Searching for the nano-Hertz stochastic gravitational wave background with the Chinese Pulsar Timing Array Data Release I

Observing and timing a group of millisecond pulsars (MSPs) with high rotational stability enables the direct detection of gravitational waves (GWs). The GW signals can be identified from the spatial correlations encoded in the times-of-arrival of widely spaced pulsar-pairs. The Chinese Pulsar Timing Array (CPTA) is a collaboration aiming at the direct GW detection with observations carried out using Chinese radio telescopes. This short article serves as a `table of contents' for a forthcoming series of papers related to the CPTA Data Release 1 (CPTA DR1) which uses observations from the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Here, after summarizing the time span and accuracy of CPTA DR1, we report the key results of our statistical inference finding a correlated signal with amplitude \log A_{\rm c}= -14.4 \,^{+1.0}_{-2.8} for spectral index in the range of $\alpha\in [-1.8, 1.5]$ assuming a GW background (GWB) induced quadrupolar correlation. The search for the Hellings-Downs (HD) correlation curve is also presented, where some evidence for the HD correlation has been found that a 4.6-$\sigma$ statistical significance is achieved using the discrete frequency method around the frequency of 14 nHz. We expect that the future International Pulsar Timing Array data analysis and the next CPTA data release will be more sensitive to the nHz GWB, which could verify the current results.Comment: 18 pages, 6 figures, submitted to "Research in astronomy and astrophysics" 22nd March 202

Composite Kernels for Semi-Supervised Clustering

A critical problem related to kernel-based methods is how to select optimal kernels. A kernel function must conform to the learning target in order to obtain meaningful results. While solutions to the problem of estimating optimal kernel functions and corresponding parameters have been proposed in a supervised setting, it remains a challenge when no labeled data are available, and all we have is a set of pairwise must-link and cannot-link constraints. In this paper, we address the problem of optimizing the kernel function using pairwise constraints for semi-supervised clustering. We propose a new optimization criterion for automatically estimating the optimal parameters of composite Gaussian kernels, directly from the data and given constraints. We combine our proposal with a semi-supervised kernel-based algorithm to demonstrate experimentally the effectiveness of our approach. The results show that our method is very effective for kernel-based semi-supervised clustering

Solar Image Restoration with the CycleGAN Based on Multi-fractal Properties of Texture Features

Texture is one of the most obvious characteristics in solar images and it is normally described by texture features. Because textures from solar images of the same wavelength are similar, we assume that texture features of solar images are multi-fractals. Based on this assumption, we propose a pure data-based image restoration method: with several high-resolution solar images as references, we use the Cycle-Consistent Adversarial Network to restore blurred images of the same steady physical process, in the same wavelength obtained by the same telescope. We test our method with simulated and real observation data and find that our method can improve the spatial resolution of solar images, without loss of any frames. Because our method does not need a paired training set or additional instruments, it can be used as a post-processing method for solar images obtained by either seeing-limited telescopes or telescopes with ground-layer adaptive optic systems

Short-term Runoff Forecasting based on Hydrological Factors at Nanchang Section of Ganjiang River, China

With the change of global climate and underlying surface characteristics, and increasing human activities, hydro-meteorological factors such as precipitation, evaporation, and runoff. Etc., are directly affected, therefore the assumption of stationarity may no longer exist. In a changing environment, the conventional runoff forecasting methods become invalid, which brings challenges to accurate hydrometeorological forecast. A hydrological model based on the changing environment was employed to forecast the runoff at Nanchang Section of Ganjiang River in this paper, and the rationality and validity of the built model were verified. The results shows that the built hydrological model has high accuracy in the short-term runoff forecasting, and better forecasting effect has been obtained after the parameters calibration and the real-time correction of the predicted runoffs, which can provide the strong support for the scientific water resources operation decision and also provide the boundary conditions of water level and water quality for the hydrodynamic and water-quality simulation at the Nanchang Section of the Ganjiang River

Review and prospect about water resources operation research

The concept of water resources operation is expatiated and classified and the theories and methods with regard to water resources operation are also summarized. Research progress of water resources operation exists to analyse the problems and to take a look to the future of research directions in the field of water resources operation. In conclusion, the research on water resources operation needs a combination with the actual state of projects, climate change and increasing human activities, actually considering water resources demands and employing uniform control of water quantity and quality, which could ensure the sustainable utilization of water resources in China

PSF–NET: A Nonparametric Point-spread Function Model for Ground-based Optical Telescopes

Ground-based optical telescopes are seriously affected by atmospheric turbulence induced aberrations. Understanding properties of these aberrations is important both for instrument design and image restoration method development. Because the point-spread function can reflect performance of the whole optic system, it is appropriate to use the point-spread function to describe atmospheric turbulence induced aberrations. Assuming point-spread functions induced by the atmospheric turbulence with the same profile belong to the same manifold space, we propose a nonparametric point-spread function—PSF–NET. The PSF–NET has a cycle convolutional neural network structure and is a statistical representation of the manifold space of PSFs induced by the atmospheric turbulence with the same profile. Testing the PSF–NET with simulated and real observation data, we find that a well trained PSF–NET can restore any short exposure images blurred by atmospheric turbulence with the same profile. Besides, we further use the impulse response of the PSF–NET, which can be viewed as the statistical mean PSF, to analyze interpretation properties of the PSF–NET. We find that variations of statistical mean PSFs are caused by variations of the atmospheric turbulence profile: as the difference of the atmospheric turbulence profile increases, the difference between statistical mean PSFs also increases. The PSF–NET proposed in this paper provides a new way to analyze atmospheric turbulence induced aberrations, which would benefit the development of new observation methods for ground-based optical telescopes

Review and prospect about water resources operation research

The concept of water resources operation is expatiated and classified and the theories and methods with regard to water resources operation are also summarized. Research progress of water resources operation exists to analyse the problems and to take a look to the future of research directions in the field of water resources operation. In conclusion, the research on water resources operation needs a combination with the actual state of projects, climate change and increasing human activities, actually considering water resources demands and employing uniform control of water quantity and quality, which could ensure the sustainable utilization of water resources in China

Infrared Free Induction Decay (IR-FID) of Non-Interfacial Origin Observed in the Interfacial Sum-Frequency Generation Vibrational Spectroscopy (SFG-VS)

We report the observation of infrared free induction decay (IR-FID) signal of the anti-symmetric modes around ~ 2350 cm-1 of the gaseous CO2 molecules in the air in the sum-frequency generation vibrational spectroscopy (SFG-VS) measurement from the gold surface. These signals appeared with time-dependent interference pattern in the 15-73 ps range and beyond after the time-zero of the SFG-VS process. The interference pattern was found to reflect the rotational coherence of the gaseous CO2 molecules. Similar IR-FID and rotational coherence was also observed for the symmetric and asymmetric stretching modes of gaseous H2O molecules in air. The gold surface in this case serves as the up-conversion agent with the visible pulse as the time-gate for the ultrafast IR-FID emissions. We tested this hypothesis by replacing the gold surface with a β-BBO (beta-barium borate, β-BaB2O4) and found a five orders of magnitude increase of the signal in the reflecting geometry. The up-conversion of the IR-FID radiation of non-interfacial origin into the SFG-VS signal also provides the mechanistic understanding of the ‘abnormal spectral bands’ in broadband SFG-VS induced by bulk absorption and refraction reported in the literature

Experimental Study and Numerical Simulation of W/O Emulsion in Developing Heavy Oil Reservoirs

In the process of waterflooding development of heavy oil, W/O emulsion has a strong ability to improve the mobility ratio and block the high-permeability layer, which can effectively improve the sweep coefficient and enhance oil recovery. In this paper, the stability and droplet size distribution of emulsions under different conditions were studied by taking heavy oil and formation water from Jimusar Oilfield in Xinjiang as samples. On this basis, double-pipe core flooding experiments were carried out to study the shut-off ability and oil displacement efficiency of W/O emulsion, and then a numerical simulation was carried out. The results show that oil and water can be completely emulsified when the stirring speed is higher than 4000 r/min. A stable emulsion can be formed when the experimental temperature is lower than 60 °C. A lower water cut results in a more stable emulsion. The emulsion is difficult to stabilize after the salinity exceeds 10,000 mg/L. When the pH value is about 7, the stability of the emulsion is the worst. With the increase in stirring speed, the increase in temperature, and the decrease in water content and salinity, the emulsion droplet size range is relatively concentrated, and the average particle size is smaller. In heterogeneous reservoirs, the permeability of different percolation channels is quite different, such that the displacement fluid only percolates along the high-permeability channel and cannot drive oil effectively. The results of displacement experiments show that the emulsion with a water cut of 60% has high viscosity and obvious sweep ability, but its stability is very poor; the effect is opposite when the water cut is less than 40%. The shut-off ability of W/O emulsion disappears gradually when the permeability contrast is more than 5.92. The research results are of great significance for improving oil recovery in heterogeneous heavy oil reservoirs

RAB31 in glioma‐derived endothelial cells promotes glioma cell invasion via extracellular vesicle‐mediated enrichment of MYO1C

Extracellular vesicles (EV), important messengers in intercellular communication, can load and transport various bioactive components and participate in different biological processes. We previously isolated glioma human endothelial cells (GhECs) and found that GhECs, rather than normal human brain endothelial cells (NhECs), exhibit specific enrichment of MYO1C into EVs and promote the migration of glioma cells. In this study, we explored the mechanism by which MYO1C is secreted into EVs. We report that such secretion is dependent on RAB31, RAB27B, and FAS. When expression of RAB31 increases, MYO1C is enriched in secretory EVs. Finally, we identified an EV export mechanism for MYO1C that promotes glioma cell invasion and is dependent on RAB31 in GhECs. In summary, our data indicate that the knockdown of RAB31 can reduce enrichment of MYO1C in extracellular vesicles, thereby attenuating the promotion of glioma cell invasion by GhEC‐EVs