Theory Of Acceleration Research Articles

Plasma Dynamics and Nonthermal Particle Acceleration in 3D Nonrelativistic Magnetic Reconnection

Understanding plasma dynamics and nonthermal particle acceleration in 3D magnetic reconnection has been a long-standing challenge. In this paper, we explore these problems by performing large-scale fully kinetic simulations of multi-X-line plasmoid reconnection with various parameters in both the weak- and strong-guide-field regimes. In each regime, we have identified its unique 3D dynamics that lead to field-line chaos and efficient acceleration, and we have achieved nonthermal acceleration of both electrons and protons into power-law spectra. The spectral indices agree well with a simple Fermi acceleration theory that includes guide-field dependence. In the low-guide-field regime, the flux rope kink instability governs the 3D dynamics for efficient acceleration. The weak dependence of the spectra on the ion-to-electron mass ratio and β (≪1) implies that the particles are sufficiently magnetized for Fermi acceleration in our simulations. While both electrons and protons are injected at reconnection exhausts, protons are primarily injected by perpendicular electric fields through Fermi reflections and electrons are injected by a combination of perpendicular and parallel electric fields. The magnetic power spectra agree with in situ magnetotail observations, and the spectral index may reflect a reconnection-driven size distribution of plasmoids instead of the Goldreich–Sridhar vortex cascade. As the guide field becomes stronger, the oblique flux ropes of large sizes capture the main 3D dynamics for efficient acceleration. Intriguingly, the oblique flux ropes can also experience flux rope kink instability, to drive extra 3D dynamics. This work has broad implications for 3D reconnection dynamics and particle acceleration in heliophysics and astrophysics.

Integrating sheath and radiation-based acceleration using scaling coefficients for tailoring radiation dominant hybrid acceleration.

An optimal target condition for generating GeV-energy ions with linearly polarized laser pulse is revealed by a hybrid acceleration theory based on the fractional contributions of the target normal sheath acceleration (TNSA) and the radiation pressure acceleration (RPA) mechanisms in the RPA-dominant regime. The theory is established with two scaling coefficients, which scale the TNSA and RPA velocities, and are sophisticated through two-dimensional particle-in-cell simulations where GeV-energy ions are obtained by RPA-dominant hybrid acceleration. By imposing limits on the scaling coefficients, three separate acceleration regions are obtained including a RPA-dominant acceleration region, which is optimal to generate GeV-energy ions. The past experiment/simulation results are in good agreement with the acceleration regions obtained. This RPA-dominant region is narrower than previously reported, and this region becomes even narrower with increasing material density.

Spectral cleaving in solar type II radio bursts: Observations and interpretation

Context. Shock waves in the solar corona are associated with solar flares and coronal mass ejections (CMEs). Type II solar bursts are radio signatures of shock waves in the solar corona. They are driven by solar flares or CMEs. Despite extensive studies, the intricate spectral patterns observed in type II solar bursts occasionally pose new challenges for the theory of electron acceleration in shocks. Aims. We study a newly identified feature in type II solar bursts called spectral cleaving. This feature is characterized by the actual branching of a type II radio emission lane in radio spectral data. Methods. We analyzed the type II burst exhibiting spectral cleaving in high-fidelity dynamic spectra obtained using the URAN-2 radio telescope (8.25–33 MHz; Poltava region, Ukraine) on 2011 February 14. The high-resolution spectrograms were examined to ascertain its spectral morphology. Results. Our research represents the first recognition of spectral cleaving as a peculiarity of type II bursts that is yet to be classified. This effect occurs due to the shift (or migration) of radio source(s) along a shock front, which in turn is caused by changes in the magnetic field orientation ahead of the propagating shock front. Conclusions. The spectral cleaving observed in solar type II bursts reveals a distinct phenomenon that indicates complex interactions between shock waves and magnetic fields in the solar corona. This discovery enhances our understanding of the mechanisms behind solar radio emissions and emphasizes the need for further observational studies to verify these findings.

Flat Spectra of Energetic Particles in Interplanetary Shock Precursors

The observed energy spectra of accelerated particles at interplanetary shocks often do not match the diffusive shock acceleration (DSA) theory predictions. In some cases, the particle flux forms a plateau over a wide range of energies, extending upstream of the shock for up to seven flux e-folds before submerging into the background spectrum. Remarkably, at and downstream of the shock we have studied in detail, the flux falls off in energy as ϵ −1, consistent with the DSA prediction for a strong shock. The upstream plateau suggests a particle transport mechanism different from those traditionally employed in DSA models. We show that a standard (linear) DSA solution based on a widely accepted diffusive particle transport with an underlying resonant wave–particle interaction is inconsistent with the plateau in the particle flux. To resolve this contradiction, we modify the DSA theory in two ways. First, we include a dependence of the particle diffusivity κ on the particle flux F (nonlinear particle transport). Second, we invoke short-scale magnetic perturbations that are self-consistently generated by, but not resonant with, accelerated particles. They lead to the particle diffusivity increasing with the particle energy as ∝ϵ 3/2 that simultaneously decreases with the particle flux as 1/F. The combination of these two trends results in the flat spectrum upstream. We speculate that nonmonotonic spatial variations of the upstream spectrum, apart from being time-dependent, may also result from non-DSA acceleration mechanisms at work upstream, such as stochastic Fermi or magnetic pumping acceleration.

A race against time: A critical analysis of elite student-athletes’ accelerated temporality through story completion

Numerous elite student-athletes (ESA) engaged in a dual career, balancing athletic pursuits with education, find themselves grappling with the perception of insufficient time to fulfil their demands. Existing research advocates for the implementation of programs promoting academic flexibility, alongside measures aimed at achieving balance between academic and sport-related activities. Other studies underscore the significance of equipping ESA with skills such as time management. Nonetheless, challenges persist in balancing the escalating demands of sports and education. Drawing upon Hartmut Rosa's theory of social acceleration, this study aims to analyse how ESA perceive and respond to time pressure. Employing the story completion method, data was gathered from seven ESA who crafted narratives in response to three story stems. Through reflexive thematic analysis, two overarching themes were identified: (1) no time to waste; and (2) it is what it is. ESA faced incessant pressure to optimise their time and performance and resorted to instrumentalising personal relationships, using them as a tool for career development. Nevertheless, this pressure was not universally perceived as oppressive; rather, it was often accepted as an inherent aspect of their reality. Our conclusion is that as long as capitalist societies and their accelerating impositions persist, any assistance that can be provided to ESA will inherently be limited.

Effect of lay theory of climate change on coping strategies: Stability and variability of information-induced results

Individuals' explanations for the cause of global climate change are based on their life experiences and acquired climate knowledge, namely the lay theories of climate change by this study. This explanation could related with their coping on climate change, but previous research has paid less attention to this issue. Study 1 conducted two national surveys (1a: n = 978, 1b: n = 933) to explore Chinese people’s lay theories of climate change and their relationship to coping strategies. In Study 2, three sub-studies were conducted to investigate the variability of lay theories of climate change and its impact on coping strategies, respectively, using the priming experiment (2a: n = 150) and the daily experience method (2b: n = 76, 2c: n = 138). The results suggest that lay theories of climate change can be divided into natural cycle theory and human-made acceleration theory. Human-made acceleration theory positively predicts problem- and meaning-focused coping strategies, and negatively predicts emotion-focused coping strategies. Participants' lay theories of climate change, while stable, are subject to change, which in turn affects their coping strategies. It is harder to get participants to switch to natural cycle theory than to human-made acceleration theory. This study puts forward the viewpoint of lay theories of climate change, which enriches the research on coping strategies of climate change.

Introducing Point-of-Care PCR technology in general practice: Ambiguities, experiences, and perceptions among health care professionals.

In this paper we present findings from a qualitative ethnographic study investigating the experiences and perceptions of general practitioners and other practice staff when introducing a new point of care diagnostic test technology (point of care polymerase chain reaction (POC PCR)) in general practice in Denmark. The ethnographic study was conducted in five general practice clinics, involving observations in four of the clinics and interviews with general practitioners and practice staff in all five clinics. Following an initial analytic phase in which barriers and facilitators in the implementation process of the Point-of-Care test were identified, we developed theoretically informed themes, drawing upon Hartmut Rosa's social theory of technological acceleration. These themes included ambiguous experiences and perceptions of: (i) diagnostic specification and inflation embedded in diagnostic practices; (ii) empowerment and erosion of professional judgment; (iii) strategies of security and insecurity in communication; (iv) the interdependence between professional autonomy and economic structures associated with organizational power; and (v) subjective and organizational time. We discuss how diagnostic technologies simultaneously contribute to and disrupt treatment safety, efficiency, and medical decision-making. Using Rosa's sociological concepts of alienation and resonance, this article furthermore explores how these ambiguous dynamics are experienced in general practice settings. It also examines the implications of navigating a heterogeneous socio-technical and medical landscape and what it means to be a health professional in a contemporary general practice environment that is increasingly shaped by diagnostic technologies.

In biased and soft-walled channels: Insights into transport phenomena and damped modulation.

The motion of a particle along a channel of finite width is known to be affected by either the presence of energy barriers or changes in the bias forces along the channel direction. By using the lateral equilibrium hypothesis, we have successfully derived the effective diffusion coefficient for soft-walled channels, and the diffusion is found to be influenced by the curvature profile of the potential. A typical phenomenon of diffusion enhancement is observed under the appropriate parameter conditions. We first discovered an anomalous phenomenon of quasi-periodic enhancement of oscillations, which cannot be captured by the one-dimensional effective potential, under the combination of sub-Ohmic damping with two-dimensional restricted channels. We innovatively develop the effective potential and the formation mechanism of velocity variance under super-Ohmic and ballistic damping, and meanwhile, ergodicity is of concern. The theoretical framework of a ballistic system can be reinterpreted through the folding acceleration theory. This comprehensive analysis significantly enhances our understanding of diffusion processes in constrained geometries.

Socialized into depression – toward a social phenomenological psychopathology

ABSTRACT The article aims at expanding the horizon of phenomenological psychopathology of depression from a social theoretical perspective. Based on Merleau-Ponty’s phenomenological ontology, in the first section, depression is reinterpreted as a disruption of chiasm: it is not merely the illness of the body, the disorder of the mind, or a specific form of social suffering, but the interrelated distortion of time consciousness, agency, and interaffectivity. The phenomenological clarification of these components provides opportunity for connecting sociological and psychopathological insight. In the second part, contemporary critical theories of acceleration, globalization, biopolitics, and system colonization are reinterpreted to highlight the structural and cultural context of late modern time consciousness, agency, and interaffectivity. In the third section, it is analyzed, how these social constituents shape the space of contemporary socialization processes, including the emergence of those intersubjective distortions, which potentially affect the entirety of chiasm in a depressive way. In the final section, the conclusions for therapy are explored, including the potentials for expanding the epistemological, substantive, and emancipatory horizon of phenomenological psychopathology.

Magnesium ion corrosion in subsea tunnel grouting: Insights, mechanisms, and optimization strategies for enhanced durability

In the construction of subsea tunnels, grouting reinforcement is crucial for enhancing tunnel strength, impermeability, and stability. This article investigates the impact of prolonged exposure to seawater, specifically magnesium ion corrosion, on the degradation of the C-S-H gel and the weakening of grouting compounds. Utilizing erosion acceleration theory, an experimental setup simulating seawater flow is designed to explore erosion patterns and mechanisms. Macroscopic and microscopic experiments and analyses reveal that magnesium ion corrosion products, Mg(OH)2 and M-S-H, lack cementation ability, leading to detachment from the grouting compound. This detachment results in increased porosity, crack formation, and reduced strength and impermeability. The study recommends reducing the water–cement ratio and increasing grouting pressure to enhance composite strength and impermeability, with attention to boundary effects and prevention of magnesium ion corrosion product shedding. These findings have significant implications for optimizing subsea tunnel construction by improving grouting reinforcement design and ensuring long-term durability.

Intermittency and Dissipative Structures Arising from Relativistic Magnetized Turbulence

Kinetic simulations of relativistic turbulence have significantly advanced our understanding of turbulent particle acceleration. Recent progress has highlighted the need for an updated acceleration theory that can account for particle acceleration within the plasma’s coherent structures. Here, we investigate how intermittency modeling connects statistical fluctuations in turbulence to regions of high-energy dissipation. This connection is established by employing a generalized She–Leveque model to characterize the exponents ζ p for the structure functions Sp∝lζp . The fitting of the scaling exponents provides us with a measure of the codimension of the dissipative structures, for which we subsequently determine the filling fraction. We perform our analysis for a range of magnetizations σ and relative fluctuation amplitudes δ B 0/B 0. We find that increasing values of σ and δ B 0/B 0 allow the turbulent cascade to break sheetlike structures into smaller regions of dissipation that resemble chains of flux ropes. However, as their dissipation measure increases, the dissipative regions become less volume filling. With this work, we aim to inform future turbulent acceleration theories that incorporate particle energization from interactions with coherent structures within relativistic turbulence.

Electron Acceleration at Earth's Bow Shock Due to Stochastic Shock Drift Acceleration

AbstractWe use the Magnetospheric Multiscale mission (MMS) to study electron acceleration at Earth's quasi‐perpendicular bow shock to address the long‐standing electron injection problem. The observations are compared to the predictions of the stochastic shock drift acceleration (SSDA) theory. Recent studies based on SSDA predict electron distribution being a power law with a cutoff energy that scales with upstream parameters. This scaling law has been successfully tested for a single Earth's bow shock crossing by MMS. Here we extend this study and test the prediction of the scaling law for seven MMS Earth's bow shock crossings with different upstream parameters. A goodness‐of‐fit test shows good agreement between observations and SSDA theoretical predictions, thus supporting SSDA as one of the most promising candidates for solving the electron injection problem.

Deep learning approaches for modeling laser-driven proton beams via phase-stable acceleration

Deep learning (DL) has recently become a powerful tool for optimizing parameters and predicting phenomena to boost laser-driven ion acceleration. We developed a neural network surrogate model using an ensemble of 355 one-dimensional particle-in-cell simulations to validate the theory of phase-stable acceleration (PSA) driven by a circularly polarized laser driver. Our DL predictions confirm the PSA theory and reveal a discrepancy in the required target density for stable ion acceleration at larger target thicknesses. We discuss the physical reasons behind this density underestimation based on our DL insights.

Improved modelling of SEP event onset within the WSA–Enlil–SEPMOD framework

Multi-spacecraft observations of solar energetic particle (SEP) events not only enable a deeper understanding and development of particle acceleration and transport theories but also provide important constraints for model validation efforts. However, because of computational limitations, a given physics-based SEP model is usually best suited to capture a particular phase of an SEP event, rather than its whole development from onset through decay. For example, magnetohydrodynamic (MHD) models of the heliosphere often incorporate solar transients only at the outer boundary of their so-called coronal domain – usually set at a heliocentric distance of 20–30 R⊙. This means that particle acceleration at coronal mass ejection (CME)-driven shocks is also computed from this boundary onwards, leading to simulated SEP event onsets that can be many hours later than observed, since shock waves can form much lower in the solar corona. In this work, we aim to improve the modelled onset of SEP events by inserting a “fixed source” of particle injection at the outer boundary of the coronal domain of the coupled WSA–Enlil 3D MHD model of the heliosphere. The SEP model that we employ for this effort is Solar Energetic Particle MODel (SEPMOD), a physics-based test-particle code based on a field line tracer and adiabatic invariant conservation. We apply our initial tests and results of SEPMOD’s fixed-source option to the 2021 October 9 SEP event, which was detected at five well-separated locations in the inner heliosphere – Parker Solar Probe, STEREO-A, Solar Orbiter, BepiColombo, and near-Earth spacecraft.

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Phenomenologies of ‘social acceleration’: some consequences and opportunities for education studies in an unknown future

ABSTRACTSocial acceleration, the rapidly increasing speeding up of the pace of life, has been described and theorised by contemporary social theorists including Paul Virilio, Ben Agger, Thomas Hylland Eriksen, and Hartmut Rosa. While these theorists use illustrations from education, and others such as Foucault and Adam have considered the relationship between education and time, there has been little theorisation of dromology (a term Virilio coined to describe the ‘science’ of speed) in education studies itself. Given its growing importance as a ‘grand theory’ in social science, this paper calls for educationalists to recognise the value of theories of social acceleration to gain a better understanding of contemporary educational practices and how the COVID-19 pandemic is illustrative of this.

Analyses of ∼0.05–2 MeV Ions Associated with the 2022 February 16 Energetic Storm Particle Event Observed by Parker Solar Probe

We present analyses of 0.05–2 MeV ions from the 2022 February 16 energetic storm particle event observed by Parker Solar Probe's (PSP) IS⊙IS/EPI-Lo instrument at 0.35 au from the Sun. This event was characterized by an enhancement in ion fluxes from a quiet background, increasing gradually with time with a nearly flat spectrum, rising sharply near the arrival of the coronal mass ejection (CME)–driven shock, becoming nearly a power-law spectrum, then decaying exponentially afterward, with a rate that was independent of energy. From the observed fluxes, we determine diffusion coefficients, finding that far upstream of the shock the diffusion coefficients are nearly independent of energy, with a value of 1020 cm2 s−1. Near the shock, the diffusion coefficients are more than 1 order of magnitude smaller and increase nearly linearly with energy. We also determine the source of energetic particles, by comparing ratios of the intensities at the shock to estimates of the quiet-time intensity to predictions from diffusive shock acceleration theory. We conclude that the source of energetic ions is mostly the solar wind for this event. We also present potential interpretations of the near-exponential decay of the intensity behind the shock. One possibility we suggest is that the shock was overexpanding when it crossed PSP and the energetic particle intensity decreased behind the shock to fill the expanding volume. Overexpanding CMEs could well be more common closer to the Sun, and this is an example of such a case.

A Review on Durability Analysis of FRP Bars based on Different Factors in Alkaline Environment

The primary issue with concrete structures is steel bar corrosion. Therefore, FRP (Fiber Reinforced Polymer) bars are often to substitute steel bars to tackle the issue of concrete swelling and cracking brought about by steel corrosion. FRP bars feature improved corrosion resistance, a stronger strength-to-quality ratio, and better fatigue resistance. However, the alkaline environment will affect the long-term strength and durability of FRP, according to certain research, which will cause the FRP bars mechanical characteristics to deteriorate. In this paper, the properties of FRP bars under alkaline conditions are reviewed, considering the harsh external environment and physical properties of FRP bars. Comprehensive investigation concludes that lowering the PH value of concrete and changing the kind of fiber material may considerably increase the endurance of FRP in alkaline environments. By demonstrating the microscopic breakdown process of FRP bars in an alkaline conditions using scanning electron microscopy. The Arrhenius acceleration theory was used to construct the present model for forecasting the long-term mechanical behavior of FRP bars, which shows how this material degrades under alkaline circumstances. This study may be utilized as a reference for FRP bars used in alkaline environments in terms of durability studies.

Analysis of Verilog-based improvements to the memory transfer

Memory copy technology is widely used for data transfer between CPU and memory, and is an important step in all types of operating systems and drivers, and is one of the bottlenecks in the current speed-up of computing. This paper has done more research on the historical development, theoretical basis and experimental details of different memory copy accelerators and related knowledge, and summarised and compared them, with emphasis on reviewing two related papers that provide an overview of their acceleration theory and experiments. The paper concludes that memory copy accelerators using a variety of innovative technologies have largely improved copy speeds and reduced energy consumption, laying a solid foundation for the future development of memory copy acceleration technology, which has been successful in improving and enhancing the user experience with the performance gains of this technology. At the same time, the development of memory copy accelerators has advanced more advanced technologies, such as machine learning, to power the development of human technology.

The Sun’s Alfvén Surface: Recent Insights and Prospects for the Polarimeter to Unify the Corona and Heliosphere (PUNCH)

The solar wind is the extension of the Sun’s hot and ionized corona, and it exists in a state of continuous expansion into interplanetary space. The radial distance at which the wind’s outflow speed exceeds the phase speed of Alfvénic and fast-mode magnetohydrodynamic (MHD) waves is called the Alfvén radius. In one-dimensional models, this is a singular point beyond which most fluctuations in the plasma and magnetic field cannot propagate back down to the Sun. In the multi-dimensional solar wind, this point can occur at different distances along an irregularly shaped “Alfvén surface.” In this article, we review the properties of this surface and discuss its importance in models of solar-wind acceleration, angular-momentum transport, MHD waves and turbulence, and the geometry of magnetically closed coronal loops. We also review the results of simulations and data-analysis techniques that aim to determine the location of the Alfvén surface. Combined with recent perihelia of Parker Solar Probe, these studies seem to indicate that the Alfvén surface spends most of its time at heliocentric distances between about 10 and 20 solar radii. It is becoming apparent that this region of the heliosphere is sufficiently turbulent that there often exist multiple (stochastic and time-dependent) crossings of the Alfvén surface along any radial ray. Thus, in many contexts, it is more appropriate to use the concept of a topologically complex “Alfvén zone” rather than one closed surface. This article also reviews how the Polarimeter to Unify the Corona and Heliosphere (PUNCH) mission will measure the properties of the Alfvén surface and provide key constraints on theories of solar-wind acceleration.