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High-frequency Oscillations in Small Magnetic Elements Observed with Sunrise/SuFI
Jafarzadeh, S.,Solanki, S. K.,Stangalini, M.,Steiner, O.,Cameron, R. H.,Danilovic, S. American Astronomical Society 2017 The Astrophysical journal Supplement series Vol.229 No.1
<P>We characterize waves in small magnetic elements and investigate their propagation in the lower solar atmosphere from observations at high spatial and temporal resolution. We use the wavelet transform to analyze oscillations of both horizontal displacement and intensity in magnetic bright points found in the 300. nm and the Ca II H 396.8 nm passbands of the filter imager on board the SUNRISE balloon-borne solar observatory. Phase differences between the oscillations at the two atmospheric layers corresponding to the two passbands reveal upward propagating waves at high frequencies (up to 30 mHz). Weak signatures of standing as well as downward propagating waves are also obtained. Both compressible and incompressible (kink) waves are found in the small-scale magnetic features. The two types of waves have different, though overlapping, period distributions. Two independent estimates give a height difference of approximately 450 +/- 100 km between the two atmospheric layers sampled by the employed spectral bands. This value, together with the determined short travel times of the transverse and longitudinal waves provide us with phase speeds of 29 +/- 2 km s(-1) and 31 +/- 2 km s(-1), respectively. We speculate that these phase speeds may not reflect the true propagation speeds of the waves. Thus, effects such as the refraction of fast longitudinal waves may contribute to an overestimate of the phase speed.</P>
Kinematics of Magnetic Bright Features in the Solar Photosphere
Jafarzadeh, S.,Solanki, S. K.,Cameron, R. H.,Barthol, P.,Rodrí,guez, J. Blanco,Iniesta, J. C. del Toro,Gandorfer, A.,Gizon, L.,Hirzberger, J.,Knö,lker, M.,Pillet, V. Martí,nez,Su&aacut American Astronomical Society 2017 The Astrophysical journal Supplement series Vol.229 No.1
<P>Convective flows are known as the prime means of transporting magnetic fields on the solar surface. Thus, small magnetic structures are good tracers of turbulent flows. We study the migration and dispersal of magnetic bright features (MBFs) in intergranular areas observed at high spatial resolution with SUNRISE/IMaX. We describe the flux dispersal of individual MBFs as a diffusion process whose parameters are computed for various areas in the quiet-Sun and the vicinity of active regions from seeing-free data. We find that magnetic concentrations are best described as random walkers close to network areas (diffusion index, gamma = 1.0), travelers with constant speeds over a supergranule (gamma = 1.9-2.0), and decelerating movers in the vicinity of flux emergence and/or within active regions (gamma = 1.4-1.5). The three types of regions host MBFs with mean diffusion coefficients of 130 km(2) s(-1), 80-90 km(2) s(-1), and 25-70 km(2) s(-1), respectively. The MBFs in these three types of regions are found to display a distinct kinematic behavior at a confidence level in excess of 95%.</P>
Transverse Oscillations in Slender Ca ii H Fibrils Observed with Sunrise/SuFI
Jafarzadeh, S.,Solanki, S. K.,Gafeira, R.,Noort, M. van,Barthol, P.,Rodrí,guez, J. Blanco,Iniesta, J. C. del Toro,Gandorfer, A.,Gizon, L.,Hirzberger, J.,Knö,lker, M.,Suá,rez, D. Orozco American Astronomical Society 2017 The Astrophysical journal, Supplement series Vol.229 No.1
<P>We present observations of transverse oscillations in slender Ca II H fibrils (SCFs) in the lower solar chromosphere. We use a 1 hr long time series of high- (spatial and temporal-) resolution. seeing-free observations in a 1.1 angstrom wide passband covering the line core of Ca II H 3969 angstrom from the second flight of the SUNRISE balloon-borne solar observatory. The entire field of view, spanning the polarity inversion line of an active region close to the solar disk center, is covered with bright, thin, and very dynamic fine structures. Our analysis reveals the prevalence of transverse waves in SCFs with median amplitudes and periods on the order of 2.4 +/- 0.8 km s(-1) and 83 +/- 29 s, respectively (with standard deviations given as uncertainties). We find that the transverse waves often propagate along (parts of) the SCFs with median phase speeds of 9 +/- 14 km s(-1). While the propagation is only in one direction along the axis in some of the SCFs, propagating waves in both directions, as well as standing waves are also observed. The transverse oscillations are likely Alfvenic and are thought to be representative of magnetohydrodynamic kink waves. The wave propagation suggests that the rapid. high-frequency transverse waves,. often produced in the lower photosphere, can penetrate into the chromosphere. with an estimated energy flux of approximate to 15 kW m(-2). Characteristics of these waves differ from those reported for other fibrillar structures, which, however, were observed mainly in the upper solar chromosphere.</P>
Slender Ca ii H Fibrils Mapping Magnetic Fields in the Low Solar Chromosphere
Jafarzadeh, S.,Rutten, R. J.,Solanki, S. K.,Wiegelmann, T.,Riethmü,ller, T. L.,Noort, M. van,Szydlarski, M.,Rodrí,guez, J. Blanco,Barthol, P.,Iniesta, J. C. del Toro,Gandorfer, A.,Gizon, L. American Astronomical Society 2017 The Astrophysical journal, Supplement series Vol.229 No.1
<P>A dense forest of slender bright fibrils near a small solar active region is seen in high-quality narrowband Ca II H images from the SuFI instrument onboard the SUNRISE balloon-borne solar observatory. The orientation of these slender Ca II H fibrils (SCF) overlaps with the magnetic field configuration in the low solar chromosphere derived by magnetostatic extrapolation of the photospheric field observed with SUNRISE/IMaX and SDO/HMI. In addition, many observed SCFs are qualitatively aligned with small-scale loops computed from a novel inversion approach based on best-fit numerical MHD simulation. Such loops are organized in canopy-like arches over quiet areas that differ in height depending on the field strength near their roots.</P>
H. Jafarzadeh,K. Abrinia 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.2
A novel severe plastic deformation (SPD) technique entitled repetitive tube expansion and shrinking (RTES) has been developed tofabricate ultra-fine grained and nanostructured AZ91 tubular components. This method includes two different half-cycles and is based onpressing a tubular part through an angular channel die with two shear zones. In order to primarily demonstrate the deformation behaviorand refinement ability of RTES method, the FE simulations and experimental analyses were both done. Analytical calculations and FEsimulations of this method accompanied by Abaqus/explicit indicate that the large amount of equivalent plastic strain of 5.8 is imposed ineach cycle. In experimental investigations of a single-cycle of RTES, microstructural observations showed a significant grain refinementfrom the initial value of ~150 μm to ~700 nm. The distribution characteristic of refinement and hardness were consistent with that ofsimulated effective strain. This novel SPD method seems to be very promising for future commercial practice.
Oscillations on Width and Intensity of Slender Ca ii H Fibrils from Sunrise/SuFI
Gafeira, R.,Jafarzadeh, S.,Solanki, S. K.,Lagg, A.,van Noort, M.,Barthol, P.,Rodrí,guez, J. Blanco,del Toro Iniesta, J. C.,Gandorfer, A.,Gizon, L.,Hirzberger, J.,Knö,lker, M.,Suá,rez, American Astronomical Society 2017 The Astrophysical journal, Supplement series Vol.229 No.1
<P>We report the detection of oscillations in slender Ca II H fibrils (SCFs) from high-resolution observations acquired with the SUNRISE balloon-borne solar observatory. The SCFs show obvious oscillations in their intensity, but also their width. The oscillatory behaviors are investigated at several positions along the axes of the SCFs. A large majority of fibrils show signs of oscillations in intensity. Their periods and phase speeds are analyzed using a wavelet analysis. The width and intensity perturbations have overlapping distributions of the wave period. The obtained distributions have median values of the period of 32 +/- 17 s and 36 +/- 25 s, respectively. We find that the fluctuations of both parameters propagate in the SCFs with speeds of 11(-11)(+49)+ km s(-1) and 15(-15)(+34) km s(-1), respectively. Furthermore, the width and intensity oscillations have a strong tendency to be either in anti-phase. or, to a smaller extent, in phase. This suggests that the oscillations of both parameters are caused by the same wave mode and that the waves are likely propagating. Taking all the evidence together, the most likely wave mode to explain all measurements and criteria is the fast sausage mode.</P>
M. Fekri,K. Jafarzadeh,S. A. Khalife Soltani,Z. Valefi,H. Mazhari Abbasi 한국탄소학회 2023 Carbon Letters Vol.33 No.7
In this research, in order to increase the oxidation resistance of graphite, kaolin and alumina powder with different ratios (26A-74S, 49A-51S, 72A-28S) and slurry method were used to create an aluminosilicate coating on the graphite substrate. In order to reduce the difference in the coefficients of thermal expansion of graphite with aluminosilicate coating, aluminum metaphosphate coating as an interlayer was prepared on the surface of graphite by cathodic electrochemical treatment. The isothermal oxidation test of the samples was carried out in air at a temperature of 1250 °C for 1, 3 and 5 h. The microstructure, chemical composition, and phase components of the coating were, respectively, analyzed by scanning electron microscope equipped with an energy-dispersive spectrometer and X-ray diffraction. The results indicated that, by increasing the withdrawal speed of the samples in slurry method, the amount of changes in the weight of the samples has increased and therefore had a direct effect on oxidation. In addition, it was approved that, at high-temperature oxidation, AlPO4 glass phase forms on aluminum metaphosphate interlayer which retards graphite oxidation. Along with aluminum metaphosphate, aluminosilicate coating also produces a glass phase which fills and seals the voids on the surface which prevents the oxygen to reach the surface of graphite. The created double-layer coating including an interlayer of aluminum metaphosphate + slurry coating prepared with the ratio of 26A-74S as the optimal coating in this research was able to increase the oxidation resistance of graphite by 73% at a temperature of 1250 °C.