Browsing by Author "Li, J."
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Item COPE: Interactive Exploration of Co-Occurrence Patterns in Spatial Time Series(IEEE Computer Society) Li, J.; Chen, S.; Zhang, Kang; Andrienko, G.; Andrienko, N.; 65983012 (Zhang, K); Zhang, KangSpatial time series is a common type of data dealt with in many domains, such as economic statistics and environmental science. There have been many studies focusing on finding and analyzing various kinds of events in time series; the term ‘event’ refers to significant changes or occurrences of particular patterns formed by consecutive attribute values. We focus on a further step in event analysis: finding and exploring events that frequently co-occurred with a target class of similar events having occurred repeatedly over a period of time. This type of analysis can provide important clues for understanding the formation and spreading mechanisms of events and interdependencies among spatial locations. We propose a visual exploration framework COPE (Co-Occurrence Pattern Exploration), which allows users to extract events of interest from data and detect various co-occurrence patterns among them. Case studies and expert reviews were conducted to verify the effectiveness and scalability of COPE using two real-world datasets.Item Enhanced Thermal Conductivity in Cu/Diamond Composites by Tailoring the Thickness of Interfacial TiC Layer(Elsevier Ltd) Wang, Luhua; Li, J.; Catalano, Massimo; Bai, G.; Li, N.; Dai, J.; Wang, X.; Zhang, H.; Wang, Jinguo; Kim, Moon J.; Wang, Luhua; Catalano, Massimo; Wang, Jinguo; Kim, Moon J.Diamond particles reinforced Cu matrix (Cu/diamond) composites were fabricated by gas pressure infiltration using Ti-coated diamond particles with Ti coating from 65 nm to 850 nm. The scanning transmission electron microscopy (STEM) characterizes that the Ti coating transforms from elemental Ti to TiC after infiltration, and the crystallographic orientation relationship between diamond and TiC is [1 1 0]_{diamond}//[1 1 0]_{TiC} and (1 1 1)_{diamond}//(1 1 1)_{TiC}. The thermal conductivity of the Cu/Ti-diamond composites firstly increases and then decreases with increasing Ti coating thickness, giving a maximal value of 811 W m⁻¹ K⁻¹ at 220 nm Ti-coating layer. The results clearly manifest the effect of interfacial layer thickness on the thermal conductivity of Cu/diamond composites.Item Multi-Responsive and Multi-Motion Bimorph Actuator Based on Super-Aligned Carbon Nanotube Sheets(Elsevier Ltd) Li, J.; Mou, L.; Zhang, Rui; Sun, J.; Wang, R.; An, B.; Chen, H.; Inoue, K.; Ovalle-Robles, R.; Liu, Z.; Zhang, RuiMulti-responsive actuators have recently aroused intensive research for the requirements of being used in various environments. However, their actuation performances are generally lower than their single responsive counterparts because of the restriction of material selection and complicated structural design. Here, for the first time, a multi-responsive actuator that can respond to four types of stimuli including electricity, near infrared light, humidity, and organic vapors was designed by attaching superaligned carbon nanotubes sheets and coating an ink layer on the both sides of the PET film. The multi-responsive actuator shows fast and reversible actuation with high displacement-to-length ratio of 0.79 under electrical stimulus, and large bending angle of 212⁰ in 0.55 s at a bending speed of 646⁰/s under near infrared light irradiation. The actuator also shows fast response exposing to moisture and volatile organic vapors. The actuator shows a large bending angle within ∼0.1 s when exposed to different organic solvents and recovered its initial shape when the solvent was removed. These performances are in the same level of the record values of the thermal-based bimorph actuators. We demonstrated this actuator as a smart electric-control frequency switch at relatively high on/off frequency up to 17.5 Hz. ©2019 Elsevier LtdItem Photothermal Bimorph Actuators with In-Built Cooler for Light Mills, Frequency Switches, and Soft Robots(Wiley-VCH Verlag) Li, J.; Zhang, Rui; Mou, L.; Jung de Andrade, Monica; Hu, X.; Yu, K.; Sun, J.; Jia, T.; Dou, Y.; Chen, H.; Fang, Shaoli; Qian, Dong; Liu, Z.; 295272933 (Qian, D); Zhang, Rui; Jung de Andrade, Monica; Fang, Shaoli; Qian, DongPhotothermal bimorph actuators are widely used for smart devices, which are generally operated in a room temperature environment, therefore a low temperature difference for actuation without deteriorating the performance is preferred. The strategy for the actuator is assembling a broadband-light absorption layer for volume expansion and an additional water evaporation layer for cooling and volume shrinkage on a passive layer. The response time and temperature-change-normalized bending speed under NIR, white, and blue light illumination are at the same level of high performance, fast photothermal actuators based on polymer or polymer composites. The classical beam theory and finite element simulations are also conducted to understand the actuation mechanism of the actuator. A new type of light mill is designed based on a wing-flapping mechanism and a light-modulated frequency switch. A fast-walking robot (with a speed of 26 mm s -1 ) and a fast-and-strong mechanical gripper with a large weight-lifting ratio (˜2142), respectively, are also demonstrated. ©2019 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimItem Reactivity of Atomic Layer Deposition Precursors with OH/H₂O-Containing Metal Organic Framework Materials(American Chemical Society) Tan, Kui; Jensen, S.; Feng, L.; Wang, H.; Yuan, S.; Ferreri, M.; Klesko, Joseph P.; Rahman, Rezwanur; Cure, Jeremy; Li, J.; Zhou, H. -C; Thonhauser, T.; Chabal, Yves J.; 0000-0002-5167-7295 Tan, K); 0000-0003-3989-8009 (Klesko, JP); 0000-0002-8109-4787 (Rahman, R); 0000-0002-6080-6909 (Cure, J); 0000-0002-6435-0347 (Chabal, YJ); Tan, Kui; Klesko, Joseph P.; Rahman, Rezwanur; Cure, Jeremy; Chabal, Yves J.Metal organic frameworks (MOFs) are a class of three-dimensional porous architectures that can be chemically functionalized. The ability of atomic layer deposition (ALD) to incorporate metal atoms or functional groups into MOFs offers an interesting alternative to chemically modify MOFs for applications such as catalysis and gas separation, for which transport, adsorption, and the reaction of gases are critical. Optimization of these deposition processes requires an understanding of the underlying reaction mechanisms that is best derived from in situ characterization. We have therefore combined in situ infrared spectroscopy, X-ray photoelectron spectroscopy with in situ sputtering, and ab initio calculations to elucidate the reaction mechanisms of the common ALD precursors trimethylaluminium (TMA), diethylzinc (DEZ), and TiCl 4 with several Zr-MOFs containing hydroxyl (OH) and water (H₂O) groups. Focusing on the OH and H₂O groups is particularly revealing because it makes it possible to explore the reactivity dependence on the chemical and structural (i.e., sterics) environments. We find that the reactivity of the OH groups in the Zr₆(μ₃ -OH)₄ (μ₃ -O)₄ (OH)ₓ (OH₂) y cluster node is highly dependent on their location, accessibility, and chemical environment. For instance, the activation temperature for the reaction of the OH groups of Zr₆ clusters with TMA decreases with the node connectivity: 200, 150, and 24 °C for UiO-66-NH₂ , Zr-abtc, and MOF-808, respectively. Interestingly, the hydroxyl groups in unfunctionalized UiO-66 do not react with TMA molecules. Ab initio calculations reveal that the NH₂ group is directly responsible for catalyzing this reaction by anchoring the TMA molecule in close proximity to the target OH group. Finally, we show that TMA easily reacts with water adsorbed on the external surfaces of wet MOF crystals at room temperature, forming a thick Al₂O₃ blocking layer on the periphery of the MOF crystals. These findings provide a basis for the design and modification of MOFs by ALD processes. © 2019 American Chemical Society.Item Understanding and Controlling Water Stability of MOF-74(Royal Society of Chemistry, 2018-06-01) Zuluaga, S.; Fuentes-Fernandez, Erika M. A.; Tan, Kui; Xu, F.; Li, J.; Chabal, Yves J.; Thonhauser, T.; 0000 0000 4239 3958 (Chabal, YJ); Fuentes-Fernandez, Erika M. A.; Tan, Kui; Chabal, Yves J.Metal organic framework (MOF) materials in general, and MOF-74 in particular, have promising properties for many technologically important processes. However, their instability under humid conditions severely restricts practical use. We show that this instability and the accompanying reduction of the CO2 uptake capacity of MOF-74 under humid conditions originate in the water dissociation reaction H2O → OH + H at the metal centers. After this dissociation, the OH groups coordinate to the metal centers, explaining the reduction in the MOF's CO2 uptake capacity. This reduction thus strongly depends on the catalytic activity of MOF-74 towards the water dissociation reaction. We further show that - while the water molecules themselves only have a negligible effect on the crystal structure of MOF-74 - the OH and H products of the dissociation reaction significantly weaken the MOF framework and lead to the observed crystal structure breakdown. With this knowledge, we propose a way to suppress this particular reaction by modifying the MOF-74 structure to increase the water dissociation energy barrier and thus control the stability of the system under humid conditions.Item Visual Exploration of 3d Geospatial Networks in a Virtual Reality Environment(Oxford University Press) Zhang, M. -J; Zhang, Kang; Li, J.; Li, Y. -N; 65983012 (Zhang, K); Zhang, KangClassic geospatial network visualization tends to limit itself to 2D representation by organizing edges and nodes on a 2D map or the external surface of a traditional 3D globe model. Visual clutters and occlusions due to edge crossings and node-edge overlaps make efficient and effective exploration of geospatial networks a challenge. This paper proposes an interactive visualization approach for the intuitive exploration of geospatial networks inside a spherical virtual reality environment. To reduce visual clutter and reveal network patterns, we also propose a parameterized 5-step 3D edge-bundling algorithm and a set of techniques to avoid collision of network edges with the viewpoint. Our spherical interaction and 3D edge-bundling approach have been implemented in an Oculus Rift VR system. We demonstrate the usefulness of our approach with two case studies on real-world network data and usability experiments. ©2018 The British Computer Society. All rights reserved.Item Water Interactions In Metal Organic Frameworks(Royal Society of Chemistry) Tan, Kui; Nijem, Nour; Gao, Yuzhi; Zuluaga, S.; Li, J.; Thonhauser, T.; Chabal, Yves J.; 0000 0000 4239 3958 (Chabal, YJ); 89624105 (Chabal, YJ); A-5998-2011 (Chabal, YJ)Metal organic frameworks (MOFs) have a strong potential for gas adsorption and separation such as H2 and CH4 storage, and CO2 capture. However, their instability in the presence of water vapor (many MOFs are hygroscopic) is one of the key issues that limit their large-scale application. Previous studies of water adsorption in MOFs have mainly relied on isotherm measurements that provide useful parameters such as adsorption uptake and isosteric heat of adsorption. The structural stability of MOFs in water vapor was also evaluated by powder X-ray diffraction measurements (PXRD). However, more studies are required to unravel the water interaction or reaction mechanisms within MOFs, which would be beneficial for the development of more robust frameworks. This review highlight focuses on water adsorption in two representative MOFs: M(bdc)(ted)0.5 [M = Cu2+, Zn2+, Ni2+, Co2+; bdc = 1,4-benzenedicarboxylate; ted = triethylenediamine] with saturated metal centers and MOF-74 [M2(dobdc), M = Mg2+, Zn2+, Ni2+, Co2+ and dobdc = 2,5-dihydroxybenzenedicarboxylic acid] with unsaturated metal centers. It shows how vibrational spectroscopy combined with van der Waals density functional (vdW-DF) calculations makes it possible to elucidate the details of water reaction in MOFs. The results presented in this highlight suggest that the reactivity and initial decomposition pathway of MOFs in water vapor critically depend on their structure and the specific metal cation in the building units. Water interaction with a hydrophobic MOF, in this case FMOF-1, is also reviewed. This information provides a framework for understanding water interactions or reactions within different types of MOFs.