Dynamic secondary electron emission in dielectric/conductor mixed

Secondary Emission Yield (SEY) of dielectric materials is of great importance for prediction and testing of the Multipaction discharge in RF components for space applications. An atypical behavior of the SEY of coatings composed by a mixture of conductor and dielectric microparticles was reported and modeled in [1]; in this original model, the interactions between dielectric and conductor particles were not taken into account, but an effective action of the surface voltage generated within the sample was included. The aim of the present contribution is to more accurately model the effect the electric fields between dielectric and conductor particles have on secondary electrons emitted by the sample. One of the most prominent features of the coatings is their roughness, so a model is proposed here that takes into account both the roughness and the charging of the dielectric particles to explain the unusual charging behavior of these coatings

Dynamic secondary electron emission in dielectric/conductor mixed coatings

An unexpected behavior of the Secondary Emission Yield (SEY) on coatings composed by a mixture of conductor and dielectric microparticles was reported and modeled in [1]. As a follow up, we measured for a fixed primary energy the dynamic evolution of the SEY in similar samples and proposed a charging-roughness coupled model to simulate the experimental results. Two different coatings were selected: 1) TMM and Al microparticles (type 1), and 2) zeolites and gold nanoparticles (type 2). Pulsed and continuous tests were used to obtain the SEY as a function of the primary energy. In both types of samples extremely large first cross-over energy, E*1, values (around 1000 eV) and very low-SEY at energies lower than E*1 (~0.2) was observed when a \u27normal\u27 electron dose (nC) was used, continuous method. This was maintained for the type 1 coatings when a ‘low’ dose (fC, single pulse method with a pulse duration of 180 ns) was used. However, type 2 coatings exhibited usual E1 values (\u3c100eV) and shape of the SEY curve, when measured by the single pulse method. When type 2 samples were irradiated at a fixed primary energy (E) by 100 μs-wide pulses with a frequency of 100Hz the SEY transient was registered. For primary energies \u3c E*1, the SEY values decreased from the one measured by the single pulse method to the SEY measured with the normal dose (continuous method). Conversely, it was observed for energies larger than E*1 that the SEY increased as the charge built up from the values rendered by the single pulse method to the continuous method\u27s values. In all instances the behavior of the SEY did not approach to 1 as the charge built up, as it should do in a usual isolating material. In addition, ~100 s after the electron irradiation was stopped, the sample had recovered its initial SEY, pointing to a charging explanation of this phenomenon. To simulate this SEY behavior, a model based in both charging and surface roughness is proposed. In this work, conductive and dielectrics materials with different SEY parameters are considered. This mixture of conductor and dielectric materials leads to charge being accumulated at different rates in the different particles or regions of the coating. Together with roughness, these different charging rates, lead to the appearance of electric potentials over the surface that need to be climbed by the secondary electrons in order to be emitted. Two bi-dimensional profiles of the sample roughness are studied, square and triangular models. For the squared profile the different materials were placed at the top and bottom of the wells and, for the triangular profile, they were placed at the left slope and right slope of each triangular hill. Different values for the initial SEYs of the materials were used and it was found that for specific pairs of values the total SEY of the sample can be strongly diminished and for others it can be enhanced, in accordance with the experimental results

Extremely low secondary electron emission from metal/dielectric particulate coatings

Research on low secondary electron emission coatings is essential for the design and manufacture of space high-power RF devices without multipactor discharge. This paper discusses some of the factors that reduce secondary electron emission for metal-dielectric surfaces. We have studied the total electron yield (TEY) behavior of a particulate coating composed of a mixture of a metal (aluminum) nanoparticulates in solid state contact with a particulate dielectric material (polyimide thermosetting resin). Surface charging, roughness, and volume fraction are utilized as the main parameters to characterize the electron emission behavior, which can effectively be determined by continuous (total dose 42.5 nC/mm2) and pulsed (1,1 fC/mm2/pulse) electron irradiation methods. Apart from the important role played by surface composition in the TEY, the influence of the dielectric volume fraction has demonstrated to be critical to achieve a significant reduction of TEY. Analytical surface techniques such as field emission scanning microscopy and X-ray photoelectron spectroscopy were used, because they are very effective in providing insight into the effect of charging on the surface. Typical TEY parameters of the aluminum foil exposed to the air are: the first crossover energy, E1=20 eV, TEY maximum, σmax = 2.9, and Emax = XXX eV; these contrast with the dielectric values: E1= 30 eV, σmax = 2.5, and Emax = XXX eV. However, it was found that E1 of the particulate sample increased with increasing dielectric volume fraction. An extremely high first crossover energy, E1\u3e1000eV, was obtained after the gold metallization of the metal/dielectric coatings of 0.75 volume fraction. It is also remarkable that TEY was 0.2 for E\u3c1000\u3eeV, the low energy emitted electrons appear to be reabsorbed. Another remarkable fact is that TEY curves measured by using either the continuous or the pulsed methods overlap in the whole primary energy range, dissipate the much larger electron dose of the continuous method as compared to the very low dose of the pulsed method; this result is usually understood as an indication of minimal influence of charging on TEY

Significant Release of Dissolved Inorganic Nutrients From the Shallow Submarine Volcano Tagoro (Canary Islands) Based on Seven-Year Monitoring

Tagoro, the shallow submarine volcano that erupted south of El Hierro (Canary Islands, Spain) in October 2011, has been intensely monitored for over 7 years, from the early eruptive stage to the current degassing stage characterized by moderate hydrothermal activity. Here, we present a detailed study of the emissions of inorganic macronutrients (NO2– + NO3–, PO4, and Si(OH)4) comprising a dataset of over 3300 samples collected through three different sampling methodologies. Our results show a significant nutrient enrichment throughout the whole studied period, up to 8.8-fold (nitrate), 4.0-fold (phosphate), and 16.3-fold (silicate) in the water column, and larger enrichments of phosphate (10.5-fold) and silicate (325.4-fold), but not of nitrate, in the samples collected directly from the vents. We also provide some preliminary results showing ammonium (NH4+) concentrations up to 1.97 μM in the vent fluids as compared to 0.02 μM in the surrounding waters. Nutrient fluxes from the volcano during the degassing stage were estimated as 3.19 ± 1.17 mol m–2 year–1 (NO2– + NO3–), 0.02 ± 0.01 mol m–2 year–1 (PO4), and 0.60 ± 1.35 mol m–2 year–1 (Si(OH)4), comparable to other important nutrient sources in the region such as fluxes from the NW-African upwelling. Nutrient ratios were affected, with a minimum (NO3– + NO2–):PO4 ratio of 2.36:1; moreover, a linear correlation between silicate and temperature enabled the use of this nutrient as a mixing tracer. This study sheds light on how shallow hydrothermal systems impact the nutrient-poor upper waters of the ocean.En prens

Donepezil alone and combined with intensive language-action therapy on depression and apathy in chronic post-stroke aphasia: A feasibility study

This study explored the feasibility and effectiveness of a short-term (10-week) intervention trial using Donepezil administered alone and combined with intensive language action therapy (ILAT) for the treatment of apathy and depression in ten people with chronic post-stroke aphasia. Outcome measures were the Western Aphasia Battery and the Stroke Aphasia Depression Questionnaire-21. Structural magnetic resonance imaging and 18fluorodeoxyglucose positron emission tomography were acquired at baseline and after two endpoints (Donepezil alone and Donepezil-ILAT). The intervention was found to be feasible to implement. Large treatment effects were found. Donepezil alone and combined with ILAT reduced aphasia severity, while apathy and depression only improved with Donepezil-ILAT. Structural and functional neuroimaging data did not show conclusive results but provide hints for future research. Given these overall positive findings on feasibility, language and behavioral benefits, further studies in larger sample sizes and including a placebo-control group are indicated.This work was supported as an independent research grant funded by Pfizer and Eisai. The funders were not involved in the study design, collection, analysis, or interpretation of the data. The work was also supported in part by the Ministerio de Economía, Industria y Competitividad, Instituto de Salud Carlos III, Spain (under Grant: PI16/01514; MLB and GD), and the Junta de Andalucía, Spain (under Grant: P20_00501; GD). MLB has been supported by funds from the European Social Fund (FEDER). LE and FJL-G have been funded by a PhD scholarship from the Spanish Ministry of Education, Culture, and Sport under the FPU program (FPU17/04136; FJL-G: FPU17/04470). DL-B was supported by I + D + i Project Andalusia and European Union Funds (FEDER) (UMA18-FEDERJA-221) and by Ramón y Cajal Program (RYC2020-029495-I) from the Spanish Ministry of Science and Innovation. MT-P has been funded by a postdoctoral fellowship under the program Plan Andaluz de Investigación, Desarrollo e Innovación (PAIDI 2020) (DOC_00421). FP and BM were supported by the Deutsche Forschungsgemeinschaft [Pu 97/15-1 and 15-2 to FP, Mo 697/5-2 to BM]. FP was also supported by the European Research Council [ERC-2019-ADG 883811] // Funding for open access charge: Universidad de Málaga / CBUA

Donepezil alone and combined with intensive language-action therapy on depression and apathy in chronic post-stroke aphasia: A feasibility study

This study explored the feasibility and effectiveness of a short-term (10-week) intervention trial using Donepezil administered alone and combined with intensive language action therapy (ILAT) for the treatment of apathy and depression in ten people with chronic post-stroke aphasia. Outcome measures were the Western Aphasia Battery and the Stroke Aphasia Depression Questionnaire-21. Structural magnetic resonance imaging and 18fluorodeoxyglucose positron emission tomography were acquired at baseline and after two endpoints (Donepezil alone and Donepezil-ILAT). The intervention was found to be feasible to implement. Large treatment effects were found. Donepezil alone and combined with ILAT reduced aphasia severity, while apathy and depression only improved with Donepezil-ILAT. Structural and functional neuroimaging data did not show conclusive results but provide hints for future research. Given these overall positive findings on feasibility, language and behavioral benefits, further studies in larger sample sizes and including a placebo-control group are indicated