scholarly journals Effect of coronal loop structure on wave heating through phase mixing

2020 ◽  
Vol 643 ◽  
pp. A73
Author(s):  
P. Pagano ◽  
I. De Moortel ◽  
R. J. Morton
Keyword(s):  
Coronal Loop ◽  
Magnetic Energy ◽  
Thermal Structure ◽  
Initial Density ◽  
Mhd Waves ◽  
Transverse Waves ◽  
Phase Mixing ◽  
Wave Heating ◽  
Subsequent Effect ◽  
The Impact

Context. The mechanism(s) behind coronal heating still elude(s) direct observation and modelling of viable theoretical processes and the subsequent effect on coronal structures is one of the key tools available to assess possible heating mechanisms. Wave heating via the phase mixing of magnetohydrodynamic (MHD) transverse waves has been proposed as a possible way to convert magnetic energy into thermal energy, but MHD models increasingly suggest this is not an efficient enough mechanism. Aims. We modelled heating by phase mixing transverse MHD waves in various configurations in order to investigate whether certain circumstances can enhance the heating sufficiently to sustain the million degree solar corona and to assess the impact of the propagation and phase mixing of transverse MHD waves on the structure of the boundary shell of coronal loops. Methods. We used 3D MHD simulations of a pre-existing density enhancement in a magnetised medium and a boundary driver to trigger the propagation of transverse waves with the same power spectrum as measured by the Coronal Multi-Channel Polarimeter. We consider different density structures, boundary conditions at the non-drive footpoint, characteristics of the driver, and different forms of magnetic resistivity. Results. We find that different initial density structures significantly affect the evolution of the boundary shell and that some driver configurations can enhance the heating generated from the dissipation of the MHD waves. In particular, drivers coherent on a larger spatial scale and higher dissipation coefficients can generate significant heating, although it is still insufficient to balance the radiative losses in this setup. Conclusions. We conclude that while phase mixing of transverse MHD waves is unlikely to sustain the thermal structure of the corona, there are configurations that allow for an enhanced efficiency of this mechanism. We provide possible signatures to identify the presence of such configurations, such as the location of where the heating is deposited along the coronal loop.

scholarly journals Transverse waves in coronal flux tubes with thick boundaries: The effect of longitudinal flows

2019 ◽  
Vol 623 ◽  
pp. A32
Author(s):  
Roberto Soler
Keyword(s):  
Singular Term ◽  
Mhd Waves ◽  
Transverse Waves ◽  
Flux Tubes ◽  
Cascade Energy ◽  
Kink Waves ◽  
Frobenius Series ◽  
The Impact ◽  
The Waves ◽  
Boundary Approximation

Observations show that transverse magnetohydrodynamic (MHD) waves and flows are often simultaneously present in magnetic loops of the solar corona. The waves are resonantly damped in the Alfvén continuum because of plasma and/or magnetic field nonuniformity across the loop. The resonant damping is relevant in the context of coronal heating, since it provides a mechanism to cascade energy down to the dissipative scales. It has been theoretically shown that the presence of flow affects the waves propagation and damping, but most of the studies rely on the unjustified assumption that the transverse nonuniformity is confined to a boundary layer much thinner than the radius of the loop. Here we present a semi-analytic technique to explore the effect of flow on resonant MHD waves in coronal flux tubes with thick nonuniform boundaries. We extend a published method, which was originally developed for a static plasma, in order to incorporate the effect of flow. We allowed the flow velocity to continuously vary within the nonuniform boundary from the internal velocity to the external velocity. The analytic part of the method is based on expressing the wave perturbations in the thick nonuniform boundary of the loop as a Frobenius series that contains a singular term accounting for the Alfvén resonance, while the numerical part of the method consists of solving iteratively the transcendental dispersion relation together with the equation for the Alfvén resonance position. As an application of this method, we investigated the impact of flow on the phase velocity and resonant damping length of MHD kink waves. With the present method, we consistently recover results in the thin boundary approximation obtained in previous studies. We have extended those results to the case of thick boundaries. We also explored the error associated with the use of the thin boundary approximation beyond its regime of applicability.

Wave-Based Heating Mechanisms for the Solar Corona

1994 ◽  
Vol 144 ◽  
pp. 443-451 ◽  
Author(s):  
F. Malara ◽  
M. Velli
Keyword(s):  
Solar Corona ◽  
Nonlinear Effects ◽  
Resonant Absorption ◽  
Mhd Waves ◽  
Small Scale ◽  
Phase Mixing ◽  
Low Dissipation ◽  
Wave Heating ◽  
Lower Solar Atmosphere ◽  
Small Scale Structures

AbstractDissipation of MHD waves generated in the lower solar atmosphere has long been proposed as a means to heat the solar corona. Because of the extremely low dissipation coefficients of the coronal plasma large gradients are necessary to efficiently dissipate such waves. Interactions with the inhomogeneities of the background medium may represent a way to create small scale structures, phase-mixing and resonant absorption being important examples. The generalization of such ideas to propagation in complex geometries (e.g., containing X type neutral points) and the extension to nonlinear effects are paramount to the development of wave-heating theories.

scholarly journals Contribution of observed multi frequency spectrum of Alfvén waves to coronal heating

2019 ◽  
Vol 623 ◽  
pp. A37 ◽  
Author(s):  
P. Pagano ◽  
I. De Moortel
Keyword(s):  
Active Region ◽  
Power Spectrum ◽  
Solar Corona ◽  
Coronal Loop ◽  
Alfven Waves ◽  
Mhd Waves ◽  
Alfvén Waves ◽  
Coronal Loops ◽  
Phase Mixing ◽  
Transverse Oscillations

Context. Whilst there are observational indications that transverse magnetohydrodynamic (MHD) waves carry enough energy to maintain the thermal structure of the solar corona, it is not clear whether such energy can be efficiently and effectively converted into heating. Phase-mixing of Alfvén waves is considered a candidate mechanism, as it can develop transverse gradient where magnetic energy can be converted into thermal energy. However, phase-mixing is a process that crucially depends on the amplitude and period of the transverse oscillations, and only recently have we obtained a complete measurement of the power spectrum for transverse oscillations in the corona. Aims. We aim to investigate the heating generated by phase-mixing of transverse oscillations triggered by buffeting of a coronal loop that follows from the observed coronal power spectrum as well as the impact of these persistent oscillations on the structure of coronal loops. Methods. We considered a 3D MHD model of an active region coronal loop and we perturbed its footpoints with a 2D horizontal driver that represents a random buffeting motion of the loop footpoints. Our driver was composed of 1000 pulses superimposed to generate the observed power spectrum. Results. We find that the heating supply from the observed power spectrum in the solar corona through phase-mixing is not sufficient to maintain the million-degree active region solar corona. We also find that the development of Kelvin–Helmholtz instabilities could be a common phenomenon in coronal loops that could affect their apparent life time. Conclusions. This study concludes that is unlikely that phase-mixing of Alfvén waves resulting from an observed power spectrum of transverse coronal loop oscillations can heat the active region solar corona. However, transverse waves could play an important role in the development of small scale structures.

Experimental Study of the Impact of Alisma plantago-aquatica Secretions on Pathogenic Bacteria

2014 ◽  
Vol 1 (3) ◽  
pp. 3-7
Author(s):  
O. Zhukorskyy ◽  
O. Hulay
Keyword(s):  
Pathogenic Bacteria ◽  
Initial Density ◽  
Biologically Active ◽  
Erysipelothrix Rhusiopathiae ◽  
Natural Focus ◽  
Test Species ◽  
Popula Tions ◽  
And Control ◽  
The Impact

Aim. To estimate the impact of in vivo secretions of water plantain (Alisma plantago-aquatica) on the popula- tions of pathogenic bacteria Erysipelothrix rhusiopathiae. Methods. The plants were isolated from their natural conditions, the roots were washed from the substrate residues and cultivated in laboratory conditions for 10 days to heal the damage. Then the water was changed; seven days later the selected samples were sterilized using fi lters with 0.2 μm pore diameter. The dilution of water plantain root diffusates in the experimental samples was 1:10–1:10,000. The initial density of E. rhusiopathiae bacteria populations was the same for both experimental and control samples. The estimation of the results was conducted 48 hours later. Results. When the dilution of root diffusates was 1:10, the density of erysipelothrixes in the experimental samples was 11.26 times higher than that of the control, on average, the dilution of 1:100 − 6.16 times higher, 1:1000 – 3.22 times higher, 1:10,000 – 1.81 times higher, respectively. Conclusions. The plants of A. plantago-aquatica species are capable of affecting the populations of E. rhusiopathiae pathogenic bacteria via the secretion of biologically active substances into the environment. The consequences of this interaction are positive for the abovementioned bacteria, which is demon- strated by the increase in the density of their populations in the experiment compared to the control. The intensity of the stimulating effect on the populations of E. rhusiopathiae in the root diffusates of A. plantago-aquatica is re- ciprocally dependent on the degree of their dilution. The investigated impact of water plantain on erysipelothrixes should be related to the topical type of biocenotic connections, the formation of which between the test species in the ecosystems might promote maintaining the potential of natural focus of rabies. Keywords: Alisma plantago-aquatica, in vivo secretions, Erysipelothrix rhusiopathiae, population density, topical type of connections.

Browsing behaviour as a mediator: the impact of multi-sensory cues on purchasing

2019 ◽  
Vol 36 (2) ◽  
pp. 253-263 ◽  
Author(s):  
Miralem Helmefalk
Keyword(s):  
Design Methodology ◽  
Consumer Behaviour ◽  
Retail Store ◽  
Sensory Cues ◽  
Content Type ◽  
Sensory Marketing ◽  
Group Data ◽  
Subsequent Effect ◽  
The Impact ◽  
Empirical Contribution

PurposeThis paper aims to examine how multi-sensory cues, when store-congruent, influence consumer browsing behaviour and its subsequent effect on purchasing.Design/methodology/approachTwo studies were used with a field experimental design in a furnishing retail store to examine browsing behaviour and purchasing in a visual, auditory, olfactory and a multi-sensory treatment group. Data were gathered over 12 weeks. This study was a set of studies comprising my dissertation thesis (Helmefalk, 2017).FindingsFindings show that multi-sensory cues in a retail atmosphere are evidently influencing purchasing via browsing behaviour as a mediator.Originality/valueThe findings evidence browsing behaviour as a mediator and predictor for purchasing, which emphasizes its conceptual and empirical contribution in terms of modifying retail atmospheres. The work contributes to the field of retailing, sensory marketing and consumer behaviour, a novel view on the linkages between multi-sensory cues, browsing behaviour and purchasing.

scholarly journals Beyond second-order convergence in simulations of magnetized binary neutron stars with realistic microphysics

2019 ◽  
Vol 490 (3) ◽  
pp. 3588-3600 ◽  
Author(s):  
E R Most ◽  
L Jens Papenfort ◽  
L Rezzolla
Keyword(s):  
Neutron Stars ◽  
Fourth Order ◽  
Finite Temperature ◽  
Equations Of State ◽  
Magnetic Energy ◽  
Second Order ◽  
Conservative Finite Difference Scheme ◽  
Order Scheme ◽  
Convergence Orders ◽  
The Impact

ABSTRACT We investigate the impact of using high-order numerical methods to study the merger of magnetized neutron stars with finite-temperature microphysics and neutrino cooling in full general relativity. By implementing a fourth-order accurate conservative finite-difference scheme we model the inspiral together with the early post-merger and highlight the differences to traditional second-order approaches at the various stages of the simulation. We find that even for finite-temperature equations of state, convergence orders higher than second order can be achieved in the inspiral and post-merger for the gravitational-wave phase. We further demonstrate that the second-order scheme overestimates the amount of proton-rich shock-heated ejecta, which can have an impact on the modelling of the dynamical part of the kilonova emission. Finally, we show that already at low resolution the growth rate of the magnetic energy is consistently resolved by using a fourth-order scheme.

Distribution functions for Galactic disc stellar populations in the presence of non-axisymmetric perturbations

2017 ◽  
Vol 13 (S334) ◽  
pp. 195-198
Author(s):  
B. Famaey ◽  
G. Monari ◽  
A. Siebert ◽  
J.-B. Fouvry ◽  
J. Binney
Keyword(s):  
Stellar Population ◽  
Distribution Functions ◽  
Galactic Disc ◽  
Trapping Region ◽  
Phase Mixing ◽  
Spiral Arms ◽  
First Order ◽  
The Impact ◽  
Action Variables ◽  
Axisymmetric Perturbations

AbstractThe present-day response of a Galactic disc stellar population to a non-axisymmetric perturbation of the potential, in the form of a bar or spiral arms, can be treated, away from the main resonances, through perturbation theory within the action-angle coordinates of the unperturbed axisymmetric system. The first order moments of such a perturbed distribution function (DF) in the presence of spiral arms give rise to non-zero radial and vertical mean stellar velocities, called breathing modes. Such an Eulerian linearized treatment however diverges at resonances. The Lagrangian approach to the impact of non-axisymmetries at resonances avoids this problem. It is based on the construction of new orbital tori in the resonant trapping region, which come complete with a new system of angle-action variables. These new tori can be populated by phase-averaging the unperturbed DF over the new tori. This boils down to phase-mixing the DF in terms of the new angles, such that the DF for trapped orbits only depends on the new set of actions. This opens the way to quantitatively fitting the effects of the bar and spirals to Gaia data with an action-based DF.

Numerical Analysis of Droplet Impact on a Smooth Slippery Surface

2018 ◽  
Author(s):  
F. Yeganehdoust ◽  
I. Karimfazli ◽  
A. Dolatabadi
Keyword(s):  
Droplet Impact ◽  
Immiscible Fluid ◽  
Oil Viscosity ◽  
Air Bubble ◽  
Air Cushion ◽  
Subsequent Effect ◽  
Interfacial Surfaces ◽  
The Stability ◽  
Moderate Range ◽  
The Impact

Spontaneous bouncing of a droplet that impacts a surface is a mechanism that occurs for the moderate range of droplet impact velocities and is caused by the formation of a stable air layer (cushion) between the droplet and the surface. This bouncing behavior is more pronounced on Lubricant Impregnated Surfaces (LISs) inspired by the natural non-wetting surface of the pitcher plant, which relies on the stable formation of a thin lubricant film across its surface. In this study, we performed modeling of the water-oil–air interfacial surfaces using the volume of fluid (VOF) methodology to simulate the impact of a water droplet onto a lubricant smooth surface with an oil as the lubricant. To resolve the effects of the air surrounding the droplet, computational cells were extensively small to capture the presence of the sub-micron layer of air trapped underneath the droplet during the impact. The model was able to capture the initiation and subsequent effect of the air cushion on the droplet hydrodynamics. We found that the stability of the air cushion and the impact dynamics are independent of the oil viscosity for specific thicknesses of lubricant layers, whereas the impact conditions such as velocity and droplet properties played a significant role on the outcome of droplet impact. Hence, the dynamics of a droplet falling on a specific thickness of oil film was influenced by the squeezed air trapped between the two immiscible fluid (water and oil). In addition, the formation of high pressure dimple region was evident, which in some cases lead to entrapment of the air bubble. Finally, we validated the results with the existing experimental data in the literature.

scholarly journals Heating of Solar and Stellar Chromospheres and Coronae by MHD Waves

1992 ◽  
Vol 9 ◽  
pp. 665-666
Author(s):  
Z. E. Musielak
Keyword(s):  
Primary Source ◽  
Stellar Atmospheres ◽  
Satellite Observations ◽  
Mhd Waves ◽  
Observational Constraints ◽  
Strong Magnetic Fields ◽  
Stellar Convection ◽  
Wave Heating ◽  
Recent Developments ◽  
The Mean

Ground-based and satellite observations have shown that all late-type dwarfs possess hot outer envelopes, and that the chromospheric and coronal emissions observed from these envelopes vary significantly for a given, fixed spectral type. In addition, there is growing evidence for nonhomogeneous and locally strong magnetic fields in the atmospheres of these stars. It is obvious that any heating theory must account for these two observational constraints as well as for the mean level of heating.There are at least two general classes of models that deal with the required heating. The first class assumes that outer stellar atmospheres are heated by hydrodynamic (mainly acoustic) or magnctohydrodynamic (MHD) waves, and that these waves are generated by turbulent motions in the stellar convection zones. The second class considers dissipation of currents generated by photospheric motions as the primary source of energy. Neither observation nor theory has been able to definitively determine which one of these two general classes of models dominates in the atmospheric heating. The main aim of this paper is to briefly present recent developments in the MHD wave heating theory. The key problems that will be addressed are: where and how efficiently are MHD waves generated, and how do these waves propagate and dissipate energy?

scholarly journals Increasing the utilisation of grain when fed whole to ruminants

1999 ◽  
Vol 50 (5) ◽  
pp. 737 ◽  
Author(s):  
A. G. Kaiser
Keyword(s):  
Seed Coat ◽  
Animal Production ◽  
Enzyme Treatment ◽  
Sufficient Evidence ◽  
Whole Grain ◽  
Beneficial Effects ◽  
Grain Damage ◽  
Subsequent Effect ◽  
Physical And Chemical ◽  
The Impact

Feeding grain whole to cattle generally results in a lower digestibility than that obtained with processed grain. If this problem could be overcome, feeding with whole grain would reduce processing costs, and the slower rate of starch digestion in the rumen could improve fibre digestion with potential beneficial effects on intake and animal production. Two strategies are available to increase the digestibility of whole grain. The first, longer term strategy relies on the selection or breeding of feed grains that are efficiently digested by cattle when fed whole. The review considers the chemical and physical properties of grains likely to increase the degree of grain damage during mastication, and increase the digestibility of the seed coat fraction. Research is required to determine the feasibility of selecting feed grains with these characteristics. The second strategy is to treat whole grain with chemicals or enzymes to increase digestibility of the seed coat and consequently whole grain digestion within the rumen. Considerable research has been conducted on the sodium hydroxide (NaOH) treatment of grain, and there is sufficient evidence from cattle experiments to indicate that digestibility, liveweight gain, and milk production on NaOH-treated whole grain can be similar to that on rolled grain, provided sufficient NaOH is applied. However, a number of practical and commercial considerations have limited the more widespread adoption of this technology on farms. Although ammonia treatment offers a more practical alternative to NaOH, digestibility and animal production responses have been highly variable, and research is required to identify effective ammoniation procedures. The increased availability of enzymes for livestock feeding has potentially provided another grain treatment option. The application of fibrolytic enzymes to whole grain prior to high-moisture storage or feeding, and their subsequent effect on grain digestibility, require research. The impact of grain characteristics, both physical and chemical, on the response to alkali or enzyme treatment also requires research.

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