The observed properties (i.e., source size, source position, time duration, decay time) of solar radio emission produced through plasma processes near the local plasma frequency, and hence the interpretation of solar radio bursts, are strongly influenced by propagation effects in the inhomogeneous turbulent solar corona. In this work, a 3D stochastic description of the propagation process is presented, based on the Fokker-Planck and Langevin equations of radio-wave transport in a medium containing anisotropic electron density fluctuations. Using a numerical treatment based on this model, we investigate the characteristic source sizes and burst decay times for Type III solar radio bursts. Comparison of the simulations with the observations of solar radio bursts shows that predominantly perpendicular density fluctuations in the solar corona are required, with an anisotropy factor ∼ 0.3 for sources observed at around 30 MHz. The simulations also demonstrate that the photons are isotropized near the region of primary emission, but the waves are then focused by large-scale refraction, leading to plasma radio emission directivity that is characterized by a half-width-half-maximum of about 40 degrees near 30 MHz. The results are applicable to various solar radio bursts produced via plasma emission.

Red blood cells (RBCs) during microcirculation, aging and storage, lose N-acetylneuraminic acid (NANA) and other biomaterials thereby altering cell structures, some properties and functions. Such cell damage very likely underlies the serious adverse effects of blood transfusion. However, a controversy has remained since 1961–1977 as to whether with aging, the RBCs, suffering loss of NANA, do have a decreased charge density. Any correlation between the changes in the cell properties with cell aging is also not clear. Therefore, to remove the ambiguity and uncertainty, we carried out multiparameteric studies on Percoll fractions of blood of 38 volunteers (lightest-young-Y-RBCs, densest-old-O-RBCs, two middle fractions).We found that there were striking differences between the properties of Y-RBCs and O-RBCs. The ζ-potential of Y-RBCs decreased gradually with aging. Studies in parallel on RBC fractions incubated with both positively charged quantum dots and Sambucus Nigra-fluorescein isothiocyanate (FITC) along with their ζ-potentials provide for the first time direct visual evidence about the lesser amount of charge density and NANA on O-RBCs, and a collinear decrease in their respective ζ-potentials. Close correlation was found between the surface charge on an aging RBC and its structure and functions, from the cell morphology, the membrane deformability to the intracellular Hb structure and oxidation ability. This quantitative approach not only clarifies the picture but also has implications in biology and medicine.

Quasi-periodic pulsations (QPPs) are frequently observed in solar flares, which may reveal some essential characteristics of both thermal and nonthermal energy releases. This work presents multi-wavelength imaging observations of an M8.7 flare in active region AR 12242 on 2014 December 17. We found that there were three different QPPs: UV QPPs with a period of about 4 minutes at 1600 Å images near the center of the active region lasting from the preflare phase to the impulsive phase; EUV QPPs with a period of about 3 minutes along the circular ribbon during the preflare phase; and radio QPPs with a period of about 2 minutes at frequencies of 1.2–2.0 GHz around the flaring source region during the impulsive phase. The observations include the radio images observed by the Mingantu Spectral Radioheliograph in China at frequencies of 1.2–2.0 GHz for the first time, microwave images by the Nobeyama Radioheliograph, UV and EUV images by AIA/SDO, and a magnetogram by HMI/SDO. We suggest that the 4 minute UV QPPs should be modulated by the sunspot oscillations, and the 3 minute EUV QPPs are closely related to the 2 minute radio QPPs for their source regions connected by a group of coronal loops. We propose that the intermittent magnetic reconnecting downward and upward plasmoids may be the possible trigger of both the preflare 3 minute EUV QPPs and the impulsive 2 minute radio QPPs. The other possible mechanism is LRC oscillation, which is associated with the current-carrying coronal loops. The latter mechanism implies that the existence of preflare QPPs may be a possible precursor to solar flares.

Solar radio type III bursts are believed to be the most sensitive signature of near-relativistic electron beam propagation in the corona. A solar radio type IIIb-III pair burst with fine frequency structures, observed by the Low Frequency Array (LOFAR) with high temporal (∼ 10 ms) and spectral (12.5 kHz) resolutions at 30 -80 MHz, is presented. The observations show that the type III burst consists of many striae, which have a frequency scale of about 0.1 MHz in both the fundamental (plasma) and the harmonic (double plasma) emission. We investigate the effects of background density fluctuations based on the observation of striae structure to estimate the density perturbation in solar corona. It is found that the spectral index of the density fluctuation spectrum is about −1.7, and the characteristic spatial scale of the density perturbation is around 700 km. This spectral index is very close to a Kolmogorov turbulence spectral index of −5/3, consistent with a turbulent cascade. This fact indicates that the coronal turbulence may play the important role of modulating the time structures of solar radio type III bursts, and the fine structure of radio type III bursts could provide a useful and unique tool to diagnose the turbulence in the solar corona.

Recent developments in astronomical radio telescopes opened new opportunities in imaging and spectroscopy of solar radio bursts at sub-second timescales. Imaging in narrow frequency bands has revealed temporal variations in the positions and source sizes that do not fit into the standard picture of type III solar radio bursts, and require a better understanding of radio-wave transport. In this paper, we utilise 3D Monte Carlo ray-tracing simulations that account for the anisotropic density turbulence in the inhomogeneous solar corona to quantitatively explain the image dynamics at the fundamental (near plasma frequency) and harmonic (double) plasma emissions observed at ∼32 MHz. Comparing the simulations with observations, we find that anisotropic scattering from an instantaneous emission point source can account for the observed time profiles, centroid locations, and source sizes of the fundamental component of type III radio bursts (generated where f pe ≈ 32 MHz). The best agreement with observations is achieved when the ratio of the perpendicular to the parallel component of the wave vector of anisotropic density turbulence is around 0.25. Harmonic emission sources observed at the same frequency (∼32 MHz, but generated where f pe ≈ 16 MHz) have apparent sizes comparable to those produced by the fundamental emission, but demonstrate a much slower temporal evolution. The simulations of radio-wave propagation make it possible to quantitatively explain the variations of apparent source sizes and positions at sub-second time-scales both for the fundamental and harmonic emissions, and can be used as a diagnostic tool for the plasma turbulence in the upper corona.

No abstract

The Chinese Spectral Radioheliograph (CSRH) covering 400 MHz-15 GHz frequency range was constructed during 2009–2016 in Mingantu Observing Station, National Astronomical Observatories, Chinese Academy of Sciences at Zhengxiangbaiqi, Inner Mongolia of China. The CSRH is renamed as MingantU SpEctral Radioheliograph (MUSER) after its accomplishment. Currently, MUSER consists of two arrays spreading over three spiral-shaped arms. The maximum baseline length is ∼3 km in both east-west and north-south directions. The MUSER array configuration is optimized to meet the needs of observing the full-disk Sun over ultrawide wavebands with images of high temporal, spatial and spectral resolutions and high dynamic range. The low frequency array, called MUSER-I, covers 400 MHz-2.0 GHz with 40 antennas of 4.5-m-diameter each and the high frequency array, called MUSER-II, covers 2–15 GHz with 60 antennas of 2-m-diameter each. The MUSER-I can obtain full-disk solar radio images in 64 frequency channels with a time cadence of 25 ms and a spatial resolution of 51.6″ to 10.3″ (corresponding to the frequency range 400 MHz to 2 GHz), whereas the MUSER-II can obtain full-disk solar images in 520 channels with a time cadence of 206.25 ms and a spatial resolution of 10.3″ to 1.3 (corresponding to the frequency range 2 to 15 GHz). A dynamic range of 25 dB can be obtained with snapshot images produced with the MUSER. An extension of MUSER in the further lower frequency range covering 30–400 MHz with an array of 224 logarithm-periodic dipole antennas (LPDAs) has been approved and will be completed during the next 4 years. The MUSER, as a dedicated solar instrument, has the following advantages providing simultaneous images over a wide frequency range with a unique high temporal-spatial-spectral resolutions; high-performing ultrawide-band dual-polarization feeds for wide-band signal collection; advanced high data-rate, large-scale digital correlation receiver for multiple-frequency and faster snapshot observations; and applications of new technologies such as using optical fiber to obtain remote antenna and wide-band analog signal transmission. The MUSER thus provides a unique opportunity to measure solar magnetic fields and trace dynamic evolution of energetic electrons in several radio frequencies, which, in turn, will help to have better understandings of the origin of various solar activities and the basic drivers of space weather.

Membrane sialic acid (SA) plays an important role in the survival of red blood cells (RBCs), the age‐related reduction in SA content negatively impacts both the structure and function of these cells. We have therefore suggested that remodelling the SA in the membrane of aged cells would help recover cellular functions characteristic of young RBCs. We developed an effective method for the re‐sialylation of aged RBCs by which the cells were incubated with SA in the presence of cytidine triphosphate (CTP) and α‐2,3‐sialytransferase. We found that RBCs could be re‐sialylated if they had available SA‐binding groups and after the re‐sialylation, aged RBCs could restore their membrane SA to the level in young RBCs. Once the membrane SA was restored, the aged RBCs showed recovery of their biophysical and biochemical properties to similar levels as in young RBCs. Their life span in circulation was also extended to twofold. Our findings indicate that remodelling membrane SA not only helps restore the youth of aged RBCs, but also helps recover injured RBCs.