We report a further investigation of the optical low frequency quasi periodic oscillations(LF QPOs)detected in the black hole transient MAXI J1820+070 in the 2018 observations with the YFOSC mounted on Lijiang 2.4 m t...We report a further investigation of the optical low frequency quasi periodic oscillations(LF QPOs)detected in the black hole transient MAXI J1820+070 in the 2018 observations with the YFOSC mounted on Lijiang 2.4 m telescope(LJT).In addition,we make use of the Insight-HXMT/HE observations to measure the properties of the quasi-simultaneous X-ray LF QPOs of MAXI J1820+070 on the same day.We compared the centroid frequency,the full width at half maximum(FWHM)and the fractional rms of the LF QPOs in both wavelength ranges.We found that the centroid frequency of the optical QPO is at a frequency of 51.58 m Hz,which is consistent with that of the X-ray LF QPO detected on the same day within 1 m Hz.We also found that the FWHM of the optical LF QPO is significantly smaller than that of the X-ray LF QPO,indicating that the optical QPO has a higher coherence.The quasi-simultaneous optical and the X-ray LF QPO at a centroid frequency of about 52 m Hz suggests that the actual mechanisms of these LF QPOs as the Lense-Thirring precession should work in the vicinity of a radius of about 80-117 gravitational radii(R_(g)=GM/c^(2),M is the mass of the black hole)from the black hole if the QPO frequency is related to a proxy of the orbital frequency in the accretion fiow as the Lense-Thirring precession model suggests.Furthermore,the apparent higher coherence of the optical QPO favors that it is a more original signal as compared with the X-ray QPO.展开更多
Thermophysical analysis of the crustal rocks is important for heat transfer determination and insulation purposes to save energy in buildings.In the presented work,thermophysical properties of four limestones were inv...Thermophysical analysis of the crustal rocks is important for heat transfer determination and insulation purposes to save energy in buildings.In the presented work,thermophysical properties of four limestones were investigated in dry and moist state under ambient conditions by using a transient plane source method.A thermal constant analyzer was used to raise the sample temperature and to measure the thermal properties in the temperature range of 300 K to 433 K.Thermal conductivity and diffusivity were measured by developing a linear relationship between temperature response of TPS (transient plane source) sensor and dimensionless time function through least-square fitting method.The experimental observations and predicted thermal conductivity of samples have shown that in-situ observations are important to determine the thermal properties accurately.The effect of temperature on thermal properties of limestone was defined by considering the chemical composition of the samples and associated heat transfer mechanism.Both thermal conductivity and diffusivity of limestone decreased while specific heat capacity increased with a rise in temperature.The overall findings indicate that the spinoff of this research is useful in studying the reliance of thermophysical properties of rocks on their structures and lithology.展开更多
基金Supported by the National Natural Science Foundation of China。
文摘We report a further investigation of the optical low frequency quasi periodic oscillations(LF QPOs)detected in the black hole transient MAXI J1820+070 in the 2018 observations with the YFOSC mounted on Lijiang 2.4 m telescope(LJT).In addition,we make use of the Insight-HXMT/HE observations to measure the properties of the quasi-simultaneous X-ray LF QPOs of MAXI J1820+070 on the same day.We compared the centroid frequency,the full width at half maximum(FWHM)and the fractional rms of the LF QPOs in both wavelength ranges.We found that the centroid frequency of the optical QPO is at a frequency of 51.58 m Hz,which is consistent with that of the X-ray LF QPO detected on the same day within 1 m Hz.We also found that the FWHM of the optical LF QPO is significantly smaller than that of the X-ray LF QPO,indicating that the optical QPO has a higher coherence.The quasi-simultaneous optical and the X-ray LF QPO at a centroid frequency of about 52 m Hz suggests that the actual mechanisms of these LF QPOs as the Lense-Thirring precession should work in the vicinity of a radius of about 80-117 gravitational radii(R_(g)=GM/c^(2),M is the mass of the black hole)from the black hole if the QPO frequency is related to a proxy of the orbital frequency in the accretion fiow as the Lense-Thirring precession model suggests.Furthermore,the apparent higher coherence of the optical QPO favors that it is a more original signal as compared with the X-ray QPO.
基金Authors would like to thank the Deanship of Scientific Research at King Saud University,Saudi Arabia,for financing this research under Research Group Project No.RG-1440-095.
文摘Thermophysical analysis of the crustal rocks is important for heat transfer determination and insulation purposes to save energy in buildings.In the presented work,thermophysical properties of four limestones were investigated in dry and moist state under ambient conditions by using a transient plane source method.A thermal constant analyzer was used to raise the sample temperature and to measure the thermal properties in the temperature range of 300 K to 433 K.Thermal conductivity and diffusivity were measured by developing a linear relationship between temperature response of TPS (transient plane source) sensor and dimensionless time function through least-square fitting method.The experimental observations and predicted thermal conductivity of samples have shown that in-situ observations are important to determine the thermal properties accurately.The effect of temperature on thermal properties of limestone was defined by considering the chemical composition of the samples and associated heat transfer mechanism.Both thermal conductivity and diffusivity of limestone decreased while specific heat capacity increased with a rise in temperature.The overall findings indicate that the spinoff of this research is useful in studying the reliance of thermophysical properties of rocks on their structures and lithology.
