High-energy photons from the Crab Nebula
The Crab Nebula contains a pulsar that excites the surrounding gas to emit high-energy radiation. The combination of the pulsar's youth and nearby location ...makes the nebula the brightest gamma-ray source in the sky. The LHAASO Collaboration report observations of this source at energies of tera– to peta–electron volts, extending the spectrum of this prototypical object. They combine these data with observations at lower energies to model the physics of the emission process. The multiwave-length data can be explained by a combination of synchrotron radiation and inverse Compton scattering.
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Detection of the Crab Nebula at peta–electron volt energies constrains the gamma-ray emission mechanism.
The Crab Nebula is a bright source of gamma rays powered by the Crab Pulsar’s rotational energy through the formation and termination of a relativistic electron-positron wind. We report the detection of gamma rays from this source with energies from 5 × 10
−4
to 1.1 peta–electron volts with a spectrum showing gradual steepening over three energy decades. The ultrahigh-energy photons imply the presence of a peta–electron volt electron accelerator (a pevatron) in the nebula, with an acceleration rate exceeding 15% of the theoretical limit. We constrain the pevatron’s size between 0.025 and 0.1 parsecs and the magnetic field to ≈110 microgauss. The production rate of peta–electron volt electrons, 2.5 × 10
36
ergs per second, constitutes 0.5% of the pulsar spin-down luminosity, although we cannot exclude a contribution of peta–electron volt protons to the production of the highest-energy gamma rays.
Although significant advances have recently been made in the diagnosis and treatment of cervical carcinoma, the long-term survival rate for advanced cervical cancer remains low. Therefore, an urgent ...need exists to both uncover the molecular mechanisms and identify potential therapeutic targets for the treatment of cervical cancer. MicroRNAs (miRNAs) have important roles in cancer progression and could be used as either potential therapeutic agents or targets. miR-506 is a component of an X chromosome-linked miRNA cluster. The biological functions of miR-506 have not been well established. In this study, we found that miR-506 expression was downregulated in approximately 80% of the cervical cancer samples examined and inversely correlated with the expression of Ki-67, a marker of cell proliferation. Gain-of-function and loss-of-function studies in human cervical cancer, Caski and SiHa cells, demonstrated that miR-506 acts as a tumor suppressor by inhibiting cervical cancer growth in vitro and in vivo. Further studies showed that miR-506 induced cell cycle arrest at the G1/S transition, and enhanced apoptosis and chemosensitivity of cervical cancer cell. We subsequently identified Gli3, a hedgehog pathway transcription factor, as a direct target of miR-506 in cervical cancer. Furthermore, Gli3 silencing recapitulated the effects of miR-506, and reintroduction of Gli3 abrogated miR-506-induced cell growth arrest and apoptosis. Taken together, we conclude that miR-506 exerts its anti-proliferative function by directly targeting Gli3. This newly identified miR-506/Gli3 axis provides further insight into the pathogenesis of cervical cancer and indicates a potential novel therapeutic agent for the treatment of cervical cancer.
Two-dimensional (2D) materials have been studied extensively as monolayers, vertical or lateral heterostructures. To achieve functionalization, monolayers are often patterned using soft lithography ...and selectively decorated with molecules. Here we demonstrate the growth of a family of 2D materials that are intrinsically patterned. We demonstrate that a monolayer of PtSe
can be grown on a Pt substrate in the form of a triangular pattern of alternating 1T and 1H phases. Moreover, we show that, in a monolayer of CuSe grown on a Cu substrate, strain relaxation leads to periodic patterns of triangular nanopores with uniform size. Adsorption of different species at preferred pattern sites is also achieved, demonstrating that these materials can serve as templates for selective self-assembly of molecules or nanoclusters, as well as for the functionalization of the same substrate with two different species.
By combining angle-resolved photoemission spectroscopy and quantum oscillation measurements, we performed a comprehensive investigation on the electronic structure of LaSb, which exhibits ...near-quadratic extremely large magnetoresistance (XMR) without any sign of saturation at magnetic fields as high as 40 T. We clearly resolve one spherical and one intersecting-ellipsoidal hole Fermi surfaces (FSs) at the Brillouin zone (BZ) center Γ and one ellipsoidal electron FS at the BZ boundary X. The hole and electron carriers calculated from the enclosed FS volumes are perfectly compensated, and the carrier compensation is unaffected by temperature. We further reveal that LaSb is topologically trivial but shares many similarities with the Weyl semimetal TaAs family in the bulk electronic structure. Based on these results, we have examined the mechanisms that have been proposed so far to explain the near-quadratic XMR in semimetals.
Abstract Background and aims Curcumin has been reported to lower plasma lipids and glucose in diabetic rats, and to decrease body weight in obese rats, which may partly be due to increased fatty acid ...oxidation and utilization in skeletal muscle. Methods and results Diabetic rats induced by high-fat diet plus streptozotocin (STZ, 30 mg/kg BW) were fed a diet containing 50, 150, or 250 mg/kg BW curcumin for 7 wk. Curcumin dose-dependently decreased plasma lipids and glucose and the dose 150 mg/kg BW appeared to be adequate to produce a significant effect. Curcumin supplementation reduced glucose and insulin tolerance measured as areas under the curve. L6 myotubes were treated with palmitate (0.25 mmol/L) in the presence of different levels of curcumin for 24 h in our in vitro experiment. Curcumin at 10 μmol/L was adequate to cause a significant increase in 2-deoxy-3 H d -glucose uptake by L6 myotubes. Curcumin up-regulated expression of phosphorylated AMP-activated protein kinase (AMPK), CD36, and carnitine palmitoyl transferase 1, but down-regulated expression of pyruvate dehydrogenase 4 and phosphorylated glycogen synthase (GS) in both in vivo and in vitro studies. Moreover, curcumin increased phosphorylated acetyl COA carboxylase in L6 myotubes. The effects of curcumin on these enzymes except for GS were suppressed by AMPK inhibitor, Compound C. LKB1, an upstream kinase of AMPK, was activated by curcumin and inhibited by radicicol, an LKB1 destabilizer. Conclusion Curcumin improves muscular insulin resistance by increasing oxidation of fatty acid and glucose, which is, at least in part, mediated through LKB1-AMPK pathway.
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.
Abstract Previous data demonstrate that traumatic brain injury (TBI) activates autophagy, and increases microtubule-associated protein 1 light chain 3 (LC3) immunostaining mainly in neurons. However, ...the role of autophagy in traumatic brain damage remains elusive. The aim of the present study was to investigate the autophagic mechanisms participating in traumatic brain injury. The autophagy inhibitors 3-methyladenine (3-MA) and bafliomycin A1 (BFA) were administered with a single i.c.v. injection before TBI. We first examined the protein levels of Beclin-1 and LC3 II, which have been found to promote autophagy previously. Immunoblotting analysis showed that 3-MA pretreatment reduced post-TBI Beclin-1 and LC3-II levels, and maintained p62/SQSTM1 (p62) levels. In addition, double immunolabeling showed that the increased punctate LC3-II dots colocalizing with Propidium Iodide (PI)-stained nuclei at 24 h after injury, were partially inhibited by 3-MA pretreatment. Furthermore, inhibition of autophagy could reduce TBI-induced cell injury assessed with i.p. injection of PI and lesion volume, and attenuate behavioral outcome evaluated by motor test and Morris water maze. The neuroprotective effects were associated with an inhibition on TBI-induced up-regulation of LC3, Beclin-1, cathepsin B, caspase-3 and the Beclin-1/Bcl-2 ratio. Taken together, these data imply that the autophagy pathway is involved in the pathophysiologic responses after TBI, and inhibition of this pathway may help attenuate traumatic damage and functional outcome deficits.
Four extreme haze episodes occurred in October 2014 in the North China Plain (NCP). To clarify the formation mechanism of hazes in autumn, strengthened observations were conducted in Beijing from 5 ...October to 2 November. The meteorological parameters, satellite data, chemical compositions and optical properties of aerosols were obtained. The hazes originated from the NCP, developing in the southwest and northeast directions, with the highest concentration of PM2.5 of 469 mu g m-3 in Beijing. The NCP was dominated by a weak high pressure system during the haze episode, which resulted in low surface wind speed and relatively stagnant weather. Moreover, the wind slowed down around Beijing city. The secondary aerosols NO3- was always higher than that of SO42-, which indicated the motor vehicles played a more important part in the hazes in October 2014, even though the oxidation rate from SO2 to SO42- was faster than that of NOx to NO3-. Sudden increases of the concentrations of organic matter, Cl- and BC (black carbon) before each haze episode implied that regional transport of pollutants by biomass burning was important for haze formation during autumn. A satellite map of fire points and the backward trajectories of the air masses also indicated this pollution source. The distinct decrease in the PBL (planetary boundary layer) height during four haze episodes restrained the vertical dispersion of the air pollutants. Water vapor also played a vital role in the formation of hazes by accelerating the chemical transformation of secondary pollutants, leading to hygroscopic growth of aerosols and altering the thermal balance of the atmosphere.
Submicron aerosol particles (PM1) were measured in-situ using a High-Resolution Time-of-Flight Aerosol Mass Spectrometer during the summer 2009 Field Intensive Study at Queens College in New York, ...NY. Organic aerosol (OA) and sulfate are the two dominant species, accounting for 54% and 24%, respectively, of the total PM1 mass. The average mass-based size distribution of OA presents a small mode peaking at ~150 nm (Dva) and an accumulation mode (~550 nm) that is internally mixed with sulfate, nitrate, and ammonium. The diurnal cycles of both sulfate and OA peak between 01:00–02:00 p.m. EST due to photochemical production. The average (±σ) oxygen-to-carbon (O/C), hydrogen-to-carbon (H/C), and nitrogen-to-carbon (N/C) ratios of OA in NYC are 0.36 (±0.09), 1.49 (±0.08), and 0.012 (±0.005), respectively, corresponding to an average organic mass-to-carbon (OM/OC) ratio of 1.62 (±0.11). Positive matrix factorization (PMF) of the high resolution mass spectra identified two primary OA (POA) sources, traffic and cooking, and three secondary OA (SOA) components including a highly oxidized, regional low-volatility oxygenated OA (LV-OOA; O/C = 0.63), a less oxidized, semi-volatile SV-OOA (O/C = 0.38) and a unique nitrogen-enriched OA (NOA; N/C = 0.053) characterized with prominent CxH2x + 2N+ peaks likely from amino compounds. Our results indicate that cooking and traffic are two distinct and mass-equivalent POA sources in NYC, together contributing ~30% of the total OA mass during this study. The OA composition is dominated by secondary species, especially during high PM events. SV-OOA and LV-OOA on average account for 34% and 30%, respectively, of the total OA mass. The chemical evolution of SOA in NYC appears to progress with a continuous oxidation from SV-OOA to LV-OOA, which is further supported by a gradual increase of O/C ratio and a simultaneous decrease of H/C ratio in total OOA. Detailed analysis of NOA (5.8% of OA) presents evidence that organic nitrogen species such as amines might have played an important role in the atmospheric processing of OA in NYC, likely involving both acid-base chemistry and photochemistry. In addition, analysis of air mass trajectories and satellite imagery of aerosol optical depth (AOD) indicates that the high potential source regions of secondary sulfate and aged OA are mainly located in regions to the west and southwest of the city.
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