cycle maximum
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Roman Brajša ◽  
Giuli Verbanac ◽  
Mario Bandić ◽  
Arnold Hanslmeier ◽  
Ivica Skokić ◽  

2020 ◽  
Vol 494 (2) ◽  
pp. 2166-2177 ◽  
B Filippov

ABSTRACT We analyse 16 failed filament eruptions observed near 24 solar cycle maximum from 2013 May to 2014 July. No significant rotation of filament spines is observed during the ascent in all studied failed eruptions, which does not support kink-instability mechanism of triggering the eruptions. We calculate potential magnetic field distributions in the corona above the initial locations of the filaments to study their height dependence. In seven events, the vertical profiles of the decay index n are monotonic. The other nine events occur in the regions with the switchback or saddle-like n-profiles. The direction of the horizontal field near the saddle bottom is turned through more than 100° relative its direction at the initial filament position, which reveals the quadrupolar magnetic configuration with null points in these regions. The eruptive filaments stop above the null points where the total Lorentz force is directed upward. The most reasonable force that can terminate filament ascending and balance the Lorentz force seems the gravity.

2020 ◽  
Vol 8 (6) ◽  
pp. 5679-5684

Filler metal addition has been verified as an effective way to refine mechanical behaviour of cold rolled mild steel in resistance spot welding.Negligible quantity of filler metal if added to the spot weld is found to improve mechanical properties of spot weldments , if no variation in composition of base metal and filler metal is allowed.. Looking at practical applications, sensitivity of the Resistance Spot Welding process with filler metal to variation in preheating treatment were experimentally investigated.Filler metal quantity was from 30 mg to 70 mg and preheat heat treatment was kept between 20% to 60%.The material of the filler metal is same as that of base metal and was added at the centre of overlap in lap joint.The experimentation was carried out by spot welding of specimen varying filler metal from 30 mg to 70 mg maintaining preheating cycle constant at 20%.The experimentation was then repeated for different preheat cycles.For 20% to 60% of preheat cycle, maximum breaking point was found to be varying linearly with increase in preheat level. Overall improvement in load bearing and energy absorption capability was observed as majority of specimen fail under the button pullout mode

2020 ◽  
Michael Danielides ◽  
Jaroslav Chum

<p>Earth's ionosphere is formed mainly due to solar radiation, precipitating particles and cosmic rays. Its behavior is directly dependent on solar variation and the change of solar activity through out each solar cycle. The solar activity is measured by the number of sunspots and the solar radiation flux expressed by the F10.7 index. The earlier variation in electron density from solar cycle maximum to solar cycle minimum has been noted by Hargreaves (1992). He utilized the F10.7 index as a proxy for Lyman- radiation flux, which ionizes at D-region heights mainly O<sub>2</sub> and N<sub>2</sub> also NO. Utilizing the IRI model the atmospheric densities of O<sub>2</sub> and N<sub>2</sub> are assumed to be constant, NO density is the unknown. Also, it is known that the ionospheric reflection height depends on, e.g. diurnal variations [Pal & Chakrabarti, 2010] and other sudden ionospheric disturbances. Its longer term variations are not well enough studied.</p><p>Utilizing passive VLF ground based measurements with data coverage for almost the entire solar cycle 24, we compare monthly averaged solar quiet absorption curves fitted by a cosine dependence. This cosine dependence includes fixed parameters based on geography and setup of the instrument. The variables are only the solar zenith angle and the D-region absorption. This approach offers an indirect value of NO density change.</p><p>For the present study we utilize VLF monitors, which are located in northern Germany and at Czech Republic. The latter station also offers data from ionospheric sounder and continuous Doppler sounding. A simple 1-D ionospheric model is applied to compute ionospheric electron densities for daytime conditions based on solar F10.7 radiation fluxes.</p><p>The aim of this study is a comparison of solar quiet VLF curves of the solar cycle 24 maximum and minimum. Beside the change of NO density, also the variation of height of the D-region reflective layer will be discussed.</p>

2020 ◽  
Vol 635 ◽  
pp. A178 ◽  
S. Boro Saikia ◽  
M. Jin ◽  
C. P. Johnstone ◽  
T. Lüftinger ◽  
M. Güdel ◽  

Context. Due to the effects that they can have on the atmospheres of exoplanets, stellar winds have recently received significant attention in the literature. Alfvén-wave-driven 3D magnetohydrodynamic models, which are increasingly used to predict stellar wind properties, contain unconstrained parameters and rely on low-resolution stellar magnetograms. Aims. In this paper, we explore the effects of the input Alfvén wave energy flux and the surface magnetogram on the wind properties predicted by the Alfvén Wave Solar Model (AWSoM) model for both the solar and stellar winds. Methods. We lowered the resolution of two solar magnetograms during solar cycle maximum and minimum using spherical harmonic decomposition. The Alfvén wave energy was altered based on non-thermal velocities determined from a far ultraviolet spectrum of the solar twin 18 Sco. Additionally, low-resolution magnetograms of three solar analogues, 18 Sco, HD 76151, and HN Peg, were obtained using Zeeman Doppler imaging and used as a proxy for the solar magnetogram. Finally, the simulated wind properties were compared to Advanced Composition Explorer (ACE) observations. Results. AWSoM simulations using well constrained input parameters taken from solar observations can reproduce the observed solar wind mass loss and angular momentum loss rates. The simulated wind velocity, proton density, and ram pressure differ from ACE observations by a factor of approximately two. The resolution of the magnetogram has a small impact on the wind properties and only during cycle maximum. However, variation in Alfvén wave energy influences the wind properties irrespective of the solar cycle activity level. Furthermore, solar wind simulations carried out using the low-resolution magnetogram of the three stars instead of the solar magnetogram could lead to an order of a magnitude difference in the simulated solar wind properties. Conclusions. The choice in Alfvén energy has a stronger influence on the wind output compared to the magnetogram resolution. The influence could be even stronger for stars whose input boundary conditions are not as well constrained as those of the Sun. Unsurprisingly, replacing the solar magnetogram with a stellar magnetogram could lead to completely inaccurate solar wind properties, and should be avoided in solar and stellar wind simulations. Further observational and theoretical work is needed to fully understand the complexity of solar and stellar winds.

2020 ◽  
Vol 12 (3) ◽  
pp. 553
Richard W. Gould ◽  
Stephanie Anderson ◽  
M. David Lewis ◽  
W. David Miller ◽  
Igor Shulman ◽  

Optically-active constituents vary over short time and space scales in coastal waters, and they are impacted by a variety of complex, inter-related forcing processes. As part of the Integrated Coastal Bio-Optical Dynamics (ICoBOD) project, we conducted a field campaign in Mississippi Sound in the northern Gulf of Mexico during spring 2018 to examine the impact of the passage of atmospheric and tidal fronts on fine-scale physical and bio-optical property distributions in a shallow, dynamic, coastal environment. During a 25-day experiment, we deployed eight moorings over a roughly 7 × 7 km box encompassing a frontal zone, to collect a time series of physical and bio-optical measurements. We describe changes in diver visibility related to the passage of a short-duration, high-turbidity surface plume and nepheloid layer development/decay during a tidal cycle. Maximum nepheloid layer development was observed during low tide and lasted about 9–12 h. The strongest turbidity signal extended about 4–5 m above the bottom (approximately half of the water column), although anomalously elevated values were observed all the way to the surface. In addition, high-resolution (50 m) hydrodynamic model simulations provide insight into the frontal dynamics and aid interpretation of the observed patterns. Mooring observations confirmed model-predicted heat flux changes associated with the passage of an atmospheric cold front.

2019 ◽  
Vol 71 (1) ◽  
Alexander V. Koustov ◽  
Sydney Ullrich ◽  
Pavlo V. Ponomarenko ◽  
Nozomu Nishitani ◽  
Federica M. Marcucci ◽  

Abstract Observations by six Super Dual Auroral Radar Network (SuperDARN) polar cap radars, three in the northern hemisphere and three in the southern hemispheres, are considered to assess F region echo occurrence rates over solar, season, and day cycles and to establish relationship between the echo occurrence rate and the background electron density and plasma flow velocity magnitude. The echo occurrence rate is shown to increase toward the solar cycle maximum, more distinctly on the nightside, consistent with a general trend of the background electron density. Over the last 5 years, the echo occurrence rates decline at a rate of 5–10% per year. The pattern of seasonal and diurnal variations in echo occurrence is found to be consistent with previous SuperDARN publications. Minor dips in echo occurrence rate are observed in winter solstices, and these are related to an overall decrease in the electron density. In most of the time sectors, the echo occurrence rate increases with the electron density but only up to a certain threshold value after which the dependence saturates. The level of the saturation depends on season, local time, and average plasma flow velocity magnitude. For the summer daytime observations, the echo occurrence rate correlates with variations of both electron density and plasma flow velocity magnitude.

Nanomaterials ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 122 ◽  
Haissam Abou-Saleh ◽  
Nadin Younes ◽  
Kashif Rasool ◽  
Manaf Younis ◽  
Rafael Prieto ◽  

The use of chitosan nanoparticles (ChNPs) in various biological and environmental applications is attracting great interest. However, potential side effects related to ChNP toxicity remain the major limitation hampering their wide application. For the first time, we investigate the potential organ-specific (cardiac, hepatic, and neuromuscular) toxicity of ChNPs (size 100–150 nm) using the zebrafish embryo model. Our data highlight the absence of both acute and teratogenic toxic effects of ChNPs (~100% survival rate) even at the higher concentration employed (200 mg/L). Although no single sign of cardiotoxicity was observed upon exposure to 200 mg/L of ChNPs, as judged by heartbeat rate, the corrected QT interval (QTc, which measures the time between the start of the Q wave and the end of the T wave in the heart's electrical cycle), maximum cardiac arrest, and ejection fraction assays, the same dosage elicited the impairment of both liver size (decreased liver size, but without steatosis and lipid yolk retention) and neurobehavioral activity (increased movement under different light conditions). Although the observed toxic effect failed to affect embryo survival, whether a prolonged ChNP treatment may induce other potentially harmful effects remains to be elucidated. By reporting new insights on their organ-specific toxicity, our results add novel and useful information into the available data concerning the in vivo effect of ChNPs.

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