Shock Waves

In this study, the Landau and cyclotron growth rates of whistler mode waves in earth's bow shock are calculated by using electron distribution functions obtained with the fast plasma experiment on ISEE 2. Three electron distribution functions measured within the transition region of the shock are analyzed. An important feature of these electron distribution functions is the presence of a field‐aligned beam with a T⊥ > T∥ anisotropy. The beam velocity vector is directed toward the magnetosheath. The calculations show that the electron distribution functions spontaneously generate whistler mode waves with plasma rest frame frequencies between about 0.1 and 100 Hz. The wave normal angles of the generated whistlers range from 0° to the resonance cone angle. Electromagnetic Landau resonance and/or cyclotron resonance contribute to wave growth over the range of velocity distributions observed. The waves that are generated by the normal cyclotron resonance have wave vectors directed...

Homogeneous second-order Aw-Rascle-type models have demonstrated greater effectiveness than their non-homogeneous counterparts in traffic flow modeling. This study addresses the numerical solution of hyperbolic conservation laws governing these models by coupling the second-order HLLE Riemann solver, a Godunov-type finite volume approach, with the wave propagation algorithm. A novel wave-speed selection strategy is proposed by comparing characteristic velocities with Roe speeds, yielding solutions with guaranteed positive density and speed. The proposed IWP-HLLE method is applied to simulate shock, rarefaction, and contact discontinuity waves under homogeneous long-road conditions, eliminating the influence of external source terms and ensuring the homogeneity of the governing hyperbolic equations. Its performance is benchmarked against the MacCormack scheme supplemented by two standard stabilization techniques, namely artificial viscosity (AV) and central differencing (CD). Spatiotemporal distributions and density profiles are examined across four representative traffic scenarios: free flow, congested traffic flow, queue dissolution, and congested flow with non-equilibrium velocity and uniform density. The results demonstrate that the IWP-HLLE approach substantially suppresses numerical oscillations compared to both AV and CD methods while maintaining stability across all test cases.

This paper deals with the calculation of the discrete approximation to the full spectrum for the tangent operator for the stability problem of the symmetric flow past a circular cylinder. It is also concerned with the localization of the Hopf bifurcation in laminar flow past a cylinder, when the stationary solution loses stability and often becomes periodic in time. The main problem is to determine the critical Reynolds number for which a pair of eigenvalues crosses the imaginary axis. We thus present a divergencefree method, based on a decoupling of the vector of velocities in the saddle-point system from the vector of pressures, allowing the computation of eigenvalues, from which we can deduce the fundamental frequency of the time-periodic solution. The calculation showed that stability is lost through a symmetry-breaking Hopf bifurcation and that the critical Reynolds number is in agreement with the value presented in reported computations.

Objective. A study was conducted to investigate the possible eects of fatigue on the heel strike-initiated shock accelerations and on attenuation of these shocks along the body during eccentric muscle contractions. Design. Level and decline running on a treadmill were used to acquire the experimental data on the foot strike-initiated shock accelerations. Background. Eccentric contractions of the lower limb muscles in combination with shock generation and propagation during downhill running and muscle fatigue may diminish their ability to dissipate and attenuate loading on the system. Methods. Fourteen young healthy males ran on a treadmill at a speed exceeding their anaerobic threshold by 5% for 30 min, as follows: (a) level running and (b) downhill running with a decline angle of À4°. The foot strike-induced shock accelerations were recorded every ®ve minutes on the tibial tuberosity and sacrum. Fatigue was monitored by means of the respiratory parameters. Results. The downhill running related with eccentric muscle contractions was associated with increased shock propagation from the tibial tuberosity to the sacrum levels, even though fatigue did not develop. Conclusions. Shock propagation from the tibial tuberosity to the sacrum is augmented due to the eccentric action of the muscles, without metabolic fatigue development. Eccentric muscle contraction in downhill running reduces the musculoskeletal ability to attenuate the heel strike-induced shock waves. Knowledge about the eect of fatigue on the shock propagation between the shank and the sacrum levels may help in understanding the mechanism of stress fractures and joint damage.

Proton radiography is the unique experimental technique for obtaining direct information about important material characteristics of real solid objects under dynamic conditions. The aim of the present work is the application of this method to the investigation of evolution of density in ...

We investigate the propagation of a dark beam in a defocusing medium in the strong nonlinear regime. We observe for the first time a shock fan filled with non-interacting one-dimensional grey solitons that emanates from a gradient catastrophe developing around a null of the optical intensity. Remarkably this scenario turns out to be very robust, persisting also when the material nonlocal response averages the nonlinearity over dimensions much larger than the emerging soliton filaments.

The problem of combustion stabilization in a duct with supersonic flow at the entrance is studied by means of numerical simulation, with the use of experimental data if available. The influence of the transient process of combustion development on the final flow structure is demonstrated. Four examples are considered and analyzed: oscillations of a pseudoshock with combustion in an asymmetric duct under asymmetric heat exchange conditions, hysteresis of flow in a model combustor of a high-speed civil aircraft engine, various ways of flame stabilization in a model high-speed combustor with a step, and formation of asymmetric flow structures in a symmetric high-speed combustor. These examples include cases with a stationary final state, with periodic oscillations, and with flameout. Influence of the kinetic mechanism, of the wall heat exchange, and of the flow symmetry is shown. Physical mechanisms of combustion stabilization in high-speed flow are analyzed. The possibility of multiple solutions with stabilized heat release is demonstrated for the considered class of flows.

Unsteady two-dimensional simulations were performed for hydrogen/air mixtures in order to evaluate the effects of the detailed chemical reaction model on detonations. The reaction models in the present study are Petersen and Hanson model, and Koshi model. The pressure, specific heat release, and OH mass fraction are not affected by the reaction models, however, HO2 and H2O2 mass fractions are dependent on them. These features also appear in the results of the zero-dimensional ignition simulation for the high pressure gas mixture. Therefore the chemical kinetic models for the high pressure affects the results of detonation simulations because the chemical properties in high pressure are significant different between them.

The interaction between interplanetary coronal mass ejection (ICME) structures can alter the geoeffectiveness of the ICME events in myriad ways. Many aspects of these interaction processes are not well understood. Using the energy spectra measured in two mutually orthogonal top-hat analyzers (THA-1 and 2), which are part of the Solar Wind Ion Spectrometer subsystem of the Aditya Solar Wind Particle EXperiment (ASPEX) on board India's Aditya-L1 mission, we gain insights into intricate features of ICME-ICME interactions during the 2024 May solar event. We report here an unprecedented two-orthogonal-plane perspective of ICME-ICME interactions for the first time from the L1 point. The investigation reveals a special interaction region formed by the propagation of the forward shock driven by complex ejecta in the preceding ICME. The interaction causes the formation of a downstream region spanning over 13 hr, which propagates in the interplanetary medium. The observations reveal that this region serves as a site for proton and alpha particle energization, and the particles within this region get distributed from one plane to the other. The presence of forward shock and particle energization is confirmed by the energetic particle flux measurements by the SupraThermal and Energetic Particle Spectrometer of ASPEX. These observations provide an unprecedented perspective on how solar wind ions become energized and distributed in an ICME-ICME interaction region. Unified Astronomy Thesaurus concepts: Solar coronal mass ejections (310); Solar wind (1534); Interplanetary shocks (829); Solar storm (1526); Solar physics (1476)

This roadmap note consolidates the EDD Field 1.2–1.4 sequence into an execution-oriented research program for testing path-dependent directional stability in model and agent behavior. EDD Field 1.2-alpha introduced the Non-Commutative Intervention Test and the operational commutator C
AB
​

for evaluating whether measured stability differs when valid requalification and false evidence or proxy mimicry are applied in reversed order. Subsequent materials added a minimal replication scaffold, a locked pilot protocol, a manual execution and blinding layer, and synthetic runless falsification controls.

The present note clarifies what this runless methodology can and cannot support. It can support methodological readiness, falsification design, blinding architecture, and planning for external execution. It cannot support empirical claims about model behavior before real outputs are collected and scored under controlled conditions. The roadmap specifies minimum requirements for future external execution, including locked scenarios, condition-key separation, blinded scoring, sham-order controls, recency controls, sign-flip controls, paraphrase families, raw-output retention, and transparent GREEN/YELLOW/RED reporting.

The contribution is a disciplined bridge from runless protocol design to future empirical testing. It frames the EDD 1.2–1.4 sequence as an execution-ready but not yet results-bearing methodology.

Context. Sheath regions ahead of coronal mass ejections (CMEs) are large-scale heliospheric structures that form gradually with CME expansion and propagation from the Sun. Turbulent and compressed sheaths could contribute to the acceleration of charged particles in the corona and in interplanetary space, but the relation of their internal structure to the particle energization process is still a relatively little studied subject. In particular, the role of sheaths in accelerating particles when the shock Mach number is low is a significant open research problem. Aims. This work seeks to provide new insights on the internal structure of CME-driven sheaths with regard to energetic particle enhancements. A good opportunity to achieve this aim was provided by multi-point, in-situ observations of a sheath region made by radially aligned spacecraft at 0.8 and ∼1 AU (Solar Orbiter, the L1 spacecraft Wind and ACE, and BepiColombo) on April 19−21, 2020. The sheath was preceded by a weak and ...

Ablative Richtmyer-Meshkov (ARM) instability develops while a strong radiation pulse, rapidly rising to its constant peak intensity, drives a constant-strength shock wave from the rippled irradiated surface of a solid target into its volume. For the direct laser irradiation, the theory, experiment, and simulations have demonstrated that the development of the ARM results in decaying oscillations of the areal mass/optical thickness modulation amplitude. Much less is known about the ARM with the indirect drive. This effect causing oscillations of the ablation front is the physical basis of the recently proposed [D. S. Clark et al., Phys. Plasmas 21, 112705 (2014)] and successfully demonstrated [H. F. Robey et al., Phys. Plasmas 23, 056303 (2016)] adiabat-shaping approach to improving the NIF target performance. We report a theoretical and numerical stability analysis of the indirectly-driven shock-piston flow performed to investigate the physical mechanism of the ablation-front oscillations detected in the simulations and the NIF experiments on adiabat shaping.