Image denoising based on deep learning has undergone significant advances in recent years. However, existing deep learning methods lack quantitative control of the deviation or error of denoised images. The neural network Self2Self was designed to denoise single images. It is trained on single images and then denoises them, although training is costly. In this work, we explore training Self2Self on an astronomical image and denoising other images of the same kind, a process that is also suitable for quickly denoising immense images in astronomy. To address the deviation issue, the abnormal pixels whose deviation exceeds a predefined threshold are restored to their initial values. The noise reduction is due to training, denoising and restoring and is, therefore, named the TDR method. With the TDR method, the noise level of solar magnetograms improved from about 8 to 2 G. Furthermore, the TDR method was applied to galaxy images from the Hubble Space Telescope, making weak galaxy structures much clearer. This capability of enhancing weak signals makes the TDR method applicable to various disciplines.
The space weather event from September 5-11, 2017, was marked by high activity, with multiple solar flares and a geomagnetic storm. This study investigates the impact of solar flares and the associated geomagnetic storm on the equatorial and low-latitude region of Africa, utilizing data from the Global Navigation Satellite System (GNSS), in-situ electron density observations from the SWARM-A satellite, and ground-based magnetometer data from Mbour (mbo, 14.39∘S, 16.96∘W), Dakar, as well as the real-time prompt penetration equatorial electric field model (PPEFM). The analysis of ionospheric total electron content (TEC) disturbances involves comparing storm-time TEC with the mean of the quiet days of the month. The rate of change of TEC index (ROTI) and the rate of plasma density irregularity index (RODI) are employed to examine ionospheric irregularities on the equatorial and low-latitude African longitude. In order to analyze the TEC changes in the ionosphere due to solar flares, difference between the TEC value before the flare and the peak TEC value during the flare were used. Results of the study show that while the X2.2 solar flare did not significantly increase TEC, the X9.3 flare caused a notable enhancement, with TEC increase of 2.47 and 1.66 TECU in the East and West African sectors, respectively. While the X1.3 solar flare caused TEC increase of 1.03 and 0.44 TECU in the East and West African sectors, respectively. Sometimes, reduction in ionospheric TEC were also observed. The ionospheric TEC response during the first stage of the storm’s main phase was minimal, but significant variations were noted during the second stage of the storm’s main phase, in both Eastern and Western African sectors. Ionospheric irregularities during the first stage of the storm’s main phase were suppressed/enhanced in the Eastern/Western African sectors. On the other hand, during the second stage of the storm’s main phase, the occurrence of ionospheric irregularities were inhibited in both African sectors. This may be likely due to the decrease in the pre-reversal enhancement of the ionospheric zonal electric field. Lastly, the study also examines disturbances in ionospheric currents inferred from ground-based data, extracted from magnetometer located in the West African sector. Unfortunately, there is no magnetometer located in the East African sector.
In this paper, we study the four-point celestial leaf amplitudes of massless scalar and MHV gluon scattering. These leaf amplitudes are non-distributional decompositions of the celestial amplitudes associated with a hyperbolic foliation of the Klein spacetime. Bulk scale invariance imposes constraints on the total conformal weights of the massless scalars or gluons. Using this constraint we show that the four-point leaf amplitudes have a simple pole singularity at z = ( overline{z} ), where, z, ( overline{z} ) are two real independent conformal cross ratios. The distributional nature of the four-point celestial amplitudes is recovered by adding the leaf amplitudes in the timelike and spacelike wedges of the spacetime. We also verify that the MHV gluon leaf amplitudes satisfy a set of differential equations previously obtained for celestial MHV gluon amplitudes by considering the soft gluon theorems and the subleading terms in the OPE expansion between two positive helicity gluons.
The effect of the parameters of a medium, which is formed by a set of gas jets, on the generation of elliptically polarized harmonics during nonlinear optical interaction with two-color femtosecond laser fields has been studied. The calculations have been performed for a laser field formed by linearly polarized first and second harmonics of a Cr:forsterite laser with the polarization of the field components making an angle of π/4. The generation of elliptically polarized harmonics by single Ar atoms in such fields has been demonstrated with a nonperturbative theoretical approach. Using the interference model, the efficiency and polarization properties of the generated harmonics under both phase and quasi-phase matching conditions have been calculated. The possibility of quasi-phase amplification of elliptically polarized harmonics has been demonstrated.
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：