PROBING LOCAL VACANCY-DRIVEN RESISTIVE SWITCHING IN METAL OXIDE NANOSTRUCTURES

Novel nonvolatile memory technologies garner intense research interest as conventional ash devices approach their physical limit. Memristors, often comprising an insulating thin film between two metal electrodes to constitute a class of two-terminal devices, enable a variety of important large data storage and data-driven computing applications. In addition to nonvolatile behavior, other features such as high scalability, low power consumption, and sub-nanosecond response times make memristors among the most attractive candidate systems. Their strength in electronic storage relies on the unique properties of the tunable variations in resistance induced from the accumulation of charged defects based on the applied bias history. Metal oxides serve as the most common storage materials, demonstrating advantages including simple fabrication, high reliability, and fast operation speeds. While the basic working concepts and the underlying conduction mechanisms have been established through combined experimental and simulation studies, the role of metal insulator interface, which acts as the crux of coupled electronic-ionic interactions, has not been fully understood. Continuous scaling, for the purpose of high density memories, also requires a detailed understanding of the switching behavior and transport mechanism. Other technical challenges include the development of innovative, low-cost fabrication methods that effectively enable high-performance structures as an alternative to complicated process modules. Stable retention and endurance of the switching characteristics, as well as uniformity of the switching parameters to ensure a valid program/read operation also represent significant challenges. Studies in device and materials optimization remain in the formative stages, and thus motivate this work to drive progress in the most attractive areas, including size dependent behavior and switching performance of memristors. This collection of work aims to correlate resistive switching within metal oxide based memristors with the fundamental physical mechanisms and material properties on a highly localized scale. Chapter 3 relates the device size and the resulting performance matrix of memory cells in the first step towards fully understanding the scaling projection and reliability issues that affect nanoscale architectures. Chapter 4 demonstrates a convective self-assembly, transferable approach that enables the fabrication of highly-controlled nanoribbon comprising solution-processed nanocrystals, providing multiple degrees of freedom for understanding the interfacial memristive behavior of functional oxide nanostructures. As a powerful tool in the study of resistive switching, conductive AFM probes the homogeneity of the charge transport properties, thus offering electrical information by locally applied bias when it is placed in direct contact with desired regime. Finally we also focus on the improving the cycle-to-cycle uniformity by embedding nanostructure into conventional metal-insulator-metal (MIM) geometry in Chapter 5. This improvement is attributed to the concentration of electric field when metal nanoislands are inserted into the oxide film matrix. The details of this work will highlight the tunable and optimizable template-driven method that can be applied on any memristive systems, yielding a superior uniformity of operating voltage and resistance states. In summary, this thesis promotes the development of novel, high-performance metal oxide based memristors enabled by the availability of new, nanostructured materials and innovations in device structure engineering. The switching performance, underlying mechanisms, area/defect concentration effects, development of solution-processed nanocrystals assemblies and chemistries, and highly enhanced uniformity in memristors are addressed by combining systematic deposition approaches with the advanced nanoscopic observation of the conducting filament, leading to the strongest competitor among future nonvolatile memory solution

Rooted in topsoil

Disillusioned by my transnational identity, I have come to realize that my sense of belonging is no longer attached to any physical location, but instead to a state of mind, to an intimacy with the world. My notion of home is an obscure and unsettled—at times utopian—idea, which can be infinitely decoded, re-positioned and re-established psychologically. This thesis is an investigation of that liminal state, questioning the paradoxical place at the intersection of longing and belonging, interior and exterior, rootedness and uprootedness. Through a collection of short essays that accompany projects, I seek to unpack the precarious emotional complexities that surface in the experience of conflicting realities. As I navigate between nostalgia for the “native” culture of the past and search for affinity in the adopted culture of the present, I use material processes to forge a zone of stability and comfort, a “homecoming” in disguise. Although it is not possible to map all the shattered fragments, my work makes an attempt. In it I explore how the quest for personal reconciliation makes space for compassionate experimentation with materiality informed by place and sense. Mundane objects act as transitional souvenirs that are manifestations of my personal history, and indexes of multiple belongings. Through casting, digital media and site-interventions, I construct a space for finding, connecting, attaching and detaching

Factors Hindering Implementation of Communicative Language Teaching in Secondary Vocational Schools of Science and Engineering in China

Without the pressure to help more students to be competitive in College Entrance Examinations, teachers in secondary vocational schools are supposed to spend more time improving students’ communicative competence in English which is more practical for students’ future career. Although communicative language teaching (CLT) approach has been added to the syllabus for over 30 years in China, however, the implication of it is hardly witnessed in English classes in secondary vocational schools of science and engineering (SVSSEs). By handing out questionaries to eight English teachers and over 300 students in my school, four restraints which prevent the application of CLT in SVSSEs have been concluded which are knowledge restraints, restraints related to the educational system, restraints by students and restraints related to teachers’ attitude and concerns

Methylglyoxal Influences Development of Caenorhabditis Elegans via Heterochronic Pathway

Methylglyoxal is a highly reactive dicarbonyl compound, which is widely distributed in food products and beverages, and is particularly high in Manuka honey. In addition to its antibacterial effects, methylglyoxal is also known as a major precursor of advanced glycation end products (AGEs), that produces altered macromolecules (such as proteins and DNA), leading to abnormal physiological changes. However, the effects of methylglyoxal on development is unclear. Thus, this study aimed to determine the role of methylglyoxal in this aspect using Caenorhabditis elegans (C. elegans). Treatment of methylglyoxal at 0.1 mM and 1 mM for 48 h significantly inhibited development of C. elegans and reduced pumping rate. Activity, measured by moving speed, was increased with 0.1 mM methylglyoxal, but reduced with 1 mM methylglyoxal. Lifespan of C. elegans was not influenced by methylglyoxal at 0.1 mM, but was shortened at 1 mM. Treatment methylglyoxal on the mutant, lin-41, which has a precocious phenotype, could alleviate the implication on wild-type worms. These results suggested that methylglyoxal significantly influenced the development of C. elegans through the heterochronic pathway

Influence of Solution Temperature on Chemical Deposited Magnesium and Corrosion Behavior of Bare and Coated Magnesium in Simulated Body Fluid

Magnesium (Mg) is a promising biomedical material due to its suitable mechanical properties and biocompatibility. The rapid dissolution in the physiological environment limits its application. There has been growing attention to pure Mg with different microstructures and coated Mg by chemical bath deposition method for bone tissue clinical use. However, the influences of microstructure on mechanical property and corrosion resistance of Mg and the relationships among the substrate, bath temperature, and coating quality are undetermined. This research achieved the pure Mg sheet by rolling and post-heat treatment. The in-situ coating was produced in a chemical solution containing Ca2+ and HPO42- under different temperatures of 37 °C-100 °C. The polarization and 30-day immersion tests were carried out to study the anti-corrosion performance of bare and coated Mg. The Mg mechanical property and the coating formation mechanism were discussed. According to the test results, it was concluded that the grain boundaries played a dual role in the mechanical property and corrosion behavior. Because they worked as physical barriers to improve strength and corrosion resistance, they also acted as crystallographic defects resulting in the adverse function when the crystalline size was super fine. The corrosion products were primarily Mg(OH)2. Calcium/magnesium phosphates and carbonates were deposited as thin outer precipitates. For the coated Mg, although improving the applied temperature offered more energy for the nucleation and growth of the precipitations, the substrate dissolution was accelerated. The coated Mg obtained at 70 ℃ on the substrate rolled at 200 ℃ had the best anti-corrosion behavior. The coating was in a double-layer structure. The inner layer was Mg(OH)2, and the outer one contained good-crystallized CaHPO4.2H2O and a small amount of Ca10(PO4)6(OH)2 and MgO. Due to plenty of Ca and P from the coating dissolution, the newly formed corrosion products had the same element content as the outer layer of the coating. They could retard the further erosion of the inner substrate. Because of this self-healing effect, the substrate was protected during the whole immersion process. This dissertation provides a combined strategy of substrate preparation and coating deposition to develop Mg-based materials for practical applications

TET-GAN: Text Effects Transfer via Stylization and Destylization

Text effects transfer technology automatically makes the text dramatically more impressive. However, previous style transfer methods either study the model for general style, which cannot handle the highly-structured text effects along the glyph, or require manual design of subtle matching criteria for text effects. In this paper, we focus on the use of the powerful representation abilities of deep neural features for text effects transfer. For this purpose, we propose a novel Texture Effects Transfer GAN (TET-GAN), which consists of a stylization subnetwork and a destylization subnetwork. The key idea is to train our network to accomplish both the objective of style transfer and style removal, so that it can learn to disentangle and recombine the content and style features of text effects images. To support the training of our network, we propose a new text effects dataset with as much as 64 professionally designed styles on 837 characters. We show that the disentangled feature representations enable us to transfer or remove all these styles on arbitrary glyphs using one network. Furthermore, the flexible network design empowers TET-GAN to efficiently extend to a new text style via one-shot learning where only one example is required. We demonstrate the superiority of the proposed method in generating high-quality stylized text over the state-of-the-art methods.Comment: Accepted by AAAI 2019. Code and dataset will be available at http://www.icst.pku.edu.cn/struct/Projects/TETGAN.htm

Demystifying Neural Style Transfer

Neural Style Transfer has recently demonstrated very exciting results which catches eyes in both academia and industry. Despite the amazing results, the principle of neural style transfer, especially why the Gram matrices could represent style remains unclear. In this paper, we propose a novel interpretation of neural style transfer by treating it as a domain adaptation problem. Specifically, we theoretically show that matching the Gram matrices of feature maps is equivalent to minimize the Maximum Mean Discrepancy (MMD) with the second order polynomial kernel. Thus, we argue that the essence of neural style transfer is to match the feature distributions between the style images and the generated images. To further support our standpoint, we experiment with several other distribution alignment methods, and achieve appealing results. We believe this novel interpretation connects these two important research fields, and could enlighten future researches.Comment: Accepted by IJCAI 201

Survival Outcomes In T3 Laryngeal Cancer Based On Staging Features At Diagnosis

Stage T3 laryngeal cancer is defined by the presence of vocal cord fixation and/or invasion into any of the following: pre-epiglottic space, paraglottic fat, post-cricoid space, or inner cortex of the thyroid cartilage. These cancers are usually treated with chemoradiation rather than upfront total laryngectomy. To our knowledge, no studies have directly compared differences in survival among the varied features within the T3 staging category. This study aims to determine how the presence of each of these staging features impacts overall and laryngectomy-free survival.Patients with clinically-diagnosed T3 laryngeal squamous cell carcinoma seen at our institution between 2010-2021 were retrospectively identified. Medical record information was collected for patient demographics, tumor characteristics, treatment course, and survival. Records were reviewed with head and neck surgeons and neuroradiologists when there was uncertainty. Patients were excluded if tumor and/or treatment information was incomplete, if metastatic disease was present at diagnosis, or if they were treated with upfront laryngectomy. For statistical analysis, the cohort was stratified in two ways: by number of T3 staging features and by type of feature. Pre-epiglottic, paraglottic, and post-cricoid space invasion were grouped together as “soft tissue invasion”. The primary outcome was overall survival (OS), and the secondary outcome was laryngectomy-free survival (LFS, the proportion of patients alive without laryngectomy, out of all alive patients at a certain timepoint). 102 patients met inclusion criteria for analysis, who were 79.4% male (81) and were diagnosed at a mean age of 65.3 ± 11.4 years. 68.4% of patients (67) presented with a single T3 staging feature. 48.0% of patients (49) had vocal cord fixation (either alone or in combination with other features), 63.7% (65) had soft tissue invasion, and 10.8% (11) had thyroid cartilage involvement. OS was 68.6% at 2 years and 47.9% at 5 years. LFS was 74.2% at 2 years and 72.1% at 5 years. On Kaplan-Meier survival analysis comparing different staging features, thyroid cartilage involvement had a significant impact on OS (p\u3c0.001). Cox proportional hazard regression analysis showed that older age at diagnosis (p\u3c0.001), higher overall cancer stage (p=0.003), and thyroid cartilage involvement (p\u3c0.001) all had significant impacts on OS. There were no demographic or clinical features which had a significant impact on LFS, i.e. features of patients who were more likely to receive salvage laryngectomy. Our results suggest that overall survival may be worse for patients with thyroid cartilage invasion. The difficulty of radiologically determining the degree of thyroid cartilage invasion, which distinguishes stage T3 from stage T4 laryngeal cancer, may contribute to this finding. However, the possibility that any thyroid cartilage invasion portends worse survival cannot be excluded. In order to optimize survival for patients with T3 laryngeal cancer, our findings should be further validated with larger datasets and prospective studies to assess the need for potential changes in tumor staging or treatment guidelines