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Three-minute oscillations are a common phenomenon in the solar chromosphere above a sunspot. Oscillations can be affected by the energy release process related to solar flares. In this paper, we report on an enhanced oscillation in flare event SOL2012-07-05T21:42 with a period of around 3 minutes that occurred at the location of a flare ribbon at a sunspot umbral–penumbral boundary and was observed in both chromospheric and coronal passbands. An analysis of this oscillation was carried out using simultaneous ground-based observations from the Goode Solar Telescope at the Big Bear Solar Observatory and space-based observations from the Solar Dynamics Observatory. A frequency shift was observed before and after the flare, with the running penumbral wave that was present with a period of about 200 s before the flare coexisting with a strengthened oscillation with a period of 180 s at the same locations after the flare. We also found a phase difference between different passbands, with the oscillation occurring from high-temperature to low-temperature passbands. Theoretically, the change in frequency was strongly dependent on the variation of the inclination of the magnetic field and the chromospheric temperature. Following an analysis of the properties of the region, we found the frequency change was caused by a slight decrease of the magnetic inclination angle with respect to the local vertical. In addition, we suggest that the enhanced 3 minute oscillation was related to the additional heating, maybe due to the downflow, during the EUV late phase of the flare.

 

Abstract A magnetic object subject to an external rotating magnetic field would be rotated due to the alignment tendency between its internal magnetization and the field. Based on this principle, 12 shapes of swimming microrobots around 1 mm long were designed and 3D-printed using biodegradable materials Poly (ethylene glycol) diacrylate (PEDGA). Their surface was decorated with superparamagnetic iron oxide nanoparticles to provide magnetic responsivity. An array of 12 permanent magnets generated a rotating uniform magnetic field (∼100 mT) to impose magnetic torque, which induces a tumbling motion in the microrobot. We developed a dynamic model that captured the behavior of swimming microrobots of different shapes and showed good agreement with experimental results. Among these 12 shapes, we found that microrobots with equal length, width, and depth performed better. The observed translational speed of the hollow cube microrobot can exceed 17.84 mm s −1 (17.84 body lengths/s) under a rotating magnetic field of 5.26 Hz. These microrobots could swim to the targeted sites in a simplified vessel branch. And a finite element model was created to simulate the motion of the swimming microrobot under a flow rate of 0.062 m s −1 . 

Multiple-surface segmentation in optical coherence tomography (OCT) images is a challenging problem, further complicated by the frequent presence of weak image boundaries. Recently, many deep learning-based methods have been developed for this task and yield remarkable performance. Unfortunately, due to the scarcity of training data in medical imaging, it is challenging for deep learning networks to learn the global structure of the target surfaces, including surface smoothness. To bridge this gap, this study proposes to seamlessly unify a U-Net for feature learning with a constrained differentiable dynamic programming module to achieve end-to-end learning for retina OCT surface segmentation to explicitly enforce surface smoothness. It effectively utilizes the feedback from the downstream model optimization module to guide feature learning, yielding better enforcement of global structures of the target surfaces. Experiments on Duke AMD (age-related macular degeneration) and JHU MS (multiple sclerosis) OCT data sets for retinal layer segmentation demonstrated that the proposed method was able to achieve subvoxel accuracy on both datasets, with the mean absolute surface distance (MASD) errors of 1.88 ± 1.96μmand 2.75 ± 0.94μm, respectively, over all the segmented surfaces.

 

Solar jets are well-collimated plasma ejections in the solar atmosphere. They are prevalent in active regions, the quiet Sun, and even coronal holes. They display a range of temperatures, yet the nature of the cool components has not been fully investigated. In this paper, we show the existence of the precursors and quasi-periodic properties for two chromospheric jets, mainly utilizing the He  I 10 830 Å narrowband filtergrams taken by the Goode Solar Telescope (GST). The extreme ultraviolet (EUV) counterparts present during the eruption correspond to a blowout jet (jet 1) and a standard jet (jet 2), as observed by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO). The high-resolution He  I 10 830 Å observation captures a long-lasting precursor for jet 1, signified by a series of cool ejections. They are recurrent jet-like features with a quasi-period of about five minutes. On the other hand, the cool components of jet 2, recurrently accompanied by EUV emissions, present a quasi-periodic behavior with a period of about five minutes. Both the EUV brightening and He  I 10 830 Å absorption show that there was a precursor for jet 2 that occurred about five minutes before its onset. We propose that the precursor of jet 1 may be the consequence of chromospheric shock waves, since the five-minute oscillation from the photosphere can leak into the chromosphere and develop into shocks. Then, we find that the quasi-periodic behavior of the cool components of jet 2 may be related to magnetic reconnections modulated by the oscillation in the photosphere. 

Using Malliavin calculus, this paper establishes asymptotic Bismut formulae for stochastic functional differential equations with infinite delay. Both nondegenerate and degenerate diffusion coefficients are treated. In addition, combined with the corresponding exponential ergodicity, stabilization bounds for ∇ P t f \nabla P_{t}f as t → ∞ t\rightarrow \infty are derived.