Fast radio bursts (FRBs) are millisecond-duration radio transients
of unknown origin. Two possible mechanisms that could generate extremely coherent emission from FRBs invoke neutron star ...magnetospheres
or relativistic shocks far from the central energy source
. Detailed polarization observations may help us to understand the emission mechanism. However, the available FRB polarization data have been perplexing, because they show a host of polarimetric properties, including either a constant polarization angle during each burst for some repeaters
or variable polarization angles in some other apparently one-off events
. Here we report observations of 15 bursts from FRB 180301 and find various polarization angle swings in seven of them. The diversity of the polarization angle features of these bursts is consistent with a magnetospheric origin of the radio emission, and disfavours the radiation models invoking relativistic shocks.
Fast radio bursts (FRBs) are millisecond-duration radio transients of unknown physical origin observed at extragalactic distances
. It has long been speculated that magnetars are the engine powering ...repeating bursts from FRB sources
, but no convincing evidence has been collected so far
. Recently, the Galactic magnetar SRG 1935+2154 entered an active phase by emitting intense soft γ-ray bursts
. One FRB-like event with two peaks (FRB 200428) and a luminosity slightly lower than the faintest extragalactic FRBs was detected from the source, in association with a soft γ-ray/hard-X-ray flare
. Here we report an eight-hour targeted radio observational campaign comprising four sessions and assisted by multi-wavelength (optical and hard-X-ray) data. During the third session, 29 soft-γ-ray repeater (SGR) bursts were detected in γ-ray energies. Throughout the observing period, we detected no single dispersed pulsed emission coincident with the arrivals of SGR bursts, but unfortunately we were not observing when the FRB was detected. The non-detection places a fluence upper limit that is eight orders of magnitude lower than the fluence of FRB 200428. Our results suggest that FRB-SGR burst associations are rare. FRBs may be highly relativistic and geometrically beamed, or FRB-like events associated with SGR bursts may have narrow spectra and characteristic frequencies outside the observed band. It is also possible that the physical conditions required to achieve coherent radiation in SGR bursts are difficult to satisfy, and that only under extreme conditions could an FRB be associated with an SGR burst.
Fast radio bursts (FRBs) are highly dispersed, millisecond-duration radio bursts1-3. Recent observations of a Galactic FRB4-8 suggest that at least some FRBs originate from magnetars, but the origin ...of cosmological FRBs is still not settled. Here we report the detection of1,863 bursts in 82 h over 54 days from the repeating source FRB 20201124A (ref.9). These observations show irregular short-time variation ofthe Faraday rotation measure (RM), which scrutinizes the density-weighted line-of-sight magnetic field strength, of individual bursts during the first 36 days, followed by a constant RM. We detected circular polarization in more than half of the burst sample, including one burst reaching a high fractional circular polarization of 75%. Oscillations in fractional linear and circular polarizations, as well as polarization angle as a function of wavelength, were detected. All of these features provide evidence for a complicated, dynamically evolving, magnetized immediate environment within about an astronomical unit (au; Earth-Sun distance) ofthe source. Our optical observations of its Milky-Way-sized, metal-rich host galaxy10-12 show a barred spiral, with the FRB source residing in a low-stellar-density interarm region at an intermediate galactocentric distance. This environment is inconsistent with a young magnetar engine formed during an extreme explosion of a massive star that resulted in a long gamma-ray burst or superluminous supernova.
In order to address the present difficulty in experimentally generating the relativistic Laguerre-Gaussian laser, primarily due to damage caused to optical modulators, a high-reflectivity phase ...mirror is applied in the femtosecond petawatt laser system to generate a relativistic hollow laser at the highest intensity of 6.3 × 1019 W / cm2 for the first time. A simple optical model is used to verify that the vortex laser may be generated in this new scheme; using such a relativistic vortex laser, the hollow plasma drill and acceleration are achieved experimentally and proven by particle-in-cell simulations. With the development of the petawatt laser, this scheme opens up possibilities for the convenient production of the relativistic hollow laser at high repetition and possible hollow plasma acceleration, which is important for a wide range of applications such as the generation of radiation sources with orbital angular momentum, fast ignition for inertial confinement fusion, and jet research in the astrophysical environment.
Background:
MicroRNAs (miRNAs) are known to regulate the inflammatory response in various cell types. However, the ability of miRNAs to modulate dendritic cells (DCs) function for allergen ...immunotherapy is unclear.
Objective:
To assess the role of miR‐23b in the regulation of ovalbumin (OVA)‐induced DC differentiation and function and to investigate the related molecular mechanisms.
Methods:
Bone marrow‐derived dendritic cells (BMDCs) were generated from murine bone marrow progenitor cells and subsequently stimulated with OVA to examine the profile of miRNA expression. After transfection with miR‐23b reagents, DCs were evaluated for endocytic ability, surface marker expression, cytokine secretion and CD4+ T‐cell differentiation. The possible roles of the Notch and NF‐κB signalling pathways were also evaluated. Human monocyte‐derived dendritic cells (MDDCs) were similarly evaluated as well.
Results:
Significant upregulation of miR‐23b was observed in BMDCs pulsed with OVA. Following miR‐23b transfection, BMDCs showed decreased OVA uptake, increased IL‐10 production, decreased IL‐12 production and an enhanced capacity to promote FoxP3+ CD4+ T regulatory cells (Tregs) differentiation. In addition, inactivation of the Notch1 and NF‐κB signalling pathways were observed. Conversely, inhibition of miR‐23b in BMDCs resulted in the opposite effects. In human MDDCs, miRNA23b transfection similarly increased IL‐10 and decreased IL‐12 production, and that treated human MDDCs induced increased FoxP3+ CD4+ T cells.
Conclusion:
Our findings provide evidence that miR‐23b is capable of inducing tolerogenic DC activity and Treg responses in vitro through the inhibition of the Notch1 and NF‐κB signalling pathways; thus, miR‐23b might represent a therapeutic target for the management of allergic diseases.
•HPLC separation of PEGs and amino-terminated PEGs due to ion-exchange mechanism.•Acetonitrile in water, common silica-based C18 or phenyl RP columns and ELSD used.•No obvious effect of molar mass by ...isocratic LCCC with optimal volatile buffer.
The separation and characterization of polyethylene glycols (PEGs) and amino-substituted derivatives on common silica-based reversed-phase packing columns using isocratic elution is described. This separation is achieved by liquid chromatography under the near critical conditions (LCCC), based on the number of amino functional end groups without obvious effect of molar mass for PEGs. The mobile phase is acetonitrile in water with an optimal ammonium acetate buffer. The separation mechanism of PEG and amino-substituted PEG under the near LCCC on silica-based packing columns is confirmed to be ion-exchange interaction. Under the LCCC of PEG backbone, with fine tune of buffer concentration, the retention factor ratios for benzylamine and phenol in buffered mobile phases, α(benzylamine/phenol)-values, were used to assess the ion-exchange capacity on silica-based reversed-phase packing columns. To the best of our knowledge, this is the first report on separation of amino-functional PEGs independent of the molar mass by isocratic elution using common C18 or phenyl reversed-phase packing columns.
Deposition current during fabrication plays an important role in the microstructure and properties of titanium alloy components prepared by multi-wire arc additive manufacturing (MWAAM) technology. ...In this study, Ti basic heterogeneous alloy with Ti-6.5Al-3.5Mo-1.5Zr-0.3Si (TC11) as the main component was deposited using the MWAAM method with the deposition current ranging from 360 A to 400 A. The effects of deposition current on the microstructural evolution, mechanical and corrosion properties of the MWAAM titanium alloys were investigated, and the process-microstructure-property relationship was analyzed. The results show that the microstructure of as-received Ti basic heterogeneous alloy was mainly composed of lamellar primary α phase (αP) and transformed β phase (βT), and increasing the deposition current during the MWAAM process would result in the increased width of α phase and the decreased aspect ratio of α phase. The mechanical properties of MWAAM-deposited specimens decrease with increasing current, which means that phase composition played a dominant role in determining hardness. When increasing the deposition current during the MWAAM process the ultimate tensile strength (UTS) decreased from 843.75 to 804.38 MPa. The MWAAM-deposited Ti basic heterogeneous alloy featured excellent corrosion properties, the corrosion potential of the best specimen was − 311 mV SCE and the corrosion current density was 1.23 × 10−8 Acm−2. This study provides a better understanding of the effect of deposition current on the targeted deposition property in the MWAAM process, which will contribute to future process control, improvement and optimization.
The impact of impurity ions on a pedestal has been investigated in the HL-2A Tokamak, at the Southwestern Institute of Physics, Chengdu, China. Experimental results have clearly shown that during the ...H-mode phase, an electromagnetic turbulence was excited in the edge plasma region, where the impurity ions exhibited a peaked profile. It has been found that double impurity critical gradients are responsible for triggering the turbulence. Strong stiffness of the impurity profile has been observed during cyclic transitions between the I-phase and H-mode regime. The results suggest that the underlying physics of the self-regulated edge impurity profile offers the possibility for an active control of the pedestal dynamics via pedestal turbulence.
An extruded Mg-5Zn-2.5Y-1Ce-0.5Mn alloy with uniform fine α-Mg grains, dispersed W-phase and T-phase and weak basal texture was prepared by the semi-continuous casting and one-pass extrusion methods. ...The deformation behaviors of the extruded alloy were tested at a temperature range from room temperature (RT) to 350 °C and a strain rate range from 1×10−2s−1 to 4×10−4s−1. The results and relevant mechanisms were analyzed by using the measured data of the strain rate sensitivity (m) and the activation energy (Q) and the observations of the morphologies of deformation and fracture surfaces. It was demonstrated that the tensile strengths decrease, while the elongation to failure tends to increase with increasing temperature or decreasing strain rate. The variation in mechanical properties with increasing temperature mainly arises from a change in opening deformation mechanisms from the dislocation slip at RT to the dislocation climb at 250 °C to the grain boundary (GB) sliding at 350 °C. At RT, the slightly decreased tensile strengths and slightly increased elongation to failure with decreasing strain rate are mainly attributed to the weak sensitivity of the dislocation slip to strain rate. At 250 °C, the lower tensile strengths and the larger elongation to failure at 4×10−4s−1 than that at 1×10−2s−1 are mainly attributed to the occurrence of the dynamic recrystallization (DRX) at lower strain rate, while such DRX does not occur at higher strain rate. At 350 °C, the lower tensile strengths and the much larger elongation to failure at 4×10−4s−1 than that at 1×10−2s−1 are attributed to the GB sliding accommodated by the lattice diffusion at lower strain rate, while the GB sliding at higher strain rate is accommodated by the GB diffusion.
ABSTRACT
We constrain the equation of state of quark stars within the Bayesian statistical approach using the mass and radius measurements of PSR J0030+0451 from NICER. Three types of bag models, ...with and without non-zero finite quark mass and/or superfluidity, are employed for quark stars made up with self-bound strange quark matter. We find the $90{{\ \rm per\ cent}}$ posterior credible boundary around the most probable values of the quark star maximum mass is $M_{\rm TOV}=2.38_{-0.23}^{+0.26}\, M_{\odot }$, within the model flexibility of the finite quark mass, the quark pairing gap, and the perturbative contribution from the one-gluon exchange. The radius of a canonical $1.4 \, M_{\odot }$ quark star is $R_{\rm 1.4}\sim 12.3\, {\rm km}$, smaller than the results based on neutron star models.
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