Interchange reconnection associated with a confined filament eruption: Implications for the source of transient cold-dense plasma in solar winds

The cold-dense plasma is occasionally detected in the solar wind with in situ data, but the source of the cold-dense plasma remains illusive. Interchange reconnections (IRs) between closed fields and nearby open fields are well known to contribute to the formation of solar winds. We present a confined filament eruption associated with a puff-like coronal mass ejection (CME) on 2014 December 24. The filament underwent successive activations and finally erupted, due to continuous magnetic flux cancellations and emergences. The confined erupting filament showed a clear untwist motion, and most of the filament material fell back. During the eruption, some tiny blobs escaped from the confined filament body, along newly-formed open field lines rooted around the south end of the filament, and some bright plasma flowed from the north end of the filament to remote sites at nearby open fields. The newly-formed open field lines shifted southward with multiple branches. The puff-like CME also showed multiple bright fronts and a clear southward shift. All the results indicate an intermittent IR existed between closed fields of the confined erupting filament and nearby open fields, which released a portion of filament material (blobs) to form the puff-like CME. We suggest that the IR provides a possible source of cold-dense plasma in the solar wind

Parametric estimation of non-minimum phase switch mode power converters

PhD ThesisNowadays, switching mode power converters (SMPCs) are widely used in many applications. The advanced control technique for converters, such as adaptive control is also spread-used in many converter control scheme designs. System identification as a tool for estimating the converter operating conditions, and providing the information to the controller is a key technique for these applications; and parametric estimation, which is part of the system identification technique, is an advanced identification technique which can allow on-line system identification and adaptive control design. However, most of the research over the past decades has only covered parametric estimation of buck converters and there is barely anything about boost converters or other non-minimum phase converters. The reason behind this is that the parametric estimation results of non-minimum phase converters are not fitted to the calculated model weights, especially for the numerator weights of the model transfer function. Thus, the controller gains cannot be determined correctly by the wrong estimated model weights. It has been a big problem in the application of parametric estimation for decades. In this research, a modelling method which is based on trailing-edge PWM off-time sampling (TEOS) is introduced in order to address this problem. The objective of this research is to develop an approach to resolve the existing accuracy problems of non-minimum phase SMPC parametric estimation. The problem, which has existed for decades, is that commonly used state-space averaged model numerator weights are not fitted to the non-minimum phase SMPC parametric estimation results. There are several possible ways to address this problem, including modification of converter modelling, modification of parametric estimation mechanism, or with the help of compensators. In this research, the TEOS modelling method has been verified by both simulation and practical experiment to provide the best-fit model weights for the parametric estimation of buck converters and boost converters; and it has also been verified, by simulation, to be used for buck-boost converter parametric estimation, which has opened up great possibilities for its use on other non-minimum phase converters. The experimental results have shown that the proposed modelling approach has improved the accuracy of parametric estimation for boost converters by more than 20% compared with the commonly used state-space averaged modelling approach. IV In addition, the TEOS model will also present a thorough inspection of the relationships between system parameters (load resistance, capacitance and inductance) and the model transfer function parameters, which can then realise the sensor-less on-line system parameters estimation or monitoring. This function is also a novel approach to the area of system component monitoring. In this thesis, the reason behind the problem of non-minimum phase converter parametric estimation is analysed for the first time. The system parametric estimation of three converters (buck, boost and buck-boost) were tested with on-line simulation and off-line experimental tests for both the averaged model and the proposed model. Then, system parameters estimation was also tested for the buck converter and boost converter in the simulation and practical experiment. In addition, the platform setup, the interface build between the Matlab Simulink and the Code Composer Studio (CCS), the settings of the Digital Signal Processor (DSP) TMS320F28335, the parameters design of boost SMPC, and the design of the Printed Circuit Board (PCB) schematics and layout are also presented in this thesis. The outcome of the research should be able to further benefit many applications of advanced control systems, fault detection, and system component monitoring

Barrier Inhomogeneity of Schottky Diode on Nonpolar AlN Grown by Physical Vapor Transport

An aluminum nitride (AlN) Schottky barrier diode (SBD) was fabricated on a nonpolar AlN crystal grown on tungsten substrate by physical vapor transport. The Ni/Au-AlN SBD features a low ideality factor n of 3.3 and an effective Schottky barrier height (SBH) of 1.05 eV at room temperature. The ideality factor n decreases and the effective SBH increases at high temperatures. The temperature dependences of n and SBH were explained using an inhomogeneous model. A mean SBH of 2.105 eV was obtained for the Ni-AlN Schottky junction from the inhomogeneity analysis of the current-voltage characteristics. An equation in which the parameters have explicit physical meanings in thermionic emission theory is proposed to describe the current-voltage characteristics of inhomogeneous SBDs.Comment: 6 pages, 6 figure

Semantic Parsing with Dual Learning

Semantic parsing converts natural language queries into structured logical forms. The paucity of annotated training samples is a fundamental challenge in this field. In this work, we develop a semantic parsing framework with the dual learning algorithm, which enables a semantic parser to make full use of data (labeled and even unlabeled) through a dual-learning game. This game between a primal model (semantic parsing) and a dual model (logical form to query) forces them to regularize each other, and can achieve feedback signals from some prior-knowledge. By utilizing the prior-knowledge of logical form structures, we propose a novel reward signal at the surface and semantic levels which tends to generate complete and reasonable logical forms. Experimental results show that our approach achieves new state-of-the-art performance on ATIS dataset and gets competitive performance on Overnight dataset.Comment: Accepted by ACL 2019 Long Pape

Composition Comparison between ICMEs from Active Regions and Quiet-Sun Regions

The composition, including the ionic charge states and elemental abundances of heavy elements, within interplanetary coronal mass ejections (ICMEs) has tight correlations with their source regions and eruption processes. This can help analyze the eruption mechanisms and plasma origins of CMEs, and deepen our understanding of energetic solar activities. The active regions and quiet-Sun regions have different physical properties, thus from a statistical point of view, ICMEs originating from the two types of regions should exhibit different compositional characteristics. To demonstrate the differences comprehensively, we conduct survey studies on the ionic charge states of five elements (Mg, Fe, Si, C, and O) and the relative abundances of six elements (Mg/O, Fe/O, Si/O, C/O, Ne/O, and He/O) within ICMEs from 1998 February to 2011 August through the data of advanced composition explorer. The results show that ICMEs from active regions have higher ionic charge states and relative abundances than those from quiet-Sun regions. For the active-region ICMEs, we further analyze the relations between their composition and flare class, and find a positive relationship between them, i.e., the higher classes of the associated flares, the larger means of ionic charge states and relative abundances (except the C/O) within ICMEs. As more (less) fractions of ICMEs originate from active regions around solar maximum (minimum), and active-region ICMEs usually are associated with higher-class flares, our studies might answer why ICME composition measured near 1 au exhibits the solar cycle dependence.Comment: 13 pages, 4 figure

ASTormer: An AST Structure-aware Transformer Decoder for Text-to-SQL

Text-to-SQL aims to generate an executable SQL program given the user utterance and the corresponding database schema. To ensure the well-formedness of output SQLs, one prominent approach adopts a grammar-based recurrent decoder to produce the equivalent SQL abstract syntax tree (AST). However, previous methods mainly utilize an RNN-series decoder, which 1) is time-consuming and inefficient and 2) introduces very few structure priors. In this work, we propose an AST structure-aware Transformer decoder (ASTormer) to replace traditional RNN cells. The structural knowledge, such as node types and positions in the tree, is seamlessly incorporated into the decoder via both absolute and relative position embeddings. Besides, the proposed framework is compatible with different traversing orders even considering adaptive node selection. Extensive experiments on five text-to-SQL benchmarks demonstrate the effectiveness and efficiency of our structured decoder compared to competitive baselines