scholarly journals Analysis of Pseudo-Lyapunov Exponents of Solar Convection Using State-of-the-Art Observations

Entropy ◽  
2021 ◽  
Vol 23 (4) ◽  
pp. 413
Author(s):  
Giorgio Viavattene ◽  
Mariarita Murabito ◽  
Salvatore L. Guglielmino ◽  
Ilaria Ermolli ◽  
Giuseppe Consolini ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Lyapunov Exponents ◽  
Outer Layer ◽  
State Of The Art ◽  
Solar Photosphere ◽  
Estimation Technique ◽  
Solar Convection ◽  
Convective Motions ◽  
The Mean ◽  
Definition Of

The solar photosphere and the outer layer of the Sun’s interior are characterized by convective motions, which display a chaotic and turbulent character. In this work, we evaluated the pseudo-Lyapunov exponents of the overshooting convective motions observed on the Sun’s surface by using a method employed in the literature to estimate those exponents, as well as another technique deduced from their definition. We analyzed observations taken with state-of-the-art instruments at ground- and space-based telescopes, and we particularly benefited from the spectro-polarimetric data acquired with the Interferometric Bidimensional Spectrometer, the Crisp Imaging SpectroPolarimeter, and the Helioseismic and Magnetic Imager. Following previous studies in the literature, we computed maps of four quantities which were representative of the physical properties of solar plasma in each observation, and estimated the pseudo-Lyapunov exponents from the residuals between the values of the quantities computed at any point in the map and the mean of values over the whole map. In contrast to previous results reported in the literature, we found that the computed exponents hold negative values, which are typical of a dissipative regime, for all the quantities derived from our observations. The values of the estimated exponents increase with the spatial resolution of the data and are almost unaffected by small concentrations of magnetic field. Finally, we showed that similar results were also achieved by estimating the exponents from residuals between the values at each point in maps derived from observations taken at different times. The latter estimation technique better accounts for the definition of these exponents than the method employed in previous studies.

scholarly journals Simulating Solar Global Magnetism in 3-D

2012 ◽  
Vol 10 (H16) ◽  
pp. 101-103
Author(s):  
A. S. Brun ◽  
A. Strugarek
Keyword(s):  
Magnetic Field ◽  
Recent Progress ◽  
Convection Zone ◽  
Thermal Structure ◽  
Solar Convection ◽  
Self Consistent ◽  
The Mean ◽  
The Magnetic Field

AbstractWe briefly present recent progress using the ASH code to model in 3-D the solar convection, dynamo and its coupling to the deep radiative interior. We show how the presence of a self-consistent tachocline influences greatly the organization of the magnetic field and modifies the thermal structure of the convection zone leading to realistic profiles of the mean flows as deduced by helioseismology.

scholarly journals On the Dynamics of the Solar Convection Zone

1980 ◽  
Vol 51 ◽  
pp. 15-16
Author(s):  
Bernard R. Durney ◽  
Hendrik C. Spruit
Keyword(s):  
Distribution Function ◽  
Energy Equation ◽  
Convection Zone ◽  
Turbulent Viscosity ◽  
Rotating Stars ◽  
Solar Convection Zone ◽  
Solar Convection ◽  
Convective Motions ◽  
The Mean ◽  
Convective Cells

AbstractWe derive expressions for the turbulent viscosity and turbulent conductivity applicable to convection zones of rotating stars. We assume that the dimensions of the convective cells are known and derive a simple distribution function for the turbulent convective velocities under the influence of rotation. From this distribution function (which includes, in particular, the stabilizing effect of rotation on convection) we calculate in the mixing-length approximation: i) the turbulent Reynolds stresstensor and ii) the expression for the heat flux in terms of the superadiabatic gradient. The contributions of the turbulent convective motions to the mean momentum and energy equation are treated consistently, and assumptions about the turbulent viscosity and heat transport are replaced by assumptions about the turbulent flow itself. The free parameters in our formalism are the relative cell sizes and their dependence on depth and latitude.

scholarly journals Helicity transport from solar convection zone to interplanetary space

2012 ◽  
Vol 8 (S294) ◽  
pp. 505-518
Author(s):  
Mei Zhang
Keyword(s):  
Magnetic Field ◽  
Convection Zone ◽  
Interplanetary Space ◽  
Magnetic Helicity ◽  
Solar Photosphere ◽  
Solar Magnetic Fields ◽  
Solar Convection Zone ◽  
Solar Convection ◽  
Magnetic Flux Ropes ◽  
Solar Winds

AbstractMagnetic helicity is a physical quantity that describes field topology. It is also a conserved quantity as Berger in 1984 demonstrated that the total magnetic helicity is still conserved in the corona even when there is a fast magnetic reconnection. It is generally believed that solar magnetic fields, together with their helicity, are created in the convection zone by various dynamo processes. These fields and helicity are transported into the corona through solar photosphere and finally released into the interplanetary space via various processes such as coronal mass ejections (CMEs) and solar winds. Here I will give a brief review on our recent works, first on helicity observations on the photosphere and how to understand these observations via dynamo models. Mostly, I will talk about what are the possible consequences of magnetic helicity accumulation in the corona, namely, the formation of magnetic flux ropes, CMEs taking place as an unavoidable product of coronal evolution, and flux emergences as a trigger of CMEs. Finally, I will address on in what a form magnetic field in the interplanetary space would accommodate a large amount of magnetic helicity that solar dynamo processes have been continuously producing.

scholarly journals Helicity–vorticity turbulent pumping of magnetic fields in the solar dynamo

2012 ◽  
Vol 8 (S294) ◽  
pp. 367-368
Author(s):  
V. V. Pipin
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Differential Rotation ◽  
Large Scale ◽  
Convection Zone ◽  
Solar Dynamo ◽  
Solar Convection Zone ◽  
Solar Convection ◽  
Large Scale Magnetic Field ◽  
Convective Motions

AbstractThe interaction of helical convective motions and differential rotation in the solar convection zone results in turbulent drift of a large-scale magnetic field. We discuss the pumping mechanism and its impact on the solar dynamo.

scholarly journals The Solar Dynamo

1990 ◽  
Vol 121 ◽  
pp. 385-402 ◽  
Author(s):  
K.-H. Rädler
Keyword(s):  
Magnetic Field ◽  
Differential Rotation ◽  
Mean Field ◽  
Solar Dynamo ◽  
Back Reaction ◽  
Dynamo Theory ◽  
Open Questions ◽  
Convective Motions ◽  
The Mean ◽  
Basic Ideas

AbstractThe phenomena of solar activity are connected with a general magnetic field of-the Sun which is due to a dynamo process essentially determined by the α-effect and the differential rotation in the convection zone. A few observational facts are summarized which are important for modelling this process. The basic ideas of the solar dynamo theory, with emphasis on the mean-field approach, are explained, and a critical review of the dynamo models investigated so far is given. Although several models reflect a number of essential features of the solar magnetic cycle there are many open questions. Part of them result from lack of knowledge of the structure of the convective motions and the differential rotation. Other questions concern, for example, details of the connection of the α-effect and related effects with the convective motions, or the way in which the behaviour of the dynamo is influenced by the back-reaction of the magnetic field on the motions.

Is solar convection responsible for the local amplification and structuring of magnetic fields? (Observational test of the hypothesis)

2006 ◽  
Vol 2 (S239) ◽  
pp. 496-498
Author(s):  
A. V. Getling ◽  
X. M. Bao
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Field Component ◽  
Vertical Component ◽  
Solar Photosphere ◽  
Vertical Magnetic Field ◽  
Solar Convection ◽  
Induction Equation ◽  
The Right ◽  
Full Vector

AbstractFull-vector magnetograms and Dopplergrams of selected areas of the solar photosphere are used to compute the vertical component of the right-hand side of the vector induction equation. We attempt to find a criterion for the action of the convective mechanism of amplification and structuring of magnetic fields using the distributions of this quantity and of the vertical magnetic-field component.

Comparison between a new ultrasound probe with a capacitive micromachined transducer (CMUT) and a traditional one in musculoskeletal pathology

2020 ◽  
Vol 61 (12) ◽  
pp. 1653-1660
Author(s):  
Ferdinando Draghi ◽  
Pascal Lomoro ◽  
Chandra Bortolotto ◽  
Luca Mastrogirolamo ◽  
Fabrizio Calliada
Keyword(s):  
State Of The Art ◽  
Doppler Signal ◽  
Ultrasound Probe ◽  
Linear Transducer ◽  
Significant Difference ◽  
Mems Technology ◽  
The Mean ◽  
Flexible Imaging ◽  
Definition Of ◽  
Musculoskeletal Pathology

Background The capacitive micromachined ultrasound transducer (CMUT) is a new ultrasound (US) probe manufactured by state-of-the-art cutting-edge semi-conductor micromachined electro-mechanical systems (MEMS) technology. Purpose To demonstrate the peculiar characteristics of each probe and the limitations that should be improved. Material and Methods This study was performed from March to April 2018. The only inclusion criterion was the presence of disease, so all patients with musculoskeletal, skin, and subcutaneous pathology were included. A total of 66 patients entered this study. The exams of each patient, with both probes, were evaluated retrospectively and independently by three radiologists. Panoramicity of the images, the definition of superficial structures (<2 cm of depth), the definition of deep structures (>2 cm), and Doppler signal were assessed. A 5-point scale was used for each parameter. Results A total of 89 pathologies were detected. The mean of score for 4G-CMUT was higher than L64 for the panoramicity of the images and the definition of the deep structures. Instead, the mean score for L64 was higher than for 4G-CMUT in the evaluation of superficial structures and Doppler signal. A statistically significant difference was found ( P < 0.05). Conclusion CMUT is a breakthrough in US technology. It allows the use of a single probe for different US examinations. The musculoskeletal, skin, and subcutaneous US can be evaluated with a piezoelectric linear transducer or CMUT. In the present study, the overall diagnostic performance was similar. Improvements in CMUT will provide even more dynamic and flexible imaging capabilities by a transducer, with a wider bandwidth.

scholarly journals Non-Linear Diamagnetic Transport of the Large-Scale Magnetic Field in the Solar Convection Zone

1993 ◽  
Vol 157 ◽  
pp. 49-50
Author(s):  
V.N. Krivodubskij
Keyword(s):  
Magnetic Field ◽  
Turbulence Intensity ◽  
Large Scale ◽  
Convection Zone ◽  
Back Reaction ◽  
Solar Convection Zone ◽  
Solar Convection ◽  
Large Scale Magnetic Field ◽  
Magnetic Buoyancy ◽  
The Mean

The mean magnetic field transport due to inhomogeneity of the turbulence intensity is considered taking the field back reaction on motion into account. In spite of the magnetic quenching, the downward diamagnetic pumping is still powerful enough to keep the fields of 3 to 4 kG strength near the SCZ base against the magnetic buoyancy.

Comparison of Fluorine(18)-fluorodeoxyglucose and Gallium(68)-citrate PET/CT in patients with tuberculosis

2019 ◽  
Vol 58 (05) ◽  
pp. 371-378
Author(s):  
Alfred O. Ankrah ◽  
Ismaheel O. Lawal ◽  
Tebatso M.G. Boshomane ◽  
Hans C. Klein ◽  
Thomas Ebenhan ◽  
...  
Keyword(s):  
Tracer Uptake ◽  
Pet Ct ◽  
The Mean ◽  
18F Fdg ◽  
Definition Of ◽  
Gallium 68 ◽  
Attending Physician ◽  
Pet Scans ◽  
The Brain

Abstract 18F-FDG and 68Ga-citrate PET/CT have both been shown to be useful in the management of tuberculosis (TB). We compared the abnormal PET findings of 18F-FDG- and 68Ga-citrate-PET/CT in patients with TB. Methods Patients with TB on anti-TB therapy were included. Patients had a set of PET scans consisting of both 18F-FDG and 68Ga-citrate. Abnormal lesions were identified, and the two sets of scans were compared. The scan findings were correlated to the clinical data as provided by the attending physician. Results 46 PET/CT scans were performed in 18 patients, 11 (61 %) were female, and the mean age was 35.7 ± 13.5 years. Five patients also had both studies for follow-up reasons during the use of anti-TB therapy. Thirteen patients were co-infected with HIV. 18F-FDG detected more lesions than 68Ga-citrate (261 vs. 166, p < 0.0001). 68Ga-citrate showed a better definition of intracerebral lesions due to the absence of tracer uptake in the brain. The mean SUVmax was higher for 18F-FDG compared to 68Ga-citrate (5.73 vs. 3.01, p < 0.0001). We found a significant correlation between the SUVmax of lesions that were determined by both tracers (r = 0.4968, p < 0.0001). Conclusion Preliminary data shows 18F-FDG-PET detects more abnormal lesions in TB compared to 68Ga-citrate. However, 68Ga-citrate has better lesion definition in the brain and is therefore especially useful when intracranial TB is suspected.

Germination and initial growth of triticale seeds under stationary magnetic fields

2014 ◽  
Vol 2 (2) ◽  
pp. 72-79 ◽  
Author(s):  
Mercedes Florez ◽  
Elvira Martinez ◽  
Victoria Carbonell
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Seed Vigor ◽  
Initial Growth ◽  
Practical Application ◽  
Biochemical Processes ◽  
Mean Germination Time ◽  
Nutrition Value ◽  
The Mean ◽  
Growth Of Seedlings

The main objective of this study is to determine the effects of 125 mT and 250mT magnetic treatment on the germination and initial growth of triticale seeds. This objective has a practical application in agriculture science: early growth of triticale. An increase in the percentage and rate of germination of seeds and a stimulation of growth of seedlings as positive response to magnetic field treatment in rice, wheat, maize and barley seeds have been found in previous studies. Germination tests were carried out under laboratory conditions by exposing triticale seeds to magnetic field for different times. The effect was studied by exposure of seeds prior sowing. The mean germination time were reduced for all the magnetic treatments applied. Most significant differences were obtained for time of exposure of 1 and 24 hours and maximum reductions was 12%. Furthermore, seedlings from magnetically treated seeds grew taller than control. The longest mean total length was obtained from seedlings exposed to 125 and 250 mT for 24 hours. External magnetic fields are assumed to enhance seed vigor by influencing the biochemical processes by stimulating activity of proteins and enzymes. Numerous studies suggested that magnetic field increases ions uptake and consequently improves nutrition value.

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