436 research outputs found


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    This paper provides two scenarios of population change and its spatial distribution at the county level in the Beijing-Tianjin-Hebei Metropolitan Region: three residential patterns and three population growth groups. The findings show that population change in this region mainly agglomerated to the urban districts and areas of fast population growth in the period of 1990-2000. Regression results also provide details on the contribution of a number of determinants to the population change in the divisions of each scenario. This research concludes by arguing the necessity of future population studies in terms of different regional or local conditions.Decomposition; Population change; Determinants; Beijing-Tianjin-Hebei

    Zero-Shot Certified Defense against Adversarial Patches with Vision Transformers

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    Adversarial patch attack aims to fool a machine learning model by arbitrarily modifying pixels within a restricted region of an input image. Such attacks are a major threat to models deployed in the physical world, as they can be easily realized by presenting a customized object in the camera view. Defending against such attacks is challenging due to the arbitrariness of patches, and existing provable defenses suffer from poor certified accuracy. In this paper, we propose PatchVeto, a zero-shot certified defense against adversarial patches based on Vision Transformer (ViT) models. Rather than training a robust model to resist adversarial patches which may inevitably sacrifice accuracy, PatchVeto reuses a pretrained ViT model without any additional training, which can achieve high accuracy on clean inputs while detecting adversarial patched inputs by simply manipulating the attention map of ViT. Specifically, each input is tested by voting over multiple inferences with different attention masks, where at least one inference is guaranteed to exclude the adversarial patch. The prediction is certifiably robust if all masked inferences reach consensus, which ensures that any adversarial patch would be detected with no false negative. Extensive experiments have shown that PatchVeto is able to achieve high certified accuracy (e.g. 67.1% on ImageNet for 2%-pixel adversarial patches), significantly outperforming state-of-the-art methods. The clean accuracy is the same as vanilla ViT models (81.8% on ImageNet) since the model parameters are directly reused. Meanwhile, our method can flexibly handle different adversarial patch sizes by simply changing the masking strategy.Comment: 12 pages, 5 figure

    Superconducting properties of novel BiSe2_{2}-based layered LaO1x_{1-x}Fx_{x}BiSe2_{2} single crystals

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    F-doped LaOBiSe2_{2} superconducting single crystals with typical size of 2×\times4×\times0.2 mm3^{3} are successfully grown by flux method and the superconducting properties are studied. Both the superconducting transition temperature and the shielding volume fraction are effectively improved with fluorine doping. The LaO0.48_{0.48}F0.52_{0.52}BiSe1.93_{1.93} sample exhibits zero-resistivity at 3.7 K, which is higher than that of the LaO0.5_{0.5}F0.5_{0.5}BiSe2_{2} polycrystalline sample (2.4K). Bulk superconductivity is confirmed by a clear specific-heat jump at the associated temperature. The samples exhibit strong anisotropy and the anisotropy parameter is about 30, as estimated by the upper critical field and effective mass modelComment: 5 pages, 5 figures, 2 tables, accepted for publication in Europhysics Lette

    Comprehensive Analysis, Discussion and Suggestion on the Current Situation of Cardiopulmonary Resuscitation and Automatic External Defibrillator in General Public in China

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    The number of sudden cardiac death (SCD) has increased year by year, which has become one of the main causes of death in China. Timely cardiopulmonary resuscitation (CPR) and timely and accurate use of automatic external defibrillator (AED) can greatly improve the survival rate of patients with sudden cardiac death. Because the large probability of sudden cardiac death occurs outside the hospital, it is very important for the general public to master first aid skills. This paper will mine all kinds of data from multi-dimensional and multi-angle, analyze the mastery of public first aid skills in China, and provide practical suggestions and ideas for popularizing first aid skills in the future

    On the Active Components in Crystalline Li-Nb-O and Li-Ta-O Coatings from First Principles

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    Layered-oxide LiNixMnyCo1xyO2\mathrm{LiNi_xMn_yCo_{1-x-y}O_2} (NMC) positive electrodes with high Nickel content, deliver high voltages and energy densities. However, a high nickel content, e.g., xx = 0.8 (NMC 811), can lead to high surface reactivity, which can trigger thermal runaway and gas generation. While claimed safer, all-solid-state batteries still suffer from high interfacial resistance. Here, we investigate niobate and tantalate coating materials, which can mitigate the interfacial reactivities in Li-ion and all-solid-state batteries. First-principles calculations reveal the multiphasic nature of Li-Nb-O and Li-Ta-O coatings, containing mixtures of LiNbO3\mathrm{LiNbO_3} and Li3NbO4\mathrm{Li_3NbO_4}, or of LiTaO3\mathrm{LiTaO_3} and Li3TaO4\mathrm{Li_3TaO_4}. The concurrence of several phases in Li-Nb-O or Li-Ta-O modulates the type of stable native defects in these coatings. Li-Nb-O and Li-Ta-O coating materials can form favorably lithium vacancies VacLi\mathrm{Vac^{'}_{Li}} and antisite defects NbLi\mathrm{Nb^{\bullet \bullet \bullet \bullet}_{Li}} (TaLi\mathrm{Ta^{\bullet \bullet \bullet \bullet}_{Li}}) combined into charge-neutral defect complexes. Even in defective crystalline LiNbO3\mathrm{LiNbO_3} (or LiTaO3\mathrm{LiTaO_3}), we reveal poor Li-ion conduction properties. In contrast, Li3NbO4\mathrm{Li_3NbO_4} and Li3TaO4\mathrm{Li_3TaO_4} that are introduced by high-temperature calcinations can provide adequate Li-ion transport in these coatings. Our in-depth investigation of the structure-property relationships in the important Li-Nb-O and Li-Ta-O coating materials helps to develop more suitable calcination protocols to maximize the functional properties of these niobates and tantalates