58 research outputs found

    CHINA-ARAB ENERGY COOPERATION: CONSTRUCT NEW ENERGY SILK ROAD

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    Arab countries are one of the most important energy supply bases in the world and a key area for China's ‘Belt and Road’" initiative(BRI). China and Arab countries have long been committed to enhancing energy cooperation. While the global energy transition is the background of China-Arab energy cooperation, the international situation in the region is still in flux, but there is a good political foundation for China-Arab energy cooperation. These are the basic conditions for China-Arab energy cooperation. Against the backdrop of energy transition and continuous changes in the international situation, China and Arab countries are working together to promote energy cooperation in terms of policy design, mechanism improvement, industry chain layout, human resource support and project implementation, combining the BRI and ‘a Community with a Shared Future for Mankind’, and the ‘China-Arab Community with a Shared Future’ in order to promote the building of a China-Arab community of energy cooperation. China-Arab cooperation in the oil and gas sector continues at a high level, while new energy sources are becoming the highlight of China-Arab energy cooperation, which is the ‘new’. In addition, despite frequent changes in the international situation, China and Arab countries have insisted on promoting a community-based approach to cooperation, which is a ‘new’ way of cooperation compared to the energy strategies of Western countries

    How Mask Matters: Towards Theoretical Understandings of Masked Autoencoders

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    Masked Autoencoders (MAE) based on a reconstruction task have risen to be a promising paradigm for self-supervised learning (SSL) and achieve state-of-the-art performance across different benchmark datasets. However, despite its impressive empirical success, there is still limited theoretical understanding of it. In this paper, we propose a theoretical understanding of how masking matters for MAE to learn meaningful features. We establish a close connection between MAE and contrastive learning, which shows that MAE implicit aligns the mask-induced positive pairs. Built upon this connection, we develop the first downstream guarantees for MAE methods, and analyze the effect of mask ratio. Besides, as a result of the implicit alignment, we also point out the dimensional collapse issue of MAE, and propose a Uniformity-enhanced MAE (U-MAE) loss that can effectively address this issue and bring significant improvements on real-world datasets, including CIFAR-10, ImageNet-100, and ImageNet-1K. Code is available at (https://github.com/zhangq327/U-MAE)

    Identifiable Contrastive Learning with Automatic Feature Importance Discovery

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    Existing contrastive learning methods rely on pairwise sample contrast zxzxz_x^\top z_{x'} to learn data representations, but the learned features often lack clear interpretability from a human perspective. Theoretically, it lacks feature identifiability and different initialization may lead to totally different features. In this paper, we study a new method named tri-factor contrastive learning (triCL) that involves a 3-factor contrast in the form of zxSzxz_x^\top S z_{x'}, where S=diag(s1,,sk)S=\text{diag}(s_1,\dots,s_k) is a learnable diagonal matrix that automatically captures the importance of each feature. We show that by this simple extension, triCL can not only obtain identifiable features that eliminate randomness but also obtain more interpretable features that are ordered according to the importance matrix SS. We show that features with high importance have nice interpretability by capturing common classwise features, and obtain superior performance when evaluated for image retrieval using a few features. The proposed triCL objective is general and can be applied to different contrastive learning methods like SimCLR and CLIP. We believe that it is a better alternative to existing 2-factor contrastive learning by improving its identifiability and interpretability with minimal overhead. Code is available at https://github.com/PKU-ML/Tri-factor-Contrastive-Learning

    Nonintegrability-driven Transition from Kinetics to Hydrodynamics

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    Nonintegrability plays a crucial role in thermalization and transport processes in many-body Hamiltonian systems, yet its quantitative effects remain unclear. To reveal the connection between the macroscopic relaxation properties and the underlying dynamics, the one-dimensional diatomic hard-point model as an illustrating example was studied analytically and numerically. We demonstrate how the system transitions from kinetic behavior to hydrodynamic behavior as the nonintegrability strength increases. Specifically, for the thermalization dynamics, we find a power-law relationship between the thermalization time and the perturbation strength near integrable regime, whereas in the far from integrable regime, the hydrodynamics dominates and the thermalization time becomes independent of the perturbation strength and exhibits a strong size-dependent behavior. Regarding transport behavior, our results further establish a threshold for the nonintegrable strength of this transition. Consequently, we can predict which behavior dominates the transport properties of the system. Especially, an explicit expression of the thermal conductivity contributed by the kinetics is given. Finally, possible applications were briefly discussed.Comment: 6 pages;5figure

    Dynamical Controls of the Eastward Transport of Overwintering Calanus finmarchicus From the Lofoten Basin to the Continental Slope

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    Diapausing populations of Calanus finmarchicus at depth in the Lofoten Basin (LB) return to the continental shelf and slope off the Lofoten-Vesterålen Islands during the phytoplankton spring bloom to feed and spawn, forming surface swarms with a great abundance. To study how overwintering populations of C. finmarchicus move with the deep currents and return to the shelf, Lagrangian transport characteristics of particles in deep water between 2008 and 2019 were analyzed using Global Ocean Reanalysis and Simulation re-analysis data and Lagrangian Coherent Structures (LCSs). Our analyses revealed that persistent eastward transport of diapausing C. finmarchicus between LB and continental slope occurred mainly between 600 and 1,100 m in the Arctic Intermediate Water. The consistency of the vertical distributions of C. finmarchicus abundance and salinity further suggests that physical factors control the horizontal distribution of the species. Hovmöller diagrams of kinetic energy indicate that there is an eastward advection of mean current at depth. The co-occurrence between the eastward transport of LCSs and the eastward advection of the mean current provides direct evidence that the life history of C. finmarchicus is subjected to physical control in the Norwegian Sea

    Efficacy of LVIS vs. Enterprise Stent for Endovascular Treatment of Medium-Sized Intracranial Aneurysms: A Hemodynamic Comparison Study

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    Background: We conducted a computational fluid dynamics (CFD) study and compared the treatment of medium-sized intracranial aneurysms with LVIS and Enterprise stent-assisted coil embolization (SACE) to determine the effects of hemodynamic changes caused by different stent and coil packing densities (PDs) in endovascular treatment.Methods: We enrolled 87 consecutive patients, with 87 medium-sized intracranial aneurysms (≥7, ≤ 12 mm), who underwent LVIS or Enterprise SACE. Aneurysms treated with LVIS SACE were allocated to the LVIS group, and the remainder were allocated to the Enterprise group. CFD were performed to assess hemodynamic alterations between before treatment, after stent deployment, and after SACE.Results: One aneurysm recanalized in the LVIS group (n = 42), and five recanalized in the Enterprise group (n = 45) (recanalization rate: 2.4 vs. 11.1%, respectively; P = 0.108). Higher complete obliteration rate (P = 0.069) was found in the LVIS group. Velocity at the neck plane showed a greater reduction ratio than velocity and WSS of the aneurysm in both groups after stent deployment, while velocity and WSS of the aneurysm showed a greater reduction ratio after coil placement. Further, there was a greater reduction in velocity at the neck plane (59.52 vs. 39.81%), aneurysmal velocity (88.46 vs. 69.45%), and wall shear stress (WSS) (85.45 vs. 69.49%) on the aneurysm in the LVIS group (P < 0.001 for all). Specifically, the reduction ratio of velocity at the neck plane showed significant difference between the groups in the multivariate analysis (P = 0.013).Conclusions : LVIS SACE showed a lower recanalization for endovascular treatment of medium-sized intracranial aneurysms, and the greater hemodynamic alterations might be the key factors

    High Yield and Packing Density Activated Carbon by One-Step Molecular Level Activation of Hydrophilic Pomelo Peel for Supercapacitors

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    Highly hydrophilic pomelo peel is used as an activated carbon (AC) precursor so that KOH can be homogeneously absorbed within it. Subsequent cryodesiccation retains the original morphology of the pomelo peel and distribution of KOH, which provides the precondition of the one-step molecular level activation. The resulting AC has a high yield of 16.7% of the pomelo peel. The specific surface area of the AC prepared by the one-step molecular activation of cryodesiccated mixture of pomelo peel and KOH (CAC-1) is 1870 m2 g-1, which is higher than that of the AC by the one-step activation of oven-dried mixture (AC-1) and AC by the two-step calcination (AC-2). CAC-1 has the highest specific capacitance of 219 F g-1 at 1 A g-1 among all the three samples. Importantly, the CAC-1 electrode has a high packing density of 0.63 g cm-3. The aqueous supercapacitor based on CAC-1 has a volumetric cell capacitance of 30.7 F cm-3, which corresponds to 123 F cm-3 for a single electrode. When the ionic liquid of 1-ethyl-3-methyl-imidazolium tetrafluoroborate is used as electrolyte, CAC-1 shows maximum specific energy of 40.5 Wh kg-1 and energy density of 25.5 Wh l-1

    Application of the Pipeline Embolization Device for Giant Vertebrobasilar Dissecting Aneurysms in Pediatric Patients

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    Objective: To evaluate the feasibility and effectiveness of the pipeline embolization device (PED) for the treatment of pediatric giant vertebrobasilar dissecting aneurysms (VBDAs).Methods: We retrospectively reviewed our institutional clinical database and identified 2,706 patients who presented with a diagnosis of intracranial aneurysms from January 2016 to June 2018. Among this group, 153 patients were diagnosed with VBDAs, and 54 of these patients underwent PED therapy. The PED technique was used in four patients who were 18 years old or younger at the time of presentation (two males, two females; mean age 9.25 years; age range 8–11 years).Results: All four included pediatric patients were managed with the PED. One patient (25%) was treated with the PED alone, while three (75%) were treated with the PED and coils. One patient died from brainstem infarction or compression of the brainstem, while follow-up of the other three patients revealed favorable outcomes. The mass effect was reduced in cases 1, 2, and 3 on follow-up MRI performed 6 months after the PED procedure.Conclusions: PEDs could be feasible in the treatment of pediatric giant VBDAs. However, the safety and efficacy of this method have not been clarified in this special pediatric population, and long-term follow-up is still necessary
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