Hong Kong Polytechnic University

About: Hong Kong Polytechnic University is a education organization based out in Hong Kong, China. It is known for research contribution in the topics: Tourism & Population. The organization has 29633 authors who have published 72136 publications receiving 1956312 citations. The organization is also known as: HKPU & PolyU.

Toward Practical High-Areal-Capacity Aqueous Zinc-Metal Batteries: Quantifying Hydrogen Evolution and a Solid-Ion Conductor for Stable Zinc Anodes.

Abstract: The hydrogen evolution in Zn metal battery is accurately quantified by in situ battery-gas chromatography-mass analysis. The hydrogen fluxes reach 3.76 mmol h-1 cm-2 in a Zn//Zn symmetric cell in each segment, and 7.70 mmol h-1 cm-2 in a Zn//MnO2 full cell. Then, a highly electronically insulating (0.11 mS cm-1 ) but highly Zn2+ ion conductive (80.2 mS cm-1 ) ZnF2 solid ion conductor with high Zn2+ transfer number (0.65) is constructed to isolate Zn metal from liquid electrolyte, which not only prohibits over 99.2% parasitic hydrogen evolution but also guides uniform Zn electrodeposition. Precisely quantitated, the Zn@ZnF2 //Zn@ZnF2 cell only produces 0.02 mmol h-1 cm-2 of hydrogen (0.53% of the Zn//Zn cell). Encouragingly, a high-areal-capacity Zn@ZnF2 //MnO2 (≈3.2 mAh cm-2 ) full cell only produces maximum hydrogen flux of 0.06 mmol h-1 cm-2 (0.78% of the Zn//Zn cell) at the fully charging state. Meanwhile, Zn@ZnF2 //Zn@ZnF2 symmetric cell exhibits excellent stability under ultrahigh current density and areal capacity (10 mA cm-2 , 10 mAh cm-2 ) over 590 h (285 cycles), which far outperforms all reported Zn metal anodes in aqueous systems. In light of the superior Zn@ZnF2 anode, the high-areal-capacity aqueous Zn@ZnF2 //MnO2 batteries (≈3.2 mAh cm-2 ) shows remarkable cycling stability over 1000 cycles with 93.63% capacity retained at ≈100% Coulombic efficiency.

The application of highly doped single-layer graphene as the top electrodes of semitransparent organic solar cells.

Abstract: A single-layer graphene film with high conductance and transparency was realized by effective chemical doping. The conductance of single-layer graphene was increased for more than 400% when it was doped with Au nanoparticles and poly(3,4-ethylenedioxythiophene): poly(styrene sulfonic acid). Then semitransparent organic solar cells based on poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) were fabricated with single-layer graphene and indium tin oxide (ITO) as the top and bottom electrodes, respectively. The performance of the devices was optimized by tuning the active layer thickness and doping the single-layer graphene electrodes. The maximum efficiency of 2.7% was observed in the devices with the area of 20 mm2 illuminated from graphene electrode under the AM1.5 solar simulator. It is notable that all of the devices showed higher efficiency from the graphene than ITO side, which was attributed to the better transmittance of the graphene electrodes. In addition, the influence...

Group-by skyline query processing in relational engines

Abstract: The skyline operator was first proposed in 2001 for retrieving interesting tuples from a dataset. Since then, 100+ skyline-related papers have been published; however, we discovered that one of the most intuitive and practical type of skyline queries, namely, group-by skyline queries remains unaddressed. Group-by skyline queries find the skyline for each group of tuples. In this paper, we present a comprehensive study on processing group-by skyline queries in the context of relational engines. Specifically, we examine the composition of a query plan for a group-by skyline query and develop the missing cost model for the BBS algorithm. Experimental results show that our techniques are able to devise the best query plans for a variety of group-by skyline queries. Our focus is on algorithms that can be directly implemented in today's commercial database systems without the addition of new access methods (which would require addressing the associated challenges of maintenance with updates, concurrency control, etc.).