The extension of the cosmic-ray spectrum beyond 1 petaelectronvolt (PeV; 10
electronvolts) indicates the existence of the so-called PeVatrons-cosmic-ray factories that accelerate particles to PeV ...energies. We need to locate and identify such objects to find the origin of Galactic cosmic rays
. The principal signature of both electron and proton PeVatrons is ultrahigh-energy (exceeding 100 TeV) γ radiation. Evidence of the presence of a proton PeVatron has been found in the Galactic Centre, according to the detection of a hard-spectrum radiation extending to 0.04 PeV (ref.
). Although γ-rays with energies slightly higher than 0.1 PeV have been reported from a few objects in the Galactic plane
, unbiased identification and in-depth exploration of PeVatrons requires detection of γ-rays with energies well above 0.1 PeV. Here we report the detection of more than 530 photons at energies above 100 teraelectronvolts and up to 1.4 PeV from 12 ultrahigh-energy γ-ray sources with a statistical significance greater than seven standard deviations. Despite having several potential counterparts in their proximity, including pulsar wind nebulae, supernova remnants and star-forming regions, the PeVatrons responsible for the ultrahigh-energy γ-rays have not yet been firmly localized and identified (except for the Crab Nebula), leaving open the origin of these extreme accelerators.
Ionospheric outflow has been shown to be a dominant ion source of Earth's magnetosphere. However, most studies in the literature are about ionospheric outflow injected into the nightside ...magnetosphere. We still know little about ionospheric outflow injected into the dayside magnetosphere and its further energization after it enters the magnetosphere. Here, with data from Magnetospheric Multiscale mission, we report direct observations of the modulation of dayside ionospheric outflow ions by ultralow frequency (ULF) waves. The observations indicate that the modulation is mass dependent, which demonstrates the possibility of using ULF waves as a mass spectrometer to identify ion species. Moreover, the measurement suggests that polarization drift may play a role in O+ modulation, which may lead to a true acceleration and even nonadiabatic behavior of O+. This interaction scenario can work throughout the whole magnetosphere and impact upon the plasma environment and dynamics.
Key Points
Interaction between ULF waves and ionospheric outflow ions injected into the dayside magnetosphere was observed by MMS
ULF waves can serve as an auxiliary diagnostic for the detection of ionospheric outflow ions and inference of their mass species
Polarization drift plays a role in the modulation of oxygen ions
Dissimilar lap joints of 1060 aluminum and T2 copper were obtained by friction stir spot welding (FSSW) at various rotational speeds. The measured process variables during welding revealed that an ...increasing rotational speed leads to a higher peak temperature but a lower torque and plunging force due to the greater softening degree of material. A continuous CuAl2-CuAl-Al4Cu9 laminated layer developed at the Al-Cu interface under the highest rotational speed, while the interface was characterized by the interruptedly distributed CuAl2 layer under lower rotational speeds. Intermetallic compound (IMC) formation sequence for CuAl2, CuAl and Al4Cu9 was predicted according to thermodynamic principles, which is consistent with the interfacial microstructure evolution identified by the transmission electron microscope (TEM). Besides the metallurgical bonding through the IMC layer at the Al-Cu interface, joints have a Cu hook extruded upward by the pin tool from the lower Cu sheet into the upper Al sheet, which provided additional mechanical interlocking between the sheets. Tensile properties of the joints were closely related to the thickness of the IMC layer and geometric features of the hook, higher tensile properties were found in joints owning a continuous interfacial IMC layer with a proper thickness as well as a high penetration depth of the hook into the upper Al sheet.
•A higher rotational speed leads to a lower torque and plunging force.•CuAl2-CuAl-Al4Cu9 laminated layer forms at the hook interface at high heat input.•IMC formation sequence for CuAl2, CuAl and Al4Cu9 is predicted.•The joints are both metallurgical and mechanical bonded.•Hook morphology influences fracture path and shear strength.
Some gamma-ray bursts (GRBs) have a tera-electron volt (TeV) afterglow, but the early onset of this has not been observed. We report observations with the Large High Altitude Air Shower Observatory ...(LHAASO) of the bright GRB 221009A, which serendipitously occurred within the instrument's field of view. More than 64,000 photons >0.2 TeV were detected within the first 3000 seconds. The TeV flux began several minutes after the GRB trigger and then rose to a peak ~10 seconds later. This was followed by a decay phase, which became more rapid ~650 seconds after the peak. We interpret the emission using a model of a relativistic jet with half-opening angle of ~0.8°. This is consistent with the core of a structured jet and could explain the high isotropic energy of this GRB.
Aims
The aim of this study was to determine the effects of unsaturated fatty acids on clinical plasmids.
Methods and Results
Two unsaturated fatty acids, linoleic acid (LA) and α‐linolenic acid (ALA) ...at final concentration 0, 0·03, 0·3 and 3 mmol l−1, respectively, were used to assess the effects on conjugative transfer of a mcr‐1‐harbouring plasmid pCSZ4 (IncX4) in conjugation experiment. The inhibitory mechanisms were analysed by molecular docking and the gene expression of virB11 was quantitated by qRT‐PCR. Target plasmid diversity was carried out by TrwD/VirB11 homology protein sequence prediction analysis. Our results showed that LA and ALA inhibit plasmid pCSZ4 transfer by binding to the amino acid residues (Phe124 and Thr125) of VirB11 with dose‐dependent effects. The expression levels of virB11 gene were also significantly inhibited by LA and ALA treatment. Protein homology analysis revealed a wide distribution of TrwD/VirB11‐like genes among over 37 classes of plasmids originated from both Gram‐negative and Gram‐positive bacteria.
Conclusions
This study demonstrates representing a diversity of plasmids that may be potentially inhibited by unsaturated fatty acids.
Significance and Impact of the Study
Our work reported here provides additional support for application of curbing the spread of multiple plasmids by unsaturated fatty acids.
Asymptomatic patients, together with those with mild symptoms of coronavirus disease 2019 (COVID-19), may play an important role in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) ...transmission. However, the dynamics of virus shedding during the various phases of the clinical course of COVID-19 remains unclear at this stage.
A total of 18 patients found to be positive for SARS-CoV-2 infection by real-time reverse transcription PCR (RT-PCR) assay and admitted to Chongqing University Central Hospital between 29 January and 5 February 2020 were enrolled into this study. Medical data, pulmonary computed tomographic (CT) scan images and RT-PCR results were periodically collected during the patients' hospital stay. All participants were actively followed up for 2 weeks after discharge.
A total of nine (50%) asymptomatic patients and nine (50%) patients with mild symptoms of COVID-19 were identified at admission. Six patients (66.7%) who were asymptomatic at admission developed subjective symptoms during hospitalization and were recategorized as being presymptomatic. The median duration of virus shedding was 11.5, 28 and 31 days for presymptomatic, asymptomatic and mildly symptomatic patients, separately. Seven patients (38.9%) continued to shed virus after hospital discharge. During the convalescent phase, detectable antibodies to SARS-CoV-2 and RNA were simultaneously observed in five patients (27.8%).
Long-term virus shedding was documented in patients with mild symptoms and in asymptomatic patients. Specific antibody production to SARS-CoV-2 may not guarantee virus clearance after discharge. These observations should be considered when making decisions regarding clinical and public health, and when considering strategies for the prevention and control of SARS-CoV-2 infection.
We present an analysis of “boomerang‐shaped” pitch angle evolutions of outer radiation belt relativistic electrons observed by the Van Allen Probes after the passage of an interplanetary shock on 7 ...June 2014. The flux at different pitch angles is modulated by Pc5 waves, with equatorially mirroring electrons reaching the satellite first. For 90° pitch angle electrons, the phase change of the flux modulations across energy exceeds 180° and increasingly tilts with time. Using estimates of the arrival time of particles of different pitch angles at the spacecraft location, a scenario is investigated in which shock‐induced ULF waves interact with electrons through the drift resonance mechanism in a localized region westward of the spacecraft. Numerical calculations on particle energy gain with the modified ULF wavefield reproduce the observed boomerang stripes and modulations in the electron energy spectrogram. The study of boomerang stripes and their relationship to drift resonance taking place at a location different from the observation point adds new understanding of the processes controlling the dynamics of the outer radiation belt.
Key Points
Boomerang‐shaped pitch angle evolutions of relativistic electrons in Pc5 band is observed for the first time in the outer radiation belt
Electrons' drift resonating with azimuthally localized ULF waves can produce boomerang‐shaped pitch angle stripes
Nonlocal effects in drift‐resonant process on outer belt dynamics
Al-Ti-B is the most widely used grain refiner for many Al alloys. However, the precise mechanism of grain refinement is still not clear after 60years of intensive research. This work aims to further ...our understanding on the grain refining mechanism involving Al-Ti-B-based grain refiners. Extensive high-resolution electron microscopy investigation has confirmed the existence of a Ti-rich monolayer on the (0001) TiB2 surface, which is most likely to be a (112) Al3Ti two-dimensional compound (2DC). Further experimental investigation was carried out to understand the potency of TiB2 particles and the stability of the Al3Ti 2DC. Our results showed that the potency of TiB2 particles is significantly increased by the formation of a monolayer of Al3Ti 2DC on their surface. The Al3Ti 2DC forms at the liquid-Al/TiB2 interface in concentrated Al-Ti solutions, but dissolves in dilute Al-Ti solutions, although the kinetics of both the formation and dissolution of Al3Ti 2DC are relatively sluggish. Effective grain refinement by the Al-5Ti-1B grain refiner is directly attributed to the enhanced potency of TiB2 particles with the Al3Ti 2DC and sufficient free Ti solute in the melt after grain refiner addition to achieve the columnar-to-equiaxed transition.
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