Graph Transformer for Recommendation

This paper presents a novel approach to representation learning in recommender systems by integrating generative self-supervised learning with graph transformer architecture. We highlight the importance of high-quality data augmentation with relevant self-supervised pretext tasks for improving performance. Towards this end, we propose a new approach that automates the self-supervision augmentation process through a rationale-aware generative SSL that distills informative user-item interaction patterns. The proposed recommender with Graph TransFormer (GFormer) that offers parameterized collaborative rationale discovery for selective augmentation while preserving global-aware user-item relationships. In GFormer, we allow the rationale-aware SSL to inspire graph collaborative filtering with task-adaptive invariant rationalization in graph transformer. The experimental results reveal that our GFormer has the capability to consistently improve the performance over baselines on different datasets. Several in-depth experiments further investigate the invariant rationale-aware augmentation from various aspects. The source code for this work is publicly available at: https://github.com/HKUDS/GFormer.Comment: Accepted by SIGIR'202

Carbonaceous matter in the atmosphere and glaciers of the Himalayas and the Tibetan plateau: An investigative review

Carbonaceous matter, including organic carbon (OC) and black carbon (BC), is an important climate forcing agent and contributes to glacier retreat in the Himalayas and the Tibetan Plateau (HTP). The HTP – the so-called “Third Pole” – contains the most extensive glacial area outside of the polar regions. Considerable research on carbonaceous matter in the HTP has been conducted, although this research has been challenging due to the complex terrain and strong spatiotemporal heterogeneity of carbonaceous matter in the HTP. A comprehensive investigation of published atmospheric and snow data for HTP carbonaceous matter concentration, deposition and light absorption is presented, including how these factors vary with time and other parameters. Carbonaceous matter concentrations in the atmosphere and glaciers of the HTP are found to be low. Analysis of water-insoluable organic carbon and BC from snowpits reveals that concentrations of OC and BC in the atmosphere and glacier samples in arid regions of the HTP may be overestimated due to contributions from inorganic carbon in mineral dust. Due to the remote nature of the HTP, carbonaceous matter found in the HTP has generally been transported from outside the HTP (e.g., South Asia), although local HTP emissions may also be important at some sites. This review provides essential data and a synthesis of current thinking for studies on atmospheric transport modeling and radiative forcing of carbonaceous matter in the HTP

Black carbon and organic carbon dataset over the Third Pole

The Tibetan Plateau and its surroundings, also known as the Third Pole, play an important role in the global and regional climate and hydrological cycle. Carbonaceous aerosols (CAs), including black carbon (BC) and organic carbon (OC), can directly or indirectly absorb and scatter solar radiation and change the energy balance on the Earth. CAs, along with the other atmospheric pollutants (e.g., mercury), can be frequently transported over long distances into the inland Tibetan Plateau. During the last decades, a coordinated monitoring network and research program named “Atmospheric Pollution and Cryospheric Changes” (APCC) has been gradually set up and continuously operated within the Third Pole regions to investigate the linkage between atmospheric pollutants and cryospheric changes. This paper presents a systematic dataset of BC, OC, water-soluble organic carbon (WSOC), and water-insoluble organic carbon (WIOC) from aerosols (20 stations), glaciers (17 glaciers, including samples from surface snow and ice, snow pits, and 2 ice cores), snow cover (2 stations continuously observed and 138 locations surveyed once), precipitation (6 stations), and lake sediment cores (7 lakes) collected across the Third Pole, based on the APCC program. These data were created based on online (in situ) and laboratory measurements. High-resolution (daily scale) atmospheric-equivalent BC concentrations were obtained by using an Aethalometer (AE-33) in the Mt. Everest (Qomolangma) region, which can provide new insight into the mechanism of BC transportation over the Himalayas. Spatial distributions of BC, OC, WSOC, and WIOC from aerosols, glaciers, snow cover, and precipitation indicated different features among the different regions of the Third Pole, which were mostly influenced by emission sources, transport pathways, and deposition processes. Historical records of BC from ice cores and lake sediment cores revealed the strength of the impacts of human activity since the Industrial Revolution. BC isotopes from glaciers and aerosols identified the relative contributions of biomass and fossil fuel combustion to BC deposition on the Third Pole. Mass absorption cross sections of BC and WSOC from aerosol, glaciers, snow cover, and precipitation samples were also provided. This updated dataset is released to the scientific communities focusing on atmospheric science, cryospheric science, hydrology, climatology, and environmental science. The related datasets are presented in the form of excel files. BC and OC datasets over the Third Pole are available to download from the National Cryosphere Desert Data Center (10.12072/ncdc.NIEER.db0114.2021; Kang and Zhang, 2021)

A tight sandstone trapezoidal pore oil saturation model

Abstract: “Non-Archie” phenomena are common in tight sandstone reservoirs with complicated pore structure, bringing challenges to the logging evaluation of tight sandstone. Based on the characteristics of tight sandstone pore structure, a new trapezoidal pore saturation model considering the effect of pore structure on rock conductivity is presented, in which the pore in tight sand is divided into straight pore with constant cross-sectional area and trapezoidal pore with variable cross-sectional area, and the total rock resistance is taken as the parallel resistance of these two parts to compressively consider the influence of pore structure and conductive volume on rock conductivity. The model parameters are studied by reconstructing the trapezoidal pore structure. Based on the trapezoidal pore reconstruction, characterization methods of model parameters were studied under the constraint of rock electrical properties test, and the variation was revealed of tortuosity, straight pore proportion and trapezoidal factors. The model was used in logging evaluation of tight sandstone of several wells, the results show the oil saturation obtained from the new model considering the effect of pore structure on electrical properties from the aspects of pore length and pore cross-section is in good accordance with the real regularity and petrophysical characteristics of the reservoir, and much closer to the formation oil-bearing conditions than that from the Archie model. Key words: Ordos Basin, Triassic Yanchang Formation, tight sandstone, pore structure, trapezoidal pore, saturation mode

Relative contribution of mineral dust versus black carbon to Third Pole glacier melting

Large-scale glaciers in the Third Pole are experiencing significant thinning and retreat, partly due to the increased deposition of black carbon (BC) and mineral dust (MD). At present, BC is generally considered a more important contributing factor than MD to glacier melting. Based on a deep analysis of published data, the relative contribution of MD versus BC to snow/ice melting increases rapidly, because BC is more likely than MD to be discharged during the melting process. As a result, the contribution of MD to glacier melting is comparable to or even higher than that of BC when the glacier surface appears as aged snow and bare ice. The importance of MD to glacier melting must therefore be emphasized in the water tower of Asia

Porous highly fluorinated polyimide/polydopamine nanocomposite films with simultaneously enhanced toughness, UV-shielding and photostability for aerospace applications

Polydopamine (PDA), also known as artificial melanin, was adopted as ultraviolet absorbent to prepare a series of porous highly fluorinated polyimide/polydopamine (FPI/PDA) films by cyclodehydration via chemical and thermal imidization. The hydrogen bond and porous structure endowed the reinforced thermal, mechanical, UV-shielding and photostability. The initial decomposition and glass transition temperatures of FPI/PDA (1 wt %) film were as high as 461.5 °C and 341.5 °C, respectively beyond pure FPI by 54.1 °C and 26.0 °C. The stress-strain curves indicated that tensile strength and fracture elongation first increased and then decreased with the increase of PDA content, and reached the maximum at 0.5 wt % PDA content, which were 1.41 and 29.47 times of FPI, respectively. UV–vis transmittance spectra, curcumin photolysis and recyclability measurement confirmed the splendid UV-shielding properties with simultaneous excellent visible light transmittance and durability of porous FPI/PDA film. FTIR and AFM manifested its superior photostability with mild variation in carbonyl absorption peaks and surface roughness after 720 h UV irradiation. The above enhancement mechanisms included synergistic UV absorption of porous FPI and PDA, photothermal conversion in a stable FPI, and PDA's free radical trapping, promoting porous FPI/PDA film as an aerospace UV shielding material

Well logging evaluation of Triassic Chang 7 Member tight reservoirs, Yanchang Formation, Ordos Basin, NW China

Taking the Triassic Chang 7 Member tight reservoirs of the Yanchang Formation in the Ordos Basin as study object, transverse relaxation simulation was made using nuclear magnetic resonance (NMR) experimental data, CT images and random-walker algorithm to evaluate microscopic pore-throats of the tight reservoirs. The smoothing degree of well logging curves was utilized to evaluate sand structure of the tight reservoirs; and through multi-well analysis and the calibration of well testing data, a grading chart of tight reservoir productivity was established based on sand structure. Reservoir quality was judged and analyzed by pore level: Transverse surface relaxivity ρ2 was obtained by comparing transverse relaxation time T2 of numerical simulation and that of NMR experiment, and the distribution of pore-throat radius was obtained according to the corrected NMR logging curves. The study shows there is an obvious correlation between productivity and sand structure of Chang 7 tight reservoirs. The more homogeneous the distribution of lithology, physical property and oiliness of the massive sand, and the smoother the well logging curves, the more likely the high oil yield will occur. Based on well logging evaluation and grading chart of productivity of tight reservoirs, sweet spots in well area W of Jiyuan Oilfield in Ordos Basin were identified, the comparison of the evaluation results and well testing data shows the accuracy rate is as high as 94.7%. Key words: tight oil, well logging evaluation, microscopic pore-throat distribution, sand structure, sweet spot distribution, Ordos Basi

Fluid identification method based on 2D diffusion-relaxation nuclear magnetic resonance (NMR)

Based on current acquisition modes of MRIL-Prime NMR logging tool, 2D NMR signals could be obtained by the combination of logging data from different modes, then the fluid properties in complicated reservoirs could be distinguished by 2D diffusion-relaxation NMR logging data distribution of pore fluids, generated by multi-echotrain joint inversion. In comparison with 1D NMR logging, this method could increase fluid information in diffusion regime, separate oil, gas and water signals in 2D space and enhance the identification capacity of fluid properties from NMR logging. The 2D NMR logging in the multi-echowave interval was applied in the oil pays in Well A and the water layers in Well B in the Nanpu Sag by MRIL-Prime tool, and the interpretation matches the well testing result. It indicates that 2D NMR logging has advantages on the identification of light oil, and fluids in macropore reservoirs than 1D NMR logging. Key words: 2D NMR logging, acquisition mode, joint multi-echotrain inversion, diffusion coefficien

A new permeability calculation method using nuclear magnetic resonance logging based on pore sizes: A case study of bioclastic limestone reservoirs in the A oilfield of the Mid-East

It is difficult to accurately obtain the permeability of complex lithologic reservoirs using conventional methods because they have diverse pore structures and complex seepage mechanisms. Based on in-depth analysis of the limitation of classical nuclear magnetic resonance (NMR) permeability calculation models, and the understanding that the pore structure and porosity are the main controlling factors of permeability, this study provides a new permeability calculation method involving classifying pore sizes by using NMR T2 spectrum first and then calculating permeability of different sizes of pores. Based on this idea, taking the bioclastic limestone reservoir in the A oilfield of Mid-East as an example, the classification criterion of four kinds of pore sizes: coarse, medium, fine and micro throat, was established and transformed into NMR T2 standard based on shapes and turning points of mercury intrusion capillary pressure curves. Then the proportions of the four kinds of pore sizes were obtained precisely based on the NMR logging data. A new NMR permeability calculation model of multicomponent pores combinations was established based on the contributions of pores in different sizes. The new method has been used in different blocks. The results show that the new method is more accurate than the traditional ones. Key words: reservoir, pore structure, nuclear magnetic resonance, permeability, bioclastic limestone, well loggin