Structure Of Corona Research Articles

Detailed insight into the formation of protein corona: Conformational change, stability and aggregation

In a physiological fluid (e.g., blood), nanomaterials will strongly interact with proteins to form “protein corona”. The structure and aggregation of protein corona around the nanoparticles are of vital importance in the safe application of nanomaterials in living organisms. Here, we combined systematic methods, including transmission electron microscopy, scanning electron microscopy equipped with energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, hydrogen/deuterium exchange techniques and fluorescence quenching to explore the conformational change, stability and aggregation of protein corona bound on magnetic nanoparticles. For the first time we observed that the conformational change of protein corona could induce proteins to aggregate. We believe that these findings will deepen our understanding of the protein corona.

Effect of nanoparticle size and PEGylation on the protein corona of PLGA nanoparticles

Upon intravenous administration of nanoparticles (NP) into the bloodstream, proteins bind rapidly on their surface resulting in a formation of a so-called ‘Protein Corona’. These proteins are strongly attached to the NP surface and provide a new biological identity which is crucial for the reaction at the nano-biointerface. The structure and composition of the protein corona is greatly determined by the physico-chemical properties of the NP and the characteristics of the biological environment. The overall objective of this study was to characterize the role of NP size/surface curvature and PEGylation on the formation of the protein corona. Therefore, we prepared NP in a size of 100 and 200 nm using the biodegradable polymers poly(DL-lactide-co-glycolide) (PLGA) and poly(DL-lactide-co-glycolide)-co-polyethylene glycol diblock (PLGA-PEG) and subsequently incubated them with fetal bovine serum (FBS) to induce the formation of a protein corona. After removal of unbound protein, we employed different analytical approaches to study the corona in detail. Sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) was performed to gain a first impression about amount and composition of the corona proteins. Identification was carried out after tryptic in-solution digestion and liquid chromatography–mass spectrometry/mass spectrometry (LC–MS/MS). In addition, we successfully established the Bradford protein assay as a suitable colorimetric method to quantify total adsorbed protein amount after alkaline hydrolysis of PLGA based NP. Our results revealed that protein adsorption on PLGA- and PLGA-PEG-NP didn’t depend on NP size within the range of 100 and 200 nm. PEGylation led to a significant reduced amount of bound proteins. The depletion of proteins which are involved in immune response was remarkable and indicated a prolonged circulation time in body.

Predicting the Structure of the Solar Corona and Inner Heliosphere during Parker Solar Probe's First Perihelion Pass

Abstract NASA’s Parker Solar Probe (PSP) spacecraft reached its first perihelion of 35.7 solar radii on 2018 November 5. To aid in mission planning, and in anticipation of the unprecedented measurements to be returned, in late October, we developed a three-dimensional magnetohydrodynamic (MHD) solution for the solar corona and inner heliosphere, driven by the then available observations of the Sun’s photospheric magnetic field. Our model incorporates a wave-turbulence-driven model to heat the corona. Here, we present our predictions for the structure of the solar corona and the likely in situ measurements that PSP will be returning over the next few months. We infer that, in the days prior to first encounter, PSP was immersed in wind emanating from a well-established, positive-polarity northern polar coronal hole. During the encounter, however, field lines from the spacecraft mapped to a negative-polarity equatorial coronal hole, within which it remained for the entire encounter, before becoming magnetically connected to a positive-polarity equatorial coronal hole. When the PSP data become available, these model results can be used to assist in their calibration and interpretation, and, additionally, provide a global context for interpreting the localized in situ measurements. In particular, we can identify what types of solar wind PSP encountered, what the underlying magnetic structure was, and how complexities in the orbital trajectory can be interpreted within a global, inertial frame. Ultimately, the measurements returned by PSP can be used to constrain current theories for heating the solar corona and accelerating the solar wind.

Frequency–Distance Structure of Solar Radio Sources Observed by LOFAR

Abstract Low-frequency radio observations make it possible to study the solar corona at distances up to 2–3 R ☉. Frequency of plasma emission is a proxy for electron density of the emitting plasma and, therefore, observations of solar radio bursts can be used to probe the density structure of the outer corona. In this study, positions of solar radio sources are investigated using the Low-Frequency Array (LOFAR) spectral imaging in the frequency range 30–50 MHz. We show that there are events where apparent positions of the radio sources cannot be explained using the standard coronal density models. Namely, the apparent heliocentric positions of the sources are 0.1–0.7 R ☉ further from the Sun compared with the positions predicted by the Newkirk model, and these shifts are frequency-dependent. We discuss several possible explanations for this effect, including enhanced plasma density in the flaring corona, as well as scattering and refraction of the radio waves.

Contribution of observed multi frequency spectrum of Alfvén waves to coronal heating

Context. Whilst there are observational indications that transverse magnetohydrodynamic (MHD) waves carry enough energy to maintain the thermal structure of the solar corona, it is not clear whether such energy can be efficiently and effectively converted into heating. Phase-mixing of Alfvén waves is considered a candidate mechanism, as it can develop transverse gradient where magnetic energy can be converted into thermal energy. However, phase-mixing is a process that crucially depends on the amplitude and period of the transverse oscillations, and only recently have we obtained a complete measurement of the power spectrum for transverse oscillations in the corona. Aims. We aim to investigate the heating generated by phase-mixing of transverse oscillations triggered by buffeting of a coronal loop that follows from the observed coronal power spectrum as well as the impact of these persistent oscillations on the structure of coronal loops. Methods. We considered a 3D MHD model of an active region coronal loop and we perturbed its footpoints with a 2D horizontal driver that represents a random buffeting motion of the loop footpoints. Our driver was composed of 1000 pulses superimposed to generate the observed power spectrum. Results. We find that the heating supply from the observed power spectrum in the solar corona through phase-mixing is not sufficient to maintain the million-degree active region solar corona. We also find that the development of Kelvin–Helmholtz instabilities could be a common phenomenon in coronal loops that could affect their apparent life time. Conclusions. This study concludes that is unlikely that phase-mixing of Alfvén waves resulting from an observed power spectrum of transverse coronal loop oscillations can heat the active region solar corona. However, transverse waves could play an important role in the development of small scale structures.

Electron Heating by Kinetic Alfvén Waves in Coronal Loop Turbulence

Abstract A test-particle model describing the energization of electrons in a turbulent plasma is presented. Parameters are chosen to represent turbulence in a magnetic structure of the solar corona. A fluctuating electric field component parallel to the background magnetic field, with properties similar to those of Kinetic Alfvén Waves, is assumed to be present at scales of the order of the proton Larmor radius. Electrons are stochastically accelerated by multiple interactions with such fluctuations, reaching energies of the order of 102 eV within tens to hundreds of seconds, depending on the turbulence amplitude. For values of the large-scale plasma velocity fluctuation of the order of tens of kilometers per second, the power absorbed by electrons per surface unit is of the order of that typically necessary to heat the corona. The power that electrons absorb from fluctuations is proportional to the third power of the large-scale velocity amplitude, and is comparable with the power associated with the turbulent cascade. Therefore, this mechanism can be considered as an equivalent kinetic dissipation for turbulence, and it can play a relevant role in the heating of electrons in the corona.

Solar physics with the Square Kilometre Array

The Square Kilometre Array (SKA) will be the largest radio telescope ever built, aiming to provide collecting area larger than 1 km2. The SKA will have two independent instruments, SKA-LOW comprising of dipoles organized as aperture arrays in Australia and SKA-MID comprising of dishes in South Africa. Currently the phase-1 of SKA, referred to as SKA1, is in its late design stage and construction is expected to start in 2020. Both SKA1-LOW (frequency range of 50–350 MHz) and SKA1-MID Bands 1, 2, and 5 (frequency ranges of 350–1050, 950–1760, and 4600–15,300 MHz, respectively) are important for solar observations. In this paper we present SKA’s unique capabilities in terms of spatial, spectral, and temporal resolution, as well as sensitivity and show that they have the potential to provide major new insights in solar physics topics of capital importance including (i) the structure and evolution of the solar corona, (ii) coronal heating, (iii) solar flare dynamics including particle acceleration and transport, (iv) the dynamics and structure of coronal mass ejections, and (v) the solar aspects of space weather. Observations of the Sun jointly with the new generation of ground-based and space-borne instruments promise unprecedented discoveries.

Safety considerations for nanoparticles in tumor treatment.

Safety considerations for nanoparticles in tumor treatment.

Contribution of phase-mixing of Alfvén waves to coronal heating in multi-harmonic loop oscillations

Context. Kink oscillations of a coronal loop are observed and studied in detail because they provide a unique probe into the structure of coronal loops through magnetohydrodynamics (MHD) seismology and a potential test of coronal heating through the phase mixing of Alfvén waves. In particular, recent observations show that standing oscillations of loops often involve higher harmonics in addition to the fundamental mode. The damping of these kink oscillations is explained by mode coupling with Alfvén waves. Aims. We investigate the consequences for wave-based coronal heating of higher harmonics and which coronal heating observational signatures we may use to infer the presence of higher harmonic kink oscillations. Methods. We performed a set of non-ideal MHD simulations in which we modelled the damping of the kink oscillation of a flux tube via mode coupling. We based our MHD simulation parameters on the seismological inversion of an observation for which the first three harmonics are detected. We studied the phase mixing of Alfvén waves, which leads to the deposition of heat in the system, and we applied seismological inversion techniques to the MHD simulation output. Results. We find that the heating due to phase mixing of Alfvén waves triggered by the damping of kink oscillation is relatively small. We can however illustrate how the heating location drifts from subsequent damping of lower order harmonics. We also address the role of higher order harmonics and the width of the boundary shell in the energy deposition. Conclusions. We conclude that the coronal heating due to phase mixing does not seem to provide enough energy to maintain the thermal structure of the solar corona even when multi-harmonic oscillations are included; these oscillations play an inhibiting role in the development of smaller scale structures.

Production of Sunspots and Their Effects on the Corona and Solar Wind: Insights from a New 3D Flux-Transport Dynamo Model

We present a three-dimensional numerical model for the generation and evolution of the magnetic field in the solar convection zone, in which sunspots are produced and contribute to the cyclic reversal of the large-scale magnetic field. We then assess the impact of this dynamo-generated field on the structure of the solar corona and solar wind. This model solves the induction equation in which the velocity field is prescribed. This velocity field is a combination of a solar-like differential rotation and meridional circulation. We develop an algorithm that enables the magnetic flux produced in the interior to be buoyantly transported towards the surface to produce bipolar spots. We find that those tilted bipolar magnetic regions contain a sufficient amount of flux to periodically reverse the polar magnetic field and sustain dynamo action. We then track the evolution of these magnetic features at the surface during a few consecutive magnetic cycles and analyze their effects on the topology of the corona and on properties of the solar wind (distribution of streamers and coronal holes, and of slow and fast wind streams) in connection with current observations of the Sun.

Synthesis, Structure, and Properties of Corona[6]arenes and Their Assembly with Anions in the Crystalline State.

The synthesis, conformational structure, electronic property, and anion complexation of novel coronarenes were systematically studied. A number of corona[4]arene[2]tetrazines that contain different combinations of nitrogen atoms with O, S, SO2, and CH2 as bridging units were synthesized conveniently by means of a fragment coupling strategy based on efficient nucleophilic aromatic substitution reaction of easily available aromatic dinucleophiles and 3,6-dichlorotetrazine. The resulting macrocycles adopt crownlike conformational structures with the nitrogen bridge(s) forming conjugation with carbonyl and the other heteroatom linkages with tetrazine. CV and DPV measurements showed that the tetrazine-bearing coronarenes were electron deficient with reduction potentials ranging from -896 to -960 mV. Owing mainly to noncovalent anion-π attractive interactions, N2,O4-corona[4]arene[2]tetrazine formed complexes with anions of varied geometries and shapes yielding diverse assembled structures in the solid state.

The Analysis of Total Solar Eclipse Pictures on August 21, 2017 at Wyoming, USA

Total Solar Eclipse has become a magnet for everyone, especially scientists. That’s because every eclipse will have their own characteristics. Even using simple instrument such as digital camera, tripod, tele lens, and solar filter, the eclipse pictures obtained. The digital picture of solar corona taken several times with different shutter speed to get the best solar corona composite with radial blur procedure and stacking technique. From that editing procedure, the structure of solar corona can be analyzing and also the maximum height of solar corona determined which is 502513.53 km or equal with 0.72 times radius of the sun.

Comparative Study of the Three-Dimensional Thermodynamical Structure of the Inner Corona of Solar Minimum Carrington Rotations 1915 and 2081

Using differential emission measure tomography (DEMT) based on time series of EUV images, we carry out a quantitative comparative analysis of the three-dimensional (3D) structure of the electron density and temperature of the inner corona ( $r<1.25\,\mathrm{R}_{\odot}$ ) between two specific rotations selected from the last two solar minima, namely Carrington Rotations (CR)1915 and CR-2081. The analysis places error bars on the results because of the systematic uncertainty of the sources. While the results for CR-2081 are characterized by a remarkable north–south symmetry, the southern hemisphere for CR-1915 exhibits higher densities and temperatures than the northern hemisphere. The core region of the streamer belt in both rotations is found to be populated by structures whose temperature decreases with height (called “down loops” in our previous articles). They are characterized by plasma $\beta\gtrsim1$ , and may be the result of the efficient dissipation of Alfven waves at low coronal heights. The comparative analysis reveals that the low latitudes of the equatorial streamer belt of CR-1915 exhibit higher densities than for CR-2081. This cannot be explained by the systematic uncertainties. In addition, the southern hemisphere of the streamer belt of CR-1915 is characterized by higher temperatures and density scale heights than for CR-2081. On the other hand, the coronal hole region of CR-1915 shows lower temperatures than for CR-2081. The reported differences are in the range ${\approx}\,10\,\mbox{--}\,25\%$ , depending on the specific physical quantity and region that is compared, as fully detailed in the analysis. For other regions and/or physical quantities, the uncertainties do not allow assessing the thermodynamical differences between the two rotations. Future investigation will involve a DEMT analysis of other Carrington rotations selected from both epochs, and also a comparison of their tomographic reconstructions with magnetohydrodynamical simulations of the inner corona.

Polyglycerolated nanocarriers with increased ligand multivalency for enhanced in vivo therapeutic efficacy of paclitaxel.

Despite the excellent biocompatibility and antifouling effect of poly(ethylene glycol) (PEG), the high steric hindrance, limited chemical functionality, and low ligand multivalency of PEGylated nanocarriers often lead to inefficient cell targeting and intracellular trafficking. Hence, a new structure of hydrophilic corona allowing a higher ligand density without loss of excellent biocompatibility is highly desirable. Here we introduce tumor-targeted polyglycerolated (PGylated) nanocarriers that dramatically enhance the invivo therapeutic efficacy of incorporated paclitaxel simply by increasing the surface density of hydrophobic tumor-targeting ligands. Linear polyglycerol-poly (ε-caprolactone) block copolymer (PG-b-PCL) is used to prepare PGylated lipiodol nanoemulsions, where PG serves as a corona conjugated with a large number of folic acid (FA) for efficient tumor targeting. Unlike FA-PEGylated nanoemulsions, FA-PGylated nanoemulsions can display a larger number of FA without structural destabilization. This property enables excellent anti-cancer activities and effective tumor regression in a cervical cancer xenograft murine model at a cumulative drug dose of ∼5mgkg-1, which is about four fold smaller than that of commercial Taxol formulation. This study highlights the importance of surface chemistry of nanocarriers that enable multivalent ligand functionalization and high tolerance to the conjugation of hydrophobic ligands, which make PG as a very effective hydrophilic corona for invivo drug delivery.

Unveiling the Molecular Structure of Pulmonary Surfactant Corona on Nanoparticles.

The growing risk of human exposure to airborne nanoparticles (NPs) causes a general concern on the biosafety of nanotechnology. Inhaled NPs can deposit in the deep lung at which they interact with the pulmonary surfactant (PS). Despite the increasing study of nano-bio interactions, detailed molecular mechanisms by which inhaled NPs interact with the natural PS system remain unclear. Using coarse-grained molecular dynamics simulation, we studied the interaction between NPs and the PS system in the alveolar fluid. It was found that regardless of different physicochemical properties, upon contacting the PS, both silver and polystyrene NPs are immediately coated with a biomolecular corona that consists of both lipids and proteins. Structure and molecular conformation of the PS corona depend on the hydrophobicity of the pristine NPs. Quantitative analysis revealed that lipid composition of the corona formed on different NPs is relatively conserved and is similar to that of the bulk phase PS. However, relative abundance of the surfactant-associated proteins, SP-A, SP-B, and SP-C, is notably affected by the hydrophobicity of the NP. The PS corona provides the NPs with a physicochemical barrier against the environment, equalizes the hydrophobicity of the pristine NPs, and may enhance biorecognition of the NPs. These modifications in physicochemical properties may play a crucial role in affecting the biological identity of the NPs and hence alter their subsequent interactions with cells and other biological entities. Our results suggest that all studies of inhalation nanotoxicology or NP-based pulmonary drug delivery should consider the influence of the PS corona.

Sparse Bayesian Inference and the Temperature Structure of the Solar Corona

Abstract Measuring the temperature structure of the solar atmosphere is critical to understanding how it is heated to high temperatures. Unfortunately, the temperature of the upper atmosphere cannot be observed directly, but must be inferred from spectrally resolved observations of individual emission lines that span a wide range of temperatures. Such observations are “inverted” to determine the distribution of plasma temperatures along the line of sight. This inversion is ill posed and, in the absence of regularization, tends to produce wildly oscillatory solutions. We introduce the application of sparse Bayesian inference to the problem of inferring the temperature structure of the solar corona. Within a Bayesian framework a preference for solutions that utilize a minimum number of basis functions can be encoded into the prior and many ad hoc assumptions can be avoided. We demonstrate the efficacy of the Bayesian approach by considering a test library of 40 assumed temperature distributions.

In Situ Characterization of Protein Adsorption onto Nanoparticles by Fluorescence Correlation Spectroscopy.

Nanotechnology holds great promise for applications in many fields including biology and medicine. Unfortunately, the processes occurring at the interface between nanomaterials and living systems are exceedingly complex and not yet well understood, which has significantly hampered the realization of many nanobiotechnology applications. Whenever nanoparticles (NPs) are incorporated by a living organism, a protein adsorption layer, also known as the "protein corona", forms on the NP surface. Accordingly, living organisms interact with protein-coated rather than bare NPs, and their biological responses depend on the nature of the protein corona. In recent years, a wide variety of biophysical techniques have been employed to elucidate mechanistic aspects of NP-protein interactions. In most studies, NPs are immersed in protein or biofluid (e.g., blood serum) solutions and then separated from the liquid for analysis. Because this approach may modify the composition and structure of the protein corona, our group has pioneered the use of fluorescence correlation spectroscopy (FCS) as an in situ technique, capable of examining NP-protein interactions while the NPs are suspended in biological fluids. FCS allows us to measure, with subnanometer precision and as a function of protein concentration, the increase in hydrodynamic radius of the NPs due to protein adsorption. This Account aims at reviewing recent progress in the exploration of NP-protein interactions by using FCS. In vitro FCS studies of the adsorption of important serum proteins onto water-solubilized luminescent NPs always showed a stepwise increase of the NP radius upon protein binding in the form of a binding isotherm, regardless of the type of NP and its specific surface functionalization. This observation indicates formation of a protein monolayer on the NP. Structure-based calculations of protein surface potentials revealed that positively charged patches on the proteins interact electrostatically with negatively charged NP surfaces, and the observed protein layer thickness always matched the known molecular dimensions of the proteins binding in certain orientations. Temperature and NP surface functionalization have also been identified as important parameters controlling protein corona formation. Notably, while the corona formed from a single type of serum protein was reversible, protein adsorption from complex biological media such as blood serum was entirely irreversible. These quantitative in vitro studies are of great relevance to the bio-nano community and especially to researchers developing engineered nanomaterials for biological and biomedical applications. Future efforts will be directed toward elucidating kinetic aspects of protein corona formation and the detailed structure of the adsorbed proteins at the molecular level. To better appreciate the biological responses triggered by NP exposure, more efforts will be devoted to the exploration of the biomolecular corona as it forms on NPs in contact with living cells, tissues, and even entire model organisms. These studies are challenging when performed in a well-controlled and quantitative fashion and rely on the availability of sophisticated analytical tools, particularly, quantitative optical imaging techniques including FCS and related fluctuation methods.

THE ROLE OF MAGNETIC HELICITY IN STRUCTURING THE SOLAR CORONA

ABSTRACT Two of the most widely observed and striking features of the Sun's magnetic field are coronal loops, which are smooth and laminar, and prominences or filaments, which are strongly sheared. Loops are puzzling because they show little evidence of tangling or braiding, at least on the quiet Sun, despite the chaotic nature of the solar surface convection. Prominences are mysterious because the origin of their underlying magnetic structure—filament channels—is poorly understood at best. These two types of features would seem to be quite unrelated and wholly distinct. We argue that, on the contrary, they are inextricably linked and result from a single process: the injection of magnetic helicity into the corona by photospheric motions and the subsequent evolution of this helicity by coronal reconnection. In this paper, we present numerical simulations of the response of a Parker (1972) corona to photospheric driving motions that have varying degrees of helicity preference. We obtain four main conclusions: (1) in agreement with the helicity condensation model of Antiochos (2013), the inverse cascade of helicity by magnetic reconnection in the corona results in the formation of filament channels localized about polarity inversion lines; (2) this same process removes most complex fine structure from the rest of the corona, resulting in smooth and laminar coronal loops; (3) the amount of remnant tangling in coronal loops is inversely dependent on the net helicity injected by the driving motions; and (4) the structure of the solar corona depends only on the helicity preference of the driving motions and not on their detailed time dependence. We discuss the implications of our results for high-resolution observations of the corona.

Shape parameters of the solar corona from 1991 to 2016

The global structure of the solar corona observed in the optical window is governed by the global magnetic field with different characteristics over a solar activity cycle. The Ludendorff flattening index has become a popular measure of global structure of the solar corona as observed during an eclipse. In this study, 15 digital images of the solar corona from 1991 to 2016 were analyzed in order to construct coronal flattening profiles as a function of radius. In most cases, the profile can be modeled with a 2nd order polynomial function so that the radius with maximum flattening index (Rmax) can be determined. Along with this value, Ludendorff index (a + b) was also calculated. Both Ludendorff index and Rmax show anti-correlation with monthly sunspot number, though the Rmax values are more scattered. The variation in Rmax can be regarded as the impact of the changing coronal brightness profile over the equator.

Time-dependent tomographic reconstruction of the solar corona

Solar rotational tomography (SRT) applied to white-light coronal images observed at multiple aspect angles has been the preferred approach for determining the three-dimensional (3D) electron density structure of the solar corona. However, it is seriously hampered by the restrictive assumption that the corona is time-invariant which introduces significant errors in the reconstruction. We first explore several methods to mitigate the temporal variation of the corona by decoupling the "fast-varying" inner corona from the "slow-moving" outer corona using multiple masking (either by juxtaposition or recursive combination) and radial weighting. Weighting with a radial exponential profile provides some improvement over a classical reconstruction but only beyond 3 Rsun. We next consider a full time-dependent tomographic reconstruction involving spatio-temporal regularization and further introduce a co-rotating regularization aimed at preventing concentration of reconstructed density in the plane of the sky. Crucial to testing our procedure and properly tuning the regularization parameters is the introduction of a time-dependent MHD model of the corona based on observed magnetograms to build a time-series of synthetic images of the corona. Our procedure, which successfully reproduces the time-varying model corona, is finally applied to a set of of 53 LASCO-C2 pB images roughly evenly spaced in time from 15 to 29 March 2009. Our procedure paves the way to a time-dependent tomographic reconstruction of the coronal electron density to the whole set of LASCO-C2 images presently spanning 20 years.