of complete spermatogenesis, whereas control testis grafts mostly degenerated and did not restore complete spermatogenesis. Conclusion(s): These results indicate that complete spermatogenesis at the time of grafting has a negative effect on graft survival. Grafting of adult testis tissue from donors with suppressed spermatogenesis leads to spermatogenic recovery and may provide a tool to study and preserve fertility and for conservation of genetic resources in individuals that lack complete germ cell differentiation. © 2012 American Society for Reproductive Medicine.Peer Reviewe

Observational evidence favors a resistive wave heating mechanism for coronal loops over a viscous phenomenon

Context. How coronal loops are heated to their observed temperatures is the subject of a long standing debate. Aims. Observational evidence exists that the heating in coronal loops mainly occurs near the loop footpoints. In this article, analytically and numerically obtained heating profiles produced by resonantly damped waves are compared to the observationally estimated profiles. Methods. To do that, the predicted heating profiles are fitted with an exponential heating function, which was also used to fit the observations. The results of both fits, the estimated heating scale heights, are compared to determine the viability of resonant absorption as a heating mechanism for coronal loops. Results. Two results are obtained. It is shown that any wave heating mechanism (i.e. not just resonant absorption) should be dominated by a resistive (and not a viscous) phenomenon in order to accomodate the constraint of footpoint heating. Additionally it is demonstrated that the analytically and numerically estimated heating scale heights for the resonant absorption damping mechanism fit the observations very well

Resonantly damped oscillations of longitudinally stratified coronal loops

Soon after coronal loop oscillations were observed by TRACE spacecraft for the first time in 1999, various theoretical models have been put forward to explain the rapid damping of the oscillations of these intriguing objects. Coronal loop oscillations are often interpreted as fast kink modes of a straight cylindrical magnetic flux tube with immovable edges modelling dense photospheric plasma at the ends of the loop. Taking this model as a basis we use cold plasma approximation and consider the tube to be thin to simplify the problem and be able to deal with it analytically. In its equilibrium state the tube is permeated by a homogeneous magnetic field directed along the tube axis. We include the effect of stratification in our model supposing that plasma density varies along the tube. There is also density inhomogeneity in the radial direction confined in a layer with thickness much smaller than the radius of the tube. Considering the system of linearized MHD equations we study the dependence of the spectrum of tube oscillations and its damping due to resonant absorption on the parameters of the unperturbed state. The implication of the obtained results on coronal seismology is discussed