A group preference-based privacy-preserving POI recommender system

Xiwei Wang,Minh Nguyen,Jonathan Carr,Longyin Cui,Kiho Lim 한국통신학회 2020 ICT Express Vol.6 No.3

Ubiquitous smartphones with their built-in location services enable people to explore various points-of-interest (POIs) through location-based apps, e.g., Yelp and Foursquare City Guide. With these apps, users can receive personalized recommendations on nearby places, e.g., restaurants and arcades, which not only saves them searching time, but also helps find POIs that are of interest to them. One issue with these apps and almost all existing recommender systems is that they require users to share their preference data with the service providers. This information, if not properly used, can leak users’ privacy. In this paper, we propose a group preference-based POI recommendation scheme which fuses matrix factorization and clustering techniques to provide quality recommendations without sacrificing users’ privacy.

Key Mechanisms of the Effect of Atomization on Lean Blow-Out Limits of Aero Engines

Xiwei Wang,Yong Huang 한국항공우주학회 2023 International Journal of Aeronautical and Space Sc Vol.24 No.2

The appearance of the lean blow-out (LBO) will seriously threaten the aircraft from safety. For an aero engine using liquid fuel, the atomization characteristics such as mean droplet size (SMD), spray pattern and initial droplet velocity will impact the combustion performance. In this paper, the influence of atomization characteristics on flame stability is studied by using two types of swirlers and nine atomizers. Data from relevant literature are also cited for analysis. The experimental results show that the structure of the swirler is the main factor that determines the spray spatial distribution. The flame pattern of the combustors with the same swirler is similar. The relationship between the LBO limit and the atomization characteristics is derived in this paper. Compared with the Lefebvre’s relation that only considers SMD, the correlation factor of the relation between the atomization characteristics and the LBO limit in this paper is increased from 0.2496 to 0.836. Further analysis shows that the influence of atomization characteristics on LBO performance can be divided into two aspects. On the one hand, the different atomization affects the performances of the spray flame. Among these performances, the minimum heat release required to maintain the flame corresponds to the ideal LBO limit. On the other hand, the SMD and initial droplet velocity affect the combustion efficiency, that is, the degree of the combustion close to the ideal LBO limit. Considering the influence of the above two aspects on LBO performance, the actual LBO limit can be obtained.

magnetostratigraphy, 26Al-10Be, Yx02 borehole, tectonic evolution, Daxing Uplift, Beijing Sub-plain

Fubing He,Xiwei Xu,Fang Tian,Zhenhua Liu,Yueze Zhang,Lingyan Bai,Yubin Cui,Kai Wang,Wenzhi Niu,Jingbo Ni,Xiaoyong Liu,Mengmeng Cao 한국지질과학협의회 2024 Geosciences Journal Vol.28 No.2

The buried Daxing Uplift connects the Beijing Sag and Dachang Sag, which is the critical tectonic unit for understanding the structural evolution of the Beijing Sub-plain and its linkages to regional tectonics. This study combines paleomagnetic, 26Al-10Be isochron dates and sedimentary analyses from a new borehole (Yx02) in the northeastern Beijing Sub-plain to shed fresh light on regional tectonic processes and the sedimentary history since the Pliocene. The main findings are as follows: (1) the Daxing Uplift had formed three depositional episodes: alluvial-fan, lacustrine-delta, and alluvial-fan sedimentation since the Cenozoic; (2) The borehole records the Brunhes, Gauss normal chron, and the Matuyama, Gilbert reversed chron in the Daxing Uplift, the corresponding depths are 0–148.9 m, 148.9–315.0 m, 315.0–520.5 m and 520.5–650 m; (3) An important tectonic event started in ~4.3 Ma, disintegrated NE-trending basin and range terrain, reactivated the NW-trending Nankou-Sunhe fault, and formed Shunyi fault in Beijing Sub-plain. Sedimentation occurs exclusively in the Beijing Sag and the northeastern Daxing Uplift during ~4.3–1.77 Ma; (4) During ~1.77–1.07 Ma, a transition from an extension to a strike-slip occurred, and is described not only in a progressively higher increase of the overall deposition rate, but also in a decrease of the relative deposition disparity between sags and uplifts. Since then, the Beijing Sub-plain has been shaped, associated with an overall subsidence depression in the Bohai Bay Basin. This work enhances our understanding of the formation and evolution of the Beijing Sub-plain, the division of tectonic episodes, and the initiation time of the latest tectonic movement in the break-up region, North China Craton, since the Neogene.

Preparation of Non-Planar-Ring Epoxy Thermosets Combining Ultra-Strong Shape Memory Effects and High Performance

Qiong Li,Songqi Ma,Jingjing Wei,Sheng Wang,Xiwei Xu,Kaifeng Huang,Binbo Wang,Wangchao Yuan,Jin Zhu 한국고분자학회 2020 Macromolecular Research Vol.28 No.5

Non-planar-ring epoxies together with non-planar-ring hardeners could achieve thermosets combining ultra-high shape recovery speed and excellent thermal properties. High shape recovery speed reflected high efficiency, and could decrease the energy consumption and the harmful effect of external stimuli on the materials, while it often conflicts with the thermal properties of shape memory polymers. In this paper, for the first time, epoxy resins with the super-short shape recovery time within 3 s were developed from non-planar-ring epoxies and hardeners, and their glass transition temperature (T g) were ~127 °C much higher than their benzene ring analogues. The effects of non-planar-ring structures of the epoxies and hardeners on the curing behavior, thermal properties as well as the shape memory properties of the thermosets were systematically investigated; the structure-property relationships were disclosed with the help of computational simulation of structure parameters and ESP maps. The faster shape recovery speed of the non-planar-ring epoxy thermosets is from their higher molecular mobility contributed by the conformational transition of non-planar-rings as well as their higher recovery force compared with benzene ring analogs. Their higher T gs are from the steric hindrance by the larger molecular volume of the non-planar-rings than benzene ring. This work will provide an effective method to produce shape memory polymers with excellent shape memory effects and high performance.

High‑speed growth of high‑quality polycrystalline diamond films by MPCVD

Kai Chen,Tao Tao,Wenxiao Hu,Yucong Ye,Kaiwen Zheng,Jiandong Ye,Ting Zhi,Xiwei Wang,Bin Liu,Rong Zhang 한국탄소학회 2023 Carbon Letters Vol.33 No.7

High-quality diamond films have attracted extensive attentions due to their excellent optical and electrical properties. However, several issues, such as random orientation, stress accumulation, and slow growth rate, severely limit its applications. In this paper, high-quality polycrystalline diamond films with highly ordered (100) orientation were prepared by microwave plasma chemical vapor deposition. The effects of growth parameters on the microstructure, quality and residual stress of diamond films were investigated. Experimental results indicate that relatively high temperature at low methane concentration will promote the formation of (100) oriented grains with a low compressive stress. Optimized growth parameters, a methane concentration of 2% along with a pressure of 250 Torr and temperature at 1050 ℃, were used to acquire high growth rate of 7.9 μm/h and narrow full width at half maximum of Raman peak of 5.5 cm? 1 revealing a high crystal quality. It demonstrates a promising method for rapid growth of high-quality polycrystalline diamond films with (100) orientation, which is vital for improving the diamond related applications at low cost.