Ellerman bombs and UV bursts: transient events in chromospheric current sheets

Ellerman bombs (EBs) and UV bursts are both brightenings related to flux emergence regions and specifically to magnetic flux of opposite polarity that meet in the photosphere. These two reconnection-related phenomena, nominally formed far apart, occasionally occur in the same location and at the same time, thus challenging our understanding of reconnection and heating of the lower solar atmosphere. We consider the formation of an active region, including long fibrils and hot and dense coronal plasma. The emergence of a untwisted magnetic flux sheet, injected $2.5$~Mm below the photosphere, is studied as it pierces the photosphere and interacts with the preexisting ambient field. Specifically, we aim to study whether EBs and UV bursts are generated as a result of such flux emergence and examine their physical relationship. The Bifrost radiative magnetohydrodynamics code was used to model flux emerging into a model atmosphere that contained a fairly strong ambient field, constraining the emerging field to a limited volume wherein multiple reconnection events occur as the field breaks through the photosphere and expands into the outer atmosphere. Synthetic spectra of the different reconnection events were computed using the $1.5$D RH code and the fully 3D MULTI3D code. The formation of UV bursts and EBs at intensities and with line profiles that are highly reminiscent of observed spectra are understood to be a result of the reconnection of emerging flux with itself in a long-lasting current sheet that extends over several scale heights through the chromosphere. Synthetic diagnostics suggest that there are no compelling reasons to assume that UV bursts occur in the photosphere. Instead, EBs and UV bursts are occasionally formed at opposite ends of a long current sheet that resides in an extended bubble of cool gas.Comment: 10 pages, 8 figures, accepted by A&

Caffeine increases strength and power performance in resistance‐trained females during early follicular phase

The effects of 4 mg·kg‐1caffeine ingestion on strength and power were investigated for the first time, in resistance‐trained females during the early follicular phase utilizing a randomized, double‐blind, placebo‐controlled, crossover design. Fifteen females (29.8±4.0 years, 63.8±5.5 kg [mean±SD]) ingested caffeine or placebo 60 minutes before completing a test battery separated by 72 hours. One‐repetition maximum (1RM), repetitions to failure (RTF) at 60% of 1RM, were assessed in the squat and bench press. Maximal voluntary contraction torque (MVC) and rate of force development (RFD) were measured during isometric knee‐extensions, while utilizing interpolated twitch technique to measure voluntary muscle activation. Maximal power and jump height were assessed during countermovement jumps (CMJ). Caffeine metabolites were measured in plasma. Adverse effects were registered after each trial. Caffeine significantly improved squat (4.5±1.9%, effect size [ES]: 0.25) and bench press 1RM (3.3±1.4%, ES: 0.20), and squat (15.9±17.9%, ES: 0.31) and bench press RTF (9.8±13.6%, ES: 0.31), compared to placebo. MVC torque (4.6±7.3%, ES: 0.26), CMJ height (7.6±4.0%, ES: 0.50) and power (3.8±2.2%, ES: 0.24) were also significantly increased with caffeine. There were no differences in RFD or muscle activation. Plasma [caffeine] was significantly increased throughout the protocol and mild side‐effects of caffeine were experienced by only 3 participants. This study demonstrated that 4 mg·kg‐1 caffeine ingestion enhanced maximal strength, power and muscular endurance in resistance‐trained and caffeine‐habituated females during the early follicular phase, with few adverse effects. Female strength and power athletes may consider using this dose pre‐competition and ‐training as an effective ergogenic aid

Three-dimensional modeling of chromospheric spectral lines in a simulated active region

Because of the complex physics that governs the formation of chromospheric lines, interpretation of solar chromospheric observations is difficult. The origin and characteristics of many chromospheric features are, because of this, unresolved. We focus here on studying two prominent features: long fibrils and flare ribbons. To model them, we use a 3D MHD simulation of an active region which self-consistently reproduces both of them. We model the H$\alpha$, Mg II k, Ca II K, and Ca II 8542 {\AA} lines using the 3D non-LTE radiative transfer code Multi3D. This simulation reproduces long fibrils that span between the opposite-polarity sunspots and go up to 4 Mm in height. They can be traced in all lines due to density corrugation. Opposite to previous studies, H$\alpha$, Mg II h&k, and Ca II H&K, are formed at similar height in this model. Magnetic field lines are aligned with the H$\alpha$ fibrils, but the latter holds to a lesser extent for the Ca II 8542 {\AA} line. The simulation shows structures in the H$\alpha$ line core that look like flare ribbons. The emission in the ribbons is caused by a dense chromosphere and a transition region at high column mass. The ribbons are visible in all chromospheric lines, but least prominent in Ca II 8542 {\AA} line. In some pixels, broad asymmetric profiles with a single emission peak are produced, similar to the profiles observed in flare ribbons. They are caused by a deep onset of the chromospheric temperature rise and large velocity gradients. The simulation produces long fibrils similar to what is seen in observations. It also produces structures similar to flare ribbons despite the lack of non-thermal electrons in the simulation. The latter suggests that thermal conduction might be a significant agent in transporting flare energy to the chromosphere in addition to non-thermal electrons.Comment: 17 pages, 15 figures, accepted for publication by A&

Synthesis of reaction-adapted zeolites as methanol-to-olefins catalysts with mimics of reaction intermediates as organic structure-directing agents

[EN] Catalysis with enzymes and zeolites have in common the presence of well-defined single active sites and pockets/cavities where the reaction transition states can be stabilized by longer-range interactions. We show here that for a complex reaction, such as the conversion of methanol-to-olefins (MTO), it is possible to synthesize reaction-adapted zeolites by using mimics of the key molecular species involved in the MTO mechanism. Effort has focused on the intermediates of the paring mechanism because the paring is less favoured energetically than the side-chain route. All the organic structure-directing agents based on intermediate mimics crystallize cage-based small-pore zeolitic materials, all of them capable of performing the MTO reaction. 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Effect of Cage Size on the Selective Conversion of Methanol to Light Olefins

Zeolites that contain eight-membered ring pores but different cavity geometries (LEV, CHA, and AFX structure types) are synthesized at similar Si/Al ratios and crystal sizes. These materials are tested as catalysts for the selective conversion of methanol to light olefins. At 400 °C, atmospheric pressure, and 100% conversion of methanol, the ethylene selectivity decreases as the cage size increases. Variations in the Si/Al ratio of the LEV and CHA show that the maximum selectivity occurs at Si/Al = 15–18. Because lower Si/Al ratios tend to produce faster deactivation rates and poorer selectivities, reactivity comparisons between frameworks are performed with solids having a ratio Si/Al = 15–18. With LEV and AFX, the data are the first from materials with this high Si/Al. At similar Si/Al and primary crystallite size, the propylene selectivity for the material with the CHA structure exceeds those from either the LEV or AFX structure. The AFX material gives the shortest reaction lifetime, but has the lowest amount of carbonaceous residue after reaction. Thus, there appears to be an intermediate cage size for maximizing the production of light olefins and propylene selectivities equivalent to or exceeding ethylene selectivities

Index of refraction for cold lithium- and diatomic sodium waves traveling through cold noble gases

In the present paper we propose to measure the index of refraction for diatomic sodium molecules traveling through a cold helium gas. Theoretical calculations of the index of refraction for this system are presented as a function of the molecule velocity and atom gas temperature. Whereas previous theoretical efforts to compute the refractive index have been concerned with atomic systems and atomic matter waves, we extend the investigation to diatomic molecules in the present work. To enable such calculations the potential energy surface for the atom-molecule interaction is calculated ab initio, along with the long range dispersion coefficients for the atom-molecule system. The full close-coupled equations, describing the atom-molecule collisions, are solved numerically to work out the influence of the collisions on the matter waves. We investigate the sensitivity of the results upon changes and inaccuracies in the potential energy surface. Several molecular rotational levels are included in the present study, and the index of refraction is found to depend on the rotational state. In addition, the index of refraction for atomic lithium matter waves traveling through the cold noble gases helium and argon are computed, motivated by a recent experiment with atomic lithium matter waves. Different resonances (glory- and scattering resonances) are identified from the results. Such resonances offer an important opportunity for the comparison of experiment and theory

Anatomy, immunology, digestive physiology and microbiota of the salmonid intestine: Knowns and unknowns under the impact of an expanding industrialized production

Increased industrialized production of salmonids challenges aspects concerning available feed resources and animal welfare. The immune system plays a key component in this respect. Novel feed ingredients may trigger unwarranted immune responses again affecting the well-being of the fish. Here we review our current knowledge concerning salmon intestinal anatomy, immunity, digestive physiology and microbiota in the context of industrialized feeding regimes. We point out knowledge gaps and indicate promising novel technologies to improve salmonid intestinal health.publishedVersio