scholarly journals Excess H, Suppressed He, and the Abundances of Elements in Solar Energetic Particles

Solar Physics ◽  
2019 ◽  
Vol 294 (10) ◽  
Author(s):  
Donald V. Reames
Keyword(s):  
Shock Waves ◽  
Power Law ◽  
Solar Energetic Particle ◽  
Coronal Plasma ◽  
Charge Ratio ◽  
Element Abundance ◽  
Power Law Distribution ◽  
Element Abundances ◽  
New Information ◽  
Order Of Magnitude

Abstract Recent studies of the abundances of H and He relative to those of heavier ions in solar energetic particle (SEP) events suggest new features in the underlying physics. Impulsive SEP events, defined by uniquely large enhancements of Fe/O, emerge from magnetic reconnection in solar jets. In small, “pure,” shock-free, impulsive SEP events, protons with mass-to-charge ratio $A/Q = 1$A/Q=1 fit the power-law dependence of element abundance enhancements versus$A/Q$A/Q extrapolated from the heavier elements $6 \leq Z \leq 56$6≤Z≤56. Sometimes these events have order-of-magnitude suppressions of He, even though H fits with heavier elements, perhaps because of the slower ionization of He during a rapid rise of plasma from the chromosphere. In larger impulsive SEP events, He fits, but there are large proton excesses relative to the power-law fit of $Z > 2$Z>2 ions, probably because associated coronal mass ejections (CMEs) drive shock waves fast enough to reaccelerate the impulsive SEPs but also to sample protons from the ambient solar plasma. In contrast, gradual SEP events are accelerated by wide, fast CME-driven shock waves, but those with smaller, weaker shocks, perhaps quasi-perpendicular, favor impulsive suprathermal residue left by many previous jets, again supplemented with excess protons from ambient coronal plasma. In the larger, more common gradual SEP events, faster, stronger shock waves sample the ambient coronal plasma more deeply, overwhelming any impulsive-ion component, so that proton abundances again fit the same power-law distribution as all other elements. Thus, studies of the power-law behavior in $A/Q$A/Q of SEP element abundances give compelling new information on the varying physics of SEP acceleration and properties of the underlying corona.

scholarly journals Element Abundances of Solar Energetic Particles and the Photosphere, the Corona, and the Solar Wind

Atoms ◽  
2019 ◽  
Vol 7 (4) ◽  
pp. 104 ◽  
Author(s):  
Donald V. Reames
Keyword(s):  
Solar Wind ◽  
Shock Waves ◽  
Solar Corona ◽  
Plasma Temperature ◽  
Energetic Particles ◽  
Solar Energetic Particles ◽  
Charge Ratio ◽  
Ambient Plasma ◽  
Element Abundances ◽  
Resonant Wave

From a turbulent history, the study of the abundances of elements in solar energetic particles (SEPs) has grown into an extensive field that probes the solar corona and physical processes of SEP acceleration and transport. Underlying SEPs are the abundances of the solar corona, which differ from photospheric abundances as a function of the first ionization potentials (FIPs) of the elements. The FIP-dependence of SEPs also differs from that of the solar wind; each has a different magnetic environment, where low-FIP ions and high-FIP neutral atoms rise toward the corona. Two major sources generate SEPs: The small “impulsive” SEP events are associated with magnetic reconnection in solar jets that produce 1000-fold enhancements from H to Pb as a function of mass-to-charge ratio A/Q, and also 1000-fold enhancements in 3He/4He that are produced by resonant wave-particle interactions. In large “gradual” events, SEPs are accelerated at shock waves that are driven out from the Sun by wide, fast coronal mass ejections (CMEs). A/Q dependence of ion transport allows us to estimate Q and hence the source plasma temperature T. Weaker shock waves favor the reacceleration of suprathermal ions accumulated from earlier impulsive SEP events, along with protons from the ambient plasma. In strong shocks, the ambient plasma dominates. Ions from impulsive sources have T ≈ 3 MK; those from ambient coronal plasma have T = 1 – 2 MK. These FIP- and A/Q-dependences explore complex new interactions in the corona and in SEP sources.

scholarly journals The Evolution of Research on Abundances of Solar Energetic Particles

Universe ◽  
2021 ◽  
Vol 7 (8) ◽  
pp. 292
Author(s):  
Donald V. Reames
Keyword(s):  
Shock Waves ◽  
Power Laws ◽  
Energetic Particles ◽  
Solar Energetic Particles ◽  
Charge Ratio ◽  
Particle Interactions ◽  
Solar Cosmic Rays ◽  
Element Abundances ◽  
Resonant Wave ◽  
Field Lines

Sixty years of study of energetic particle abundances have made a major contribution to our understanding of the physics of solar energetic particles (SEPs) or solar cosmic rays. An early surprise was the observation in small SEP events of huge enhancements in the isotope 3He from resonant wave–particle interactions, and the subsequent observation of accompanying enhancements of heavy ions, later found to increase 1000-fold as a steep power of the mass-to-charge ratio A/Q, right across the elements from H to Pb. These “impulsive” SEP events have been related to magnetic reconnection on open field lines in solar jets; similar processes occur on closed loops in flares, but those SEPs are trapped and dissipate their energy in heat and light. After early controversy, it was established that particles in the large “gradual” SEP events are accelerated at shock waves driven by wide, fast coronal mass ejections (CMEs) that expand broadly. On average, gradual SEP events give us a measure of element abundances in the solar corona, which differ from those in the photosphere as a classic function of the first ionization potential (FIP) of the elements, distinguishing ions and neutrals. Departures from the average in gradual SEPs are also power laws in A/Q, and fits of this dependence can determine Q values and thus estimate source plasma temperatures. Complications arise when shock waves reaccelerate residual ions from the impulsive events, but excess protons and the extent of abundance variations help to resolve these processes. Yet, specific questions about SEP abundances remain.

scholarly journals A Semianalytic Afterglow with Thermal Electrons and Synchrotron Self-Compton Emission

2022 ◽  
Vol 924 (1) ◽  
pp. 40
Author(s):  
Donald C. Warren ◽  
Maria Dainotti ◽  
Maxim V. Barkov ◽  
Björn Ahlgren ◽  
Hirotaka Ito ◽  
...  
Keyword(s):  
Power Law ◽  
Gamma Ray ◽  
Early Time ◽  
Spectral Structure ◽  
Power Law Distribution ◽  
X Ray ◽  
Broadband Emission ◽  
Dependent Form ◽  
Order Of Magnitude ◽  
Tev Gamma Rays

Abstract We extend previous work on gamma-ray burst afterglows involving hot thermal electrons at the base of a shock-accelerated tail. Using a physically motivated electron distribution based on first-principles simulations, we compute the broadband emission from radio to TeV gamma rays. For the first time, we present the effects of a thermal distribution of electrons on synchrotron self-Compton emission. The presence of thermal electrons causes temporal and spectral structure across the entire observable afterglow, which is substantively different from models that assume a pure power-law distribution for the electrons. We show that early-time TeV emission is enhanced by more than an order of magnitude for our fiducial parameters, with a time-varying spectral index that does not occur for a pure power law of electrons. We further show that the X-ray closure relations take a very different, also time-dependent, form when thermal electrons are present; the shape traced out by the X-ray afterglows is a qualitative match to observations of the traditional decay phase.

scholarly journals Sixty Years of Element Abundance Measurements in Solar Energetic Particles

2021 ◽  
Vol 217 (6) ◽  
Author(s):  
Donald V. Reames
Keyword(s):  
Solar Corona ◽  
Magnetic Reconnection ◽  
Extreme Ultraviolet ◽  
Chemical Elements ◽  
Energetic Particles ◽  
Solar Energetic Particles ◽  
Charge Ratio ◽  
Element Abundance ◽  
Shock Acceleration ◽  
Element Abundances

AbstractSixty years ago the first observation was published showing solar energetic particles (SEPs) with a sampling of chemical elements with atomic numbers $6 \leq Z \leq 18$ 6 ≤ Z ≤ 18 above 40 MeV amu−1. Thus began study of the direct products of dynamic physics in the solar corona. As we have progressed from 4-min sounding-rocket samples to continuous satellite coverage of SEP events, we have extended the observations to the unusual distribution of element abundances throughout the periodic table. Small “impulsive” SEP events from islands of magnetic reconnection on open magnetic-field lines in solar jets generate huge enhancements in abundances of 3He and of the heaviest elements, enhancements increasing as a power of the ion mass-to-charge ratio as ($A$ A /$Q$ Q )3.6, on average. Solar flares involve the same physics but there the SEPs are trapped on closed loops, expending their energy as heat and light. The larger, energetic “gradual” SEP events are accelerated at shock waves driven by fast, wide coronal mass ejections (CMEs). However, these shocks can also reaccelerate ions from pools of residual suprathermal impulsive ions, and CMEs from jets can also drive fast shocks, complicating the picture. The underlying element abundances in SEP events represent the solar corona, which differs from corresponding abundances in the photosphere as a function of the first ionization potential (FIP) of the elements, distinguishing low-FIP (<10 eV) ions from high-FIP neutral atoms as they expand through the chromosphere. Differences in FIP patterns of SEPs and the solar wind may distinguish closed- and open-field regions of formation at the base of the corona. Dependence of SEP acceleration upon $A$ A /$Q$ Q allows best-fit estimation of ion $Q$ Q -values and hence of the source plasma temperature of ∼1 – 3 MK, derived from abundances, which correlates with recent measures of temperatures using extreme ultraviolet emission from jets. Thus, element abundances in SEPs have become a powerful tool to study the underlying solar corona and to probe physical processes of broad astrophysical significance, from the “FIP effect” to magnetic reconnection and shock acceleration. New questions arise, however, about the theoretical basis of correlations of energy-spectral indices with power-laws of abundances, about the coexistence of separate resonant and non-resonant mechanisms for enhancements of 3He and of heavy elements, about occasional events with unusual suppression of He and about the overall paucity of C in FIP comparisons.

scholarly journals Set-Min sketch: a probabilistic map for power-law distributions with application to k-mer annotation

2020 ◽  
Author(s):  
Yoshihiro Shibuya ◽  
Gregory Kucherov
Keyword(s):  
Power Law ◽  
Error Rate ◽  
Explicit Representation ◽  
The Other ◽  
Memory Usage ◽  
Power Law Distribution ◽  
Space Efficiency ◽  
Order Of Magnitude ◽  
Power Law Distributions ◽  
Probabilistic Map

Motivation: In many bioinformatics pipelines, k-mer counting is often a required step, with existing methods focusing on optimizing time or memory usage. These methods usually produce very large count tables explicitly representing k-mers themselves. Solutions avoiding explicit representation of k-mers include Minimal Perfect Hash Functions (MPHFs) or Count-Min sketches. The former is only applicable to static maps not subject to updates, while the latter suffers from potentially very large point-query errors, making it unsuitable when counters are required to be highly accurate. Results: We introduce Set-Min sketch, a sketching technique inspired by Count-Min sketch, for representing associative maps, more specifically, k-mer count tables. We show that Set-Min sketch provides a very low error rate, both in terms of the probability and the size of errors, much lower than a Count-Min sketch of similar dimensions. On the other hand, Set-Min sketches are shown to take up to an order of magnitude less space than MPHF-based solutions, especially for large values of k. Space-efficiency of Set-min takes advantage of the power-law distribution of k-mer counts in genomic datasets.

scholarly journals Gradual SEP Events

2021 ◽  
pp. 97-133
Author(s):  
Donald V. Reames
Keyword(s):  
Plasma Temperature ◽  
Solar Energetic Particle ◽  
Abundance Ratio ◽  
Element Abundance ◽  
Ion Flow ◽  
Element Abundances ◽  
Magnetically Trapped ◽  
The Face ◽  
Suprathermal Ions ◽  
Magnetic Bottle

AbstractGradual solar energetic-particle (SEP) events are “big proton events” and are usually much more “gradual” in their decay than in their onset. As their intensities increase, particles streaming away from the shock amplify Alfvén waves that scatter subsequent particles, increasing their acceleration, eventually limiting ion flow at the “streaming limit.” Waves generated by higher-speed protons running ahead can also throttle the flow of lower-energy ions, flattening spectra and altering abundances in the biggest SEP events. Thus, we find that the A/Q-dependence of scattering causes element-abundance patterns varying in space and time, which define source-plasma temperatures T, since the pattern of Q values of the ions depends upon temperature. Differences in T explain much of the variation of element abundances in gradual SEP events. In nearly 70% of gradual events, SEPs are shock-accelerated from ambient coronal plasma of ~0.8–1.6 MK, while 24% of the events involve material with T ≈ 2–4 MK re-accelerated from residual impulsive-suprathermal ions with pre-enhanced abundances. This source-plasma temperature can occasionally vary with solar longitude across the face of a shock. Non-thermal variations in ion abundances in gradual SEP events reaccelerated from the 2–4 MK impulsive source plasma are reduced, relative to those in the original impulsive SEPs, probably because the accelerating shock waves sample a pool of ions from multiple jet sources. Late in gradual events, SEPs become magnetically trapped in a reservoir behind the CME where spectra are uniform in space and decrease adiabatically in time as the magnetic bottle containing them slowly expands. Finally, we find variations of the He/O abundance ratio in the source plasma of different events.

scholarly journals On the Correlation between Energy Spectra and Element Abundances in Solar Energetic Particles

Solar Physics ◽  
2021 ◽  
Vol 296 (1) ◽  
Author(s):  
Donald V. Reames
Keyword(s):  
Shock Waves ◽  
Solar Energetic Particle ◽  
Heavy Ion ◽  
Temporal Variations ◽  
Energy Spectra ◽  
Shock Acceleration ◽  
Physical Processes ◽  
Element Abundances ◽  
New Perspective ◽  
Interesting Behavior

AbstractIn solar energetic particle (SEP) events, the physical processes of both shock acceleration and scattering during transport can cause energy-spectral indices to be correlated with enhancement or suppression of element abundances versus mass-to-charge ratios $A/Q$ A / Q . We observe correlations for those “gradual” SEP events where shock waves accelerate ions from the ambient coronal plasma, but there are no such correlations for “impulsive” SEP events produced by magnetic reconnection in solar jets, where abundance enhancement in different events vary from $(A/Q)^{+2}$ ( A / Q ) + 2 to $(A/Q)^{+8}$ ( A / Q ) + 8 , nor are there correlations when shock waves reaccelerate these residual impulsive ions. In the latter events the abundances are determined separately, prior to the accelerated spectra. Events with correlated spectra and abundances show a wide variety of interesting behavior that has not been described previously. Small and moderate gradual SEP events, with relative abundances typically depending approximately upon $(A/Q)^{-1}$ ( A / Q ) − 1 and the spectra upon energy $E^{-2.5}$ E − 2.5 , vary little with time. Large SEP events show huge temporal variations skirting the correlation line; in one case O spectra vary with time from $E^{-1}$ E − 1 to $E^{-5}$ E − 5 while abundances vary from $(A/Q)^{+1}$ ( A / Q ) + 1 to $(A/Q)^{-2}$ ( A / Q ) − 2 during the event. In very large events, streaming-limited transport through proton-generated resonant Alfvén waves flattens the spectra and enhances heavy ion abundances prior to local shock passage, then steepens the spectra and reduces enhancements afterward, recapturing the typical correlation. Systematic correlation of spectra and element abundances provide a new perspective on the “injection problem” of ion selection by shocks and on the physics of SEP acceleration and transport.

scholarly journals X-ray Radiation from Flare-heated Coronal Plasma

2000 ◽  
Vol 195 ◽  
pp. 395-396
Author(s):  
M. Güdel
Keyword(s):  
Power Law ◽  
Coronal Loop ◽  
Emission Measure ◽  
Magnetic Loop ◽  
Coronal Plasma ◽  
Power Law Distribution ◽  
Temperature Dependent ◽  
X Ray

We investigate the reaction of a coronal loop in the case of repetitive flares, with a power-law distribution in energy, injected into a rigid magnetic loop. Emission measure distributions and temperature-dependent modulations of the radiation are briefly discussed.

scholarly journals The structure of co-publications multilayer network

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Ghislain Romaric Meleu ◽  
Paulin Yonta Melatagia
Keyword(s):  
Power Law ◽  
Degree Distribution ◽  
Preferential Attachment ◽  
Small World ◽  
Generation Model ◽  
Small World Network ◽  
Power Law Distribution ◽  
Multilayer Networks ◽  
Multilayer Network ◽  
Scientific Papers

AbstractUsing the headers of scientific papers, we have built multilayer networks of entities involved in research namely: authors, laboratories, and institutions. We have analyzed some properties of such networks built from data extracted from the HAL archives and found that the network at each layer is a small-world network with power law distribution. In order to simulate such co-publication network, we propose a multilayer network generation model based on the formation of cliques at each layer and the affiliation of each new node to the higher layers. The clique is built from new and existing nodes selected using preferential attachment. We also show that, the degree distribution of generated layers follows a power law. From the simulations of our model, we show that the generated multilayer networks reproduce the studied properties of co-publication networks.

scholarly journals Power-law behavior of transcription factor dynamics at the single-molecule level implies a continuum affinity model

2021 ◽  
Author(s):  
David A Garcia ◽  
Gregory Fettweis ◽  
Diego M Presman ◽  
Ville Paakinaho ◽  
Christopher Jarzynski ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Single Molecule ◽  
Power Law ◽  
Dwell Time ◽  
Specific Binding ◽  
Power Law Distribution ◽  
Single Molecule Level ◽  
Binding Behavior ◽  
Chromatin Template ◽  
Nuclear Domains

Abstract Single-molecule tracking (SMT) allows the study of transcription factor (TF) dynamics in the nucleus, giving important information regarding the diffusion and binding behavior of these proteins in the nuclear environment. Dwell time distributions obtained by SMT for most TFs appear to follow bi-exponential behavior. This has been ascribed to two discrete populations of TFs—one non-specifically bound to chromatin and another specifically bound to target sites, as implied by decades of biochemical studies. However, emerging studies suggest alternate models for dwell-time distributions, indicating the existence of more than two populations of TFs (multi-exponential distribution), or even the absence of discrete states altogether (power-law distribution). Here, we present an analytical pipeline to evaluate which model best explains SMT data. We find that a broad spectrum of TFs (including glucocorticoid receptor, oestrogen receptor, FOXA1, CTCF) follow a power-law distribution of dwell-times, blurring the temporal line between non-specific and specific binding, suggesting that productive binding may involve longer binding events than previously believed. From these observations, we propose a continuum of affinities model to explain TF dynamics, that is consistent with complex interactions of TFs with multiple nuclear domains as well as binding and searching on the chromatin template.

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