6,580 research outputs found
Native p-type transparent conductive CuI via intrinsic defects
No full textThe ability of CuI to be doped p-type via the introduction of native defects has been investigated using first-principles pseudopotential calculations based on density functional theory. The Cu vacancy has a lower formation energy than any of the other native defects, which include I vacancy (V(I)), Cu interstitial (Cu(i)), I interstitial (I(i)), Cu antisite (Cu(I)), and I antisite (I(Cu)). Combined with its shallow acceptor level, it offers sufficient hole concentrations in CuI. The natural band alignments as compared to zinc-blende ZnS, ZnSe, and ZnTe have also been calculated in order to further identify the p-type dopability of CuI. It is found that CuI has a relatively high valence band maximum and conduction band minimum, which also makes it easy to dope CuI p-type in terms of the doping limit rule. In addition, the small effective mass of the light hole-about 0.303m(0)-can provide high mobility and p-type conductivity in CuI. All of these results make CuI an ideal candidate for native p-type materials (C) 2011 American Institute of Physics. [doi:10.1063/1.3633220
Tuning the Performance of Nanocarbon-Based Gas Sensors Through Nanoparticle Decoration
No full textTin dioxide (SnO2) is a well–known gas sensing material, but it becomes sensitive only at elevated temperatures (e.g., above 200 °C). Nanoparticles (NPs) combined with nanocarbons, such as carbon nanotubes (CNTs) and graphene, form a new class of hybrid nanomaterials that can exhibit fascinating gas sensing performance due to tunable electron transfer between NPs and nanocarbons induced by gas adsorption. Indeed, sensors made of SnO2 NPs&ndascoated CNTs have shown outstanding room–temperature sensing performance to various gases, including those that are undetectable by either SnO2 or CNTs alone.
The objectives of this dissertation study are to synthesize various NP–nanocarbon hybrid materials and to fabricate and characterize sensing platforms based on the resulting hybrid nanomaterials. Two simple and efficient methods have been used for the hybrid synthesis. One is a simple NP synthesis and assembly system for NP–nanocarbon hybrid nanomaterials production through combining a mini–arc plasma reactor with electrostatic force–directed assembly. The other is a simple wet–chemical method for direct fabrication of doped SnO2 NP–decorated reduced graphene oxide (RGO) sheets. In particular, CNT/Ag NP and RGO/Ag NP hybrids have been produced for fast, sensitive, and selective detection of NH3. Furthermore, a ternary hybrid of Ag NPs and SnO2 NPs–decorated CNTs has been demonstrated and showed better sensing performance than CNT/SnO2 NP hybrids likely due to the enhanced gas adsorption and electron transfer. Additionally, hybrid sensors of In–doped SnO2 NPs on RGO are shown to exhibit high selectivity to NO2 sensing. Finally, the sensing mechanism for the NP–nanocarbon system has been extensively discussed.
Based on this study, we conclude that the sensing performance (including sensitivity, selectivity, and response time) can be fine–tuned by coating nanocarbons with carefully–selected NPs (pure or doped). An attempt has been made to compare the sensing performance of hybrids based on various types of nanocarbons (e.g., multiwalled CNTs, semiconducting single–walled CNTs, RGO). Nanocarbons with superior semiconducting properties as building blocks of hybrid nanomaterials are shown to exhibit better gas sensing performance. This study provides a scientific foundation to engineer practical room–temperature gas sensors with enhanced performance
Tuning the Performance of Nanocarbon-Based Gas Sensors Through Nanoparticle Decoration
No full textTin dioxide (SnO2) is a well–known gas sensing material, but it becomes sensitive only at elevated temperatures (e.g., above 200 °C). Nanoparticles (NPs) combined with nanocarbons, such as carbon nanotubes (CNTs) and graphene, form a new class of hybrid nanomaterials that can exhibit fascinating gas sensing performance due to tunable electron transfer between NPs and nanocarbons induced by gas adsorption. Indeed, sensors made of SnO2 NPs&ndascoated CNTs have shown outstanding room–temperature sensing performance to various gases, including those that are undetectable by either SnO2 or CNTs alone. The objectives of this dissertation study are to synthesize various NP–nanocarbon hybrid materials and to fabricate and characterize sensing platforms based on the resulting hybrid nanomaterials. Two simple and efficient methods have been used for the hybrid synthesis. One is a simple NP synthesis and assembly system for NP–nanocarbon hybrid nanomaterials production through combining a mini–arc plasma reactor with electrostatic force–directed assembly. The other is a simple wet–chemical method for direct fabrication of doped SnO2 NP–decorated reduced graphene oxide (RGO) sheets. In particular, CNT/Ag NP and RGO/Ag NP hybrids have been produced for fast, sensitive, and selective detection of NH3. Furthermore, a ternary hybrid of Ag NPs and SnO2 NPs–decorated CNTs has been demonstrated and showed better sensing performance than CNT/SnO2 NP hybrids likely due to the enhanced gas adsorption and electron transfer. Additionally, hybrid sensors of In–doped SnO2 NPs on RGO are shown to exhibit high selectivity to NO2 sensing. Finally, the sensing mechanism for the NP–nanocarbon system has been extensively discussed. Based on this study, we conclude that the sensing performance (including sensitivity, selectivity, and response time) can be fine–tuned by coating nanocarbons with carefully–selected NPs (pure or doped). An attempt has been made to compare the sensing performance of hybrids based on various types of nanocarbons (e.g., multiwalled CNTs, semiconducting single–walled CNTs, RGO). Nanocarbons with superior semiconducting properties as building blocks of hybrid nanomaterials are shown to exhibit better gas sensing performance. This study provides a scientific foundation to engineer practical room–temperature gas sensors with enhanced performance
Youthhood
No full textTESTING-GROUND issue 03, Youthhood, examines worlds through youthful eyes, makes evident young ambitions, and questions how we can better empower young people to design cities, landscapes, and a planet that works for them. The issue includes contributions from: Carmel Keren, Jude Daniel Smith, Claire Edwards, Kazeem Kuteyi, Emmanuel Adarkwah, Reza Nik, Dan Cui, Kristofer Cullum-Fernandez, Fida Sassi, Simeon Shtebunaev, Daze Aghaji, Averill Dimabuyu, Sarri Elfaitouri, Rebecca McDonald-Balfour, and Ed Wall.
Rebecca McDonald-Balfour (Author), Jude Daniel Smith (Author), Daze Aghaji (Author), Carmel Keran (Author), Alexis Liu (Author), Dan Cui (Author), Kristofer Cullum-Fernandez (Author), Fida Sassi (Author), Averill Dimabuyu (Author), Ed
Impact damage of composite laminates with high-speed waterjet
No full textRain erosion may cause substantial damage to aircrafts during supersonic flight. Such event is investigated here via high-speed waterjet impact on composite laminates. An experimental setup is developed to produce waterjets with the speed up to 700m/s and a finite element model of the waterjet-composite impact event is established. The consistency of experiment and simulation results validates the adopted numerical methods. The distribution of the water-hammer pressure is non-uniform and the maximum pressure occurs near the contact periphery when the water is about to eject laterally. After a high-speed (300∼560m/s) waterjet impacts a composite laminate, the impacted surface depression is observed, and the typical surface damage presents a central region with no visible surface damage surrounded by a faded “failure ring” with resin removal, matrix cracking and minor fiber fracture. Delamination occurs at the interfaces of adjacent layers with unequal dimensions and longitudinal matrix cracking appears on the back surface. Both the velocity and the diameter of waterjets are crucial factors on CFRP damage extents. Water-hammer pressure, the stagnation pressure and propagation of stress waves are failure mechanisms for most matrix damage in CFRP impacted by waterjets.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Structural Integrity & Composite
Sampling and Reconstruction of Signals on Product Graphs
No full textIn this paper, we consider the problem of subsampling and reconstruction of signals that reside on the vertices of a product graph, such as sensor network time series, genomic signals, or product ratings in a social network. Specifically, we leverage the product structure of the underlying domain and sample nodes from the graph factors. The proposed scheme is particularly useful for processing signals on large-scale product graphs. The sampling sets are designed using a low-complexity greedy algorithm and can be proven to be near-optimal. To illustrate the developed theory, numerical experiments based on real datasets are provided for sampling 3D dynamic point clouds and for active learning in recommender systems.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Signal Processing System
Ban dao ti yi zhi jie gou zai guang cui hua he guang dian cui hua zhong de yan jiu
No full textLi, Qian = 半導體异质结构在光催化和光電催化中的研究 / 李乾.Thesis Ph.D. Chinese University of Hong Kong 2015.Includes bibliographical references (leaves 145-162).Abstracts also in Chinese.Title from PDF title page (viewed on 30, December, 2016).Li, Qian = Ban dao ti yi zhi jie gou zai guang cui hua he guang dian cui hua zhong de yan jiu / Li Qian
A Conversational User Interface for Instructional Maintenance Reports
No full textMaintaining a complex system, such as a modern production line, is a knowledge-intensive task. Many firms use maintenance reports as a decision support tool. However, reports are often poor quality and tedious to compile. A Conversational User Interface (CUI) could streamline the reporting process by validating the user's input, eliciting more valuable information, and reducing the time needed. In this paper, we use a Technology Probe to explore the potential of a CUI to create instructional maintenance reports. We conducted a between-groups study (N = 24) in which participants had to replace the inner tube of a bicycle tire. One group documented the procedure using a CUI while replacing the inner tube, whereas the other group compiled a paper report afterward. The CUI was enacted by a researcher according to a set of rules. Our results indicate that using a CUI for maintenance reports saves a significant amount of time, is no more cognitively demanding than writing a report, and results in maintenance reports of higher quality. Internet of ThingsHuman-Centred Artificial Intelligenc
The Logic of Knowledge-Based Cooperation in the Social Dilemma
No full textComputer Science, Artificial IntelligenceComputer Science, Theory & MethodsCPCI-S(ISTP)
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