28 research outputs found
On the scaling of the damping time for resonantly damped oscillations in coronal loops
There is not as yet full agreement on the mechanism that causes the rapid
damping of the oscillations observed by TRACE in coronal loops. It has been
suggested that the variation of the observed values of the damping time as
function of the corresponding observed values of the period contains
information on the possible damping mechanism. The aim of this Letter is to
show that, for resonant absorption, this is definitely not the case unless
detailed a priori information on the individual loops is available
Influence of Butterfly and Gate Valves Upstream Large Water Meters
[EN] The research presented was conducted to quantify the effects of butterfly and gate valves located upstream water meters with diameters larger than 50 mm. Errors caused by these valves can have an enormous financial impact taking into consideration that a small percentage of variation in the error of a large meter is typically related to a significant volume of water. The uncertainty on the economic impact that a valve installed upstream of a medium size water meter leads to many water utilities to oversize the meter chambers in order to mitigate the potential negative errors. Most manufacturers approve their meters for a specific flow disturbance sensitivity class according to the standard ISO 4064-1:2018. Under this classification, a correct operation of the meters requires a certain length of straight section of pipe upstream the meter. However, this classification of the meters cannot consider all types of flow perturbances. For this study, two types of valves, butterfly and gate, were tested upstream ten brand-new water meters from six different manufacturers constructed in four different metering technologies: single-jet, Woltmann, electromagnetic and ultrasonic. In each meter unit was tested at five flow rates, from minimum to the overload flow rates. The tests were conducted with valves set in different orientations, closing degrees, and upstream distances from the water meters under study. The research shows that the valves used can produce significant deviations in the measuring errors with respect the errors found for undistorted working conditions.A. would like to thank Fernando Legarda for the original idea and support to install the test bench. Also, would like to thank Cesar Samperio and Iker Bidaurratzaga from Amvisa, Koldo Urkullu and Juan Luis Mozo from Udal Sareak, Unai Lerma and Joaquin Soler from CABB and Francesc Gavara from FACSA for providing the water meters required to carry out this research and their support during the whole process. I.A. and I.B. would like to thank also to the Basque Government research group IT1314-19.Albaina, I.; Arregui De La Cruz, F.; Bidaguren-Alday, C.; Bidaguren, I. (2020). Influence of Butterfly and Gate Valves Upstream Large Water Meters. Water. 12(9):1-24. https://doi.org/10.3390/w12092563S12412
Damping of Fast Magnetohydrodynamic Oscillations in Quiescent Filament Threads
High-resolution observations provide evidence about the existence of
small-amplitude transverse oscillations in solar filament fine structures.
These oscillations are believed to represent fast magnetohydrodynamic (MHD)
waves and the disturbances are seen to be damped in short timescales of the
order of 1 to 4 periods. In this Letter we propose that, due to the highly
inhomogeneous nature of the filament plasma at the fine structure spatial
scale, the phenomenon of resonant absorption is likely to operate in the
temporal attenuation of fast MHD oscillations. By considering transverse
inhomogeneity in a straight flux tube model we find that, for density
inhomogeneities typical of filament threads, the decay times are of a few
oscillatory periods only.Comment: 11 pages, 2 figures, ApJL accepte
Damping mechanisms for oscillations in solar prominences
Small amplitude oscillations are a commonly observed feature in
prominences/filaments. These oscillations appear to be of local nature, are
associated to the fine structure of prominence plasmas, and simultaneous flows
and counterflows are also present. The existing observational evidence reveals
that small amplitude oscillations, after excited, are damped in short spatial
and temporal scales by some as yet not well determined physical mechanism(s).
Commonly, these oscillations have been interpreted in terms of linear
magnetohydrodynamic (MHD) waves, and this paper reviews the theoretical damping
mechanisms that have been recently put forward in order to explain the observed
attenuation scales. These mechanisms include thermal effects, through
non-adiabatic processes, mass flows, resonant damping in non-uniform media, and
partial ionization effects. The relevance of each mechanism is assessed by
comparing the spatial and time scales produced by each of them with those
obtained from observations. Also, the application of the latest theoretical
results to perform prominence seismology is discussed, aiming to determine
physical parameters in prominence plasmas that are difficult to measure by
direct means.Comment: 36 pages, 16 figures, Space Science Reviews (accepted
Coronal Heating by MHD Waves
The heating of the solar chromosphere and corona to the observed high temperatures, imply the presence of ongoing heating that balances the strong radiative and thermal conduction losses expected in the solar atmosphere. It has been theorized for decades that the required heating mechanisms of the chromospheric and coronal parts of the active regions, quiet-Sun, and coronal holes are associated with the solar magnetic fields. However, the exact physical process that transport and dissipate the magnetic energy which ultimately leads to the solar plasma heating are not yet fully understood. The current understanding of coronal heating relies on two main mechanism: reconnection and MHD waves that may have various degrees of importance in different coronal regions. In this review we focus on recent advances in our understanding of MHD wave heating mechanisms. First, we focus on giving an overview of observational results, where we show that different wave modes have been discovered in the corona in the last decade, many of which are associated with a significant energy flux, either generated in situ or pumped from the lower solar atmosphere. Afterwards, we summarise the recent findings of numerical modelling of waves, motivated by the observational results. Despite the advances, only 3D MHD models with Alfvén wave heating in an unstructured corona can explain the observed coronal temperatures compatible with the quiet Sun, while 3D MHD wave heating models including cross-field density structuring are not yet able to account for the heating of coronal loops in active regions to their observed temperature
Brain fog of post-COVID-19 condition and Chronic Fatigue Syndrome, same medical disorder?
Background: Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is characterized by persistent physical and mental fatigue. The post-COVID-19 condition patients refer physical fatigue and cognitive impairment sequelae. Given the similarity between both conditions, could it be the same pathology with a different precipitating factor? Objective: To describe the cognitive impairment, neuropsychiatric symptoms, and general symptomatology in both groups, to find out if it is the same pathology. As well as verify if the affectation of smell is related to cognitive deterioration in patients with post-COVID-19 condition. Methods: The sample included 42 ME/CFS and 73 post-COVID-19 condition patients. Fatigue, sleep quality, anxiety and depressive symptoms, the frequency and severity of different symptoms, olfactory function and a wide range of cognitive domains were evaluated. Results: Both syndromes are characterized by excessive physical fatigue, sleep problems and myalgia. Sustained attention and processing speed were impaired in 83.3% and 52.4% of ME/CFS patients while in post-COVID-19 condition were impaired in 56.2% and 41.4% of patients, respectively. Statistically significant differences were found in sustained attention and visuospatial ability, being the ME/CFS group who presented the worst performance. Physical problems and mood issues were the main variables correlating with cognitive performance in post-COVID-19 patients, while in ME/CFS it was anxiety symptoms and physical fatigue. Conclusions: The symptomatology and cognitive patterns were similar in both groups, with greater impairment in ME/CFS. This disease is characterized by greater physical and neuropsychiatric problems compared to post-COVID-19 condition. Likewise, we also propose the relevance of prolonged hyposmia as a possible marker of cognitive deterioration in patients with post-COVID-19.This study has been funded by Instituto de Salud Carlos III (ISCIII) through the project PI20/01076 and co-funded by the European Union, EITB maratoia (BIOS21/COV/006) and grants for health research projects from the Basque Government (2021111006). Azcue, N. received a pre-doctoral research grant from the basque government (PRE_2021_1_0186)
Evaluation of the Optimal Utility of Some Investment Projects with Irreversible Environmental Effects
Impacte de la combinació de fonts de dades obertes i experimentals en l'anàlisi de les aigües subterrànies a la Illa Margarita
El projecte estudiarà la qualitat de l'aigua en uns pous de la Illa Margarita de Veneçuela utilitzant informació d'una campanya experimental on es disposa de característiques del pou i qualitat de l'aigua en diversos paràmetres físico-químics. Tanmateix, es completarà la base de dades amb informació de contexte disponible, com les pluges de la zona, qüestions de clima, ús del sol, etc, per enriquir l'anàlisi i entendre l'impacte de l'activitat humana en el deteriorament de la qualitat de l'aigua de la illa. L'anàlisi es farà utilitzant eines de data scienc