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Force-free magnetic fields can be used to compute the magnetic structure above active regions where the field strength is large. Using vector magnetograms for two active regions that gave rise to solar flares, the force-free fields are obtained for times before and after the flare. The current density in the upper atmosphere obtained from nonlinear force-free fields is analyzed using Singular Value Decomposition (SVD) methods to determine how it is distributed around the times of flare occurrence. Regions of localized and relatively intense currents are sought at the different scales since these are usually linked to magnetic reconnection. It is found that the probability distribution functions (PDF) for small scales exhibit long tails and they are compared for times before and after the flare. Previous to the flare they seem to be slightly wider but not significant enough to draw a definite conclusion. This is likely due to break down of the applicability of the Force-Free fields after the flare. The effect of having long-tailed PDFs is equivalent to the one found in temperature fluctuations about the flare occurrence (1) which could point to a correlation between electrical currents and temperature. It is also obtained that the energy content in the middle scales of the currents is larger before than after the flare which would point to a magnetic dissipation at those scales during the flare. [ABSTRACT FROM AUTHOR]

Topological data analysis (TDA) provides a set of data analysis tools for extracting embedded topological structures from complex high-dimensional datasets. In recent years, TDA has been a rapidly growing field which has found success in a wide range of applications, including signal processing, neuroscience and network analysis. In these applications, the online detection of changes is of crucial importance, but this can be highly challenging since such changes often occur in low-dimensional embeddings within high-dimensional data streams. We thus propose a new method, called PERsistence diagram-based ChangE-PoinT detection (PERCEPT), which leverages the learned topological structure from TDA to sequentially detect changes. PERCEPT follows two key steps: it first learns the embedded topology as a point cloud via persistence diagrams, then applies a nonparametric monitoring approach for detecting changes in the resulting point cloud distributions. This yields a nonparametric, topology-aware framework which can efficiently detect online geometric changes. We investigate the effectiveness of PERCEPT over existing methods in a suite of numerical experiments where the data streams have an embedded topological structure. We then demonstrate the usefulness of PERCEPT in two applications on solar flare monitoring and human gesture detection. [ABSTRACT FROM AUTHOR]

We report spin-resolved hard X-ray photoelectron spectroscopy (spin-HAXPES) for a buried Fe thin film in the valence band region. For the spin-HAXPES experiments, we developed an ultracompact built-in Mott-type spin-filter in a sample carrier, which enabled us to use the merit of two-dimensional (2D) multi-channel detector in a recent photoelectron analyser without modifying an apparatus for HAXPES. The effective Sherman function and the singlechannel figure of merit (FOM) of the spin-filter were assessed to be -0.07 and 2.0 × 10-4, respectively. By utilizing the 2D detector of the photoelectron analyser, the effective FOM increased by a factor of ~4 × 104 compared to the case when only 1 channel of the 2D detector was used. We have applied spin-HAXPES to MgO(2 nm)/Fe(50 nm)/MgO(001) structures. The spin-HAXPES experiments revealed the majority and minority spin electronic states and the spin polarisation of the buried Fe thin film. Due to the large photoionization cross-section of the 4s orbital of Fe in HAXPES, the spin-resolved spectra mainly reflected the Fe 3d and 4s states. The observed spin-HAXPES and spin polarisation spectral shapes agreed well with the calculated spin-resolved cross-section weighted densities of states and spin polarisation spectra. In contrast, a small discrepancy in the energy scale was recognised due to the electron correlation effects. These results suggest that the electron correlation effects are important in the electronic structure of bulk Fe, and spin-HAXPES is useful for detecting genuine spinresolved valence band electronic structures of buried magnetic materials. [ABSTRACT FROM AUTHOR]

Effective process monitoring of high-dimensional data streams with embedded spatial structures has been an arising challenge for environments with limited resources. Utilizing the spatial structure is key to improve monitoring performance. This article proposes a correlation-based dynamic sampling technique for change detection. Our method borrows the idea of Upper Confidence Bound algorithm and uses the correlation structure not only to calculate a global statistic, but also to infer unobserved sensors from partial observations. Simulation studies and two case studies on solar flare detection and carbon nanotubes (CNTs) buckypaper process monitoring are used to validate the effectiveness of our method. [ABSTRACT FROM AUTHOR]

In many applications of modern quality control, process monitoring involves a large number of process variables and quality characteristics. Practitioners are desired to attain complete information about the process in order to assure quick detection of shifts that may possibly occur at any variable. However, full information is not always available during online monitoring of big data streams due to limitations of monitoring resources in practice. In this paper, a rank-based monitoring and sampling algorithm based on data augmentation is proposed to quickly detect the mean shifts in a process when only a limited portion of observations are available online. Specifically, at each observation time, the proposed method will automatically augment information for unobservable variables based on the online observations, and then intelligently allocate the monitoring resources to the most suspicious data streams. Comparing to the existing literature, this method is able to accurately infer the status of all variables in a process based on a small number of observable variables and effectively construct a global monitoring statistic with the proposed augmented vector, which leads to a quick detection of the out-of-control status even if limited shifted variables are observed in real time. Simulation studies as well as a real case study on real-time solar flare detection are conducted to demonstrate the efficacy and applicability of the proposed method. [ABSTRACT FROM AUTHOR]

Flare tip is an important safety feature of most oil and gas producing and processing facilities. They are used extensively in the hydrocarbon and petrochemical industries as a system to achieve safe and reliable gas release during a plant upset or emergency situation. In this study, a detailed metallurgical investigation of failed smokeless flare tip stack drums at natural gas liquid fractionation plant was performed. Environmental scanning electron microscopy coupled with energy-dispersive X-ray microanalysis and Vicker's microhardness measurement analysis showed severe intergranular cracking damage initiated from the edge of the barrel. Formation of non-protective oxide and Ni-rich sulphide was detected along with the formation of corrosion products and scale primarily at cracks. These findings suggested that the flare tip stack drums have experienced frequent flame impingement or internal burning which promoted microstructural changes in the material and high-temperature corrosion, leading to crack initiation and growth and subsequently resulted in failure. [ABSTRACT FROM AUTHOR]

By the line ratio of Oxygen IV 1399.776.50 Å and 1401.163 Å lines in a flare ribbon in the solar transition region, the principle of the electron density diagnostics using the collisional radiative model is discussed, and the relationship of the electron density with the line ratio is obtained, for both Maxwellian and Kappa distributions. By the observed line ratio, the diagnostic result of the electron density in the flare ribbon for the Maxwellian distribution are log (N e) = 11.41 − 0.33 + 0.46 c m − 3 , 11.42 − 0.33 + 0.46 c m − 3 and 11.45 − 0.33 + 0.46 c m − 3 at the temperature of log T = 4.88 K, 5.0 K and 5.17 K, respectively, which are slightly smaller than reported 11.96 − 0.22 + 0.35 c m − 3 using the method of differential emission measure. The electron density for the Kappa distributions are log (N e) = 11.18 − 0.30 + 0.42 c m − 3 , 11.29 − 0.31 + 0.43 c m − 3 , and 11.34 − 0.32 + 0.45 c m − 3 for κ = 2, 3 and 5, respectively. With increasing κ, the electron density for the Kappa distribution will be close to that for the Maxwellian distribution. This discussion is significant in the electron density diagnostics in the solar transition region, which will be also important for diagnostics for non-Maxwellian distribution. [ABSTRACT FROM AUTHOR]

The goal of this minisymposium was to bring together, in one forum, researchers from very different areas of magnetohydrodynamics and dynamo theory who do not normally share the same stage. This special issue is a continuation of the minisymposium and collates five original research articles that span several diverse and fascinating areas of theoretical magnetohydrodynamics. This special issue sprung from the minisymposium "Recent Developments in Magnetohydrodynamics and Dynamo Theory", which formed part of the 2021 Combined British Mathematical Colloquium (BMC) and British Applied Mathematics Colloquium (BAMC) hosted online by the University of Glasgow in April 2021. [Extracted from the article]

The article focuses on the effects of space weather on the earth. Topics discussed include the 1989 solar storm stages, the unwanted electricity from solar storms, the discovery of space weather, the plan in addressing the dangers of space weather, and the observation of solar flare by the U.S. National Aeronautics and Space Administration (NASA).

Temporally and spatially dense data-rich environments provide unprecedented opportunities and challenges for effective process control. In this article, we propose a systematic and scalable adaptive sampling strategy for online high-dimensional process monitoring in the context of limited resources with only partial information available at each acquisition time. The proposed adaptive sampling strategy includes a broad range of applications: (1) when only a limited number of sensors is available; (2) when only a limited number of sensors can be in “ON” state in a fully deployed sensor network; and (3) when only partial data streams can be analyzed at the fusion center due to limited transmission and processing capabilities even though the full data streams have been acquired remotely. A monitoring scheme of using the sum of top-rlocal CUSUM statistics is developed and named as “TRAS” (top-rbased adaptive sampling), which is scalable and robust in detecting a wide range of possible mean shifts in all directions, when each data stream follows a univariate normal distribution. Two properties of this proposed method are also investigated. Case studies are performed on a hot-forming process and a real solar flare process to illustrate and evaluate the performance of the proposed method. [ABSTRACT FROM PUBLISHER]

The energy flux released into the corona is estimated from magnetic reconnection events in all spatial scales, covering down to nanoflares. The reconnection model used is based on a quasi-3D configuration that approximates the braiding of magnetic field lines which is produced by photospheric motions and includes both resistive and collisionless reconnection, depending on the event size [Martinell, J.J. Rad. Effects Defec. Solids2010, 165, 114]. This model is applied to all length scales involved in the energy release adding all them up. In order to obtain the size distribution, the observations of the Solar Dynamics Observatory (SDO) are used for two wavelengths in the far UV, together with the corresponding magnetograms and look for correlations brightness-magnetic field. Since the resolution limit of the SDO is just above the nanoflare scales, the spectral index of the energy distribution is determined and it is used to extrapolate down to nanoflare scales. An upper limit of the energy flux is obtained following two different methods, as well as an estimate for the aspect ratio of the current sheets. The energy flux estimates are in the range of which is of the order needed to maintain the hot corona. [ABSTRACT FROM AUTHOR]

Purpose: To determine the effect of dose-rate on induction of neoplastic transformation in  vitro by low doses of 232 MeV protons. Materials and methods: The experimental system used was the human hybrid cell assay. The dose-rates examined were 50 cGy/min and 20 cGy/h. The dose-rate 20 cGy/h was chosen as this is in the range of the maximum dose-rate that can be experienced in an unshielded space environment following a solar flare. At low dose-rate (LDR), doses from 0.5--100 cGy were studied. At high dose rate (HDR), the dose range was 0.5--200 cGy. Results: The data indicated no significant differences between the two dose-rates at doses up to 100 cGy. Conclusion: For the endpoint of neoplastic transformation in  vitro, high dose-rate data may be sufficient to estimate low dose-rate effects (20 cGy/h) in the dose range up to 100 cGy from 232 MeV protons. The data are of relevance to risk estimation for space travel. [ABSTRACT FROM AUTHOR]

Purpose: Astronauts on missions are exposed to low-dose/low-dose-rate (LDR) radiation and could receive high doses during solar particle events (SPE). This study investigated T cell function in response to LDR radiation and simulated SPE (sSPE) protons, alone and in combination. Materials and methods: C57BL/6 mice received LDR γ-radiation (57Co) to a total dose of 0.01 Gray (Gy) at 0.179 mGy/h, either with or without subsequent exposure to 1.7 Gy sSPE protons delivered over 36 h. Mice were euthanised on days 4 and 21 post-exposure. T cells with cluster of differentiation 4 (CD4+) were negatively isolated from spleens and activated with anti-CD3 antibody. Cells and supernatants were evaluated for survival/signalling proteins and cytokines. Results: The most striking effects were noted on day 21. In the survival pathway, nuclear factor-kappaB (NF-κB; total and active forms) and p38 mitogen activated protein kinase (p38MAPK; total) were significantly increased and cJun N-terminal kinase (JNK; total and active) was decreased when mice were primed with LDR γ-rays prior to sSPE exposure ( P < 0.001). Evaluation of the T cell antigen receptor (TCR) signalling pathway revealed that LDR γ-ray exposure normalised the high sSPE proton-induced level of lymphocyte specific protein tyrosine kinase (Lck; total and active) on day 21 ( P < 0.001 for sSPE vs. LDR + sSPE), while radiation had no effect on active zeta-chain-associated protein kinase 70 (Zap-70). There was increased production of interleukin-2 (IL-2) and IL-4 and decreased transforming growth factor-β1 in the LDR + sSPE group compared to the sSPE group. Conclusion: The data demonstrate, for the first time, that protracted exposure to LDR γ-rays can significantly modify the effects of sSPE protons on critical survival/signalling proteins and immunomodulatory cytokines produced by CD4+ T cells. [ABSTRACT FROM AUTHOR]

Nigeria has recorded a long history of petroleum exploration, but gas flaring associated with this activity is contributing immensely to air pollution in the Niger-Delta area and beyond. Hence, this work is aimed at quantifying the extent of air pollution from gas flaring, i.e., CO2, CO, SO2, NO2, and THC. Volume of gas flare and conditions of flare as well as experimental data on concentration were collated. The dispersion model based on the principle of Gaussian distribution was developed. The simulated results of the dispersion model shows the dispersion pattern of pollutants from gas flaring, and the effect of changes in the volume of gas flared, stack efficiency, wind speed, and atmospheric stability on the concentrations of pollutants from gas flaring were investigated. It was observed that the simulated result is in good agreement with dispersion pattern and that continuous gas flaring irrespective of the quantity will, in the long run, lead to change in the quality of the physical atmosphere. [ABSTRACT FROM AUTHOR]

We address an important inverse problem in solar plasma physics by means of an 'ad hoc' implementation of the Tikhonov regularization method. Our approach is validated in the case of different modifications of the mathematical model of the problem based on physical motivations, and for data sets obtained with synthetic experiments. Finally, an application to a real observation recorded by the NASA mission 'Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI)' is considered. [ABSTRACT FROM AUTHOR]

We investigate the motion of a charged particle in the process of acceleration up to relativistic energies in a superhot turbulent current layer with three components of the magnetic field. We solve analytically the relativistic equation of motion that has been averaged over the particle gyration in the magnetic field. The obtained results are compared with numerical solution of the ordinary (without averaging) equation of motion. The analytical solution describes a stable motion, i.e. when a particle remains in the reconnecting current layer until it reaches its edges. The stability conditions are found imposed on the electric and magnetic fields in the layer. Particles with positive and negative charges have different behaviours. The numerical solution has confirmed the conclusions of the analytical approach. Applications to solar flares are discussed. [ABSTRACT FROM AUTHOR]

The problem of energy transport by magnetohydrodynamic (MHD) solitons to the local region of a solar flare is considered within the framework of a new concept on the nature of solar flares as an effect of the unloading of matter and energy under self-organized criticality. The high-resolution observations (±1?) by the TRACE spacecraft are used. The characteristics of the small-scale discrete flare elements are shown to correspond to the properties of MHD solitons. Therefore, the above-mentioned concept represents conclusive evidence of the fractal-cluster structure of the solar magnetized plasma. [ABSTRACT FROM AUTHOR]

We present a method of chromospheric flux simulation for 13 late-type main-sequence stars. These Sun-like stars have well-determined cyclic flux variations similar to an 11 year solar activity cycle. Our flux prediction is based on chromospheric HK emission time series measurements from Mount Wilson Observatory and comparable solar data. We show that solar three-component modelling explains the stellar observations well. We find that 5–10% of the disc surfaces of K stars are occupied by bright active regions. [ABSTRACT FROM AUTHOR]

The dynamic properties of solar flares are considered on the basis of the spectral observations of soft X-rays of more than 180 flares obtained during the last two decades. The random non-thermal velocities are in the range from 60 to 580 km s[SUP-1] but mainly change from 110 to 190 km s[SUP-1]. The mean value of the x calculated for flares being mainly of C1-M5 X-ray classes are equal to 160.8 4.7 km s[SUP-1]. The directed velocities in flares are from several dozen to several hundred kilometres per second. The relationships between x and other flare characteristics are discussed. Investigations of flare dynamics help us to understand the nature of energy transport in them. [ABSTRACT FROM AUTHOR]

Postflare loops, which fill by hot plasma from chromospheric sources, are numerically simulated. The PERESVET code is used to solve the system of resistive magnetohydrodynamic equations. The possible mechanisms of plasma heating in the loop are discussed. It is shown that plasma heating can be produced by magnetic line reconnection. The stable plasma confinement in the arch magnetic field of the solar corona is determined by field-aligned current generation. [ABSTRACT FROM AUTHOR]

The oblique interaction of the solar chromospheric rotational or Alfven discontinuity with the transition region, described as a contact discontinuity, is studied. The appearance of the refracted magnetohydrodynamic shock wave going through the solar corona is shown. This wave makes the dissipation of the magnetic field energy inside the coronal plasma possible and may cause explosive events. [ABSTRACT FROM AUTHOR]

Focuses on internal energy spectra of solar soft X-ray flares in the three solar activity cycles. Temporal variations in the power-law spectrum of X-ray flares over three solar cycles; Parameters of the energy spectrum; Quantitative analysis of limiting energy of flares.

Investigates the modelling of long duration x-ray flares on late-type subgiant stars. Examination of thermal conduction and radiative losses during plasma heating; Explanation of duration of soft x-ray flare radiation; Discussion of the peculiar features of the temporal behavior of temperature.

Investigates the spatial anisotropy of flares relative to sunspot groups and vector butterfly diagrams in solar activity cycles numbers 17 to 19 and 23. Revelation of global anisotropy of the flare process; Construction of vector diagrams; Interpretation of the opposite shifts of flares.

Investigates the evolution and forecast of flare activity in the solar cycle 23. Presentation of the effective method for the prediction of the solar cycle; Explanation of the method to predict geoeffective solar flare events; Prediction of the period of flare energy release.

Investigates the generalized concept of flares on late-type stars. Description of the different kind of stellar flares; Effect of impulsive heating on outer atmosphere of the star; Comprehension of the origin of x-ray and optical flare.

Presents the He I 10830 Armstrong data of observations of the flare that occurred on July 9, 1996. Achievement of images of the active region at the Crimean Astrophysical Observatory at the BST-2 telescope; Implication of the presence of long-lived emission kernels and extended loop structures.

Analyzes the stability of the turbulent current sheet of a flare. Instability of the equilibrium state of the current sheet; Inclusion of clusters of bad turbulent low conductive domains and good normal ones in the final state of the flare current sheet.

Reports on the use of data on location of flares covering solar cycles 17-20 to construct vector diagrams for the mean position of the flare scattering center in the coordinate system of the sunspot center. Exhibition of a westward displacement by the high-latitude sunspots; Interpretation of results in terms of a global-scale excitation of flares by wave-lie disturbances.

Examines the Fe I and Fe II line emissions in solar flare models. Origination of Fe I and Fe II lines from the coronal photosphere; Comparison between theoretical and observed profiles for Fe I and Fe II line agreement; Description of the derived models.

Examines the behavior of a long-lived extended filament in active region NOAA 5669 with a complex magnetic structure. Relation between filament behavior and flare activity; Behavior of filament during the generation of the flare; Factors of triggered separations and eruptions of superficial layers.

The article offers information on the impact of violent solar activity over earth's upper atmosphere as well as impact of snowstorms over health. Topics discussed include role played by solar flares and coronal mass ejections (CMEs) in bring electrically charged plasma blasting toward the earth; increase in the chances of cardiovascular diseases by snowstorms; and information on energy-efficient supercomputers.

Reports on a study on space weather conducted by researchers at the Johns Hopkins University's Applied Physics Laboratory in Baltimore, Maryland. Data used in predicting future electromagnetic solar storms; Effects of solar storm on Earth; Application of the Iridium satellite constellation.

Reports on a major geomagnetic storm called flare that occurred on the sun on April 6 and 7, 2000. Origin of the flare; Power of the flare; Potential causes of future flares.

Compares the energy distribution between solar and ultraviolet ceti stellar flares. Increase of solar flare energy spectrum in the epoch of maximum; Correlation between solar 11-year cycle phase and cyclic variation of integral energy spectrum on the epoch of minimum; Implication of flare activity on red dwarf stars.

The article focuses on technologies and methods that can enable aviation businesses adapt to solar storms. Virgin Atlantic pilot Bryn Jones told that possible effects of solar storms on the airline industry were disruption of Global Positioning System and other electronics, as passenger airplanes are being modified with electronics in place of hydraulics. Satellites like the In-Orbit Validation Element monitor space weather and are affected by solar storms, which can be managed by shielding.

Presents information on the solar flare that occurred on November 4, 2003. Size of the solar flare according to researchers from the University of Otago in New Zealand; Classification of flares; Effect of solar flares on communication systems and power resources.