By using a coupled acoustic emission (AE) and digital image correlation (DIC) technique, the failure behavior of air plasma sprayed thermal barrier coatings (TBCs) was investigated. The in-situ DIC ...observations show that the characteristics of AE signals, extracted from the fast Fourier transform, are closely related to the failure modes of a TBC system, which was applied to real-time reveal its damage evolution during tension. It is shown that there is a typical power-law relationship between the vertical crack density in coating and strain in substrate. A damage variable defined as a function of the cumulative AE events can be used to characterize the different fracture stages of a TBC system. With the increase of strain in substrate, the AE-b value estimated by the Gutenberg–Richter law varies from 2.0 at the initial regime to a plateau value of 1.2.
•Tensile failure of APS TBCs system has been in-situ monitored by two techniques.•We further clarified several good correlations between AE data and fracture modes.•Evolution of crack density and damage was analyzed by AE and strain test results.•Relationship of AE-b change and failure modes was successfully established.
The focal plane camera is the core component of the Wide Field-of-view Cherenkov/fluorescence Telescope Array (WFCTA) of the Large High-Altitude Air Shower Observatory (LHAASO). Because of the ...capability of working under moonlight without aging, silicon photomultipliers (SiPM) have been proven to be not only an alternative but also an improvement to conventional photomultiplier tubes (PMT) in this application. Eighteen SiPM-based cameras with square light funnels have been built for WFCTA. The telescopes have collected more than 100 million cosmic ray events and preliminary results indicate that these cameras are capable of working under moonlight. The characteristics of the light funnels and SiPMs pose challenges (e.g. dynamic range, dark count rate, assembly techniques). In this paper, we present the design features, manufacturing techniques and performances of these cameras. Finally, the test facilities, the test methods and results of SiPMs in the cameras are reported here.
The intraday optical variability of the BL Lacertae object S5 0716+714 is studied using historical light curves. The well-sampled intranight data set is selected. In total, 19 333 data points have ...been collected over 208 nights. The source exhibits strong variability in the optical band. At a confidence level of 99.9 per cent, for 162 of the 208 nights the source shows intranight variability. The source varies with an increasing rate of 0.043 mag h−1 and a decreasing rate of 0.036 mag h−1 during the observations, with no evident difference between rising and falling parts. The fast variability is found on JD 245 1909, with a decreasing rate of 0.015 mag min−1 over 6 min. The temporal characteristic is studied by using the structure function method. The result shows that the source varies with an 11.5-min time-scale. For this source, the emission size is estimated to be 1.39 × 1014 cm, the mass of the central black hole is estimated to be 107.87 M⊙ and the magnetic field strength is estimated to be 10.6 G.
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.
We report the discovery of an extended very-high-energy (VHE) gamma-ray source around the location of the middle-aged (207.8 kyr) pulsar PSR J 0622 + 3749 with the Large High-Altitude Air Shower ...Observatory (LHAASO). The source is detected with a significance of 8.2 σ for E > 25 TeV assuming a Gaussian template. The best-fit location is (right ascension, declination) = ( 95.47 ° ± 0.11 ° , 37.92 ° ± 0.09 ° ) , and the extension is 0.40 ° ± 0.07 ° . The energy spectrum can be described by a power-law spectrum with an index of − 2.92 ± 0.17stat± 0.02sys. No clear extended multiwavelength counterpart of the LHAASO source has been found from the radio to sub-TeV bands. The LHAASO observations are consistent with the scenario that VHE electrons escaped from the pulsar, diffused in the interstellar medium, and scattered the interstellar radiation field. If interpreted as the pulsar halo scenario, the diffusion coefficient, inferred for electrons with median energies of ∼ 160 TeV , is consistent with those obtained from the extended halos around Geminga and Monogem and much smaller than that derived from cosmic ray secondaries. The LHAASO discovery of this source thus likely enriches the class of so-called pulsar halos and confirms that high-energy particles generally diffuse very slowly in the disturbed medium around pulsars.
Detections of Jupiter-like giant planets in orbit around short-period white dwarf binaries should provide insight into the formation and evolution of circumbinary planets (planets orbiting both ...components of short-period binaries), as well as into the ultimate fate of planets and the late evolutionary stage of binary stars (e.g. the evolution of the common envelope). However, to date no planets have been detected as companions to such close binaries. Here, we report the discovery of a giant planet orbiting the only known hibernating cataclysmic variable (CV), QS Vir, with a period of 7.86 yr. We analysed the variations of the orbital period of the eclipsing white dwarf–red dwarf binary, and a very small-amplitude cyclic change is found to be superimposed on a long-term period decrease. The period oscillation has the smallest amplitude among close binary stars and can be plausibly interpreted as the light-travel time effect via the presence of a third body. We found that the tertiary component is a giant planet with a mass of ∼6.4 MJupiter at a distance of ∼4.2 astronomical units (au) from the binary. The continuous decrease is explained as angular momentum loss via magnetic braking which is driving the evolution of the hibernating CV into a normal cataclysmic binary.
The long baseline simultaneous multiband (BVRI) observations of blazar 3C 273 are presented. We have made 758 optical multiband observations with the Yunnan Astronomical Observatory (YAO) 103 cm and ...Shanghai Astronomical Observatory (SHAO) 156 cm from 2003 January to 2005 April. In our observational campaign, the average colour indices are B−V= 0.21, V−R= 0.26 and R−I= 0.31. The mean magnitudes in B, V, R and I are 12.895, 12.698, 12.441 and 12.139, respectively. The source is in a steady state over observational campaign. The correlations between colour index and brightness are discussed. We find that the correlations of B−V versus B, V−R versus V and R−I versus R have significant negative correlation, while B−V versus V, V−R versus R and R−I versus I have positive correlation. These strong correlations imply that the spectrum becomes bluer (flatter) when the source becomes brighter, and redden (softer) when the source fades both in intraday and long-term variability. The spectral evolution trends of 3C 273 are consistent with those of BL Lac objects.
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