717 research outputs found
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Renewable Polymeric Energy Harvesters from Moisture and Heat
No full textElectricity is indispensable in our daily life and batteries are the widely used energy sources for portable devices in the modern world. However, harmful chemicals and wastes in batteries can lead to serious environmental and health problems without proper dispositions. As such, renewable energy sources such as solar cells have drawn lots of interests with great progresses in recent years. In this work, two forms of renewable energy harvesters based on polymers are studied based on moistures and thermal gradients in the environment. Material properties, fundamental operation mechanisms, and application demonstrations of these two renewable energy harvesters are investigated in the dissertation. The moisture-based electric generators have long working time and high energy density output by utilizing the mechanism of the proton transportation and proton concentration oscillation. The specific polymer used in the generator has a moisture-induced oscillation surface potential from the functional groups of the polymer. Both dynamic simulation and oscillation theory have been developed to analyze this phenomenon. The self-oscillation behavior help extending the operation period of the energy harvester under the constant feeding of moistures. Experimental results show the short-circuit current density can reach 1.5 μA/cm2 and a maximum open-circuit voltage of 0.4 V with a long operation period up to 15,000 seconds with an energy density of 16.8 mJ/cm2. The thermoelectric energy harvester has an ultra-high Seebeck coefficient and self-healing properties, which is suitable for harvesting energy from temperature gradients such as wearable devices between the human skin and the environment. The energy generator is based on the material of ionogel, which has different pore sizes and polarities to results in the very different diffusion coefficients of anions and cations. Specifically, the diffusion coefficients are characterized and simulated by using the molecular dynamic simulation under different temperatures and tested experimentally. The whole device has a measured Seebeck coefficient at 298 μV/K, which is generally higher than those of traditional thermoelectric materials. Furthermore, the prototype device is flexible, bendable and self-healable for potential applications in harvesting electrical energy for wearable devices
Visualizing the Landscape of Indo-Pacific Strategy Research in China (2013-2023) A CiteSpace-Based Analysis
No full textThis study conducted a systematic analysis of 531 articles on the “Indo-Pacific Strategy”, published in CSSCI and Peking University Core journals between 2013 and 2023, sourced from the China National Knowledge Infrastructure (CNKI) database. By employing CiteSpace visualization software and bibliometric methods, we constructed networks of author collaboration, institutional collaboration, and keyword co-occurrence. This approach revealed the developmental trajectory, research hotspots, and evolutionary trends within this field. The key findings indicate that: (1) Research interest in the “Indo-Pacific Strategy” has shown a consistent upward trend since 2018; (2) Primary research themes encompass the Belt and Road Initiative (BRI), India, the United States, China-U.S. relations, the Indo-Pacific region, and regional order; (3) High-frequency keywords such as “Trump (Administration)”, “U.S.-Japan Alliance”, and “India-U.S. relations” delineate the current research frontiers; (4) Research outputs are highly concentrated in 15 core journals; (5) A stable core research community has yet to emerge, as evidenced by the fragmented nature of the author collaboration network. Based on these findings, this paper proposes several future research directions, aiming to provide empirical data and theoretical references for further exploration in this field
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Two-Dimensional, Individually-Addressable Nanostructure Arrays
No full textAbstractTwo-Dimensional, Individually-Addressable Nanostructure ArraysbyChu-Yeu Peter YangDoctor of Philosophy in Mechanical EngineeringUniversity of California, BerkeleyProfessor Liwei Lin, Chair Assembly and integration of vertically-oriented, one-dimensional nanostructures into a two-dimensional array platform has been demonstrated. This 2D architecture is realized using top-down semiconductor and microelectro-mechanical system (MEMS) processes as well as bottom-up catalyst-assisted 1D nanostructure synthesis methods. Two prototype demonstrations include: (1) a 15×12 carbon nanotube (CNT) array and (2) a 2×5 ZnO nanowire array systems. Arrays based on CNT structures have been developed to verify the feasibility of the 2D architecture using vertically-oriented nanostructures. A trench process is conducted by dry etching into a silicon substrate. A CNT growth process follows to fill the trenches while top electrodes are defined by metallization with a shadow mask. Measurement results show that the average resistance value from the 15×12 CNT electrodes with a contact area of 500×400 um^2 was several tens of ohms. To get a better understanding for the electrical characteristics of the as-fabricated CNT structures, a single 1 um-long CNT sample with measured diameter of 30 nm was attached to two nanoprobes inside a scanning electron microscope. Its resistivity was characterized as 0.056 ohm-m and the overall resistance value of the CNT nodes in the 2D array was estimated at 41 ohms;. This result correlates well with measured resistance values from the CNT nodes, suggesting that there are successful electrical connections between the top and bottom electrodes through the CNT bundles. Individual-addressability of the 2D architecture has been enabled by replacing the metallic CNTs with semiconducting ZnO nanowires and creating rectifying, Schottky diodes at the array nodes. A 2×5 array featuring asymmetric bottom platinum-nZnO Schottky junctions and top nZnO-titanium/gold ohmic contacts was fabricated. ZnO nanowires were first synthesized atop of metal electrodes on a silicon substrate. After applying spin-on-glass, the tips of the nanowires were exposed by plasma etching and top metal electrodes were deposited. The I-V characteristics of a 150×500 um^2 node under forward and reverse biases with and without a 40 um-wide UV laser beam were tested. It is found that a photogenerated current is detectable from the 2D array with an estimated responsivity of 3×10^-4 A/W. Moving the laser beam to neighboring nodes did not result in an increased current from the interrogated node, demonstrating the individual-addressability of the 2D ZnO nanowire array and its capability for discrete pattern recognition as a UV photodetector. This marks the first successful demonstration of vertically integrating ZnO nanowires into an individually-addressable 2D array for possible ultrahigh-density applications in nanoelectronic memory, information displays, photodetectors, and nano-lithography
ForceClicks
No full textForceClicks is a novel touch button input technique for consecutive clicking which incorporates touch force sensors. From force data of a single continuous touch over time, ForceClicks detects peaks and generates discrete clicks. Compared to typical button interaction, this is effective in a sense that consecutive clicks do not require finger positional movements. Additionally, stable force over a certain time threshold can trigger an alternate state, long press, and can be mapped to other actions. The usability of ForceClicks has been evaluated in terms of a) scattering level and b) efficiency. Results suggest higher stability than typical touch, especially when the task requires visual engagement on remote content. The relatively scatter-free characteristic of ForceClicks allows it to be applied on rapid clicking while gaming, and reduce of visual dedication allows easier control of external devices, and two applications, a shooting game and a number picker, are presented for demonstration
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Metal Oxides for Solid State Electronics: Transparent Electrodes, Photoanodes and Transistors
No full textAbstractMetal Oxide for Solid State Electronics: Transparent Electrodes, Photoanodes and TransistorsbyHyun Sung ParkDoctor of Philosophy in Engineering - Mechanical Engineering University of California, BerkeleyProfessor Liwei Lin, ChairMetal oxides have unique characteristics for a variety of modern applications such as thin films and nano-structured materials in optoelectronic devices and renewable energy productions. In this dissertation, three different metal oxides are developed: solution processed antimony doped tin oxide (ATO) thin films for transparent electrodes; high aspect-ratio ZnO nanowires with ALD (Atomic Layer Deposition) TiO2 for stabilizations as photo-anodes; and spin-coated SnO2 films for TFTs (Thin Film Transistors) in the applications of display devices.In the first part of this dissertation, solution processed ATO electrodes show high conductivity (~21000 S/m) and optical transparency (~95%) suitable for the state-of-art optoelectronic devices such as displays, solar cells, and smart windows. The high quality thin films are made by the low-cost solution-based process with multiple spin-coating steps using sol-gel precursors. In order to obtain better electrical and optical performances, a parametric study has been performed on four key processing parameters: doping concentration, film thickness, ambient gases and temperatures. Studies on the film surface morphology using scanning electron microscopy together with electrical, and optical characterizations elucidate the dominant factors for the conductivity and transmittance of the films. Further examinations under X-ray photoelectron spectroscopy reveal the required annealing temperature to form Sb+5 species in the Sn+4 lattices. It is found that improved mechanical flexibility is achieved and the elastic modulus of 35GPa is obtained by using the nano-indentation test. A 3D finite element analysis shows ATO films can resist 4x more deformation than those of commercial vacuum-processed indium tin oxide (ITO) films under the four-point bending simulations.The high aspect-ratio and vertically ordered ZnO nanowires as long as 10μm in length and 50nm in the cross-sectional width are constructed by using a hydrothermal process. A conformal TiO2 film of 40nm in thickness is deposited afterwards by ALD to stabilize the ZnO nanowires in a solar-powered hydrogen gas harvester. Two key innovations have been achieved using the favorable geometry and high quality nanowires in this work: (1) improved stability over bare ZnO nanowires during the photocatalytic reactions, and (2) excellent low bias voltages.In the work of using SnO2 films to make TFTs for display devices, a multiple spin coating is developed in order to obtain better gate modulation properties. The effects of annealing condition on the electrical performances and the surface morphologies of TFTs have been investigated. Experimentally, a value of 6.3cm2/Vs of the extracted field effect mobility for solution processed SnO2 TFTs has been achieved and this value is 6x higher than that of a-Si:H TFTs
Freight service network design with heterogeneous preferences for transport time and reliability
No full textValue of time and value of reliability are two important user attributes that reflect shippers’ behavioral preferences, and as such influence the design of transport service networks. As shippers preferences will vary widely, it is important to consider these variations between users in the design of service networks. Up to now, network design research has ignored the combined use of time and reliability valuations for heterogeneous user populations. The objective of this paper is to address these attributes in a model for freight service network design targeting service performance improvement. We present a new frequency based service network design model with transshipments, capacity constraints and heterogeneous users. We apply the model to demonstrate that including heterogeneity explicitly in network design pays off in terms of an improved user performance of the network. A case study is conducted for a railway network in China. Values of time and reliability are estimated from a recent Stated Preference survey and used to determine distinct user classes. The proposed optimization problem is solved using an improved Simulated Annealing based heuristic method, for the case of the aggregate user group and the case of two distinct classes. Results show that by taking variations in shippers’ VOT and VOR into account, users’ total generalized cost is reduced while service levels improve. We conclude that incorporating heterogeneous VOT and VOR into the service network design problem is of interest for decisions on network investments.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.Transport and PlanningTransport and Logistic
Functionalized Inorganic Semiconductor Nanomaterials: Characterization, Properties, and Applications
No full textThis eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contac
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Continuous and Cuffless Blood Pressure Monitoring by Piezoelectric Micromachined Ultrasonic Transducers
No full textHypertension is a major risk factor for chronic diseases such as heart disease and stroke, which cost billions of dollars in health care expenses in America. Long-term and continuous blood monitoring system is an effective way for blood pressure management to reduce the risk of adverse health outcomes. However, the current cuff inflation-based monitoring schemes are cumbersome and inconvenient, which leads to limited ambulatory blood pressure monitoring for patients to only 24 to 48 hours.Ultrasound has been used in medical applications for a long time, known for its harmless nature and good tissue penetrative performances. This dissertation focuses on the development of a subcutaneous continuous blood pressure monitoring system without a cuff, utilizing AlN-based piezoelectric micromachined ultrasonic transducers (PMUTs). The principle of using PMUTs for continuous blood pressure monitoring is based on tracking the artery diameter through the pulse-echo method. Requirements for monitoring the targeted brachial artery, with a diameter of approximately 4 mm, are discussed, and a small form factor PMUT sensor of 5×5 mm2 is designed through a CMOS-compatible fabrication process.
The backside deep reactive ion etching (DRIE) process has been optimized to achieve a vertical sidewall for PMUTs with a high aspect-ratio. PMUT diaphragms with a radius of 29 μm and good AlN crystallinity of a full width at half maximum (FWHM) of only 1.56° have been constructed. Prototype devices exhibit a displacement at the center of the diaphragms of around 35 nm/V and a resonance frequency of 8.5 MHz in air and 6.3 MHz in water. Electrical impedance characterizations indicate a magnitude at resonance of 184.2 ohm and an electromechanical coupling factor of 2.0%.
The working principle is validated through in vitro experiments and a silicone tube with a geometry similar to the targeted artery is utilized to extend and contract under the applied pressure. The minimum detectable tube diameter variation of 2.3 μm (normal artery extension ~100 μm) is achieved under a dynamic frequency of 60 beats per minute, similar to the heart rate. An in vivo animal test is conducted on an ambulatory sheep to measure blood pressure continuously with a diastolic/systolic pressure error of only 1.6 mmHg when compared to results from a direct arterial line reference sensor result. A package design consisting of epoxy drop casting and oxide/parylene coating is proposed to result in only a 15% displacement drop for future long-term biomedical monitoring applications
Functionalized Inorganic Semiconductor Nanomaterials: Characterization, Properties, and Applications
No full textThis eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contac
Evaluation of soybean cyst nematode (SCN) resistance in perennial glycine species and genome-wide association mapping and genomic prediction study for SCN resistance in common bean and prediction of the short distance movement of soybean rust urediniospores through machine learning
No full textSince agriculture started, there have been numerous occasions when plant diseases of crops had severe impact on human activities. From the famine caused by potato late blight (Phytophthora infestans) in Ireland in 1846, to the dramatic economic loss caused by downy mildew of grapes (Plasmopara viticola) in the Mediterranean in 1865, to the loss of the valuable banana cultivar ‘Gros Michel’ caused by Fusarium oxysporum Schlect. f. sp. cubense, plant diseases have caused significant historical and economic importance. The goal of plant disease management is to reduce the economic and aesthetic damage caused by plant diseases, and the focus of my thesis centers around studying diseases and their pathogen in an effort to supplement long-term effective management strategies for important diseases of soybean.
Soybean cyst nematode (SCN; Heterodera glycines; HG) is a widely occurring and damaging pathogen with a wide host range. SCN is the leading cause of soybean yield loss in the US and it will likely become a major yield-limiting threat to common bean (Phaseolus vulgaris L.), another highly susceptible host of SCN. Developing resistant cultivars is the most cost-effective method for managing this disease. In the first chapter of my thesis, I focused on identifying additional sources of resistance to SCN in perennial Glycine species which can be potentially used for improving resistance of soybean to SCN. 13 perennial Glycine species of 282 PIs were inoculated with HG types 0, 2, and 1.2.3 first, and then 36 PIs out of this set were further evaluated by inoculating with HG type 1.2.3.4.5.6.7, a population that overcomes all the resistance genes in soybean. The Glycine species evaluated contains many PIs that are highly resistant to SCN with 10 species classified as immune or highly resistance to three HG types, indicating a much broader resistance in these PIs. With additional work on hybridizing the perennial Glycine species and soybean along with techniques of gene cloning and gene transfer, many of the genes in the perennial Glycine species could be used to develop additional soybean genotypes with SCN resistance. In the second chapter of my thesis, genome-wide association study (GWAS) was used to detect SNPs significantly associated with SCN resistance in the core collection of P. vulgaris and to make genomic predictions (GPs) of SCN resistance to two HG types. GWAS identified SNPs that are significantly associated with resistance to two HG types, and GP for resistance to two SCN HG types achieved high prediction accuracy. The findings in this chapter demonstrated GWAS and GP as valuable tools for developing new resistant common bean varieties with SCN resistance in the future.
Epidemiology studies concerning the environmental and biological factors affecting disease entry, establishment and development are also extremely important for the successful management of diseases. The third chapter of my thesis focuses on developing mathematical models to predict the disease epidemic of soybean rust (Phakopsora packyrhizi), another devastating fungal disease of soybean with rapid establishment and development in the fields, using environmental and biological variables. Four machine learning models, including Absolute Shrinkage and Selection Operator (LASSO) method, zero-inflated Poisson/regular Poisson regression model, random forest, and neural network were built and compare to describe deposition of urediniospores collected in passive and active traps. The high prediction accuracy of some of the models demonstrated the applicability of machine learning in disease risk assessment, and the finding of this project is potentially helpful in guiding farmers to make proper and in-time disease management decisions.Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2017-09-29 without embargo termsThe student, Liwei Wen, accepted the attached license on 2017-06-30 at 15:10.The student, Liwei Wen, submitted this Dissertation for approval on 2017-06-30 at 15:26.This Dissertation was approved for publication on 2017-07-03 at 17:36.DSpace SAF Submission Ingestion Package generated from Vireo submission #11291 on 2017-09-29 at 11:27:27Made available in DSpace on 2017-09-29T16:38:07Z (GMT). No. of bitstreams: 3
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Previous issue date: 2017-07-0
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