Positron Plasma Research Articles

Self-consistent Strong Screening Applied to Thermonuclear Reactions

Self-consistent strong plasma screening around light nuclei is implemented in the Big Bang nucleosynthesis (BBN) epoch to determine the short-range screening potential, e ϕ(r)/T ≥ 1, relevant for thermonuclear reactions. We numerically solve the nonlinear Poisson–Boltzmann equation incorporating Fermi–Dirac statistics, adopting a generalized screening mass to find the electric potential in the cosmic BBN electron–positron plasma for finite-sized α particles (4He++) as an example. Although the plasma follows Boltzmann statistics at large distances, Fermi–Dirac statistics is necessary when work performed by ions on electrons is comparable to their rest-mass energy. While self-consistent strong screening effects are generally minor owing to the high BBN temperatures, they can enhance the fusion rates of high-Z (Z > 2) elements while leaving fusion rates of lower-Z (Z ≤ 2) elements relatively unaffected. Our results also reveal a pronounced spatial dependence of the self-consistent strong screening potential near the nuclear surface. These findings about the electron–positron plasma’s role refine BBN theory predictions and offer broader applications for studying weakly coupled plasmas in diverse cosmic and laboratory settings.

Newly formed solitary wave solutions and other solitons to the (3+1)-dimensional mKdV–ZK equation utilizing a new modified Sardar sub-equation approach

In this paper, we are going to investigate the (3+1)-dimensional nonlinear modified Korteweg–de Vries-Zakharov–Kuznetsov (mKdV–ZK) equation, which governs the behavior of weakly nonlinear ion acoustic waves in magnetized electron–positron plasma. By taking advantage of the newly proposed modified Sardar sub-equation method, we derive a comprehensive set of exact soliton solutions to the mKdV–ZK equation. Additionally, we provide graphical representations of the solutions, including 2D, 3D, and contour plots, to visualize the characteristics and features of these nonlinear wave structures. These solutions encompass a diverse range of wave patterns, including traveling waves, bright solitons, periodic waves, dark–bright solitons, lump-type solitons, and multi-soliton solutions. The obtained solutions provide valuable insights into the nonlinear behaviors and dynamics exhibited by the mKdV–ZK equation. The success of the new modified Sardar sub-equation method in obtaining a diverse range of solutions for the [Formula: see text]-dimensional mKdV–ZK equation highlights its potential for applications in the analysis of various nonlinear systems in plasma physics and beyond. Also, the study reviewed the superiority of the modified method compared to the Sardar sub-equation method.

Steady state stability features of the electron–positron plasma diode in a mode with particle reflection from potential extrema

Steady state stability features of a diode with electrons and positrons entering from opposite boundaries and moving without collisions in plasma are numerically studied. The most complex regime when charged particles are reflected from potential barriers is considered. This problem arises, in particular, when modeling pulsar diodes. A small perturbation evolution is studied. It has been established that at the initial stage of the process the perturbation amplitude changes in time according to an exponential law. It is shown that stationary solutions with a potential barrier for electrons located near the electron-emitting electrode and a potential barrier for positrons located near the opposite electrode are stable when the inter-electrode distance is below a certain threshold. As the inter-electrode distance increases, the solutions become unstable. Solutions of another type when barriers reflecting particles are located in the opposite to the emitting electrode parts of the gap are also studied. However, these solutions turned out to be unstable.

Physical function is associated with cognitive status, brain amyloid-beta deposition, and blood biomarkers in Chinese Han population.

The physical function of elderly individuals reflects whether they have had a history of regular physical activity over the long term. Such indicators have been found to have a certain connection with cognitive function these years. However, there is limited research that associates it with mechanisms such as cerebral Aβ deposition. We aim to investigate this relationship and unveil the underlying mechanisms. Physical function and cognition data of 4189 participants were obtained from the Chinese preclinical Alzheimer's disease study. Participants were divided into six groups according to disease severity. Among them, 1048 participants underwent the positron emission tomography-computed tomography (PET-CT) and plasma biomarker test. Grip strength and gait were combined into a score indicating physical function. Multiple linear regression models and logistic regression models were mainly used to conduct the analysis. There was a significant positive correlation between physical function and cognitive function (R = 0.48, p < 0.001), independent of sex, age, apolipoprotein E-ε4 genotype, and disease stages (p < 0.001). Physical function was effective in distinguishing individuals with cognitive impairment from those without (AUC = 0.835). Physical function was negatively associated with brain Aβ deposition (p = 0.008) and brain Aβ had an intermediary effect (p < 0.01) on the association between physical function and cognition in women. This association was mainly evident in the lateral parietal, lateral temporal, posterior cingulate, frontal, occipital, and precuneus regions. Physical function was negatively associated with plasma neurofilament light-chain (Nfl) level (p < 0.001). Physical function is strongly associated with cognitive function in the Chinese elderly, and brain Aβ deposition partly mediates the linkage in women. Plasma Nfl can be used as a potential target for exercise intervention in cognitive function. Improving physical function will contribute to the alleviation of cognition decline.

Collisionless Shock in a Relativistically Hot Unmagnetized Electron–Positron Plasma

In this work, we investigate collisionless shocks propagating in a relativistically hot unmagnetized electron–positron plasma. We estimate the dissipation fraction at shocks in the relativistically hot plasma, showing that it is sufficiently large to explain the observation of gamma-ray bursts even when the shock is not highly relativistic. It is shown by two-dimensional particle-in-cell simulations that magnetic fields are generated around the shock front by the Weibel instability, as in the cold upstream plasma. However, in contrast to the cold upstream plasma, no particles are accelerated at the shock in the simulation time of t=3600ωp−1 . The decay of the magnetic field in the downstream region is slower for slower shock velocities in the hot plasma cases. Applying the slow decay of the downstream magnetic field, we propose a model that generates magnetic fields in the large downstream region, which is required from the standard model of the gamma-ray burst afterglow.

Amyloid and SCD jointly predict cognitive decline across Chinese and German cohorts.

Subjective cognitive decline (SCD) in amyloid-positive (Aβ+) individuals was proposed as a clinical indicator of Stage 2 in the Alzheimer's disease (AD) continuum, but this requires further validation across cultures, measures, and recruitment strategies. Eight hundred twenty-one participants from SILCODE and DELCODE cohorts, including normal controls (NC) and individuals with SCD recruited from the community or from memory clinics, underwent neuropsychological assessments over up to 6 years. Amyloid positivity was derived from positron emission tomography or plasma biomarkers. Global cognitive change was analyzed using linear mixed-effects models. In the combined and stratified cohorts, Aβ+ participants with SCD showed steeper cognitive decline or diminished practice effects compared with NC or Aβ- participants with SCD. These findings were confirmed using different operationalizations of SCD and amyloid positivity, and across different SCD recruitment settings. Aβ+ individuals with SCD in German and Chinese populations showed greater global cognitive decline and could be targeted for interventional trials. SCD in amyloid-positive (Aβ+) participants predicts a steeper cognitive decline. This finding does not rely on specific SCD or amyloid operationalization. This finding is not specific to SCD patients recruited from memory clinics. This finding is valid in both German and Chinese populations. Aβ+ older adults with SCD could be a target population for interventional trials.

Association of glial fibrillary acid protein, Alzheimer's disease pathology and cognitive decline.

Increasing evidence shows that neuroinflammation is a possible modulator of tau spread effects on cognitive impairment in Alzheimer's disease. In this context, plasma levels of the glial fibrillary acidic protein (GFAP) have been suggested to have a robust association with Alzheimer's disease pathophysiology. This study aims to assess the correlation between plasma GFAP and Alzheimer's disease pathology, and their synergistic effect on cognitive performance and decline. A cohort of 122 memory clinic subjects with amyloid and tau positron emission tomography, MRI scans, plasma GFAP, and Mini-Mental State Examination (MMSE) was included in the study. A subsample of 94 subjects had a follow-up MMSE score at least one year after baseline. Regional and voxel-based correlations between Alzheimer's disease biomarkers and plasma GFAP were assessed. Mediation analyses were performed to evaluate the effects of plasma GFAP on the association between amyloid and tau PET, and tau PET and cognitive impairment and decline. GFAP was associated with increased tau PET ligand uptake in the lateral temporal and inferior temporal lobes in a strong left-sided pattern independently of age, gender, education, amyloid, and APOE status (β=0.001, p < 0.01). The annual rate of MMSE change was significantly and independently correlated with both GFAP (β=0.006, p < 0.01) and global tau SUVR (β=4.33, p < 0.01), but not with amyloid burden. Partial mediation effects of GFAP were found on the association between amyloid and tau pathology (13.7%), and between tau pathology and cognitive decline (17.4%), but not on global cognition at baseline. Neuroinflammation measured by circulating GFAP is independently associated with tau Alzheimer's disease pathology and with cognitive decline, suggesting neuroinflammation as a potential target for future disease-modifying trials targeting tau pathology. Peretti et al. show that a circulatory marker of neuroinflammation-glial fibrillary acidic protein-is associated with tau pathology in lateral temporal and frontal regions in patients with Alzheimer's disease, independent of amyloid load. Neuroinflammation appears to modulate the association between amyloid and tau biomarkers.

Nonplanar ion acoustic waves in e-p-i plasmas with non-Maxwellian distributed electrons and positrons

The process of propagation of cylindrical and spherical ion acoustic solitary waves in an electron, positron, and ion plasma system is studied. The electrons are considered to have the generalized (r, q) distribution, while the positrons are supposed to have the kappa distribution, also known as the Lorentzian distribution. The classic nonlinear equation, Korteweg de-Vries (KdV), has been numerically solved by employing appropriate mathematical transformations. The role of various plasma parameters and nonplanar geometry on the widths and amplitudes of nonlinear ion acoustic structures has been numerically investigated. The current study could be helpful to understand the significance of cylindrical and spherical solitary waves in laboratory, astrophysical as well as in space plasmas.

The energy dissipation of a test-charge particle within a dense, degenerate electron- positron-ion plasma

The energy loss of a moving test-charge particle is studied in a degenerate quantized plasma, whose constituents are the electrons, positrons, and ions. The electrons and positrons are assumed to be quantized and degenerate species, whereas positive ions are treated classically. Relying on the kinetic formalism, an expression for the test-charge potential is derived with a modified dielectric response function involving the ion-acoustic oscillations. The energy loss or stopping power is solvedas a function of a test-charge speed, which is significantly affected by the positron concentration, the electron and positron quantization factors and plasma parameters. It is examined that quantization and quantum parameters lead to the enhancement of energy loss in an electron-positron-ion (EPI) dense plasma. The present findings may prove useful to understand the test-charge response in degenerate dense plasmas, where electrons and positrons are quantized in the strong magnetic fields.

Tau pathology is associated with synaptic density and longitudinal synaptic loss in Alzheimer's disease.

The associations of synaptic loss with amyloid-β (Aβ) and tau pathology measured by positron emission tomography (PET) and plasma analysis in Alzheimer's disease (AD) patients are unknown. Seventy-five participants, including 26 AD patients, 19 mild cognitive impairment (MCI) patients, and 30 normal controls (NCs), underwent [18F]SynVesT-1 PET/MR scans to assess synaptic density and [18F]florbetapir and [18F]MK6240 PET/CT scans to evaluate Aβ plaques and tau tangles. Among them, 19 AD patients, 12 MCI patients, and 29 NCs had plasma Aβ42/40 and p-tau181 levels measured by the Simoa platform. Twenty-three individuals, 6 AD patients, 4 MCI patients, and 13 NCs, underwent [18F]SynVesT-1 PET/MRI and [18F]MK6240 PET/CT scans during a one-year follow-up assessment. The associations of Aβ and tau pathology with cross-sectional and longitudinal synaptic loss were investigated using Pearson correlation analyses, generalized linear models and mediation analyses. AD patients exhibited lower synaptic density than NCs and MCI patients. In the whole cohort, global Aβ deposition was associated with synaptic loss in the medial (r = -0.431, p < 0.001) and lateral (r = -0.406, p < 0.001) temporal lobes. Synaptic density in almost all regions was related to the corresponding regional tau tangles independent of global Aβ deposition in the whole cohort and stratified groups. Synaptic density in the medial and lateral temporal lobes was correlated with plasma Aβ42/40 (r = 0.300, p = 0.020/r = 0.289, p = 0.025) and plasma p-tau 181 (r = -0.412, p = 0.001/r = -0.529, p < 0.001) levels in the whole cohort. Mediation analyses revealed that tau tangles mediated the relationship between Aβ plaques and synaptic density in the whole cohort. Baseline tau pathology was positively associated with longitudinal synaptic loss. This study suggested that tau burden is strongly linked to synaptic density independent of Aβ plaques, and also can predict longitudinal synaptic loss.

Study of magnetic field evolution by Weibel instability in counter-streaming electron–positron plasma flows

Study of magnetic field evolution by Weibel instability in counter-streaming electron–positron plasma flows

Characteristics of discordance between amyloid positron emission tomography and plasma amyloid-β 42/40 positivity

Various plasma biomarkers for amyloid-β (Aβ) have shown high predictability of amyloid PET positivity. However, the characteristics of discordance between amyloid PET and plasma Aβ42/40 positivity are poorly understood. Thorough interpretation of discordant cases is vital as Aβ plasma biomarker is imminent to integrate into clinical guidelines. We aimed to determine the characteristics of discordant groups between amyloid PET and plasma Aβ42/40 positivity, and inter-assays variability depending on plasma assays. We compared tau burden measured by PET, brain volume assessed by MRI, cross-sectional cognitive function, longitudinal cognitive decline and polygenic risk score (PRS) between PET/plasma groups (PET−/plasma−, PET−/plasma+, PET+/plasma−, PET+/plasma+) using Alzheimer’s Disease Neuroimaging Initiative database. Additionally, we investigated inter-assays variability between immunoprecipitation followed by mass spectrometry method developed at Washington University (IP-MS-WashU) and Elecsys immunoassay from Roche (IA-Elc). PET+/plasma+ was significantly associated with higher tau burden assessed by PET in entorhinal, Braak III/IV, and Braak V/VI regions, and with decreased volume of hippocampal and precuneus regions compared to PET−/plasma-. PET+/plasma+ showed poor performances in global cognition, memory, executive and daily-life function, and rapid cognitive decline. PET+/plasma+ was related to high PRS. The PET−/plasma+ showed intermediate changes between PET−/plasma− and PET+/plasma+ in terms of tau burden, hippocampal and precuneus volume, cross-sectional and longitudinal cognition, and PRS. PET+/plasma− represented heterogeneous characteristics with most prominent variability depending on plasma assays. Moreover, IP-MS-WashU showed more linear association between amyloid PET standardized uptake value ratio and plasma Aβ42/40 than IA-Elc. IA-Elc showed more plasma Aβ42/40 positivity in the amyloid PET-negative stage than IP-MS-WashU. Characteristics of PET−/plasma+ support plasma biomarkers as early biomarker of amyloidopathy prior to amyloid PET. Various plasma biomarker assays might be applied distinctively to detect different target subjects or disease stages.

Accelerating self-modulated nonlinear waves in weakly and strongly magnetized relativistic plasmas

It is known that a nonlinear Schrödinger equation describes the self-modulation of a large amplitude circularly polarized wave in relativistic electron–positron plasmas in the weakly and strongly magnetized limits. Here, we show that such an equation can be written as a modified second Painlevé equation, producing accelerated propagating wave solutions for those nonlinear plasmas. This solution even allows the plasma wave to reverse its direction of propagation. The acceleration parameter depends on the plasma magnetization. This accelerating solution is different to the usual soliton solution propagating at constant speed.

Measurements of Penning-Malmberg trap patch potentials and associated performance degradation

Antiprotons created by laser ionization of antihydrogen are observed to rapidly escape the ALPHA trap. Further, positron plasmas heat more quickly after the trap is illuminated by laser light for several hours. These phenomena can be caused by patch potentials—variations in the electrical potential along metal surfaces. A simple model of the effects of patch potentials explains the particle loss, and an experimental technique using trapped electrons is developed for measuring the electric field produced by the patch potentials. The model is validated by controlled experiments and simulations. Published by the American Physical Society 2024

Shock electrostatic electron acoustic wave features in four-component electron–positron plasma

The linear (nonlinear) wave properties of dissipative electron acoustic plasma have been studied. The impacts of temperatures and densities on the properties of linear real and imaginary (growth rate) plasma frequencies have been examined. The effects of viscosities in the linear growth rate are also studied. Accordingly, the significant shock-like electrostatic field in auroral plasmas has been discussed. Furthermore, the electrostatic dissipative fields have been studied to explain experimental observations. A comparison between the obtained electrostatic dissipative fields and satellite observations in auroral plasmas is briefly discussed.

A multivariate MRI model of Alzheimer’s disease risk is associated with clinical diagnosis, PET imaging, and plasma biomarkers in a mixed dementia sample

AbstractBackgroundWe sought to validate two structural MRI‐based brain health models: Spatial Pattern of Atrophy for REcognition of Alzheimer’s disease (SPARE‐AD) and SPARE‐Brain Age Gap (SPARE‐BAG), which estimates the discrepancy between biological brain age and chronological age. These models' generalization to non‐amnestic AD (naAD) syndromes and associations with positron emission tomography (PET) and plasma biomarkers remain underinvestigated. We hypothesized that SPARE‐AD scores in naAD would be lower (less abnormal) than in amnestic AD (aAD) but elevated (more abnormal) relative to controls; and that SPARE‐AD but not SPARE‐BAG scores would be associated with PET and plasma biomarkers of AD.MethodSPARE‐AD and SPARE‐BAG scores were estimated for each of 1607 MRI scans from 277 cognitively normal adults (62.8% female; mean age = 69.5 years) and 902 clinical participants (54.2% female; mean age = 73.1 years), including 585 with amnestic mild cognitive impairment (aMCI) or aAD; 56 with naAD syndromes; 28 with vascular disease; 28 with Lewy body disorders (LBD); 18 with suspected frontotemporal lobar degeneration (FTLD); 56 with non‐amnestic MCI of uncertain etiology; and 131 with other clinical diagnoses. We used mixed effects models adjusting for age, sex, and global cognition to test group differences in SPARE‐AD and SPARE‐BAG. Additionally, we assessed associations with tau (n = 122) and amyloid‐beta (n = 199) PET imaging and plasma‐based phosphorylated tau‐181 (p‐tau181) and glial fibrillary acidic protein (GFAP) (n = 358).ResultSPARE‐AD scores were elevated vs. controls in aMCI/aAD, naAD, vascular disease, FTLD, and naMCI (all p&lt;0.003) but not in LBD or other diagnoses (p&gt;0.1). NaAD patients had lower SPARE‐AD (p&lt;0.02) but higher SPARE‐BAG scores (p&lt;0.02) than aMCI/aAD patients. SPARE‐AD scores were positively associated with mean cortical tau PET uptake, amyloid PET positivity, and plasma p‐tau181 and GFAP (all p&lt;0.001). In contrast, SPARE‐BAG scores were not associated with PET or plasma biomarkers (all p&gt;0.05).ConclusionSPARE‐AD values for naAD syndromes were intermediate between those of controls and aMCI/AD patients, likely reflecting divergent, partially overlapping cortical atrophy relative to aAD. PET and plasma biomarkers of AD neuropathologic change were associated with SPARE‐AD but not with SPARE‐BAG scores, suggesting SPARE‐BAG reflects age‐related atrophy that is largely independent of AD.

Slow positron production and storage for the ASACUSA-Cusp experiment

The ASACUSA (atomic spectroscopy and collisions using slow antiprotons) Cusp experiment requires the production of dense positron plasmas with a high repetition rate to produce a beam of antihydrogen. In this work, details of the positron production apparatus used for the first observation of the antihydrogen beam, and subsequent measurements, are described in detail. This apparatus replaced the previous compact trap design resulting in an improvement in the positron accumulation rate by a factor of $52\pm 3$ .

Instability of steady states with inhomogeneous field in electron–positron plasma diode

Instability features of steady states of the plasma diode with electron and positron counter flows are studied. There are several types of such states for each value of the inter-electrode distance. The case when charged particles moving in the diode plasma are not reflected from potential extrema is considered. We have solved an equation for the amplitude of the electric field perturbation for steady states with an inhomogeneous field distribution. Studying the dispersion equation has shown that all considered solutions are unstable. We have also confirmed this result when simulating small perturbation evolution of a steady-state solution.

Comptonization by reconnection plasmoids in black hole coronae – III. Dependence on the guide field in pair plasma

ABSTRACT We perform non-radiative two-dimensional particle-in-cell simulations of magnetic reconnection for various strengths of the guide field (perpendicular to the reversing field), in magnetically dominated electron–positron plasmas. Magnetic reconnection under such conditions could operate in accretion disc coronae around black holes. There, it has been suggested that the transrelativistic bulk motions of reconnection plasmoids containing inverse-Compton-cooled electrons could Compton-upscatter soft photons to produce the observed non-thermal hard X-rays. Our simulations are performed for magnetizations 3 ≤ σ ≤ 40 (defined as the ratio of enthalpy density of the reversing field to plasma enthalpy density) and guide field strengths 0 ≤ Bg/B0 ≤ 1 (normalized to the reversing field strength B0). We find that the mean bulk energy of the reconnected plasma depends only weakly on the flow magnetization but strongly on the guide field strength – with Bg/B0 = 1 yielding a mean bulk energy twice smaller than Bg/B0 = 0. Similarly, the dispersion of bulk motions around the mean – a signature of stochasticity in the plasmoid chain’s motions – is weakly dependent on magnetization (for σ ≳ 10) but strongly dependent on the guide field strength – dropping by more than a factor of two from Bg/B0 = 0 to Bg/B0 = 1. In short, reconnection in strong guide fields (Bg/B0 ∼ 1) leads to slower and more ordered plasmoid bulk motions than its weak guide field (Bg/B0 ∼ 0) counterpart.

Abnormal absorption of extremely intense laser pulses in relativistically underdense plasmas

It is generally believed that relativistically underdense plasmas are transparent for intense laser radiation. However, particle-in-cell simulations reveal abnormal laser field absorption above the intensity threshold of about 3×1024 Wcm−2 for the wavelength of 1 μm. Above the threshold, the further increase in the laser intensity does not lead to an increase in the propagation distance. The simulations take into account emission of hard photons and subsequent pair photoproduction in the laser field. These effects lead to onset of a self-sustained quantum electromagnetic cascade and to formation of dense electron–positron (e+e−) plasma right inside the laser field. The plasma absorbs the laser field efficiently, which ensures the plasma opacity. The role of a weak longitudinal electron–ion electric field in the cascade growth is discussed.