Compound electron acceleration at planetary foreshocks.

Shock waves, the interface of supersonic and subsonic plasma flows, are the primary region for charged particle acceleration in multiple space plasma systems, including Earth's bow shock, which is readily accessible for in-situ measurements. Spacecraft frequently observe relativistic electron populations within this region, characterized by energy levels surpassing those of solar wind electrons by a factor of 10,000 or more. However, mechanisms of such strong acceleration remain elusive.

Cross-Scale Energy Transfer from Fluid-Scale Alfvén Waves to Kinetic-Scale Ion Acoustic Waves in the Earth's Magnetopause Boundary Layer.

In space plasmas, large-amplitude Alfvén waves can drive compressive perturbations, accelerate ion beams, and lead to plasma heating and the excitation of ion acoustic waves at kinetic scales. This energy channeling from fluid to kinetic scales represents a complementary path to the classical turbulent cascade. Here, we present observational and computational evidence to validate this hypothesis by simultaneously resolving the fluid-scale Alfvén waves, kinetic-scale ion acoustic waves, and their imprints on ion velocity distributions in the Earth's magnetopause boundary layer.

Magnetospheric Control of Ionospheric TEC Perturbations via Whistler-Mode and ULF Waves.

The weakly ionized plasma in the Earth's ionosphere is controlled by a complex interplay between solar and magnetospheric inputs from above, atmospheric processes from below, and plasma electrodynamics from within. This interaction results in ionosphere structuring and variability that pose major challenges for accurate ionosphere prediction for global navigation satellite system (GNSS) related applications and space weather research. The ionospheric structuring and variability are often probed using the total electron content (TEC) and its relative perturbations (dTEC).

Identification of Coupled Landau and Anomalous Resonances in Space Plasmas.

Wave-particle resonance, a ubiquitous process in the plasma universe, occurs when resonant particles observe a constant wave phase to enable sustained energy transfer. Here, we present spacecraft observations of simultaneous Landau and anomalous resonances between oblique whistler waves and the same group of protons, which are evidenced, respectively, by phase-space rings in parallel-velocity spectra and phase-bunched distributions in gyrophase spectra. Our results indicate the coupling between Landau and anomalous resonances via the overlapping of the resonance islands.

Haemorrhagic Complications After Microsurgical Treatment for Intracranial Aneurysms Under Acetylsalicylic Acid: An Impact Analysis.

Background: Patients with intracranial aneurysms often have comorbidities that require them to take acetylsalicylic acid (ASA). In recent years, many patients with aneurysms have been prescribed ASA to prevent aneurysm enlargement. ASA is also prescribed to patients with intracranial aneurysms in preparation for surgical revascularization.

Optimal photoelectron circular dichroism of a model chiral system.

We optimize the internuclear geometry and electronic structure of a model chiral system to achieve a maximal photoelectron circular dichroism (PECD) in its one-photon ionization by circularly polarized light. The electronic structure calculations are performed by the single center method, while the optimization is done using quantum alchemy employing a Taylor series expansion. Thereby, the effect of bond lengths and uncompensated charge distributions on the chiral response of the model is investigated theoretically in some detail.

A Systematic Review and Case Illustrations of Misdiagnosing Intracranial Aneurysms.

Modern neuroimaging methods do not completely rule out false diagnoses of intracranial aneurysms which can lead to an unwarranted operation associated with risks of complications. However, surgical interventions for falsely diagnosed aneurysms are quite rare. The purpose of this study is to demonstrate two clinical cases of false-positive aneurysms and a systematic review of the literature dedicated to the incidence and etiology of false-positive aneurysms, identifying risk factors associated with false-positive aneurysms.

Real-time laser speckle contrast imaging for intraoperative neurovascular blood flow assessment: animal experimental study.

The use of various blood flow control methods in neurovascular interventions is crucial for reducing postoperative complications. Neurosurgeons worldwide use different methods, such as contact Dopplerography, intraoperative indocyanine videoangiography (ICG) video angiography, fluorescein angiography, flowmetry, intraoperative angiography, and direct angiography. However, there is no noninvasive method that can assess the presence of blood flow in the vessels of the brain without the introduction of fluorescent substances throughout the intervention.

Theoretical study of spin polarization in multiphoton ionization of Xe.

Spin polarization in the multiphoton above-threshold ionization of 5p3/2- and 5p1/2-electrons of Xe with intense 395nm, circularly polarized laser pulses, is investigated theoretically. For this purpose, we solve the time-dependent Schrödinger equation on the basis of spherical spinors. We, thus, simultaneously propagate the spin-up and spin-down single-active-electron wave packets, driven by the laser pulses in the ionic potential, which includes the spin-orbit interaction explicitly.

Amplitude Dependence of Nonlinear Precipitation Blocking of Relativistic Electrons by Large Amplitude EMIC Waves.

Recent work has shown that ElectroMagnetic Ion Cyclotron (EMIC) waves tend to occur in four distinct regions, each having their own characteristics and morphology. Here, we use nonlinear test-particle simulations to examine the range of energetic electron scattering responses to two EMIC wave groups that occur at low L-shells and overlap the outer radiation belt electrons. The first group consists of low-density, H-band region b waves, and the second group consists of high-density, He-band region c waves.

Nonresonant Scattering of Relativistic Electrons by Electromagnetic Ion Cyclotron Waves in Earth's Radiation Belts.

Electromagnetic ion cyclotron waves are expected to pitch-angle scatter and cause atmospheric precipitation of relativistic (>1  MeV) electrons under typical conditions in Earth's radiation belts. However, it has been a long-standing mystery how relativistic electrons in the hundreds of keV range (but <1  MeV), which are not resonant with these waves, precipitate simultaneously with those >1  MeV. We demonstrate that, when the wave packets are short, nonresonant interactions enable such scattering of hundred-keV electrons by introducing a spread in wave number space.

Superfast precipitation of energetic electrons in the radiation belts of the Earth.

Energetic electron precipitation from Earth's outer radiation belt heats the upper atmosphere and alters its chemical properties. The precipitating flux intensity, typically modelled using inputs from high-altitude, equatorial spacecraft, dictates the radiation belt's energy contribution to the atmosphere and the strength of space-atmosphere coupling. The classical quasi-linear theory of electron precipitation through moderately fast diffusive interactions with plasma waves predicts that precipitating electron fluxes cannot exceed fluxes of electrons trapped in the radiation belt, setting an apparent upper limit for electron precipitation.

Electron Dynamics and Correlations During High-Order Harmonic Generation in Be.

We investigate theoretically the high-order harmonic generation in beryllium atom irradiated by a short 1850 nm linearly polarized laser pulse in the intermediate strong-field ionization regime with the Keldysh parameter of 0.85. To this end, the respective time-dependent Schrödinger equation is solved by the time-dependent restricted-active-space configuration-interaction (TD-RASCI) method.

Photoelectron circular dichroism of a model chiral anion.

Photoelectron circular dichroism (PECD) in the one-photon detachment of a model chiral anionic system is studied theoretically by the single center method. The computed chiral asymmetry, characterized by the dichroic parameter β of up to about ±3%, is in good accord with the first experimental observations of the effect in photodetachment of amino acid anions [P. Krüger and K.

Spacecraft Observations and Theoretical Understanding of Slow Electron Holes.

We present Magnetospheric Multiscale observations showing large numbers of slow electron holes with speeds clustered near the local minimum of double-humped velocity distribution functions of background ions. Theoretical computations show that slow electron holes can avoid the acceleration that otherwise prevents their remaining slow only under these same circumstances. Although the origin of the slow electron holes is still elusive, the agreement between observation and theory about the conditions for their existence is remarkable.

Photoelectron circular dichroism in the multiphoton ionization by short laser pulses. III. Photoionization of fenchone in different regimes.

Photoelectron circular dichroism (PECD) in different regimes of multiphoton ionization of fenchone is studied theoretically using the time-dependent single center method. In particular, we investigate the chiral response to the one-color multiphoton or strong-field ionization by circularly polarized 400 nm and 814 nm optical laser pulses or 1850 nm infrared pulse. In addition, the broadband ionization by short coherent circularly polarized 413-1240 nm spanning pulse is considered.

Remarkable charged particle dynamics near magnetic field null lines.

The study of charged-particle motion in electromagnetic fields is a rich source of problems, models, and new phenomena for nonlinear dynamics. The case of a strong magnetic field is well studied in the framework of a guiding center theory, which is based on conservation of an adiabatic invariant-the magnetic moment. This theory ceases to work near a line on which the magnetic field vanishes-the magnetic field null line.

Controlling Dynamics of Postcollision Interaction.

A general scheme to get insight and to control postcollision interaction (PCI) by means of sequential double ionization with two high-frequency pulses is discussed. In particular, we propose to consider PCI of a slow photoelectron released by the pump pulse from a neutral atom with a fast photoelectron released by the time-delayed probe pulse from the created ion. This scheme is exemplified by the ab initio calculations performed for the prototypical helium atom.

Nonlinear resonances generate large-scale convection cells in phase space.

It is well known that resonance phenomena can destroy adiabatic invariance and cause chaos and mixing. In the present Rapid Communication, we show that a nonlinear wave-particle resonant interaction may do the opposite-generate large-scale coherent structures in phase space. The combined action of the drift due to nonlinear scattering on resonance and trapping (capture) into resonance creates a convection cell-like structure, where the areas of particle acceleration and deceleration are macroscopically separated.

Photoelectron Circular Dichroism with Two Overlapping Laser Pulses of Carrier Frequencies ω and 2ω Linearly Polarized in Two Mutually Orthogonal Directions.

Using a model methanelike chiral system, we theoretically demonstrate a possibility to access photoelectron circular dichroism (PECD) by a single experiment with two overlapping laser pulses of carrier frequencies ω and 2ω, which are linearly polarized in two mutually orthogonal directions. Depending on the relative phase, the resulting electric field can be tailored to have two different rotational directions in the upper and lower hemispheres along the polarization of the ω pulse. We predict a strong forward-backward asymmetry in the emission of photoelectrons from randomly oriented samples, which has an opposite sign in the upper and lower hemispheres.

Circular Dichroism in Fluorescence Emission Following the C 1s→π* Excitation and Resonant Auger Decay of Carbon Monoxide.

Dichroism in angle-resolved spectra of circularly polarized fluorescence from freely-rotating CO molecules was studied experimentally and theoretically. For this purpose, carbon monoxide in the gas phase was exposed to circularly polarized soft X-ray synchrotron radiation. The photon energy was tuned across the C 1s→π* resonant excitation, which decayed via the participator Auger transition into the CO⁺ A ²Π state.

Multiscale Currents Observed by MMS in the Flow Braking Region.

We present characteristics of current layers in the off-equatorial near-Earth plasma sheet boundary observed with high time-resolution measurements from the Magnetospheric Multiscale mission during an intense substorm associated with multiple dipolarizations. The four Magnetospheric Multiscale spacecraft, separated by distances of about 50 km, were located in the southern hemisphere in the dusk portion of a substorm current wedge. They observed fast flow disturbances (up to about 500 km/s), most intense in the dawn-dusk direction.

Photoelectron circular dichroism in the multiphoton ionization by short laser pulses. II. Three- and four-photon ionization of fenchone and camphor.

Angle-resolved multiphoton ionization of fenchone and camphor by short intense laser pulses is computed by the time-dependent single center method. Thereby, the photoelectron circular dichroism (PECD) in the three-photon resonance enhanced ionization and four-photon above-threshold ionization of these molecules is investigated in detail. The computational results are in satisfactory agreement with the available experimental data, measured for randomly oriented fenchone and camphor molecules at different wavelengths of the exciting pulses.