Deep Learning Based Fine-Grained Species Identification

University of Technology Sydney. Faculty of Engineering and Information Technology.Fine-Grained Visual Categorization (FGVC) is a challenging research topic in computer vision. It deals with the classification of visual data at a subordinate level. This thesis investigates four categories of FGVC methods based on deep learning, including general convolutional neural networks, object part localization methods, approaches using CNN ensemble or higher-order feature encoding, and methods utilizing recurrent visual attention. Overall performance comparison has been conducted to analyse their advantages and disadvantages. We proposed a new regression-based part detection structure and a novel part-based model, which increased the classification accuracy of PS-CNN from 76.4% to 82.4% on the CUB-200-2011 benchmark dataset. Inspired by the second-order pooling, we proposed a highly interpretable method with a compressed structure to significantly reduce the computation complexity while improving the fine-grained categorization accuracy. The proposed model provides a supervised selection of the most discriminative second-order channels. With the proposed method, the computation and the feature dimension are linearly reduced to 4% of the original bilinear pooling. By applying matrix normalization and a Fisher-Recurrent-Attention structure, we achieved the best result among the VGG-16 based FGVC models. Following the conception of attention crop and attention drop in the Fisher-Recurrent-Attention model, we proposed a forcing module to constrain the network to extract more diverse features for FGVC. The forcing module focuses more on confusion regions which are essential for the fine-grained classification. Experimental results show that the proposed forcing module can improve the attention and prediction of the network when an input image is panned or zoomed, and the double prediction performs better than the single prediction. The existing FGVC methods often come with enormous amounts of computation and require large memory space. This makes these models inadequate for mobile applications. We proposed a Category Attention Transferring Convolutional Neural Network (CAT-CNN) to transfer the attention knowledge from a large-scale FGVC network to a small but efficient network to improve its presentation capability. Using the proposed model, we improved the classification accuracy of the efficient networks by up to 5.7% on the CUB-2011-200 dataset without increasing computation time or memory cost, which makes FGVC feasible on mobile devices. We also conducted abundant studies to investigate the relationship between attention and classification accuracy of our proposed deep learning models, visualized and analysed the attentional activations of these models. We hope that our findings may inspire further research efforts to advance the FGVC for a wide range of real-world applications

Real-time Monitoring for the Next Core-Collapse Supernova in JUNO

Core-collapse supernova (CCSN) is one of the most energetic astrophysical events in the Universe. The early and prompt detection of neutrinos before (pre-SN) and during the SN burst is a unique opportunity to realize the multi-messenger observation of the CCSN events. In this work, we describe the monitoring concept and present the sensitivity of the system to the pre-SN and SN neutrinos at the Jiangmen Underground Neutrino Observatory (JUNO), which is a 20 kton liquid scintillator detector under construction in South China. The real-time monitoring system is designed with both the prompt monitors on the electronic board and online monitors at the data acquisition stage, in order to ensure both the alert speed and alert coverage of progenitor stars. By assuming a false alert rate of 1 per year, this monitoring system can be sensitive to the pre-SN neutrinos up to the distance of about 1.6 (0.9) kpc and SN neutrinos up to about 370 (360) kpc for a progenitor mass of 30$M_{\odot}$ for the case of normal (inverted) mass ordering. The pointing ability of the CCSN is evaluated by using the accumulated event anisotropy of the inverse beta decay interactions from pre-SN or SN neutrinos, which, along with the early alert, can play important roles for the followup multi-messenger observations of the next Galactic or nearby extragalactic CCSN.Comment: 24 pages, 9 figure

Effect of Zn/Y atomic ratio on precipitation behavior and dynamic recrystallization behavior of Mg–Zn–Y alloy under different extrusion temperature

Precipitation behavior and dynamic recrystallization (DRX) behavior of Mg–Zn–Y alloys with different Zn/Y atomic ratios under different extrsuion temperatures were systematically investigated in this work. The results shows that the types of precipitated phases in the casted alloys are changed with the increase of Zn/Y atomic ratio. After extrsuion, the brittle W-phases in Mg98.7Zn1Y0.3 and Mg98Zn1Y1 alloys are broken into finer particles along the extrusion direction, but the resistance of W-phases to grain growth is weak at higher extrusion temperature. However, Mg97.5Zn1Y1.5 alloy exhibits relatively stable grain size at different extrusion temperatures, due to the significant inhibitory effect of LPSO phases on grain growth at high temperatures. The banded LPSO phases with wide phase spacing can promote DRX behavior via particle stimulated nucleation (PSN) resulting in highest DRX fraction. Nevertheless, the lamellar LPSO phases could effectively hinder the grain boundary migration and dislocation motion, which is against the nucleation and growth of DRX grains. It is precisely due to the influence of LSPO phases on the DRX behavior and its own kinking effect that Mg97.5Zn1Y1.5 alloy has better heat resistance. Mg97.5Zn1Y1.5 alloy exhibits excellent tensile strength and ductility, with ultimate tensile strength (UTS) of 413 MPa, yield strength (YS) of 330 MPa and elongation (EL) of 12.1% after extrusion at 573 K. The good ductility is mainly due to the coordinated deformation ability of the LPSO phase and the activated non-basal slip effect. The synergistic effect of lamellar LPSO phase and kinking deformation effectively refines the microstructure of the alloy and improves the strength

Variable-Frequency Ultrasonic Treatment on Microstructure and Mechanical Properties of ZK60 Alloy during Large Diameter Semi-Continuous Casting

Traditional fixed-frequency ultrasonic technology and a variable-frequency ultrasonic technology were applied to refine the as-cast microstructure and improve the mechanical properties of a ZK60 (Mg-Zn-Zr) alloy during large diameter semi-continuous casting. The acoustic field propagation was obtained by numerical simulation. The microstructure of the as-cast samples was characterized by optical and scanning electron microscopy. The variable-frequency ultrasonic technology shows its outstanding ability in grain refinement comparedwith traditional fixed-ultrasonic technology. The variable-frequency acoustic field promoted the formation of small beta-Mg globular grains and changed the distribution and morphology of beta-phases throughout the castings. Ultimate tensile strength and elongation are increased to 280 MPa and 8.9%, respectively, which are 19.1% and 45.9% higher than the values obtained from billets without ultrasonic treatment and are 11.6% and 18.7% higher than fixed-frequency ultrasound treated billets. Different refinement efficiencies appear in different districts of billets attributed to the sound attenuation in melt. The variable-frequency acoustic field improves the refinement effect by enhancing cavitation-enhanced heterogeneous nucleation and dendrite fragmentation effects

The effect of double extrusion on the microstructure and mechanical properties of AZ80RE alloy

The Mg-8.10Al-0.42Zn-0.51Mn-1.52La-1.10Gd (wt%, AZ80RE alloy, RE = rare earth) alloy was subjected to double extrusion, and the influence of the double extrusion on the microstructure and mechanical properties of the extruded alloy was investigated. The secondary extrusion process could strongly refine the recrystallized grains and disperse the fine RE-containing phases. The ductility of the AZ80RE alloy was also promoted, due to the grain refinement and the basal texture weakening. The elongation was significantly prolonged from the initial 13.3% to 28.5% after secondary extrusion. The basal texture weakening slightly deteriorated the yield stress of the AZ80RE alloy. The yield stress was declined from 218 MPa to about 172 MPa after secondary extrusion. Furthermore, lower extruding temperature was beneficial for finer grains and better ductility

Microstructure and Mechanical Property Inhomogeneities of a Modified AZ80 Magnesium Alloy Wide Plate Under Horizontal Flat Die Extrusion

In the present paper, inhomogeneities in the microstructure and mechanical properties of a modified AZ80 plate under industrial production conditions were investigated. The results indicated that the microstructure of the edge and middle region shows more homogeneous and fine recrystallized grains. Additionally, more coarse recrystallized grains existed between the edge and the middle region. The ultimate tensile strength and yield strength of the edge region of the plate are maximal (287 and 162MPa), and those near the 1/8W region are minimal (259 and 152MPa). The grain size increased from 19.5 to 27.2m along the center layer to the surface layer. The ultimate tensile stress (yield stress) increases from 258 (121MPa) to 284MPa (176MPa) in the direction from the surface layer to the middle layer. The microhardness decreased from the surface layer (72HV) to the center layer (64HV). The metal strain state and temperature distribution lead to different degrees of dynamic recrystallization, which causes the microstructure and mechanical properties of the plate

Study of microstructure and mechanical properties of Mg–3Y-1REmOn composites by Y-REmOn (RE=La, Ce, Sm, Gd) in-situ reaction

The expensive cost of master alloys for preparing high-performance Mg rare-earth alloys has prevented their large-scale production and application. This paper demonstrates that some inexpensive rare-earth oxides can replace the corresponding master alloys for material preparation by thermodynamic calculations, and low-cost Mg–3Y–1La2O3, Mg–3Y–1CeO2, Mg–3Y–1Sm2O3, and Mg–3Y–1Gd2O3 composites were prepared using the melting-casting-hot extrusion method. Y can reduce some rare earth oxides to rare earth element. When the content of rare earth element is high, it can form a second phase (Mg17La2, Mg12Ce) with Mg which is well bound to the matrix, revealing that the in-situ composite has a good particle-matrix interface relationship. In addition, the in-situ Mg17La2 is coarse and has a higher volume fraction, which plays a key role in the improvement of mechanical properties. The ultimate tensile strength of Mg–3Y–1La2O3 composite is 55.1 MPa higher than that of Mg–3Y alloy. The strengthening mechanism can be attributed to the load transfer and coefficient of thermal expansion (CTE) of the Mg17La2

The simultaneous application of variable frequency ultrasonic and low frequency electromagnetic fields in semi continuous casting of AZ80 magnesium alloy

Considering the greatly significance of high quality billet in industrial manufacture and subsequent deformation process, special casting technologies are employed usually. In this present work, traditional fixed-frequency ultrasonic field (FUF), low frequency electromagnetic field (LEF), variable-frequency ultrasonic field (VUF) and the combinational field of VUF + LEF were introduced to refine the as-cast microstructure and promote the mechanical properties of AZ80 magnesium alloy during the semicontinuous casting. The results showed that all kinds of the external field treatments have their ability to refine the grain, while the combinational field represents the best efficiency in terms of grain refinement with the grain size of 116-141 mu m decreased from 679-1454 mu m (untreated billet) in the empty set 255 mm billet. The homogeneity of grains was improved dramatically as well. The main role of VUF was to promote heterogeneous nucleation and generate the large number of nuclei by enlarging cavitation area and acoustic pressure, while the main contribution of LEF was to transport these nuclei in the entire liquid cave. The same as grain size, the Mg17Al12 phases were also refined showing the increase of area fraction of tiny phase. The YS and UTS were remarkably increased after the combinational field treatment, showing the values of 96.8-105 MPa (YS) and 165.5-214.3 MPa (UTS) increased from 73.1 to 84.4 MPa (YS) and 138-153.7 MPa (UTS) of the untreated billet. Finally, the relation between UTS and grain size was established using Hall-Petch relation as a bridge. (C) 2018 Elsevier B.V. All rights reserved

Hot deformation behavior and processing map development of AZ110 alloy with and without addition of La-rich Mish Metal

In order to compare the workability of AZ110 alloy with and without addition of La-rich Mish Metal (MM), hot compression tests were performed on a Gleeble-3500D thermo-mechanical simulator at the deformation temperature range of 473−623 K and strain rate range of 0.001-1 s. The flow stress, constitutive relation, DRX kinetic model, processing map and microstructure characterization of the alloys were investigated. The results show that the flow stress is very sensitive to deformation temperature and strain rate, and the peak stress of AZ110LC (LC = La-rich MM) alloy is higher than that of AZ110 alloy. The hot deformation behavior of the alloys can be accurately predicted by the constitutive relations. The derived constitutive equations show that the calculated activation energy Q and stress exponent n for AZ110 alloy are higher than the calculated values of AZ110LC alloy. The analysis of DRX kinetic models show that the development of DRX in AZ110LC alloy is earlier than AZ110 alloy at the same deformation condition. The processing maps show that the workability of AZ110LC alloy is significantly more excellent than AZ110 alloy and the microstructures are in good agreement with the calculated results. The AZ110LC alloys can obtain complete DRX microstructure at high strain rate due to its higher stored energy and weak basal texture