136 research outputs found
Artificial neural network-based geometry compensation to improve the printing accuracy of selective laser melting fabricated sub-millimetre overhang trusses
No full textSelective laser melting processes deposit and join metal powders to near net shape in a layer-by-layer manner. The process of melting and re-solidification of several layers of deposited material can result in geometric deviations, and the impact is particularly significant for sub-millimetre structures oriented at a wide range of overhang angles with respect to the building platform. This paper assesses and benchmarks the capabilities of a neural network-based geometric compensation approach for truss lattice structures with circular cross-sections. The neural network method is capable to generate free-form cross-sections with enhanced geometric freedom for compensation compared to more established analytical compensation approaches limited to predefined geometric shapes. For neural network training, lattice dome structures composed of trusses with different overhang angles were designed and printed by selective laser melting and measured via X-ray computed tomography, resulting in point cloud data sets containing more than 20,000 data points for each overhang angle. For experimental validation, neural network-compensated dome structures were benchmarked against dome structures with elliptical parameter compensation. Results show that the neural network compensated lattice trusses achieve higher printing dimensional accuracy compared to the uncompensated structures and those compensated based on elliptical parameter estimates.Full Tex
Leadership and Management of A Jiangnan Town in Late Qing (1800-1911)
No full text本文的目的在於理解南潯作為一個繁榮的江南市鎮，如何在十九世紀的各個階段得到有效的管理，以及其領導層的組成如何隨著外界的政治經濟變遷而改變。作者選擇市鎮作為研究單位，其目的在於將市場和周邊的村落放在同一單位下檢視，以求更好地在經濟和社會層面認識中國之城鄉連續體的本質。通過細讀地方一手史料（包括地方志、族譜、報紙和文集），本文將不僅從制度的角度，同時也會通過地方權力持有者（包括地方官、下層士紳和商人）的具體活動，來觀察南潯鎮的權力結構。我的主要論點是，雖然地方的領導層從未放棄其自治權，但是該領導層的組成卻能夠靈活地在不同階段（1800-1842，1843-1864，1865-1890，1891-1911）進行重組，這造就了南潯鎮一整個世紀的社會穩定，除了其間遭受外來的太平天國戰爭的打擊。為了經營市場和經營更大的市鎮，地方領袖們成立了不同的組織且運用了不同的策略。概括而論，商人行會的成立是為了協調商業事務，而寺廟和善堂的維護則是為了建立一種社區共同體的意識并消弭潛在的社會衝突。在整個十九世紀，尤其是其後半段，地方領袖們的行政權和執法權都得到了擴張，其代價是官方權力的縮減，但其同時也確保了辛亥革命期間南潯的和平政權更迭。This paper attempts to understand how a prosperous Jiangnan town, Nanxun, was managed in different periods of the 19th century and how its leadership evolved when the broad political and economic environment changed. The choice of a town as the unit for analysis was made under the intention to bring together the marketplace and the surrounding villages for examining the nature of Chinese urban-rural continuum both economically and socially. Through scrutiny of local primary sources, i.e., local gazetteers, genealogies, newspapers and literary collections, I am going to investigate the power structure of Nanxun town not only from an institutional perspective but also through the activities of local power agents, e.g., local officials, lower gentry and merchants. My thesis is that the local leadership never gave up autonomy over town management but its constitution changed flexibly in four stages (1800-1842, 1843-1864, 1865-1890, 1891-1911), resulting in long-term stability throughout the century except the major interruption by the exogenous Taiping war. For running the marketplace and the broad town, local leaders established different institutions and adopted different strategies. Generally speaking, the merchant guilds were founded for coordinating commercial affairs while the temples and charities were maintained for building a sense of community and easing potential conflicts over the town. Through the second half of the century, especially after several major mid-century structural changes, the administrative and enforcement power of local leaders expanded at the expense of official authority and secured the peaceful regime change in the 1911 Revolution.Chen, Ruochen.Thesis M.Phil. Chinese University of Hong Kong 2016.Includes bibliographical references (leaves ).Abstracts also in Chinese.Title from PDF title page (viewed on …).Detailed summary in vernacular field only
RF micro-systems for 5G front-end signal processing
No full textThe fifth-generation (5G) communication has sparked great research interest in developing the next generation radio frequency (RF) front ends for more stringent requirements on performance, power consumption, and spectral utilization efficiency. More parallel RF bands and paths are added in the same form factor, along with which come more components and tighter integration. Designing portable systems faces the new challenge of reducing component size while still operating at RF, where the path attenuation is low and fading is readily manageable. Satisfactory size reduction is particularly difficult for passive components that rely on the principle of waveguiding and thus scale with electromagnetic (EM) wavelength at RF (typical ~10s cm). Hence, radical size reduction by several orders of magnitude can only be attained by resorting to a physical domain other than EM, namely acoustic waves with wavelengths 4~5 orders of magnitude smaller. In fact, acoustic devices at RF, such as surface or bulk acoustic wave devices, have been widely used for mobile phone applications. Other acoustic elements, such as couplers, correlators, and impedance matching networks, have also shown promising potential to outperform the state-of-the-art EM counterparts. However, the past developments often battled the challenge of efficiently accessing the acoustics over a sufficiently wide bandwidth and subsequently producing application-worthy performance, because of the fundamental limitations from the lack of high electromechanical coupling (k2) and low damping piezoelectric platforms. Recently, thanks to the advances in materials, design, and fabrication, LiNbO3 thin-film has been proved as a promising low-loss, wideband, and frequency-diverse acoustic platform for novel functions toward high-performance 5G front-end signal processing.
Based on acoustic devices in LiNbO3 thin films, this thesis aims to design and demonstrate several classes of novel RF microsystems that can enable conventional signal processing functions with better performance or new tasks for emerging applications. First, the acoustic systems are used as passive signal processing elements for the Internet of Things (IoT) applications. The high figure of merit (FoM) LiNbO3 resonator array is used as the impedance matching element for interfacing with the high impedance CMOS rectifiers in the IoT-inspired wake-up radio. The high FoM, adequately large static capacitance and spurious free performance collectively contribute to a high voltage gain over 20. Another type of microsystem for IoT applications is 1-dB IL acoustic delay lines (ADLs) on the S0 mode in thin-film LiNbO3, showing record-breaking low IL over a larger bandwidth, opening new horizons for low-power RF acoustic signal processing. Second, the miniature nonreciprocal component based on switched high-performance delay elements is demonstrated for full duplex radio. The wideband and long delay featured by the high-performance LiNbO3 ADLs significantly benefit the performance, including the dynamic switching induced IL and intra-modulations, while relaxing the requirements for synthesizing and synchronizing the control signals. The demonstrated 4 port circulator shows a highly symmetric performance across the 4-ports with 18.8 dB nonreciprocal contrast between the IL (6.6 dB) and isolation (25.4 dB) over an FBW of 8.8% at a center frequency 155 MHz, all of which are accomplished with a record low switching frequency of 877.22 kHz. Upon further optimizations, such circulators can potentially outperform ferrite-based devices in loss, bandwidth, and isolation while offering more compact size and reconfigurable operation. Third, low-loss wideband GHz S0 mode ADLs are explored for self-interference cancellation in full-duplex radio. The fabricated miniature acoustic delay lines show a fractional bandwidth of 4% and a minimum IL of 3.2 dB at a center frequency of 0.96 GHz. Various delays ranging from 20 ns to 900 ns have been obtained for digitally addressable delay synthesis. Multiple acoustic delay lines with center frequencies from 0.9 to 2 GHz have been demonstrated. The demonstrated ADLs can potentially provide wide-range and high-resolution reconfigurable delays for future SIC applications. Finally, design and measurement of 5 GHz antisymmetric mode acoustic delay lines for 5G enhanced mobile broadband (eMBB) applications are presented; the demonstrated ADLs significantly surpass the state of the art with similar feature sizes in center frequency. The implemented ADLs at 5 GHz show a minimum insertion loss of 7.94 dB and a fractional bandwidth around 4%. In addition to the remarkable device performance, these designs also point out the opportunities to advance the operation frequencies of acoustic devices toward the wideband and high-frequency signal processing functions required for future 5G applications.
RF acoustic microsystems demonstrated in this thesis have shown promising prospects for 5G front-end signal processing applications. Thanks to the simultaneously low damping and wideband performance at RF, acoustic devices based on LiNbO3 thin films are auspicious candidates to provide the design flexibilities and high performance required for various 5G application scenarios. Further development in high-performance RF acoustic devices may put on the horizon an RF front-end synthesized either purely or predominantly from an RF acoustic component kit.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2021-12-01The student, Ruochen Lu, accepted the attached license on 2019-09-12 at 09:43.The student, Ruochen Lu, submitted this Dissertation for approval on 2019-09-12 at 10:03.This Dissertation was approved for publication on 2019-09-13 at 16:52.DSpace SAF Submission Ingestion Package generated from Vireo submission #14451 on 2020-02-28 at 17:35:17Made available in DSpace on 2020-03-02T22:38:37Z (GMT). No. of bitstreams: 4
LU-DISSERTATION-2019.pdf: 41135901 bytes, checksum: d53219a4453f36fb646113ee6c675878 (MD5)
20190912_thesis_version04_format_check_4.docx: 86478459 bytes, checksum: 9f010d92462f29b038d1c4cfc2694ffe (MD5)
LICENSE.txt: 4207 bytes, checksum: 1ad070f4f17db180272819881c06afdb (MD5)
PROQUEST_LICENSE.txt: 4553 bytes, checksum: 98e0eafa7b6c5cf3d66f91e35aef082c (MD5)
Previous issue date: 2019-09-13Embargo set by: Seth Robbins for item 113969
Lift date: 2022-03-02T22:39:04Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemLimited Restriction Lifted for Item 113969 on 2022-03-03T10:15:08Z
Influence of geometric defects on the compression behaviour of thin shell lattices fabricated by micro laser powder bed fusion
No full textMicro laser powder bed fusion (μLPBF) is an additive manufacturing process enabling the fabrication of thin-walled metallic shell lattices at the micrometre scale. With wall thicknesses reduced down to 100 µm, this process significantly enhances the structural design freedom, enabling the design of multi-functional, lightweight, stiff, and strong components. However, from a manufacturing perspective, as the wall thicknesses approach the printing resolution, this process is likely to introduce geometric defects, and informed quality assurance of the 3D-printed structures becomes critical. From a structural perspective, the mechanical properties of thin-walled structures are known to be highly sensitive to manufacturing defects. To quantify the process-induced geometric defects and to understand the influences of the geometric defects on the mechanical properties of thin shell lattices, we propose a micro X-ray computed tomography (XCT) based finite element (FE) modelling methodology, which is validated here for Primitive-type shell lattices fabricated by μLPBF in stainless steel. Four types of geometric defects, namely thickness variations, through-thickness defects (holes) on shell surfaces, surface waviness and roughness, are incorporated into the shell element-based FE models. The detailed evaluation of numerical and experimental compression test results shows that the defect-informed simulation approach provides significantly improved prediction accuracy compared to the ideal geometry model in terms of stiffness, peak stress, plateau stress and densification behaviour. The respective influences of each type of defect and their combinations on the mechanical properties of the shell lattices are studied, highlighting that surface roughness and thickness variations lead to prominent impact on the reduction of both linear and nonlinear mechanical properties.</p
Low-loss and wideband acoustic delay lines
No full text This paper demonstrates low-loss acoustic delay lines (ADLs) based on shear-horizontal waves in thin-film LiNbO 3 for the first time. Due to its high electromechanical coupling, the shear-horizontal mode is suited for producing devices with large bandwidths. Here, we show that shear-horizontal waves in LiNbO 3 thin films are also excellent for implementing low-loss ADLs based on unidirectional transducers. The high acoustic reflections and large transducer unidirectionality induced by the mechanical loading of the electrodes on a LiNbO 3 thin film provide a great tradeoff between delay line insertion loss and bandwidth. The directionality for two different types of unidirectional transducers has been characterized. Delay lines with variations in the key design parameters have been designed, fabricated, and measured. One of our fabricated devices has shown a group delay of 75 ns with an IL below 2 dB over a 3-dB bandwidth of 16 MHz centered at 160 MHz (fractional bandwidth = 10%). The measured insertion loss for other devices with longer delays and different numbers of transducer cells are analyzed, and the loss contributing factors and their possible mitigation are discussed. Accepted Author ManuscriptDynamics of Micro and Nano System
ANALYSIS OF PRINTING ACCURACY IN ADDITIVE MANUFACTURING FOR LATTICE STRUCTURES
No full textPh.DDOCTOR OF PHILOSOPHY (CDE-ENG
Privacy-aware electric vehicle load forecasting via blockchain-based federated transfer learning
No full textAbstract Electric vehicle (EV) load forecasting has become critical with the rapid growth of EVs and fast-charging technologies. However, privacy concerns pose challenges to traditional forecasting methods. Our work proposes a novel blockchain-based federated transfer learning framework for privacy-aware probabilistic EV load forecasting. Our approach uses secure aggregation via blockchain to prevent gradient leakage, with smart contracts aggregating masked vectors to produce a global model without exposing individual data. Our work introduces transfer learning to adapt the global model to varying charging scenarios by transferring layer-wise weights. The framework integrates machine learning, pattern recognition, and big data analytics methodologies. Experimental results with datasets of varying client numbers demonstrate that our method outperforms baselines in prediction accuracy and communication efficiency, particularly for large-scale scenarios. By combining advanced techniques in data mining, machine learning, and blockchain, this framework provides a scalable solution for privacy-preserving EV load forecasting while ensuring robust performance in dynamic environments. Our innovations include secure parameter aggregation using homomorphic encryption, blockchain-based secure aggregation, and transfer learning for model adaptability, resulting in significant improvements in privacy protection, communication overhead, and prediction accuracy
Thin-Film Lithium Niobate Acoustic Delay Line Oscillators
No full textIn this work, thin-film lithium niobate (LiNbO3) acoustic delay line (ADL) based oscillators are experimentally investigated for the first time for the application of single-mode oscillators and frequency comb generation. The design space for the ADL-based oscillator is first analyzed, illustrating that the key to low phase noise lies in high center frequency (fo), large delay (τ G), and low insertion loss (IL) of the delay. Therefore, two self-sustained oscillators employing low noise amplifiers (LNA) and a low IL, long delay (fo=157MHz, IL =2.9dB, τG= 200-440ns) SH0 mode ADLs are designed for a case study. The two SH0 ADL oscillators show measured phase noise of -109 dBc/Hz and -127 dBc/Hz at 10-kHz offset while consuming 16 mA and 48 mA supply currents, respectively. Although the carrier power of the proposed oscillator is lower than published state-of-the-art ADL oscillators, competitive phase noise performance is still attained thanks to the low IL. Finally, frequency comb generation is also demonstrated with the same delay line and a commercial RF feedback amplifier, showing a comb spacing of 3.4 MHz that matches the open-loop characterization.Accepted Author ManuscriptDynamics of Micro and Nano System
A Multi-Task Learning Based Runoff Forecasting Model for Multi-Scale Chaotic Hydrological Time Series
No full textAccurately predicting runoff is crucial for managing water resources, preventing and mitigating floods, scheduling hydropower plant operations, and protecting the environment. The hydrological dynamic composite system that forms runoff is complex and random, and seemingly random behavior may be caused by nonlinear variables in a simple deterministic system, which poses a challenge to runoff prediction. In this paper, we construct parallel and multi-timescale reservoirs from a chaotic theory perspective to simulate the stochasticity of chaotic systems. We propose a multi-task-based "Decomposition-Integration-Prediction" (Multi-SDIPC) model for runoff prediction. To validate our research results, we use the Catchment Attributes and Meteorology for Large-Sample Studies (CAMELS) dataset and compare our proposed model with 10 baseline models. The results show that our model has an average NSE metric of 0.83 and exhibits higher accuracy, better generalization, and greater stability than the other models in multi-step forecasting. Based on our findings, we recommend wider application of the Multi-SDIPC model in different regions of the world for medium or long-term runoff prediction.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 Engineering and Logistic
Optical dating of young lacustrine sediment from Manas Lake in northwestern China
No full textManas Lake is a closed and dried lake in Junggar Basin with catchment area of 11,000 square kilometers. The lake is particularly sensitive and important to the study of paleo‐climate changes, because the climate in the catchment area is dominantly influenced by the Westlies. Dating of lake paleo-shorelines and lacustrine sediments can provide chronological evidence of water level and climate changes. No evidence for Holocene high lake level was found by previous studies.
The ages of samples were determined using Optical Stimulated Luminescence methodologies. Slope method was used for the determination of equivalent dose of quartz. Series of Lx and Tx from a number of aliquots for each regenerative dose are analyzed to obtain an averaged slop value of the Lx/Tx, by separately fitting Lx-Tx plots under each regenerative dose. In this thesis, slope method was tested for a series of young lacustrine sediment. It is found that using the slope method can save 40% time of conventional SAR procedure. The errors were reduced with large number of natural aliquots. This approach can effectively improve the reliability of optical dating. It is preferred for dating of young samples, because of weak signals and poor precision.
Fifteen lacustrine sediments and shoreline deposits were dated. These samples were from a borehole, a profile section and shoreline deposits of the latest high lake level. High-resolution data were achieved by using slope method of OSL signals from quartz for the lacustrine sediments. Magnetic susceptibility of these samples was measured as a proxy for revealing paleo-climate changes. The OSL ages suggested that the lake had experienced a rapid deposition process during 200~600 years ago. Such ages agreed well with the ages of last high lake level, which was the age of little ice age. It is concluded that the paleo-climate of Lake Manas was cold and wet during the little ice age. Sedimentation gaps with age gap of 70ka were found between sediments of little ice age and sediments beneath, from both the lacustrine borehole and paleo‐shorelines. It implies that Lake Manas probably drained for a considerable time.published_or_final_versionEarth SciencesMasterMaster of Philosoph
- …
