A mathematical model of p62-ubiquitin aggregates in autophagy

Aggregation of ubiquitinated cargo by oligomers of the protein p62 is an important preparatory step in cellular autophagy. In this work a mathematical model for the dynamics of these heterogeneous aggregates in the form of a system of ordinary differential equations is derived and analyzed. Three different parameter regimes are identified, where either aggregates are unstable, or their size saturates at a finite value, or their size grows indefinitely as long as free particles are abundant. The boundaries of these regimes as well as the finite size in the second case can be computed explicitly. The growth in the third case (quadratic in time) can also be made explicit by formal asymptotic methods. In the absence of rigorous results the dynamic stability of these structures has been investigated by numerical simulations. A comparison with recent experimental results permits a partial parametrization of the model.

Quantum Entanglement of Free Particles

In this paper, the Schrödinger equation is solved for many free particles and their quantum entanglement is studied via correlation analysis. Converting the Schrödinger equation in the Madelung hydrodynamic-like form, the quantum mechanics is extended to open quantum systems by adding Ohmic friction forces. The dissipative evolution confirms the correlation decay over time, but a new integral of motion is discovered, being appropriate for storing everlasting quantum information.

Fast Particle Acceleration in Three-dimensional Relativistic Reconnection

Magnetic reconnection is invoked as one of the primary mechanisms to produce energetic particles. We employ large-scale 3D particle-in-cell simulations of reconnection in magnetically dominated (σ = 10) pair plasmas to study the energization physics of high-energy particles. We identify an acceleration mechanism that only operates in 3D. For weak guide fields, 3D plasmoids/flux ropes extend along the z-direction of the electric current for a length comparable to their cross-sectional radius. Unlike in 2D simulations, where particles are buried in plasmoids, in 3D we find that a fraction of particles with γ ≳ 3σ can escape from plasmoids by moving along z, and so they can experience the large-scale fields in the upstream region. These “free” particles preferentially move in z along Speiser-like orbits sampling both sides of the layer and are accelerated linearly in time—their Lorentz factor scales as γ ∝ t, in contrast to γ ∝ t in 2D. The energy gain rate approaches ∼eE rec c, where E rec ≃ 0.1B 0 is the reconnection electric field and B 0 the upstream magnetic field. The spectrum of free particles is hard, dN free / d γ ∝ γ − 1.5 , contains ∼20% of the dissipated magnetic energy independently of domain size, and extends up to a cutoff energy scaling linearly with box size. Our results demonstrate that relativistic reconnection in GRB and AGN jets may be a promising mechanism for generating ultra-high-energy cosmic rays.

The optical properties and in-situ observational evidence for the formation of brown carbon in cloud

Atmospheric brown carbon (BrC) makes a substantial contribution to aerosol light-absorbing and thus the global radiative forcing. Although BrC may change the lifetime of the cloud and ultimately affect precipitation, little is known regarding the optical properties and formation of BrC in the cloud. In the present study, the light-absorption properties of cloud droplet residual (cloud RES) were measured by coupled a ground-based counterflow virtual impactor (GCVI) and an Aethalometer (AE-33), in addition to the cloud interstitial (cloud INT) and ambient (cloud-free) particles by PM2.5 inlet-AE-33, at Mt. Tianjing (1690 m a.s.l.), a remote mountain site in southern China, from November to December 2020. Meanwhile, the light-absorption and fluorescence properties of water-soluble organic carbon (WSOC) in the collected cloud water and PM2.5 samples were also obtained, associated with the concentration of water-soluble ions. The mean light-absorption coefficient (Abs370) of the cloud RES, cloud INT, and cloud-free particles were 0.25 ± 0.15, 1.16 ± 1.14, and 1.47 ± 1.23 Mm−1, respectively. The Abs365 of WSOC was 0.11 ± 0.08 Mm−1 in cloud water and 0.40 ± 0.31 Mm−1 in PM2.5, and the corresponding mass absorption efficiency (MAE365) was 0.17 ± 0.07 and 0.31 ± 0.21 m2·g−1, respectively. A comparison of the light-absorption coefficient between BrC in the cloud RES/cloud INT and WSOC in cloud water/PM2.5 indicates a considerable contribution (48–75 %) of water-insoluble BrC to total BrC light-absorption. Secondary BrC estimated by minimum R squared (MRS) method dominated the total BrC in cloud RES (67–85 %), rather than in the cloud-free (11–16 %) and cloud INT (9–23 %) particles. It may indicate the formation of secondary BrC during cloud processing. Supporting evidence includes the enhanced WSOC and dominant contribution of secondary formation/biomass burning factor (> 80 %) to Abs365 in cloud water provided by Positive Matrix Factorization (PMF) analysis. In addition, we showed that the light-absorption of BrC in cloud water was closely related to humic-like substances and tyrosine/proteins-like substances (r > 0.63, p < 0.01), whereas only humic-like substances for PM2.5, as identified by excitation-emission matrix fluorescence spectroscopy.

The Research of GIS Discharge Influence Based on Particle Properties in Installation Environment

In order to explore the influence of atmospheric free particles that exit during GIS installation on the stable operation of GIS, the size, shape and inner properties of the particles contained in the air are analyzed. And based on 500kV GIS equipment, the GIS gas chamber model and the model of free particles were established. By using the finite element simulation software, the surface electric field distribution when the free particles remain on the insulator surface is solved. The results show that the electric field distribution of particles which exist along the surface of insulator is directly related to the relative permittivity of the material of the particles themselves, and the intensity of the electric field along the surface increases with the increase of the relative permittivity. with the fact that the relative permittivity of air particles is almost below 20, as a result, the existence of 10µm grade non-metallic free particles will not cause flashover discharge. But, when a small number of Fe3O4 particles which size over 1mm or when them accumulate regularly, it will lead to flashover discharge. Therefore, the suspended atmospheric particles in the installation environment have little impact on the stable operation of GIS. When considering the installation environmental conditions, the installation can be carried out on a clear, windless day which can save costs.

Particle Uptake Driven Phagocytosis in Macrophages and Neutrophils Enhances Bacterial Clearance

Humans are exposed to numerous synthetic foreign particulates in the form of environmental pollutants and diagnostic or therapeutic agents. Specialized immune cells (phagocytes) clear these particulates by phagocytosing and attempting to degrade them. The process of recognition and internalization of the particulates may trigger changes in the function of phagocytes. Some of these changes, especially the ability of a particle-loaded phagocyte to take up and neutralize pathogens, remains poorly studied. Herein, we demonstrate that the uptake of non-stimulatory cargo-free particles enhances the phagocytic ability of monocytes, macrophages and neutrophils. The enhancement in phagocytic ability was independent of particle properties, such as size or the base material constituting the particle. Additionally, we show that the increased phagocytosis was not a result of cellular activation or cellular heterogeneity but was driven by changes in cell membrane fluidity and cellular compliance. A consequence of the enhanced phagocytic activity was that particulate-laden immune cells neutralize E. coli faster in culture. Moreover, when administered in mice as a prophylactic, particulates enable faster clearance of E. coli and S. epidermidis. Together, we demonstrate that the process of uptake induces cellular changes that favor additional phagocytic events. This study provides insights into using non-stimulatory cargo-free particles to engineer immune cell functions for applications involving faster clearance of phagocytosable particulates.

Study of the Behavior of Gold and Accompanying Chemical Elements in Weathering Profile on a Quartz Vein in Mintom (South Cameroon, Central Africa)

The present study, which focuses on the behavior of gold and its accompanying chemical elements developed on an alteration profile, is carried out in a humid equatorial zone at Mintom in South Cameroon (Central Africa). The methodology used to achieve the results obtained focused on the description of the morphology of the outcrop, the petrography of the rock studied, the study of heavy minerals accompanying gold in the weathering materials on smear slides, mineralogical analysis of weathering materials by X-ray diffraction (XRD), scanning electron microscopy (SEM) analysis of gold and geochemical analyzes by ICP - AES and ICP - MS of weathering materials. The main results obtained from this methodology inform us that on the petrographic level the main rock studied is the gold-bearing quartz vein located in Zom, consisting mainly of quartz and opaque minerals. Morphologically, the weathering materials developed on this granite basement present an advanced ABC-type profile characterized by a significant thickness (4 to 6 m). The morphological and chemical characters of the gold particles have evolved from the mineralized zone to the surface. This development was marked by an increase in blunt, rounded grains. Morphoscopy and scanning electron microscopy of the gold particles have shown hollow, blunt to sub-blunt grains, non-evolved free particles, and evolved free particles, respectively. In most samples of weathered material gold is found in association with chemical elements such as Ag, Cr, Co, Cu, Ni, V and figure 10 show identical behavior between these chemical elements and gold, but particularly between silver and gold, which would testify to an identical origin. Au concentrations are very high in most samples of weathering material. Also, these samples of altered materials with a high proportion of gold (0.01 to 2.28 ppm) also present high concentrations of silver (Ag) which justifies that the occurrence or the gold deposit is associated with silver and can be exploited as a geochemical parameter to prospect for gold in the study area.